FIELD The present invention relates to methods and materials of making three dimensional articles via 3d printing.

BACKGROUND Three dimensional printers for printing three dimensional articles are set forth in US Published Patent Applications Nos. 20100140849, or 20130241114, or 20140110872 or 2.0140036455 to Stratasys, inc., the subject matter of each being incorporated herein in their entirety. 3D printing in multiple colors is set forth in US Patent Application Publication No. 20140034214 to Makerbot Industries, the subject matter of which is incorporated herein in its entirety by reference. Other additive 3D printing systems, such as the ProJet additive printing systems with UV curing by 3D Systems, Inc. could also be used with the materials herein, Stereolithographic 3D printing systems, such as the KudoSD Titan 1, could also be used.

Further art is represented by US 20030157435, US 5929130, US 20130056910, US 20110262711 and US 5629133.

SUMMARY OF INVENTION It is an aim of the present invention to provide a three dimensional printing process.

It is another aim of the present invention to provide 3D printed article, which comprises a first portion that is electrically insulating and comprises a siloxane polymeric material; and a second portion that is electrically conductive and comprises a siloxane polymeric material. Further, it is an aim of the present invention to provide a 3D printed article which comprises a cured siloxane material having therein a first group of particles and a second group of particles, and wherein the first group is different from the second group based on average particle size, shape or particle material. The invention is based on the concept of concurrently or sequentially depositing electrically conductive and electrically insulating materials in a printing process so as to form a 3D printed article. Both the electrically conductive and electrically insulating materials comprise a siloxane polymer that is cured upon deposition by electromagnetic radiation or heat.

More specifically, the present invention is characterized by what is stated in the characterizing parts of the independent claims. Siloxane materials as disclosed herein can be used for printing three dimensional articles. The siloxane materials can be provided with or without particles therein. The materials can be concurrently deposited or sequentially deposited.

The materials can be electrically conducting or electrically insulating, transparent, hard or soft materials, of different refractive indices, and/or of different colors. By providing similar siloxane materials but with the variability in color, transparency, hardness, conductivity, etc., mismatch between materials (e.g. CTE mismatch) can be minimized.

DESCRIPTION OF EMBODIMENTS

Various example embodiments will be described more fully hereinafter. The present inventive concept may, however, be embodied in many different forms and should not be construed as limited to the example embodiments set forth herein. Rather, these example embodiments are provided so that this description will be thorough and complete, and will fully convey the scope of the present inventive concept to those skilled in the art.

It will be understood that when an element or layer is referred to as being "on", "connected to" or "coupled to" another element or layer, it can be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on", "directly connected to" or "directly coupled to" another element or layer, there are no intervening elements or layers present. Like numerals refer to like elements throughout. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. It will also be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region., layer or section without departing from the teachings of the present inventive concept. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well., unless the context clearly indicates otherwise, it will be further understood that the terms "comprises" and/or "comprising," or "includes" and/or "including" when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. Furthermore, relative terms, such as "lower" or "bottom" and "upper" or "top," may be used herein to describe one element's relationship to other elements, it will be understood that relative terms are intended to encompass different orientations of the device. For example, if the device is turned over, elements described as being on the "lower" side of other elements would then be oriented on "upper" sides of the other elements. The exemplary term "lower." can therefore, encompasses both an orientation of "lower" and "upper". Similarly, if the device is turned over, elements described as "below" or "beneath" other elements would then be oriented "above" the other elements. The exemplary terms "below" or "beneath" can, therefore, encompass both an orientation of above and below, Unless otherwise defined, ail terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries., should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Electrically Insulating 3D Material: Electrically non-conductive siloxane materials can be deposited in an additive 3D printing process. Particles can be provided with the deposited siloxane material, such as ceramic particles. The non conductive material can be provided as an opaque, reflecting or translucent or transparent material. If particles are provided, the particles can be nitride or oxide particles. For example, the particles can comprise an electrically non-conductive material such as silica, quartz, alumina, aluminum nitride, aluminum nitride coated with silica, barium sulfate, alumina trihydrate, boron nitride, etc. The particles can be any suitable shape, such as substantially round or shaped as flakes, and can be micro-sized or nano-sized. The filler may comprise ceramic compound particles that are nitrides, oxides, or oxynitrides, In particular, the filler can be particles that are ceramic particles that are an oxide of silicon, zinc, aluminum, yttrium, ytterbium, tungsten, titanium silicon, titanium, antimony, samarium, nickel, nickel cobalt, molybdenum, magnesium, manganese, lanthanide, iron, indium tin, copper, cobalt aluminum, chromium, cesium or calcium. The particles could instead be nitride particles, such as aluminum nitride, tantalum nitride, boron nitride, titanium nitride, copper nitride, molybdenum nitride, tungsten nitride, iron nitride, silicon nitride, indium nitride, gallium nitride or carbon nitride.

The curing mechanism in the 3D printing process can be heat and/or electromagnetic radiation, e.g. UV light. Also, the dielectric siloxane layer can be provided as a liquid or viscous material and exposed to UV light for curing. The film can be crosslinked by UV only without any heat being applied, or it can be curable with a combination of UV and heat, such as where the heat is less than 120 °C or even less than 100 °C for heat sensitive devices. It is also possible to provide only heating for the siloxane curing.

The siloxane composition may comprise coupling agents, curing agents, antioxidants, adhesion promoters and the like, as disclosed herein. In particular, the siloxane material comprises reactive groups on the Si-0 backbone that are reactive upon the application of incident UV light. It is also possible to provide two different types of particles within the non conductive siloxane material, such as ceramic particles having different sizes, or two different types of particles loaded within the siloxane prior to 3D printing. Electrically Conductive 3D Materia! : The siloxane material can also be deposited as an electrically conductive material, preferably having within the siloxane, such as metallic particles. The particulate filler may be a conductive material, such as carbon black, graphite, graphene, gold, silver, copper, platinum, palladium, nickel, aluminum, silver plated copper, silver plated aluminum, bismuth, tin, bismuth-tin alloy, silver plated fiber, nickel plate copper, silver and nickel plated copper, gold plated copper, gold and nickel plated copper, or it may be gold, silver-gold, silver, nickel, tin, platinum, titanium plated polymer such as polyacrylate, polystyrene or silicone but not limited to these. The filler can be also a semiconductor material such as silicon, n or p type doped silicon, Ga N, InGaN, GaAs, InP, SiC but not limited to these. Furthermore, the filler can be quantum dot or a surface plasmonic particle or phosphor particle. Other semiconductor particles or quantum dots, such as Ge, Ga P, InAs, CdSe, ZnO, ZnSe, Ti02, ZnS, CdS, CdTe, etc. are a lso possible. However metallic particles are preferred. More particularly, the particles can be comprised of any suitable metal or semi-metal such as those selected from gold, silver, copper, platinum, palladium, indium, iron, nickel, aluminum, carbon, cobalt, strontium, zinc, molybdenu m, titanium, tungsten, silver plated copper, silver plated aluminum, bismuth, tin, bismuth-tin alloy, silver plated fiber or alloys or combinations of these. Metal particles that are transition metal particles (whether early transition metals or late transition metals) are envisioned, as are semi metals and metalloids. Semi-metal or metalloid particles such as arsenic, antimony, tellurium, germanium, silicon, and bismuth are envisioned. it is also possible to provide two different group of particles to the siloxane material used for 3D printing, where a first group of partic les having an average particle size of greater than 200 nm are provided together with a second group of particles that have an average pa rticle size of less than 200 nm, e.g. where the first group has an average particle size of greater than 500 nm and the second group has an average particle size of less than lOOnm (e.g. average particle size of first group greater than 1 micron, particle size of second group less than 50 nm , or even less than 25 nm). The smaller pa rticles have a lower melting point than the larger particles and melt or sin ter at a tempera ture less than particles or mass of the same material having a plus micron size. In one example, the smaller pa rticles have an average particle size of less than 1 micron and mel t or sinter at a temperature less than the bulk temperatu re of the same material. Depending upon the particle material selected, and the average particle size, the melting and sintering temperatures will be different. As one example, very small silver nanoparticies can melt at less than 120 °C, and sinter at even lower temperatures. As such, if desired, the smaller particles can have a melting or sintering temperature equal to or lower than the polymer curing temperature, so as to form a web of melted or sintered particles connecting the larger particles together prior to full cross-linking and curing of the siloxane polymeric material. In one example, the smaller particles are melted or sintered with the larger particles at a temperature of less than 130 °C, e.g. less than 120 °C, or even sintered at less than 110 °C, whereas the siloxane material undergoes substantial cross-linking at a higher temperature, e.g. substantial sintering or melting at less than 110 °C, but substantial polymerization at greater than 110 °C (or e.g. substantial sintering or melting at less than 120 °C (or 130 °C), but substantial polymerization at greater than 120 °C (or 130 °C). The sintering or melting of the smaller particles prior to substantial polymerization of the siloxane material, allows for greater interconnectivity of a formed metal "lattice" which increases the final electrical conductivity of the cured layer. Substantial polymerization prior to substantial sintering or melting of the smaller particles decreases the amount of formed metal "lattice" and lowers the electrical conductivity of the final cured layer. Of course, it is also possible to provide only the particles of the smaller average particle size, e.g. sub micron size, which can still achieve the benefits of lower sintering and melting points as compared to the same bulk material (or the same particles having an average particle size of greater than 1 micron for example).

3D printing of both electrically conductive and electrically insulating materials is desirable for forming electrically leads or traces within the article being printed, or more complex electricaly components, including touch sensitive surfaces that have different layers of electrically conductive and insulating materials that form a capacitor that can detect the position of touch on the 3D article. Printing of both electrically conductive and insulating materials allows for the printing of modular devices, such as modular telephones where various components, such as the memory or camera can be removed and upgraded without replacing the entire phone. Such 3D printable modular devices can be smartphones, tablets, laptops, e-books, etc Transparent or reflective 3D Printed Materials: The siloxane materials deposited by 3D printing can be highly transmissive to visible light. Transparent articles such as eyeglasses, drinking glasses or cups, transparent cases or other portions, e.g. modular portions for electronics devices (e.g.

smartphones, cameras, tablets, laptops etc) can be printed, or any article desired that is suitable for 3D printing in a transparent material can be envisioned. In many examples, the light transmitted through the transparent layer in the 3D article is at least 85%, preferably 90% or more, or even 95% or more. The refractive index can be modified based on the types of organic groups attached to the siloxane backbone (e.g. aiky! chains for lower refractive indices, aryl groups for higher refractive indices), as well as selection of the type of particles if presen t. Layers in the 3D printed article can be printed with transparent siloxane layers having different refractive indices. If particles are present in the transparent printed layers, they can be e.g. oxide particles having an average particle size less than visible light, e.g. less than 400 rsrn, or preferably less than 200nm or even less than lOOnm. If a reflective layer is desired to be printed, metallic particles can be provided within the siloxane material, and which metallic particles can have any suitable size, e.g. an average particle size greater than visible light e.g. greater than 7G0nm. such as greater than 1 micron, or greater than 10 microns. A combination of reflective and transparent portions of the 3D article can be printed, as well as including combinations of electrically conductive and non- conductive portions.

More particularly with regard to the siloxane composition referred to hereinabove, a composition is made where at a siloxane polymer is provided. Preferably the polymer has a silicon oxide backbone, with aryl (or alkyl) subsitutents as well as functional cross-linking substituents. An optional filler material is mixed with the siloxane polymer. The filler material is preferably particulate material comprising particles having an average particle size of 100 microns or less, preferably 10 microns or less. A catalyst is added, the catalyst being reactive with the functional cross-linking groups in the siloxane polymer when heat or UV light (or other activation method) is provided to the composition. A monomeric (or oligomeric) coupling agent(s) are included in the composition, preferably having functional cross-linking groups that are likewise reactive upon the application of heat or light as in the siloxane polymer. Additional materials such as stabilizers, antioxidants, dispersants, adhesion promoters, plasticizers, softeners, and other potential components, depending upon the final use of the composition, can also be added. Though a solvent could be added, in a preferred embodiment the composition is solvent-free and is a viscous fluid without solvent which is stored and shipped as such.

As noted above, the composition being made as disclosed herein, comprises a siloxane polymer. To make the siloxane polymer, a first compound is provided having a chemical formula where a is from 1 to 3, R ¹ is a reactive group, and R ² is an alkyl group or an aryl group. Also provided is a second compound that has the chemical formula SiR ³ _b R ⁴ _c R -(b+c) where R ³ is a cross-linking functional group, R ⁴ is a reactive group, and R ⁵ is an alkyl or aryl group, and where b = 1 to 2, and c = 1 to (4-b). An optional third compound is provided along with the first and second compounds, to be polymerized therewith. The third compound may have the chemical formula Si R ⁹ _f R ¹⁰ _g where R ⁹ is a reactive group and f = 1 to 4, and where R ¹⁰ is an alkyl or aryl group and g = 4-f. The first, second and third compounds may be provided in any sequence, and oligomeric partially polymerized versions of any of these compounds may be provided in place of the above-mentioned monomers.

The first, second and third compounds, and any compounds recited hereinbelow, if such compounds have more than one of a single type of "R" group such as a plurality of aryl or alkyl groups, or a plurality of reactive groups, or a plurality of cross-linking functional groups, etc., the multiple R groups are independently selected so as to be the same or different at each occurrence. For example, if the first compound is SiR ¹ ₂ R ² ₂ , the multiple R ¹ groups are independently selected so as to be the same or different from each other. Likewise the multiple R ² groups are independently selected so as to be the same or different from each other. The same is for any other compounds mentioned herein, unless explicitly stated otherwise.

A catalyst is also provided. The catalyst may be a base catalyst, or other catalyst as mentioned below. The catalyst provided should be capable of polymerizing the first and second compounds together. As mentioned above, the order of the addition of the compounds and catalyst may be in any desired order. The various components provided together are polymerized to create a siloxane polymeric material having a desired molecular weight and viscosity. After the polymerization, particles, such as microparticles, nanoparticles or other desired particles are added, along with other optional components such as coupling agents, catalyst, stabilizers, adhesion promoters, and the like. The combination of the components of the composition can be performed in any desired order.

More particularly, in one example, a siloxane polymer is made by polymerizing first and second compounds, where the first compound has the chemical formula where a is from 1 to 3, R ¹ is a reactive group, and R ² is an alkyl group or an aryl group, and the second compound has the chemical formula SiR ³ _b R ⁴ _c R -(b+c) where R ³ is a cross-linking functional group, R ⁴ is a reactive group, and R ⁵ is an alkyl or aryl group, and where b = 1 to 2, and c = 1 to (4-b). The first compound may have from 1 to 3 alkyi or aryl groups (R ² ) bound to the silicon in the compound. A combination of different alkyi groups, a combination of different aryl groups, or a combination of both alkyi and aryl groups is possible. If an alkyi group, the alkyi contains preferably 1 to 18, more preferably 1 to 14 and particularly preferred 1 to 12 carbon atoms. Shorter alkyi groups, such as from 1 to 6 carbons (e.g. from 2 to 6 carbon atoms) are envisioned. The alkyi group can be branched at the alpha or beta position with one or more, preferably two, C _x to C ₆ alkyi groups. In particular, the alkyi group is a lower alkyi containing 1 to 6 carbon atoms, which optionally bears 1 to 3 substituents selected from methyl and halogen. Methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl and t-butyl, are particularly preferred. A cyclic alkyi group is also possible like cyclohexyl, adamantyl, norbornene or norbornyl.

If R ² is an aryl group, the aryl group can be phenyl, which optionally bears 1 to 5 substituents selected from halogen, alkyi or alkenyl on the ring, or naphthyl, which optionally bear 1 to 11 substituents selected from halogen alkyi or alkenyl on the ring structure, the substituents being optionally fluorinated (including per-fluorinated or partially fluorinated). If the aryl group is a polyaromatic group, the polyaromatic group can be for example anthracene, naphthalene, phenanthere, tetracene which optionally can bear 1-8 substituents or can be also optionally 'spaced' from the silicon atom by alkyi, alkenyl, alkynyl or aryl groups containing 1-12 carbons. A single ring structure such as phenyl may also be spaced from the silicon atom in this way.

The siloxane polymer is made by performing a polymerization reaction, preferably a base catalyzed polymerization reaction between the first and second compounds. Optional additional compounds, as set forth below, can be included as part of the polymerization reaction. The first compound can have any suitable reactive group R ¹ , such as a hydroxyl, halogen, alkoxy, carboxyl, amine or acyloxy group. If, for example, the reactive group in the first compound is an -OH group, more particular examples of the first compound can include silanediols such as

diphenylsilanediol, dimethylsilanediol, di-isopropylsilanediol, di-n-propylsilanediol, di-n- butylsilanediol, di-t-butylsilanediol, di-isobutylsilanediol, phenylmethylsilanediol and

dicyclohexylsilanediol among others.

The second compound can have any suitable reactive group R ⁴ , such as a hydroxyl, halogen, alkoxy, carboxyl, amine or acyloxy group, which can be the same or different from the reactive group in the first compound. In one example, the reactive group is not -H in either the first or second compound (or any compounds that take part in the polymerization reaction to form the siloxane polymer - e.g. the third compound, etc.), such that the resulting siloxane polymer has an absence of any, or substantially any, H groups bonded directly to the Si in the siloxane polymer. Group R ⁵ , if present at all in the second compound, is independently an alkyi or aryl groups such as for group R ² in the first compound. The alkyi or aryl group R ⁵ can be the same or different from the group R ² in the first compound.

The cross-linking reactive group R ³ of the second compound can be any functional group that can be cross-linked by acid, base, radical or thermal catalyzed reactions. These functional groups can be for example any epoxide, oxetane, acrylate, alkenyl or alkynyl group.

If an epoxide group, it can be a cyclic ether with three ring atoms that can be cross-linked using acid, base and thermal catalyzed reactions. Examples of these epoxide containing cross-linking groups are glycidoxypropyl and (3,4-Epoxycyclohexyl)ethyl) groups to mention few.

If an oxetane group, it can be a cyclic ether with four ring atoms that can be cross-linked using acid, base and thermal catalyzed reactions. Examples of such oxetane containing silanes include 3-(3- ethyl-3-oxetanylmethoxy)propyltriethoxysilane, 3-(3-Methyl-3-oxetanylmethoxy)propyltriethoxysilan e, 3-(3-ethyl-3-oxetanylmethoxy)propyltrimethoxysilane or 3-(3-Methyl-3-oxetanylmethoxy) propyltrimethoxysilane, to mention a few.

If an alkenyl group, such a group may have preferably 2 to 18, more preferably 2 to 14 and particularly preferred 2 to 12 carbon atoms. The ethylenic, i.e. two carbon atoms bonded with double bond, group is preferably located at the position 2 or higher, related to the Si atom in the molecule. Branched alkenyl is preferably branched at the alpha or beta position with one and more, preferably two, Ci to C ₆ alkyi, alkenyl or alkynyl groups, optionally fluorinated or per-fluorinated alkyi, alkenyl or alkynyl groups. If an alkynyl group, it may have preferably 2 to 18, more preferably 2 to 14 and particularly preferred 2 to 12 carbon atoms. The ethylinic group, i.e. two carbon atoms bonded with triple bond, group is preferably located at the position 2 or higher, related to the Si or M atom in the molecule. Branched alkynyl is preferably branched at the alpha or beta position with one and more, preferably two, C _x to C ₆ alkyl, alkenyl or alkynyl groups, optionally per-fluorinated alkyl, alkenyl or alkynyl groups.

If a thiol group, it may be any organosulfur compound containing carbon-bonded sulfhydryl group. Examples of thiol containing silanes are 3-mercaptopropyltrimethoxysilane and 3- mercaptopropyltriethoxysilane.

The reactive group in the second compound can be an alkoxy group. The alkyl residue of the alkoxy groups can be linear or branched. Preferably, the alkoxy groups are comprised of lower alkoxy groups having 1 to 6 carbon atoms, such as methoxy, ethoxy, propoxy and t-butoxy groups. A particular examples of the second compound is an silane, such as 2-(3,4-Epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 3-(Trimethoxysilyl)propylmethacrylate, 3-(Trimethoxy- silyl)propylacrylate, (3-glycidyloxypropyl)trimethoxysilane, or 3-glycidoxypropyl-triethoxysilane, 3- methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, among others.

A third compound may be provided along with the first and second compounds, to be polymerized therewith. The third compound may have the chemical formula Si R ⁹ _f R ¹⁰ _g where R ⁹ is a reactive group and f = 1 to 4, and where R ¹⁰ is an alkyl or aryl group and g = 4-f. One such example is

tetramethoxysilane. Other examples include phenylmethyldimethoxysilane, trimethylmethoxysilane, dimethyldimethoxysilanesilane, vinyltrimethoxysilane, allyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyl tripropoxysilane, propylethyltrimethoxysilane, ethyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, among others.

Though the polymerization of the first and second compounds can be performed using an acid catalyst, a base catalyst is preferred. The base catalyst used in a base catalyzed polymerization between the first and second compounds can be any suitable basic compound. Examples of these basic compounds are any amines like triethylamine and any barium hydroxide like barium hydroxide, barium hydroxide monohydrate, barium hydroxide octahydrate, among others. Other basic catalysts include magnesium oxide, calcium oxide, barium oxide, ammonia, ammonium perchlorate, sodium hydroxide, potassium hydroxide, imidazone or n-butyl amine. In one particular example the base catalyst is Ba(OH) ₂ . The base catalyst can be provided, relative to the first and second compounds together, at a weight percent of less than 0.5%, or at lower amounts such as at a weight percent of less than 0.1%. Polymerization can be carried out in melt phase or in liquid medium. The temperature is in the range of about 20 to 200 °C, typically about 25 to 160 °C, in particular about 40 to 120 °C. Generally polymerization is carried out at ambient pressure and the maximum temperature is set by the boiling point of any solvent used. Polymerization can be carried out at refluxing conditions. Other pressures and temperatures are also possible. The molar ratio of the first compound to the second compound can be 95:5 to 5:95, in particular 90:10 to 10:90, preferably 80:20 to 20:80. In a preferred example, the molar ratio of the first compound to the second compound (or second plus other compounds that take part in the polymerization reaction - see below) is at least 40:60, or even 45:55 or higher.

In one example, the first compound has -OH groups as the reactive groups and the second compound has alkoxy groups as the reactive groups. Preferably, the total number of -OH groups for the amount of the first compound added is not more than the total number of reactive groups, e.g. alkoxy groups in the second compound, and preferably less than the total number of reactive groups in the second compound (or in the second compound plus any other compounds added with alkoxy groups, e.g. an added tetramethoxysilane or other third compound involved in the polymerization reaction, ad mentioned herein). With the alkoxy groups outnumbering the hydroxyl groups, all or substantially all of the -OH groups will react and be removed from the siloxane, such as methanol if the alkoxysilane is a methoxysilane, ethanol if the alkoxysilane is ethoxysilane, etc. Though the number of -OH groups in the first compound and the number of the reactive groups in the second compound (preferably other than -OH groups) can be substantially the same, it is preferably that the total number of reactive groups in the second compound outnumber the -OH groups in the first compound by 10% or more, preferably by 25% or more. In some embodiments the number of second compound reactive groups outnumber the first compound -OH groups by 40% or more, or even 60% or more, 75% or more, or as high as 100% or more. The methanol, ethanol or other byproduct of the polymerization reaction depending upon the compounds selected, is removed after polymerization, preferably evaporated out in a drying chamber.

The obtained siloxane polymers have any desired (weight average) molecular weight, such as from 500 to 100,000 g/mol. The molecular weight can be in the lower end of this range (e.g., from 500 to 10,000 g/mol, or more preferably 500 to 8,000 g/mol) or the organosiloxane material can have a molecular weight in the upper end of this range (such as from 10,000 to 100,000 g/mol or more preferably from 15,000 to 50,000 g/mol). It may be desirable to mix a polymer organosiloxane material having a lower molecular weight with an organosiloxane material having a higher molecular weight.

The obtained siloxane polymer may then be combined with additional components depending upon the final desired use of the polymer. Preferably, the siloxane polymer is combined with a filler to form a composition, such as a particulate filler having particles with an average particle size of less than 100 microns, preferably less than 50 microns, including less than 20 microns. Additional components may be part of the composition, such as catalysts or curing agents, one or more coupling agents, dispersants, antioxidants, stabilizers, adhesion promoters, and/or other desired components depending upon the final desired use of the siloxane material. In one example, a reducing agent that can reduce an oxidized surface to its metallic form, is included. A reducing agent can remove oxidation from particles if they are metallic particles with surface oxidation, and/or remove oxidation from e.g. metallic bonding pads or other metallic or electrically conductive areas that have oxidized, so as to improve the electrical connection between the siloxane particle material and the surface on which it is deposited or adhered. Reducing or stabilization agents can include ethylene glycol, beta-D- glucose, poly ethylene oxide, glycerol, 1,2-propylene glycol, N,N dimethyl formamide, poly- sodium acyrylate (PSA), betacyclodextrin with polyacyrylic acid, dihydroxy benzene, poly vinyl alcohol, 1,2 - propylene glycol, hydrazine, hydrazine sulfate, Sodium borohydride, ascorbic acid, hydroquinone family, gallic acid, pyrogallol, glyoxal, acetaldehyde, glutaraldehyde, aliphatic dialdehyde family, paraformaldehyde, tin powder, zinc powder, formic acid. An additive such as a stabilization agent, e.g. an antioxidant such as Irganox (as mentioned hereinbelow) or a diazine derivative can also be added.

Cross-linking silicon or non-silicon based resins and oligomers can be used to enhance cross linking between siloxane polymers. The functionality of added cross-linking oligomer or resin is chosen by functionality of siloxane polymer. If for example epoxy based alkoxysilanes were used during polymerization of siloxane polymer, then epoxy functional oligomer or resin can be used. The epoxy oligomer or resin can be any di, tri, tetra, or higher functionality epoxy oligomer or resin. Examples of these epoxy oligomers or resins can be l,l,3,3-tetramethyldisiloxane-l,3-bis2-(3,4- epoxycyclohexyl)ethyl, l,l,3,3-tetramethyldisiloxane-l,3-bisglycidoxypropyl, Bis(3,4- epoxycyclohexylmethyl) adipate, 3,4-Epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, 1,4- Cyclohexanedimethanol diglycidyl ether, Bisphenol A diglycidyl ether, Diglycidyl 1,2- cyclohexanedicarboxylate, to mention a few. The curing agent added to the final formulation is any compound that can initiate and/or accelerate the curing process of functional groups in siloxane polymer. These curing agents can be either heat and/or UV activated (e.g. a thermal acid if the polymerization reaction is heat activated or a photoinitiator if UV activated). The cross-linking groups in the siloxane polymer, as mentioned above, are preferably epoxide, oxetane, acrylate, alkenyl or alkynyl groups. The curing agent is selected based on the cross-linking group in the siloxane polymer.

In one embodiment, the curing agent for epoxy and oxetane groups can be selected from nitrogen- containing curing agents, such as primary and/ or secondary amines which show blocked or decreased activity. The definition "primary or secondary amines which show blocked or decreased reactivity" shall mean those amines which due to a chemical or physical blocking are incapable or only have very low capability to react with the resin components, but may regenerate their reactivity after liberation of the amine, e.g. by melting it at increased temperature, by removing sheath or coatings, by the action of pressure or of supersonic waves or of other energy types, the curing reaction of the resin components starts.

Examples of heat-activatable curing agent include complexes of at least one organoborane or borane with at least one amine. The amine may be of any type that complexes the organoborane and/or borane and that can be decomplexed to free the organoborane or borane when desired. The amine may comprise a variety of structures, for example, any primary or secondary amine or polyamines containing primary and/ or secondary amines. The organoborane can be selected from alkyl boranes. An example of these heat particular preferred borane is boron trifuoride. Suitable

amine/(organo)borane complexes are available from commercial sources such as King Industries, Air products, and ATO-Tech.

Other heat activated curing agents for epoxy groups are thermal acid generators which can release strong acids at elevated temperature to catalyze cross-linking reactions of epoxy. These thermal acid generators can be for example any onium salts like sulfonium and iodonium salts having complex anion of the type BF ₄ ^" , PF ₆ ^" , SbF ₆ ^" , CF ₃ S0 ₃ ^" , and (C ₆ F ₅ ) ₄ B\ Commercial examples of these thermal acid generators are K-PURE CXC - 1612 and K-PURE CXC - 1614 manufactured by King Industries. Additionally, with respect to epoxy and/or oxetane containing polymers, curing agent, co-curing agents, catalysts, initiators or other additives designed to participate in or promote curing of the adhesive formulation like for example, anhydrides, amines, imidazoles, thiols, carboxylic acids, phenols, dicyandiamide, urea, hydrazine, hydrazide, amino-formaldehyde resins, melamine- formaldehyde resins, quaternary ammonium salts, quaternary phosphonium salts, tri-aryl sulfonium salts, di-aryl iodonium salts, diazonium salts, and the like, can be used.

For acrylate, alkenyl and alkynyl cross linking groups curing agent can be either thermal or UV activated. Examples of thermal activated are peroxides and azo compounds. Peroxide is a compound containing unstable oxygen-oxygen single bond which easily split into reactive radicals via hemolytic cleavage. Azo compounds have R-N=N-R functional group which can decompose to nitrogen gas and two organic radicals. In both of these cases, the radicals can catalyze the polymerization of acrylate, alkenyl and alkynyl bonds. Examples of peroxide and azo compounds are di-tert-butyl peroxide, 2,2- Bis(tert-butylperoxy)butane, tert-Butyl peracetate, 2,5-Di(tert-butylperoxy)-2,5-dimethyl-3-hexyne, Dicumyl peroxide, Benzoyl peroxide, Di-tert-amyl peroxide, tert-Butyl peroxybenzoate, 4,4'-Azobis(4- cyanopentanoic acid), 2,2'-Azobis(2-amidinopropane) dihydrochloride, diphenyldiazene, Diethyl azodicarboxylate and l,l'-Azobis(cyclohexanecarbonitrile) to mention a few

Photoinitiators are compounds that decompose to free radicals when exposed to light and therefore can promote polymerization of acrylate, alkenyl and alkynyl compounds. Commercial examples of these photoinitiators are Irgacure 149, Irgacure 184, Irgacure 369, Irgacure 500, Irgacure 651, Irgacure 784, Irgacure 819, Irgacure 907, Irgacure 1700, Irgacure 1800, Irgacure 1850, Irgacure 2959, Irgacure 1173, Irgacure 4265 manufactured by BASF. One method to incorporate curing agent to the system is to attach a curing agent or a functional group that can act as curing agent, to a silane monomer. Therefore the curing agent will accelerate curing of the siloxane polymer. Examples of these kind of curing agents attached to a silane monomer are to γ-lmidazolylpropyltriethoxysilane, γ-lmidazolylpropyltrimethoxysilanel, 3- mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3- (triethoxysilyl)propylsuccinicanhydride, 3-(trimethoxysilyl)propylsuccinicanhydride, 3-aminopropyl- trimethoxysilane and 3-aminopropyltriethoxysilane to mention a few. An adhesion promoter can be part of the composition and can be any suitable compound that can enhance adhesion between cured product and surface where product has been applied. Most commonly used adhesion promoters are functional silanes where alkoxysilanes and one to three functional groups. Examples of adhesion promoter used in die attach products can be octyltriethoxy- silane, mercaptopropyltriethoxysilane, cyanopropyltrimethoxysilane, 2-(3,4-Epoxycyclohexyl) ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 3-(Trimethoxysilyl)propyl- methacrylate, 3-(Trimethoxysilyl)propylacrylate, (3-glycidyloxypropyl)trimethoxysilane, or 3- glycidoxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane and 3-acryloxypropyl- trimethoxysilane.

The polymerized siloxane formed will have a [Si-0-Si-0] _n repeating backbone (i.e. a backbone of repeating units of formula [Si-O-Si-O]), with organic functional groups thereon depending on the silicon containing starting materials. However it is also possible to achieve a [Si-0-Si-C] _n or even a [Si- 0-Me-0] _n (where Me is a metal) backbone. In the formulas, n is an integer of typically 1 to 1,000,000, in particular 1 to 100,000, for example 1 to 10,000, or even 1 to 5,000 or 1 to 1,000.

To obtain a [Si-O-Si-C] backbone, a chemical with formula R can be polymerized together with the first, second, and third compounds or any combination of these, as mentioned above, where a is from 1 to 3, b is from 1 to 3, R ¹ is a reactive group like explained above, R ² is an alkyi, alkenyl, alkynyl, alcohol, carboxylic acid, dicarboxylic acid, aryl, polyaryl, polycyclic alkyi, hetero cyclic aliphatic, hetero cyclic aromatic group and R ¹¹ is independently an alkyi group or aryl group, or an oligomer thereof having a molecular weight of less than 1000 g/mol. Examples of these compound are l,2-bis(dimethylhydroxylsilyl)ethane, l,2-bis(trimethoxylsilyl)ethane, l,2-Bis(dimethoxymethyls ilyl)ethane, l,2-Bis(methoxydimethylsilyl)ethane, l,2-bis(triethoxylsilyl)ethane, 1,3- bis(dimethylhydroxylsilyl)propane, l,3-bis(trimethoxylsilyl)propane, l,3-Bis(dimethoxymethyls ilyl)propane, l,3-Bis(methoxydimethylsilyl)propane, l,3-bis(triethoxylsilyl)propane, 1,4- bis(dimethylhydroxylsilyl)butane, l,4-bis(trimethoxylsilyl)butane, l,4-Bis(dimethoxymethylsilyl) butane, l,4-Bis(methoxydimethylsilyl)butane, l,4-bis(triethoxylsilyl)butane, 1,5- bis(dimethylhydroxylsilyl)pentane, l,5-bis(trimethoxylsilyl)pentane, 1,5- Bis(dimethoxymethylsilyl) pentane, l,5-bis(methoxydimethylsilyl)pentane, l,5-bis(triethoxylsilyl)pentane, 1,6- bis(dimethylhydroxylsilyl)hexane, l,6-bis(trimethoxylsilyl)hexane, l,6-Bis(dimethoxymethylsilyl) hexane, l,6-Bis(methoxydimethylsilyl)hexane, l,6-bis(triethoxylsilyl)hexane 1,4- bis(trimethoxylsilyl)benzene, bis(trimethoxylsilyl)naphthalene, bis(trimethoxylsilyl)anthrazene, bis(trimethoxylsilyl)phenanthere, bis(trimethoxylsilyl)norbornene, l,4-Bis(dimethylhydroxysilyl) benzene, l,4-bis(methoxydimethylsilyl)benzene and l,4-bis(triethoxysilyl)benzene to mention few.

In one embodiment to obtain [Si-O-Si-C] backbone, a compound with formula R

R ⁴ _d R ³ _c SiR ¹¹ SiR ³ _e R ⁴ fR -(e ₊ f) is polymerized together with the first, second, third compounds as mentioned herein, or any combinations of these, where R ³ is a cross-linking functional group, R ⁴ is a reactive group, and R ⁵ is an alkyl, alkenyl, alkynyl, alcohol, carboxylic acid, dicarboxylic acid, aryl, polyaryl, polycyclic alkyl, hetero cyclic aliphatic, hetero cyclic aromatic group, R ¹² is independently an alkyl group or aryl group, and where c = 1 to 2, d = 1 to (3-c), e = 1 to 2, and f = 1 to (3-e),or an oligomer thereof having a molecular weight of less than 1000 g/mol. Examples of these compounds are l,2-bis(ethenyldimethoxysilyl)ethane, l,2-bis(ethynyldimethoxysilyl)ethane, 1,2- bis(ethynyldimethoxy)ethane, l,2-bis(3-glycidoxypropyldimethoxysilyl)ethane, l,2-bis[2-(3,4- Epoxycyclohexyl)ethyldimethoxysilyl]ethane, l,2-bis(propylmethacrylatedimethoxysilyl)ethane, 1,4- bis(ethenyldimethoxysilyl)benzene, l,4-bis(ethynyldimethoxysilyl)benzene, 1,4- bis(ethynyldimethoxysilyl)benzene, l,4-bis(3-glycidoxypropyl dimethoxysilyl)benzene, l,4-bis[2-(3,4- epoxycyclohexyl)ethyldimethoxysilyl]benzene, l,4-bis(propyl methacrylatedimethoxysilyl)benzene, to mention few.

In one embodiment a siloxane monomer with molecular formula R ¹ _a R ² _b R ₎ Si-0-SiR -0-Si R ¹ _a R ² _b R where R ¹ is reactive group like explained above, R ² is alkyl or aryl like explained above, R ³ is cross linking functional group like explained above and a = 0 to 3, b = 0 to 3, is polymerized with previously mentioned silanes or added as an additive to the final formulation. Examples of these compounds are l,l,5,5-tetramethoxy-l,5-dimethyl-3,3-diphenyltrisiloxane, l,l,5,5-tetramethoxy-l,3,3,5- tetraphenyltrisiloxane, l,l,5,5-tetraethoxy-3,3-diphenyltrisiloxane, l,l,5,5-tetramethoxy-l,5-divinyl- 3,3-diphenyltrisiloxane, l,l,5,5-tetramethoxy-l,5-dimethyl-3,3-diisopropyltrisiloxane , 1,1,1,5,5,5- hexamethoxy-3,3-diphenyltrisiloxane, l,5-dimethyl-l,5-diethoxy-3,3-diphenyltrisiloxane, 1,5- bis(mercaptopropyl)-l,l,5,5-tetramethoxy-3,3-diphenyltrisilo xane, l,5-divinyl-l,l,5,5-tetramethoxy- 3-phenyl-3-methyltrisiloxane, l,5-divinyl-l,l,5,5-tetramethoxy-3-cyclohexyl-3-methyltrisil oxane, l,l,7,7-tetramethoxy-l,7-divinyl-3,3,5,5-tetramethyltetrasil oxane, l,l,5,5-tetramethoxy-3,3- dimethyltrisiloxane, l,l,7,7-tetraethoxy-3,3,5,5-tetramethyltetrasiloxane, 1,1,5,5- tetraethoxy-3,3- dimethyltrisiloxane, l,l,5,5-tetramethoxy-l,5-[2-(3,4-epoxycyclohexyl)ethyl]-3,3- diphenyltrisiloxane, l,l,5,5-tetramethoxy-l,5-(3-glycidoxypropyl)-3,3-diphenyltri siloxane, l,5-dimethyl-l,5-dimethoxy- l,5-[2-(3,4-epoxycyclohexyl)ethyl]-3,3-diphenyltrisiloxane, l,5-dimethyl-l,5-dimethoxy-l,5-(3- glycidoxypropyl)-3,3-diphenyltrisiloxane to mention few examples.

An additive added to the composition (after polymerization of the siloxane material as noted above) can be a silane compound with formula of R ¹ is reactive group like hydroxyl, alkoxy or acetyloxy, R ² is alkyl or aryl group, R ³ is crosslinking compound like epoxy, oxetane, alkenyl, acrylate or alkynyl group, a = 0 to 1 and b = 0 to 1. Examples of such additives are tri-(3- glycidoxypropyl)phenylsilane, tri-[2-(3,4-epoxycyclohexyl)ethyl]phenylsilane, tri-(3- methacryloxypropyl)phenylsilane, tri-(3-acryloxypropyl)phenylsilane, tetra-(3-glycidoxypropyl)silane, tetra-[2-(3,4-epoxycyclohexyl)ethyl]silane, tetra-(3-methacryloxypropyl)silane, tetra-(3- acryloxypropyl)silane, tri-(3-glycidoxypropyl)p-tolylsilane, tri-[2-(3,4-epoxycyclohexyl)ethyl]p- tolylsilane, tri-(3-methacryloxypropyl)p-tolylsilane, tri-(3-acryloxypropyl)p-tolylsilane, tri-(3- glycidoxypropyl)hydroxylsilane, tri-[2-(3,4-epoxycyclohexyl)ethyl]hydroxylsilane, tri-(3- methacryloxypropyl)hydroxylsilane, tri-(3-acryloxypropyl)hydroxylsilane.

The additives can be also any organic or silicone polymers that may react or may not react with the main polymer matrix therefore acting as plasticizer, softener, or matrix modifier like silicone. The additive can be also an inorganic polycondensate such as SiOx, TiOx, AIOx, TaOx, HfOx, ZrOx, SnOx, polysilazane.

As mentioned above, the particulate material is selected for including in the siloxane material depending upon the desired characteristics of the pixel/voxel being deposited by the 3D printer (electrically conductive/electrically insulating, soft/hard, transparent/opaque/reflecting, with colors, etc. The particulate filler may be a conductive material, such as carbon black, graphite, graphene, gold, silver, copper, platinum, palladium, nickel, aluminum, silver plated copper, silver plated aluminum, bismuth, tin, bismuth-tin alloy, silver plated fiber, nickel plate copper, silver and nickel plated copper, gold plated copper, gold and nickel plated copper, or it may be gold, silver-gold, silver, nickel, tin, platinum, titanium plated polymer such as polyacrylate, polystyrene or silicone but not limited to these. The filler can be also a semiconductor material such as silicon, n or p type doped silicon, GaN, InGaN, GaAs, InP, SiC but not limited to these. Furthermore, the filler can be quantum dot or a surface plasmonic particle or phosphor particle. Other semiconductor particles or quantum dots, such as Ge, GaP, InAs, CdSe, ZnO, ZnSe, Ti02, ZnS, CdS, CdTe, etc. are also possible. The filler can be particles that are any suitable metal or semi-metal particles such as those selected from gold, silver, copper, platinum, palladium, indium, iron, nickel, aluminum, carbon, cobalt, strontium, zinc, molybdenum, titanium, tungsten, silver plated copper, silver plated aluminum, bismuth, tin, bismuth-tin alloy, silver plated fiber or alloys or combinations of these. Metal particles that are transition metal particles (whether early transition metals or late transition metals) are envisioned, as are semi metals and metalloids. Semi-metal or metalloid particles such as arsenic, antimony, tellurium, germanium, silicon, and bismuth are envisioned.

Or alternatively it may be an electrically nonconductive material, such as silica, quartz, alumina, aluminum nitride, aluminum nitride coated with silica, barium sulfate, alumina trihydrate, boron nitride, etc. The fillers can be the form of particles or flakes, and can be micro-sized or nano-sized. The filler may comprise ceramic compound particles that are nitrides, oxynitrides, carbides, and oxycarbides of metals or semimetals are possible. In particular, the filler can be particles that are ceramic particles that are an oxide of silicon, zinc, aluminum, yttrium, ytterbium, tungsten, titanium silicon, titanium, antimony, samarium, nickel, nickel cobalt, molybdenum, magnesium, manganese, lanthanide, iron, indium tin, copper, cobalt aluminum, chromium, cesium or calcium.

Also possible are particles that comprise carbon and are selected from carbon black, graphite, graphene, diamond, silicon carbonitride, titanium carbonitride, carbon nanobuds and carbon nanotubes. The particles of the filler can be carbide particles, such as iron carbide, silicon carbide, cobalt carbide, tungsten carbide, boron carbide, zirconium carbide, chromium carbide, titanium carbide, or molybdenum carbide. The particles could instead be nitride particles, such as aluminum nitride, tantalum nitride, boron nitride, titanium nitride, copper nitride, molybdenum nitride, tungsten nitride, iron nitride, silicon nitride, indium nitride, gallium nitride or carbon nitride.

Particles of any suitable size can be used, depending upon the final application. In many cases small particles having an average particle size of less than 100 microns, and preferably less than 50 or even 20 microns are used. Sub-micron particles, such as those less than 1 micron, or e.g. from 1 to 500 nm, such as less than 200nm, such as from 1 to 100 nm, or even less than 10 nm, are also envisioned. In other examples, particles are provided that have an average particle size of from 5 to 50 nm, or from 15 to 75nm, under 100 nm, or from 50 to 500nm. Particles that are not elongated, e.g.

substantial spherical or square, or flakes with a flattened disc shaped appearance (with smooth edges or rough edges) are possible, as are elongated whiskers, cylinders, wires and other elongated particles, such as those having an aspect ratio of 5:1 or more, or 10:1 or more. Very elongated particles, such as nanowires and nanotubes having a very high aspect ratio are also possible. High aspect ratios for nanowires or nanotubes can be at 25:1 or more, 50:1 or more, or even 100:1 or more. The average particle size for nanowires or nanotubes is in reference to the smallest dimension (width or diameter) as the length can be quite long, even up to centimeters long. As used herein, the term "average particle size" refers to the D50 value of the cumulative volume distribution curve at which 50% by volume of the particles have a diameter less than that value.

To enhance the coupling with filler and siloxane polymer, a coupling agent can be used. This coupling agent will increase the adhesion between filler and polymer and therefore can increase thermal and/or electrical conductivity of the final product. The coupling agent can be any silane monomer with a formula of R ¹³ _h R ¹⁴ |SiR ¹⁵ _j where R ¹³ is a reactive group like halogen, hydroxyl, alkoxy, acetyl or acetyloxy, R ¹⁴ is alkyl or aryl group and R ¹⁵ is a functional group including like epoxy, anhydride, cyano, oxetane, amine, thiol, allyl, alkenyl or alkynyl, h = 0 to 4, I = 0 to 4, j = 0 to 4 and h + i + j = 4. The coupling agent can be either mixed directly with filler, siloxane polymer, curing agent, and additives when final product is prepared or the filler particles can be treated by the coupling agent before they are mixed with particles.

If the particles are treated with coupling agent before using them in the final formulation, different methods like deposition from alcohol solution, deposition from aqueous solution, bulk deposition onto filler and anhydrous liquid phase deposition can be used. In the deposition from alcohol solution, alcohol / water solution is prepared and the solution pH is adjusted to slightly acidic (pH 4.5- 5.5). Silane is added to this solution and mixed for few minutes to allow partly hydrolyzing. Then filler particles are added and the solution is mixed from to RT to refluxing temperature for different time periods. After mixing, the particles are filtered, rinsed with ethanol and dried in an oven to obtain surface treated particles by the coupling agent. Deposition from aqueous solution is similar compared to deposition from alcohol solution but instead of alcohol, pure water is used as a solvent. pH is again adjusted by acid if non amine functionalized is used. After mixing particles with water/silane mixture, the particles are filtered, rinsed and dried.

Bulk deposition method is a method where silane coupling agent is mixed with solvent without any water or pH adjustment. The filler particles are coated with the silane alcohol solution using different methods like spray coating and then dried in an oven. In the anhydrous liquid phase deposition, silane are mixed with organic solvent like toluene, tetrahydrofuran or hydrocarbon and filler particles are refluxed in this solution and the extra solvent is removed by vacuum or filtering. The particles can be also dried afterwards in an oven but it is not sometimes need due to direct reaction between particles and filler under refluxing conditions.

Examples of such silane coupling agents are bis (2-hydroxyethyl)-3-aminopropyltriethoxysilane, Allyltrimethoxysilane, N-(2-Aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-Aminoethyl)-3- aminopropyltrimethoxysilane, 3-Aminopropylmethyldiethoxysilane. 3-Aminopropyltriethoxysilane, 3- Aminopropyltrimethoxysilane, (N-Trimethoxysilylpropyl)polyethyleneimine, Trimethoxysilylpropyl- diethylenetriamine, Phenyltriethoxysilane, Phenyltrimethoxysilane, 3-Chloropropyltrimethoxysilane, l-Trimethoxysilyl-2(p,m-chloromethyl)phenylethane, 2-(3,4-Epoxycyclohexyl)ethyltrimethoxysilane, 3-Glycidoxypropyltrimethoxysilane, Isocyanatepropyltriethoxysilane, Bis[3-(triethoxysilyl)propyl]- tetrasulfide, 3-Mercaptopropylmethyldimethoxysilane, 3-Mercaptopropyltrimethoxysilane, 3- Methacryloxypropyltrimethoxysilane, 2-(Diphenylphosphino)ethyltriethoxysilane, 1,3-Divinyl- tetramethyldisilazane, Hexamethyldisilazane, 3-(N-Styrylmethyl-2-aminoethylamino)propyl- trimethoxysilane, N-(Triethoxysilylpropyl)urea, 1,3-Divinyltetramethyldisilazane, Vinyltriethoxysilane and Vinyltrimethoxysilane to mention a few. Depending on the type of particles added, the siloxane-particle cured final product can be a layer or pattern that is thermally conductive, such as having a thermal conductivity, after final heat or UV curing, of greater than 0.5 watts per meter kelvin (W/(m-K)). Higher thermal conductivity materials are possible, depending upon the type of particles selected. Metal particles in the siloxane composition can result in a cured final film having a thermal conductivity greater than 2.0 W/(m-K), such as greater than 4.0 W/(m-K), or even greater than 10.0 W/(m-K). Depending upon the final application, much higher thermal conductivity may be desired, such as greater than 50.0 W/(m-K), or even greater than 100.0 W/(m-K). However in other applications, particles may be selected to result, if desired, in a material having low thermal conductivity. Also, if desired the final cured product can have low electrical resistivity, such as less than 1 x 10 ^"3

Ω-m, preferably less than 1 x 10 ^"5 Ω-m, and more preferably 1 x 10 ^"7 Ω-m. Also the sheet resistance of a deposited thin film is preferably less than 100000, more preferably less than 10000. However a number of desired final uses of the material may have high electrical resistivity. In some cases, particularly if the composition will be applied in a device that requires optical characteristics, though it may be desirable in some cases for the final cured siloxane to have optically absorbing properties, it is more likely that the material would desirably be highly transmissive to light in the visible spectrum (or in the spectrum in which the final device is operated), or would desirably be highly reflective to light in the visible spectrum (or in the spectrum in which the device is to be operated). As an example of a transparent material, the final cured layer or pattern in the 3D printed article having a thickness of from 1 to 50 microns will transmit at least 85% of the visible light incident perpendicularly thereto, or preferably transmit at least 90%., more preferably at least 92.5% and most preferably at least 95% As an example of a reflective layer, the final cured layer can reflect at least 85% of the light incident thereon, preferably reflect at least 95% of the light incident thereon at an angle of 90 degrees.

The material of the present invention may also contain a stabilizer and/or an antioxidant. These compounds are added to protect the material from degradation caused by reaction with oxygen induced by such things as heat, light, or residual catalyst from the raw materials.

Among the applicable stabilizers or antioxidants included herein are high molecular weight hindered phenols and multifunctional phenols such as sulfur and phosphorous-containing phenol. Hindered phenols are well known to those skilled in the art and may be characterized as phenolic compounds which also contain sterically bulky radicals in close proximity to the phenolic hydroxyl group thereof. In particular, tertiary butyl groups generally are substituted onto the benzene ring in at least one of the ortho positions relative to the phenolic hydroxyl group. The presence of these sterically bulky substituted radicals in the vicinity of the hydroxyl group serves to retard its stretching frequency, and correspondingly, its reactivity; this hindrance thus providing the phenolic compound with its stabilizing properties. Representative hindered phenols include; l,3,5-trimethyl-2,4,6-tris-(3,5-di-tert- butyl-4-hydroxybenzyl)-benzene; pentaerythrityl tetrakis-3(3,5-di-tert-butyl-4-hydroxyphenyl)- propionate; n-octadecyl-3(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate; 4,4'-methylenebis(2,6-tert- butyl-phenol); 4,4'-thiobis(6-tert-butyl-o-cresol); 2,6-di-tertbutylphenol; 6-(4-hydroxyphenoxy)-2,4- bis(n-octyl-thio)-l,3,5 triazine; di-n-octylthio)ethyl 3,5-di-tert-butyl-4-hydroxy-benzoate; and sorbitol hexa[3-(3,5-d i- tert-butyl-4-hydroxy-phenyl)-propionate]. Commercial examples of antioxidant are for example Irganox 1035, Irganox 1010, Irganox 1076, Irganox 1098, Irganox 3114, Irganox PS800, Irganox PS802, Irgafos 168 manufactured by BASF. The weight ratio between siloxane polymer and filler is between 100:0 to 5:95 depending of the final use of the product. The ratio between siloxane polymer and cross-linking silicon or non-silicon based resin or oligomer is between 100:0 to 75:25. The amount of curing agent calculated from siloxane polymer amount is from 0.1 to 20%. The amount of adhesion promoter based on total amount of formulation is from 0 to 10%. The amount of antioxidant based on total weight of the formulation is from 0 to 5%.

Depending upon the type of curing mechanism and catalyst activation the final formulation can be cured such as by heating the material to higher temperature. For example if thermal acid generator is used, the material is placed in oven for specific time period. Also possible is curing with

electromagnetic radiation, such as UV light, or both heat and UV light.

As deposited by the 3D printer, the molecular weight of the siloxane polymer formed from polymerization of the first and second compounds is from about 300 to 10,000 g/mol, preferably from about 400 to 5000 g/mol, and more preferably from about 500 to 2000 g/mo!. The polymer can be combined with particles of any desired size, preferably having an average particle size of less than 100 microns, more preferably less than 50 microns, or even less than 20 microns. The siloxane polymer is added at a weight percent of from 10 to 90%, and the particles are added at a weight percent of from 1 to 90%. If the final use of the siloxane material requires optical transparency, the particles may be ceramic particles added at a lower weight percent, such as from 1 to 20% by weight. If the siloxane material is to be used where electrical conductivity is desired, the particles may be metal particles added at from 60 to 95% by weight. Polymerization of the first and second compounds is performed, and the particles mixed therewith, to form a viscous fluid having a viscosity of from 50 to 100000 mPa-sec, preferably from 1000 to 75000 mPa-sec, and more preferably from 5000 to 50000 mPa-sec. The viscosity can be measured with a viscometer, such as a Brookfield or Cole-Parmer viscometer, which rotates a disc or cylinder in a fluid sample and measures the torque needed to overcome the viscous resistance to the induced movement. The rotation can be at any desired rate, such as from 1 to 30 rpm, preferably at 5 rpm, and preferably with the material being measured being at 25 °C. After polymerization, any additional desired components can be added to the composition, such as particles, coupling agents, curing agents, etc. The composition is shipped to customers as a viscous material in a container, which may be shipped at ambient temperature without the need for cooling or freezing. As a final product, the material can be applied via an additive 3D printer with the siloxane material being heat or UV cured with each deposited pixel (or volumetric pixel "voxel") to form a solid cured polymeric siloxane portion in the 3D article.

The composition as disclosed herein is preferably without any substantial solvent. A solvent may be temporarily added, such as to mix a curing agent or other additive with the polymerized viscous material. In such a case, the e.g. curing agent is mixed with a solvent to form a fluid material that can then be mixed with the viscous siloxane polymer. However, as a substantially solvent free composition is desired for shipping to customers, and later application on a customer's device, the solvent that has been temporarily added is removed in a drying chamber. There may however be trace amounts of solvent remaining that were not able to be removed during the drying process, though the composition is substantially free of solvent. This solvent removal aids in the deposition of the composition disclosed herein, by reducing shrinkage during the final curing process, as well as minimizing shrinkage over time during the lifetime of the device, as well as aiding thermal stability of the material during the lifetime of the device. Knowing the final application of the composition, the desired viscosity of the composition, and the particles to be included, it is possible to fine tune the siloxane polymer (starting compounds, molecular weight, viscosity, etc.) such that, upon incorporation into the composition having particles and other components, the desired final properties are achieved for subsequent delivery to the customer. Due to the stability of the composition, it is possible to ship the composition at ambient temperature without any substantial change in molecular weight or viscosity, even after a one week, or even one month, time period from making till final use by the customer.

EXAMPLES The following siloxane polymer examples are given by way of illustration and are not intended to be limitative. The (dynamic) viscosity of the siloxane polymer was measured by Brookfield viscometer (spindle 14). The molecular weight of the polymer was measured by Agilent GPC.

Siloxane polymer i: A 500 mL round bottom flask with stirring bar and reflux condenser was charged with diphenylsilanediol (60g, 45 mol%), 2-(3,4-Epoxycyclohexyl)ethyl]trimethoxysilane (55.67g,

36,7mol%) and tetramethoxysilane (17.20g, 18,3 mol%). The flask was heated to 80 °C under nitrogen atmosphere and 0.08g of barium hydroxide monohydrate dissolved in 1 mL of methanol was added dropwise to the mixture of silanes. The silane mixture was stirred at 80 °C for 30min during the diphenylsilanediol reacted with alkoxysilanes. After 30 min, formed methanol was evaporated off under vacuum. The siloxane polymer had viscosity of 1000 mPas and Mw of 1100.

Siloxane polymer ii: A 250 mL round bottom flask with stirring bar and reflux condenser was charged with diphenylsilanediol (30g, 45 mol%), 2-(3,4-Epoxycyclohexyl)ethyl]trimethoxysilane (28. lg, 37mol%) and dimethyldimethoxysilane (6,67g, 18 mol%). The flask was heated to 80 °C under nitrogen atmosphere and 0.035g of barium hydroxide monohydrate dissolved in 1 mL of methanol was added dropwise to the mixture of silanes. The silane mixture was stirred at 80 °C for 30min during the diphenylsilanediol reacted with alkoxysilanes. After 30 min, formed methanol was evaporated under vacuum. The siloxane polymer had viscosity of 2750 mPas and Mw of 896. Siloxane polymer iii: A 250 mL round bottom flask with stirring bar and reflux condenser was charged with diphenylsilanediol (24,5g, 50 mol%), 2-(3,4-Epoxycyclohexyl)ethyl]trimethoxysilane (18,64g, 33,4mol%) and tetramethoxysilane (5,75g, 16,7 mol%). The flask was heated to 80 °C under nitrogen atmosphere and 0.026g of barium hydroxide monohydrate dissolved in 1 mL of methanol was added dropwise to the mixture of silanes. The silane mixture was stirred at 80 °C for 30min during the diphenylsilanediol reacted with alkoxysilanes. After 30 min, formed methanol was evaporated under vacuum. The siloxane polymer had viscosity of 7313 mPas and Mw of 1328.

Siloxane polymer iv: A 250 mL round bottom flask with stirring bar and reflux condenser was charged with diphenylsilanediol (15g, 50 mol%), 2-(3,4-Epoxycyclohexyl)ethyl]trimethoxysilane (13,29g, 38,9mol%) and bis(trimethoxysilyl)ethane (4,17g, 11,1 mol%). The flask was heated to 80 °C under nitrogen atmosphere and 0.0175g of barium hydroxide monohydrate dissolved in 1 mL of methanol was added dropwise to the mixture of silanes. The silane mixture was stirred at 80 °C for 30min during the diphenylsilanediol reacted with alkoxysilanes. After 30 min, formed methanol was evaporated under vacuum. The siloxane polymer had viscosity of 1788 mPas and Mw of 1590.

Siloxane polymer v: A 250 mL round bottom flask with stirring bar and reflux condenser was charged with diphenylsilanediol (15g, 45 mol%), 2-(3,4-Epoxycyclohexyl)ethyl]trimethoxysilane (13,29g,

35mol%) and vinyltrimethoxysilane (4,57g, 20 mol%). The flask was heated to 80 °C under nitrogen atmosphere and 0.018g of barium hydroxide monohydrate dissolved in 1 mL of methanol was added dropwise to the mixture of silanes. The silane mixture was stirred at 80 °C for 30min during the diphenylsilanediol reacted with alkoxysilanes. After 30 min, formed methanol was evaporated off under vacuum. The siloxane polymer had viscosity of 1087 mPas and Mw of 1004.

Siloxane polymer vi: A 250 mL round bottom flask with stirring bar and reflux condenser was charged with di-isopropylsilanediol (20.05g, 55.55 mol%), 2-(3,4-Epoxycyclohexyl)ethyl]trimethoxysilane (20.0g, 33.33mol%) and bis(trimethoxysilyl)ethane (7.3g, 11,11 mol%). The flask was heated to 80 °C under nitrogen atmosphere and 0.025g of barium hydroxide monohydrate dissolved in 1 mL of methanol was added dropwise to the mixture of silanes. The silane mixture was stirred at 80 °C for 30min during the diphenylsilanediol reacted with alkoxysilanes. After 30 min, formed methanol was evaporated off under vacuum. The siloxane polymer had viscosity of 150 mPas and Mw of 781. Siloxane polymer vii: A 250 mL round bottom flask with stirring bar and reflux condenser was charged with di-isobutylsilanediol (18.6g, 60 mol%) and 2-(3,4-Epoxycyclohexyl)ethyl]- trimethoxysilane (17.32g, 40mol%). The flask was heated to 80 °C under nitrogen atmosphere and 0.019g of barium hydroxide monohydrate dissolved in 1 mL of methanol was added dropwise to the mixture of silanes. The silane mixture was stirred at 80 °C for 30min during the diphenylsilanediol reacted with alkoxysilanes. After 30 min, formed methanol was evaporated off under vacuum. The siloxane polymer had viscosity of 75 mPas and Mw of 710.

COMPOSITION EXAMPLES The following composition examples are given by way of illustration and are not intended to be limitative. Comp. example 1, Silver filled adhesive: A siloxane polymer with epoxy as a crosslinking functional group (18.3g, 18.3%), silver flake with average size (D50) of 4 micrometer (81g, 81%), 3- methacrylatepropyltrimethoxysilane (0.5g, 0.5%) and King Industries K-PURE CXC - 1612 thermal acid generator (0.2%) where mixed together using high shear mixer. The composition has a viscosity of 15000 mPas.

Comp. example 2, Alumina filled adhesive: A siloxane polymer with epoxy as a crosslinking functional group (44.55, 44.45%), aluminium oxide with average size (D50) of 0.9 micrometer (53g, 53%), 3- methacrylatepropyltrimethoxysilane (lg, 1%), Irganox 1173 (lg, 1%) and King Industries K-PURE CXC - 1612 thermal acid generator (0.45g, 0.45%) where mixed together using three roll mill. The composition has a viscosity of 20000 mPas.

Comp. example 3, BN filled adhesive: A siloxane polymer with epoxy as a crosslinking functional group (60g, 60%), boron nitride platelet with average size (D50) of 15 micrometer (35g, 35%), Irganox 1173 (1.3g, 1.3%), 2-(3,4-Epoxycyclohexyl)ethyltrimethoxysilane (3.4g, 3.4%) and King Industries K- PURE CXC - 1612 thermal acid generator (0,3g, 0.3%) where mixed together using three roll mill. The composition has a viscosity of 25000 mPas.

Comp. example 4, Translucent material: A siloxane polymer with methacrylate as a functional group (89g, 89%), fumed silica with average size (D50) of 0.007 micrometer (5g, 5%), Irganox 1173 (2g, 2%) and Irgacure 917 photoinitiator (4g, 4%) where mixed together using three roll mill. The composition has a viscosity of 25000 mPas.

In view of the disclosed methods and materials, a stable composition is formed. The composition may have one part that is a siloxane polymer having a [-Si-0-Si-0] _n repeating backbone, with alkyl or aryl groups thereon, and functional cross-linking groups thereon, and another part that is particles mixed with the siloxane material, wherein the particles have an average particle size of less than 100 microns, the particles being any suitable particles such as metal, semi-metal, semiconductor or ceramic particles. The composition as shipped to customers may have a molecular weight of from 300 to 10,000 g/mol, and a viscosity of from 1000 to 75000 mPa-sec at 5 rpm viscometer.

The viscous (or liquid) siloxane polymer is substantially free of -OH groups, thus providing increased shelf-life, and allowing for storing or shipping at ambient temperature if desired. Preferably, the siloxane material has no -OH peak detectable from FTIR analysis thereof. The increased stability of the formed siloxane material allows for storage prior to use where there is a minimal increase in viscosity (cross-linking) during storage, such as less than 25% over the period of 2 weeks, preferably less than 15%, and more preferably less than 10% over a 2 week period stored at room temperature. And, the storage, shipping and later application by the customer can be all performed in the absence of a solvent (except for possible trace residues that remain after drying to remove the solvent), avoiding the problems of solvent capture in the layer later formed in the final product, shrinkage during polymerization, mass loss over time during device usage, etc. No substantial cross-linking occurs during shipping and storage, without the application of heat preferably greater than lOOC or UV light.

When the composition is deposited and polymerized, e.g. by the application of heat or UV light, very small shrinkage or reduction in mass is observed. In Fig. 6, the x-axis is time (in minutes), the left y axis is the mass of the layer in terms of % of the starting mass, and the right y-axis is temperature in Celsius. As can be seen in Fig 6, a siloxane particle mixture as disclosed herein is heated rapidly to

150C, then held at 150C for approximately 30 minutes. In this example, the siloxane particle has a Si- O backbone with phenyl group and epoxy groups, and the particles are silver particles. The mass loss is less than 1% after heat curing for over this time period. Desirably the mass loss is typically less than 4%, and generally less than 2% - however in many cases the difference in mass of the siloxane particle composition between before and after curing is less than 1%. The curing temperature is generally at less than 175 °C, though higher curing temperatures are possible. Typically the curing temperature will be at 160 °C or below, more typically at 150 °C or below. However lower curing temperatures are possible, such as at 125 °C or below. Regardless of whether the 3D printed material is deposited as an electrically insulating layer, an electrically conductive layer, as a thermally conductive layer, a transparent layer, a light reflecting layer, opaque or colored layer etc., once the composition is deposited and polymerized and hardened as desired, the siloxane particle layer or pattern is thermally very stable. As an example, heating the in situ material after hardening by heat or UV polymerization up to 600 °C at a ramp rate of 10 °C increase per minute, a mass loss of less than 4.0%, preferably less than 2.0%, e.g. less than 1.0% is observed at both 200 °C and 300 °C (typically a mass loss of less than 0.5% is observed at 200 °C, or a mass loss of less than 0.2% at 200 °C is observed). At 300 °C, a mass loss of less than 1% is observed, or more particularly less than 0.6%. Similar results can be observed by simply heating the polymerized material for 1 hour at 200 °C, or at 300 °C. Results of less than 1% mass loss by heating the polymerized deposited material at 375C or more for at least 1 hour are possible. Even at temperatures of greater than 500 °C, a mass loss of 5% or less is observed. Such a thermally stable material is desirable, particularly one as disclosed herein that can be deposited at low temperatures (e.g. less than 175 °C, preferably less than 150 °C, or less than 130 °C at e.g. 30 min curing / baking time), or that can be polymerized by UV light.

As can be seen from the above, various 3D articles can be printed with siloxane materials.

Transparent articles, or portions or articles, with or without particles therein, reflective articles, and opaque articles are possible. In addition, electrically insulating and electrically conducting articles, or portions or articles, can be printed. A mixture of transparent materials, e.g. with different refractive indices, or a mixture of reflective and transparent materials, can be used for 3D printing an article. Colors can also be added to the siloxane materials being printed. It is possible to print continuously, or pixel by pixel (voxel by voxel). It is also possible to first print entirely one siloxane material (e.g one color, or e.g. electrically insulating) followed by entirely another color or e.g. electrically conductive. It is also possible to print layer by layer, where first all of a first color (or electrically insulating) is printed in a layer, followed by all of a second color (or electrically conductive) is printed in that layer. For faster printing, it is desirable to have multiple print heads such that the different materials (different colors, different refractive indices, different conductivities, etc.) are printed at the same time, or immediately sequentially such that when the reciprocating or rotary platform of the 3D printing machine need not repeat movement over the same area.

The foregoing is illustrative of example embodiments and is not to be construed as limiting thereof. Although a few example embodiments have been described, those skilled in the art will readily appreciate that many modifications are possible in example embodiments without materially departing from the novel teachings and advantages. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. Therefore, it is to be understood that the foregoing is illustrative of various example embodiments and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims.

The following embodiments can be particularly mentioned. 1. A three dimensional printing process comprising,

concurrently or sequentially depositing electrically conductive and electrically insulating materials so as to form a 3D printed article;

wherein both the electrically conductive and electrically insulating materials comprise a siloxane polymer that is cured upon deposition by electromagnetic radiation or heat.

2. The process of embodiment 1, wherein the electrically conductive siloxane polymer is cured by heat and the electrically insulating siloxane polymer is cured by UV light. 3. The process of embodiment 1 or 2, wherein the electrically conductive siloxane polymer comprises particles, such as metal particles.

4. The process of any of the preceding embodiments, wherein the electrically insulating siloxane polymer comprises particles, selected from nitride or oxide particles.

5. The process of any of the preceding embodiments, wherein the particles in the electrically insulating siloxane comprise silica, quartz, alumina, aluminum nitride, aluminum nitride coated with silica, barium sulfate, alumina trihydrate, or boron nitride or the particles in the electrically insulating siloxane are nitride particles and comprise aluminum nitride, tantalum nitride, boron nitride, titanium nitride, copper nitride, molybdenum nitride, tungsten nitride, iron nitride, silicon nitride, indium nitride, gallium nitride or carbon nitride.

6. The process of any of the preceding embodiments, wherein the particles in the electrically conductive siloxane comprise gold, silver, copper, platinum, palladium, indium, iron, nickel, aluminum, carbon, cobalt, strontium, zinc, molybdenum, titanium, tungsten, silver plated copper, silver plated aluminum, bismuth, tin, or alloys or combinations thereof.

7. The process of any of the preceding embodiments, wherein a first group and second group of particles are provided within the electrically conductive siloxane, wherein the first group is different from the second group based on average particle size, shape, and/or composition, the first group of particles having an average particle size of greater than 500nm, and the second group of particles having an average particle size of less than 200nm. 8. The process of any of the preceding embodiments, wherein the electrically insulating siloxane comprises first and second groups of particles, where the first group is different from the second group based on average particle size, shape and/or composition. 9. An article formed by the process of any of embodiments 1 to 8.

10. A 3D printed article, comprising:

a first portion that is electrically insulating and comprises a siloxane polymeric material; a second portion that is electrically conductive and comprises a siloxane polymeric material.

11. The article of embodiment 10, wherein the second portion comprises metal particles and the first portion comprises ceramic particles.

12. The article of embodiments 10 or 11, wherein the electrically insulating first portion is a light transmissive portion that transmits at least 85% of visible light incident thereon.

13. A 3D printed article comprising a cured siloxane material having therein a first group of particles and a second group of particles, wherein the first group is different from the second group based on average particle size, shape or particle material.

14. A 3D printed article comprising:

- a first portion that transmits at least 85% of visible light incident thereon;

- a second portion that transmits at least 85% of visible light incident thereon;

wherein the first portion and the second portion have different refractive indices.

15. The article of embodiment 14, wherein the first portion and second portion are directly contacting each other.

16. A 3D printed article comprising:

- a first portion that is light transmissive and transmits at least 85% of visible light incident thereon, and wherein the first portion has an index of refraction less than 1.4 at 632.8nm wavelength and has an optical birefringence less than 0.01. 17. The article of embodiment 16, wherein the refractive index is less than 1.3 and wherein the first portion comprises particles, for example particles of an average particle size of less than 400nm, such as less than lOOnm. 18. A 3D printed article comprising:

a light transmissive portion that transmits at least 85% of visible light incident thereon, and wherein the portion has an index of refraction greater than 1.55 at 632.8nm wavelength and has an optical birefringence less than 0.01, for example wherein the index of refraction is 1.65 or higher, such as 1.70 to 1.95.

INDUSTRIAL APPLICABILITY

The present methods can include printing both electrically insulating and electrically conducting portions, transparent, reflective or opaque portions, transparent portions having different refractive indices, portions of different colors, and where the various deposited portions are UV or heat curable, and optionally comprise particles, such as metallic particles in electrically conductive portions and ceramic particles in electrically insulating portions. A variety of 3D articles can be made, such as transparent articles such as eyeglasses, or electronics articles such as portions of smartphones, tablets or the like.

CITATION LIST

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