BACKGROUND OF THE INVENTION Latent curing agents are solid low molecular weight chemicals that are dispersed in monomers, oligomers and polymers or mixtures thereof. Those chemicals are practically inactive at ambient temperature and become active at elevated temperatures (i. e., when heated above threshold temperature).

When activated, the dispersed solid particles of latent curing agent melt, dissolves in the thermoset resin matrix and react or initiate polymerization with polymers to form a cross- linked polymeric network.

A thermoset polymer is a polymer that does not melt when heated. A cured thermoset polymer has a three dimensions network, which is usually covalent. The typical latent curing agents in thermosets, especially in epoxy systems, are solid fine powders that are dissolved in the epoxy matrix only above critical temperatures.

Epoxy based thermosets are cost effective matrices known for their low viscosity, excellent chemical and thermal properties, cost effectiveness, excellent adhesion to metals, ceramics and plastics, ease of application, low toxicity, wide spectrum of resins, diluents, modifiers and curing agents. Typical epoxy resin in electronic manufacturing are selected from bisphenol S epoxy resins, diglycidyl terephthalate resin, heterocyclic epoxy resins, bixylenol epoxy resins, biphenol epoxy resins, tetraglycidyl xylenoyl ethane resins, bisphenol A epoxy resins, hydrogenated bisphenol A epoxy resins, bisphenol F epoxy resins, brominated bisphenol A epoxy resins, Novolak epoxy resins, Novolak epoxy resins of bisphenol A, chelate epoxy resins, glyoxal epoxy resins, amino group-containing epoxy resins, rubber-modified epoxy resins, dicyclopentadiene phenolic epoxy resins, silicone-modified epoxy resins, heterocyclic ring containing polyepoxide such as tris (2,3-epoxy propyl) isocyanurate and epsilon-caprolactone-modified epoxy resins or a mixture thereof Epoxy and derivatives or combinations thereof are a major building block in the printed circuit board industry: boards and laminates, legend marking inks, solder masks and hole plugging pastes. The most common latent curing agent for epoxy resins are urea derivatives, imidazoles, modified amines, and dicyandiamide hereinafter denoted in the term'DICY', which is a commercially available ingredient in high-end electronic applications, such as adhesives, PCBs manufacturing, solder masks and hole plugging inks. DICY is characterized by a significant latency (pot life) and outstanding final properties of the cured matrix. It is activated at temperatures in the range of 160 °C to 180 °C without a catalyst and in the range of 120 °C to 150 °C with catalyst. Imidazoles and derivatives thereof are the common catalyst for DICY or used as curing agents by themselves. The catalyst usually has negative impact on a pot life of the mixed formula.

Ink jet technology enables a very precise digital printing and provides for relatively small dots of liquid e. g. , monomers, polymer solution or molten polymer material. Digital printing of high performance polymers adapted for marking, protection, coating, encapsulation and definition in electronic manufacturing has become a reality in recent years. The aforementioned ink is characterized by a low viscosity, usually less than 15 Cp, at shear rate of 0.1 to 100,000 1/s at jetting temperature. If viscosity changes during storage or operation by more than 2 to 5 Cps, the jetting quality is severely deteriorate (satellites). The ink has surface tension of 25 to 40 dyne/cm and is usually cured by drying or UV lamp that is mounted adjacent to printing head.. When UV curable thermoset resin is used, their viscosity is kept almost unchanged for long period of time, a critical issue for ink jet applications. Most of ink-jet applications in electronic manufacturing are thus UV curable acrylates due to their low viscosity and long pot life.

The major drawback of acrylate-based inks is their inferior adhesion, inferior thermal resistance and inferior chemical resistance-especially when exposed to aggressive media at elevated temperatures. In the other hand, epoxy based inks are not available for ink jet applications since only latent curing agents enable pot life long enough to remain "constant"for periods of 4 to 30 days at ambient temperature, and even the finest particle size latent curing agents are too big for ink jet usage (the finest commercially available DICY powders are characterized by an average particle size of 4 to 6 micron), thus their use in ink-jet application is limited. When solid particles are used, e. g. , pigments, fillers, catalyst, latent curing agent, their maximal size need to be small enough so it is not because clogging of ink jet head nozzles or disrupt the drop formation. For most ink jet heads, the maximal particle size need to be less than about 5 micron, more preferred less than about 1 e. A finer version of latent curing agents and catalyst, characterized for example by maximal particle size of less than 5 micron, and more preferably by size less than 1 micron, is hence a critical component for high performance digital printing ink-jet inks and its commercial availability is a long felt need.

BRIEF DESCRIPTION OF THE INVENTION In order to understand the invention and to see how it may be implemented in practice, a plurality of embodiments shall now be described, in a non-limiting manner only, with reference to the accompanying drawings, in which figure 1 schematically illustrates a top view of a portion of the reactive fine particle according to one embodiment of the present invention; figure 2 schematically illustrates a lateral cross section of a portion of the reactive fine particle according to said embodiment of the present invention ; figure 3 schematically illustrates a lateral cross section of a portion of the reactive fine particle according to yet another embodiment of the present invention, wherein a multi-laminar heterogamous coating is provided; figure 4 schematically illustrates a lateral cross section of a portion of the reactive fine particle according to another embodiment of the present invention wherein the reactive particles are located in the inner and the outer portion of the inert particle; and figure 5 schematically illustrates a lateral cross section of a reactive fine particle according to another embodiment of the present invention, wherein at step A is comprises a physical support of the inert particle, and at the subsequent step B is comprises only the reactive particles.

SUMMARY OF THE INVENTION It is thus the object of the present invention to provide a novel and cost effective A reactive fine particle comprising one or more functional compounds A, selected from latent curing agents, accelerators for epoxy resins, mixtures or precursors thereof, having a maximal size of less than 5 microns; adapted for curing, cross-linking, or initiating of polymerization of active group containing polymers; and one or more inert particles B having a least the maximal size of about 5 microns carrying said functional compounds A at the outer surface and/or in its inner portion; wherein said compounds A to inert particles B weight ratio is ranging from about 0.01/100 to about 3/1.

It is in the scope of the present invention wherein the one or more of the functional compounds A is selected from a group comprising modified amines, urea derivatives, imidazoles, dicyandiamide, its derivatives or any mixture thereof.

It is also in the scope of the present invention wherein at least a portion of the epoxy comprising polymers selected from a group comprising aromatic, heterocyclic, cycloaliphatic ring and at least two oxirane (epoxy) groups, commercially available bisphenol A based novolac products, bisphenol S epoxy resins, diglycidyl terephthalate resin, heterocyclic epoxy resins, bixylenol epoxy resins, biphenol epoxy resins, tetraglycidyl xylenoyl ethane resins, bisphenol A epoxy resins, hydrogenated bisphenol A epoxy resins, bisphenol F epoxy resins, brominated bisphenol A epoxy resins, Novolak epoxy resins, Novolak epoxy resins of bisphenol A, chelate epoxy resins, glyoxal epoxy resins, amino group-containing epoxy resins, rubber-modified epoxy resins, dicyclopentadiene phenolic epoxy resins, silicone-modified epoxy resins, heterocyclic ring containing polyepoxide, tris (2,3-epoxy propyl) isocyanurate and epsilon- caprolactone-modified epoxy resins or any mixture thereof.

It is also in the scope of the present invention wherein liquid thermosetting compound is provided. This compound is comprised of one or more functional compounds A, selected from latent curing agents for polymers comprising at lest one epoxy group, accelerators for epoxy resins, mixtures or precursors thereof, having a maximal size of less than about 5 microns; adapted for curing, cross-linking or initiating of polymerization of active group containing polymers; and one or more inert particles B having a least the maximal size of about 5 microns carrying said functional compounds A at the outer surface and/or in its inner portion. Said compounds A to inert particles B weight ratio is ranging from about 0.01/100 to about 3/1. At least a portion of the polymers comprising at least one epoxy group are selected from a group comprising aromatic, heterocyclic, cycloaliphatic ring and at least two oxirane (epoxy) groups, commercially available bisphenol A based novolac products, bisphenol S epoxy resins, diglycidyl terephthalate resin, heterocyclic epoxy resins, bixylenol epoxy resins, biphenol epoxy resins, tetraglycidyl xylenoyl ethane resins, bisphenol A epoxy resins, hydrogenated bisphenol A epoxy resins, bisphenol F epoxy resins, brominated bisphenol A epoxy resins, Novolak epoxy resins, Novolak epoxy resins of bisphenol A, chelate epoxy resins, glyoxal epoxy resins, amino group-containing epoxy resins, rubber-modified epoxy resins, dicyclopentadiene phenolic epoxy resins, silicone-modified epoxy resins, heterocyclic ring containing polyepoxide, tris (2,3-epoxy propyl) isocyanurate and epsilon-caprolactone-modified epoxy resins or any mixture thereof. Such a liquid thermosetting compound comprising an ink and ink jet ink is also provided useful.

It is also in the scope of the present invention wherein one or more of the inert particles is selected from BaS04, CaS04, Talk, kaolin, mica, carbon black and synthetic silica, silica, quartz, calcium carbonate, dolomite, glass or any combination thereof.

It is also in the scope of the present invention to provide a reactive fine particle, which is adapted for curing thermoset polymers; wherein at least a portion of the functional compounds are curing agents, or curing catalyst.

It is also in the scope of the present invention wherein the reactive fine particle as defined in any of the above is adapted for curing thermoset polymers, especially wherein at least a portion of the functional compounds are latent curing agents or catalysts adapted to initiate cross linking and/or polymerization of said thermoset polymers when heated to a temperature higher than a threshold temperature.

It is also in the scope of the present invention wherein a liquid thermosetting compound is provided. This compound is especially adapted to be cured by the curing agents and/or catalyst as defined above, comprising reactive fine particles A, inert particles B and compounds selected from thermosetting resins, oligomers, monomers, thermoplastic resins, fillers, fibers, whiskers, flakes, spheres, nano-particles, wetting agents, reactive diluents, photoinitiators, impact modifiers, flexibilizers, heat stabilizers, elastomers, surface tension modifiers, adhesion promoter, flame retardants, matting agents, rheology modifiers, dispersants or any combination thereof.

The liquid thermosetting compound is additionally or alternatively adapted for applications in microelectronic devices manufacturing selected from dielectrics, resistors, optical waveguides, conductive modules, capacitance layers, adhesives, protective coatings, solder resists, marking inks, hole plugging inks, encapsulants or any combination thereof. the liquid thermosetting is preferably adapted to protect, mark, seal, encapsulate, define, and/or insulate electronic circuits from their environment and/or form aggressive media.

It is further in the scope of the present invention wherein the liquid thermosetting compound defined above is adapted to be applied as ink jet inks by ink jet printers ; characterized by a viscosity lower 50 Cp at shear rate of 0. 1 to 100,000 1/s at application temperature, surface tension lower than 50 dyne/cm at application temperature, being thermally cured at 100 to 170 °C for period ranging from 10 min to 2 hr, and glass transition temperature of cured ink of greater than 80 °C.

It is also in the scope of the present invention wherein the liquid thermosetting compound defined above is adapted to protect, mark, seal, encapsulate, define and/or insulate electronic circuits from their environment and/or form aggressive media. More specifically, this liquid thermosetting compound is adapted to bond electronic, electric, optic and/or electro optic devices; to mark and notate features on the outer layers of PCB and/or the surface of discrete compounds; to define the feature of capacitors, resistors and/or conductors on a PCB layer.

It is also in the scope of the present invention wherein the liquid thermosetting compound defined above is adapted to be applied by ink jet to bond electronic, electric, optic and/or electro optic devices.

It is also in the scope of the present invention wherein the liquid thermosetting compound defined above is adapted to be applied by ink jet to mark and notate features on the outer layers of PCB and/or the surface of discrete compounds.

It is also in the scope of the present invention wherein the liquid thermosetting compound defined above is adapted to be applied by ink jet to define the feature of capacitors, resistors and/or conductors on a PCB layer.

It is also in the scope of the present invention wherein the liquid thermosetting compound defined above is adapted to be applied by ink jet as solder resist or solder mask onto outer layer of printed circuit board or printed wired board to protect from environment the define pads.

It is still another object of the present invention to provide a useful method for producing reactive fine particles as defined in any of the above, comprising inter alia the steps of : dissolving one or more functional compounds A or its precursors in a solvent to form a clear solution; admixing one or more kind of inert particles B with the solution obtained above to form a homogenized dispersion such that weight ratio between compounds A to inert particles B weight is ranging from about 0.01/100 to about 3/1; evaporating said solvent and precipitating said functional compounds as a layer or in the form of small crystals onto and/or into the surface of said inert particles B; and, milling said particles in a solvent or in a polymeric resin or in the final ink composition until all particles have maximal diameter of less than 5 micron; in the manner that reactive fine particles comprising said compounds A and inert particles B in a weight ratio which is ranging from about 0. 01A : 100B to about 3A: 1B is obtained.

It is also in the scope of the present invention wherein the deposition of the functional compounds A onto the inert particles B is provided by means selected from introducing of at least one another solvent to the said admixture ; changing the temperature; pH shifting ; altering electrolytes concentration, spraying agent solution on filler particles, precipitating A by reacting one or more precursors to form A on surface of B, applying catalyst on surface of that initiate or catalyze formation or deposition of A, or any combination thereof.

It is also in the scope of the present invention wherein the previously mentioned method additionally comprising the step of stabilizing the obtained slurry by means of admixing a sufficient measure of dispersing agents and/or rheology modifiers.

It is still another object of the present invention to provide a useful method for producing reactive fine particles, wherein the inert particles B are coated in at least a significant portion of their surface with functional compounds A; said method comprising inter alia the steps of admixing at least one functional compound or its precursors in a solvent to form a clear solution; spraying the same towards particles of the inert filler, having potentially maximal particle size of about 5 microns after milling; and, milling said particles in a solvent or in a polymeric resin or in the final ink composition until all particles have maximal diameter of less than about 5 micron.

In order to create an ink that can be applied by ink jet, further steps are taken : milling with monomers, polymers, pigments, epoxy resins, solvents, photo initiators, adhesion promoters, rheology modifiers, dispersing agents, wetting agents, filler, heat stabilizers, corrosion inhibitors, by media mill, rotor stator homogenizer or atttritor to an ink having particles lower than 2 microns, as indicated by filterability through filter of 2 micron pore size.

It is also in the scope of the present invention wherein the reactive fine particles obtained by those methods are characterized by monolayer or multilayers of functional compounds.

DETAILED DESCRIPTION OF THE INVENTION The following description is provided, alongside all chapters of the present invention, so as to enable any person skilled in the art to make use of said invention and sets forth the best modes contemplated by the inventor of carrying out this invention. Various modifications, however, will remain apparent to those skilled in the art, since the generic principles of the present invention have been defined specifically to provide sub micron reactive particles, a method for their production and any use or end product comprising said novel particles or said method.

The term'fine particle'is referring according to the preset invention to any small particle; compound, matrix or a composition encapsulated, burriered, crystallized or packed in a predetermined three dimensional (3D) envelop characterized by a maximal external diameter lower than about 5 micrometer. More specifically, the powder should have maximal aggregate (conglomerate) size of about 700 nm. The term'about'refers hereinafter to i 25% of the defined value. More specifically, the term refers to i 5% of the defined value.

The term'reactive fine particle'is referring according to the preset invention to fine particle, either prime particle or aggregate or agglomerate as defined above, comprising at least one type of inert particle (hereinafter'B') and at least type of functional component (hereinafter'A'), wherein the maximal size of said particle is less than about 5 micrometer). Component A is in physical and/or chemical connection with said inert particle B. It is further in the scope of the present invention wherein said reactive fine particle is comprised of various types of functional components (As) and inert particles (Bs), differ by their size, 3D structure, surface activity, reactivity, latency property, chemical composition, specific area or any other physical, chemical or biological properties. It is further in the scope of the present invention wherein said functional components (As) are only temporary comprised of at least a portion of the inert particles (Bs), in the manner the content of the said inert particles in the end product is significantly lower than its content at the beginning of the production process. It is still in the scope of the present invention wherein the nature of the said portion of inert particles is differing, altering or changing along the said production process.

According to the present invention, the term'polymer'is refereeing hereinafter to any monomer, oligomer or polymer, their mixture, or to any combination thereof. Moreover, this term is also referring to block polymers, co-polymers and to all product and by- products of polymerization reactions.

According to one embodiment of the present invention, the aforementioned fine particles are comprised of at least one inert particle B that is either inorganic material, e. g., comprising in anon limiting manner mineral metal oxides, mineral natural fillers, synthetic metal oxides, ceramics, metallic compositions, glass or sol-gel matrices, chemical element or any mixture thereof, or organic material, such as cellulose, natural polymer, synthetic polymer or any mixture thereof. The said fine powder B is characterized by a specific surface area ranges from about 1 to about 300 m2/g.

According to yet another embodiment of the present invention, said powder is characterized by a specific surface area ranges from about 10 to about 50 m2/g.

The said fine particles may further comprised of at least one latent reactive composition A, e. g. , a solid latent curing agent and/or catalyst) which is dissolved in the solution in a, and then mixed with the powder of inert particles B, weight ratio ranging from about 0.01/100 to about 3/1 A to B. According to yet another embodiment of the present invention, the said ratio is ranging form about 5 Ato about 100 B; to about 1A to 1B. It is acknowledged in this respect that additives of any type are potentially comprised in the said particle. Hence, presence of commercially available dispersing agents and rheology controlling agents is recommended to avoid agglomeration during concentration and storage.

The carrier inert particle B is selected in a non-limiting manner form one or more of the following criteria: having a specific surface area between about 1 to about 300 m2/gr, wherein the most favorable powder is the one characterized by a specific surface area ranging between about 10 and about 50 m2/gr ; since it is non-abrasive, and hence avoid damage to application tooling, especially to an ink-jet print head. Moreover, the carrier is preferably non-corrosive; it has a good thermal stability and chemical resistance; it is not reacting with the reactive particle and with the monomers, oligomers, polymers, solvents and/or additives in the ink. The inert particle B is further of sub-micron prime particle size, most favorably between about 0.03 to about 0.5 micron mean diameter; the maximal agglomerate size after milling of said reactive submicron compound (A onto B) in atttritor, media mill or similar machine is about 2 micron or less, it has a good compatibility with the monomers, oligomers, polymers, solvents and additives in the ink.

Typical powders that meet these criteria are sulfates, e. g., BaS04 or CaS04, carbonates such as CaCO3, talc, kaolin, mica, silicates, carbon black and synthetic silica.

The carrier medium is optimized for effectively dissolving the functional component A and is selected in a non-limiting manner form one or more of the following criteria: it is not toxic or is characterized by a very low toxicity; it is cost effective since it is at least partially re-usable and/or recyclable; it is a good solvent for the reactive latent curing agent and/or catalyst; it has a low boiling point and a low specific heat of evaporation; and further, it is practically non reactive with either the inert or the reactive particles.

Reference is made now to figure 1, presenting a simplified top view reactive fine particles according to the present invention, wherein an relatively large inert particle B (1) is coated by a plurality of functional component A (see 2 for example). Said functional component (2) was crystallized on top the inert particle (1) and is characterized by a specific, defined and relative crystal 3D structure.

Reference is made now to figure 2, presenting a lateral cross-section of one portion of homogeneously coated reactive fine particle (20). Said portion comprising a central inert particle (1) and a plurality of functional components (see 2 for example). Said functional components may by either homogenous or heterogeneous nature, morphology or size, and may be set as an individual crystalline (portion a) or may be attached physically or chemically one to the others so a thin coating is provided (portion b).

Reference is made now to figure 3, presenting a lateral cross-section of one portion of heterogeneously coated reactive fine particle (30). Said portion comprising a central inert particle (1) and a plurality of functional components of type 2A (first and internal coating layer), type 2B (second coating layer) and type 2C (third and external coating layer). It is in the scope of the present invention wherein such a heterogeneous system is arranged as a plurality of layers in the manner at least one layer is homogeneous; a conglomerate comprising two or more types of reactive particles or any combination or mixture thereof.

Here, the three coating layer perform a contentious multi-component layer. Nevertheless, a porosive or other discontinuous layered or embedded structures are easily to be tailor made according to the description of the present invention.

Reference is made now to figure 4, presenting a lateral cross-section of one portion of homogeneously embedded reactive fine particle (40). Said portion comprising a central inert particle (1) and a plurality of functional components, some are entrapped, immobilized, encapsulated, soaked, doped or bonded into the inner portion of the inert particle (2D); and some are coated on the outer rim of the inert particle (2E). A reactive fine particle incorporating either homogenous or heterogeneous systems located in the inner portion, outer portion or a combination thereof is also possible according to the description of the present invention Reference is now made to figure 5, presenting a lateral cross-section of one portion of homogeneously coated reactive fine particle (50). Illustration 5A presents the said portion, wherein it is initially comprised of a central inert particle (1) and a plurality of functional components (see 2 for example). Illustration 5B however presents the said portion, whereat the inert particle is removed (51) in he manner it is currently comprised of the thin layer of the functional components. The removal of the said inert particle (1) in step (51) is provided by many known techniques of the art, such as physical treatments (temperature change, UV emission, sonication etc. ), chemical reactions (pH shifting in the manner solubility is altered, oxidation, liquid-liquid extraction, etc), controlled biological response etc. Such a vehicle-like vesicle may be further processed in any manner.

It is acknowledged that other novel systems are disclosed by the present invention, such as a system wherein at least one precursor is reacted in a solvent to form the reactive compound A that is later deposited onto B.

It is in the scope of the present invention to provide a useful method for the production of the reactive fine particles A as defined in any of the above. Hence, the general approach for the production of the reactive fine particles according to the present invention is a simple process comprised inter alia of the following five steps: (a) dissolving at least one reactive latent curing agent or catalyst or its precursors, characterized by fine particles, in a solvent to form a clear solution; (b) admixing an inert filler B having maximal prime particle size of about 2 microns with the solution obtained above to form a homogenized dispersion; (c) evaporating said solvent and precipitating said reactive fine particles as a layer or in the form of small crystals onto said filler surface and/or inside the internal porosity of said filler ;; and lastly, (d) drying or concentrating the same.

Additionally, a method for producing coated filler particles is hereto provided. Those filler particles B are coated the reactive fine particles A in at least a significant portion of their surface. Said method comprising inter alia the steps of admixing at least one reactive latent curing agent/catalyst or its precursors in a solvent to form a clear solution, and then spraying the same towards particles of the inert filler, having maximal particle size of about 2 microns. After removing the solvent, dried coated filler is obtained. The spraying is referring for any applicable means for jetting components A over components B, such as using an atomizer and a stream of hot carrier of air or gas.

It is in the scope of the present invention wherein sprayed suspension or solution comprising the reactive fine particle A or its precursors is sprayed onto a stream of B powder so a about 0. 01/100 to about 3/1 A to B and coated dispersion is provided.

It is further acknowledged in this respect that since the surface area the inert particle B is high and the amount of the functional component A is limited, crystals or films of functional component A are small or thin so crystallization of particles to a non-desired big size is effectively limited.

The presence of organic dispersant (e. g. , dispersing agent), assures that the particles are covered by a layer that minimize the tendency to re-agglomerate. The powder or slurry is then milled in pearl mill, sand mill or attritor in the presence of additional amount of dispersing agent to a smooth paste, so fine particles are obtained, such as fine particles carrying latent curing agents. Another way to disperse the reactive fine particles in a manner that they do not re-agglomerate is to mill the concentrated slurry or dried powder of A on B in the final ink composition comprising of monomers, polymers, pigments, epoxy resins, solvents, photo-initiators, adhesion promoters, rheology modifiers, dispersing agents, wetting agents, filler, heat stabilizers, corrosion inhibitors, by media mill, rotor stator homogenizer or atttritor to an ink having particles lower than about 2 microns, as indicated by filterability through filter of 2 micron pore size.

It is in the scope of the present invention wherein the reactive fine particles as defined in any of the above are applicable in the various electronic technologies, especially for electronic and/or microelectronic and/or optical components or devices manufacturing processes suitable to be applied by ink jet technology. More specifically, the electronic technologies defined above may be selected from solder masks, dielectrics, resistors, optical waveguides, conductive modules, capacitance layers, adhesives, protective coatings, encapsulants or any combination thereof.

EXAMPLE 1 Preparation of latent curing agent for epoxy resin that has prime particles smaller than about 1 micron: 53. 34 gr of DICY, such as commercially available Dyhard UR100 SF by Degussa were dissolved in 1,013. 39 gr of solvent, e. g. , commercially available Dowanol PM by DOW by slow RPM mixer until clear solution obtained. 35.56 gr of BaS04 powder with prime particles smaller than 1 micron, e. g. , commercially available Blank-Fixe micro by Sachtelben Chemie GMBH is admixed, and then disperse for 20 min using a high shear mixer. The slurry is transferred to rotavapor and the DICY is slowly precipitated onto BaS04 fine particles during evaporation of solvent. The resulted fine powder was analyzed for optimal curing level vs. epoxy resin having EEW value of 190 and found to be optimal at 56 PHR. The latency was good, but somewhat inferior relatively to that of original DICY, as indicated from TABLE 1. The DICY-BaSO4 compound is called hereinafter 6116/1 compound.

Table 1: viscosity change of epoxy, e. g. , the commercially available Epalloy 8220 by CVC Specialty Chemicals Inc. resin with DICY, e. g. , the commercially available Dyhard 100SF, byDegussa and Submicron-DICY 6116/1 <BR> <BR> <BR> <BR> <BR> <BR> Samplename Epalloy8220 Propylene Dyhard 100SF 6116/1 carbonate Control 100 20 7 Nano-DICY 100 20 56 The relative viscosity at 50°C (measured divided by original and multiplied by 100) of each was measured at different times (accelerated at 50°C): Sample name original 3 days 6 days 9 days <BR> <BR> Control 100 97 100 110<BR> <BR> <BR> <BR> Nano-DICY 100 100 104 120 Since some thixotrophy was observed with the nano size 6116/1 DICY, the increase in viscosity is a combination of reaction and particles-resin interaction. Nevertheless, the nano-size material is still latent and may be applicable as latent curing agent for ink-jet applied epoxy based inks.

The 6116/1 was milled in epoxy resin and solvent by media mill and easily filtered through 1 micron filter. Original DICY failed to be filtered under same milling conditions.

EXAMPLE 2 Preparation of nano-size curing accelerator for epoxy resin that has prime particles smaller than about 1 micron: Latent imidazole compound, i. e. , commercially available Curezol 2MZ-A by Shikoku Japan is deposited onto BaS04 : 16.19 gr of Curezol 2MZ-A and 1237.58 gr of Methanol were mixed by slow RPM mixer until clear solution obtained. 46.24 gr of BaS04 powder was admixed by means of Blank-Fixe micro by Sachtelben Chemie GMBH, with prime particles smaller than 1 micron, and subsequently disperse for 20 min using a high shear mixer. The slurry was transferred to rotavapor and the imidazole was slowly precipitated onto BaS04 fine particles during evaporation of solvent. The latency was similar to that of original 2MZ-A as evident from Table 2. The Curezol 2MZ-A-BaS04 compound is denoted hereinafter'6116/2 compound'.

Table 2: viscosity change of epoxy, i. e. , commercially available Epalloy 8220 by CVC Specialty Chemicals Inc. resin with Curezol 2MZ-A (Shikoku) and Submicron-2MZ-A 6116/2 Sample name Epalloy 8220 Propylene 2MZ-A 6116/2 carbonate Control 100 20 2 Nano-2MZ-A 100 20 16 The relative viscosity at 50 °C (measured divided by original and multiplied by 100) of each was measured at different times (accelerated at 50 °C) : <BR> <BR> <BR> <BR> <BR> Sample name original 3 days 6 days 9days<BR> Sample name original 3 days 6 days 9 days Control 100 109 115 130 Nano-2MZ-A 100 120 136 170 Since some thixotrophy was observed with the nano-size 6116/2 2MZ-A, the increase in viscosity is a combination of reaction and particles-resin interaction. Nevertheless, the nano-size material is still latent and may be applicable as latent curing agent for ink-jet applied epoxy based inks.

The 6116/2 was milled in epoxy resin and solvent by media mill and easily filtered through 1 micron filter. Original 2MZ-A failed to be filtered under same milling conditions.

EXAMPLE 3 Latency of combination of DICY and 2-MZ-A Table 3: viscosity change of epoxy, namely commercially available Epalloy 8220 by CVC Specialty Chemicals Inc. resin with DICY/2MZ-A and Submicron DICY 6116/1 and Submicron-2MZ-A 6116/2 <BR> <BR> <BR> <BR> <BR> <BR> Sample name Epalloy Propylene DICY 6116/1 2MZ-A 6116/2 8220 carbonate Control 100 20 7 2 Nano-21VI-A + 100 20 56 16 Nano DICY The relative viscosity at 50 °C (measured divided by original and multiplied by 100) of each was measured at different times (accelerated at 50 °C) : Sample name original 3 days 6 days 9 days <BR> <BR> Control 100 100 180 251<BR> <BR> <BR> <BR> Nano-2MZ-A+ 100 80 133 Above 300<BR> <BR> Nano DICY Examples 1 to 3 shows that the novel submicron solid curing agent and catalyst are latent, but less than their parent raw materials. It is suggested that the higher surface area and the intimate contact with epoxy cause the deterioration in latency. Nevertheless, this combination is still very applicable as latent curing agent for ink-jet applied epoxy based inks.

EXAMPLE 4 A solder mask ink having solids content of 47 to 48 % is latent at ambient temperature so viscosity increase by less than 1 cps within 2 weeks at ambient temperature, can be applied by ink jet onto PWB board, gels under UV irradiation, i. e. , so drop size is set, to a tack free film, cures within 0.5 to 1 hour at 150 °C, and has viscosity of less than 15 cps at 100 1/s at 47 °C degrees, surface tension of 35 dynes/cm and meets all IPC SM840C requirements is formulated form the DICY-BaSO4 6116/1 and imidazole-BaS04 6116/2 powders: 21.91 gr of epoxy novolac resin, namely commercially available Epon 161 by Resolution Performance Products, 30.94 gr of solid DGEBA epoxy, i. e. , commercially available EPON 1001F by Resolution Performance Products, 10.31 gr of rubber-modified epoxy resin, such as commercially available HYPOX RF1320 by CVC Specialty Chemicals, 32.13 gr of liquid epoxy resin, i. e., commercially available Epalloy 8220 by CVC Specialty Chemicals, 36.01 gr of diacrylate monomer, namely commercially available SR238 by Sartomer, 42.02 gr of tetra-acrylate monomer, i. e. , commercially available SR295 by Sartomer, 4 to 9 gr photo initiator for UV and/or UV-visible range, for example commercially available Darocur 1173 by Ciba, wetting and dispersing agents in amount sufficient for stabilization of filler, 42.60 gr of 6116/1 (i. e. DICY-BaSO4) and 15.26 gr of 6116/2 (i. e., imidazole-BaS04) and pigments namely commercially available Phthallocyanine green and Ti02, 62.3 gr of ether-ester solvent by commercially available Dowanol PMA of Dow, and 189.6 gr cyclic ester solvent such as commercially available Propylene Carbonate by Lyondell.

The mixture was milled using a Dynomill KDL horizontal mill, media size 0.4 to 0.5 mm; media type Zr-Y, 4000 RPM, residence time of 15 minutes. The resulted ink is easily filtered through 1 micron filter and has excellent storage stability, ie. , low sedimentation rate, soft cake etc.

The ink was printed by means of commercially available Printar LGB809 printer, printing at 45 °C, 100V, 2 KHz, 6 lls pulse width onto PWB board having bare glass- epoxy laminate and copper conductors. The ink wets very well both materials and the propagation of ink was easily controlled by timed UV pulse that initiated the photo initiator, and cured the acrylate monomers so a tack free film was obtained. The film was the dried and cured in oven for 60 minutes at 150 °C. The cured film has excellent mechanical and physical properties and passes all requirements listed in IPC-SM 840 C protocol for solder-resists for PWB. The Tg of cured film was analyzed by DSC and found to be above 120 °C. The ink has good latency for 1 to 2 weeks at ambient temperature, viscosity raised by less than 1 cps at ambient within 2 weeks and less than 5 cps within 4 weeks.

When ink was manufactured according same procedure but based on original commercially available Dyhard UR100 SF DICY and Curezol 2MZ-A imidazole, the ink was difficult to filter. Since filtration was poor, this composition was not applicable to ink jet application.