This invention relates to a radiation-curable monoethylenically unsaturated liquid non-aqueous composition.

Such a composition is known from US-A- .575.330. US-A-4,575,330 discloses the optical fabrication of three-dimensional objects of complex shape using computer guided radiation to solidify superposed layers of a liquid, radiation-curable, ethylenically unsaturated material at the surface of a reservoir of such material to a thermoset polymer that is cross-linked with covalent bonds. Dimensionally accurate objects are formed by this method. Attempts to utilize such optically fabricated objects as patterns for investment casting have been unsuccessful because the thermoset pattern does not melt when heated, but instead thermally expands causing the refractory material in which the pattern is invested to crack or distort before the pattern can be heated sufficiently to cause it to be removed from the mold. The patterns produced from these materials are insoluble and therefore cannot be removed by solvents.

Therefor the disadvantage of the composition as described in US-A-4.575.330 is that it is not possible to use such a composition for investment casting.

Object of the invention is to overcome the disadvantage of the prior art composition.

This is achieved, according to the invention, in that the composition comprises an ionomeric composition comprising a monoethylenically unsaturated acid wherein at least a portion of the acid groups thereof is neutralized by a metal ion-producing component.

The term 'composition' as used herein in its various grammatical forms, refers to the radiation curable monoethylenically unsaturated liquid non-aqueous composition.

The term "ionomeric composition" as used herein in its various grammatical forms, defines a composition from which an ionomer can be formed.

Ionomers are polymers having pendant ionic functional groups attached to a non-crosslinked polymeric backbone chain and can be produced by copolymerization of a nonionic backbone component and an ionizable monomer having a pendant acid group followed by neutralization of the acid group to form the ionomer. This is described e.g. in Bazuin et al., "Modification of Polymer Properties Through Ion Incorporation", Ind. Eng. Chem. Prod. Res. Dev., 1981, Vol. 20, No. 2, pp 271 to 286 at p 272. See also Lundberg, "Ionic Polymers", Encyclopedia of Polymer Science and Engineering, Vol. 8 (1987), pp 393 to 423 at pp 395 to 400, and Rees, "Cross-linking, Reversible", Encyclopedia of Polymer Science and Engineering, Vol. 4, pp 395 to 417, at p 396. Neutralization is conducted after copolymerization because the unneutralized acid copolymerizes much more readily than the neutralized acid. See, Lundberg, ∑&. at p 397.

The ions of the ionic functional group aggregate with each other to form strong ionic bonds between ionomers that result in the ionomers having characteristics normally associated with cross-linked thermoset polymers. The ionic bonds decompose upon exposure to solvents and/or heat causing the ionomers to have characteristics normally associated with uncrosslinked thermoplastic polymers. The ionomers can also be cross-linked together with covalent bonds. Bazuin et al., Lundberg and Rees, J&. , describe ionomers in more detail.

These known ionomers are solids and cannot be utilized in applications, such as optical fabrication, wherein free-flowing liquids capable of polymerization upon exposure to radiation are required.

Also, these ionomers cannot be utilized in applications, such as optical fabrication, wherein rapid copolymerization is required and neutralization cannot be performed after copolymerization.

The composition according to the invention does not have these drawbacks. investment casting produces dimensionally accurate parts using a disposable pattern to produce a mold in which the part is cast. The pattern is normally made by injecting a heat-softenable pattern material, such as a wax, into a pattern die. The pattern is removed from the die after the material solidifies. A refractory material, e.g., an agueous ceramic slurry, is then built up around the pattern to invest the pattern therein. The mold is produced by melting and removing the invested pattern at an elevated temperature that can also fuse the refractory material. Removal of the pattern produces a cavity defined by the refractory material into which molten metal is introduced. After the metal cools, the mold is broken away to release the part.

Investment casting is described in more detail in Casting Kaiser Aluminium, Second Edition, Kaiser Aluminum & Chemical Sales, Inc., Oakland, CA 94604, 1965, pp. 243 to 247 and 495 to 509.

Investment casting is impractical when only a few parts are desired and can be expensive even when many parts are desired because of the time and money required to make the pattern die.

The production of pattern dies is time consuming and expensive because the size of the pattern and the pattern die must be determined by trial and error to compensate for shrinkage of the pattern or shrinkage and machining of the cast part. Thus, several sets of pattern dies having varying dimensions have to be prepared.

Also, modification of the part cannot be easily- made because even a slight modification of the part requires modification of the pattern die or a new pattern die. An additional problem with investment casting is that relatively large parts cannot be made because the accuracy in the production of the part diminishes as the size of the part increases.

US-A-4,844,144 discloses investment casting utilizing optically fabricated patterns produced from compositions that include both a polyethylenically unsaturated material and an inert thermoplastic material*. However, US-A-4.844.144 does not disclose or suggest the ionomeric compositions of the present invention or their use in the production of patterns for investment casting as are taught herein. US-A-4.844.144 is incorporated herein by reference.

A further object of the patterns of the present invention, produced by optical fabrication, is to eliminate the shortcomings of the prior art investment casting methods, especially the need for pattern dies. It is also an object to overcome the shortcomings of a composition utilized to produce optically fabricated patterns for use in investment casting.

The composition can further include at least one monoethylenically unsaturated monomer or oligomer that copolymerizes with the ethylenically unsaturated group of the monoethylenically unsaturated acid upon exposure to radiation.

This invention is also directed to a composition that comprises said ionomeric composition and a radiation cure initiator.

The composition can be used in applications, such as the production of dimensionally accurate objects/patterns utilizing the optical fabrication method of US-A-4.575.330 and coatings, that require a liquid ionomeric composition that polymerizes upon exposure to radiation. Coatings can be applied to substrates such as glass, metal, wood, plastic, rubber, paper, concrete, fabrics and the like.

The composition can be utilized to produce objects that can be utilized as patterns in the investment casting method of the present invention.

This invention is also directed to a radiation-cured material that results from curing the composition. This cured material exhibits improved conversion, improved green strength, and reduced distortion as compared to compositions that do not utilize the ionomeric composition. When the radiation dose is maintained at a constant level, the cure speed is improved and the radiation is used efficiently. This cured material is not an absorbent material.

The ionomer obtained by polymerising an ionomeric composition has a non-crosslinked polymeric backbone and pendant ionic functional groups wherein the ions aggregate with each other creating strong ionic bonds that reversibly cross-link the ionomers with each other to provide structural rigidity to the cured material. The ionic bonds decompose upon exposure to solvents and/or heat, thus weakening the cured material and patterns produced therefrom. Preferably, there is little or no crosslinking of the ionomers by covalent bonds.

US-A-4,167,464 discloses an UV photo polymerized interpoly er prepared from an aqueous onomeric mixture including acrylic acid having the carboxylate groups neutralized prior to polymerization, a higher acrylic esther monomer having an alkyl group of 10 to 30 carbon atoms, a lower acrylic ester having an alkyl group containing 1 to 8 carbon atoms and a photoinitiator.

EP-A-0.047.009 discloses an interpolymer obtained from a monomeric mixture of acrylic acid having a large percentage of the carboxylate acid groups neutralized prior to polymerization and α-olefins, styrene or a substituted styrene. The monomeric mixtures are aqueous dispersions. Films and fibers produced from the monomeric mixtures of US-A-4.167.464 and EP-A-0.047.009 are applied in e.g. disposable non woven products, because they have a high degree of absorption of water and body fluids. This is undesirable for many applications of the present invention including optical fabrication and coatings.

The invention further relates to a process of curing of a composition according to the invention. The composition of the present invention is cured by exposure to a curing amount of radiation to produce ionomers. The ionic functional groups of the ionomers aggregate with each other to ionically bond and reversibly cross-link the ionomers. There is preferably no cross-linking via irreversible covalent bonds because preferably only monoethylenically unsaturated materials are utilized. Polyethylenically unsaturated materials, which cause covalent bond cross-linking, can be present in the composition. However, the degree of covalent bond cross-linking must permit weakening of the pattern to the extent that the pattern can be utilized in investment casting.

The term "curing amount", as used in its various grammatical forms, identifies an amount of radiation that causes crosslinking sufficient to convert the composition from a liquid, free-flowing condition to at least a semisolid condition.

Suitable radiation for curing includes actinic radiation, preferably in the form of ultraviolet light, visible light, or both, and electron beam radiation.

The invention also comprises a method of investment casting that produces a mold from a pattern by investing the object produced by using a composition according to the invention in a refractory material. The pattern is produced from the composition, preferably utilizing optical fabrication. The pattern is removed from the mold without cracking or distorting the mold preferably by exposure to a solvent for a time period sufficient to weaken the pattern followed by exposure to an elevated temperature. After exposure to a solvent as mentioned above, the pattern does not undergo the thermal expansion that optically fabricated patterns produced from conventional materials undergo and therefore does not crack or distort

the mold. The present investment casting method eliminates the need to produce a pattern die which results in a savings of time and money. The present investment casting method is cost-effective even if only a few parts are desired because a pattern die is not required and because modifications of a part are readily made by. reprogramming the computer utilized in the optical fabrication method. Also, since large patterns can be accurately produced utilizing optical fabrication relatively large parts can be made utilizing the present investment casting method.

The term "ionomer", as used herein in its various grammatical forms to describe a polymer, identifies an ionized polymer having a preferably non-crosslinked polymeric backbone and pendant ionic functional groups. Ionomers can also be described as metal carboxylate salts.

The term "ionic functional", as used herein in its various grammatical forms, indicates that the ionomer contains one or more atoms that have lost or gained one or more electrons.

Representative ethylenically unsaturated acids include: carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, crotonic acid, elaidic acid and itaconic acid; a saturated acid partially esterified with an ethylenically unsaturated alcohol; carboxyalkyl acrylates; carboxyalkyl methacrylates; compounds of hydroxyalkyl acrylate or methacrylate and an anhydride such as succinic anhydride, maleic anhydride and phthalic anhydride; and the like. Examples of the saturated acids that are esterified with an ethylenically unsaturated alcohol include oxalic acid, succinic acid, adipic acid and the like. Suitable ethylenically unsaturated alcohols include allyl alcohol, crotyl alcohol, and the like. Mixtures of the acids can also be utilized. The alkyl groups of the above acids are preferably Cl to C4 alkyl groups. Preferably the acid is a (meth)acrylate. The carboxyalkyl(meth)acrylates preferably have C, to C ₄ alkyl groups and are represented by

carboxymethylacrylate, carboxyethylacrylate, carboxybutylmethacrylate, and the like. The hydroxy alkyl(meth)acrylates that are reacted with an anhydride preferably have C. to C . alkyl groups and are represented by hydroxymethylmethacrylate, hydropropylacrylate, hydroxybutylacrylate and the like. Representative anhydrides are succinic anhydrides, maleic anhydrides, phthalic anhydrides, and the like.

The number average molecular weight of the acid is preferably about 50 to about 600, more preferably about 70 to about 300, daltons.

The term "dalton", as used in its various grammatical forms, identifies an atomic mass that is one-twelfth the mass of carbon-12.

The metal ion-producing component provides at least one metal ion. The ion is preferably monovalent, divalent or trivalent. Representative of the metal ions are those of the Group la, lb, Ila, lib. Ilia, IVa, Vb and VIII elements of the Periodic Table of Elements. Preferred metal ions are sodium, lithium, barium, magnesium, calcium, zinc and aluminum.

Preferred metal ion-producing components are metal hydroxides, metal carbonate hydroxides, metal acetates, the like and mixtures thereof. Representative of these metal ion-producing components are magnesium hydroxide, zinc hydroxide, calcium carbonate, sodium acetate and barium acetate. Preferably, the metal ion-producing component is a metal hydroxide.

The metal ion-producing component and the amount utilized are selected to achieve the desired percent neutralization of the acid groups of the ethylenically unsaturated acid. When the percent neutralization of acid groups is too high the ions of the ionic functional groups are unable to form strong ionic bonds and therefore do not form aggregates. While not desiring to be bound by a

theory, it is presently believed that the formation of aggregates enhances the polymerization of the ethylenically unsaturated metal carboxylate partial salt. When the percent neutralization is too high the cured material becomes brittle. Therefore, the metal ion-producing component is present in .an amount sufficient to neutralize a percentage of the acid groups and the percent neutralization does not prevent the formation of aggregates.

Preferably, about 2 to about 80, more preferably about 5 to about 65, percent of the acid groups are neutralized. Most preferably, about 10 to about 50 percent of the acid groups are neutralized. Neutralization can be accomplished by admixing the acid and the metal ion-producing component at ambient o temperature and pressure, i.e., a temperature of about 20 o to about 30 C and a pressure of about 1 atmosphere. A solvent can be utilized to facilitate admixing. Preferably, the solvent is reactive with the other materials of the composition. Representative solvents include vinyl pyrrolidone, vinyl caprolactam and the like.

Representative of the other materials that copolymerize with the ethylenic unsaturation of the acid are monoethylenically unsaturated monomers and monoethylenically unsaturated oligomers. Preferably, the composition contains at least one of the monomer or oligomer.

The monomers and oligomers can have acid groups that can be neutralized by the metal ion-producing component. The percent of the acid groups in the composition that are neutralized has been previously discussed.

The number average molecular weight of the monomer is preferably about 50 to about 500, more preferably about 100 to about 300, daltons.

The number average molecular weight of the oligomer is preferably about 200 to about 2000, more preferably about 300 to about 1000, daltons.

The composition can further comprise many nonaqueous copolymerizable, radiation-curable liquid materials that are distinct from the ethylenically unsaturated acid and can be admixed with the ethylenically unsaturated acid. Representative of the radiation-curable liquid materials are mono- and polyethylenically unsaturated monomers and oligomers, poly(meth)acrylate copolymerizable and cross-linkable components t (meth)acrylate components], allyl oligomers, the like and mixtures thereof.

The term "(meth)acrylate component", and various grammatical forms thereof, includes (meth)acrylates and monomers and polymers that have a radiation-polymerization mechanism similar to (meth)acrylates. Representative mono- and polyethylenically unsaturated monomers and oligomers include esters of ethylenically unsaturated carboxylic acids, vinyl compounds, preferably other than styrene and substituted styrenes, the like and mixtures thereof. Representative of these monomers and oligomers are alkyl acrylates, phenoxyalkyl acrylates, phenoxyalkyl methacrylates, aleates, fu arates, vinyl caprolactam, vinyl pyrrolidone, monoacrylate oligomers, as for example the reaction product of 1 mole of cyclohexanol, 1 mole of Tone M-100 (a hydroxy functional caprolactone ester of acrylic acid that is commercially available from Union Carbide, New York, NY) and 1 mole of isophorone diisocyanate, the like and mixtures thereof. The above alkyl groups are lower alkyl groups, preferably alkyl groups that contain 1 to 4 carbon atoms. The (meth)acrylate component can contain monomers and oligomers and is preferably of a resinous nature and contains an average of at least about 1.2, and more

preferably at least about 2.0, (meth)acrylate groups per oligomer unit. The ( eth)acrylate component should have a flowable viscosity and be stable at the conditions at which it is utilized.

The resinous (meth)acrylate component can be a poly(meth)acrylate of aa epoxy functional resin. These poly(meth)acrylates have an average of about two or more (meth)acrylate groups per polymer unit. These poly(meth)acrylates are exemplified by the commercial product Ebecryl 3700, available from Radcure Specialties, which is the diester of Epon 828 (an epoxy functional resin that is a diglycidyl ether of bisphenol A that is commercially available from Shell Chemicals,

New York, NY). The number average molecular weight of Ebecryl 3700 is about 500 daltons and the number average molecular weight of Epon 828 is about 390 daltons.

Diacrylate-modified polyurethanes, especially those that have a polyester-containing backbone, are also useful as the resinous (meth)acrylate component. Representative are acrylate-capped polyurethanes that are the urethane reaction products of a hydroxy-functional polyester, especially one having an average of about 2 to about 5 hydroxy groups per molecule, with a monoacrylate monoisocyanate. These acrylate-capped polyurethanes are illustrated by a polyester having a number average molecular weight of about 600 daltons that is made by reacting trimethylol propane with caprolactone followed by reacting three molar equivalents of the reaction product of 1 mole of 2-hydroxyethyl acrylate with 1 mole of isophorone diisocyanate therewith. The end product is a polyurethane triacrylate. The urethane-forming reaction is generally performed at about 60°C in the presence of about 1% by weight of dibutyl tin dilaurate. A commercial, polyester-based polyacrylate-modified polyurethane that is useful herein is Uvithane 893 available from Thiokol

Chemical Corp., Trenton, NJ. The polyester in Uvithane 893 is a polyester of adipic acid with about 1.2 molar equivalents of ethylene glycol polyesterified to an acid number of less than about 5. This polyester is converted as described above to a polyacrylate-modified polyurethane that is a semi-solid at room temperature and that has an average unsaturation equivalent of about 0.15 to about 0.175 ethylenically unsaturated groups per 100 grams of resin.

In polyester processing, the acid number, defined as the number of milligrams of base required to neutralize one gram of polyester, is used to monitor the progress of the reaction. The lower the acid number, the further the reaction has progressed.

Triacrylates, such as the glycerylpropoxy triacrylate commercially available from Radcure Specialties under the trade designation GPTA, are also suitable. A polyacrylate-modified polyurethane that is suitable as the (meth)acrylate component is the reaction product of 1 mole of isophorone diisocyanate, 1 mole of 2-hydroxyethyl acrylate and about 1 weight percent dibutyl o tin dilaurate reacted at a temperature of about 40 C for a time period of 4 hours that is subsequently reacted with 1 mole of a commercial hydroxy end-functional caprolactone o polyester at a temperature of about 60 C for a time period of about 2 hours. A suitable caprolactone polyester is the reaction product of 2 moles of caprolactone and 1 mole of o ethylene glycol reacted at a temperature of about 60 C for a time period of 4 hours. A suitable commercial caprolactone polyester is available from Union Carbide Corp., Danbury,

CT, under the trade designation Tone M-100 which has a number average molecular weight of about 345 daltons. The (meth)acrylate component can be admixed with a liquid N-vinyl monomer that has a radiation-polymerization mechanism similar to (meth)acrylates.

The term "N-vinyl monomer", as used herein in its

various grammatical forms, describes a monomer having a nitrogen atom adjacent to a vinyl group. Representative N-vinyl monomers include N-vinyl pyrrolidone and N-vinyl caprolactam, with N-vinyl pyrrolidone being preferred.

The resinous ( eth)acrylate component can be dissolved in a reactive solvent that preferably is an ethylenically unsaturated liquid that can comprise liquid mono(meth)acrylates, liquid poly(meth)acrylates or admixtures thereof. More preferably the reactive solvent includes an ethylenically unsaturated liquid poly(meth)acrylate. Liquid tri(meth)acrylates, e.g., trimethylol propane triacrylate, and di(meth)acrylates, e.g., 1,6-hexanediol di(meth)acrylate, are suitable. Liquid tetra(meth)acrylates, e.g., pentaerythritol tetraacrylate, are also useful. Another representative liquid poly(meth)acrylate is Sartomer C 9003 which is a diacrylate of neopentyl glycol polypropoxylate with an average of two propylene oxide units per molecule and having a number average molecular weight of about 330 daltons that is commercially available from Sartomer, Westchester, PA. This liquid reactive solvent is preferably a mixture of monoethylenically and polyethylenically unsaturated materials in a weight ratio of about 4:1 to about 1:4, respectively.

A non-reactive diluent can also be present in the composition to adjust the viscosity. Representative of the non-reactive diluents is Acryloid B44 (a butyl acrylate/methyl methacrylate copolymer commercially available from Rohm & Haas Inc., Philadelphia, PA) and the like.

The term "non-reactive diluent", and various grammatical forms thereof, identifies a diluent capable of dissolving the monoethylenically unsaturated acids, monomers and oligomers.

The viscosity of the composition can also be adjusted utilizing an inert diluent that is non-reactive with respect to the ethylenically unsaturated material. A representative inert diluent is n-hexanol or butanol.

The (meth)acrylate component is preferably present in an amount in the range of about 15 to about 80, more preferably about 40 to about 70, weight percent based on the total weight of the radiation-curable liquid material.

The liquid reactive solvent is preferably present in an amount in the range of about 20 to about 85, more preferably about 30 to about 60, weight percent based on the total weight of the radiation-curable liquid material. The optional N-vinyl monomer, when utilized, replaces a like amount of the (meth)acrylate component and is present in an amount in the range of about 5 to about 40 weight percent based on the total weight of the radiation-curable liquid material. The non-reactive diluent, when utilized, replaces a like amount of the (meth)acrylate component and is present in an amount up to about 50 weight percent based on the total weight of the radiation-curable liquid material.

Representative allyl oligomers that can be utilized as the radiation-curable liquid materials are: allyl esters, e.g. diallyl maleate and diallyl phthalate; allyl ethers, e.g. trimethylol propane diallyl ether; allyl urethanes, e.g., the reaction product of two moles of allyl alcohol and one mole of toluene diisocyanate; allyl carbonates, e.g., bisallyl diglycol carbonate; heterocyclic allyl oligomers resins, e.g., triallyl cyanurateε and triallyl isocyanunates; and allyl and diallyl amine adducts of polyepoxide compounds, e.g., the allyl or diallyl amine adduct of the diglycidyl ether of bisphenol A. Further representative of the allyl resins is the commercial product APU6007 from Reichhold Chemicals which is a solution containing 65 weight percent of the terminal allyl

unsaturated polyester resin Polylite TM 13-831, also a commercial product of Reichhold Chemicals, in the solvent methylethyl ketone.

The composition can also include a conventional, photoinitiator that initiates cure of the composition upon exposure to radiation such as actinic energy. The radiation cure initiator is preferably utilized with actinic radiation and preferably is not utilized with electron beam radiation. These photoinitiatorε are usually ketonic, and frequently aromatic, such as the benzophenones. Darocur 1173 is an illustrative, commercially available benzyl ketal-based photoinitiator from EM Chemicals that contains 2-hydroxy-2-methyl-l-phenyl-propane-l-one as the active ingredient. A suitable aryl ketone photoinitiator is Irgacure 184 which contains hydroxycyclohexyl phenyl ketone as the active ingredient and which is commercially available from Ciba Geigy Corp. Further representative initiators include: admixtures of camphorquinone and amines; photoreducible dyes; admixtures of photoreducible dyes and amines; ketonic photoinitiators; and admixtures of ketonic photoinitiators, photoreducible dyes and amines. The combination of camphorquinone and an amine is a known initiator that is sensitive to visible light.

Camphorquinone is commercially available from Aldrich Chemical Co. Inc., Milwaukee, WI, USA.

The amines are preferably tertiary amines, more preferably alkyl, cycloalkyl or alkanol tertiary amines, or mixtures thereof. Preferred tertiary amines have from about 1 to about 12 carbon atoms in the alkyl, cycloalkyl or alkanol group. Examples of tertiary amines that are useful herein are triethyl amine, tributyl amine, dimethylethanol amine, methyldiethanol amine, triethanol amine, dimethyl benzyl amine, trioctyl amine, ethyldiethanol amine, didodecyl diethylenediamine and dimethyl diethylenediamine.

The weight ratio of camphorquinone to amine is preferably in the range of about 2:1 to about 8:5. The photoreducible dye suitable for use herein is preferably a photoreducible phthalein dye. Representative dyes are fluorescein (CA 2321-07-05);

2' ,4' ,5' ,7'-tetrabromofluorescein, disodium salt, e.g., eosin, commercially available from Aldrich Chemical Co. Inc., Milwaukee, WI, USA; and tetraiodofluorescein, e.g., erythrosin, also commercially available from Aldrich Chemical Co. Inc. and riboflavin, also commercially available from Aldrich Chemical. Other halogen-modified fluorescein dyes such as dibromo-, dichloro-, diiodo- or tetrachlorofluorescein are also suitable for use in the present invention.

Representative amines suitable in admixture with the dyes are described hereinabove.

The weight ratio of photoreducible dye to amine is preferably in the range of about 1:10 to about 1:5.

The ketonic photoinitiator is effective to initiate polymerization upon exposure to actinic energy such as light in or near the ultraviolet and visible ranges. Representative of the ketonic photoinitiator is Darocur 1173, a commercially available benzyl ketal-based photoinitiator from EM Chemicals that contains 2-hydroxy-2-methyl-l-phenyl-propane-l-one as the active ingredient. Also representative is a commercially available aryl ketone photoinitiator, Irgacure 184, from Ciba Geigy Corp., Ardsley, NY, USA, that contains hydroxycyclohexyl phenyl ketone as the active ingredient. Further representative is Irgacure 651, also available from Ciba Geigy Corp, that contains dimethoxyphenyl acetophenone as the active ingredient. Representative photoreducible dyes and amines that can be utilized in admixture with the ketonic photoinitiator are described hereinabove.

The weight ratio of the photoreducible dye to amine

to ketonic photoinitiator is preferably in the range of about 1:5:10 to about 2.5:5:4. The weight ratio of ionomeric composition to optional radiation cure initiator is preferably in the range of about 500:1 to about 9:1.

The term "actinic energy", as used herein in its various grammatical forms, defines a type of light radiation capable of producing chemical change in the ionomeric composition. Preferably, the light radiation has a wavelength in or near the ultraviolet and visible ranges, e.g., light having a wavelength of about 200 to about 600 nanometers (nm). A suitable source for the ultraviolet light is a helium-cadmium laser having an output of 15 milliwatts at a wavelength of 325 nm focused to a 350 micron diameter, such as a Liconix Model 4240 N laser. A suitable source for visible light is an argon ion laser having an output of 488 to 514 nm. Typically, cure to at least a semisolid condition can be attained at a dose of about 0.5 to about

2 1.5 Joules/square centimeter (J/cm ).

Electron beam radiation suitable for use herein can be generated by a CB-150 Lab Unit commercially available from Energy Science. Typically, cure to at least a semisolid condition can be attained at a dose of about 1 to about 10 megarads per square centimeters.

The weight ratio of the ionomeric composition to the radiation-curable liquid material is preferably in the range of about 1:50 to about 3:1, more preferably about 1:10 to about 2:1.

The optimum amount of ionomeric composition utilized in the composition containing photoreducible dye is the amount that results in an increase in the percent conversion of the liquid to a solid, as compared to the percent conversion of a control composition. The percent conversion is determined by a constant dose test that is

described in EXAMPLE 2, below. This optimum amount is dependent upon the equivalent weight of the acid utilized to produce the ionomeric composition and will change in direct proportion to a change in the equivalent weight of the acid. For example, when the ionomeric composition is prepared from 92 parts by weight of carboxyethyl acrylate (equivalent weight of about 144) and 8 parts by weight of magnesium hydroxide, the optimum amount is preferably up to about 25, more preferably up to about 10, weight percent of the composition with the remainder of the composition being the initiator and the radiation-curable material.

The monoethylenically unsaturated acid is preferably present in an amount in the range of about 2 to about 50, more preferably about 10 to about 30, weight percent based on the total weight of the ethylenic unsaturation-containing material in the composition.

At least one of the monoethylenically unsaturated monomer or monoethylenically unsaturated oligomer is preferably present in an amount in the range of about 40 to about 98, more preferably about 70 to about 90, weight percent based on the total weight of the ethylenic unsaturation-containing material present in the composition.

The non-reactive diluent can be present in the composition in an amount in the range of about 5 to about 50, preferably about 10 to about 40, weight percent based on the total weight of the ethylenic unsaturation-containing material present in the composition.

The photoinitiator is preferably present in an amount in the range of about 0.1 to about 10, more preferably about 1.0 to about 6, weight percent based on the total weight of the composition. The viscosity of the composition is preferably about 300 to about 2000 centipoise (cp).

An object or pattern can be produced utilizing the composition of the present invention in an optical fabrication method as disclosed in US-A-4.575.330. In this method, the surface of a reservoir of a liquid composition is cured by exposure to radiation to produce a cross section of the pattern. The cured portion is then coated with a body of additional liquid composition. A substantial portion of the body of additional composition is reduced from a fluid layer of excessive thickness to a successive fluid layer of less thickness and cured by exposure to radiation to produce a subsequent cross section of the pattern that adheres to the previous cross section. The steps of coating the cured portion and then exposing it to radiation to cause curing are repeated until the desired pattern is produced.

When the pattern is removed from the reservoir it at least has adequate green strength and can then be conventionally post-cured by further exposure to actinic energy. Alternatively, the pattern can be thermally post-cured. A free-radical polymerization catalyst can be utilized to make the thermal cure more rapid or effective at lower temperature. The term "adequate green strength," as used herein in its various grammatical forms, indicates that the pattern is strong enough to maintain its dimensional accuracy prior to post-cure.

The present invention is also directed, as indicated hereabove, to a method of investment casting wherein the pattern is invested in a refractory material. The invested pattern is then placed, and maintained, in a solvent to weaken the pattern by decomposing the ionic bonds between the ionomers. Preferred solvents are highly polar solvents such as aqueous ammonia solutions and aqueous ammonia solutions containing other solvents such as methylethyl ketone and iεopropyl alcohol. A preferred solvent solution contains about one-third of a 28 percent aqueous ammonia solution, about one-third methylethyl ketone

and about one-third isopropyl alcohol.

The time period sufficient to weaken the pattern will depend upon the composition utilized, the size of the pattern, the thickness of the refractory material, the solvent utilized and the temperature at which the invested pattern is maintained in the solvent.

The weakened, invested pattern is then removed from the cavity defined by the refractory material to produce the mold. Removal can be accomplished by discharging the weakened pattern through an opening in the refractory material. Alternatively, removal can be effected by exposing the weakened, invested pattern to an elevated temperature to decompose any remaining ionic bonds and/or decompose or breakdown the non-crosslinked polymeric backbone with any residue of the pattern being removed through an opening in the refractory material. The weakening of the pattern permits any thermal expansion of the thermoset polymeric backbone to occur without cracking or distorting the mold. The temperature to which the weakened, invested pattern is exposed is preferably about 50 to about 400, more preferably about 100 to about 200, °C. After the pattern is removed the mold can be conventionally fired to fuse the refractory material.

The composition can optionally be admixed with an inert thermoplastic material that preferably is a low molecular weight oligomer. This admixture can also be utilized in an investment casting process such as that described in US-A-4,844,144. Representative thermoplastic materials are disclosed in more detail in US-A-4.844.144. When utilized, the thermoplastic materials preferably are present in an amount in the range of about 5 to about 50, more preferably about 15 to about 35, weight percent based on the total weight of the metal carboxylate partial salt or the composition.

The composition of the present invention can be utilized in optical fabrication methods such as the method disclosed in US-A-4,575,330.

The composition can be applied to substrates, e.g., glass, metal, wood, plastic, rubber, paper, concrete, fabrics and the like, as a coating, covering and the like to produce articles. The following Examples are provided as an illustration, and not as a limitation, of the present invention.

EXAMPLE 1: PREPARATION OF THE IONOMERIC COMPOSITION

An ionomeric composition was prepared by admixing 92 parts by weight of carboxyethyl acrylate commercially available from Radcure Specialties and 8 parts by weight of magnesium hydroxide commercially available from Aldrich Chemical, Milwaukee, Wisconsin at ambient conditions.

Admixing was continued until substantial homogeneity was achieved. Approximately, 40% of the acid groups of the carboxyethyl acrylate were neutralized.

EXAMPLE 2:

COMPARISON OF A CONTROL COMPOSITION, A SR-9003 CONTAINING COMPOSITION, AND A RADIATION-CURABLE LIQUID COMPOSITION

A base resin composition was prepared by admixing 45 parts by weight of Ebecryl 3700 commercially available from Radcure Specialties, 40 parts by weight of N-vinyl pyrrolidone commercially available from GAF and 15 parts by weight of glycerylpropoxy triacrylate commercially available from Radcure Specialties under the trade designation GPTA. An aliquot of the base resin served as the control composition which was not admixed with the ionomeric composition or SR-9003.

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SR-9003 is a neopentylglycol propoxy diacrylate commercially available from Sartomer that is non-ionic but possesses a structure, viscosity, and acrylate equivalent weight similar to the metal carboxylate partial salt of EXAMPLE 1. SR-9003 is embodying comparative examples.

Various amounts of the ionomeric composition of EXAMPLE 1 or SR-9003 were admixed with aliquots of the base resin to produce the radiation-curable liquid compositions or the SR-9003 containing compositions, respectively. The percent ionomeric composition of EXAMPLE 1 and SR-9003 utilized relative to the base resin are provided in TABLES I and II, below. Aliquots of these three compositions were photosensitized for cure by visible light from an argon ion laser having an output of 488 to 514 nm utilizing 0.4 weight percent of erythrosin dye and 2 weight percent of ethyldiethanol amine commercially available from Pennwalt. The weight percents are based on the total weight of the composition. Aliquots of the control and radiation-curable liquid compositions were photosensitized for cure by ultraviolet light from a helium-cadmium laser having an output of 325 nm using 4 weight percent of Darocur 1173 commercially available from EM Industries.

Photosensitized aliquots of the compositions were tested at a constant dose for thickness and percent conversion and at a constant thickness for relative dose and percent conversion. The test results are provided in TABLES I and II, below.

Table I

VISIBLE LIGHT-LASER CURED COMPOSITIONS

NR Weight % Constant Doze Tests Constant Thickness Tests ionomer SR-90032 Thickn. (mm) % Conv. Rel. dose % Conv.

2.1. 0.0 22.5 74 100 62

2.2 3.5 18.5 84 120 75

10 2.3 7.0 16.5 85 140 76

2.4 14.0 13.5 82 200 75

2.5 28.0 12.0 72 200 67 ϋi 2.6 0.0 21.0 73

03 15 2.7 3.5 21.0 73 0) 2.8 7.0 20.0 73 H 2.9 14.0 19.5 71

H 2.10 28.0 17.5 62

____| 20 1. The ionomeric composition of example 1 m 2. Commercially available from Sartomer ø The numbers 2.1 and 2.6 are the control composition.

{ XTj TABLE II

HI 25 UV LIGHT-LASER CURED COMPOSITIONS

-I Weight % Constant Dose Tests Constant Thickness Tests

Ionomer Thickn.(mm) % Conv. Rel. Dose % Conv.

30 0.0 19.0 64 100 68

3.5 20.5 66 67 66

₁ The ionomeric composition of EXAMPLE 1.

The constant dose test included exposing the surface of a reservoir of each composition to a constant dose of radiation. The thickness of the cured layer was then measured microscopically and is expressed in mils. The percent conversion was determined by removing a sample of the cured material from the reservoir and blotting the sample to remove adherent liquid composition. The sample was then weighed to obtain the initial weight before being placed in a methylethyl ketone (MEK) bath at ambient temperature for a time period of 120 minutes. At the end of this time period the sample was removed from the MEK bath, dried, and reweighed to obtain the final weight. The percent conversion was calculated by dividing the difference between the final weight of the sample by the initial weight of the sample and then multiplying the quotient by 100. A higher percent conversion indicates increased conversion of a liquid composition to a solid. The constant thickness test consisted of exposing the surface of a reservoir of the control composition to radiation in an amount sufficient to achieve a thickness of 20 mils. This amount of radiation was designated X. The surfaces of reservoirs of the ionomeric composition or SR-9003 containing compositions were exposed to radiation in an amount sufficient to achieve the same thickness. This amount of radiation was designated Y. The relative dose was calculated by deviding Y by X and then multiplying the quotient by 100. The test results for the constant dose tests for visible light-laser cure indicate that as the percent ionomeric composition utilized is increased up to an optimum amount the percent conversion also increases as compared to the control composition. When this optimum amount is exceeded the percent conversion decreases as compared to the control composition. In contrast, as the amount of SR-9003 utilized is increased, the percent conversion remains constant or undesirably decreases. Thus, no increase in percent conversion is achieved utilizing SR-9003.

It is presently believed that the relative dose for the constant thickness test increases with increasing ionomeric composition content because the polarity of the ionomeric composition changes the absorbance characteristics of the dye. However, the percent conversion is still improved.

Constant dose tests for UV light-laser cure indicate that the thickness and percent conversion are greater for the radiation-curable liquid compositions as compared to the control composition. The increase in thickness at a constant dose indicates a more efficient use of the radiation. The increase in percent conversion indicates an increase in green strength.

The constant thickness test for UV light-laser cure shows that the relative dose decreases, and the percent conversion remains about constant, as the weight percent of the metal carboxylate partial salt utilized increases. The reduction in the dose required to obtain a constant thickness indicates an increase in cure speed. The maintaining of the percent conversion at a constant level indicates that the green strength remains constant and therefore the green strength is not sacrificed to increase cure speed.

EXAMPLE 3: PREPARATION OF IONOMERIC COMPOSITIONS

Four acrylate ionomeric compositions were prepared by admixing the diluent vinyl pyrrolidone with a metal hydroxide followed by admixing carboxyethyl acrylate, commercially available from Radcure Specialties, thereto until a substantially homogeneous acrylate ionomeric composition was produced. The formulations for the production of the acrylate ionomeric compositions are provided in TABLE III, below.

TABLE III ACRYLATE IONOMERIC COMPOSITIONS Parts By Weight

Ionomeric A B C D compositions:

Carboxyethyl acrylate 69.3 68.0 65.0 70.0 Vinyl pyrrolidone 25.0 25.0 25.0 25.0

Magnesium hhyyddrrooxxiiide 5.7

Calcium hydroxide ¹ 7.0

Zinc carbonate hydroxide 10.0

Aluminum hydroxide hydrate ¹ 5.0

Commercially available from Aldrich Chemical Co.

EXAMPLE 4: COMPARISON OF A CONTROL COMPOSITION

TO RADIATION-CURABLE LIQUID COMPOSITIONS Aliquots of the base resin of EXAMPLE 2 were admixed with a photosensitizer comprising erythrosin dye. and ethyldiethanol amine and either SR-9003 to produce the control composition, or an ionomeric composition of EXAMPLE 3 to produce radiation-curable liquid compositions. The formulae of the compositions are provided in TABLE IV,below. Each composition was formulated to obtain a carboxyethyl acrylate or SR-9003 concentration of 10 parts by weight.

TABLE IV COMPOSITIONS Parts By Weight

Component Composition: E F G H I

. l Base resin 90.0 85.6 85.3 84.6 85.7

Ethyldiethanol amine 2.0 2.0 2.0 2.0 2.0

CO c 0 Erythrosin dye 0.4 0.4 0.4 0.4 0.4

SR-9003 ² 10.0

0) Ionomeric composition A 14.4

Ionomeric composition B~ 14.7 c Ionomeric composition C ^~ 15.4 m 15 Ionomeric composition D ^~ 14.3

CD

I IT! Base resin of EXAMPLE 2.

_ Commercially available from Sartomer.

Acrylate ionomeric composition of EXAMPLE 3.

The compositions were cured utilizing an argon ion laser having a visible wave length output of 488 to 514 nm at a dosage of about one Joule per square centimeter. The percent conversion for these compositions are provided in TABLE V.

TABLE V PERCENT CONVERSION TEST RESULTS

Composition Percent Conversion

E 50.1

F 66.9

G 66.8 H 56.5

I 59.4

The percent conversion was determined in accordance with the method described in EXAMPLE 2, above. The percent conversion test results indicate that the radiation-curable liquid compositions exhibit a substantial improvement in percent conversion as compared to a SR-9003 containing control composition.

EXAMPLE 5: Radiation-Curable Monoethylenically Unsaturated Liquid Compositions Patterns suitable for use in the present investment casting method were optical fabricated utilizing the compositions of the present invention disclosed in TABLE VI, below.

TABLE VI Radiation-Curable Monoethylenically Unsaturated Liquid Compositions

Parts by Weight

Component & Q £ g g

Methacrylic acid — — — — — 14

Carboxyethyl acrylate 20 20 20 20 20

Magnesium hydroxide 1.8 3.2 -- 1.6 1.6 1.9 Calcium hydroxide — — 2.0 — — —

DSO 4259-118 ¹ 40 40 40

Acryloid B44 ² — — — 20 — 20

Polyvinyl pyrrolidone — — — — 20 —

Vinyl pyrrolidone 40 40 40 50 50 50

Vinyl caprolactam — — — 10 — 16 Phenoxyethyl acrylate — — — — 10 —

Darocure 1173 ¹ 5 5 5 5 5 5

A monoacrylate oligomer commercially available from DeSoto, Inc., Des Plaines, IL that is a reaction product of 1 mole of cyclohexanol, 1 mole of Tone M-100 (a hydroxy functional caprolactone ester of acrylic acid commercially available from Union Carbide Corp., New

York, NY) and 1 mole of isophorone diisocyanate. 2 A butyl acrylate/methyl methacrylate copolymer commercially available from Rohm & Haas Co.,

Philadelphia, PA. 3

A benzyl ketal-based photoinitiator commercially available from EM Chemicals.

The compositions all experienced good reactivity to ultraviolet laser radiation and the patterns exhibited adequate to excellent green strength when removed from the reservoir of composition. The post-cured patterns were hard and non-tacky.

A pattern .produced from Composition D was placed in a solution of one-third of a 28 percent aqueous ammonia solution, one-third methyl ketone and one-third isopropyl alcohol for 24 hours which resulted in the weakening of the pattern to a point whereby the pattern lost its shape.