WO1998013729A1

WO1998013729A1 - A hydrolyzable, radiation-curable monomer or oligomer, a radiation-curable resin composition, an article, and improved rapid prototyping methods

Info

Publication number: WO1998013729A1
Application number: PCT/NL1997/000534
Authority: WO
Inventors: Stephen C. Lapin; Michael G. Sullivan
Original assignee: Dsm N.V.
Priority date: 1996-09-26
Filing date: 1997-09-25
Publication date: 1998-04-02

Abstract

The present invention discloses a hydrolyzable, radiation-curable monomer or oligomer, which when suitably cured is hydrolyzable in an aqueous medium, and a method of making the hydrolyzable radiation-curable monomer or oligomer. Also disclosed is a radiation-curable resin composition, which when suitably cured is hydrolyzable in the presence of an aqueous medium, and a method of removing the hydrolyzable portion. The invention also provides an improved rapid prototyping method for making a mold suitable for investment cast molding.

Description

A HYDROLYZABLE, RADIATION-CURABLE MONOMER OR OLIGOMER, A RADIATION-CURABLE RESIN COMPOSITION, AN ARTICLE, AND IMPROVED RAPID PROTOTYPING METHODS

1. Field of the Invention

The present invention provides a hydrolyzable, radiation-curable monomer or oligomer, which when suitably cured retains the property of being hydrolyzable in an aqueous medium, and a method of making the hydrolyzable radiation-curable monomer or oligomer. The invention also provides a radiation-curable, resin composition, which when suitably cured exhibits the property of being hydrolyzable in an aqueous medium. The invention further relates to an article having at least a portion of which is formed of a radiation-curable, resin composition, which when suitably cured exhibits the property of being hydrolyzable in the presence of an aqueous medium, and to a method of removing the hydrolyzable portion. The invention also provides an improved rapid prototyping method for making a mold suitable for investment cast molding.

2. Background of the Invention

In general, radiation-curable monomers and oligomers are not hydrolyzable. For example, radiation- curable monomers and oligomers are commonly formulated so as to be suitable for coatings to protect optical glass fibers from moisture. Thus, hydrolyzability is usually not a desired property of radiation-curable monomers and oligomers.

Coatings made from such radiation-curable monomers and oligomers, which have been cross-linked by exposure to radiation, generally are difficult to remove from the coated substrate surface. Usually, such coatings are removed by heating or scraping. These methods of removing coatings are largely unsuitable for delicate surfaces which can be damaged by scraping or where the temperature resistance or stability of the substrate surface is low. While such methods can damage delicate surfaces, heating and scraping are currently used to strip the coating of coated optical glass fibers. Thus, there is a need for an improved method for removal of radiation cured coatings from delicate surfaces, for instance, by development of a radiation-curable monomer or oligomer that can be used to make a radiation-curable, resin composition which when suitably cured can be easily removed from the coated substrate surface.

U.S. patent No. 5,072,029 discloses a process for catalyzing the reaction of certain cyclic vinyl ethers with carboxylic acids, for use in making photoresists. Vinyl ethers are well known protecting groups for carboxylic acids, therefore it is not surprising to find a reference that includes the use of methacrylic acid. However, there is no disclosure of using this material for UV-curing. Instead, when photoresists are exposed to radiation they degrade by scission of the polymer bonds, rather than crosslink. Furthermore, only certain monofunctional monomers are disclosed, thus, there cannot. be any crosslinking in the final cured coating.

Published European patent application 053 690-A1 discloses certain positive photoresist compositions that contain a vinyl ether compound and a polymer containing carboxylic acid or phenolic groups. However, the polymer does not contain functional groups that undergo a crosslinking reaction when exposed to radiation. Rather, the polymer is applied from an organic solvent and dried, before exposure to radiation. Furthermore, radiation is used to degrade the polymer by scission of the polymer bonds, and not to crosslink the polymer.

U.S. patent No. 5,420,171 discloses a UV- curable, water soluble composition. However, the coatings formed from this composition are not crosslinked. Rather, a monofunctional monomer is combined with a non-reactive water soluble polymer such as polyvinyl alcohol. The water-soluble composition is used to make a temporary solder mask.

A. Darrou, et. al., "Lost Wax and Stereolithography Process" (English Language Translation), Ch. II, Foundry Applications, 3rd European Conference of Rapid Prototyping, Paris, France (Oct. 5 & 6, 1994), discloses a degradable photopolymer for rapid prototyping. The polymer is degraded in a solvent. Two process are disclosed:

(1) make a photopolymer mold, fill the mold with hot wax, degrade photopolymer, make a ceramic casting from wax pattern, and use the ceramic mold to cast metal parts; and

(2) make a photopolymer model, make a polymer shell around the model, degrade the model, and use the shell for injection molding of thermoplastics. However, this article has no disclosure of the solvent used, nor of any chemical compositions for the polymeric material. The only specific disclosure refers to a trademark Highlink SPL.

A radiation-curable, resin composition, which can be easily removed from a substrate surface or shaped article after being suitably cured, would be very useful in a rapid prototyping process to make a support form for investment casting. Rapid prototyping is the automatic production of three-dimensional physical prototypes made directly from coordinate information, such as from computer aided design ("CAD") software.

An example of a rapid prototyping process is the Cubital process described in U.S. patent No. 5,031,120 (Pomerantz). In the Cubital process, light is passed through an erasable mask to solidify a layer of a radiation-curable, resin composition in selected areas. The non-solidified portions are removed and replaced by a removable support material, such as wax. Additional layers are added until the desired three-dimensional object is completely formed. The removable support material is commonly a wax which can be removed by melting or dissolving to provide the thereby formed, free three- dimensional object.

Another example of a rapid prototyping process is disclosed in U.S. Pat. No. 4,575,330 (Hull). The Hull process is a scanning method, in which a concentrated beam of ultraviolet light is focused on the surface of a container filled with a liquid radiation-curable, resin composition. The light beam, moving under computer control, scribes a layer of the object onto the surface of the liquid. Wherever the beam strikes the surface, a very thin layer of the radiation-curable, resin composition is crosslinked to form a solid. To make a three-dimensional object, the entire operation is repeated, with the position of the object shifted slightly each time, whereby the object is built up layer by layer. Examples of radiation-curable, resin compositions that have been used in rapid prototyping methods are disclosed in U.S. patent numbers 5,418,112 and 5,434,196.

Investment casting is a very old and well known technique for the fabrication of ceramic molds which can be used for the production of metal tools and parts. The material most commonly used to create a support form for forming the ceramic mold is wax. After the ceramic mold is created, the wax can be easily removed from the mold by melting.

The combination of rapid prototyping and investment casting has been known since the introduction of rapid prototyping technology in the mid-1980s. The prospect of creating molds that are suitable for manufacturing directly from rapid prototypes is very attractive because it affords a significant time savings. Models produced by many rapid prototyping systems, including the Hull process and the Cubital process, are made of crosslinked, radiation-cured, resin compositions, which have been used to produce a polymeric support form to be used in investment casting. The polymeric support form produced replaces the wax support form. However, there are many problems associated with using such crosslinked, radiation-cured, resin compositions as the investment casting support forms. Because the polymers are crosslinked in the polymeric support form they do not melt and flow out of the ceramic mold formed on the polymeric support. The crosslinked polymers must be removed by thermal decomposition and burning, which in turn can leave an undesirable residue that affects the accuracy of the ceramic mold. Another problem is that the coefficient of thermal expansion is generally greater for the crosslinked polymer than the ceramic material, so the ceramic mold is easily cracked during the casting process. Many schemes have been tried to adapt radiation-curable, resin compositions for investment casting support forms. However, wax remains the presently preferred material for investment casting support forms because of the easy removal via melting.

Thus, there is a need for a radiation-curable, resin composition that is suitable for use in a rapid prototyping process and which when suitably cured can nonetheless be easily removed from a ceramic mold without being thermally decomposed or burned.

Wax is usually used as a support form in the Cubital method. It is possible to invert the coordinate information from the computer software so that the desired three-dimensional object is created in wax, which can then be used as the wax support form in investment casting. However, the wax support form is surrounded by the solidified and crosslinked, radiation-cured, resin composition. Currently there is no way to remove the crosslinked polymers without damaging the delicate wax support form.

Thus, there is a need for a radiation-curable, resin composition that is suitable for use in a rapid prototyping process, and which can be easily removed from a support form contained within the cured polymers without damaging the support form.

SUMMARY OF THE INVENTION An objective of the present invention is to provide a hydrolyzable radiation-curable monomer or oligomer that can be used to make a radiation-curable, resin composition that when suitably cured can be easily removed. Another objective is to provide a radiation- curable, resin composition that is suitable for use in rapid prototyping and which when suitably cured can easily be removed from a mold, without requiring thermal decomposition or burning away. A further objective is to provide a radiation- curable, resin composition that is suitable for use in a rapid prototyping process and that can be easily removed from a wax support form contained within the cured polymer formed. Surprisingly, it has been found that the above objectives, and other objectives, can be achieved by the following.

The invention provides a novel hydrolyzable radiation-curable monomer or oligomer, which when suitably cured retains the property of being hydrolyzable in a suitable aqueous medium, said monomer or oligomer compr ising: at least two radiation-curable functional groups; and at least one hydrolyzable group that hydrolyzes in the presence of a suitable aqueous medium, said two radiation-curable functional groups being connected to said monomer or oligomer via said at least one hydrolyzable group.

The invention also provides a novel radiation- curable, resin composition, which when suitably cured exhibits the property of being hydrolyzable in a suitable aqueous medium. The radiation-curable, resin composition comprises: a radiation-curable, hydrolyzable monomer or oligomer in an amount sufficient to provide said suitably cured resin composition with the ability to hydrolyze in the presence of a suitable aqueous medium, and thereby being removable, said hydrolyzable monomer or oligomer having at least two radiation-curable functional groups and at least one hydrolyzable group, and said two radiation-curable functional groups being connected to said monomer or oligomer via said hydrolyzable group.

The invention further provides a novel rapid prototyping method for generating a polymeric support form for making molds, in which a radiation-curable, resin composition is cured into the shape of a polymeric support form, wherein the improvement comprises: incorporating a radiation-curable, hydrolyzable monomer or oligomer into said radiation-curable, resin composition in an amount sufficient to provide a hydrolyzable, polymeric support form, said hydrolyzable oligomer having at least one hydrolyzable group and at least two radiation-curable groups, wherein said two radiation-curable functional groups being connected to said monomer or oligomer via said hydrolyzable group; and removing said hydrolyzable support form by hydrolyzing said polymeric support form in a suitable aqueous medium.

The invention also provides a rapid prototyping method for generating a support form for making molds, in which a radiation-curable, resin composition is cured in a shape of a polymeric mold for forming said support form, a support form is formed from said polymeric mold, and the polymeric mold is removed from said support form, wherein the improvement comprises: incorporating a radiation-curable, hydrolyzable monomer or oligomer into said radiation- curable, resin composition in an amount sufficient to provide the property of hydrolyzability to said polymeric mold, said hydrolyzable monomer or oligomer having at least one hydrolyzable group and at least two radiation- curable groups, wherein said two radiation-curable functional groups being connected to said monomer or oligomer via said hydrolyzable group; and removing said hydrolyzable polymeric mold by hydrolyzing said hydrolyzable polymeric mold in a suitable aqueous medium.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The term "hydrolyzable" is used herein to describe the property of being hydrolytically decomposable in the presence of a suitable aqueous medium. For solid cured compositions, the term "hydrolytically decomposable" as used herein includes the property of becoming a gel which is easily removable. As used herein, a monomer or oligomer refers to a radiation-curable compound.

Examples of suitable aqueous mediums include, water and mixtures of water and water-miscible organic solvents, such as ketones and alcohols. The aqueous medium can also contain additives, such as dispersants, acids, bases, buffers, salts, dyes, and surfactants. Preferably, the aqueous medium is acidic or basic in order to promote catalyzation of the hydrolysis reaction.

One skilled in the art will easily be able to select an aqueous medium which is suitable for the desired application. For example, the ability of a specific aqueous medium to hydrolyze and remove a hydrolyzable, radiation-cured, resin composition can be easily tested without undue experimentation. Hydrolyzable, Radiation-Curable Monomers and Oligomers

The hydrolyzable, radiation-curable monomer or oligomer contains as essential components at least two radiation-curable functional groups and at least one hydrolyzable group. Two radiation-curable functional groups should be connected, either directly or indirectly, via at least one hydrolyzable group. Thus, when the hydrolyzable group is hydrolyzed, any bonding between polymers achieved by the cross-linked radiation-cured functional groups will be destroyed.

One skilled in the art will easily be able to select the desired amount of hydrolyzable groups without undue experimentation. In general, the greater the number of hydrolyzable groups present in the monomer or oligomer, the easier the cured resin will hydrolytically decompose in the presence of a suitable aqueous medium. For example, the amount of hydrolyzable groups present in the monomer or oligomer should be sufficient to provide the desired level of hydrolyzability when suitably cured. Preferably, the number of hydrolyzable groups is sufficient to provide the desired level of- hydrolyzability when suitably cured, but few enough to prevent undesirable effects, such as rapid hydrolysis in ambient atmospheric humidity.

For small monomers, one hydrolyzable group may be sufficient to provide the desired level of hydrolyzability. However, for larger oligomers, which contain a polymeric backbone, more than one hydrolyzable group may be required to provide the desired level of hydrolyzability. For certain applications, a suitable amount of hydrolyzable groups in the polymeric backbone is from 1 to about 10, preferably from about 2 to about 6.

Various types of hydrolyzable groups may be used in the monomer or the oligomer backbone. An example of a suitable hydrolyzable group is an acetal ester group, as follows: 0

II -O-C-

where R_x is a hydrogen, or lower alkyl having from about 1 to about 10 carbon atoms. The ring shown by the dotted line is optional.

Preferably, R_x is a methyl group. The acetal ester group(s) can be an integral part of the carbon backbone of the hydrolyzable, radiation-curable oligomer. Alternatively, the acetal ester group can be connected to one or more radiation-curable functional groups to form a hydrolyzable, radiation-curable monomer.

The acetal-ester group can readily undergo hydrolysis as follows:

CH₃ 0 0 0

I II II »

RO-CH-O-C-R' + H₂0 - CH₃CH + R'-C-OH + ROH

This hydrolysis reaction allows cured coatings and three-dimensional objects made from the hydrolyzable, radiation-curable monomers and oligomers to be easily removed (hydrolytically decomposed) after curing.

Simple carboxylic acid esters are not considered to be hydrolyzable groups as described herein. For example, suitable hydrolyzable groups include those groups which are capable of providing a solid radiation-cured composition in the shape of a 1/8 inch by 1/2 inch by 1 inch bar with the ability to hydrolytically decompose in a static 1 normal aqueous potassium hydroxide solution at 25°C in about 5 days or less, preferably about 3 days or less. Hydrolytic decomposition has been reached when the solid has been substantially completely transformed into a soft gel that is easily separable.

The polymeric backbone of the hydrolyzable oligomer can contain hydrolyzable group(s). For example, - li ¬

the polymeric backbone can comprise one or more types of polymer blocks coupled with each other via one or more hydrolyzable groups. Thus, when the hydrolyzable groups are hydrolyzed in the cured resin, the polymer blocks are free to dissociate.

Alternatively, the polymeric backbone comprises a polymer or copolymer, to which the radiation-curable functional group(s) is connected via one or more hydrolyzable groups. Thus, when the hydrolyzable groups are hydrolyzed in the cured resin, any bonding between the polymers and/or copolymers will be destroyed, thereby allowing the polymers and copolymers to dissociate, and thereby, there is a reduction of cross-link density.

The types and molecular weight of the polymer (s) and/or copolymer (s) that can be present in the polymeric backbone will depend on the particular application and may or may not be limited. One skilled in the art will easily be able to select the type and molecular weight of the polymer (s) or copolymer (s) used to provide the desired viscosity and the desired properties of the radiation- cured resin, such as Tg, modulus, flexibility and hardness.

Suitable examples of polymers and copolymers include, but are not limited to, polyethers, polyolefins, polyesters, polycarbonates, polyurethanes and copolymers thereof. The polymers and copolymers can also be fluor inated.

Preferably, the hydrolyzable radiation-curable monomers and oligomers used have a weight-average molecular weight of about 100 to about 10,000, and more preferably about 200 to about 5,000, with the monomers having a molecular weight closer to 100 and the oligomers having a molecular weight closer to the higher end of the ranges. The radiation-curable functional groups can be any functional group capable of polymerization when exposed to actinic radiation. Suitable radiation-curable functional groups are now well known and within the skill of the art.

Commonly, the radiation-curable functionality used is ethylenic unsaturation, which can be polymerized through radical polymerization or cationic polymerization. Specific examples of suitable ethylenic unsaturation are groups containing acrylate, methacrylate, styrene, vinyl ether, vinyl ester, N-substituted acrylamide, N-vinyl amide, maleate esters, and fumarate esters. Preferably, the ethylenic unsaturation is provided by a group containing acrylate, methacrylate, or styrene functionality.

Another type of radiation-curable functionality generally used is provided by, for example, epoxy groups, or thiol-ene or amine-ene systems. Epoxy groups can be polymerized through cationic polymerization, whereas the thiol-ene and amine-ene systems are usually polymerized through radical polymerization. The epoxy groups can be, for example, homopolymer ized. In the thiol-ene and amine- ene systems, for example, polymerization can occur between a group containing allylic unsaturation and a group containing a tertiary amine or thiol.

For example, the radiation-curable, hydrolyzable monomer or oligomer can be formed by the addition reaction of a carboxylic acid with a vinyl ether, as follows:

0 CH, 0

II I II R-0-CH=CH₂ + R'-C-OH → R-O-CH-O-C-R '

In order to render these compounds radiation- curable, they can be readily terminated with any radiation-curable functional group, such as those described above. A person skilled in the art will easily be enabled to add a radiation-curable functional group to these compounds. For example, a radiation-curable, hydrolyzable monomer can be prepared by reacting two moles of acrylic acid with one mole of triethylene glycol divinyl ether.

The specific hydrolyzable radiation-curable monomer or oligomer need not contain all identical radiation-curable functional groups. The radiation-curable functional groups can be mixed as desired for the particular application.

Suitable oligomeric compounds can be formed by including polyfunctional carboxylic acids in the oligomer. For example, an oligomer of the following structure can be formed by reacting acrylic acid (AA), a dicarboxylic acid (DA) and a divinyl ether (VE) :

AA-(VE-DA)_n-VE-AA

The molecular weight of the oligomer can be easily controlled by adjusting the ratio of VE to DA. The desired molecular weight of the oligomer will depend upon the application. For rapid prototyping processes, in general, n values from 0 (monomer) to about 20 will be most useful because of the resulting viscosity and film properties. However, greater n values can be used.

Oligomers having more than two radiation-curable end-groups can be prepared by using higher functionality vinyl ethers and/or carboxylic acids.

When preparing these monomers and oligomers it is desirable to use a slight excess of vinyl ether groups compared to the stoichiometr ic amount of vinyl ether groups. When an excess of vinyl ether is used, a fraction of the monomer and oligomer compounds will have terminal vinyl ether groups. This is usually not detrimental since it is known from C. Decker, RadTech 94 Conference Proceedings, p. 602, that vinyl ethers can copolymerize to some extent with acrylates upon curing. Furthermore, the excess of vinyl ether groups insures that all of the free acrylic acid is reacted. Radiation-Curable Composition

Radiation-curable, resin compositions are now well known in the art and one skilled in the art knows how to formulate these compositions to provide the desired properties of the cured composition, such as Tg, modulus, flexibility, abrasion resistance, and organic solvent resistance.

Based on the disclosure provided herein, one skilled in the art will now be able to easily reformulate known radiation-curable, resin compositions to also provide the property of hydrolyzability to the radiation- cured, resin composition. For example, radiation-curable, resin compositions that are suitable for use in rapid prototyping methods are now well known in the art. U.S. patent Nos. 5,418,112 and 5,434,196 disclose examples of radiation-curable compositions which are suitable for rapid prototyping methods. The complete disclosure of these patents is incorporated herein by reference. A hydrolyzable, radiation-curable monomer or oligomer according this invention can be incorporated in the known radiation-curable, resin compositions in an amount sufficient to provide the cured resin composition with the desired level of hydrolyzability. Another way of providing the property of hydrolyzability to the cured resin composition, is to incorporate one or more hydrolyzable functional groups into one or more of the monomers or oligomers present in the radiation-curable, resin composition.

In general, the greater the quantity of hydrolyzable groups present in the radiation-curable composition, the easier the cured composition can be hydrolyzed in the presence of a suitable aqueous medium.

Monofunctional monomers may added as diluents to lower the viscosity of the composition. Such monofunctional monomers can copolymerize with the hydrolyzable monomer or oligomer. Since monofunctional monomers do not contribute to crosslinking they should not affect the hydrolyzability of the cured resin.

Suitable examples of monomer diluents comprise a monomer having a radiation-curable functionality as described above and an C₄-C₂₀ alkyl or polyether moiety. Specific examples of such monomer diluents include: hexylacrylate, 2-ethylhexylacrylate, isobornylacrylate, isodecylacrylate, laurylacrylate, stearylacrylate, ethoxyethylacrylate, laurylvinylether , 2-ethylhexylvinyl ether, and the like.

Suitable examples of polyether type monomers include diet yleneglycolmonoacrylate, tr iethylglycolmonoacrylate, di-propyleneglycol monoacrylate, and tri- propyleneglycolmonoacrylate. The diluent can also be a compound comprising an aromatic group. Specific examples of a diluent having an aromatic group that can be used include: ethyleneglycolphen let eraerylate, polyethyleneglycolphenyletheraer late, polypropyleneglycolphenyletheracrylate, and alkyl-substituted phenyl derivatives of the above exemplary monomers, such as polyethyleneglycolnonyl- phenyletheracrylate. Ethoxylated or propoxylated nonylphenolacrylates can also be used.

The monomer diluent, if present, is preferably present in an amount between about 1 and about 35 wt.%, and more preferably in an amount of less than 10 wt.%.

In addition to radiation-curable, hydrolyzable monomers and oligomers, and photoinitiators, the compositions may also contain various additives and fillers. Particularly advantageous are additives and fillers that enhance the removal of the solidified, hydrolyzable, radiation-curable, resin composition. These may include surfactants, salts, polyethylene glycols, ethoxylated nonylphenol, sodium bicarbonate, fillers, pigments and dyes. Rapid Prototyping Methods

The hydrolyzable, radiation-curable, resin compositions according to this invention can be used in three different novel rapid prototyping methods. In a first embodiment, the hydrolyzable, radiation-curable resin compositions can be used to produce a hydrolyzable, polymeric support form for making molds, for example ceramic molds, clay molds, silicone rubber molds, and epoxy molds. For example, the Cubital method described in

U.S. patent No. 5,031,120, which is incorporated herein by reference, is well known in the art. The hydrolyzable, radiation-curable, resin compositions according to this invention can be used in the Cubital method in place of known radiation-curable, resin compositions, as follows. In an improved Cubital method according to this invention, light is passed through an erasable mask to solidify a layer of the hydrolyzable, radiation-curable, resin composition in selected areas. The non-solidified portions of the hydrolyzable, radiation-curable, resin composition are removed and replaced by a removable support material, such as wax. Additional layers are added until the desired three-dimensional polymeric object is completely formed. The removable support material is usually a wax which is removed by melting or dissolving to provide the free three-dimensional polymeric object made of cured hydrolyzable, polymeric material.

The hydrolyzable, polymeric support form can then be coated with a molding material to form a mold, such as an investment casting mold. The hydrolyzable, polymeric support form can then be easily removed from the mold by hydrolyzing the polymeric support form in a suitable aqueous medium. Various agitation techniques including stirring, ultrasound, or water jets may be used to accelerate removal of the hydrolyzable, polymeric support form. In this improved method, damage to the mold by heat or contamination from burned polymeric materials is avoided.

In a second embodiment, the hydrolyzable, radiation-curable, resin compositions according to this invention can also be used in rapid prototyping methods to directly produce a conventional removable support form for making molds, such as investment casting molds. The conventional removable support form can be made from any conventionally used removable support material and will depend on the desired application. For example, if the conventional removable support form is to be used in making a ceramic mold for investment casting, wax can be used to make the conventional support form.

The coordinate information from the computer software in the above improved Cubital method can be inverted so that the desired three-dimensional object is created in the conventional removable support material, instead of the radiation-cured resin. The conventional removable support material can then be directly used as the removable support form to make a mold, such as an investment casting mold.

In this method, the conventional removable support form is surrounded by the solidified and crosslinked, hydrolyzable, radiation-cured, resin composition, which can be easily removed by hydrolyzing the radiation-cured resin composition in a suitable aqueous medium. Damage to the fragile conventional removable support form is avoided because scraping and heating to remove cured resin are avoided. However, the removal of the cured, hydrolyzable, resin composition may be accelerated by slight heating at temperatures below the melting point of the conventional removable support mater ial .

In a third embodiment, the hydrolyzable, radiation-curable resin compositions can be used to produce a hydrolyzable, polymeric mold which can be used to mold a removable support form for making molds, for example ceramic molds, clay molds, silicone rubber molds, and epoxy molds. In an improved method according to this embodiment, light is passed through an erasable mask to solidify a layer of the hydrolyzable, radiation-curable, resin composition in selected areas. The non-solidified portions of the hydrolyzable, radiation-curable, resin composition are removed and replaced by a removable support material, such as wax. Additional layers are added until the desired three-dimensional polymeric mold is completely formed. The removable support material is usually a wax which is removed by melting or dissolving to provide the free three-dimensional polymeric mold made of cured hydrolyzable, polymeric material.

The hydrolyzable, polymeric mold can then be used to make a removable support form for making a mold. The hydrolyzable, polymeric mold can then be easily removed from the removable support form by hydrolyzing the polymeric mold in a suitable aqueous medium. Various agitation techniques including stirring, ultrasound, or water jets may be used to accelerate removal of the hydrolyzable, polymeric mold. In this improved method, damage to the delicate removable support form by heat or contamination from burned polymeric materials is avoided. The above first and third embodiments can also be conducted using an improved Hull process, as follows. In an improved Hull method according to this invention, a concentrated beam of radiation is focused on the surface of a hydrolyzable, radiation-curable, resin composition. The radiation beam, moving under computer control, draws a layer of the object on the surface of the liquid. Wherever the radiation strikes the surface, a very thin layer of the hydrolyzable, radiation-curable resin composition is crosslinked to form a solid. To make a three-dimensional object, the entire operation is repeated, with the position of the object shifted slightly each time, whereby the object is built up layer by layer. In this case the object can be a hydrolyzable, polymeric support form. The hydrolyzable, polymeric support form can then be coated with a molding material to form a mold, such as an investment casting mold. The hydrolyzable, polymeric support form can then be easily removed from the mold by hydrolyzing the polymeric support form in a suitable aqueous medium. Various agitation techniques including stirring, ultrasound, or water jets may be used to accelerate removal of the hydrolyzable, polymeric support form. In this improved method, damage to the mold by heat or contamination from burned polymeric materials is avoided.

Alternatively, the object made in the improved Hull method can be a hydrolyzable, polymeric mold which can be used to form a removable support form. The hydrolyzable, polymeric mold can then be easily removed from the removable support form by hydrolyzing the polymeric mold in a suitable aqueous medium. Various agitation techniques including stirring, ultrasound, or water jets may be used to accelerate removal of the hydrolyzable, polymeric mold. In this improved method, damage to the delicate removable support form by heat or contamination from burned polymeric materials is avoided.

Other Uses The hydrolyzable, radiation-curable resin compositions can be used to make a removable, cured coating on an article to protect the article, for example, during shipping or handling. Once the article is no longer exposed to damage, the coating can be easily removed by hydrolyzing the cured coating.

The hydrolyzable, radiation-curable resin compositions can also be used to make a temporary solder mask, as described in U.S. patent No. 5,420,171, the complete disclosure of which is incorporated herein by reference.

The invention will be further explained by the following non-limiting examples. Example 1

A monomer was prepared by slowly adding 400.0 grams (5.56 mol) of acrylic acid to 629.2 grams (3.11 mol) of triethylene glycol divinyl ether under a dry air atmosphere. An exotherm to a temperature of 84°C was observed. After the temperature returned to 50°C the mixture was heated to 60 to 65°C for two hours. The product was a low viscosity, clear, colorless liquid. IR, --H and ¹³C NMR were consistent with the expected structure, shown as follows:

0 CH₃ CH₃ 0

II I I II CH₂= CH - C- 0 - CH - (0-CH₂-CH₂ ) ₃- 0 - CH - 0 - C - CH = CH₂

Example 2 and Comparative Example A

The monomer from Example 1 was combined with a free-radical photoinitiator (Darocur 1173, 3%) and coated on a glass plate with a 3 mil Bird bar. For comparison, a common acrylate monomer ( tr ipropylene glycol diacrylate, TPGDA) was combined with the same photoinitiator and cured under the same conditions. Both films were slightly tacky after irradiation at 2.0 J/cm² with a Fusion D Lamp in air. In a nitrogen atmosphere the compound from Example 1 was tack=free at 0.35 J/cm² while TPGDA required 0.5 J/cm². Both films were hard and brittle and resisted >200 double rubs with MEK after curing at 2.0 J/cm² in nitrogen. After 9 days at ambient room conditions, the film from the monomer of Example 1 was soft and pliable and could easily be removed by wiping with a wet towel, while the film from the Comparative Example A remained hard and was unaffected by wet wiping.

Example 3

An oligomer was prepared by reacting 173.9 grams (0.861 mol) of triethylene glycol divinyl ether with 40.0 grams (0.556 mol) of acrylic acid and 104.6 grams (0.556 mol) of azealic acid. The resulting oligomer was a clear liquid with a viscosity of 435 mpa.s. GPC analysis (polystyrene standards) showed a M_w of 2151 and M_n of 1139 and only traces of residual starting materials.

Example 4

The oligomer from Example 3 was combined with Darocur 1173 (3%) and cured at 2 J/cm² in 3 mil films and also in 1/8" x 1/2" x 1" thick bars. The cured oligomer was submerged in distilled water and IN KOH. In distilled water the film turned to a weak gel in about 4 days and the bar formed a gel in about 7 days. In IN KOH the film dissolved after standing overnight at room temperature while the bar was gone in about 4 days.

Example 5

An oligomer was prepared by reacting 168.7 grams (0.861 mol) of 1, 4-cyclohexanedimethanol divinyl ether with 40.0 grams (0.556 mol) of acrylic acid and 73.4 grams (0.556 mol) of glutaric acid. The resulting oligomer was a clear liquid with a viscosity of 9300 mPa.s.

Example 6

The oligomer from Example 5 was combined with Darocur 1173 (4%) and cured at 2 J/cm² in 1/8" x 1/2" x 1" bars. The cured material was tested for decomposition as shown in Table 1 below.

Table 1

This example demonstrates that the rate of decomposition may be increased by heating and ultrasonic treatment.

Example 7

A hydrolyzable resin composition suitable for use in rapid prototyping was prepared using the oligomer formed in Example 5. The following components were blended at room temperature:

93.14 wt% oligomer from Example 5

4.9 wt% diethoxy ethyl acrylate

(as a monofunctional diluent)

1.96 wt% benzyl dimethyl ketal (Irgacure 651, Ciba Geigy)

The composition had a viscosity of 1700 mPa.s at 32°C. A Cubital model NO. 5600 Solider unit was used. Investment casting wax was used in place of the normal Solider wax. Three second exposures through perforations the erasable mask were used to cure each layer of the hydrolyzable composition. The uncured sections of the hydrolyzable composition were removed and replaced with a layer of investment casting wax. The coordinate information was adjusted to produce 20 layer thick solid wax objects including cylinders, cubes and gears. The wax objects were encased in the solid cured hydrolyzable composition. Sections of the encased wax objects were placed in a water bath at 40°C overnight. The sections of the solid cured hydrolyzable composition exposed to the water bath transformed into a soft gel thereby allowing easy removal to liberate clean investment wax models.

Claims

C L A I M S

1. A hydrolyzable radiation-curable monomer or oligomer, comprising at least two radiation-curable functional groups; and at least one hydrolyzable group that hydrolyses in the presence of said aqueous medium, wherein said two radiation-curable functional groups are connected to said monomer or oligomer via said hydrolyzable group, and said monomer or oligomer when suitably cured retains the property of being hydrolyzable in said aqueous medium.

2. A radiation-curable monomer or oligomer according to claim 1, wherein said hydrolyzable group is an acetal ester group.

3. A radiation-curable monomer or oligomer according to any one of claims 1-2, wherein said hydrolyzable group hydrolyzes in the presence of an alkaline aqueous medium.

4. A radiation-curable monomer or oligomer according to any one of claims 1-3, wherein said radiation-curable functional group is selected from the group consisting of acrylate, methacrylate, vinyl ether, styrene, vinylester, N-substituted acrylamide, N- vinylamide, maleate esters and fumarate esters.

5. A radiation-curable monomer or oligomer according to any one of claims 1-4, wherein said monomer or oligomer, when suitably cured as part of a solid radiation-cured composition, in the shape of a 1/8 inch by 1/2 inch by 1 inch bar is capable of hydrolytically decomposing in a static 1 normal aqueous potassium hydroxide solution at 25°C in about 5 days or less.

6. A method of making a radiation curable monomer or oligomer comprising the steps of: combining a first compound containing a carboxylic acid group with a second compound containing a vinyl ether group under conditions whereby an addition reaction occurs between said carboxylic acid group and said vinyl ether group to form a third compound containing an acetal ester functional group? and introducing at least two radiation-curable functional groups onto said third compound such that said radiation-curable functional groups are connected to said monomer or oligomer via said acetal ester functional group, to thereby form said radiation- curable monomer or oligomer, and wherein said radiation-curable monomer or oligomer, when suitably cured exhibits the property of being hydrolyzable in a suitable aqueous medium.

7. A method according to claim 6, wherein said second compound is present in an amount greater than the stoichiometric amount required to react with said first compound.

8. A method according to any one of claim 6-7, further comprising the step of adjusting the ratio between said first compound and said second compound to control the molecular weight of said hydrolyzable monomer or oligomer.

9. A radiation-curable resin composition, which when suitably cured exhibits the property of being hydrolyzable in a suitable agueous medium, said radiation-curable resin composition comprising: a radiation-curable, hydrolyzable monomer or oligomer according to any one of claims 1-5, or obtainable by the method according to any one of claims 6-9, and at least one reactive diluent

10. A radiation-curable resin composition according to claim 9, further comprising a photoinitiator.

11. A radiation-curable resin composition according to any one of claims 9-10, further comprising a salt or surfactant to facilitate hydrolysis of said suitably cured resin.

12. An article having at least a portion which is hydrolyzable in the presence of a suitable aqueous medium, said portion comprising a radiation-cured resin composition having the property of being hydrolyzable in a suitable aqueous medium, wherein said radiation-cured resin composition prior to curing is a resin composition according to any one of claims 9-11.

13. A coated article having a coating which is hydrolyzable in the presence of a suitable aqueous medium, said coating comprising a radiation-cured resin composition having the property of being hydrolyzable in a suitable aqueous medium, wherein said radiation-cured resin composition prior to curing is a resin composition according to any one of claims 9-11.

14. A method of removing a hydrolyzable portion or layer from an article, said hydrolyzable portion or layer comprising a suitably radiation-cured resin composition having the property of being hydrolyzable in a suitable aqueous medium, said radiation-cured resin composition prior to curing is a resin composition according to any one of claims 9-11, wherein said method comprises the steps of: contacting said hydrolyzable portion or layer with a suitable aqueous medium under conditions whereby said aqueous medium hydrolyzes said hydrolyzable portion or layer to thereby remove said hydrolyzable portion or layer .

15. A method according to claim 14, further comprising the step of agitating said aqueous medium during said contacting step.

16. A method according to any one of claims 14-15, further comprising the step of heating said aqueous medium during said containing step.

17. In a rapid prototyping method for generating a removable polymeric support form for making molds, in which a radiation-curable resin composition is cured into the shape of a removable polymeric support form, wherein the improvement comprises: incorporating a radiation-curable, hydrolyzable monomer or oligomer into said radiation-curable, resin composition in an amount sufficient to provide a hydrolyzable, polymeric support form, said hydrolyzable monomer or oligomer having at least one hydrolyzable functional group and at least two radiation-curable groups, wherein said two radiation-curable functional groups are connected to said monomer or oligomer via said hydrolyzable functional group; and removing said hydrolyzable polymeric support form by hydrolyzing said hydrolyzable polymeric support form in a suitable aqueous medium.

18. The method according to claim 17, wherein said rapid prototyping method is a Cubital type method in which said hydrolyzable polymeric support form is formed in layers.

19. The method according to claim 17, wherein said rapid prototyping method is a Hull type method in which said hydrolyzable polymeric-support is formed in layers.

20. In a rapid prototyping method for generating a removable support form for making molds, in which a radiation-curable resin composition is cured in a shape of a polymeric mold for forming said support form, a removable support form is formed from said polymeric mold, and the polymeric mold is removed from said support form, wherein the improvement comprises : incorporating a radiation-curable hydrolyzable monomer or oligomer into said radiation-curable, resin composition in an amount sufficient to provide the property of hydrolyzability to said polymeric mold, said hydrolyzable monomer or oligomer having at least one hydrolyzable group and at least two radiation-curable functional groups, wherein said two radiation-curable functional groups are connected to said monomer or oligomer via said hydrolyzable functional group; and removing said hydrolyzable polymeric mold by hydrolyzing said hydrolyzable polymeric mold in a suitable aqueous medium to provide said removable support form.

21. The method according to claim 20, wherein said removable support form comprises a wax.

22. The method according to any one of claims 20-21, wherein said rapid prototyping method is a Cubital type method in which said polymeric mold and said removable support form are formed in layers.

23. The method according to any one of claims 20-21, wherein said rapid prototyping method is a Cubital type method in which said polymeric mold is produced, and said removable support form is formed in said polymeric mold.

24. The method according to any one of claims 20-21, wherein said rapid prototyping method is a Hull type method.

25. A method of making a radiation-curable monomer or oligomer comprising the step of: combining a first compound comprising at least one carboxylic acid functional group and a second compound comprising at least one vinyl ether functional group under conditions whereby an addition reaction occurs between said carboxylic acid functional group and said vinyl ether functional group to thereby form said radiation-curable monomer or oligomer comprising at least one acetal ester functional group; and wherein said first compound is selected such that upon reaction with said second compound, a radiation- curable functional group which is directly connected to said acetal ester functional group forms, and wherein said radiation-curable monomer or oligomer when suitably cured exhibits the property of being hydrolyzable in a suitable aqueous medium.

26. A method according to claim 25, wherein said first compound is acrylic acid.

27. A method according to any one of claims 25-26, wherein said second compound is triethylene glycol divinyl ether or 1 , 4-cyclohexanedimethanol divinyl ether .

28. A method according to any one of claims 25-27, wherein a thord compound comprising at least two carboxylic functional groups is combined with said first and second compounds in said combining step.

29. A method according to claim 28, wherein said third compound is azelaic acid or glutaric acid.