CA1314425C - Photopolymerizable films containing plasticizer silica combinations - Google Patents

Abstract

0437p PATENT
C. C. Fifield, R. T. Mayes, M. Tate, and D. F. Varnell Case 1 PHOTOPOLYMERIZABLE FILMS CONTAINING
PLASTICIZER SILICA COMBINATIONS
ABSTRACT OF THE DISCLOSURE
Disclosed is an aqueous developable, photopolymerizable composition having increased flexibility and reduced cold flow comprising a unique mixture of a siliceous material and a plasticizer in combination with known photopolymerizable monomers, polymeric binders, thermal polymerization inhib-itors, and photoinitiators.

Description

131~25 This invention relates to aqueous-developable photo-polymerizable compositions.
Photopolymerizable compositions comprising a carbo~yl-group-containing, film-forming polymeric binder, a polyfunc tional addition-photopolymerizable monomer, a thermal poly-merization inhibitor and a free radical photoinitiator are knowh. Referred to as "dry films", these compositions are developable by aqueous media because of the presence of the carboxyl groups in the polymeric binder. They are often sold as a roll of dry film sandwiched between a flexible support or substrate and a flexible cover member.
A problem encountered in the use of aqueous developable dry films is maintaining flexibility of the composition after polymerization while controlling cold flow in the unpolymer-ized composition.
It is desirable to have post-polymerization flexibility in compositions used as photoresists in the manufacture of printed circuit boards. Line trimming, and the use of flexi-ble circ~lit boards require a flexible, polymerized photore-sist. The more flexible the composition is in the polymer-ized state, the less likely it is to crack and break away from the circuit board during board flexing or line trimming.
In the past maintaining post~polymerization flexibility has been accomplished by the addition of plasticizers. How-ever, the plasticizers used in the past have tended to in-crease cold flow in the unpolymerized composition.
The undesirability of cold flow is particularly pro-nounced when the compositions are commercially supplied as laminated rolls of photopolymerizable relief-forming layers -2~ 25 of film sandwiched between flexible suppoets and flexible cover members. Cold flow causes the composition to ooze out rom between successive layers of the support and cover mem-beL, and the composition then hardens on the edge Oe the roll, a phenomenon known as "edge fusion". Edge fused rolls are difficult, and sometirnes impossible to unroll. When they are unrolled, some of the composition is often delaminated.
Therefore, it is desirable to reduce the cold flow of photopolymerizable dry film, using known photopolymerizable monomers, thermal polymerization inhibitors, and free radical photoinitiators, while increasing the post-polymerization flexibility oE the dry film.
European Patent 0 133 265 attempts to deal with the prob-lem of cold flow of photopolymerizable dry film for use in re-lief printing plates, in which the photopolymerizable layersare based on nitrile rubbers, by incorporating in those layers I 1 to lO weight percent of a pyrogenic silicic acid. Because ; of the inheeently flexible nature of the elastomeric photo-polymerizable layers, plasticizers are not necessary, but , 20 optionally they may contain dialkylphthalate plasticizers.
'I The European Patent points out that in the flexible, rel-atively thick (0.5 to 7 mm) multilayered materials it dis-closes, precipitated silicic acid can not be successfully used in place of the pyrogenic silicic acid.
In "Thixotropes", Plastics Compounding, May/June 1984, pp. 53-66, ~d Galli discusses both eumed silica and precipi-tated silica, and points out that precipitated silica differs from fumed silica in significant respects, including a larger average particle size.

.~

2a 1 3!~`25 Th~ invention is used in a photopolymerizable composition comprising a carboxyl group-containing film-forming polymeric binder, a free radical photoinitiator, an addition photopolymerizable monomer, and a thermal polymerization inhibitor. The invention relates to the improvement wherein the composition further comprises: (a) at least one plasticizer in an amount of about 5% to about 20%
by weight, wherein the plasticizer is tri-n-bukyl citrate, N-ethyltoluene sulfonamide, glycerol tri-acetate, or reaction product of (i) an isocyanate terminated block copolymer of polyesterdiol blocks selected from the group comprising polyalkylene adipatediol and polyalkylene succinatediol with polyetherdiol blocks comprising polyalkylene ~lycol/ethylene oxide and (ii) at least one hydroxy substituted acrylate or methacrylate; and (b) a siliceous material having a particle size of less than about 10 microns, in an amount of about 13%
to 25% by weight, wherein the material is precipitated silica, a combination of fumed silica and aluminum oxide, or a mixture thereof.

rn/

-3- 131~425 Precipitated silica, as is well known in the art, is made by the controlled neutralization (with a mineral acid) of a sodium silicate solution. The precipitated silica used in the composition according to the invention has a particle size of less than about 10 rnicrons, preferably less than about .02 microns.
Fumed silica (also known as pyrogenic silica), as also well known in the art, and is a product of high temperature pyrolysis of silicon-containing compounds, such as silicon tetrachloride. The fumed silica used in compositions accord-ing to the invention has a particle size of less than about 10 microns, preferably less than about .012 microns, and must be used in combination with aluminum oxide, presumably to form larger particles by hydrogen bonding .
The aluminum oxide used in the compositions according to the invention with the fumed silica has an average particle size of less than about 10 microns, preferably less than about .02 microns. The ratio, in parts by weight, of fumed silica to aluminum oxide is from about 4/1 to about 2/3, preferably from about 3/1 to about 2/1 respectively.
Based on the total weight of the photopolymerizable com-position of this invention: ~a) the amount of precipitated silica or combination of fumed silica and aluminum oxide varies from about 10~ to about 25%, preferably from about 13%
to about 19%; (b) the amount of plasticizer varies from about 5% to about 20~ preferably from about 9% to about lS~; the amount of photopolymerizable monomer varies from about 5~ to about 40%, pre~erably from about 15~ to about 2S%: the amount of photoinitiator varies from about 2% to about 10%, prefer-ably, from about 3% to about 7%; the amount of the polymeric ~' -4~ 25 binding agent.varies from about 30~ to about 75%, preferably 45% to about 60%, and the amount of thermal polymerization inhibitor varies from about .003% to about .04~, preferably from about .01~ to about .02~.
S Plasticizers other than tri-n-butyl citrate, glycerol triacetate, the reaction products of isocyanate-terminated block copolymers of polyesterdiol blocks and polyalkylene glycol/ethylene oxide blocks and the hydroxy-subs~ituted ac-rylate or methacrylate, and N-ethyl-toluene sulfonamide (which includes N-ethyl-ortho-toluene sulfonamide and N ethyl-para-toluene sulfonamide or a mixture of both), do not work in the compositions according to the invention. In particular, the dialkylphthalate plasticizers disclosed in European Patent 0 133 265 are not effective.
The reaction products of isocyanate terminated block co-polymers of polyesterdiol blocks and polyalkylene glycol/
ethylene oxide blocks and hydroxy-substituted acrylates or methacrylates, and their preparation, are well known, for in-stance rom U.S. Patent No. 3,960,572. Polyesterdiols that may be used in the reaction include, for example, polyethylene adipatediol, polypropylene adipatediol, polybutylene adipate-diol, polyhexamethylene adipatediol, and polyethylene suc-cinatediol. Of these, polyethylene adipatediol is preferred.
Polyalkylene glycols that may be used in the reaction include, 2S for example, ethylene glycol and propylene glycol~ Of these, the ethylene glycol is preferred, ~iisocyanates that may be used in terminating the block copolymer are, for example, tol-uene diisocyanate and paraphenylene diisocyanate, of which the former is preferred.
Hydroxy-substituted acrylates or methacrylates that may be used in the reaction are, for example, 2-hydroxyethyl acry-late or methacrylate, hydroxypropyl acrylate or methacrylate, and polypropylene glycol monomethacrylate. ~ydroxypropyl methacrylate and polypropylene glycol monomethacrylate are 3S preferred.
All these examples of reaction products of isocyanate terminated block copolymers and hydroxy substituted acrylates -5- 1 31 ~a~25 or methacrylates that may be used in compositions according to the inventioh are disclosed in the above-mentioned U.S. Pat~
No. 3,960,572.
Preferred molar ratios for the reaction are 1:1:3-2 ~polyesterdiol: polyalkylene glycol/ethylene oxide: isocya-nate) and 1:2-2.5 (isocyanate: hydroxy substituted acrylate or methacrylate).
The free-radical photoinitiator used in compositions ac-cording to the invention is a conventional photoinitiator activatable by actinic radiation that is thermally inacti~e below about 185C. Examples of useful photoinitiators are well known, for instance from U.S. Patent 4,268,61G. Prefer-able photoinitiators are aromatic ketones, such as benzophe-none.
lS The conventional addition-photopolymerizable monomers that contain at least 2 ethylenic double bonds, used in the compositions according to the invention, are non-gaseous ac-rylate esters. They are polyfunctional, i.e., capable of cross-linked polymerization, and preferably they contain 3 or 4, more preferably 3, ethylenic double bonds. They have num-ber average of molecular weights from about lO0 to about 500.
Suitable monomer~ include ethylene diacrylate; dlethylene glycol diacrylate; glycerol diacrylate; glycerol triacrylate, 1,3-propanediol dimethacrylate; 1,2,4-butane-triol trimethac-rylate; 1,4-benzenediol dimethacrylate; 1,4-cyclohexanediol diacrylate; pentaerythritol tri- and tetramethacrylate; pen-taerythritol tri- and tetraacrylate; tetraethylene glycol dimethacrylate; trimethylolpropane trimethacrylate; tri-ethylene glycol diacrylate; tetraethylene glycol diacrylate, pentaerythritol triacrylate, trimethylol propane teiacrylate;
pentaerythritol tetraacrylate; 1,3-propanediol diacrylate;
1,5-pentanediol dimethacrylate; and the bis-acrylates and bis-methacrylates of polyethylene glycols, polypropylene glycols, and copolymers thereof. Monomers containing vinylidene groups conjugated with ester linkages are preferred.
A conventional thermal polymerization inhibitor is used in compositions according to the invention to prevent thermal -6- 1 3 1 ~r 4 2 ) polymerization during drying and storage. Examples of useful thermal polymerization inhibitors are p-methoxyphenol, hydro-quinone, alkyl and aryl-substituted hydroquinones ~nd qui-nones, tertbutyl ~atechol, pyrogallol, copper resinate, 3-naphthol, 2,6-di-tert-butyl-p-cresol, 2,2'~methylene-bis (4-ethyl-6-t-butylphenol), p-tolylquinone, chloranil, aryl phosphites, and aryl alkyl phosphites.
The carboxyl-group-containing film-forming polymeric binder used in compositions according to the inven~ion and its preparation are well known,for instance from U.S. Pat.
No, 4,539,286. They are prepared from one or more film-forming, vinyl type monomers and one or more alpha, beta ethylenically unsaturated monomers containing carboxyl groups and having 3-15 carbon atoms, which makes the binder soluble in aqueous media. Vinyl type monomers that may be used are alkyl and hydroxyalkyl acrylates and methacrylates having 3-15 caebon atoms, styrene, and alkyl substituted styrenes. The acrylates and methacrylates are preferred, Examples of carboxyl-group-containing monomers that may be used are cin-namic acid, crotonic acid, sorbic acid, acrylic acid, metha-crylic acid, itaconic acid, propiolic acid, maleic acid, fumaric acid, and half esters and anhydrides of these acids.
Acrylic acid and methacrylic acid are preferred.
Preferably, a monofunctional carboxyl-group-containing addition-photopolymerizable monomer (i.e., one containing one ethylenic double bond) i5 additionally added to compositions according to the inventionO The photopolymerized material made from the photopolymerizable composition then has better adhesion to the copper surfaces of conventional substrates, and is strippable from a substrate in small pieces. Without this monomer, the photopolymerized material can be stripped well, but in large sheets. Stripping in small pieces is pre-ferred since the photopolymerized material~between fine lines is more easily removed. Also, some stripping apparatuses have filtration systems that could have clogging problems if strip-ping occurs in large sheets.

_7~ 131 ~a,25 Examples of such monofunctional carboxyl-group-containing addition~photopolymerizable monomers are itaconic acid, beta-carboxyethylacrylate, citraconic acid, crotonic acid, monomethacryloyloxyethyl phthalate, monoacryoyloxyethyl phthalate, and fumaric acid. Itaconic acid and beta-carboxy-ethylacrylate are preferred.
Based on the weight of the photopolymerizable composi-tion according to the invention, the amount of the monofunc-tional carboxyl group-containing addition photo-polymerizable monomer used is preferably from about 1% to about 10%, more preferably from about 1.5~ to about 6%.
The photopolymerizable compositions of this invention optionally include additives well known in the art of photo-polymerizable compositions, such as leuco (i.e., printout) dyes, background dyes, adhesion promoters, and antioxidants as disclosed in U.S. Patent 4,297,~35, and the above-mentioned U.S. Patent 4,268,610. Other optional additives will be ap-yarent to those skilled in the art.
The compositions are prepared by mixing the various com-ponents in a solvent. ~ixing must be sufficient to evenlydisperse the siliceous material throughout the mixture. Suit-able solvents are alcohols, ketones, halogenated hydrocarbons, and ethers. Other solvents will be apparent to those skilled in the art. After mixing, the composition is coated onto a support, and the solvent is evaporated.
The methods for using the photopolymerizable composi-tions of this invention, as rolls of dry film sandwiched between a flexible support member and a flexible cover member are well known, as for instance from U.S. Patent Nos.
30 3,4~9,982 and 4,293,635.
Dry films of the instant invention can be made on inflex-ible supports as well as flexible supports and may be supplied in the form of stacks of laminated sheets (as disclosed in the above-mentioned U.S. Patent 4,268,610~ as well as in rolls.
Preferably, the photopolymerizable compositions of this invention are used in a conventional way as a photoresist in -8- 1 31~425 the manufacture of printed circuit boards. The composition is coated onto the copper surface of a copper clad substrate, exposed to actinic radiation through a negative to create a latent image of photopolymerized material, and developed in a known aqueous developing solution to remove the unpolymerized composition from the copper surface. The portions of the sur-face not covered by the photopolymerized material are then modifiable by known processes, e.g., by plating or etching procedures, while the photoresist protec~s the covered sur face~ The photopolymerized material can be ultimately re-moved from the substrate by washing with known stripping solutions.
The photopolymerizable compositions according to the in-vention are applied to the copper clad substrate by known pro-cedures, such as hot shoe or hot roll lamination of the dryfilm attached to a transparent, peelable support, which sup-port is removed after polymerization, as disclosed in the above-mentioned U.S. Patent No. 4,293,635. Generally, the amount of actinic radiation used to polymerize the composition varies from about 35 to about 150 mJ/cm , with precise amounts determinable by those skilled in the art based on the specific composition used.
The copper clad substrate is any known copper/dieletric laminate used in circuit board manufacture, such as a copper clad board of fiberglass reinforced epoxy resin.
The aqueous developing solutions used in accordance with this invention have, by weight, about .5-10~ alkaline agents, preferably about .5-1~, and the latent-imaged board is washed in the solution for a time sufficient to remove the unpoly-merized composition. Useful alkaline agents are alkalai metalhydroxides, eOg., lithium, sodium and potassium hydroxide, the base reacting alkalai metal salts of weak acids, e.g., sodium carbonate and bicarbonate, and alkalai metal phosphates and pyrophosphates. Sodium carbonate is preferred. The circuit board can be submerged in the developing solution or, prefera-bly, the solution is sprayed under high pressure on the board.

9 131~425 In general, the stripping solutions useful in removing the photopolymerized material in accordance with the instant invention are heated aqueous alkaline solutions, using the same alkaline agents as the developing solutions, but having a higher alkaline concentration, i.e., generally, by weight, fro~ about 1% - 10~, preferably from about 1~ - 3%. General-ly, the stripping solution is heated to a temperature of about 45C - 65C, preferably about 50C - 55C. Washing the sub-strate to remove the photopolymerized material is by methods well known to those skilled in the art, such as spraying the substrate with the heated stripping solution or, preferably, agitating the substrate in a heated bath of the stripping solution.
Examples of the photoimaging techniques and equipment, including radiation sources, exposure intensity and duration, developing and stripping solutions and techniques, and lami-nated board compositions useful in the preferred embodiment are all well known, for instance from the U.S. patents 3,469,982, ~,293,635, and 4,268,610 already mentioned.
The ability of compositions according to the invention to remain flexible upon photopolymerization is particularly important in the processing steps commonly encountered in circuit board manufacture. In particular, flexing of lami-nated substrates will not cause cracking when using the photo-polymerized material of this invention. Even where flexible substrates are not employed, the flexible nature of the photo-polymerized material helps to prevent chipping as the lami-nated boards are handled.
The compositions according to the invention are useful in solvated form. For example, in silk screen printing tech-niques for circuit board manufacture, which are well known for instance from the textbook '~ CL ~ C ~~n~,b~, 2nd edition, ed. by Clyde F. Coombs, Jr., (1979), the compositions are applied to circuit boards in solvated form, Alsot in photoimaging techniques as described in the preferred embodi-ment herein, the composition can be coated onto the substrate in solvated form, and the solvent then evaporated.

13 ~ ~D,25 To more a.dequately describe the invention, the following Examples and Controls are included. ~11 parts and percentages in the Examples and Controls are by weight unless otherwise indicated.

EX~MPI.E 1 ~ his example illustrates a photopolymerizable composi-tion of this invention and its reduced cold flow. The photo-polymerizable composition is prepared using the ingredients listed below:
Parts Control butylated hydroxy toluene (antioxidant) .008 .01 DMPAP (photoinitiator) 4 4 PBCH (print-out dye developer).656 .8 15 TDA3 (polymerizable monomer)5.04 6.15 TMPT~4 (polymerizable monomer)5.04 6.15 acrylic binder 34.25 41.75 precipitated silica6 8.52 --glycerol triacetate (plasticizer) 8.94 __ 20 leuco crystal violet (print-out dye) .115 .14 blue dye solution7 (background dye) .39 .48 methyl ethyl ketone (solvent)27.5 20 .

1. dimethoxyphenyl acetophenone 2. pentabromo monochloro cyclohexane 3. triethylene glycol diacrylate 4. trimethylol propane triacrylate 5. prepared from 49.5% ethyl methacrylate, 35.5~ ethyl acrylate, and 15% methacrylic acid, dissolved in methyl ethyl ketone 0 ~. median agglomerate size= 1.4 micrometers' average particle size= 21 nanometers, surface size area= 150m2/gm 7. methanol, victorian blue, and brilliant green 1 3 1 ~4 25 The ingredients are mixed thoroughly using a mechanical stirrer at room temperature for six hours at lOOOrpm.
Sample rolls of film using the compositions of Example 1 and the Control are made, and the films are sandwiched be-tween a polyester film support and a polyethylene cover sheet.The rolls are dried in forced hot air ovens at 155-212F.
The resulting dry film thickness is about 40 micrometers.
Samples of these films are tested for complex viscosity.
Complex viscosity measurements are made with a RheometricS
Mechanical Spectrometer (RMS) at 60C. To take the measure-ments, the support and cover sheets are removed and successive layers of dry film are stacked to make an 80 mil thick test sample.
Edge fusion tests are run at 85F in 50~ relative humid-ity and 80~ relative humidity. Two Examples and two Controlrolls are tested at both humidity levels. Complex viscosity is recorded in Table 1 and Edge fusion tests are recorded in Tables 2 and 3 below. Edge fusion i5 recorded as 0 = none, 1 = very slight, 2 ~ slight, 3 = moderate and somewhat function-ally defective, and 4 = severe and un~uestionably a rejectfilm. Edge fusion is measured up to 28 days.

-12- 131~25 , TABLE 1 ~ C~L~

Example 1 7.8 x 106 Control 2.2 x 106 Edge Fusion @85F and 50% RH

DAYS

3 5 7 10 1~21 28 Example 0 0 1 2 22 2 Control 1 1 2 2 2-3 3-4 0 1 2 2 2-3~ -Edge Fusion @85F and 80% RH

DAYS

Example 1 0 0 1 1 2 2-3 3 Control 0 1 2-3 3 3-4 - - --13- 13~25 Tables l,.2, and 3 show that the composition of this in-vention has reduced cold flow over the sarne composition with-out plasticizer and precipitated silica. Furthermore, the Tables show that an increase in complex viscosity results in an increased resistance to cold flow.

EX~PLE 2 To show the superiority of the precipitated silica/
plasticizer containing compositions of the instant invention over compositions containing precipitated silica alone and plasticizer alone, a composition is prepared using the formu-la~ion of Example l and three control films are prepared that are identical except that one contains no precipitated silica and plasticizer, one contains precipitated silica alone (no plasticizer), and the third contains plasticizer alone (no precipitated silica). The ingredients are intimately mixed for several hours at l,OOOrpm. The mixture is then coated with a doctor blade onto a polyester support film and the solvent evaporated by air drying for about 16 hr. Dry film thickness is about 38 micrometers.
Complex viscosity mesurements (RMS @60C) are made.
Samples of the films are laminated to scrubbed copper lami-nate panels, using a hot shoe laminator at 235F at four feet per minute. The films are then exposed to a medium pressure Hg lamp and developed in a .15~ sodium carbonate solution at 85F.
Chipping of polymerized films is an indication of poor flexibility. To test for flexibility, the sample polymer-ized films are cut with a razor blade drawn at a 90 angle to the plane of the films.
An attempt to laminate the control film containing sili-ca alone is unsuccessful hecause it has poor adhesion and it is so brittle it cracks, even in its unpolymerized state.
Complex viscosity cannot be measured either Eor the same reasons.

1 3 ~ ~25 Complex viscosities and eazor test results are recorded in Table ~ below:

Complex Viscosity ~azor Co~

Example 2 5.2 x 10 no chipping Control (no silica 1.5 x 106 chips badly and plasticizer) Control with silica ~too brittle to test) (too brittle to test) Control with 1.35 x 105 no chipping plasticizer The results show that adding precipitated silica and plasticizer according to the instant invention increases the complex viscosity, which is a measure of resistance to cold flow and decreases chipping, which is a measure of increased post-polymeriæation flexibility, while using precipitated silica alone actually increases chipping and using plas-ticizer alone actually decreases complex viscosity.
EX~MP~E 3 A film of the composition of this invention is prepared using the procedures of Example 2 and the following formu-lation:

-15- 13~ 25 = Parts ___ butylated hydroxy toluene .008 PBCH .65 5 acrylic binder (as in Example l) 34.3 T~5PTA 5.1 TDA 5.1 precipitated silica 8.52 (as in Example 1) 10 plasticizer ~described below)13.3 leuco crystal violet .23 blue dye solution .39 methyl ethyl ketone 40 The plasticizer used is a block copolymer of polyethylene adipatediol and polypropylene glycol/ethylene oxide, termi-nated with toluene diisocyanate, at a mole ratio of 1:1:3 respectively, and capped with hydroxypropylmethacrylate, at a mole ratio o~ 2:1 (hydroxypropylmethacrylate: diisocyanate).
The capped terminated block copolymer has a molecular weight o~ 2439.
A control is prepared in like manner but without plas-ticizer and precipitated silica.
The films are exposed and developed as in Example 2 and razor blade tests show that the control chips badly while the Example prepared according to this invention doesn't chip, i.e., the Example is more flexible than the control.

EX~MPLE 4 Example and control films are prepared as in Example 3 except that the plasticizer used is N-ethyl-toluene sulfon-amide (9.16 parts), and 10.1 parts of precipitated silica areused. The complex viscosity (RMS @60C) of Example 4 is 4 x 106 poise while the control (no precipitated slicia and plasticizer) measures 7.8 x lO5 poise, showing the Example more resistant to cold flow than the control. After exposure -16- 131~425 and development as in Example 3, the Example film doesn't chip when razor tested while the control chips badly showing that the control is less flexible than the Example.

To show that fumed silica, by itself, does not work in the instant invention, a film is prepared using the same formulation as Example 1. A control is prepared using fumed silica (8.S2 parts) instead of precipitated silica. Films are prepared as in Example 2. The film containing fumed sili-ca showed extensive streaking and visible particles, making it unsuitable for photoimaging purposes. The film containing precipitated silica was of good ~uality having no streaks or visible particles. The fumed silica used has an average pri-mary particle size of 12 nanometers and a surface area of 200 m2/gm.

To show the use of fumed silica and aluminum oxide in the instant invention, a film is prepared as in Example 2 using the following ingredients:

20 ~ Parts butylated hydroxy toluene .01 PBCH .97 acrylic binder (as in Example 1) 50.78 25 TMPTA 7.48 TDA 7.48 leuco crystal violet .34 blue dye solution .S8 fumed silical 6.33 30 aluminum oxide 6,33 tri-n-butyl citrate (plasticizer)13.26 methyl ethyl ketone 50 -17- 131~425 l. average particle size = 12 nanometers, surface area of 200 m2/gm 2. average particle size = 20 nanometers: surface area =
100 m2/gm A control is prepared without fumed silica, i.e., aluminum oxide alone. The complex viscosity of Example 6 (RMS @ 60C) is lcl x 107 poise while the control measured 1.7 x 106 poise showing that the control does not exhibit good resistance to cold flow as does the Example.
The Example 6 film is exposed and developed as in Example 2 and shows a flexible polymerized film that does not chip when razor-cut.

To show the use of the monofunctional carboxyl group-containing addition photopolymerizable monomer in a pre-ferred embodiment of the instant invention, the following photopolymerizable composition is prepared:

C m~y~ Grams butylated hydroxytoluene0.01 PBCH 0.80 acrylic binder (as in Example 1) 41.75 TMPTA 6.15 25 TDA 6.15 precipitated silica (as in Example l) 10.4 glyceroltriacetate 10.9 itaconic acid 1.89 30 leuco crystal violet 0.56 blue dye solution 0.48 methyl ethyl ketone 27,5 -1~- 1 31 ~425 A composition of the instant invention is prepared with-out itaconic acid. soth compositions are stirred several hours at 1000 rpm at room temperature. Films are cast onto polyester film using appropriate doctor blades to obtain a thickness of 37.5 microns. The films are allowed to dry overnight at room temperature. Copper laminate panels are cleaned and scrubbed, and the dry films are laminated to the~ using a hot shoe laminator at 235F at an approximate rate of 4O0 feet per minute. Films are exposed through diazo artwork with a medium pressure mercury vapor arc lamp.
The developing is done in dilute alkaline solution at 85F.
Stripping of the cured resist is carried out in a 2 liter beaker equipped with a mechanical stirrer in 3% aqueous potassium hydroxide at 50C to evaluate particle size. The panels are examined under a microscope for cleanliness of polymerized material removal ~etween fine lines.
The Example of the instant invention that contains itaconic acid strips in small pieces and the removal of polymerized material from between fine lines is complete.
The composition without itaconic acid strips in a large sheet and there is polymerized material between fine lines indicating that further stripping is required.

Claims (12)

1. In a photopolymerizable composition comprising a carboxyl group-containing film-forming polymeric binder, a free radical photoinitiator, an addition photopolymerizable monomer, and a thermal polymerization inhibitor, the improvement wherein the composition further comprises:
a. at least one plasticizer in an amount of about 5% to about 20% by weight, wherein the plasticizer is tri-n-butyl citrate, N-ethyltoluene sulfonamide, glycerol tri-acetate, or reaction product of (i) an isocyanate terminated block copolymer of polyesterdiol blocks selected from the group comprising polyalkylene adipatediol and polyalkylene succinatediol with polyetherdiol blocks comprising polyalkylene glycol/ethylene oxide and (ii) at least one hydroxy substituted acrylate or methacrylate; and b. a siliceous material having a particle size of less than about 10 microns, in an amount of about 13% to 25%
by weight, wherein the material is precipitated silica, a combination of fumed silica and aluminum oxide, or a mixture thereof.

2. The composition of claim 1, wherein the plasticizer is tri-n-butyl citrate.

3. The composition of claim 1, wherein the plasticizer is N-ethyl-toluene sulfonamide.

4. The composition of claim 1, wherein the polyesterdiol blocks are polyethylene adipatediol blocks.

5. The composition of claim 1, wherein the polyalkylene glycol is polypropylene glycol.

6. The composition of claim 1, wherein the hydroxy substituted acrylate or methacrylate is hydroxypropyl-methacrylate or polypropylene glycol monomethacrylate.

7. The composition of claim 1, wherein the siliceous material is precipitated silica.

8. The composition of claim 1, wherein the siliceous material is a combination of fumed silica and aluminum oxide.

9. In a photopolymerizable element comprising a photopolymerizable composition sandwiched between a support member and a cover member, the improvement wherein the photopolymerizable composition is the photopolymerizable composition of claim 1.

10. The composition of claim 1 further comprising a monofunctional carboxyl group-containing addition photo-polymerizable monomer.

11. The composition of claim 10, wherein the monofunctional carboxyl group-containing addition photo-polymerizable monomer is itaconic acid.

12. The composition of claim 10, wherein the monofunctional carboxyl group-containing addition photo-polymerizable monomer is beta-carboxyethylacrylate.