JPH0528825B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to photopolymerizable resist materials. More particularly, it relates to aqueous processable resist compositions that can be laminated to copper surfaces.

Photopolymerizable resist materials are known from US Pat. No. 3,469,982, which describes the production of film resists in the form of a sandwiched photopolymerizable layer between a cover sheet and a temporary support. . This film resist is then laminated to a copper or copper laminate and exposed and processed to provide a photopolymerizable layer that serves as a resist for subsequent etching.

Aqueous processable photopolymerizable resists offer significant advantages to the printed circuit industry in terms of lower cost and environmental safety, and acid binders play an important role in such resist devices. , the acid binder is German Patent No. 2123702 and U.S. Patent No.
4273857, UK Patent No. 3458311 and UK Patent No. 1507704
It is stated in each specification.

In the manufacture of printed circuit boards from film resist elements, it is necessary to laminate the photosensitive layer of the element to a substrate board. US Patent No.
No. 3,547,730 discloses a lamination process in which the laminated layers achieve sufficient adhesion to the substrate to withstand subsequent photoresist processing steps of development, etching, and plating. One of the problems with resist use is adhesion. US Patent No.
No. 3,622,334 describes the addition of heterocyclic nitrogen-containing compounds such as benzimidazole to polymerizable compositions to improve the adhesion of photopolymer resist films used in aqueous plating solutions. Although this technique is advantageous for resists that are removed with organic solvents, it may be useful to deposit aqueous processable acid binder resist compositions, especially if several days elapse between deposition and development. It causes stain and scum formation on copper surfaces.

According to the present invention, the photopolymerizable resist composition comprises a copper substrate and a processable photopolymerizable resist composition, the photopolymerizable resist composition comprising a photopolymerizable ethylenically unsaturated monomer, a photoinitiated agent or photoinitiator system and
consisting of a binder having an acid value of 100 or more, and a molecular weight not exceeding 300, a solubility of at least 0.01 g in 100 g of water at 20°C, and a solubility of 1 x 10 ^-5 to 5 x 10 ^-2 An improved element comprising a copper substrate laminated with the processable polymerizable resist composition described above is proposed, the improvement being the incorporation into the composition of an acid having a dissociation constant in the range of . The acid is present in an amount sufficient to prevent stain or scum formation on the copper surface.

First definition for conventional aqueous processable photopolymerizable resist compositions containing a photopolymerizable ethylenically unsaturated monomer, a photoinitiator or initiator system, and a binder having an acid number greater than or equal to 100. A particularly undesirable result of the binder is the formation of an undesirable scum or stain on the copper surface to which the composition is laminated. If the resist remains in contact with the copper for more than a few hours, acceptable results will not be obtained.
Although it is possible to minimize the problem by quickly processing the laminated resist,
This is not a practical solution if a large number of laminates must be processed in a single processing machine. In such cases, where more than one processing step is required for the stacked resist, development must be delayed.

In resist lay-up and removal tests using various binder components, a light tan stain was observed on the copper surfaces used. The most significant stains occur when low molecular weight (approximately 6000) binders with high acid numbers, such as at least 100, and more commonly at least 200, are used. Further testing on samples in which the resist formulation was deposited on a copper surface for a week or more revealed that the copper surface remained coated with irregular residual coverage after the resist was dissolved away with an alkaline solution. Ta.

According to the invention, at least 0.01 g of at least 0.01 g in 100 g at 20° C., even if the molecular weight does not exceed 300.
The addition of an acid having a solubility of 1×10 ⁻⁵ to 5×10 ⁻² and a dissociation constant in the range of 1×10 −5 to 5×10 −2 reduces or minimizes scum or stain formation.
Generally, the acid will have a molecular weight of no more than 250. The acid is incorporated into the photopolymerizable resist composition (usually present as a film) in an amount sufficient to improve resistance to scum or stain formation. 0.01〜
Addition of 1.0% by weight of acid (based on the weight of the other components of the photopolymerizable composition, i.e. photopolymerizable monomer, photoinitiator or initiator system and binder) is satisfactory. . The preferred range is 0.1-0.5% to provide resistance to appreciable scum or stain formation. However, higher acid concentrations can also be used. The upper limit on the amount of acid is not critical, other than that the acid should not appreciably interfere with the adhesion of the photopolymerizable composition. This acid is preferably a carboxylic acid.

Desirable properties of the acids of this invention are that they are water soluble and readily release pronto. Weak organic acids with dissociation constants below 1×10 ⁻⁵ are excluded. The protection from stain and scum formation provided by the present invention is due to the ability of these acids to diffuse to the copper surface and create a protective coating before the acid groups on the binder become bound to the copper surface. It is believed that. This result should not be too strong. Otherwise, the acid will not be removed by the aqueous nature of the resist. This undesirable effect occurs in the case of oxalic acid (dissociation constant 5.4×10 ⁻² ), which forms strong bonds with the copper surface.

Acids that have been found to be particularly useful in the practice of this invention are citric acid, malonic acid, malic acid, and maleic acid. Also found to be useful are sebacic acid, benzoic acid, chlorosuccinic acid, pimelic acid, azelaic acid, adipic acid, glutaric acid, phthalic acid and succinic acid.

This aqueous processable resist composition is required to be compatible directly with copper substrates. In this text, "direct" refers to the absence of the type of interlayer that would inhibit stain formation on the copper substrate of comparable resist compositions, i.e., compositions without the presence of acid. It means. For example, a small amount of adhesive between the copper and the resist composition may be acceptable. Generally no intervening material is present and the resist composition is contacted with the copper substrate.

Without wishing to be bound by any theory, it is believed that the addition of the acids of the present invention into aqueous photopolymerizable compositions may play a role distinct from the effect of increasing coating adhesion to copper substrates. it is conceivable that. US Patent No.
No. 3,622,334 discloses compounds such as benzotriazole and 5-chlorobenzotriazole for increasing the adhesion of photopolymerizable resists to substrates.

Chelators such as benzotriazole can bind strongly to copper surfaces. G.
Corros.Sci. by W. Polling, 10 (5), 359,
(1970), X-ray diffraction and electromechanical studies have shown that benzotriazole functions by forming a chemical complex with copper ions on the surface, creating a highly impermeable physical barrier layer. This indicates that it will be generated. Initially, it was believed that the addition of benzotriazole into resist formulations containing high acid value binders was a method of inhibiting stain and scum formation on copper. The results show that benzotriazole and 5-chlorobenzotriazole can provide some improvement, but
However, it was shown that a sample with a binder having an acid number of 200 and a time period of two weeks did not give completely satisfactory results. A sample resist of this same formulation left in laminate to a copper circuit board for 4 weeks left a higher degree of deposits on the copper than observed previously, i.e. surface interactions were slow but continuous. It showed that it was hot.
Although excellent results can be obtained when using benzotriazole and 5-chlorobenzotriazole with binders with acid numbers below 100, this technique has been tested with binders of much greater acidity. was unsuccessful.

Stain and scum become surface residues that can inhibit etching if they cannot be removed by the etching agent or if they are not attacked by the etching agent.
Soaking and/or cleaning steps can also be used for stain or scum removal prior to etching, but this negates the benefits of faster or lower temperature processing associated with highly acidic binders. I end up making it.

By comparing the etching time of the test formulation to the time required to etch a freshly scrubbed control specimen under the same conditions, a rough idea of the effect of surface stain or scum residue on etching can be obtained. It is possible. However, this was not a sensitive test to these residues. And more sensitive tests have been developed.

A contact angle test determines the amount of residue. It involves measuring how the equilibrium contact angle for water or an aqueous solution on a copper panel changes with etchant dip time. Contact angle is a sensitive measure of how clean a copper panel is compared to a freshly scrubbed and etched panel, which consistently gives a contact angle of 10 degrees or less. For comparison, on laminated and developed panels, the contact angle is approximately 60° to 70°
, which indicates the presence of residue. The length of immersion time in the etching agent to obtain an angle of less than 10° then represents a quantitative measure of the extent of the residue; for certain results, the temperature of the etching agent, the agitation, the etching agent Careful control over the time and measurements between removal and washing must be implemented. Because of the effect of air oxidation on the copper surface, measurements should be performed within 5 minutes of etching and cleaning. Although water is the most convenient wetting agent to use, the sensitivity of this test can be increased by the use of a 2% ethyl cellosolve solution in water.

Photopolymerizable resist compositions are prepared from a polymer component (binder), a monomer component, an initiator, and optionally a polymerization inhibitor.

Suitable binders which can be used as sole binders or in combination with others include polyacrylates and alpha-alkyl polyacrylate esters such as polymethyl methacrylate and polyethyl methacrylate, polyvinyl esters. For example, polyvinyl acetate, polyvinyl acetate/acrylate, polyvinyl acetate/methacrylate and hydrolyzed polyvinyl acetate, ethylene/vinyl acetate copolymers, polystyrene polymers and their copolymers with e.g. maleic anhydride and its esters, vinylidene chloride. Copolymers such as vinylidene chloride/acrylonitrile,
vinylidene chloride/methacrylate and vinylidene chloride/vinyl acetate copolymers,
Polyvinyl chloride and copolymers such as polyvinyl chloride/vinyl acetate, saturated and unsaturated polyurethanes, synthetic rubbers such as butadiene/acrylonitrile, acrylonitrile/butadiene/styrene, methacrylate/acrylonitrile/butadiene/styrene copolymers, 2-chlorobutadiene 1,3 polymer, chlorinated rubber and styrene/
Butadiene/styrene, styrene/isoprene/
Styrene block copolymers, high molecular weight polyglycol polyethylene oxides with an average molecular weight of approximately 4,000 to 1,000,000, epoxides such as those containing acrylate or methacrylate groups, copolyesters such as those of the formula HO(CH ₂ ) _o −
OH (where n is an integer from 2 to 10) polymethyl glycol and (1) hexahydroterephthanic acid, sebacic acid, and terephthalic acid, (2) terephthalic acid,
(3) terephthalic acid and sebacic acid; (4) terephthalic acid and isophthalic acid; Acids and () mixtures of copolyesters made from terephthalic acid, isophthalic acid, sebacic acid and adipic acid, nylons or polyamides such as N-methoxymethyl polyhexamethylene adipamide, cellulose esters such as cellulose acetate, cellulose acetate succinate and Mention may be made of cellulose acetate butyrate, cellulose ethers such as methylcellulose, ethylcellulose and benzylcellulose, polycarbonates, polyvinyl acetals such as polyvinyl butyral, polyvinyl formal, polyformaldehyde.

Preferably, the binder should contain sufficient acidic or other groups to render the composition processable in aqueous developer solutions. Useful aqueous processable binders include U.S. Pat.
Examples include those disclosed in specification No. 1507704. Useful amphoteric polymers include interpolymers derived from N-alkylacrylamides or methacrylamides, acidic film-forming comonomers, and alkyl or hydroxyalkyl acrylates, such as those disclosed in U.S. Pat. No. 3,927,199. can give.

Suitable monomers that may be used as sole monomers or in combination with others include:
Namely, t-butyl acrylate, 1,5-pentadiol diacrylate, N,N-diethylaminoethyl acrylate, ethylene glycol diacrylate, 1,4-butanediol diacrylate, diethylene glycol diacrylate, hexamethylene glycol diacrylate, 1,3 −
Propanediol diacrylate, decamethylene glycol diacrylate, decatotylene glycol diacrylate, 1,4-cyclohexanediol diacrylate, 2,2-dimethylolpropane diacrylate, glycerol diacrylate, tripropylene glycol diacrylate, glycerol triacrylate , trimethylolpropane triacrylate, pentaerythritol triacrylate, polyoxyethylated trimethylolpropane triacrylate, and trimethacrylate, and U.S. Pat.
Similar compounds disclosed in No. 3380831, 2,2
-di(p-hydroxyphenyl)-propane diacrylate, pentaerythritol tetraacrylate, 2,2-di-(p-hydroxyphenyl)
-Propane dimethacrylate, triethylene glycol diacrylate, polyoxyethyl-
2,2-di-(p-hydroxyphenyl)-propane dimethacrylate, di-(3-methacryloxy-2-hydroxypropyl) ether of bisphenol-A, di-
(2-methacryloxyethyl) ether, di-(3-methacryloxy-2-hydroxypropyl) ether of bisphenol-A, di-(2-acryloxyethyl) of bisphenol-A
Ether, di-(3-methacryloxy-2-hydroxypropyl) ether of tetrachlorobisphenol-A, di-(2-methacryloxyethyl) of tetrachloro-bisphenol-A
Ether, di-(3-taacryloxy-2-hydroxypropyl)ether of tetrabromobisphenol-A, tetrabromobisphenol-A
Di-(2-methacryloxyethyl) ether of A, di-(3-methacryloxy-2-hydroxypropyl) ether of 1,4-butanediol, di-(3-methacryloxy-2-hydroxypropyl) ether of diphenolic acid -Hydroxypropyl) ether, triethyl glycol dimethacrylate, polyoxypropyltrimethylolpropane triacrylate (462), ethylene glycol dimethacrylate, butylene glycol dimethacrylate, 1,3-propanediol dimethacrylate, 1,2, 4-butanetriol trimethacrylate, 2,2,4-trimethyl-1,3-pentanediol dimethacrylate, pentaerythritol trimethacrylate, 1-phenylethylene-1,2-dimethacrylate, pentaerythritol tetramethacrylate acrylate, trimethylolpropane triacrylate, 1,5-pentanediol dimethacrylate, diallyl fumarate, styrene, 1,4-benzenediol dimethacrylate, 1,4-diisopropenylbenzene and 1,3,5-tri Examples include isopropenylbenzene.

In addition to the ethylenically unsaturated monomers, this layer may also contain at least one of the following free radical-initiated chain-extending addition polymerizable ethylenically unsaturated compounds having a molecular weight of at least 300: Preferred monomers of this type are alkylene or polyalkylene glycol diacrylates prepared from 2 to 15 alkylene glycols or polyalkylene ether glycols of 1 to 10 ether linkages and as disclosed in U.S. Pat. No. 2,927,022. For example, those having a plurality of addition-polymerizable ethylene bonds, especially when present as terminal bonds. Particularly preferred are those in which at least one, and preferably most, of such carbons are conjugated with coarse double-bonded carbons, including carbon-carbon double bonds and double bonds between carbon and heteroatoms such as nitrogen, oxygen and sulfur. This is what we are doing. Notable are those in which ethylenically unsaturated groups, especially vinylidene groups, are conjugated with ester or amide structures.

Preferred free radical-generating addition initiators that are activatable by actinic radiation and thermally inert at and below 185°C include substituted compounds having two endocyclic carbons in a conjugated carbocyclic ring system. or unsubstituted polynuclear quinone, such as 9,10-anthraquinone, 1-chloroanthraquinone, 2-chloroanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, octamethylanthraquinone,
1,4-naphthoquinone, 9,10-phenanthrenequinone, 1,2-benzanthraquinone, 2,3
-Benzanthraquinone, 2-methyl-1,4-
naphthoquinone, 2,3-dichloronaphthoquinone,
1,4-dimethylanthraquinone, 2,3-dimethylanthraquinone, 2-phenylanthraquinone, 2,3-diphenylanthraquinone, anthraquinone α-sulfonic acid sodium salt, 3-chloro-2-methylanthraquinone, retenquinone, 7 , 8,9,10-tetrahydronaphthacenequinone, 1,2,3,4-tetrahydronaphthacenequinone and 1,2,3,4-tetrahydrobenz(a) anthracene-7,12-dione. Other photoinitiators that are also useful are described in U.S. Pat. No. 2,760,863, although some of them can be thermally active at temperatures as low as 85°C, including vicinal keto Aldonyl alcohols such as benzoin, pivaloin,
Acilloin ethers, such as benzoin methyl and ethyl ether, α-methylbenzoin, α
α-hydrocarbon-substituted aromatic acyloins, including -allylbenzoin and α-phenylbenzoin. U.S. Patent No. 2850445, U.S. Patent No. 2875047,
Photoreducible dyes and reducing agents disclosed in Patent Nos. 3097096, 3074974, 3097097 and 3145104, as well as dyes of the phenazine, oxazine and quinone groups, Michler's ketones, benzophenones, 2,4,5 -Triphenylimidazylyl duplex and hydrogen donor combinations and mixtures thereof described in US Pat. Nos. 3,427,161, 3,479,185 and 3,549,367 can also be used as initiators. Sensitizers also useful in conjunction with photoinitiators and photoinhibitors are disclosed in U.S. Pat.
It is disclosed in the specification of No.

Thermal polymerization inhibitors that can be used in the photopolymerizable composition include p-methoxyphenol, hydroquinone and alkyl- and aryl-substituted hydroquinones, and quinones, tert-butylcatechol, pyrogallol,
Copper resinate, naphthylamine, β-naphthol, cuprous chloride, 2,6-di-tert-butyl-p-cresol, phenothiazine, pyridine, nitrobenzene and dinitrobenzene, p-torquinone and chloranil. Also, U.S. Patent No.
The nitroso compositions disclosed in US Pat. No. 4,168,982 are also useful for preventing thermal polymerization.

Various dyes and pigments can be added to increase the visibility of resist images. All colorants used should however preferably be transparent to the activating radiation used.

Generally suitable substrates for the methods of the present invention involving printed circuit formation are those that have mechanical strength, chemical resistance, and good dielectric properties. That is, most board materials for printed circuits are thermoset or thermoflex resins, usually in combination with reinforcing fillers. Thermoset resins with reinforcing fillers are typically used for rigid boards, while thermoflex resins without reinforcement are typically used for flexible circuit boards.

Typical structures include phenolic or epoxy resins on paper, paper-glass composites, and combinations such as polyester, epoxy, polyimide, polytetrafluoroethylene or polyethylene on glass. In most cases, the plates are coated with a layer of strongly electrically conductive metals, copper being the most common of these metals.

It will be appreciated by those skilled in the art that the surface of the printed circuit substrate to be laminated is preferably clean and free of extraneous materials that could render any appreciable portion of the surface non-wetting. It is being recognized. For this reason, it is often desirable in the printed circuit board manufacturing field to clean printed circuit substrates prior to lamination using one or more of several cleansers known in the art. The particular type of cleaning depends on whether the contamination is organic, particulate, or metallic. Such methods include degreasing with solvents and solvent emulsions, mechanical scrubbing, alkali impregnation, acid treatment, etc. and subsequent cleaning and drying.

A variety of substrates can be used for resist elements in the practice of the present invention. Suitable supports having a high degree of dimensional stability against temperature changes are, for example, polyamides, polyolefins,
One can choose from a wide variety of films constructed from high polymers such as polyesters, vinyl polymers, and cellulose esters. A preferred support for the present invention is polyethylene terephthalate.

Suitable protective cover sheets can be selected from the same group of polymeric films listed as supports. Polyethylene and polyethylene terephthalate are particularly useful as cover sheets for resist elements of the present invention.

The invention will be more clearly understood by reference to the following examples.

Example 1 A water-based resist film was manufactured by the following method.

The following ingredients were added to a vessel equipped with an air agitator for mixing.

(1) Methylene chloride 810.00g (2) Methanol 80.00g (3) Styrene butyl maleate, acid value 185, molecular weight 20000 (script set from Monsanto Company)
640) 157.50g (4) Styrene acrylic acid, acid value 200, softening point 144°C
(Available as Jyonkryl from Jyonson Wax Co., Ltd.) 114.80g This was stirred for 30 minutes.

(5) 2,2'-bis-(o-chlorophenyl)-4,
4',5,5'-tetraphenylbiimidazole
7.60g This was stirred for 5 minutes.

(6) Benzophenone 22.50g (7) Michler's Ketone 22.50g (8) Leuco Crystal Violet CI 42555
1.80g (9) p-Toluenesulfonic acid 0.45g This was stirred for 5 minutes.

(10) Trimethylolpropane triacrylate
126.00g (11) Triethylene glycol dimethacrylate 13.50g This was stirred for 5 minutes.

(12) CI Basic Green 0.14g (13) 1,4,4-trimethyl-2,5-diazobicyclo[3.2.2]-non-2-ene-N,N
-Dioxide 0.45g This was stirred for 30 minutes.

298 g of this final composition was then added to each of three containers containing the following solids dissolved in 5 g of methanol.

A 0.4g benzotriazole B 0.4g 5-chlorobenzotriazole C 0.4g anhydrous citric acid A and B are comparative examples and are based on U.S. Pat.
No. 3,622,334.

C containing citric acid as a low molecular weight water-soluble acid represents the idea of the present invention.

These solutions were coated onto a polyethylene terephthalate support using a 0.0152 cm doctor knife to produce a 0.0035-0.0038 cm thick coating.

These resist films were then laminated to copper coated epoxy resin boards and held for various times to measure scum formation or surface stain on the copper. Lamination was carried out with the aid of rubber coated roller operation at a speed of 2 feet/minute at 100 DEG -115 DEG C. and a nip pressure of 3 pounds/linear inch.

Exposure of the plate was performed using a scanning mercury arc as the irradiation source,
DMVL (Corite, Inc., Minneapolis, MN) was used. After the 15 second exposure, the polyethylene terephthalate support film was stripped off and discarded, leaving the exposed resist adhered to the copper surface.
The plate was then developed by placing it in a 30 lb/in2 spray of 105ⓓ 0.04N NaOH at a distance of 6 inches from the spray nozzle.
This step left a raw resist pattern on the copper in the transparent areas of the exposed transparency. For this method to be most useful, no resist should remain in the complementary opaque areas.

No stain or scum was observed when the resist was held on copper once. In the case of composition B, strong staining was observed after being kept for 4 days. On the other hand, composition A showed weak staining, but composition C of the present invention showed no staining. Comparative examples of compositions A and B had severe staining and scum on the copper surface when held for the same three week period.

The substitution of citric acid of the present invention for benzotriazole or 5-chlorobenzotriazole provides an improved film that is much better in its ability to hold onto copper surfaces without staining or scum formation upon aging. Ta. A decrease in line retention was observed for the experimental film relative to the comparative example. i.e. 2-3 for A and B
The mil line was 4-5 mil line for C. Etching speed, sensitivity, flexibility and wettability and other properties were equal to or better than the comparative example.

A Rame-Haet contact angle goniometer (Model A100) was used to measure the contact angle of a 0.01 cm ³ drop of 2% ethyl cellosolve in water after etching the treated plate in ammonium persulfate for 10 seconds. It was measured. A lower contact angle indicates a cleaner surface. Table 1 shows the contact angle results obtained on laminated films subjected to equal treatments but for different times.

Table 1 Film 1 day 4 days 7 days Nakatsuta. The comparative examples, on the other hand, exhibited higher and more elevated contact angles that correlated with stain formation. Contact angle tests show differences in the films after being laminated to a copper surface for one day, while visual observation did not observe any staining on any of them.

Example 2 Example 1 was repeated, but instead of succinic acid
Malonic, malic and maleic acids were used in amounts of 0.4g. Improvements in resistance to stain and scum formation similar to those observed in Example 1 for citric acid were obtained.

Example 3 Resistance to scum and stain formation when sebacic acid, benzoic acid, oxalic acid, chlorosuccinic acid, pimelic acid, azelaic acid, adipic acid, glutaric acid, phthalic acid and succinic acid were combined in the resist formulation of Example 1. improvement was obtained. For stain inhibition for up to one week, these were not as effective as were the acids described in Examples 1 and 2.

Claims (1)

[Scope of Claims] 1 Consists of a copper substrate and a film of an aqueous processable photopolymerizable resist composition directly laminated thereon, the resist composition comprising a photopolymerizable ethylenically unsaturated monomer. a photoinitiator or photoinitiator system, a binder having an acid value of 100 or more, and a molecular weight not exceeding 300 and a solubility of at least 0.01 g in 100 g of water at 20°C and 1 x 10 ^-5 ~5×
an acid having a dissociation constant in the range of ^10-2 , said acid being present in an amount sufficient to inhibit stain or scum formation of said composition on the copper surface. and thus partially exposed to a scanning mercury arc and 0.04N at 105F.
After development with NaOH, the film was made to have the property of being adhesive in areas where it was exposed to a mercury arc, but non-adhesive in areas that were not exposed to a mercury arc. An element comprising the above-mentioned copper base material and a film of a resist composition. 2. The element according to claim 1, wherein the acid has a molecular weight not greater than 250. 3. The element of claim 1, wherein the resist composition is in contact with the copper substrate. 4. The element according to claim 1, wherein the acid is a carboxylic acid. 5. The element of claim 1, wherein the acid is present in an amount of 0.01 to 1.0% by weight of the monomer, photoinitiator or photoinitiator system and binder. 6 the acid is present in an amount of 0.1 to 5% by weight of said monomer, photoinitiator or photoinitiator system and binder;
An element according to claim 1. 7. The element of claim 1, wherein the acid is selected from the group consisting of citric acid, malonic acid, malic acid and maleic acid. 8. The element of claim 1, wherein the acid is selected from the group consisting of sebacic acid, benzoic acid, chlorosuccinic acid, pimelic acid, azelaic acid, adipic acid, glutaric acid, phthalic acid and succinic acid. 9. The element of claim 8, wherein the acid is present in an amount of 0.01 to 1.0% by weight of the monomer, photoinitiator or photoinitiator system and binder. 10. The element according to claim 1, comprising a cover sheet in contact with the film. 11. The element according to claim 10, wherein the cover sheet is made of polyethylene or polyethylene terephthalate.