MXPA97006886A - Method to improve photo-ima quality - Google Patents

Abstract

The present invention relates to a method for improving the resolution quality of photo images by incorporating a selected amount of a polymerization inhibitor into the photocurable resin composition that is employed so that the photo polymerization of the photo curable resin is inhibits in those areas not directly initiated by the

Description

The present invention relates to a method for improving the quality and resolution of photo images by incorporating a selected amount of a polymerization inhibitor into the photocurable resin composition that is employed, such that the photopolymerization of the photo curable resin is inhibits in those areas not directly affected by light. The light can be visible, infrared, actinic or laser light. The Patents of the U.S.A. Nos. 4,264,705; 4,427,759; 4,431,723; 4,442,302; 4,517,279; 4,540,649 and 4,716,094; Canadian Patent No. 1,267,475 and EP 335,245 disclose multilayer elastomeric printing plates, flexographic printing plates and related photopolymerizable compositions used to prepare such plates. It is evident from these representative patents that there are many requirements for the preparation of acceptable printing plates, but principal among these requirements is that the quality of the photo image is of the highest quality. That is, good resolution or a sharply defined image is essential along with durability and resistance to degradation or erosion by solvent or water based inks. EP 335,247 discloses that a hindered amine should also be present to provide stability to the cured product.

The U.S. Patent No. 4,216,019; EP 252,150 and WO 95/12148 describe the preparation of compositions for screen printing with stencil, giving stencils with solvent / water resistance. These stencils are intended for use in order to give silk screen images with good resolution and quality. The general method for using a stencil composition, includes applying or coating a photosensitive stencil composition on a screen, drying the composition, exposing the stencil appropriately through a photo mask to actinic radiation to form an image, optionally drying the image, treat the stencil with an alkaline developing solution or treat the dried stencil with an aqueous, alkaline ink and print a substrate. The U.S. Patent No. 4,517,279 illustrates the use of high molecular weight butadiene / acrylonitrile sopolymers, with a selected carboxyl and acrylonitrile content, a photopolymerizable ethylenically unsaturated monomer and photo initiator as the photopolymerizable resin composition. The U.S. Patent No. 4,716,094 illustrates the use of ethylenically unsaturated prepolymers, ethylenically unsaturated monomers, a photoinitiator and a surface adhesion modifier (to provide an adhesion free surface) as the photopolymerizable composition.

The U.S. Patent No. 4,666,821 describes the preparation of masks for hot melt welding using photopolymerizable compositions. The U.S. Patent No. 4,824,765 describes the use of water-soluble photoinitiators in general image-forming processes, useful for preparing printing plates, screen printing stencils, welding masks, lithographic and lithographic printing plates, acid-resistant materials. etching or etching, UV cured inks, final coating plates, and coatings resistant to abrasion or wear. The U.S. Patent No. 5,501,942, gives a typical procedure for the preparation of welding masks or resistant materials, which includes applying a photosensitive composition to a substrate, removing water from the composition to form a photosensitive film on the substrate, exposing the substrate coated with actinic light. in a desired pattern, remove the unexposed areas from the coating with an aqueous or alkaline aqueous solution to discover the substrate in the unexposed areas and subject the coating on the substrate to an optional UV or thermal curing. EP 261,910 and EP 295,944 both describe the photosensitive resin plate which is developed with water suitable for producing printing plates with high resistance to water-based inks.

From each of these references and the technique in general, it is clear that the steps to produce printing plates, welding masks and any other end-use application mentioned above, involve a photopolymerizable composition having the following components: (a) a polymer or prepolymer containing some polymerizable or crosslinkable groups; (b) an ethylenically unsaturated monomer; (c) a photoinitiator or cationic catalyst activated by light; and optionally (d) other compounds directed to modify some aspects of the final polymerized or cured product. These references note that actinic radiation is employed to polymerize the liquid polymerizable resin composition to produce stencil, plate and pressure, etch resistant material or welding mask, but none of the references illustrates or suggests that the quality or stability of the image picture can be greatly improved by inclusion of a polymerization inhibitor in the photopolymerizable resin composition. The image photoformation technique is used in many fields such as printing plates, materials resistant to etching acids and welding mask applications. Photo masks have always been employed in this application to transfer an image onto a material sensitive to light-curing use. The process begins with the irradiation of actinic light on the light sensitive material placed under a photo mask. When the incident light passes through the transparent or open part of the photo mask on the light sensitive material, the material hardens by stages of polymerization or entanglement. When the irradiated light is blocked by the photo mask, the light sensitive material below the photo mask will not receive incident actlnic light and should remain in an unpolymerized state. During development of the photo image, the non-polymerized material is then removed from the polymerized material which subsequently becomes the photo image. Theoretically, this image should be clear, clear and with the highest quality. However, in practice there is a problem caused by the scattering of the light as it passes through the photo mask or when the laser beam impinges, causing the light to diffuse outward suando leaves the photo mask. This result is caused by the fact that any photo mask has a finite thickness that leads some diffusion of incident light. Also, impurities or fillers in the formulation itself may cause some scattering of incident light. The diffuse incident light causes some polymerization to occur outside of the discrete dimensions of the open portions of the photo mask, where polymerization is not desired. In the case of printing plates, the undesired polymerization will cause the reverse image to be filled with excess polymer, so that the printed image loses its definition and clarity. In the case of electronic applications, the undesired polymerization will fill the space between two lines also reducing the resolution of the desired image. It is noted that the present process pertains to both acid-resistant, positive and negative materials, since each of the types of materials resistant to etching acids requires high-resolution images. The present invention relates to a method for preventing or at least mitigating the unwanted polymerization of photopolymerizable material caused by diffuse incident light. The method involves the addition of an effective inhibitory amount of a monomer polymerization inhibitor in the photopolymerizable material. This inhibitor is sufficient to prevent polymerization when the incident light is diffuse and not directly incident on the material, but not enough to avoid polymerization, when incident light hits the material directly. The effective inhibitory amount may be in the range of 0.1 to 20% by weight of the photoinitiator concentration or between 0.0001 and 0.2% by weight of the resin composition.

More specifically, the present invention is a method for reducing unwanted polymerization caused by scattered or diffused light in a photopolymerizable material and for improving the quality and resolution of the final developed image that is formed by the irradiation of the photopolymerizable material by light, in wherein the process comprises adding to the photopolymerizable material an effective inhibitory amount of an inhibitor selected from the group consisting of N-oxyl or nitroxide compounds, quinone methides, nitroso compounds, phenothiazine, hydroquinone and selected phenols, wherein the amount of the inhibitor is sufficient for avoid and mitigate the polymerization by diffused or scattered light, but it is insufficient to avoid polymerization of the light-curing material irradiated directly by light. It is noted that the present invention is not in the exact definition of the photopolymerizable composition, or in the identity of the equipment for actinic radiation employed, or in the nature of the photoinitiator or other component of the photopolymerizable solution that all are conventional but in fact that A polymerization inhibitor is added to improve the quality of the photoimage obtained. The composition useful in the present process may also contain an effective stabilizing amount of a hindered mine that is different from the N-oxyl inhibitor described above. This hindered amine and any residue of the N-oxyl inhibitor can also improve the storage stability of the printing plate made by the present process. The residual radical inhibitor in the plate can act as a radical scavenger to prevent the plate from being damaged by oxidation and / or photodegradation. It is noted that the present N-oxyl inhibitor can purify a radical to form a NOR-hindered amine. The ÑOR hindered amines are known as effective stabilizers in their own right by organic substrates. In this way, there is an added bonus with the use of the N-oxyl polymerization inhibitors present, since they can impart some additional stabilizing efficacy to the products present. It is noted that most typographic presses are operated at high speed, which generates heat of friction between the printing plate and the printing substrate. In this way, oxidation can easily occur. Any residual radical inhibitor or hindered amine stabilizer added may be advantageous to provide protection against plaque degradation. The addition of the radical inhibitor also increases the water resistance of the printing plate. In this way, it is possible to maintain its image resolution when a water-based ink is used since the image swells less. In this way, the addition of the radical inhibitor also increases the chemical resistance of the printing plate. The presence of an additional hindered amine allows for improved resistance of the printing plate against both thermal and actinic induced degradation. Preferably, the polymerization inhibitor is present in an effective inhibitory amount of 0.0001 to 0.2% by weight of the total composition. Inhibitors useful in the present invention are nitroxyl radicals, quinone ethiures, phenothiazine, selected hydroquinones or phenols, nitroso compounds, galvinoxil [2,6-di-tert-butyl- (3,5-di-tert-butyl) 4-oxo-2, 5-cyclopentadien-l-ylidene-p-tolyoxy free radical] and the like Some nitroxyl compounds of special interest are listed below as follows: di-tert-butyl nitroxyl, l-oxyl-2, 2 , 6,6-tetramethylpiperidine, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-ol, l-oxyl-2, 2,6,6-tetra-tetrapiperidin-4-one, l-oxyl-2, 2 , 6,6-tetramethylpiperidin-4-yl acetate, l-oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl-2-ethylhexanoate, l-oxyl-2, 2,6,6-tetramethylpiperidin-4- il estereate, l-oxyl-2, 2,6,6-6-tetramethylpiperidin-4-yl benzoate, 1-oxy 1-2, 2,6,6-tetramethylpiperidin-4-yl 4-tert-butylbenzoate, bis (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) succinate, bis (l) -oxyl-2,2,6,6-tetramethylpiperidin-4-yl) adipate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) sebacate, bis (l-oxyl-2,2 , 6,6-tetramethylpi eridin-4-yl) n-butylmalonate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) phthalate, bis (l-oxyl-2, 2, 6, 6-tetramethylpiperidin-4-yl) isoftallate, bis (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) terephthalate, bis (l-oxyl-2, 2,6,6,6-tetramethylpiperidin-4) -yl) hexahydroteref talato, N, N'bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) adipamide, N- (l-oxyl-2,2,6,6-tetramethylpiperidin-4) -yl) -caprolactam, N- (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) -dodecyl succinimide, 2,4,6-tris (l-oxyl-2, 2,6,6- tetramethylpiperidin-4-yl isocyanurate, 2,4,6-tris [N-bUtil-N- (l-? Xl-2, 2,6,6,6-tetramethylpiperidin-4-yl] -s * -triazine, and 4, '-ethylenebis (l-oxyl-2, 2,6,6-tetramethylpiperazin-3-one).

Especially preferred is the polymerization inhibitor bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) sebacate; 4-benzylidene-2,6-di-tert-butyl-cyclohexa-2,5-dienon; or l-oxyl-2, 2,6,6-tetramethyl-4-hydroxypiperidine. A method is preferred where light is actinic light. A method is also preferred where irradiation occurs through a photo mask. A particularly preferred embodiment of the present invention involves a photosensitive resin composition for preparing a slab plate comprising: (A) from 5 to 98% by weight, based on the total weight of the components (A), (B) , (C) and (D), of a polymer selected from the group consisting of pre-polymer, a binder polymer and its mixture. (B) from 1.0 to 94% by weight, based on the total weight of the components (A), (B), (C) and (D), of an ethylenically unsaturated monomer or its mixture. (C) from 0.001 to 10% by weight, based on the total weight of the components (A), (B), (C) and (D), of a photopolymerization initiator selected from the group consisting of acetophenone and its derivatives, benzoin and its derivative, benzophenone and its derivative, anthraquinone and its derivative, xanthone and its derivative, thioxanthone and a mixture thereof, and a mixture of one or more of these initiators, and (D) from 0.001 to 0.2 % by weight, based on the total weight of components (A), (B), (C) and (D), of a polymerization inhibitor selected from the group consisting of nitroxyl radicals, quinone methyl, phenothiazine, hydroquinones, Selected phenols, galvinoxino or nitroso compounds. An especially preferred embodiment is when the composition described above additionally contains the component (E) which is from 0.05 to 10% by weight, based on the total weight of the composition, of a hindered amine containing a portion 2,2,6. , 6-tetramethylpiperidine. Ethylenically unsaturated monomers or oligomers that may be employed in the present process include natural rubber, synthetic rubber, epoxy (meth) acrylate, urethane (meth) acrylate, polyester (meth) acrylate, unsaturated polyester styrene, vinyl ethers and vinyl functional resins and derivatives of the aforementioned classes of monomers, oligomers or their copolymers. The different classes of photoinitiators that may be employed in the present process include benzoin and benzoin ether derivatives, benthenyl ketal derivatives, a-dialcoxyacetophenone, derivatives -hydroalkylphenone, aa-n-alkylphenone, acylphosphine oxides, acylphosphine sulfates, phenyloxylate derivatives, O-derivatives. acyl-oxiaminoxetone, benzophenone and its derivatives, Michler's ketone, thioxanthone and derivatives, metallocene compounds, bisimidazole and derivatives and all the compounds bound with polymer of the type mentioned above. More specifically, suitable examples of photoinitiating systems are aromatic carbonyl compounds such as benzoin, benzoin alkyl ethers such as isopropyl or n-butyl ether, acetophenol substituted, benzyl ketals preferably such as benzyl dimethyl ketal or acetophenones substituted with halogen, such as trichloromethyl-p -tert-butylphenyl ketone or morphonyl methyl phenyl ketone or dialcoxyacetophenones such as diethoxyacetophenone or α-hydroxyacetophenone, such as 1-hydroxycyclohexyl phenyl ketone, or benzophenones, such as benzophenone or bis (4-dimethylamino) benzophenone; or metallocene initiators such as the titanocene initiators, for example bis (pi-methylcyclopentanediyl) is (tr-pentafluorophenyl) titanium (IV); or a stannane together with a photoreducible dye, for example dimethyl benzyl stannane in conjunction with methylene blue or rose bengal; or a quinone or thioxanthone in conjunction with an amine that carries at least one hydrogen atom in carbon atoms such as anthraquinone benzoquinone or thioxanthone in conjunction with bis (4-dimethylamino) -enophenone or triethanolamine; or a thioxanthone for example a thioxanthone substituted with alkyl or halogen, such as 2-isopropylthioxanthone or 2-chlorothioxanthone; or acyl phosphide; or electron transfer systems such as borates in combination with electron acceptors that absorb light; or photoreducible dyes in combination with amines or other coinisiators. Suitable photopolymerizable acrylate or methacrylate monomers and oligomers are also known as described in EP 115,354. Diethylene glycol diacrylate, trimethylolpropane triacrylate, pentathritol triacrylate or epoxy acrylates, bisphenol A, phenol or cresol novolaks, urethane acrylates or polyether acrylates are very suitable. The epoxy acrylates can also be modified in a conventional manner with carboxylic anhydride. In addition to the stabilizer which is a hindered amine of component (E), any amount of other additives may also be present such as colorants, plasticizers, adhesion promoters, emulsifiers, pigments, chain transfer agents, sensitizers, cure improvers such as amines, solvents, flow control agents and the like. Preferred is a composition further comprising component (E) wherein the polymerization inhibitor is selected from the group consisting of nitroxyl radicals, quinone methyl, phenothiazines, hydroquinones, selected phenols, nitroso and galvinoxyl compounds.

More preferred is a composition which additionally contains the component (E) wherein the nitroxyl compound is: di-tert-butyl nitroxyl, l-oxyl-2, 2,6,6-tetramethylpiperidine l-oxyl-2, 2,6, 6-tetramethylpiperidin-4-ol, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-one, l-oxyl-2, 2,6,6-6-tetramethylpiperidin-4-yl acetate, l-oxyl-2 , 2, 6, 6-tetramethylpiperidin-4-yl-2-ethexanoate, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl stearate, l-oxyl-2, 2,6,6-tetramethylpiperidin- 4-yl benzoate, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl-4-tert-butylbenzoate, bis (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) succinate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) adipate, bis (l-oxyl-2,6,6,6-tetramethylpiperidin-4-yl) sebacate, bis (l-oxyl- 2,2,6,6-tetramethylpiperidin-4-yl) n-butymalonate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) phthalate, bis (l-oxyl-2, 2, 6,6-tetramethylpiperidin-4-yl) isophthalate, bis (l-oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl) terephthalate, bis (l) -oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl) hexahydrotereftallate, N, N'bis (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) adipamide, N- (l -oxyl-2,2,6,6-tetramethylpiperidin-4-yl) -caprolactam, N-bis (l-oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl) odecyl succinic acid, 2,4, 6-tris (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl isocyanurate, 2,4,6-tris [N-butyl-N- (l-OXYl-2,2,6,6- tetramethylpiperidin-4-yl] -s-triazine, and 4,4'-ethylenebis (l-oxyl-2, 2,6,6-tetramethylpiperidin-3-one). Particularly preferred is a composition which additionally contains component (E) wherein the polymerization inhibitor is: bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) sebacate; 4-benzylidene-2,6-di-tert-butyl-cyclohexa-2,5-dienone; or l-oxyl-2, 2,6,6-tetramethyl-4-hydroxypiperidine. Regarding the radiation sources, any source capable of giving appropriate light irradiation is convenient such as Hg lamps, fluorescent lamps, lasers and the like.

Although photoindicators are primarily employed, hybrid systems involving free radical initiators and cations, or photo / thermo initiators are also useful in the present invention. Although scattering of light through photo masks is a common problem, light can also be dispersed by impurities from fillers that may be present in the formulation. This is especially the case in thick printing plates. Additionally, there are techniques of image formation where photo masks are not required. For example, imaging can be performed by dispersing a laser through the photopolymerizable formulation or by focusing a laser on a solid photopolymerizable material to form a three-dimensional image. This is used in applications such as stereolithography and holography. A further objective of the present invention is the use of a polymerization inhibitor selected from the group consisting of N-oxyl or nitroxide compounds, quinone methyls, nitroso compounds, inoxyl gal, phenothiazine, hydroquinones and selected phenols, to reduce the undesired polymerization caused by scattered or diffused light in a photopolymerizable material and to improve the quality and resolution of the final revealed image that is formed by the irradiation of the photopolymerizable material by light.

The following examples are intended to illustrate the present invention and are not to be construed as limiting the invention of the present invention in any way. fiJBHPQ l Application of Printing Plate A liquid photopolymer mixture comprising 70 parts of an aliphatic diacrylate, 20 parts by weight of epoxidized soybean oil acrylate, and 10 parts of 1,6-hexanediol diacrylates are used as the sensitive material to light to produce a printing plate. The light source is a unit NAPP Model 9000 Napprinter equipped with 12 black light lamps VHO. The photo mask is a Logarithmic Sayce test diagram (Sayce Logarithmic Test Chart = SLTC). The SLTC gives a series of bars after the photopolymer is imaged and subsequently revealed. The depth between the two relief bars is measured and compared between various test formulations with and without a radical polymerization inhibitor. The space between two bars is progressively narrower when the bar identification number becomes larger. Consequently, the depth between two relief bars looks shallower. A Flexo Piat test diagram is also used as a test objective to give the image quality. The Flexo Piate test chart consists of inverse bars that are progressively narrower as their number of identification lines becomes smaller. Table I below shows that under the same exposure conditions, the reverse image quality can be improved by adding a small amount of radical polymerization inhibitor to the test formulation. Without the radical inhibitor in the fornulation, the inverse image depth of space # 15 is 0.61 mm; by adding 0.001% by weight in an Inhibitor A to the test formulation to prevent scattered light from initiating undesirable polymerization, the inverse image depth for the same space # 15 is 0.71 mm. This represents an improvement of 17.4% in image quality obtained by the use of a radical inhibitor. This means that there is less filling between bars so that the image is clearer, cleaner and deeper and with better resolution. In the case where 0.001% by weight of inhibitor B is used, the inverse image depth for space # 15 is now 1.26 mm or an improvement of 107% compared to the image depth when no inhibitor is used in the formulation .

Use of Different Inhibitors * Inhibitor Inhibitor # 15 # 16 # 17 # 18 # 19 # 20 Conc.% None 0 0.61 0.56 0.53 0.47 0.44 0.40 A 0.0001 0.88 0.78 0.73 0.65 0.62 0.53 A 0.001 0.71 0.67 0.59 0.59 B 0.0001 0.67 0.58 0.55 0.52 0.48 0.43 BB 0 0 ..000011 1.26 1.24 1.20 1.11 0.95 1.04 C 0.0001 0.64 0.57 0.53 0.49 0.45 0.43 C 0.001 0.79 0.73 0.68 0.65 0.58 0.54 D 0.0001 0.39 0.63 0.59 0.51 0.49 0.42 D 0.001 0.57 0.51 0.48 0.44 0.42 0.37 DD 0 0..0011 0.59 0.53 0.50 0.49 0.43 0.39 E 0.0001 0.37 0.35 0.32 0.30 0.30 0.30 E 0.001 0.39 0.36 0.38 0.28 0.34 0.34 E 0.01 0.49 0.41 0.45 0.40 0.38 0.35 F 0.0001 0.50 0.47 0.44 0.39 0.38 0.34 FF 0 0..000011 0.50 0.46 0.44 0.40 0.39 0.34 F 0, 01 0.49 0.40 0.41 0.39 0.35 0.32 * The photoinitiator used is 1.5% by weight of 2,2-dimethoxy-2-phenylacetophenone, Irgacure1"1 651 (Ciba-Geigy Corporation). The exposure time is 60 seconds per floor and 30 seconds for image. The formulation for liquid printing plate model requires two exposures to complete the plaque formation process. An exhibition is designed for the formation of the floor and another exhibition is designed for the stage of image formation. There are several ways to evaluate the effect of inhibitors on plaque. An example is to give a constant exposure time regardless of the influence of inhibitors to the photopolymerization process. It can be said that due to the constant exposure time either the floor thickness or the relief of the image may not be the same for the examples given in Tables I and II. Therefore, the improvement of image resolution may not be able to be attributed to the inhibitors in the formulation. To validate the results in Tables I and II, another experiment is conducted as shown in Table III. Two types of liquid printing plate are made. Its total thickness of plate includes the floor thickness and the thickness of relief is 6.35 mm (250 mils) and 1.70 mm (67 mils) these two thicknesses are usually seen in commercial plates. The purpose of this experiment is to make similar floor thickness and relief thickness and to evaluate the effect of inhibitor in image resolution. To achieve this, different fusion times have to be used. The results shown in Table III demonstrate that the inhibitor is useful for improving the resolution of the image. The depth between the two bars in each space is measured in millimeters (mm). The test objective is the Sayse logarithmic test diagram (SLTC): A is bis (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate; B is a quinone methyl, 4-benzylidene-2,6-di-tert-butyl-cyclohexa-2,5-dienone. C is l-oxyl-2,2,6,6-tetramethyl-4-hydroxypiperidine. D is n-octadecyl 3, 5-di-tert-but i 1-4 -hydroxyhydrocinnamate, Irganox "* 1076 (Ciba-Geigy Corp) E is 2,6-dinitro-4-methylphenol F is 4-methoxyphenol. Under different test conditions, it is possible to adjust the exposure time in such a way that the test formulations with or without the inhibitor will give the same floor thickness as seen in Table 2. It is evident that even when different concentrations of photoinitiator use, the addition of a photopolymerization inhibitor to the formulation improves the depth of the inverse images formed r hh tt use of Different Initialization zadoree * Space [ni Photo- Inhibitor # 15 # 16 # 17 # 18 # 19 # 20 started Cpn,% 1 0 0.61 0.58 0.53 0.47 0.44 0.40 1 0.0001 0.88 0.78 0.73 0.65 0.62 0.53 1 0.001 0.71 0.67 0.59 0.59 TABLE II fCont.) Use of Different Photoinitiators * Space fmn1 Photo- Inhibitor # 15 # 16 # 17 # 18 # 19 # 20 Initiator Conc.% 2 0 0.32 0.30 0.28 0.25 0.22 2 0.0001 0.36 0.36 0.34 0.31 0.2 6 0.26 3 0 0.32 0.32 0.24 0.26 0.24 3 0.0001 0.33 0.36 0.29 0.28 0.26 0.24 ** Inhibitor A is bis' (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) sebacate. The depth between the two bars is measured in millimeters (mm) and the test objective is the Sayce logarithmic test diagram. The floor thickness for runs with the photoinitiator is 1.91 mm (75 mils) and for initiator 3 it is 2 mm (79 mils). Photoinitiator 1 is 2,2-dimethoxy-2-phenylacetophenone, IrgacureHR 651 (Ciba-Geigy Corp.). Photoinitiator 2 is bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylphenyl) phosphine oxide. Photoinitiator 3 is 2-benzyl-2- (N, N-dimethylamino) -l- (4-morpholinophenyl) -l-butanone, Irgacure ™ 369 (Ciba-Geigy Corp.).

TABIA UX Effect of the Inhibitor on the Liquid Print Plate Plate with Thickness of 6.3 mm (250 mils) Line% of Photo Concentration of Thickness of # 30 # 15 Initiator ** Inhibitor A% Pjso mm f jls) 0.8 0 2.98 (118) 11.5 3.35 0.8 0.005 2.73 (108) 16.5 5.65 0.5 0 3.26 (129) 3.95 2.65 0.5 0.005 3.03 (120) 17.7 5.85 Plate with thickness 1.7 mm fß7 milsl 0.8 0 1.14 (45) 5.4 2.25 0.8 0.005 0.84 (33) 13.5 3.75 0.8 0.001 1.22 (48) 8.9 3.9 TAllaLA lll (contal Effect of the Inhibitor on the Liquid Print Plate Plate with Thickness of 6.3 nun (250 mils) Line% of Photo Concentration of Thickness of # 10 # 7 Initiator ** Inhibitor A% Piso mfmils ^ 0.8 or 2.98 (118) 1.8 1.4 0.8 0.005 2.73 (108) 2.8 2.0 0.5 0 3.26 (129) 2.1 1.45 0.5 0.005 3.03 (120) 2.45 2.3 TABLE III fcont.l Effect of the Inhibitor on the Liquid Print Plate Plate with Thickness of 6.3 mm (250 mils) Line% of Photo Concentration of Thickness of # 10 # 7 Initiator ** Inhibitor A% pjsp mmfmjlg) lacquer with thickness 1 mm (67 mils) 0.8 or 1.14 (45) 2.1 1.5 0.8 0.005 0.84 (33) 1.5 0.8 0.001 1.22 (48) 2.8 1.9 TAB A III pofft.) Effect of the inhibitor in the Liquid Print Plate Plate with Thickness of 6.3 mm (250 mils) Line% of Photo Concentration of Thickness of # 5 Initiator ** Inhibitor A% Pjsp mm (TO lS) 0.8 0 2.98 (118) 0.8 0.005 2.73 (108) 1.25 0.5 0 3.26 (129) 0.5 0.005 3.03 (120) 1.8 Í Plate with thickness 1.7 mm 6767 mils) 0.8 0 1.14 (45) 0.8 0.005 0.84 (33) 0.8 0.001 1.22 (48) Inhibitor A is bis (l-oxyl) -2,6,6,6-tetramethylpiperidin-4-yl) sebacate. The depth between the two bars is measured in millimeters (mm) and the test objective is the Sayce logarithmic test diagram. ** Photoinitiator 1 is 2,2-dimethoxy-2-phenylacetophenone, Irgacure ™ 651 (Ciba-geigy Corp.). In summary, the data given in example 2 show that under the same exposure condition, different floor thickness can be had or the exposure time can be adjusted to obtain the same floor thickness. In any case, the inverse image quality can be improved by the addition of a small effective amount of polymerization inhibitor in the photocurable formulation and this improvement is independent of the floor thickness. EXAMPLE 2 Application in Electronics A two-pack welding mask formulation is prepared according to the following procedure. A first composition is prepared by mixing 25.4 parts by weight of a partial ester of hydroxyethyl methacrylate and a copolymer of aleic-styrene anhydride [SMA 1000 (Arco Chemical); 45:55 ratio] 6.44 parts of ethylene glycol monobutyl ether acetate? 4.97 parts of an epoxy resin acid-modified acrylate ester based on bisphenol-A (Novacuré 3800, Interez Inc.)) 184 parts ethoxylated detrimethylolpropane triacrylate; 2.0 parts of trimethylolpropopane triacrylate; 0.93 part of Modaflow flow promoter agent; 0.92 part of a release agent; 7.37 parts of 2-methy1-1, 4- [methylthio) phenyl-morpholinopropanone-1 (Irgacure ™ 908 Ciba-Geigy Corp.) and 1.33 parts of a thioxanthone photoinitiator at room temperature. A second composition is prepared to mix 14.89 parts of an epoxy cresol novolac resin (Epon "* DPS 164 Shell); 7.35 phenolic novolak (Araldite" * EPN 1138 Ciba-Geigy Corp); and 9.10 parts of monobutyl ether ethylene glycol acetate. The mixture is then melted to reduce viscosity for easy processing. Finally 3.66 parts of fumed silica (Carbosil ** M-5, cabot) are added. The two compositions are mixed at room temperature with stirring and then ground using a three roll mill. A coating with a thickness of 0.0254 to .0508 mm (1 to 2 mils) of the resulting mixture is deposited on a copper plate using a # 3 rod. After the coating is dried at 80 ° C for approximately 25 minutes and after cooling to room temperature, a tack-free coating is obtained. The coated board is then placed on a vacuum plate with a negative mask photo placed on top. The board is then covered with a transparent polyethylene film, thin and subjected to approximately 400 milliijoules of UV radiation. The image is revealed by washing with a 1% aqueous sodium carbonate solution for 1 minute at 50 ° C. the resulting polymer cured board image is given a post-curing of 2.4 joules using a medium pressure Hg lamp and finally baked in a 150 ° C oven for one hour. A "micro-copy resolution test chart" is used as a photo mask to evaluate the image resolution. The test diagram consists of 18 patterns with different numbers assigned to each pattern. Each number represents the resolution of the next pattern. The higher the number obtained, the better the image resolution achieved. The results are shown in Table III below.

Effect of Inhibitor in Welding Hash Resolution Inhibitor A fConcentration%) Stage of Resolution 0 2.5 0.005 2.5 0.01 2.5 0.05 4 0.1 9 0.15 9 0.2 10 0.3 10 0.5 10 Inhibitor A is bis (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacato From the results given in Table IV, it is evident that adding a small amount of free radical inhibitor to the solder mask formulation significantly improves the image resolution. The best image resolution that can be obtained for the formulation without inhibitors 2.5, but when adding 0.05% or 0.1 of inhibitor A to the formulation, the image resolution becomes 4 and 9 respectively.

Claims (11)

1. CLAIMS 1.- Process for reducing unwanted polymerization by scattered and diffused light in a light-curing material and for improving the resolution quality of the final developed image formed by the irradiation of the light-curing material by light, characterized in the method because it comprises adding to the material light-curing an effective inhibitory amount of an inhibitor selected from the group consisting of N-oxyl or nitroxide compounds, quinone methides, nitroso compound, galvinoxyl, phenothiazine, hydroquinones and selected phenols, wherein an amount of the inhibitor is sufficient to prevent or mitigate the polymerization by diffused or scattered light, but it is insufficient to prevent polymerization of the photopolymerizable material irradiated directly by light.
2. 2.- Procedure in accordance with the claim 1, characterized in that the polymerization inhibitor is present in an effective inhibitory amount of 0.0001 to 02% by weight of the total composition.
3. 3. Method according to claim 1, characterized in that the polymerization inhibitor is: di-tert-butyl nitroxyl, l-oxyl-2,2,6,6-tetramethylpiperidine, l-oxyl-2, 2,6, 6-tetramethylpiperidin-4-ol, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-one, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl acetate, l-oxyl-2 , 2, 6, 6-tetramethylpiperidin-4-yl-2-ethexanoate, l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl stearate, l-oxyl-2, 2,6,6-tetramethylpiperidin- 4-yl benzoate, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl 4-tert-butylbenzoate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) -succinate , bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) adipate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) sebacate, bis (l-oxyl) -2, 2, 6, 6-tetramethylpiperidin-4-yl) n-butylmalonate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) phthalate, bis (l-oxyl-2,2 , 6,6-tetramethylpiperidin-4-yl) isoftallate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) terephthalate, bis (l-oxyl-2, 2,6, 6-tetramet and lpipe Ridin-4-yl) hexahydroteref talato, N, N'bis (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) adipamide, N- (l-oxyl-2, 2,6,6- tetramethylpiperidin-4-yl) -caprolactam, N-bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) dodecyl succinimide, 2,4,6-tris (1-oxyl-2,2,6 , 6-tetramethylpiperidin-4-yl isocyanurate, 2,4,6-tris [N-butyl-N- (l, oxyl-2,2,6,6-tetramethylpiperidin-4-yl] -s-triazine, and 4, 4'-ethylenebis (l-oxyl-2, 2,6,6-tetramethylpiperidin-3-one).
4. 4. Method according to claim 1, characterized in that the polymerization inhibitor is: bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) sebacate; 4-bincillidene-2,6-di-tert-butyl-cyclohexa-2,5-dienone; or l-oxyl-2, 2,6,6-tetramethyl-4-hydroxypiperidine.
5. 5. Method according to claim 1, characterized in that the light is actinic light.
6. 6. - Method according to claim 1, characterized in that the irradiation occurs through a photomask.
7. 7. A composition of photosensitive resin for preparing a relief printing plate, a material resistant to etching or etching acids, a welding mask or a stencil for stenciling, characterized in that: (A) from 5 to 98% by weight, based on the total weight of the components (A), (B), (C) and (D), of a polyomer selected from the group consisting of pre-polymer, a binder polymer and its mixture; (B) from 1.0 to 94% by weight, based on the total weight of the components (A), (B), (C) and (D), of an ethylenically unsaturated monomer or its mixture; (C) from 0.001 to 10% by weight, based on the total weight of components (A), (B), (C) and (D), of a photopolymerization initiator selected from the group consisting of acetophenone and its derivative, benzoin and its derivative, benzophenone and its derivative, anthraquinone and its derivative, xanthone and its derivative, thioxanthone and a mixture thereof, and a mixture of one or more of these initiators; and (D) from 0.001 to 0.2% by weight, based on the total weight of the components (A), (B), (C) and (D), of a polymerization inhibitor selected from the group consisting of nitroxyl radicals , quinone, methylated, phenothiazine, hydroquinones, selected phenols, galvinoxyl or nitroso compounds.
8. 8. - A composition according to claim 7, characterized in that it additionally contains a component (E) which is 0.05% by weight, based on the total weight of the composition of a hindered amine containing a 2,2,6 moiety, 6-tetramethylpiperidine.
9. 9. A composition according to claim 7, characterized in that the nitroxyl compound is: di-tert-butyl nitroxyl, l-oxyl-2,2,6,6-tetramethylpiperidine, 1-oxyl-2,2,6, 6-tetramethylpiperidin-4-ol, 1-oxy-2, 2,6,6-tetramethylpiperidin-4-one, l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl acetate, l-oxyl- 2, 2, 6, 6-tetramethylpiperidin-4-yl-2-ethexanoate, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl stearate, l-oxyl-2, 2,6,6-tetramethylpiperidine -4-yl benzoate, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl 4-tert-butylbenzoate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) - succinate, bis (l-oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl) adipate, bis (lo-2,2,6,6-tetramethylpiperidin-4-yl) sebacate, bis (l-oxyl) -2,6,6,6-tetramethylpiperidin-4-yl) n-butylmalonate, bis (l-oxyl-2,6,6,6-tetramethylpiperidin-4-yl) phthalate, bis (l-oxyl-2, 2 , 6,6-tetramethylpiperidin-4-yl) isophthalate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) terephthalate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin -4-il) h exahydroteref talato, N, N'bis (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) adipamide, N- (l-oxyl-2,6,6,6-tetramethylpiperidin-4-yl) -caprolactam, N-bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) dodecyl succinimide, 2,4,6-tris (l-oxyl-2,2,6,6-tetramethylpiperidin-4) -isocyanurate, 2,4,6-tris [N-butyl-N- (l, oxyl-2,2,6,6-tetramethylpiperidin-4-yl] -s-triazine, and 4,4'-ethylenebis (l -oxyl-2, 2,6,6-tetramethylpiperidin-3-one).
10. 10. A composition according to claim 9, characterized in that the polymerization inhibitor is: bis (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate; 4-benzylidene-2,6-di-tert-butyl-cyclohexa-2,5-dienone; or l-oxyl-2,2,6,6-tetramethyl-4-hydroxypiperidine.
11. 11.- Use of a polymerization inhibitor selected from the group consisting of N-oxyl or nitroxide compounds, quinone metuyres, nitroso compound, galvinoxyl, phenothiazine, hydroquinones and selected phenols, to reduce unwanted polymerization caused by scattered and diffused light in a material light-curing and to improve the quality and resolution of the final revealed image that is formed by the irradiation of light-curing material.