PHOTOSENSITIVE EMULSION FOR COATING PLASTIC FILM

Abstract: Photosensitive emulsion contains (A) emulsion contg. (a) a film-forming polymer, (B) photo-crosslinking polyvinyl alcohol contg. photo-crosslinking constitutional unit of formula (I), (IV) or (V) and (C) acetyleneglycol series or acetylene alcohol series cpd. as antiformer. In formulae, A is gp. (II) or (III); R1 is H, alkyl or aralkyl and may contain OH, carbamoyl, ether bonding or unsatd. bonding; R2 is H or lower alkyl; X- is anion; m is 0 or 1; n is integer of 1-6; B is aromatic or heterocyclic contg. at least one kind of polar gp.. Pref. cpd. (C) is, e.g., 2,4,7,9-tetramethyl -5-decyne-4,7-diol or its ethyleneoxide adduct or 3,6-dimethyl-4-octyne -3,6-diol and is used in a concn. of 0.01-5, pref. 0.1-1.0 wt.% based on total amt. of photosensitive emulsion. Mixed ratio of (A) to (B) is 100:10-200 by wt. as solid content.

Description: The present invention relates to a photosensitive coating emulsion for a plastic film which is suitable for image formation to give a coating film free from unevenness due to foaming or cissing during coating. A photosensitive material obtained by coating a plastic film with a photosensitive emulsion comprising a polyvinyl alcohol or polyvinyl acetate emulsion and a dichromate and/or a diazo compound has been known as a photosensitive image-forming material suitable for various fields such as screen processing or the like. However, though the dichromate which is used in the above photosensitive emulsion as a sensitizer is highly sensitive, the photosensitive emulsion tends to readily undergo dark reaction after coating, so that the operation step is restricted. Further, the use of the dichromate itself is also restricted, because chromium (VI) causes environmental pollution. On the other hand, the diazo compound is less sensitive than the dichromate and undergoes dark reaction though slowly. Consequently, the diazo compound is not alway satisfactory as a sensitizer. Further, some highly photosensitive compositions which neither cause dark reaction nor contain any metal which acts as a source of environmental pollution were proposed. For example, Japanese Patent Publication No. 40814/1981 discloses a photosensitive emulsion for screen processing which comprises a stilbazolium group-containing photocrosslinkable polyvinyl alcohol and a film-forming polymer, while Japanese Patent Laid-Open No. 194905/1983 discloses an emulsion which comprises a chalcone group-containing photocrosslinkable polyvinyl alcohol and a film-forming polymer. When, however, such a photosensitive emulsion is applied to a plastic film such as polyethylene terephthalate film with an ordinary device such as a roll, air knife, curtain or slit coater and dried, significant unevenness of coating due to foaming and cissing which is caused in the preparation step of the photosensitive emulsion or the coating step is present on the surface of the coating, thus giving no precise images. The inventors of the present invention have studied various anti-foaming agents to prevent foaming and cissing. Generally, mineral oils, fatty oils, fatty acids, fatty acid estrs, alcohols, silicones, polyalkylene glycols, fluorine compounds or a mixture thereof are used as an anti-foaming agent in various steps of textile, dye, paper pulp, synthetic rubber latex, paint or synthetic resin industry. The inventors of the present invention attempted to coat a substrate such as a polyethylene terephthalate film with a composition obtained by adding an ordinary anti-foaming agent such as the one described above to a photosensitive emulsion comprising a film-forming polymer and a photocrosslinkable polyvinyl alcohol and found that some of the ordinary anti-foaming agents effectively prevented foaming but caused cissing, while the others prevented cissing but could not sufficiently prevent foaming. It is the object of the present invention to provide a photosensitive coating emulsion for a plastic film resulting in a coating film havng an excellent appearance, good sensitivity, resolving power, resitance to printing and solvent resistance. Said object is achieved by a photosensitive coating emulsion for a plastic film comprising an emulsion containing a film-forming polymer and a photocrosslinkable polyvinyl alcohol containing at least one photocrosslinkable unit of the general formula (I), (II) or (III) the general formula (I) wherein A is a group represented by the general formula (a) or (b) or wherein R¹ is a hydrogen atom or an alkyl or aralkyl group which may contain a hydroxyl or carbamoyl group or an ether or unsaturated bond, R² is a hydrogen atom or a lower alkyl group, and X⁻ is an anion, m is 0 or 1, and n is a positive number of 1 to 6; wherein B is an aromatic or heterocyclic group having at least one polar group and m and n are as defined above, characterized by further containing an acetylenic glycol or alcohol as an anti-foaming agent. The presence of the anti-foaming agent does not adversely affect the state of the emulsion. Further, when this photosensitive emulsion is applied to a plastic film and dried, the drying characteristics are not remarkably lowered and neither foaming nor cissing is observed on the surface of the coating film. The screen processing with the above photosensitive emulsion of the present invention is carried out as follows: The photosensitive emulsion of the present invention is applied to a plastic film such as polyethylene terephthalate film to prepare a photosensitive film. This film is stuck on a screen plate with water or a photosensitive emulsion. After drying, the plastic film is removed to form a photosensitive coating film having a uniform thickness on the screen plate. Now the present invention will be described in more detail by referring to examples where the emulsion will be used in screen processing. Examples of the emulsion containing a film-forming polymer to be used in the present invention include a vinyl acetate emulsion, an acrylic emulsion, an ethylene-vinyl acetate emulsion, an ethylene-acrylic emulsion, a SBR (styrene butadiene rubber) latex, a vinyl chloride emulsion and a vinylidene chloride emulsion. The photocrosslinkable polyvinyl alcohol to be used in the photosensitive emulsion of the present invention can be prepared by introducing the photocrosslinkable unit represented by the general formula (I), (II) or (III) into a polyvinyl alcohol prepared by completely or partially saponifying a polyvinyl acetate. The introduction of the photocrosslinkable unit can be carried out by a known method, such as the one described in Japanese Patent Publication Nos. 5761/1981 or 5762/1981 and Japanese Patent Publication Nos. No. 194905/1983. Now, the synthesis of the polyvinyl alcohol containing the photocrosslinkable unit represented by the general formula (I) will be described as a representative example. Polyvinyl alcohol is reacted with a stilbazolium or styrylquinolinium salt represented by the general formula (IV) or (V): wherein A, m and n are as defined above and R³ is a lower alkyl group or two R³ groups may together form a lower alkylene group, in the presence of an acid catalyst to obtain a photocrosslinkable polyvinyl alcohol. Examples of the compound of the general formula (IV) include 1-methyl-2-(p-formylstyryl)pyridinium, 1-methyl-4-(p-formylstyryl)pyridinium, 1-ethyl-2-(p-formylstyryl)pyridinium, 1-ethyl-4-(p-formylstyryl)pyridinium, 1-allyl-4-(p-formylstyryl)pyridinium, 1-(2-hydroxyethyl)-2-(p-formylstyryl)pyridinium, 1-(2-hydroxyethyl)-4-(p-formylstyryl)pyridinium, 1-carbamoylmethyl-2-(p-formylstyryl)pyridinium, 1-carbamoylmethyl-4-(p-formylstyryl)pyridinium, 1-methyl-2-(m-formylstyryl)pyridinium, 1-benzyl-2-(p-formylstyryl)pyridinium, 1-benzyl-4-(p-formylstyryl)pyridinium, 1-methyl-4-(p-formylstyryl)-5-ethylpyridinium, 1-methyl-2-(p-formylstyryl)quinolinium, 1-ethyl-2-(p-formylstyryl)quinolinium and 1-ethyl-4-(p-formylstyryl)quinolinium. The compound represented by the general formula (V) may be an acetal of the compound represented by the general formula (IV). Further, examples of the anion X⁻ include halide, phosphate, sulfate, methosulfate and p-toluenesulfonate ions. The substituent "B" of the photocrosslinkable unit represented by the general formula (II) or (III) may be an aromatic or heterocyclic group substituted with a carboxyl group or its salt, a sulfo group or its salt or a primary, secondary or tertiary amine or their salt including a quaternary salt of a tertiary amine. It is preferred that the photocrosslinkable polyvinyl alcohol has a degree of saponification of 75 mol % or above and an average degree of polymerization of 300 to 3000. If the average degree of polymerization is less than 300, the mechanical strength and the water resistance are poor, while if it exceeds 3000, the solution of the composition exhibits a remarkably high viscosity to result in difficult coating. Further, the solubility in water in the development step is low, so that an unexposed part will be hardly washed out, which is unfavorable. If a polyvinyl alcohol having a degree of saponification of less than 75 mol % is used, the solubility in water is low and the obtained coating film will be soft and have an insufficient strength. The content of the photocrosslinkable unit is preferably 0.5 to 10 mol % based on the unit of the polyvinyl alcohol. If the content is higher than 10 mol %, the reaction mixture exhibits a remarkably high viscosity to result in a difficult preparation. Further, the solubility of the obtained photosensitive resin composition in water is poor. The weight ratio (on a solid basis) of the emulsion containing the film-forming polymer to the photocrosslinkable polyvinyl alcohol in the photosensitive emulsion of the present invention is preferably between 100 : 10 and 100 : 200. If the amount of the photocrosslinkable polyvinyl alcohol to be added per 100 parts by weight of the emulsion is less than 10 parts by weight, the resulting coating films exhibits a low solvent resistance to result in a poor resistance to printing. Further, the unexposed part is difficultly washed out to result in an insufficient development. On the contrary, if the amount exceeds 200 parts by weight, the water resistance and smoothness of the surface are poor and the sensitivity is lowered. According to the present invention, an aliphatic alcohol having eight carbon atoms may be added to the anti-foaming agent Further, the dispersion medium of the photosensitive emulsion containing the anti-foaming agent may contain a mixture of water with methyl, ethyl, propyl or isopropyl alcohol. According to the present invention, the photosensitive emulsion containing the anti-forming agent is applied to a substrate by a coating device such as a roll, air-knife, curtain or slit coater and dried to give a photosensitive material having an excellent foam-free appearance. The plastic film to be used as a substrate may, for example, be a film made of polyethylene terephthalate, polycarbonate, polystyrene, polyvinyl chloride, cellulose acetate. The acetylenic glycol or alcohol to be used as an anti-foaming agent in the present invention may be 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, solutions thereof in ethylene glycol or 2-ethylhexyl alcohol, adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol with 3 to 30 mol of ethylene oxide and a combination of two or more of them. The amount of the anti-foaming agent is 0.01 to 5% by weight, preferably 0.1 to 1.0% by weight based on the amount of the photosensitive emulsion. These acetylenic glycols or alcohols may be used together with other ordinary anti-foaming agents. Now, the present invention will be described in more detail by referring to the following Examples. Referential Example 1 110 g of N-methyl-γ-picolinium methosulfate and 200 g of terephthalaldehyde were dissolved in 400 ml of methanol under heating and 6 ml of piperidine was added thereto. The obtained mixture was refluxed for 3 h, cooled and distilled under a reduced pressure to remove the ethanol. The residue was washed with ethyl acetate to obtain a precipitate. The precipitate was dissolved in hot ethanol and ethyl acetate was gradually added thereto to obtain a crystal. This crystal was washed with ethyl acetate and dried to obtain 120 g of N-methyl-γ-(p-formylstyryl)pyridinium methosulfate. Referential Example 2 (Preparation of a photocrosslinkable polyvinyl alcohol) 9 g of the N-methyl-γ-(p-formylstyryl)pyridinuim methosulfate prepared in Referential Example 1 and 100 g of a polyvinyl alcohol having a degree of saponification of 88 mol % and a degree of polymerization of 1700 were dissolved in 900 ml of water under heating. 5 g of 85% phosphoric acid was added to the resulting solution. The obtained mixture was stirred at 60°C under heating for 5 h and then at an ordinary temperature for 24 h and poured into a large amount of acetone to obtain a precipitate. This precipitate was sufficiently washed with methanol twice and dried to obtain 98 g of a resin. The resin contained about 1.2 molar % of stilbazolium units based on the total constituent unit of the polyvinyl alcohol. Examples 1 to 5 and Comparative Examples 1 to 4 A photosensitive emulsion having the following formulation was prepared: polyvinyl acetate emulsion (solid content: 50% by weight) 140 parts by weight photocrosslinkable polyvinyl alcohol (Referential Example 2) (solid content: 10% by weight) 300 parts by weight coloring material a slight amount water 200 parts by weight Four acetylenic glycols and four commercially available anti-foaming agents were added to 1000 parts by weight of the above photosensitive emulsion each in an amount shown in Table 1, followed by mixing. The obtained mixture was applied to one surface of a biaxially oriented film made of polyethylene terephthalate having a thickness of 75 µm with a curtain coater and dried with a hot air of 60°C to form a photosensitive coating film having a thickness of 30 µm. The coating film was examined for surface appearance and the results are shown in Table 1. The photosensitive materials for screen processing prepared in Examples 1 to 5 were each applied to a 63um (250-mesh) polyester screen stuck on a wooden frame with water and dried by ventilation to peel the polyester film. The obtained screen plate was contacted with a positive original, irradiated with an ultra-high pressure mercury vapor lamp of 3 kW at a distance of 1 m for 30 s and washed with water shower of an ordinary temperature to carry out the development. The developed screen plate was dried to give a pinhole-free screen printing plate having an excellent edge sharpness wherein a fine line having a width of about 100 µm was reproduced. On the other hand, many pinholes were observed on the surface of the screen printing plates produced with the photosensitive materials of Comparative Examples 1 to 4. Example 6 One part by weight of a solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol in ethylene glycol having a solid content of 50% by weight was added to 1000 parts by weight of the same photosensitive emulsion as the one used in Examples 1 to 5. A photosensitive coating film was prepared by use of the obtained mixture. This coating film had an excellent surface free from foaming or cissing and exhibited good image-forming characteristics.

Claims: A photosensitive coating emulsion for a plastic film comprising an emulsion containing a film-forming polymer and a photocrosslinkable polyvinyl alcohol containing at least one photocrosslinkable unit of the general formula (I), (II) or (III): wherein A is a group represented by the general formula (a) or (b) wherein R¹ is a hydrogen atom or an alkyl or aralkyl group which may contain a hydroxyl or carbamoyl group or an ether or unsaturated bond, R² is a hydrogen atom or a lower alkyl group, and X⁻ is an anion, m is 0 or 1, and n is a positive number of 1 to 6; wherein B is an aromatic or heterocyclic group having at least one polar group, and m and n are as defined above, characterized by further containing an acetylenic glycol or alcohol as an anti-foaming agent. The emulsion of claim 1 characterized in that the photocrosslinkable polyvinyl alcohol has a degree of saponification of 75 mol % or above and an average degree of polymerization of 300 to 3000. The emulsion of claim 1 characterized in that the amount of the photocrosslinkable unit is 0.5 to 10 mol % based on the unit of the polyvinyl alcohol.

Inventors: ICHIMURA, KUNIHIRO, KUBO, KEIJI
Applicants: DAICEL CHEMICAL INDUSTRIES, LTD., JAPAN AS REPRESENTED BY DIRECTOR-GENERAL, AGENCY OF INDUSTRIAL SCIENCE AND TECHNOLOGY
Application year: 1986
Main classification: G03F7
IPC codes: G03F7, G03C1