JPS6245972B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved positive-working photosensitive composition that provides a highly sensitive yet easily distinguishable visible image upon exposure of a photosensitive lithographic printing plate to ultraviolet light. O-quinonediazide photosensitizers have the property of being decomposed by ultraviolet light to produce carboxylic acids. Taking advantage of this property, only the exposed areas are removed with an alkaline aqueous solution and an image is formed in the unexposed areas to give a positive image.This photosensitizer is currently used in many positive photosensitive lithographic printing plates and photoresists. ing. When this o-quinonediazide photosensitizer is irradiated with ultraviolet light, it photodecomposes as described above, and the film changes from yellow to slightly red. This hue is discernible under natural light or white light, but is nearly invisible under the yellow safe light commonly used in printing-related prepress rooms. In particular, in printing plate making, it is difficult to determine the position when performing overprinting or multi-sided printing, and when the same plate is exposed to light more than once, the positioning tends to be ambiguous. Image generation is an important element in making photosensitive lithographic printing plates. Special Publication No. 40-21093, No. 45-9611, No. 46-
42446, JP-A No. 54-72103, JP-A No. 54-72728,
Specifications such as German Patent No. 1803712 and British Patent No. 1154716 describe methods for obtaining visible images upon exposure, but most of these are photochromic methods; Because the absorption wavelength of the color overlaps with the sensitivity wavelength range of the o-quinonediazide-based photosensitizer, light is absorbed by the color that develops as it is exposed to light, and although a visible image is obtained, it is essentially the photosensitive lithographic printing. It has the disadvantage of reducing the sensitivity of the plate. In particular, Japanese Patent Publication No. 40-21093 discloses that a visible image can be obtained by mixing a dye that changes color tone in the pH range of 2.5 to 6.5, such as diethylaminoazobenzole, in the photosensitive layer of a positive photosensitive lithographic printing plate. However, all of the dyes described in this publication are photochromic, so it is possible to obtain a visible image under yellow safe light, but in order to obtain a better visible image, it is necessary to add There was a drawback that the amount had to be increased, and the sensitivity of the photosensitive planographic printing plate decreased accordingly. Therefore, in order to obtain a visible image under yellow safe light without reducing the sensitivity of the photosensitive lithographic printing plate, it is sufficient to add a photobleachable dye that changes the exposed area from colorless to yellow. Moreover, if the yellow color produced by photobleaching does not have absorption in the wavelength range (300 to 450 nm) sensitive to o-quinonediazide photosensitizers, no decrease in sensitivity will occur. Based on the above findings, the present inventors have developed a photosensitive composition that does not cause a decrease in the sensitivity of the o-quinone diazide photosensitizer and can provide a positive image that can be identified even under yellow safe light when exposed to ultraviolet light. As a result of intensive research, we found that o-quinonediazide photosensitizers contain sulfophthalein PH expressed by the general formula below.
It has been found that the above objectives can be achieved by adding an indicator and a basic substance soluble in an organic solvent: (In the above formula, A ₁ to _{A 4} are the same or different and represent a hydrogen atom or a halogen atom, and R ₁ to _{R 4}
and R ₁ ′ to R ₄ ′ are the same or different hydrogen atoms,
Represents a halogen atom or a lower alkyl group. ) The o-quinonediazide photosensitizer used in the present invention may be one that is commonly used, for example,
-22062, No. 38-12083, No. 49-34681, and U.S. Pat. A type phenol resin and an alkali-soluble resin such as vinyl methyl ether/maleic anhydride copolymer are mixed in a ratio of 1:2 to 1:6, and oil blue, crystal violet, and cyanine blue are added to make the image easier to see. It is possible to use dyes added with dyes such as The structure of the sulfophthalein PH indicator used in the present invention changes as follows depending on the acidic side and alkaline side in an aqueous solution: This sulfophthalene-based PH indicator generally has the structure of formula (), that is, the structure on the acidic side in the crystalline state, unless it is specifically made into a salt.
This property is also the same when dissolved in an alcoholic solvent, and the alcoholic solution does not exhibit an alkaline color. The above-mentioned Japanese Patent Publication No. 40-21093 describes that o-naphthoquinone diazide compounds photodecompose to produce carboxylic acid, and this is used to cause a color change in the PH indicator on the acidic side to obtain a visible image. It is expected that. However, the sulfophthalein-based PH indicator used in the present invention takes the structure of formula () when coexisting in an organic solvent in which an o-quinonediazide-based photosensitizer is dissolved. No change in color tone occurs depending on the formation of . Therefore, in order for a sulfophthalein-based PH indicator to change color in a positive photosensitive film, it must have a structure as shown in formula () in advance. For this purpose, a basic substance soluble in an organic solvent may be added to a photosensitive solution containing a sulfophthalein PH indicator. As a result, the positive photosensitive layer containing the sulfophthalein-based PH indicator undergoes a color change upon irradiation with light, giving a very clear positive image. While the photosensitive layer of Japanese Patent Publication No. 40-21093 mainly obtains photochromic images (negative images), the photosensitive layer of the present invention is also characterized in that photobleaching images (positive images) are obtained. Therefore, the photosensitive agent of the present invention differs from Japanese Patent Publication No. 40-21093 in that it does not cause a decrease in sensitivity, and is a new and improved invention. The sulfophthalein PH indicator used in the present invention changes color sufficiently on the alkaline side as shown in Table 1 below, and the amount added may be 0.1 to 0.5% based on the o-quinonediazide photosensitizer.

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[Table] The organic solvent-soluble basic substance used in the present invention is preferably one with low volatility, and the stronger the basicity, the more effective it is. For example, guanidine carbonate, monoethanolamine, diethanolamine, p-phenylenediamine, hexamethylenetetramine, benzidine, N-aminoethylethanolamine, etc. are used, and the amount added is the same as that of o-quinonediazide photosensitizer and sulfophthalein PH. It is adjusted in terms of the color tone caused by the indicator and the color change caused by light irradiation, but it may be added in an amount of 0.05 to 2.7% based on the o-quinonediazide photosensitizer. The organic solvent used in the present invention is a polar solvent that dissolves the o-quinone diazide photosensitizer, such as alcohols such as methanol and ethanol, acetone,
These include ketones such as methyl ethyl ketone, and glycols such as methyl cellosolve and ethyl cellosolve. The photosensitive lithographic printing plate coated with the photosensitive composition according to the present invention does not reduce the sensitivity of the o-quinonediazide-based photosensitizer, and the exposed non-image areas are photobleached, and moreover, it can be developed with a weak alkaline aqueous solution. To,
The image area has the characteristic of further increasing the density to provide a clear colored image. The present invention will be explained in detail below with reference to Examples, but the present invention is not limited thereto. Example 1 1 g of novolak type phenolic resin esterified with 50 mol% o-naphthoquinonediazide-5-sulfonyl chloride, 3.5 g of novolak type cresol resin (softening point 82°C), promthymol blue 0.07
A photosensitive solution was obtained by dissolving 0.05 g of guanidine carbonate in 50 g of ethylene glycol monoethyl ether. This photosensitive solution was applied to an aluminum plate for a lithographic printing plate to a dry film thickness of 2.7 μm, and dried at 80° C. for 10 minutes. When a positive film was attached closely to this photosensitive planographic printing plate and exposed for 60 seconds from a distance of 1 meter using a 1KW ultra-high pressure mercury lamp, the exposed area changed from green to pale yellow, and a positive image appeared on the plate surface. Ta. The image thus obtained was further clearly identified under yellow safe light because the pale yellow color of the exposed area was canceled out by the safe light. Next, when the exposed plate was developed with a 5% sodium metasilicate aqueous solution, the exposed areas were washed away, and an image was obtained in which the unexposed areas were a slightly darker green color. Incidentally, a photosensitive film prepared by removing guanidine carbonate from this photosensitive composition exhibited a yellowish brown color, and although it turned pale red after exposure, the image could not be distinguished at all under yellow safe light. Furthermore, when comparing the gray scale sensitivity of this photosensitive composition with promthymol blue and guanidine carbonate removed, the complete white-out sensitivity of the gray scale was the same as 4.0, and no decrease in sensitivity was observed. Example 2 1 g of brominated polyhydroxystyrene esterified with 20 mol% of o-naphthoquinonediazide-5-sulfonyl chloride, 3 g of novolak type cresol resin esterified with 50 mol% of o-naphthoquinonediazide-5-sulfonyl chloride, novolak type Cresol resin (softening point 82℃) 10g, promphenol blue 0.1g, monoethanolamine
0.07 g of crystal violet and 0.05 g of crystal violet were dissolved in 100 g of ethylene glycol monoethyl ether and filtered to obtain a photosensitive solution. This photosensitive solution was applied to an aluminum plate for lithographic printing plate in the same manner as in Example 1, and when exposed with a positive film in close contact, the exposed non-image area changed from dark green to light purple, and under yellow safety light. But I could clearly identify it. Next, this was developed with a 5% aqueous sodium silicate solution, resulting in a very visible positive image with a dark green image area. When this printing plate was printed using an offset printing machine and a dampening solution containing 20% isopropyl alcohol, the result was 5.
Thousands of good prints were obtained.

Claims (1)

[Claims] 1 The o-quinonediazide photosensitizer has the following formula: (In the formula, A ₁ to _{A 4} are the same or different and represent a hydrogen atom or a halogen atom, and R ₁ to _{R 4} and
R ₁ ' to _{R 4} ' are the same or different and represent a hydrogen atom, a halogen atom, or a lower alkyl group. ) A positive photosensitive composition comprising a sulfophthalein PH indicator represented by: and a basic substance soluble in an organic solvent.