JPS61258255A - Positive type photosensitive lithographic printing plate - Google Patents

Abstract

PURPOSE:To make faithful the reproducibility of a tone and to improve the reproduction of min. dots by coating the layer of a positive type photosensitive compsn. having the specified absorption intersity after exposure onto an aluminum plate which is subjected to surface roughening and anodic oxidation treatment. CONSTITUTION:Such layer of the positive type photosensitive compsn. of which the absorption intensity at 400nm after exposure is >=0.06 for each 1mum is coated on the surface of the aluminum plate subjected to the surface roughening then to the anodic oxidation treatment. The aluminum plate is cleaned and degreased by trichloroethylene and then the surface thereof is sand-grained by using a nylon brush and 400 mesh pumice-water suspension. The aluminum plate is thereafter thoroughly washed with water. Such plate is immersed for 9sec in an aq. 25% sodium hydroxide soln. kept at 45 deg.C and is thereby etched. The plate is rinsed and is further immersed in a 20% nitric acid then the plate is rinsed. A DC anodic oxide film is provided on the plate with a 7% sulfuric acid as an electrolyte and thereafter the plate is rinsed and dried. The positive type photosensitive compsn. is coated on the aluminum plate and is dried by which the positive type lithographic printing plate is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a positive-working photosensitive lithographic printing plate, and more specifically, the present invention relates to a positive-working photosensitive lithographic printing plate. formed by applying a layer of the composition,
The present invention relates to a positive-working photosensitive lithographic printing plate that has halftone dot reproducibility faithful to the original film, that is, has a small dot reduction effect.

[Conventional technology]

A positive-working photosensitive lithographic printing plate (hereinafter abbreviated as "positive-working PS plate") comprising a layer of a positive-working photosensitive resin composition provided on an aluminum support which has been grained and anodized in advance. ), when exposed through a positive transparent original image, the exposed area increases its solubility in a developing solution, and when it is treated with a developing solution of a positive-working photosensitive resin composition, the exposed area of the photosensitive layer is removed and the hydrophilicity of the support is increased. It is known that surfaces are exposed and thus a positive image is formed. When the lithographic printing plate obtained in this manner is used, the halftone dots become thick during printing. In order to prevent this, during plate making, sufficient exposure is performed to make the halftone dots thinner on the plate, and center line surface roughness as disclosed in Japanese Patent Publication No. 59-26479 is Ha) is 0.6 to 1.
An aluminum support having a diameter of 2μ and a surface reflectance of 50% or more was used. However, in recent years, with the use of scanners in creating original films,
It has become possible to reduce the area of halftone dots on film, and there is no longer a need to reduce the number of dots. Furthermore, in a lithographic film with a low solid density, if the dots are reduced, the minimum halftone dot will disappear. In addition, when the exposure amount is reduced in order to obtain the smallest halftone dot, light is scattered at the edge of the film, so an unnecessary image is formed in that area on the plate, which must be erased with an erasing liquid after development. The need arises. For this reason, plates with large dot reduction have traditionally been desired, but in recent years, plates with more faithful halftone dot reproducibility have been desired.

JP-A-57-118238 discloses a method for increasing sensitivity and faithfully reproducing tone by adding a compound of general formula [I] to a photosensitive layer. In this method, the effect of faithfully reproducing tone is not so great, and furthermore, it has the disadvantage of worsening development tolerance.

(In the general formula [I], R,, R2, and R each represent a hydrogen atom, an alkyl group, an alkoxy group, an aryl group, a substituent aryl group, an acyl group, a halogen group, a nitro group, or a hydroxyl group. (R1 can be the same or different.) U.S. Pat. A positive-working 28 plate is proposed using an aluminum support with a surface exhibiting a dark steel-gray tone obtained by oxidation. However, the surface of the aluminum support of this positive type 28 plate has a low reflectance in the entire range from ultraviolet to visible light, which makes it difficult to see the printed image obtained during image exposure, and also makes it difficult to see the printed image that is formed after development. The contrast between the sensitive image and the surface of the support is low, resulting in poor plate inspection properties, which has the disadvantage of causing problems in correction operations such as erasing and additions.

On the other hand, a negative photosensitive lithographic printing plate (hereinafter abbreviated as "negative 23 plate"), which is formed by providing a layer of a negative photosensitive resin composition on a support having a hydrophilic surface, is a negative transparent original. When exposed to light through the photosensitive layer, the photosensitive layer hardens in the exposed areas and the adhesive strength with the support changes, and when this is treated with a developer of a negative photosensitive resin composition, the unexposed areas of the photosensitive layer are removed. It is known that the hydrophilic surface of the support is exposed, thus forming an oil-sensitive positive image composed of a cured negative photosensitive resin composition on the support. In this negative type 23 plate, increasing the exposure time causes the exposed portion of the photosensitive layer to harden further and also improves the adhesion to the support, so this is due to changes in development processing conditions (e.g. development time, etc.). This is advantageous in that changes in image strength are reduced, a stable image is ensured, and the strength of the image is also increased, so that a lithographic printing plate with high stiffness resistance can be obtained. However, on the other hand, increasing the exposure time has serious drawbacks such as the effects of halation and irradiation, which thicken the image, reduce resolution, and make it impossible to obtain printed matter with good tone reproducibility. . These drawbacks are particularly noticeable when using supports that scatter well, such as roughened aluminum supports or paper supports.
It was known that this tendency becomes even greater when a roughened aluminum plate is subjected to anodizing treatment.

For example, in the above-mentioned U.S. Pat. No. 3,891,516, a negative plate 23 that overcomes these drawbacks is made by graining an aluminum plate with a wet abrasive such as a slurry of pumice, and then immediately soaking it in sulfuric acid. A negative-working 28 plate has been proposed using an aluminum support with a surface exhibiting a dark steel-gray tone obtained by anodizing with. However, the surface of the aluminum support for the negative 28th plate also has a low reflectance in the entire range from ultraviolet to visible light, just as in the case of the positive 23rd plate. In addition to making the printed image difficult to see, the contrast between the oil-sensitive image formed after development and the surface of the support is low, resulting in poor plate inspection performance, which poses a new problem that hinders correction work such as erasing and additions. There was a drawback that caused

On the other hand, U.S. Pat. No. 3,458,311 discloses a negative type in which a photosensitive layer made of a photopolymerizable composition is provided on an aluminum support that has been roughened and hydrophilized and then subbed with a dibasic acid dye. A 28th edition is disclosed, but the negative 28th edition, in which a negative photosensitive resin composition containing a photosensitive diazo resin is provided on an aluminum support, has a significant decrease in sensitivity on the surface of the aluminum support. It was found that the bonding force with the aluminum support was insufficient, so that it could not be put to practical use.

Further, in U.S. Pat. No. 3,280,734, an aluminum plate is anodized and then immediately colored with an aqueous solution of Mordant Blue 69 or Mordant Yellow 59 on an aluminum support. .066
No. 28 discloses a negative plate coated with diazo resin as described in U.S. Pat. No. 4,277.
, No. 555 has a negative type 28 in which an aluminum plate is anodized, then treated with an aqueous sodium silicate solution, and then a diazo resin is placed under an aluminum support colored with a basic dye.
These 28 negative-working plates all have the surface of the support colored for the purpose of visualizing the oil-sensitive image obtained after development, and improve the tone reproducibility as described above. It is not intended for that purpose. This means that the photosensitive layer is made only of diazo resin,
The coating amount is extremely thin, approximately 10 to 30 mg/m'.
This is also supported by the fact that in the case of such a thin photosensitive layer, since halation and irradiation do not substantially occur, there is essentially no inherent problem of deterioration in tone reproducibility. Furthermore, a negative photosensitive resin composition containing a diazo resin is provided on an aluminum support made of a colored aluminum plate that has been hydrophilically treated with a mordant dye or a basic dye as specifically exemplified in these patents. It has been found that the Type 28 plate has serious drawbacks in that when it is subjected to plate-making processing after being stored for a long period of time, it tends to leave behind color from the dye in non-image areas and also causes scumming on the printed matter.

As described above, many attempts have been made to improve tone reproducibility in the negative 28 plate, but all of them have had serious drawbacks.

Further, in the positive type 23rd edition, no attempt has been made to faithfully reproduce the tone except in Japanese Patent Application Laid-Open No. 57-118238 and U.S. Pat. No. 3,891,516 mentioned above.

[Purpose of the invention]

Therefore, an object of the present invention is to provide a positive type 23 plate with faithful tone reproducibility and good reproduction of the minimum halftone dot.

Another object of the present invention is to provide a positive type 23 plate which has faithful tone reproducibility and is less likely to produce film edge marks.

[Structure of the invention]

The inventors of the present invention have made various studies to achieve the above object, and as a result, they have completed the present invention.

In the present invention, an aluminum plate whose surface has been roughened and then anodized has an absorption intensity of 1 μm at 400 nm after exposure.
This is a positive-working photosensitive planographic printing plate coated with a layer of a positive-working photosensitive composition having a density of 0.06 or more per m.

Positive-working photosensitive compositions usually contain an 0-quinonediazide compound. The photosensitive absorption band of this 0-quinonediazide compound is from 350 to 450 nm, and it is particularly efficiently photodecomposed at 400 nm. Therefore, increasing the absorption intensity at 400 nm will reduce the sensitivity of the photosensitive composition. However, the positive-working 23rd plate of the present invention, which uses a photosensitive composition with an absorption intensity of 0.06 per μm or more at 400 nm after exposure, has lower sensitivity compared to the conventional positive-working 23rd plate. However, when the exposure amount is adjusted so that the halftone dot area on the plate is the same, film edge marks occur in the conventional PS plate, whereas film edge marks do not occur in the PS plate of the present invention. When the exposure amount is adjusted so that film edge marks do not occur, the PS plate of the present invention exhibits more faithful tone reproducibility than the conventional PS plate.

Hereinafter, the method for manufacturing a lithographic printing plate according to the present invention will be explained in detail in order.

The aluminum plate used in the present invention includes pure aluminum and aluminum alloy plate. Various aluminum alloys can be used, such as silicon,
An alloy of copper, manganese, magnesium, chromium, zinc, lead, bismuth, nickel diode and aluminum is used. These compositions contain some iron and titanium as well as other negligible impurities.

Before graining the aluminum plate, if necessary, the surface may be pretreated to remove rolling oil from the surface and expose a clean aluminum surface. For the former, solvents such as trichlene, surfactants, etc. are used.

For the latter, a method using an alkaline etching agent such as sodium hydroxide or potassium hydroxide is widely used.

Mechanical, chemical, and electrochemical methods are all effective as methods for forming a grain chamber that can be used in the present invention. Mechanical methods include the ball polishing method, blast polishing method, and brush polishing method in which a water-dispersed slurry of an abrasive such as pumice is rubbed with a nylon brush, and chemical methods include the method described in JP-A-55-31. A method of immersion in a saturated aqueous solution of an aluminum salt of a mineral acid as described in Publication No. 187 is suitable, and an electrochemical method using hydrochloric acid,
Alternating current electrolysis in an acidic electrolyte such as nitric acid or a combination thereof is preferred. Among these surface roughening methods,
In particular, the surface roughening method that combines mechanical roughening and electrochemical roughening as described in JP-A-55-137993 has a strong adhesion of the oil-sensitive image to the support. preferable.

When forming a grain chamber by the above method, it is preferable that the graining is performed in such a range that the center line surface roughness (Ha) of the surface of the aluminum plate is 0.3 to 1.0μ.

The thus grained aluminum plate is washed with water and chemically etched as necessary.

The etching solution used in the present invention is usually selected from aqueous base or acid solutions that dissolve aluminum.

In this case, it is necessary that no film different from aluminum derived from the etching solution components is formed on the etched surface. Examples of preferred etching agents include basic substances such as sodium hydroxide, potassium hydroxide, trisodium phosphate, disodium phosphate, tripotassium phosphate, and dipotassium phosphate; acidic substances such as sulfuric acid and persulfuric acid. , phosphoric acid, hydrochloric acid, and their salts, but salts of metals having a lower ionization tendency than aluminum, such as zinc, chromium, cobalt, nickel, copper, etc., are not preferred because they form an unnecessary film on the etched surface.

These etching agents have a dissolution rate of 0.3 to 40 g/m' per minute of immersion time for the aluminum or alloy used, depending on the concentration and temperature settings.
It is most preferable to carry out the process as follows, but it may be more or less than this.

Etching is performed by immersing the aluminum plate in the above etching solution or applying the etching solution to the aluminum plate, and the etching amount is 0.5 to 10 g.
/ m'.

As the above-mentioned etching agent, it is desirable to use an aqueous base solution because of its high etching rate. In this case, since smut is generated, desmut processing is usually performed. Acids used for desmutting include nitric acid,
Sulfuric acid, phosphoric acid, chromic acid, butic acid, hydrofluoric acid, etc. are used.

The etched aluminum plate is washed with water if necessary, and then anodized. Anodic oxidation can be performed by methods conventionally practiced in this field.

Specifically, when a direct or alternating current is passed through aluminum in an aqueous or non-aqueous solution containing sulfuric acid, phosphoric acid, chromic acid, oxalic acid, sulfamic acid, benzenesulfonic acid, etc. or a combination of two or more of these, aluminum supports An anodic oxide film can be formed on the body surface.

The processing conditions for anodic oxidation vary depending on the electrolyte used and cannot be determined unconditionally, but generally the electrolyte concentration is 1 to 80% by weight, the solution temperature is 5 to 70°C, and the current density is 0.
．． Appropriate ranges are 5 to 60 amperes/dm'', voltage 1 to 100 µ, and electrolysis time 30 seconds to 50 minutes.

Among these anodizing treatments, the British Patent No. 1.
412.768 and the method of anodizing at high current density in sulfuric acid and U.S. Pat. No. 3.51
Preferred is the method of anodizing using phosphoric acid as an electrolytic bath, as described in No. 1.661.

The aluminum plate roughened as described above and further anodized may be subjected to a hydrophilic treatment if necessary. Preferred examples thereof include U.S. Pat. Nos. 2,714.066 and 3.181. Alkali metal silicates, such as aqueous sodium silicate solutions as disclosed in Japanese Patent Publication No. 36-22063 and potassium fluorozirconate as disclosed in U.S. Pat.
There is a method of treatment with polyvinylphosphonic acid as disclosed in No. 3.461.

A layer of a positive-working photosensitive composition is provided on the aluminum support thus treated. The positive photosensitive composition used in the present invention is preferably one consisting of an 0-quinonediazide compound and a phenolic resin.

The O-quinonediazide compound used in the present invention is a compound having at least one O-quinonediazide group, and its alkali solubility is increased by active irradiation, and examples of such compounds include compounds with a wide variety of structures. be able to. Examples of such O-quinonediazide compounds are described in J.

"Light-Sensitive Systems" by John Corser (John Wille & Sons)
ey & 5ons, Inc.), pages 339-352. Particularly suitable are sulfonic acid esters or sulfonamides of O-quinonediazide reacted with various aromatic polyhydroxy compounds or amines. Among such 0-quinonediazide compounds,
Ester of benzoquinone (1,2)-diazidosulfonic acid chloride and polyhydroxyphenyl or naphthoquinone-(1,2)-diazidosulfonic acid chloride and pyrogallol as described in Japanese Patent Publication No. 43-28403 Etching with acetone resin is most preferred. Other suitable O-quinonediazide compounds include U.S. Pat.
8.Benzoquinone described in specification No. 8.210
There are esters of (1,2)-diazide sulfonic acid chloride or naphthoquinone-(1,2)-diazide sulfonic acid chloride and phenolform and aldehyde resins. Other useful O-quinonediazide compounds for use in the present invention include those reported in numerous patents and known. For example, JP-A-47-530
No. 3, No. 48-63802, No. 63803, No. 48-63803
No., No. 48-96575, No. 38701-1970, No. 13354-1973, No. 11222-1971,
Publication No. 45-9610, Publication No. 17481-1973,
U.S. Patent No. 2.797.213, U.S. Patent No. 3.454.4
No. 00, No. 3.544.323, No. 3.573.
No. 917, No. 3.674.495, No. 3.785
．． No. 825, British Patent No. 1, '227.602;
1.251.345, 1.267, 005
No. 1.329.888, No. 1.330.93
Examples include those described in various specifications such as No. 2 and German Patent No. 854.890.

The phenolic resin used in the present invention refers to a novolak resin and a polyvinyl compound having a phenolic hydroxyl group, and the novolak resin is a resin obtained by condensing phenols and formaldehydes in the presence of an acidic catalyst. , including those modified with silene and mesitylene. Such novolak resins include phenol-formaldehyde resin, talesol-formaldehyde t'N resin < p-tert-butylphenol-
Typical examples include formaldehyde resin and phenol-modified xylene resin.

Examples of the polyvinyl compound having a phenolic hydroxyl group include polyhydroxystyrene polymers and copolymers thereof, and halogenated polyhydroxystyrene polymers and copolymers.

The amount of Q-quinonediazide compound in the total photosensitive composition is 1
It is 0 to 50% by weight, more preferably 20 to 40% by weight. The amount of the phenolic resin blended is 45 to 79% by weight, preferably 50 to 70% by weight, based on the total photosensitive composition.

The positive photosensitive composition used in the present invention has a
Absorption intensity at 00 nm is 0.06 or more per 1 μm,
A compound is added to make the ratio preferably 0.08 or more, more preferably 0.10 or more. Such a compound may be any ultraviolet absorber that absorbs ultraviolet light, particularly in the 350 to 450 nm absorption band of 0-quinonediazide. For example, yellow oil-soluble dye Aizen 5pilon
Yellow) G RH [Hodogaya Chemical Industry■] Diaresin Yellow
w> FC Mitsubishi Chemical ■], Orient Oil IX O-((lrient [lil Yello
w) 3G [Orient Chemical Industry ■], Paris Fast
Ix Low (Vali Fast Yellow) #
3104 C Orient Chemical Industry■], Vali Fast Yellow
#3105 C Orient Chemical Industry■], Soldan Yellow GRN
(Chugai Kasei), Primoflavine 8 GC Sumitomo Chemical Co., Ltd. as a yellow basic dye, Aizen Aura
mine) 0-125 [Hodogaya Chemical Industry ■], Aizen Cathilo Yellow (Aizen Cathilo
n Yellow) 3GLH [Hodogaya Chemical Industry■]
, Eisen Cachiron Brilliant E-r-D
(Aizen Cathilon Br1lliant
Ye! low> 50 L H [Hodogaya Chemical Industry ■]
, Aizen Cat Yellow
hilon Yellow-ow) GLH [Hodogaya Chemical Industry ■], Sumiacryl Yellow (Sumiacryl Yellow)
Yellow) 3 R [: Jumi Kagaku Kogyo ■] Guiacryl Supra Brilliant Yellow (Diacry
l 5upra Br1lliant Yellow)
2 GLC Mitsubishi Kasei ■], Diacryl Supra Yellow (Diacryl 5upra Yel
low) 5 RL C Mitsubishi Chemical ■] Aizen CathilonYe
low) 3 RL H [Hodogaya Chemical Industry side]. The amount of such an ultraviolet absorber used is such that the absorption intensity at 400 nm after exposure is 0.06 or more, and is generally 0.3 to 0.3 in the total photosensitive composition.
15% by weight is suitable.

In addition, the absorption intensity was low before exposure, and after exposure it was 400n
A combination of compounds that increases the absorption intensity of m, for example, 0-naphthoquinonediazide-4-sulfonic acid halide described in JP-A-50-36209, trihalomethyl described in JP-A-53-36223 -2-
Pyrone and trihalomethyltriazine, JP-A-55-62
Acidic substances such as various 0-naphthoquinonediazide compounds described in JP-A No. 444, 2-trihalomethyl-5-aryl-1,3,4-oxadiazole compounds described in JP-A-55-77742, etc. 400 by interacting with this acidic substance and generating 400
Combinations with PH indicators and dyes that increase absorption at nm can also be used. Examples of this include substances that turn yellow on the acidic side, such as bromophenol blue and tetrabromophenol blue.
ol Blue), bromochlorophenol blue (
Bromochlorophenol Blue), Bromocresol Green
Green).

In any of the above methods, the absorption intensity at 400 nm is 0.06 per μm after exposure, that is, at an exposure amount higher than the minimum exposure amount at which the non-image area is eluted by the developer.
or more, preferably 0.08 or more,
More preferably, it is 0.10 or more. Generally, the amount of exposure required to obtain the desired absorption intensity is
A photosensitive layer of up to three times the minimum exposure is useful, and the smaller the exposure required to obtain the desired absorption intensity, the more
This is preferable because it provides more faithful tone reproducibility.

In the specification of this application, "absorption intensity" refers to a photosensitive composition applied to a transparent support with a thickness of 100 μm at a dry weight of 2.5 g/m2, after drying, an exposure amount of at least 10 times the minimum exposure amount is applied. The absorption intensity at 400 nm was measured using a transparent support to which no photosensitive composition was applied as a control. For convenience, the thickness of the photosensitive composition is 1 μm = 1
Measured as g/m2.

The positive photosensitive composition used in the present invention includes dyes for image identification, such as crystal violet, methyl violet, malachite green, tsuksin, para tsuksin, Victoria Blue BH [Hodogaya Chemical Co., Ltd.]
], Victoria Pure Blue BOH [manufactured by Hodogaya Chemical Industry ■] Oil Blue 603 [manufactured by Orient Chemical Industry ■] Oil Pink #312 [manufactured by Orient Chemical Industry ■] Oil Red 5B [Orient Chemical Industry ■]
], Oil Green #502 [Orient Chemical Industry ■
], etc. may be added in an amount of about 0.3 to 15% by weight based on the total photosensitive composition. Furthermore, compounds that interact with these dyes to generate photodecomposition products that change the color tone,
For example, 0-naphthoquinonediazide-4,-sulfonic acid halide described in JP-A-50-36209, trihalomethyl-4,- as described in JP-A-53-36223,
2-pyrone and trihalomethyltriazine, JP-A-55-
Various 0-naphthoquinone diazide compounds described in JP-A No. 62444, 2 described in JP-A-55-77742
-Trihalomethyl-5-aryl-1,3,4=oxadiazol compounds and the like can be added. These compounds can be used alone or in combination, and the amount added is preferably 0.3 to 15% by weight.

The sensitivity can be increased by adding an acid anhydride compound described in JP-A-55-80022 to the composition of the present invention. The composition of the Ikemizu invention contains fillers, cellulose alkyl ethers for improving coating properties, ethylene oxide surfactants (FC-430, FC-431 manufactured by 3M), and physical properties of the coating film. In order to improve the properties, various additives can be added depending on various purposes, such as plasticizers such as dibutyl phthalate, butyl glycolate, tricresyl phosphate, and dioctyl adipate. By adding fillers, not only can the physical properties of the coating film be further improved, but also
It becomes possible to make the surface of the photosensitive layer matte, and the vacuum adhesion during image printing improves, making it possible to prevent so-called printing blur. Such fillers include talcum powder, glass powder, clay, starch, flour, corn flour,
There are Teflon powders, etc.

The above-mentioned photosensitive composition is dissolved or dispersed in a solvent that dissolves or disperses each of the above-mentioned components, and then applied onto a support. The solvents used here include ethyl, dichloride, cyclohexanone, methyl ethyl ketone, methyl cellosolve acetate, propylene glycol monomethyl ether acetate, n-butyl propionate, 3,3-dimethyl butyl acetate, 2-ethoxytetrahydrobilane, and ethylene glycol. - Solvents for dissolving or dispersing the photosensitive composition, such as mono-t-butyl ether, toluene, ethyl acetate, 2-heptanone, and 2,4-pentanedione, can be used alone or in combination, but are applied to the aluminum surface. It is necessary to select a solvent that will form a fairly uniform halation layer without substantially redissolving the dye. For this purpose, it is preferable to apply the coating using a solvent based on esters.

The appropriate concentration of solids in the coating liquid is 2 to 50% by weight. In addition, the appropriate coating amount is generally 0.5 to 3.0 g/m'' in terms of solid content. Physical properties such as physical strength, development latitude, and oil sensitivity are reduced.

Examples of the developer for the positive photosensitive composition of the present invention include sodium silicate, potassium silicate, sodium hydroxide, potassium hydroxide, lithium hydroxide, tribasic sodium phosphate, dibasic sodium phosphate, triphosphoric acid ammonium, ammonium diphosphate, sodium metasilicate,
Aqueous solutions of inorganic alkaline agents such as sodium bicarbonate, aqueous ammonia, etc. and organic alkaline agents such as monoethanolamine or jetanolamine are suitable, and their concentration is preferably 0.1 to 10%, preferably is 0.5
It is added in an amount of ~5% by weight.

Moreover, a surfactant and an organic solvent such as alcohol can be added to the alkaline aqueous solution as necessary.

〔Example〕

Next, the present invention will be explained in more detail by giving examples.

In addition, all "%" in the following examples are weight % unless otherwise specified.

Examples 1 to 4 and Comparative Examples A and B After washing and degreasing an aluminum plate (material 1050) with a thickness of 0.3 mm with triclean, it was washed with a knife brush and a
The surface was grained using 0 mesh of pumice water suspension and thoroughly washed with water. This board was heated to 25% at 45℃.
Etch by immersing in a sodium hydroxide aqueous solution for 9 seconds, washing with water, and then immersing in 20% nitric acid for 20 seconds and washing with water. The amount of etching on the grained surface at this time is approximately 8g.
/m2. Next, this plate was coated with a DC anodic oxide film of 3 g/rn2 at a current density of 15 Δ/dm2 using 7% sulfuric acid as an electrolyte, and then washed with water and dried. The aluminum plate was coated with the following positive photosensitive liquid and dried to obtain positive planographic printing plates (Examples) 1 to 4 and (Comparative Examples) A and B, respectively. The coating pot for the photosensitive layer after drying is all 2.5 g/m"
Met.

Photosensitive liquid methyl ethyl ketone ・・・・・・・・・ 8
g Methyl cellosolve acetate 1
5g Note ■ What is described in Example 1 in the specification of U.S. Patent No. 3.635.709 Note ■ What is described in the specification of U.S. Patent No. 4.123.279 ■ Example 1・・・・・・・・・・・・・・・・0.
04 g2・・・・・・・・・・・・0.08
g3・・・・・・・・・・・・0.12 g4・
・・・・・・・・・・・・・・・0.16 g Comparative example A・
・・・・・・・・・・・・・・・No additive B・・・・・・
......0.02 g After exposing these positive photosensitive printing plates with a 3KW metal halide lamp from a distance of 70cm, DP-4 (product name: manufactured by Fuji Photo Film ■) was used. Automatic development for 40 seconds at 25°C with 8-fold dilution (800U: using an automatic development machine manufactured by Fuji Photo Film ■)
I did this. There are two types of appropriate exposure at this time: the exposure that completely eliminates film edge marks (at this time, gray scale with a density difference of 0.15 (manufactured by Fuji Photo Film))
The exposure amount (ie, the point at which the Fogler film's value (line width: 2 μm) is 15) when the 5th step is completely clear) and the tone reproduction are taken as 1). The lower the value reproduced, the more faithful the tone reproducibility. In addition, after coating and drying each photosensitive composition on a transparent support with a thickness of 100 μm, a sufficient amount of light exposure (7 on a gray scale) was applied.
After the step became completely clear), the absorption intensity at 400 nm was measured using a self-recording spectrophotometer model 340 manufactured by Hitachi, Ltd., using a transparent support not coated with the photosensitive composition as a control.

These results are shown in Table 1.

As can be seen from Table 1, Examples 1 to 4, in which the absorption intensity after exposure is 0.06 or more, are the conventional positive PS plate comparative example A.
(absorption intensity 0.04), it shows more faithful tone reproducibility at an exposure amount that does not cause film edge marks. In other words, the values are reproduced more precisely. Furthermore, since the value is reproduced even after sufficient exposure, it is possible to completely prevent the occurrence of film edge marks even in the case of a film that is more prone to film edge marks than the film used in this experiment. On the other hand, in Comparative Example B in which an ultraviolet absorber was also added, the absorption intensity after exposure was 0.055, resulting in an unsatisfactory result.

Example 5 In Examples 1 to 4, Aizen 5pilon Yellow GRH
Orient Oil Yellow (Orie'
nt Oil Yellow) 3G [Orient Chemical ■
When 0.08 g of the product was used, the absorption intensity after exposure was 0.07.

The results showed that the tone reproducibility of this positive PS plate was also faithful.

Example 6 In Examples 1 to 4, Crampons Spiron Yellow (
81zen 5pilon Yellow)
When the sample was changed to GLH (manufactured by Hodogaya Chemical Industry Co., Ltd.) (0.04 g), the absorption intensity after exposure was 0.08, and good results with faithful tone reproducibility were obtained.

〔Effect of the invention〕

The positive-working photosensitive lithographic printing plate of the present invention has excellent tone reproducibility and is less likely to produce film edge marks.

Claims (3)

[Claims] (1) After exposure to light on the roughened and then anodized aluminum plate surface, the absorption intensity at 400 nm is 1μ
A positive-working photosensitive lithographic printing plate coated with a layer of a positive-working photosensitive composition having a density of 0.06 or more per m. (2) The positive-working photosensitive lithographic printing plate according to claim 1, wherein the absorption intensity at 400 nm after exposure is 0.06 or more per 1 μm by adding an ultraviolet absorber. (3) The positive-working photosensitive lithographic printing plate according to claim 2, wherein the ultraviolet absorber is a yellow dye.