JPH0570813B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a positive-working photosensitive lithographic printing plate, and more specifically, after coloring an aluminum support that has been roughened and anodized in advance with an ultraviolet absorbing dye, a positive-working photosensitive lithographic printing plate is produced. The present invention relates to a positive-working photosensitive lithographic printing plate coated with a layer of a composition, which has halftone dot reproducibility faithful to the original film, that is, has a small dot reduction effect. [Prior Art] Positive-working photosensitive lithographic printing plates (hereinafter referred to as
It is abbreviated as "Positive PS version". ), 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 using the lithographic printing plate obtained in this way,
Printing causes thickening of halftone dots. In order to prevent this, during plate making, the halftone dots on the plate are narrowed by sufficient exposure, and
An aluminum support as disclosed in Japanese Patent No. 26479 having a center line surface roughness (Ha) of 0.6 to 1.2 μ and a surface reflectance of 50% or more has been used. However, in recent years, when creating original films, it has become possible to reduce the area of halftone dots on the film by using scanners, and there is no need to reduce the dots. Furthermore, in the case of a lithographic film with a low solid density, if the dots are reduced, the minimum halftone dot will disappear.
Additionally, when the exposure amount is reduced to produce the smallest halftone dot, light is scattered at the edges of the film, resulting in unnecessary images being formed on the plate and disappearing with the erasing solution after development. The need arises. For this reason, a plate with a large dot reduction has conventionally been desired, but in recent years, a plate with more faithful halftone dot reproducibility has been desired. JP-A-57-118238 discloses a method of increasing sensitivity and faithfully reproducing tone by adding a compound of the general formula [] to the photosensitive layer. The method of adding a specific compound to the toner is not very effective in faithfully reproducing the tone, and has the disadvantage of worsening development tolerance. General formula []

[Purpose of the invention]

Therefore, an object of the present invention is to provide a positive PS plate with faithful tone reproducibility and good reproduction of the smallest halftone dot. Another object of the present invention is to provide a positive PS plate that has faithful tone reproducibility and is less likely to produce film edge marks. [Structure of the Invention] In order to achieve the above object, the present inventors have made various studies and as a result have accomplished the present invention. In the present invention, the surface of an aluminum plate that has been roughened and then anodized is coated with an ultraviolet absorbing paint.
At the absorption maximum wavelength of 340 to 450 nm, the reflected optical density Ds is higher than that of the case without dyeing.
This is a positive-working photosensitive lithographic printing plate obtained by coating a layer of a positive-working photosensitive composition containing o-quinonediazide after coloring the plate to a height of 0.08 to 0.4. Furthermore, when using this positive-working photosensitive lithographic printing plate, not only does the tone reproducibility become faithful, but also, unexpectedly, residual color (dye added to the photosensitive layer is strongly adsorbed to the anodic oxide film, resulting in exposure, It has been found that the image contrast is high, and the erasing workability is very good. Hereinafter, the method for manufacturing a lithographic printing plate according to the present invention will be explained in detail one by one. The aluminum plate used in the present invention includes pure aluminum and aluminum alloy plate. Various aluminum alloys can be used; for example, alloys of aluminum and metals such as silicon, copper, manganese, magnesium, chromium, zinc, lead, bismuth, and nickel are used. These compositions contain some iron and titanium as well as other negligible impurities. Prior to 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 the graining method that can be used in the present invention. Mechanical methods include ball polishing, blast polishing, and brush polishing in which a water-dispersed slurry of an abrasive such as pumice is rubbed with a nylon brush. A method of immersion in a saturated aqueous solution of an aluminum salt of a mineral acid as described in the publication is suitable, and an electrochemical method is a method of alternating current electrolysis in an acidic electrolyte such as hydrochloric acid, nitric acid, or a combination thereof. is preferred. Among these surface roughening methods, a surface roughening method that combines mechanical roughening and electrochemical roughening as described in Japanese Patent Application Laid-open No. 137993/1983 is particularly suitable for using dyes as described below. This method is preferable because a large amount of dye is adsorbed in the coloring step, and the adhesion of the oil-sensitive image to the support is strong. Graining using the method described above has a center line surface roughness (Ha) of 0.3 to 1.0μ on the surface of the aluminum plate.
It is preferable that the treatment be carried out within a range such that: The thus grained aluminum plate is washed with water and chemically etched as required. The etching solution used in the present invention is usually selected from aqueous base or acid solutions that dissolve aluminum. In this case, the etched surface must not be coated with aluminum or a film different from aluminum derived from the etching solution components. Examples of preferred etching agents include basic substances such as sodium hydroxide, potassium hydroxide, trisodium phosphate,
Disodium phosphate, tripotassium phosphate, dipotassium phosphate, etc.; acidic substances include sulfuric acid, persulfuric acid,
Examples include 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. It is most preferable to use these etching agents in such a way that the concentration and temperature used are such that the rate of dissolution of the aluminum or alloy used is from 0.3 to 40 g/ ^m2 per minute of immersion time. There is no problem even if it exceeds or falls below. Etching is carried out by immersing an aluminum solution in the above-mentioned etching solution or applying the etching solution to the aluminum plate, and the etching amount is preferably in the range of 0.5 to 10 g/m ² . For the above-mentioned etching, it is desirable to use an aqueous base solution because of its high etching speed. In this case, since smut is generated, desmut processing is normally performed. The acids used in the desmut treatment include nitric acid, sulfuric acid, phosphoric acid, chromic acid, hydrofluoric acid, and hydrofluoric acid. 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, benzyl sulfonic acid, etc. or a combination of two or more of these, aluminum An anodic oxide film can be formed on the surface of the support. The processing conditions for anodic oxidation vary depending on the electrolyte used, so they cannot be determined unconditionally, but in general, the concentration of the electrolyte is 1 to 80% by weight, and the temperature of the solution is 5 to 80%.
70℃, current density 0.5 to 60 ampere/dm ² , voltage 1
A range of ~100V and electrolysis time of 30 seconds to 50 minutes is appropriate. Among these anodizing processes, in particular, the method of anodizing at high current density in sulfuric acid used in the invention described in British Patent No. 1,412,768 and the method described in US Pat. No. 3,511,661 Preferred is the method of anodic oxidation using phosphoric acid as an electrolytic bath. The aluminum plate roughened as described above and further anodized may be subjected to a hydrophilic treatment if necessary.
Alkali metal silicates such as those disclosed in Japanese Patent Publication No. 2714066 and No. 3181461, such as aqueous sodium silicate solutions or potassium fluorozirconate as disclosed in Japanese Patent Publication No. 36-22063 and U.S. Pat. No. 4,153,461. There is a method of treatment with polyvinylphosphonic acid, such as the one described in
A UV-absorbing dye is applied onto the aluminum support thus obtained. The absorption wavelength of ultraviolet rays should be approximately the same as the absorption wavelength of the photosensitive material, and should preferably have an absorption wavelength of 340 to 450 nm, which is the absorption wavelength of commonly used O-quinone diazide, and should have an absorption maximum in 340 to 450 nm. Some are particularly preferred. Such a dye is applied without water, as an organic solvent, or as a mixed solution of water and an organic solvent, by a known method such as a dip method, a roll coating method, a bar coating method, or the like. The amount of application is O
- The reflection optical density Ds at the dye absorption maximum wavelength in the quinonediazide absorption band is 0.08 to 0.4 higher than when no dye is applied, and 30mg/
It is preferable to keep it below ^m2 . If the increase in Ds is less than 0.08, the effect of increasing tone reproducibility is weak;
If it is 0.4 or more, the sensitivity will decrease significantly. The reflection optical density was measured using an integrating sphere reflection spectrophotometer. Moreover, if the coating amount is 30 mg/m ² or more, printing durability will deteriorate. Various types of ultraviolet absorbing dyes can be used as dyes, but using monobasic acid type acid dyes, that is, acid dyes that have only one sulfonic group or carboxyl group in one dye molecule, has the effect of reducing residual color. is large. Specific examples of such monobasic acid type acid dyes include:

【table】

〔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 and 2 and Comparative Example A After degreasing an aluminum plate (material 1050) with a thickness of 0.3 mm with triclean, the surface was grained using a nylon brush and 400 mesh of pumice water suspension, and thoroughly washed with water. I washed it with This board
Etch by immersing in 25% sodium hydroxide aqueous solution at 45℃ for 9 seconds, washing with water, and then immersing in 20% nitric acid.
Dipped for 20 seconds and rinsed with water. The amount of etching on the grained surface at this time was approximately 8 g/m ² . Next, this plate was heated to a current density of 15 A/dm ² using 7% sulfuric acid as an electrolyte.
After applying a 3 g/m ² DC anodic oxide film, it was washed with water and dried. Next, after applying the following dye solutions 1 and 2 (see Table 1) to this aluminum plate, the following positive photosensitive liquid was applied and dried on the dried one and the one without dye coating. Positive planographic printing plates (Examples) 1 and 2 and (Comparative Example) A were obtained, respectively.
The coating weight of the photosensitive layer after drying was 2.5 g/m ² in all cases. Photosensitive liquid Ester compound of naphthoquinone-1,2-diazide-5-sulfonyl chloride and pyrogallol-acetate resin (Note)...0.90g Cresol-formaldehyde resin...2.00g T-Butylphenol-formaldehyde resin (Note)...0.05g Naphthoquinone -1,2-diazide-4-sulfonic acid chloride...0.03g Oil Blue #603 (manufactured by Orient Chemical Industry Co., Ltd.)
…0.05g Methyl ethyl ketone …8g Methyl cellosolve acetate …15g Note: As described in Example 1 of U.S. Patent No. 3,635,709 Note: As described in U.S. Pat. No. 4,123,279 Positive-working photosensitivity of these After exposing the printing plate to a 3KW metal halide lamp from a distance of 70cm,
By diluting DP-4 (trade name: manufactured by Fuji Photo Film Co., Ltd.) 8 times, automatic development was carried out at 25° C. for 40 seconds (800U: using an automatic developing machine manufactured by Fuji Photo Film Co., Ltd.). The appropriate exposure time at this time is the point at which the fourth step becomes completely clear on a gray scale with a density difference of 0.15 (manufactured by Fuji Photo Film Co., Ltd.), and the exposure amount at which the film edge marks completely disappear (at this time, the point at which the fifth step is cleared). ). Note that the gray scale sensitivity of the three types of plates was exactly the same, and the exposure time was the same for all three types. The K value (line width: .mu.m) of the fogler film was used to judge the tone reproducibility under these plate-making conditions. A residual color test was also conducted using a developing solution in which 4 m ² /processing was carried out. These results are shown in Table-1.

[Table] As can be seen from the results in Table 1, Examples 1 and 2 were undercoated with ultraviolet absorbing dye Acid Yellow 25.
Compared to Comparative Example A, tone reproducibility is more faithful, and the minimum halftone dot (thin line of K value) is better reproduced at the same exposure. In addition, under the conditions for reproducing 15 μm, in Examples 1 and 2, the film edge marks completely disappeared with the 5-stage clear, whereas
In Comparative Example A, a 4-stage clear was required, and film edge marks were generated. Furthermore, the residual color of the fatigue solution treated with 4 m ² was also different from that of Example 1 and Comparative Example A.
In No. 2, the difference was low, and the minimum halftone dot and film edge marks had good inspection properties and easy erasing work. Also, when comparing Examples 1 and 2, Example 2 in which the pH was adjusted by adding triethanolamine hydrochloride
Example 1 (PH: 5.2) was not adjusted.
Compared to 6.83), the optical density after dye application is higher, tone reproducibility is slightly improved, and residual color is further reduced. When printing using these three types of plates, there was no staining and all had the same printing durability (100,000 sheets printed).
Good results were obtained. Examples 3 and 4 and Comparative Examples B, C, and D Examples 3 and 4 and Comparative Examples B, C, and D were prepared in the same manner as in Example 1 except that the amount of Acid Yellow 25 added was changed. We obtained the results shown below. This is summarized in Table 2.

【table】

[Table] Since the optical density of Comparative Example B is low, the effect of improving tone reproducibility is not observed as in Comparative Example A without an undercoat of ultraviolet absorbing dye. Good results were obtained in all Examples 3, 2, and 4, and the tone reproducibility improved as the optical density increased. In Example 4, there was a slight decrease in sensitivity (-0.3 steps) and a decrease in printing durability (×98), but this is within a range that causes no practical problems. In Comparative Example C, where the optical density increase was 0.45, the sensitivity decreased (-1 step), and the coating amount was as large as 28 mg/ ^m2 , so the printing durability (x95) was at the limit of the allowable range, and the coating amount was 36 mg/m2. Comparative example D of /m ²
There is a clear decrease in printing durability (×85). Example 5 and Comparative Examples E and F Example 5 and Comparative Example E were carried out in the same manner as in Example 2 except that 1N hydrochloric acid was added to the undercoating liquid to adjust the pH of the undercoating liquid to 3, 2, and 1. The results shown in ,F were obtained. This is shown in Table 3.

[Table] As you can see from Table 3, Acid Yellow 25
If the pH is lower than 2, dye residual color will occur.
Furthermore, the optical density is highest when the pH is 2, and decreases when the pH is set to 1. However, the addition of triethanolamine hydrochloride resulted in a high optical density even at PH: 5.2. On the other hand, when 1N hydrochloric acid was added to the formulations of Examples 1 and 2 (Acid Yellow 25 alone), the optical density was measured, and the results shown in Table 4 were obtained.

[Table] From Table 4, the optical density increase is lower than that with triethanolamine hydrochloride at pH 4 or higher;
It can be seen that although there is no effect of pH change, an increase in optical density is observed at pH 3 to 2. However, the optical density of the formulation containing triethanolamine hydrochloride is more stable against pH fluctuations. Also alone
When setting the pH to 3, if the pH becomes a little lower than 2.5, a yellow residual color will occur due to the undercoat dye instead of the residual color of the photosensitive layer, making it difficult to use in practice. Therefore, adding a pH adjuster such as triethanolamine hydrochloride to the UV-absorbing dye coating solution not only increases the optical density but also reduces residual color and allows stable production without being affected by pH fluctuations. It is desirable to make it possible. Examples 6, 7, and 8 In Example 2, the following yellow dyes were used in place of Acid Yellow 25, and the same good results as in Example 2 were obtained. Example 6 Acid Yellow 29 Example 7 Acid Yellow 76 Example 8 Compound () Comparative Example G In Example 1, an aqueous tartrazine solution was applied instead of the Acid Yellow 25 solution. At this time, the increase in optical density at 400 nm was 0.16. At this time, improvement in tone reproducibility was observed as in Example 1, but there was no effect of reducing residual color, and on the contrary, residual color increased. Tartrazine (CI acid yellow 23)

〔Effect of the invention〕

The positive-working photosensitive lithographic printing plate of the present invention has faithful tone reproducibility, good reproduction of the minimum halftone dot, and is less likely to produce film edge marks. Furthermore, when a monobasic acid type acid dye is used as the ultraviolet absorbing dye, residual color is reduced, image contrast is high, and erasing workability is very good.

Claims (1)

[Claims] 1 The surface of the aluminum plate, which has been roughened and then anodized, is coated with ultraviolet absorbing paint at 340~
At the absorption maximum wavelength of 450 nm, the reflected optical density Ds is 0.08 to 0.08 lower than that of the case without dyeing.
A positive-working photosensitive lithographic printing plate, which is colored to have a height of 0.4 and then coated with a layer of a positive-working photosensitive composition containing o-quinonediazide.