JPS63149640A - Photosensitive composition and photosensitive lithographic printing plate - Google Patents

Abstract

PURPOSE:To improve the stability of sensitivity after exposing of a printing plate and reproducibility of small dots by incorporating amine which captures the acid generated by active rays and is not decomposed by said rays into a titled compsn. CONSTITUTION:The compd. (A) which generates the acid when irradiated with the active rays, the compd. (B) which has >=1 bonds to be decomposed by said acid, and the amine compd. (C) which captures the acid and is not decomposed by the irradiation of the active rays are incorporated into the titled compsn. A 2-halomethyl-1,3,4-oxadiazole compd. is used as the component A and the compd. expressed by the formula as the component B. 4-dimethylaminopyridine, etc., are used as the component C. A high mol.wt. binder such as novolak resin is usable as a binder and if necessary, a dye, plasticizer, sensitizer, etc., may be added thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a photosensitive lithographic printing plate and a photosensitive composition used in the printing plate.

[Background of the Invention] As a positive photosensitive composition, a first reaction in which an acid is generated by irradiation with actinic rays, a second reaction with the generated acid,
That is, various types of photosensitive adhesives are known that utilize the principle that exposed areas become soluble in a developer through an acid decomposition reaction. The acid-decomposed compound used in the second reaction is
No. 8-89003, No. 51-120714, No. 53
-133429, 55-12995, 55-1
Compounds having a C-0-C bond described in specifications such as No. 26236 and No. 56-17345, JP-A No. 6
Compounds having a 5i-0-C bond described in specifications such as No. 0-37549 and No. 60-121446,
Other examples include compounds described in the specifications of JP-A-60-3625 and JP-A-60-1024γ.

All of these photosensitive compositions had different sensitivities depending on whether they were developed immediately after exposure or developed some time after exposure, that is, the stability of sensitivity after exposure was low. In order to improve the stability of sensitivity after exposure, a technique for adding a compound that generates radical inhibiting species upon irradiation with light is disclosed in JP-A-61-167945, but the stability of sensitivity is still insufficient. No, further improvements were desired.

[Object of the Invention] Therefore, the object of the present invention is to provide a photosensitive lithographic printing plate which has high sensitivity stability after exposure and excellent reproducibility of small dots (small halftone dots) and tone reproducibility, and a photosensitive lithographic printing plate used therein. An object of the present invention is to provide a photosensitive composition.

Another object of the present invention is to provide a photosensitive planographic printing plate whose sensitivity stabilizing effect does not decrease even after long-term storage of the photosensitive planographic printing plate, and a photosensitive composition used therein. .

[Structure of the Invention] The object of the present invention is to provide a compound that can generate an acid when irradiated with actinic rays, a compound that has at least one bond that can be decomposed by the acid, and a compound that can capture the acid and generate an acid when irradiated with actinic rays. This was achieved using a photosensitive lithographic printing plate having a photosensitive composition containing an amine compound that does not decompose, and a photosensitive layer formed from the photosensitive composition on the main support.

[Specific Structure of the Invention] A compound that generates an acid upon irradiation with actinic rays (hereinafter referred to as the acid-generating compound of the present invention) will be described.

The acid generating compound of the present invention includes various known compounds and mixtures. For example, diazonium salts, phosphonium salts, sulfonium salts, and iodonium BF4
-1PFs-1Sb Fs-1Si Fs-1CI O
4-nato(7)li, Wli-O1'n compound, orthoquinone-diazide sulfonyl chloride, and organometallic/
Organic halogen compounds are also actinic light-sensitive components that form or separate acids upon irradiation with actinic light, and can be used as acid-generating compounds in the present invention. All organic halogen compounds, which are known in principle as free-radical-forming photoinitiators, are compounds which form hydrohalic acids and can be used as acid-generating compounds according to the invention.

Examples of compounds forming the above-mentioned hydrohalic acids are U.S. Pat. Nos. 3.515.552 and 3.536.4
89 and 3.779.778 and West German Patent Application No. 2,243,621;
．． Compounds that generate acids upon photolysis as described in US Pat. No. 6,100,842 can also be used.

Furthermore, JP-A-54-74728, JP-A-55-
24113, JP 55-77742, JP 60-3626, JP 60-138539
Specifically, the 2-halomethyl-1,3,4-oxadiazole-based compounds described in the above publication include 2-tric0methyl-5-[β(2-benzofuryl)vinyl]1,3.4
-Oxadiazoles can be used.

Specific examples of the acid generating compound of the present invention include JP-A-56-
Examples include those described in Japanese Patent No. 17345.

Further, O-naphthoquinonediazide-4-sulfonic acid halide described in JP-A-50-36209 can also be used.

The acid-generating compound of the present invention can vary widely depending on its chemical properties and the composition or physical properties of the photosensitive composition of the present invention, but is approximately A range of 0.1 to about 20% by weight is suitable, preferably a range of 0.2 to 10% by weight.

A compound having at least one bond that can be decomposed by the acid generated by the acid-generating compound of the present invention (hereinafter referred to as 1, the acid-decomposable compound of the present invention) will be described.

Specifically, the acid-decomposed compound of the present invention includes JP-A No. 4
No. 8-89003, No. 5l-120714Ji3, No. 5
No. 3-133429, No. 55-12995, No. 55
Compounds having a C-〇-C bond described in the specifications of JP-A-126236 and JP-A-56-17345; compounds described in the specifications of JP-A-60-37549 and JP-A-60-121446 A compound having a 5i-0-C bond,
Mei I of JP-A-60-3625 and JP-A-60-10247
Other acid-degradable compounds listed in the book m. Furthermore, the compound having an Si--N bond described in the specification of Japanese Patent Application No. 16687/1987,
Carbonic esters described in the specification of Japanese Patent Application No. 603, orthocarbonic esters described in the specification of Japanese Patent Application No. 1983-125473, orthotitanate esters, orthosilicate esters described in the specification of Japanese Patent Application No. 125474/1980, acetals and ketals described in the specification of Japanese Patent Application No. 155481/1981, C described in the specification of No.-87769
Examples include compounds having -8 bonds.

Among these acid-decomposed compounds, in the present invention, JP-A-48-89003, JP-A-51-120714, JP-A-5
No. 3-133429, No. 55-12995, No. 55
．． -126236, No. 56-17345, and the compounds described in Japanese Patent Applications No. 60-251744 and No. 61-155481 are preferred; More preferred are the compounds described in Japanese Patent Application No. 60-251744 and No. 61-155481.

Further, specific exemplary compounds and synthesis methods of the acid-decomposed compound of the present invention are described in each of the above-mentioned specifications.

The content of the acid-decomposed compound of the present invention is preferably 5 to 70% by weight, particularly preferably 10 to 50% by weight, based on the total solid content of the photosensitive composition of the present invention.

Further, the acid decomposition compound of the present invention may be used alone, or two
A mixture of more than one species may be used.

Examples of synthesis of the acid-decomposed compound of the present invention are shown below.

Synthesis Example 1> 1.1-dimethoxycyclohexane (manufactured by Tokyo Kasei Kogyo ■) 72. IG (0.5 mol), triethylene glycol (manufactured by Kanto Kagaku n)? 5.1 (1 (0.5 mol)) and 180 mg of p-toluenesulfone were mixed with 10
The reaction was carried out at 0°C for 1rR, then the temperature was gradually raised to 150°C, and the reaction was further carried out at 150°C for 4 hours.

Methanol produced by the reaction was distilled off during this time. After cooling, 500 μ12 of tetrahydrofuran and 2.59 μl of anhydrous potassium carbonate were added, stirred, and filtered. The solvent was distilled off from the filtrate under reduced pressure, and low-boiling components were further distilled off at 150° C. under high vacuum to obtain a viscous oily product D-1.

D-1; Mw =980. Mw /Mn = 2.3 <Synthesis Example 2> Benzaldehyde (Kanto Kagaku II) 53.1 g (0.5
mol), triethylene glycol 75.1 (1(0,5
2.59 mol of sulfuric acid was added to a solution of 500 ilf of benzene, and the mixture was reacted under reflux for 200 hours. The reaction water produced by the reaction was separated as an azeotrope.

After the reaction was completed, 250 g of anhydrous potassium carbonate was added, and the mixture was stirred at room temperature for 2 hours, and then filtered. Benzene was distilled off from the filtrate under reduced pressure, and low-boiling components were further distilled off at about 150° C. under high vacuum to obtain a viscous oily product D-2.

D-2: Synthesis Example 3> 53.1 g of methyl orthoformate and 55.8 CI of 1,2,6-hexandriol were reacted in the same manner as in Synthesis Example 1 to produce polymer orthocarboxylic acid ester D-3 having the following structural unit. I got it.

D-3; Mw ” 1700. Mw /Mn = 2.1 Synthesis Example 4> Thioglycerol 10.9g (0.1 mol), methyl orthoformate 10.6Q, (0.1 mol) and as an acid catalyst 0.16 g (0,001 mol) of p-toluenesulfonic acid was gradually heated while stirring for 5 hours, and the temperature was raised to 130°C while distilling off methanol as a by-product.The amount of methanol distilled off was 8.6 g. Met.

Thereafter, the reaction was stopped by cooling, and anhydrous potassium carbonate 1.
1 g was added and filtered to obtain a colorless and transparent viscous liquid.

This liquid was then heated under vacuum (approximately 11IIIHg) for approximately 8
It was dried at 0° C. for 10 hours to obtain about 16 g of orthothioformate D-4 having the following structural unit.

D-4: Synthesis Example 5> To a mixture of 34.5Q of p-xylylene glycol, 48.6Q of tetraethylene glycol, 87g of pyridine and 6001g of ethyl acetate, 6 of dichlorodimethylsilane was added.
After adding 4.5 g of ethyl acetate 15 (hj2 solution) dropwise at room temperature with stirring, stirring was continued at 50° C. for 3 hours.

The generated pyridine hydrochloride was filtered off and treated with 5% NaHCO.

The aqueous solution was washed with saturated brine. After drying the solution over anhydrous sodium sulfate, the solvent was distilled off under reduced pressure to obtain a product, silyl ether polymer D-5.

D-5: Mw =16,000. Mw/Mn=1
, 7 Synthesis Example 6> 89 g of orthomethyl carbonate 6B, 1Q, 1, 2,6-hexanetriol and 0.1 p-toluenesulfonic acid
Gradually heat the mixture to 90°C while stirring.

After stirring at 90°C for 3 hours, the mixture is further gradually heated to 150°C over 3 hours. During this time, methanol produced by the reaction is distilled off. After cooling, 500 g of tetrahydrofuran was added to the reaction product, followed by 3 g of anhydrous potassium carbonate, stirred, and then filtered. The solvent was distilled off from the filtrate under reduced pressure to obtain Polymer Ol 1 to Carbonate D-6 having the following structural units.

D-6: Mw = 48 + 000 + Mll / Mn = 33
<Synthesis Example 7> 1.1-dimethoxycyclopentane 13, Og(0,5
mole), triethylene glycol monomethyl ether 1
64.2g (1.0 mol) and 80Il1g of p-toluenesulfonic acid were reacted at 100°C for 1 hour at 11/2 W, then the temperature was gradually raised to 150°C, and further reacted at 150°C for 4 hours.

Methanol produced by the reaction was distilled off during this time.

After cooling, 5001β of tetrahydrofuran and 2.59 g of anhydrous potassium carbonate were added, stirred and filtered. The solvent was distilled off from the filtrate under reduced pressure, and low-boiling components were further distilled off at 150°C under high vacuum to obtain a viscous oily product D-7.

D-7: <Synthesis Example 8> 1.1-Dimethoxycyclohexane and phenyl cellosolve were reacted in the same manner as in Synthesis Example G to produce a viscous oily product D-
I got 8.

D-8: An amine compound (hereinafter referred to as the amine compound of the present invention) that can supplement acid and does not decompose upon irradiation with actinic rays will be described.

The amine compound of the present invention has the property of compensating for the acid generated from the acid generating compound of the present invention, and is an amine compound that does not absorb light with a wavelength of 500 nm or more. Specifically, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, n-propylamine, di-n-propylamine, tri-n-propylamine, isopropylamine, n-butylamine, isobutylamine, 5ec-butylamine, tert-butylamine, cyclohexylamine, benzylamine, α-phenylethylamine, β
- phenylethylamine, ethylenediamine, tetramethylenediamine, hexamethylenediamine, tetramethylammonium hydroxide, aniline, methylaniline, dimethylaniline, diphenylamine, triphenylamine, 0-toluidine, m-toluidine, p-toluidine, O-anisidine, m-anisidine, p-anisidine,
0-chloroaniline, m-chloroaniline, p-chloroaniline, O-bromoaniline, m-bromoaniline,
p-bromoaniline, 0-nitroaniline, m-nitroaniline, p-nitroaniline, 2.4-dinitroaniline, 2.4.6-dolinitroaniline, 0-phenylenediamine, m-phenylenediamine, p-phenylene Examples include diamine, benzidine, p-aminobenzoic acid, sulfanilic acid, sulf7nylamide, pyridine, 4-dimethylaminopyridine, piperidine, piperazine, urea and the like.

The amount of the amine compound of the present invention added is 1/100 to 10 times the equivalent, preferably 1/20 to the equivalent of the amount of the acid generating compound of the present invention, and A suitable amount is 0.1% to 10% by weight based on the total strain.

In the present invention, in addition to the acid-generating compound of the present invention, the acid-decomposing compound of the present invention, and the radical scavenger of the present invention, a high molecular weight binder may be used. Examples of the high molecular weight binder include novolac resins, polymers having hydroxystyrene units, and polymers having structural units represented by the general formula [E].

Examples of the novolak resin include phenol formaldehyde resin, cresol formaldehyde resin,
Phenol-cresol-formaldehyde copolycondensate resin as described in JP-A No. 55-57841, p-substituted phenol and phenol as described in JP-A-55-127553, or
Examples include copolycondensate resins of cresol and formaldehyde.

Examples of polymers having hydroxystyrene units include polyhydroxystyrene and hydroxystyrene copolymers described in Japanese Patent Publication No. 52-41050.

A polymer having a structural unit represented by the general formula [I] refers to a homopolymer having a repeating structure of only the structural unit,
Alternatively, it is a copolymer in which the structural unit is combined with one or more structural units having a structure in which the unsaturated double bonds of other vinyl monomers are opened.

General formula [I] +CRI R2-CR3+ CoNR → X 5 Y -OH In general formula [I], R1 and R2 each represent a hydrogen atom, an alkyl group such as a methyl group or an ethyl group, or a carboxylic acid group, and is a hydrogen atom. R3 represents a hydrogen atom, a halogen atom such as a chlorine atom or a bromine atom, or an alkyl group such as a methyl group or an ethyl group, preferably a hydrogen atom or a methyl group. R4 represents a hydrogen atom, an alkyl group such as a methyl group or an ethyl group, a phenyl group or a naphthyl group.

Y represents a phenylene group or a naphthylene group, including those having substituents, and examples of substituents include alkyl groups such as methyl and ethyl groups, halogen atoms such as chlorine and bromine, carbon MWk, methoxy and ethoxy groups, etc. alkoxy group, hydroxyl group, sulfonic acid group, cyano group, nitro group,
Examples include acyl groups, but preferably those that have no substituent or are substituted with a methyl group.

X is a divalent organic group that connects a nitrogen atom and an aromatic carbon atom, and n represents an integer of O to 5, preferably when n is O.

A polymer having a structural unit represented by general formula [I] is
More specifically, for example, expressed as a) to h), 1=Y- or '! Ru.

I) In a) to h), R1-R5 are each a hydrogen atom,
It represents an alkyl group or a halogen atom, and X represents an alkyl group or a halogen atom. Moreover, m, n, l, k and S represent the mole % of each structural unit.

Further, a novolak resin, a polymer having a hydroxystyrene unit, and a polymer having a structural unit represented by the general formula [Il] can also be used in combination.

The photosensitive composition of the present invention may further contain pigments such as dyes and pigments, plasticizers, etc., as necessary. Furthermore, if necessary depending on the purpose of use, a sensitizer (as described above) may be added to the photosensitive composition of the present invention. Compound that increases the acid generation efficiency of the acid generation compound of the present invention)
etc. can also be added.

Furthermore, a lipophilic resin can be added to the photosensitive composition of the present invention in order to improve the oil sensitivity of the photosensitive composition.

The lipophilic resin (hereinafter referred to as a liposensitizing agent) is, for example, a phenol substituted with an alkyl group having 3 to 15 carbon atoms, as described in JP-A-50-125806. A condensate of aldehyde and t-butylphenol formaldehyde resin can be added. It is also possible to add a photosensitive resin obtained by condensing a lipophilic substituted phenol formaldehyde resin with a sulfonic acid polychloride of O-quinonediazide. These oil sensitizing agents are preferably contained in an amount of 0.1 to 5% by weight of the photosensitive composition of the present invention.

In the photosensitive composition of the present invention, a photosensitive layer is provided by dissolving each of the above-mentioned components in the following solvents and coating and drying them on the surface of a suitable support. A photosensitive planographic printing plate (hereinafter referred to as the photosensitive planographic printing plate of the present invention) can be formed using the photosensitive composition.

Solvents that can be used to dissolve each component of the photosensitive composition of the present invention include cellosolves such as methyl cellosolve, methyl cellosolve acetate, ethyl cellosolve, and ethyl cellosolve acetate, 1,2-propanediol monomethyl ether, and its like. Examples include acetate, 1,2-propanediol monoethyl ether or its acetate, dimethylformamide, dimethyl sulfoxide, dioxane, acetone, cyclohexanone, trichloroethylene, methyl ethyl ketone, and the like.

Alternatively, the method described in JP-A No. 60-208750, that is, the photosensitive composition is dissolved in an organic solvent, the aqueous solvent solution is emulsified and dispersed in water, and the fertilized solvent is substantially removed. A method for producing a liquid coating solution can also be used.

As the coating method, a conventionally known method can be used.

The support provided with the photosensitive layer using the photosensitive composition of the present invention may be a metal plate made of aluminum, zinc, steel, copper, etc., or a support plate plated or vapor-deposited with chromium, zinc, copper, nickel, aluminum, iron, etc. Examples include metal plates, paper, plastic films, glass plates, paper coated with resin, paper covered with metal foil such as aluminum, and plastic films subjected to hydration treatment. Among these, preferred is an aluminum plate treated to make it hydrophilic. As the support for the photosensitive lithographic printing plate of the present invention, it is more preferable to use an aluminum plate that has been subjected to surface treatments such as graining, anodizing, and, if necessary, sealing.

In the present invention, the active light rays may be any light rays sufficient to cause the acid-generating compound of the photosensitive composition of the present invention to form an acid. A conventional exposure and printing apparatus can be used, for example, an apparatus that uses a light source such as an ultra-high pressure mercury lamp, a metal halide lamp, a xenon lamp, or a tungsten lamp, or an apparatus that performs scanning exposure using a laser beam may be used as appropriate. . The exposure amount is 0.1
It can be appropriately selected within the range of mJ to 2000 mJ.

The photosensitive lithographic printing plate of the present invention is exposed and baked using the above-mentioned exposure baking apparatus, and then developed with a developing solution, so that only the unexposed areas remain on the surface of the support, forming a positive-positive type relief image.

Aqueous alkaline developers can be suitably used for developing the photosensitive lithographic printing plate of the present invention, such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate,
Examples include aqueous solutions of alkali metal salts such as sodium metasilicate, potassium metasilicate, sodium diphosphate, and sodium triphosphate.

[Effects of the Invention] The present invention has the effect of providing high sensitivity stability after exposure, excellent reproducibility of small dots and tone reproducibility, and stabilizing sensitivity even after long-term storage of photosensitive planographic printing plates. A photosensitive lithographic printing plate that does not cause a decrease in the lithographic printing plate and a photosensitive composition used therein were obtained.

[Examples] Specific examples of the present invention will be shown below, but the embodiments of the present invention are not limited thereto.

[Preparation of photosensitive lithographic printing plate sample] After degreasing an aluminum plate (material 1050, tempering H16) with a thickness of 0.241 in a 5% caustic soda aqueous solution at 60°C for 1 minute, 0.5 mol 1ffi In an aqueous hydrochloric acid solution, temperature: 25°C, current density: 60. Electrolytic etching treatment was performed under the conditions of A/d 12 and treatment time 230 seconds. Next, after desmutting in a 5% caustic soda aqueous solution at 60°C for 10 seconds, desmutting was performed in a 20% sulfuric acid solution at a temperature of 2.
The anodic oxidation treatment was performed at 0° C., current density: 3 A/dv', and treatment time: 1 minute. Furthermore, with hot water at 30℃
Hot water sealing treatment was performed for 0 seconds to produce an aluminum plate as a support for lithographic printing plate material.

Next, a photosensitive composition coating solution having the following composition was applied to this aluminum plate using a rotary coater and dried at 90° C. for 4 minutes to obtain a positive-working photosensitive lithographic printing plate sample.

Example 1 Photosensitive liquid (I) - Acid decomposition compound 2.14 (tonovolac resin Copolycondensation resin of phenol, m-cresol, p-cresol and formaldehyde (molar ratio of each of phenol, m-cresol and p-cresol) is 2.0:
4.8: 3.2, lylw = 10,000, M
Y/Mn = 6.7) 5.74 (J・
2-Trichloromethyl-5-[β-(2-benzofuryl)vinyl]1゜3.4-oxadiazole (exemplified compound (1) described in JP-A-60-138539) 0.279・Invention 1001 g of amine compound listed in Table 1 ・Methyl cellosolve 1001 g Step tablet for sensitivity measurement (
Eastman Kodak No. 2, concentration difference 0.
21 levels of gray scale (15 each) in close contact, 4
Exposure was carried out for 30 seconds from a distance of 70 cm using a KW metal halide lamp (Idolfin 2000 manufactured by Iwasaki Electric Co., Ltd.) as a light source.

Next, the samples that had been exposed for 1 minute and 60 minutes after exposure were developed for 40 seconds at 25°C with a developer prepared by diluting 5DR-1 (Konishi Roku Photo Industry (floor rack)) 8 times with water, and
-1 (manufactured by Konishi Rokushapage Kogyo (+M)).The clear sensitivity was then evaluated.The results are shown in Table 1.

In order to further examine the raw storage stability, the temperature was 55℃ and the humidity was 10%.
The clear sensitivity of the photosensitive lithographic printing plates degraded under forced degradation conditions for 3 days was similarly evaluated. The results are shown in Table 1.

As is clear from Table 1, in Comparative Examples 1 to 7 in which no amine compound was added, the difference in the number of clear steps over time was large and the sensitivity was not stable. Furthermore, in Comparative Example 8 in which a compound other than the amine compound of the present invention was added, the sensitivity was similarly unstable. On the other hand, in Examples 1 to 12 of the present invention, sensitivity stability is high, and stability is well maintained even after forced deterioration.

Example 13 A printing test was conducted using the lithographic printing plates obtained in Examples 1 to 12 and Comparative Examples 1 to 8. However, in addition to the elapsed time from exposure to development of 1 minute, 1 hour, 3.5 hours, 6 hours,
The test was also carried out for 10 hours.

In the lithographic printing plates using the photosensitive compositions of the compositions of Comparative Examples 1 to 8, when developed 6 hours and 10 hours after exposure, so-called "skipping small dots" occurred in the printed matter and the tone reproducibility of the printed matter deteriorated. did. On the other hand, with the compositions of Examples 1 to 12, printed matter with good dot reproducibility and tone reproducibility was obtained regardless of the elapsed time from exposure to development and even after forced deterioration.

Example 14 In Examples 1 to 12, Comparative Examples 1 to 8, and Example 13, Victoria Pure Blue BOH was added to the photosensitive liquid (I).
Using a photosensitive liquid containing osg and using the same method except that no inking was applied, tests were conducted on the difference in the number of clear steps, the difference in the number of clear steps after forced deterioration, and the reproducibility of small dots.

As with the results of Examples 1 to 12, Comparative Examples 1 to 8, and Example 13, the results showed that the present invention had high stability after exposure and excellent dot reproducibility and tone reproducibility.

Claims (2)

[Claims] (1) Contains a compound that can generate an acid when irradiated with active light, a compound that has at least one bond that can be decomposed by the acid, and an amine compound that can capture the acid and does not decompose when irradiated with the active light. A photosensitive composition characterized by: (2) In a photosensitive lithographic printing plate having a photosensitive layer formed from a photosensitive composition on a support, the photosensitive composition is a compound capable of generating an acid upon irradiation with actinic rays, and is decomposed by the acid. A compound having at least one bond capable of
and a photosensitive lithographic printing plate characterized by containing an amine compound capable of capturing the acid and not decomposed by irradiation with actinic rays.