JPS6347773A - Preparation of lithographic plate - Google Patents

Abstract

PURPOSE:To use semiconductor laser beams low in output and to form a lithographic plate high in resolution and printing resistance and free from background stains with high sensitivity by forming an antihalation means under emulsion layers, exposing the lithographic plate to the scanning light of >=700nm wavelength, and processing it with a developing solution containing thiocyanate. CONSTITUTION:The lithographic plate material has on a support at least the silver halide emulsion layer containing silver halide grains composed of at least silver bromide and a sensitizing dye having maximum spectral sensitivity in a long wavelength region of >=700nm in an amount of 3X10<-5>-3X10<-4>mol per mol of silver halide, and a physical development nucleus layer as a surface layer, and further, the antihalation means having a reflectivity of 13-40% of the scanning exposure light. This plate material is exposed to the high- illuminance short-time scanning exposure light of >=700nm wavelength and processed with the developing solution containing at least the thiocyanate for use in the silver complex salt diffusion transfer process.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Industrial Application Field The present invention relates to a method for making a lithographic printing plate using a silver complex diffusion transfer method suitable for using a laser beam, particularly a semiconductive laser beam, as a light source. .

(B) Prior art and its problems Planographic printing plates in which the transferred fli image obtained by the silver complex diffusion transfer method can be immediately used for ink receptivity have already been developed in Japanese Patent Publications No. 48-30562 and No. 53-216.
02, 1972-103104, 1977-9750, etc., and are well known.

According to a typical implementation method of the silver complex diffusion transfer method suitable for the plate-making method of such a lithographic printing plate, a support is coated with a subbing layer that also serves as a halide prevention layer, a silver halide emulsion M, and a physical dye λ. When the Sensitive 1 material consisting of the core layer is imagewise exposed and developed, the silver halide on which the latent image has been formed becomes blackened silver in the emulsion layer. At the same time, silver halide on which no latent image has been formed is dissolved by the action of a silver halide complexing agent contained in the processing solution and diffused onto the surface of the photosensitive material. The dissolved and diffused silver complex salts are deposited as a silver image by the reducing action of the developing agent on the physical development nuclei of the surface layer.Subsequently, a development process is performed to modulate the ink receptivity of the resulting silver image. After being subjected to oil sensitization treatment if necessary, it is set in an offset printing machine and the ink image is transferred to the printed material.

In the conventional method, the silver halide emulsion layer is spectrally sensitized using a merocyanine dye, cyanine hexaelement, etc. so that it has a maximum sensitivity in the green region around 550 nm, and a plate-making camera with a normal light source such as a tungsten light source is used. Exposure was given for several seconds to several tens of seconds. However, the above conventional method has limitations even though the lithographic printing plate originally has excellent sharpness and resolution. Moreover, when trying to obtain color printed matter from a color original, there are problems in that not only the resolution is insufficient, but also the production of printing plates and plate-making operations are complicated.

Today, as one method for solving the above-mentioned problems, plate making using laser light has been proposed.

For example, U.S. Patent No. 4,501,811, JP-A-59
-71055, 1986-75838, 1986-10
No. 0148 and the like disclose a lithographic printing plate for use in helium-neon lasers or light-emitting diodes.

As described in these patent specifications, in these lithographic printing plates using the silver complex diffusion transfer method, the surface physical development nucleus layer has a large effect on the spectral sensitization.
Sensitivity to the target laser beam has decreased, storage stability has deteriorated, and as a result of silver complex salt diffusion transfer development, a soft transferred deposited silver image has been formed, resulting in decreased sharpness and resolution, and furthermore, background smearing has occurred. It is difficult to obtain a lithographic printing plate of high quality as desired because the silver image was removed during printing and sufficient printing durability could not be obtained.

JP-A-60-75838 discloses that when plate making with 632.8 nm helium-neon laser light, resolving power and printing durability can be improved by providing an antihalation layer with a reflectance of 10 inches or less. has been done.

A method using a laser beam such as helium-neon or argon as a light source in a scanner system can provide high output, but has drawbacks such as large and expensive equipment and low power consumption efficiency. On the other hand, semiconductor lasers have advantages such as being small, inexpensive, easy to modulate, and have a long life. Semiconductor lasers include Ga/As/P; Ga/A
Semiconductors of systems such as t/As; Ga/As: In/P: In/As are used, and the wavelength of this laser light is generally longer than 700 nm, and in particular, is often as long as 750 nm.

Photosensitive planographic printing plates that use such long-wavelength semiconductor laser light as a light source for image exposure are known, for example, from
0-61752. This patent specification describes, as a particularly preferred embodiment, a non-silver-sensitive F5 (for example, a photosensitive film having a photosensitive layer consisting of an 0-naphthoquinone diazide compound and a photosensitive silver halide emulsion layer) that can sequentially form a lipophilic image on a support. A lithographic printing plate is shown, and the sensitizing dyes having maximum spectral sensitivity in the long wavelength region (700 nm and above) used in such an emulsion layer have general formulas (I) to (1'V).
).

However, a lithographic printing plate having a silver halide emulsion layer containing such a sensitizing dye, an antihalation layer with a reflectance of 10% or less for semiconductor laser diode light in the near-infrared region, and a surface physical development nucleus layer, Although it had sufficiently high printing durability, its sensitivity to laser diode output machines was extremely low, and if the reflectance of the anti-halation layer was increased to improve sensitivity to some extent, the printing durability would deteriorate. As a result, it has been extremely difficult to satisfy all of the requirements of high sensitivity, high resolution, and high printing durability based on conventional knowledge.

(C) Object of the invention The object of the invention is lithographic printing that uses a silver complex diffusion transfer method that has high sensitivity, can use low-output semiconductor laser light, has high resolution, high printing durability, and is free from scumming. The purpose of the present invention is to provide a plate making method.

CD) Structure of the Invention The above-mentioned object of the present invention is to apply a lithographic printing plate having at least a silver halide emulsion 1 and a physical development nucleus layer as a surface layer on a support by high illuminance, short time scanning exposure diameter, silver complex salt diffusion transfer. In a plate-making method in which development is performed using a commercially available developer, the reflectance of scanning exposure light of 700 nm or more is 13% to 4% below the emulsion layer.
Furthermore, the emulsion layer contains silver halide grains containing at least silver bromide and a sensitizing dye having maximum spectral sensitivity in a long wavelength region of 700 nm or more. per mole, 93 Xl0-
' to 700n of lithographic printing plates containing in an amount of 3
This was achieved by a plate-making method characterized by exposing to scanning light of m or more and then developing with a developer containing at least a thiocyanate.

The present invention will be explained in more detail below.

The support used in the lithographic printing plate of the present invention is, for example, paper, film, for example, cellulose acetate film, polyvinyl acetal film, polystyrene film, polypropylene film, polyethylene terephthalate film, or polyester, polypropylene or polystyrene film, etc. The support can be a coated composite film, metal, metallized paper or metal/paper laminate. Paper supports coated on one or both sides with an alpha-olefin polymer, such as polyethylene, are also useful.

It is preferable to provide an undercoat layer between the support and the silver halide emulsion layer.

At least one of the subbing layer, the support, and the backing layer is provided with antihalation, such that scanning exposure light, for example, 780 nm laser diode light, is reflected onto the emulsion layer at a rate of 13 to 40 inches. .

A highly preferable reflectance is 14% to 35%.

This method of preventing surface hareshi from being exposed is disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 60-7
Compared to the 3-inch and 8-inch reflectance halation prevention methods described in 5838, the sensitivity has been increased, and contrary to expectations, it has been found that the reduction in resolution due to the laser scanner method can be ignored in practice. did. However, there is a drawback that the printing durability of fine line images is poor.

The amount of a sensitizing dye having a maximum spectral sensitivity of 700 nm or more is 3X per mole of silver halide containing at least silver bromide.
When combined with the above-mentioned halation prevention in the range of 10-' to 3X10-' moles, and development with a developer containing at least thiocyanate, high sensitivity can be achieved that is sufficiently applicable to a laser diode output device, and the above-mentioned resistance can be achieved. It has been found that the drawback of reduced printing force is completely resolved, and a lithographic printing plate with high printing durability and high resolution can be obtained.

The preferred amount of sensitizing dye is 1 mole of silver halide,
94×10 to 2×10 mol.

In the present invention, the antihalation applied to at least one of the subbing layer, the support, and the backing layer is 700%
A substance capable of absorbing laser light with a wavelength of at least 750 nm, preferably at least 750 nm, is used, such as a black pigment such as carbon black, a penta or hebutamethine oquinol dye, and the like.

Preferably, antihalation is applied at least to the subbing layer adjacent to the emulsion layer.

The sensitizing dye used in the present invention, which has maximum spectral sensitivity in a wavelength region longer than 700 nm, is disclosed in, for example, U.S. Pat.
No. 095,854, No. 2,095,856, No. 2
, No. 955,939, No. 3,482,978, No. 3,552,974, No. 3,573,921, No. 3,582,344, No. 3,623,881 It can be as stated in the specification etc.

Preferably, for example, dyes represented by the following general formulas (1) to (IV) are used.

(Hereinafter, all white) -''≧ In the general formulas (1) to (IV), Zl and Z2 may be the same or different, and each may form a 5-negative or 6-membered nitrogen-containing heterocycle. Represents the necessary atomic group.R
1 and R2 may be the same or different, and each represents an alkyl group or an alkenyl group. R3 represents an alkyl group, an alkenyl group, or an aryl Mk. R4-R
10 may be oriented or different, and each represents a hydrogen atom, a hydrogen atom, an alkyl group, an aryl group, or an alkoxy group. However, R6 and R7 or R8 and R9 can also be connected to each other to form a 5- or 6-membered ring. R11 and R42 may be the same or different, and each represents an alkyl group or an aryl group,
R11 and R12 can also be connected to each other to form a 5- or 6-membered ring. Y is a sulfur atom, an acid atom 1. 'N
R+3 (Ru is an alkyl group).

X represents an acid anion. 2%m, n, p and q each represent 1 or 2.

Specific examples of Zl and Z2 include thiazole, pemenzothiazole, naphtho(1,2-4:l thiazole,
Naphtho[:2.1-d:]thiazole, Nando[2,3
-〆4] Thiazole, selenazole, penzo selenazole, naphtho [2,1-t, l selenazole, nantho [1,2-t] selenazole, oxazole, pembele oxazole, naph) [1,2-d:l Oxazole, naph[2,1-el'=:l oxazole, naphtho[2.3-11] oxazole, 2-quinoline, 4-quinoline, 3,3-dialkylindolenine, imidazole, benz Nitrogen-containing d-rings such as imidazole, naph)[1,2-d]imidazole and pyridine can be mentioned. These 'fJJ, purple rings are alkyl groups (for example, methyl, ethyl, butyl, trifluoromethyl, etc.)
, aryl groups (e.g., phenyl, tolyl, etc.), hydroxy groups, alkoxy groups (e.g., methoxy, ethoxy,
(butoxy, etc.), carboxy groups, alkoxycarbonyl groups (e.g., methoxycarbonyl, ethoxycarbonyl), halogen atoms (e.g., fluorine, chlorine, bromine, iodine), aralkyl groups (e.g., benzyl, phenethyl, etc.)
, a cyano group, an alkenyl group (for example, allyl), or the like may have one or more substituents.

In R1 and "2, the alkyl group includes a lower alkyl group such as methyl, ethyl, propyl, butyl, a hydroxyalkyl group such as β-hydroxyethyl, γ-hydroxyglobil, β-methoxyethyl, γ-methoxyglobil, etc. Alkoxyalkyl groups such as bir, β-acetoxyethyl, γ-
Acyloxyalkyl groups such as acetoxyglobil and β-benzoyloxyethyl; carboxyalkyl groups such as carboxymethyl and β-carboxyether; alkoxycarbonylalkyl groups such as methoxycarbonylmethyl, ethoxycarbonylmethyl and β-ethoxycarbonylethyl; β- Examples of the alkenyl group include sulfoalkyl groups such as sulfoether, γ-sulfopropyl, and δ-sulfobutyl, aralkyl groups such as benzyl, phenethyl, and sulfobenzyl, and allyl.

Examples of R3 include alkyl groups and alkenyl groups as described above for R1 and R2, as well as aryl groups such as phenyl, tolyl, methoxyphenyl, chlorophenyl, and naphthyl.

R4-R10 are hydrogen atoms, halogen atoms (e.g. chlorine, bromine, iodine, fluorine), alkyl groups and aryl groups as described in R1 and 'PL2, or alkoxy groups having alkyl as described in R1 and R2 ( That is, the 5- or 6-membered ring formed by R6 and R7 or R8 and R9 may be substituted with a lower alkyl group or the like. R11 and R12 represent an alkyl group or an aryl group as described for R1 and R2, and R11 and R1
2 can also be introduced in succession to form a 5- or 6-membered ring. R15 is an alkyl group as described for R1 and R2.

Examples of the acid anion of It does not exist when it has a betaine-like structure.

Specific examples of 0 violet sensitization used in the present invention are illustrated below.

l1 O3 CHs+SOs- C2H5 (CH2)4 SO, - CH3 The sensitizing dye used in the present invention can be synthesized by a method known to those skilled in the art. It can be added to the silver halogenide emulsion at any time before coating.

The silver halide emulsion used in the present invention consists of silver halide containing at least silver bromide. Silver chlorobromide and silver chloroiodobromide containing about 3 to about 60 moles of silver bromide are preferred, and those containing about 5 to about 50 moles of silver bromide are particularly preferred. Silver iodide is preferably in the range of about 0.01 to about 2 mole. The average particle size of these silver halide grains is preferably in the range of 0.2 to 0.8 microns, but ranges other than this can also be used. Further, the silver halide is preferably a monodispersed emulsion in which 90 percent or more of the total number of grains has a grain size within ±30% of the average grain size.

Further, although halogenated 0 grains are preferably substantially cubic to tetradecahedral grains, /'10 silver genide having other crystal habits can also be used.

The binder used in the silver halide emulsion of the lithographic printing plate of the present invention is usually gelatin. One or two hydrophilic polymer binders such as pyrrolidone, carboxymethyl cellulose, polyacrylamide, styrene-maleic anhydride copolymer, polyvinyl methyl ether-maleic anhydride copolymer, etc.
It is also possible to substitute more than one species. Furthermore, an aqueous vinyl polymer dispersion (latex) can also be used.

Silver halide emulsions can be sensitized in a variety of ways when they are manufactured or coated. Preferably, it is chemically sensitized by methods well known in the art, such as with sodium thiosulfate, alkylthioureas, or with gold compounds such as gold rhodan, gold chloride, or a combination of both. In addition, Zhou JvJ
By using a compound of metal chips belonging to the PG group of the Table of Laws, such as salts of cobalt, nickel, rhodium, palladium, iridium, platinum, etc., it is made with particularly high sensitivity, high sharpness, and high dissolving power. It is possible to obtain favorable characteristics for an M printing plate.

The amount added is 10-8 to 10-5 per mole of silver halide.
It is in the molar range. The silver halide emulsion layer can contain other additives, such as coating aids, hardeners, anti-capri agents, matting agents (water retention agents), developing agents, and other conventional additives.

The image-receiving layer is the upper side of the silver halide emulsion layer, that is, the outermost surface.
It is established as a When provided below the emulsion layer, the effect of the present invention is either absent or small.

As the physical development nucleus, known metals such as antimony, bismuth, cadmium, cobalt, palladium, nickel, silver, lead, zinc, and their sulfides can be used. The image-receiving layer contains hydrophilic colloids such as gelatin, carboxymethyl cellulose, gum arabic, sodium alginate, hydroxyethyl starch, dialdehyde starch, dextrin, hydroxyethyl cellulose, polystyrene sulfonic acid, a copolymer of vinylimidazole and acrylamide, and polyvinyl alcohol. It may contain one kind or two or more kinds. The hydrophilic colloid contained in the image is 0.5g/rr? It is preferable that it is the following.

Hygroscopic substances such as humectants such as sorbitol, glycerol, etc. may be present in the image-receiving layer. Furthermore, the image-receiving layer may also contain pigments for preventing scumming such as barium sulfate, titanium dioxide, china clay, and silver, developing agents such as hydroquinone, and hardening agents such as formaldehyde and dichloro-8-triazine.

The DTR processing solution used in the present invention contains at least thiocyanate as a silver halide solvent. As the thiocyanate, potassium thiocyanate, sodium thiocyanate, ammonium thiocyanate, etc. are used. The amount of thiocyanate to be used is about 0.05 to about 0.3 mol, preferably about 0.1 to about 0.3 mol, per 1 treatment solution.
It is 25 moles.

U.S. Patent No. 4,297,429, U.S. Patent No. 4,297,4
30, Specification No. 4,355,090, etc., 2-
Silver halide solvents such as mercaptobenzoic acid and cyclic imides (e.g. uracil) have been described as capable of producing lithographic printing plates with good printing durability, and have been put into practical use.
The printing durability of a lithographic printing plate using a silver chloride (iod)ide emulsion containing a sensitizing dye as described above was insufficient to reach a practical level. Further, although silver chloride emulsions are generally advantageous in terms of printing durability, it has been found that they are unsuitable because of the large decrease in printing durability caused by the sensitizing dye as described above. However, in addition to the thiocyanate, silver halide solvents such as 2-mercaptobenzoic acid, uracil, various volatile amines, and thiosulfates may be used in combination as necessary.

In addition to the above-mentioned silver halide solvent, the DTR processing solution used in the present invention includes alkali agents such as sodium hydroxide, potassium hydroxide, lithium hydroxide, and trisodium phosphate.
Preservatives, such as sodium sulfite, potassium sulfite, etc.
Thickening agents such as hydroxyethyl cellulose, carboxymethyl cellulose, antifouling agents such as potassium bromide, 1-phenyl-5-mercaptotetrasol, benzotriazole, compounds described in JP-A-47-26201, developers such as hydroquine /, 1-phenyl-3
- pyrazolidones, development modifiers such as polyoxyalkylene compounds, onium compounds, etc.

When applying the silver complex diffusion transfer method, for example, British Patent No. 1,000,115, British Patent No. 1,012,476,
No. 1,017,273, No. 1,042,477, etc. F! As described in Specification A, it has been practiced to incorporate a developer into the silver halide emulsion layer and/or the image-receiving layer or other water-permeable layer adjacent thereto. Therefore, for such materials, the processing solution used in the development step may be a so-called "alkaline activating solution" that does not contain a developer.

The lithographic printing plate manufactured according to the present invention is, for example,
8-29723, US Pat. No. 3,721,539, etc., the ink receptivity can be changed or enhanced.

The printing method, the desensitizing liquid, the dampening liquid, etc. used can be any commonly known method.

CB) Examples The present invention will be explained below with reference to examples, but of course the present invention is not limited to these.

Example 1 A matting layer containing silica particles with an average particle size of 5 microns was provided on one side of a subbed polyester film support, and a matting layer containing carbon black and hydroquinone on the other side and 20 times heavier than photographic gelatin. Undercoat layer containing silica powder with an average particle size of 7 μm (adjusted to pH 4.5)
and after being chemically sensitized with gold compound and hypo, 2-
A silver halide emulsion layer (CpH 4,5 IC adjustment) containing mercaptobenzoic acid and silica powder having an average particle size of 7 μm at a ratio of 5 weight % to photographic gelatin was provided.

The silver halide emulsion contains the sensitizing dye (15) in an amount of 5.4X10-' mole per mole of silver halide, and also contains 5X10-7 mole of chloride per mole of silver halide during physical ripening. Added iridium, average particle size 0
．． It was a silver chlorobromide emulsion with a diameter of 7 μm and containing 23 moles of silver bromide.

Is it 1.0P/ly? , silver chloride, converted to silver nitrate, was coated at a rate of 1°O. The undercoat layer and emulsion layer contain formalin as a hardening agent at a ratio of 5°01 to gelatin.
Contains an amount of gelatin.

The optical reflection of the undercoat layer at 7130 nm is 9 degrees.
It was 14. After drying and heating at 40°C for 14 days,
On this emulsion layer, hydroquinone 0.8P/;t? A solution added so as to be prepared is prepared in the same manner and applied (lithographic printing plate A).

On the other hand, except for setting the optical reflectance of the undercoat layer to 0.71,
A lithographic printing plate B was prepared in exactly the same manner as the lithographic printing plate.

A dark red filter (Fuji Photo Film FF1SC-70) was attached to the light source to pass light with a wavelength longer than about 700 nm, and the film original containing the K (B) image was brought into close contact with each of the above lithographic printing plates. It was exposed to light for 10 seconds.

This was used as a sample for printing test.

Furthermore, a wedge with a convexity difference of 0.15 was used to perform Km light in the same manner as above. This was used as a sample for sensitometry.

Each image-exposed printing plate was heated with the following DTR developer at 25°C.
Developed for 30 seconds. After the development process, the original plate is subjected to two apertures of 90
- roller to remove excess developer, immediately treated with a neutralizing solution having the following composition at 25° C. for 20 seconds, remove excess solution with a squeeze roller, and dry at room temperature.

Neutralizing liquid〉 Paste each printing sample on a sheet, load this sheet into an offset printing machine, apply the following desensitizing liquid all over the plate surface, and apply the following Printing was performed using a dampening liquid.

The printing machine is N.B.Dick 350CD (A・B@
An offset printer manufactured by Dick Company (Moyo) was used.

Non-greasy liquid> Humidifying liquid> The results were as follows.

The sensitivity is expressed as a relative sensitivity, with the sensitivity of printing plate A being 100.

On the other hand, the lithographic printing plates A and B were scanned using a laser diode scanner that emits light at 780 nm,
Although laser printing was performed using a lithographic printing plate A (manufactured by IU1TRE Inc.) in the United States, not only lithographic printing plate A, but even B could not be printed satisfactorily under the conditions of maximum output.

Next, in lithographic printing plate B, sensitizing dye (13) was added per mol of silver halide, 91×10 −' mol (lithographic printing plate C).
, same < 2.7 X 10-' mol (lithographic printing plate D)
A lithographic printing plate was prepared in exactly the same manner except that the same <9×10 −5 mol (lithographic printing plate E) was used, and the same test was performed.

The results are shown in Table 1.

Compared to printing plate A, printing plates C-E in Table 1 had poor resolution by contact exposure, and the running durability in Table 1 was also low.

However, the lithographic printing plate and E are Ultra 5
Printing was possible with Etter 9, the printing durability was 10,000 sheets or more in all cases, and the resolution was also good.

Example 2 Sensitizing dye (22) fj! instead of sensitizing dye (13) :
The same procedure as in Example 1 was carried out except for using. Results similar to those in Example 1 were obtained.

Example 3 Example 1 was repeated except that sensitizing dye (2) was used in place of sensitizing dye (13). Results similar to those in Example 1 were obtained.

Example 4 In lithographic printing plate B of Example 1, sensitizing dye (13) t per mole of silver halide, 96×10 mol (lithographic printing plate F), same (3×10 mol (lithographic printing plate G), same) A lithographic printing plate was prepared in the same manner except that the amount was 1×10 6 mol (lithographic printing plate H), and tested in the same manner.

Printing plate F showed similar results to printing plate B, and printing plate G showed similar results to printing plate.

The printing plate H had a sensitivity comparable to that of the printing plate, but even if the sensitivity was increased by increasing the reflectance to prevent halation, the printing durability was significantly inferior.

Example 5 In the lithographic printing plate E of Example 1, the reflection density of the undercoat layer was set to 0.
．． 58 (lithographic printing plate craftsman) and 0.32 (lithographic printing plate J)
A lithographic printing plate was prepared in the same manner except for the following, and tested in the same manner.

Although the lithographic printing plate was more sensitive than the lithographic printing plate E, there was almost no decrease in resolution, and the results of printing durability were also the same as that of the printing plate E.

Although the lithographic printing plate J had higher sensitivity than the lithographic printing plate, the resolution was significantly lowered and
In all 5etters, fine line silver images were missing by the time 5,000 sheets were printed.

(F) Effects of the Invention According to the present invention, in the direct plate making method of a semiconductor laser diode scanner system, lithographic printing using a silver complex diffusion transfer method with high sensitivity and high printing durability with virtually no reduction in resolution is possible. It is now possible to obtain a copy.

Claims (1)

[Claims] (1) In a plate-making method in which a lithographic printing plate having at least a silver halide emulsion layer and a surface physical development nucleus layer on a support is exposed to high-intensity, short-time scanning, and then developed with a developer for silver complex diffusion transfer, An antihalation means is provided below the emulsion layer so that the reflectance of scanning exposure light of 700 nm or more is 13% to 40%, and the emulsion layer further includes silver halide grains containing at least silver bromide and a 700 nm layer. A silver halide sensitizing dye having maximum spectral sensitivity in the long wavelength region
A lithographic printing plate containing 3 x 10^-^5 to 3 x 10^-^4 mol per mole is exposed to scanning light of 700 nm or more, and then developed with a developer containing at least thiocyanate. A plate-making method.