JP2548736B2 - Lithographic printing plate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a lithographic printing plate capable of plate making by an electrophotographic recording method, and in particular, it is sensitive to a wavelength range of a semiconductor laser for making a plate directly from a computer. The present invention relates to a lithographic printing plate having

[Prior Art] Conventionally, as a lithographic printing plate capable of plate making by an electrophotographic method, a lithographic printing plate provided with a photosensitive layer made of zinc oxide and a binder resin on a conductive support has been widely used.
However, since the photosensitive wavelength range of these is in the visible range, exposure with a semiconductor laser having a wavelength range in the infrared was impossible.

Japanese Patent Application No. 57-225959 discloses a lithographic printing plate having a photosensitive layer containing a phthalocyanine pigment, zinc oxide and a binder resin as a lithographic printing plate capable of being exposed by a semiconductor laser. However, in this specification, the binder resin is not particularly limited.

The binder resin is required to disperse a photoconductive pigment such as zinc oxide so as to have mechanical strength, retain electrophotographic characteristics, and ensure printability. In the lithographic printing plate of the present invention, the phthalocyanine pigment has electrophotographic properties and zinc oxide has printability, but the phthalocyanine pigment has no printability because it is lipophilic. Commonly used binder resins cannot be applied in the lithographic printing plate of the present invention due to lack of photographic properties. Further, those satisfying only electrophotographic characteristics and printability tend to have low mechanical strength, scratch the surface with slight rubbing or pressure, and as a result, only printed matter with a lot of background stains tends to be obtained.

Acrylic resins, that is, copolymers of radically polymerizable monomers such as acrylic acid esters, methacrylic acid esters and styrene, are widely used as binder resins for pigment-resin-dispersed electrophotographic photoreceptors.

Acrylic resins include copolymers such as methyl (meth) acrylate, ethyl (meth) acrylate, styrene, n-butyl (meth) acrylate, isobutyl acrylate, 2-ethylhexyl (meth) acrylate, and n-octyl (meth) methacrylate. , But generally
Particularly in a lithographic printing plate containing a phthalocyanine pigment as in the present invention, in a composition having excellent electrophotographic properties,
The mechanical strength was poor.

In order to improve the surface strength, JP-B-55-6217 and JP-A-59-40654 disclose, in addition to zinc oxide fine particles, large particles of zinc oxide having a diameter of 30 to 50 μm, or some kinds of resin. By mixing the zinc oxide particles coated with, and by providing projections on the surface of the photoreceptor, pressure is selectively applied to the projections, preventing wear of the photoreceptor itself and preventing background contamination and image flow. Described photoreceptor. However, with this method, it is difficult to reproduce a fine pattern of 50 μm or less because there are projections of several tens to 100 μm.

Further, Japanese Unexamined Patent Publication (Kokai) No. 58-127932 discloses a photoconductor in which a binder resin is a photocurable type, and a photosensitive layer is coated and then irradiated with light to improve the mechanical strength of the surface. But,
Since the photoconductive pigment absorbs light, a strong light source is required to cure the entire photosensitive layer, and not only the number of steps is increased, but only the surface is cured and the inside tends to be uncured.
It was difficult to obtain sufficient mechanical strength.

Also, Japanese Patent Application Laid-Open No. 54-1747838 discloses a photoconductor in which a (meth) acrylic resin and an epoxy resin are blended to form a binder resin. This is because the acrylic resin is the main component for maintaining the electrophotographic characteristics although it is cured to some extent, and the effect was insufficient only in the drying zone of a commonly used coating machine.

In order to solve such a drawback, a resin in which a radical-polymerizable organic acid, an epoxy group-containing (meth) acrylic acid ester, and acrylamide are introduced into a copolymer of methacrylic acid ester and acrylic acid ester forms a photosensitive layer. It has been confirmed to give good results as a constituent binder resin. However, although this resin shows good characteristics at low temperature and low humidity and medium temperature and humidity, it has a drawback that electrophotographic characteristics, especially receptive potential and dark decay are lowered at high temperature and high humidity.

[Object of the Invention] The present inventors have achieved the present invention as a result of earnest researches focusing on the composition of the photosensitive layer of a lithographic printing plate in order to solve the above drawbacks.

An object of the present invention is to provide a lithographic printing plate which has a long mechanical strength, is suitable for printing, can obtain a good image, and has little deterioration in electrophotographic characteristics even at high temperature and high humidity.

SUMMARY OF THE INVENTION The present invention provides a conductive support, at least zinc oxide,
In a lithographic printing plate having a photosensitive layer containing a phthalocyanine pigment and a binder resin, the binder resin is
A) 0.1-10 wt% of acrylamide, (B) 0.1-10 wt% of (meth) acrylic acid ester containing epoxy resin,
(C) A lithographic printing plate characterized by being an acrylic copolymer containing 0.1 to 5 wt% of itaconic acid.

Hereinafter, the present invention will be described in detail.

The lithographic printing plate of the present invention is provided with a photosensitive layer containing a zinc oxide, a phthalocyanine pigment and the like and a binder resin on a conductive support. Is described.

The conductive support used in the present invention is aluminum,
Aluminum, chromium, palladium, metal oxide, etc. vacuum-deposited on a metal plate or metal sheet such as brass, copper, stainless steel, plastic sheet, plastic sheet or paper, etc., and metal oxide An object plate or sheet can be used.

As the phthalocyanine pigment, ε-type copper phthalocyanine, α-type metallocyanine, β-type copper phthalocyanine, α-type metal-free phthalocyanine, chloroindium phthalocyanine, magnesium phthalocyanine and the like can be applied.

The zinc oxide is not particularly limited, but has an average particle size of 0.2.
It is possible to use a powdery material having a particle size of about 0.5 μm, which is generally used for electrophotography.

As the binder resin, a special acrylic resin described below is used. That is, it is a copolymer containing acrylamide, (meth) acrylic acid ester containing an epoxy group, and itaconic acid. Examples of the (meth) acrylic acid ester containing an epoxy group include glycidyl (meth) acrylate, (meth)
Epoxy stearyl acrylate, (meth) acrylic acid (3,4-epoxycyclohexyl) ethyl, (meth)
Examples thereof include glycidoxy acrylate. Itaconic acid is a dibasic acid among radically polymerizable organic acids,
Only itaconic acid was found to have particularly good characteristics at high temperature and high humidity. Further, because of mechanical strength, charge potential retention, flexibility, photosensitivity, residual potential, hydrophilicity, etc., as a partner of copolymerization, methyl methacrylate, ethyl methacrylate, -n-propyl methacrylate, methacrylic acid-t- Butyl, styrene, methyl acrylate, ethyl acrylate,
Copolymerize acrylic acid-n-propyl, acrylic acid-i-propyl, acrylic acid-n-butyl, acrylic acid-i-butyl, acrylic acid-t-butyl, acrylic acid pentyl, acrylic acid-2-ethylhexyl, etc. It is preferable.

Next, the copolymerization ratio of the acrylic copolymer having the above structure will be described.

Acrylamide has the effects of improving printability and accelerating heat curing, but if it is too large, the electrophotographic characteristics at high humidity deteriorate, and if it is too small, it becomes difficult to heat cure and mechanical strength deteriorates. , 0.5 ~ 10w due to poor printability
t% is suitable, preferably 2-8 wt%. Epoxy group-containing (meth) acrylic acid ester is the main agent for thermosetting, and if it is too small, it becomes difficult to thermoset and the mechanical strength deteriorates. If it is too large, unreacted substances remain and cause economic changes. 0.1-10 wt% is suitable, preferably 1-7 wt%. Further, if itaconic acid is too small, it becomes difficult to heat-cure, and if it is too large, electrophotographic properties deteriorate, so 0.1-10 w
t% is suitable, preferably 0.3-3 wt%. The amount of the copolymerization partner is not particularly limited, but the glass transition point of the copolymer is preferably about 0 ° C to 70 ° C.

This copolymer can be easily manufactured. That is, a plurality of the corresponding monomers are subjected to solution polymerization using an organic solvent such as an aromatic hydrocarbon, a ketone, an ester, or cellosolve in the presence of a reaction initiator such as azobisisobutyronitrile or benzoyl peroxide. I just need.

Next, a method for producing a lithographic printing plate of the present invention will be described. First, a composition for forming a photosensitive layer is prepared by kneading a phthalocyanine pigment, zinc oxide, a binder resin and a solvent. Next, a photosensitive layer is provided by applying this coating liquid onto a conductive support to obtain the lithographic printing plate of the present invention. As a method for kneading the coating liquid, a ball mill, a paint shaker, an ultrasonic homogenizer, a sand mill, or the like can be applied. For application, an applicator, a spray coater, a bar coater, a dip coater, a doctor blade or the like can be used. Drying is performed after coating, and it is preferable to heat with hot air at 100 ° C. or higher for 400 seconds or longer.

As for the composition ratio, the phthalocyanine pigment holds 2 to 20 wt% for maintaining electrophotographic sensitivity, and zinc oxide holds 40 to 85 wt% for satisfying printability such as water retention, mechanical strength and electrophotographic characteristics. Therefore, the binder resin is 5 to 50
wt% is preferred.

The plate making and printing method using the lithographic printing plate thus obtained will be described below. First, the entire surface is positively charged in a dark place, image exposure is performed to form a latent image, and then charged particles are adhered by development, and if necessary, dried and fixed to perform plate making. The lithographic printing plate of the present invention can perform image exposure by scanning with a semiconductor laser. The development is preferably a wet development method with good image quality. Next, offset printing is performed after first desensitizing with a desensitizing liquid. The desensitizing liquid can be used for both commercially available cyan type and non-cyan type.

[Operation] According to the present invention, as a binder resin, a (meth) acrylic acid ester having a reactive epoxy group, which is desired to be a monomer component having well-balanced electrophotographic properties, a radical-polymerizable itaconic acid and acrylamide are copolymerized. It is characterized by using a resin. That is, a copolymer having a well-balanced electrophotographic property is thermoplastic and plastically deforms when rolled and left for a long time after being stacked, which causes scumming. Due to the presence of
It does not deform with respect to heat and pressure thereafter. In addition, acrylamide has an effect of improving hydrophilicity, so that even if it contains a lipophilic phthalocyanine pigment, printability is sufficiently good. In addition, acrylamide seems to act as an accelerator for the thermosetting reaction, and due to the presence of acrylamide, it cures only when heated to a dry degree. Itaconic acid is one of radical-polymerizable organic acids and participates in the curing reaction by heating together with acrylamide and epoxy groups, but it is not only that, but it is evenly distributed in the copolymerization unit, so it has moisture resistance. , The receptive potential and the dark decay hardly decrease even in the presence of acrylamide which is slightly weak in high temperature and high humidity. As described above, the intended function is first obtained by the copolymerization of this combination. Furthermore, since it is not a blend of a plurality of resins but a copolymer of monomers having respective functions, there is no need to worry about compatibility, and a stable pigment dispersion system can be obtained. Further, the presence of the appropriate polar component improves the dispersibility of the pigment. Further, since the mechanical strength is improved by curing the binder resin itself, not by the unevenness of the surface, the image quality such as resolution is improved.

[Examples] Hereinafter, the present invention will be described in detail with reference to Examples.

Example 1 A monomer, a solvent and a reaction initiator were mixed in the following blending ratio, and the mixture was stirred and heated in a nitrogen atmosphere to synthesize a binder resin.

N-Butyl acrylate 46 g Methyl methacrylate 46 g Glycidyl methacrylate 1 g Acrylamide 5 g * Itaconic acid 2 g 2-Butanone 100 g Benzoyl peroxide 0.2 g The following compounds were used as itaconic acid.

Binder resin solution (50wt%), zinc oxide (SAZEX2000 manufactured by Sakai Kagaku), copper phthalocyanine (Heliogen manufactured by BASF)
Each of Blue L 6700F) and methyl ethyl ketone was placed in a mayonnaise bottle together with 18 g, 18 g, 3 g and 80 g of glass beads and dispersed for 2 hours with a paint shaker (Red Devil) to prepare a coating solution.

Next, a water-soluble acrylic resin was applied as a sealing material to the surface of the 110 g / m ² paper that had been subjected to conductive treatment, and the above coating solution was applied to a dry film thickness of 10 μm, and the mixture was placed in an oven at 140 ° C. It was dried for 5 minutes to obtain a lithographic printing original plate.

The electrophotographic characteristics of this lithographic printing plate were measured with an Electrostatic Paper Analyzer 8100 (manufactured by Kawaguchi Electric Co., Ltd.) in an atmosphere of 20 ° C. 65% RH (medium temperature / humidity) and 30 ° C. 80% RH (high temperature / high humidity). .

The measurement was performed with STATIC-1, and corona potential +5 vV exposure was performed at 780 nm monochromatic light at ² μW / cm ² .

 The results are shown in the table below.

As described above, in the system containing itaconic acid, deterioration of electrophotographic properties at high temperature and high humidity is small.

Also, with a blocking stirrer at a pressure of 5.0 kg / cm ² , pressure-bond so that the front surface and the back surface are in contact, 30 ° C, 50%
The change of the surface was observed when left standing for 24 hours in an RH environment, and it was easy to make indentations, but both samples were good.

Also, place a weight on a chrome-plated metal piece and apply 100g / c
The surface of the photosensitive layer was observed by observing the surface of the photosensitive layer after sliding the surface of the photosensitive layer at m ² and at a speed of 10 cm / Sec.

(Comparative Example 1) 50 g of methyl methacrylate, 50 g of n-butyl acrylate,
From 2-butanone 100 g and benzoyl peroxide 0.2 g,
A copolymer sample 3 was produced in the same manner as in Example 1.

Lithographic printing plates (A) and (B) were prepared in the same manner as in Example 1 using the copolymer samples 1 and 3 as binder resins, respectively.

(A) The easiness of indentation and the rubbing strength of (A) were examined.
In (a), in the indentation test,
Many crushes with a diameter of 50 to 300 μm were observed. Also in the rubbing test, there were many rubbing marks.

Also, after rubbing an iron whose temperature was adjusted to about 70 ° C on part of (a) and (a), the beam diameter was 40 μm × 80 μm,
The main scanning can be 180 m / sec and the sub-scanning can be 45 mm / sec and can be modulated at 3600 Hz. Using a laser plate making machine using a liquid development method, equipped with a 5 mW GaAsP semiconductor laser, (a) (a)
Made against. The corona charging potential was +6 kV, and a negative polarity developer was used.

Furthermore, a commercially available etchant (# 300 manufactured by Ryobi Printing Machine Co., Ltd.)
A printing test was conducted by automatic etching with a commercially available light offset printing machine (AD-80 manufactured by Ryobi Printing Co., Ltd.) equipped with (0).

As a result, in (a), good printed matter was obtained from the beginning, but in (a), the stain became worse at first, but 10
After printing 0 sheets, it was a little dirty.

Also, the marks of the iron were clearly stained in (a), but were not stained in (a).

[Effects of the Invention] As described above, according to the present invention, in a lithographic printing plate writable by a semiconductor laser, the mechanical strength of its surface is improved, and the lithographic printing plate can be manufactured, transported, stored or used. It becomes strong against rubbing, pressure and winding pressure.
In addition, the deterioration of the electrophotographic characteristics under high temperature and high humidity is significantly reduced. In addition, printability such as hydrophilicity or water retention is improved.

Front Page Continuation (72) Yoshiaki Matsuura, Inventor Yoshiaki Matsuura, 3-1 Somoe-cho, Shizuoka-shi, Shizuoka Inside the Tomagawa Paper Mill Co., Ltd. Company Tomagawa Paper Mill Processing Paper Mill (72) Inventor Masaaki Iwai 3-1 Somune-cho, Shizuoka City, Shizuoka Prefecture Tomagawa Nakazawa Examiner, Tomagawa Paper Mill Processing Paper Mill Co., Ltd.

Claims (2)

(57) [Claims] (1) at least zinc oxide on a conductive support;
In a lithographic printing plate having a photosensitive layer containing a phthalocyanine pigment and a binder resin, the binder resin is
(A) 0.1-10 wt% acrylamide, (B) 0.1-10 wt% (meth) acrylic acid ester containing epoxy resin
%, (C) an acrylic copolymer containing 0.1 to 5 wt% of itaconic acid. 2. The lithographic printing plate according to claim 1, wherein the (meth) acrylic acid ester containing an epoxy group is glycidyl methacrylate.