JPH0358504B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an offset printing original plate, and more particularly to a direct-printing type offset printing original plate in which a specific adhesive is applied to the image-receiving layer.

Currently, offset printing original plates used in office printing have (1) a printing layer (image-receiving layer) on the base paper;
(2) an electrophotographic type with a photoconductive layer (image-receiving layer) provided on the base paper; (3) a silver salt photographic type with a silver halide emulsion layer provided on the base paper. It can be cited as a representative example. Above all,
For the original plate (1), to form the image on the printing plate, write it by hand with lipophilic ink on the printing layer, print it by type, or print it with a wire dot type or thermal transfer printer. , or can be easily done using the xerography method, etc.
It has advantages compared to the other original plates mentioned in (2) and (3) above.

By the way, the image-receiving layer of this direct-printing type offset printing original plate, like that of other types of offset printing original plates, is made hydrophilic enough to repel ink during printing by the offset printing original after being desensitized. At the same time, it must be water resistant enough to withstand the repeated application of dampening water during printing.

In order to satisfy both hydrophilicity and water resistance, conventional direct printing offset printing plates have the following properties:
It is known that an image-receiving layer is provided on a support by adding a melamine formaldehyde resin as a crosslinking agent to a water-soluble resin such as polyvinyl alcohol, and further adding an inorganic pigment (U.S. Pat. No. 2,532,865). There is. However, in such original plates, either the hydrophilicity or the water resistance of this layer may be insufficient due to the mixing ratio of the water-soluble resin and the crosslinking agent, or due to slight fluctuations in the drying conditions after forming the image-receiving layer. The selection range of conditions for simultaneously achieving both printing and water resistance was narrow, and the quality of the products (direct printing type offset printing original plates) tended to vary widely.

An object of the present invention is to provide a direct printing type offset printing original plate in which the hydrophilicity and water resistance of the image-receiving layer are stably obtained and the quality of the printing material is less variable.
Another object of the present invention is to provide a direct printing type offset printing original plate which prevents scumming during printing and improves printing durability, and which allows a large number of clear prints to be obtained at all times.

That is, the direct printing type offset printing original plate of the present invention is characterized in that an image-receiving layer containing an inorganic pigment and acetoacetylated polyvinyl alcohol as a binder as a main component is provided on a support.

Note that the above-mentioned and later-described "direct-printing type offset printing original plate" refers to an image that is directly formed on the surface image-receiving layer of the original plate using oil-based ink, a typewriter, a printer, etc., or a dry toner is formed on the image-receiving layer. Alternatively, an image is formed by transferring a toner image using a plain paper copying machine using wet toner, and then the non-image area is desensitized with an etchant (desensitizing liquid) to create a printing plate. , refers to the original plate used to obtain printed matter by applying it to an offset printing machine.

As described above, the original plate of the present invention has an image-receiving layer provided on a support.

Examples of the support used here include paper substrates, paper substrates wet-strengthened using melamine-formalin resins, urea-formalin resins, polyamide epichlorohydrin resins, etc., resin-coated papers, plastic films, and the like.

In the original plate of the present invention, the appropriate ratio of the pigment and binder constituting the image-receiving layer is 2 to 8 parts by weight of the pigment to 1 part by weight of the binder. As pigments here, clay, calcium carbonate, zinc oxide, silica, aluminum oxide, barium sulfate, lithopone, titanium oxide, and all other inorganic pigments used in conventional direct-drawing offset printing plates can be used. These pigments may be used alone or in combination of two or more.

Furthermore, the binder in the image-receiving layer is mainly acetoacetylated polyvinyl alcohol;
For the purpose of further improving printing durability, aldehydes,
Amines, melamine resin, hydrazides, persulfates, Ni ²⁺ , Cu ²⁺ , Al ³⁺ , Fe ³⁺ , Sb ³⁺ , NH4 ⁺ ,
One or more salts containing cations such as Mg ²⁺ , Ca ²⁺ , and Zn ²⁺ may be added in an amount of 50% by weight or less based on the total amount of the binder.

The acetoacetylated polyvinyl alcohol used in the present invention can be obtained by adding liquid diketene to polyvinyl alcohol powder and reacting it.
(manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd.), etc., and can be easily obtained.

In order to actually produce a direct-printing type offset printing plate according to the present invention, an aqueous solution containing acetoacetylated polyvinyl alcohol, an inorganic pigment, and, if necessary, the above additives is applied onto a support and dried at 100 to 150°C. Then, an image-receiving layer having a thickness of about 5 to 20 μm may be formed.

In this case, a water-resistant intermediate layer may be provided between the support and the image-receiving layer to further improve printing durability, and a back coat layer may be provided on the back side of the support to prevent curling. It may also be provided.

The intermediate layer (1 to 20 μm thick) may be an emulsion type resin such as acrylic resin, SBR, MBR, NBR, or vinyl acetate-ethylene copolymer, or a solvent-soluble resin such as epoxy resin, polyvinyl butyral, polyvinyl acetate, or polyvinyl chloride. Resins and the like may be used alone or in combination of two or more. Also, a suitable amount of pigment may be added to this intermediate layer.

The back coat layer (5 to 20 μm thick) may be starch or starch derivatives, cellulose derivatives such as CMC or HEC, polyvinyl alcohol, casein, vinyl acetate-crotonic acid copolymer, water-soluble resin such as ammonium polyacrylate, or acrylic resin. , SBR, MBR, emulsion type resins such as vinyl acetate-ethylene copolymer, etc. may be used alone or in combination of two or more. Also, a suitable amount of pigment may be added to this backcoat layer.

As mentioned above, since the offset printing original plate according to the present invention uses acetoacetylated polyvinyl alcohol as a binder in the image-receiving layer,
When this image-receiving layer is formed, the acetoacetylated polyvinyl alcohol is made water resistant by heat or a crosslinking agent, and furthermore, due to the excellent surface strength and hydrophilicity of polyvinyl alcohol, printing plates made using it are A large number of clean, clear prints can be obtained.

Next, examples will be shown. Note that all parts are parts by weight.

Example 1 An image-receiving layer coating solution having the following composition was coated on the surface of a support (90 g/m ² wet reinforced paper) and heated at 130°C.
The layer was dried for 3 minutes to form an image-receiving layer of about 20 g/m ² .

[Image-receiving layer coating liquid]

10% aqueous solution of acetoacetylated polyvinyl alcohol (trade name Gocephaimer Z-200, manufactured by Nippon Gosei Kagaku Co., Ltd.) 100 parts 80% aqueous solution of melamine formalin resin (trade name Sumirezu Resin-613, manufactured by Sumitomo Chemical Co., Ltd.) 1.5 parts 1.2 parts of a 10% aqueous solution of ammonium chloride 100 parts of a 50% aqueous dispersion of clay Next, a back coat layer coating solution having the following composition was applied to the back side of this support, and dried at 130°C for 3 minutes to form a coating solution of approximately 10 g/m ² A back coat layer was provided and this was supercalendered to produce a direct-printing type offset printing original plate.

[Back coat layer coating liquid]

SBR latex (solid content 50%) 10 parts 10% aqueous solution of polyvinyl alcohol (product name
DVA-117, manufactured by Kuraray Co., Ltd.) 50 parts 50% clay dispersion 100 parts 80% melamine formalin resin aqueous solution 2 parts 10% ammonium chloride aqueous solution 1.6 parts This original plate was imaged using a thermal transfer printer. Etch liquid (diaphragm etch liquid)
When a printing plate was obtained by desensitizing it with oil and printing on an offset printing machine (Toko Model 810), more than 1000 clear prints with no background smudges were obtained.

Comparative Example 1 Offset printing was performed in the same manner as in Example 1, except that the acetoacetylated polyvinyl alcohol in the image-receiving layer coating solution in Example 1 was replaced with the same amount of polyvinyl alcohol (trade name PVA-117, manufactured by Kuraray Co., Ltd.). When I obtained the master plate and printed it, the image-receiving layer peeled off from about the 10th sheet onwards, and background stains were observed.

Comparative Example 2 Offset was produced in the same manner as in Example 1, except that the acetoacetylated polyvinyl alcohol in the image-receiving layer coating solution in Example 1 was replaced with the same amount of modified polyvinyl alcohol (trade name KL-118, manufactured by Kuraray Co., Ltd.). When I obtained the original printing plate and printed it, the image-receiving layer peeled off from about the 100th page, and background stains were observed.

Example 2 An intermediate layer coating solution having the following composition was coated on the surface of a support (100 g/m ² wet reinforced paper) and dried at 130° C. for 3 hours to form an approximately 15 g/m ² intermediate layer.

[Intermediate layer coating liquid]

Carboxyl-modified SBR latex (50% solids)
60 parts 10% aqueous solution of oxidized starch 50 parts 50% aqueous dispersion of clay 100 parts 80% aqueous solution of melamine-formalin resin 6 parts 10% aqueous solution of ammonium chloride 4.8 parts Further, apply an image-receiving layer coating solution with the following composition on top of this. It was then dried at 130° C. for 3 minutes to form an image-receiving layer of about 15 g/m ² .

[Image-receiving layer coating liquid]

10% aqueous solution of acetoacetylated polyvinyl alcohol (trade name: Gocephaimer Z-200, manufactured by Nippon Gosei Kagaku Co., Ltd.) 100 parts 40% glyoxal solution 10 parts 10% aqueous solution of ammonium chloride 20 parts 50% aqueous dispersion of clay 100 Next, the same back coat layer as in Example 1 was provided on the back side of this support to prepare a direct-printing type offset printing original plate.

When this master plate was made into plates in the same manner as in Example 1 and printed, more than 2000 clear prints were obtained.

Claims (1)

[Claims] 1. An offset printing original plate comprising an image-receiving layer containing an inorganic pigment and acetoacetylated polyvinyl alcohol as main components on a support.