JPH0336675B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a lithographic printing plate, and more particularly to a lithographic printing plate having a polyester film coated on both sides with a resin and having excellent printing durability and transparency. Supports for lithographic printing plates include aluminum,
Metal plates such as zinc, paper materials, plastic films, etc. are used. When making a lithographic printing plate,
There are various plate-making methods, but in order to obtain a normal finished printing paper (for example, no left-right reverse images), in silver plate, etc., which utilizes the diffusion transfer method, devices such as reversing mirrors are used during plate-making. In this case, the lithographic printing plate support is not particularly required to be transparent, so metal plates, paper materials, etc. can be used. However, in the above-mentioned plate-making method without special innovations, if imagewise exposure is performed from the emulsion-coated side of the lithographic printing plate, the image will be reversed, so exposure must be performed from the back side, which is not coated with the emulsion layer. . Therefore, in this case, if the support itself is opaque,
Since the emulsion layer is not exposed to light, it is not exposed and cannot be used for plate making. The so-called back-baking plate-making method, which uses a plate-making camera without a built-in reversing mirror or the like and performs imagewise exposure from the back side of the lithographic printing plate (i.e., the side opposite to the silver halide emulsion layer with respect to the transparent support), is known, for example, as described in Japanese Patent Application Laid-Open No. 48−
It is described in Publication No. 89007. The present invention thus provides a lithographic printing plate that is particularly suitable for exposing from the back side of the lithographic printing plate to which the emulsion layer is not coated (hereinafter sometimes referred to as "back-baking plate making" or "back-baking plate"). It is something. Plastic films are suitable for back printing because of their excellent transparency; for example, triacetate films, polycarbonate films, polystyrene films, polypropylene films, polyvinyl chloride films, polyester films, etc. can be used. Among these, when used as a support for lithographic printing plates, properties such as elongation and rigidity are strictly required, so plastic films that meet these properties include:
Examples include polyester film. However, since polyester film itself has poor surface activity, it is not only difficult to apply emulsion directly to its surface, but even if emulsion is applied after surface activation treatment such as corona discharge treatment. Due to the difference in heat shrinkability between the polyester film and the emulsion layer, serious problems such as peeling of the emulsion layer occur during a series of photographic processing steps. Furthermore, in order to overcome these obstacles, attempts have been made to provide a so-called subbing layer between the polyester film and the emulsion layer, but it has not been possible to obtain sufficient adhesive strength between the polyester film and the emulsion layer. A strong undercoat layer, such as an undercoat layer treated with an organic titanate, cannot be used for back printing because the transparency of the support itself is significantly reduced. Therefore, in order to firmly adhere the polyester film and the emulsion layer without impairing the transparency, it is possible to achieve this by providing another resin layer, such as a resin layer such as polyolefin, on the surface of the polyester film. Since lithographic printing plates are extremely prone to curling, which tends to cause trouble in automatic plate making and automatic printing processes, when polyester film is resin-treated, both sides of the polyester film are usually treated with resin. As a lithographic printing plate support for back printing, it is particularly preferable to provide a mirror resin layer such as polyolefin on both sides of a polyester film from the viewpoint of transparency. After that, severe blocking (stickiness on the front and back surfaces) occurs, making it completely impractical. Therefore, in order to improve this point, it may be possible to provide a rough resin layer such as polyolefin on both sides of the polyester film, but in this case, the roughening causes a significant decrease in transparency, making it difficult to use it for back printing. I can't do that.
For the same reason, even if the emulsion coated surface is a mirror layer and the back surface is a rough layer, it cannot be used for back printing. Even if polyethylene resin layers such as ordinary polyolefin resin such as low density polyethylene, medium density polyethylene, and high density polyethylene are provided on both sides of a polyester film, it is true that an emulsion layer is provided on the rough surface resin layer as in the embodiment of the present invention. However, when ordinary polyolefin resin is used, the lithographic printing plate is sometimes attached to an offset printing machine for printing. In some cases, peeling of the film on the printing plate (separation between the polyester film and polyolefin resin layer) may occur before the desired number of prints is obtained, and the industry is demanding the use of a resin that has sufficient adhesion to the polyester film layer. That is the reality. In order to solve this problem, the inventors of the present invention have made extensive studies and have arrived at the present invention. That is, a double-sided resin-coated polyester in which a rough resin layer of carboxy-modified polyethylene (which may be used in combination with polyethylene resin) is provided on one side of a polyester film, and a mirror-surface resin layer of carboxy-modified polyethylene and/or polyethylene is provided on the other side. The present invention provides a lithographic printing plate in which an emulsion layer is provided on a rough resin layer in the film. According to the present invention, since the emulsion layer is provided on the rough surface resin layer, there is no deterioration in transparency to the extent that it causes actual damage, and a plate of good quality can be obtained, especially as a back-printing lithographic printing plate. Moreover, since the adhesion between the polyester film surface layer and the carboxy-modified polyethylene resin layer is extremely strong, a lithographic printing plate with an excellent number of printing sheets can be obtained.

[Formula] refers to polyethylenes containing groups, such as polyethylenes modified by grafting unsaturated carboxylic acids onto polyethylenes. Examples of unsaturated carboxylic acids include a-, β-, such as maleic acid, acrylic acid, and methacrylic acid.
These include unsaturated carboxylic acids or alicyclic polycarboxylic acids having an unsaturated bond in the ring, and anhydrides, amides, esters, etc. of these acids are used. In the present invention, it is preferable to provide the specular resin layer of the polyester film with a back coat layer containing gelatin as a main component for fine curl adjustment. In this case, various inorganic pigments such as silica, talc, etc. may be added to the extent that the transparency for back-burning plate making is not impaired. The polyester film in the present invention may be unstretched, uniaxially stretched, biaxially stretched, etc., but biaxially stretched polyester film is preferred from the viewpoint of ductility, rigidity, thermal stability, etc. The thickness of the film used is approximately 75 to 350 .mu.m, but from the viewpoint of performance and cost, a film thickness of approximately 100 to 188 .mu.m is preferable. As the carboxy-modified polyethylene resin in the present invention, as mentioned above, various unsaturated carboxylic acid-modified polyethylenes are used, and various densities,
Melt viscosity index (hereinafter referred to as MI)
(sometimes abbreviated as ) can be used alone or in combination, but low-density carboxy-modified polyethylene is particularly preferred. Further, other resins, such as low density polyethylene, medium density polyethylene, and high density polyethylene, may be mixed as appropriate within a range that does not impair adhesiveness. The thickness of each polyolefin resin layer on the front and back surfaces of the polyester film is not particularly limited, but is usually 10 to 70μ, preferably 20 to 40μ. The method of providing a rough resin layer in the present invention is to roughen the surface of a cooling roll normally used for melt extrusion coating, and the degree of roughness is such that it overlaps with the mirror resin layer on the back side. From those with a lightly roughened surface to the extent that no blocking occurs when combined, to those with an emulsion layer on the roughened resin layer, and to the extent that transparency is not adversely affected when used for back printing plate making. Any material with a highly roughened surface can be used. Further, as the method for providing the mirror-finished resin layer on the back surface, a mirror-finished surface of a cooling roll used for melt extrusion coating is usually used, as described above. The back coat layer in the present invention has gelatin as its main component, and can contain a hardening agent and other various inorganic pigments to the extent that the transparency for back-baking plate making is not impaired. In addition, antistatic agents, surfactants, latex, etc. may be contained. Next, examples will be described in order to explain the present invention more specifically. Example 1 While corona discharge treatment was applied to one side of a 100μ thick polyester film, carboxy-modified polyethylene (density 0.96, MI5) was extruded from a melt extruder die at 335°C, and a 30μ thick polyester film was extruded using a roughened cooling roll. It was melt-extruded and coated to a thickness of . At that time, corona discharge treatment was performed on the rough resin surface. Subsequently, the other side was similarly subjected to corona discharge treatment and melt extrusion coated using a mirror-finished cooling roll to a thickness of 30μ. The lithographic printing plate support thus obtained is designated as Sample A. or,
Separately, for comparison of suitability for back-burning, a sample was also prepared in which a mirror resin surface was subjected to corona discharge treatment (referred to as sample B). A lithographic printing emulsion was applied to the rough resin layer of sample A obtained in this way (about 6 g/m ² in solid content),
After drying, it was exposed to light from the side opposite to the emulsion side, baked, and then subjected to a series of photographic processing steps to obtain a lithographic printing plate. When this lithographic printing plate surface was observed with a magnifying glass, it was found to be in good condition with no blurring (unsharp image or print area), but when this lithographic printing plate was installed in an offset printing machine and printed, it was found that the finished print The paper had a good finish with no blurring, and it was possible to print more than 10,000 sheets. On the other hand, sample B (mirror emulsion coating, back surface rough resin layer)
A lithographic printing plate was also obtained through the same processing steps as Sample A. When this lithographic printing plate surface was observed in the same manner as Sample A, blurring was observed, and when the lithographic printing plate was mounted on an offset printing machine and printing was performed, only a blurred finish was obtained on the printed paper. Separately, low-density polyethylene (density 0.92, MI5) was applied to both sides of the polyester film at 335°C.
Sample C was obtained in exactly the same manner as Sample A except for melt extrusion coating. A lithographic printing plate was prepared from this sample C in the same manner as in the case of sample A, and when the surface of this lithographic printing plate was observed with a magnifying glass, it was found to be good with no blurring. Furthermore, when this lithographic printing plate was attached to an offset printing machine and printed, the printed paper had a good finish with no blurring, but after printing more than 5,000 sheets, the film on the plate surface peeled (polyester film and polyethylene resin delamination) occurred. Example 2 While corona discharge treatment was applied to one side of a 188μ thick polyester film, carboxy-modified polyethylene (density 0.91, MI4) was extruded from a melt extruder die at 335°C, and a 30μ thick polyester film was extruded using a roughened cooling roll. It was melt-extruded and coated to a thickness of . At that time, corona discharge treatment was applied to the rough resin surface. Next, low-density polyethylene (density 0.92,
While extruding MI5) from a melt extruder die at 335°C, it was melt-extruded and coated using a mirror-finished cooling roll to a thickness of 30μ. A lithographic printing emulsion was coated on the rough surface resin layer of the lithographic printing plate support thus obtained in the same manner as in Example 1, and a lithographic printing plate was obtained in the same manner as in Example 1. This lithographic printing plate has no blurring, and when this lithographic printing plate is mounted on an offset printing machine and printed, the printed paper has a good finish with no blurring, and it is possible to print more than 20,000 sheets. It was hot. Example 3 A resin composition consisting of 50 parts by weight of carboxy-modified polyethylene (density 0.91, MI4) and 50 parts by weight of low-density polyethylene (density 0.92, MI5) was prepared by corona discharge treatment on one side of a 100μ thick polyester film. While extruding through a melt extruder die at 350°C, melt extrusion coating was applied using a roughened cooling roll to a thickness of 40μ. Next, apply medium density polyethylene (density 0.93, MI7) to the other side.
While extruding through a melt extruder die at 350°C, melt extrusion coating was performed using a mirror cooling roll to a thickness of 40μ. At that time, corona discharge treatment was performed on the mirror resin surface. A back coat layer consisting of gelatin and a small amount of hardening agent is provided on the specular resin layer of the lithographic printing plate support obtained in this way (about 4
g/m ² ) A lithographic printing plate was prepared and printed in the same manner as in Example 1 except for the following. As a result, as in Example 1, a lithographic printing plate and finished printing paper without blur were obtained, and printing of 15,000 sheets or more was possible. Example 4 A resin consisting of 75 parts by weight of carboxy-modified polyethylene (density 0.97, MI 0.7) and 25 parts by weight of high-density polyethylene (density 0.97, MI 7) was subjected to corona discharge treatment on one side of a 175μ thick polyester film. While extruding the composition through a melt extruder die at 350°C, it was melt-extruded and coated using a roughened cooling roll to a thickness of 30μ. Next, the other side was subjected to the same corona discharge treatment while extruding from a melt extruder die at 350°C using exactly the same resin as the above resin (however, the blending weight ratio was 50:50).
Melt extrusion coating was performed using a mirror cooling roll to a thickness of 20μ. At that time, corona discharge treatment was performed on the mirror resin surface. A back coat layer consisting of gelatin, a small amount of hardening agent, and some silica was provided on the specular resin layer of the lithographic printing plate support obtained in this way (about 5 g/m ² in solid content). Example 1
A lithographic printing plate was prepared using the same procedure as above. As a result, as in Example 1, a lithographic printing plate and finished printing paper without blur were obtained, and printing of 10,000 sheets or more was possible.

Claims (1)

[Claims] 1. A rough resin layer of carboxy-modified polyethylene (which may be used in combination with polyethylene resin) is provided on one side of a polyester film, and a mirror-finished resin layer of carboxy-modified polyethylene and/or polyethylene is provided on the other surface. A lithographic printing plate in which an emulsion layer is provided on the rough resin layer in a double-sided resin-coated polyester film. 2. The lithographic printing plate according to claim 1, wherein the specular resin layer is provided with a back coat layer containing gelatin as a main component. 3. The lithographic printing plate according to claim 1 or 2, wherein the double-sided resin layer is a double-sided resin-coated polyester film formed by melt extrusion coating.