JPH0569415B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to photographic materials, and more specifically, after the surface of a plastic film is coated with a resin,
This invention relates to a photographic material in which very few pits occur on the resin surface. As supports for photographic materials, such as lithographic printing plates, metal plates such as aluminum and zinc, plastic films, paper materials, etc. are used.
These problems include problems with printing durability, other printing characteristics, such as ink stains during printing, the relationship between the adhesion between the lithographic printing layer and the support, and in some cases, manufacturing costs and ease of handling. An appropriate support is selected according to need. BACKGROUND ART In recent years, automatic plate making and automatic printing systems have become widespread in light office printing, and lithographic printing plates with excellent printing durability and compatible with various plate making methods are being used. Lithographic printing plates are usually plate-made by applying imagewise exposure from the front side of the lithographic printing plate (image-forming layer side with respect to the support) using a plate-making camera with a reversing mirror (hereinafter referred to as the front-burning method). ). In this case, the lithographic printing plate support does not need to be transparent, and various metal plates and paper materials can be used. However, plate making is performed by applying imagewise exposure from the back side of the lithographic printing plate (the side opposite to the image forming layer with respect to the support) using a plate making camera that does not have a reversing mirror (hereinafter referred to as the back baking method). In some cases, transparency is required as a lithographic printing plate support, so various metal plates and paper materials cannot be used.
A plastic film with good transparency is used. The present invention can of course be applied to lithographic printing plates produced by the usual front-burning method, and is particularly suitable for lithographic printing plates produced by the back-burning method. A so-called back-baking plate-making method in which imagewise exposure is performed from the back side of a lithographic printing plate using a plate-making camera without a built-in reversing mirror or the like is described, for example, in Japanese Patent Application Laid-open No. 89007/1989. Because of its excellent transparency, plastic film is used in various photographic materials, and is also suitable as a lithographic printing plate support using a back-burning method. Various plastic films, such as triacetate films,
Among polycarbonate films, polystyrene films, polypropylene films, polyvinyl chloride films, polyester films, etc., properties such as elongation and stiffness are strictly required when used as supports for lithographic printing plates. A conformal polyester film is preferred. Because photographic materials, especially lithographic printing plates, are used under high printing pressure, the image forming layer (hereinafter referred to as
The surface of the support (sometimes referred to as the emulsion layer) and the emulsion must be sufficiently adhered to each other. 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. Therefore, as a method of strengthening the adhesion between the polyester film and the emulsion layer, it is possible to provide another resin layer on the surface of the polyester film, for example, a resin layer of polyolefin, which is a thermoplastic resin. Generally, a melt extrusion coating method is used to provide such a resin layer. Further, the temperature of the molten resin during extrusion coating is usually 200 to 350°C. Of course, a resin layer may be provided only on the emulsion layer side of the lithographic printing plate, but in order to prevent curling, which can easily cause problems in automatic plate making and automatic printing processes, it is usually necessary to apply a resin layer to polyester film. Resin processing is applied to both sides of the polyester film. As a back-burning lithographic printing plate support, it is particularly preferable to provide a polyolefin mirror resin layer on both sides of a polyester film from the viewpoint of transparency. Severe blocking (stickiness on the front and back surfaces) occurs, making it completely impractical. Of course, if a back coat layer is provided in-line during melt extrusion coating, both sides may have a mirror finish. Therefore, in order to improve this point, it is possible to provide a polyolefin roughened resin layer on both sides of the polyester film, but in this case, the roughening may reduce transparency and blur (unclear images or printed lines). ), so it cannot be used in the back firing method.
Furthermore, for the same reason, even if the emulsion-coated side is a mirror layer and the back side is a rough layer, it cannot be used in the back baking method. Therefore, as a back-burning lithographic printing plate support, it is necessary to provide a mirror-finished resin layer on the side to which the emulsion is not coated, that is, the back side. In this case, as mentioned above, the melt coating method is generally used, and when ordinary low-density polyethylene resin is coated on the surface of the polyester film using this coating method, fine particles often appear on the surface of the melt-extrusion coated resin. A hole (referred to as a pit in the present invention) is generated. When these pits occur, the microscopic uniformity of the mirror-like resin layer on the back side is impaired, so in the case of the back-burning method, when exposing from the back side, the light does not pass through uniformly, resulting in blurring (image or drawing area). This means that only a lithographic printing plate with a blurred appearance will be obtained. As a result of intensive research aimed at improving this point, the present inventors have found that a resin composition containing 50 parts by weight or more of a polyolefin resin that has been kneaded at least once is applied to at least the side of the plastic film opposite to the side on which the image forming layer is provided. Photographic materials that are coated with a transparent resin layer by melt extrusion have fewer pits.
It has been found that a support particularly suitable for a back-burning lithographic printing plate can be obtained. Further, 50 to 95 parts by weight of polyolefin and 5 to 50 parts by weight of high-density polyethylene which have been kneaded at least once.
A photographic material in which a transparent resin layer is provided by melt-extrusion coating a resin composition containing parts by weight on at least the side opposite to the side on which the image forming layer is provided of a plastic film has extremely little occurrence of pits. Furthermore, it has been found that a resin composition containing 10 to 30 parts by weight of high-density polyethylene produces even fewer pits and is particularly suitable as a support for a back-burning lithographic printing plate. Moreover, if the surface resin layer is made to have a rough surface and the back surface resin layer is made to have a mirror surface, there is an advantage that runnability during the process is improved. Usually, various photographic materials have a mirror surface on the surface resin layer and a rough surface on the back surface resin layer, but in this case there is a problem in runnability. That is, in various photographic materials, it is common to provide a back coat layer on the back side for fine curl adjustment and addability, and in this case, it is often done to first provide the back coat layer and then provide the emulsion layer. However, when back-coating, the mirror layer is on the lower side, so the guide roll surface and the mirror layer come into contact, which often causes scratches, and because the mirror surface is a mirror surface, slips with the guide roll may occur. There were problems such as meandering. However, if the emulsion-coated surface is made of a rough resin layer, the above-mentioned problems will not occur and good running properties will be obtained. The polyolefin resin in the present invention includes:
A homopolymer such as low-density polyethylene, medium-density polyethylene, polypropylene, polybutene, polypentene, etc., or a copolymer consisting of two or more olefins such as ethylene/propylene copolymer, or a copolymer of ethylene and α-olefin. Linear low-density polyethylene and mixtures thereof, with various densities and melt viscosity indexes (melt index: hereinafter sometimes abbreviated as MI) can be used singly or in combination. Particularly preferred are low density polyethylene and medium density polyethylene. The high density polyethylene used in the present invention has a density of
So-called high-density polyethylene of 0.94 g/m ² or more may be used, and various MI can also be used, but MI 2 to 10 is preferable. Furthermore, high-density polyethylene of various densities and various types of MI may be used in appropriate combinations. Melt-extrusion coating of only the polyolefin resin that has been kneaded one or more times on at least the side opposite to the side on which the image forming layer is provided is effective in preventing the formation of pits. Several types of polyethylene resins, such as low-density polyethylene and medium-density polyethylene, may be combined in consideration of the adhesiveness between the plastic film and polyolefin, the surface hardness of the resin, and the like. In these cases, unless the resin contains 50 parts by weight or more of the resin that has been kneaded once or more, the pitting prevention effect cannot be obtained. Other thermoplastic resins, such as carboxy-modified polyethylene, ethylene-ethyl acrylate copolymer, and ethylene-vinyl acetate copolymer, may be mixed as appropriate in the resin composition, as long as the amount is 50 parts by weight or less. In the present invention, the polyolefin which has been kneaded a predetermined number of times may be produced by using a Banbury mixer, which is usually used as a kneader, or by using an extruder for kneading. Furthermore, these kneaders may be used in combination. The kneading temperature is preferably 140 to 230°C, preferably 200°C or lower in order to prevent resin deterioration, and a heat stabilizer may be added in advance. There are no particular restrictions on the heat stabilizer, but for example, 3,5-di-tert-
Butyl-4-hydroxytoluene, tetrakis[methylene(3,5-di-tert-butyl-4-hydroxy-hydrocinnamate]methane, 2,6
-di-tert-butyl-4-methyl-phenol,
Examples include 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanuric acid. The number of times of kneading is preferably as large as possible without causing thermal deterioration, but it is necessary to decide the number of times of kneading in consideration of the required quality and cost. In the present invention, the number of times polyolefin is kneaded refers to the number of kneading times that the manufacturer performs in an extruder for granulation (pelletization) after polymerization, and the number of times that the user performs kneading in an extruder for extrusion coating. shall not be included. Therefore, for example, in the present invention, if a user purchases polyolefin impellets that are usually commercially available, and after kneading them in a Banbury mixer (first kneading) and granulating them through an extruder (second kneading), the number of times of kneading is It is called double polyolefin. Of course, this also includes, for example, the case where the manufacturer performs the above-mentioned two kneading operations and then supplies the product to the user, or the case where the manufacturer and the user perform kneading separately. When the photographic material of the present invention is used, for example, in a lithographic printing plate, a high number of printing sheets is usually required, so the adhesiveness between the resin layer on the emulsion layer side and the plastic film, such as polyester, must be sufficient. It won't happen. When a thermoplastic resin such as polyolefin is used as the resin layer on the emulsion layer side, the adhesiveness between the resin layer and polyester is weak;
Although delamination (a phenomenon in which a resin layer peels off from a polyester surface) often occurs, delamination does not occur when carboxy-modified polyethylene, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate, etc. are used as the thermoplastic resin. In order to further increase the adhesive strength, the surface of the polyester on which the emulsion layer is to be provided can be subjected to a surface treatment, such as a slight corona discharge treatment (contact angle of 42 to 55 degrees, preferably 42 to 50 degrees). Of course, the side opposite to the side on which the emulsion layer is provided does not require as much adhesive strength as the left side, but the resin composition of the present invention [i.e., the resin composition containing 50 parts by weight or more of polyolefin that has been kneaded at least once, Furthermore, the polyolefin 50
When applying a resin composition containing ~95 parts by weight and 5 to 50 parts by weight of high-density polyethylene on one side of polyester, if strong adhesive strength is required, a mild corona discharge as described above is recommended. Processing may be performed. The contact angle in the present invention was determined by a droplet method using distilled water using a FACE contact angle meter (manufactured by Kyowa Kagaku Co., Ltd.). That is, after the surface of the polyester film is subjected to corona discharge treatment using a corona discharge device installed in-line of the melt extrusion coating machine, the surface of the polyester film is treated with FACE, which is installed in a constant temperature and humidity room (20℃-65%RH). Measured using a contact angle meter. In the present invention, carboxy-modified polyethylene means that the polyethylene molecular structure contains

[Formula] contains a group, and refers to, for example, polyethylene modified by grafting an unsaturated carboxylic acid to polyethylene. Examples of unsaturated carboxylic acids include α,β-unsaturated carboxylic acids such as maleic acid, acrylic acid, and methacrylic acid, and alicyclic polyhydric carboxylic acids having an unsaturated bond in the ring, and acid anhydrides of these acids. ,
Amides, esters, etc. are used. As the carboxy-modified polyethylene resin in the present invention, as mentioned above, various unsaturated carboxylic acid-modified polyethylenes and the like can be used, and those having various densities and melt viscosity indexes can be used alone or in combination. Furthermore, other resins may be mixed as appropriate within a range that does not significantly impair adhesiveness. The ethyl acrylate content in the ethylene-ethyl acrylate copolymer of the present invention is not particularly limited, but is usually 5 to 20%, preferably 7 to 18%.
are used. Further, materials having various densities and melt viscosity indexes can be used alone or in combination. Furthermore, other resins may be mixed as appropriate within a range that does not significantly impair adhesiveness. The vinyl acetate content in the ethylene-vinyl acetate copolymer of the present invention is usually 6 to 40% by weight, preferably 6 to 28% by weight. Further, materials having various densities and melt viscosity indexes can be used alone or in combination. Furthermore, other resins may be mixed as appropriate within a range that does not significantly impair adhesiveness. Further suitable are carboxy-modified polyethylene, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer, mixtures thereof, and mixtures of these with polyolefin, if necessary. As the plastic film in the present invention, as mentioned above, films of triacetate, polycarbonate, polystyrene, polypropylene, polyvinyl chloride, polyester, etc. can be used, but polyester films are particularly preferred in the present invention. 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, stiffness, 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. There are no particular regulations regarding the thickness of each resin layer on the front and back sides of polyester film, but
Usually 10-70μ, preferably 15-40μ. 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 the extent that there is no adverse effect on transparency etc. when used as a back-burning method after providing an emulsion layer on the roughened resin layer. 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. A back coat layer may be provided on the back resin layer for fine curl adjustment and addition of additional writing. The back coat layer has gelatin as its main component, and may contain a hardening agent and various other inorganic pigments such as silica and talc. In addition, antistatic agents, surfactants, etc. may also be contained (in the case of the back-burning method, to the extent that no reduction in transparency or blurring occurs). When the photographic material of the present invention is used, for example, as a lithographic printing plate (not only by the front-burning method, but especially by the back-burning method), the best mode is to apply a slight corona discharge treatment to the emulsion layer side of the plastic film, such as polyester. (contact angle of 42 to 55°), carboxy-modified polyethylene, ethylene-ethyl acrylate copolymer, and ethylene-vinyl acetate copolymer (polyolefin if necessary) alone or in combination with these resins using an extrusion coating machine. A lithographic printing plate in which an image forming layer is provided on a rough resin layer using polyester, and a mirror resin layer of the resin composition of the present invention is provided on the opposite side of the polyester layer is extremely susceptible to pitting. It is possible to obtain a product with a small amount of printing and an excellent number of printing sheets. The reason for using polyolefin in the resin layer on the image forming layer side is that when ethylene-ethyl acrylate copolymer or ethylene-vinyl acetate is used alone, it often has poor peelability from the cooling roll. It may be used in combination with polyolefin as appropriate in order to improve the above-mentioned problems and when a high number of printing sheets is not required. In some cases, polyolefin may be used alone. Furthermore, an embodiment in which the above embodiment is reversed, that is, the resin composition of the present invention (however, it is made opaque by kneading titanium dioxide or the like) is applied to one side of a plastic film, for example, polyester, by subjecting it to a mild corona discharge treatment.ゝAn image forming layer is further provided on the mirror resin layer, and on the other side, carboxy-modified polyethylene, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer, polyolefin, etc. are used alone or in combination. When a photographic material provided as a rough surface resin layer is used, for example, in a photographic print film, a photographic material with excellent sharpness can be obtained because of its high smoothness. The image forming layer provided in the thermoplastic resin layer of the photographic material in the present invention is usually an image receiving layer having a silver halide emulsion layer or a physical development nucleus layer formed by a silver complex diffusion transfer method, and can be used as various photographic materials. The photographic material of the present invention is particularly suitable as a photosensitive material for printing such as lithographic printing plates because of the extremely high adhesiveness between the polyester film and the thermoplastic resin. In addition, as a special application, it can also be used in photographic materials produced by the silver dye bleaching method, which require high adhesion. Furthermore, the polyester film and/or resin layer of the photographic material of the present invention made semi-transparent or opaque by, for example, titanium dioxide, can be used as a photographic print film or print film (material for advertising display at stations, etc.) (with built-in lighting), etc. Next, examples will be described in order to explain the present invention more specifically. The method for measuring the number of pits described in Examples is as follows. The resin surface of plastic film coated with polyolefin resin is manufactured by Olympus BH-2.
After magnifying it 500 times using a microscope and photographing it on a Polaroid plate, a diameter of 1 mm within the equivalent of 1 cm ² (actual diameter 2 μ) is obtained.
I counted more pits. When the number of pits exceeds 50, blurring occurs when using the back firing method. Example 1 Low density polyethylene (MI6, density 0.92) was kneaded repeatedly at 190°C using a kneading extruder as many times as shown in Table 1. While applying corona discharge treatment to one side of a 150μ thick polyester film, each resin listed in Table 1 was extruded from an extrusion coating machine at 335°C, using a mirror-finishing cooling roll to obtain a thickness of 30μ. Coated by melt extrusion. Next, the other side was similarly subjected to corona discharge treatment and melt-extrusion coated at a resin temperature of 335℃ using the same resin as sample 1 using a roughened cooling roll to a thickness of 30μ. I worked on it.
Table 1 shows the results of determining the number of pits for the four types of samples thus obtained by the method described in the specification. Next, emulsion for planographic printing plates was applied to the four types of rough resin layers while subjecting them to corona discharge treatment (about 6 g/m ² in solid content), and after drying, a plate-making camera without a built-in reversing mirror was installed. imagewise exposed from the back side of the lithographic printing plate (the side opposite to the emulsion layer with respect to the support),
After baking, a lithographic printing plate was obtained through a series of photographic processing steps. When these planographic printing plates were observed with a magnifying glass, samples 2 to 4 were in good condition with no blur, but on the other hand,
Sample 1 showed blur. Furthermore, when these lithographic printing plates were mounted on an offset printing machine and printed, it was found that when the lithographic printing plates of Samples 2 to 4 were used, the finished printed paper had a good finish without blurring, but on the other hand, When the lithographic printing plate of Sample 1 was used, the finished printed paper could only have a blurred finish.

[Table] Example 2 200 ppm of 3,5-di-tert-butyl-4 based on the resin was added to medium density polyethylene (MI3, density 0.93).
The mixture to which -hydroxytoluene was added was kneaded at 140°C in a Banbury mixer, and then further kneaded at 160°C using a kneading extruder. The above-mentioned resin kneaded twice and the resin kneaded 0 times, which was not subjected to any treatment after the Banbury mixer, were dry-mixed so as to have the compounding ratios shown in Table 2. While applying corona discharge treatment to one side of a 100μ thick polyester film, each resin listed in Table 2 was extruded from a melt extrusion coating machine at 350℃, using a mirror finishing cooling roll to obtain a thickness of 20μ. Coated by melt extrusion. Next, the other side was similarly subjected to corona discharge treatment and melt extrusion coated at a resin temperature of 350°C using the same resin as Sample 9 using a roughened cooling roll to a thickness of 20μ. I worked on it.
Table 2 shows the results of determining the number of pits for the five types of samples thus obtained by the method described in the specification. Next, for five types of samples, the mirror resin layer was subjected to corona discharge treatment, and a back coat layer consisting of gelatin and a small amount of hardening agent was provided (about 4 g/m ² in solid content), but the same as in Example 1. A lithographic printing plate was prepared and printed using the same procedure. As a result, samples 5 to 7 yielded lithographic printing plates and finished printed paper without blur, while samples 8 and 9 yielded only lithographic printing plates and finished printed paper with blur.

[Table] Example 3 Tetrakis [methylene 3,5
-di-tert-butyl-4-hydroxy-hydrocinnate] to which methane had been added was kneaded at 200°C using a kneading extruder. The resin kneaded once above and the various resins listed in Table 3 were dry mixed so as to have the blending ratios listed in Table 3. While applying corona discharge treatment to one side of a polyester film with a thickness of 188μ, each resin listed in Table 3 was extruded from a melt extruder at 320℃ and melted using a mirror-finished cooling roll to a thickness of 40μ. Extrusion coated. Next, the other side was similarly subjected to corona discharge treatment, using a roughened cooling roll, and using only the carboxy-modified polyethylene used in sample 14, the resin temperature was 320℃ to a thickness of 40μ. Coated by melt extrusion. Table 3 shows the results of determining the number of pits for the five types of samples thus obtained by the method described in the specification. Next, lithographic printing plates were prepared and printed using the same procedure as in Example 1 for the five samples. As a result, lithographic printing plates and finished printing papers without blur were obtained for all samples 10 to 14.

[Table] Example 4 Low density polyethylene (MI6, density 0.92g/cm ³ )
were kneaded at 190°C using a kneading extruder. The above-mentioned resin kneaded once and high-density polyethylene and the resin kneaded 0 times and high-density polyethylene were dry-mixed so as to have the blending ratios shown in Table 4. While applying corona discharge treatment to one side of a 100μ thick polyester film, each resin listed in Table 4 was extruded from a melt extruder at 320°C and melted using a mirror-finished cooling roll to a thickness of 30μ. Extrusion coated. Next, the other side was similarly subjected to corona discharge treatment and melt-extrusion coated at a resin temperature of 320℃ using the same resin as sample 1 using a roughened cooling roll to a thickness of 30μ. I worked on it.
Table 4 shows the results of determining the number of pits for the 10 types of samples thus obtained by the method described in the specification. Next, lithographic printing plates were obtained using the same procedure as in Example 1 for 10 types of samples. When these planographic printing plates were observed with a magnifying glass, Samples 4 to 10 were in good condition with no blur, while Samples 1 to 3 had blur. Furthermore, when these lithographic printing plates were mounted on an offset printing machine and printed, the finished printed paper when using the lithographic printing plates of Samples 4 to 10 had a good finish without blurring, but on the other hand, When the lithographic printing plates of Samples 1 to 3 were used, the finished printed paper could only have a blurred finish. It should be noted that Sample 4 had some curling after being subjected to a series of photographic processing steps after coating the emulsion, and it was found that there were some problems in workability.

[Table] Example 5 100 ppm of 1,3,5-tris (4-tert) was added to medium density polyethylene (MI3, density 0.93) based on the resin.
-Butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanuric acid was kneaded in a Banbury mixer at 140°C, and then further kneaded at 160°C using a kneading extruder. The twice-kneaded resin and high-density polyethylene (MI5, density 0.96) were dry-mixed at the blending ratio shown in Table 5. While applying corona discharge treatment to one side of a 150μ thick polyester film, each resin listed in Table 5 was extruded from a melt extruder at 335°C, using a mirror-finishing cooling roll to obtain a thickness of 15μ. Coated by melt extrusion. Next, the other side was treated with corona discharge in the same way, and a roughened cooling roll was used to coat the other side with carboxy-modified polyethylene (MI4, density
0.91) and adjust the resin temperature to a thickness of 15μ.
Melt extrusion coating was performed at 320°C. Table 5 shows the results of determining the number of pits for the six types of samples thus obtained by the method described in the specification. Next, while applying corona discharge treatment to the specular resin layer of six types of samples, a back coat layer consisting of gelatin, a small amount of hardening agent, and some silica was provided (about 5 g/m ² in solid content). A lithographic printing plate was prepared and printed using the same procedure as in 1.
As a result, good lithographic printing plates and finished printing papers without blur were obtained for Samples 11 to 16.

[Table] Example 6 Using the various resins shown in Table 6, one side of a 100μ thick polyester film was subjected to corona discharge treatment at 320°C so as to obtain the desired contact angle shown in Table 6. While extruding from the melt extruder die,
Extrusion coating was performed using a roughened cooling roll so that the resin thickness was as shown in Table 6. At that time, corona discharge treatment was also applied to the rough surface resin layer at a constant intensity. Next, the other side of the polyester film was also treated with the same resin as Sample No. 14 in Example 5 using a mirror-finished cooling roll while applying corona discharge treatment at a constant intensity so that the resin thickness was the same as that of the surface resin layer. The formulation was extrusion coated. Lithographic printing plates were obtained using the same procedure as in Example 1 for the 25 types of samples thus obtained. When this lithographic printing plate was observed with a magnifying glass, it was in good condition with no blurring, and when this lithographic printing plate was mounted on an offset printing machine and printing was performed, the printed paper had a good finish without blurring. . Furthermore, polyester films with contact angles of 40° and 60° had a printing durability of 5,000 to 8,000 sheets. On the other hand, those with a contact angle of 42 to 55° have a printing durability of more than 10,000 sheets, especially those with a contact angle of 42 to 55°.
The number of items was 20,000 to 50,000 or more.

【table】

[Table] Example 7 One side of a 150μ thick polyester film was lightly corona discharge treated (contact angle
50°) carboxy-modified polyethylene (MI4, density
0.91 g/cm ³ ) was extruded from an extrusion coating machine at a resin temperature of 325°C and melt-extrusion coated using a roughened cooling roll to a thickness of 15 μm. Next, the other surface was subjected to corona discharge treatment with a constant intensity, and the sample in Example 1 was prepared using a mirror-finished cooling roll.
Using the same resin as No. 2, melt extrusion coating was performed at a resin temperature of 325°C to a thickness of 15μ. Further, the rough surface resin layer and the mirror surface resin layer were respectively subjected to corona discharge treatment at a constant intensity, and the rough surface resin layer was provided with a lithographic printing emulsion layer, and the mirror surface resin layer was provided with a back coat layer, respectively, in the same manner as in Example 5. Using a plate-making camera with a built-in reversing mirror, the lithographic printing plate was imagewise exposed from the front side (emulsion layer side with respect to the support), and after baking, a lithographic printing plate was obtained through a series of photographic processing steps. When this lithographic printing plate was observed with a magnifying glass, it was in good condition with no blur.
Furthermore, when this lithographic printing plate was installed in an offset printing machine and printing was performed, the finished printed paper had a good finish without blurring, and a printing life of more than 50,000 sheets was obtained.

Claims (1)

[Scope of Claims] 1. In a photographic material in which both sides of a plastic film are coated with resin, a resin composition containing 50 parts by weight or more of a polyolefin that has been kneaded at least once is applied to at least the side opposite to the side on which the image forming layer is provided. A photographic material with a transparent resin layer coated on the surface by extrusion. 2. The photographic material according to claim 1, comprising 50 to 95 parts by weight of the polyolefin and 5 to 50 parts by weight of high density polyethylene. 3. The photographic material according to claim 1, wherein the plastic film is a polyester film. 4. The photographic material according to claim 1, comprising a plastic film having the polyolefin layer on one side and a thermoplastic resin layer on the other side. 5 The thermoplastic resin layer is made of carboxy-modified polyethylene, ethylene-ethyl acrylate copolymer,
The photographic material according to claim 4, comprising at least one of an ethylene-vinyl acetate copolymer and a polyolefin.