JPH0421177B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a support for photographic paper. More specifically, the present invention relates to a support for photographic paper that is useful for obtaining photographic paper that has electrical conductivity on its back surface and that does not lose its conductivity during development or the like. be. [Prior Art] Baryta paper has traditionally been used as a support for photographic paper, but in recent years, water-resistant supports have come to be used, in which a coating layer made of polyolefin resin is provided on both sides of a base made of paper. It's here. This water-resistant support shortens washing and drying times during development, eliminates the need for ferrotypes, reduces chemical consumption, maintains high levels of rigidity and strength, and reduces staining due to chemical penetration. It has the following advantages. The paper base of the support is made of high-purity, high-whiteness pulp that contains virtually no impurities, and is further treated with strong size treatment, rigidity enhancement treatment, and other treatments to prevent stains caused by chemical liquid penetration from the edges. And anti-static treatment has been applied. In addition, the polyolefin resin coating layer that forms the surface of the support to which the photographic emulsion is applied (hereinafter referred to as the support surface) has the following properties: Titanium oxide, colored pigments, fluorescent whitening agents, antioxidants,
Various additives such as antifoggants are kneaded. On the other hand, the polyolefin resin coating layer formed on the opposite side of the support to which the photographic emulsion is to be coated (hereinafter referred to as the back side of the support) is coated with polyolefin resin, which is used on the front side of the support, to prevent curling of photographic paper. Polyolefin resin is used, which has a slightly higher density than resin. Additionally, the back side of the support is given a suitable matte finish to give it a paper-like appearance. However, the resin of the coating layer and the surface of the resin coating layer were generally not subjected to any treatment. Recently, as the cutting speed of photographic paper in color photographic processing laboratories has increased, troubles due to the generation of static electricity have started to occur in photographic paper using the above-mentioned water-resistant support. These problems include static electricity that accumulates during handling and attracts dirt and dust, which causes various spots such as water repellency, desensitization, and fogging, and when the accumulated static electricity is discharged. This may also cause fogging, called static marks, on the emulsion. Furthermore, after chemical processing such as development and bleach-fixing, cutting is carried out.
Although they can be stacked, they may not be stacked neatly due to static electricity, or multiple sheets may stick together, making handling inconvenient. Various proposals have been made to solve the above problems. For example, Tokuko Sho 57-53940, US.PAT3033679,
As described in US Pat. No. 3,437,484, attempts have been made to apply a conductive agent to the back surface of the support to perform antistatic treatment. However, although these attempts are effective in preventing static electricity before processing, they are not effective in preventing static electricity after processing such as development because the conductivity is lost due to chemical processing such as development and bleach-fixing. This method was completely ineffective in solving problems in handling photographic paper after processing such as development. [Problems to be Solved by the Present Invention] The present invention solves the drawbacks of conventional photographic paper, namely the problem of electrostatic charging, and does not lose its conductivity through chemical processing such as development and bleach-fixing. The object is to provide a support useful for obtaining photographic paper. [Means for Solving the Problems] The photographic paper support of the present invention has a base made of paper and a coating layer formed on both sides of the base and made of polyolefin resin, On the surface of the coating layer on the back side of the support, a back coat layer containing hydroxyethylcellulose having an average number of added moles of ethylene oxide per glucose unit in the range of 2.0 to 2.8,
It is characterized by being formed with a dry weight of 0.01 to 5.0 g/m ² . As mentioned above, the support of the present invention includes a paper base,
It has a polyolefin resin coating layer formed on both sides thereof, and a hydroxyethylcellulose-containing back coat layer formed on the coating layer on the back side of the support (the side opposite to the side on which the photographic emulsion layer is formed). . The paper substrate used in the support sheet of the present invention can be selected from base papers generally used for photographic paper supports, such as natural pulp paper, synthetic pulp paper, mixed paper of natural pulp and synthetic pulp, etc. Various types of laminated paper can be mentioned. This base paper may contain additives such as sizing agents, fixing agents, paper strength enhancers, fillers, antistatic agents, dyes, etc. that are generally used in paper manufacturing, and may also contain surface sizing agents, surface strength agents, etc. The surface may be appropriately coated with an antistatic agent or the like. The paper substrate used usually has a weight of 100 to 300 g/m ² . The polyolefin resin used to coat both sides of the paper substrate can be a homopolymer of ethylene, α-olefins such as propylene, a copolymer of at least two of the aforementioned olefins, and
It can be selected from mixtures of at least two of these various polymers. Particularly preferred polyolefin resins are low density polyethylene, high density polyethylene, and mixtures thereof. Although there is no particular restriction on the molecular weight of the polyolefin resin, a molecular weight in the range of 20,000 to 200,000 is usually used. Each coating layer is generally applied to a paper substrate with a weight of 10 to 40 g/m ² . It is already known to add various additives such as white pigments, colored pigments, fluorescent whitening agents, and antioxidants to the polyolefin resin used for the coating layer.
That is, in the present invention, there is no problem in adding these additives to the polyolefin resin coating layer on the surface side of the support to which the photographic emulsion is coated. A back coat layer containing hydroxyethyl cellulose is formed on the surface of the polyolefin resin coating layer on the back side of the support. At this time, in order to improve the adhesion of the surface of the coating layer to the back coat layer, this surface may be subjected to corona discharge treatment, low temperature plasma treatment, or the like. The present inventors provided an electrically conductive back coat layer on the back side of a photographic paper support and investigated various means for preventing the problems caused by the generation of static electricity as described above. In particular, we investigated ways to maintain electrical conductivity even after processing photographic paper with chemicals such as developer and bleach-fix solution.
The average number of moles of ethylene oxide added (average number of moles substituted) per glucose unit as a conductive agent is
It has been found that using 2.0 to 2.8 hydroxyethyl cellulose achieves the above objective. Conventionally commonly used sodium chloride, potassium chloride, calcium chloride, magnesium chloride, sodium sulfate, other inorganic salts, quaternary ammonium salts, amide type cations, alkyl amine derivatives, tertiary amines, fatty acid amide derivatives, etc. A back coat layer that has been imparted with conductivity using a cationic conductive agent or an anionic conductive agent such as an alkali salt of polyacrylic acid or an alkali salt of polystyrene sulfonic acid can provide sufficient conductivity before developing the photographic paper. It will be done. However, due to the above-mentioned conductive components being eluted into the chemical solution during processing with developing solutions, bleach-fixing solutions, etc.
The electrical conductivity of the photographic paper cannot be maintained after these treatments. However, the average number of moles of ethylene oxide added (average number of moles substituted) per glucose unit is 2.2~
Photographic paper with a back coat layer containing 2.8% hydroxyethyl cellulose is not only conductive before development, but also does not lose its conductivity even when treated with chemicals such as developing solutions and bleach-fixing solutions, and also has excellent conductivity during development and bleach-fixing. It is possible to prevent problems caused by static electricity during stacking and handling after processing. Hydroxyethyl cellulose is one type of cellulose
Its properties change depending on the number of ethylene oxides added to the unit (glucose) (average number of substituted moles). Usually commercially available hydroxyethyl cellulose has an average number of added moles of ethylene oxide (average number of substituted moles) per glucose unit that is less than 2.0 and more than 1.6, and such hydroxyethyl cellulose is used as a conductive agent in the back coat layer. Then, the conductivity of the back coat layer is lost due to processing such as development, bleaching and fixing, and there is no effect in preventing the generation of static electricity. Furthermore, hydroxyethyl cellulose in which the average number of ethylene oxide additions (average number of substituted moles) is greater than 2.8 per glucose unit is difficult to produce industrially and is therefore not suitable for practical use. The molecular weight of the hydroxyethyl cellulose used in the present invention may be within the usual range of 30,000 to 200,000. The content of hydroxyethyl cellulose in the back coat layer of the present invention is preferably in the range of 1 to 100% by weight. That is, the back coat layer may be made of only hydroxyethyl cellulose (100% by weight), but it may also be made of 99% (by weight) of other binder resins, conductive agents, pigments, etc. in order to provide other functions. ) The effect can be achieved even when mixed at the following total content. For example, natural paper properties (paper-like), silica, clay, calcium carbonate, amorphous aluminium silicate, amorphous aluminium silicate,
Pigments such as amorphous calcium silicate may be mixed, and in order to improve the strength of the coating film,
Emulsions such as synthetic rubber latex, polyvinyl acetate, vinyl acetate-acrylic copolymer, vinyl acetate-ethylene copolymer, polyacrylate ester polyvinyl chloride, vinyl chloride-vinylidene chloride copolymer, water-soluble polyester, acrylic resin , polyvinyl alcohol, starch, casein, gelatin, and other binder resins. Further, in order to further improve the conductivity of the photographic paper before processing such as development, the previously described inorganic salts, cationic conductive agents, and anionic conductive agents may be mixed. The back coat layer has a dry weight of 0.01 to 5.0
g/m ² , preferably 0.1 to 2.0 g/m ² . If this dry weight is less than 0.01 g/ ^m2 , the conductivity of the back coat layer obtained will be insufficient for practical use, and if it is more than 5 g/ ^m2 , the feel and appearance of the back side of the support will differ from those of plain paper. This has the drawback that the manufacturing cost is also high. To form the back coat layer, a coating solution having a desired composition is prepared and applied to the back side of the support simultaneously with or after the formation of the polyolefin resin coating layer. There are no particular limitations on the coating method, and any of ordinary bar coating, gravure coating, air knife coating, blade coating, etc. may be employed. [Function] The back coat layer formed on the back side of the support sheet according to the present invention imparts excellent electrical conductivity to the back side of the support sheet that is not lost by chemical processing such as developing, bleaching, and fixing of photographic paper. do. [Examples] The present invention will be further explained by examples. Examples 1 to 4 and Comparative Examples 1 to 4 In each of Examples 1 to 4 and Comparative Examples 1 to 4, both sides of a 175 g/m ² base paper were each coated with a 30 g/m ² polyethylene film. The polyethylene coating layer on the back side of the support sheet was subjected to corona discharge treatment. Next, a coating liquid having the composition shown in Table 1 is applied to the surface of the coating layer modified by this corona discharge treatment using a bar coater so that the dry weight becomes the value shown in Table 1, and the drying temperature is 80°C. , drying time 60
Dried in seconds. Thereafter, the surface electrical resistance of the back surface of the support and the surface electrical resistance of the back surface after processing with a color developer, bleach-fix solution, etc. were measured in an environment of 20° C. and 65% RH. The results are shown in Table 1.

【table】

〔Effect of the invention〕

In the support for photographic paper of the present invention, the specific hydroxyethylcellulose-containing back coat layer formed on the back side of the support has a great effect on preventing electrostatic charging of the photographic paper, and this effect is due to the chemical solution used in developing, bleaching, fixing, etc. It is not lost during processing.

Claims (1)

[Scope of Claims] 1. A support for photographic paper comprising a base made of paper and a coating layer made of polyolefin resin formed on both sides of the base, comprising: the coating on the back side of the support; A back coat layer containing hydroxyethylcellulose having an average number of added moles of ethylene oxide per glucose unit in the range of 2.0 to 2.8 is formed on the layer surface.
A support for photographic paper, characterized in that it is formed with a dry weight of 5.0 g/m ² . 2 The hydroxytylulose has a molecular weight of 30,000 to
Support according to claim 1, having a molecular weight of 200,000. 3. The support according to claim 1, wherein the content of hydroxyethylcellulose in the back coat layer is in the range of 1 to 100% by weight. 4. The support according to claim 1, wherein the polyolefin resin is selected from homopolymers of ethylene and propylene, copolymers thereof, and mixtures of two or more of these polymers. 5. The support according to claim 1, wherein the back coat layer contains 99% by weight or less of an additive consisting of at least one selected from pigments and binder resins. 6. The support according to claim 1, wherein the surface of the coating layer having the back coat layer is modified by corona discharge treatment.