JPS6219732B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to photographic resin-coated papers, and in particular to methods for making resin-coated papers using polyolefin resins. The purpose of this is to eliminate step-like unevenness that occurs in the lateral direction on the surface of the coated paper when the polyolefin resin film is peeled off from the cooling roll in the process of melt-extrusion coating the paper substrate with polyolefin resin.
In other words, the purpose is to prevent "uneven peeling steps". In recent years, as the development process for photographic paper has become more rapid, polyolefin resin-coated paper has come to be used as a support for photographic paper in place of baryta paper. In this case, smooth polyolefin resin-coated paper is usually used as the support for smooth-surface type photographic paper, and smooth polyolefin resin-coated paper is
It was manufactured by using a cooling roll with a smooth surface in the melt extrusion coating process. However, with this method, when the extrusion coating speed increases, the polyolefin resin film extruded from the die is peeled off from the cooling roll without being sufficiently cooled, resulting in "uneven peeling", which results in a product that is not satisfactory in terms of quality. The disadvantage was that it was not possible to obtain A commonly known method for preventing "uneven peeling" is to add a surfactant to the polyolefin resin, but this method reduces the adhesive strength between the polyolefin resin and the paper, and requires melt extrusion. However, this method has the disadvantage of increasing smoke generation, and cannot be said to be the optimal method. After extensive research, we discovered that in the process of melt-extrusion coating polyolefin resin onto a paper substrate, we used a cooling roll with a finely textured surface to mold the surface of the polyolefin resin with minute textures, thereby making it possible to apply the photographic emulsion. We have discovered that "uneven peeling" can be prevented without reducing the surface gloss of photographic paper. The reasons why "uneven peeling" can be prevented by using a cooling roll with fine irregularities on its surface are as follows: (1) The surface irregularities increase the surface area of the cooling roll, which increases the cooling power of the cooling roll. (2) The presence of air between the polyolefin resin and the cooling roll reduces the adhesion area, making it easier to separate the polyolefin from the cooling roll. This is thought to be due to the following reasons. The polyolefin resin used in the present invention includes homopolymers such as polyethylene, polypropylene, and polyisobutylene, ethylene-vinyl acetate copolymers,
Copolymers such as ethylene-propylene copolymers, polyolefin derivatives such as ionomers, or mixtures thereof can be used. Its thickness is about 5 to 200 μm, preferably about 20 to 50 μm. In addition, white pigments, fluorescent brighteners, dispersants, antioxidants, antistatic agents, etc. may be added to these resins as desired. The paper used in the present invention can be made of natural pulp, synthetic pulp, or a mixture thereof. Its thickness is about 20 to 400μ,
In particular, about 70 to 250μ is preferable. Its basis weight is about 15 to 350 g/m ² , preferably about 50 to 200 g/m ² . Moreover, paper strength enhancers, sizing agents, colorants, fluorescent whitening agents, etc. may be added to these papers as desired. The cooling roll according to the present invention has fine irregularities on its surface. More specifically, the shape of the fine unevenness may be regular or irregular, and the average depth of the unevenness is about 0.05 to 0.7μ, particularly about 0.1 to 0.5μ. A value of approximately μ is suitable. If the average depth of the unevenness is smaller than 0.05μ, it is impossible to prevent "uneven peeling steps", and if it is larger than 0.7μ, the gloss of the surface of the photographic paper coated with the photographic emulsion is reduced. The average pitch of the unevenness is about 0.1 to 100 μm, and particularly preferably about 1 to 20 μm. The depth and pitch of minute irregularities on the surface of the cooling roll were directly measured using a SURFCOM surface roughness meter manufactured by Tokyo Seimitsu Co., Ltd. The depth was measured between A and B shown in Figure 1, and the average depth was determined by simply averaging the sum of the depths at 10 consecutive locations. Shown in Figure 1
Measured as a pitch between CDs, any consecutive 10
The average pitch was calculated by simply averaging the sum of the pitches at each location. In order to form fine irregularities on the surface of the cooling roll, any method such as surface polishing of the roll, vapor deposition method, sandblasting method, etching method, electroporation method, plating method, etc. may be used, but among these, sandblasting method is the most popular. suitable. There are various materials for the cooling roll, such as stainless steel, nickel or chrome plating made of metal such as iron, enameling, and Teflon coating.
Each material and molding method can be selected arbitrarily, and chrome plating is suitable for sandblasting. The effectiveness of the present invention will be explained in more detail by way of examples. Example A base paper of LBKP 100%, basis weight 175 g/m ² and thickness 180 μm was melt-extruded and coated with polyethylene having a density of 0.920 g/cc to a thickness of 30 μm. Using the cooling roll shown in Table 1, in each case, the speed at which "uneven peeling stage" occurs at a coating speed higher than that, that is, the upper limit coating speed was measured. After the surface of the polyethylene resin-coated paper obtained from each cooling roll was subjected to corona discharge treatment, a color silver halide photographic emulsion was applied, and the surface of the developed photographic paper was observed with the naked eye. The results are shown in Table 1. When the cooling roll of the present invention was used, the upper limit coating speed could be increased without reducing the gloss of the photographic paper surface. 【table】

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the unevenness on the surface of the cooling roll.

Claims (1)

[Claims] 1. In the process of melt extrusion coating a paper substrate with polyolefin resin, the surface has an average depth of 0.05 to 0.7
A method for producing resin-coated paper for photography, which is characterized by cooling the polyolefin resin-coated paper using a cooling roll having fine irregularities with an average pitch of 0.1 to 100 μ, and at the same time molding the polyolefin resin surface with fine irregularities. .