JPH0428290B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention prevents blocking with a cooling roll and staining of the cooling roll in the production of a photographic support made by coating one or both sides of paper with a polyolefin resin, and does not cause a decrease in the adhesive strength between the paper and the polyolefin resin. The present invention relates to a method for manufacturing a photographic support. Furthermore, it relates to a manufacturing method that does not cause these problems even when the coating speed is increased. Current photographic supports are generally made waterproof by coating one or both sides of the paper with a polyolefin resin in order to speed up the development process of photographic paper. A method for coating paper with polyolefin resin such as polyethylene or polypropylene is so-called extrusion, in which molten polyolefin resin is extruded into a film from the T-die of an extruder, allowed to flow onto the traveling paper, and then bonded together using cooling rolls and press rolls. A coating method is used. Photographic supports contain pigments, dispersants, etc. in the polyolefin resin for performance reasons, and problems such as blocking due to poor peeling between the resin and cooling roll during extrusion coating and product contamination due to cooling roll stains occur. Especially as a photographic support, this poses a serious quality problem. Furthermore, although it is important to increase the coating speed to increase productivity and reduce costs, increasing the coating speed significantly increases product contamination due to blocking and cooling roll stains, and also increases the risk of problems between the polyolefin resin and the paper substrate. The problem of reduced adhesion also occurs. The problem of blocking with a cooling roll causes striped or linear uneven gloss on the surface of the product, or small convex swellings called blisters, which make the product unusable from the viewpoint of image formation for photography. Furthermore, the coated paper is cut at the part where it peels off from the cooling roll where blocking occurs strongly, making it impossible to process. This is a particular problem in photographic supports, which include mirror-finished supports, rough-surfaced (matte) supports, silky-grained supports, fine-grained supports, etc., depending on the state of the surface patterning. In addition, the problem of product contamination due to cooling roll dirt is that low molecular weight substances, stabilizers, dispersants, etc. in the polyolefin resin adhere to the cooling roll, and this is transferred to the product, causing surface glare and uneven gloss, making it impossible to commercialize the product. , the extrusion process must be stopped and the cooling roll must be cleaned, which significantly impedes processability. As is the case with laminated papers such as general wrapping paper and printing paper, blocking and cooling roll stains increase as the coating speed increases. or,
The same goes for the reduction in adhesive strength between resin and paper substrate, but the paper substrate used as a photographic support has a high moisture content in the base paper to prevent discharge fog due to static electricity, the addition of conductive agents, strong size, etc. The need for high smoothness and the fact that the resin contains pigments, dispersants, etc. are also factors that reduce the adhesive strength between the resin and the paper substrate, and this decreases significantly as the coating speed increases.
Photographic paper with low adhesion deteriorates the appearance, and particularly during the development process, processing liquid may penetrate through the cut edges of the paper, causing problems such as discoloration and distortion of images. Furthermore, if the adhesion is insufficient when cutting the photographic paper into a predetermined size, whisker-like stretched polyolefin products will occur at the cut end, resulting in poor cutting and poor appearance. It has been known that blocking and cooling stains can be improved by lowering the resin temperature; however, lowering the resin temperature worsens adhesion. Lowering the temperature of the cooling roll is also an improvement, but there are limits. For example, if the temperature is lowered too much, moisture in the air will condense, causing other problems. There is also a method of adding a release agent, but none is sufficiently suitable for use as a photographic support. There is a method of creating a temperature difference on both sides of the film using the T-die of the extruder, but the fluidity of the molten resin in the T-die of the extruder is disturbed, making it difficult to obtain a stable film, and there is a limit to the temperature difference. No effect. For adhesion, corona treatment, flame treatment, heating treatment of the base paper surface, ozone treatment of the molten film, etc. are known, but any method requires lowering the resin temperature to a level that does not cause blocking or cooling roll stains. Moreover, it was difficult to obtain the desired adhesion. As a result of various studies on these countermeasures, we have found a method that solves the problem of blocking with the cooling roll and cooling stains without impairing the adhesion between the resin and the paper body even when the coating speed is increased, resulting in the present invention. That is, the surface of the paper base in contact with the resin is activated in advance, and the surface of the molten polyolefin resin film extruded from the T-die of the extruder is blown onto the surface on the cooling roll side to cool the surface of the molten film.
This is a method for producing a photographic support, which comprises coating a paper substrate with the molten polyolefin resin. More specifically, the temperature of the molten resin at the T-die outlet of the extruder is set to 280 to 320°C, and the surface of the paper base in contact with the resin is activated by corona treatment, and the molten polyolefin resin film is extruded from the T-die of the extruder. The temperature on the side of the cooling roll is 15℃~30℃.
The surface of the molten film is cooled by blowing cold air at ℃ through a slit-shaped bar or a cylindrical bar with predetermined holes. The speed of the cold air at this time is 6 m/sec ~ 14
m/sec is preferred. A molten film with only the surface cooled is allowed to flow down onto the paper base and the two are bonded together using a cooling roll and a press roll, thereby preventing blocking with the cooling roll and staining the cooling roll without reducing the adhesion between the resin and the paper base. I found something to do. It is effective to blow cold air at a temperature of 15 to 30°C; if it exceeds 30°C, it will be less effective, and if the temperature is less than 15°C, the cost will increase. The speed of cold air is 6m/
sec to 14 m/sec is preferred, but any speed may be used as long as the surface of the molten film can be cooled. When blowing cold air, the resin temperature at the exit of the T-die of the extruder is preferably 260°C to 340°C, and 280°C to 320°C is particularly effective; adhesive strength tends to decrease below 280°C, and temperatures higher than 320°C However, as the coating speed increases, the effectiveness against blocking and cooling stains tends to decrease. Examples will be described below. Note that the present invention is not limited to the examples. Examples 1 to 8 and Comparative Examples 1 to 4 75% by weight of low-density polyethylene with a density of 0.918 g/cm ³ and high-density polyethylene with a density of 0.962 g/cm ³ on paper used for a photographic support with a basis weight of 170 g/m ² 25% by weight
The mixed resin is extruded and coated with a polyethylene resin composition in which 10% by weight of anatase titanium dioxide and 0.5% by weight of zinc stearate are uniformly dispersed in the mixed resin. The other side is made of 50% by weight low density polyethylene with a density of 0.918g/ ^cm3 .
A photographic support is prepared by extrusion coating a polyethylene composition consisting of 50% by weight of high-density polyethylene with a density of 0.962 g/cm ³ . At this time, the traveling speed of the paper base was set to 150 m/min and 180 m/min.
m/min, resin temperature at extruder exit from 260℃ to 340℃
The conditions were set at .degree. C., and the paper substrate was activated by corona treatment, and the cold air blown onto the surface of the molten resin film on the cooling side was used by cooling compressed air from a compressor. The cold air was blown using a cylindrical bar with holes of 1.5 mm in diameter spaced at 5 mm intervals. The results are shown in Table-1. The evaluation of the effects shown in Table 1 was as follows: Blocking property was evaluated by observing the fluctuation when separated from the cooling roll and the surface condition of the photographic support, and classifying it into classes from 1 to 10. The cooling stain resistance was evaluated by observing the staining condition of the cooling roll and the cloudy condition of the surface of the photographic support, and classifying the samples into classes from 1 to 10. Adhesion was determined by storing the photographic support at 50° C. for 12 hours, then peeling off the resin from the base paper surface, measuring the area of fuzz on the base paper surface, and grading the results into 1 to 10 classes. As a photographic support, a support with a score of 4 or less in any of the above three evaluations is rejected as a product.

[Table] As described above, according to the present invention, blocking and cooling roll staining can be significantly improved, and productivity can be improved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Paper base, 2... Molten polyolefin film, 3... T die, 4... Cold air blowing bar, 5...
...Pressure roll, 6...Cooling roll, 7...
Takeover roll.

Claims (1)

[Scope of Claims] 1. In a method for manufacturing a photographic support in which one surface of a paper substrate is activated and then a polyolefin resin is extruded and coated on the surface of the running paper substrate through a T-die of an extruder, the extruder 1. A method for producing a photographic support, which comprises blowing cold air at 15°C to 30°C onto the cooling roll side surface of a molten polyolefin resin film extruded from a T-die. 2 The temperature of the molten resin at the T-die exit of the extruder is 280℃
The method for producing a photographic support according to claim 1, wherein the temperature is 320°C. 3. The method for producing a photographic support according to claim 1, wherein the activation treatment on the paper substrate is a corona discharge treatment.