DE2129680C3 - Process for the production of photographic paper supports - Google Patents

Description

The invention relates to a process for the production of photographic paper supports by extrusion coating of paper with polyethylene.

Baryta papers have hitherto been used as photographic paper supports. Such paper backings however, have the disadvantage that the treatment speed is limited and the photographic emulsion layers during storage of the treated photographic paper often turn yellow as the treatment solutions get into the paper during treatment, for example during the development or fixation, penetrate and partially remain therein after the treatment.

In order to avoid this disadvantage, a resin-coated paper for photographic paper supports is used used. A coated paper is a paper with resin layers on a surface or Both surfaces and due to the water resistance, in particular those on both surfaces resin coated papers are used for photographic supports. Such resin-coated Papers are made by extrusion coating, using a theinioplastic resin, for example Polyethylene is melted in the extruder, the melted resin is extruded through the extruder head and the resin against the paper in the gap that exists between the cooling roller and the pressure roller, is pressed.

In the case of resin-coated paper as the photographic paper support, there is sufficient adhesion required between the paper and the resin layers so that the resin layers do not separate from the paper during treatment, d. H. Developing, fixing, washing and drying, are stripped off. on the other hand The resin must not affect the photographic emulsions in order to improve the performance of the photographic paper.

Good adhesion between the paper and the resin layers is achieved at high resin temperatures obtained as the viscosity of the molten resin decreases and the surface of the resin is activated. On the other hand, however, the higher the extrusion temperature, the more decomposition and oxidation occur of the resin and the resulting products cause fogging of the photographic emulsion and prevent adhesion between the resin layers and the photographic emulsion. in the Hence, in terms of maintaining the good properties of photographic papers, they are low Extrusion temperatures desirable.

The object of the invention is therefore to provide a method for producing photographic Paper backings by extrusion coating of paper with polyethylene, a satisfactory one Adhesion between the paper and the polyethylene layer is achieved and a fogging of the photographic emulsion is avoided and thus polyethylene papers with good photographic properties can be obtained.

This object is achieved according to the invention in that a first layer of polyethylene on an extrusion temperature of above 320 ° C is mounted on a side of the paper and then a second layer of polyethylene is mounted at an extrusion temperature of below 300 ⁰ C to this first Polyathylenschicht.

By the invention that good adhesion between the paper and the first layer is obtained by drawing the first Polyathylenschicht to the paper at temperatures above 320 ⁰ C is reached. On the other hand, the second polyethylene layer at a low temperature below 320 ⁰ C, the decomposition and oxidation is prevented by the raising of the polyethylene, and the polyethylene layer thus obtained does not affect the photographic emulsions. The adhesion between the first layer and the second layer is very good at temperatures below 300 ° C.

When extrusion coating should generally ^{be avoided temperatures above 350 0} C, since the polyethylene is decomposed in the extruder or in the extruder head, and temperatures below 260 ⁰ C should also be avoided, since the adhesion between the polyethylene layers is poor, even if a polyethylene on one Polyethylene layer is pulled up.

In the method according to the invention, it is preferred to use high quality photographic paper Purposes used with a thickness of 100 to 250 microns. For the formation of the first layer of polyethylene a low density, high melt index polyethylene is preferably used. For the second polyethylene layer is preferred in view of the good adhesion properties between the first layer and the second layer and the good properties of a photographic material thus obtained The base used is a low-density or high-density polyethylene. It will Polyethylene classified as follows according to its density (see Römpps Chemielexikon, 6th edition, p. 5026):

Polyethylene
medium density
Polyethylene
high density

0.927-0.940 g / cm ³

0.941-0.965 g / cm ³

The polyethylene pulp for the first layer and the Second layer can be conventional pigments, such as titanium oxide, zinc oxide or zinc sulfide, dyes such as chromophthal Blue A3R C.I. No. 69,800, contain fluorescent brighteners or antistatic agents.

The following examples serve to further illustrate the invention, in which the adhesive strength and the Fog density was determined according to the following procedures.

Determination of the adhesive strength

The determination was made according to ASTM D-903. A test piece 2.5 cm wide was used and the polyethylene layer was stripped from the paper surface at a rate of 15 cm / min. The resistive force against strip at an angle of? 8O ⁰ C was defined as adhesive strength. The atmosphere at the time of the determination was 25 ° C with 50% relative humidity.

Determination of the haze density

A support sample was subjected to corona discharge (voltage 20,000 V, treatment amount 1 kW / cm ² · 10 m / min), and a conventional chlorobromide emulsion for photographic papers was coated on the thus treated sample. The specimen was cut into two parts, one of which was fixed without development and the other for 48 hours at 50 ° C under 80% relative humidity was allowed to stand, then was developed at 2O ⁰ C for 90 sec. And then fixed. The difference between the two samples was defined as fog or fog density.

The emulsion used in this experiment was prepared according to the following procedure:

Thickness of 15 microns drawn onto a paper with a unit weight of 170 g / m ² at 335 ^° C. and a high-pressure polyethylene with a density of 0.925 g / cm ³ and a melt index of 2, which titanium dioxide in an amount of 7.5 % incorporated, drawn up to a thickness of 25 microns at 280 ° C. The obtained polyethylene coated paper was named Sample 1.

On the other hand, the high-pressure polyethylene with a density of 0.925 g / cm ³ and a titanium dioxide content of 7.5% was drawn onto the paper in the same amount to a thickness of 40 microns at 320 ^° C. in a similar manner to the cover layer of sample 1 . The obtained polyethylene-coated paper was named Sample 2.

The bond strength between the paper and the polyethylene layer was as follows:

Solution 1

Distilled water
gelatin
Sodium chloride
Potassium bromide
Citric acid (10%)

Distilled water
Silver nitrate

Solution 2

600 cm ³

74 g
7.6 g
8.9 g

10 cm ³

200 cm ³
25 g

40

45

Solution 2 kept at 40 ° C. was poured into solution 1 kept at 62 ° C. over 2 minutes. The mixed solution was ripened at 62 ° C for 30 minutes, cooled, coagulated, cut into small pieces and washed with running water at 15 ⁰ C for 30 minutes. 10 g of gelatin was added to the obtained emulsion, and water was added to make a total of 1 kg. The emulsion was then ripened again at 62 ° C. for 30 minutes (cf. Photographic Material and Method of Handling, Goro Miyamoto, Kyoritsu Publishing Co., Ltd., Tokyo [Japan], 1963, p. 80).

65 Example 1

A high pressure polyethylene having a melt index of 7 and a density of 0.919 g / cm ³ became an adhesive strength

Sample 1
Sample 2

232 *)
148

*) No stripping was observed at the interface of the polyethylene layer.

The above-mentioned photographic emulsion was coated onto these two layers and then left to stand for 48 hours at 50 ^° C. and 80% relative humidity. The fog density of sample 1 was 0.2 while that of sample 2 was 1.3.

As a result, the carrier made in accordance with the present invention has superior adhesion between Paper and polyethylene layer shows and a photographic paper with good photographic properties compared to conventional photographic paper supports.

Example 2

A designated as Sample 1 polyäthylenbeschichtetes paper was produced under the same conditions as in Example 1, except that 10% titanium oxide were added to the polyethylene used for the cover layer, then this was extruded onto the first layer of polyethylene at 270 ⁰ C in a thickness of 15 microns.

One designated as Sample 2 Comparative Sample was used by extruding the same as the polyethylene for the outer layer of the sample 1 prepared in a thickness of 40 microns at 320 ⁰ C.

The adhesive strength: between the paper and the resin layer and the fog density were determined. It the following results were obtained:

Sample 1
Sample 2

Adhesion Strength

232

148

Haze density

0.3
1.5

Sample 2 proved to be inferior in terms of the two properties tested.

Example 3

A polyethylene, density 0.916 g / cm ^J, melt index 5, was coated on a paper having a unit weight of 170 g / cm ² in a thickness of 10 microns at 340 ⁰ C

drawn up and then a low-pressure polyethylene (density 0.96 g / cm ³ , melt index 5) in a thickness of 30 microns at 290 ^° C. was drawn up. The obtained polyethylene-coated paper was named Sample 1.

As a comparative sample, the same polyethylene as used for the cover layer of the specimen 1, mounted on the same paper to a thickness of 40 microns at 340 ⁰ C. The paper obtained was named Sample 2.

and the paper and the fog density were determined. The following results were obtained:

Sample 1
Sample 2

Adhesion Strength

250 85

Haze density

0.3

1.5

The comparative sample 2 proved to be in terms of efficiency

The "adhesive strength between the polyethylene layer" is considered to be inferior to both certain properties.

Claims (5)

Patent claims: 1. A process for the production of photographic paper support by extrusion coating of paper with polyethylene, characterized in that a first layer of polyethylene on an extrusion temperature of above 32O ⁰ C is mounted on a side of the paper and then on this first Polyathylenschicht a second Polyathylenschicht at an extrusion temperature of is drawn up below 300 ⁰ C. 2. The method according to claim 1, characterized in that the paper is a paper with a thickness 100 to 250 microns is used. 3. The method according to claim 1 or 2, characterized in that for the first polyethylene layer a high melt index low density polyethylene is used. 4. The method according to any one of claims) to 3, characterized in that the second polyethylene layer is a low density polyethylene or a high density polyethylene is used. 5. The method according to any one of claims 1 to 4, characterized in that a first polyethylene layer and / or a second polyethylene layer can be used, the usual pigments, dyes, contain fluorescent whitening agents or antistatic agents.