GB2109705A

GB2109705A - Photographic paper

Info

Publication number: GB2109705A
Application number: GB08231489A
Authority: GB
Inventors: Yoshimasa Asanuma
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 1981-11-11
Filing date: 1982-11-04
Publication date: 1983-06-08
Also published as: GB2109705B; JPS5882242A; FR2516270B1; DE3241598A1; FR2516270A1

Abstract

A photographic paper improved in the antistatic property, which comprises a paper sheet to which a polymer containing, as structural unit, a metal salt of styrene-sulfonic acid is provided and a thermoplastic polymer coated over the paper sheet.

Description

SPECIFICATION Photographic paper This invention relates to a photographic paper comprising a thermoplastic polymer layer, and more particularly relates to a photographic paper in which a thermoplastic polymer is coated on a paper sheet so treated as to decrease accumulation of electrostatic charge.

It has been known that a photographic paper can be substantially waterproofed by placing various kinds of thermoplastic polymers such as polyethylene, polypropylene, polystyrene and polyacrylate over a paper sheet thereof. In fact, the thermoplastic polymer-coated photographic paper that is capable of repelling water (referred to hereinafter as waterproof photographic paper) is advantageous, as compared with the conventionally employed baryta paper comprising barium sulfate etc. coated over the paper sheet, in that period of times required for the developing and washing stages can be greatly shortened. Therefore, the waterproof photographic paper have been widely used at present.

However, in the waterproof photographic paper, the surface of which is coated with the nonelectroconductive thermoplastic polymer, electrostatic charge tends to accumulate in the course of manufacturing, handling and using the waterproof photographic material. For this reason, the waterproof photographic paper is not considered to be fully satisfactory. Moreover, the waterproof photographic paper has a defect that sparks caused by the accumulated electrostatic charge produce irregular fog patterns on the radiation-sensitive photographic emulsion layer placed on the nonelectroconductive thermoplastic polymer. Such irregular fog patterns are extremely detrimental to the photographic material.Further, another problem caused by the accumulated electrostatic charge resides in that the photographic paper on which the electrostatic charge accumulates is apt to collect dust and contaminant from the surroundings. The so collected dust and contaminant not only spoils the appearance of the photographic paper, but also disturbs the operation of the control devices for processing the photographic materials such as a device for detecting a mark provided at a predetermined position on the photographic material for the purpose of facilitating the print-cutting operation performed after completion of the final processing and drying stages.

To overcome the above-described problems, various kinds of substances have been proposed as antistatic agent to be incorporated into the photographic paper.

It is known that an antistatic agent can be applied to the photographic paper in the following manners: (1) a method involving kneading an antistatic agent into the thermoplastic polymer to be coated over the paper sheet; (2) a method involving coating an antistatic agent over the surface of the thermoplastic polymer layer; and (3) a method involving coating an antistatic agent over the surface of a support such as a paper sheet (referred to hereinafter as substrate) on which the thermoplastic polymer is placed.

In the method (1), however, a large amount of an antistatic agent is necessarily incorporated into the polymer. Further, there has not yet been found an antistatic agent having sufficiently high heat resistance and being stable under severe conditions employed for processing the thermoplastic polymer. Accordingly, satisfactory effect can hardly be accomplished by this method.

According to the method (2), preparation of the accumulation of electrostatic charge can be attained by coating the thermoplastic polymer layer with a small amount of an antistatic agent.

Moreover, it is advantageous that the effect given by the method (2) is not influenced by the conditions for processing the thermoplastic polymer. For these reasons, the method (2) has been mainly adopted for imparting the antistatic property to the photographic paper. However, this method also has defects that the antistatic agent-coating layer is apt to fall off or separate from the polymer layer under contact with a passroll, and that the friction coefficient of the so-coated polymer layer is remarkably reduced so that adhesion between the polymer layer and a photographic emulsion layer is rendered unsatisfactorily weak.

The method (3) is free from the defects described in the method (2), because an antistatic agent is not exposed outside. However, this method is based on a pseudo-destaticizing effect and, accordingly, is fundamentally different from the methods (1) and (2). More in detail, either of the method (1) and the method (2) is based on a direct destaticizing effect involving suppressing the accumulation of electrostatic charge on the surface of the thermoplastic polymer layer or accelerating leakage of the accumulated electrostatic charge therefrom, while the method (3) involves inducing an electric charge opposite to the electric charge produced on the surface of the thermoplastic polymer layer, on the surface of a substrate such as a paper sheet so as to produce an electric double layer, whereby reducing the apparent electric field strength in the surroundings.Accordingly, the surface resistance of the substrate in the method (3) should be controlled to reach much lower level than the surface resistance of the thermoplastic polymer layer in the method (1) or method (2).

According to the study by the present inventor, it has been found that the surface resistance of the substrate in the method (3) is required to be not higher than 5 x 10752 (200 C, RH 10%) in order to prevent troubles caused by the accumulation of electrostatic charge. However, such a desirable surface resistance is not accomplished by the antistatic agent employed conventionally in the method (3).

United States Patent No. 4,173,480 discloses a destaticizing method in which an antistatic composition comprising a synthetic hectorite clay is applied onto a paper sheet and then polyethylene or the like is coated thereover so as to prevent the accumulation of electrostatic charge.

United States Patent No. 3,253,922 also discloses a destaticizing method in which sodium salt of naphthalenesulfonic acid is employed in place of the abovementioned synthetic hectorite clay.

However, an antistatic composition comprising either the synthetic hectorite clay or the sodium salt of naphthalenesulfonic acid is only able to provide a surface resistance to the substrate at a value much higher than the desired borderline value identified hereinbefore. Therefore, the method (3) employing the above-mentioned antistatic agent still gives unsatisfactory result.

Accordingly, the primary object of this invention is to provide a waterproof photographic paper coated with a thermoplastic polymer such as polyethylene which is able to effectively prevent accumulation of electrostatic charge thereon.

Another object of the invention is to provide a waterproof photographic paper which is provided with an antistatic agent free from falling off or separation from the photographic paper in a variety of stages such as an emulsion coating stage, a slitting stage, and a printing stage.

A further object of the invention is to provide a waterproof photographic paper which is provided with an antistatic agent free from disturbing the photosensitivity of a silver halide photographic emulsion to be placed thereon.

A still further object of the invention is to provide a waterproof photographic paper which is provided with an antistatic agent, the provision of which does not reduce the friction coefficient of the surface of the thermoplastic polymer coating layer.

The above-described objects are now accomplished by the present invention residing in a photographic paper comprising a paper sheet to which a polymer containing, as structural unit, a metal salt of styrenesulfonic acid is provided, and a thermoplastic polymer coated over the paper sheet.

In the invention, the polymer containing as structural unit a metal salt of styrenesulfonic acid preferably is a polymer having the formula (I):

in which A is a monomer unit forming the polymer in conjunction with the metal salt of styrenesulfonic acid, and M is a metal atom.

In the formula (I), the configuration and sequence of the monomer unit represented by

and the monomer unit represented by A are optionally arranged.

The monomer unit A is derived from a monomer copolymerizable with the metal salt of styrenesulfonic acid. Examples of the copolymerizable monomer include acrylic acid, a lower alkyl-ester of acrylic acid such as methyl acrylate or ethyl acrylate, methacrylic acid, and a lower alkyl-ester of methacrylic acid such as methyl methacrylate or ethyl methacrylate. The lower alkyl group for constituting the above-described ester is an alkyl group containing 1-6 carbon atoms. Particularly preferred are methyl methacrylate and methacrylic acid.

The metal atom represented by M preferably is a monovalent metal atom, for instance, an alkali metal such as sodium, potassium or lithium. Particularly preferred is sodium.

There is no limitation on the values x and y representing the polymerization degree of the polymer of the formula (I). However, x and y are preferably selected from the values in the ranges of 20-5,000, and 5-8,000, respectively. More preferred ranges for x and y are 300 4,000 and 200-7,000, respectively, and particularly preferred ranges for x and y are 640-3,500 and 710-6,000, respectively.

The copolymerization ratio xly can be optionally varied. Generally, the xly ratio ranges from 5/95 to 80/20, more preferably ranges from 10/90 to 65/35.

Representative examples of the compound represented by the formula (I) are set forth below.

These compounds, however, are given only as examples of the compound of the formula (I), and the compounds of the invention are not restricted by these examples.

The amount of the antistatic composition comprising the polymer containing as structural unit a metal salt of styrenesulfonic acid to be coated on the paper sheet varies with the nature of the polymer (antistatic agent). Generally, the antistatic composition is coated on the paper sheet in such an amount that 0.05-10 g. of the solid content (antistatic agent) is coated over 1 m2 of the surface of the paper sheet. Preferred range for the solid content is 0.1-6 g. per 1 m2 of the surface, and particularly preferred range is 0.5~4 g. per 1 m2 of the surface. If the coating amount is less than 0.05 g./m2, the prevention of accumulation of electrostatic charge is unsatisfactorily poor.On the other hand, the coating amount of more than 10 g./m2 renders the adhesion between the paper sheet and a thermoplastic polymer layer to be coated thereover extremely weak.

It is most general that the antistatic agent is applied onto the surface of the paper sheet by a sizing method which is generally employed in the final stage of the manufacture of a paper sheet. The sizing method can be carried out by placing on a paper sheet a sizing solution such as an aqueous sizing solution containing the desired antistatic agent. The antistatic agent can be coated over the surface of the paper sheet by a conventional coating method such as roll coating, bar coating, air-knife coating, bead coating, spray coating or gravure coating. The antistatic agent employed in the invention is generally soluble in water. If desired, an organic solvent miscible with water can be employed in combination with water for the preparation of the coating solution.

Examples of the thermoplastic polymer coated over the paper sheet for the preparation of the waterproof photographic paper include polyolefins such as polyethylene and polypropylene; copolymers between olefins such as ethylene and propylene and other copolymerizable monomers; mixtures of these polymers; cellulose esters; polyamide; and linear polyester. Other thermoplastic polymers than those mentioned above can be also employed.

The present invention will be described in detail by the following examples, but the invention is not restricted to these examples.

The measurements of the surface resistance, electrostatic field strength and fog were carried out on a test sample which had been allowed to stand 6 hours at 250C and RH 10%, in the following manners.

1) Measurement of surface resistance A substrate coated with an antistatic agent was held between brass electrodes (length: 10 cm, space between the electrodes: 0.14 cm, portions to be touched by the test sample were made of stainless steel), and the voltage and current were read upon supplying therebetween an electric current for one minute by means of an electrometer TR-8651 (manufactured by Takeda Riken Co., Ltd., Japan).

The so obtained values were converted to the surface resistance according to the equation of Ohm's Rule. Smaller value of the surface resistance means higher antistatic property. Satisfactory antistatic property was accomplished when the surface resistance was not higher than 5 X 107( ).

2) Measurements of electrostatic field strength and fog A substrate was coated with a thermoplastic polymer (resin) on both surfaces and a silver halide photographic emulsion was placed on one surface thereof to prepare a test piece.

The so prepared test piece was passed through urethane rubber rollers rotating at a rate of 50, 1 00, 1 50, 200 or 300 m/min., within a dark room. The electrostatic field strength produced on the test piece after passing between the rollers was measured by a surface electrometer SSVI1-40 (manufactured by Kawaguchi Electric Co., Ltd., Japan). The so treated test piece was then developed in conventional manner and conditions, and the surface of the developed test piece was observed. The conditions of the surface of the test piece were rated as follows: I: No fog was observed on the surface of the emulsion layer; II: Fog was observed in part on the surface of the emulsion layer; and ill: Fog was observed almost all over the surface of the emulsion layer.

Example 1 Each of the antistatic compositions A, B, C, D and E set forth below was coated on a fine quality paper sheet weighing 1 30 gum2, in such an amount that 3 g. of the solid content was coated over 1 m2 of the surface of the paper sheet for the antistatic composition A, B, C or D.

The so treated paper was then allowed to stand for 6 hours at 250C and RH 10%, and measured for the surface resistance on the antistatic agent-coated surface.

Subsequently, the paper sheet was coated on both surfaces with a polyethylene layer of 0.03 mm thick to prepare a polyethylene-coated paper. One surface of the polyethylene coating layer was run under corona discharge at discharge voltage 4 kW at a rate of 100 m/min., and then coated with a silver halide photographic emulsion.

The so prepared photographic material was allowed to stand for 6 hours at 250C and RH 10%, and measured for the electrostatic field strength and the fog.

The results are set forth in Tables 1,2 and 3.

Composition A

parts by weight 30 water 70 Composition B

30 [x=560, y=360 ] water 70 Composition C Sodium naphthalenesulfonate 30 water 70 Composition D Laponite S (synthetic hectorite clay, 30 produced by Laporte Industry Ltd.) water 70 Composition E water 100 Table 1 Surface resistance on surface of paper sheet (S#) Composition Sufface resistance (S?) A 7x106 B 8x106 C 7x108 D 1 x1010 E 1 X1013 F 9x1013 Remark: Composition F means that no antistatic agent was applied onto the paper sheet.

Table2 Electrostatic field strength (V) Rate(m/min.) 50 100 150 200 300 Composition A 21 36 41 68 83 B 26 41 58 70 88 C 160 250 380 530 700 D 850 1100 1360 1520 1800 E 2000 3000 3800 4400 5600 F 2500 3400 5000 5900 6900 Remark: Composition F has the same meaning as above.

Table 3 Fog Aate(m/min.) 50 100 150 200 300 Composition A I I I B I I I C II 11 Ill 111 111 Ill Ill lil Ill Ill E lil lil lil Ill Ill F lil Ill III Ill Ill Remark: Composition F has the same meaning as above.

The results set forth in the above Tables indicate that the photographic paper coated with Composition A or B according to the invention produced no fog even after passing between the urethane rubber rollers at a rate of 300 m/min. In contrast, the photographic paper coated with Composition C produced fog almost all over the surface when passed at a rate of 150 m/min. or more, although the rank II was given when passed at a rate of 50 or 100 m./min. Accordingly, the photographic paper coated with Composition C still cannot be employed in practice when the photographic paper is to be conveyed in the photographic processing stages at a high speed.

Example 2 A mixture of starch (CATO Size 50: produced by Ohji National Co., Ltd., Japan) and one of the antistatic compositions G, H, I and J was coated on a fine quality paper sheet weighing 130 g./m2. The ratio between the starch and the antistatic composition and the coating amount were adjusted in such a manner that the starch was coated in the amount of 5 g./m2 (solid content basis) and the antistatic composition (solid content basis) was coated in the amount of 2.5 g./m2. Thus, the sizing was applied onto the paper sheet.

Subsequently, the paper sheet was coated on both surfaces with a polyethylene layer of 0.035 mm thick to prepare a polyethylene-coated paper. One surface of the polyethylene coating layer was run under corona discharge at discharge voltage 4 kW at a rate of 100 m/min., and then coated with a silver halide photographic emulsion.

The results are set forth in Tables 4, 5 and 6.

Composition G Composition H

[x=780, y=480 ] Composition I Na2SO4 Composition J CaCl2 Table 4 Surface resistance on surface of paper sheet (52) Composition Surface resistance (#) G 1 x107 H 9x106 1x109 J 9x107 Table 5 Electrostatic field strength (V) Rate(m/min.) 50 100 150 200 300 Composition G 30 43 65 75 101 H H 45 55 75 80 120 I 260 300 320 470 760 J 130 180 200 300 480 Table 6 Fog Rate(m/min.) 50 100 150 200 300 Composition G I I I I H I I I III Ill III Ill III J I II I II III II II III III The compounds employed in Compositions I and J were both conventional antistatic agents generally employed for destaticizing a paper.

The results set forth in the above Tables indicate that the photographic paper coated with Composition J produced fog almost all over the surface when passed at a rate of 200 m/min. or more, although the rank I was given when passed at a rate of 50 m/min. and the rank II was given when passed at a rate of 100 or 150 m/min.

Moreover, the photographic paper coated with Compositions I or J showed poor adhesion between the paper sheet and the polyethylene layer, and the polyethylene layer fell off in the developing stage for either case.

In contrast to the above, the photographic paper coated with Composition G or H according to the invention produced no fog, and the adhesion between the paper sheet and the polyethylene layer was satisfactory. These results mean that the antistatic agent according to the invention is remarkably effective.

Claims

1. A photographic paper comprising a paper sheet to which a polymer containing, as structural unit, a metal salt of styrenesulfonic acid is provided, and a thermoplastic polymer coated over the paper sheet.

2. The photographic paper as claimed in Claim 1, in which the polymer containing, as structural unit, a metal salt of styrenesulfonic acid has the formula (I):

in which A is a monomer unit forming the polymer in conjunction with the metal salt of styrenesulfonic acid; M is a metal atom; x is an integer ranging from 20 to 5,000; and y is an integer ranging from 5 to 8,000; and the configuration and sequence of the monomer unit

and the monomer unit A are optionally arranged.

3. The photographic paper as claimed in Claim 2, in which M in the formula (I) is an alkali metal.

4. The photographic paper as claimed in Claim 3, in which the alkali metal is sodium.

5. The photographic paper as claimed in Claim 2, in which x and y in the formula (I) are integers of 300 4,000 and 200-7,000, respectively.

6. The photographic paper as claimed in Claim 2, in which x and y in the formula (I) are integers of 640-3,500 and 710-6,000, respectively.

7. The photographic paper as claimed in Claim 2, in which the ratio of x against y in the formula (I) ranges from 5/95 to 80/20.

8. The photographic paper as claimed in Claim 2, in which the ratio of x against y in the formula (I) ranges from 10/90 to 65/35.

9. The photographic paper as claimed in Claim 2, in which the monomer unit A in the formula (I) is derived from acrylic acid, its lower alkyl-ester, methacrylic acid, or its lower alkyl-ester.

10. The photographic paper as claimed in Claim 1, in which the polymer containing, as structural unit, a metal salt of styrenesulfonic acid is coated in the amount of 0.05-10 g. over 1 m2 of the surface of the paper sheet.

11. The photographic paper as claimed in Claim 1, in which the polymer containing, as structural unit, a metal salt of styrenesulfonic acid is coated in the amount of 0.1-6 g. over 1 m2 of the surface of the paper sheet.

12. The photographic paper as claimed in Claim 1, in which the polymer containing, as structural unit, a metal salt of styrenesulfonic acid is coated in the amount of 0.5-4 g. over 1 m2 of the surface of the paper sheet.