Process For The Preparation Of Photographic Materials

Abstract

An improvement in adhesion strength between a polystyrene resin support and a gelatin-containing photographic emulsion layer is attained by the pretreatment of the support in two steps in which the first step comprises a surface-roughening treatment of the polystyrene support and the second step comprises a subsequent flame-treatment of the roughened polystyrene support carried out by contacting the roughened surface of the support with a flame from a combustible gas burner.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for the preparation of a photographic material.

2. Description of the Prior Art

Heretofore, baryta paper has been commonly used as a support base for various photographic materials such as photographic printing paper and diffusion transfer photographic paper. This baryta paper is prepared by coating paper made from pulp with a kneaded mixture consisting of fine particles of barium sulfate, a binder such as gelatin and water. However, such a support material has often suffered from a number of drawbacks such as poor dimensional stability against varying moisture, shrinking which occurs after development, delay in drying time after development and poor resistance to water.

SUMMARY OF THE INVENTION

After elaborate studies for overcoming the above-mentioned difficulties encountered upon the use of known baryta papers, we reached the present invention.

The process of this invention is characterized by a two step pretreatment, in sequence, of a polystyrene support which comprises firstly roughening the surface of the polystyrene film support and then flame-treating the roughened surface of the support. The resulting support is then coated with an emulsion or suspension containing gelatin as a binder.

The expression "emulsion or suspension containing gelatin as a binder" used throughout the specification of this invention defines such materials as are commonly used in this art and which are an aqueous emulsion or aqueous suspension of gelatin containing one or more silver halides such as silver chloride, silver bromide, silver chlorobromide or silver iodobromide; or a light-sensitive diazo compound, or a development nucleating substance for an image-receiving composition used in a silver salt diffusion transfer photographic process with or without any other substances which may be admixed therewith as are commonly used in this art.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be more fully explained in the following description.

First, the support material used in this invention must be so selected as to have equal or superior or mechanical or optical characteristics to conventional paper since the purpose of the present invention essentially resides in the provision of a material to be used as a photographic printing paper. Nevertheless, there has been found, up to the present, no synthetic resin which possesses nearly the same degree of "toughness" or "crispiness" as paper, with the exception of polystyrene. The present invention now provides a process whereby a novel photographic material is obtained by the use of polystyrene resin.

The polystyrene resin used in the process of the present invention can be a homopolymer of styrene, or a copolymer of styrene with other monomers, for example, styrene-butadiene copolymers, acrylonitrile-styrene copolymers, styrene-propylene copolymers, methylmethacrylate-styrene copolymers, .alpha.-methylstyrene homopolymers, etc. More particularly, the use of impact-resistant polystyrene, which is a copolymer of styrene with butadiene, is the most desirable material for meeting the objects of the present invention. To the above-mentioned polystyrene resin, one or more resins of the resins such as ethylene-vinylacetate copolymers, ethylene-acrylate copolymers, ethylene methacrylate ionomers, ethylene-acrylic acid ionomers, butadiene-acrylonitrile copolymers, ethylene-propylene copolymers, natural rubbers, synthetic isoprene rubbers, butadiene rubbers, styrene-butadiene rubbers, highstyrene content rubbers, polybutadienes, polybutene rubbers, chloropreno rubbers, butyl rubbers, or various kinds of nitrile rubbers, may be added and mixed therewith. The use of such resins is effective to improve the surface flatness, molding or extruding properties, control stiffness and increasing anti-tearing strength. These materials are used in art-accepted amounts to improve the properties recited.

No novelty per se is attached to the polystyrenes used in the present invention, and they are best selected from those polystyrenes known to the art to have excellent film forming abilities. Such materials, and their properties, are so well established that no further discussion will be offered thereon.

Throughout the specification, the term "polystyrene" or "polystyrene resin" is used to include all of such homopolymers and copolymers of styrene, unless otherwise specified.

When using polystyrene resin as the support material for photographic printing paper, it must be preliminarily converted into a white and opaque support. One method for effecting such conversion comprises preliminarily admixing a white pigment into the polystyrene resin and extruding the resultant resin compound into a film. The white pigment used includes titanium dioxide, barium sulfate, calcium sulfate barium carbonate, lithopone, alumina white, calcium carbonate silica white etc. The particle size of the white pigment is preferably less than about 1 .mu. and the pigment may be incorporated in the range of from about 2 to about 40 weight parts, preferably 5 to 30 weight parts, based on 100 weight parts of the resin component. Other dyestuffs or fluorescent brightenining agents known to the art may be further added to increase the whiteness of the resulting resin.

The polystyrene thus filled with the above pigments is then extruded in a conventional manner, and if desired, biaxially stretched to give a white and opaque film having excellent properties such as textural strength, water repellency, dimensional stability etc., which are most desirable in a support material for photographic materials.

However, since polystyrene is inherently hydrophobic and chemically inactive, it is most difficult to ensure firm adhesion between the support and a hydrophilic photographic emulsion containing gelatin which is to be applied onto the surface of the support.

The use of a polystyrene support as a transparent support material for negative photographic films having flat surface has been proposed. However, it has only been unsuccessfully utilized because no practical or effective method for firmly bonding the photographic emulsion layer to the support base has been yet establised. In this respect, we have discovered an improved process whereby strong adhesion between the roughened polystyrene support and the gelatin-containing photographic emulsion layer can be attained successfully.

The process of the present invention comprises the combination, in sequence, of the following two steps:

1. A first step in which the surface of polystyrene support is subjected to roughening treatment; and

2. a subsequent step in which the roughened surface of the polystyrene support is subjected to flame-treatment.

By employing these two steps in combination, a polystyrene support can be readily and firmly bonded to a layer of an emulsion or suspension containing gelatin.

It should be noted that the adhesion between the polystyrene support and the gelatin-containing layer fails if only one of the above two steps is applied to the support.

Flame-treatment itself has hitherto been applied to polyolefin resins for the purpose of improving printability and adhesiveness. In the case of polyolefin resins which have an inherently smooth surface, a marked improvement in adhesion strength can be attained with the use of flame-treatment alone. On the ohter hand, as will be shown in the examples, the adhesiveness of a polystyrene resin is not at all improved by the application of the flame-treatment alone.

According to the process of this invention, an outstanding increase in the adhesion strength is achieved only by carrying out flame-treatment in combination with a preceeding roughening treatment of the surface of the polystyrene support, and such a result is quite surprising and unexpected from prior teachings.

In addition, it is quite an unexpected benefit that the polystyrene support treated in accordance with the process of this invention never loses its strong adhesion even after extended periods of time. This is contrary to what occurs in the case of the flame-treatment of smooth-surfaced polyolefin resins. Accordingly, the aging stability of the adhesiveness of the polystyrene support obtained by the process of this invention is quite unique and satisfactory for the practical use thereof.

The details of steps (1) and (2) are described below.

The surface-roughening treatment of polystyrene support, i.e., step (1), is carried out by contacting the polystyrene film with a solvent capable of dissolving or swelling the polystyrene resin, such as tetrahydrofuran, methyl acetate, ethyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, methylene chloride, ethylene chloride, cyclohexane, benzene, dimethyl formamide and mixtures thereof, to thereby form a swollen layer on the surface of the polystyrene, and then contacting the resultant film with a liquid which is miscible with the above solvent but which is not comparible with or dissolves the polystyrene resin, i.e., non-solvent for polystyrene, to thereby coagulate the swollen layer while forming a roughened surface with minute protruding and recessed portions. The contact of the film with the solvent or with the non-solvent is practically conducted by dipping the film in the organic solvent or by applying the organic solvent to the film with the use of roller coaters, brushes or by spraying it, etc. The details of the procedure are disclosed in U.S. Pat. No. 3,515,567.

The support thus treated now has formed on its surface a layer with a number of minute pores each having a diameter and depth of from 0.1 .mu. to 50 - 60 .mu., so that incident light striking the surface is randomly reflected to give a white and opaque surface which can be satisfactorily utilized as a material for supporting a gelatin-containing photographic emulsion to give a desirable photographic printing paper, even if the support is originally transparent.

Accordingly, it is not always necessary to preliminarily admix a white pigment with the polystyrene support. It will thus be understood that the polystyrene support used in this invention is substantially white and opaque regardless of whether it is filled with white pigment or not, and the only important factor is that the support be a white and opaque film.

Roughening treatments other than the above-described process which can also be used in the practice of this invention include, for example, roughening by mechanical abrasion, foaming upon film-forming procedure by the expansion of a suitable thermally expanding foaming agents, roughening by selective dissolution of a soluble foreign substance added in the support, such as ethylene oxide, after the resin is formed into a film and the like. Any of these known surface-roughen treatments may be employed in the practice of the present invention without substantially impairing the advantageous features of the invention.

The flame-treatment of this invention, i.e., step (2), is carried out by using a burner placed transversely to the running web and by blowing a flame generated by the combustion of a fuel gas and oxygen onto the roughened surface of the film while optionally cooling the opposite side of the web by contacting it with a chilled roller.

The gaseous fuel can be a paraffinic hydrocarbon, olefinic hydrocarbon, carbon monoxide, hydrogen or a like combustible gas. However, the use of a paraffinic hydrocarbon is most desirable in view of its safeness and economy.

The mixing ratio of the fuel gas to oxygen is determined so that oxygen is present in a greater than equivalent amount to the fuel gas. In general, the larger the proportion of oxygen, the better will be the flame stability and the higher will be the effectiveness of the flame-treatment. However, too much oxygen will cause "flash back" or "back fire" and will lead to the extinguishment of the flame. It is therefore important to appropriately adjust the amount of oxygen so as not to invite such an undesirable phenomenon whatever gaseous fuel is used. The limit of oxygen ratio will be easily determined by the results of simple experiments, i.e., if flash back occurs, decrease oxygen until steady burning is achieved.

It is supposed that the surface treatment of the polystyrene film during the flame-treatment reaches as high as 300.degree.-2,000.degree.C at instantaneous moments, and the degree of the surface temperature is dependent not only on the flow rates of the fuel gas and oxygen or air but also on the running speed of the web. The exact conditions chosen will, of course, depend to a certain extent upon the exact apparatus used, but optimum conditions can always be determined empirically, if necessary. Generally speaking, one can select one or more variables to be held constant and then alter one other variable, e.g., hold fuel gas and oxygen flow rate constant while varying web speed, to determine optimum conditions which yield the most suitable product for the specific end use proposed.

In the case when the support treated is a stretched polystyrene film, care must be taken so as not to heat the film to a temperature over the glass transition point to prevent the film from softening and shrinking.

As long as the flame-treatment of the roughened polystyrene support is carried out under carefully controlled conditions in the manner as described above it is not only possible to impart excellent adhesion over relatively wide conditions as opposed to the rather narrow conditions employed in case of the flame-treatment of polyolefins which is conducted under strictly restricted conditions such as controlled oxygen content, flame temperature and temperature difference between the film surface and back of the film during the treatment.

The invention will be more fully illustrated in detail by referring to the following examples. The method for testing the adhesion strength between the polystyrene support and the layer of the emulsion or suspension coated thereon employed in the following examples was as follows:

1. Test of Adhesion Strength in the Dry State

Onto a sample piece prepared by coating a polystyrene support with an emulsion containing gelatin as a binder to form coated film there was bonded a cellulose triacetate film 0.14 mm thick with an epoxy resin adhesive. The bonded film was allowed to stand for 24 hours at a temperature of 23.degree.C under a relative humidity of 65 percent and then cut into a strip 1 cm wide and 15 cm long. Thereafter, the cellulose triacetate film was stripped off by peeling it at a drawing speed of 7.38 cm/min. The stripping strength was measured with the use of a resistance strain meter. In the examples, the expression "good adhesion" means that the test sample had an adhesion strength of at least 8 g/mm, which corresponds to a sufficient stripping strength for the practical use of the film as a photographic material.

2. Test of Adhesion Strength in the Wet State

A polystyrene/emulsion sample as was used in the test (1) was wetted after it had been developed, fixed or water-rinsed, and a cellulose triacetate film was bonded thereto with a cyanoacrylate adhesive in the same manner as in test (1). The bonded film was then directly subjected to measurement of the stripping resistance. In the wet test, the expression "good adhesion" means, similarly to test (1), a stripping strength of more than 2 g/mm. In the following examples, "part" or "parts" means "part or parts by weight."

EXAMPLE 1

An impact resistant biaxially stretched polystyrene film 0.2 mm was dipped in acetone for 3 seconds than immersed in methanol for another 30 seconds to give a white, opaque support having on its surface a minute porous layer. The support was then conveyed at a running speed of 80 m/min. while blowing flame onto the roughened surface from a burner placed at a distance (burner tip to the film) of 8 mm and having a 10 cm nozzle (flame width) with a slit gap of 0.2 mm. The burner was fed with a gaseous mixture of propane and oxygen at a rate of 80 lit./hr. and 500 lit./hr., respectively.

The thus flame-treated film was then coated with a black-and-white silver halide photographic emulsion having the following composition (material per square meter of the film):

Silver Chlorobromide 3.5 g Gelatin (binder) 13.0 g Formaldehyde 0.1 g Saponi (wetting agent) 0.03 g Water to make the entire emulsion 130 cc.

The results of a stripping test of the film coated with the above emulsion to examine the adhesion strength between the film support and the coated emulsion layer showed that the film had good adhesion, i.e., a stripping strength of 19 g/mm in the dry state and 6 g/mm in the wet state.

On the other hand, another photographic material prepared by coating the surface-roughened impact-resistant polystyrene support with the above photographic emulsion without flame treatment had a stripping strength of 0.5 g/mm in the dry state and 0 g/mm in the wet state. A similar experiment under the same condition but without the surface roughening treatment showed a complete absence of adhesive strength in both the dry state and the wet state.

EXAMPLE 2

An impact resistant polystyrene film containing 13 percent titanium dioxide having a thickness of 0.25 mm was treated with methyl ethyl ketone on one side and dried to give a support film having a lustrous surface with an extremely minute porous structure. The solvent-treated side of the support was subjected to flame-treatment with the use of the burner described in Example 1 at a support conveying speed of 80 m/min. while feeding propane and oxygen to the burner at a rate of 100 lit./hr. and 1,600 lit./hr., respectively. The distance of the support to the burner tip was 5 cm.

The thus treated surface of the film was coated with an aqueous gelatin solution of the follwing composition as an undercoat liquid:

Gelatin 10 g Formalin (a 20 % aqueous solution) 4 cc Water 190 cc

Onto the resultant undercoat layer, there was coated a color-type photographic silver halide emulsion of the following composition:

Silver chlorobromide 3.0 g Gelatin 3.5 g Emulsified dispersion containing an aqueous solution containing 1 g of benzoylaceto-2-chloro-5-dodecyloxycarbonyl anilide (yellow coupler)., 1 g of gelatin and 0.5 g of dibutylphthalate 14.0 g Triethylene phosphamide (3 % solution in acetone) 3.0 ml. Polyvinyl pyrolidone 0.7 g

A stripping test on the resultant film coated with the above color photographic emulsion indicated an adhesion strength as required in a color photographic material.

On the other hand, a similar photographic material prepared by coating with the same liquids used above onto a roughened, filler-containing and impact resistant polystyrene film without a flame treatment completely failed to bonding in the dry or wet state.

EXAMPLE 3

A polystyrene support 0.1 mm thick was dipped in methyl isobutyl ketone for 2 seconds, dried in air for 30 seconds and then soaked for 30 seconds in ethanol to give a white and opaque polystyrene film having a microporous layer on the support surface. The thus roughened polystyrene support was flame-treated under the same conditions as employed in Example 2 and thereafter coated with the following liquid (per square meter of film) so as to form an image receiving layer to be used in a silver salt diffusion transfer process.

______________________________________ Gelatin (binder) 3 g Colloidal silver sulfide (developing nuclei) 0.001 g Phenyl mercaptotetrazol (toning agent) 0.001 g Saponin (wetting agent) 0.02 g ______________________________________

A stripping test on the thus prepared image-receiving material proved that it had a sufficiently high adhesion strength for use as an image-receiving material in a silver salt diffusion transfer photographic process, whereas, an otherwise identical support to which flame-treatment had not been applied or on which the surface-roughening treatment had not been effected showed a complete lack of adhesiveness between the coated layer and the support.

EXAMPLE 4

A roughened, white and opaque impact resistant polystyrene support obtained in the same manner as Example 2 was flame-treated under the following conditions:

Propane flow rate: 200 lit./hr. Oxygen flow rate: 2500 lit./hr. Distance between burner tip and film: 3 cm

During the flame treatment the temperature of a chilling roll contacting the film at the opposite side of the suppport with respect to the burner was kept at 35.degree.C.

The thus treated film was coated with a black-and-white silver halide emulsion as in Example 1, dried and then subjected to a strippint test. The film exhibited good adhesion between the coated emulsion layer and the support.

The resultant black-and-white photographic film formed a beautiful positive picture image after being printed with a negative picture.

EXAMPLE 5

On a polystyrene film 0.2 mm thick filled with 10 percent by weight titanium dioxide there were blown fine particles of silica sand of a specific gravity of 2.2 and a particle size of 80 mesh at the distance of 60 cm. to give a roughened polystyrene support having a number of minute cavities of a depth of 1-3 .mu.. The thus roughened film was flame-treated under the same conditions as employed in Example 4 and then coated with a black-and-white silver halide emulsion as used in Example 1 to give coated film with extremely good adhesion. A picture printed on the resultant photographic material through a negative picture gave a positive picture image with a beautiful mat face and magnificient feeling.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims

What is claimed is:

1. A process for the preparation of a photographic material which consists essentially of a combination in sequence of the steps of firstly forming a plurality of minute pores having a diameter and depth of from 0.1.mu. to 60.mu. in the surface of a polyetyrene support by roughening, secondly subjecting the roughened surface of the polystyrene support to flame-treatment, coating the resulting flame-treated surface of the polystyrene support with an emulsion or suspension containing gelatin, and drying the resulting coating.

2. A process as claimed in claim 1 where the roughening is performed by contacting the polystyrene with a solvent which dissolves or swells the surface of the polystyrene to provide a swollen surface layer and then contacting the polystyrene with a non-solvent for the polystyrene which is miscible with the solvent, whereby the swollen surface layer is coagulated.

3. A process as claimed in claim 1 where the polystyrene is a homopolymer.

4. A process as claimed in claim 1 where the polystyrene is a styrene-butadiene, styrene-acrylonitrile, styrene-propylene or styrene-methyl methacrylate copolymer.

5. A process as claimed in claim 1 where the polystyrene contains a white pigment.

6. A process as claimed in claim 1 where the flame treatment is accomplished by continuously passing the polystyrene in web form in contact with a flowing fuel gas/oxygen combustion flame.

7. A process as claimed in claim 6 where the emulsion or suspension contains a silver halide.

8. A process as claimed in claim 6 where the emulsion or suspension contains developing nuclei for a silver salt diffusion transfer process.