JPH0610738B2 - Method for producing layered support of photographic paper with polyolefin coating on both sides - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for producing a photographic paper support in which a substrate paper is coated with a polyolefin resin on both sides.

PRIOR ART The coating is provided with a light-sensitive emulsion layer in a special working step, which after development is developed in several baths connected in series to give a photographic image.

The polyolefin layer, such as polyethylene, polypropylene or other thermoplastic, protects the paper support against moisture penetration from the developing bath, thereby reducing the wash, fix and dry times required for the developing process. .

Usually, the polyolefin layer is continuously poured from the melt to the paper surface on both sides by an extrusion molding method, and solidified by cooling to form a film, which is fixed to the paper.

The different surface tensions of the non-polar polyolefin polymer and the paper, which is composed primarily of natural cellulosic fibers and sizes to render it hydrophobic, govern the adhesion of the polyolefin polymer to the paper surface. The uniform maximum deposition of this bond is of decisive importance for the subsequent use of the photographic support material. This is because, under mechanical loading, the binder should not be peeled off under the simultaneous chemical action of the developing reagents when the exposed image support is transported to the developing bath. The corners or edges of the cut of the photographic support material are especially affected in this case. This is because the alkaline chemical containing the penetrant can penetrate the cellulose material, which is not protected by the polyolefin, to some extent and swell it. If the bond between the polyolefin film and the paper surface is insufficiently adhered, the film will peel and fray at the corners of the cut, which renders the photographic image unusable and significantly reduces its utility value. In the same way, at this point the developer penetrates into the paper support and discolors it, whereby the automated rapid drying is delayed after development and the edges of the finished image are discolored.

Various methods are known for adjusting these requirements for photographic paper supports. In the case of extruded coatings, the temperature of the molten polyolefin can be increased, which enhances its adhesion to the paper. In fact, in the case of polyethylene, temperatures up to 320 ° C., a temperature range in which the unwanted thermal decomposition of thermoplastics takes place with particularly long residence times, i.e. with slow progress rates.

Another way to improve this adhesion is the emission of paper webs by corona discharge or gas treatment with ozone. When fixing the loosening of the polyolefin resin during application,
The action time of corona discharge or ozone gassing is increased by reducing the velocity of the strips, which improves the adhesion. However, the disadvantage is that the production efficiency is significantly reduced on the one hand, and the residence time of the polyolefin resin in the critical temperature range is increased on the other hand, and there is a risk of thermal decomposition. The action of too strong radiation or ozone exerts a detrimental sizing of the substrate paper, i.e. its hydrophobization by chemical additives as well as its detrimental use on the surface moisture, whereby the developer of its cutting angle of the paper Resistance to penetration is compromised.

Attempts have been made to apply an adhesion promoter, a so-called primer, to the base paper before applying the polyolefin. Thus, for example, a polyethylene-imine that is sufficiently water-soluble and can be applied to the surface either alone or in combination with starch or polyvinyl alcohol to reinforce the surface significantly enhances the adhesion of the paper to the polyolefin. Is known for. However, polyethylene-imine has a detrimental effect on the light-sensitive emulsions and causes the formation of veil, which has been found to be unsuitable for photographic paper supports. Attempts have also been made to apply low molecular weight polyethylene, polyethylene waxes and other polymers having a sufficient affinity for polyolefins in the form of water emulsions to the substrate paper as adhesion promoters. However,
A surfactant emulsifier is required for the stability of this emulsion, which has a detrimental effect on sizing,
This enhances the penetration of the developer into the cutting angle under the discoloration. Therefore, in general, the use of primers, which must contain a surfactant for stabilization, is ruled out due to the instability of the hydrophobizing sizing with respect to horn penetration.

These drawbacks are caused by Japanese Patent Publication No. 15423 (1).
1974), the molar ratio of ethylene to sodium acrylate, -potassium or -ammonium is 85: 1.
5 or the molar ratio of ethylene to ammonium acrylate and vinyl alcohol 60:25:15
The copolymerization product can be avoided if it is applied to the base paper before the polyolefin is applied. This can result in a reinforcement of the adhesion of the polyolefin to the paper surface, or the extrusion temperature can be significantly reduced with the same adhesion.

However, the practical use of this copolymerization product suspended in water is that the suspension is unstable for use in, for example, paper machine sizing machines, and when circulated it precipitates due to interaction with the paper surface. I'm at odds with what to do.

This precipitation is large when other components are added to the suspension. The other constituents are, in particular, the electrolytes necessary for adjusting the required electrical conductivity of the paper, such as sodium chloride or sodium sulphate, as well as starches, starch derivatives or polyvinyl alcohol, by means of which the paper is reinforced and used. The toughness of the paper support is improved. Also, the hydrophobization of the base paper is impaired on the surface. Because conventional hydrophobizing agents cannot be applied due to their incompatibility with the suspension of the copolymer. In the same way
This coating does not allow the use of the optical brighteners required to control the color of the photographic support. Because it is also incompatible with the suspension.

DE-A-2326759 describes a mixture of a polymer aqueous dispersion and an inorganic electrolyte, such as an alkali metal salt and an optical brightener and an organic film-forming polyelectrolyte to which an antioxidant may be added. Application of substrate paper is described. By this method, improved adhesion of polyethylene was achieved and the photographic fog density was retained.

Adjusting the mixture of the various polymer dispersions proposed in this case results in different pH of the aqueous dispersion, which is due to the interaction of the evolving strip with the paper surface, the instability of the precipitate and the circulation of the sizing machine. Can give rise to

In this known technique, it can actually be added to a sizing machine, and the dispersion produced at that time is stable even under the conditions of circulation in the sizing machine of a papermaking machine. Exists.

In particular, the object of the invention is to avoid all the above-mentioned known disadvantages of primer coatings on base papers, while at the same time obtaining sufficient adhesion of the polyolefin to the paper surface. Furthermore, it is possible to obtain the actual application effect of the sizing machine on the substrate paper surface, that is, increase in conductivity, increase toughness and strengthening of the surface, optical brightener effect in some cases, and photochemical stability. It does not impair the hydrophobicity of the substrate paper with respect to the penetration of the developer at the cutting angle of the support.

As a surprising solution according to the invention, a copolymer of ethylene and 15 to 25% by weight of acrylic acid with a high acidity on paper is combined with an electrolyte, starch or polyvinyl alcohol and optionally an optical brightener to give a stable suspension. It has been found that it can be applied as a liquid and added to the cellulosic suspension when making paper, before dehydration on a sieve and subsequent drying in a paper machine. An important point of the invention is the application of the mixture according to the invention to the surface of the paper. The addition of paper to the material can be done additionally.

The present invention is well dispersible in water in the range of alkaline or ammoniacal alkaline pH, without any addition of surface-active emulsifiers and suspended in view of the addition of other necessary additives. It is based on the property of this polymer to be fully soluble in liquid. When the pH is lowered to the neutral or weakly acidic range by other processing methods, the copolymer precipitates and forms an interference film on the paper surface, which is bonded to the fiber surface in the texture of the paper.

The polyethylene component of this precipitated polymer on the paper surface has a greater affinity for the polyethylenes (HDPE and LDPE) used in the conventional photographic paper support, in particular, for the polyethylene, compared to the extruded polyolefin. Good adhesion is obtained.

The solution to the problem according to the invention is by adjusting the proportion of acrylic acid in the copolymer and the pH with a subsequent drop in pH when mixing the other ingredients. The adjustment of the alkaline pH can be carried out with a caustic soda solution or other alkali, but the use of ammonia has proved to be particularly preferred.
This is because ammonia evaporates well at the subsequent drying temperature, which leads to a decrease in pH.

The main advantage of the invention described in the following examples is the use of the commercially available corporimers as surface coatings (plittermers) in combination with electrolytes, starches, starch derivatives, polyvinyl alcohol and optical brighteners. , A stable suspension was prepared in this case by adjusting the alkalinity of solutions or suspensions of these components with ammonia and the addition of the desired amount of ethylene / acrylic acid copolymer, and by applying it to the paper surface all known disadvantages And a sufficient increase in the attachment of the conjugate is obtained.

According to the invention, this action is additionally obtained by using an ethylene / acrylic acid copolymer having a proportion of acrylic acid of 15 to 25% by weight as the base paper, in the customary sizing agent, for example as a single sizing agent at neutral pH. It can be increased by sizing in combination with a range of alkyl / ketene dimers and stearic acid in the weakly acidic pH range.

To this end, an alkaline or ammoniacal alkaline solution of ethylene / acrylic acid copolymer having 15-25% by weight of acrylic acid (adjusted to pH 8.5-10) is used, with a fiber density of 4-6% and a ground cellulose of conventional composition. Mix vigorously with. Then the pH of the mixture is lowered to pH 6-7 with dilute sulfuric acid,
This causes the copolymer to settle into fibers with a uniform material density. It can then be additionally sized or made hydrophobic with stearic acid and aluminum sulphate in the weakly acidic range or with alkyl / ketene dimers in the neutral range with the polyamine-epichlorohydrin as retentive agent.

The advantage of such a combination sizing is that the surface application of the ethylene / acrylic acid copolymer according to the invention and the synergistic effect by the reinforcement of the adhesive effect of the bond of the support together with the necessary components in the material-precipitated copolymer are Hydrophobicization of the paper substrate to permeation of the developer into the corners of a later development process of the photographic image support.

The known sizing method, in combination with stearic acid in the range of weakly acidic pH and aluminum sulfate or a retention agent in the neutral range with alkyl / ketene dimers, does not increase the affinity of the paper for the extruded polyolefin and does not increase the excess on the surface. In the case of quantity, the affinity can be reduced rather.

The sizing efficacy of the cut angle on the developer is determined by the resistance to the alkaline components contained therein which, when wetting the fiber, causes its swelling, as well as the alcoholic surface activity contained therein, which promotes such undesired wetting. It is measured by the resistance to the agent. It must have good wetting suppression, must be alkali resistant up to a pH of about 10, and finally have sufficient affinity for the extruded polyolefin on both sides of the substrate paper to fix the film. Must have. The method according to the invention fulfills this condition in a surprising way.

Examples Example 1 Photographic base papers sized with an alkyl / ketene dimer in the material in the neutral range and polyamino-epichlorohydrin as retentive material and having a plane weight of 170 g / m ² were listed below on a sizing machine of a paper machine. It was impregnated with the substance of an aqueous solution or dispersion, dried and coated by extrusion at 290 ° C. with 30 g / m ² per side of polyethylene. Conventional radiation in a corona discharge was applied to this experimental series due to paper adhesion prior to application of polyethylene.

After this treatment method, the polyethylene layer was adhered to the paper surface by cutting a polyethylene strip with a width of 1 cm each for 4 minutes and 10 minutes after extrusion under the same conditions with a knife by hand and then by hand. The test was carried out by cutting out a length of about 20 cm in the traveling direction. The cut-out is visually determined by the amount of fiber torn from the paper with polyethylene strips, number 1
Add ~ 5. In this case, the number 1 represents the complete splitting of the paper and the number 5 represents the fiberless release of the polyethylene film. Numbers 2-4 represent intermediate stages due to fiber tear thickness and uniformity.

Various measurements of the force that must be taken when removing a strip of polyethylene from a paper surface described in the literature are:
It merely indicates the bond strength or split strength of the paper, not the adhesion that exists between the paper and the polyethylene layer. The bond strength between the polyethylene and the paper must be greater than the bond strength of the fibers in order to fulfill the above-mentioned purpose of use, because the bond strength of the substrate paper is totally different depending on the type of cellulose used and its grinding. . This gives a clear attachment of the bond, which is not dependent on the bond strength of the paper, by the test method of visual judgment of tearing of polyethylene.

The solution for coating the surface is prepared according to the invention as follows in order to eliminate the precipitate and obtain a stable dispersion: Individual components, such as starch, polyvinyl alcohol, electrolytes and optical brighteners. Is added to water sequentially with stirring according to the desired concentration, and completely dissolved. Next, concentrated ammonia was added to the solution to contain 4 to 8 g of ammonia,
Add in an amount to yield 9-10. Ethylene / acrylic acid copolymer is added as final component to the finished solution gradually with vigorous stirring at a concentration of 25% by weight in water, in an amount corresponding to the desired batch. With this addition according to the invention, a stable solution or suspension is obtained without precipitation. With ammonia or alkali
Without pH control, the solution becomes unstable and the individual components aggregate.

The optical brighteners used in the examples are merely from an aesthetic point of view and are not a component that characterizes the solution of the present invention. An optical brightener may or may not be included.

Other alkalis, such as caustic soda solution or potassium carbonate, were also used to adjust the pH of the solution, resulting in comparable stability of the dispersions. Ammonia turned out to be preferred. This is because the impregnated paper evaporates sufficiently when it is dried, which lowers the pH again, which makes the copolymer insoluble in water.

To produce the following solution for this example, it was applied to both sides of the paper with a sizing machine: (1) oxidized starch 5% = 0.85g / m ² (per one side) sodium chloride 2.5% = 0.43g / m ² (one side per) optical brightener 0.2% = 0.035g / m ² (per one side) (2) polyvinyl alcohol 4% = 0.63g / m ² (per one side) sodium chloride 2.5% = 0.43g / m ² (per one side) optical brightener 0.2% = 0.035g / m ² (per one side) (3) oxidized starch 1% = 0.17g / m ² (per one side) ethylene / acrylic acid copolymer 2% = 0.34 g / m
² (per one side) sodium chloride 2.5% = 0.43g / m ² (per one side) optical brightener 0.2% = 0.035g / m ² (per one side) of concentrated ammonia 0.5% = 5g / l (solution) (4) Polyvinyl alcohol 1% = 0.17g / m ² (per side) Ethylene / acrylic acid copolymer 2% = 0.34g / m
² (per one side) sodium chloride 2.5% = 0.43g / m ² (per one side) optical brightener 0.2% = 0.035g / m ² (per one side) of concentrated ammonia 0.5% = 5g / l (solution) (5) Polyvinyl alcohol 0.5% = 0.08g / m ² (per side) Ethylene / acrylic acid copolymer 2% = 0.34g / m
² (per one side) sodium chloride 2.5% == 0.43g / m ² (per one side) optical brightener 0.2% = 0.035g / m ² (per one side) of concentrated ammonia 0.5 = 5 g / l (solution) (6) oxidized starch 1% = 0.17g / m ² (per side) Ethylene / acrylic acid copolymer 2% = 0.34g / m
² (per side) sodium chloride 2.5% = 0.43g / m ² (per one side) optical brightener 0.2% = 0.035g / m ² (per one side) polyamino - 0.4% epichlorohydrin = 0.07 g / m
² (per side) Concentrated ammonia 0.5% = 5g / l (in solution) Results Comparative samples 1 and 2 without corona radiation do not actually give polyethylene deposits, but the samples coated according to the invention show very good polyethylene deposits on the paper surface under the same extrusion conditions. Be done.

Example 2 Neutral sizing of substrate paper.

To a commercially available pulverized cellulose mixture used for photographic paper, a solution of ethylene / acrylic acid copolymer and starch ester at a material density of 5% and a ratio of 1: 1 was added with 5 g of concentrated ammonia / 0.2% of polyamino-epichlorohydrin.
With vigorous stirring and then pH with dilute sulfuric acid.
Adjusting to 7, the copolymer should be 0.
5% was present. It is then sized in a known manner with 0.5% of alkyl / ketene dimer as hydrophobizing agent and 0.5% of polyamino-epichlorohydrin as retentive agent, and the suspension is laid on a laboratory paper machine at a flat weight of 170 g / m ²
Was used for the paper. Dry paper strip using sizing machine Oxidized starch 1% = 0.17g / m ² (per side) Ethylene / acrylic acid copolymer 1% = 0.17g / m
² solution was applied to (per side) sodium chloride 2.5% = 0.43g / m ² (per one side) optical brightener 0.2% = 0.035g / m ² (per one side) of concentrated ammonia 0.5% = 5g / l (in solution) It is dried and polyethylene is extruded in the usual way, but without corona radiation at 290 ° C.
Each side was coated with 30 g / m ² . Comparative samples were prepared by the same method, but without the addition of ethylene / acrylic acid copolymer and ammonia to the cellulose mixture and acidification with sulfuric acid, but with the same surface coating.

Again, it was confirmed that there was sufficient deposition of polyethylene without corona radiation. However, the additional sizing with ethylene / acrylic acid copolymers still enhances the hydrophobization of the substrate paper against the penetration of developer into the corners of the polyethylene coated photographic image support, and the paper surface coated according to the invention. Does not impair the adhesion of polyethylene to the.

Example 3 Acid stearate sizing.

As in Example 2, in the same ground cellulose mixture, a solution of ethylene / acrylic acid copolymer and starch ester in a 1: 1 ratio with a material density of 5% and 5 g of concentrated ammonia /
As well, 0.2% of polyamino-epichlorohydrin was added with vigorous stirring, and then pH 7 was adjusted with sulfuric acid, again 0.5% of copolymer was present on the fiber. To this mixture, add sodium stearate in the usual way.
1.3% was added and aluminum sulfate was added at pH 4.5 to precipitate stearic acid on the fibers. After dilution, polyamino-epichlorohydrin still as a moisture-proofing agent and a retention agent.
5% was added and a paper with a plane weight of 170 g / m ² was produced on a laboratory paper machine and dried.

A sizing machine was applied to the dried strip of paper with the solution as in Example 2, the paper was dried and polyethylene was conventionally applied by extrusion at 290 ° C. without corona radiation on both sides.

Comparative sample 2 was prepared by the same method, but without the addition of ethylene / acrylic acid copolymer, starch ester and ammonia to the cellulose mixture, but with the same surface coating.

This comparison is also clearly related to the improved adhesion of the extruded polyethylene film to the surface of the substrate paper precoated with the ethylene / acrylic acid copolymer according to the invention,
Figure 4 shows the advantages of sizing the material with the ethylene / acrylic acid copolymer according to the invention in combination with the sizing of stearic acid in acidic medium for the enhancement of hydrophobization against developer penetration into the cutting angle of the photographic paper support.

Claims (10)

[Claims] 1. A method for producing a layer support for photographic paper, comprising a polyolefin coating on both sides, wherein a substrate paper is treated with a polymer aqueous dispersion prior to application of the polyolefin, the aqueous dispersion having a pH of 8.5-10. A method for producing a layer support for photographic paper, characterized in that it comprises an ethylene / acrylic acid copolymer, an electrolyte and a binder and the dispersion is applied to both sides of a paper which has been previously made hydrophobic. 2. An aqueous dispersion having a pH of 8.5 to 10 and containing an ethylene / acrylic acid copolymer, an electrolyte, a binder and an optical brightener, the dispersion being pre-hydrophobicized on both sides of a paper. The method according to claim 1, wherein the coating is performed. 3. The ethylene / acrylic acid copolymer has a proportion of acrylic acid of 15 to 25% by weight, preferably 18 to 2.
A method according to claim 1 or 2 having 2% by weight. 4. The method according to claim 1 or 2, wherein the surface of the paper is coated with an amount of 0.1 to 1.8 g / m ² of ethylene / acrylic acid copolymer per side. 5. A simple salt, preferably N, after adjusting the pH to 8.5-10 with a caustic soda solution or ammonia in the coating solution.
The method according to claim 1 or 2, wherein aCl or Na ₂ SO ₄ is contained at a concentration of 10 to 50 g /. 6. The method according to claim 1 or 2, wherein the binder comprises a group of starch, starch derivative or polyvinyl alcohol and is contained at a concentration of 0.5 to 5%. 7. The method according to claim 1 or 2, wherein the coating solution contains a polyamino-epichlorohydrin resin at a concentration of 0.1 to 5%. 8. An optical brightener having a concentration of 0.05 in the coating solution.
The method of claim 2, wherein the method is included at ˜0.5%. 9. Ethylene / acrylic acid copolymer is adjusted to pH 9 with ammonia, and the fibers of the crushed paper have a density range of 4 to 6% of the material and a proportion of 0.3 to 1.5% by weight with respect to the fibers and polyamino acid. -Mixing 0.05-0.5% by weight of epichlorohydrin, acidifying with mineral acid or aluminum sulphate and precipitating on the fiber, adding 0.1-1.0% by weight of a holding agent to make the material hydrophobic, then forming the paper, Further processing,
The method according to any one of claims 1 to 8. 10. A method according to claim 9 wherein the ethylene / acrylic acid copolymer polymer solution added to the paper material contains up to a 1: 1 ratio of starch, starch derivative or polyvinyl alcohol.