EP0114973A2 - Water-proof photographic paper - Google Patents

Abstract

A multilayer, waterproof photographic paper support is described, the paper support being coated with a lacquer layer made of a radiation-hardened lacquer and a further barrier layer being arranged between the paper and lacquer layer, which consists of a polymeric, film-forming material or of an extrusion coating or an application of an aqueous solution or an aqueous dispersion.

Description

The invention relates to a multilayer waterproof photographic paper support with very high _O berflä- chenebenheit and good photographic properties and a method for its production.

Water-proof coated photographic paper supports are known in various embodiments. DE-AS 14 47 815 describes a paper support for photosensitive layers coated on both sides with polyolefin resin. DE-OS 30 22 451 describes a paper support which is coated on both sides with lacquer layers hardened by electron beams. DE-OS 30 22 709 finally describes a paper carrier coated with curable mixtures, in which a coating is cured in contact with a shaping surface, and which is consequently distinguished by high flatness of the surface. The new waterproof lacquer coatings hardened by electron beams described in DE-OS 30 22 451 and DE-OS 30 22 709 are above all more scratch-resistant than the polyolefin coatings according to DE-AS 14 47 815 which have been customary to date. In addition, there is the possibility of higher pigmentation which results in better image sharpness in supervisory images, and the improvement of the surface structure according to DE-OS 30 22 709 contributes decisively to the fact that thinner photographic layers can be applied evenly. This also results in an improvement in the image quality.

A disadvantage of backing materials with radiation-hardened coatings has hitherto been that with normal storage of the photographic products there is a slight shift in the sensitivity of the photographic layers and a measurable haze occurs during longer storage times. This disadvantage becomes noticeable after a few months of storage.

So far it is unclear why the storage stability is not guaranteed, because the starting materials have no measurable influence on the photographic layers. It is assumed that a photochemically active low molecular monomer or impurity by diffusion gets into the photographic layers and reacts there after it has only become photochemically active due to the radiation. Such low molecular weight monomers are contained in the hardenable or unhardened layer.

In order to counter this disadvantage, the layer hardened by electron beams according to DE-OS 30 46 130 was covered with an additional polyolefin layer. As a result, it was possible to ensure a storage stability of several months while maintaining the good surface characteristics of the support and to obtain a product that was usable under normal conditions. As a disadvantage, a reduction in sharpness due to the polyolefin coverage had to be accepted. The scratch sensitivity of the polyolefin surface is again disadvantageous in this embodiment. It also increases the durability of the photographic material limited by the polyolefin, which, in terms of its aging resistance, lags significantly behind the classic photo substrates with baryta layers.

It is therefore an object of the present invention to provide a waterproof and scratch-resistant photographic support element with high durability, which not only has a stable, consistently flat surface, but also has no influence on the sensitivity of overlying photographic layers after long periods of storage and has no disturbing haze in the photographic layers.

This object is achieved by the features characterized in the claims.

The paper support is asispapier of a fully sized _B, which is covered with radiation-hardened lacquer layer. At least one barrier layer is arranged between the paper and the lacquer layer. The base paper preferably consists of fiber pulp or synthetic fibers or other constituents, also in a mixture, it is hydrophobized and equipped with other customary glues and strengthening agents. The barrier layer lies on the base paper and is described in detail below.

The permeability of the barrier layer for acrylate monomer is expediently so low that more than 100 seconds are required when testing with the Hercules sizing tester until the remission has dropped to 70%.

According to the invention, the barrier layer can be on below can be made in different ways from different materials.

It should only be noted that the permeability for an acrylate monomer does not fall significantly below the stated value of 100 seconds, and that the layer contains only minimal amounts of free wetting agent, preferably no free wetting agent.

In a particular embodiment, the barrier layer consists of a polyolefin film which has been applied by extrusion coating. The thickness of the layer in this case is 5 to 30 μm, preferably 7 to 20 μm. The polyolefin is, for example, polypropylene or polyethylene or an ionomer resin or another ethylene copolymer resin. However, the barrier layer can also consist of a mixture of the thermoplastic resins mentioned with one another or with other thermoplastic resins. The front side barrier layer preferably contains pigments.

In a further embodiment, the barrier layer is applied as an aqueous solution of a water-soluble film-forming polymer and dried. Suitable water-soluble polymers are, for example, polyvinyl alcohols, film-forming starch derivatives, film-forming cellulose derivatives, copolymers or acrylic acid with other vinyl monomers, alginates, casein, polyacrylamide, polystyrene sulfonate or mixtures of these polymers with one another or with other substances dissolved or dispersed in water. The thickness of the dried barrier layer is each depending on the type of polymer between 3 and 30 µ.

In a third embodiment, the barrier layer is produced from the aqueous dispersion of a water-insoluble polymer or from a mixture of such a polymer dispersion with a water-soluble binder dissolved in water. Suitable polymer dispersions are dispersions of ethylene polymers and copolymers, acrylate or methacrylate polymers and copolymers, vinyl acetate copolymers and mixtures of such polymer dispersions with one another which are film-forming at the drying temperatures customary in the paper machine or in the coating machine. The thickness of the dried barrier layer is between 4 and 30 μ when produced from an aqueous dispersion.

In principle, the barrier layer can contain all the usual additives and auxiliaries such as pigments, dyes, brighteners, plasticizers, electrolytes and others. The only exception is the use of larger amounts of free wetting agents. Specifically, this means that the surface tension of an aqueous coating mixture is preferably not less than 55 dynes. cm ^-1 should be. In particular, nonionic wetting agents in the barrier layer should be avoided as far as possible.

Either directly or after an adhesion-improving pretreatment, an electron beam curable layer is applied to the water-free barrier layer Mixture drawn up and solidified by the action of electron beams. Conventional photographic layers based on photocatalytic redox systems, for example silver salts, are applied to this layer hardened by means of electron beams, optionally also after applying an adhesive layer.

In addition to the binder, the coating solidified by means of electron beams preferably contains pigments and optionally small amounts of dyes and / or other additives. A coating has a basis weight of about 10 to 60 g / m ² (preferably 15 to 40 g / m ² ).

The curable mixture is applied using one of the known coating methods, leveled and, after being covered with a protective gas, cured by means of electron beams. However, according to DE-OS 30 22 709, it can also be pressed against a shaping surface after application and then solidified by means of electron beams through paper and barrier layers without the use of a protective gas. Finally, the two-sided layers according to DE-OS 30 22 709 can also be applied in one operation and solidified at the same time.

The binder of the layer which can be hardened by electron beams essentially consists of substances which, before hardening, contain c = _c double bonds, for example in the form of acrylate or methacrylate groups.

It can also contain smaller proportions of non-curable polymeric, oligomeric or low molecular weight substances, provided that such additives are useful for improving certain properties and do not fundamentally change the character of a mixture that is hardened by electron beams. Preferred pigments in a layer to be hardened by means of electron beams are white pigments, e.g. Titanium oxide, zirconium oxide, zinc oxide, zinc sulfide, antimony oxide, barium sulfate, calcium carbonate. Color pigments, carbon black or soluble dyes can also be contained in the layer for special purposes or for taste considerations. However, the layer can also be transparent.

In general, the back of the paper of the multi-layer carrier material produced according to the invention is also coated with a barrier layer and a hardenable layer and optionally further layers. However, the single-sided multilayer structure according to the invention is sufficient for simple applications.

One or more photographic layers based on silver salt emulsions for black / white or color photography are arranged over the front layer hardened by electron beams, optionally after applying a further intermediate layer.

For a better understanding of the structure of the carrier material according to the invention, different embodiments are shown in cross-section in FIGS. 1-3. In the drawings, 1 denotes the photographic layer, which in turn can consist of several layers. 2 designates an optional _Y- promoting intermediate layer, 3 designates the front layer which is solidified by means of electron beams and preferably contains pigment, 4 designates the front blocking layer, 5 designates the photographic base paper with a hydrophobizing inner sizing and / or optionally a surface sizing, 6 designates the back barrier layer, 7 denotes another electron beam-cured layer, and 8 designates a weiterefunkti ^tionally e _R e _i-ckse tenschicht.

The invention is now explained in more detail with reference to the following examples.

example 1

A photographic base paper weighing approx. 80 g / m ² , which is glued on the inside with alkyl ketene dimer and polyamide epichlorohydrin resin and which has been given a surface sizing from anionic starch with NaCl, is coated on both sides by means of extrusion coating with approx. 12 g / m ^{2 of} a polyethylene mixture. The polyethylene mixture contains approximately 10% by weight of titanium dioxide and 0.2% by weight of cobalt violet pigment.

It has been shown that the type, the thickness or the molecular weight or any blends with other thermoplastic substances have no influence have the blocking effect. Polyethylene represents all extrudable thermoplastic polymers.

Parts of the thus pre-coated paper are then respectively, according to the coated after corona treatment of the Polyäthylenoberflächen on both sides in the DE-OS No. 30 22 709 with 25 g / m ² of radiation-curable mixtures of these and solidified by means of electron beams. The coating on one side is solidified through the paper in contact with a high-gloss cylinder, and the coating on the opposite side after leveling is solidified under nitrogen as a protective gas. The solidification takes place by means of electron beams with an energy dose of 40 J / g.

The curable mixtures used in the different samples of the example were composed as follows:

Example 2

A photographic base paper weighing approximately 110 g / m ² and sized as in Example 1 is coated on both sides by means of a doctor blade with a mixture of the following composition and dried:

The dried barrier coating has a weight per unit area of approximately 15 g / m ² . It is smoothed with the aid of a calendering device and, according to Example 1, recipe F, is coated on both sides with 20 g / m ^{2 of} a layer hardened by electron beams.

Example 3

An approx. 100 g / m ² heavy photographic base paper as sized in Example 1 is coated on both sides in a paper machine with the aid of a Twinblade coating device with a solution of the following composition:

The barrier coating obtained after drying and smoothing has a weight per unit area of approximately 7 g / m ² . The paper precoated in this way is then coated on both sides with 30 g / m ^{2 of} a layer hardened by electron beams in accordance with Example 1, recipe F.

Example 4

A photographic base paper weighing approximately 100 g / m ² and sized as in Example 1 is coated on one side with a mixture of the following composition:

After drying, the layer application is approx. 10 g / m ² . The dried layer is smoothed by means of a warmed calender and with about 20 g / m ² of a curable mixture formulation F coated according to Example 1, ochglanzzylinder pressed against a _H and from the uncoated paper side by means of electron beams with an energy dose of 40 J / g solidified.

Example 5

A photographic base paper weighing approx. 70 g / m ² , which is sized with epoxidized difatty acid amide (R = C ₁₄ or greater), starch / polyacrylamide and aluminum stearate, is coated on both sides in the size press of the paper machine with a mixture of the following composition:

After drying and smoothing, the layer application is approximately 6 g / m ² per side.

The pre-coated paper is 25 g / m ^{2 of} a curable mixture corresponding to formulation F from Example 1, the uncured mixture pressed against a high-gloss cylinder and solidified from the uncoated paper side by means of electron beams at 40 J / g. Then the opposite side is coated with about 25 g / m ^{2 of} a curable mixture, which has the following composition:

The layer is solidified under nitrogen by means of electron beams with an energy dose of 30 J / g and forms the back of the photographic support.

Example 6

A photographic base paper weighing approx. 170 g / m ² , which is sized with alkyl ketene dimer, aluminum stearate, gelatin and polyamide epichlorohydrin resin, is coated on both sides with a coating mixture which has the following composition:

After drying, the weight per unit area of the barrier layer is approx. 25 g / m ² . The precoated paper is smoothed and, according to Example 1, recipe F, coated on one side with about 15 g / m ^{2 of} a curable mixture. The mixture is pressed against a high-gloss cylinder and solidified from the back by means of electron beams at 50 J / g.

Comparative examples

As comparisons 7-12, the base papers used in Examples 1-6 were coated directly with the radiation-curable mixtures given in the examples without prior application of the barrier layers. The coating weight was increased by the amount that makes up half the barrier layer. As in the associated examples, the coatings were solidified by means of electron beams with the energy dose given in the examples.

A comparative example 13 was taken from a photographic carrier paper coated on both sides with polyethylene as standard, which according to comparative example A from DOS 30 22 451 on the front side with a 15/85 titanium dioxide / polyethylene mixture and was coated on the back with a non-pigmented polyethylene layer.

Examination of the carrier materials

The effect of the barrier layers was determined with the Hercules sizing tester using hexanediol diacrylate ( _H DDA) as test equipment. The device and its function are described in the leaflet "Hercules - Glue Level Tester" from Hercules NV. The Hague (Holland). These tests were carried out on the papers before the curable coating was applied

The effect of the barrier layers on fog and sensitivity of the photographic layers was determined in two ways. First, the pattern coated with radiation-hardened layers examples and comparative examples as well as samples of the associated _B were asispapiere each between two sheets of commercially available photographic Bromsilberpapiers set and so in the dark for four days at 60 ° C and 80% relative humidity stored. In this contact bearing test, the sheets were exposed to a pressure load of approximately 300 g / m ² . After the 4-day contact test had ended, the test specimens were removed and the photographic papers that had been in contact with the test specimens were exposed and developed to a medium shade of gray, and the areas that had been in contact with the test specimens were compared with the surrounding areas. A possibly existing ne deviation in the shade of gray was assessed and graded on a 6-point scale. Here means:

A deviation from the comparison gray tone always showed itself as sensitization (= darker).

In the second photographic test, the papers coated with radiation-hardened layers were coated with a conventional fine-grained black and white silver halide emulsion layer with high resolution after corona treatment of the surface.

Parts of the light-sensitive papers produced in this way were packed light-tight and stored for one year at room temperature. Then they were developed as standard and the respective veil was measured with the densitometer. The measured values obtained are summarized in Table 1 with the other test data.

Other parts of the photosensitive papers prepared as described were imagewise exposed through a test negative and developed and fixed in a conventional manner.

The test negative used was a line grid, which was made in the form of a gradient wedge. From the different course of the optical density over the gradient wedge, the line grid copied on enables a comparative statement about the sharpness performance of the different samples. The relative sharpness figures are also shown in Table 1. All values are based on the sample with the relatively highest sharpness. (di example 1 F = 100%).

Further refinements of the invention are possible. In a variant, the mixture curable by means of electron beams can be used to increase the whiteness in addition to white pigment and optionally color pigment, an optical brightener, e.g. of the aminocoumarin type, as marketed by ACC under the name "Calcofluor White RW", can be added. It is also possible to color the base paper and to coat one side of the paper with a layer containing carbon black while the other is coated with a white layer.

In a special embodiment, it is also possible to apply an aqueous barrier layer and to coat it with the radiation-curable mixture without intermediate drying. Surprisingly, the curable mixture can also be cured without adverse side effects, while the water is first absorbed by the base paper and removed from the back after the curing has been carried out.

Papers coated on both sides with water resistance are generally only coated on the side with a barrier layer and an electron beam hardened layer which is intended for coating with light-sensitive layers. The opposite side can be coated in any waterproof manner according to one of the methods described in the literature. All known types of surface design can be practiced, which are required by the use of the papers, ie roughness, Be Writability, antistatic properties and rolling behavior of the papers are preferably controlled via the back coating.

Claims (23)

1. Waterproof, photographic paper support with several layers, the paper support being coated with a lacquer layer made of a radiation-hardened lacquer, characterized in that at least one barrier layer is arranged between the paper and the lacquer layer. 2. Paper support according to claim 1, characterized in that the barrier layer is designed so that the permeability for the acrylate monomer does not fall below 100 seconds and the barrier layer preferably contains no free wetting agent. 3. _P apierträger according to claim 1 and 2, characterized in that the barrier layer has a thickness of 2 - 30 u, preferably 4 - 20 u. 4. _P apierträger according to claim 1-3, characterized in that the barrier layer is made a-TERIAL of a polymeric film-forming _M, which is made by extrusion coating or by application of an aqueous solution or an aqueous dispersion. 5. Paper support according to claims 1-4, characterized in that the barrier layer contains pigments, dyes, brighteners, plasticizers, electrolytes and other known additives. In that the barrier layer of white pigments such as titanium dioxide, _Z ircon- oxide containing 6. Paper carrier according to claim 5, characterized in that zinc oxide, zinc sulfide, antimony oxide, barium sulfate and calcium carbonate. 7. Paper support according to claims 1-6, characterized in that the barrier layer consists of a polyolefin or polyolefin copolymer. 8. Paper support according to claims 1-7, characterized in that the barrier layer consists of a (meth) acrylate polymer or copolymer. 9. Paper support according to claims 1-8, characterized in that the barrier layer consists of a film-forming starch derivative with a proportion of a synthetic film-forming polymer. 10. Paper support according to claims 1-9, characterized in that the barrier layer consists of polyvinyl alcohol or a combination with other water-soluble or water-dispersible polymers. 11. A method for producing a multilayer photo- g _ra fishing support material on a paper basis, according to claim ₁ to 10, characterized by the combination of the following process steps: _a ) applying a barrier layer with low permeability to monomeric acrylic acid esters on at least one surface of a base paper, b) coating the barrier layer with a flowable mixture curable by means of electron beams, c) curing the layer arranged over the barrier layer by means of electron beams. 12. The method according to claim 11, characterized by the combination of the following process steps: a) applying a barrier layer with low permeability to monomeric acrylic acid esters on at least one surface of a base paper, b) pretreatment of the surface of the barrier layer in order to improve the adhesion of the subsequently applied curable coating, c) coating the pretreated surface of the barrier layer with a flowable mixture curable by means of electron beams, d) curing the curable layer arranged above the barrier layer by means of electron beams. 13) Method according to claim 11 or 12, characterized in that the barrier layer is produced by means of an extrusion coating process from a thermoplastic resin. 14) Method according to claim 11 or 12, characterized in that the barrier layer is formed by applying an aqueous dispersion of a film-forming substance or mixture of substances with subsequent drying. 15) Method according to claim 11 or 12, characterized in that the barrier layer is formed by applying an aqueous solution of a film-forming substance or mixture of substances. 16) Method according to claim 12 to 15, characterized in that the pretreatment of the surface of the barrier layer is an oxidizing pretreatment. 17) Method according to claim 16, characterized in that the oxidizing pretreatment is a corona treatment. 18) Method according to claim 12 to 15, characterized in that the pretreatment of the surface of the barrier layer is a separate adhesive coating. 19) The method according to claim 11 or 12, characterized in that the curable by electron layer having a _E nergiedosis 5-60 Joule / g is hardened (preferably 20. The method according to claim 11 - 19, characterized in that the surface of the layer hardened by means of electron beams is subjected to an adhesion-improving pretreatment before application of a photographic layer. 21. A method for producing a multi-layer photographic base material on paper, according to claim 11-20, characterized by the combination of the following process steps: a) applying a coating consisting essentially of polyolefin on both surfaces of a base paper, b) oxidizing pretreatment of one of the two polyolefin surfaces, c) coating the pretreated polyolefin surface with a flowable mixture curable by means of electron beams, d) curing the curable layer by means of electron beams. 22. The method according to claim 11 - 21, characterized in that the layer curable by means of electron beams is brought into contact with a shaping surface, then hardened through the paper by means of electron beams and then separated from the shaping surface. 23. The method according to claim 11-21, characterized in that the layer curable by means of electron beams in contact with is brought to a shaping surface, then hardened through the shaping material by means of electron beams and then separated from the shaping surface.

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