EP0176656B1 - Support material for black and white and colour photography - Google Patents

Abstract

Described is a photographic support material for black-and-white and color photographic emulsions, which support material is coated at least on one side with a layer containing a white pigment ad a binder component that predominantly includes unsaturated organic compounds and that is hardened by means of high energy radiation, while the white pigment, which is preferably a titanium oxide or titanium mixed oxide, carries an inorganic surface deposit which consists of oxides or hydrated oxides that make up at least about 2% by weight of the total pigment. The oxides and hydrated oxides include those of aluminum, silicon, zinc, magnesium, tin, zirconium, antimony or alkaline-earth metals.

Description

The invention relates to a carrier material for black / white and color photographic layers which contains at least one coating hardened by means of electron beams.

A variety of substrates for photographic layers are known. The most common media include film materials and papers. Papers are usually additionally coated. Waterproof papers coated in particular with synthetic resin layers have found wide use as supports for photographic layers. Resin films and laminates coated with special layers are also known. Papers coated on both sides with polyolefin resin and film materials coated with pigmented layers (DAS 14 47 815, US 38 33 380, US 36 30 742, US 39 28 037) were most widespread. However, such coatings only have a limited pigment absorption, are not scratch-resistant and are unsuitable for thermal image development.

More recently, particularly advanced paper supports have been described in DAS 30 22 451, DAS 30 22 709 and GB-A 2 078 236, which consist of base paper with at least one coating produced in situ with the aid of electron beam curing. The advantages of a coating hardened with electron beams are its scratch resistance, the high pigment absorption capacity and the higher surface smoothness compared to polyolefin coatings.

Resin coatings are not only resistant to water, but also to acidic and alkaline photographic process solutions and thus prevent these solutions from penetrating into any underlying paper. As a result, the time-consuming washing process for paper or nonwoven base is significantly shortened.

All resin coatings, whether on paper or on film, can contain pigments, dyes, optical brighteners, image stabilizers, antioxidants or other additives, insofar as this is desirable or necessary in view of the desired properties of an overlay photographic image. Of the possible additives, pigments and dyes are of the greatest importance for the visual impression of a photographic image on the coating. They determine the color character of color images and are decisive for the sharpness of the photographic images.

After suitable pretreatment of the resin surface, the photographic layers are applied to the surface of the resin layer either directly or after previously applying an adhesion-promoting intermediate layer. These photographic layers are preferably layers which are known under the term silver salt photography and which are used either to produce black / white or color images.

Resin coatings hardened with electron beams in accordance with DOS 30 22 451 or DOS 30 22 709 are produced by applying a flowable mixture to the surface of a paper or other base support, distributing it uniformly there and then solidifying it with high-energy electron beams under a protective gas or other covering. The mixtures contain as a crucial component at least one substance with ethylenically unsaturated double bonds, which have the ability to polymerize with one another when this is initiated by radiation.

The layers hardened with electron beams now have many advantages compared to polyolefin layers, but so far they have also had disadvantages. Despite the wide range of variations in the composition of radiation-hardened layers, it was not possible to create a layer that showed equally good behavior in all photographic process solutions. Rather, it was found that the layers hardened with electron beams behave differently towards different process solutions. There are commercially available color developer preparations which, in combination with subsequent exposure to oxygen, lead to a yellowish discoloration of the surface of the radiation-hardened layer. This discoloration is slight, but clearly visible and can neither be prevented by the stop bath, nor by thorough washing. It occurs especially when using photographic developer solutions containing an aromatic amine derivative (e.g. derivatives of phenylenediamine, toluidine, etc.). As a result, the use of radiation-hardened-coated papers has so far been limited to processes in which other chemicals are used for image development, e.g. Hydroquinone.

This yellowing by color developers does not occur with polyolefin surfaces which contain rutile or anatase or another white pigment, nor is it observed on classic baryta papers which have at least one coating consisting essentially of barium sulfate and gelatin. Also other coatings consisting of different synthetic resins and white pigment do not show this staining, while previously described radiation-hardened coatings based on acrylates, methacrylates or allyl compounds are always visibly colored with color developers. Decisive for the discoloration with developer therefore seems to be the proportion of binder, especially a possible presence of unsaturated organic compounds.

The discoloration of radiation-hardened coatings with color developer is evident both with pigment-free coatings and with coatings that contain white pigment. As a rule, the discoloration is even stronger with pigment-containing coatings than with pigment-free coatings, as shown in Table 1 below. (The binder used here consisted of 62% by weight of polyester tetraacrylate, 22.5% by weight of glycerol propoxitriacrylate and 15.5% by weight of hexanediol diacrylate).

DE-A-34 15 215 has already shown a way of obtaining layers with reduced staining by means of the special composition of the curable components of a coating mixture. The process described there is based on the fact that unsaturated hydroxyl-functional compounds are contained in the coating mixtures in a molar concentration of 2 or more than 2.

The technical teaching from DE-A-34 15 215 is basically applicable to both pigment-free and pigmented coating mixtures. However, pigment-containing coating mixtures usually stain somewhat more strongly than pigment-free coatings. Therefore, the OH concentration in pigmented coatings should generally be a little higher than in comparable pigment-free coatings.

A disadvantage of this solution given in DE-A-34 15 215, however, is the severe limitation in the selection of the mixture components that can be used. This disadvantage is particularly noticeable in the case of layers with a higher pigmentation which, in order to avoid undesirable brittleness with an increasing pigment content, require an increasing amount of flexibilizing additives.

It is therefore an object of the present invention to provide a radiation-hardened coating layer which enables the coated carrier to be used in as many ways as possible and in particular shows little or no staining even after customary treatment with commercially available color developers.

This object is achieved in that a titanium dioxide is used as the white pigment which bears an inorganic surface coating which makes up at least 2% by weight of the total pigment.

Titanium dioxide pigments used in coating layers can be untreated like the Ti0 ₂ (rutile 2) contained in Table 1. In many cases, however, they are surface-treated to improve dispersibility with inorganic oxides (Al ₂ O ₃ , AIO (OH), SiO ₂ , ZnO, etc.), ie coated. Oxides in the broader sense are also understood to mean oxide hydrates. Such surface-coated types are, for example, the Ti0 ₂ (anatase) and Ti0 ₂ (rutile 1) contained in Table 1, which are coated with 0.6 and 1.0% by weight Al oxide, and like the other white pigments in Table 1 lead to increased discoloration with color developers.

Even the use of such titanium dioxides, which are treated alone or in addition to the inorganic surface covering with organic substances, does not lead to a reduction in the coloration with color developer, unless at the same time OH-containing compounds according to DE-A-34 15 215 are present.

Surprisingly, however, the discoloration with color developer is significantly less if a titanium dioxide is used which is surface-coated with 2% by weight or more than 2% by weight of an inorganic oxide or hydrated oxide. The inorganic oxide or hydrated oxide can be an aluminum oxide or silica or zinc oxide or magnesium oxide or tin oxide or zirconium oxide or antimony oxide or one of the alkaline earth metal oxides or mixtures of such compounds. Due to the surface coverage, the titanium dioxide particles are provided with a more or less closed coating of foreign oxide or oxide hydrate. The coating can consist of one or more layers and contain other oxides in addition to those mentioned, provided that these are not coloring.

Titanium dioxide pigments coated in this way can be produced by any process. They can also exist as mixed oxides with another white oxide under the surface coverage, and they can additionally be treated in any way with organic compounds. It is crucial that the pigment particles contain a sufficiently strong coating of an inorganic oxide or hydrated oxide other than Ti0 ₂ .

Surface coatings with titanium dioxide pigment with various inorganic coatings are described in "Titanium" by J. Barksdale (New York, 1966) and in various patents and patent applications. It is also known from Japanese Patent Application Laid-Open No. 57-108849 / 1982 to use titanium dioxide aftertreated with 0.2 to 1.2% by weight of aluminum oxide hydrate in polyolefin coatings on photographic papers.

"Patent Abstracts of Japan, Vol. 1, No. 103, p. 3238 E77" describes recording materials which contain titanium dioxide pigment in non-hardening binders, which surface covers with 0.5-5% by weight aluminum and / or silicon oxide is. This surface coating serves both to improve the adhesion on the base paper and to improve the adhesion of emulsion layers applied later.

However, it is surprising and not described that titanium dioxide pigments, which are coated with 2 or more% by weight of any white oxides or hydrated oxides, have a particularly advantageous effect in the radiation-hardened coating mixtures on the coloring of the hardened coating layer with photographic color developer. This is all the more surprising since the corresponding oxides and hydrated oxides lead to increased discoloration even when used alone in radiation-hardened layers (see Table 1).

The advantages of using titanium dioxide pigments with 2 or more% by weight of other oxide or oxide hydrate coatings in radiation-hardened layers according to the invention can be seen both in layers which are hardened by means of electron beams and in layers of unsaturated starting component hardened in another way. The coating layers can be on paper, film, metal foil, paper laminate or any other support and contain known other additives.

In a special embodiment of the invention, titanium dioxide pigment is used, the surface covering of which consists largely or even predominantly of silica. In addition, a small proportion of an aluminum oxide and / or zinc oxide and / or antimony oxide and / or zirconium oxide and / or alkaline earth metal oxide can be present. It is of minor importance whether the coating of the Ti0 _{2 is} more or less closed. The degree of occupancy is obviously decisive.

An additional organic surface covering e.g. with polyhydric alcohol, (poly) siloxane, organic titanates, organophosphates, lactone, amino compounds etc. Substances which generally serve to improve the dispersibility are possible and also have their known advantages in the case of the titanium dioxide pigments coated with inorganic oxides.

Titanium dioxide pigment in the sense of the invention is not only to be understood to mean the known Ti0 ₂ modifications rutile and anatase, but also other pure or mixed titanium oxides and white pigment-like titanates.

It can be particularly advantageous if titanium dioxide surface-coated with at least 2% by weight of foreign oxide is used in a hardenable mixture which contains hydroxyl-functional unsaturated substances. The particular advantage of this combination lies in the fact that the molar concentration of the OH groups in the mixture can be less than 2 and still layers are obtained which show no visible coloring with color developer.

The invention has a particularly advantageous effect if the substances curable by electron beams are mixtures which contain at least one substance which contains two or more double bonds. In addition, non-reactive substances without double bonds can also be contained in a mixture to a limited extent.

Substances containing acrylate or methacrylate groups are primarily used as reactive components. However, esters of maleic acid, fumaric acid, mesaconic acid, citraconic acid or itaconic acid, other derivatives of these acids, allyl compounds and linear and cyclic dienes or trienes are also suitable as reactive mixture components. Those esters of the acids mentioned which are derived from polyhydric alcohols are preferred. Examples are hexanediol diacrylate, trimethylolpropane triacrylate, polyester acrylates, polyurethane acrylates, polyether acrylates, polyepoxy diacrylates, alkyd resin acrylates or the methacrylates corresponding to the acrylates mentioned.

The flow properties of such curable mixtures are adjusted according to the invention by mixing constituents of higher molecular weight with low molecular weight substances. The hardness and flexibility of the hardened layers is determined by the ratio of double bonds to the molecular size in the starting material and can be varied widely by mixing different substances.

Support materials according to the invention are suitable as supports for all known photographic layers containing at least one silver compound. In particular, they are suitable for all types of wet development processes as well as for thermal image development processes.

The concept of the invention is explained in more detail with the following examples.

example 1

A mixture of 62 wt .-% polyester tetraacrylate (average molecular weight = _c a. 1000), 22.5 wt% and 15.5 wt .-% Glycerinpropoxitriacrylat hexanediol diacrylate was added to a hand without added pigment and secondly with the addition of 20 wt .-% Titanium dioxide pigment with 2 or more wt .-% inorganic surface coating evenly brought onto a polyethylene / paper laminate and by means of Hardened electron beams. The hardened coating had a thickness of approximately 20 pm.

The layer coatings were then treated with commercially available photographic developer for color paper, washed and the samples were stored for four days at room temperature with access to air. The discoloration of the layer surface that occurred during storage was determined according to DIN 4512 as a change in the optical density compared to the initial value and is listed in Table 2.

This series shows that the discoloration of the layer can be reduced by titanium oxide pigments with 2% by weight and more than 2% by weight of foreign oxide coating. Experiment 1a serves as a comparison, and the remaining experiments show the decrease in discoloration with increasing occupancy.

Example 2

A basic mixture of 50% by weight tripropylene glycol diacrylate, 45% by weight trimethylolpropane triacrylate and 5% by weight glycidil methacrylate was placed on a photographic base paper on the one hand without the addition of pigment (2a) and on the other hand with the addition of 30% by weight of titanium oxide pigment (2b), leveled to a thickness of approx. 35 pm with the aid of a doctor rod and hardened in a known manner by means of electron beams.

The layer coatings were treated with color developer as in Example 1 and the discoloration was determined. The results are summarized in Table 3.

This series also confirms that the color discoloration caused by color developers is reduced by those titanium oxide pigments which contain at least 2% by weight of a foreign oxide coating. Even in the case of a layer which strongly stains as a result of the addition of glycidyl methacrylate, the discoloration can be reduced so much by covering the titanium oxide surface to such an extent that the layer appears almost white (tests 2h and 2p). It is crucial in the context of the invention that the turning point with regard to the discoloration is an occupancy of 2% by weight.

Example 3

A basic mixture of 45% by weight of pentaerythritol triacrylate, 50% by weight of triethylene glycol diacrylate and 5% by weight of hydroxyethyl acrylate was uniformly applied to a polyethylene on the one hand without pigment addition and on the other hand with the addition of 40% by weight of different titanium oxide pigments / Paper laminate brought and cured by means of electron beams. The hardened coating had a thickness of approx. 20 pm each. The OH molality of the basic mixture is 2.

The layers were tested as in Example 1. The test results are summarized in Table 4.

This series of experiments, in which hydroxyl-functional curable components were used, also confirms the advantage of using titanium oxides with a foreign oxide content of at least 2% by weight. At the same time, this series demonstrates the special advantages of combining hydroxy-functional curable materials together with an externally coated titanium oxide with at least 2% coating.

Claims (10)

1. Photographic carrier material for coatings for black-and-white and coloured photography, which is coated on at least one side with a coating containing a white pigment and in which the white pigment contains a surface coating and the binder component of which is produced predominantly from unsaturated compounds and hardened by means of energy-supplying radiation, characterised in that as white pigment a pigment is used which carries an inorganic surface covering which amounts to at least 2% wt. of the total pigment.

2. Carrier material according to claim 1, characterised in that the inorganic surface covering amounts to 3 to 20% wt. of the total pigment.

3. Carrier material according to claim 1, characterised in that the white pigment is a titanium dioxide or titanium mixed oxide or a white pigment-type titanate.

4. Carrier material according to claim 1, characterised in that the inorganic surface covering of the white pigment particles consists of an oxide or oxyhydrate of aluminium, silicon, tin, zirconium, antimony, or the alkaline earth metals, or of mixtures of these oxides and oxyhydrates.

5. Carrier material according to claims 1 to 3, characterised in that the titanium oxide surface coated with at least 2% wt. of foreign oxide is worked into a hardenable binder component which contains unsaturated substances with hydroxy-functional groups.

6. Carrier material according to claims 1 to 4, characterised in that the particles of the white pigment have a covering consisting predominantly of silicic acid.

7. Carrier material according to claim 5, characterised in that the titanium dioxide particles are provided with a surface coating which consists predominantly of silicic acid and small proportions of an aluminium oxide and/or antimony oxide and/or zirconium oxide and/or alkaline earth metal oxide.

8. Carrier material according to claims 1 to 6, characterised in that the binder component in which the white pigment is dispersed contains at least one substance which contains two or more double bonds.

9. Use of a carrier material according to claim 1 as carrier for photographic layers which contain at least one inorganic or organic silver compound.

10. Use of a carrier material according to claim 1 as carrier for coatings for black-and-white or colour photography, which can be developed by the action of heat.