EP0507068A1 - Polyolefin coated photographic support - Google Patents

Abstract

The application relates to photographic supports (film bases) having a two-sided coating which is composed at least on one side of a polyolefin mixture and optionally contains further auxiliaries, for example white pigment, which favourably modify the use of the photographic support. To increase the working speed in the production of the support, the polyolefin mixture contains at least one copolymer of an alpha -olefin and an alpha , beta -carboxylic acid, the proportion of the copolymer in the polyolefin mixture being not less than 5 % by weight, preferably 20-80 % by weight.

Description

The invention relates to a photographic support with a two-sided coating which consists of a polyolefin mixture on at least one side and optionally further auxiliaries which have a positive influence on the use of the photographic support, e.g. White pigment, contains.

It is known to coat base papers with thermoplastic synthetic resins and then to use them as layer supports for photographic layers, with water resistance, dimensional stability and economy being the main focus for the manufacturer. Among other things, Coatings are used, which consist of polyolefins and olefin copolymers, which are usually applied by the process of extrusion coating in the melt state on both surfaces of the base paper. The "base paper" of the layer support can also comprise paper-resin mixtures or so-called synthetic papers instead of paper. In the following we speak of "base paper", even if it is not a "paper" in the actual sense.

The base papers to be used for the purpose according to the invention do not differ from those which are usually used for such substrates, for example photo base papers with a basis weight of 170 g / m 2. It is preferably an on paper provided with hydrophobic resin layers (predominantly polyolefin layers) on both surfaces, of which the resin layer closest to the photographic layers usually contains at least one light-reflecting pigment and is thus flatly protected against the ingress of water or photographic processing solutions. At the edges, however, the paper core is unprotected against the penetration of aqueous processing solutions. To prevent this, the base paper is usually hard sized. Both reactive substances such as alkyl ketene dimer and non-reactive substances such as higher fatty acids are known as sizing agents for photographic base papers.

The reactive sizing agents are usually processed in a neutral environment using a cationic resin (neutral sizing). The non-reactive sizing agents are processed in an acidic environment with the addition of aluminum ions.

A combination of both sizing processes is also known (e.g. DE-OS 32 38 865).

The sizing agents with a hydrophobic effect are added to the fiber suspension and deposited on the fiber surface by adding auxiliaries. An example of such an aid in the case of acidic sizing is an aluminum salt; in the case of neutral sizing, this can be a cationic polyamide-polyamine-epichlorohydrin resin. However, other cationic substances such as cationic polyacrylamides, cationized starches or polyethylene imines are also suitable in certain cases for improving the retention of the reactive sizing agents in the paper sheet.

Since the hard sizing of the base paper causes a loss of strength, the paper pulp becomes additional Added substances that improve paper strength, such as polyvinyl alcohol, anionic polyacrylamide and various starch derivatives.

In addition to the internal hydrophobization, the surface of the paper can also be glued by applying high-molecular substances (surface sizing). The high molecular weight compounds that have been used include substances such as e.g. Gelatin, oxidized starch and other starch derivatives, carboxymethyl cellulose, polyvinyl alcohol and others.

The surface of the base paper is treated with an aqueous coating composition, which may contain other additives in addition to the above-mentioned high-molecular substances, such as e.g. optical brighteners, pigments, consumables, etc.

Both types of sizing (internal sizing and surface sizing) have a disadvantageous effect on the adhesion of the polyolefin coating subsequently applied to the sized base paper. As a result, according to the state of the art, only limited working speeds are possible for the extrusion coating, which are generally at most 150-180 m / min.

A water-resistant layer support for light-sensitive, photographic materials is known in which a base paper is coated on one or both sides with polyolefin resin (for example US Pat. No. 3,411,908), and those in which the coating consists of polyolefin mixtures with a copolymer of ethylene and another α -Olefin consists (eg EP-OS 290 852) or consists exclusively of an ionomer resin with pigment content, in which the ionomer resin consists of α-olefins and α, β-unsaturated monocarboxylic acids (DE-OS 15 72 189).

A light-sensitive layer containing silver halide is then applied to one of the synthetic resin layers. The light-sensitive layer can be a black and white as well as a color photography layer. The coating underneath, which is to carry the aforementioned light-sensitive emulsion layer, has special requirements with regard to light reflection, whiteness, smoothness and sensitometric properties. For this reason, this coating may contain auxiliaries, such as white pigment, lubricants, antioxidants, optical brighteners, dispersing aids, antistatic agents and others, which have a positive effect on the use of the photographic support.

The subsequent application of hydrophilic layers, such as gelatin-containing adhesion-promoting layers or light-sensitive layers, and the use of aqueous photographic baths for development and fixation, require the coating to be particularly firmly adhered to the base paper. The cut edges or edges of the photographic layer support are particularly stressed here, since the chemicals of the photographic process can penetrate into the unprotected material. If the adhesion between the coating and the paper surface is insufficient, the substrate delaminates and fringes occur at the cut edges. Developer liquid can also penetrate the base paper at these points and discolor it.

Various measures are known for improving the adhesion of the coating, which mainly consists of polyolefins, to a base paper. For example, increasing the extrusion temperature of the molten polyolefin can increase adhesion. However, extrusion temperatures that are too high have an unfavorable effect, because they make them especially in the presence of titanium dioxide as a white pigment, which is also catalytically active, the degradation of the synthetic resins is accelerated. This decomposition manifests itself on the one hand as yellowing, and on the other hand through the formation of decomposition products which lead to the formation of fog in the photographic layer.

Another measure to improve adhesion is to irradiate the paper web with a corona discharge. For example, in US Pat. Nos. 3,411,908 and 3,501,298, and in British Pat. No. 1,005,631, treatment of the base paper with a corona discharge before coating is proposed in order to improve the binding of the polyolefin to the base paper. However, the corona process has some disadvantages. Corona discharge surface processing requires relatively expensive high voltage equipment. Too much surface treatment has a detrimental effect on the inner sizing of the base paper, as a result of which the resistance of the base paper at its cut edges to penetration of the developer liquid is impaired.

Adhesion can also be improved by using chemical adhesion promoters. These include ethylene / vinyl acetate copolymers, ethylene / acrylamide copolymers, ionomers, terpolymers and the like. The adhesion promoters are applied to the base paper in the form of an adhesive layer (intermediate layer) made of aqueous dispersion. However, the use of such adhesion promoters, as is known for example from DE-PS 23 26 759 or Japanese laid-open specification 49-15423, usually does not create optimal liability. Another step is required to apply the adhesive coat, which in turn requires further installation. Here, too, the photographic properties of the entire substrate can be adversely affected.

Finally, as a measure to improve the adhesion, it is known to incorporate synthetic fibers into the mass of the base paper. This measure is described for example in DE-PS 23 44 367. The disadvantage here is that a special paper mixture has to be prepared separately.

It is also known that only limited working speeds, approximately 150-180 m / min, are possible in the extrusion coating of photographic base papers.

It is therefore an object of the invention to improve the adhesion between a base paper and the polyolefin layer in a layer support of the type mentioned above and to avoid costly and cumbersome additional measures, as described above. In addition, reliable adhesion is to be ensured both without corona discharge and at extrusion speeds above 180 m / min.

The object is achieved by a photographic support of the type mentioned at the outset, which is characterized in that the polyolefin mixture for the coating contains at least one copolymer of an α-olefin with an α, β-unsaturated carboxylic acid.

The polyolefin is preferably a polypropylene (PE) or polypropylene (PP). The polyethylene used here can be HDPE (High Density Polyethylene), LDPE (Low Density Polyethylene), LLDPE (Linear Low Density Polyethylene) or a mixture of these PE types. The proportion of the copolymer in the mixture is at least 5% by weight, preferably between 20 and 80% by weight. It is a copolymer whose α-olefin is preferably ethylene or propylene. The α, β-unsaturated carboxylic acid has a proportion in the copolymer of at least 0.1% by weight, preferably between 0.5 to 15% by weight.

It has surprisingly been found that the addition of an α-olefin / α, β-unsaturated carboxylic acid copolymer of the aforementioned type improves the adhesion of the coating to the surface of the base paper in an outstanding manner.

The excellent adhesion properties of the coating can also be converted into an economic advantage in particular in that the working speed in the production of the photographic layer support according to the invention is significantly improved compared to that in other adhesion-promoting measures. The hardness (crystallinity) of the polyolefin layer is not measurably changed. However, the processing speed is significantly increased compared to the processing speed with other coatings. This processing speed can be increased again by a certain amount if the base paper additionally has an adhesion-improving structure produced by corona discharge.

It is also possible to treat the coating itself on the outside with a corona discharge in order to improve the adhesion with respect to the emulsion lying thereon.

The α, β-unsaturated carboxylic acids are monocarboxylic acids, such as acrylic and methacrylic acid, or else dicarboxylic acids, such as itaconic acid (methylene succinic acid). In the case of dicarboxylic acids, those are suitable which do not tend to form anhydrides.

The following examples illustrate the invention. The test results compiled in the table document the advantages of the photographic layer support produced according to the invention.

example 1

A 170 g / m² heavy, surface-sized photographic base paper was coated on the front with approx. 30 g / m² of a mixture of 45% by weight HDPE (Vestolen AV 7172, d = 0.963 g / cm³, MFI (melt flow index) = 8 and 55 wt .-% ethylene / methacrylic acid copolymer (1.2 wt .-% carboxylic acid, d = 0.922 g / cm³, MFI = 8) at an extrusion temperature of approx. 295 ° C and machine speeds of 180, 200, 220, 240, 270 and 290 m / min coated.

Example 2

A photographic base paper weighing 175 g / m² and surface-sized with polyvinyl alcohol was coated on the front with approx. 40 g / m² of a mixture of 95% by weight of polyethylene and 5% by weight of ethylene / methacrylic acid copolymer (10.0% by weight). % Carboxylic acid content) coated under the same conditions as in Example 1.

Example 3

A base paper weighing 170 g / m² was coated on the front with about 20 g / m² of a mixture of 20% by weight of polyethylene (Vestolen AV 7172) and 80% by weight of ethylene / itaconic acid copolymer (0.5% by weight Carboxylic acid portion) coated under the same test conditions.

Example 4

A 170 g / m² heavy, surface-sized photographic base paper was coated on the front approx. 30 g / m² of a mixture of 25% by weight HDPE (Vestolen AV 7172, d = 0.963 g / cm³, MFI = 8), 20 TiO₂ masterbatch (PPM 2073/1 with 50% rutile, MFI = 20) and 55% by weight of ethylene / methacrylic acid copolymer (1.2% by weight of carboxylic acid, d = 0.922 g / cm³, MFI = 8) at an extrusion temperature of approx. 295 ° C. and machine speeds of 180, 200, 220, 240, 270 and 290 m / min coated.

Comparative Example 1

The surfaces of a 175 g / m² photographic base paper were treated with an aqueous dispersion of an ethylene-vinyl acetate copolymer (Vinnapas EP1) (5 g / m²) and then with a polyethylene mixture (50% by weight HDPE, 50% by weight). LDPE) coated under the same extrusion conditions as in Example 1.

Comparative Example 2

A 180 g / m² heavy, surface-sized photographic base paper was extrusion-coated with approx. 35 g / m² of a polyethylene mixture (45% HDPE and 55% LDPE) (test conditions as in Example 1).

The test of the adhesion of the polyolefin resin to the paper base was carried out according to a test method customary for the applicant. For this purpose, a 1 cm wide PE strip was immediately lifted from the surface with a knife immediately after 1 hour and after 2 hours after the extrusion under the same conditions and then pulled off further by hand for about 20 cm in both directions of the paper.

The demolition will be based on the amount of that with the PE strip The fiber web torn out of the paper is assessed visually and graded with the numbers 1 to 5. The grade 1 means a complete split in the paper plane, the grade 5 a delamination of the PE film without fiber tear.

The results of the liability test are summarized in the table. The results show that the machine speed can be increased significantly without reducing the quality of the products.

Claims (14)

Photographic support with a two-sided coating which consists of a polyolefin mixture on at least one side and, if appropriate, further auxiliaries which have a positive influence on the use of the photographic support, for example white pigment,
characterized in that the polyolefin mixture contains at least one copolymer of an α-olefin with an α, β-unsaturated carboxylic acid. Photographic support according to claim 1, characterized in that the proportion of the copolymer in the polyolefin mixture is at least 5% by weight. Photographic support according to claim 2, characterized in that the proportion of the copolymer in the polyolefin mixture is between 20 and 80% by weight. Photographic support according to one of claims 1 to 3, characterized in that the α-olefin in the copolymer is ethylene or propylene. Photographic support according to claim 1, characterized in that the proportion of α, β-unsaturated carboxylic acid in the copolymer is at least 0.1% by weight. Photographic support according to claim 1 or 5, characterized in that the proportion of α, β-unsaturated carboxylic acid in the copolymer is between 0.5 and 15% by weight. Photographic support according to one of claims 1 to 6, characterized in that the α, β-unsaturated carboxylic acid is a monocarboxylic acid. Photographic support according to claim 7, characterized in that the α, β-unsaturated carboxylic acid is acrylic or methacrylic acid. Photographic support according to one of claims 1 to 6, characterized in that the α, β-unsaturated carboxylic acid is a dicarboxylic acid. Photographic support according to claim 9, characterized in that the α, β-unsaturated dicarboxylic acid is itaconic acid. Photographic support according to one of claims 1 to 10, characterized in that the application quantity of the mixture per side is between 10 and 45 g / m². Photographic support according to one of claims 1 to 11, characterized in that the photographic base paper used is surface-sized in the area of the coating with starch, gelatin, carboxymethylcelullose or polyvinyl alcohol. Photographic layer support according to one of claims 1 to 12, characterized in that the coating has an adhesion-improving structure produced by corona discharge on at least one side. Photographic support according to one of claims 1 to 13, characterized in that at least one of the sides of the base paper has an adhesion-improving structure produced by corona discharge.