EP0697620B1 - Photographic support material comprising a back-side coating - Google Patents

Description

The invention relates to a carrier material for photographic Layers in the form of a plastic-coated paper or a plastic film with a back layer, and one aqueous coating composition for the production of this Back layer.

• Antistatik, damit bei der Weiterverarbeitung keine Verblitzungen, keine Sortierprobleme und keine verstärkten Schmutzanziehungen stattfinden.
• Beschreib- und Bedruckbarkeit, damit die Materialien gekennzeichnet werden können.
• Geringe Schmutzaufnahme gegenüber teerartigen Oxydationsprodukten fotografischer Entwicklungsbäder.
• Klebebandhaftung, damit beim Entwicklungsprozeß die Rollenwaren aneinander fixiert werden können.

Backing layers are those layers which are opposite to the photographic emulsion to be applied later. The back layers of such carrier materials should impart the following properties to the plastic surfaces:

• Antistatic, so that no flashes, no sorting problems and no increased dirt build-up occur during further processing.
• Writeability and printability so that the materials can be labeled.
• Low dirt absorption compared to tar-like oxidation products of photographic processing baths.
• Adhesive tape adhesion so that the roll goods can be fixed to one another during the development process.

Some customers require backing layers with optimization all of the above properties, other customers prefer Back layers with particularly good individual properties. The two patents JP-63 004 231 and DE-PS 37 35 871 prove this.

JP-63 004 231 describes a back layer which Has antistatic properties, printability and low dirt absorption. It is produced using a coating compound Polymer latex (e.g. carboxyl-containing acrylate copolymer), Conductivity agents (e.g. polystyrene sulfonic acid) and colloidal Silica. The coating composition can additionally Contain auxiliaries (e.g. hydroxyethyl cellulose).

However, the back layer thus obtained has no writability with pencils on.

DE-PS 37 35 871 describes a back layer in which all properties have been optimized, that is, this layer can also be described with pencils. The coating mass for this back layer is composed of one Terpolymer of predominantly styrene and butadiene, a conductivity agent (e.g. polystyrene sulfonic acid), a colloidal Silica and a silica with an average particle size from 3 to 6 µm. With very good antistatic properties the pencil writability is almost good to good and the dirt absorption is still low to very low. Both properties can still be improved.

EP-A-496 037 relates to a coating material for the Back of photographic support materials used as components an aluminum-modified colloidal silica Alkali salt of an organic polyacid, a polyfunctional Aziridine and a plastic dispersion containing a Has a residual monomer content of <200 ppm,> 50 mol% hard Monomers in the polymer has free carboxyl groups in the polymer contains and as a dried film an interfacial tension of> 50 dynes / cm. This coating mass leads to a Back that has good properties in terms of Printability with thermal printers having.

It is therefore an object of this invention to provide a carrier material for to provide photographic layers that are sufficient good overall properties on the back a very has good writability with pencils and none Dirt absorption by photographic developer solutions shows.

Another object of this invention is to provide a coating composition to provide, with the one on the back of plastic-coated papers or plastic films desired rear layer can be achieved above.

• einem carboxylgruppenhaltigen Acrylat-Copolymer, das zu mehr als 80 Gew.% aus einem oder mehreren der Monomeren Acrylsäureester, C₁ bis C₆-Alkylacrylsäureester und Styrol besteht, wobei die freien Carboxylgruppen des Acrylat-Copolymeren unvernetzt bleiben,
• einer Naphtalinsulfonsäure oder einer organischen Polysäure mit freien oder salzartig gebundenen Carbonsäuregruppen oder Sulfonsäuregruppen,
• einer grobkörnigen Kieselsäure mit einer Korngröße von 3 bis 6 µm, einem Porenvolumen von < 1 ml/g und einer Oberfläche von > 400 m²/g (nach BET) und
• einem gut salzverträglichen Verdickungsmittel.

This task is solved by a coating compound or by a backing layer

• a carboxyl-containing acrylate copolymer which consists of more than 80% by weight of one or more of the monomers acrylic acid ester, C ₁ to C ₆ -alkyl acrylate and styrene, the free carboxyl groups of the acrylate copolymer remaining uncrosslinked,
• a naphthalene sulfonic acid or an organic polyacid with free or salt-bonded carboxylic acid groups or sulfonic acid groups,
• a coarse-grained silica with a grain size of 3 to 6 µm, a pore volume of <1 ml / g and a surface area of> 400 m ² / g (according to BET) and
• a good salt-compatible thickener.

In a special embodiment of the invention, the Coating compound or the back layer additionally an colloidal aluminum modified silica.

The ratio of acrylate copolymer: conductivity agent preferably 90:10 to 70:30.

The ratio of acrylate copolymer: coarse-grained silica is preferably 90:10 to 40:60.

The ratio of acrylate copolymer: colloidal silica is preferably 100: 0 to 30:70

In the acrylate copolymer, the free carboxyl groups are through Polymerization of unsaturated carboxylic acids produced, e.g. of acrylic acid, methacrylic acid or maleic acid. These free Carboxyl groups contribute in addition to the conductivity agents for the antistatic treatment of the back layer. she are therefore also not by reaction with crosslinking agents blocked.

Binding agents (copolymers), which form soft plastic films, have a disadvantageous effect on the writeability with pencils. A copolymer is therefore used whose monomers form hard films. The copolymer according to the invention is composed of more than 80% by weight of one or more of the monomers acrylic acid ester, C ₁ to C ₆ -alkyl acrylate and styrene.

Hard homopolymers made from the above monomers, such as polystyrene or polymethyl methacrylate, have ball indentations of 120-200 N / mm ² , measured according to DIN 53456, while soft homopolymers, such as polyolefins, have ball indentations of 10-100 N / mm ² .

The organic polyacid used as a conductivity agent, or the salt of this acid is preferably the alkali salt Acid, the acid being a carboxylic acid such as polyacrylic acid or can be a sulfonic acid such as polystyrene sulfonic acid.

The addition of coarse-grained silica generally has a positive effect on the writeability with pencils. Surprisingly, it has been found that the indication of the particle size of this silica is not a clear yardstick for this positive effect. The pore volume and in particular the surface have a significant influence (compare example B1 with comparison V1). According to the invention, the coarse-grained silica has a particle size of 3 to 6 μm, a pore volume of <1 ml / g and a surface area of> 400 m ² / g. In a particularly preferred embodiment, the silica has a surface area of 600 to 800 m ² / g.

Examples of well-tolerated thickeners are hydroxyethyl cellulose or water-soluble carboxyl-containing Acrylate-based copolymers. Others that are not well tolerated by salt Thickeners such as carboxymethyl celluloses lead to flocculation in the coating compound.

All components become a coating compound with water mixed together, the mixture still small overall, non-disturbing amounts, i.e. <5% by weight of wetting agents, dispersing agents, added water-soluble binders or dyes can be.

The coating composition can be applied to the back of the carrier material to be coated using all customary application units and then dried, the amount applied being selected so that an application weight of 0.2 to 2.0 g / m ² is present after drying.

The aqueous coating composition can vary in the following amounts by weight: % By weight Acrylate copolymer, 50% by weight dispersion 3.0-10.0 Conductivity agent, 30% by weight solution 1.5 - 4.0 coarse-grained silica 0.5 - 4.0 colloidal silica, 30% by weight sol 0.0 - 20.0 Thickener, 2% by weight solution 25.0 - 40.0 water Rest up to 100.0

The following examples are intended to illustrate the invention:

A base paper of 175 g / m ² basis weight, which was coated on the front with 30 g / m ^{2 of} polyethylene, which contained 10% by weight of titanium dioxide, and on the back with 30 g / m ^{2 of} polyethylene, only became one on the back Subjected to corona discharge and then coated with the coating compositions listed in Table 1. A 10-piece doctor blade (= 0.1 mm diameter of the winding wire) was used to meter the application weight. The layers applied were dried in the hot air duct to the application weights listed in Table 1. Components of the coating composition in% by weight Examples B1 B2 B3 B4 water 53.5 39.5 61.5 37.0 Copolymer dispersion containing carboxyl groups, C1 to C6 alkyl acrylate: styrene is 1: 1, 49% by weight (Carboset GA 1086 from BF Goodrich) 6.0 9.0 3.0 5.0 Na polystyrene sulfonate, 30% by weight 2.5 2.0 3.5 3.0 Coarse-grained silica, 4.9 µm particle size 0.4 ml / g pore volume, 750 m ² / g surface (Gasil 200 DF from Crosfield Chem.) 2.0 4.0 3.0 1.0 Colloidal aluminum-modified silica 30% by weight (Ludox AM from Du Pont) 5.0 4.5 - 18.0 Hydroxyethyl cellulose, 2% by weight in water (Tylose H 300 from Hoechst) 30.0 40.0 28.0 35.0 Wetting agent, 10% by weight in methanol (Surfynol 440 from Air Reduct. Chem.) 1.0 1.0 1.0 1.0 Application weight after drying in g / m ² 0.6 1.7 0.3 0.8

Comparative examples:

For comparison, the same conditions as in the examples, variants of the coating composition B1 were applied. Components of the coating composition in% by weight Comparative examples V1 V2 V3 water 53.5 83.5 53.2 Acrylate copolymer from Example B1 6.0 6.0 6.0 Na styrene sulfonate from Example B1 2.5 2.5 2.5 Coarse-grained silica from Example B1 - 2.0 2.0 Colloidal silica from Example B1 5.0 5.0 5.0 Hydroxyethyl cellulose from Example B1 30.0 - 30.0 Wetting agent from example B1 1.0 1.0 1.0 Coarse-grained silica, 4.1 µm particle size, 1.2 ml / g pore volume, 320 m ² / g surface (Gasil 644 M from Crosfield) 2.0 - - Trifunctional aziridine, 50% by weight in isopropanol as crosslinking agent (Xama 7 from Celanese) - - 0.3 Application weight after drying in g / m ² 0.6 0.3 0.6

Those with the coating compositions of the examples and comparative examples Carrier materials were manufactured subjected to the following tests:

The antistatic properties were tested by measuring the surface resistance with a comb electrode according to DIN-VDE 303T3.

The printability was checked using the commercial ribbons "New Cherry Ribbon" and "Kodak Back Printer CAT 1402114". The samples were printed on the typewriter on a typewriter with a type stop and then placed in the Kodak developer EP2 at 38 ° C. for 3.5 minutes. Then the flattened samples were 5 times with a velvet covered and water-soaked 180 g roll at a speed of 10 cm / sec. smeared. The smudge resistance of the typeface was assessed visually.

The writability with pencils was carried out with pencil hardness HB and assessed visually.

To check the dirt absorption , 250 ml of the commercially available color developer CP-1R18P at 40 ° C in a beaker at 500 rpm for 12 hours. touched. A dark tar-like layer of oxidation products formed on the surface. The developer was then poured onto ABS plates (acrylonitrile-butadiene-styrene copolymer) on which the tar-like layer was deposited. The back of the samples were placed on the plates, covered with paper and rolled over 3 times with a 2 kg roller. The samples were then rinsed with running water for 1 minute and hung up to dry. The dirt adhered was assessed visually as dirt pick-up.

To test the adhesive tape adhesion , the 5 cm wide commercially available 3M adhesive tape No. 8422 was pressed onto the back side layer and pressed on with an 8 kg roller. The adhesive tape was removed from the sample from punched-out 15 mm wide strips of this composite in a breaking load tester at an angle of 180 ° C. at a speed of 20 cm / min and with constant wetting of the separation point with water. The pulling force was measured. A value of> 2.0 N / 15 mm means good adhesion, a value of> 1.0 N / 15 mm means sufficient adhesion.

The test results are summarized in Table 3 below and the following paragraph. Examples Comparative examples B1 B2 B3 B4 V1 V2 V3 Surface resistance Ω / cm before bath run 9x109 4x1010 5x109 8x109 8x109 9x109 3x1010 after passing the bath 7x1012 9x1012 1x1013 9x1011 7x1012 6x1012 8x1012 Printability Well Well Well Well Well Well Well Pencil writability very good very good very good very good bad very good very good Dirt pick-up none none none none very low very low low Adhesive tape adhesion N / 15 mm 1.7 1.5 2.1 1.6 1.5 2.3 2.8

The coating composition of comparative example V2 (without hydroxyethyl cellulose) showed little stability. Beautiful after 1-2 hours there was significant sedimentation of the coarse-grained Silica while the other coating materials (with Hydroxyethyl cellulose) is stable after 24 hours, i.e. without were significant sedimentation.

The examples show that with good general properties Dirt pickup and the writeability with pencils excellent values could be improved. The stability of the coating compositions according to the invention ensures easy processing.

Claims (13)

1. Support material for photographic layers in the form of a plastic-coated paper or a plastic film having a backlayer containing a naphtalene sulphonic acid or an organic polyacid having free or salt-like bound carbonic acid groups or sulphonic acid groups, characterized in that the backlayer consists of at least

   an acrylate copolymer containing carboxyl groups, which consists to the extent of more than 80% by weight of one or more of the monomers acrylate, C₁ to C₆-alkylacrylate and styrene, wherein the free carboxyl groups of the acrylate copolymer are not crosslinked,

   a readily salt-compatible thickener and

   a coarse-grained silica of 3 to 6 µm particle size, a pore volume of < 1 ml/g and a surface area of > 400 m²/g.
2. Support material according to claim 1,
   characterized in that the acrylate copolymer/organic polyacid weight ratio is 90 : 10 to 70 : 30.
3. Support material according to claim 1,
   characterized in that the acrylate copolymer/coarse-grained silica weight ratio is 90 : 10 to 40 : 60.
4. Support material according to claim 1,
   characterized in that, for producing the backlayer, a colloidal aluminium-modified silica is used in addition.
5. Support material according to claims 1 and 4,
   characterized in that the acrylate copolymer/aluminium-modified silica weight ratio is 100 : 0 to 30 : 70.
6. Support material according to claim 1,
   characterized in that the organic polyacid is a free acid or the alkali metal salt of a free acid of the type of polyacrylic acid or polystyrenesulphonic acid.
7. Support material according to claim 1,
   characterized in that the readily salt-compatible thickener is hydroxy-ethylcellulose or a water-soluble acrylate-based copolymer containing carboxyl groups.
8. Support material according to claim 1,
   characterized in that the backlayer has a weight per unit area of 0.2 to 2.0 g/m².
9. Coating composition for producing a backlayer on a support material for photographic layers which support material consists of a plastic-coated paper or a plastic film, wherein the coating composition contains a naphtalene sulphonic acid or an organic polyacid having free or salt-like bound carbonic acid groups or sulphonic acid groups, characterized in that the coating composition further contains at least the following components:

   an acrylate copolymer containing carboxyl groups, which consists to the extent of more than 80% by weight of one or more of the monomers acrylate, C₁ to C₆-alkylacrylate and styrene, wherein the free carboxyl groups of the acrylate copolymer are not crosslinked,

   a readily salt-compatible thickener and

   a coarse-grained silica of 3 to 6 µm particle size, a pore volume of < 1 ml/g and a surface area of > 400 m²/g.
10. Coating composition according to claim 9,
    characterized in that the coating composition contains colloidal aluminium-modified silica in addition.
11. Coating composition according to claim 9,
    characterized in that the organic polyacid is a free acid or the alkali metal salt of a free acid of the type of polyacrylic acid or polystyrenesulphonic acid.
12. Coating composition according to claim 9,
    characterized in that the readily salt-compatible thickener is hydroxyethylcellulose or a water-soluble acrylate-based copolymer containing carboxyl groups.
13. Coating composition according to claims 9 and 10,
    characterized in that the individual components are present in the following quantities by weight: wt.% Acrylate-copolymer, 50 wt.% dispersion 3,0 - 10,0 Organic polyacid, 30 wt.% solution 1,5 - 4,0 Thickener 2 wt.% solution 25,0 - 40,0 Coarse-grained silicic acid 0,5 - 4,0 Colloidal silicic acid, 30 wt.% sol 0,0 - 20,0 Water remainder up to 100,0