EP0356531B1 - Water-resistant photographic-paper support - Google Patents

Description

The invention relates to a paper support coated on both sides with polyolefin for photographic layers.

Due to the high demands of today's development processes, waterproof photographic supports have to be produced that are resistant to the penetration of developer and fixing solutions, as well as have other mechanical properties such as specific rigidity, splitting strength, breaking load etc.

It is known to use paper coated on both sides with hydrophobic resin layers as a support material for photographic layers. Such a carrier material usually consists of a paper core with a polyolefin coating applied to both surfaces. The top polyolefin coating layer to which a photosensitive emulsion layer is to be applied usually contains at least one white pigment to increase the sharpness of the photographic image. In addition, the polyolefin layer can also contain color pigments and other additives such as dispersing aids, antioxidants and antistatic compounds.

The paper backing, which is covered on both sides with water-impermeable polyolefin, is then protected on both surfaces against the action of treatment solutions, but is still exposed to the liquids at the edges. The penetration of treatment liquids discolour due to the influence of air and light and thus reduce the value of the photographic support.

In order to counteract the problem of soiling of the edges of the photographic support, the paper core is "hard glued" in the mass. In addition to the internal hydrophobization of the paper core, attempts have also been made to glue the surface of the base paper by applying various high-molecular substances. The high molecular weight compounds that have been used for this include substances such as gelatin, oxidized starch and other starch derivatives, carboxymethyl cellulose, modified polyvinyl alcohols and other binders. The surface of the base paper can be treated with the aid of an aqueous coating compound (coating solution) which, in addition to the abovementioned binders, can also contain other additives, such as, for example, B. optical brighteners (whiteners), pigments, defoamers, crosslinking agents, etc.
A coating solution can be applied to the surface of the paper using a size press, or other application methods can also be used, e.g. B. blade or rotary scraper method.

Starch has long been used primarily to improve the surface properties and as additional protection for the surface of the size-glued paper against external influences. Modified, degraded starches such as cationic, anionic or oxidized starches are used for the coating.

The use of starch in the surface treatment (DE 25 15 823) ensures good adhesion between the paper support and the polyolefin layer, it leads however, with regard to edge penetration not to optimal results. In addition, other physical values, in particular the gap strength, are insufficient.

In DE-OS 32 41 599 it was proposed to glue the paper core by applying a polyvinyl alcohol modified with dicarboxylic acids. This method does not guarantee a uniformly good adhesion between the polyolefin coating and the paper core and is also unsatisfactory with regard to the so-called edge penetration. In addition, the method is not without problems because of the poor electrolyte compatibility of the polyvinyl alcohol.

The process of DE-A 34 00 125, in which an ethylene-acrylic acid copolymer with an alkaline or ammoniacal adjustment to pH is used, also serves to improve the adhesion of the polyolefin films to the base paper which has already been hydrophopized in bulk and to avoid delamination in the subsequent processing stages 8.5 to 10 as an aqueous stable dispersion in combination with electrolytes, starch, starch derivatives, polyvinyl alcohol and optical brighteners applied to the paper surfaces, dried and then coated with polyolefin extrusion.

The attempt to use a polyvinyl alcohol modified with monocarboxylic acids (DE-OS 35 43 597) offers good results with regard to edge penetration, internal strength and polyolefin adhesion, but it causes problems in the preparation of the coating slip. The polyvinyl alcohol tends to flake in the presence of salts because of its poor electrolyte compatibility.

These flakes, which form under the influence of the salts used to improve the conductivity, are difficult to dissolve again in the course of the mixing process in the preparation of the coating solution (coating composition). The application of such a coating solution results in a reduction in the surface quality of the photographic paper support, since the above-mentioned flakes cause surface unevenness. On the other hand, the removal of these flakes by filtering, however, reduces the binder content and thereby deteriorates the values of the wear resistance of the carrier.

The object of the invention is therefore to develop a waterproof photographic support which, in addition to high splitting resistance, resistance to the penetration of photographic treatment liquids and good polyethylene adhesion, also has a good surface obtained by applying flake-free coating solution.

This object is achieved with a waterproof photographic paper support made from a base paper coated on both sides with polyolefin and hydrophopized in the mass, which is provided with a coating which is an anionic, cationic or amphoteric polyacrylamide or a mixture thereof, modified starch and at least one soluble inorganic salt from the group of chlorides and sulfates of an alkali or alkaline earth metal.

Surprisingly, it has been found that the advantages, namely reducing the penetration of photographic treatment solutions, increase the internal Strength of the paper core and improvement of the polyethylene adhesion is achieved in particular by the combination of polyacrylamide and oxidized starch in the coating composition.

The preferred weight ratio of polyacrylamide to modified, especially oxidized, starch is 1/3 to 3/1.

The paper core is produced in the usual way using a paper machine. The pulp is sized in bulk using known sizing agents. These include Alkyl ketene dimers or fatty acids or salts of the fatty acids. In addition, the pulp can contain fillers, pigments, optical brighteners, wet strength agents, antioxidants and other additives customary for the production of photographic supports.

The polyacrylamide used is an anionic, cationic, amphoteric polyacrylamide or a mixture of these.

The anionic polyacrylamide can e.g. B. a partially hydrolyzed product of polyacrylamide, an acrylamide-acrylic acid copolymer, an acrylamide / methacrylic acid copolymer, an acrylamide / maleic anhydride copolymer, an acrylamide / acrylic acid ether copolymer.

An anionic polyacrylamide with an anion content between 0% and 85% is preferred.

The cationic polyacrylamide can e.g. B. a degradation product of polyacrylamide, a reaction product of polyacrylamide with polyethyleneimine, a copolymer of acrylamide with a cationic monomer.

The amphoteric polyacrylamide is a polyacrylamide that contains both anionic groups and cationic groups in the macromolecule. The anionic groups are carboxylate or alkali carboxylate groups. The cationic groups can be any cationic groups such as quaternized or protonated alkylaminoalkylene acrylate or alkylaminoalkylene acrylamide groups.

The modified starch used here can be an esterified, etherified, acid-hydrolytically or enzymatically degraded starch or oxidized starch.
The esterified starch can be, for example, a starch phosphate ester, starch acetate, citrate or formate.
Among the etherified starches, for example, the alkyl starch ether, hydroxyalkyl starch ether, carboxyalkyl starch ether or allyl starch ether can be considered.
The acid hydrolytically degraded starch can be a starch degraded in the presence of acids such as hydrochloric acid, sulfuric acid or phosphoric acid.
The oxidized starch is a starch degraded by alkaline oxidation, and hypochlorite or periodate can serve as the oxidizing agent.
According to the invention, the oxidized starch is preferred here.

In addition, the effect according to the invention is only achieved if soluble inorganic salts from the group of chlorides and sulfates of an alkali or alkaline earth metal are added to the aqueous solution, for example calcium chloride, magnesium chloride, sodium chloride, potassium chloride, magnesium sulfate, sodium sulfate, potassium sulfate or any mixtures thereof . Sodium chloride is preferred according to the invention. In the examples illustrating the invention, calcium and sodium chloride are used as a representative of all the salts specified above, but other salts also confirm the effect according to the invention. The weight ratio salt / polyacrylamide is 2/3 to 2/1.

The mixture according to the invention is applied from an aqueous solution using known and customary application methods.

The total application amount is preferably 1.5 to 6 g / m².

The invention is illustrated by the following examples.

example 1

An aqueous pulp suspension (100% hardwood sulfate pulp, consistency: 4% freeness: 35 ° SR) was sized in bulk by adding:
2% by weight of anionic starch
0.75% by weight of anionic polyacrylamide
0.75% by weight of cationic polyacrylamide
0.60% by weight alkyl ketene dimer (Aquapel C 101, Herkules GmbH)
0.10% by weight of epoxidized fatty acid amide (Baysynthol CA 36 029, Bayer AG)
1.30% by weight of polyamide-polyamine-epichlorohydrin resin (Kymene 557 HP, Herkules GmbH)

From this an approximately 170 g / m² heavy base paper was produced, which was surface-sized with an aqueous coating composition according to Table 1. The application quantity was approx. 2.5 ± 0.2 g / m².

The coated papers were dried and coated with polyethylene for testing on a laboratory extruder (HDPE, density: 0.950 g / cm³, temperature: 295 ° C., contact pressure: 3.2 atm).

Example 2

A base paper (170 g / m 2) produced as in Example 1 was sized with an aqueous coating composition according to Table 2 below. The application quantity was approx. 3 ± 0.25 g / m². The coated paper was dried and extrusion coated with polyethylene as in Example 1.

Comparative Example V1

A base paper produced according to Example 1 was surface-sized with an aqueous coating master according to Table 3. The order quantity was 3 ± 0.2 / m². The coated paper was dried and extrusion coated with polyethylene according to Example 1.

Comparative example V2

A base paper produced according to Example 1 was surface-sized with an aqueous coating composition according to Table 4. The application quantity was 2.5 ± 0.2 g / m². The coated paper core was dried and extrusion coated with polyethylene according to Example 1.

Comparative Example V3

Base paper produced as in Example 1 was surface-sized with an aqueous coating composition. The composition of the coating composition is given in Table 6.
The application quantity was 2.5 ± 0.2 g / m². The coated paper core was dried and extrusion coated with polyethylene as in Example 1.

Examination of the paper samples produced according to Examples 1-2 and Comparative Examples 1-3

• 1. Innere Festigkeit (Spaltfestigkeit)
  Die Bestimmung wird nach TAPPI RC 308 mit einem Scott Bond Spaltfestigkeitsprüfer (Internal Bond Impact Tester Model B) durchgeführt. Die Meßwerte werden in ft · 1b x 10⁻³ angegeben.
• 2. Kanteneindringen (KE)
  Die mit Polyethylen beschichteten Papierproben werden mit einem handel süblichen Entwickler bei einer Temperatur von 30°C über eine Zeitdauer von 25 Minuten behandelt. An beiden Kanten der Probe wird das Eindringen der fotografischen Flüssigkeit gemessen. Die Meßwerte werden als Kanteneindringen (KE) in mm angegeben.
• 3. Haftung zwischen der Polyethylenschicht und dem gestrichenen Papierkern
  Die Prüfung wird mit einem Bruchlast-Meßgerät der Fa. Lorentzen & Wettre durchgeführt. Die Papierproben (15 x 180 mm) werden bei einer Abzugsgeschwindigkeit von 70 mm/min und einem Abzugswinkel von 180°C geprüft. Die Meßergebnisse werden in mN/15 mm angegeben.
• 4. Flockenbildung durch Elektrolytzusatz
  Die zur Beschichtung des Basispapiers erzeugten Streichlösungen werden auf Glasplättchen aufgebracht, getrocknet und anschließend visuell auf Flockenbildung begutachtet.

A part of the paper samples produced was tested without a polyolefin coating, another part was first coated as indicated and then subjected to various tests. The following test methods were used to examine the paper samples:

• 1. Internal strength (gap strength)
  The determination is carried out according to TAPPI RC 308 with a Scott Bond splitting strength tester (Internal Bond Impact Tester Model B). The measured values are given in ft · 1b x 10⁻³.
• 2. Edge penetration (KE)
  The paper samples coated with polyethylene are treated with a commercially available developer at a temperature of 30 ° C. for a period of 25 minutes. The penetration of the photographic liquid is measured on both edges of the sample. The measured values are given as edge penetration (KE) in mm.
• 3. Adhesion between the polyethylene layer and the coated paper core
  The test is carried out with a breaking load measuring device from Lorentzen & Wettre. The paper samples (15 x 180 mm) are tested at a take-off speed of 70 mm / min and a take-off angle of 180 ° C. The measurement results are given in mN / 15 mm.
• 4. Flake formation due to the addition of electrolytes
  The coating solutions produced for coating the base paper are applied to glass plates, dried and then visually examined for flaking.

Rigidity, breaking load and water absorption (Cobb test) were also tested. The results are in the usual range and were not used to evaluate the invention.

The results of the tests described are summarized in Tables 6-8. Table 6 shows the test results obtained on the paper samples produced according to the invention. Tables 7 and 8 contain the results of the comparative examples.

As can be seen from the tables, the best results were obtained with a coating solution consisting of polyacrylamide, oxidized starch and calcium or sodium chloride (Table 6).
The use of the coating compositions described according to the invention on the one hand improves the mechanical properties of the paper backing, but at the same time it allows the required antistatic agents (salts) to be used without problems. Table 6 Test results according to the invention (obtained from Examples 1 and 2) sample Splitting strength ft · lb · 10⁻³ Edge penetration mm Adhesion mN / 15mm Electrolyte compatible. (Flaking 1a 265 0.60 0.9 - 1b 182 0.60 0.9 - 1c 229 0.50 0.8 - 1d 230 0.60 0.9 - 1e 225 0.55 0.9 - 1f 220 0.60 1.1 - 1g 231 0.60 0.9 - 1h 215 0.60 0.8 - 1i 230 0.60 0.8 - 1y 228 0.65 0.9 - 1k 230 0.60 1.0 - 1l 229 0.60 1.0 - 2a 240 0.60 1.70 - 2 B 258 0.60 1.60 - 2c 262 0.60 1.60 - 2d 255 0.60 1.50 - 2e 260 0.55 1.60 - 2f 258 0.50 1.50 - 2g 245 0.50 1.50 - 2h 259 0.55 1.60 - 2i 261 0.50 1.50 - 2y 260 0.60 1.60 - 2k 255 0.55 1.60 - 2l 258 0.50 1.50 - 2m 255 0.60 1.20 - Test results (obtained from comparative examples V1-V3) sample Splitting strength ft · lb · 10⁻³ Edge penetration mm Adhesion mN / 15mm Electrolyte compatible. (Flaking) V1 a 162 0.88 0.6 - V1 b 164 0.92 1.0 - V1 c 160 1.03 0.6 - V1 d 165 0.90 0.8 - V1 e 165 1.00 0.7 - V1 f 166 0.90 0.6 - V1 g 168 0.80 0.7 - V1 h 170 0.80 0.7 - V1 i 166 0.80 0.8 - V1 j 177 0.90 0.5 - V2 a 219 1.00 0.2 + V2 b 208 1.10 0.2 + V2 c 264 0.90 0.2 + V2 d 256 0.90 0.2 + V2 e 214 1.10 0.2 + V2 f 220 0.83 0.3 + V2 g 256 0.85 0.2 + V2 h 248 0.85 0.2 + V2 i 245 1.03 0.3 + V2 j 256 0.70 0.2 + V2 k 274 0.70 0.2 + V2 l 269 0.80 0.3 + V2 m 284 0.80 0.5 + V2 n 273 0.80 0.5 + V2 or 267 0.90 0.5 + V2 p 287 0.80 0.7 + V2 q 295 0.80 0.4 + V2 r 287 0.70 0.5 + Test results (obtained from comparative example V4) sample Splitting strength ft · lb · 10⁻³ Edge penetration mm Adhesion mN / 15mm Electrolyte compatible. (Flaking) V4 a 220 0.60 1.0 - V4 b 230 0.60 0.9 - V4 c 228 0.50 0.8 - V4 d 225 0.60 0.8 - V4 e 231 0.55 0.9 - V4 f 230 0.60 1.0 - V4 g 240 0.60 1.0 - V4 h 236 0.65 1.1 - V4 i 225 0.55 1.0 - V4 j 227 0.60 0.9 - V4 k 232 0.60 0.9 - V4 l 229 0.60 1.0 -

Claims (8)

1. A waterproof photographic paper support consisting of a base paper, coated on both sides with polyolefin and made water-repellant in the pulp, which is provided with a coating which contains modified starch and electrolytes, characterised in that the coating contains an anionic, cationic or amphoteric polyacrylamide or a mixture thereof and the electrolyte is at least one soluble inorganic salt from the group of the chlorides and sulphates of an alkali metal or alkaline-earth metal.
2. A waterproof photographic paper support according to claim 1, characterised in that the polyacrylamide is an anionic polyacrylamide and has an anion content of 0% up to 85%.
3. A waterproof photographic paper support according to claim 1, characterised in that the modified starch is an oxidised starch.
4. A waterproof photographic paper support according to claim 1, characterised in that the polyacrylamide and the modified starch stand in a weight ratio of 1 : 3 up to 3 : 1.
5. A waterproof photographic paper support according to claim 1, characterised in that the coating composition is applied to the base paper in an overall amount of 1.5 up to 6 g/qm.
6. A waterproof photographic paper support according to claim 1, characterised in that the salt is calcium chloride, magnesium chloride, sodium chloride, potassium chloride, sodium sulphate, potassium sulphate or an arbitrary mixture of these.
7. A waterproof photographic paper support according to claim 1, characterised in that the salt is sodium chloride.
8. A waterproof photographic paper support according to claim 1, characterised in that the weight ratio of salt to polyacrylamide is 2 : 3 up to 2 : 1.