EP0268751B1 - Water-resistant photographic paper support - Google Patents

Abstract

A waterproof, polyolefin coated paper support for photographic coatings is disclosed, wherein the paper base contains an alkylketene dimer as a hydrophobizing sizing agent. The alkylketene dimer consists to the greater part of behenyl ketene and contains no more than 40% residues originating from alkylketenes having chains shorter than C20-alkyl.

Description

The invention relates to a waterproof coated paper support for photographic layers.

It is known to use paper coated with polyolefin on both sides as a waterproof support material for photographic layers. Such a carrier material is known to consist of a sized base paper with synthetic resin coatings applied to both surfaces. The synthetic resin coatings can consist of polyolefin and have been applied to the paper by means of extrusion coating.

Papers coated on both surfaces with a polyolefin resin are protected against the ingress of water and aqueous processing solutions for photographic materials: only the open edges of the laminates allow aqueous processing solutions to penetrate into the paper core, because the pulp fibers of the paper core, which are naturally hydrophilic , exposed there. For this reason, the base papers for a synthetic resin coating are usually sized to be extremely hydrophobic in order to keep the penetration of the photographic processing solutions as low as possible.

Known glues for photographic base papers that are highly hydrophobic for the paper are dimeric alkyl ketene. These dimerized alkyl ketenes are generally used in the neutral pH range together with cationic retention agents or strengthening resins and at least partially react with superficial OH groups of the cellulose fibers. (J.Appl.Photographic Engineering 3 (1981), Issue 7, pp.68 / 69) It is also possible to use dimeric alkylketenes together with fatty acid soaps or fatty acid anhydrides, which are precipitated with aluminum salts and fixed to the fibers to achieve an optimal glue effect will.

The hydrophobic effect of the dimeric alkyl ketene is, according to the prevailing view, essentially dependent on the alkyl groups. In practice, alkyl ketene dimers with alkyl chains of different lengths ("mixed" alkyl ketene dimers) are usually used. The alkyl group contains between 12 and 18 carbon atoms, as in R.D. November 1978, communication 17516 is communicated. Mixed alkyl ketene dimers with 16 and 18 carbon atoms are predominantly used.

definiert sind.DE-OS 33 06 768 also shows that a mixed alkyl ketene dimer with predominantly C _J6 and C, ₈ alkyl radicals and smaller proportions of C ₂ o and more alkyl radicals is best suited, while C _i4 or CJ2 alkyl radicals are less suitable are suitable to obtain a good hydrophobizing sizing of the base paper. DE-OS 33 06 768 more or less precisely claims the use of alkyl ketene dimers with alkyl chain compositions by the equation

are defined.

• 1,06
• 2,69
• 1,26
• 4,34
• und 14,3
  für eine gute Leimwirkung, während die Leimwirkung bei A-Werten unter 1 weniger gut ist (A=O, 27; 0,54 und 0,82). Die Leimwirkung ist durch die Eindringtiefe einer fotografischen Entwicklösung bestimmt. Entsprechend der Tabelle II auf Seite 13 nimmt die Eindringtiefe mit größer werdendem A-Wert nach Art einer Hyperbel ab. Der Wendepunkt der Hyperbel liegt etwa beim A-Wert von 1. Beim A-Wert on 14,3 wurde eine Eindringtiefe von 0,2 mm erreicht.

According to its structure, this equation of DE-OS 33 06 768 corresponds to an open scale. The value of the equation labeled "A value" should be equal to or greater than 1. The examples of DE-OS 33 06 768 that justify this equation demonstrate actual A values of

• 1.06
• 2.69
• 1.26
• 4.34
• and 14.3
  for a good glue effect, while the glue effect is less good at A values below 1 (A = O, 27; 0.54 and 0.82). The glue effect is determined by the penetration depth of a photographic processing solution. According to Table II on page 13, the depth of penetration decreases with increasing A value in the manner of a hyperbola. The inflection point of the hyperbola lies approximately at the A value of 1. With the A value at 14.3, a penetration depth of 0.2 mm was achieved.

Despite numerous attempts, it has now not been possible to reproduce the results published in DE-OS 33 06 768. In particular, penetration depths of 0.2 mm or 0.32 mm according to Table II of DE-OS 33 06 768 could not be obtained. In replication of the manufacturing conditions for the paper given there, values for the penetration depth that were smaller than 0.4 mm were never obtained. This is not unusual in papermaking because the same technical units and the same manufacturing conditions are certainly not used at another manufacturing location.

Regardless of the absolute values for the depth of penetration disclosed in DE-OS 33 06 768, it was also not possible to simulate the hyperbolic curve of the glue effect. Rather, an absolute limit value was always obtained, which apparently depends on pulp and degree of grinding with constant sizing.

Even though alkyl ketene dimers, because of their good gluing effect, alone or in combination with other glue agents, are widely used for the production of photographic base papers for synthetic resin found stratification, they still have disadvantages that previously seemed insurmountable. This applies to all alkyl ketene dimers previously used for photographic papers.

One disadvantage is that the alkyl ketene dimer does not fully react as it passes through the paper mixture. In practice, only a small part reacts with OH groups of the pulp. A larger part of the alkyl ketene dimer added to the pulp suspension for sizing is not chemically, but only physically bound in the paper fleece and therefore does not develop its full hydrophobic effect. This physically bound part consists partly of ketone, but partly of unreacted alkyl ketene dimer (Wochenblatt für Papierfabrikation 1983, p.215 f). In order to compensate for this low degree of reaction, the practice in the production of photographic base papers is carried out with additions of alkyl ketene dimer of 0.5 to 0.7% by weight, based on pulp. This amount is significantly higher than would theoretically be necessary to make the fibers hydrophobic if the reaction with OH groups described in the literature were to proceed faster and more completely.

Another disadvantage is that because of the large proportion of physically bound alkyl ketene dimer in the paper, the hydrogen bond between the cellulose fibers (fiber-fiber bond) is disturbed and the internal strength and rigidity of the paper are reduced as a result.

Finally, it is also disadvantageous that unreacted alkyl ketene dimer migrates to the paper surface during a short storage period of the paper, accumulates there and malfunctions in the subsequent application of synthetic resin layers, e.g. Polyolefin layers. The accumulation of the unreacted alkyl ketene dimer (dust) on the surface of the paper can be so strong that deposits of alkyl ketene dimer occur on the rolls and rollers of the coating unit during extrusion coating with polyolefin. As a result, rolls that come into contact with uncoated paper must be cleaned up to several times a day. This is not only a cost factor but also a quality problem.This can be seen, for example, in the fact that the adhesion of the extruded resin layer to the paper, which decreases and diffuses strongly with the amount of ketene dimer, or in the fact that ketene dimer gets onto the surface of the synthetic resin layers and is subsequently applied to the photographic layers Leads to usage errors. All of the disadvantages described here also appeared with only slight differences for all papers which, according to DE-OS 3 306 768, were sized with alkyl ketene dimers of the alkyl chain compositions listed in Table 11 of the document.

It is therefore an object of the present invention to produce a photographic paper support whose base paper is sized using an alkyl ketene dimer and which does not have the disadvantages described above. In particular, it is an object of the invention to produce a base paper for synthetic resin coating which has been sized using alkyl ketene dimer and which does not show any harmful enrichment of the alkyl ketene dimer on the surface and does not have any adverse effects when the paper is extrusion-coated with polyolefin.

This object is achieved in that the base paper is sized with an alkyl ketene dimer, which is predominantly formed from behenyl ketene.

The paper core is preferably sized with an alkyl ketene dimer which consists of at least 60% behenyl ketene dimer with C ₂ o-alkyl residues and has a maximum of 40% alkyl residues derived from shorter-chain fatty acids than C ₂₀ .

Papers produced according to the invention using a behenyl ketene dimer with more than 60% C ₂₀ alkyl radicals did not show the disadvantages set out in the description of the prior art. The papers according to the invention showed neither a blooming of alkyl ketene dimer (dust) nor disproportionate disturbances in the subsequent coating with polyolefin and with photographic layers. Above all, there were no adhesion problems and no wetting problems due to the transfer of alkyl ketene dimer to the polyolefin surface.

Papers according to the invention showed an excellent sizing effect even with smaller additions of behenyl ketene dimer than previously customary for the pulp suspension and thus a low edge penetration of photographic treatment solutions.

This result is surprising. It is particularly surprising that despite the greater length of the alkyl chains than in the known alkyl ketene dimers with alkyl chains between C ₁₂ and C _20, the reactivity of this alkyl ketene dimer is greater, contrary to general rules. In contrast to the alkyl ketene dimers previously used, no free alkyl ketene dimer was detected in papers produced according to the invention, while papers produced under the same production conditions with predominantly C) ₄ -, C ₁₆ - or CJs-alkyl radicals always contained free alkyl ketene dimers. This was even the case with a pure stearyl ketene dimer with 98% stearyl ketene content, which would be characterized according to DE-OS 33 06 768 mentioned above by an A value of approx. 34.

The alkylketene dimer essentially containing behenyl chains is added to the pulp suspension in the form of an aqueous emulsion. The amount of alkyl ketene dimer to be added, based on the pulp, is between 0.1 and 1.0% by weight in the product according to the invention.

In a preferred embodiment, the addition of alkyl ketene dimer with at least 60% of C2o-alkyl chains is between 0.2 and 0.7% by weight, based on the paper stock.

In addition to the alkyl chain dimer according to the invention, the base paper can contain the known cationic resins such as polyamide-epichlorohydrazine resin, polyacrylamide or starch derivatives. It can contain a combination of cationic and anionic resins, such as in DE-OS 33 28 463, DE-OS 32 10 621 or DE-OS 32 16 840 described, and it may contain additional other sizes such as soaps of higher fatty acids, fatty acid anhydrides or epoxidized higher fatty acid amides. In addition, the additives customary in photographic base papers, such as pigments, fillers, dyes and optical brighteners, can be present in the paper in the known amounts.

The finished, usually also surface-sized base paper is coated on both sides with synthetic resin, e.g. with polyolefin, extrusion-coated and used as a base material for photographic layers.

The invention is explained in more detail in the examples.

example 1

A bleached short fiber pulp (hardwood sulfate pulp) was ground at a consistency of 4% to 35 _° SR. The fabric was sized with the amounts of alkyl ketene dimer according to the invention (with 87% C ₂ o-alkyl radicals) and 1% by weight of polyamide-polyamine-epichlorohydrin given in Table 1 under Example 1. The fabric was processed in the usual way on a paper machine to photo raw paper of 175 g / m2 basis weight, the surface of the paper being sized with the following aqueous solution using a size press:

The application of surface sizing was 1.5 g / m2 and side of dry matter.

A portion of the base paper was then extrusion coated on both sides with polyethylene of 30 g / m ² each, as described, for example, in Example 4 of US 38 33 380.

Example 2

A short fiber pulp according to Example 1 was _sized with the amounts of alkyl ketene _dimer according to the invention mentioned in Table 1 under Example 2 (with 87% C _2o alkyl radicals), 1% by weight polyamide-polyamine-epichlorohydrin and sodium stearate and aluminum sulfate at pH 4.5. The base paper was produced in a known manner in the paper machine, the impregnation solution from Example 1 being applied in the same amount as surface sizing in the size press. Part of the 175 g / m ² paper was coated with polyethylene as in Example 1.

Ver ^g ieich 1V

A paper was produced under the conditions described in Example 1, but the alkyl ketene dimer was a commercial product based on palmitic / stearic acid.

The amounts of alkyl ketene dimer added are given in Table 1 under comparison 1.1 V to 1.4V.

Comparison 2V

A paper was produced under the conditions described in Example 2, but the alkyl ketene dimer was a commercially available product based on palmitic / stearic acid.

The amounts of alkyl ketene dimer added are given in Table 1 under comparison 2.1 V to 2.3V.

Compare 3V

A paper was produced under the conditions described in Example 1, but the alkyl ketene dimer was a product based on pure stearic acid (98% stearyl ketene content).

The additional amounts of stearyl ketene dimer are given in Table 1 under comparison 3.1 V and 3.2V.

Example 3

A pulp mixture (hardwood / softwood = 2/1) was ground at a consistency of 4% to 40 _° SR. The substance was mixed with the amounts of alkyl ketene dimer according to the invention (with 87% C ₂ o-alkyl radicals), 1% by weight polyamide-polyamine-epichlorohydrin and epoxidized stearic acid amide and / or cationic and / or anionic polyacrylamide given in Table 2 under Example 3 and processed on the paper machine in the usual way to form a base paper, a surface sizing with the following aqueous formulation being applied in the size press:

The application of the size press solution after drying was 1.7 g / m ² . The entire base paper had a weight of 110 g / m ² . Part of this base paper was extrusion-coated on both sides with 20 g / m ² polyethylene, as is known from corresponding processes.

Example 4

A cellulose mixture (hardwood / softwood = 1/1) was a mixed sizing from alkyl ketene dimer according to the invention (with 87% C ₂ o-alkyl residues), 1 wt .-% polyamide-polyamine-epichlorohydrin, sodium stearate and aluminum sulfate at pH 4.5 with the addition of epoxidized stearic acid amide and / or anionic and / or cationic polyacrylamide. The variable amounts are listed in Table 2 under Example 4. Surface sizing, basis weight and polyethylene coating corresponded to those from Example 3.

Comparison 4V

A paper was produced according to the conditions described in Example 3, but the alkyl ketene dimer was a product based on palmitic / stearic acid.

The varied additional amounts are given in Table 2 under comparison 4.1V to 4.3V.

Comparison 5V

A paper was produced according to the conditions described in Example 4, but the alkyl ketene dimer was a product based on palmitic / stearic acid.

The varied additional quantities are given in Table 2 under comparison 5.1V and 5.2V.

Example 5

A short fiber pulp (hardwood sulfate pulp) was ground at a consistency of 4% to 30 _° SR. The fabric was sized with the alkyl ketene dimer according to the invention (87% C ₂ o-alkyl radicals), 1% by weight polyamide-polyamine-epichlorohydrin, starch and the auxiliaries listed in Table 3 under Example 5. The solution from Example 1 was applied in the size press of a paper machine in an amount of 1.5 g / m ² and side based on dry substance (i). The raw paper weight was 75 g / m ² . Part of the base paper was extrusion coated on both sides with 20 g / m ² polyethylene.

Example 6

A base paper was produced in accordance with Example 1. The alkyl ketene dimer used differed in its C ₂ o-alkyl radical content as follows:

Comparison 6V

A paper was produced under the conditions described in Example 5, but the alkyl ketene dimer was a product based on palmitic / stearic acid.

The additional quantities are given in Table 3 under comparison 6.1V to 6.3.

Comparison 7V (according to DE-OS 33 06 768)

A pulp mixture (hardwood / softwood = 2/1) was ground at a consistency of 4% to 43 ° SR. The fabric was sized with 0.7% by weight alkyl ketene dimer and 0.7% by weight polyamide-polyamine-epichlorohydrin and produced on the paper machine, the impregnating liquid from Example 1 being applied in the amount specified there using the size press. Part of the 170 g / m2 heavy base paper was extrusion coated on both sides with 30 g / m ² polyethylene. The composition of the alkyl ketene dimers used was as follows:

The following test methods were used to test the papers: Dust test function

• 0 = kein Staub
• + = geringes Stauben
• ++ = mäßiges Stauben
• +++ = starkes Stauben.

Samples of the base paper were stored at constant atmospheric humidity (50% RH) and 35 _° C for seven days. The developing amount of diketene dust on the paper surface was then assessed visually in the grazing light. The individual notes mean:

• 0 = no dust
• + = little dusting
• ++ = moderate dusting
• +++ = heavy dusting.

Structural strength

The internal strength of the base papers was determined using the Scott Bond gap strength tester (Internal Bond Impact Tester Model B) according to TAPPI RC 308.

Stiffness

The stiffness values of the base papers were determined with the bending stiffness tester from Lorentzen & Wettre, Stockholm, according to standard SCAN-P 29.69 and converted to specific stiffness.

Edge penetration of developer solution

The papers coated with polyethylene were cut to the required test sample size and immersed in a commercially available color developer tape (T = 30 _° C.) for 25 minutes. After intermediate washing, immersion in a commercially available fixing bath and dewatering, the samples were dried and the penetration depth (in mm) of the developer solution from the cut edge was measured with a measuring magnifier.

Polyethylene adhesion

The coated papers were scratched on the surface with a razor blade so that the polyethylene could be peeled off in 25 mm wide strips. The force required for pulling was measured with an Alwetron TH 1 tensile testing machine (Lorentzen & Wettre, Stockholm).

The test results are summarized in Tables 4 and 5.

The test results prove that the base papers sized according to the invention with behenyl ketene dimer do not show the "dusting" of the alkyl ketene dimer which is disadvantageous for the further processing of the paper. Papers according to the invention also have a comparatively higher structural strength (Scott Bond) and a generally higher level of polyethylene adhesion on the base paper.

In addition, it was found that when using behenyl ketene dimer as a glue, the total amount of glue added can be reduced without the edge penetration deteriorating. This enables the physical properties of the base paper (structural strength, stiffness) to be improved even further. With regard to polyethylene adhesion, the tests always showed uniform adhesion values with fiber tears from the paper surface and no separation without fiber tears. No transmission of alkyl ketene dimer to the resin surface was observed.

The base papers produced according to the invention are preferably coated on both sides with polyolefin resin layers in order to produce the waterproof backing papers for photographic layers, as described in US Pat. The resin-coated paper supports are then, if appropriate after pretreatment and application of further auxiliary layers, coated in a known manner with black / white or color photographic layers.

Claims (20)

1. Waterproof paper carrier for photographic coatings, which contains a base paper, sized using dimeric alkyl ketenes, characterized in that the base paper is sized with an alkyl ketene dimer, which is preponderantly formed from behenyl ketene.

2. Paper carrier according to claim 1, characterized in that the alkyl ketene dimer is at least 60% formed from behenyl ketene with C₂o-alkyl radicals and that the alkyl ketene dimer contains a maximum of 40% alkyl radicals from shorter-chain fatty acids than C₂₀.

3. Paper carrier according to claim 1, characterized in that the base paper is produced using 0.1 to 1% by weight alkyl ketene dimers.

4. Paper carrier according to claim 1, characterized in that the base paper is produced using 0.2 to 0.7% by weight alkyl ketene dimers.

5. Paper carrier according to claim 1, characterized in that the base paper is produced using 0.1 to 1.0% by weight alkyl ketene dimers containing at least up to 80% C₂₀.

6. Paper carrier according to claim 1, characterized in that the base paper additionally contains a cationic resin.

7. Paper carrier according to claim 1, characterized in that the base paper additionally contains both a cationic and also at least one anionic resin.

8. Paper carrier according to claim 1, characterized in that, apart from alkyl ketene dimers, the base paper contains further sizes.

9. Paper carrier according to claim 8, characterized in that a further size is an epoxidized, higher fatty acid amide.

10. Paper carrier according to claim 9, characterized in that the epoxidized higher fatty acid amide is an epoxidized stearic acid amide.

11. Paper carrier according to claim 9, characterized in that the epoxidized fatty acid amide is an epoxidized behenic acid amide.

12. Paper carrier according to claim 8, characterized in that a further size is a soap of a higher fatty acid.

13. Paper carrier according to claim 1, characterized in that, apart from alkyl ketene dimers, the base paper contains an aluminium salt.

14. Paper carrier according to claim 13, characterized in that, apart from alkyl ketene dimers and aluminium salt, the base paper contains at least one further size.

15. Paper carrier according to claims 3 and 6, characterized in that the base paper is produced using 0.1 to 1% by weight alkyl ketene dimers and contains at least one cationic resin.

16. Paper carrier according to claim 6, characterized in that the cationic resin is a polyamide- polyamine-epichlorohydrin resin.

17. Paper carrier according to claim 6, characterized in that the cationic resin is a cationic polyacrylamide.

18. Paper carrier according to claim 7, characterized in that the anionic resin is an anionic polyacrylamide or an anionic starch.

19. Paper carrier according to claim 14, characterized in that the base paper additionally contains a cationic resin.

20. Paper carrier according to claim 14, characterized in that the base paper aditionally contains at least one cationic resin and at least one anionic resin.