EP2428840A1 - Support material for photographic silver halide double coated paper - Google Patents

Abstract

Support material for the coating on both sides of silver-halide photographic recording layers comprises at least one base paper with resin layers arranged on both sides and functional layers on the sides of the synthetic resin layers opposite to the base paper, where the functional layers comprise at least one water-soluble binder, a polyhydric alcohol, a salt of an inorganic acid and synthetic resin particles.

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to a support material for a silver halide control material for the high-quality reproduction of photographs. In particular, it relates to a substrate for the photographic production of photo books whose individual pages may contain photographs on the front and back.

STATE OF THE ART

Photo books can be personalized using digital image data. The pages are exposed to sheets or webs of photosensitive photographic paper using digital exposure techniques and bound to a book after photographic development. This saves the user from sticking and labeling individual pictures in photo albums.

Known photographic papers are designed for single-sided imaging, the silver halide-containing imaging layers are only applied to one side of the substrate, and after exposure and processing, an image is displayed on one side only. The support materials used for the preferred production of color images are usually coated on both sides with synthetic resins papers. The properties and the preparation of such support materials is described, for example, in Science and Technology of Photograph. 1st edition. Editor KELLER, Karlheinz. Weinheim: VCH Verlagsgesellschaft mbH, 1993. p. 69 to 74 ,

The production of photobooks using conventional one-sided imaged photographic papers can be accomplished by gluing second sheets or webs back to back, a method and apparatus therefor being known, for example, in US Pat EP 1 955 866 A1 described. But the bonding is an additional costly step in the book production dar. The book pages available through this also have more than twice the thickness of the photo paper used, which is often not desired. Particularly thin photographic papers, which are used to reduce the thickness of the book pages, have the disadvantage that they often lead to transport problems in conventional photographic exposure and development equipment because of their low stiffness.

Other digital printing techniques are also known for making the book pages of photo books, such as inkjet printing or electrophotographic printing processes using toners. So far, the image pages produced with such printing techniques are somewhat different in some aspects such as gloss, haptics, and long-term image stability than the image pages produced photographically using photosensitive material, and therefore less desirable.

The invention has for its object to provide a support material for the double-sided coating with one or more photoemulsion layers, which gives an image impression after coating with photoemulsion, exposure of an image and wet-chemical development on both sides, the comparable to that on a conventional one-sided imageable carrier material.

Furthermore, a good adhesion of the photoemulsion layers on both sides of the carrier material is to be achieved.

The carrier material may not stick together when rolled up or show a strong tendency for the surfaces to adhere to one another.

The carrier material according to the invention must not be electrostatically charged during further processing, in particular during unwinding, since the resulting discharge processes can damage and blacken the photoemulsion layers.

Finally, the support material should have a high whiteness and a high opacity in order to give an image impression comparable to a one-sided imageable support material, and to avoid a show through of the image applied on the back side.

This object is achieved by a support material for the double-sided coating with photographic silver halide recording layers comprising at least one base paper with synthetic resin layers formed on both sides and functional layers on the sides of the synthetic resin layers facing away from the base paper, the functional layers at least one water-soluble binder, a polyhydric alcohol, a salt of a inorganic acid and particles of a synthetic resin dispersion.

The invention provides a support material having on both sides with one or more photosensitive Image recording layers can be coated and the production of high-quality double-sided imaged pages, for example, allows for the production of photo books. The carrier material can be handled as a roll as well as a sheet material in the entire subsequent process of coating with light-sensitive layers, exposure, wet-chemical photographic development and further processing into a photo book, without adhesions or strong adhesion of the material surfaces to one another, electrostatic charges and Discharges are avoided. At the same time, good adhesion of the photographic emulsion layers is ensured.

The support material according to the invention, after being coated on both sides with photoemulsion layers, two-sided exposure and wet-chemical development, gives images on both sides whose image impression resembles that of one-sided images on a conventional support. It shows no sticking and no disturbing adhesion of the surfaces to each other during winding and unwinding under industrial production conditions. Furthermore, in the further coating with photoemulsion, it shows no electrostatic charge which leads to damage and blackening of the photoemulsion layers. The adhesion of a photoemulsion applied on both sides to the support material according to the invention is ensured.

The resin layers applied, for example, by extrusion may have a roughness, measured as Rz value according to DIN 4768, of less than 2 .mu.m for a support material which serves to produce glossy images, or less than 15 .mu.m for a support material which is dull for the production Pictures is used.

The functional layers applied to the synthetic resin layers on both sides contain at least one water-soluble polymer, a water-miscible polyhydric alcohol, a salt of an inorganic acid and synthetic resin particles. These may have a mean particle size of 2 microns to 20 microns. They can have a melting range of over 110 ° C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of the invention, the term base paper is understood to mean an uncoated or surface-sized paper. It can be made using a bleached pulp.

A base paper may, in addition to pulp fibers, sizing agents such as Alkylkendendimere, fatty acids and / or fatty acid salts, epoxidized fatty acid amides, alkenyl or alkyl succinic anhydride, wet strength agents such as polyamine-polyamide-epichlorohydrin, dry strength agents such as anionic, cationic or amphoteric polyamides, starch, optical brighteners, pigments, dyes, Defoamer and other known in the paper industry tools may contain. The base paper can be surface-sized. Examples of suitable sizing agents are polyvinyl alcohol or oxidized starch. The base paper can be produced on a Fourdrinier or a Yankee paper machine (cylinder paper machine). The weight per unit area of the base paper may be 50 to 250 g / m ² , in particular 50 to 150 g / m ² . The raw paper can be used in uncompacted or compacted form (smoothed). Particularly suitable are base papers having a density of 0.8 to 1.05 g / cm ³ , in particular 0.95 to 1.02 g / cm ³ .

Particular preference is given to base papers which contain mineral fillers. Such fillers may, for example, kaolins, calcium carbonate in its natural form such as limestone, marble or dolomite, precipitated calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, talc, silica, alumina and mixtures thereof are used in the base paper. Such base papers can have a higher opacity compared to base papers without fillers, which can advantageously prevent a bleeding through of the photographic image formed on one side while viewing the image on the other side.

A base paper according to the invention is a base paper coated on both sides with a thermoplastic resin, for example a polyolefin or polyolefin mixture. The application of the resin layers to the base paper can be effected by extrusion.

In a further embodiment of the invention, a further layer which contains a hydrophilic binder can be arranged between the base paper and the synthetic resin layers arranged on both sides of the base paper at least on one side. Particularly suitable for this purpose are film-forming starches such as thermally modified starches, in particular corn starches or hydroxypropylated starches. Preferably, low-viscosity starch solutions can be used, the Brookfield viscosities in a range of 50 to 600 mPas (25% solution 50 ° C / 100 rpm), in particular 100 to 400 mPas, preferably 200 to 300 mPas lie. The Brookfield viscosity is measured according to ISO 2555. Preferably, the binder does not contain a synthetic latex. The absence of a synthetic binder allows the recycling of waste material without prior treatment.

In a further embodiment of the invention, at least one pigment is contained in the further layer containing a hydrophilic binder. The pigment may be selected from the group of metal oxides, silicates, carbonates, sulfides and sulfates. Particularly suitable are kaolins, talc, calcium carbonate and / or barium sulfate.

Particularly preferred is a pigment having a narrow particle size distribution, wherein at least 70% of the pigment particles have a size of less than 1 micron. In order to develop the desired effect, the proportion of the pigment with the narrow particle size distribution of the total amount of pigment should be at least 5% by weight, in particular from 10 to 90% by weight. Particularly good results can be achieved with a proportion of 30 to 80% by weight of this pigment in the total pigment.

According to the invention, a pigment having a narrow particle size distribution also comprises pigments having a particle size distribution in which at least about 70% by weight of the pigment particles have a size of less than about 1 μm and at 40 to 80% by weight of these pigment particles the difference between the pigment having the largest grain size (diameter) and the pigment of the smallest grain size is smaller than about 0.4 μm. Particularly advantageous proved to be a calcium carbonate with a d _50% value of about 0.7 microns.

According to one embodiment of the invention, a pigment mixture containing calcium carbonate and kaolin can be used. The quantitative ratio calcium carbonate / kaolin is preferably 30:70 to 70:30.

The ratio of binder to pigment in the further layer can be from 0.1 to 2.5, preferably from 0.2 to 1.5, but in particular from 0.9 to 1.3.

The layer containing a hydrophilic binder may preferably contain further polymers such as polyamide copolymers and / or polyvinylamine copolymers. The polymer can be used in an amount of 0.4 to 5 wt .-%, based on the mass of the pigment. According to a preferred embodiment, the amount of the polymer is 0.5 to 1.5 wt .-%.

The layer containing the hydrophilic binder may be disposed directly on one or both sides of the base paper. It can be formed as a single layer or as a multilayer on the base paper. The coating composition can be applied in-line or off-line with all customary in papermaking application units, the amount is chosen so that after drying the coating weight per layer at most 20 g / m ² , in particular 8 to 17 g / m ² , or according to a particularly preferred embodiment is 2 to 6 g / m ² .

This further layer can also be smoothed by mechanical methods such as calendering or ferrotyping, but it can also be applied by cast coating.

The synthetic resin layers can be applied by extrusion on both sides of the base paper. According to one embodiment of the invention, the synthetic resin layers may contain the same polymer on both sides. In a further embodiment of the invention, the polymers used in the synthetic resin layers of the two sides are different.

The resin layers arranged on both sides of the base paper preferably contain a polymer having a water vapor permeability of at most 150 g / m ² × 24 h at a layer thickness of 30 μm, measured at 40 ° C. and 90% relative atmospheric humidity.

The polymer is preferably a thermoplastic polymer. Suitable thermoplastic polymers include, for example, polyolefins, especially low density polyethylene (LDPE), high density polyethylene (HDPE), ethylene / α-olefin copolymers (LLDPE), polypropylene, polyisobutylene, polymethylpentene, and mixtures thereof. However, other thermoplastic polymers such as (meth) acrylic acid ester homopolymers, (meth) acrylic acid ester copolymers, vinyl polymers such as polyvinyl butyral, polyamides, polyesters, polyacetals and / or polycarbonates may also be used.

Particularly preferred is low-density polyethylene (LDPE) or a polyethylene mixture of low-density polyethylene (LDPE) and high-density polyethylene (HDPE), wherein the ratio LD / HD 9: 1 to 1: 9, in particular 9: 1 to 9: 3, can be.

In a preferred embodiment of the invention, the sides of the base paper are coated with a polymer layer comprising at least 50% by weight, in particular at least 80% by weight of a low density polyethylene having a density of 0.910 to 0.930 g / cm ³ and a melt index of 1 to 20 g / 10 min, based on the polymer layer.

In a preferred embodiment of the invention, the resin layers on one or both sides of the base paper may further contain white pigments such as titanium dioxide.

The proportion of a white pigment in one or both synthetic resin layers can advantageously increase the opacity of the support material and improve the sharpness of the photographic image produced. In addition, one or both synthetic resin layers may contain further auxiliaries, such as optical brighteners, dyes and dispersing aids.

The coating weight of the polymer layers on the front and back may be 5 to 50 g / m ² , preferably 20 to 50 g / m ² or more preferably 30 to 50 g / m ² .

In one embodiment of the invention in which the support material can be used for the production of glossy images, a roughness of the surface is produced by using correspondingly structured cooling cylinders with a value of less than 2 μm, measured as Rz value according to DIN 4768. A roughness of 0.80 μm to 1.90 μm, in particular 1.00 μm to 1.70 μm, with a particularly uniform roughness depth distribution with a standard deviation of Rz between 0.050 μm and 0.120 μm, preferably at 0.060 μm to 0.100, is particularly preferred microns.

In a further preferred embodiment of the invention, in which the carrier material is used for the production of matt images, a roughness of the surface can be determined by using correspondingly structured cooling cylinders having a value of 2 μm to 15 μm, measured as Rz value according to DIN 4768, be generated.

On at least one side of the base paper, but preferably on both sides, functional layers are applied. These functional layers are designed such that they have an antistatic effect, have antiblocking properties and promote the adhesion of the silver salt emulsion to the resin surface. The functional layers contain at least one water-soluble polymer, a water-miscible polyhydric alcohol, an inorganic acid salt and fine synthetic resin particles.

The water-soluble polymer in the functional layer according to the invention may be polyvinyl alcohol, starch or another water-soluble polymer. Particularly preferred is gelatin.

The water-miscible polyhydric alcohol may be a glycol such as ethylene glycol or propylene glycol or other polyhydric alcohol, and particularly preferred is glycerol.

The salt of an inorganic acid may according to a preferred embodiment be an alkali metal chloride or alkali metal nitrate, more preferably sodium nitrate or lithium nitrate.

The resin particles may be a synthetic resin having a melting range above 110 ° C. The synthetic resin particles may have an average particle size of from 2 μm to 20 μm, more preferably from 4 μm to 10 μm. In a preferred embodiment, the synthetic resin particles contain polyethylene.

The functional layer is produced from a coating liquid which, in addition to a synthetic resin dispersion which delivers the synthetic resin particles and the aforementioned constituents of the functional layers, may contain further auxiliaries, such as wetting agents or thickeners. The coating liquid preferably contains water as a main component as a solvent.

The two-sided application of the functional layer can be carried out inline or offline with all customary in papermaking application units. The amount applied after drying per layer is at most 2.0 g / m ² , in particular 100 mg / m ² to 1 g / m ² .

It is preferable to treat the base paper surface or the base paper surface by corona irradiation or with a gas plasma before applying the synthetic resin layer to the base paper or the functional layer on the resin layer.

The following examples serve to further illustrate the invention.

example

To prepare the base paper A, a base paper made of eucalyptus pulp was used. For grinding, the pulp was ground as an approximately 5% aqueous suspension (thick matter) with the aid of a refiner to a freeness of 36 ° SR. The mean fiber length was 0.64 mm. The concentration of pulp fibers in the thin was 1 wt .-%, based on the mass of the pulp suspension. The thin stock additives were added as a neutral sizing agent alkylketene dimer (AKD) in an amount of 0.48 wt .-%, wet strength agents polyamine-polyamide-epichlorohydrin resin (Kymene ^®) gene in an amount of 0.36 6 -.% And a natural CaCO ₃ in an amount of 10% by weight. The quantities are based on the pulp mass. The thinstock, whose pH was adjusted to about 7.5, was transferred from the head box to the wire of the paper machine, followed by sheet formation by dewatering the web in the wire section of the paper machine. In the press section the further dewatering of the paper web was carried out to a water content of 60% by weight, based on the web weight. Further drying took place in the dryer section of the paper machine with heated drying cylinders. The result was a base paper with a basis weight of 160 g / m ² and a humidity of about 7%.

The base paper is coated on both sides with a coating, a styrene-acrylate binder and a pigment mixture of 50 wt .-% calcium carbonate and 50 wt .-% kaolin with a coating weight of 15 g / m ² on both sides, dried and then smoothed with a calender. The material thus obtained is referred to below as base paper A.

The base paper B is a base paper prepared in the same manner as the base paper in base paper A from eucalyptus pulp. In the pulp dispersion, however, it additionally contains titanium dioxide in an amount such that the base paper web after completion contains 10% by weight of TiO _2, based on dry mass. This base paper was used directly, without applying another coating slip, as base paper B for the subsequent extrusion coating.

Both sides of the base papers A and B were coated with a polyethylene-titania mixture of 90% by weight of a low density polyethylene (LDPE, 0.923 g / cm ³ ), 10% by weight of titanium dioxide (rutile) with a coating weight of about 20 g / m ² coated in the laminator at a speed of about 250 m / min. The cooling cylinders were chosen so that the resulting surfaces on both sides have a roughness Rz of 1.2 microns with a standard deviation of 0.08 microns, measured as Rz value according to DIN 4768. The materials obtained are in Described below as A1 and B1, they show a high-gloss surface.

Similarly, the base papers A and B were extrusion-coated with the same polyethylene-titanium dioxide mixture, but the cooling cylinders were chosen so that the resulting surfaces on both sides had a roughness Rz of 11.2 μm with a standard deviation of 1.3 μm. The resulting materials are referred to below as A2 and B2, they have a matt textured surface.

The surfaces of the obtained extrusion-coated materials after coating with a corona discharge were coated with coatings a, b, c, and d and dried, the coating weight after drying in all cases being 0.5 g / m ² on each of the two surface sides of each material amounted to.

The composition of the coating compositions a to d is shown in the following table. As acrylate is a mixture of Carboset ^® GA 1161 and GA 1339 (manufacturer Lubrizol) and as PE wax dispersion Lubaprint ^® VP 760 / D (manufacturer LPBader, Rottweil, Germany) was used, all amounts refer to the solid used: Coating slip a gelatin 6.0 g (usual adhesive layer) alum 1.0 g Isopropanol + butanol 10.0 g + 7.0 g water 76.0 g Coating composition b acrylate 7.7 g (usual backside layer) Colloidal silicic acid 4.2 g Fallen silica 0.3 g Polystyrolsulfonsaure 0.9 g water 86.9 g Coating c gelatin 5.2 g (Invention) Isopropanol + butanol 10.0 g + 6.6 g glycerin 1.0 g sodium nitrate 1.5 g alum 0.1 g PE wax dispersion 2.6 g water 73.0 g Coating composition d gelatin 5.2 g (Invention) Ispropanol butanol + 10.0 g + 6.6 g glycerin 1.0 g lithium nitrate 1.5 g alum 0.1 g PE wax dispersion 2.6 g water 73.0 g

The resulting support materials were subjected to the tests described in the table below: Surface resistance Measured with a comb electrode according to DIN 53483 bonding test Two sheets of the carrier material in A4 size are stacked at 23 ° C and 50% RH and loaded with a 10 kg weight. After 65, the leaves are separated manually and the sticking / gluing is evaluated. +: No bonding, o: easy bonding, -: strong bonding emulsion liability The surfaces of the materials are coated with a silver bromide gelatin photographic emulsion and, after drying at 23 ° C./50% RH, the adhesion is assessed by sticking and peeling off a TESA 4104 adhesive strip. +: Emulsion remains undamaged, o: emulsion slightly torn off, -: emulsion completely torn off from the carrier.

The test results are summarized in Table 1 below. <b> Table 1 </ b> material Surface Log (surface resistance / ohms / cm) bonding test emulsion liability Ala (comparison) glittering 13.2 - + A1b (comparison) glittering 10.1 + - A1c (invention) glittering 9, 9 + + A1d (invention) glittering 8, 9 + + A2a (comparison) frosted 13, 3 - + A2b (comparison) frosted 10.2 + - A2c (invention) frosted 10.0 + + A2d (invention) frosted 9.1 + + B1a (comparison) glittering 13.2 - + B1b (comparison) glittering 9, 9 + - B1c (invention) glittering 9, 8 + + B1d (invention) glittering 9.1 + + B2a (comparison) frosted 13.1 - + B2b (comparison) frosted 10.1 + - B2c (invention) frosted 10.2 + + B2d (invention) frosted 9.0 + +

Claims (15)

Support material for the double-sided coating with photographic silver halide recording layers comprising at least one base paper with synthetic resin layers arranged on both sides and functional layers on the sides of the synthetic resin layers facing away from the base paper, the functional layers comprising at least one water-soluble binder, a polyhydric alcohol, a salt of an inorganic acid and synthetic resin particles contain. Support material according to claim 1, characterized in that the water-soluble binder is gelatin. Support material according to claim 1 or 2, characterized in that the polyhydric alcohol is glycerol. A carrier material according to any one of claims 1 to 3, characterized in that the synthetic resin particles are polyolefin particles. Support material according to claim 4, characterized in that the polyolefin have a melting range above 110 ° C. Support material according to one of claims 1 to 5, characterized in that the average particle size of the synthetic resin particles is 2 μm to 20 μm. Support material according to one of claims 1 to 6, characterized in that the average particle size of the synthetic resin particles is 4 μm to 10 μm. Support material according to one of claims 1 to 7, characterized in that the functional layers have a coating weight of 0.1 g / m ² to 1 g / m ² on each side. Support material according to one of claims 1 to 8, characterized in that plastic layers have a surface roughness of 0.80 μm to 3.0 μm, measured as Rz. Support material according to one of claims 1 to 8, characterized in that the plastic layers have a surface roughness of 6.0 microns to 15.0 microns, measured as Rz. Support material according to one of claims 1 to 10, characterized in that the plastic layers contain low density polyethylene (LDPE). Support material according to one of claims 1 to 11, characterized in that the plastic layers contain a white pigment. Support material according to claim 1, characterized in that the base paper contains a base paper with an inorganic pigment as filler. Support material according to claim 13, characterized in that the inorganic pigment is titanium dioxide, calcium carbonate, or kaolin. A carrier material according to claim 13, characterized in that the base paper is a base paper with a filler content of 2 wt .-% to 15 wt .-%, based on the mass of the base paper is.