JPH0121495B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to base materials for photographic layers, particularly water-resistant base materials having a paper core. The photographic base material consists of film or paper or laminated paper. Film bases are advantageously used when high surface quality is required and the flexibility and cost of the material are less important, or when images are viewed or evaluated in transmitted light. This is especially true for negative materials, which generally have to be thin and transparent. Positive materials are much thicker for reasons of use and are viewed in reflected light. The positive material is therefore particularly based on paper, which is still sufficiently flexible despite its large thickness and has the necessary opacity for reflection viewing of the image. Conventional photographic paper generally has a coating layer containing a white pigment, the composition of which is important to the sharpness of the photographic image produced in the overlying photosensitive layer. Rapid automated processing methods for producing photographic images have increasingly led to the use of water-resistant coated papers as positive materials. In particular, according to German Patent No. 14 47 815, papers with extruded plastic coatings on both sides are used as the basis for various photographic layers.
In this case, the plastic coating placed between the paper and the photographic layer above it contains in particular highly reflective white pigments, such as titanium dioxide, and optionally nuance dyes and/or brighteners and/or other lubricants. Contains functional additives such as , antistatic agents, and anti-deterioration agents. As plastic coatings used are coatings made of polyolefins which have the special advantage of being able to be effectively processed for the attachment of photographic layers, especially by simple corona treatment. Additionally, polyolefin coatings are photochemically inert and inexpensive to manufacture. A disadvantage of all paper-based base materials produced by extrusion coating is the relatively low amount of white pigment in the pigmented coating layer. In the case of polyolefinic extrusion coating materials, for example, titanium dioxide generally cannot be used in an amount greater than about 20% by weight. This is because continuous film coatings cannot be produced with high pigment contents. Furthermore, the high temperature of the coating material, which reaches the paper in a molten state of approximately 300° C., has a disadvantageous effect on the process conditions. Due to the rapid heating of the paper surface, the cellulose fibers on the surface are dehydrated. The partial readjustment of the fibers that occurs after this rapid dewatering and cooling results in undesirable deformations of the paper surface that are reflected in the plastic coating on the paper. Therefore, melt-coated photographic paper bases always exhibit a surface structure that can be called a fine non-planarity, which appears as a cloudy pattern or unevenness in the photographic image. Another cause of the non-planarity of plastic coatings produced by extrusion coating onto paper from a melt and subsequent cooling on the roll surface is the non-uniformity of the coated paper core. Depending on the paper density variations, differences in the adhesion strength of the plastic layer to the chill roll are observed, and when the coated paper leaves the chill roll, different strengths of deformation forces act on the still plastic plastic coated surface. The disadvantages with respect to surface structure and image sharpness of such papers coated with a thermoplastic layer have been addressed according to German Patent Applications P3022451.2 and P3022709.9 by coating the photographic base paper with a curable mixture and by curing it. can be avoided by carrying out the process with an electron beam at room temperature. The water-resistant photographic paper base produced by this method provides photographic images with good sharpness due to improved pigment addition, and has a non-planar surface due to the structure of the paper that appears as unevenness in the produced photographic image. do not. However, such base materials with one or more coatings of mixtures cured by electron beams always have the disadvantage that small amounts of monomer compounds remain in the coating. These are monomers or depolymerization products that were not fixed during electron beam curing. Many of these different structures are volatile, but in any case the proportion of migratory compounds is relatively small. However, due to their chemical reactivity, these low-molecular-weight compounds can affect the photographic layer, changing its sensitivity, especially on storage. It has been found that conventional bonding promoting layers based on gelatin or mixtures of gelatin and other polymers do not provide a sufficient barrier to inhibit the migration of this harmful reactive compound. Subsequent coatings of polyethylene sheets also do not prevent migration and therefore adverse effects on the overlying photographic layers. It is therefore an object of the present invention to provide a water-resistant photographic base element which has the mechanical properties of a paper base and an always planar surface, which does not have a detrimental effect on the photosensitive layer and which provides photographic images of good quality. It is to obtain. This purpose consists of a paper coated with plastic on both sides and optionally other coatings, the plastic coating on the photographic layer side being cured by means of an electron beam, at least one first coating containing a pigment and an extrusion coating. at least one pigment comprising:
The solution is a multilayer photographic base material consisting of two second coatings. The electron beam cured coating is surface treated and then coated with polyolequin by extrusion coating. The coating, which is initially applied on one side and cured by means of an electron beam, contains, in addition to the binder, a pigment in particular,
g/m ² (in particular 15 to 30 g/m ² ). The binder mainly consists of a substance containing C═C double bonds and is therefore polymerized and hardened by the accelerated electron beam. Small amounts of non-curable polymers or low molecular weight substances may be included in the binder mixture as long as such additives serve to improve certain properties and do not essentially alter the properties of the mixture that is cured by electron beams. can. Preferred pigments in the layer hardened by electron beams are white pigments such as titanium dioxide, barium sulfate,
These are zinc oxide and calcium carbonate. For special applications, colored pigments or carbon black can be included in the layer, alone or together with white pigments. The first layer cured by electron beam is then subjected to surface oxidation treatment and then extrusion coated to 8-40 g/m ²
(in particular 12 to 25 g/m ² ) of polyolefin layer. Known surface treatments of layers hardened by electron beams are also simply carried out in the form of corona or flame treatments. However, surface treatment with ozone, various wet chemical surface oxidations (e.g. U.S. Pat.
3317330) or UV irradiation are likewise possible. After surface treatment of the hardened layer by electron beam,
This layer is coated with a polyolefin layer using a wide slit nozzle in a melt extrusion process at 280-320°C.
Polyethylene is used in particular as polyolefin, but ethylene copolymers consisting mainly of ethylene or polypropylene may also be used. Furthermore, mixtures of polyolefins and other polymeric substances, such as mixtures of about 5% polyethylene and polystyrene, are particularly suitable. Polyolefin coating materials generally contain from 5 to 20% by weight of one or more white pigments. A preferred white pigment is titanium dioxide in the rutile or anatase form. However, it is also possible to use mixtures of titanium dioxide and calcium carbonate and/or zinc oxide. Additionally, small amounts of blue, violet, or red pigments may be included in the mixture to adjust the particular nuance of white color. Other brighteners and other functional additives may be present in small amounts in the polyolefin layer. For special purposes, in particular as a negative material for silver salt diffusion printing, the amount of polyolefin can also contain from 0.5 to 8% by weight of carbon black. The surface of the polyolefin layer is likewise subjected to an oxidative surface treatment and/or coated with a bond-promoting layer, thereby making it ready for photosensitive layer coating. Usually, the paper back side of the multilayer base material thus produced is likewise coated with a polyolefin or protected against the ingress of photographic processing liquids by any other coating. Although the structure and composition of the backside coating is diverse and complex, it is of no great significance within the scope of the present invention. In order to clarify the structure of the photographic base material of the present invention, it will be explained with reference to a drawing (FIG. 1). In the figure 1 represents a photographic layer which may itself be multilayer. 2 is the oxidized surface of the bond promoting layer or polyolefin layer. 3 is the polyolefin layer, 4 is the treated surface of the e-beam hardened layer, 5 is the e-beam hardened layer, 6 is the photo paper with the hydrophobic inner surface size and/or surface size, and 7 is the treated surface of the e-beam hardened layer. Represents a back seal layer, which itself may be multilayer. The invention will now be explained by way of example. Example 1 Inner surface sized with alkyl ketene dimer
A photographic paper having an areal weight of about 170 g/m ² carrying a conductive surface layer containing Na ₂ SO ₄ was coated with about 15 g/m ² of the electron beam curable mixture by means of a doctor blade. The composition of the mixture is polyester acrylate (4 2
Polystyrene resin (=approx. 350) 10% by weight Oligotriacrylate (=approx. 480) 20% by weight Hexanediol diacrylate 10% by weight TiO ₂ -rutile form 20 It was % by weight. The coating was cured by electron beam under nitrogen with an energy dose of 40 J/g. The surface was subsequently corona treated in a known manner and coated with approximately 25 g/m ² of pigmented polyethylene mixture by extrusion coating. The composition of this polyethylene mixture was 85% by weight polyethylene (density 0.924, melt index 4), 15% by weight titanium dioxide-rutile form, and 0.1% by weight ultramarine blue. Example 2 A photographic paper having an areal weight of about 170 g/m ² was coated with about 7 g/m ² of the electron beam curable mixture by means of a doctor blade. The composition of the mixture was the same as in Example 1. Apply the coating to the energy dose as in Example 1.
After curing at 40 J/g and corona treatment of the surface, about 30 g/m ² of the same polyethylene mixture as in Example 1 was applied. Example 3 Electron beam curable mixture 25 on a photo paper with an areal weight of approximately 170 g/m ² with a doctor blade.
g/m ² was coated. The composition of the mixture was as in Example 1. Apply the coating to the energy dose as in Example 1.
After curing at 40 J/g and corona treatment of the surface, Example 1
Approximately 15 g/m ² of the same polyethylene mixture was coated. Example 4 A photographic paper having an areal weight of approximately 160 g/m ² was coated on one side with approximately 20 g/m ² of the electron beam curable mixture. The composition of the mixture was as follows. Polyester acrylate (4 2 per molecule
Contains double bonds (= approximately 1000) 43% by weight Hexanediol diacrylate 22% by weight Oligotriacrylate 20% by weight Titanium dioxide 15% by weight Blue nuance dye 0.007% by weight Purple nuance dye 0.003% by weight Coating with West German Patent Application P3022709 It was pressed onto a cooled mirror-finish cylinder by the method described in 9. It was cured by an accelerated electron beam with an energy dose of 30 J/g from the back side of the paper, and after curing, it was peeled off from the cylinder. The electron beam hardened layer was then corona treated as in Example 1 and the same polyethylene mixture as in Example 1
g/m ² was coated. Example 5 A photographic paper having an areal weight of approximately 160 g/m ² was coated on one side with approximately 35 g/m ² of an electron beam curable mixture. The composition of the mixture was as follows. Polyester acrylate 25% by weight Hydroxyethyl acrylate 5% by weight Neopentyl glycol diacrylate 20% by weight Oligotriacrylate 10% by weight Calcium carbonate 40% by weight The coating was coated with a polyester sheet by changing the method described in West Germany patent application P3022709.9. The polyester sheet was coated and cured by an accelerated electron beam with an energy dose of 50 J/g from the back side of the paper, and after curing was peeled off from the polyester sheet. The surface of the layer hardened by means of an electron beam is then flame treated according to DE 2138033 and then about 10 g of polyethylene mixture/
m ² was coated. The composition of the polyethylene mixture extrusion coated through a wide slit nozzle was as follows. Polyethylene (density 0.923, melt index 4) 85% by weight Titanium dioxide (anatase form) 14% by weight Calcium carbonate 1% by weight Ultramarine blue 0.07% by weight Brightener 2.5-di(5-tert-butyl-benzoxazoli) 2') Thiophene 0.1 part by weight Comparative Example A A photographic paper having an areal weight of about 170 g/m ² was coated on one side with about 40 g/m ² of a polyethylene mixture by extrusion coating. The composition of the mixture was 85% by weight polyethylene, 15% by weight titanium dioxide-rutile form, and 0.1% by weight ultramarine blue. COMPARATIVE EXAMPLES B-F Further comparative examples were made using the same papers as in Examples 1 to 5, in each case coated on one side with about 30 g/m ² of the electron beam curable mixture described therein. Curing was performed using an electron beam in the same manner as in 1 to 5. The papers of Examples 1 to 5 were uniformly coated on the uncoated back side with 30 g/m ² of a polyethylene mixture having the following composition. Low pressure polyethylene (density 0.96, melt index 10) 75% by weight High pressure polyethylene (density 0.92, melt index 4) 25% by weight Test To carry out photographic tests, each of the inventive and comparative examples was first coated. The front side was treated with a high frequency corona and coated with a gelatin and silver halide based photographic emulsion for conventional black and white processes. After storing the photographic material thus produced for three months,
The gray scale was exposed and developed and the density curve of this gray scale is shown graphically in FIG. This density curve shows a change in sensitivity without changing the gradation in Comparative Examples B-F in which the front surface was covered only with a lacquer layer hardened by an electron beam, but the example according to the present invention shows no change in sensitivity. Almost corresponds to Comparative Example A. In another test, the photosensitively coated material was lightly exposed to light, developed to a gray tone, and then the haze (unevenness) of the gray surface was compared and judged. In this case, comparative example A (polyethylene coating only) showed a relatively strong unevenness, whereas the example according to the invention showed a clearly higher uniformity. The subsequent surface properties of the non-photosensitively coated base material revealed the surprising fact that the inventive example was significantly superior to Comparative Example A, especially with regard to surface quality. A method for measuring surface quality is described in German Patent Application P3022709.9. A selection of test results are shown in the table below.

[Table] Examples include papers with a weight of 160-170 g/m ² .
However, the present invention is suitable for paper weighing up to 50 g/m ² and e.g.
It is also very advantageously suitable for papers up to 250 g/m ² . Coating and curing of the mixture curable by electron beam takes place at room temperature without external heat supply, so that
The paper is processed almost unchanged. The subsequent melt extrusion coating is as described above.
It is carried out at a temperature of 280-320 ° C.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the structure of a multilayer photographic base of the present invention, and FIG. 2 is a graph showing grayscale density curves of photographic bases according to examples of the present invention and comparative examples. DESCRIPTION OF SYMBOLS 1... Photographic layer, 2... Bond promotion layer, 3... Polyolefin layer, 4... Surface of electron beam hardening layer,
5... Electron beam hardening layer, 6... Photographic paper, 7...
...Water-resistant coating on the back side.

Claims (1)

Claims: 1. A photographic multilayer base material consisting of paper coated on both sides with plastic, comprising at least one first coating containing a pigment and an extrusion, the plastic coating on the photographic layer side being cured by means of an electron beam. Photographic multilayer base material, characterized in that it consists of at least one second coating provided by coating. 2. The base material according to claim 1, wherein the first coating cured by electron beam consists mainly of a compound containing C═C double bonds and a white pigment. 3. The first coating cured by electron beam comprises, in addition to the curable compound and the white pigment, an inert resin and/or a plasticizer.
The base material according to item 1 or 2. 4. Base material according to one of claims 1 to 3, wherein the first coating cured by means of an electron beam is corona treated before application of the further coating. 5. Base material according to claim 1, wherein the first coating cured by means of an electron beam is surface treated with a gas flame before applying the further coating. 6. Base material according to claim 1, wherein the second coating provided by extrusion coating consists essentially of polyolefin and white pigment. 7. Base material according to one of claims 1 to 6, in which at least one coating comprises a small amount of colored pigment. 8 At least one pigment present in the coating is 2
Base material according to one of claims 1 to 7, which is titanium oxide. 9. Base material according to one of claims 1 to 6, in which at least one coating comprises carbon black. 10. Base material according to one of claims 1 to 8, wherein the second coating applied by extrusion coating comprises a brightener. 11. Base material according to one of claims 1 to 10, wherein the surface of the second coating applied by extrusion coating is oxidized before application of the next coating.