FI111920B - Procedure for making print paper - Google Patents

Description

111920

A method for producing printing paper

The invention relates to a method for producing printing paper, in particular ink-jet printing paper (so-called ink-jet paper).

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As inkjet printers become more common, the demand for printing paper has begun to improve. Such printing papers generally comprise a substrate, which is most commonly a paper-based substrate, so-called. base paper, with an absorbent layer on top. The purpose of the absorption layer 10 is to receive the color of the ink jet printer ink (ink jet) and to absorb the liquid in the ink, whereby the ink in the ink remains on the surface of the printing paper to form a sharp image. Due to the requirements for the absorption layer, the development of printing papers has specifically focused on the development of materials and methods of application for the absorption layer. Although the layer on top of the substrate may be referred to as an absorption layer, it may often have two or more layers which may differ in composition and / or application step and have different purposes in the printing paper. At its best, such an absorption layer is such that it rapidly absorbs ink in a vertical (z-direction) direction of the fluid layer, but does not spread the liquid in the x-y direction, i.e., the image plane of the print paper.

A long known method of making printing paper is to apply an aqueous solution or dispersion of an • absorbent material to the substrate by any known coating method which, upon drying, forms an absorbent layer on the substrate. The printing paper produced in this way is shown e.g. EP-650850.

It has been attempted to avoid drying by selecting the material of the absorption layer so that it can be applied by extrusion coating, whereby, rather than dewatering, it is sufficient to allow the layer applied in the melt to cool. The basic raw material for the absorption layer is then a melt-applied polymer which, when solidified, forms 35 absorption layers. For example, EP-1018438 and WO 01/62510 disclose the formation of an absorption layer by extrusion coating technique, for example, from polyvinyl alcohol of extrudable quality. Pigments may also be doped with the polymer to be applied by extrusion. In the same publications, it is mentioned that a thinner surface layer containing pigment and binder can be applied over the applied layer during the extrusion step, which first receives the ink jet of the printer and forms the dye image. The separately applied surface layer can be used to adjust the surface properties (smoothness, gloss) of the print paper. It is required of the receiving layer that the ink dyes permanently bind to it and not change it to such an extent that their color shades 10, but on the other hand the receiving layer must be highly permeable to the ink fluid medium.

The surface pigments improve the absorbency of the surface as compared to the binders alone, which, on the other hand, can achieve better gloss. 15 For inkjet printing purposes, a paper with a good water absorption and good gloss and smoothness would be the optimal solution.

Ink-jet printing papers are also presented, e.g. U.S. Patent Nos. 6,262,108,88; 6,228,475; 6,290,814; and 6,248,432.

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EP-826510 and US-6180219 disclose a method for improving the gloss of a printing paper surface in particular. For methods ·; · *; characterized by the use of a special film having a smooth surface to obtain the desired properties on the surface of the absorption layer of the printing paper. In US-6180219, an ink-receiving layer is formed on top of the film to form a surface layer in the finished printing paper. Absorbent sugar is applied over the substrate (base paper) of the printing paper as a mixture of binder and pigment, and this layer *. An additional adhesive layer may be applied over the top. The film is laminated onto the layers applied to the substrate using moisture and the pressure of the nip between the rollers, and after drying the film initially: V: the former surface layer is permanently adhered to the substrate layer, for example to the very top adhesive layer. As the film 35 is pulled off, it is peeled off at the interface between the topsheet and the film, and the surface of the topsheet facing the film surface forms a smooth glossy surface of the printing paper. In EP-826510, surface 3111920 is in turn applied to an absorbent layer applied to the substrate, and while the surface layer is still wet, the film is superimposed in contact with the surface layer and after drying is removed with the same results as above.

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Em. it is particularly well known in the publications to use pigments in the surface layer. US-6180219 uses a hydrogel obtained from an inorganic metal oxide, and EP-826510 uses colloidal silica. Although these publications provide a high quality smooth surface, the process requires the use of moisture in lamination and subsequent drying.

U.S. Patent No. 5,958,168 (Example I-3) further discloses a method of compressing a surface layer applied to a smooth surface film and a polyethylene laminated paper onto a calender nip at 80 ° C, whereby the surface layer adheres to the laminated paper, its polyethylene surface, and surface. Synthetic amorphous silica particles of less than 1 µm in size are used in the surface layer.

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The production of smooth and glossy printing paper requires several steps when using any of the film laminating fabrics described above. Smooth transfer film with absorption layer and absorption layer * ·· '; the substrate coated therewith must be manufactured separately in its own processes, whereupon the substrate and surface layer are bonded together in a separate process which generally utilizes pressure, humidity and heat together (in the case of US 5,958,168 only pressure and heat).

· * ": Pigments capable of accelerating the penetration of a large amount of water contained in the ink jet can be incorporated in the absorption layer 30 (EP-1018438; WO 01/62510) applied by the extrusion technique. The problem is that the water-soluble polymer forms a thin surface layer, free of pigments, which leaves a water-absorbing swellable polymer on the surface of the printing paper.

4, 111920

It is an object of the invention to provide a process which makes it possible to produce high gloss and smooth printing paper by a simpler method. It is a further object of the invention to provide a process suitable for the industrial manufacture of printing paper 5 as a continuous process. To accomplish this purpose, the method according to the invention is essentially characterized in what is set forth in the characterizing part of the appended claim 1.

The general principle is to intervene in the formation of the surface of the absorption layer when the outer surface of the absorption layer is still in a state due to the extrusion process that it is not finally solidified and the various components are arranged in relation to one another. Thus, in one way, the method "interferes" with the free formation of the outer surface of the absorption layer.

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The invention utilizes the deformation properties of the outer surface of an absorbent layer material extruded onto a substrate by contacting it, for example, with the surface of a smooth transfer film or an additional layer applied to that surface. Due to the extrusion, the material 20 of the absorption layer is still at a temperature such that its surface area. topography and surface structure, in particular the ordering of the various components (inert pigment, hydrophilic polymer) relative to one another, can be influenced. The surface of the transfer film can then act as the outer surface of the pigment doped absorption layer applied to the substrate so that the adhesive polymer of the absorption layer does not cover the pigment particles close to the surface, leaving the surface with better ink reception. The transfer film prevents a coating of absorption coefficient on the pigment particles due to different surface forces. 30 of a polymer that has not yet solidified.

The transfer film can also be used to provide a separate, in-process: V: additional layer formed by combining a smooth transfer film ·: ··: top surface layer (future surface of printing paper) with absorbent layer material while still extruding at a temperature that promotes adhesion of the surface layer. When the material of the absorption layer cools from this temperature, the surface layer adheres to the absorption membrane permanently and with greater adhesion to the transfer film. In the final step, the transfer film may be peeled off to reveal a smooth glossy surface of the printing paper. The outer surface of the printing paper is thus formed by the surface layer facing the surface of the transfer film during application.

According to a preferred embodiment, the material of the absorption layer is fed by extrusion to a point where a transfer film optionally provided with a surface layer and a continuous web formed by the substrate are combined. The molten absorption layer material from the extrusion nozzle is then trapped between the transfer film and the substrate in the composite web, and the resulting composite web is then transported through cooling, for example a certain distance in contact with the cooling surface.

The pigments can also be imported from outside by means other than a separate transfer film. They can be applied as evenly as possible to the member which, after extrusion, comes into contact with the outer surface of the absorption layer, e.g. the surface of the cooling roll.

In addition, there are some advantageous alternatives to the surface layer and absorption layer materials and compositions discussed below.

The invention will be described in more detail below with reference to the accompanying drawings; · '; in the drawings showing the industrial manufacture of printing paper, in which Figure 1 shows the transfer film with a layer of printing paper, * ♦ * · '; Figure 2 shows the transfer film, the absorbent layer material and the substrate 30, Figure 3 shows the final step of forming a web of finished printing paper: Y:, * »35 Figure 4 schematically shows the formation of a finished printing paper in Figures 1-3. and 6111920 Figure 5 schematically illustrates the formation of a finished printing paper according to another embodiment.

In the printing paper, the proportion of pigment in the surface is increased by introducing pig-5 pigment from the outside onto the surface of the absorption layer. One possibility is to use a continuous transfer film for this.

Figure 1 illustrates a coating station in which a layer 3 forming a surface layer in a ready-to-use printing paper of suitable thickness is applied over a transfer film 4 of a plastic material, at least having an application surface. The film thickness is preferably from 12 to 50 pm and the film applikointipuolen normaalisileysarvoina a surface roughness (PPS smoothness), expressed is preferably less than 0.3, more preferably less than 0.04 pm. The film 4 passes through the applicator roll A, which spreads the surface layer in the form of a dispersion or solution 15 on the smooth surface of the film. The film may be polyethylene, polypropylene, polyester or other plastic material or other flexible material which may be transported through various process steps in a continuous web and, if necessary, rolled up. The plastic film may be unoriented or oriented monoaxially or Biak-20 socially. Em. the film coated with the dispersion or solution is subjected to drying. The figure shows the roll coating method, but other application methods can also be used.

Before application, the surface energy of the transfer film 4 is adjusted, if necessary, to allow the aqueous solution or dispersion to spread evenly in the application, but the film is subsequently successfully removed from the surface layer after it has dried. The treatment to obtain the correct surface energy can be: flame corona. The film may also be primed to a suitable surface, whereby no pre-treatment is required.

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Figure 2 shows an extrusion step in which a continuous transfer film 4 coated with a surface layer 3 is laminated to form a continuous y. rather, the web is conveyed by means of an absorbent layer forming material 35 fed to the nip formed by the guide roller O and the cooling roller J so that the topsheet 3 remains inside the film 4 in the composite web. The transfer film 4 and the substrate 1 are continuously fed between rollers O, J where they are laminated together as a result of feeding a molten polymer M from the extruder E to the junction of the webs formed by the extruder E in the form of a wide material web. according to the slot die of extruder E. If the transfer film 4 is roll-loaded after coating and drying, the tray 1 and the film 4 are fed to rolls O and J on their own rolls, but it is also possible that the transfer film 4 is continuously fed from step 1 of Figure 1 to extrusion step 2.

Due to melting in the extruder, the polymer fed has a certain temperature which, after lamination, facilitates the adherence of the surface layer 3 on the transfer film 4 to the absorption layer 2 which is formed in a molten state in the nip between the rolls O, J. After the nip, the transfer film 4 and the web formed by the substrate 1 pass between the solidifying and cooling absorption layer 2 and the adhering surface layer 3 along the cooling peripheral surface of the cooling roll J, from which the composite web is further processed by the second guide roll O The transfer film 4 is guided to the nip by means of a cooling roll J, and after the nip cooling of the composite web takes place from the side 20 of the film 4, since the film is against the cooling roll. At this point, .v. the surface of the absorption layer 2 on the transfer membrane side cools faster and the surface layer 3 adheres to the absorption layer 2. The guide 1 guided to the nip by the guide roller O remains on the cooling roller J ·; *; outermost, and cooling is effected on that side mainly by the ambient '·' 25 air. The layer applied in the extrusion cools and thus solidifies between the webs and forms a finished absorption layer 2 adhered to the substrate 1 with a surface layer 3 adhered thereto.

Figure 3 shows the formation of a web of finished printing paper. Extreme. A web of 30 rosettes is guided between two rollers T, one of which is used to collect, in the final step, a removable, "peel-off" transfer film 4 from the composite web; V: having a tray 1 and an absorption layer 2 having a topsheet 3 has a smooth and shiny surface due to being 35 against the 4 smooth surfaces of the transfer film. This release step may be performed with a reel or winder or prior to any reel that continuously forms a feed web to roll finished 111920 8 printing paper. The release of the film 4 can also be performed on a sheeting machine.

The transfer film 4 may be retained in the web as long as it is convenient to protect the sensitive surface of the printing paper from mechanical stress during the various process steps and thereby ensure that the surface of the printing paper is finally formed. The detached transfer film 4 can be reused for applying the topsheet 3 in step 1 of Figure 1. The release liner may also be recycled as a continuous material 10 from the release back to the surface layer application step of Figure 1 and, if necessary, subjected to a pre-treatment to make the surface suitable for application of the surface layer 3 material. The transfer film then forms a continuous loop of material passing through the application, extrusion and release steps.

Figure 4 shows the steps described above in sectional views of printing paper. Each step is indicated by a dashed line and a Roman numeral corresponding to the one cited above.

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The following describes various materials that can be used to make printing paper as described above.

»* ·»; · "In the extrusion step of Figure 2, it is possible for the film to be extruded between the webs to consist of two or more layers, the materials of which can be selected e.g. according to which material they come into contact with. For example, in so-called coextrusion, a layer on the side of the substrate 1 improves the adhesion of the absorption layer to the substrate, such a layer on the side of the substrate 1 can also act as a barrier layer to prevent the ink from absorbing water up to the substrate.

: This is particularly advantageous if the substrate 1 is made from a fibrous raw material: ':'; made of paper.

The surface layer 3 is usually thinner in weight basis than the absorption layer 2 applied by extrusion, which may comprise more layers as described above. Also, the topsheet 3 may comprise several layers, e.g. because the layers are applied successively to the transfer film 4 in the step of Figure 1. The compositions of such layers may be different.

The thin surface layer 3 provided by the transfer film 4 differs in composition from the absorption layer and is designed to provide the desired properties of the outer surface of the printing paper with respect to inkjet printing. The surface layer 3 acts as an ink-receiving layer (Tintenaufnahme-10 schicht) on the finished printing paper. Such a layer, when it has good smoothness and luster, reproduces, for example, the ink formed in inkjet printing with good resolution and high color density. The top layer has a pigment for absorbency and a binder for attaching the pigment. The pigment to binder ratio and the casting of the above ingredients can influence the surface properties. Excipients that improve the printing performance, such as cationic agents for chemical bonding of the ink to the surface and a binder such as polyacrylamide, polydimethylammonium chloride, or known quaternary ammonium salts, or polyethyleneimine or mixtures thereof may also be included in the surface layer 3. Preferably, the topsheet 3 is formed from a coating composition comprising a binder and a pigment to be applied in the step of Figure 1, wherein the amount of pigment is relatively large. The finished dried surface layer 3 may contain more than 50% by weight of pigment by dry weight. The pigment may have a mean particle size of 25 µm, preferably less than 1 µm. Colloidal silica is one example of a pigment having a small particle size. Other inorganic pigments, such as alumina, aluminum hydroxide or kaolin, may also be used. When a smooth transfer film is used to form the outer surface of the printing paper, the outer surface '' replicates ', not the pigments it'. The particle size need not be small in order to maintain the gloss.

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The topsheet 3 may be applied as an aqueous solution to which any of the above pigments have been dispersed and the binder is a hydrophilic polymer, such as: polyvinyl alcohol, polyvinylpyrrolidone, carboxymethylcellulose, polyethylene oxide or polyoxyalkylene. The solution is preferably prepared so that the pigment content in the finished layer is at least 50% by weight, preferably more than 50% by weight, on a dry weight basis. If necessary, other additives such as crosslinkers and antifoams may be used. As mentioned above, the topsheet 3 may also be formed on the transfer film 4 in multiple layers. The total thickness of the topsheet 3 may be from 1 to 20 g / m2, typically from 1 to 8 g / m2.

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The material of the absorption layer 2 beneath the surface layer 3 may be of suitable polymer grade to be extruded. When selecting an absorption layer, it should be borne in mind that in printing, the colors are mostly retained on the surface layer 3 and the water acting as a solvent penetrates into the underlying absorption layer, and water may return to the surface as the ink dries. Hydrophilic polymers such as starch, ethylcellulose, methylcellulose, and gelatin, or synthetic water-soluble polyisolated poly (poly (vinyl alcohol), polyvinyl alcohol, , polyethyleneimine and polymers of various acrylic acid and methacrylic acid. A mixture of polymers may also be used. The polymer or polymer blend of the absorption layer has a certain melt-processing temperature at which it can be applied by extrusion, and this temperature may be e.g. 100-300 ° C, preferably 160-220 ° C. Extruded quality ♦ · · polyvinyl alcohol is a particularly preferred material for the absorption layer 2. The above-mentioned hydrophilic polymers or mixtures thereof are preferably such that they do not dissolve in water until after printing paper; 25 normal operating temperatures at temperatures above 1 ·. ·; At 50 ° C.

• V ·: The absorption layer may also contain pigments with absorption properties. to adjust the sponges. The material to be extruded is blended in the desired ratio; . 30 in pigments prior to extrusion and then acts as a binder for pigments. The pigments are preferably up to 50% by weight in the absorption layer, preferably 10-50% by weight. In this way, the absorption capacity 0, 10 is obtained. get better. The pigment is preferably silica or talc or a mixture of these:: ··: The above amounts are expressed relative to the mass of the absorption layer minus the proportion of the barrier layer that may be present on the substrate side. Advantageously, the surface layer on the absorption layer has a higher proportion of pigments.

11 111920

It is preferred that the pigments contain at least 50 wt%, preferably between 50 and 80 wt%. Further, it is preferred that the binder of the surface layer 3 is less water-swellable than the binder of the absorption layer 2. Although the binder-pigment layer of the topsheet 3 absorbs water more slowly for 5 minutes than the lower absorbent layer, which binder is more hydrophilic than the topsheet, the topsheet is thin enough to allow the ink jet water to absorb into the absorbent layer sufficiently quickly. Similarly, the use of a highly water-absorbing pigment in the surface layer in a high proportion of the binder (e.g., 50-80 wt.% Of the mass of the surface layer 10) also provides rapid water absorption through the surface layer.

The absorption layer may be formed by coextrusion of two or more layers, preferably of different compositions. For example, on the side of the absorption layer 2 facing the substrate 1, a suitable extrudable polymeric layer may be formed which promotes adhesion to the substrate and possibly also acts as a barrier to prevent the passage of water. One example of such a material which can be used in particular for coextruding an absorbent layer of paper or board substrate 1, 'v. on top is a maleic anhydride / ethylene / acrylic ester terpolymer.

This random copolymer of ethylene, alkyl acrylate and maleic anhydride is suitable for use in coextrusion, for example with polyvinyl alcohol, due to its good adhesion. Other polyolefin-based copolymers or terpolymers or ionomers may also be used to provide good adhesion to substrate 1 and other material applied by coextrusion and coming to the surface of the absorption layer 2: ': 3. The amount of barrier layer can be 2-20 g / m2.

• · 30 The size of the absorption layer 2 extruded on the substrate 1

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the female amount can be 5-40 g / m2. The amount of the surface layer 3 is chosen so that it is less than the amount of the absorption layer in basis weight by Y: The thickness of the surface layer is preferably in the range of 0.1 to 0.25 parts ·: ·; the total thickness of the absorption layer (including a possible 35 barrier layer).

12 111920

The transfer film 4 is preferably made of plastic, in particular polyester, polyamide, polypropylene (e.g. OPP), polycarbonate, polyamide or HD-polyethylene, a surface siliconized polymer material, or also a surface siliconized metal strip. The smoothness of the surface involved in forming the outer surface of the printing paper 5 in the transfer film is preferably in accordance with the above PPS smoothness values.

The pigments can be applied externally to the surface of the printing paper by other means than by first coating the transfer film. Pigments 10 may be applied to a surface which comes into contact with the surface of the absorption layer applied by extrusion and moves with this surface along a certain distance, for example a cooling roll. Pigments adhere from the surface of the cooling roll to the surface of the absorption layer. Again, the pigments may be the same as those mentioned above with the transfer film.

The invention also encompasses the idea that a separate surface layer is not formed by transfer film, but utilizes the forming properties of the absorbent layer material 20 extruded by contacting it with a smooth transfer film.

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! ·. ·, Von with bare surface. The transfer film "" moves "the surface smoothness ab-

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on the outer surface of the sorption layer. Due to the extrusion, the material of the absorption layer is still at such a temperature that its surface topography and surface structure, in particular the arrangement of the various components relative to one another, can be affected. The surface of the transfer film can then act as a molding of the outer surface of the absorption layer applied to the substrate by pigment-doped melt extrusion so that the polymer of the absorption layer does not cover the pigment particles near the surface, but the surface remains exposed thereto. 30 capacity to improve. The transfer film prevents a thin coating of the absorption layer polymer from forming on the pigment particles due to different surface forces. Thus, in this embodiment, the absorption layer applied by extrusion always contains a pigment.

·: ··: The material to be extruded is doped in the desired proportions with pigments 35 before extrusion. The pigments are preferably up to 50% by weight in the absorption layer, preferably 10-50% by weight. The above amounts are expressed relative to the mass of the absorbent layer minus the proportion of the barrier layer which may be present on the substrate side of 13111920. Figure 5 is a diagram illustrating the use of a smooth transfer film 4 without a layer containing pigment.

5 When using plain transfer film 4, its smoothness may be of the order shown above and may be made of the same plastic or other materials as those mentioned above. However, the smooth transfer membrane, which is free of adherent solids in the absorption layer, may be used to introduce the substance such that, in the same liquid form, a surface-enhancing agent is absorbed into the absorption layer and absorbed at least onto the surface of the absorption layer.

When used as a transfer membrane alone, it can be guided to the surface 15 of the absorption layer 2 as in Figure 2 and removed from the cooling roller J as part of the composite path of the substrate 1, the absorption layer 2 and the transfer film 4. The release may also take place in the same steps as the transfer film 4 provided with a special topsheet 3.

·. ·. 20 »· *

As mentioned above, the surface energy of the transfer film 4 can be adjusted ···. by known methods, so that the desired substance, either a liquid or a mixture of liquid and pigments, can easily penetrate therein.

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Iti

The purpose of Tray 1 in each of the above alternatives is to provide a support and support structure for the printing paper. : /; Although paper or board made from a variety of fiber raw materials are commonly used materials, non-paper materials such as plastic films can also be used. When used with paper or cardboard, it may be coated. The paper or board may also be coated with plastics on the side in contact with the ν ': absorption layer 2. When selecting a plastic coating, ·: ·: Adequate adhesion to the material of the absorption layer 2 should be taken into account. The plastic coating on paper 35 or cardboard can also act as a barrier layer to prevent water from being absorbed from the absorption layer to the paper.

14 111920

On the back of the paper or board tray 1 (opposite side to the print side), a plastic protective layer can be used to prevent water from being absorbed from that side. Again, this layer is provided in the web formed by the substrate 1 before being fed to the extrusion lamination.

• · • · »« 1 • · »<· * t« t * ·. · • · · · * | • »1 • · · ·

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Claims (11)

A process for the production of printing paper, in particular ink jet printing paper, in which on a substrate (1) formed and a binder polymer, in particular a hydrophilic binder polymer containing absorbent layer (2), is post-treated to adjust its properties to be suitable for printing, characterized in that the material of the absorption layer (2) is spread on the substrate (1) in a molten state by extrusion, and the position and / or amount of pigment on the surface of the print paper is adjusted - by bringing the surface of the pigment mixed the absorbent layer (2) in contact with a continuous surface, when the absorbent layer is after the extrusion still at such a temperature at which the surface has not settled to its final shape, and said continuous surface is detached from the surface of the absorption layer, after the surface has settled to its final shape against said smooth surface, or - by bringing pigments from outside through the continuous surface to the surface of the absorption layer (2), when the absorption layer is after the extrusion still at a temperature which promotes the adhesion of the pigment. 20 The method according to claim 1, characterized in that it is continuous; The flat surface is a smooth transfer film (4), which will later be loosened to: v * expose the surface of the print paper which has been against the surface of the transfer film. ; 25 A method according to claim 2, characterized in that a pigment containing surface layer is spread on the surface of the transfer film (4), after which the transfer film (4) is placed with the surface layer (3) against the absorption layer ... (2) so that the surface layer contacts the material of the absorption layer (2) when, after extrusion at an adhesion promoting temperature, and after the material of the absorption layer has cooled, the transfer film (4) is released from the absorption layer (2). to expose the surface: "*; the surface of the layer (3) which has been against the transfer film (4). Method according to claim 2 or 3, characterized in that the material of the absorption layer (2) is measured by extrusion to a point in which the transfer film (4) 111920 and the substrate (1) formed with the surface layer (3) continuous web is combined so that the material of the absorption layer (2) becomes between the transfer film (4) and the substrate (1). Method according to any of the preceding claims 2, 3 or 4, characterized in that after the transfer film (4) has been placed against the absorption layer, the transfer film (4) and the substrate (1) with the absorption layer (2) between them are cooled. 10 Method according to claim 5, characterized in that the cooling takes place mainly from the side of the film (4). Process according to claim 6, characterized in that the transfer film (4) is in contact with the cooling surface. 15 Process according to any of the preceding claims 3-5, characterized in that the surface layer (3) is spread as a pigment and binder containing aqueous-based coating composition on the surface of the transfer film (4). 20 Method according to any of the preceding claims, characterized in that the absorbent layer (2) contains pigment and pigment: it is assumed that the proportion of pigment in weight percent of the dry weight is greater in the non-absorbed pigment containing layer than in the absorbent layer. 25 (2). Method according to claim 9, characterized in that the surface layer (3) contains pigments at least 50% by weight, preferably 50-80% by weight of the dry weight. , V 30 : 11. A method according to any of the preceding claims, characterized in that the absorption layer (2) is spread on the substrate (1) in coextrusion.