FIELD OF THEINVENTION The present invention relates to a recording material for thermosublimation printing.

Abstract

The present invention relates to a recording material for thermal sublimation printing, comprising a base paper (1) having a front surface and a back surface, at least one synthetic resin layer (4) on at least the back surface of the base paper (1), a dye receiving layer (2) arranged on the front surface of the base paper (1), at least one plastic film (3) arranged between the base paper (1) and the dye receiving layer (2), and optionally a barrier layer arranged between the plastic film (3) and the dye receiving layer (2), wherein the synthetic resin layer (4) has an elastic modulus of at least 0.8 GPa.

Description

[Technical field]

[0001] Thermal sublimation printing serves to reproduce digitally created images in the form of printed images, the image quality of which is comparable to that of silver halide photography. The digital image is preprocessed pointwise for the basic colors cyan, magenta, yellow and black, and converted into corresponding electrical signals, which are then converted locally into heat by the thermal head of the printer. Under the action of the local heat, dyes sublimate from the donor layer of the ink ribbon or ink sheet, which is in contact with the recording material to be printed, and diffuse into the dye-receiving layer of the recording material.

[0002] Initially, it was assumed that dyes in dye sublimation printing were converted directly from a solid state to a gaseous state by the action of heat, i.e. sublimated. However, it has since been shown that dyes can be liquefied to a certain extent in dye sublimation printing, and a more plausible explanation for the process that takes place has been given in terms of a diffusion effect (so-called dye diffusion thermal transfer; D2T2). Depending on the thermal energy supplied to the image spot, different amounts of dye are transferred to the recording material.

[0003] In order to achieve photographic quality images, the recording material for thermal sublimation printing must have, inter alia, a good surface, low thermal conductivity, good heat resistance, good compressibility, and good dimensional stability. In addition, the recording material for thermal sublimation printing must have good storage resistance after printing to prevent migration of dyes in the carrier over time and the associated deterioration of image quality.

[0004] The compressibility of the recording material is important to ensure good contact between the thermal head of the printer and the recording material. During the printing process, accurate positioning of the recording material in relation to the print head is important. for each printing pass. since only one of the four basic colors (cyan, magenta, yellow and black) can be applied simultaneously. For this reason, the printed image must be created by application of dyes in four successive cycles (so-called multi-pass method). Since the same color pixel must then be produced up to four times at the same printing position to produce the desired tone, any change in the positioning of the recording material in relation to the print head during dye application leads to a deterioration of the image quality. Such changes in positioning (so-called misregistration) can occur, for example, due to transport problems of the recording material in the printer.

[0005] The transport rollers used in printers specially developed for thermal dye sublimation printing, such as Mitsubishi's WXL-1852017, DNP DS-621 and Citizen CX, have a surface roughness with needle-shaped protuberances that should act for a good relationship with the recording material. However, with currently widely used recording materials, due to the characteristics of the contact surface between the recording material and the transport rollers of the printer, friction occurs during the transport of the recording material in the printer, so that the best positioning of the recording material relative to the print head cannot be guaranteed. During successive printing processes, a misregistration occurs between the already applied print image and the print image to be applied in the subsequent printing process, with an associated deterioration in image quality.

[0006] Recording materials for thermosublimation printing have already been thoroughly described in the prior art. Such recording materials essentially consist of a support material, a dye-receiving layer and possibly further functional layers.

[0007] The support material can be, for example, uncoated or coated paper, with particular preference being given to papers coated with synthetic resins, in particular polyolefin-coated papers, or papers provided with a multi-layer plastic film, as described, for example, in EP 3028866 A1.

[0008] The dye receiving layer mainly contains a resin having an affinity for the dyes coming from the donor layer of the ink ribbon or sheet. For this purpose, for example, plastics having ester bonds, such as polyester resins, polyacrylic ester resins, polycarbonate resins, polyvinyl acetate resins, styrene acrylate resins, plastics having amide bonds, such as polyamide resins, or polyvinyl chloride, as well as mixtures of the above-mentioned plastics, are used. The use of copolymers containing at least one of the above-mentioned plastics as the main component, such as vinyl chloride / vinyl acetate copolymers, is also known in the prior art.

[0009] As a further functional layer, a so-called anti-curl layer is used, for example, to counter the curling of the recording material after passing through a thermal printer. A plastic film, for example, which is applied or laminated to the back side of the recording material, is well suited for this purpose. However, the application or lamination of a plastic film to the back side of the recording material requires an additional method step, which increases the complexity of the recording material, and the resulting surface properties of the recording material do not allow slip-free and therefore misalignment-free transport in the printer, which is disadvantageous. Furthermore, there is a risk of delamination with recording materials to which a plastic film is applied.

[0010] Another option described in the prior art to deal with the curl of the recording material after passing through a thermal printer is to apply a functional layer with a higher coating weight and associated higher thickness that deals with the curl or curvature. The disadvantage of this method embodiment is that it requires a large amount of material and is therefore uneconomical.

[0011] JP 2015-193251 describes a recording material in which a polyolefin layer is applied to both sides of a support material, the polyolefin layers being different in density and application weight from each other on both sides of the support material. However, the application of polyolefin still leads to transport problems in printers known from the prior art. In this case, a position-free transport of the recording material in the printer is therefore not guaranteed.

[0012] Therefore, against the background of the above-mentioned prior art, there exists a need for a recording material for thermosublimation printing which does not have the above-mentioned printer transport problems, or has them to a lesser extent.

[0013] The object of the present invention is therefore to provide a recording material for thermal sublimation printing which, whilst maintaining the usual requirements imposed on recording materials in thermal printing processes, has improved behaviour with regard to transport properties in the printer, in particular reduced misregistration compared to prior art recording materials and thus improved print quality.

[0014] This issue is a. a base paper having a front surface and a back surface; b. at least one synthetic resin layer on at least the back surface of the base paper; c. a dye receiving layer disposed on the front surface of the base paper; d. at least one plastic film disposed between the base paper and the dye receiving layer; e. optionally, a barrier layer disposed between the plastic film and the dye receiving layer; Including, The synthetic resin layer has an elastic modulus of at least 0.8 GPa; This problem is solved by a recording material for thermal sublimation printing.

[0015] Surprisingly, it has been found that such recording materials do not have the transport problems in printers described in the prior art, or have them to a significantly reduced extent, and therefore with the recording material according to the invention a significantly improved print quality can be achieved compared to the recording materials of the prior art. For the purposes of the present invention, the term base paper is understood to mean uncoated or surface-sized paper.

[0016] The base paper may contain pulp fibers, sizing agents such as alkyl ketene dimers, fatty acids and / or fatty acid salts, epoxidized fatty acid amides, alkenyl succinic anhydrides or alkyl succinic anhydrides, wet strength agents such as polyamine-polyamide-epichlorohydrin, dry strength agents such as anionic, cationic or amphoteric polymers or cationic starch, as well as optical brighteners, fillers, pigments, dyes, defoamers and other auxiliaries known in the paper industry. The base paper may be produced on a Fourdrinier or Yankee machine (drum machine). The basis weight of the base paper is between 50 and 250 g / m 2 , especially 80 to 180 g / m 2 The base paper can be used in uncompressed or compressed form (smoothed). 3 density, especially between 0.9 and 1.1 g / cm 3 A base paper having a density of 0.1 to 100% is particularly well suited.

[0017] Pulp fibres may be, for example, bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), bleached hardwood sulphite pulp (LBSP) or bleached softwood sulphite pulp (NBSP). Pulp fibres obtained from waste paper may also be used. Mixtures of the abovementioned pulp fibres may also be used, for example with a proportion of other fibres, such as synthetic fibres. However, pulp fibres made of 100% hardwood pulp are preferably used. The average fibre length of the uncomminuted pulp is preferably between 0.5 and 0.85 mm (Kajaani measurement).

[0018] Fillers that can be used in the base paper include, for example, kaolin, natural forms of calcium carbonate such as limestone, marble, or dolomite, precipitated calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, talc, silica, aluminum oxide, and mixtures thereof.

[0019] The base paper may be surface-sized. Suitable sizing agents for this purpose are, for example, polyvinyl alcohol or oxidized starch. In one particular embodiment of the invention, the sizing agent may additionally comprise at least one pigment. The pigment is preferably selected from the group consisting of metal oxides, silicates, carbonates, sulfides, sulfates, and mixtures thereof. In practice, pigments such as kaolin, talc, calcium carbonate and / or barium sulfate have proven to be particularly effective. The addition of pigments to the sizing agent can improve the surface properties of the base paper, in particular its smoothness.

[0020] The recording material according to the present invention has at least one synthetic resin layer at least on the back side of the base paper, the synthetic resin layer having an elastic modulus of at least 0.8 GPa. The determination of the elastic modulus can be carried out by techniques well known to those skilled in the art. The elastic modulus is preferably determined using a Lorentzen & Wettre Tensile Tester based on the tensile strength test described in the experimental section.

[0021] In the present invention, the reverse side of the base paper is understood to be the side of the base paper which faces the transport rollers of the printer.

[0022] In one preferred embodiment of the invention, the synthetic resin layer has an elastic modulus of at least 0.90 GPa, particularly preferably at least 0.95 GPa, very particularly preferably at least 1.0 GPa.

[0023] The synthetic resin layer may preferably comprise a thermoplastic polymer. In one embodiment of the invention, a biotechnologically produced polymer is used as the thermoplastic polymer. In an alternative embodiment of the invention, a polymer produced from renewable raw materials is used as the thermoplastic polymer. In another alternative embodiment of the invention, polylactic acid (PLA) and natural or modified starch, and mixtures thereof, are used as the thermoplastic polymer. Preferred thermoplastic polymers are, for example, low density polyethylene (LD-PE), high density polyethylene (HD-PE), polypropylene (PP), 4-methylpentene-1 homopolymers and copolymers (TPX), and mixtures thereof, as well as polyesters, such as, for example, polycarbonate.

[0024] In one preferred embodiment of the invention, the synthetic resin layer comprises HD-PE, LD-PE, 4-methylpentene-1 homopolymers and copolymers (TPX) and mixtures thereof. It has been found to be particularly useful if the synthetic resin layer contains at least 40% by weight of HD-PE, in particular 60 to 80% by weight of HD-PE. The HD-PE used in the synthetic resin layer has a density of 0.95 g / cm. 3 It has further been found to be particularly practical if the synthetic layer contains up to 25% by weight of LD-PE. The LD-PE used in the synthetic layer has a density of 0.935 g / cm 3 It is preferred that the density of the cellulose acylate is less than 100 μm.

[0025] In another preferred embodiment of the invention, the synthetic resin layer comprises at least 5% by weight, in particular at least 10% by weight, preferably 5 to 20% by weight, particularly preferably 5 to 15% by weight, of TPX, based on the dry weight of the synthetic resin layer. The addition of TPX leads to a further improvement of the surface properties of the synthetic resin layer.

[0026] In a particularly preferred embodiment of the present invention, the synthetic resin layer on the back side is composed of 0 to 25% by weight of TPX, 55 to 85% by weight of HD-PE, and 5 to 25% by weight of LD-PE, based on the dry weight of the synthetic resin layer. The recording material of the present invention having a synthetic resin layer composed in this way has particularly good transport properties in a printer, which makes it possible to almost completely prevent the misregistration of the printed image during printing.

[0027] The synthetic resin layer may contain white pigments, such as titanium dioxide, and other pigments, as well as auxiliaries, such as optical brighteners, dyes, and dispersing aids.

[0028] It has proven to be particularly advantageous in practice if the synthetic resin layer has a pigment content of at least 5% by weight, in particular at least 10% by weight, preferably at least 20% by weight, based on the dry weight of the synthetic resin layer.The pigment is preferably selected from calcium carbonate, aluminum oxide, aluminum silicate or mixtures thereof.By adding pigments, the surface properties of the synthetic resin layer can be further optimized.

[0029] In a particularly preferred alternative embodiment of the invention, the synthetic resin layer on the back side is composed of 5 to 25% by weight of a pigment, in particular calcium carbonate, 75 to 85% by weight of HD-PE and 0 to 15% by weight of LD-PE, based on the dry weight of the synthetic resin layer. A synthetic resin layer thus composed on the back side of the recording material according to the invention leads to a significantly lower friction with the surface of the transport roller of the printer, so that misregistration of the printed image during printing can be significantly reduced or even almost prevented.

[0030] The coating weight of the synthetic resin layer is 5 to 50 g / m 2 , especially 5 to 30 g / m 2 , preferably 10 to 20 g / m 2 It may be.

[0031] In one preferred embodiment, the synthetic resin layer is extruded or applied as a film.

[0032] The synthetic resin layers are extruded onto the base paper in a single layer or coextruded in multiple layers. Extrusion coating can be carried out at machine speeds of up to 600 m / min.

[0033] The recording material according to the present invention further comprises a dye receiving layer disposed on the front side of the base paper.

[0034] In the present invention, the front side of the base paper is understood to be the side of the base paper which faces the print head of the printer.

[0035] Basically, any dye receiving layer known from the prior art for thermal sublimation printing is suitable as the dye receiving layer. The dye receiving layer preferably comprises a polymer selected from polyesters, polyacrylic esters, polycarbonates, styrene acrylates, vinyl homopolymers and / or vinyl copolymers or mixtures thereof. The use of vinyl polymers such as polyvinyl chloride, vinyl chloride / acrylate copolymers, vinyl chloride / vinyl acetate copolymers and / or vinyl chloride / vinyl acetate / vinylidene chloride, and mixtures thereof, in the dye receiving layer has proven to be particularly practical.

[0036] The dye receiving layer may contain a polar binder, such as polyvinyl alcohol, and an optical brightener. As polar binders, starch, polyethylene glycol (PEG) and polyvinyl alcohol are particularly preferably used. Polyvinyl alcohols modified with carbonyl or carboxyl groups and mixtures thereof are particularly preferred. The use of these modified polyvinyl alcohols has the advantage that they are very compatible with the usual optical brighteners used in dye receiving layers, and therefore their use does not cause a deterioration in print quality.

[0037] The amount of polar binder in the dye-receiving layer may be from 1 to 25% by weight, especially from 5 to 20% by weight, based on the dry weight of the dye-receiving layer.

[0038] As optical brighteners it is particularly preferred to use stilbenes, ethylene derivatives, phenylethylene derivatives or thiophene derivatives. The amount of optical brightener may be from 0.01 to 10% by weight, in particular from 0.05 to 5% by weight, based on the dry weight of the dye receiving layer.

[0039] The dye-receiving layer may further comprise inorganic and / or organic pigments. Particularly well suited are fine-grained inorganic pigments such as silicon dioxide, aluminum oxide, aluminum oxide hydrate, aluminum silicate, calcium carbonate, zinc oxide, tin oxide, antimony oxide, indium oxide or mixed oxides of these oxides, as well as mixtures thereof. The amount of pigment in the dye-receiving layer may be from 10 to 90% by weight, in particular from 30 to 70% by weight, based on the dry weight of the dye-receiving layer. In one preferred embodiment of the invention, the dye-receiving layer comprises silicon oxide as fine-grained inorganic pigment, in particular fine-grained silicic acid.

[0040] The dye-receiving layer may optionally also contain other auxiliaries, such as inorganic or non-ionic surfactants, matting agents, dyes, crosslinking agents, lubricants, antiblocking agents, and other conventional additives. The amount of auxiliaries may be from 0.01 to 10% by weight, in particular from 0.05 to 5% by weight, based on the dry weight of the dye-receiving layer.

[0041] The coating material for forming the dye receiving layer can be applied in-line or off-line using any coating equipment that is conventional in papermaking. The coating weight of the dye receiving layer is at most 5 g / m2 after drying. 2 , especially 0.1 to 3 g / m 2 In a particularly preferred embodiment, the dye receiving layer has a dried coating weight of from 0.3 to 1.0 g / m 2 Such coat weights have been found to improve ink density in prints. It has proven particularly useful if the synthetic resin layer and / or the dye receiving layer contains a substance with antistatic action.

[0042] In one preferred embodiment of the invention, the synthetic resin layer and / or the dye receiving layer comprises an antistatic substance, in particular a conductive inorganic pigment. Such an antistatic substance can be added in addition to the above-mentioned pigments optionally contained in the synthetic resin layer and / or the dye receiving layer. The antistatic substance is preferably selected from semiconductors, betaines or ampholytes. The addition of such an antistatic substance to the synthetic resin layer and / or the dye receiving layer has been found to be favorable in order to counter the charging of the recording material during storage, transportation and in the printer, and thus to prevent a loss of print quality due to an already charged recording material.

[0043] The recording material according to the invention comprises at least one plastic film arranged between the base paper and the dye receiving layer. The plastic film is preferably a biaxially oriented plastic film. The plastic film may be a single layer, but preferably has a multi-layer structure comprising a porous core layer and at least one non-porous surface layer. The porous core layer serves for thermal insulation, whereas the non-porous surface layer serves for a surface as smooth as possible. In a particularly preferred embodiment, the plastic film is a biaxially oriented polypropylene film.

[0044] It has proven particularly advantageous if plastic films having a thickness of 30 to 60 μm, in particular 35 to 50 μm, are used.

[0045] In order to ensure good coverage of the recording material and uniform colour, the use of a plastic film having an opacity of 70 to 90% (measured in accordance with JIS-P-8148) has proven particularly practical according to the invention.

[0046] In yet another embodiment of the invention, the plastic film comprises organic and / or inorganic fillers, with preference given to carbonates such as calcium carbonate, carboxylic acids and other fillers with the potential to generate gas leading to foaming of the layer.

[0047] The recording material according to the present invention optionally comprises a barrier layer located between the plastic film and the dye receiving layer.

[0048] Besides the barrier properties which serve to prevent ink strike-through, such barrier layers usually also have an adhesion function to ensure good adhesion of the dye receiving layer on the plastic film. Such barrier layers are described, for example, in EP 3028866 A1.

[0049] In one embodiment of the invention, the barrier layer is a mixture of gelatin and a polymeric binder dispersible in water.

[0050] The water-dispersible polymeric binder in the barrier layer is preferably a water-dispersible polyester-polyurethane-copolymer.

[0051] In another embodiment, a crosslinker that improves internal and intermediate adhesion is applied in the barrier layer, which is preferably a polyaziridine.

[0052] The coating materials for forming the barrier layer and the dye receiving layer can be applied separately to the plastic film by gravure roll, blade coating, curtain coater, or any other commonly used application method, i.e., the coating material prepared for forming the barrier layer is applied to the plastic film first, and in the next step, the coating material for forming the dye receiving layer is applied to the dried barrier layer and dried.

[0053] Alternatively, the coatings described above can be applied "wet-in-wet", for example by a multi-layer curtain coater.

[0054] A drawback of applying separate coatings to the barrier layer and the plastic film is that delamination can occur between the individual layers.

[0055] For this reason, in one particular embodiment of the present invention, a plastic film that already contains a barrier layer is used. The use of such a plastic film can prevent delamination between individual layers. Furthermore, there is the advantage that raw materials and process steps can be saved in the production of recording material.

[0056] In another embodiment of the present invention, there is an adhesive layer between the base paper and the dye receiving layer. In one preferred embodiment of the present invention, the adhesive layer is made of low density polyethylene (LD-PE).

[0057] In an alternative embodiment of the invention, the adhesive layer may be constructed in the same way as the synthetic resin layer, meaning that the adhesive layer is identical in terms of its construction to the synthetic resin layer, or may be constructed from the materials described above for the synthetic resin layer in the amounts described.

[0058] The adhesive layer can be applied to the base paper, for example by extrusion, and serves as an adhesive layer for a plastic film applied thereon. The thickness of the adhesive layer is preferably 10 to 30 μm, in particular 15 to 25 μm.

[0059] The invention will now be described in more detail with reference to examples by way of illustration. [Brief description of the drawings]

[0060] [Figure 1] FIG. 1 is a schematic structure of an embodiment of a recording material according to the present invention. [Diagram 2] FIG. 2 is an SEM photograph of a synthetic resin layer on the back side of a prior art recording material having misaligned transport roller needle incisions. [Diagram 3] FIG. 3 is an SEM photograph of a synthetic resin layer on the back side of a recording material according to the invention having the incisions of a transport roller needle that is not misaligned. [Figure 4]FIG. 4 shows crosshairs for determining misalignment.

[0061] Fig. 1 shows a schematic structure of a preferred embodiment of a recording material according to the present invention. In this preferred embodiment, the recording material includes a base paper 1, on whose front surface a dye receiving layer 2 is disposed. A plastic film 3 is disposed between the base paper 1 and the dye receiving layer 2. This recording material has a synthetic resin layer 4 on the back surface of the base paper 1. On the front surface of the base paper 1, a barrier layer 5 is disposed between the plastic film 3 and the dye receiving layer 2. Furthermore, on the front surface of the base paper 1, an adhesive layer 6 is disposed between the plastic film 3 and the base paper 1.

[0062] 2 shows an SEM photograph of the surface of the synthetic resin layer on the back side of a recording material of the prior art after successive printing steps. This back side has indentations of the transport roller needles, which indicate a misalignment. Due to friction between the recording material and the transport roller, optimal positioning of the recording material relative to the print head is no longer guaranteed, so that during successive printing steps misalignments occur between the already applied print image and the print image to be applied in the following printing step, with an associated decrease in the print image quality. Such misalignments can be recognized by means of SEM photography of the surface of the synthetic resin layer on the back side of the recording material, with reference to the misaligned transport needle indentations.

[0063] Fig. 3 shows an SEM photograph of the surface of the synthetic resin layer 4 on the back side of the recording material according to the invention after successive printing steps. In contrast to the SEM photograph shown in Fig. 2 of the back side of a recording material of the prior art after successive printing steps, it can be seen from Fig. 3 that the surface of the synthetic resin layer 4 on the back side of the recording material according to the invention does not have a misalignment of the incisions of the transport roller needles. The recording material according to the invention therefore ensures an optimal positioning of the recording material relative to the print head during transport in the printer, which results in an outstanding print image quality under successive printing steps.

[0064] Figure 4 shows a printed image of the crosshairs for determining misregistration. The misregistration can be determined with a microscope by looking at the cyan, yellow and magenta colour shifts in the crosshairs (see crosshairs on the right). The sum of all the colour shifts gives the misregistration. The misregistration is a measure of the transport characteristics of the printer. Small or no misregistration (crosshairs on the left) is highly desirable.

[0065] Working Example Base paper manufacturing Base paper A was made from eucalyptus pulp. For grinding, the pulp was ground in an aqueous suspension of about 5% (high-density material) using a refiner to a grinding degree of 36°SR. The concentration of pulp fibers in the low-density material was 1% by weight based on the mass of the pulp suspension. The low-density material was added with additives such as cationic starch in an amount of 0.4% by weight, alkyl ketene dimer (AKD) as a neutral size in an amount of 0.48% by weight, wet strength agent polyamine-polyamide-epichlorohydrin resin (Kymene®) in an amount of 0.36% by weight, and natural CaCO3 in an amount of 10% by weight. The amounts are expressed with respect to the absolute dry pulp material. The low-density material, with its pH adjusted to approximately 7.5, was transferred from the headbox to the wire of the papermaking machine, and then sheet formation was carried out in the wire part of the papermaking machine while the web was dewatered. Further dewatering of the paper web was carried out in the press part of the papermaking machine to a moisture content of 60% by weight based on the web weight. Further drying was carried out in the dryer part of the papermaking machine by means of heated drying cylinders. 2 A base paper having a basis weight of about 100 g and a moisture content of about 7% was obtained.

[0066] Preparation of the recording material according to the invention and also a control example The side of the base paper facing the side to be printed (reverse side) was coated in an extruder with a synthetic resin layer consisting of the polymer mixture listed in Table 1. The cooling cylinder was cooled so that the resulting reverse side surface was R 200 mm or less as specified in DIN 4768. Z It was chosen to have a roughness of 0.9 μm measured as a value.

[0067] The surface of the base paper intended for printing (front side) was laminated with three layers of biaxially oriented polypropylene film (plastic film, HIPHANE BOPP, Hwaseung Industries Co. Ltd) in an extruder after corona discharge irradiation, during which a film made of low density polyethylene (LD-PE) was extruded between the front side of the base paper and the biaxially oriented polypropylene film. The thickness of the polyethylene film (adhesive layer) acting as an adhesion medium was 20 μm.

[0068] The resulting support material was then coated with a barrier layer (with a No. 25 wire bar) on the side coated with the plastic film and dried at 78°C for 3 minutes. The composition of each barrier layer is shown in Table 2. The coating weight of each barrier layer was 1.6 g / m2. 2 The dry coating was selected to produce a coating of 0.01%.

[0069] In the next step, the dye-receiving layer was applied to the barrier layer (with a #15 wire bar) and dried (2 min, 78°C). The coating weight of the dye-receiving layer was 0.5 g / m 2 The composition of the dye receiving layer coating is given in Table 3. Preparation of the paint for the dye receiving layer

[0070] 31.70 g of a vinyl chloride / acrylate copolymer dispersion (PrintRite® DP281.E, manufacturer Lubrizol) with a solids content of 56% by weight and 13.58 g of a vinyl chloride / vinyl acetate / vinylidene chloride dispersion (Vycar® 577E, manufacturer Lubrizol) with a solids content of 56% by weight were mixed with 3.15 g of a 30% aqueous suspension of colloidal silicic acid (Ludox® AM X4931, manufacturer Grace), 0.95 g of polydimethylsiloxane (TegoGlide® 482, manufacturer Evonik Industries), 0.25 g of a defoamer (Tego Foamex® 825, manufacturer Evonik Industries), 0.08 g of a wetting agent (Capstone® FS30, 25%, manufacturer DuPont) and 50.29 g of water.

[0071] The composition of the recording materials obtained based on the examples and the control can be seen in Table 4. With the recording materials thus obtained the misregistration in the printer was determined as well as the dye migration and mottling were evaluated by the methods described below.

[0072] As can be clearly seen from the results in Table 4, the properties of the synthetic resin layer on the back side of the recording material play a major role with regard to the critical misregistration in the printing process. Acceptable behavior in multi-pass printing processes, i.e. little or no misregistration, is only achieved with recording materials according to the invention, in which the synthetic resin layer has an elastic modulus of at least 0.8 GPa.

[0073] Measurement method Dye Migration Test The samples are printed on a Mitsubishi printer CP-D70DW with standard donor ribbons in maximum color density for yellow, cyan, magenta and black. The print format is 10x15cm, the colored area is 1x1cm. The samples are hung in an oven at 80°C for 5 days. After 5 days, the back side of the printed samples is evaluated for dye strike-through, which is done by school grading.

[0074] The evaluation is done as follows: no ink bleed-through on the reverse side is given a rating of 1, whereas a larger area and stronger ink bleed-through is given a rating of 5. To this end, a relative scale of ratings from 1 to 5 is used.

[0075] Mottling evaluation (unevenness) The samples and a Mitsubishi CP-D70DW printer are preconditioned for 12 hours at 40°C and 80% relative humidity. A full-surface print of 10x15cm in black is then printed in the same climate. The samples are assessed for mottling using a school scale of 1 to 5. School scale 1 means no mottling, school scale 5 means strong mottling. The scale of 1 to 5 is relative to the scales 1 and 5.

[0076] Elasticity The modulus of elasticity is determined according to the tensile strength test using a Lorentzen&Wettre Tensile Tester. For this purpose, a sample of the synthetic resin layer is cut to a width of 50 mm and a length of 120 mm. The measuring length is set to 100 mm. The measuring speed is 100 mm / min. The thickness of the sample and the weight per unit area are determined and recorded in the test program "Modulus of Elasticity" of the Lorentzen&Wettre Tensile Tester. A tensile strength test is then carried out on the sample. The modulus of elasticity is determined from the ratio between the mechanical stress and the elongation in the linear region of the stress-elongation graph.

[0077] How to measure misregistration using printed images The misregistration is determined with reference to the crosshairs. First, a print image with various crosshairs is printed. The print image then has the crosshairs printed out. The misregistration is determined with a microscope with reference to the color shifts of cyan, yellow, and magenta in the crosshairs (see Fig. 4, right crosshairs). The misregistration is calculated from the sum of all color shifts. The misregistration is an indicator of the printer's transport characteristics. In this case, slight or no misregistration (see Fig. 4, left crosshairs) is highly desirable.

[0078] [Table 1]

[0079] [Table 2]

[0080] [Table 3]

[0081] [Table 4]

Claims

1. A recording material for thermal sublimation printing, comprising: a. A base paper (1) having a front surface and a back surface; b. at least one synthetic resin layer (4) on at least the back surface of the base paper; c. a dye receiving layer (2) disposed on the front surface of the base paper; d. at least one plastic film (3) disposed between the base paper and the dye receiving layer; e. optionally, a barrier layer disposed between said plastic film (3) and said dye receiving layer (2); In a recording material comprising The synthetic resin layer (4) has an elastic modulus of at least 0.8 GPa, The synthetic resin layer (4) is (i) comprising 5% to 25% by weight of one of 4-methylpentene-1 homopolymer and copolymer (TPX) polymers, 55% to 85% by weight of HD-PE, and 5% to 25% by weight of LD-PE, based on the dry weight of the synthetic resin layer; or (ii) A recording material comprising, based on the dry weight of the synthetic resin layer, 5 to 25% by weight of a pigment, 75 to 85% by weight of HD-PE, and 0 to 15% by weight of LD-PE.

2. 2. Recording material according to claim 1, characterized in that the synthetic resin layer (4) has an elastic modulus of at least 0.90 GPa.

3. 3. Recording material according to claim 2, characterized in that the synthetic resin layer (4) has an elastic modulus of at least 0.95 GPa.

4. 3. Recording material according to claim 1 or 2, characterized in that the synthetic resin layer (4) has a pigment proportion of at least 5% by weight relative to the dry weight of the synthetic resin layer.

5. 5. Recording material according to claim 4, characterized in that the synthetic resin layer (4) has a pigment proportion of at least 10% by weight relative to the dry weight of the synthetic resin layer.

6. 6. Recording material according to claim 4 or 5, characterized in that the pigment is selected from calcium carbonate, aluminium oxide, aluminium silicate or mixtures thereof.

7. 7. Recording material according to any one of claims 1 to 6, characterized in that the plastic film (3) is a biaxially oriented plastic film.

8. 8. Recording material according to claim 7, characterized in that the plastic film (3) is a biaxially oriented polypropylene film.

9. 9. Recording material according to any one of the preceding claims, characterized in that as the barrier layer (5) a mixture of a water-dispersible polymeric binder and gelatin is used.

10. 10. Recording material according to claim 9, characterized in that the water-dispersible polymeric binder in the barrier layer (5) is a polyester-polyurethane-copolymer.

11. Recording material according to any one of the preceding claims, characterized in that the dye receiving layer (2) comprises a polar binder comprising polyvinyl alcohol modified with carbonyl or carboxyl groups.

12. 12. Recording material according to claim 11, characterized in that the polar binder represents 5-20% by weight of the dye receiving layer (2).

13. The recording material according to any one of claims 1 to 12, characterized in that on the front side of the base paper (1) there is additionally applied an adhesive layer (6) which is arranged between the base paper (1) and the plastic film (3).

14. 14. Recording material according to claim 13, characterised in that the adhesive layer (6) consists of LD-PE.

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