EP4039486A1 - Thermal sublimation print recording material with improved transport properties - Google Patents

Abstract

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

Description

The invention relates to a recording material for thermal sublimation printing.

Thermal sublimation printing is used to reproduce a digitally generated image in the form of a printed image, the image quality of which corresponds to that of a silver salt photograph. The digital image is selectively processed with regard to the basic colors cyan, magenta, yellow and black and converted into corresponding electrical signals, which are then locally converted into heat using a thermal head in the printer. Due to the local effect of heat, the dye sublimates from the donor layer of an ink ribbon or ink sheet that is in contact with the recording material to be printed and diffuses into the dye-receiving layer of the recording material.

Originally, it was assumed for thermal sublimation printing that the heat would transform the dye directly from the solid directly into the gaseous state, i.e. it would sublimate. It later turned out, however, that a certain degree of liquefaction of the dye can occur during thermal sublimation printing, so that a more accurate description of the ongoing process is given by diffusion effects (so-called Dye Diffusion Thermal Transfer; D2T2). Depending on the thermal energy applied to the pixel, a different amount of dye is transferred to the recording material.

In order to achieve images in photo quality, a recording material for thermal sublimation printing must have a good surface, low thermal conductivity, good heat resistance, good compressibility and good dimensional stability, among other things. In addition, the recording material for dye-sublimation prints have good shelf life after printing to prevent migration of dyes through the substrate over time and consequent deterioration in image quality.

The compressibility of the recording material is important to ensure good contact between the printer's thermal head and the recording material. During the printing process, the exact positioning of the recording material in relation to the print heads is important, since only one of the four primary colors (cyan, magenta, yellow and black) can be applied at the same time in each printing process. For this reason, the print image must be created by applying dye in four consecutive passes (so-called multi-pass process). Since the same color pixel has to be precisely controlled up to four times at the same print position in order to generate the desired color tone, changing the positioning of the recording material in relation to the print heads during the colorant application leads to a deterioration in image quality. Such a change in positioning (so-called offset) can be caused, for example, by difficulties in transporting the recording material in the printer.

The transport rollers used in printers specially developed for thermal sublimation printing, such as the WXL - 185 2017 from Mitsubishi, DNP DS-621 or Citizen CX, have a surface roughness with needle-shaped elevations that are intended to ensure a good connection to the recording material. With the recording materials currently in use, however, due to the properties of the contact surfaces of the recording material and the transport rollers of the printer, friction occurs during transport of the recording material in the printer, so that optimal positioning of the recording material to the print head cannot be guaranteed. In successive printing processes, there is an offset between the print image already applied and the print image applied in the subsequent printing process, and the print image quality is thus impaired.

Recording materials for thermal sublimation printing have already been sufficiently described in the prior art. They essentially consist of a carrier material, a dye-receiving layer and optionally other functional layers.

For example, uncoated or coated papers are used as the carrier material, with synthetic resin-coated, in particular polyolefin-coated papers or papers provided with a multi-layer plastic film being particularly suitable. Such carrier materials are, for example, in EP 3 028 866 A1 described.

The dye-receptive layer mainly contains a resin which has an affinity with the dye from the donor layer of the ink ribbon. Plastics with ester compounds, such as polyester resins, polyacrylic acid ester resins, polycarbonate resins, polyvinyl acetate resins, styrene acrylate resins, or plastics with amide compounds, such as polyamide resins, or polyvinyl chloride and mixtures of the plastics mentioned are used for this purpose. The use of copolymers which contain at least one of the abovementioned plastics as the main component, such as vinyl chloride/vinyl acetate copolymer, is also known in the prior art.

So-called anti-curl layers, for example, are used as further functional layers in order to counteract a buckling of the recording material after it has passed through the thermal printer. Well suited for this are, for example, plastic foils that are laminated on the back of the recording material. However, laminating the plastic films onto the back of the recording material has the disadvantage that it requires an additional process step, this increases the complexity of the recording material and the resultant surface quality of the recording material allows slip-free and thus offset-free transport in the printer not allowed. In addition, there is a risk of delamination in the case of recording materials laminated with plastic films.

Another possibility, described in the prior art, of counteracting the buckling of the recording material after it has passed through the thermal printer consists in applying a functional layer with a higher application weight and associated greater thickness, which counteracts the curl or buckling. The disadvantage of this procedure is that it requires a large amount of material and is therefore uneconomical.

the JP 2015 193251 describes a recording material in which a polyolefin layer has been applied to both sides of the carrier material, the densities and application weights of the polyolefin layers applied to both sides of the carrier material differing. However, the application of polyolefins still leads to the transport difficulties in the printer known from the prior art. A displacement-free transport of the recording material in the printer is therefore not guaranteed.

Against the background of the prior art described, there is therefore a need for recording materials for thermal sublimation printing which do not have the transport difficulties described in the printer, or only do so to a small extent.

It is therefore the object of the invention to provide a recording material for thermal sublimation printing which, with regard to its transport properties in the printer, has improved behavior, in particular less offset, compared to recording materials of the prior art and thus improved print quality, while retaining the others a recording material in the thermal printing process.

1. a. ein Rohpapier mit einer Vorder- und einer Rückseite
2. b. mindestens eine Kunstharzschicht auf zumindest der Rückseite des Rohpapiers
3. c. eine farbstoffaufnehmende Schicht, die auf der Vorderseite des Rohpapiers angeordnet ist,
4. d. mindestens eine Kunststofffolie, die zwischen dem Rohpapier und der farbstoffaufnehmenden Schicht angeordnet ist sowie
5. e. optional eine Barriereschicht, die zwischen der Kunststofffolie und der farbstoffaufnehmenden Schicht angeordnet ist,

wobei die Kunstharzschicht einen E-Modul von mindestens 0,8 GPa aufweist.This problem is solved by a comprehensive recording material for thermal sublimation printing

1. a. a base paper with a front and a back
2. b. at least one synthetic resin layer on at least the back side of the base paper
3. c. a dye-receptive layer arranged on the front side of the base paper,
4. i.e. at least one plastic film which is arranged between the base paper and the dye-receiving layer and
5. e. optionally a barrier layer arranged between the plastic film and the dye-receiving layer,

wherein the synthetic resin layer has a modulus of elasticity of at least 0.8 GPa.

Surprisingly, it was found that such a recording material does not have the transport difficulties in the printer described in the prior art, or only to a significantly lesser extent. A significantly improved print quality can therefore be achieved with the recording material according to the invention compared to the recording material of the prior art.

For the purposes of the invention, the term base paper means uncoated or surface-sized paper.

In addition to cellulose fibers, a base paper can contain sizing agents such as alkylkentene dimers, 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 or cationic starches, optical brighteners, fillers, pigments , dyes, defoamers and other auxiliaries known in the paper industry. The base paper can be made on a Fourdrinier or a Yankee paper machine (cylinder paper machine). The basis weight of the raw paper can be 50 to 250 g/m ² , in particular 80 to 180 g/m ² . The base paper can uncompacted or compressed (smoothed) form. Raw papers with a density of 0.8 to 1.2 g/cm ³ , in particular with a density of 0.9 to 1.1 g/cm ³ , are particularly suitable.

For example, bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), bleached hardwood sulfite pulp (LBSP) or bleached softwood sulfite pulp (NBSP) can be used as pulp fibers. Pulp fibers obtained from waste paper can also be used. The cellulose fibers mentioned can also be used in a mixed form and proportions of other fibers, for example synthetic resin fibers, can be mixed in. However, pulp fibers made from 100% hardwood pulp are preferably used. The average fiber length of the unbeaten pulp is preferably 0.5 to 0.85 mm (Kajaani measurement).

Kaolins, calcium carbonate in its natural forms such as limestone, marble or dolomite, precipitated calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, talc, silica, aluminum oxide and mixtures thereof in the raw paper can be used as fillers.

The base paper can be surface sized. Sizing agents suitable for this purpose are, for example, polyvinyl alcohol or oxidized starch. According to a particular embodiment of the invention, the sizing agent can additionally contain at least one pigment. The pigment is preferably selected from the group consisting of metal oxides, silicates, carbonates, sulfides or sulfates and mixtures thereof. Pigments such as kaolins, talc, calcium carbonate and/or barium sulfate have proven particularly useful in practice. By adding pigment to the sizing agent, the surface quality of the raw paper, in particular its smoothness, can be improved.

The recording material according to the invention has at least one synthetic resin layer on at least the reverse side of the raw paper, the synthetic resin layer having a modulus of elasticity of at least 0.8 GPa. The determination of the modulus of elasticity can be carried out using the methods known to those skilled in the art. The modulus of elasticity is preferably determined using the Lorentzen & Wettre Tensile Tester in accordance with the tensile strength test described in the test section.

According to the invention, the back of the base paper is understood to mean the side of the base paper facing the transport rollers in the printer.

According to a preferred embodiment of the invention, the synthetic resin layer has a modulus of elasticity of at least 0.90 GPa, particularly preferably at least 0.95 GPa, very particularly preferably at least 1.0 GPa.

The synthetic resin layer may preferably contain a thermoplastic polymer. According to one embodiment of the invention, biotechnologically produced polymers are used as thermoplastic polymers. According to an alternative embodiment of the invention, the thermoplastic polymers used are polymers that have been produced from renewable raw materials. According to a further alternative embodiment, polylactic acid (PLA) and native or modified starches and mixtures thereof are used as thermoplastic polymers. Preferred thermoplastic polymers are polyolefins, for example low-density polyethylene (LD-PE), high-density polyethylene (HD-PE), polypropylene (PP), 4-methylpentene-1 homo- and copolymers (TPX) and mixtures thereof, and also polyesters, for example polycarbonates .

According to a preferred embodiment of the invention, the synthetic resin layer contains HD-PE, LD-PE, 4-methylpentene-1 homo- and copolymers (TPX) and mixtures thereof. It has proven to be particularly practical if the synthetic resin layer contains at least 40% by weight HD-PE, in particular 60 to 80% by weight HD-PE. The HD-PE used in the synthetic resin layer preferably has a density of more than 0.95 g/cm ³ . It has also proven to be particularly practical if the synthetic resin layer contains up to 25% by weight of LDPE. Preferred the LD-PE used in the synthetic resin layer has a density of less than 0.935 g/cm ³ .

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

According to a particularly preferred embodiment of the invention, the rear synthetic resin layer consists of 0 to 25% by weight TPX, 55 to 85% by weight HD-PE and 5 to 25% by weight LD-PE, based on the dry weight of the synthetic resin layer. A recording material according to the invention with a synthetic resin layer designed in this way on the back has particularly good transport properties in the printer, so that offsetting of the printed image during printing can be largely prevented.

The synthetic resin layer can contain white pigments such as titanium dioxide and other pigments as well as other auxiliaries such as optical brighteners, dyes and dispersants.

It has proven 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 pigments are preferably selected from calcium carbonate, aluminum oxides, aluminum silicates or mixtures thereof. The surface properties of the synthetic resin layer can be further optimized by adding the pigments.

According to a particularly preferred alternative embodiment of the invention, the synthetic resin layer on the back consists of 5 to 25% by weight of 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 designed in this way on the back of the recording material according to the invention leads to significantly less friction with the surfaces of the transport rollers of the printer, so that offset of the printed image during printing can be significantly reduced or largely prevented.

The application weight of the synthetic resin layer can be 5 to 50 g/m ² , in particular 5 to 30 g/m ² , preferably 10 to 20 g/m ² .

According to a preferred embodiment, the synthetic resin layer is extruded or applied as a film.

The synthetic resin layer can be extruded onto the base paper in a single layer or co-extruded in multiple layers. Extrusion coating can take place at machine speeds of up to 600 m/min.

The recording material according to the invention also comprises a dye-receiving layer which is arranged on the front side of the base paper. According to the invention, the front side of the base paper is understood to mean the side of the base paper facing the print head of the printer.

In principle, 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 contains a polymer selected from polyesters, polyacrylic acid esters, polycarbonates, styrene acrylates, vinyl homo- and/or vinyl copolymers or mixtures thereof. The use of vinyl polymers such as polyvinyl chloride, vinyl chloride/acrylate copolymer, vinyl chloride/vinyl acetate copolymer and/or Vinyl chloride/vinyl acetate/vinylidene chloride and mixtures thereof in the dye-receiving layer.

The dye-receiving layer may contain a polar binder such as polyvinyl alcohol and optical brighteners. Starch, polyethylene glycol (PEG) and polyvinyl alcohol are particularly preferably used as polar binders. 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 optical brighteners customarily used in dye-receiving layers and their use therefore does not impair the print quality.

The amount of the polar binders in the dye-receiving layer can be 1 to 25% by weight, in particular 5 to 20% by weight, based on the dry weight of the dye-receiving layer.

Particular preference is given to using stilbenes, ethylene, phenylethylene or thiophene derivatives as optical brighteners. The amount of the optical brighteners can be 0.01 to 10% by weight, in particular 0.05 to 5% by weight, based on the dry weight of the dye-receiving layer.

The dye-receptive layer may further contain an inorganic and/or organic pigment. Finely divided inorganic pigments such as silicon dioxide, aluminum oxide, aluminum oxide hydrate, aluminum silicate, calcium carbonate, zinc oxide, tin oxide, antimony oxide, titanium dioxide, indium oxide or a mixed oxide of these oxides and mixtures thereof are particularly suitable. The amount of the pigment in the dye-receptive layer may be 10 to 90% by weight, particularly 30 to 70% by weight, based on the dry weight of the dye-receptive layer. According to a preferred embodiment of the invention contains the dye-receiving layer as a finely divided inorganic pigment silicon dioxide, in particular finely divided silicic acids.

The dye-receptive layer can optionally also contain other auxiliaries, for example anionic or nonionic surface-active agents, matting agents, dyes, crosslinking agents, lubricants, anti-blocking agents and other customary additives. The amount of the auxiliaries can be 0.01 to 10% by weight, in particular 0.05 to 5% by weight, based on the dry weight of the dye-receiving layer.

The coating composition for forming the dye-receiving layer can be applied inline or offline using any of the application units customary in papermaking. After drying, the application weight of the dye-receiving layer can be at most 5 g/m ² , in particular 0.1 to 3 g/m ² . According to a particularly preferred embodiment, the application weight after drying of the dye-receiving layer is 0.3 to 1.0 g/m ² . It has been found that these application weights improve the color densities in the print.

It has proven to be particularly practical if the synthetic resin layer and/or the dye-receiving layer contain antistatic substances.

According to a preferred embodiment of the invention, the synthetic resin layer and/or the dye-receiving layer contains/contain antistatic substances, in particular electrically conductive inorganic pigments. These antistatic substances may be added in addition to the above pigments optionally contained in the synthetic resin layer and/or dye-receptive layer. The antistatic substances are preferably selected from semiconductors, betaines or ampholytes. The addition of such antistatic substances to the synthetic resin layer and/or dye-receiving layer has proven to be advantageous in preventing charging of the recording material during storage, transport and in the printer and thus prevent the print quality from being impaired by recording material that has already been loaded.

The recording material according to the invention comprises at least one plastic film which is arranged between the base paper and the dye-receiving layer. The plastic film is preferably a biaxially oriented plastic film. The plastic film can be single-layer, but preferably has a multi-layer structure with a porous core layer and at least one non-porous surface layer. The porous core layer is used for thermal insulation, while the non-porous surface layer ensures the smoothest possible surface. According to a particularly preferred embodiment, the plastic film is a biaxially oriented polypropylene film. It has proven particularly advantageous if a plastic film with a thickness of 30 to 60 μm, in particular 35 to 50 μm, is used.

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

According to a further embodiment of the invention, the plastic film comprises organic and/or inorganic fillers. In this context, preference is given to carbonates, such as calcium carbonate or carboxylic acids, and also other fillers with the potential for gas development, which cause foaming of the layer.

The recording material according to the invention optionally comprises a barrier layer which is arranged between the plastic film and the dye-receiving layer.

In addition to the barrier property, which serves to prevent the color from bleeding through, such a barrier layer usually also has an adhesive function in order to ensure good adhesion of the colorant-receiving layer to the plastic film. Such barrier layers are, for example, in EP 3 028 866 A1 described.

According to one embodiment of the invention, a mixture of gelatin and a water-dispersible polymeric binder is used as the barrier layer. The water-dispersible polymeric binder in the barrier layer is preferably a water-dispersible polyester-polyurethane copolymer. According to a further embodiment, crosslinkers are used in the barrier layer which improve the intrinsic and intermediate adhesion. These are preferably polyaziridines.

The coating masses for forming the barrier layer and the dye-receiving layer can be applied to the plastic film separately from one another and using gravure rollers, blades, curtains or all common application methods, i.e. the coating mass produced to form the barrier layer is first applied to the plastic film. In the next step, the coating composition for forming the dye-receiving layer is applied to the dried barrier layer and dried.

However, the coating compositions described above can also be applied "wet-on-wet", for example by means of a multi-layer curtain coating unit.

A disadvantage of the separate application of the barrier layer and the plastic film is that delamination can occur between the individual layers.

For this reason, according to a particular embodiment of the invention, a plastic film is used that already includes a barrier layer. through the Using such a plastic film, delamination between the individual layers can be prevented from occurring. Furthermore, raw material and one process step can advantageously be saved in the production of the recording material.

According to a further embodiment of the invention, there is an adhesive layer between the base paper and the dye-receiving layer. According to a preferred embodiment of the invention, the adhesive layer consists of low-density polyethylene (LD-PE).
According to an alternative embodiment of the invention, the adhesive layer can be constructed like the synthetic resin layer. This means that the structure of the adhesive layer is identical to that of the synthetic resin layer or it can be composed of the materials described above for the synthetic resin layer in the specified amounts.

The adhesive layer can be applied to the base paper, for example by extrusion, and can serve as an adhesive layer for the plastic film applied over it. The thickness of the adhesive layer is preferably 10 to 30 μm, in particular 15 to 25 μm.

Fig.1

Schematischer Aufbau einer Ausführungsform eines erfindungsgemäßen Aufzeichnungsmaterials

Fig.2

SEM-Aufnahme der Kunstharzschicht auf der Rückseite eines Aufzeichnungsmaterials des Standes der Technik mit Transportwalzennadel Einstichen mit Versatz

Fig. 3

SEM-Aufnahme der Kunstharzschicht auf der Rückseite eines erfindungsgemäßen Aufzeichnungsmaterials mit Transportwalzennadel Einstichen ohne Versatz

Fig. 4

Fadenkreuze für die Versatzbestimmung

The invention is described in more detail below using exemplary embodiments.

Fig.1

Schematic structure of an embodiment of a recording material according to the invention

Fig.2

SEM photograph of the synthetic resin layer on the back of a prior art recording material with transport roller needle punctures with offset

3

SEM photograph of the synthetic resin layer on the back of a recording material according to the invention with transport roller needle punctures without offset

4

Crosshairs for offset determination

figure 1 shows a schematic structure of a preferred embodiment of a recording material according to the invention. According to this preferred embodiment, the recording material comprises a base paper 1, on the front of which a dye-receiving layer 2 is arranged. A plastic film 3 is arranged between the base paper 1 and the dye-receiving layer 2 . The recording material has a synthetic resin layer 4 on the back of the base paper 1 . A barrier layer 5 is arranged on the front of the base paper 1 between the plastic film 3 and the dye-receiving layer 2 . Furthermore, an adhesive layer 6 is arranged on the front of the base paper 1 between the plastic film 3 and the base paper 1 .

figure 2 Fig. 13 shows an SEM photograph of the surface of the synthetic resin layer on a back side of a prior art recording medium after successive printing processes. The back shows punctures from the transport roller needles that show an offset. Due to friction between the recording material and the transport rollers, an optimal positioning of the recording material to the print head could not be guaranteed, so that in successive printing processes there is an offset between the print image that has already been applied and the print image that is applied in the subsequent printing process, and thus the print image quality is impaired. This offset can be seen on the surface of the synthetic resin layer on the reverse side of the recording material using the SEM image from the offset feed needle punctures.

figure 3 FIG. 12 shows an SEM photograph of the surface of the synthetic resin layer 4 on the reverse side of a recording material according to the invention after successive printing processes. In contrast to the in figure 2 shown SEM image of a reverse side of a recording material of the prior art after successive printing processes figure 3 be taken that the surface of the synthetic resin layer 4 on the back of the recording material according to the invention no offset of the punctures Has transport roller needles. The recording material according to the invention therefore ensures optimal positioning of the recording material in relation to the print head during transport in the printer, so that excellent print image quality is achieved in successive printing processes.

figure 4 shows two printed images of a crosshair to determine the offset. The offset is determined using the microscope based on the color shift of cyan, yellow, magenta (see crosshairs on the right) in the crosshairs. The sum of all color shifts gives the offset. The offset is a measure of transport properties in the printer. A small offset or no offset (left crosshair) is very desirable.

examples Production of a base paper

A base paper A was made from eucalyptus pulp. For beating, the cellulose was ground as an approximately 5% aqueous suspension (high-density stock) using a refiner to a degree of beating of 36° SR. The concentration of the cellulose fibers in the thin stock was 1% by weight, based on the mass of the cellulose suspension. Additives were added to the thinstock such as cationic starch at 0.4% by weight, as a neutral sizing agent alkyl ketene dimer (AKD) at 0.48% by weight, wet strength agent polyamine-polyamide-epichlorohydrin resin (Kymene ^® ) in an amount of 0.36% by weight and a natural CaCO ₃ in an amount of 10% by weight. The amounts given relate to the dry pulp mass. The thin stock, the pH of which was adjusted to about 7.5, was transferred from the headbox to the wire of the paper machine, whereupon sheet formation took place with dewatering of the web in the wire section of the paper machine. In the press section of the paper machine, the paper web was further dewatered to a water content of 60% by weight, based on the web weight. Further drying took place in the drying section of the paper machine with heated drying cylinders. A raw paper with a basis weight of 132 g/m ² and a moisture content of about 7% was produced.

Production of the recording materials according to the invention and the comparative examples

The side of the base paper opposite the side to be printed (rear side) was coated in the extruder with a layer of synthetic resin composed of the polymer mixtures listed in Table 1. The cooling cylinder was chosen so that the resulting rear surface has a roughness of 0.9 µm, measured _as the Rz value according to DIN 4768.

The surface intended for printing (front side) of the raw paper was, after irradiation with a corona discharge, treated with a three-layer biaxial oriented polypropylene film (Plastic Film, HIPHANE BOPP, Hwaseung Industries Co. Ltd) was laminated in an extruder, with a low-density polyethylene (LD-PE) film being extruded between the face of the base paper and the biaxially oriented polypropylene film. The thickness of the adhesion-promoting polyethylene film (adhesive layer) was 20 μm.

The carrier material obtained was then coated with a barrier layer on the side coated with the plastic film (25 gauge wire doctor) and dried at 78° C. for three minutes. The composition of the respective barrier layer is given in Table 2. The applied amounts of the barrier layer were chosen such that a dry application of 1.6 g/m ² resulted in each case.

In the next step, a dye-receiving layer was applied to the barrier layer (15 gauge wire squeegee) and dried (2 minutes, 78° C.). The application amount of the coating slip of the dye-receiving layer was chosen so that a dry application of 0.5 g/m ² resulted. The composition of the coating slip for the dye-receptive layer is given in Table 3.

Preparation of the coating slip for the dye-receptive layer

31.70 g of a vinyl chloride/acrylate copolymer dispersion with a solids content of 56% by weight ( ^PrintRite® DP 281.E, manufacturer Lubrizol) and 13.58 g of a vinyl chloride/vinyl acetate/vinylidene chloride dispersion with a solids content of 56% by weight % (Vycar ^® 577 E, manufacturer Lubrizol) were mixed with 3.15 g of a 30% aqueous suspension of colloidal silica (Ludox ^® AM X4931, manufacturer Grace), 0.95 g polydimethylsiloxane (TegoGlide ^® 482, manufacturer Evonik Industries), 0.25 g of a defoaming agent (Tego ^Foamex® 825, manufacturer Evonik Industries), 0.08 g of a wetting agent ( ^Capstone® FS 30, 25%, manufacturer DuPont) and 50.29 g of water were mixed.

Table 4 shows the structure of the recording materials obtained according to the examples and comparative examples. To the one thus obtained The offset in the printer was determined for the recording materials, and the dye migration and cloudiness (mottling) were evaluated using the methods described below.

As can be clearly seen from the results in Table 4, the nature of the synthetic resin layer on the back of the recording material plays a significant role with regard to the offset, which is critical in the printing process. Acceptable behavior in the multipass printing process, i.e. little or no offset, is only achieved with the recording materials according to the invention, the synthetic resin layer of which has a modulus of elasticity of at least 0.8 GPa.

measurement methods Dye Migration Test

The samples are printed with the maximum color densities of yellow, cyan, magenta and black on the Mitsubishi CP-D70DW printer with standard donor ribbon. The print format is 10 x 15 cm and the colored areas are 1 x 1 cm. These samples are hung for 5 days at an oven temperature of 80°C. After 5 days, the dye bleed through on the back of the printed sample is assessed using school grades.

The assessment is made as follows: no color bleeding on the back is given a rating of 1, heavy color bleeding over a large area is given a rating of 5. For this purpose, the relative gradation from grade 1 to grade 5 takes place.

Mottle rating (cloudiness)

Samples and printer CP-D70DW from Mitsubishi are preconditioned for 12 hours at 40°C and 80% relative humidity. A 10 x 15 cm full-surface black print is then carried out with the existing climate. The mottle evaluation of the patterns takes place in grades from 1 to 5. The grade 1 means no mottle (no cloudiness) and grade 5 means strong mottle (strong cloudiness). The grade gradation between 1 and 5 is relative to grades 1 and 5.

Young's modulus

The modulus of elasticity is determined according to the tensile strength test using the Lorentzen & Wettre Tensile Tester. For this purpose, samples of the synthetic resin layer are cut to a width of 50 mm and a length of 120 mm. The gauge length is fixed at 100 mm. The measuring speed is 100 mm/min. The thickness and basis weight of the samples are determined and included in the "E-modulus" test program of the Lorentzen & Wettre Tensile Tester. The tensile strength test is then carried out on the samples. The modulus of elasticity is determined from the relationship between mechanical stress and strain in the linear area of the stress-strain diagram.

Method for offset measurement in the printed image

The offset is determined using a crosshair. First, a print image with different crosshairs is printed. The printed crosshairs are then located on the printed image. The offset is based on the color shift of cyan, yellow, magenta (see FIG. 4 , right crosshairs) in the crosshairs determined using a microscope. The sum of all color shifts gives the offset. The offset is a measure of transport properties in the printer. A small offset or no offset (see FIG. 4 , left crosshair) very desirable. <b>Table 1:</b> Composition of the synthetic resin layer and modulus of elasticity of the respective synthetic resin layer A B C D E f G H I HD-PE / wt% 80 75 70 60 80 80 80 0 100 LDPE / wt% 20 20 20 20 15 10 0 100 0 TPX / wt% 0 5 10 20 0 0 0 0 0 Calcium carbonate /% by weight 0 0 0 0 5 10 20 0 0 thickness / µm 20 20 20 20 20 20 20 20 20 solid content / % 100 100 100 100 100 100 100 100 100 Modulus of elasticity / GPa 0.63 0.83 0.97 0.98 0.82 0.99 1.55 0.49 0.67 spread J Coating compound K desalinated water 79.16 79.00 Gelatine (Imagel ^® AP 71979, 290 bloom, isoelectr. point =8, Gelita AG) 5.80 5.80 NH ₃ solution, 5% 1.20 1.20 TiO ₂ (Ti-Pure RPS Vantage 71% in water, DuPont) 2.75 2.91 Optical brightener (Leucophor ^® UO, 25% Archroma International) 3.26 3.26 Polyester polyurethane copolymer (PU-Coat DMP 105, 40% in water, Baumeister Chemicals & Consulting GmbH & Co. KG) 5.00 5.00 Wetting agent (Capstone ^® FS 30, 25% in water, DuPont) 0.07 0.07 Polyaziridine (PZ-33, 50% in IPA, Flevo Chemie BV) 2.76 2.76 solids content 10.04 12:31 PH value 8.5 8.5 Coating L Spread M Coating compound N spread O desalinated water 50.86 41.76 34.38 47.92 Defoaming agent (TegoFoamex 825) 0.25 0.29 0.24 0.17 Vinyl chloride/acrylate copolymer dispersion (Printrite DP-281E) 31:37 37.18 48.28 40.08 Vinyl chloride/vinyl acetate/vinylidene chloride dispersion (Vycar 577 E) 13.44 15.93 13:11 9.07 Colloidal Silica (Ludox AM X4931) 3:12 3.69 3.04 2.10 Polydimethylsiloxane (Tego Glide 482) 0.89 1.06 0.87 0.60 Wetting agent (Capstone FS 30) 0.08 0.09 0.08 0.05 solids content 27.00 32 36.4 29 pH 9 9 9 9 Construction comparison 1 Invention 1 Invention 2 Invention 3 Invention 4 dye-receptive layer L L M M M barrier layer J J J K K plastic film HIPHAN BOPP HIPHAN BOPP HIPHAN BOPP HIPHAN BOPP HIPHAN BOPP Polymer blend of the adhesive layer H H H H H base paper base paper base paper base paper base paper base paper Polymer mixture of the synthetic resin layer A f G G D Modulus of elasticity of the synthetic resin layer/GPa 0.61 0.99 1.55 1.55 0.98 offset 6mm 1 mm 0mm 0mm 0mm Migration (Grade) 1 1 1 1 1 Mottle Test (Grade) 1 1 1 1 1

Claims (15)

Recording material for thermal sublimation printing comprising a. a base paper (1) with a front and a back b. at least one synthetic resin layer (4) on at least the back of the base paper c. a dye-receiving layer (2) which is arranged on the front side of the base paper, i.e. at least one plastic film (3) which is arranged between the base paper and the dye-receiving layer and e. optionally a barrier layer which is arranged between the plastic film (3) and the dye-receiving layer (2). characterized in that the synthetic resin layer (4) has a modulus of elasticity of at least 0.8 GPa. Recording material according to Claim 1 , characterized in that the synthetic resin layer (4) has a modulus of elasticity of at least 0.90 GPa, preferably at least 0.95 GPa. Recording material according to one of the preceding claims, characterized in that the synthetic resin layer (4) has a proportion of pigments of at least 5% by weight, preferably at least 10% by weight, based on the dry weight of the synthetic resin layer. Recording material according to Claim 3, characterized in that the pigments are selected from calcium carbonate, aluminum oxides, aluminum silicates or mixtures thereof. Recording material according to one of the preceding claims, characterized in that the synthetic resin layer (4) contains HD-PE, LD-PE, 4-methylpentene-1 homo- and copolymers (TPX) and mixtures thereof. Recording material according to one of the preceding claims, characterized in that the synthetic resin layer (4) contains a proportion of at least 5% by weight of one of the polymers 4-methylpentene-1 homo- and copolymers (TPX). Recording material according to one of the preceding claims, characterized in that the plastic film (3) is a biaxially oriented plastic film, in particular a biaxially oriented polypropylene film. Recording material according to one of the preceding claims, characterized in that the plastic film (3) comprises a barrier layer (5). Recording material according to Claim 8, characterized in that a mixture of a water-dispersible polymeric binder and gelatin is used as the barrier layer (5). Recording material according to Claim 9, characterized in that the water-dispersible polymeric binder in the barrier layer (5) is a polyester-polyurethane copolymer. Recording material according to one of the preceding claims, characterized in that the dye-receiving layer (2) contains an optical brightener and a polar binder. Recording material according to Claim 11, characterized in that the polar binder in the dye-receiving layer (2) contains polyvinyl alcohol modified with carbonyl or carboxyl groups. Recording material according to Claim 12 or 13, characterized in that the polar binder makes up a proportion of 5 to 20% by weight of the dye-receiving layer (2). Recording material according to one of the preceding claims, characterized in that an adhesive layer (6) is additionally applied to the front side of the base paper (1) and is arranged between the base paper (1) and the plastic film (3). Recording material according to Claim 14, characterized in that the adhesive layer (6) consists of LD-PE.

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