EP4053333B1 - Transfer material for sublimation printing based on paper having barrier function against inks - Google Patents

Description

The invention relates to a transfer material for the dye sublimation process and a process for its production. The invention further relates to a method for transferring an inkjet printed image from the transfer paper according to the invention to a receiving material.

For printing materials such as textiles or rigid bodies that are difficult to print using direct printing processes for mechanical reasons, transfer printing processes are available, in which a flexible sheet-shaped transfer material is first printed and the printed image is transferred from this to the object to be printed. A special embodiment of such a transfer printing process is the dye sublimation process, which is described, for example, in B. Thompson: Printing Materials - Science and Technology (1998) on page 468. In this process, the image to be printed is applied to the transfer material using printing inks which, after the print has dried, are evaporated under the influence of heat and are image-wise deposited again from the gas phase on the material to be finally printed. The sublimation colors can advantageously be applied to the transfer material using digital printing, in particular the inkjet printing process, which enables individual and personalized prints, for example on textiles. Printing inks for the inkjet printing process with dyes that can be transferred to the final print medium by sublimation are, for example, in the DE 102 46 209 A1 described.

Common transfer materials onto which the printed image to be transferred is printed using inkjet printing technology include a carrier, for example a base paper, which is coated with an ink-receiving layer.

A transfer material suitable for the dye sublimation process should, on the one hand, enable good absorption of the ink liquid when printing with the image to be transferred, otherwise the print sharpness will suffer, and on the other hand, the loss of sublimable dye should be as small as possible when the printed image is transferred to the image to be printed material occur. Ideally, a loss of sublimable dye through penetration into the paper interior of the carrier and onto the surfaces of the transfer presses, so-called ink strikethrough, should be completely prevented when the printed image is transferred from the transfer material to the material to be printed.

The transfer materials used on the market for sublimation printing can basically be divided into two groups. On the one hand, there is the group of transfer materials in which film-forming binders are used in the ink-receiving layer and which already have a certain barrier function against the penetration of inks due to the film-forming binders. On the other hand, microporous ink-receiving layers are used, which predominantly use non-film-forming binders in the ink-receiving layer. In these latter products, ink bleed-through is solved by applying at least one barrier layer to the back of the carrier or between the carrier and the ink-receiving layer. However, problems arise both during production and later use due to the stickiness of the barrier layers. Another problem in use is the significant deterioration in curl properties (undesirable rolling up of the paper) by applying a barrier layer.

In the EP 1 101 682 A1 describes a coated paper that has low air permeability on the side to be printed. This is intended to prevent part of the sublimable dyes from penetrating the porous paper interior of the carrier during the sublimation transfer step and thus being lost for transfer to the material to be finally printed. However, such papers with a low porosity on the side to be printed absorb the inkjet ink liquid very slowly and lead, especially at high levels Printing speeds, slow drying and the ink running on the surface and thus unsatisfactory print sharpness.

This also applies to those in the EP 1 878 829 A1 described transfer materials with swellable, non-porous ink receiving layers. The EP 1 878 829 A1 describes that the use of synthetic polymers such as polyethylene (PE), polyester (PES), polyacrylates and other synthetic thermoplastic polymers as an additional coating on the backing paper leads to a deterioration in the quality properties of the print image transferred to the material to be printed using the dye sublimation process because these polymers have a disadvantageously high color retention capacity and thus lead to a lower transfer rate of the dye.

In the US 2008/229962 A1 A coating for a backing paper is proposed which contains silica and a comparatively small amount of binder and thus has considerable air permeability. Although this achieves good absorption of the ink liquid when printing the transfer material with the image to be transferred, there is no bleed-through of the dye, ie a loss of sublimable dye due to penetration into the interior of the paper and onto the surfaces of the transfer presses during transfer to the final image to be imaged Material, however, is not sufficiently prevented by this coating.

In the EP 3 302 991 A2 will also describe a porous ink-receiving layer with a small amount of binder and inorganic fillers, which is characterized by good ink absorption and print quality. To avoid the loss of sublimable dye, barrier layers are described on the back of the transfer material or between the backing paper and the dye-receiving layer. However, due to the polymer-based barrier layers applied on one side, the curling properties of the backing paper increase, which is problematic in further processing. In addition, a barrier layer applied to the back can lead to the back being sticky and therefore undesirable Adhesion of the transfer material to the surfaces of the transfer presses when used in the dye sublimation process.

A so-called thermal transfer material is also available DE 10 2014 116550 A1 described. In particular, it is proposed to use thermoplastic particles with a melting point of 35 ° C to 150 ° C and an average particle size of 0.3 to 5 μm in the ink-receiving layer. The thermoplastic particles are intended to optimize the adhesion of the printed ink-receiving layer to the front of the thermal transfer material when transferring the printed image to flat textiles using the dye sublimation process. The color receiving layer of the DE 10 2014 116550 A1 has a binder content of 55 to 80% dry and can also contain pigments. With this proportion of binder in the ink-receiving layer, even in the presence of pigments, there is a closed, film-like layer that is not porous. Disadvantageous to the in DE 10 2014 116550 A1 The procedure described is therefore that the drying speed is significantly lower than when using microporous ink-receiving layers, so that the inkjet ink liquid is only absorbed very slowly. At high printing speeds, the slow drying leads to the ink running on the surface of the transfer material and thus to unsatisfactory print sharpness of the printed image. In addition, a large amount of thermoplastic particles must be used in the ink-receiving layer in order to achieve any noticeable adhesion of the front side of the thermal transfer material to the textile. Due to the high amount of thermoplastic particles in the ink-receiving layer, the print quality (line sharpness) and the transfer quality (optical densities on textile) of the transfer material can be severely impaired. With this approach it is also not possible to control textile adhesion independently of the print and transfer quality.

Against the background of the prior art, the invention is based on the object of providing a transfer material for the dye sublimation process which allows little or no penetration of sublimable dyes through the carrier of the transfer material in which the known problems of the prior art transfer materials do not occur.

This problem is solved by a transfer material for the dye sublimation process, comprising a carrier paper which is coated on one side with a dye-receiving layer, the carrier paper containing at least 1.5% by weight, based on the dry weight of the pulp, of a polymer dispersion selected from the Group consisting of polyacrylates, polyesters, polyolefins or mixtures thereof.

Surprisingly, it was found that the introduction of at least the specified amount of specific polymer dispersions and mixtures thereof into the backing paper of the transfer material according to the invention leads to a significant improvement and even prevention of the breakthrough of sublimable dyes when used in the dye sublimation process. Without wishing to be bound to scientific theories, the polymer dispersion in the carrier paper of the transfer material according to the invention appears to form a barrier to the sublimable dye inks without the need for complete closure of the carrier paper by means of an additional barrier layer. The barrier effect appears to be based on sorption processes between the sublimable dyes and the specific polymers. Because it is not necessary to apply an additional barrier layer to the transfer material according to the invention, the transfer material according to the invention has the disadvantages associated with the application of this barrier layer, such as stickiness, impaired curl properties and insufficient porosity of the ink-receiving layer and, associated with this, slow drying and bleeding Ink on the surface and unsatisfactory print sharpness, not on.

The transfer material according to the invention comprises a backing paper.

The backing paper is preferably an uncoated or surface-sized paper. In addition to cellulose fibers, the backing paper can contain sizing agents such as Alkyl kentenedimers, fatty acids and/or fatty acid salts, epoxidized fatty acid amides, alkenyl or alkyl succinic anhydride, starch, tree resins, wet strength agents such as polyamine-polyamide-epichlorohydrin, dry strength agents such as anionic, cationic or amphoteric polyamides, optical brighteners, pigments, dyes, defoamers and others in the paper industry contain known chemical additives. Usually in paper production, sizing agents with an added amount of 0.2% or less, wet strength agents with an added amount of 0.5% or less and dry strength agents with an added amount of 1.0% or less are used. The amounts added are dosed as low as possible in order to avoid costs and unnecessary and uncontrolled multiple circulation of the agents in the material cycle.

The backing paper can be surface-sized. Suitable sizing agents for this are, for example, polyvinyl alcohol or starch dextrins or modified starches such as oxidized starches or starch ethers. The backing paper can be produced on a fourdrinier machine with or without a top wire. The basis weight of the backing paper can be 30 to 200 g/m ² , in particular 40 to 120 g/m ² . The backing paper can be used in uncompacted or compressed form (smoothed). Backing papers with a density of 0.6 to 1.05 g/cm ³ , particularly 0.70 to 0.9 g/cm ³ , are particularly suitable. The smoothing can be done in the usual way with calendering.

All pulps commonly used for this purpose can be used to produce the backing paper. The pulp for producing the backing paper is preferably a eucalyptus pulp with a fiber content of less than 200 μm after grinding of 10 to 35% by weight and an average fiber length of 0.5 to 0.75 mm. It has been shown that the use of a pulp with a limited proportion of fibers smaller than 200 µm reduces the loss of stiffness that occurs when using filler.

Hardwood pulp (NBHK - Northern Bleached Hardwood Kraft Pulp) and softwood pulp can also be used.

According to the invention, the backing paper contains at least 1.5% by weight, based on the mass of the pulp, of a polymer dispersion selected from the group consisting of polyacrylates, polyesters, polyolefins or mixtures thereof. (hereinafter also polymer dispersion according to the invention).

The use of at least 1.5% by weight of the polymer dispersion according to the invention surprisingly leads to a significant improvement in the barrier properties of the transfer material without the need for an additional barrier layer, as in the prior art. The amounts used of the polymer dispersion according to the invention are significantly above the amounts used for conventional polymer dispersions used in the production of a backing paper, such as sizing agents, wet strength agents or dry strength agents.

The polyacrylates used according to the invention are, for example, styrene-alkyl acrylate copolymer or methyl methacrylate. The alkyl in the styrene-alkyl acrylate copolymer preferably has the meaning methyl, ethyl, propyl, butyl and/or hexyl. Preferably the alkyl in the styrene-alkyl acrylate copolymer is ethyl or butyl. Copolymers can be used as mixtures of the aforementioned alkyl groups in the alkyl acrylate portion of the styrene-alkyl acrylate copolymer. The polyesters used according to the invention are preferably selected from the group consisting of polybutylene terephthalate, polyethylene terephthalate, polylactide, polytrimethylene terephthalate, polyethylene naphthalate, polycarbonate, polyester carbonate. Polyethylene, polybutylene, polymethylpentene and polyisobutylene, for example, can be used as polyolefins.

According to a preferred embodiment of the invention, the backing paper contains at least 2% by weight, in particular at least 2.5% by weight, preferably at least 3% by weight, based on the mass of the pulp, of a polymer dispersion according to the invention. It has been found that such a transfer material has a further improved barrier effect, so that there is a further significant reduction in ink bleed-through with such a transfer material. It has proven to be particularly practical if the polymer dispersion is evenly distributed within the thickness of the backing paper. This ensures a particularly high level of consistent barrier effect over the entire surface of the carrier material.

In addition to cellulose fibers, portions of other natural or synthetic fibers can also be used to produce the backing paper. The proportion of other fibers in the total fiber mass is preferably less than 40% by weight; proportions of other fibers are particularly preferred below 20% by weight.

According to a preferred embodiment, the backing paper contains at least 5% by weight, in particular between 5 and 20% by weight, most preferably between 8 and 15% by weight. based on the mass of the pulp, synthetic fibers, in particular polyethylene fibers or polyethylene terephthalate fibers. The synthetic fibers preferably have a length of between 2 and 6 mm, preferably between 4 and 6 mm. The diameter of the synthetic fibers can be between 30 and 110 µm, preferably between 50 and 100 µm.

It has been found that the barrier effect of the transfer material according to the invention can be further enhanced by the additional use of synthetic fibers in the backing paper.

According to a preferred embodiment of the invention, the ink penetration of the transfer material according to the invention is below 30%, preferably below 20%, particularly preferably below 15%. In practice, ink bleed-through of up to 30% is acceptable, but leads to a loss of sublimable dye. A transfer material with an ink penetration of less than 20% or less results in significantly less dye loss and is therefore more efficient overall.

The backing paper may contain fillers and pigments.

Fillers and pigments for the production of the backing paper can be, for example, kaolins, calcium carbonate in its natural form such as limestone, marble or dolomite stone, precipitated calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, talc, silica, aluminum oxide, aluminum and magnesium silicates or silicas and mixtures thereof Raw paper can be used.

According to a preferred embodiment, the backing paper according to the invention contains at least 5% by weight, based on the mass of the pulp, of one or more pigments. The use of hydrophobic pigments, in particular those selected from the group consisting of kaolin, calcium carbonate, aluminum and magnesium silicates or silicas and mixtures thereof, has proven to be particularly practical. It has been found that the use of such hydrophobic pigments in the backing paper according to the invention further improves the barrier effect for sublimable dyes. Without wishing to be bound to scientific theories, this also appears to be based on interactions or sorption processes between the sublimable dyes and the hydrophobic pigments, which significantly reduce the migration speed of the sublimable dyes. This interaction can be further strengthened by using hydrophobic pigments with a high specific surface area. The hydrophobic pigment therefore preferably has a specific surface area of greater than 80 m ² /g.

The backing paper of the transfer material according to the invention is coated on one side with an ink-receiving layer. The ink-receiving layer is arranged on the side of the backing paper to be printed.

The ink-receiving layer can be a porous or microporous layer. A porous ink-receiving layer in the sense of the invention contains before printing. connected air-filled cavities (pores). These pores can Ink liquid is absorbed very quickly by capillary forces and this leads to the printed image drying quickly. In contrast to film-like ink-receiving layers, such porous ink-receiving layers contain a high proportion of pigment particles and comparatively only small proportions of (film-forming) binder.

Porous ink-receiving layers have a high air permeability, which can be determined using the Bendtsen method. Their pore volume can be detected and determined, for example, by liquid absorption measurements or by mercury porositometry.

The porous ink-receiving layer thus contains inorganic pigment and binder. Pigments with an anionic, neutral or only weakly cationic surface such as silica, calcium carbonate, kaolin, talc, bentonite, aluminum oxides or aluminum oxide hydrates are particularly preferred. However, finely divided polymeric compounds can also be included, with high-melting thermoplastic or thermoset polymers being preferred. In a further embodiment of the invention, the ink-receiving layer can also contain a mixture of two or more pigments. The pigments preferably have an average particle size of 100 nm to 30 µm, particularly preferably 200 nm to 10 µm.

The ink-receiving layer preferably additionally contains a polymeric binder, preferably a hydrophilic polymeric binder. The binder may be a water-soluble or water-dispersed binder. Preferred binders are styrene copolymers, polyvinyl alcohol, starch, modified starch, polyvinyl acetate, acrylates or polyurethane dispersions. The mass ratio of pigment to binder is 100:1 to 100:50, preferably 100:40 to 100:2.

The application weight of the ink-receiving layer is preferably 1 g/m ² to 50 g/m ² , particularly preferably 3 g/m ² to 30 g/m ² . The air permeability of the Color receiving layer, measured according to Bendtsen, is preferably greater than 100 ml/min, particularly preferably 200 ml/min to 500 ml/min.

The ink-receiving layer is preferably applied to the paper carrier by applying aqueous coating slip, whereby all application methods common in the paper industry can be used. Application using a blade, squeegee, film press or curtain coating is preferred. A multi-layer curtain coating process is particularly preferred:

The coating slips can contain other common additives such as wetting agents, thickeners, rheology aids, dyes and optical brighteners.

One or more further layers can be arranged between the backing paper and the ink-receiving layer in the transfer material according to the invention. These are preferably layers containing a hydrophilic binder.

1. (a) Herstellen eines Trägerpapiers auf einer Papiermaschine, wobei mindestens 1,5 Gew.-%, bezogen auf die Masse des Zellstoffes, einer Polymerdispersion, ausgewählt aus der Gruppe, bestehend aus Polyacrylaten, Polyestern, Polyolefinen oder deren Mischungen, während der Herstellung des Trägerpapiers der Zellstoffsuspension zugegeben werden;
2. (b) Trocknen und Glätten des Trägerpapiers;
3. (c) Aufbringen der Farbempfangsschicht auf eine Oberfläche des Trägerpapiers; und
4. (d) Trocknen des in Schritt (c) erhaltenen Transfermaterials.

A further subject of the invention is a method for producing the carrier material according to the invention, comprising the following steps:

1. (a) Producing a backing paper on a paper machine, wherein at least 1.5% by weight, based on the mass of the pulp, of a polymer dispersion selected from the group consisting of polyacrylates, polyesters, polyolefins or mixtures thereof, during the production of the Backing paper is added to the pulp suspension;
2. (b) drying and smoothing the backing paper;
3. (c) applying the ink-receiving layer to a surface of the backing paper; and
4. (d) drying the transfer material obtained in step (c).

The method according to the invention is characterized in comparison to the methods known in the prior art for producing transfer materials for the dye sublimation process in that the step of additionally applying a barrier layer between the ink-receiving layer and the backing paper or on the back (which is not with a Ink receiving layer coated side) of the backing paper is omitted since the barrier effect is created by the addition of the polymer dispersion during the production of the backing paper. This saves process steps and raw materials in the production of the transfer material. The method according to the invention is therefore significantly more efficient than the procedures known from the prior art.

The information already given above in connection with the transfer material according to the invention applies accordingly to the method according to the invention.

According to a preferred embodiment of the method according to the invention, the method comprises the following additional step (a1) between step (a) and step (b):
(a1) Impregnation of the backing paper with an impregnation solution which comprises at least 1.0 g/m ² of a polymer dispersion selected from the group consisting of polyacrylates, polyesters, polyolefins or mixtures thereof, in a size or film press.

The impregnation solution can comprise the same polymer dispersion that was already added to the pulp suspension to produce the backing paper in step (a). Additional impregnation of the backing paper leads to a further reduction in ink bleed through without any loss of productivity in the wet section of the paper machine. The use of large amounts of polymer dispersion in the wet part of the paper machine is usually avoided, as this leads to disruptions in the sensitive balance of the white water cycle in terms of charge and colloidal interactions of the particles, which has a negative impact on the productivity of the manufacturing process. The possibility of adding the polymer dispersion both in the wet part of the paper machine and in the size or film press The process-related risk of a deterioration in production efficiency can be reduced, since two different times can be used during paper production to introduce a certain total amount of polymer dispersion, so that there is no locally excessive concentration of the polymer dispersion in the wet part of the paper machine or in the glue - or film press and therefore does not suffer from the disadvantages described above.

According to a preferred embodiment, the backing paper is impregnated in step (a1) with an impregnation solution which has at least 1.5 g/m ² , preferably at least 2.0 g/m ² , particularly preferably at least 2.5 g/m ² , very particularly preferably comprises at least 3.0 g/m ² of the polymer dispersion according to the invention.

In addition to the polymer dispersion according to the invention, the impregnation solution used in step (a1) can contain the additives commonly used in paper production and described above in connection with the production of the backing paper, such as sizing agents, wet strength agents, dry strength agents, optical brighteners, fillers, pigments, dyes, defoamers and others contain chemical additives known in the paper industry.

Finally, the present invention also relates to a method for transferring an image to a receiving material by sublimation, wherein a transfer material according to the invention is printed with an image using the ink-jet printing process and the image is transferred to a receiving material by sublimation.

According to a preferred embodiment of the method according to the invention, the receiving material is selected from polyester fabric, polyester fleece or a polyester-coated material.

Fig. 1 shows schematically a cross section through a transfer material according to the invention. 1 denotes a paper carrier. The backing paper contains the polymer dispersion according to the invention. The backing paper is coated on one side with an ink-receiving layer 2 for inkjet printing.

The following examples serve to further explain the invention.

Examples Production of a backing paper

Eucalyptus pulp was used to produce the backing paper. For grinding, the pulp was ground as an approximately 5% aqueous suspension (thick matter) using refiners to a grinding degree of 25 °SR. The concentration of the pulp fibers in the thin material was approximately 1% by weight, based on the mass of the pulp suspension. Further additives were added to the thin material, such as a neutral sizing agent alkyl ketene dimer (AKD) in an amount of 0.15% by weight, wet strength agent polyamine-polyamide-epichlorohydrin resin (Kymene ^® ) in an amount of 0.60% by weight, starch ( C-Bond HR 35845) in an amount of 1.0% by weight and a natural ground CaCOa in an amount of 30% by weight. The quantities refer to the pulp mass. The thin stock, whose pH 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, 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. The result was a base paper with a basis weight of 63 g/m ² , a filler content of 18% by weight and a moisture content of approximately 5.5%.

Production of a coating slip for the color receiving layer

To 441 g of a diluted dispersion of precipitated calcium carbonate (Precarb ^® 800 from Schaefer Kalk) with a solids content of 48% by weight, 557g of an aqueous 9.5% by weight solution of a partially saponified polyvinyl alcohol (Mowiol ^® 18-88 from the company Kuraray) was added and the mixture was mixed with a dissolver stirrer. Then 0.5 g of surfactant Surfynol ^® 440 from Air Products is added. The coating slip obtained has a solids content of 26.6% by weight, a viscosity of 150 mPas, a pH of 7.5 and a surface tension of 36 mN/m.

Production of the transfer material

The resulting surface-sized, dried and smoothed backing paper is coated on one side with the coating material for the color-receiving layer.

Preparation of the examples according to the invention and the comparative examples

The transfer materials listed in the following table were produced according to the process described above. When producing the backing paper, the barrier component mentioned in the first column of Table 1 was used in exchange for eucalyptus pulp. The first comparative example corresponds to the one produced. Carrier material without the addition of a further barrier component in the production of the carrier paper in exchange for pulp and is accordingly referred to as “without barrier component”. The comparative example, which is referred to in the first column of the table as "without barrier component with an additional barrier layer", was produced according to the above-mentioned process, but here no barrier component was added to the backing paper during its production and the backing paper was additionally added to the side opposite the ink-receiving layer provided with a barrier layer made of a thermoplastic polymer, such as a fully saponified polyvinyl alcohol (eg Mowiol ^® 28-99). Table 1: Transfer materials /*Advansa Standard 1.7-6-309 NSD was used Added barrier component in the backing paper Barrier component / wt.% Optical density Ink Throughput /% Stickiness in the transfer process Curl mean without barrier component 0 Comparison 4.31 80 Note 1 0 without barrier component with additional barrier layer 0 Comparison 4.45 20 Note 3 5 PE fibers (Advansa*) 5 Comparison 4.38 50 Note 1 0 Styrene-alkyl acrylate copolymer / PE fibers (Plextol DV 544/ Advansa*) 1/5 Inventive 4.37 30 Note 1 0 Styrene-alkyl acrylate copolymer (Plextol DV 544) 1 Comparison 4.35 50 Note 1 1 Styrene-alkyl acrylate copolymer (Plextol DV 544) 3 Inventive 4.32 25 Note 1 0 Styrene-alkyl acrylate copolymer (Plextol DV 544) 5 Inventive 4.51 10 Grade 2 0 Cationic styrene-alkyl acrylate copolymer (Eurocryl 2324) 1 Comparison 4.33 50 Note 1 1 Cationic styrene-alkyl acrylate copolymer (Eurocryl 2324) 5 Inventive 4.47 0 Grade 2 0

The data listed in Table 1 show that the use of at least 1.5% by weight, based on the mass of the pulp, of a polymer dispersion according to the invention in the backing paper of the recording material according to the invention leads to the desired barrier effect, i.e. to a low ink penetration. Positive properties such as good optical densities are retained during printing and very good curl behavior and low stickiness can be observed in the transfer process. The combination of good barrier properties, low stickiness in the transfer process and very good curling behavior can only be achieved with the recording materials according to the invention. The results in Table 1 show that this combination of properties with the recording materials described in the prior art without a barrier layer or with an additional barrier layer as well as with recording materials which contain less than 1.5% by weight, based on the mass of the pulp, of the polymer dispersion according to the invention Have backing paper, cannot be reached.

Methods

The resulting transfer materials were printed with a color image using the EPSON Workforce Pro WF 5110 inkjet printer with SubliJet IQ sublimation color inks from Sawgrass.

Determination of ink penetration

The sublimation transfer paper to be tested is stored in DIN A 4 format for at least 1 hour in the printing room at a standard climate of 23°C and 50% humidity.

Printing is done on standard sublimation desktop printers. The print file contains 10 round color fields with different sloping amounts of ink to be printed in black. The print field at the top left is printed with 100% ink and the following areas are printed with 10% less ink. Below the print fields is the name of the field in % and is stated as 100% - amount of ink applied in %. For example, the ink field that is printed with 80% ink is labeled 20%. The following image shows the print file.

After printing, the paper is left to dry in a standard climate for 1 hour. The sublimation process then takes place in the Sefa ROTEX AUTO X REL transfer press with a height indicator. For this purpose, the open transfer press is heated to 200°C. Once the temperature has been reached, the textile is first placed on the floor heating plate and the printed paper is placed on top with the printed side towards the textile. Immediately afterwards, the so-called cover paper, which is an 80 g/m ² copy paper made from bleached cellulose, is placed on the back of the printed sublimation paper and the transfer press is closed. The sublimation time is 30 seconds with medium contact pressure.

After the sublimation period has expired, the transfer press is opened and the 3 layers are carefully separated from each other. The textile is discarded. If there is poor ink penetration, the sublimation ink sublimates to the back and, depending on the intensity of the ink penetration, is deposited more or less on the copy paper. The amount of ink plays an important role. The higher the amount of ink on the printed sublimation paper, the higher the tendency for ink to bleed through towards the back or cover page.

Since there are color patches with different amounts of ink on the printed sublimation paper, the gradation of the ink transfer is on the cover sheet equally visible. To assess the ink penetration, a visual inspection of the cover sheet is carried out. The color field that is just visible in daylight is marked and given as a % value for ink bleed through.

Sublimation paper with poor ink penetration results in values of 70-90%. Values of 60-40% are obtained on papers with improved ink penetration. Papers with very good resistance to ink bleed-through receive values of 30-0%. An exact scaling of the tendency to ink bleed through can be specified in % values. Figure 2 shows an example of the cover sheet, with the gray haze that is just visually visible at 80%, which corresponds to a poor value in terms of ink penetration. With a paper that has a very good barrier effect against sublimation ink, nothing can be seen on the cover sheet (Figure 3).

Determination of stickiness in the transfer process

• Note 1: keine Klebrigkeit
• Note 2: geringe Klebrigkeit
• Note 3: mittlere Klebrigkeit
• Note 4: hohe Klebrigkeit
• Note 5: sehr starke Klebrigkeit

The stickiness of the back of the transfer material is determined using haptic evaluation. To do this, place the transfer material between two fingers positioned and fixed with as even pressure as possible. When removing the fingers, the stickiness is determined in comparison to known transfer material patterns on a grading system from 1 to 5. For a smooth implementation of the transfer process, a grade of 2 or better is desirable.

• Grade 1: no stickiness
• Grade 2: low stickiness
• Grade 3: medium stickiness
• Grade 4: high stickiness
• Grade 5: very strong stickiness

Determination of the curl average

1. 1. FS-Rand: DINA4-Muster ca. 1,5 cm vom Führerseite-Rand
2. 2. M: DINA4-Muster aus der Mitte der Papierbahn
3. 3. AS: DINA4-Muster ca. 1,5 cm vom Antriebs-Rand (AS-Rand)

The curl mean value test is carried out using three DINA4 samples of the transfer materials according to the invention or transfer materials of the prior art (comparative examples) listed in Table 1. When producing the DINA4 samples from the test strip of the paper machine, it should be noted that they are taken from the following points (see also the explanatory illustration below):

1. 1. FS edge: DINA4 pattern approx. 1.5 cm from the driver side edge
2. 2nd M: DINA4 pattern from the middle of the paper web
3. 3. AS: DINA4 pattern approx. 1.5 cm from the drive edge (AS edge)

The prepared samples are labeled on the customer side (FS, M, AS) and stored with the customer side up on a smooth surface for 30 minutes at 50 ± 2% relative humidity and 23 ± 1 °C.

• 0 = kein Curl
• 1 -3 cm = geringer Curl
• > 3 cm = Curl nicht akzeptabel

The average curl value is determined by calculating the average value for each DIN A4 pattern from the measured 4 corner points of the respective pattern, which are designated with the numbers 1 - 4, 5 - 8 and 9 -12 as shown in the figure above and the mean value is formed from these 3 mean values of the individual DINA4 patterns, ie the curl mean value is the mean value of the 3 calculated mean values of the individual DINA4 patterns. The following evaluation scheme applies to the determination of each individual curl value at an individual corner point of the DINA4 pattern:

• 0 = no curl
• 1 -3 cm = low curl
• > 3 cm = curl not acceptable

What is measured is the distance from the point at which the corner point was before the start of the determination, ie before storage at the above-mentioned conditions (temperature, relative humidity) for 30 minutes, to the part of the DINA4 sample that is after 30 minutes under the above-mentioned given conditions (temperature, relative humidity) starting from the original point of the corner point diagonally to the center of the DINA4 pattern (intersection in the middle of the DINA4 pattern, which is formed when you draw mental straight lines from each corner point diagonally to the next corner point) just barely lies flat on the smooth surface, ie the part of the DINA4 pattern that still lies on the smooth surface after the corner of the pattern has been rolled up.

Claims (13)

1. Transfer material for the dye sublimation process, comprising a base paper, which is coated on one side with a color-receiving layer, characterized in that the base paper contains at least 1.5 wt%, relative to the mass of the pulp, of a polymer dispersion selected from polyacrylates, polyesters, polyolefins, or mixtures thereof.
2. Transfer material according to claim 1, characterized in that the base paper contains at least 3 wt%, relative to the mass of the pulp, of a polymer dispersion.
3. Transfer material according to one of the preceding claims, characterized in that the ink penetration of the transfer material is less than 30%, preferably less than 20%.
4. Transfer material according to one of the preceding claims, characterized in that the base paper further contains at least 5 wt%, relative to the mass of the pulp, of pigment.
5. Transfer material according to claim 4, characterized in that the pigment is a hydrophobic pigment.
6. Transfer material according to claim 5, characterized in that the hydrophobic pigment is selected from the group consisting of kaolin, calcium carbonate, aluminum and magnesium silicates, silicas, or mixtures thereof.
7. Transfer material according to claim 5 or 6, characterized in that the hydrophobic pigment has a specific surface area greater than 80 m²/g.
8. Transfer material according to one of the preceding claims, characterized in that the base paper further contains at least 5 wt%, relative to the mass of the pulp, of synthetic fibers.
9. Transfer material according to one of the preceding claims, characterized in that the polymer dispersion is distributed uniformly within the thickness of the base paper.
10. Method for producing a transfer material according to claim 1, comprising the following steps:

    (a) producing a base paper on a paper machine, wherein at least 1.5 wt%, relative to the mass of the pulp, of a polymer dispersion selected from the group consisting of polyacrylates, polyesters, polyolefins, or mixtures thereof are added to the pulp suspension during production of the base paper;

    (b) drying and smoothing the base paper;

    (c) applying the color-receiving layer to a surface of the base paper; and

    (d) drying the transfer material obtained in step (c).
11. Method according to claim 10, characterized in that the process between step (a) and step (b) comprises the following additional step (a1) :
    (a1) impregnating the base paper with an impregnation solution comprising at least 1.0 g/m² of a polymer dispersion selected from the group consisting of polyacrylates, polyesters, polyolefins, or mixtures thereof, in a size press or film press.
12. Method for transferring an image onto a receiving material by sublimation, characterized in that a transfer material according to one of claims 1 through 9 is printed with an image by means of the inkjet printing process, and the image is transferred onto a receiving material by sublimation.
13. Method according to claim 12, characterized in that the receiving material is selected from polyester fabric, polyester nonwoven, or a material coated with polyester.

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