TRANSFER MATERIAL FOR SUBLIMATION PRINTING BASED ON PAPER AS THE CARRIER, WITH AN INK BLOCKING FUNCTION

Abstract

The invention relates to a transfer material for dye sublimation processes, comprising a base paper, which is coated on one side with a color-receiving layer, wherein the base 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. The invention further relates to a process for producing a transfer material according to the invention, comprising the steps of: (a) producing a base 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 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). The invention further relates to a process for transferring an image onto a receiving material by sublimation, wherein a transfer material according to the invention is printed with an image by way of the inkjet printing process, and the image is transferred onto a receiving material by sublimation.

Claims

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%, and 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 m.sup.2/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/m.sup.2 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.

Description

[0053] FIG. 1 schematically shows a cross-section through a transfer material according to the invention. In this case, 1 denotes a base made of paper. The base paper contains the polymer dispersion according to the invention. The base paper is coated on one side with a color-receiving layer 2 for inkjet printing.

[0054] The following examples are used to further explain the invention.

EXAMPLES

Production of a Base Paper

[0055] A eucalyptus pulp was used to produce the base paper. For grinding, the pulp was ground as an approximately 5% aqueous suspension (thick stock) with the aid of refiners to a grinding degree of 25? SR. The concentration of the pulp fibers in the thin material was about 1 wt %, relative to the mass of the pulp suspension. Further additives were added to the thin stock, such as 0.15 wt % of a neutral sizing agent, alkyl ketene dimer (AKD), 0.60 wt % of a wet strength agent, polyamine-polyamide epichlorohydrin resin (Kymene?), 1.0 wt % starch (C-Bond HR 35845), and 30 wt % of a natural milled CaCO.sub.3. The quantities refer to the pulp mass. The thin stock, the pH of which was adjusted to approximately 7.5, was brought from the headbox onto the wire of the paper machine, whereupon the sheet was formed with dewatering of the web in the wire section of the paper machine. In the press section, the paper web was dewatered further to a water content of 60 wt %, relative to the web weight. Further drying was carried out in the drying section of the paper machine using heated drying cylinders. A base paper having a basis weight of 63 g/m.sup.2, a filler content of 18 wt %, and a moisture of about 5.5% was produced.

Production of a Coating Material for the Color-Receiving Layer

[0056] 557 g of an aqueous 9.5 wt % solution of a partially saponified polyvinyl alcohol (Mowiol? 18-88 from Kuraray) are added to 441 g of a dilute dispersion of precipitated calcium carbonate (Precarb? 800 from Schaefer Kalk) having a solids content of 48 wt %, and the mixture is mixed using a dissolver stirrer. 0.5 g of wetting agent, Surfynol? 440, from Air Products is then added. The coating material obtained has a solids content of 26.6 wt %, a viscosity of 150 mPas, a pH of 7.5, and a surface tension of 36 mN/m.

Production of the Transfer Material

[0057] The surface-sized, dried, and smoothed base paper obtained is coated on one side with the coating material for the ink receiving layer.

Preparation of the Examples According to the Invention and the Comparative Examples

[0058] The transfer materials listed in the following table were prepared according to the method described above. In each case, the barrier component given in the first column of Table 1 was used in exchange for eucalyptus pulp during the production of the base paper. The first comparative example corresponds to the base material produced, without addition of a further barrier component during the production of the base 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 additional barrier layer, was produced according to the above-mentioned method, but, in this case, no barrier component was added to the base paper during its production, and the base paper on the side opposite the color-receiving layer was additionally provided with a barrier layer made of a thermoplastic polymer, such as, for example, a fully-hydrolyzed polyvinyl alcohol (e.g., Mowiol? 28-99).

TABLE-US-00001 TABLE 1 Transfer materials/*Advansa Standard 1.7-6-309 NSD was used Added barrier Barrier Ink Tackiness in component in the base component/ Optical penetration/ the transfer Curl paper wt % density % process average without barrier 0 Comparison 4.31 80 Rating 1 0 component without barrier 0 Comparison 4.45 20 Rating 3 5 component with additional barrier layer PE Fibers (Advansa*) 5 Comparison 4.38 50 Rating 1 0 Styrene-alkyl acrylate 1/5 Inventive 4.37 30 Rating 1 0 copolymer/PE fibers (Plexthol DV 544/ Advansa*) Styrene-alkyl acrylate 1 Comparison 4.35 50 Rating 1 1 copolymer (Plexthol DV 544) Styrene-alkyl acrylate 3 Inventive 4.32 25 Rating 1 0 copolymer (Plexthol DV 544) Styrene-alkyl acrylate 5 Inventive 4.51 10 Rating 2 0 copolymer (Plexthol DV 544) Cationic styrene-alkyl 1 Comparison 4.33 50 Rating 1 1 acrylate copolymer (Eurocryl 2324) Cationic styrene-alkyl 5 Inventive 4.47 0 Rating 2 0 acrylate copolymer (Eurocryl 2324)

[0059] The data listed in Table 1 show that the use of at least 1.5 wt %, relative to the mass of the pulp, of a polymer dispersion according to the invention in the base paper of the recording material according to the invention results in the desired barrier effect, i.e., in a low ink penetration. In this case, positive properties, such as the good optical densities, are maintained during the print, and a very good curl behavior and a low tackiness are to be observed in the transfer process. The combination of good barrier properties, low tackiness in the transfer process, and very good curl characteristics is achievable only with the recording materials according to the invention. The results in Table 1 show that this combination of properties cannot be achieved with the recording materials described in the prior art without a barrier layer or with an additional barrier layer and with recording materials having less than 1.5 wt %, relative to the mass of the pulp, of the polymer dispersion according to the invention in the base paper.

Methods

[0060] The resulting transfer materials were printed with a color image; in this case, the inkjet printer EPSON Workforce Pro WF 5110 with sublimation ink SubliJet IQ from Sawgrass was used.

Determining the Ink Penetration

[0061] The sublimation transfer paper to be tested is stored in DIN A4 format for at least 1 h under standard climatic conditions 23? C. and 50% humidity in the print chamber.

[0062] The printing is done on commercially available sublimation desktop printers. The print file includes 10 round color fields with differently declining amounts of ink to be printed in black. The print field at the top left is printed with 100% ink quantity, and the following ones with 10% less ink quantity in each case. Under the print fields, the designation of the field is in % and is specified as 100%applied ink quantity in %. For example, the ink field printed with 80% ink quantity is denoted by the inscription 20%. FIG. 2 shows the print file.

[0063] After printing has taken place, the paper is placed under standard climatic conditions to dry for 1 h. Subsequently, the sublimation process is carried out in the Sefa ROTEX AUTO X REL transfer press with height indicator. For this purpose, the open transfer press is heated to 200? C. After the temperature has been reached, the textile is first placed on the base heating plate, and thereafter the printed paper with the printed side in the direction of the textile. Directly thereafter, the so-called cover paper, which is an 80 g/m.sup.2 copy paper made of bleached pulp, is placed on the rear side of the printed sublimation paper, and the transfer press is closed. Sublimation lasts for 30 seconds at medium contact pressure.

[0064] After the sublimation time has elapsed, the transfer press is opened, and the 3 layers are carefully separated from one another. The textile is discarded. The sublimation ink sublimes in the case of poor ink penetration to the rear side and, depending upon the intensity of the ink penetration, precipitates more or less on the copying paper. The amount of ink plays an important role. The higher the amount of ink on the printed sublimation paper, the higher the tendency towards ink penetration in the direction of the rear side or cover sheet.

[0065] Since color fields in different amounts of ink are located on the printed sublimation paper, the gradation of the ink penetration on the cover sheet is also visible. A visual inspection of the cover sheet is carried out to evaluate the ink penetration. The color field, which is still recognizable in daylight, is marked and indicated as a % value with respect to ink penetration.

[0066] Values of 70-90% are obtained for a sublimation paper with poor ink penetration. For papers with improved ink penetration, values of 60-40% are obtained. Papers with very good behavior against ink penetration achieve values of 30-0%. An exact scaling of the tendency towards ink penetration can be specified in % values. FIG. 3 shows, by way of example, the cover sheet, with marking of the bloom, which is just visually discernible at 80% and constitutes a poor value in terms of ink penetration. With a paper which has a very good barrier effect against sublimation ink, there is nothing to be seen on the cover sheet (FIG. 4).

Determining the Tackiness in the Transfer Process

[0067] The tackiness of the rear side of the transfer material is determined by means of a haptic evaluation. For this purpose, the transfer material is positioned between two fingers and fixed with as uniform a pressure as possible. When the fingers are detached, the tackiness compared to known transfer material samples is determined in a rating system from 1 to 5. A rating of 2 or more is desirable for the transfer process to run smoothly. [0068] Rating 1: no tackiness [0069] Rating 2: slight tackiness [0070] Rating 3: average tackiness [0071] Rating 4: strong tackiness [0072] Rating 5: very strong tackiness

Determining the Curl Average

[0073] The curl average is tested with three DIN A4 samples of the transfer materials according to the invention or transfer materials of the prior art (comparative examples) listed in Table 1. In preparing the DIN A4 samples from the test strip of the paper machine, it should be ensured that they are taken at the following points (see also FIG. 5): [0074] 1. FS edge: DIN A4 sample approx. 1.5 cm from tender side edge [0075] 2. M: DIN A4 sample from the middle of the paper web [0076] 3. AS: DIN A4 sample approx. 1.5 cm from the drive edge (AS edge)

[0077] The prepared samples are labeled on the client side (FS, M, AS) and stored with the client side facing upwards for 30 minutes at 50?2% relative humidity and 23?1? C. on a smooth surface.

[0078] The curl average value is determined by calculating for each DIN A4 sample the mean value from the measured four corner points of the respective sample, which are designated as shown in the above illustration with the numbers 1-4, 5-8, and 9-12, and by forming the average value from these 3 average values of the individual DIN A4 samples, i.e., the curl average value is the average value of the 3 calculated average values of the individual DIN A4 samples. The following evaluation scheme applies to the determination of each individual curl value at a single corner point of the DIN A4 sample: [0079] 0=no curl [0080] 1-3 cm=slight curl [0081] >3 cm=curl not acceptable

[0082] In this case, the distance from the point at which the corner point was located prior to the start of the determination is measured, i.e., prior to storage under the above-mentioned predefined conditions (temperature, relative humidity) for 30 minutes, to the part of the DIN A4 sample, which, after 30 minutes at the above-mentioned predefined conditions (temperature, relative humidity), starting from the original point of the corner point diagonally to the center of the DIN A4 sample (intersection point in the center of the DIN A4 sample, which forms when imaginary straight lines are drawn from each corner point diagonally to the next corner point), is still resting flat on the smooth surface, i.e., the part of the DIN A4 sample which still rests on the smooth surface after the rolling upwhich may occurof the corner of the sample.

[0083] The curl average value is determined by calculating for each DIN A4 sample the mean value from the measured four corner points of the respective sample, which are designated as shown in the above illustration with the numbers 1-4, 5-8, and 9-12, and by forming the average value from these 3 average values of the individual DIN A4 samples, i.e., the curl average value is the average value of the 3 calculated average values of the individual DIN A4 samples. The following evaluation scheme applies to the determination of each individual curl value at a single corner point of the DIN A4 sample: [0084] 0=no curl [0085] 1-3 cm=slight curl [0086] >3 cm=curl not acceptable

[0087] In this case, the distance from the point at which the corner point was located prior to the start of the determination is measured, i.e., prior to storage under the above-mentioned predefined conditions (temperature, relative humidity) for 30 minutes, to the part of the DIN A4 sample, which, after 30 minutes at the above-mentioned predefined conditions (temperature, relative humidity), starting from the original point of the corner point diagonally to the center of the DIN A4 sample (intersection point in the center of the DIN A4 sample, which forms when imaginary straight lines are drawn from each corner point diagonally to the next corner point), is still resting flat on the smooth surface, i.e., the part of the DIN A4 sample which still rests on the smooth surface after the rolling upwhich may occurof the corner of the sample.