Heat sensitive recording material

Abstract

The invention relates to a heat-sensitive recording material having a flat support, a thermal reaction layer on at least one face of the flat carrier, and optionally an intermediate layer formed between the flat support and the respective thermal reaction layer, and optionally other layers, a crosslinked biopolymer material in the form of nanoparticles being used as a binder in at least one of the layers. The invention also relates to the production and the use thereof.

Claims

1. A heat-sensitive recording material with a flat support, at least one thermal reaction layer on at least one side of the flat support and optionally an intermediate layer, which is formed between the flat support and the respective thermal reaction layer, and selectively a topcoat protection layer and a backcoat protection layer, wherein a cross-linked biopolymer material in the form of nanoparticles is used as the binder in at least one of the layers and wherein the cross-linked biopolymer material in the form of nanoparticles is obtainable by means of a method, in which a biopolymer material is plasticized using shear forces and in the presence of a cross-linking agent and then dispersed in a hydroxylic solvent, wherein the cross-linked biopolymer material in the form of nanoparticles has a degree of swelling of less than 2, wherein the degree of swelling relates to a volume expansion when the cross-linked biopolymer material in the form of nanoparticles swells in water when a sample of a water-free quantity of 2 g is added to 200 ml pure water, dispersed therein and directly thereafter this is heated in a water bath that is boiling well for 30 minutes and cooled to room temperature, the part of the water that was evaporated is added and the sample is dispersed again and 100 ml of the dispersion are placed precisely in a measuring cylinder, the measuring cylinder is allowed to stand for 24 hours at room temperature and a precipitate is measured visually with respect to its quantity (ml).

2. A recording material according to claim 1, characterised in that the cross-linked biopolymer material in the form of nanoparticles has a degree of swelling of less than 1.

3. A recording material according to claim 1, characterised in that the cross-linked biopolymer material in the form of nanoparticles is used in the thermal reaction layer(s) and/or the intermediate layer(s).

4. A recording material according to claim 1, characterised in that the cross-linked biopolymer material in the form of nanoparticles is used in the intermediate layer(s).

5. A recording material according to claim 1, characterised in that the cross-linked biopolymer material in the form of nanoparticles is a starch, a starch derivative or a polymer mixture with at least about 50% by weight starch or starch derivative.

6. A recording material according to claim 1, characterised in that the cross-linked biopolymer material in the form of nanoparticles is starch.

7. A recording material according to claim 1, characterised in that the average mean particle size of the nanoparticles is between about 10 nm and 600 nm.

8. A recording material according to claim 1, characterised in that the cross-linked biopolymer material in the form of nanoparticles is present in the respective layer(s) in a quantity of about 1 to 50% by weight, based on the total weight of the respective layer.

9. A recording material according to claim 1, characterised in that the flat support has a weight per unit area of about 20 to 600 g/m.sup.2, the respective intermediate layer(s) has/have a weight per unit area of about 1 to 14 g/m.sup.2, and/or the thermal reaction layer(s) has/have a weight per unit area of about 1 to 8 g/m.sup.2.

10. A recording material according to claim 1, characterised in that at least one further binder is additionally present in the layer(s), in which the cross-linked biopolymer material in the form of nanoparticles is present.

11. A recording material according to claim 1, characterised in that it comprises a flat support, a thermal reaction layer and an intermediate layer formed between the flat support and the thermal reaction layer, wherein the intermediate layer contains, as the cross-linked biopolymer material in the form of nanoparticles comprising a starch or a starch derivative as the cross-linked biopolymer material in the form of nanoparticles, a hollow sphere pigment or an inorganic pigment or a mix of the two and a co-binder.

12. A recording material according to claim 11, characterized in that the co-binder is polyvinyl alcohol, latex, or a starch which differs from the starch that can be used as a cross-linked biopolymer material in the form of nanoparticles.

13. A method for producing a heat-sensitive recording material according to claim 1, characterised in that a cross-linked biopolymer material in the form of nanoparticles is used.

14. A recording material according to claim 13, characterized in that the cross-linked biopolymer material in the form of nanoparticles is used as a powder.

15. A paper for fax printing, the printing of sales slips or receipts, car park tickets, entry and travel tickets, medical investigation programs and barcode labels comprised of the heat-sensitive recording material of claim 1.

16. A recording material according to claim 1, characterized in that the average mean particle size of the nanoparticles is between about 40 nm and 400 nm.

17. A recording material according to claim 1, characterized in that the average mean particle size of the nanoparticles is between about 40 and 200 nm.

18. A recording material according to claim 1, characterized in that the cross-linked biopolymer material in the form of nanoparticles is present in the respective layer(s) in a quantity of about 1 to 40% by weight, based on the total weight of the respective layer.

19. A recording material according to claim 1, characterized in that the cross-linked biopolymer material in the form of nanoparticles is present in the respective layer(s) in a quantity of about 2 to 30% by weight, based on the total weight of the respective layer.

20. A recording material according to claim 1, characterized in that the flat support has a weight per unit area of about 30 to 300 g/m.sup.2, the respective intermediate layer(s) has/have a weight per unit area of about 2 to 9 g/m.sup.2 and/or the thermal reaction layer(s) has/have a weight per unit area of about 2 to 6 g/m.sup.2.

Description

EXAMPLES

(1) Production of Heat-Sensitive Recording Materials

(2) An intermediate layer formulation according to Table 1 (Formulation 1) or an intermediate layer formulation according to Table 2 (Formulation 2), was applied using a dry application of about 3 g/m.sup.2 by means of a doctor blade to a conventional flat support (thermal crude paper) with a respective weight per surface area of 44 g/m.sup.2.

(3) The paper substrates thus produced were then coated with a thermal coating compound according to Table 3 (Formulation 3). The coat application was about 4.5 g/m.sup.2 (otro) by means of a doctor blade. The coating dispersion A mentioned there was produced by grinding 30 parts by weight 2-anilino-3-methyl-6-di-n-butylamino-fluoran with 55 parts by weight of a 15% aqueous polyvinyl alcohol solution in a ball mill to form an average particle size of 1.5 m. The coating dispersion B was produced by grinding 65 parts by weight 2,2-bis-(4-hydroxyphenyl)-propane together with 35 parts by weight benzyl-naphthyl-ether, 75 parts by weight of a 15% aqueous polyvinyl alcohol solution and 90 parts by weight water in a mill to an average particle size of 1.5 m.

(4) TABLE-US-00001 TABLE 1 Formulation 1 DW Wet mass 100% Furnace dry (otro) Component % g g Water 5.50 Ropaque HP-1055*.sup.1 27 71.08 19.19 Styron Latex*.sup.2 48 14.66 7.04 PV-OH*.sup.3 20 8.58 1.72 Auxiliary rheology agent*.sup.4 31 0.18 0.06 100.00 28.00 pH = 8.2; Brookfield viscosity (100 rpm; spindle 3; 20 C.) = 380 mPas *.sup.1hollow sphere pigment company Dow (styrene/acrylate copolymer) *.sup.2binder of the type styrene/butadiene latex (company Styron) *.sup.3polyvinyl alcohol low-viscous, highly saponified (company Kuraray) *.sup.4Rheocoat type from the company Coatex (acrylate copolymer)

(5) TABLE-US-00002 TABLE 2 Formulation 2 DW Wet mass 100% Furnace dry (otro) Component % g g Water 13.73 Ropaque HP-1055*.sup.1 27 70.43 19.02 Ecosphere 2240*.sup.2 95 7.35 6.98 PV-OH*.sup.3 20 8.49 1.70 100.00 27.70 pH = 8.8; Brookfield viscosity (100 rpm; spindle 4; 20 C.) = 1400 mPas *.sup.1hollow sphere pigment company Dow (styrene/acrylate copolymer) *.sup.2cross-linked starch, EcoSphere quality (company Ecosynthetix) *.sup.3polyvinyl alcohol low-viscous, highly saponified (company Kuraray)

(6) TABLE-US-00003 TABLE 3 Formulation 3 Wet mass 100% Furnace dry (otro) Component g g Water 12.35 PVA highly viscous, 10.44 1.04 highly saponified (10%) Leukophor UO (31.3%)*.sup.1 0.22 0.07 PCC slurry (55%)*.sup.2 28.92 15.91 Dispersion B 25.52 10.72 Stearic acid amide dispersion*.sup.3 11.12 2.78 Zn stearate dispersion*.sup.3 4.84 1.45 Dispersion A 5.92 2.66 Auxiliary rheology agent (25%)*.sup.4 0.67 0.16 100.00 34.8 pH = 8.3; Brookfield viscosity (100 rpm; spindle 3; 20 C.) = 480 mPas; Surface tension (static ring method according to Du Nouy) 48 mN/m; dry content about 35% by weight *.sup.1optical brightener (anionic stilbene derivative) (company Clariant) *.sup.2d.sub.50: 1.0, calcite type, *.sup.3company Chukyo *.sup.4Sterocoll type (company BASF) (copolymer of acrylic acid esters and carboxylic acids)

(7) Aging after Inscription

(8) The heat-sensitive recording materials thus obtained were subjected to an aging test (aging after inscription), in two defined climates over a time period of several weeks. The image stability was determined weekly.

(9) For this purpose, a typeface was generated on the thermal printer and its optical density was determined before aging. Thereafter, the material was aged suspended freely in different climates over a specific time period. The climates were dry heat (50 C.) and moist heat (40 C./80% ambient humidity) in each case over a time period of 1, 2, 4, 6 and 9 weeks. After aging, the remaining optical density was measured and the drop in the image stability determined in %: (OD.sup.after/OD.sup.before1)*100. Furthermore, the background white of the respective paper samples was determined after aging. The white measurement took place from the upper side using an Elrepho 3000 reflection photometer (company Datacolor). The degree of whiteness was determined here using filter R 457 (ISO 2470) without a UV-filter.

(10) The results are summarized in Table 4.

(11) TABLE-US-00004 TABLE 4 Image % drop in the optical density after Background white stability after x weeks aging % after x weeks aging 0.25 mJ/dot 0.45 mJ/dot aging Intermediate Test 40 C./80% 40 C./80% 40 C./80% layer after: duration 50 C. a.h. 50 C. a.h. 50 C. a.h. Formulation 1 1 week 24.1 25.5 1.6 3.9 77.2 81.3 2 weeks 28.4 36.4 6.6 6.3 74.3 76.4 4 weeks 40.5 42.7 18.0 11.8 72.2 72.2 6 weeks 46.6 50.9 27.0 18.1 68.5 70.3 9 weeks 49.1 56.4 31.1 19.7 67.3 69.5 Formulation 2 1 week 17.6 21.8 1.7 2.5 78.0 82.6 2 weeks 21.6 22.8 0.8 0.8 76.5 82.7 4 weeks 28.4 28.7 6.8 0.8 75.3 81.7 6 weeks 30.4 39.6 12.7 5.8 71.6 80.4 9 weeks 35.3 38.6 14.4 6.6 72.3 80.9

(12) The results show a more stable aging behaviour of the heat-sensitive recording material when using formulation 2 in comparison to a heat-sensitive recording material when using formulation 1.

(13) The increased stability of the background can be seen especially in the case of a relatively long storage period. This trend is shown in an especially reinforced manner under moist warm climatic conditions.

(14) Depositing Behaviour:

(15) The test of the depositing behaviour took place on two conventional commercial thermal printers (Epson TM-T8811 and Mettler-Waage Type L2-RT) and was evaluated after visual assessment with grades of 0 to 3:

(16) Table 5 shows the evaluation of the depositing on the thermal strip:

(17) TABLE-US-00005 TABLE 5 Note Printer A Printer B Formulation 1 2-3 2-3 Formulation 2 0.5-1 0.5-1 0 = no deposits, 1 = slight/visible, 2 = average, 3 = strong

(18) The heat-sensitive recording material with formulation 2 exhibited significantly better depositing behaviour than the heat-sensitive recording material using formulation 1.

(19) Aging Before Inscription:

(20) To determine the storage stability, i.e. the stability of a heat-sensitive recording material before inscription, a conventional thermal paper with its thermal reaction layer (reference paper) was brought into contact with a pure binder layer, which was applied to a raw paper (counter-paper). The reference paper is a standard POS paper (obtainable from the paper factory August Koehler SE). The binder to be investigated was provided as a solution or as a dispersion. The binder solution or dispersion was applied to a thermal raw paper by means of a doctor blade. The application weight was in the range from 2 to 3 g/m.sup.2 (dry). The paper was then stored at 35 C./75% ambient humidity between Plexiglas plates at a defined pressure of 7 kg. After defined time intervals of 4, 8, 12, 16, 20, 28 weeks, a sample was removed and printed on a thermal printer to determine the remaining writing performance. For this purpose, the optical density was measured before or after the aging of the paper and the writing performance [(OD.sup.after/OD.sup.before)*100] was determined. This test method is directed at the influence of the binder on the aging of the heat-sensitive recording material. The results can be inferred from Table 6. It can be seen that the heat-sensitive recording material has a significantly improved storage stability using a cross-linked biopolymer material in the form of nanoparticles (No. 2) compared to heat-sensitive recording materials with known binders.

(21) TABLE-US-00006 TABLE 6 Writing performance [%] Writing performance [%] Aging before writing 0.25 mJ/dot; 35 C./75% a.h. 0.45 mJ/dot; 35 C./75% a.h No. Binder 4 wks 8 wks 12 wks 16 wks 20 wks 28 wks 4 wks 8 wks 12 wks 16 wks 20 wks 28 wks 1 Reference without contact 97.0 92.9 99.0 93.9 92.9 93.9 97.7 97.7 100.8 95.5 99.2 98.5 with the counter-paper 2 Reference paper in contact 97.0 91.9 99.0 89.9 90.9 93.9 99.2 94.7 99.2 94.0 92.5 92.5 with Ecosphere 2240 3 Reference paper in contact with SB- 89.8 80.8 80.8 76.8 70.7 62.6 91.7 88.0 80.5 79.7 77.4 56.4 Latex 1 4 Reference paper in contact 81.8 66.7 72.7 50.5 39.4 40.4 88.0 68.4 75.2 49.6 42.1 37.6 with SA-Latex 1 5 Reference paper in contact 87.6 84.3 75.2 66.9 70.3 95.0 90.7 84.9 77.0 69.8 with SB-Latex 2 6 Reference paper in contact 90.9 79.3 76.9 71.9 57.9 97.1 89.2 80.6 79.9 61.9 with SB-Latex 3 7 Reference paper in contact 86.0 81.0 81.0 70.3 73.6 95.0 90.7 87.8 77.7 79.9 with SB-Latex 4 8 Reference paper in contact 67.8 44.6 28.1 29.8 21.5 66.9 38.9 34.5 25.2 23.7 with SA-Latex 2 9 Reference paper in contact 92.9 86.9 88.9 79.8 77.8 74.7 97.7 87.2 91.9 85.0 75.2 77.4 with PV-OH SB-Latex 1 = XZ34946.01 styrene-butadiene copolymer (company Styron) SB-Latex 2 = Synthomer 76M10 (company Synthomer) SB-Latex 3 = Litex PX9366 (company Polymer Latex) SB-Latex 4 = XZ9182.00 (company Styron) SA-Latex 1 = Makrovil SE348 (company Indulor) SA-Latex 2 = DAL 7294 (company Styron) PV-OH = polyvinyl alcohol low-viscous, highly saponified (company Kuraray) Ecosphere 2240 = cross-linked starch, EcoSphere quality (company Ecosynthetix)