COATED PAPER

Abstract

The present invention relates to a coated paper comprising a base paper and a barrier layer applied thereto, the barrier layer comprising at least one polymer, the polymer comprising an at least partly saponified polyvinyl alcohol and/or an at least partly saponified polyvinyl alcohol copolymer, each of which has an onset temperature of less than 210° C. determined by DSC.

Claims

1. A coated paper comprising a base paper and a barrier layer applied thereto, the barrier layer comprising at least one polymer, characterised in that the polymer comprises an at least partly saponified polyvinyl alcohol and/or an at least partly saponified polyvinyl alcohol copolymer, each of which has an onset temperature of less than 210° C. determined by DSC, the onset temperature being defined by DSC according to DIN EN ISO 11357-1:2010-03 as the point of intersection of the extrapolated baseline and the inflection tangent at the beginning of the melting or crystallisation peak.

2. The coated paper according to claim 1, characterised in that a precoat comprising at least one inorganic pigment and a polymeric binder is present between the base paper and the barrier layer.

3. The coated paper according to claim 2, characterised in that the inorganic pigment is in the form of platelets, a precipitated calcium carbonate, a silicate, and/or in that the polymeric binder comprises a polymeric binder based on a polyacrylate.

4. The coated paper according to claim 1, characterised in that the at least one polymer comprises a partly saponified polyvinyl alcohol with a degree of saponification of from 30% to 95%, a mean molecular weight of greater than 0 and less than 100,000 g/mol, and with an onset temperature of less than 200° C. determined by DSC.

5. The coated paper according to claim 1, characterised in that the at least one polymer comprises a partly saponified polyvinyl alcohol with a degree of saponification of greater than 95% to 100%, a mean molecular weight of greater than 70,000 g/mol, and with an onset temperature of less than 200° C. determined by DSC.

6. The coated paper according to claim 1, characterised in that the at least one polymer comprises a partly saponified polyvinyl alcohol copolymer with a degree of saponification of from 95% to 100%, a mean molecular weight of greater than 60,000 g/mol, and with an onset temperature of less than 210° C. determined by DSC.

7. The coated paper according to claim 1, characterised in that the at least one polymer comprises a mixture of a partly saponified polyvinyl alcohol with a degree of saponification of from 30% to 95%, a mean molecular weight of greater than 0 and less than 100,000 q/mol, and with an onset temperature of less than 200° C. determined by DSC; a partly saponified polyvinyl alcohol with a degree of saponification of greater than 95% to 100%, a mean molecular weight of greater than 70,000 g/mol, and with an onset temperature of less than 200° C. determined by DSC; and a partly saponified polyvinyl alcohol copolymer with a degree of saponification of from 95% to 100%, a mean molecular weight of greater than 60,000 q/mol, and with an onset temperature of less than 210° C. determined by DSC.

8. The coated paper according to claim 1, characterised in that the partly saponified polyvinyl alcohol and/or the partly saponified polyvinyl alcohol copolymer at a dry content of 4% has a viscosity of less than 30 mPa*s.

9. The coated paper according to claim 1, characterised in that the applied area density of the barrier layer is from 5 to 20 g/m.sup.2, in relation to the dried end product (air-dried).

10. The coated paper according to claim 1, characterised in that the coated paper, is free of halogen-containing compounds.

11. The coated paper according to claim 1, characterised in that the base paper has an area density of from 20 to 120 g/m.sup.2.

12. The coated paper according to claim 1, characterised in that the base paper has a long fibre content of from 10 to 80% and a short fibre content of from 20 to 90% by weight, a long fibre being a fibre that has a fibre length of from 2.6 to 4.4 mm and a short fibre being a fibre that has a fibre length of from 0.7 to 2.2 mm.

13. The coated paper according to claim 1, characterised in that a further layer comprising aluminium, and/or metal oxides is applied to the barrier layer.

14. A method for producing a coated paper according to claim 1, characterised in that an aqueous suspension comprising the starting materials of the barrier layer is applied to the base paper, said aqueous application suspension having a solids content of from 5 to 50% by weight and is applied by a curtain coating process, preferably by a double curtain coating process, at an operating speed of the coating facility of at least 200 m/min.

15. A packaging material or a component of packaging material for foodstuffs comprised of the coated paper of claim 1.

16. A coated paper obtained by the method according to claim 14, wherein the packaging is a cold-sealed packaging, a heat-sealed packaging, or a form-fill-seal packaging.

17. The coated paper according to claim 2, characterised in that the inorganic pigment is in the form of talc platelets, a precipitated calcium carbonate, a kaolin silicate, and/or in that the polymeric binder comprises a polymeric binder based on a polyacrylate.

18. The coated paper according to claim 1, characterised in that the at least one polymer comprises a partly saponified polyethylene vinyl alcohol with a degree of saponification of from 95% to 100%, a mean molecular weight of greater than 60,000 g/mol, and with an onset temperature of less than 210° C. determined by DSC.

19. The coated paper according to claim 1, characterised in that the partly saponified polyvinyl alcohol and/or the partly saponified polyvinyl alcohol copolymer at a dry content of 4% has a viscosity of less than 15 mPa*s.

20. The coated paper according to claim 1, characterised in that the applied area density of the barrier layer is from 8 to 12 g/m.sup.2 in relation to the dried end product (air-dried).

Description

Examples

[0150] The following coatings were applied to a 60 g/m.sup.2 base paper with 40% long fibre and 60% short fibre content.

[0151] Precoat/Primer: The precoat contains 75.9% pigment (phyllosilicate), 22.8% latex (styrene-butadiene latex) and 1.3% rheology modifiers (0.2% acrylate-based thickener, 1.1% zirconium-based cross-linking agent).

[0152] Barrier Layer:

[0153] In examples 1 to 5 and in comparative example 1, polyvinyl alcohols were used. In examples 6 to 7, polyethylene vinyl alcohols were used.

[0154] The barrier layer of examples 1 to 7 and comparative example 1 comprises a pure polymeric coating. Example 1’ comprises a polymeric coating with 99.8% polyvinyl alcohol (example 1; degree of saponification: 87%; M.sub.w: 50900) and 0.2% rheology modifiers (Na-docusate).

[0155] For this purpose, the precoat was applied using a blade. The barrier layer of examples 1 to 7 and of comparative example 1 was applied with a doctor blade; the barrier layer of example 1′, in contrast to example 1, was applied with a curtain coater.

[0156] The following properties were examined:

[0157] Coating weight: Application weight of the barrier coating in g/m.sup.2. This is determined by differential weighing between coated and uncoated papers.

[0158] Viscosity: The viscosity was measured with a Brookfield viscometer, determined at 23° C. and a speed of 100 rpm, at a dry content of 4%.

[0159] WVTR: Water vapour transmission rate, determined according to ISO 15106-2.

[0160] OTR: Oxygen transmission rate, determined according to DIN 15105-2

[0161] HVTR: Hexane vapour transmission rate. Here, n-hexane is filled into a beaker (solvent-resistant), tightly sealed with the test sample, and the decrease in weight is monitored over time. In the case of creased samples, a crease of 180° is created with a roller which exerts a load of 330 g/cm on the resulting crease, it being possible for the coating to be located on the inside (inner crease) or outside (outer crease).

[0162] Palm kernel oil test: Analogous to DIN 53116. In the case of creased samples, a 180° crease is created with a roller that exerts a load of 330 g/cm on the resulting crease, it being possible for the crease to located on the inside (inner crease) or outside (outer crease).

[0163] Display paper: Evaluation of the display paper mentioned in DIN 53116. Here, grease penetration points with a diameter (d)>1<1 mm are counted.

[0164] Sample paper: Evaluation of the rear side of the sample paper mentioned in DIN 53116. This is not part of the standard, but was carried out for improved differentiation.

[0165] Sealing seam strength: The samples are sealed at 3.3 bar for 0.3 sec. in the temperature range of from 100° C. to 220° C., transverse to the running direction of the paper, and the sealing seam strength is determined according to DIN 55529 (2012). The optimum sealing temperature and, for comparison, the sealing force at 150° C. (optimum sealing temperature of example 1) are recorded.

[0166] DSC melting temperature/onset: The DSC curves were measured with a Mettler DSC 20S in cold-welded aluminium crucibles and perforated lids. The heating rates were 10 K/min in the range between 30° C. and 280° C. The melting temperatures were determined via the peak minima of the melting process.

[0167] Surface tension or energy Contact angle measuring device OCA 20 (DataPhysics) with software SCA 20 Measuring principle: OWRK method (Owens, Wendt, Rabel, Kaelble) Measuring liquids used and origin of the material constants entered: water and diiodomethane (according to Buscher) and 1,5-pentanediol (according to Gebhardt)

[0168] The obtained coated papers were examined. The results are shown in the following table.

TABLE-US-00001 Comp. Ex. 1 Ex. 1′ Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 ex. 1 Coating weight Ø g/m.sup.2 10.3 10.0 10.4 10.1 9.7 10.1 9.1 10.3 9.7 Viscosity* mPa*s 9 9 26 7 10 9 17 25 8 OTR 23.0° C./0% r.h. g/m.sup.2/d 1.86 1.12 1.33 16.64 1.53 1.12 0.04 0.04 3.05 HVTR g/m.sup.2/d <10 <10 <10 <10 <10 <10 <10 <10 <10 Creased (inside) g/m.sup.2/d <10 <10 <10 <10 <10 <10 <10 <10 <10 Creased (outside) g/m.sup.2/d <10 <10 <10 <10 <10 <10 <10 <10 <10 Palm kernel oil test Display paper (AP) d</>1 mm 0/0 0/0 0/0 0/0 0/0 0/0 0/0 1/0 0/0 Sample paper (PP) d</>1 mm 0/0 0/0 0/0 0/0 0/0 0/0 0/0 1/0 0/0 AP - inner crease d</>1 mm 0/0 0/0 0/0 0/1 0/0 0/0 0/0 0/0 0/1 PP - inner crease d</>1 mm 0/0 0/0 0/0 0.5/0   0/0 0/0 0/0 0/0 0/1 AP - outer crease d</>1 mm 0/0 0/0 0/0 0/0 2/0 0/0 0/0 0/0 0/0 PP - outer crease d</>1 mm 0/0 0/0 0/0 0/0 0/2 3/0  1/10 1/0  2/12 Cold tack at 150° C. N/15 mm 6.9 6.7 0.7 4.5 5.0 7.2 0.0 0.0 0.6 Opt. sealing temperature ° C. 150 150 200 160 130-160 150 190 190 210 WVTR Ambient, 23° C., 50% r.h. g/m.sup.2/d 8.3 7.6 12.7 26.0 9.5 16.0 1.0 1.9 8.0 DSC- Melting temp. ° C. 195 195 224 189 190 191 218 217 222 DSC - Onset ° C. 178 178 187 158 165 169 203 199 221 Degree of saponification % 87 87 99 85 88 88 99 98-99 98 Mean molecular mass g/mol 50.900 50900 91.200 38.900 56.700 64.700 87.900 35.000 Surface tension or energy mN/m 58.35 66.73 55.93 54.06 54.98 43.73 44.27 60.26

[0169] The partly saponified polyvinyl alcohols used have very low hexane and oxygen transmission rates. This is presumably due to their relatively high hydrophilicity.

[0170] The polyvinyl alcohols with a higher degree of saponification are distinguished in the coating material by a higher viscosity with the same dry content. From a chemical point of view, this only make's sense since, due to the higher polarity, each molecule interacts more strongly with the surrounding solvent (water).

[0171] This is rather disadvantageous, since a large amount of water has to be dried in the coating process at low dry contents. This not only costs in terms of energy, but can also be difficult to realise in terms of application technology, depending on the desired coating weight. In addition, the diffusion of water molecules and thus the drying itself is slowed. Furthermore, this can lead to an accumulation of gaseous water in the coating, which leads to the formation of macroscopic coating defects.

[0172] The water vapour permeability of the examined polyethylene vinyl alcohols is lower than that of the polyvinyl alcohols, which is presumably due to the ethylene content and the associated lower hydrophilicity.

[0173] In general, fully saponified PVOHs should be more brittle than partly saponified PVOHs because of the greater number of hydrogen bonds that they can form. This also applies to comparative example 1 (see palm kernel oil test).

[0174] This has not yet been proven for example 2. The reason for this is assumed to be the higher molecular weight. It has already been shown for polyvinyl alcohol fibres (e.g. Gotoh et al., Polymer Journal, vol. 32, no. 12 (2000), pp. 1049-1051: “Molecular Weight Dependence of Tensile Properties in Poly(vinyl alcohol) Fibers”) that different molecular weights among otherwise identical polyvinyl alcohols have an immense influence on their physical properties. For example, the elongation at break of higher-weight polyvinyl alcohols is lower, but the force required for this is many times higher.