PAPER ARTICLE COMPRISING A PAPER COMPONENT AND A HEAT-SEALABLE COATING

Abstract

The present invention refers to a paper article comprising a paper component having a first side and a second side, wherein the first side and/or the second side of the paper component is at least partially coated with a heat-sealable coating, wherein the heat-sealable coating comprises a first polymer comprising units derived from a (meth)acrylate and/or (meth)acrylic acid and/or a salt thereof, and a second polymer, being different from the first polymer, comprising units derived from a) a (meth)acrylate and/or (meth)acrylic acid and/or a salt thereof, and b) an alkene, wherein the first polymer and the second polymer are present in the heat-sealable coating in a weight ratio of 90:10 to 35:65, and wherein the first polymer and the second polymer are present in the heat-sealable coating in an overall amount of at least 50 wt. %, based on the total weight of the coating. Furthermore, the present invention refers to a laminate comprising a paper component, a substrate and a heat-seal layer being present between the paper component and the substrate, which is obtained by heat-sealing a paper article according to the present invention to the substrate. The invention also refers to a use of a coating for heat-sealing a paper component to a substrate.

Claims

1. A paper article comprising a paper component having a first side and a second side, wherein the first side and/or the second side of the paper component is at least partially coated with a heat-sealable coating, wherein the heat-sealable coating comprises a first polymer comprising units derived from a (meth)acrylate, and/or (meth)acrylic acid and/or a salt thereof, and a second polymer, being different from the first polymer, comprising units derived from a) a (meth)acrylate, and/or (meth)acrylic acid and/or a salt thereof, and b) an alkene, wherein the first polymer and the second polymer are present in the heat-sealable coating in a weight ratio of 90:10 to 35:65, and wherein the first polymer and the second polymer are present in the heat-sealable coating in an overall amount of at least 50 wt. %, based on the total weight of the coating.

2. The paper article according to claim 1, wherein the first polymer and the second polymer are present in the heat-sealable coating in a weight ratio of 90:10 to 45:55.

3. The paper article according to claim 1, wherein the heat-sealable coating further comprises a wax in an amount of from 0.1 to 20 wt. %, based on the total weight of the coating.

4. The paper article according to claim 1, wherein the first polymer is selected from the group consisting of (meth)acrylate/acrylic acid polymers and salts thereof, poly(meth)acrylic acids and salts thereof, and mixtures thereof.

5. The paper article according to claim 1, wherein the second polymer is selected from the group consisting of ethylene/(meth)acrylate polymers, ethylene/(meth)acrylate/(meth)acrylic acid polymers and salts thereof, ethylene/(meth)acrylic acid polymers and salts thereof, and mixtures thereof.

6. The paper article according to claim 1, wherein the first polymer and the second polymer are present in the heat-sealable coating in an overall amount of at least 60 wt. %, based on the total weight of the coating.

7. The paper article according to claim 1, wherein the heat-sealable coating further comprises a mineral material in an amount of from 0.1 to 49 wt. %, based on the total weight of the coating.

8. The paper article according to claim 1, wherein the heat-sealable coating is present on the first side and/or the second side of the paper component in an amount of from 1 to 50 g/m.sup.2 and/or wherein the first side and/or the second side of the paper component is fully coated with the heat-sealable coating.

9. The paper article according to claim 1, wherein the paper component is a paper, a cardboard or a paperboard.

10. The paper article according to claim 1, wherein the paper component is pre-coated on the first side and/or the second side with a pre-coating comprising a mineral material.

11. A laminate comprising a substrate, a paper component, and a heat-seal layer being present between the paper component and the substrate, wherein the laminate is obtained by heat-sealing a paper article according to claim 1 to the substrate.

12. The laminate according to claim 11, wherein the substrate is a cellulose-based substrate, a paper substrate or a wood substrate, a polar polymer, a polyester, a polylactic acid, a polyhydroxyalkanoate or furandicarboxylic acid-based polyester, or a nonpolar polymer, polyethylene, polypropylene, polystyrene, or mixtures thereof.

13. The laminate according to claim 11, wherein the heat-sealing is carried out at a temperature in the range of from 50 to 180° C. and/or wherein the heat-sealing is carried out by applying a force per area in the range of from 0.05 to 50 N/mm.sup.2 and/or wherein the heat-sealing is carried out one or more times over a time period in the range of from 0.1 to 100 seconds.

14. The paper article according to claim 1, wherein the first polymer is acrylate/acrylic acid polymer or a salt thereof.

15. The paper article according to claim 1, wherein the second polymer is an ethylene/acrylic acid polymer or a salt thereof.

16. The paper article according to claim 1, wherein the heat-sealable coating is present on the first side and/or the second side of the paper component in an amount of from 4 to 10 g/m.sup.2, and wherein the first side of the paper component is fully coated with the heat-sealable coating.

17. The paper article according to claim 1, wherein the paper component is pre-coated on the first side and/or the second side with a pre-coating comprising a calcium carbonate.

18. The laminate according to claim 11, wherein the substrate is a paper substrate.

19. The laminate according to claim 11, wherein the heat-sealing is carried out at a temperature in the range of from 110 to 140° C.

20. A method for forming a laminate, comprising heat sealing a paper component to a substrate to form the laminate; wherein the first side and/or the second side of the paper component is at least partially coated with a heat-sealable coating, some of the heat-sealable coating is between the paper component and the substrate prior to forming the laminate, and the heat-sealable coating comprises a first polymer comprising units derived from a (meth)acrylate, and/or (meth)acrylic acid and/or a salt thereof, and a second polymer, being different from the first polymer, comprising units derived from a) a (meth)acrylate, and/or (meth)acrylic acid and/or a salt thereof, and b) an alkene, wherein the first polymer and the second polymer are present in the heat-sealable coating in a weight ratio of 90:10 to 35:65, and wherein the first polymer and the second polymer are present in the heat-sealable coating in an overall amount of at least 50 wt. %, based on the total weight of the heat-sealable coating.

21. The method according to claim 20, wherein the substrate is a polar polymer, a polyester, a polylactic acid, a polyhydroxyalkanoate or a furandicarboxylic acid-based polyester, or wherein the substrate is a nonpolar polymer, polyethylene, polypropylene, polystyrene or mixtures thereof.

Description

[0462] According to a preferred embodiment, the paper component is pre-coated on the first side and/or the second side with a pre-coating comprising a mineral, preferably a calcium carbonate.

[0463] FIG. 1: Heat-seal strength of laminates obtained by heat-sealing each one of coated papers 1 to 10 against another paper being coated with an identical heat-sealable coating (sealing against sealing) at different temperatures.

[0464] FIG. 2: Heat-seal strength of laminates obtained by heat-sealing each one of coated papers 1 to 10 against a raw paper at different temperatures.

[0465] FIG. 3: Heat-seal strength of laminates obtained by heat-sealing each one of coated papers 1 to 10 against polyethylene at different temperatures.

[0466] FIG. 4: Heat-seal strength of laminates obtained by heat-sealing each one of coated papers 1 to 10 against polylactic acid at different temperatures.

[0467] FIG. 5: Examples of laminates obtained by heat-sealing the paper article against itself as substrate (FIGS. 5a and 5b), and against a separate substrate (FIGS. 5c and 5d).

[0468] FIG. 6: (Part of) coated paper article and substrate before heat-sealing (FIG. 6a; 1=paper article, 2=heat-sealable layer, 3=substrate) and laminate obtained by heat-sealing (FIG. 6b; 1=paper article, 2=heat-seal layer, 3=substrate).

[0469] FIG. 7: Exemplary continuous laboratory coater for coating a paper article (1=rewinding, 2=hot air dryer, 3=IR-dryer, 4=Rod/Blade, 5=Unwinding (for rod/blade), 6=metering size press, 7=unwinding (for metering size press).

EXAMPLES

[0470] 1. Methods

[0471] Particle Size Distribution

[0472] In the experiments, the weight-median particle size d.sub.50 and weight top cut particle size d.sub.98 values were measured using a Sedigraph 5125 from the company Micromeritics Instrument Corporation, USA. The method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurements were carried out in an aqueous solution comprising 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and supersonics. For the measurement of dispersed samples, no further dispersing agents were added.

[0473] Solids Content of an Aqueous Suspension

[0474] The suspension solids content was determined using a Moisture Analyser MJ33 from the company Mettler-Toledo, Switzerland, with the following settings: drying temperature of 160° C., automatic switch off if the mass does not change more than 1 mg over a period of 30 s, standard drying of 5 to 20 g of suspension.

[0475] Determination of Oil Permeation

[0476] Oil permeation tests were carried out with a commercially available 100% corn oil colored with sudan red. 30 g of oil were weighed into a beaker, and the top of the beaker was closed with a test specimen of a paper article (80 cm.sup.2; coated side down) using a tight ring. The beaker was put in an oven having a temperature of 65° C. for 10 min. The beaker was then turned upside down, so that the oil contacts the coated side of the paper article specimen. The paper article specimen is controlled over a time period of 60 min for oil permeation.

[0477] Determination of Water Absorptiveness

[0478] Cobb Unger (wl5) is measured using ISO 535:1991(E). In accordance with this method, the mass of water absorbed in a specified time by g/m.sup.2 of paper or board during 1800 s time under specified conditions is measured. The conditioning atmosphere is according to ISO 187 (23° C./50% RH).

[0479] Preparation of Formulations

[0480] All mixing steps were done with a Pendraulik Laboratory Dissolver, model LD 50.

[0481] Coating of Paper Article

[0482] The coatings were applied at a coating speed of 20 m/min using a Durrer continuous laboratory coater (Switzerland) using rod metering (X23 (23 mL/m.sup.2, rod pressure of approximately 1 bar, rod revolutions of 12 rpm). Durrer continuous laboratory coater; see FIG. 7; 1=rewinding, 2=hot air dryer, 3=IR-dryer, 4=Rod/Blade, 5=Unwinding (for rod/blade), 6=metering size press, 7=unwinding (for metering size press).

[0483] Heat-Sealing

[0484] Heat-sealing was performed on a Kopp Laboratory Sealer SGPE 3000 from the company Kopp (Reichenbach, Germany) equipped with sealing bar of 200×5 mm. The temperature was set up in a range of 90 to 160° C., with a sealing force of 100 N (0.4 N/mm.sup.2) and a time of sealing of 0.5 seconds.

[0485] Seal Strength

[0486] Seal strength of the seal layer in the laminates was measured with L&W Tensile test from the company Lorentzen & Wettre (Sweden) by an unsupported T-peel test using a test specimen having a 50 mm width. Seal strength at sealing break (peeling) were reported in Newton [N].

[0487] 2. Materials

[0488] Polymers

[0489] Polymer Mix A: Aqueous mixture of neutralized ethylene/acrylic acid polymer (second polymer; CAS: 9010-77-9). The second polymer has a comonomer content of acrylic acid of about 20 mol-%.

[0490] Polymer Mix B: Aqueous mixture of neutralized acrylate/acrylic acid polymer (first polymer; CAS: 51981-89-6).

[0491] Polymer Mix C: Aqueous emulsion of 90 wt. % (based on total dry solids) neutralized ethylene/acrylic acid polymer (second polymer; CAS: 9010-77-9) and 10 wt. % (based on total dry solids) of paraffin wax; solid content 39.5 wt. %; pH (ISO 976:2013) 8.6; Viscosity (ISO 1652:2011) 1620 mPa*s. The second polymer has a comonomer content of acrylic acid of about 20 mol-%.

[0492] Polymer Mix D: Aqueous emulsion of 90 wt. % (based on total dry solids) neutralized acrylate/acrylic acid polymer (first polymer; CAS: 51981-89-6) and 10 wt. % (based on total dry solids) of paraffin wax; solid content 50.5 wt. %; pH (ISO 976:2013) 8.1; viscosity (ISO 1652:2011) 162 mPa*s.

[0493] Mineral Material

[0494] CC: Natural ground calcium carbonate; weight-median particle size d.sub.50=1.6 μm; weight-based top cut particle size d.sub.98=10 μm; slurry with solids content 77 wt. %; available from Omya, Switzerland.

[0495] Paper Component and Substrates

[0496] Paper component: Paper, precoated, 80 g/m.sup.2, thickness 82 μm, available from SAPPI, Austria.

[0497] Substrate 1: Paper, precoated, 80 g/m.sup.2, coated on one side with one of the coating formulations 1 to 10 (see below).

[0498] Substrate 2: Paper, raw (not precoated), 60 g/m.sup.2, thickness 75 μm, available from SAPPI, Austria.

[0499] Substrate 3: Paper, grammage 120 g/m.sup.2, thickness 108 μm, coated with a polylactic acid coating (30 g/m.sup.2), available from Valuepap, Austria.

[0500] Substrate 4: Paper, grammage 130 g/m.sup.2, thickness 127 μm, coated with a polyethylene coating (50 g/m.sup.2), available from Valuepap, Austria.

[0501] Substrate 5: Wood substrate, particle board V20 8 mm, available from Coop, Switzerland.

[0502] Coating Compositions

[0503] Aqueous coating compositions 1 to 10 are shown in Table 1.

TABLE-US-00001 TABLE 1 Aqueous coating compositions Coating composition Component 1 2 3 4 5 6 7 8 9 10 Mix A 50 Mix B 50 Mix C 100 70 60 50 40 40 30 15 0 Mix D 0 30 40 50 40 60 70 85 100 CC 20 Dry weight ratio (first 0:100 30:70 40:60 50:50 50:50 60:40 70:30 85:15 100:0 50:50 polymer:second polymer) Solid content 39.1 42.1 42.8 43.9 48.2 44.6 45.0 47.5 49.8 43.3 pH 8.5 8.4 8.4 8.2 8.3 8.2 8.2 8.1 8.0 8.1 Viscosity (100 rpm) 2540 100 110 80 70 80 80 80 140 90

[0504] 3. Results

[0505] 3.1 Coated Paper Article Each one of the coating formulations 1 to 10 were used to fully coat a first side of the paper component. The coating was carried out as described above. After drying, a paper article is obtained comprising a paper component being coated fully coated on a first side with a coating.

[0506] The final coated paper articles 1 to 10 had a coating weight and a Cobb value as shown in Table 2.

TABLE-US-00002 TABLE 2 Paper articles 1 to 10 Paper article 1 2 3 (IE) 4 (IE) 5 (IE) 6 (IE) 7 (IE) 8 (IE) 9 10 (IE) Coating weight (g/m.sup.2) 7.4 8.3 8.3 7.7 9.9 8.3 9.2 8.6 9.4 7.8 COBB 1800 (g/m.sup.2) 1.4 15.6 18.4 40.8 23.8 14.3 10.0 11.0 9.2 66.5 IE = Inventive example.

[0507] Each one of the paper articles 1 to 10 was tested for heat-sealing against a) the same type of coated paper as substrate (substrate 1; heat-sealing against a substrate also coated with the heat-sealable coating; A-A), b) against a raw paper as substrate (Substrate 2; A-B Paper), c) against polyethylene as substrate (substrate 4, A-B PE), and d) against polylactic acid as substrate (substrate 3, A-B PLA).

[0508] The heat-sealing tests were carried out at different temperatures ranging from 90° C. to 160° C. and the seal strength was measured. The results of the heat-sealing tests are shown in Tables 3 to 6 and FIGS. 1 to 4.

TABLE-US-00003 TABLE 3 Seal strength for laminates obtained by heat-sealing each one of paper articles 1 to 10 against substrate 1 (A-A; coating against coating) Sealing Paper article temperature 1 2 3 4 5 6 7 8 9 10 [° C.] Seal strength [N] 90 8.9 1.2 6.8 6.5 —* 7.5 7.6 8.6 9.3 8.4 100 9.0 5.3 7.6 6.9 4.9 7.9 7.4 8.6 9.3 8.7 110 9.2 7.3 7.8 7.4 5.6 8.3 7.8 8.7 8.9 8.8 120 9.5 8.9 8.0 7.4 6.3 7.6 7.8 8.4 9.9 8.7 130 8.1 8.4 7.4 7.7 5.8 8.3 7.6 8.5 10.1 8.6 140 9.0 7.6 8.4 8.3 5.7 8.9 7.6 9.1 10.1 8.9 150 9.8 8.3 8.1 7.9 5.7 7.8 8.3 9.3 10.2 9.4 160 9.5 7.7 7.4 8.1 5.2 8.1 8.0 9.2 9.8 8.5 *= did not seal.

TABLE-US-00004 TABLE 4 Seal strength for laminates obtained by heat-sealing each one of paper articles 1 to 10 against substrate 2 (A-B; coating against raw paper) Sealing Paper article temperature 1 2 3 4 5 6 7 8 9 10 [° C.] Seal strength [N] 90 4.8 -* 5.1 5.6 —* 4.3 3.4 4.2 6.1 6.3 100 7.1 7.7 7.3 7.4 3.2 4.5 6.6 6.0 7.3 7.1 110 7.9 7.9 7.9 8.3 4.2 7.5 7.7 7.1 8.1 7.6 120 8.4 7.9 8.5 7.9 3.9 8.6 7.9 7.3 7.9 7.5 130 8.2 8.0 7.5 8.1 4.4 8.1 7.3 7.8 8.9 7.9 140 8.2 8.5 8.0 8.1 5.4 8.3 7.9 8.7 8.4 8.3 150 7.8 8.1 8.1 7.9 4.9 7.6 7.7 8.6 8.3 8.1 160 8.2 8.6 7.6 8.2 4.6 8.5 8.3 8.5 9.4 8.2 *= did not seal.

TABLE-US-00005 TABLE 5 Seal strength for laminates obtained by heat-sealing each one of paper articles 1 to 10 against substrate 4 (A-B; coating against PE) Sealing Paper article temperature 1 2 3 4 5 6 7 8 9 10 [° C.] Seal strength [N] 90 —* —* 2.0 —* —* 6.2 5.7 5.6 —* 9.1 100 —* —* 6.9 7.4 —* 9.2 9.0 9.8 9.7 9.1 110 0.9 8.6 9.8 8.4 9.9 9.1 9.0 9.3 9.7 9.9 120 1.3 8.7 9.3 8.3 9.6 9.2 6.6 9.0 10.3 10.1 130 5.2 10.1 10.0 8.2 9.5 9.8 7.3 8.9 9.6 9.6 140 7.0 10.4 10.1 8.7 9.7 9.2 8.5 8.6 10.1 10.5 150 6.9 10.5 10.7 7.3 9.6 9.6 9.8 8.6 10.8 10.0 160 8.2 9.3 9.7 9.3 8.6 9.1 9.5 8.5 10.3 10.1 *= did not seal.

TABLE-US-00006 TABLE 6 Seal strength for laminates obtained by heat-sealing each one of paper articles 1 to 10 against substrate 3 (A-B; coating against PLA) Sealing Paper article temperature 1 2 3 4 5 6 7 8 9 10 [° C.] Seal strength [N] 90 —* —* —* —* —* —* —* 9.1 9.7 —* 100 —* —* —* —* —* —* —* 9.2 9.6 —* 110 —* —* 3.2 —* —* 8.5 8.8 9.5 10.8 —* 120 —* —* 4.4 7.3 —* 9.2 8.0 9.7 10.2 10.7 130 —* —* 4.8 7.5 6.3 9.7 8.8 9.3 9.4 9.7 140 —* —* 5.2 7.5 5.5 8.9 8.7 9.3 9.5 9.4 150 —* —* 5.0 5.5 4.2 9.0 9.5 8.9 9.6 9.8 160 —* —* 4.9 7.6 6.8 9.2 9.7 9.2 9.4 9.7 *= did not seal.

[0509] As can be seen by the indicated seal strength in Tables 3 to 6 and FIGS. 1 to 4, for inventive paper articles 3 to 8 and 10 a good heat-seal strength is obtained for all types of substrates 1 to 4.

[0510] The comparison of inventive paper articles 4 and 10 shows that the addition of wax to the heat-sealable coating (paper 4) decreases the Cobb value of the paper article without negatively affecting the ability of the paper article to seal against all substrate types. The comparison of inventive paper articles 4 and 5 shows that the addition of calcium carbonate to the heat-sealable coating (paper 5) further decreases the Cobb value of the paper article and allows for modifying the seal strength without negatively affecting the ability of the paper article to seal against all substrate types.

[0511] Paper articles 1 and 2 do not seal against polylactic acid as substrate, i.e. show a seal strength of 0 N for heat-sealing at temperatures from 90° C. to 160° C. (see FIG. 4). Further, paper articles 1 and 2 only seal against polyethylene as substrate at a temperature of 110° C. or above (see FIG. 3). Paper article 9 does not seal at a temperature of 90° C. against polyethylene as substrate (see FIG. 3).