Mineral oil barrier

Abstract

The present invention is directed to a liquid coating composition comprising at least one terephthalate ionomer comprising anionic substituents selected from sulfonate, carboxylate and/or phosphate groups, wherein the at least one terephthalate ionomer has an acid value of at least 1 mg KOH/g ionomer, at least one calcium carbonate containing filler, and a buffer.

Claims

1. A liquid coating composition comprising at least one terephthalate ionomer comprising anionic substituents selected from sulfonate, carboxylate and/or phosphate groups, wherein the at least one terephthalate ionomer has an acid value of at least 1 mg KOH/g ionomer, at least one calcium carbonate containing filler, and a buffer, wherein the pH of the liquid coating composition is in the range from 6.5 to 11.

2. The composition of claim 1, wherein the at least one terephthalate ionomer comprises the anionic substituents in an amount from 0.1 to 20 mol-%, based on the total amount of the at least one ionomer.

3. The composition of claim 1, wherein the at least one terephthalate ionomer comprises the anionic substituents in an amount from 0.5 to 10 mol-%, based on the total amount of the at least one ionomer.

4. The composition of claim 1, wherein the at least one terephthalate ionomer comprises the anionic substituents in an amount from 1 to 5 mol-%, based on the total amount of the at least one ionomer.

5. The composition of claim 1, wherein the at least one terephthalate ionomer is a sulfonated terephthalate ionomer.

6. The composition of claim 1, wherein the at least one terephthalate ionomer is a sulfonated terephthalate ionomer comprising sulfonate groups in an amount from 0.1 to 6 wt.-%, based on the total weight of the at least one ionomer.

7. The composition of claim 1, wherein the at least one terephthalate ionomer is a sulfonated terephthalate ionomer comprising sulfonate groups in an amount from 1 to 5 wt.-%, based on the total weight of the at least one ionomer.

8. The composition of claim 1, wherein the at least one terephthalate ionomer is a sulfonated terephthalate ionomer comprising sulfonate groups in an amount from 2 to 4 wt.-%, based on the total weight of the at least one ionomer.

9. The composition of claim 1, wherein the at least one calcium carbonate containing filler is selected from the group consisting of calcium carbonate, calcium carbonate containing minerals, and mixtures thereof.

10. The composition of claim 1, wherein the at least one calcium carbonate containing filler is calcium carbonate.

11. The composition of claim 1, wherein the at least one calcium carbonate containing filler is ground calcium carbonate.

12. The composition of claim 1, wherein the at least one calcium carbonate containing filler is in a form of particles having a weight median particle size d50 from 0.05 to 7 ?m.

13. The composition of claim 1, wherein the at least one calcium carbonate containing filler is in a form of particles having a weight median particle size d50 from 0.1 to 5 ?m.

14. The composition of claim 1, wherein the at least one calcium carbonate containing filler is in a form of particles having a weight median particle size d50 from 0.2 to 3 ?m.

15. The composition of claim 1, wherein the at least one calcium carbonate containing filler is in a form of particles having a weight median particle size d50 from 0.3 to 2 ?m.

16. The composition of claim 1, wherein the composition has a solids content is in the range from 25 wt.-% to 75 wt.-%, based on the total weight of the composition.

17. The composition of claim 1, wherein the composition has a solids content is in the range from 30 wt.-% to 67 wt.-%, based on the total weight of the composition.

18. The composition of claim 1, wherein the composition has a solids content is in the range from 45 wt.-% to 65 wt.-%, based on the total weight of the composition.

19. The composition of claim 1, wherein the composition has a solids content is in the range from 50 wt.-% to 62 wt.-%, based on the total weight of the composition.

20. The composition of claim 1, wherein the wt.-% ratio of the at least one terephthalate ionomer to the at least one calcium carbonate containing filler is in the range from 95:5 to 20:80.

21. The composition of claim 1, wherein the wt.-% ratio of the at least one terephthalate ionomer to the at least one calcium carbonate containing filler is in the range from 60:40 to 20:80.

22. The composition of claim 1, wherein the wt.-% ratio of the at least one terephthalate ionomer to the at least one calcium carbonate containing filler is in the range from 55:45 to 30:70.

23. The composition of claim 1, wherein the wt.-% ratio of the at least one terephthalate ionomer to the at least one calcium carbonate containing filler is in the range from 50:50 to 45:65.

24. The composition of claim 1, wherein the composition further comprises a complexing agent.

25. The composition of claim 24, wherein the complexing agent is ammonium zirconium carbonate.

26. The composition of claim 1, wherein the at least one terephthalate ionomer is a polyalkylene terephthalate ionomer.

27. The composition of claim 1, wherein the at least one terephthalate ionomer is a polyethylene terephthalate ionomer.

28. The composition of claim 1, wherein the at least one terephthalate ionomer is co-polymerized with a hydrophobic compound.

29. The composition of claim 1, wherein the at least one terephthalate ionomer is co-polymerized with a hydrophobic compound comprising a C6 to C24 straight chain fatty acid, a C6 to C24 branched fatty acid, a triglyceride thereof, or any mixture thereof.

30. A process for producing the liquid coating composition of claim 1 comprising the steps of: a) providing an aqueous solution and/or dispersion of at least one terephthalate ionomer comprising anionic substituents selected from sulfonate, carboxylate and/or phosphate groups, wherein the at least one terephthalate ionomer has an acid value of at least 1 mg KOH/g ionomer, b) providing at least one calcium carbonate containing filler, c) mixing the aqueous solution and/or dispersion of the at least one terephthalate ionomer of step a) and the at least one calcium carbonate containing filler of step b), wherein a buffer is added (i) during step a), or (ii) during steps a) and b), or (iii) during steps a) and c), or (iv) during steps a), b) and c) to provide in the obtained liquid coating composition a pH in the range from 6.5 to 11.

31. The process of claim 30, further comprises the step of adding a complexing agent before, during and/or after step c).

32. A packaging material comprising a cellulose-based substrate having a first and a reverse side, and at least one barrier layer being in contact with the first side or the reverse side of the substrate, wherein the at least one barrier layer comprises at least one terephthalate ionomer and at least one calcium carbonate containing filler, and a buffer, wherein the at least one terephthalate ionomer comprises anionic substituents selected from sulfonate, carboxylate and/or phosphate groups and has an acid value of at least 1 mg KOH/g ionomer.

33. A process for producing the packaging material of claim 32 comprising of the following steps: A) providing a cellulose-based substrate having a first and a reverse side, B) applying a liquid coating composition according to claim 1 on the first side of the substrate to form a barrier layer, and C) drying the barrier layer.

34. The process of claim 33, which further comprises carrying out steps B) and C) on the reverse side of the substrate to manufacture a packaging material being coated on the first and the reverse side.

35. A barrier layer for packaging materials comprising the liquid coating composition of claim 1 comprising at least one terephthalate ionomer and at least one calcium carbonate containing filler as a barrier layer, wherein the at least one terephthalate ionomer comprises anionic substituents selected from sulfonate, carboxylate and/or phosphate groups and has an acid value of at least 1 mg KOH/g ionomer.

36. A packaging material for food packing applications and/or food displays comprising the barrier layer according to claim 35.

Description

DESCRIPTION OF THE FIGURE

(1) FIG. 1 shows a graph of the hexane migration through comparative and inventive packaging materials over 24 hours.

EXAMPLES

(2) 1. Measurement Methods

(3) In the following, measurement methods implemented in the examples are described.

(4) Brookfield Viscosity

(5) The Brookfield viscosity of the liquid coating compositions was measured after one hour of production and after one minute of stirring at 20? C.?2? C. at 100 rpm by the use of a Brookfield viscometer type RVT equipped with an appropriate disc spindle, for example spindle 2 to 5.

(6) pH Value

(7) The pH of a suspension or solution was measured at 25? C. using a Mettler Toledo Seven Easy pH meter and a Mettler Toledo InLab? Expert Pro pH electrode. A three point calibration (according to the segment method) of the instrument was first made using commercially available buffer solutions having pH values of 4, 7 and 10 at 20? C. (from Sigma-Aldrich Corp., USA). The reported pH values are the endpoint values detected by the instrument (the endpoint was when the measured signal differed by less than 0.1 mV from the average over the last 6 seconds).

(8) Particle Size Distribution

(9) The particle size distribution of the pigment particles was measured using a Sedigraph 5100 from the company Micromeritics, 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 measurement was 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.

(10) Solids Content of an Aqueous Suspension

(11) The suspension solids content (also known as dry weight) 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 sec, standard drying of 5 to 20 g of suspension.

(12) Barrier Performance Quick Test

(13) A droplet of 15 ?l hexane, which has been red-colored with sudan red, was applied for 30 s to the barrier side of the substrate. The appearance of red stains on the reverse side of the barrier paper indicated a migration of hexane through the barrier coated substrate.

(14) Barrier Performance Migration TestHexane Vapor Transmission Rate

(15) 10 g hexane was added into a migration cell, which was sealed by a coated substrate sample. The sealed migration cell was placed on an automatic balance and the weight of the migration cell was registered every 30 min for 24 h. A decrease in weight indicated a migration of hexane through the barrier coating. As a reference a migration cell sealed with an aluminum foil was used, which did not show any weight decrease over 24 h.

(16) Degree of Sulfonation

(17) The amount of sulfonate groups was determined by measuring the amount of sulfur in the ionomer using a CHNS elementary analysis. For the elementary analysis a Vario EL III CHNS elemental analyzer from Elementar Analysensysteme GmbH, Germany, was used.

(18) 2. Materials

(19) Ionomer

(20) PET1: sulfonated polyethylene terephthalate ionomer (acid value: <10 KOH mg/g ionomer; intrinsic viscosity: 0.40-0.46, degree of sulfonation: 3.5-3.7 wt.-%, based on the total weight of PET1), commercially available from The Seydel Companies, Inc. (USA).

(21) Calcium Carbonate Containing Filler

(22) CC1: ground calcium carbonate (d.sub.50: 0.6 ?m), commercially available from Omya International AG, Switzerland.

(23) CC2: pre-dispersed slurry of ground calcium carbonate (d.sub.50: 0.6 ?m, solids content: 71.5 wt.-%, pH: 10, Brookfield viscosity: 300 mPa.Math.s at 20? C.), commercially available from Omya International AG, Switzerland.

(24) CC3: pre-dispersed slurry of ground calcium carbonate (d.sub.50: 0.5 ?m, solids content: 72 wt.-%, pH: 10, Brookfield viscosity: 500 mPa.Math.s at 20? C.), commercially available from Omya International AG, Switzerland.

(25) Buffer

(26) AMP: 2-amino-2-methyl-1-propanol solution, commercially available from Angus Chemical Company, USA.

(27) Complexing Agent

(28) AZC: ammonium zirconium carbonate, commercially available from Clariant SE, Switzerland.

(29) Binder

(30) PVA1: polyvinyl alcohol Mowiol 26-88, commercially available from Kuraray Europe GmbH, Germany.

(31) PVA2: polyvinyl alcohol Mowiol 18-88, commercially available from Kuraray Europe GmbH, Germany.

(32) Other Additives

(33) Surfactant: Tecside 87, available from Trill) Emulsion Chemie AG, Ramsen, Switzerland.

(34) Thickener: Sterocoll DF, available from BASF.

(35) 3. Examples

Example 1

(36) Solubilization of Sulfonated PET Ionomer

(37) Water was placed into a beaker and under continuous stirring with a paddle mixer, terephthalate ionomer PET1 was added in an amount of 30-50 wt.-%, based on the total weight of the aqueous solution. Subsequently, the mixture was heated up to 90? C. for 30 min. The obtained solution was cooled down to 40 to 50? C. and then the pH was adjusted to 8.5 by adding buffer AMP.

(38) The obtained aqueous solution of PET1 was yellow honey colored and had a solids content of 30 wt.-%, based on the total weight of the aqueous solution, and a viscosity of less than 50 mPa.Math.s.

(39) Preparation of Liquid Coating Compositions

(40) The filler CC1 was provided in form of a filter cake having a solids content of 78 wt.-%, based on the total weight of the filter cake. The filter cake was mixed with 0.3 parts by weight of complexing agent AZC. Subsequently, the aqueous solution of PET1 was added in such an amount that a wt.-% ratio of filler to PET1 of 62 to 38 was obtained.

(41) The obtained liquid coating composition had a solids content of 48 wt.-%, based on the total weight of the composition, a pH of 8.5 and a viscosity of 200 mPa.Math.s.

(42) Preparation of Barrier Coated Substrates

(43) Virgin cellulose-based substrates of the UZ (uncoated, bleached virgin chemical pulp) or UC (uncoated, virgin mechanical pulp) type with a basis weight of 260 g/m.sup.2 (e.g. available from SAPPI, Maastricht, The Netherlands) were coated with the prepared inventive coating composition (composition B) and a comparative coating composition (composition A), which was the prepared solution of PET1. The coating was carried out with a K303 Control Coater, Model 625, from Erichsen, Germany, using the amounts, rods and speeds indicated in Table 2 below. Unlike the inventive coating composition samples, barrier coatings prepared with coating composition A (comparative example) required a long time for drying.

(44) TABLE-US-00001 TABLE 1 Liquid coating compositions. Coating Ratio filler/polymer Solids content composition Filler Polymer [wt.-%/wt.-%] [wt.-%] A (comparative) PET1 30 B (inventive) CC1 PET1 62:38 48

(45) TABLE-US-00002 TABLE 2 Composition of coated substrates Amount of applied coating Sample Coating composition composition [g/m.sup.2] Rod/Speed 1 B (inventive) 10 3/2 2 B (inventive) 15 4/2 3 B (inventive) 20 4/10 4 B (inventive) 6 0/2 5 A (comparative) 10 3/2 6 A (comparative) 5 0/2

(46) The barrier performance of the barrier coated substrate samples 1 to 6 and a blank substrate sample, was tested by determining the hexane vapor transmission rate using the barrier performance migration test, described above. The test results are shown in FIG. 1, wherein the numbers in the FIGURE correspond to the sample numbers.

(47) It can be seen from FIG. 1 that the blank substrate sample showed a bad barrier performance: the hexane was totally migrated through the barrier coating after 14 to 16 h. All substrates coated with inventive coating composition (composition B) revealed good barrier properties. The substrate coated with PET1 only (composition A) revealed also good barrier properties. However, as already mentioned above, barrier coatings containing PET1 only required long drying times, which can have a negative effect on the substrate and may delay production processes.

Example 2

(48) Two liquid coating composition samples 7 and 8 were produced, using the ingredients and amounts compiled in Table 3 below, as follows:

(49) An aqueous solution of PET1 having a solids content of 36.3 wt.-%, based on the total weight of the solution, was prepared by mixing the respective amount of PET1 with water and stirring the mixture 60 min at 95? C.

(50) The calcium carbonate suspension CC3 was mixed with the prepared aqueous solution of PET1. The obtained mixture was buffered with buffer AMP to a pH value of 8.5, and subsequently, the additive PVA1 was added under mixing conditions. The properties of the obtained liquid coating composition are given in Table 3 below.

(51) The liquid coating composition was applied on a white lined chipboard GD2 (Kondor-GD 2, Buchmann Karton, Germany) in an amount such that a layer thickness as indicated in Table 3 below was achieved and by using a rod no. 3 and a K303 Control Coater, Model 625, from Erichsen, Germany. After application of the barrier layer, the chipboard had the moisture content given in Table 3 below. The applied coating composition was dried at room temperature under infrared light for 5 seconds.

(52) TABLE-US-00003 TABLE 3 Composition and properties of coating composition samples 7 and 8 and the barrier layers produced thereof. Sam- Sam- Component ple 7 ple 8 PET1 parts by weight of solution 110.34 137.93 solid content [wt.-%] 36.3 36.3 parts by weight, based on dry coating 40 50 composition CC3 parts by weight of suspension 83.22 69.93 solid content [wt.-%] 72 72 parts by weight, based on dry coating 60 50 composition PVA1 parts by weight of solution 5.71 5.71 solid content [wt.-%] 17.5 17.5 parts by weight, based on dry coating 1 1 composition Properties solids content [wt.-%] 50.7 47.6 of obtained pH 9.0 8.95 coating viscosity [mPa .Math. s] 750 280 composition Properties layer weight per unit area [g/m.sup.2] 18.9 18.9 of barrier layer moisture content of substrate [%] 5.6 6.2

(53) The barrier performance of the coated chipboards was tested using the barrier performance quick test described above. The cardboard remained white, and thus, the applied coating composition showed good barrier properties.

Example 3

(54) Two liquid coating composition samples 9 and 10 were produced, using the ingredients and amounts compiled in Table 4 below, as follows:

(55) An aqueous solution of PET1 having a solids content of 36.3 wt.-%, based on the total weight of the solution, was prepared by mixing the respective amount of PET1 with water and stirring the mixture 60 min at 95? C. The obtained PET1 solution was buffered with buffer AMP to a pH value of 8.5.

(56) The calcium carbonate suspension CC2 was pre-mixed with 0.28 wt.-%, based on the total weight of the dried coating composition, of the complexing agent AZC and 4 parts by weight, based on the dry coating composition, (corresponding to 11.03 parts by weight of the PET1 solution) of the prepared aqueous solution of PET1. The pre-mixed calcium carbonate suspension was buffered with buffer AMP to a value of 8.5 and mixed with the remaining parts of said aqueous solution of PET1. Subsequently, additive PVA1 was added under mixing conditions. The properties of the obtained liquid coating composition are also given in Table 4 below.

(57) The liquid coating composition was applied on a white lined chipboard GD2 (Kondor-GD 2, Buchmann Karton, Germany) in an amount such that a layer thickness as indicated in Table 4 below was achieved and by using a rod no. 3 and a K303 Control Coater, Model 625, from Erichsen, Germany. After application of the barrier layer, the chipboard had the moisture content given in Table 4 below. The applied coating composition was dried at room temperature under infrared light for 5 seconds.

(58) TABLE-US-00004 TABLE 4 Composition and properties of coating composition samples 9 and 10 and the barrier layers produced thereof. Component Sample 9 Sample 10 PET1 parts by weight of solution 110.34 137.93 solid content [wt.-%] 36.3 36.3 parts by weight, based on dry 40 50 coating composition CC2 parts by weight of suspension 83.92 69.93 solid content [wt.-%] 71.5 71.5 parts by weight, based on dry 60 50 coating composition PVA1 parts by weight of solution 5.71 5.71 solid content [wt.-%] 17.5 17.5 parts by weight, based on dry 1 1 coating composition Properties of solids content [wt.-%] 51.3 47 obtained pH 8.77 8.75 coating viscosity [mPa .Math. s] 280 320 composition Properties of layer weight per unit area [g/m.sup.2] 16.5 16.0 barrier layer moisture content of substrate [%] 6.0 6.2

(59) The barrier performance of the coated chipboards was tested using the barrier performance quick test described above. The cardboard remained white, and thus, the applied coating composition showed good barrier properties.

Example 4

(60) Two liquid coating composition samples 11 and 12 were produced, using the ingredients and amounts compiled in Table 5 below, as follows:

(61) An aqueous solution of PET1 having a solids content of 41.1 wt.-%, based on the total weight of the solution, was prepared by mixing the respective amount of PET1 with water and stirring the mixture 60 min at 95? C. The obtained PET1 solution was buffered with buffer AMP to a pH value of 8.5.

(62) The calcium carbonate suspension CC2 or CC3, respectively, was pre-mixed with the complexing agent AZC, 0.2 wt.-%, based on the total weight of the dried coating composition, of buffer AMP, and 2 parts by weight, based on the dry coating composition, (corresponding to 4.83 parts by weight of the PET1 solution) of the prepared aqueous solution of PET1. Subsequently, the pre-mixed calcium carbonate suspension was mixed with the remaining parts of the aqueous solution of PET1. The properties of the obtained liquid coating composition are also given in Table 5 below.

(63) The liquid coating composition was applied on a white lined chipboard GD2 (Kondor-GD 2, Buchmann Karton, Germany) in an amount such that a layer thickness as indicated in Table 5 below was achieved and by using a rod no. 3 and a K303 Control Coater, Model 625, from Erichsen, Germany. After application of the barrier layer, the chipboard had the moisture content given in Table 5 below. The applied coating composition was dried at room temperature under infrared light for 5 seconds.

(64) TABLE-US-00005 TABLE 5 Composition and properties of coating composition samples 11 and 12 and the barrier layers produced thereof. Component Sample 11 Sample 12 PET1 parts by weight of solution 72.46 72.46 solid content [wt.-%] 41.4 41.4 parts by weight, based on dry 30 30 coating composition CC3 parts by weight of suspension 94.59 solid content [wt.-%] 74.0 parts by weight, based on dry 70 coating composition CC2 parts by weight of suspension 94.59 solid content [wt.-%] 74.0 parts by weight, based on dry 70 coating composition Properties of solids content [wt.-%] 59.0 59.4 obtained pH 8.45 8.40 coating viscosity [mPa .Math. s] 1760 3270 composition Properties of layer weight per unit area [g/m.sup.2] 22.0 14.0 barrier layer moisture content of substrate [%] 6.5 6.8

(65) The barrier performance of the coated chipboards was tested using the barrier performance quick test described above. The cardboard remained white, and thus, the applied coating composition showed good barrier properties.

Example 5

Mill Trial

(66) This example illustrates the preparation of coated substrates by use of slide die curtain coating technology in industrial scale.

(67) The base paper used in this trial was a test liner from Model AG, Weinfelden, Switzerland with a grammage of 135 g/m.sup.2.

(68) A liquid coating composition sample 13 was produced, using the ingredients and amounts compiled in Table 5 below, as follows:

(69) An aqueous solution of PET1 having a solids content of 30.0 wt.-%, based on the total weight of the solution, was prepared by mixing the respective amount of PET1 with water and stirring the mixture 60 min at 95? C. The obtained PET1 solution was buffered with buffer AMP to a pH value of 8.5.

(70) The calcium carbonate suspension CC3 was mixed with the prepared aqueous solution of PET1. The obtained mixture was buffered with buffer AMP to a pH value of 8.5, and subsequently, the additive PVA2 as well as the surfactant and the thickener were added under mixing conditions. The properties of the obtained liquid coating composition are given in Table 5 below.

(71) TABLE-US-00006 TABLE 5 Composition and properties of coating composition sample 13 Component Sample 13 PET1 solid content [wt.-%] 30.0 parts by weight, based on dry 50 coating composition CC3 solid content [wt.-%] 72.0 parts by weight, based on dry 50 coating composition PVA2 solid content [wt.-%] 13.0 parts by weight, based on dry 3 coating composition Surfactant (Tecside solid content [wt.-%] 100 87) parts by weight, based on dry 0.7 coating composition Thickener solid content [wt.-%] 50 (Sterocoll? DF) parts by weight, based on dry 0.02 coating composition Properties of solids content [wt.-%] 39.0 obtained Surface tension [mN/m] 35 coating composition viscosity [mPa .Math. s] 150

(72) The static surface tension has been analyzed with a tensiometer from the company Kr?ss GmbH, Hamburg, Germany.

(73) The curtain coating trial was conducted on a coating machine 5, at the Cham Paper Group, Cham, Switzerland.

(74) Two coating trials were run, one with a machine speed of 300 m/min and an application weight of 10 g/m.sup.2, and a second one with a machine speed of 300 m/min and an application weight of 15 g/m.sup.2.

(75) The applied coating was dried using hot air and infra-red light.

(76) Migration tests, namely MOSH (migration of mineral oil saturated hydrocarbons) and MOAH (migration of mineral oil aromatic hydrocarbons), have been conducted over 50 days on both samples (10 g/m.sup.2 and 15 g/m.sup.2 coating weight) by Eurofins Scientific AG, Switzerland, an external testing lab, according to DIN EN 14338:2004.

(77) The results are as follows:

(78) Both coating weights showed even after 50 days a MOSH value (sum of all saturated hydrocarbons with C10 to C35 chain) of less than 0.6 mg/kg, and a MOAH value (sum of all aromatic hydrocarbons with 10 to 35 C-atoms) of less than 0.15 mg/kg.