HEAT-SEALING BARRIER PAPER

Abstract

A paper including a fibrous substrate, a precoat layer including a binder and a mixture of platy filler(s) having a shape factor of at least 15 and of finer filler(s), the size of the particles of which is, for 80% by weight, less than 2 m (measured according to the ISO 13317-3 SediGraph method) and at least one covering layer applied to the precoat layer, the paper having a water vapour permeability of at most 150 g/m.sup.2/24 h and preferably of less than 100 g/m.sup.2/24 h, measured according to the ASTM F1249 standard under so-called tropical conditions of 38 C. and 90% relative humidity.

Claims

1-37. (canceled)

38. Paper comprising: a fibrous substrate, a precoat layer comprising a binder and a mixture of platy filler(s) having a shape factor of at least 15 and of finer filler(s), the size of the particles of which is, for 80% by weight, less than 2 m (measured according to the ISO 13317-3 SediGraph method), at least one covering layer applied to the precoat layer, the paper having a water vapour permeability of at most 150 g/m.sup.2/24 h, measured according to the ASTM F1249 standard under so-called tropical conditions of 38 C. and 90% relative humidity.

39. Paper according to claim 38, the weight of the covering layer not exceeding 10 g/m.sup.2 when dry.

40. Paper according to claim 39, the covering layer comprising a heat-sealable polymer, or even being constituted by a heat-sealable polymer.

41. Paper according to claim 38, the platy filler(s) and the finer filler(s) being of the same nature.

42. Paper according to claim 38, the shape factor of the platy filler particles being at least 40.

43. Paper according to claim 38, the finer filler(s) having a particle size, for 95% by weight, of less than 2 microns, measured according to the ISO 13317-3 SediGraph method.

44. Paper according to claim 38, the platy filler(s) being mineral filler(s).

45. Paper according to claim 38, the finer filler(s) being mineral filler(s).

46. Paper according to claim 38, the platy filler(s) being selected from kaolins and talc and mixtures thereof.

47. Paper according to claim 38, the finer filler(s) being selected from kaolins, calcium carbonate, barium sulphate, silica, titanium dioxide and mixtures thereof.

48. Paper according to claim 38, the finer filler(s) being selected from kaolins.

49. Paper according to claim 38, the dry weight of platy filler(s) being between 3% and 58% of the total dry weight of the precoat layer.

50. Paper according to claim 38, the dry weight of finer filler(s) being between 3% and 58% of the total dry weight of the precoat layer.

51. Paper according to claim 38, the percentage of platy filler(s), expressed by dry weight, relative to the sum of the fillers, expressed by dry weight, being between 10% and 90%.

52. Paper according to claim 38, the binder having a glass transition temperature T.sub.g below or equal to 25 C.

53. Paper according to claim 38, the binder being selected from latices of styrene-butadiene, styrene-acrylic, acrylic, butyl acrylate, butyl acrylate-styrene-acrylonitrile chemical nature, and mixtures thereof.

54. Paper according to claim 38, the binder being selected from latices of styrene-butadiene chemical nature.

55. Paper according to claim 38, the binder being introduced in latex form.

56. Paper according to claim 38, comprising in the precoat layer at least 15 parts when dry of binder relative to the weight of fillers when dry (100 parts).

57. Paper according to claim 38, the binder comprising a polymer of chemical nature not present in the covering layer.

58. Paper according to claim 38, the covering layer being substantially free of filler.

59. Paper according to claim 38, the covering layer being the only layer that covers the precoat layer.

60. Paper according to claim 38, the covering layer comprising one or more polymers selected from copolymers based on PVdC or on styrene-acrylic and mixtures thereof.

61. Paper according to claim 38, the amount of precoat layer being less than or equal to 12 g/m.sup.2 by dry weight.

62. Paper according to claim 38, comprising a printing layer on the face of the substrate opposite the one bearing the precoat layer and the covering layer.

63. Paper according to claim 38, the substrate bearing two identical precoat layers on its opposite faces.

64. Paper according to claim 38, the substrate bearing two precoat layers of different natures on its opposite faces.

65. Paper according to claim 38, a pore-filling composition being applied to the substrate, and the precoat layer being applied to the pore-filling composition.

66. Paper according to claim 38, the basis weight of the fibrous substrate being between 25 and 180 g/m.sup.2.

67. Paper according to claim 38, the paper being heat-sealable.

68. Paper according to claim 38, the final basis weight of the paper being between 45 and 200 g/m.sup.2.

69. Precoated paper suitable for the manufacture of a paper as defined in claim 38, having a water vapour permeability of at most 150 g/m.sup.2/24 h according to the ASTM F1249 standard at 38 C. and 90% relative humidity, the precoated paper being uncalendered.

70. Packaging comprising a paper as defined in claim 38, the paper being heat-sealed to itself, containing a food product.

71. Process for manufacturing a paper according to claim 38, in which a composition is applied to a fibrous substrate, the composition comprising a binder in latex form and a dispersion of a mixture of platy filler(s) having a shape factor of at least 15 and of finer filler(s), the size of the particles of which is, for 80% by weight, less than 2 m.

Description

EXAMPLE 1

[0080] A fibrous support having a basis weight of 55 g/m.sup.2 is produced on a papermaking machine operating at 400 m/min. The papermaking machine is equipped with a Yankee cylinder placed before the size press.

[0081] The fibrous support is firstly glazed then treated on-line on both its faces by a size press with a pore-filling pigment composition, containing 100 dry parts of kaolin of Amazon Premium type (Cadam), and a mixture of Merifilm 104 starch (Tate&Lyle) and of latex of DL950 type (Dow) in a proportion of 20 dry parts relative to the dry kaolin. The treatment applied is 5 g/m.sup.2 when dry in total.

[0082] It is then coated using a Meyer rod coater with a precoat formulation containing a mixture of platy fillers and of finer particulate fillers and a latex of styrene-butadiene chemical nature of Tg=7 C. (DL950 from Dow Chemical) and dried without contact in an infrared oven then a hot air oven. It is then wound on a reel with no other treatment. The dry weight of the precoat layer applied is 7 g/m.sup.2 and its formulation is given in the table below:

TABLE-US-00001 Material Reference/Nature Suppliers Parts wt % Topsperse GX-N Dispersant COATEX 0.2 0.2 Capim NP Kaolin IMERYS 60.0 45.5 (platy filler) Amazon Premium Kaolin CADAM 40.0 30.4 (finer filler) Bacote 20 Crosslinker QUARRECHIM 1.5 1.1 DL950/Styrene- Styrene-butadiene DOW 30.0 22.8 butadiene latex latex Tg 7 C. Tg 7 C.

[0083] The particles size, for 97% by weight, of Amazon Premium, measured according to the IS013317-3 SediGraph method, is less than 2 microns.

[0084] The shape factor of the Capim NP particles is 28.

[0085] The barrier to water vapour is measured by a Mocon Permatran 3/61 machine according to the ASTM F1249 standard at 38 C. and 90% relative humidity in order to determine the barrier contribution of this precoat layer. It is measured at 33413 g/m.sup.2/24 h. After coating with the covering layer, a barrier is obtained of less than 150 g/m.sup.2/24 h.

EXAMPLE 2

[0086] The fibrous support is firstly glazed then treated on-line on both its faces by a size press with a pore-filling pigment composition, containing 100 dry parts of kaolin of Amazon Premium type (Cadam), and a mixture of Merifilm 104 starch (Tate&Lyle) and of latex of DL950 type (Dow) in a proportion of 20 dry parts relative to the dry kaolin. The treatment applied is 5 g/m.sup.2 when dry in total.

[0087] It is then coated using a Meyer rod coater with a formulation containing a mixture of platy fillers and of finer particulate fillers and a latex of styrene-butadiene chemical nature of Tg=7 C. (DL950 from Dow Chemical) and dried without contact in an infrared oven then a hot air oven. It is then wound on a reel with no other treatment. The dry weight of the precoat layer applied is 7 g/m.sup.2 and its formulation is given in the table below:

TABLE-US-00002 Material Reference/Nature Suppliers Parts wt % Topsperse GX-N Dispersant COATEX 0.2 0.2 Capim NP Kaolin IMERYS 60.0 45.5 (platy filler) Hydrocarb 95 Calcium carbonate OMYA 40.0 30.4 (finer filler) Bacote 20 Crosslinker QUARRECHIM 1.5 1.1 DL950/Styrene- Styrene-butadiene DOW 30.0 22.8 butadiene latex latex Tg 7 C. Tg 7 C.

[0088] The particles size, for 95% by weight, of Hydrocarb 95, measured according to the ISO13317-3 SediGraph method, is less than 2 microns.

[0089] The barrier to water vapour is measured by a Mocon Permatran 3/61 machine according to the ASTM F1249 standard at 38 C. and 90% relative humidity in order to determine the barrier contribution of this precoat layer. It is measured at 3159 g/m.sup.2/24 h. After coating with the covering layer, a barrier is obtained of less than 150 g/m.sup.2/24 h.

EXAMPLE 3

[0090] A paper is produced on-line under the same conditions as in Example 1. But following the deposition of the precoat layer, it is coated on-line with a covering layer consisting of a dispersion of PVdC copolymer (Diofan A297 from Solvay), and dried without contact in an infrared oven then a hot air oven. It is then wound on a reel with no other treatment and no bonding between turns is observed. The dry weight of the covering layer is 6.5 g/m.sup.2.

[0091] The barrier to water vapour is measured by a Mocon Permatran 3/61 machine according to the ASTM F1249 standard at 38 C. and 90% relative humidity. It is measured at 21.02.4 g/m.sup.2/24 h.

[0092] The sealing is then simulated on a laboratory heat-sealing machine by bonding the face covered with the covering layer to itself at 110 C., under 3 bar and for 0.5 second. Next, the force necessary for detaching papers bonded to samples having a width of 15 mm is subsequently measured under an angle of 90 degrees according to the Tappi T540 standard at a speed of 100 mm/min.

[0093] A sealing force of 3.5 N/15 mm is obtained.

[0094] The invention is not limited to the examples described.

[0095] In summary, the invention may have one or more of the following advantageous features: [0096] the weight of the covering layer does not exceed 10 g/m.sup.2 when dry, in particular is strictly less than 10 g/m.sup.2, [0097] the covering layer comprises or is constituted by a heat-sealable polymer, [0098] the platy filler(s) and the finer filler(s) are of the same nature, [0099] the shape factor of the platy filler particles is at least 40, more preferably at least 60, [0100] the finer filler(s) are non-platy filler(s), [0101] the finer filler(s) are platy filler(s), [0102] the finer filler(s) have a particle size, for 95% by weight, of less than 2 microns, measured according to the ISO 13317-3 SediGraph method, [0103] the platy filler(s) are mineral filler(s), [0104] the finer filler(s) are mineral filler(s), [0105] the platy filler(s) are selected from kaolins and talc and mixtures thereof, [0106] the finer filler(s) are selected from kaolins, calcium carbonate, barium sulphate, silica, titanium dioxide and mixtures thereof, [0107] the finer filler(s) are selected from kaolins, [0108] the dry weight of platy filler(s) is between 3% and 58% of the total dry weight of the precoat layer, the weight of platy filler(s) preferably being greater than that of the finer fillers, [0109] the dry weight of finer filler(s) is between 3% and 58% of the total dry weight of the precoat layer, [0110] the percentage of platy filler(s), expressed by dry weight, relative to the sum of the fillers, expressed by dry weight, is between 10% and 90%, preferably between 40% and 90% and more preferably still between 60% and 90%, [0111] the binder has a glass transition temperature T.sub.g below or equal to 25 C. and more preferably below 10 C., [0112] the binder is selected from latices of styrene-butadiene, styrene-acrylic, acrylic, butyl acrylate, butyl acrylate-styrene-acrylonitrile chemical nature, and mixtures thereof, [0113] the binder is selected from latices of styrene-butadiene chemical nature, [0114] the binder is introduced in latex form, [0115] the precoat layer comprises at least 15 parts when dry of binder relative to the weight of fillers when dry (100 parts) and preferably more than 25, better still 30 parts, [0116] the binder comprises a polymer of chemical nature not present in the covering layer, [0117] the covering layer is substantially free of filler, [0118] the covering layer is the only layer that covers the precoat layer, [0119] the covering layer comprises one or more polymers selected from copolymers based on PVdC or on styrene-acrylic and mixtures thereof, [0120] the amount of precoat layer is less than or equal to 12 g/m.sup.2 by dry weight, [0121] the paper comprises a printing layer on the face of the substrate opposite the one bearing the precoat layer and the covering layer, [0122] the substrate bears two identical precoat layers on its opposite faces, [0123] the substrate bears two precoat layers of different natures on its opposite faces, [0124] a pore-filling composition is applied to the substrate, and the precoat layer is applied to the pore-filling composition, the pore-filling composition being applied preferably by size press or film press, [0125] the basis weight of the fibrous substrate is between 25 and 180 g/m.sup.2, [0126] the paper is heat-sealable, in particular starting from 90 C., when the sealing is carried out by hot clamps, under 3 bar and for 0.5 s, [0127] the water vapour permeability of the barrier paper is less than 100 g/m.sup.2/24 h. [0128] between 30% and 80% by weight of platy particles are of size less than or equal to 2um (measured according to the ISO 13317-3 SediGraph method), [0129] the paper is heat-sealable, notably to itself, at a manufacturing rate greater than or equal to 40 bags per minute, on vertical packaging machines of VFFS (Vertical Form, Fill and Seal) type, along longitudinal sealing lines of 330 mm per bag, [0130] the paper is heat-sealable to itself with a sealing force greater than or equal to 2 N/15 mm, measured under an angle of 90 degrees according to the Tappi T540 standard at a speed of 100 mm/min, when the sealing is carried out by hot clamps, under 3 bar and for 0.5 s, [0131] the temperature of the fibrous substrate during the application of the precoat layer is greater than or equal to 50 C., [0132] the temperature of the fibrous substrate during the application of the covering layer is greater than or equal to 70 C., [0133] the final basis weight of the paper is between 45 and 200 g/m.sup.2. The expression comprising a should be understood as being synonymous with comprising at least one.