Method for the production of heat-sealing barrier paper

Abstract

The invention relates to a method for the production of a heat-sealable paper that forms a barrier to water vapour, in particular having a water vapour permeability of at most 150 g/m.sup.2/24 h measured according to ASTM F1249 under so-called tropical conditions of 38 C. and 90% relative humidity, in which at least one coating layer comprising at least one thermoplastic film-forming polymer is applied in-line on the paper-making machine to the fibrous substrate.

Claims

1. A process for manufacturing a heat-sealable water vapor barrier paper having a water vapor permeability of at most 150 g/m.sup.2/24 h measured according to the ASTM F1249 standard under conditions of 38 C. and 90% relative humidity, in which at least one covering layer comprising at least one thermoplastic film-forming polymer is applied in-line on a papermaking machine and to a precoat layer, and in which the precoat layer is applied to a fibrous substrate in-line before the application of the covering layer to the precoat layer.

2. The process as claimed in claim 1, the production speed of the paper being greater than or equal to 300 m/min.

3. The process as claimed in claim 1, a pore-filling composition being applied in-line to the fibrous substrate before the in-line application of any layer or precoat layer.

4. The process as claimed in claim 1, the final basis weight of the paper being between 45 and 200 g/m.sup.2.

5. The process as claimed in claim 1, comprising at least one in-line drying step then one in-line winding step, in which the heating power during the drying step is sufficient so that the covering layer is sufficiently dry during the winding step so that the turns of the reel do not stick together.

6. The process as claimed in claim 5, the paper being brought during the drying of the fibrous substrate, before any surface treatment into contact with a Yankee cylinder.

7. The process as claimed in claim 5, the paper being brought during the drying of the covering layer into a zone where the drying takes place without contact.

8. The process as claimed in claim 1, in which the precoat layer comprises a mixture of platy filler(s) having a shape factor of at least 15 and of finer, non-platy filler(s), the particle size of which, for 80% by weight, is less than or equal to 2 m, measured by the ISO 13317-3 SediGraph method.

9. The process as claimed in claim 8, the platy filler(s) and the finer filler(s) being of the same nature.

10. The process as claimed in claim 8, the shape factor of the platy particles being at least 40.

11. The process as claimed in claim 8, the finer filler(s) having a particle size, for 95% by weight, of less than 2 microns.

12. The process as claimed in claim 8, the platy filler(s) being mineral filler(s).

13. The process as claimed in claim 8, the finer filler(s) being mineral filler(s).

14. The process as claimed in claim 8, the platy filler(s) being selected from kaolins and talc and mixtures thereof.

15. The process as claimed in claim 8, the finer filler(s) being selected from kaolins, calcium carbonate, barium sulphate, silica, titanium dioxide and mixtures thereof.

16. The process as claimed in claim 8, the finer filler(s) being selected from kaolins.

17. The process as claimed in claim 8, the dry weight of platy filler(s) being between 3% and 58% of the total dry weight of the precoat layer.

18. The process as claimed in claim 8, the dry weight of finer filler(s) being between 3% and 58% of the total dry weight of the precoat layer.

19. The process as claimed in claim 8, 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%.

20. The process as claimed in claim 1, the precoat layer comprising a binder comprising a polymer of chemical nature not present in the covering layer.

21. The process as claimed in claim 20, the binder having a glass transition temperature T.sub.g below or equal to 25 C. measured according to the ASTM E1356 standard.

22. The process as claimed in claim 20, the binder being selected from latices of styrene-butadiene, styrene-acrylic, acrylic, butyl acrylate, butyl acrylate-styrene-acrylonitrile chemical nature.

23. The process as claimed in claim 20, the binder being introduced in latex form.

24. The process as claimed in claim 20, the amount of binder being of at least 15 parts when dry relative to the fillers when dry (100 parts).

25. The process as claimed in claim 1, the covering layer being applied without calendering of the substrate covered by the precoat layer.

26. The process as claimed in claim 1, the covering layer being the only layer that covers the precoat layer.

27. The process as claimed in claim 1, the covering layer comprising one or more polymers selected from copolymers based on PVdC or on styrene-acrylic.

28. The process as claimed in claim 1, the amount of precoat layer being less than or equal to 12 g/m.sup.2 by dry weight.

29. The process as claimed in claim 1, the amount of covering layer being less than or equal to 10 g/m.sup.2 by dry weight.

30. The process as claimed in claim 1, in which a layer is applied in-line on the papermaking machine to the face of the fibrous substrate opposite the one bearing the covering layer.

31. The process as claimed in claim 1, the paper being heat-sealable at a production 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.

32. The process as claimed in claim 1, the paper being heat-sealable when the sealing is carried out by hot nip rolls, under 3 bar and for 0.5 s.

33. The process as claimed in claim 1, the paper being heat-sealable to itself with a sealing force of 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 nip rolls, under 3 bar and for 0.5 s.

34. A packaging process in which an article is packaged by heat-sealing the paper obtained by the manufacturing process as claimed in claim 1 to itself, at a production 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.

Description

EXAMPLE 1

(1) 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.

(2) The fibrous support is firstly glazed then treated in-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.

(3) 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:

(4) 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.

(5) The particle size, for 97% by weight of Amazon Premium, measured according to the ISO 13317-3 SediGraph method, is less than 2 microns.

(6) The shape factor of the Capim NP particles is 28.

(7) The barrier to water vapor 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

(8) 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.

(9) The fibrous support is firstly glazed then treated in-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.

(10) 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:

(11) 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.

(12) The particle size, for 95% by weight of Hydrocarb 95, measured according to the ISO 13317-3 SediGraph method, is less than 2 microns.

(13) The barrier to water vapor 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

(14) A paper is produced in-line under the same conditions as in Example 1. But following the deposition of the precoat layer, it is coated in-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.

(15) The barrier to water vapor 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.

(16) 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.

(17) A sealing force of 3.5 N/15 mm is obtained.

(18) The invention is not limited to the examples described.

(19) In summary, the invention may have the following advantageous features, alone or in combination: a precoat layer is applied in-line before the application of the covering layer to the precoat layer, the production speed of the paper is greater than or equal to 300 m/min, better still greater than or equal to 400 m/min, even better still greater than or equal to 500 m/min, a pore-filling composition is applied in-line to the fibrous substrate before the in-line application of any layer or precoat layer, the pore-filling composition being applied preferably by size press or by film press, the process comprises at least one in-line drying step then one in-line winding step, the heating power during the drying step being sufficient so that the covering layer is sufficiently dry during the winding step so that the turns of the reel do not stick together, the paper is brought during the drying of the fibrous substrate, before any surface treatment, in particular coating, into contact with a Yankee cylinder, the paper is brought during the drying of the covering layer into a zone where the drying takes place without contact, in particular using at least one infrared ramp and/or hot-air heating, the precoat layer comprises at least one platy filler having a shape factor of at least 15 and preferably a mixture of platy filler(s) having a shape factor of at least 15 and of in particular finer, in particular non-platy filler(s), the particle size of which, for 80% by weight, is less than or equal to 2 m, measured by the ISO 13317-3 SediGraph method, the platy filler(s) and the finer filler(s) are of the same nature, the shape factor of the platy particles is at least 40, more preferably at least 60, the finer filler(s) have a particle size, for 95% by weight, of less than 2 microns, the platy filler(s) are mineral filler(s), the finer filler(s) are mineral filler(s), the platy filler(s) being selected from kaolins and talc and mixtures thereof, the finer filler(s) being selected from kaolins, calcium carbonate, barium sulphate, silica, titanium dioxide and mixtures thereof, the finer filler(s) being selected from kaolins, the dry weight of platy filler(s) being between 3% and 58% of the total dry weight of the precoat layer, the amount by weight of platy filler(s) preferably being greater than that of the finer fillers, the dry weight of finer filler(s) is between 3% and 58% of the total dry weight of the precoat layer, the percentage of platy fillers, expressed by dry weight, relative to the sum of the fillers, expressed by dry weight, being between 10% and 90%, preferably between 40% and 90% and more preferably still between 60% and 90%, the precoat layer may comprise a binder, the binder having a glass transition temperature T.sub.g below or equal to 25 C. and more preferably below or equal to 10 C., measured according to the ASTM E1356 standard, the binder being selected from latices of styrene-butadiene, styrene-acrylic, acrylic, butyl acrylate, butyl acrylate-styrene-acrylonitrile chemical nature, and preferably latices of styrene-butadiene chemical nature, the binder comprises a polymer of chemical nature not present in the covering layer, the binder being introduced in latex form, the amount of binder is of at least 15 parts when dry relative to the fillers when dry (100 parts) and preferably more than 25, better still 30 parts, a covering layer may be applied without calendering of the substrate covered by the precoat layer, the covering layer may be the only layer that covers the precoat layer, the covering layer may comprise one or more polymers selected from copolymers based on PVdC or on styrene-acrylic, the amount of precoat layer is less than or equal to 12 g/m.sup.2 by dry weight, the amount of covering layer is less than or equal to 10 g/m.sup.2 by dry weight, a layer, in particular a printing layer, is applied in-line on the papermaking machine to the face of the substrate opposite the one bearing the covering layer, the covering layer is constituted by a heat-sealable polymer, the water vapor permeability of the barrier paper is less than 150 g/m.sup.2/24 h, better still less than 100 g/m.sup.2/24 h, measured according to the ASTM F1249 standard under so-called tropical conditions at 38 C. and 90% relative humidity, the basis weight of the fibrous substrate is between 25 and 180 g/m.sup.2, the paper is heat-sealable starting from 90 C., when the sealing is carried out by hot nip rolls, under 3 bar and for 0.5 s, the substrate bears two identical precoat layers on its opposite faces or two layers of different natures, between 30% and 80% by weight of platy particles have a size less than or equal to 2 m (measured according to the ISO 13317-3 SediGraph method), the paper is heat-sealable, in particular to itself, at a production 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, the paper is heat-sealable to itself with a sealing force of 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 nip rolls, under 3 bar and for 0.5 s, the temperature of the fibrous substrate during the application of the precoat layer is greater than or equal to 50 C., the temperature of the fibrous substrate during the application of the covering layer is greater than or equal to 70 C., the final basis weight of the paper is between 45 and 200 g/m.sup.2.

(20) The expression comprising a should be understood as being synonymous with comprising at least one.