Laminate

Abstract

A primary laminate including a tabstock in which a seal laminate including a foil layer and a top foam layer, a tabstock and a plastic film stock are fed to a laminating station is provided herein. At the lamination station, a curtain of polymeric adhesive is extruded between the plastics film stock and the top face of the primary substrate, which is partly comprised of the top face of the tabstock and partly comprised of the top foam layer of the seal laminate. Use of primary laminates obtained by such a process to form seals for sealing a container, for food or drink stored at low temperatures, is also described.

Claims

1. A primary laminate comprising: a seal laminate including a heat seal layer for sealing to a container, a foil layer and a top foam layer; a tabstock which has a top and a bottom face wherein the bottom face is in contact with the top foam layer of the seal laminate; a layer of plastic film adhered to the top face of the tabstock and to the top foam layer by a random copolymer of ethylene and alkyl acrylate and having a melt flow index in the range of 1 to less than 5 dg/min (190 C., 2.16 kg); and wherein the random copolymer of ethylene and alkyl acrylate bonds the layer of plastic film to the top foam layer so that the layer of plastic film does not delaminate therefrom when subjected to a low temperature freezer test by exposing a sealed container with the primary laminate to a temperature from about 0 C. to about 30 to form a cold primary laminate and when applying a removal force to the cold primary laminate for removal of the cold primary laminate from the container.

2. The primary laminate according to claim 1, wherein the random copolymer of ethylene and alkyl acrylate has a melt point of about 70 to about 100 C. and a density of about 0.92 to about 0.955 g/cm.sup.3.

3. The primary laminate according to claim 1, wherein the random copolymer of ethylene and alkyl acrylate is a copolymer of ethylene and C.sub.1-12 alkyl acrylate esters.

4. The primary laminate according to claim 1, wherein the random copolymer of ethylene and alkyl acrylate is an ethylene methyl acrylate copolymer effective to provide an initial peel strength between the layer of plastic film and the top foam layer of greater than 15N/12.5 mm at 330 mm/min.

5. The primary laminate according to claim 1, wherein the random copolymer of ethylene and alkyl acrylate has a melt point of about 70 to about 100 C. and the top foam layer has a higher melt point of about 120 C. to about 129 C.

6. The primary laminate according to claim 1, wherein the layer of plastic film is a co-extruded polyester film.

7. A pull-tab sealing member constructed to be secured to a rim surrounding an opening of a container, the pull-tab sealing member comprising: a seal laminate having a bottom heat seal layer for bonding to a rim of a container and a top foam layer; a tab having a top and a bottom face wherein the bottom face is in contact with but not bonded to the top foam layer of the seal laminate so that the tab lies wholly within a perimeter of the pull-tab sealing member; a layer of plastic film forming a portion of the tab and adhered to the top foam layer of the seal laminate by an extruded polymeric adhesive; and the extruded polymeric adhesive is a random copolymer of ethylene and alkyl acrylate and has a melt flow index in the range of 1 to less than 5 dg/min (190 C., 2.16 kg) effective to bond the layer of plastic film to the top foam layer so that the layer of plastic film does not delaminate therefrom upon a removal force applied to the tab when the pull-tab sealing member is exposed to temperatures from about 30 C. to about 0 C.

8. The pull-tab sealing member according to claim 7, wherein the polymeric adhesive has a melt point of about 70 to about 100 C. and a density of about 0.92 to about 0.955 g/cm.sup.3.

9. The pull-tab sealing member of claim 7, wherein the polymeric adhesive has a melt point of about 70 to about 100 C. and the top foam layer has a higher melt point of about 120 C. to about 129 C.

10. The pull-tab sealing member according to claim 7, wherein the polymeric adhesive is a copolymer of ethylene and C.sub.1-12 alkyl acrylate esters.

11. The pull-tab sealing member according to claim 7, wherein the polymeric adhesive is an ethylene methyl acrylate copolymer effective to provide an initial peel strength between the layer of plastic film and the top foam layer of greater than 15N/12.5 mm at 330 mm/min.

12. The pull-tab sealing member according to claim 7, wherein the layer of plastic film is a co-extruded polyester film.

13. A pull-tab sealing member constructed to be secured to a rim surrounding an opening of a container, the pull-tab sealing member comprising: a seal laminate having a bottom heat seal layer for bonding to a rim of a container and a top polymer foam layer; a layer of polymer film partially adhered to the top polymer foam layer of the seal laminate by a random copolymer of ethylene and alkyl acrylate to form a tab defined by a portion of the polymer film layer not adhered to the top polymer foam layer so that the defined tab lies wholly within a perimeter of the pull-tab sealing member; and the random copolymer of ethylene and alkyl acrylate is a random copolymer of ethylene and C.sub.1-12 alkyl acrylate esters with a mole percentage of the acrylate between 0.5 and 25 percent and has a melt flow index from 1 to less than 5 dg/min (190 C., 2.16kg) effective to bond the layer of plastic film to the top foam layer so that the layer of plastic film does not delaminate therefrom upon a removal force applied to the tab throughout a temperatures from about 30 C. to about 0 C.

14. The pull-tab sealing member according to claim 13, wherein the random copolymer of ethylene and alkyl acrylate has a melt point of about 70 to about 100 C. and a density of about 0.92 to about 0.955 g/cm.sup.3.

15. The pull-tab sealing member according to claim 14, wherein the random copolymer of ethylene and alkyl acrylate is a random copolymer of ethylene methyl acrylate in an amount effective to provide an initial peel strength between the layer of polyester film and the top polyolefin foam layer of greater than 15N/12.5 mm at 330 mm/min.

16. The pull-tab sealing member according to claim 13, wherein the layer of polymer film is a co-extruded polyester film.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An embodiment of the invention will now be described with reference to the following figures, in which:

(2) FIG. 1 is a cross section through an example of a primary laminate including a tabstock as formed according to the method of the present invention with a vertical dimension greatly exaggerated;

(3) FIG. 2 is a schematic diagram of the laminating apparatus used in the method of the present invention;

(4) FIG. 3 is a perspective view of a part of the apparatus illustrated in FIG. 2;

(5) FIG. 4 is a cross section through a sample of the primary laminate being subjected to the 180 peel test to check the strength of the extruded adhesive.

(6) FIG. 5 is a perspective view showing the seal in place on the neck of a container.

DETAILED DESCRIPTION

EXAMPLE 1

(7) A seal laminate (1) comprising heat sealable (hot-melt) layer (4) for adhesion to a container to be sealed, a foil layer (5) and a top layer of polyethylene foam (7) is obtained commercially from Isco Jacques Schindler. This seal laminate is rolled onto a first feed roll (13) in the laminating apparatus.

(8) The second feed roll (14) in the laminating apparatus is the source of the tabstock, which in this case, is a layer of polyethylene terephthalate (8). The width of the layer of polyethylene terephthalate (8) is in the range from 25-60 mm.

(9) A third feed roll (15) is loaded with the plastics film stock, in this case a PET stock (10) which can be obtained commercially from Toray, Europe. The thickness of the PET stock (10) is in the range from 23-36 m. The PET stock (10) used is a co-extruded PET material available as Lumirror 10.47 from Toray. The coextruded surface layer ensures optimal adhesion to the adjacent foam layer of the seal laminate.

(10) The seal laminate (1), tabstock (8) and PET stock (10) are simultaneously fed to the laminating station (6) where an extruder (17) is positioned vertically above the nip between rollers (18 and 19). Prior to reaching the laminating station (6), the seal laminate (1) and tabstock (8) are brought into contact to form a primary substrate (1a).

(11) Ethylene methyl acrylate copolymer (9) with a melt flow index of 2 dg/min (190 C., 2.16 kg (ASTM D1238)) is then extruded continuously as a curtain from the extruder (17) between the top face of the primary laminate (1a) and the bottom face of the PET stock (10). The height of the die head above the nip was about 20 cm. The extrusion conditions i.e. the weight of adhesive being extruded, its, speed and extruder head temperature, were such that a temperature of greater than about 200 C., for instance as much as about 250 C. is attained at the nip for adhesion. Roller 18 is a chilled stainless steel roller, while roller 19 has a Teflon coated surface with Shore A hardness of 75. The rollers (18) and (19) are moving at a speed of 70 m/min relative to the speed of application of the adhesive, the pressure between them selected to avoid the curtain creasing at the nip. The bottom face of the PET stock (10) and the resulting primary laminate (1b) including a tabstock is passed with the bottom face of the PET stock in contact with a chill roller (18) at a temperature of about 23 C. to be rolled on to a final product roll (32). This process is illustrated schematically in FIG. 2.

(12) The break-in peel strength was measured as explained above and illustrated in FIG. 4, of a primary laminate formed using a PET stock (10) thickness of 36 m and a PET tabstock thickness of 12 m onto the seal laminate upper surface of polyethylene foam, wherein the coat weight of the extruded ethylene methyl acrylate copolymer (9) was 40 gm.sup.2. The value was greater than 15N/12.5 mm at 33o mm/min.

(13) The coat weight was determined as follows: a 0.5 m to 1 m length of paper backed polyester which has a width of 1 m was passed to the laminating station between primary substrate 1a and resin 9. A curtain of the ethylene methyl acrylate copolymer was then extruded continuously between the top polyester face of the paper backed polyester and the bottom face of the PET stock (10) under the run conditions of the line. Several 1010 cm samples were then cut across the width of the web and their weight in g was recorded. The weight of the paper backed polyester and PET stock (10) were subtracted from this figure and the result was multiplied by 100 to give a coat weight in gm.sup.2.

(14) The seal stock laminate was then cut into narrow strips. From these strips, circular discs were punched to form discs of the seal stock laminate (16) i.e. seals. The seals are fixed inside screw caps. The screw cap equipped with the seal is then screwed onto the open neck of the bottle 24. The cap and bottle are then subjected to an induction heating step in which the foil is heated around its periphery by the generation of eddy currents within it, which, in turn, melts the heat sealable layer (4) to bond the seal to the open neck of the bottle.