Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
  • B32B27/10—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of paper or cardboard
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
  • B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/34—Layered products comprising a layer of synthetic resin comprising polyamides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2307/00—Properties of the layers or laminate
  • B32B2307/30—Properties of the layers or laminate having particular thermal properties
  • B32B2307/31—Heat sealable
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2377/00—Polyamides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2439/00—Containers; Receptacles
  • B32B2439/70—Food packaging

Definitions

• Lid for a food can
• the invention relates to a lid for a food can, comprising a body layer made of paper, a plastic layer composite extruded onto that surface of the body layer that faces the can and, attached to the plastic layer composite, ⁇ peelable heat-sealing layer for fastening the lid to the can by heat-sealing.
• the term 'to peel' is used herein to mean the opening of a relatively fast joint in a predetermined manner without that it tears.
• a lid for a food can as described above is known e.g. from Finnish Patent Application 914,268.
• aluminium which is conventionally used in cans for yoghurt, pudding, and other corresponding products, has been replaced with a paper-based material.
• the surface of the lid that faces the can is coated with a plastic layer composite by extruding in one step, the most essential layers of the composite being an oxygen-imper ⁇ meable layer and a heat-sealable polymer layer facing the can. Further, on both sides of the oxygen-permeable layer are extruded polymeric adhesive layers.
• Production of a lid for a food can as described above includes several contributing factors that must have a defined relationship to one another in order that the product might function as desired.
• a particular problem in the production of paper-based lids for food cans is the tendency of the lids to curl. The primary reason for this is that the plastic layers have a different crystallization degree and coefficient of heat expansion. In fact, various kinds of trial runs must be conducted to obtain a composition in which the forces that make the product curl are in balance such that the lid keeps straight. Further, the lid must comprise plastic layers that are able to adjust themselves to any unevenness on the jointing surface of the can, so that the joint is uniform and tight. Another major problem involved in joint sealing is that it must be possible to detach the lid from the can in one piece without using excessive force.
• the lid is also suitable for frozen products, such as ice lolly packs, replacing the aluminium lid conventionally used in them also.
• the glass transition temperature of the plastic layers used must be sufficiently low so that the pack functions reliably in freezing temperatures also.
• the lid being characterized in that the heat-sealing layer comprises a layer of heat-sealing lacquer, and that the plastic layer composite comprises, adjacent to the paper layer, a first plastic layer made of acid-modified ethylene-based copolymer; adjacent to the first plastic layer, a second plastic layer made of plastic that is infusible at the heat-sealing temper- ature used; and between the second plastic layer and the heat-sealing lacquer, a third plastic layer made of acid-modified ethylene-based copolymer.
• the second plastic layer advantageously com ⁇ prises a polyamide layer.
• the second plastic layer comprises a layer of polyolefin-based plastic.
• the polyolefin-based plastic is typically, for example, polyethylene, polypropylene or polybutylene.
• the acid-modified ethylene-based copolymer may be e.g. ethylmethylacrylate, ethylbutyl- acrylate, ethylvinylacetate, ethylacrylic acid or ethyl- methylacrylic acid.
• the copolymer may also be any one of the above-listed copolymers further modified with maleic acid.
• Fig. 1 shows a top view of an exemplary embodi ⁇ ment of a lid according to the invention
• Fig. 2 shows a cross-sectional view of the lid shown in Fig. 1.
• Fig. 1 shows an exemplary embodiment 1 of the lid for a food can according to the invention, com ⁇ prising a generally circular body element 8 and a tear tab 9 connected therewith.
• the lid is intended to be heat-sealed, close to the outer edge of its circular body element 8, onto a flange formed at the upper edge of a circular can.
• Fig. 2 shows a cross-section of the lid 1 shown in Fig. 1.
• the lid comprises a body layer 2 made of paper, coated with a mineral coating 3.
• a printing layer 10 On top of the mineral coating 3 is a printing layer 10, and on top of that is protective lacquer 11.
• the protective lacquer makes the print sufficiently moisture-resistant and sufficiently protects the paper layer 2 from external moisture.
• a plastic layer 4 that is made of acid-modified ethylene- based copolymer (hereinafter: EAM) and that adheres well to paper, sealing the surface that faces the can.
• the EAM layer primarily functions as an adhesive layer, making it possible for the different parts of the plastic layer composite to attach to one another.
• a polyamide layer 5 which gives the lid the properties desired, particularly as regards gas permeability. Layer 5 could not be attached directly to the paper layer 2, since its adheres to paper rather poorly.
• a third plastic layer 6 which is also made of acid-modified ethylene-based copolymer (EAM).
• EAM layer 6 also functions as an intermediate layer between layer 5 and a heat-sealing lacquer layer 7 applied to its lower surface.
• EAM layer 6 prevents moisture from entering layer 5. If moisture had an access to the polyamide layer, the layer would swell, damaging the lid.
• the characteristics of the heat-sealing lacquer 7, on the other hand, are such that the lacquer would not adhere directly to the polyamide layer 5 to the extent desired. Layer 6 is thus, in practice, essential.
• Layers 4 and 6 help to render the part of the lid comprising layers 2, 4, 5, 6 and 7 such that it does not tend to curl, nor do the layers detach from one another, not even under moist conditions.
• Layer 7 makes it possible to heat-seal the lid to the body of the can.
• the melting point of layer 5 must be such that the layer hardly melts at all at the heat-sealing temperature.
• layers 4 and 6 soften during heat- sealing to such an extent that they are able to level down any unevenness present on the adhesion surface of the can: e.g. layer 4 may penetrate to some extent between the fibres of the paper layer 2.
• the lid according to the invention also resists freezing, since the glass transition temperature of EAM is sufficiently low.
• the lid is thus also suited for cans used in packing ice-cream or ice lollies or other corresponding frozen products.
• the effectiveness of the lid according to the invention is especially based on the advantageous prop ⁇ erties of the EAM layers 4 and 6. This material adheres to both paper, polyamide and heat-sealing lacquer to a sufficient degree, and it is sufficiently watertight to protect the polyamide layer 5 against moisture. Further, it softens at the heat-sealing temperature used and is thus able to function as a levelling layer in the above manner.
• the essential feature of the lid according to the invention is that the properties (e.g.
• a lid for a food can has been described above by means of one exemplary embodiment, and it is to be understood that it can be modified in many ways without deviating from the scope defined by the attached claims.
• the polyamide layer can thus be replaced by plastic, especially propene-based plastic, having the desired properties, such as infusibility at the heat-sealing temperature used.
• the surface layers 10 and 11 can be modified as desired. It is noted, however, that protection of a mineral-coated paper against external moisture by means of protective lacquer rather than a plastic layer also renders the material used in the present lid pulpable, which is clearly advantageous.

Landscapes

• Laminated Bodies (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8538747

Family Applications (1)

Country Status (3)

Cited By (2)

Citations (2)

• 1993
  • 1993-10-11 FI FI934476A patent/FI934476A/fi not_active Application Discontinuation
• 1994
  • 1994-10-10 AU AU78144/94A patent/AU7814494A/en not_active Abandoned
  • 1994-10-10 WO PCT/FI1994/000453 patent/WO1995010413A1/en active Application Filing

Patent Citations (2)

Also Published As

Similar Documents

Legal Events