NZ244379A - Plastics laminate for food package having layer of polybutylene terephthalate laminated with layer of polystyrene - Google Patents

Description

NEW ZEALAND PATENTS ACT 1953 AFTER PROVISIONAL NO: 244379 COMPLETE SPECIFICATION DATED: 17 September 1992 IMPROVEMENTS IN AND RELATING TO BARRIER MATERIALS We, POLARCUP (NZ) LIMITED of 30 Keeling Road, Henderson, Auckland, New Zealand, a New Zealand company, hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: BACKGROUND OF THE INVENTION The present invention relates to improvements in and relating to barrier materials.

In the food packaging industry particularly, various barrier materials aire knovm for numerous purposes. Typically the barrier material will be seeking to control or stop the flow of gas, usually oxygen, into# the package and*/or to control or stop the egress of gas from the package.

Where the packaged food product is "live", as in the case of normal living yoghurt, the shelf life of the product will be determined largely by the control exercised by the packaging on the amount of oxygen being allowed into the package.

Where the packaged food product is only required for both manufacture and marketing within New Zealand then shelf life can- become less crucial especially where there is a large turnover of the packaged product. However, where there is any delay between packaging and availability for sale to the end customer, such as where the packaged product is being shipped to Australia or other export markets, shelf life becomes crucial and needs to be as long as possible. ✓ Various plastics and laminates of plastics have been proposed to achieve extended shelf life. ABS and PETG plastics have been proposed- as possible solutions but both have disadvantages in respect of price and/or physical properties.

It is thus an object of the present invention to provide a plastics laminate which can provide improved barrier properties for packaging or which at least will provide the public with a useful choice.

Further objects of this invention will become apparent from the following description.

SUMMARY OF THE INVENTION According to one aspect of the present invention there is thus provided a laminate comprising at least a first layer of a pplybutylene terephthalate based material, laminated with at least a second layer ofj. a polystyrene.

According to a further aspect of the present invention there is provided a laminate as immediately above defined wherein said first layer 2 4 4 3 79 is at least .04mm thick and said second layer is at least .8mm thick.

» Further aspects of this invention which should be considered in all its aspects will become ^ apparent from the following description given by way of example of possible embodiments thereof.

BRIEF DESCRIPTION OF DRAWINGS Figure 1: This shows very diagrammatically a 10 cross-sectional view of a laminate according to one possible embodiment of the invention.

BRIEF DESCRIPTION OF PREFERRED EMBODIMENTS In the packaging of a living food product such as yoghurt, the atmosphere within the package needs to be carefully controlled so as to in turn control the biological activity within the product. This particularly requires control of the ingress of |20 oxygen into the package. With some food products the packaging seeks to provide a total barrier to the ingress of any oxygen and then the food product is typically packaged under vacuum or in the presence of some inert gas. '44379 In the case of living yoghurt a shelf life of perhaps 3 to 4 weeks could typically be sought but to enable the product to be transported to export markets a longer shelf life of perhaps 6 weeks could be required.

In assessing transmission rates for gases through packaging materials, this is typically expressed as a transmission rate or permeability value calculated as: cc/mil 100 in 2/24 h/atm (23°C) Typically, for living yoghurt, a transmission rate value of not more than about 2 will be sought as any higher and too much oxygen may be allowed in for a given thickness. The transmission rate value for an ABS plastics layer may typically be approximately 2 while that for PETG may be about 4.

In experimentation it has been found that a polybutylene terephthalate based material such as VALOX (trade mark) manufactured by G E Plastics Europe can provide a suitable barrier layer for. inclusion in a laminate of the present invention, being laminated with a polystyrene and particularly a high impact polystyrene (HIPS).

A further advantage of this combination of materials is that they are compatible for subsequent scrapping and recycling.

In a particular embodiment of the present invention a first layer of VALOX (trade mark) and a second layer of HIPS were co-extruded with the first layer being .08mm thick and the second layer being .8mm to 1mm thick. It has been found that such a laminate is suitable for the wall of a food product container such as a yoghurt pot, and provides a transmission rate value of less than 2 while also enabling the egress from the container of carbon dioxide generated by the living yoghurt. It has also been found that the laminate facilitates the sealing across the top edge of the pot with the typical foil layer closing off the open end of the pot.

It has also been found that delamination of the laminate does not appear to be a problem as can be the case with PETG material.

Referring to Figure 1, a laminate 1 according to one possible embodiment comprises a central core 3 of HIPS and two outer layers 2 of VALOX (trade L.- ' mark). The layers 2 may each be of the order .04mm to ,06mm thick and the overall thickness may be .9 to 1.1mm for example.

Where only a single layer of VALOX (trade mark) is provided them, as mentioned previously, this will be thicker, of the order of .08mm. It is to be appreciated that any number of layers of the aforementioned materials in conjunction with » anyother materials which may be appropriate, may be used.

Where in the foregoing description reference has been made to specific components or integers of the invention having known equivalents then such equivalents are herein incorporated as if individually set,forth.

Although this invention has been described by way of example and with reference to possible embodiments thereof it is to be understood that modifications or improvements may be made thereto without departing from the scope of the invention as defined in the appended claims. 24.4379

Claims (6)

WHAT WE CLAIM IS;

1. A laminate comprising a first layer of a polybutylene terephthalate based material laminated with at least a second layer of a polystyrene.

2. A laminate as claimed in Claim 1 wherein said first layer is at least .04mm thick and said second layer is at least .8mm thick.

3. A laminate as claimed in Claim 2 wherein one layer of polybutylene terephthalate based material is provided on each side of said second layer and each layer of said polybutylene terephthalate based material is between .04mm and .06mm thick and the overall thickness of said laminate is between .9mm and 1.1mm.

4. A laminate as claimed in any one of the preceding claims wherein said polystyrene consists of a high impact polystyrene (HIPS).

A OFr- c \ A laminate substantially as herein describe^ ft' / or substantially as herein described with//'1- ;i I • < - w r-4 ^ ♦ O reference to the accompanying drawing. \ ^ ^^ ^ R Ei 2M$7f - 9 -

6. A package for a food product made from a laminate as claimed in any one of the preceding claims. (NZ) LIMITED :to^?rt^ys CAREY g/s/500191/pgsl-9i jes