WO1987005563A1

WO1987005563A1 - Plastics films

Info

Publication number: WO1987005563A1
Application number: PCT/GB1987/000168
Authority: WO
Inventors: Andrew James Matthews
Original assignee: Edeco Holdings Limited
Priority date: 1986-03-11
Filing date: 1987-03-11
Publication date: 1987-09-24
Also published as: GB8605997D0

Abstract

A multi-layer barrier film comprises separate layers having gas and moisture barrier properties. A particular use for such barrier films is as a container material for latent heat storage media. The film comprises at least one layer selected from linear low density polyethylene, polypropylene, PVC, polyurethane, polyester, polyethylene and olefin blend/styrenic compound as a water barrier and at least one of ethylene vinyl alcohol, polyvinylidene chloride, nylon and metallic foil as a gas barrier.

Description

-1-

PLASTICS FILMS

This invention relates to plastics and in particular to multi-layer plastics films.

It is known to use plastics films for encapsulating various materials. This invention is concerned with encapsulating materials that undergo a phase transformation, usually in the range of 20°C to 80°C and from which a latent heat storage medium can be formed by utilisation of the latent heat of the transformation. Such a material is described in UK patent 2134532. For optimum performance the composition of a latent heat storage medium may require careful control, and variation of the composition may have very significant effect upon performance. For example addition of 3% to 4% excess water in a sodium acetate trihydrate medium reduces the heat output per gram of medium by about 30%, and reduces the medium discharge temperature from about 57°C to about 53°C. Therefore it is important that the composition is not changed by ingress of water, gas or other contaminants and that there is no egress of the components of the medium.

It has previously been proposed to seal latent heat storage material comprising a salt hydrate in PVC bags because of the flexibility of such a package. However there are several drawbacks to use of PVC bags. In order to convert the material into the higher energy state it is necessary to heat the bag and contents above the transition temperature. One convenient way of doing this is to immerse the bag in boiling water and simmer for a period of time, typically 20 minutes or more. However during such repeated treatement a PVC bag permits a significant quantity of water to enter the bag and dilute the heat storage material. Even if an alternative heat treatment is used the recrystal lisation that takes place when the medium discharges is accompanied by a density and volume change and this together with other factors tends to -2-

cause significant quantities of air to enter the bag and disperse in the storage material, and this can significantly increase the time it takes to recharge the storage medium in addition to leading to poor appearance and reaction with 5 components of the storage medium. PVC material also tends to lack sufficient strength for repeated thermal cycling and the attendant 'handling, being vulnerable to puncture when warm and very floppy. The floppiness of the bag, even when cooled, means that the bag does not have a constant shape or volume

10 and this further aggravates air absorption and can lead to cracking along fold lines.

The absorption of extra quantities of water and air has an exaggerated effect when the latent heat storage material has 15 the minimum of additives in order to maximise thermal efficiency.

The present invention is directed towards providing a water and gas impermeable barrier film.

20

Accordingly the invention provides a barrier film comprising a plurality of plastics layers providing moisture and gas barriers, the layers being held together by adhesive or tie layers, the film comrising at least one layer selected from

25 linear low density polyethylene, polypropylene. PVC, poly rethane, polyester, polyethylene and olefin blend/styrenic compound as a water barrier and at least one of ethylene vinyl alcohol, polyvinylidene chloride, nylon and metallic foil as a gas barrier.

30

In one aspect the present invention provides a container for a latent heat storage material comprising a film having a plurality of plastics layers, the film being thermoformable and at least one of the outermost layers being weldable.

_D

The invention also provides a container for a latent heat -3-

storage material comprising a plurality of plastics layers, the film being weldable and at least one of the layers being weldable to an injection mouldable grade of similar plastics.

In a preferred aspect the invention provides a container for a latent heat storage material comprising a film having a plurality of layers at least one of which is moisture impermeable, at least one of which is gas impermeable, at least one of which is thermoformable to a semi rigid structure and at least one of the outer layers being weldable to itself and to an injection mouldable plastics filler port.

The invention is now described by way of example with reference to the accompanying drawing which shows a schematic view of an embodiment of the invention.

Referring to the Figure, there is shown a shell 1 having symmetrical upper 2 and lower 3 halves. The shell is composed of a co-extruded film comprising for example a 100 urn layer of nylon 6 SNTA PA6, an intermediate 40um layer of plexar 130 and a 150um layer of a linear low density polyethylene

(LLDPE). The combined film thickness is sufficient to withstand manhandling without special precaution and enables the film to be t her o formed to a definite semi-rigid shape while still retaining pliability. For different applications' total film thickness from 25 urn to the order of millimetres may be used. In the film the nylon layer forms an effective gas barrier and has high temperature resistance while the LLDPE forms a moisture barrier and forms strong welded bonds. The co-extruded film is oriented so that the nylon layer is on the outer surface of the shell and the LLDPE is on the inner surface. The two halves of the shell are welded together along a peripheral flange 4 with the inner LLDPE layers adjacent one another. -4 -

It h.a.s been found that an intermediate layer thickness of 40uιrr enables the filled shell to be repeatedly subjected to the cycle of immersion in boiling water for extended periods (20 to 40 minutes), cooled to ambient temperature or down to -10°C, and heated by the discharging of the medium without

05 the layers of the co-extrusion separating. The cycle may be repeated in excess of 100 times without deleterious effect to the layer structure or breakdown in the barrier properties. Thinner intermediate layers may be used, for example about 20um.

10

With a highly concentrated storage medium, that is one with the minimum of additives and little or no excess water, which is intended to function over many cycles of operation it is important to complete the encapsulation within the shell !5 without incorporating contaminants and to ensure that the final seal is also a sufficient barrier to water and air.

In the embodiment shown the two halves of the shell are preformed by a thermoforming process, the LLDPE being on the 0 inside of the moulding. In the centre of the moulding a circular step 5 is formed in which an aperture is made. Ac this circular location, on opposite halves of each shell, a filling port assembly 6 and a nucleation port assembly 7 are attached respectively. The filling port assembly 6 has a

25- channel 8 through which the medium is introduced into the shell and the nucleation port assembly 7 houses a nucleation device (not shown). Each port has a circular flange 9 that is welded to the shell adjacent the circular step. In the embodiment described the ports are made from an injection

3° mouldable grade of LLDPE (e.g. Dowlex 2553F) and the flange is located on and welded to the inside of the shell by being located in the aperture from the inside before the halves of the shel l are joined. Thus the weld between the port assemblies and the film is between two grades of LLDPE and of 5 high strength. -5-

Once the ports have been welded to the respective halves of the shells, the shell halves are welded together along their outer flanges, with the LLDPE layers confronting one another to form the weld, and the inwardly projecting portions of the two ports snap together. The shell is then ready for

Ω5 filling, which is done by introducing a filling head into the filling port. The filling head sequentially evacuates the shell, introduces a precise volume of storage medium into the shel 1 and then seals the port with a rubber seal.

10 The nucleation port houses an activation member such as a stainless steel disc, which is in in contact with the medium in the shell so that when operated the charged medium is nucleated to discharge.

1-5 in the described embodiment the nucleation port and filling ports have cooperatively interfitting parts so that when clipped together they form a substantially rigid spacer interposed between opposite sides of the shell, thus aiding retention of shape, and therefore the volume, of the shell. 20

Various combinations of materials may be suitable for the film layers and the layers may be coextrusions or laminated. For example barrier properties may be imparted by a metallic layer. In some instances the bonding between layers may

-^■ enable a two-layer system, in other circumstances three or more layers are necessary. The preferred materials are multilayer combinations of polyurethanes , polyolefins and polyamides incorporating barrier resins such as ethylene vinylalcohol copolymers (EVOH) and polyvinylidene chloride ° (PVdC) grades. Various examples are given below. -6-

Coextr sion: Example 1

material thickness (um)

LLDPE 140

EVOH 10

LLDPE 140

Example 2

material thickness (um)

Nylon 6 (PA6) 100

EVOH 10

LLDPE 150

Both examples 1 and 2 require adhesive layers between the structural polymers, thus the films have five layers in total.

Lamination: Example 3

material thickness (um]

nylon 6 150 polypropylene 150

Example 4

material thickness (um)

polyurethane 200 PVC 200 -7 -

Example 5 materia l thicknes s ( um)

polyurethane 140

PVdC 25 polyurethane 140

Adhesive is required between the layers of examples 3, 4 and 5 making respectively two three layer films and one five layer film.

The materials of examples 1 to 5 may be thermoformed and can be subjected to multiple (at least 50 to 200 times) recycling of charging and discharging of the latent heat storage medium Alternative film materials include combinations of polyolefins and polyesters utilising either vacuum mettalisation or incorporating foil laminates.

Vacuum meta11isation;

Example 6

material thickness (um)

metallised polypropylene 100- metallised polypropylene 100

the layers are laminated with the metallised surfaces internally confronting. -8-

Foil lamination:

Example 7

material thickness (um)

polyester 100 foil 25 polyethylene 150

With examples 4 and 5 shallow thermoforming is possible. The metallised layers provide extremely good barriers but the recyclability is less than for other examples.

Specialised copolymers and blends of polyolefins, including compounds with styrenic block copolymers may also be used, incorporating a barrier resin as mentioned above.

Example 8

material thickness (um)

olefin blend/ styrenic compound 150

EVOH 10 olefin blend/ styrenic compound 150

When the films of examples 1 to 6 are used in a manner similar to the described embodiment they may be matched to an appropriate port assembly material in order to give a strong weld. In some instances the examples may be modified by substitution of a compatible layer from other examples. -9 -

In the embodiment described the port assemblies are welded to the inner layer of LLDPE as this provides the strongest weld. In alternative structures the assemblies may be welded to a different layer, and may be made of a different material. In general it is preferred for the port assemblies to be made of an injection mouldable grade of the same material of either the outer or inner layer of the film.

The materials of examples 4 and 5 are of particular interest. For environments where good barrier properties to moisture and gas are required these materials are particularly useful. Polyurethane provides- a strong film with good barrier properties to gas, while the inner PVdC layer provides both a gas and moisture barrier in example 5. The PVdC is pre-shrunk before being laminated between layers of polyurethane with tie layers between the layers of laminate. In sheet form it is prefered to provide weld zones (by RF welding) to prevent layer separation if the material is to be aggresively handled. It is found that the welding strengthens the laminate in the region of the weld. With containers such as those shown in the drawings the peripheral welds and port welds act as the weld zones to aid maintainance of unity of the layers during the comparatively aggressive handling that occurs during continual thermal recycling.

Although PVC has limitations as a barier material on its own, in combination with polyurethane it has been found to provide a tolerable substitute for the polyurethane PVdC layers of example 5 when great numbers of thermal cycles are not required.

The use of the barrier films described herein is not limited to containers for latent heat storage media, although that purpose serves to demonstrate a particular need for the barrier film.

Claims

1. A barrier film comprising a plurality of plastics layers providing moisture and gas barriers, the layers being held together by adhesive or tie layers, the film comrising at least one layer selected from linear low density

05^" polyethylene, polypropylene. PVC, polyurethane, polyester, polyethylene and olefin blend/styrenic compound as a water barrier and at least one of ethylene vinyl alcohol, polyvinylidene chloride, nylon and metallic foil as a gas barrier.

10

2. A barrier film according to claim 1 in which the film comprises a polypropylene layer and a nylon layer with an intermediate tie layer of at least 20 um thickness.

15^".

3. A barrier film according to claim 2 in which the tie layer is at least 40um in thicknes .

4. A barrier film acording to claim 1 in which the film comprises two layers of polyurethane laminated with an

20 intermediate layer of pre-shrunk polyvinylidene chloride.

5. A barrier film according to claim 4 in which the film is provided with welded zones.

25 6. A barrier film according to claim 5 in which the welded zones are around the periphery of the film.

7. A barrier film according to claim 5 or claim 6 in which the polyurethane layers are in the range of 100 to 200 um in 30. thickness and the polyvinylidene chloride layer is in the range of 20 to 50 um in thickness.

8. A barrier film according to claim 1 in which the film comprises a PVC layer and a polyurethane layer.

9. A barrier film according to any one of claims 1 to 4 or 5 claim 8 in which the total film thickness is in the range of 25um to 1mm.

10. A container for a latent heat storage material comprising a barrier film according to any preceding claim. 0

11. A container according to claim 10 comprising at least two portions of barrier film welded together at the periphery.

- 12. A container according to claim 10 or claim 11 in which the barrier film is thermoformed .

13. A container according to any of claims 10 to 12 in which the container further comprises a member comprising an 0 injection moulded plastics of similar type to one of the film layers and the member is welded to one of the outer layers.

14. A container according to claim 13 in which the member is welded to a layer inwardly of the container. 5

15. A container according to claim 14 or claim 15 in which the member is a filling port.