Thermoformable composite film

Details Thermoformable composite film Thermoformable composite film

1999-07-19

2001-12-11

Nakarani, D. S. (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S517000, C428S518000, C428S520000

Reexamination Certificate

active

06329047

ABSTRACT:

The present invention relates to a thermoformable composite film, a process for producing a thermoformable composite film and the use of the film as a packaging material.
To produce high-performance packaging, flexible films are molded to the shape of a tray or capsule using the action of heat and pressure and a mechanical ram at super- and/or subatmospheric pressure. The film serves firstly to protect the contents. To protect the contents from the effects of the environment the film must therefore have a high level of barrier properties with respect to water-vapor, gases and UV. It must have mechanical stability to protect the contents from physical effects, and so that it does not itself become damaged by the contents. The quality of the contents must not be impaired by constituents released from within the film.
Blister packs are increasingly frequently chosen as packaging for a wide variety of articles since this type of pack is available in a wide variety of forms and meets the requirements of mechanized packaging processes. The starting materials used for blister packs are thermoformable films. These are plastic films which when heated can be shaped relatively readily by applying super- or subatmospheric pressure pneumatically, or using a ram. Appropriate selection of the molds can thus introduce depressions (blisters) into the film (base film) and these can be matched to the shape of the article to be packed. After this shaping step the article to be packed is introduced into the resulting blister. Once the blister has been filled, a backing film is applied to the base film and encloses the article to be packed within its blister.
If all of the requirements cannot be covered by a single material, the properties required in a film are achieved by combining more than one film to give a composite. Films produced from cycloolefin copolymers have very good impermeability to water vapor. However, these films have poor resistance to fats. Environmental-stress-cracking corrosion occurs on exposure to unsaturated fatty acids.
The film most frequently used in blister packs is polyvinyl chloride (PVC). To increase its barrier properties with respect to gases, in particular water vapor, the PVC base film is frequently coated with PVDC. Films made from unoriented polypropylene (uPP) give better water-vapor barrier properties than PVDC films and are less questionable from an environmental point of view. However, the disadvantage is that this material has poorer thermoformability and higher shrinkage.
The COC mono- or multilayer films described in EP-A-570 188 and EP-A-631 864 when used as base films give good processing and good barrier properties.
Relatively new developments in the area of blister packs for pharmaceuticals describe the use of amorphous polyolefins with good processing performance and levels of high water-vapor barrier properties. For example, EP-A-570 188 and EP-A-631 864 describe the use of polyolefins with cyclic olefins as polymeric building block. These applications describe the use of these polyolefins (cycloolefin copolymers, abbreviated to COC) in the form of mono- or multilayer films for blister packs.
Alongside automated packing and the presentation of the product protected within the blister, for example pharmaceuticals in the form of tablets, capsules or the like, the blister pack can markedly reduce exposure to atmospheric moisture and oxygen and thus increase shelf life.
The object of the present invention is to provide a composite film with a high level of barrier properties, very good thermoformability and good resistance to fats, together with a cost-effective and environmentally friendly process for its production, and also the use of the film for producing blister packs.
The object of the present invention is achieved by a thermoformable composite film comprising at least one film which comprises cycloolefin copolymer and comprising, laminated to at least one side of this film, a thermoplastic PVDC film.
At relative humidity of about 85% and at a temperature of about 23° C. the film has a water-vapor permeability of ≦0.05 gim
2
d, a puncture resistance of ≦20 N and a thickness of ≦100 &mgr;m.
For producing specific types of packaging, flexible or else rigid films are used to achieve high barrier values with respect to gases, in particular to oxygen and to water vapor. Requirements are becoming more stringent: achievement of greater protection from environmental effects, longer shelf-lives, storage, quality assurance, portioning, transport, information, transparency, printability, sterilizability and UV protection of the products to be packed.
The film has not only to protect the contents but must also have mechanical stability. Release of constituents from within the film must not be allowed to have an adverse effect on the contents. The film must not be damaged by the product. Applications which have all of these requirements to a relatively high degree are pharmaceutical blister packs, push-through packaging (PTP), bags for sensitive solutions, medical equipment, and also blisters, trays and bags for food or drink.
To achieve these specific requirements, film properties are adjusted by combining a number of different materials with one another, by printing, coating, laminating, coextruding or extrusion-coating. Films made from COC (cycloolefin copolymer) have on the one hand very good impermeability to water vapor but on the other hand very poor resistance to fats. Exposure to unsaturated fatty acids leads to corrosion by environmental stress cracking. To avoid this corrsion one or both sides of the COC film is/are preferably protected by combination with another functional plastic. Metallic or ceramic coating in vacuo is also possible.
The object has been achieved by coating the COC film, in pure form or as a blend with other polyolefins or rubbers, with PVDC. This achieves high barrier values. A supplementary surface protection may be applied, as described above, using another plastic, such as PVC, polyamide, polypropylene or polyethylene, or else a metal, such as aluminum, copper or zinc.
The novel composite film has the resistance required together with improved barrier properties. It also fulfils the required conditions for processing. COC films with PVDC coating and PVDC protective laminate can be produced more cost-effectively than PVC/PVDC coatings, PVC/PE/fluorine copolymers or homopolymer laminates or extruded modified acrylonitrile/methyl acrylate copolymers, and with the same or higher barrier values. The water-vapor permeability values for the high-barrier films, measured under DIN and ASTM conditions (23° C., 85% rh) are as shown in Table 1 below for the following film structures:
TABLE 1
Film structures
Water-vapor permeability
(Thicknesses [&mgr;m])
(g/m
2
.d [69 &mgr;m PVDC = 90 g/m
2
])
PVC/PE/PVDC (250/30/69)
0.05
PVC/homofluoropolymer (250/51)
0.02
COC/PVDC (250/51)
0.03
With PVC-PVDC coatings and to some extent with fluoropolymers, an intermediate PE layer is needed to equilibrate stresses. No intermediate PE layer is required with COC/PVDC coatings.
The films suitable for the purposes of the invention comprise at least one cycloolefin polymer selected from the class consisting of polymers containing from 0.1 to 100% by weight, preferably from 10 to 90% by weight, based on the total weight of the cycloolefin copolymer, of polymerized units of at least one cyclic olefin of the formulae I, II, II′, IlIl, IV, V or VI
where R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
and R
8
are identical or different and are a hydrogen atom or a C
1
-C
20
-hydrocarbon radical, such as a linear or branched C
1
-C
8
-alkyl radical or C
6
-C18-aryl radical or C
7
-C
20
-alkylenearyl radical, or a cyclic or acyclic C
2
-C
20
-alkenyl radical, or form a saturated, unsaturated or aromatic ring, where the same radicals R
1
to R
8
in the different formulae I to VI may have different meanings, and n may be from 0 to 5, and from 0 to 99.9 moi%, based on the total composition of the cycloolefin copolymer, of poly

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