Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1998-01-20
2001-04-17
Robinson, Ellis (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S035700, C428S036920, C428S332000, C428S474400, C428S036600, C428S036700, C528S339000, C138S118000, C264S477000
Reexamination Certificate
active
06217962
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of polymer materials which are barriers to gases and liquids and more particularly of transparent materials which are resistant to water and capable of being shaped into single- or multimaterial thin layers or films.
BACKGROUND OF THE INVENTION
Many barrier materials and in particular amorphous polyamide resins are described in the literature. Thus, the subject of EP 411,601 is multilayer films for petrol tanks in which one layer is composed of amorphous copolyamide 6,I/6,T. However, these amorphous polyamide resins require high processing temperatures, for example during thermoforming of the finished article, and when the finished article containing these amorphous polyamide resins is biaxially orientated, its barrier properties are greatly reduced.
To overcome this disadvantage, provision was then made to combine amorphous polyamide resins with other resins, such as crystalline polyamides.
The subject of EP 287,839 is multilayer films in which one layer comprises a mixture of crystalline polyamide and of amorphous polyamide (PA-6,I/6,T).
EP 366,382 describes a composition for blown or moulded bottles composed of a mixture of PA-6, PA-6,6, of amorphous PA and of a lamellar filler, and WO 93/01108 describes a food container composed of a mixture of PA-6,6, of several amorphous PAs, of a lamellar filler and of an ionomeric resin.
These technical solutions have the disadvantage of requiring an additional stage, namely the mixing of more or less compatible resins, sometimes necessitating the addition of a compatibilizing agent.
Another very widespread barrier material is composed of the family of copolymers of ethylene and of vinyl alcohol (EVOH) . However, EVOH, in addition to its high price, has low resistance to moisture, which prevents it from being used in the preparation of single-material articles and, when it is used for composite articles, necessitates the addition of at least one intermediate layer between the EVOH and the wet medium, in order to prevent direct EVOH/wet medium contact. Moreover, when multilayer containers or films are prepared with an EVOH barrier layer according to a solid-phase thermoforming process, it is found that the EVOH cannot be shaped at the relatively low temperatures required for thermoforming the other resins of the multilayer structure without rupturing the EVOH layer, resulting in a loss in the overall barrier properties. In order to limit these disadvantages, it is also possible to combine the EVOH with other resins. Thus, the subject of EP 305,146 is mixtures of EVOH (mainly) and of amorphous polyamides for the manufacture of multilayer containers obtained by thermoforming.
However, none of the abovementioned references provides a material which simultaneously possesses sufficient barrier properties to be used alone and is capable of being employed easily and processed, in particular according to thermoforming, drawing techniques, without a decrease in its barrier properties.
SUMMARY OF THE INVENTION
The invention which is the subject of the present application relates to a barrier material which satisfies these criteria and thus makes it possible to dispense with a mixture of resins in the preparation of a (single-)layer which is a barrier to liquids and to gases. This material additionally exhibits good adhesion to many resins and has good transparency, which is an advantage in the preparation of items intended for packaging, in particular food packaging.
The barrier material according to the invention comprises at least a copolyamide, essentially composed of units derived from hexamethylenediamine, iso- and terephthalic acids and optionally adipic acid, which exhibits a degree of crystallinity (&khgr;
c
) of at least 5% and preferably of at least 8%, measured by X-ray diffraction in the wide-angle range using a refractometer of &thgr;-&thgr; type (cf. Nylon Plastics Handbook, M. I. Kohan, Hanser Publishers: 1995, 4.6.2 Crystallinity, p. 98-100).
The barrier material according to the invention contains at least a PA-6,I/6,T copolyamide or a PA-6,I/6,T/6,6 terpolyamide -mentioned below as “polyamide according to the invention”- comprising, per 100 mol of copolyamide:
from 40 to 67 mol of PA-6,I,
from 30 to 45 mol of PA-6,T,
and from 0 to 20 mol of PA-6,6,
and preferably
from 46 to 62 mol of PA-6,I,
from 30 to 42 mol of PA-6,T,
and from 6 to 12 mol of PA-6,6.
The polyamide according to the invention can additionally contain up to 5% by weight of other polyamide monomers, such as one or more dicarboxylic acids and/or diamines and/or amino acids and/or lactams, among which mention may in particular be made of 1,4-diaminocyclohexane, caprolactam, dodecalactam, octamethylenediamine, decamethylenediamine, dodecamethylenediamine, 1,5-diaminohexane, 2,2,4-trimethyl-1, 6-diaminohexane, piperazine, 3,3′-dimethyl-4,4′diaminodicyclohexylmethane, 4,4′-diaminodicyclohexylmethane, 2,2′-bis(4-aminocyclohexyl)propane, isophoronediamine, or azelaic, sebacic and dodecanedioic acid.
Its level of di(6-aminohexyl)amine, a triamine resulting from the possible dimerization of hexamethylenediamine, measured by proton NMR, is preferably less than 1.5 molar %.
The intrinsic viscosity of the copolyamides according to the invention, measured at 25° C. in a 0.5 g/dl solution of polymer in meta-cresol, is between 0.75 and 1.3, preferably between 0.85 and 1.05.
The polyamide according to the invention can be polymerized according to a process similar to that employed in the continuous or batchwise synthesis of PA-6, 6.
The monomers (hexamethylenediamine, iso- and terephthalic acids and optionally adipic acid) are charged to a reactor, preferably in the form of an aqueous saline solution generally containing from 20 to 40% by weight of water, at least one of the monomers being introduced into the reaction mixture in slight excess with respect to the proportion targeted in the final copolymer. The reaction mixture is then heated to a temperature of between 200 and 240° C., and preferably in the region of 220° C., under autogenous pressure. The pressure within the reactor generally reaches 1.5 to 2.5 MPa and the temperature is maintained, while stirring the reaction mixture, for approximately thirty minutes.
The water present in the reaction mixture is then evaporated off while suppressing the appearance of surface foam and while avoiding an excessively sudden drop in the pressure. The duration of this operation is generally between 1 hour 30 and 3 hours 30, preferably in the region of 2 hours, the temperature preferably being maintained at 240° C. When the reactor has returned to atmospheric pressure, the polymerization is continued, either under reduced pressure or under a stream of nitrogen, for a period of time generally of between about twenty minutes and 1 hour 30. The polymer is recovered, for example, in the form of extruded granules at a temperature of between 250 and 300° C.
It has been found that the degree of crystallinity of the polyamide according to the invention depends on its thermal history. Thus, the degree of crystallinity of the polyamide as polymerized and extruded will increase when the said polyamide is subsequently heated at a temperature between its glass transition temperature and its maximum melting temperature. Likewise, shearing and/or drawing carried out in this temperature range have the effect of increasing the degree of crystallinity of the polyamide according to the invention and its barrier properties.
The Applicant Company has also noted that some products, in particular water, when they are in contact with the polyamide according to the invention, lower its glass transition temperature; it will be important, during any heat treatment, to take this phenomenon into account.
Besides the copolyamide or the terpolyamide described above, the barrier material according to the invention may contain various additives and/or modifiers, among which may be mentioned:
dyes and pigments, such as titanium dioxide, carbon black, cobalt oxide, iron oxides, nic
Atofina
Figueroa John J.
Millen White Zelano & Branigan
Robinson Ellis
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