Multilayer composite having a barrier action

Details Multilayer composite having a barrier action Multilayer composite having a barrier action

1999-08-24

2002-09-17

Nolan, Sandra M. (Department: 1772)

Stock material or miscellaneous articles

Hollow or container type article

Polymer or resin containing

C138S137000, C138SDIG007, C180S313000, C428S036910, C428S423300, C428S423500, C428S475200

Reexamination Certificate

active

06451395

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multilayer plastic composite having a barrier action, for example, in a pipe, in a hollow body or as a film.
2. Description of the Background
Plastic pipes made of polyamide are known and have been used in a variety of applications. In order to fulfill their task, the pipes have to be, inter alia, inert toward the medium flowing in them and resistant to high and low temperatures and to mechanical stresses.
Single-layer pipes are not always able to meet the necessary requirements. In the transport of, for example, aliphatic or aromatic solvents, fuels or the like, such pipes display considerable disadvantages such as unsatisfactory barrier action against the medium, undesired dimensional changes or unacceptably low mechanical stressability.
Attempts have been made to overcome these disadvantages by means of multilayer pipes which include a barrier layer. Well-suited barrier layer materials are, for example, polyethylene naphthalate and polybutylene naphthalate. However, the adhesion between the layers in multilayer pipes is basically problematical, because of the incompatibility of most plastics. A strong bond between the individual polymer layers is, however, absolutely necessary for industrial applications.
EP 0 637 509 and DE 42 14 383 describe multilayer pipes which have a barrier action and comprise a barrier layer of polyethylene naphthalate or polybutylene naphthalate which is joined to a polyamide layer by means of a bonding agent. However, the bonding agent presents problems in both cases. In the composites described in DE 42 14 383, the bonding agent comprising thermoplastic polyurethane is susceptible to methanol-containing fuels, so that the adhesion between the layers is lost after prolonged contact; in addition, the viscosity of the commercial thermoplastic polyurethanes is so low at the temperatures required for coextrusion with a polyalkylene naphthalate that satisfactory coextrusion presents extreme difficulties because of the high viscosity differences. Furthermore, the danger of thermal decomposition is relatively high even at low residence times. The bonding agents which are disclosed in EP 0 637 509 become embrittled on prolonged contact with methanol-containing fuels at elevated temperature, while the adhesion between the layers is likewise lost.
Essentially, composites which require additional layers of bonding agent in addition to the purely functional layers have the disadvantage that the number of layers to be extruded increases as a result of the use of a bonding agent, which leads to increased costs for procurement and operation of the extrusion plant. To this must be added the costs for quality assurance of the multilayer composite which likewise increase with increasing number of layers.
An improvement can in principle be achieved here by means of self-adhesive barrier layers. Thus, EP 0 569 681, EP 0 569 683 and EP 0 601 295 describe multilayer composites having a barrier layer which constitutes a mixture of a partially crystalline polyester such as polybutylene terephthalate and compounds which contain at least two isocyanate groups.
However, the bonding agent-free composites disclosed therein have the disadvantage that the adhesion between polyamide and polyester barrier layer is lost after prolonged contact with methanol-containing fuels at high temperature, e.g. test using test fuel CM15 at 60° C. (in accordance with Ford WSS-M98D33-A). The same result is also found when such pipes are used as cooling fluid lines. A need, therefore, continues to exist for pipes and similar such devices which possess a barrier layer of improved adhesion and barrier action against various fluid media.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a multilayer composite having a good barrier action against the medium in contact therewith, e.g. fuels, in particular methanol-containing fuels, their individual components, fuel vapors, oils and also against cooling fluids, as well as their individual components, usually glycol and water, which multilayer composite contains no additional layers of bonding agent and whose individual layers nevertheless form a strong composite in which the adhesion between the layers is maintained even after long storage exposure to methanol-containing fuels at elevated temperature or after prolonged action of cooling fluid under operating conditions.
Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by a multilayer composite comprising at least the following layers:
I. a layer I of a polyamide molding composition, and
II. a layer II of a polyalkylene 2,6-naphthalate molding composition which comprises a mixture of:
a) from 80-99% by weight of polyalkylene 2,6-naphthalate and
b) from 1-20% by weight of one or more compounds containing at least two isocyanate groups, wherein the polyalkylene 2,6-naphthalate is a polyethylene 2,6-naphthalate or a polybutylene 2,6-naphthalate and, furthermore, the isocyanate groups from component IIb are present in layer II in a concentration of from 0.03-3% by weight, whereby the layers are firmly bonded to one another without use of an additional layer of bonding agent.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Suitable polyamides first and foremost include aliphatic homopolycondensates and copolycondensates. Examples which may be mentioned include 4.6-, 6.6-, 6.12-, 8.10-, 10.10-polyamides and the like. Preference is given to 6-, 10.12-, 11-, 12- and 12.12-polyamides. [The designation of the polyamides corresponds to the international standard, where the first digit(s) indicate(s) the number of carbon atoms in the starting diamine and the last digit(s) indicate(s) the number of carbon atoms in the dicarboxylic acid. If only one figure is given, this means that an &agr;,&ohgr;-aminocarboxylic acid or the lactam derived therefrom has been used as starting material—H. Domininghaus, Die Kunststoffe und ihre Eigenschaften, page 272, VDI-Verlag (1976).]
If copolyamides are used, they are comprised of for example, adipic acid, sebacic acid, suberic acid, isophthalic acid or terephthalic acid as coacid and bis(4-aminocyclohexyl)methane, trimethylhexamethylenediamine, hexamethylenediamine or the like as the codiamine.
The preparation of these polyamides is known as described by, e.g., D. B. Jacobs, J. Zimmermann, Polymerization Processes, pp. 424-67; Interscience Publishers, New York (1977) and in DE 21 52 194.
Other suitable polyamides include mixed aliphatic/aromatic polycondensates, which are described, for example, in U.S. Pat. Nos. 2,071,250; 2,071,251; 2,130,523; 2,130,948; 2,241.322; 2,312,966; 2,512,606; 3,393,210 or in Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd edition, Vol. 18, pages 328 and 435, Wiley & Sons (1982). Other polycondensates which are likewise suitable as polyamides include poly(ether esteramides) and poly(etheramides). Such products are described, for example, in DE 27 12 987, DE 25 23 991 and DE 30 06 961.
The molecular weight (number average) of the polyamides is above 5000, preferably above 10,000, which values correspond to a relative viscosity (&eegr;
rel
) in the range from 1.5-2.8.
In a preferred embodiment, the polyamides employed in layer I include those in which at least 30% of all terminal groups are amino groups.
The polyamides mentioned are used alone or in mixtures.
If required, the polyamides and/or the polyalkylene 2,6-naphthalate can be impact-modified. Polymers suitable for this purpose include, for example, ethylene-propylene and ethylene-propylene-diene copolymers (EP 0 295 076), polypentenylene, polyoctenylene and random and block copolymers of alkenylaromatic compounds with aliphatic olefins and dienes (EP 0 261 748). Impact modifiers also include impact-modifying rubbers such as core/shell rubbers having a tough and resilient core of (meth)acrylate, butadiene or styrene-butadiene rubber having a glass transition temperature T
g

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