Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
2000-02-22
2002-01-01
Seidleck, James J. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S036910, C428S474700, C428S476300, C428S488110, C428S480000, C428S477700, C525S425000
Reexamination Certificate
active
06335101
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a composite having at least one polyamide layer and at least one polyester layer, bonded together by an adhesion promoter which adheres to both polyamide and polyester layers.
2. Discussion of the Background
Polyamides and polyesters are by themselves unsuitable for many applications. For example, polyamides are not weather-resistant, since they age when exposed to light and they also absorb atmospheric moisture. This leads to discoloration, impairment of mechanical properties, and also warping. Although polyamides have good mechanical properties, in particular good toughness, they have poor barrier properties. Polar substances in particular can easily migrate through polyamides. This is extremely disadvantageous, for example, for fuel pipes which convey alcohol-containing fuel.
Polyesters are generally highly weather-resistant and have excellent barrier properties with respect to both polar and nonpolar media. However, they are generally susceptible to impact. In particular, the notched impact strength of polyesters is frequently inadequate. Polyesters can therefore not be used by themselves in many instances in which their other properties, such as excellent barrier properties, high heat resistance and good stiffness, would be desirable.
It would therefore be desirable to combine the good mechanical properties of polyamides with the high weather-resistance and excellent barrier properties of polyesters. However, it is generally difficult to bond polyamides and polyesters to form composites which could combine the desirable properties of both materials. It would therefore be desirable to be able to produce a strong bond between polyamides and polyesters. This would allow, for example, moldings made from polyamides to be protected from light and moisture by coating them with a polyester layer. Equally, a molding made from a polyester could be protected from chemical and mechanical effects by coating it with a polyamide layer. This would also provide a way of making fuel piping, which is usually composed of a polyamide (PA), such as PA 6, PA 11 or PA 12, with a layer which can provide a barrier to fuel, in particular to alcohol-containing fuel.
Composites made from polyamides and polyesters are in principle already known. EP-A 0 336 806 describes the coextrusion of PA 12 and polybutylene terephthalate (PBT) to give a two-layer tube. DE-C 38 27 092 describes a tube having more than one layer which has, from inside to outside, layers of polyamide, polyvinyl alcohol, polyamide and polyester. However, a very large majority of polymers, including polyamides and polyesters, are incompatible with one another, meaning that no adhesion is achieved between the laminate layers when polymer laminates are produced. However, in conventional industrial applications, a strong bond between the individual polymer layers is an essential requirement.
A polyester layer and a polyamide layer may be bonded via an adhesion promoter which is composed of a mixture of polyamide and polyester. However, blends of this type, which are produced, for example, by mixing melts in an extruder, are very brittle. Attempts to coextrude such adhesion promoters onto polyamide and polyester give adhesion either to the polyamide or to the polyester, but never to both polymers simultaneously.
EP-A-0 509 211 describes thermoplastic composites having more than one layer, with one layer made from a polyamide molding composition and one layer made from a polyester molding composition, bonded via an adhesion promoter which comprises a mixture of polyamide and polyester. Since the problems discussed above also occur here, in a preferred embodiment at least part of the polyamide fraction in the adhesion promoter and also at least part of the polyester fraction are present in the form of a polyamide-polyester block copolymer. However, the preparation of block copolymers of this type is difficult, and requires the addition of auxiliaries or catalysts which can create problems when the composite is used subsequently in food and drink applications.
In addition, the preparation of such block copolymers requires precise control of the end groups, since they are prepared by linking suitable end groups. One must therefore ensure that the appropriate end groups are present in sufficient concentration. Since commercially available polymers are not adapted to these requirements, special polymer grades have to be prepared and then converted to a block copolymer. The production costs for adhesion promoters of this type are therefore unreasonably high. This applies to a still greater degree to the block copolyesteramides used as adhesion promoters in polyamide/polyester composites having more than one layer, as in the process of EP-A 0 837 088.
SUMMARY OF THE INVENTION
The object of this invention is to provide composites having polyamide and polyester layers joined by an adhesion promoter. The adhesion of the layers in composites of this type should also be retained in the presence of reagents such as fuel or solvents, and also at high temperatures.
DETAILED DESCRIPTION OF THE INVENTION
This object has been achieved by means of a thermoplastic composite having a multiplicity of layers and comprising:
I. a layer of a polyamide molding composition,
II. a layer of a polyester molding composition, and
III. a layer of an adhesion promoter adherent to I and II comprising at least 50% by weight of a blend of:
a) from 20 to 80% by weight, preferably from 30 to 70% by weight and particularly preferably from 40 to 60% by weight, of a polyamide, prepared from
&agr;) a diamine having from 6 to 12 carbon atoms, and
&bgr;) an essentially stoichiometrically equivalent amount of dicarboxylic acid, where the dicarboxylic acid comprises at least 5 mol %, preferably at least 15 mol % and particularly preferably at least 25 mol %, of a dicarboxylic acid having from 10 to 36 carbon atoms,
and
b) from 80 to 20% by weight, preferably from 70 to 30% by weight and particularly preferably from 60 to 40% by weight, of a polyester, prepared from
&agr;) a mixture of from 30 to 95 mol %, preferably from 50 to 93 mol % and particularly preferably from 70 to 90 mol %, of an aromatic dicarboxylic acid having from 6 to 20 carbon atoms and from 70 to 5 mol %, preferably from 50 to 7 mol % and particularly preferably from 30 to 10 mol %, of the same dicarboxylic acid as in the polyamide of the adhesion promoter, having from 10 to 36 carbon atoms, and
&bgr;) a diol having from 2 to 12 carbon atoms.
The blend present in the adhesion promoter is composed of components partially compatible with one another, where either the polyamide or the polyester forms a continuous phase with the other component dispersed therein, or there is an interpenetrating network in which both phases are continuous. The partial compatibility is discernible on the one hand from scanning electron micrographs and on the other hand from the good mechanical properties of the blend. Unlike physical mixtures of conventional polyamides and polyesters, the novel adhesion promoter has very good adhesion both to polyamide molding compositions and to polyester molding compositions. This very good adhesion is achieved irrespective of whether the polyamide or the polyester is the continuous phase in the adhesion promoter.
The individual components of the composite are described in more detail below.
The polyamides of layer I are mainly aliphatic homo- and copolycondensates, such as PA 46, PA 66, PA 612, PA 810, PA 1010, PA 1012, PA 1212, PA 6, PA 7, PA 8, PA 9, PA 10, PA 11 and PA 12. (The terminology for the polyamides corresponds to an international standard in which the first figure(s) give(s) the carbon atom number of the starting diamine and the second number(s) give(s) the carbon atom number of the dicarboxylic acid. If only one figure is given this means that the starting material was an &agr;,&ohgr;-aminocarboxylic acid and/or the lactam derived therefrom. Reference may be made for further information to H. Domininghaus, Die Kun
Baumann Franz-Erich
Franzmann Giselher
Haeger Harald
Oenbrink Georg
Schmitz Guido
Bagwell Melanie D
Degussa-Hüls Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seidleck James J.
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