Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1998-05-15
2004-01-20
Nolan, Sandra M. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C138S137000, C428S036700, C428S036900, C428S036910, C428S421000, C428S422000, C428S423700, C428S473500, C428S475800, C428S474700, C428S475200, C428S483000
Reexamination Certificate
active
06680093
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a three component coupling agent and a multilayer composite produced using the coupling agent.
2. Discussion of the Background
In the development of multilayer composites used, for example, as pipes for conveying liquid or gaseous media in motor vehicles, the molding compositions used have to be sufficiently resistant to the media being conveyed and the pipes have to meet all the mechanical demands placed on them. Such requirements are, for example, specified in the relevant standards (DIN 73378; SAE J2260) or else set down in the specifications of the major motor vehicle manufacturers (e.g., General Motors GM213M; Opel GNIE08100; Ford WSS-M98D33-A).
A particularly critical point is the stability of the adhesion between layers, even after long-term contact with hot, alcohol-containing liquids, such as alcohol-containing fuels or water/ethylene glycol mixtures.
In most conventional multilayer pipes, the adhesion between the polyamide layers (which give the pipes their strength) and the corresponding barrier or protective layers, is produced by the use of coupling agents. Such composites are described, for example, in DE-A-38 21 723, DE-A-42 14 383, DE-A-44 34 530, EP-A-0 618 390 and EP-A-0 649 739.
However, it has frequently been found that the bonds between the components of the composite (A and B) and a coupling agent (C) have only limited resistance to attack by the media conveyed. After prolonged contact, particularly at elevated temperatures, the bond is broken, leading to an unacceptable decrease in the adhesion forces up to and including total loss of adhesion or delamination.
For this reason, attempts have been made to achieve adhesion at the layer interfaces by means of material compatibility, by using melt mixtures of the two components A and B as the coupling agent C (EP-A-0 523 644; JP Kokai 7-53823; DE-A-44 34 530). Theoretically, if the components A and B are themselves fuel-resistant, no separation would occur at the interface A to C or B to C if it were possible, at each of the interfaces, to bond a sufficiently high proportion of the component A present in the C layer to the layer A and a sufficiently high proportion of the component B present in the C layer to the layer B.
However, such 2-component blends generally have the problem that the two incompatible components A and B demix in the shear and tensile flows occurring during processing. In general therefore, a bond to only one of the two components is obtained. Furthermore, the morphology of the coupling agent layer is usually fibrous. Thus the coupling agent has an insufficiently high mechanical strength and only relatively low peel strengths are obtained as measured in accordance with ISO 8033.
Attempts have been made to avoid demixing of the components A and B in the coupling agent C by addition of a compatibilizer. Particularly in the bonding of polyamide to fluoropolymers, preference has been given to using thermoplastic polyurethanes (TPU) (JP-A-07053824). However, if one of the two components A and B comprises a fluoropolymer, temperatures of 230° C. and above are required for processing the coupling agent. This leads, particularly at relatively long residence times, to degradation of the TPU which drastically reduces the effectiveness and the processing friendliness of the coupling agent. Furthermore, it has been found that the viscosity of conventional TPU molding compositions is too low. Thus it cannot exert a sufficiently high stress on components A and B in the compounding step to disperse A and B sufficiently finely in one another. These high stresses, however, are needed to effect an additional mechanical interlocking of the components which would be sufficient, in the case of a theoretically conceivable failure of the bond at the interfaces of the individual phases within the coupling agent, to continue to ensure a sufficiently high-quality mechanical bond.
In the case of such coupling agents, achievement of sufficient adhesion is still strongly dependent on the tensile and shear stresses that occur. This means that the adhesion of a multilayer composite in the form of a high profile, a film, a blown article or multicomponent injection molding also depends strongly on the geometry of the article, the tool design and the processing conditions.
Another alternative has been proposed in EP-A-0 618 390 and EP-A-0 649 739. In these documents, the coupling agent comprises two components, one of which is identical to the material of layer A and the other is compatible with the material of layer B. These two components of the coupling agent, likewise have a certain level of compatibility. In the concrete example of the use of polyamide as layer material A and polyvinylidene fluoride as layer material B, the coupling agent is a blend of polyamide and a poly(alkyl acrylate) or a polyglutarimide.
Although good initial strengths are obtained with these composites, upon thermal stressing of the composite, the strength is partially or even completely lost, depending on the conditions selected. This is a serious problem, for example in the thermoforming of corresponding multilayer pipes, if the customary heat treatment times are exceeded due to a fault.
Multilayer pipes that are used in the motor vehicle sector as fuel lines usually have a high stiffness. Since they cannot be laid as a straight conduit in a passenger car, these lines have to be thermofonned. In this reshaping processing, the previously straight pipe is permanently bent so that it retains bends and curvatures of the particular points required.
A method of thermoforming pipes which is currently widely employed is thermoforming using polyethylene glycol. In this process, the pipe is generally laid into a template, and together with the template, immersed in a polyethylene glycol bath. This bath is heated to a temperature appropriate for the material of which the pipe is made, so that the pipe warms up from the outside and becomes soft. The internal resistance of the pipe against bending is thus decreased, i.e. the stresses introduced by bending are relaxed. However, it has been found that this also reduces the adhesion at the interfaces of the composite to values that, in many cases, are no longer acceptable.
If multilayer pipes are used as lines for cooling fluid, such susceptibility likewise has to be expected.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a coupling agent for multilayer composites in which the two incompatible components A and B do not demix during processing and which has a high mechanical strength as an applied layer.
A further object of the present invention is to provide a coupling agent for use in preparing multilayer composites, that is made of a polymer material that is thermally stable under the processing conditions and provides a fine dispersion of components A and B in one another.
A further object of the present invention is to provide a coupling agent for use in preparing multilayer composites that gives high initial adhesion that is very largely retained on prolonged contact with organic media, such as fuels or cooling fluid, and also upon thermal stressing of the composite.
These and other objects of the present invention have been satisfied by the discovery of a coupling agent molding composition which consists essentially of the following components:
a) from 5 to 95 parts by weight of a polymer A containing amino groups;
b) from 95 to 5 parts by weight of a polymer B, preferably selected from the group consisting of thermoplastic polyesters or fluoropolymers;
wherein the sum of the components a) and b) is 100 parts by weight, and
c) from 1 to 90 parts by weight of a compatibilizer comprising an alkyl acrylate polymer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to a three component coupling agent useful for preparation of multilayer composites. The coupling agent of the present invention consists essentially of
a) from 5 to 95 parts by weight o
Ries Hans
Schlobohm Michael
Schmitz Guido
Degussa - AG
Nolan Sandra M.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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