Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-12-17
2002-12-24
Gallagher, John J. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C264S129000, C264S265000
Reexamination Certificate
active
06497782
ABSTRACT:
The invention relates to a process for producing a composite article from polar thermoplastics and polyurethane elastomers, in which the thermo-plastic material is treated with an adhesion promoter comprising solvents, and also to the composite articles which can be produced and are produced thereby. Use of the adhesion promoter makes it possible to obtain adhesion of polyurethane elastomers on plastics which do not exhibit any adhesion without use of the adhesion promoter.
The polar thermoplastics include in particular those known as engineering thermoplastics, also known as high-performance polymers. These have excellent thermal, mechanical and chemical properties and are therefore preferred materials for engineering applications. Moldings produced from these have good strength and hardness, together with excellent resilience, and are therefore applied widely and very frequently in all areas of daily life, for example in the construction of motor vehicles and other equipment, and for housings and casings, keyboards and snap connectors. Their excellent sliding-friction properties also make them useful for many moving parts, such as power train components, deflector rolls, gear wheels and shift levers.
However, moldings of this type frequently have a low mechanical damping factor, which in certain applications requires the use of soft damping elements. In addition, it is often necessary to use a seal at junctions when moldings are installed. The high surface hardness of the moldings can, under certain circumstances combined with a low sliding-friction coefficient, cause items placed thereon to slip, and this can compromise, for example, the operating reliability of switching units and control units. For these reasons, combinations of hard and soft materials are used more and more frequently in order to combine the particular properties of these materials with one another. The hard material here is intended to give the component or molding its strength, and the elastic properties of the soft material permit it to take on the functions of sealing, or of damping vibration or deadening sound, or of altering surface feel. In these applications it is important that there is adequate adhesion between the hard and the soft component.
Gaskets, damping elements, etc. are frequently provided separately, made from a soft material, and usually anchored mechanically to a thermoplastic molding or adhesive-bonded thereto in an additional operation, creating more work and in some cases considerable cost.
A newer and more cost-effective method is multicomponent injection molding, in which, for example, a second component is used for overmolding on a first, ready-molded, component. The adhesion between the two components here should be very strong, but may frequently be further improved in physical interlocks, by applying undercuts, for example. Good basic adhesion between the two components, for example as a result of chemical affinity, is generally a precondition for their practical application and is therefore of great importance for this process.
Examples which are well known are multicomponent-injection-molded combinations of polypropylene with polyolefin elastomers or with styrene-olefin elastomers, or of polybutylene terephthalate with polyester elastomers or with styrene-olefin elastomers. Polyamides, too, adhere to very many soft components.
There are also known moldings made from polyacetal with directly molded-on functional elements, produced using uncrosslinked rubbers (DE-C 44 39 766). The bond strength of composite articles of this type is, however, still unsatisfactory.
DE-A9611272 describes just such composite articles, composed, inter alia, of a polyacetal, a rubber copolymer, a reinforcing filler, a crosslinking agent and, if desired, other conventional additives. Particularly good adhesion of the polymer components is achieved here by vulcanizing the rubber fraction. However, the elevated temperatures and long times needed for vulcanization make this additional step disadvantageous.
Another application (German patent application No. 197 43 134.8) relates to a process for producing composite articles from polyacetal and a soft component, by preinjecting the polyacetal in a mold in a first step and, in a second step, using the lower-hardness material for overmolding, thereby bonding this to the polyacetal. For the lower-hardness region here, use is made of a thermoplastic polyurethane elastomer (TPE-U) with a hardness of from Shore A 65 to Shore D 75. However, this range of hardness is too high for many applications. In addition, the thermoplastic polyurethane elastomers described have the known disadvantages in processing, e.g. moisture absorption, the resultant thermal instability and variable flowability and also mold-release problems.
It is clear that softer damping elements could be obtained using foamed elastomers, which generally have a lower hardness than the corresponding compact elastomers. In processes which have become established in recent years, therefore, soft elastomer foam gaskets are applied, in a second operation, to the hard material which has been removed from an injection mold. Single-component or two-component polyurethanes are particularly suitable for this purpose. Addition-crosslinking two-component polyurethanes are particularly advantageous for achieving high production rates, as a result of relatively rapid and thorough curing without the need for prolonged drying times. However, the different chemical nature of these substances and the different processing conditions for the hard and soft component frequently give rise to adhesion problems in such cases.
The method generally used for improving adhesion to thermoplastics is to flame-treat the surface of the plastic, or to treat it with some other oxidative process, e.g. corona treatment or plasma treatment.
It is also well known that an adhesion promoter can be used to bring about adhesion between materials which do not per se adhere to one another. The makeup of the adhesion promoter here must be such that it has high chemical affinity for both of the materials to be bonded to one another, but does not subject these materials to chemical attack.
Whereas solutions have been found for a wide variety of cases, for example the adhesion of a plastic to metal, glass or other materials, there is a difficulty with particular engineering thermoplastics in achieving sufficiently strong and durable adhesion to polyurethane elastomers. However, it is precisely these engineering thermoplastics which are of interest for many applications, for example in automotive construction, where a molding, component or functional part produced from these thermoplastics is to be provided with a gasket. Polyurethane elastomers are again particularly suitable for gaskets of this type.
The object was therefore to provide a process which avoids the disadvantages and limitations mentioned and produces a composite article made from engineering thermoplastics and polyurethane elastomers.
Surprisingly, it has now been found that the use, as an adhesion promoter, of clear lacquers or primers which have been designed for use on metal surfaces gives an adhesive bond between polyurethane elastomers and engineering thermoplastics or other polar thermoplastics. Suitable adhesion-promoter systems involve acrylic-resin lacquers and polyurethane-resin lacquers which comprise solvents and which may have been modified by adding fillers, pigments or a crosslinking component.
By using these adhesion-promoter systems according to the invention, sealing or damping elements, for example, made from polyurethane elastomers can be laid down with adhesive bonding directly onto moldings made from polar thermoplastics, or be molded onto these, without any need for undercuts or other assembly steps. Without using these adhesion-promoter systems it is not possible to produce a bond between the polyurethane elastomer and, in particular, polyacetal or a polyester. Even widely used techniques, such as surface-etching, plasma treatment (corona discharge) or fl
Danilow Detlef
Krämer Norbert
Langerbeins Klaus
Link Alfred
Platz Di Reinhold
Connolly Bove & Lodge & Hutz LLP
Gallagher John J.
Ticona GmbH
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