Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1989-08-03
2002-10-29
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S177000, C525S183000, C525S184000, C525S207000, C525S221000
Reexamination Certificate
active
06472475
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an adhesives which cure by two different, successively activatable chemical reactions. More particularly, the invention relates to adhesives based on mixtures of two polymers which can be joined together by an esterification reaction or the like; the mixture may additionally be vulcanized after the esterification reaction. The adhesives are especially useful for vehicle construction applications.
2. Description of the Related Art
In vehicle construction, it is desirable to harden adhesives together with the paints at relatively high temperatures. However, since painting has to be preceded by cleaning operations after which bonding is no longer possible, the adhesives used have to develop such high strength only a short time after application that the bonds neither separate nor slip during cleaning of the bodywork to be painted.
To achieve this, many different types of adhesive have already been proposed for this application. For example, it is possible to obtain adequate early strength with two-component polyurethane adhesives. However, the disadvantage is that the cured polyurethane adhesives are difficult to stabilize against hydrolysis or similar ageing processes. Another disadvantage is that the two components, namely polydiisocyanates and polyols, have to. be used in exact quantitative ratios because otherwise bond failures occur. This is all the more difficult in practice as the two components generally differ in viscosity so that accurate dosing and mixing units have to be used. The same also applies to two-component epoxy resin systems.
Other adhesives typically used in the field in question are the plastisols. Plastisols are mixtures of polymers with a solvent in which polymer and solvent are coordinated with one another in such a way that a dispersion of a polymer in the organic solvent is present at room temperature and a dissolving process takes place on heating so that, ultimately, a polymer is present in swollen form. The disadvantage of plastisols lies in the poor variability of the systems, which means that the polymers can only be adapted to meet bonding requirements providing the solubility properties important to gellability are not lost as a result. Another disadvantage is that plastisols have to be cured in induction ovens or the like before stoving of the paint which involves additional energy consumption.
Epoxy resin adhesives formulated in the manner of plastisols are known. With systems such as these, however, it is extremely difficult to adjust reactivity in such a way that stability in storage on the one hand and reactivity in induction ovens on the other hand are obtained.
Finally, polybutadienes containing hydroxyl groups and polybutadienes containing acid anhydride groups are known and may be reacted by mixing, acidic or basic catalysts optionally being added to accelerate the reaction. However, it was not known that mixtures such as these can be formulated to adhesives which, after pregelation, can be cured by vulcanization.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a two-component adhesive system which cures by two different chemical reaction mechanisms that can be activated successively and catalyzed at least substantially independently of one another. The adhesive system was to show high application tolerances, particularly in regard to the mixing ratio between the two components. In addition, the gelation rate was to be variable. Finally, the cured adhesive was to satisfy the requirements typically imposed in the automotive industry in regard to hydrolysis and ageing stability and also thermal stability. Accordingly, the present invention provides a pregellable adhesive comprising: (a) from about 30 to about 70 parts by weight of a polymer A containing on average at least two hydroxyl groups per macromolecule; (b) from about 70 to about 30 parts by weight of a polymer B compatible with A and containing on average at least two carboxylic acid and/or carboxylic anhydride groups or at least one carboxylic acid and one carboxylic anhydride group per molecule; (c) from about 10 to about 120 parts by weight of a vulcanization promoter; wherein at least one of said polymers A or B contains vulcanizable carbon-carbon double bonds.
The present invention also relates to a process for the formation of an adhesive bond between vulcanization-stable substrates, characterized in that a polymer A, which contains esterification catalysts and/or oxidation inhibitors in solution or admixture, is thoroughly mixed with a polymer B, which contains vulcanizing agents and, optionally, fillers and/or promoters in solution and/or admixture, to form a rubber mixture, the rubber mixture thus formed is applied to the substrates to be bonded, the substrates are fitted together, the bond is precured at or just above room temperature, but always below the vulcanization temperature, and is then brought to the vulcanization temperature, optionally after temporary storage, and cured.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In its broadest embodiment, the invention relates to the concept of using as an adhesive a two-component system which pregels when the two components are mixed and which may then be finally cured by a second curing mechanism. A preferred mechanism for the second curing mechanism is vulcanization. Possible chemical reactions for pregelation, i.e. the first curing mechanism, are reactions which can lead, for example, to the formation of ester groups, more especially the esterification of carboxylic anhydride groups containing polymer-bound hydroxyl groups, the esterification of carboxylic acids or even transesterification reactions.
Accordingly, the polymers A and B present in the system on the one hand must bear chemical groups which react during pregelation; on the other hand, however, at least one of components A and B must also bear chemical groups which react during curing, i.e. for example during vulcanization.
Thus, polymer A contains on average at least two hydroxyl groups per macromolecule. However, more than two hydroxyl groups may even be present, particularly with relatively high degrees of polymerization. The hydroxyl groups may be arranged at the ends of the chain or at the ends of side groups, although they may also lie directly on the chain. Polymer A may contain vulcanizable double bonds and must contain vulcanizable double bonds when polymer B contains no such vulcanizable double bonds. Similarly, polymer B may contain vulcanizable double bonds and must contain vulcanizable double bonds when polymer A contains no such double bonds. Polymer B contains on average two carboxylic acid and/or carboxylic anhydride groups per molecule or one or more carboxylic acid groups and one or more carboxylic anhydride groups per molecule. In the preparation of the polymer mixtures, the expert must always ensure than polymers A and B are compatible with one another, i.e. the polymers must not separate.
Preferred materials for polymers A and B are liquid polyolefins containing the corresponding terminal groups, particularly liquid polydienes, for example liquid polybutadienes. However, it is also possible to use copolymers based on butadiene and olefins or copolymers based on isoprene which may optionally contain other monomers, for example copolymers of butadiene and olefins. Among such compounds, those containing halogen are less preferred.
Where little importance is attributed to hydrolysis stability, compatible polyesters and/or polyamides containing the corresponding terminal groups may also be used as polymer A or polymer B.
In one preferred embodiment of the invention, polymer A is a polybutadiene containing terminal or internal hydroxyl groups while polymer B is a polybutadiene containing carboxylic anhydride groups. Preferred polybutadienes have a molecular weight Mn (as determined by vapor pressure osmometry) in the range from 1,000 to 3,500 and preferably in the range from 1,500 to 2,000. Suitable products have acid numbers in the rang
Garnault Anne-Marie
Lanoye Thierry
Henkel Kommanditgesellschaft auf Aktien (Henkel KGAA) Henkelstra
Lipman Bernard
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