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
2000-03-28
2002-09-10
Wilson, D. R. (Department: 1733)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S193000, C427S385500, C427S388200
Reexamination Certificate
active
06448338
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to hot-pumpable, heat-curing compositions based on ethylene/vinyl acetate copolymers (EVA), to their use as sealing compounds or lining adhesives, to a process for sealing seams in vehicle manufacture and to a process for lining sandwich components in vehicle manufacture.
2. Discussion of Related Art
In machine construction, vehicle construction or equipment manufacture and particularly in car manufacture, the metal components are, for the most part, still mechanically assembled and fixed at the so-called white-shell stage. Conventional fixing methods include riveting, screwing or welding, particularly spot welding, and flanging processes. The seams between the parts thus joined have to be sealed against penetrating water, dust and the like. Conventional compounds for sealing these seams are based either on plastisols or on rubber compositions. In car manufacture, sealing is increasingly being carried out at the so-called white-shell stage for manufacturing reasons, i.e. the sealing compounds are generally applied to the uncleaned metal surface. The surfaces are often coated with various corrosion inhibiting oils or drawing oils so that the sealing compounds used thereon should not be functionally affected by these oils. The sealants are cured at a later stage in the paint drying ovens. Before curing, the joined and sealed parts pass through cleaning, phosphating and dip-priming stages. The treatment compositions used in those stages are capable of flushing the sealants from the joints. For this reason, all sealants or sealing compounds or adhesives used at the white-shell stage of vehicle manufacture are required to be resistant to washing. Hitherto, these requirements have been satisfied by various procedures including, for example, thermal/inductive precuring or pregelation of low-viscosity paste-form adhesives/sealants or sealing compositions based on plastisols. These plastisols may be PVP plastisols of the type described, for example, in DE-A-1769325 or in DE-A-2200022, although (meth)acrylate plastisols of the type described, for example, in DE-A-2454235 or DE-A-3523480 may also be used. The styrene-copolymer-based plastisols disclosed in DE-A4034725 and in DE-A-4315191 are also mentioned in this regard. Separate equipment is required for the precuring or pregelation step necessitated by the use of plastisols. In general, the equipment in question consists of special induction heaters or hot-air or infrared heaters. Besides the additional investment involved, this procedure has another disadvantage. On account of the short cycle times, the pregelation step has to be carried out by so-called heat shock so that the surfaces of the metal parts briefly assume very high temperatures. This can lead to cracking of the corrosion-inhibiting and drawing oils applied to the metal surfaces.
Rubberbased sealants and sealing compounds which are applied hot are also known. After cooling to ambient temperature, these compounds/compositions have such a high intrinsic viscosity that they are resistant to washing a few minutes after application. Hot-applied rubber compositions are widely used as adhesives, sealants and sealing compounds at the white-shell stage of car manufacture. These compositions contain rubbers, more particularly vulcanizable rubbers based on 1,4-polybutadienes and/or 1,4-polyisoprenes. The compositions preferably contain liquid polydienes of low molecular weight, sulfur and optionally accelerators for sulfur vulcanization. The compositions may additionally contain high molecular weight, so-called solid rubber, both the liquid polydienes and the solid rubber optionally containing functional groups such as, for example, hydroxyl groups, carboxyl groups, anhydride groups or epoxy groups. The use of these rubber compositions as adhesives/sealants is the subject of a number of patent applications, cf. for example EP-A-97394, EP-A-309903, EP-A-309904, DE-A-3834818, DE-A-4120502, DE-A-4122849 and EP-A-356715. Unfortunately, the rubber compositions in question have a very tacky surface and can very easily be deformed by mechanical pressure before they are cured in the paint drying ovens. This is a major disadvantage above all where they are used for fitted parts, such as for example doors, bonnets or boot lids, because such parts often have to be stacked and stored during the manufacturing process. The tacky surface binds very large quantities of dust and soil and the fact that the rubber compositions can easily be mechanically deformed often leads to handling marks on the visible part of seams in particular so that the appearance of the sealed joint is adversely affected.
Attempts have been made to solve some of the problems mentioned above by using two-component rubber systems. Thus, EP-A-181441 describes a two-component system consisting of a hydroxyfunctional 1,3-polybutadiene and a second component which consists of a polymer based on 1,3-butadiene and which contains lateral succinic anhydride groups. EP-A-356715 describes a two-component system consisting of a polymer A containing at least two hydroxyl groups per macromolecule and of a second component which is compatible with component A and which contains on average at least two carboxyl groups or carboxylic anhydride groups per molecule. Through the use of suitable catalysts, these two-component materials can develop a certain strength at room temperature through the esterification reaction alone. Ultimate strength is developed by an additionally incorporated sulfur vulcanization system during vulcanization in the paint drying ovens. However, these two-component systems only develop adequate resistance to pressure and handling about 30 minutes after application. This means that the corresponding parts can only be further processed some 30 minutes after application of the two-component system. In addition, two-component systems, particularly those of high viscosity, require elaborate metering and mixing units to be able to guarantee a reasonably dependable level of process safety.
Although conventional hotmelt adhesive compositions—through their rapid build up of strength after cooling—would enable corresponding sealing compounds rapidly to develop resistance to pressure and handling, these hotmelt adhesives have two major disadvantages:
they require very high application temperatures
on account of their thermoplastic character, they soften and flow at the temperatures prevailing in the paint drying ovens so that they would flow out from the joint.
Accordingly, the problem addressed by the present invention was to provide hot-pumpable heat-curing compositions which could be directly applied to uncleaned surfaces at the white-shell stage of car manufacture and which, when used as sealing compounds, would have adequate resistance to pressure and handling only a short time after application so that the corresponding parts could be immediately further processed. In addition, these sealing compounds would have a tack-free surface so that they would not attract dust or soil. In addition, a tack-free surface of the sealing compounds would ensure that machinery and equipment in which car parts thus sealed are further processed would not be contaminated by the sealing compounds. In addition, the binder system would be formulated in such a way that curing or crosslinking of the sealing compound could take place even over the broad temperature ranges encountered in the stoving phase of electrophoretic coating in car manufacture. In addition, it would have to be guaranteed that the cured sealing compound would have an attractive smooth surface because the corresponding joints are often visible. For reasons of corrosion control, no pores or open bubbles should occur. In addition, the surfaces would be required to lend themselves to coating with conventional automotive lacquers.
DESCRIPTION OF THE INVENTION
The solution to the problem stated above is defined in the claims and lies essentially in the use of heat-curing compositions containing at least one
Born Peter
Hoellriegel Klaus
Harper Stephen D.
Henkel Teroson GmbH
Ortiz Daniel S.
Wilson D. R.
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