Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-05-02
2003-04-15
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S506000, C524S513000, C524S589000, C526S302000
Reexamination Certificate
active
06548593
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the priority of European patent application no. 00 109 342.6, filed May 2, 2000, the disclosure of which is incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
The present invention relates to new thixotropic agents for viscous systems, in particular for the manufacturing of adhesives and sealants with migration-free properties.
BACKGROUND OF THE INVENTION
For the production of non-sag viscous systems thixotropic agents are used. Inorganic fillers such as e.g. carbon black, aerosil etc. are used. Achieving thixotropy by means of such fillers usually leads to an increase in viscosity and therefore such fillers are primarily considered for the production of compositions for mechanical processing. For the manual processing, e.g. out of a cartridge, the compositions are preferably rendered non-sag by means of organic thixotropic agents since such organic thixotropic agents cause almost no viscosity increase. Organic thixotropic agents are e.g. amide waxes, hydrolyzed castor oils, or urea derivatives that are produced in an inert carrier such as plasticizers, hydrocarbons etc. Such inert carriers, however, have the disadvantage that they can migrate even out of cross-linked systems, such as one-component polyurethane systems, thereby leading to a deterioration of quality. Dependent on the situation, this can have several consequences: For an adhesive, loss of adhesion may result; Substances diffusing out of the composition may cause health problems, a visual deterioration of porous substrates etc.
Thus, the present invention aims at providing new thixotropic agents for adhesives and sealants that overcome the above mentioned drawbacks.
BRIEF SUMMARY OF THE INVENTION
Hence, it is a general object of the invention to provide a thixotropic agent based on at least one urea derivative in a migration-free carrier material.
Another object is a viscous, at least one curable binder comprising system containing a thixotropic agent of the present invention.
Still another object is a method for the production of the thixotropic agent of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The thixotropic agents of the present invention are—as some thixotropic agents of the state of the art—based on urea derivatives. However, for the production of the thixotropic agents of the present invention a non-migrating carrier is used. Such a carrier is either intermingled or interwoven with the structure matrix after the cross-linking, has pronounced compatibility with the whole system, or is incorporated into the structure matrix and can therefore not diffuse out of the cured material. The carrier material or parts thereof should not show any migration tendency on white cement.
Carrier materials suitable in the scope of the present invention are those that do not show any migration according to the test method specified below: The thixotropic agent, or an adhesive or sealing composition comprising such thixotropic agent, respectively, are applied to white cement in form of beads. After 7 days curing at 23° C. and 50% relative humidity (r.h.), the contact zone of the adhesive bead to the substrate is visually examined for signs of migration. Thixotropic agents or carriers, respectively, that under the above mentioned conditions show no noticeable migration, will be referred to below as non-migrating etc.
The thixotropic agents of the present invention are suitable for any cross-linking system. Such cross-linking systems can be two-component systems that cross-link upon mixing of a binder—also referred to as resin component—with a curing agent. The resin component contains reactive groups such as acrylate groups, epoxy groups, isocyanate groups, silane groups, etc. Possible curing agents are e.g. amino groups or hydroxy groups or sulfur groups comprising compounds, initiators for initiating a polymerization of activated double bonds, water, catalysts, etc. The cross-linkable system can also be a one-component system that can be cured either thermally by air humidity or by radiation such as UV-radiation.
The chemistry for the production of urea derivatives is known (see e.g. DE 1805693) and is preferably based on the reaction of aromatic, monomer diisocyanates (isocyanate monomer), such as 4,4′-diphenylmethylene diisocyanate (=MDI), with an aliphatic amino compound, such as e.g. butyl amine. Since both compounds, the isocyanate as well as the amine, are highly reactive, immediately after the mixing of the components the urea derivative is formed as a solid in the carrier material. In the scope of the present invention, the high reactivity of the two reactants requires a careful choice of process parameters and an optimal selection of the carrier material, preferably a reactive carrier material, in order to exclude or at least minimize undesired side reactions as far as possible. The urea derivative can be present in the carrier material in concentration of 5 to 50% or more, preferably in the range of 15 to 30%, and the content is dependent on the processability of the resulting thixotropic agent.
For the production of the thixotropic agent of the present invention, the influence of water present in the carrier material must be considered in the stoichiometric calculation of the amount of isocyanate monomer, such as MDI, and of the amine compound.
Non reactive carrier materials are long-chain polymers with high affinity for the cross-linkable, or the cross-linked system. Said affinity can possibly be enhanced by suitable substitution, such that migration of the carrier material in the cross-linked system does not occur.
Preferred carrier materials are reactive carrier materials such as polyols, blocked isocyanate polymers (prepolymers terminated with blocked isocyanate groups), silane groups terminated prepolymers and/or acrylate groups comprising polymers.
Preferred polyols are polyols with an OH-value of <28 mg KOH/g or a Mw per OH-group of >2000, respectively, more preferably polyols with an OH-value of <10 mg KOH/g or a M
W
per OH-group of >6000, whereby such polyols much preferably are liquid at a temperature of about 20° C.-25° C.
It is also within the scope of the present invention that the carrier material is a mixture of carrier materials with the same or different reactivity, in particular a combination of a prepolymer comprising acrylate groups with a prepolymer on silane basis.
The production of the thixotropic agents of the present invention can be carried out in various ways. Two possible production methods, using illustrative examples for polyol prepolymers, are disclosed below in greater detail. In an analoguous manner, said methods can be applied to blocked isocyanate prepolymers and silane groups terminated prepolymers. The production of thixotropic agents with non-reactive carrier materials is less critical since undesired side reactions are excluded.
In a first method at least one isocyanate monomer is added to a mixture of at least one amine compound and at least one polyol. Another procedure is that at least one isocyanate monomer is dissolved in at least one polyol, and is immediately added to a mixture of at least one amine compound in the same palyol(s), optimally in an equivalent ratio of isocyanate:amine of 1:1. Experiments have shown that the quality of the resulting thixotropic agent is dependent on the OH-value since the isocyanate monomer immediately reacts with the hydroxyl groups of the polyol. A good quality results if the OH-value is below 28 mg KOH/g, preferably below 10 mg KOH/g, or the molecular weight per OH-group is above 2000. in particular above 6000.
Preferably, the polyol is liquid at room temperature, or at about 20 to 25° C., respectively, in order to avoid the costly preheating of the polyol on the one hand, and on the other hand, to avoid a removal of additional heat resulting from the pre-heating step during the exothermic production of the urea derivative. Polyethers are particularly suitable as polyols. If the polyol is a polyethylene gl
Merz Peter W.
Onuoha Ukiwo
Tsuno Shingo
Burns Doane Swecker & Mathis L.L.P.
Cheung William K.
Sika Schweiz AG
Wu David W.
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