Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Patent
1989-07-06
1991-01-08
Welsh, Maurice J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
4273855, C08G 1830
Patent
active
049837036
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a coating composition containing organic solvents, a mixture of a polyhydroxy component (A), and a polyisocyanate component (B), and a pot life extender, and to the use of this coating composition in motor car refinishing in particular.
Two-component polyurethane systems are employed in the automotive industry where they find application for example in motor car refinishing. A shortcoming of these known compositions is that their pot life is so short that a reaction between the two components can occur already while they are being applied to a substrate. This problem becomes even more acute when a catalyst for the polyurethane formation is employed. It therefore becomes desirable for the two-component polyurethane composition to possess an extended pot life and to cure rapidly after being applied to a substrate despite having an extended pot life.
The use of tertiary alcohols as pot life extenders in a system which contains isocyanate groups and hence reactive groups, is known. It is known from EP-B 1,304 that the pot life of a coating composition containing a mixture of a polyhydroxy compound and a polyisocyanate in an organic solvent can be extended by the addition of 2-methyl-2-propanol and/or 2-methyl-2-butanol if at least 0.8 equivalent of the alcohol is used to one equivalent of the polyisocyanate.
In the case of slow-reacting isocyanates in particular, the reaction must be speeded up to ensure that the applied paints crosslink rapidly and are resistant to gasoline. When dimethylethanolamine and dibutyltin dilaurate, for example, were used as catalysts in the crosslinking reaction, no desired acceleration of the crosslinking of the applied film was achieved, even though pot life was reduced to 2 hours.
It is possible to speed up the reaction by introducing carboxyl groups into the polyol components, but this suffers the disadvantage of a severely shortened pot life. A pot life extension of two-component polyurethane systems containing such acid groups by means of tertiary alcohols, as described in EP-B 1,304, is in most cases insufficient.
The object of the present invention was effectively to extend the pot life of the systems consisting of combinations of polyols with carboxyl groups and polyisocyanates.
Surprisingly, the object has been achieved by the coating composition of the type stated at the outset, wherein the polyhydroxy component has an acid value of 5 to 25 mg of KOH/g, and a mixture consisting of 0.1 to 4.0% by weight, based on the total weight of the coating composition, of a compound having a tertiary amino group or an amide group (C), and of 1 to 15% by weight, based on the total weight of the coating composition, of a tertiary monoalcohol (D) is used as pot life extender, 2-methyl-2-propanol and 2-methyl-2-butanol being excluded as the tertiary alcohols.
Suitable polyhydroxy components with an acid value of 5 to 25 mg of KOH/g are hydroxyacrylates, polyester polyols and polyether polyols. The polyhydroxy compounds generally have a hydroxyl value of at least 80.
Examples of suitable hydroxyacrylates are copolymers of styrene, vinyltoluene, acrylic acid, methacrylic acid, esters of maleic acid or fumaric acid, alkyl acrylates and alkyl methacrylates of 1 to 14 carbon atoms in the alkyl radical, such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, isopropyl acrylate, isobutyl acrylate, pentyl acrylate, isoamyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, decyl acrylate, dodecyl acrylate, pentyl methacrylate, isoamyl methacrylate, hexyl methacrylate, 2-ethylbutyl methacrylate, octyl methacrylate, decyl methacrylate, dodecyl methacrylate and methyl methacrylate, and copolymers of hydroxyl group-containing esters of acrylic or methacrylic acid, such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyamyl acrylate, hydroxyhexyl acrylate, hydroxyoctyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 3-hydroxybutyl acrylate and the corresponding methacrylates. The suitable hydroxyacryla
Moller Dieter
Vorbeck Udo
BASF Lacke & Farben Aktiengesellschaft
Mayer Richard L.
Welsh Maurice J.
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