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
2000-02-21
2002-06-04
Lovering, Richard D. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S127000, C525S920000, C526S932000, C528S065000
Reexamination Certificate
active
06399718
ABSTRACT:
The present invention relates to a polyurethane resin suitable as a Theological control additive for aqueous coating compositions.
The present specification further relates to processes for preparing this polyurethane resin and to aqueous two-component polyurethane coating compositions comprising this polyurethane resin, to the use of these coating compositions and to the use of the polyurethane resin as an additive for controlling the rheology of coating compositions.
In the field of coating plastics there is a keener desire for aqueous systems, both as primers and as topcoats. In these applications the coating materials used have to meet a large number of different requirements. In particular, for instance, in the field of coating plastics there is the requirement that the resulting coatings exhibit a good “appearance”, i.e., for example, high gloss and low haze levels. Furthermore, for example, in the wet-on-wet process for producing a basecoat/clearcoat system, clearcoats applied to the as yet uncured basecoat should not cause incipient dissolution of or otherwise disrupt the basecoat film, since otherwise finishes of poor appearance are obtained. This applies in particular to finishes produced using basecoats that contain effect pigments (e.g., metal pigments, especially aluminum flakes or pearl luster pigments).
In addition, the coating compositions ought to exhibit very little tendency toward running (curtaining, development of tears, sagging) on vertical faces, on edges and in beads, following application, especially during the baking operation or during the drying operation at temperatures generally from room temperature to about 80° C. It is known that this tendency to run can be influenced by controlling the rheology of the coating compositions. By increasing the viscosity of the known coating materials, however, the improvement which can be obtained in the tendency to run is inadequate.
It is in fact known that polyurea compounds act to stabilize running. A serious disadvantage of known polyureas, however, is haze in the baked coating film, especially when the polyureas are used in clearcoats. In order to overcome this problem, DE-A-42 36 901 proposed the use of acrylated polyurethane resins prepared by reacting a hydroxyl-containing acrylate copolymer, a hydroxy-functional microdispersion, a diisocyanate and a monoamine as an additive to control the rheology of conventional coating compositions. The polyurethane resins described in DE-A-42 36 901, however, have the disadvantage that their preparation requires a complex process comprising a plurality of synthesis steps and that they are unsuitable for aqueous coating materials.
Furthermore, DE-C-31 50 174 also discloses hydrophobic polyurethane resins containing urea groups, said resins being based on a polyalkylene oxide diol having a molecular weight of from 2000 to 20,000 and their use as thickeners for controlling the rheology of aqueous coating compositions. Because of the high level of ether groups, however, the polyurethane resins described in DE-C-31 50 174 have the disadvantage that the films become sensitive to condensation. In addition, the thickeners described therein become manageable only at high levels of dilution. Furthermore, these thickeners cannot be used as film formers. Since the polyether segments of the thickener enter into stable interactions with water, there may be instances of instability on storage above 40° C.
Moreover, German Patent Application P 196 11 646.5, unpublished at the priority date of the present specification, discloses an aqueous two-component polyurethane coating composition suitable for coating plastics. The use of monoisocyanate-modified polyurethane resins as rheology control additives, however, is not described.
Furthermore, German Patent Application P 196 06 783.9, unpublished at the priority date of the present specification, discloses polyurethane resins and their use as an additive for aqueous coating materials for the purpose of increasing the rheology stability. Monoisocyanate-modified polyurethane resins are not, however, described in that document.
The object of the present invention is therefore to provide polyurethane resins suitable as an additive, especially in aqueous coating compositions, where they can be used to control the viscosity. As far as possible, these polyurethane resins should also function as a binder component in such compositions. In particular, these polyurethane resins, especially when used in aqueous two-component polyurethane coating compositions and with particular preference when used in clearcoats, should lead to coatings having a good appearance (e.g., high gloss, low haze). At the same time, the resulting coating compositions should exhibit minimal tendency to run following application. Furthermore, the coating compositions prepared using these polyurethane resins should exhibit good basecoat wetting when used as a clearcoat for producing a multicoat paint system. In the case of two-component coating compositions, moreover, the binder component (I) of the coating composition should possess very long storage stability.
Finally, in the field of plastics coating, there is a further requirement that the coating compositions employed are curable at low temperatures (generally<100° C.) and even when cured at these low temperatures lead to films having the desired properties.
This object is surprisingly achieved by a polyurethane resin (P) obtainable by
(A) in a first reaction stage (A) reacting
(a) one or more di- and/or polyisocyanates,
(b) one or more compounds (b) which have at least one group which ensures dispersibility in water and more than one group which is reactive toward isocyanate groups, and
(c) if desired, one or more compounds having at least 2 and not more than 3 OH groups
to give an intermediate (A) having free isocyanate groups and having urethane groups,
(B) in a second reaction stage (B) adding
(d) one or more monoisocyanates
to the intermediate (A) obtained in stage (A), and
(C) subsequently reacting the resulting mixture (B) with one or more hydroxyl-containing polymers and/or oligomers (D) to give the polyurethane resin (P), using less than 20% by weight, based on the weight of the polyurethane resin (solids content), of polyalkylene oxide diols and/or polyalkylene oxide polyols to prepare the polyurethane resin.
The invention additionally provides processes for preparing these polyurethane resins and coating compositions, especially aqueous two-component polyurethane compositions, which comprise said polyurethane resin, and provides for the use of these coating compositions and for the use of the polyurethane resin as a rheology control additive.
It is surprising and was not foreseeable that the polyurethane resins both act as a binder component and possess rheology control properties and promote the formation of transparent coating films of high homogeneity. A further advantage is that the polyurethane resins, especially used in aqueous two-component polyurethane coating compositions, preferably when used in clearcoats, lead to coatings having a good appearance (e.g., high gloss, low haze) combined with minimal tendency to run. Furthermore, the coating compositions prepared using these polyurethane resins exhibit good basecoat wetting when used as a clearcoat to produce a multicoat paint system. Furthermore, the binder component (I) of the coating composition—in the case of two-component coating compositions—has a long storage stability. It is also advantageous, finally, that the coating compositions employed can be cured at low temperatures (generally<100° C.) and even when cured at these low temperatures lead to films having the desired properties.
The preparation of the polyurethane resin (P) of the invention involves
(A) in a first reaction stage (A) reacting
(a) one or more di- and/or polyisocyanates,
(b) one or more compounds (b) which have at least one group which ensures dispersibility in water and more than one group which is reactive toward isocyanate groups, and
(c) if desired, one or more comp
Hintze-Brüning Horst
Rink Heinz-Peter
Weinert Peter
BASF Coatings AG
Lovering Richard D.
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