Binders for soft feel coating materials

Details Binders for soft feel coating materials Binders for soft feel coating materials

2000-01-14

2001-04-03

Yoon, Tae (Department: 1714)

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...

C525S327200, C525S381000, C525S382000, C526S269000, C524S602000

Reexamination Certificate

active

06211286

ABSTRACT:

RELATED APPLICATION
This application claims priority of Austrian Application No. A 54/99 filed, Jan. 18, 1999, herein incorporated by reference.
BACKGROUND OF THE INVENTION
In the coating of hard substrates, such as plastics, there is frequently a desire for the coating to achieve a soft feel, where the coated surface, although feeling soft to the touch, is unimpaired in terms of the mechanical and chemical resistance in comparison with the conventional coatings.
Binders for these so-called soft feel coating materials preferably have segments of polymers having a low glass transition temperature; the crosslinking density must be high enough for there to be very little or no reduction in the mechanical and chemical resistance properties but low enough to allow the effect of the low glass transition temperature to be manifested macroscopically as well.
Two-component binders have been disclosed for soft feel coating materials based on hydroxyl-containing polyester urethanes, which are to be cured preferably with isocyanates but also, for example, with acid anhydrides or amino resins.
It has not proven possible to date to provide practicable one-component binders for soft feel coating materials. Although crosslinking with amino resins is able to take place at elevated temperature in the manner of a one-component system, the soft surface of the soft feel coating is adversely affected by the high temperatures required.
The known, polyisocyanate-based systems which cure at room temperature have the problems typical of isocyanates of limited pot life and poor acceptability from the standpoint of occupational hygiene. A further important disadvantage of isocyanate curing agents in conjunction with soft feel coating materials is the “aftercuring” which is observed. Because of the presence of water (which is itself able to react with the isocyanates), the polyfunctional isocyanates used for crosslinking have to be used in excess. Their reaction with water involves decarboxylation and formation of the corresponding amines, which in turn form ureas with isocyanates which have not yet reacted. This urea formation reaction takes place during the drying of the coating material and adversely affects the feel of the coating film, which is still soft directly following application. There was therefore a need to develop a binder for soft feel coating materials which durably retains this soft feel. A further object was to provide a one-component binder which cures at moderate temperature and yet imposes very little restriction on the pot life.
SUMMARY OF THE INVENTION
It has surprisingly been found that polymers having a predominantly aliphatic nature which contain terminal or lateral cyclic carbonate groups, possess the required low glass transition temperature and can be processed to binders in an aqueous, amine-containing dispersion crosslink in a short time and at low temperatures after drying and lead to coatings having the required soft feel without suffering rapid loss of said soft feel. These binders can be formulated as both one-component and two-component coating materials.
The invention therefore provides aqueous binders for soft feel coating materials, comprising predominantly aliphatic, water-soluble or water-dispersible polymers A having terminal or lateral cyclic carbonate groups and an amine B having at least two primary amino groups, the ratio of the number of primary amino groups in the component B to the number of cyclic carbonate groups in the component A being from about 7:3 to about 3:7, preferably from about 6:4 to about 4:6.
DESCRIPTION OF PREFERRED EMBODIMENTS
The term “predominantly aliphatic” refers to those polymers in which the mass fraction of aliphatic units in the sum of the masses of aromatic and aliphatic units is at least about 60%, preferably at least about 70%, and with particular preference at least about 75%.
By terminal cyclic carbonate groups are meant those which are located in each case at the chain end of linear or branched molecules. Lateral cyclic carbonate groups are those which are not located at the end of a chain or chain branch. Preferably, the polymers A contain on average at least about 1.5, with particular preference at least about 2, such cyclic carbonate groups per molecule.
Suitable binder components A are all known classes of aliphatic or predominantly aliphatic polymers which are soluble or dispersible in water and contain cyclic carbonate groups as end groups either as a result of their synthesis or as a result of reaction with a compound which has a cyclic carbonate group and a group which rapidly undergoes reaction with reactive end groups of the polymer. Examples of the latter class of polymers are polyacrylate polyols A11, polyester polyols A12, polyether polyols A13, polyurethane polyols A14 and polyolefin polyols A15 as hydroxyl-containing polymers A1, and polyether amines A21 and polyiminoalkylene amines A22, polyamido amines A23 and polyureas A24 as amino-containing polymers A2. Particular preference is given in this context to polyacrylate polyols A11, polyester polyols A12, polyurethane polyols A14 and polyolefin polyols A15 and also to polyamido amines A23 and polyureas A24. Likewise suitable though less preferred are polymers which contain mercapto groups as reactive groups. In this case the specific molar amount of hydroxyl or amino groups in the polymers A1 and/or A2 in question is in each case preferably from about 0.01 to about 2 mmol/g, and the polymers preferably have on average per molecule in each case at least about 1.5, preferably from about 1.8 to about 2.5, and with particular preference from about 1.9 to about 2.2, functional groups. The conversion of these hydroxyl or amino end groups of the polymers A1 and A2 into cyclic carbonate groups can be carried out, for example and preferably, by reaction with an at least bifunctional isocyanate A3, thereby providing the polymers with isocyanate end groups which are attached to the initial polymer by way of a urethane or urea group. The amount of isocyanates A3 in this case is preferably chosen such that there are on average at least about 1.5 isocyanate groups per molecule of this intermediate. In a subsequent step, these isocyanate-functional polymers can in turn be reacted with a compound A4 having at least one isocyanate-reactive group and one cyclic carbonate group, with particular preference glycerol carbonate (4-hydroxymethyl-1,3-dioxolan-2-one), to give the desired polymer A having cyclic carbonate end groups.
Examples of polymers A5, which have the required cyclic carbonate groups by virtue of their precursors, are reaction products of units having in each case two, preferably terminal, cyclic carbonate groups A51 (which can be prepared, for example, from diepoxides by reaction with carbon dioxide using appropriate catalysis) and diamines A52, the diamines being employed in a substoichiometric proportion.
The glass transition temperature of these polymers A that are suitable for the invention is from about −70 to about −30° C., preferably from about −60 to about −40° C. The polymers A preferably have an acid number of from about 5 to about 200 mg/g, in particular from about 20 to about 150 mg/g. The acid groups are preferably at least partly neutralized (at least about 10%, preferably at least about 25% neutralized). The specific cyclic carbonate group content is preferably from about 0.01 to about 2 mmol/g, with particular preference from about 0.2 to about 1.5 mmol/g.
The polyacrylate polyols A11 can be prepared in conventional manner by free-radically initiated polymerization of mixtures of olefinically unsaturated monomers, the mixture containing a mass fraction of at least about 5%, preferably at least about 10%, of hydroxyl-containing olefinically unsaturated monomers A111 and a mass fraction of at least about 1%, preferably at least about 2%, of olefinically unsaturated carboxylic acids A112. Another variety of the polyacrylate polyols that are suitable for the present invention is obtainable by polymerizing a mixture of olefinica

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