Water-dilutable binder for “soft feel” lacquers

Details Water-dilutable binder for “soft feel” lacquers Water-dilutable binder for “soft feel” lacquers

1999-08-02

2001-07-03

Short, Patricia A. (Department: 1712)

Coating processes

With post-treatment of coating or coating material

Heating or drying

C427S388400, C427S389700, C427S393500, C427S343000, C525S440030, C525S457000, C525S458000, C525S456000, C525S424000, C525S428000, C524S591000

Reexamination Certificate

active

06254937

ABSTRACT:

RELATED APPLICATIONS
This application claims priority to Austrian application No. 1343/98, filed Aug. 4, 1998, herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to binders for water-dilutable “soft feel” lacquers which remain stable on being exposed to UV radiation.
2. Background of the Invention
When coating hard substrates such as plastics it is frequently desirable sought to achieve a “soft feel” by means of a coating in such a manner that while the surface has a soft “feel” the mechanical and chemical stability of the coating is not impaired in comparison to that of the customary coatings.
Preferred binders for such “soft feel” lacquers are to be found in the segment of polymers displaying a low glass transition temperature. This means on one hand that the cross-linking density must be high enough to prevent or minimize any deterioration of the chemical and mechanical properties as far as possible, and on the other hand it must be sufficiently low to permit the manifestation of the effects of the macroscopic properties of the low glass transition temperature.
In the case of polyurethanes, for example, polyether polyols or polyester polyols which have a purely aliphatic character are frequently used as such a segment with a low glass transition temperature. Especially for top coat applications the use of aromatic components is generally avoided, as they would render the finished coating photosensitive and may lead to secondary reactions such as yellowing and embrittlement.
However, it has been established that coatings made with binders and curing agents with aliphatic constitutional units, especially polyurethane and polyester which have purely aliphatic constitutional units, become rapidly tacky on being exposed to UV radiation and lose their mechanical stability.
OBJECT OF THE INVENTION
One object of the invention was to find binders for water-dilutable “soft feel” lacquers which remain stable on being exposed to UV radiation.
Surprisingly, it was discovered that combinations of binders A and curing agents B, provided at least one of the two components A and B contain aromatic structural elements, result in coatings with excellent stability against UV radiation. This was all the more unexpected as aromatic constitutional units usually reduce the resistance to light or UV radiation.
SUMMARY OF THE INVENTION
The subject matter of the invention are combinations of binder A and curing agent B for soft feel coatings, comprising water-dilutable binders A with functional groups selected from hydroxyl, amino and carboxyl groups, and curing agents B which contain functional groups capable of reaction with the functional groups of component A and capable of forming chemical bonds as cross-linking points, wherein at least one of the components, A or B, contains aromatic structural components in such a quantity that their mass fraction, related to the mass of solids, amounts to at least about 3%, preferably at least 5% and in particularly preferred cases at least about 10%.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
All known classes of polymers featuring functional groups, selected from hydroxyl, amino, amide and carboxylic acid groups, are suitable as binder A. Examples of suitable polymers containing hydroxyl groups include polyacrylate polyols, polyester polyols, polyether polyols and polyurethane polyols. Examples of polymers containing amino groups include polyether amines, polyiminoalkylene amines, polyamide amines and polyurethane ureas. Examples of polymers for containing carboxyl groups include polyester polyols, polyurethane polyols and copolymers of acrylic or methacrylic acids. Mixtures of all the polymers described above are also contemplated. In this context, the preferred specific amount of substance of hydroxyl, amino, or carboxyl groups in the respective polymers should be about 0.01 to about 2 mmol/g, with the polymers possessing an average of at least about 1.5, preferably between about 1.8 and about 2.5 and in particularly preferred cases 1.9 to 2.2 functional groups per molecule.
Preferred binders A are combinations of polymers containing hydroxyl groups, with particular preference to polyurethanes A1, and polymers containing amino groups, with particular preference to polyurethane ureas A2. Polyesterpolyols are especially preferred constituents of the polyurethanes A1 and A2; however, others, for example, polyether polyols, polycarbonate polyols, polybutadiene polyols, polyisoprene polyols and polyesteramide polyols may also be used.
The hydroxyl number of the preferred polyester urethanes A1 amounts to about 10 to about 60, is preferred between 20 to 50 and receives particular preference between 35 to 45 mg/g; their glass transition temperature is from about −70 to about −30° C., preferably between −60 to −40° C. and particularly, at about −50° C.
The hydroxyl number of the polyester urethane ureas A2 preferably amounts from about 0 to about 10, and is particularly preferred between 0 and 5mg/g. Their amine number amounts from about 1 to about 15, preferably from 3 to 10 and particularly between 4 and 8 mg/g. The glass transition temperature of the components A1 is always lower than the glass transition temperature of A2, a difference in the glass transition temperature of about 5 K is preferred while a difference between about 7 and about 20 K receives particular preference.
Within the scope of the invention it is also possible to produce the binders A having segments with at least two different glass transition temperatures and differing functional groups in such a manner that the glass transition temperatures exhibit a difference of at least about 5 K. These A components with a block structure may in such a case possess, for example, hydroxyl as well as amino groups.
The mass ratio of the binder components A1 and A2 (solid matter) is from about 4:6 to about 9:1, preferably from 5:5 to 8:2, with particular preference from about 6:4 to 7:3.
The hydroxyl number is defined by the German Industrial Standard (DIN) 53 240 as the quotient of that mass m
KOH
of potassium hydroxide exhibiting the same number of hydroxyl groups as the sample to be tested and the mass m
B
of this sample (mass of the solid matter in the sample in the case of solutions or dispersions) and its customary unit of measurement is “mg/g”.
The amine number is defined by the German Industrial Standard (DIN) 53 176 as the quotient of the mass m
KOH
of potassium hydroxide which requires the same amount of acid for neutralization as the sample to be tested and the mass m
B
of this sample (mass of the solid matter in the sample in the case of solutions or dispersions) and its customary unit of measurement is “mg/g”.
The preferred component A 1, hereinafter designated “soft component”, comprising of polyurethane containing hydroxyl groups, may be produced in the known manner from aliphatic, aromatic or mixed aliphatic and aromatic polyols with an average of at least two hydroxyl groups per molecule and multifunctional aliphatic, aromatic or mixed aliphatic and aromatic isocyanates whereby the amount of substance of the isocyanate groups in the mixture of the reactants is less than that of the hydroxyl groups. The required dilutability by water is achieved by means of incorporating anionogenic groups, i.e. components which carry acid groups which are neutralized at least partially prior to or during the dispersion in water by the addition of neutralizing agents, such as aqueous alkali or amines, and are thus transformed into anions. As already mentioned, the preferred polyurethanes A1 are those derived from polyester urethanes which are accessible by the polyaddition of polyesters A11 containing hydroxyl groups and multifunctional isocyanates A12. In turn the polyesters A11 are produced in the known manner by means of polycondensation of polyols A111 and multifunctional acids A112 or their ester-forming derivatives, for which purpose it is preferred to use a mixture of at least two aliphatic polyols A111.
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