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
2002-08-05
2004-01-13
Gorr, Rachel (Department: 1711)
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...
C524S840000, C528S049000, C528S079000, C528S061000, C523S336000, C523S339000, C428S423500, C428S423700, C428S424200
Reexamination Certificate
active
06677400
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to polyurethane dispersions, a process for their production and solvent-free primers for substrates containing these dispersions. The invention also relates to substrates, in particular plastics, primed with the dispersions, which have improved adhesion and higher gloss.
BACKGROUND OF THE INVENTION
Paint on high-grade plastic parts is applied in three layers. Such a layered structure comprises a primer, base coat and clear coat. The primer acts as the bonding agent between substrate and paint. An important property of a primer should therefore be to ensure good bonding on different plastic substrates. Aqueous primers can sometimes not adequately fulfil this basic requirement.
A further property of the primer is the possibility of covering and/or levelling defects in the surface of the molding. Since this cannot be entirely successful for all defects, these defects are conventionally eliminated after the priming step by regrinding. Good grinding ability on the part of the primer is therefore essential. Surface defects that are not eliminated at this point in the manufacturing process must be reworked at a later stage of the production process, involving considerably greater effort and higher costs. Otherwise the molding would be unable to be used. The discovery of even the smallest surface defect is therefore of enormous significance. Since defects and irregularities are easier to detect on glossy surfaces, a good primer should display a minimum gloss.
The requirements of a primer as described above are already met by solvent based (organically dissolved) polyurethanes of the prior art. However, these organically dissolved primers contribute to a considerable extent to the overall solvent emissions of a painting line. The use of organically dissolved primers in modern painting lines is therefore not desirable in ecological and economic terms. The lowest possible contribution to the volatile organic content (VOC) is a further requirement of a suitable primer. There is thus an urgent need for solvent-free aqueous primers for plastic parts that satisfy the requirements described above.
As yet, however, no systems based on purely aqueous polyurethane dispersions are known that satisfactorily solve all of the aspects of a primer as described above.
U.S. Pat. No. 5,548,016 describes coatings containing mixtures of aqueous preparations of polyurethanes and polyacrylates. These are suitable as a primer for the painting of plastic parts if 10 to 25 wt. % of an organic, water-miscible solvent (co-solvent) are added.
DE-A 2 651 506 describes a process for the production of polyurethanes that are dispersible in water. The process products disclosed therein are not suitable as a primer in the painting process for plastic parts, however, as they do not have the necessary adhesive properties.
It is an object of the present invention to provide a solvent-free, aqueous primer for substrate surfaces, in particular plastics, that meet the requirements described above.
It has now been found that coating compositions based on the polyurethane dispersions according to the invention are outstandingly suitable as a primer for the painting of diverse substrate surfaces, preferably plastic substrates.
SUMMARY OF THE INVENTION
The present invention relates to an aqueous polyurethane resin dispersion containing
i) a polyol component with a number-average molecular weight of at least 300 daltons, containing at least one polyether diol initiated on an aromatic diol,
ii) a polyol component with a number-average molecular weight of 62 to 299 daltons,
iii) a monofunctional isocyanate-reactive compound with an ethylene oxide content of at least 50 wt. % and a molecular weight of at least 400 daltons,
iv) a polyisocyanate,
v) an aliphatic polyamine with a molecular weight of 60 to 300 daltons or hydrazine, and
vi) a hydrophilic aliphatic diamine.
The invention also relates to a coating composition containing
A) 30 to 90 parts by weight of this polyurethane resin dispersion,
B) 5 to 60 parts by weight of an inorganic filler,
C) 1 to 60 parts by weight of a water-miscible polyisocyanate,
D) 0.1 to 30 parts by weight of a pigment, and
E) 1 to 15 parts by weight of a paint additive,
whereby the sum of the components is 100 parts by weight.
The invention also relates to a process for production of the dispersions and a substrate primed with the dispersion.
DETAILED DESCRIPTION OF THE INVENTION
The coating compositions containing the polyurethane resin dispersions according to the invention show outstanding adhesion both to diverse substrate surfaces, in particular plastic substrates, and to subsequent paint films, improved resistance to condensation and solvents in the overall paint structure and an extremely low VOC.
In the context of the invention the term “polyurethane” also includes “polyurethane polyureas”, i.e., high-molecular compounds containing urea groups in addition to urethane groups.
Suitable structural components i) include organic compounds containing at least two free hydroxyl groups, which are capable of reacting with isocyanate groups. Examples of such organic compounds include higher-molecular compounds from the classes of polyester, polyester amide, polycarbonate, polyacetal and polyether polyols with a number average molecular weight of at least 300, preferably 500 to 8000, particularly preferably 800 to 5000 daltons. Preferred compounds are, for example, those containing two hydroxyl groups (difunctionally), such as polyester diols or polycarbonate diols.
Examples of polyester polyols include linear polyester diols or weakly branched polyester polyols, prepared from aliphatic, cycloaliphatic or aromatic dicarboxylic or polycarboxylic acids or anhydrides thereof, such as succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, nonane dicarboxylic, decane dicarboxylic, terephthalic, isophthalic, o-phthalic, tetrahydrophthalic, hexahydrophthalic or trimellitic acid, and acid anhydrides, such as o-phthalic, trimellitic or succinic anhydride or a mixture thereof with polyhydric alcohols, such as, e.g., ethanediol, diethylene, triethylene, tetraethylene glycol, 1,2-propanediol, dipropylene, tripropylene, tetrapropylene glycol, 1,3-propanediol, butane-1,4-diol, butane-1,3-diol, butane-2,3-diol, pentane-1,5-diol, hexane-1,6-diol, 2,2-dimethyl-1,3-propanediol, 1,4-dihydroxycyclohexane, 1,4-dimethylol cyclohexane, octane-1,8-diol, decane-1,10-diol, dodecane-1,12-diol or mixtures thereof, optionally with the additional use of higher-functional polyols, such as trimethylol propane or glycerol. Examples of polyhydric alcohols for production of the polyester polyols also include cycloaliphatic and/or aromatic dihydroxyl and polyhydroxyl compounds. Instead of the free polycarboxylic acid the corresponding polycarboxylic anhydrides or corresponding polycarboxylic acid esters of low alcohols or mixtures thereof can also be used to produce the polyesters.
The polyester polyols can also be homopolymers or copolymers of lactones, which are preferably obtained by reacting lactones or lactone mixtures, such as butyrolactone, &egr;-caprolactone and/or methyl &egr;-caprolactone with suitable difunctional and/or higher functional initiator molecules, such as the low-molecular, polyhydric alcohols mentioned above.
Polycarbonates having hydroxyl groups are also suitable as polyhydroxyl components, and include those that can be produced by reacting diols such as 1,4-butanediol and/or 1,6-hexanediol with diaryl carbonates, e.g., diphenyl carbonate, dialkyl carbonate, such as dimethyl carbonate or phosgene, with a number-average molecular weight of 800 to 5000 daltons.
Preferred structural components i) are polyester diols based on adipic acid and glycols such as 1,4-butanediol, 1,6-hexanediol and/or 2,2-dimethyl-1,3-propanediol (neopentyl glycol). Likewise preferred are copolymers of 1,6-hexanediol with &egr;-caprolactane and diphenyl carbonate with a number-average molecular weight of 1000 to 4000 daltons, and 1,6-hexanediol polycarbonate diols with a number-aver
Klippert Uwe
Kobor Frank
Kobusch Claus
Kurek Gerald
Münzmay Thomas
Bayer Aktiengesellschaft
Gil Joseph C.
Gorr Rachel
Roy Thomas W.
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