Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-12-21
2002-04-23
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S501000, C524S501000, C524S522000, C524S523000, C525S066000, C525S078000, C525S079000, C525S902000
Reexamination Certificate
active
06376575
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an aqueous coating composition based on a mixture of a dispersion of an addition polymer and a rheology modifier. Preferably, this aqueous coating composition is mixed with a metallic pigment, such as aluminum, or a pigment, such as a metal oxide-coated mica, so that coatings with a metallic appearance may be obtained. In this way there is obtained a differential light reflection effect referred to as “flop”. A problem with coating systems having a metallic appearance is to obtain a high flop as well as a high gloss.
BACKGROUND OF THE INVENTION
To obtain a high flop, the metallic pigment on application of the coating composition should be and remain well oriented. To obtain a high gloss, the metallic pigment-containing coating is provided with an unpigmented, so-called clear coat. This system is generally called a “base coat/clear coat” system. In actual practice, the base coat will be sprayed with the clear coat, without prior curing of the base coat (“wet-on-wet”). Since the clear coat usually contains organic solvents, steps should be taken to prevent disorientation of the metallic pigment in the base coat as a result of the base coat being weakened up by the organic solvents in the clear coat (“strike-in”).
An aqueous base coat composition is known from EP-A-0 038 127, i.e., a crosslinked core-shell dispersion whereby the shell, when swollen, provides the desired rheological properties. The crosslinking reduces the strike-in. A disadvantage to this system, however, is that the coating composition will have poor film-forming properties, which may manifest itself in poor mechanical properties.
Another aqueous base coat composition is known from EP-A-0 287 144, i.e., a swellable non-crosslinked core-shell dispersion having an amount of (meth)acrylic acid in the shell of 10-60 mole %. Exemplified are swellable non-crosslinked core-shell dispersions having more than 2 wt. % (meth)acrylic acid in 100 parts of the addition polymer. Also in this embodiment a decrease in strike-in is observed.
Both systems disclosed in EP-A-0 038 127 and EP-A-0 287 144 contain in the shell a lot of carboxylic groups, neutralized by an amine to provide the desired rheological properties. However, because of this large amount of salt groups, coatings based on these compositions especially when applied and cured at ambient temperature, show a poor water-resistance.
SUMMARY OF THE INVENTION
The present invention now provides an aqueous coating composition which may be used as base coat in a base coat/clear coat system, having good mechanical properties, a high flop, a high gloss, practically no strike-in, and a good water-resistance. Due to the fact that higher solid contents can be achieved with the aqueous coating composition of the present invention, a reduction in drying times and number of coats is obtained. In one or more of these properties the aqueous coating composition of the present invention shows improvement over those disclosed in EP-A-0 038 127 and EP-A-0 287 144.
The aqueous coating composition according to the invention comprises a mixture of
90 to 99 wt. % of a filmforming binder composition comprising an alkali non-swellable core-shell addition polymer dispersion (I), and
1-10 wt. % of a rheology modifying addition polymer dispersion (II),
the sum of the wt. % indicated for the filmforming binder composition and dispersion (II) always being 100 wt. %,
wherein
the polymer dispersion (I) is prepared in two or more steps by emulsion polymerization, and obtained by copolymerization in a first step of
(1) 60-95 parts by weight (calculated on 100 parts by weight of the total addition polymer (I)) of a monomer mixture A consisting of
(i) 65-100 mole % of a mixture of
(a) 10-98 mole % of a (cyclo)alkyl (meth)acrylate of which the (cyclo)alkyl group contains 4-12 carbon atoms,
(b) 0-55 mole % styrene,
(c) 2-15 mole % hydroxy alkyl (meth)acrylate, and
(d) 0-20 mole % of a di(cyclo)alkyl maleate and/or fumarate of which the (cyclo)alkyl groups contain 4-12 carbon atoms,
the sum of the mole % indicated for the monomers (a), (b), (c), and (d) always being 100 mole %, and
(ii) 0-35 mole % of a different copolymerizable monoethylenically unsaturated monomer,
the sum of the mole % indicated for the components (i) and (ii) always being 100 mole %,
and by copolymerization in a subsequent step of
(2) 5-40 parts by weight (calculated on 100 parts by weight of the total addition polymer (I)) of a monomer mixture B consisting of
(e) 1-10 mole % (meth)acrylic acid,
(f) 2-20 mole % hydroxy alkyl (meth)acrylate,
(g) 0-55 mole % styrene, and
(h) 15-97 mole % of a different copolymerizable monoethylenically unsaturated monomer,
the sum of the mole % indicated for the monomers (e), (f), (g), and (h) always being 100 mole %,
with the carboxylic acid groups derived from the (meth)acrylic acid being at least partially neutralized,
resulting in a non-crosslinked addition polymer I,
whereby the total amount of (meth)acrylic acid in 100 parts of the total addition polymer (I) is less than 1.75 wt. %, and
wherein
the polymer dispersion (II) is prepared by emulsion polymerization, and obtained by copolymerization of
(iii) 99.5-99.99 parts by weight (calculated on 100 parts by weight of the total addition polymer (II)) of a monomer mixture C consisting of
(j) 10-80 wt. % (cyclo)alkyl (meth)acrylate,
(k) 20-50 wt. % (meth)acrylic acid,
(m) 0-20 wt. % hydroxyalkyl (meth)acrylate, and
(n) 0-20 wt. % of a different copolymerizable monoethylenically unsaturated monomer,
the sum of the wt. % indicated for the monomers (j), (k), (m), and (n) always being 100 wt. %, and
(iv) 0.01-0.5 parts by weight (calculated on 100 parts by weight of the total addition polymer (II)) of a compound having at least two unsaturated groups,
with the carboxylic acid groups derived from the (meth)acrylic acid being at least partially neutralized.
DETAILED DESCRIPTION OF THE INVENTION
Preferably, in the first step of the preparation of the polymer dispersion (I), a monomer mixture A is used, consisting of
(i) 80-100 mole %, more preferred 100 mole %, of a mixture of
(a) 30-95 mole % of a (cyclo)alkyl (meth)acrylate of which the (cyclo)alkyl group contains 4-12 carbon atoms,
(b) 0-50 mole % styrene,
(c) 5-12 mole % hydroxy alkyl (meth)acrylate, and
(d) 0-8 mole % of a di(cyclo)alkyl maleate and/or fumarate of which the (cyclo)alkyl groups contain 4-12 carbon atoms, and
(ii) 0-20 mole %, more preferred 0 mole %, of a different copolymerizable monoethylenically unsaturated monomer.
As examples of (cyclo)alkyl (meth)acrylates suitable for use in monomer mixture A and having a (cyclo)alkyl group with 4-12 carbon atoms may be mentioned: butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, octyl acrylate, octyl methacrylate, isobornyl acrylate, isobornyl methacrylate, dodecyl acrylate, dodecyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, and mixtures thereof. Butyl acrylate, butyl methacrylate, and mixtures thereof are preferred.
Examples of hydroxyalkyl (meth)acrylates are 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 6-hydroxyhexyl acrylate, p-hydroxycyclohexyl acrylate, p-hydroxycyclohexyl methacrylate, hydroxypolyethylene glycol (meth)acrylates, hydroxypolypropylene glycol (meth)acrylates, and mixtures thereof. 2-Hydroxyethyl methacrylate is preferred.
As examples of di(cyclo)alkyl maleates and/or fumarates with the (cyclo)alkyl groups having 4-12 carbon atoms suitable for use in monomer mixture A may be mentioned dibutyl maleate, dibutyl fumarate, 2-ethylhexyl maleate, 2-ethylhexyl fumarate, octyl maleate, isobornyl maleate, dodecyl maleate, cyclohexyl maleate, and mixtures thereof.
As suitable copolymerizable monoethylenically unsaturated monomers to be used in monomer mixture A may be mentioned: alkyl (meth)acrylates having fewer than 4 carbon atoms in the alkyl group, such as methyl methacrylate, methyl acrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate,
Buter Roelof
Roelofs Andreas Henricus J.
Akzo Nobel N.V.
Egwim Kelechi
McGillycuddy Joan M.
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