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
2000-12-21
2003-04-22
Cain, Edward J. (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...
C524S501000, C524S507000, C524S589000
Reexamination Certificate
active
06552117
ABSTRACT:
The invention relates to an aqueous coating composition comprising an addition polymer and a polyurethane. Preferably, this aqueous coating composition also comprises a metallic pigment, such as aluminium, or a pigment, such as a metal oxide-coated mica, so that coatings with a metallic appearance may be obtained. In this way a differential light reflection effect referred to as “flop” is obtained. 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 well oriented and remain so. 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 softened by the organic solvents in the clear coat (“strike-in”).
An aqueous base coat composition is known from EP-A-0 287 144, i.e. a non-cross-linked core-shell dispersion where the shell, when swollen, provides the desired rheological properties. A decrease in strike-in is observed. However, it has been established that this coating composition needs improvement in respect of several coating properties, such as covering power and drying times.
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 which has good mechanical properties, a high flop, a high gloss, practically no strike-in, and a good water-resistance. Due to the fact that higher solids 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 the one disclosed in EP-A-0 287 144.
The aqueous coating composition according to the invention comprises 5 to 95 wt. % of at least one alkali-swellable core-shell addition polymer (I), and 95 to 5 wt. % of at least one polyurethane (II),
the sum of the wt. % indicated for the polymers (I) and (II) always being 100 wt. %.
DETAILED DESCRIPTION OF THE INVENTION
Preferably, the aqueous coating composition comprises
10 to 90 wt. % of at least one addition polymer (I), and
90 to 10 wt. % of at least one polyurethane (II).
More preferably, the aqueous coating composition comprises
25 to 75 wt. % of at least one addition polymer (I), and
75 to 25 wt. % of at least one polyurethane (II).
Preferably, the alkali-swellable core-shell addition polymer (I) is a copolymer prepared in two or more steps by emulsion polymerization, and is obtained by the copolymerization in a first step of
A) 60-95 parts by weight (based on 100 parts by weight of addition polymer) of a monomer mixture A consisting of
i) 65-100 mole % of a mixture of
a) 60-100 mole % of a (cyclo)alkyl (meth)acrylate of which the (cyclo)alkyl group contains 4-12 carbon atoms, and
b) 0-40 mole % of a di(cyclo)alkyl maleate and/or a di(cyclo)-alkyl fumarate of which the (cyclo)alkyl groups contain 4-12 carbon atoms,
the sum of the mole % indicated for the monomers (a) and (b) always being 100 mole %, and
ii) 0-35 mole % of another copolymerizable, monoalkylenically unsaturated monomer,
the sum of the mole % indicated for the monomers (i) and (ii) always being 100 mole %, and
by the copolymerization in a subsequent step of
B) 5-40 parts by weight (based on 100 parts by weight of addition polymer) of a monomer mixture B comprising
iii) 10-60 mole % of (meth)acrylic acid and
iv) 40-90 mole % of another copolymerizable, monoalkylenically unsaturated monomer,
the sum of the mole % indicated for the monomers (iii) and (iv) always being 100 mole %,
with the carboxylic acid groups derived from the (meth)acrylic acid being at least partially ionized;
resulting in a non-cross-linked, alkali-swellable core-shell addition polymer (I).
Such alkali-swellable core-shell addition polymers are known from EP-A-0 287 144.
Preferably, the addition polymer is obtained by the copolymerization of
80-90 parts by weight of monomer mixture A and
10-20 parts by weight of monomer mixture B.
Optionally, different monomer mixtures A and/or B may be used successively.
By emulsion polymerization is meant here the polymerization of an ethylenically unsaturated monomer in water in the presence of a water-soluble or water-insoluble initiator and using an emulsifier.
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. It is preferred that monomer mixture A should contain 70-95, more particularly 80-95, mole % of the aforementioned (cyclo)alkyl (meth)acrylate. Preferred monomers are butyl acrylate, butyl methacrylate, and mixtures thereof.
As examples of di(cyclo)alkyl maleates and/or fumarates with (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, monoalkylenically unsaturated monomers of which maximally 35, and preferably 5-20, mole % may 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, propyl methacrylate, and isopropyl acrylate; alkyl maleates and fumarates having fewer than 4 carbon atoms in the alkyl groups, such as dimethyl maleate, diethyl maleate, diethyl fumarate, and dipropyl maleate; (meth)acrylates having ether groups such as 2-methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, 3-methoxypropyl acrylate; hydroxy-alkyl (meth)acrylates, e.g., 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 the corresponding alkoxy derivatives thereof; epoxy (meth)acrylates, such as glycidyl acrylate and glycidyl methacrylate; monovinyl aromatic hydrocarbons, such as styrene, vinyl toluene, &agr;-methyl styrene, and vinyl naphthalene; also acrylamide and methacrylamide, acrylonitrile, methacrylonitrile, N-methylol acrylamide, and N-methylol methacrylamide; N-alkyl (meth)acrylamides, such as N-isopropyl acrylamide, N-isopropyl methacrylamide, N-t-butyl acrylamide, N-t-octyl acrylamide, N,N-dimethyl aminoethyl methacrylate, and N,N-diethyl aminoethyl methacrylate; monomers, such as vinyl chloride, vinyl acetate, vinyl pyrrolidone, and vinyl propionate, and monomers containing one or more urea or urethane groups, for instance the reaction product of 1 mole of isocyanatoethyl methacrylate and 1 mole of butylamine, 1 mole of benzylamine, 1 mole of butanol, 1 mole of 2-ethylhexanol, and 1 mole of methanol, respectively. Mixtures of these compounds may also be used. Preferred are alkyl (meth)acrylates, such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, and mixtures thereof, and hydroxyalkyl (meth)acrylates, such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, and mixtures thereof.
Since the addit
Broekroelofs Gertrude A.
Ernst Moos Jan Wilhelm
Van Diemen Johannes Hubertus
Akzo Nobel N.V.
Cain Edward J.
McGillycuddy Joan M.
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