Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an improved process for the
preparation of paint compositions. ~lore particularly, the pres-
ent invention relates to an improved process for preparing a paint
composition composed of an emulsion containing polymer-coated
pigment particles in the dispersed state.
There have heretofore been known a process for preparing
a polymer composition comprising a pigment such as filler pigments,
inorganic pigments, metal pigments and carbon black by utilizing a
Friedel-Crafts catalyst (see Japanese Patent Publication No.
6985/62 to Continental Oil Company) and a process for preparing an
emulsion by polymerizing a vinyl monomer in water in which a white
inorganic pigment incorporated with an organic chelating agent is
dispersed (see ~apanese Patent Publication No. 14584t~6 to
Kobunshi-Kagaku Kogyo Kabushiki l~aisha).
However, since in each of these compositions comprising
a pigment and a polymer, which are prepared according to these
known processes, the pigment and polymer are in the merely mixed
state, such undesired phenomena as heterogeneous dispersion of the
pigment and non-uniformity of the particle size cannot be avoided.
20 Accordingly, when these compositions are used as paints, such un-
desired defec~s as uneven color concentration and for~ation of
pigment specks are brought about.
It is the object of this invention to provide a paint
composition which overcomes the above defects and provides homo-
geneous pigment particles in a uniformty dispersed state.
In accordance with this invention, the above object
is achieved by contacting a finely divided pigment other than
elemental carbon-containing material with a radical-polymerizable
vinyl monomer in an aqueous or alcoholic medium containing bi-
30 sulfite ions (also called acid sulfite ions) in the absence of r
additional polymerization initiators. The pigment particles
themselves in combination with the bisulfite ions act as a
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polymerization initiator, and, the polymerization will proceed
at room or slightly elevated temperatures. If desired, a
polymer can be incorporated into the aqueous or alcoholic medium
prior to the polymerization of the vinyl monomer, e.g. polyvinyl
alcohol.
~ By the term "radical~polymerizable vinyl monomer" used
in the instant specification and claims is meant a compound that
can be vinyl-polymerized in the presence of a radical polymerization
initiator to form a polymer.
The polymer-coated pigment obtained according to this t
invention can be clearly distinguished from polymer-pigment
compositions prepared by conventional processes due to the fact
that the polymer is tightly bonded to the pigment surface and
hence, the polymer-coated pigment can provide a very stable .
coating film. Further, in case a polymer is incorporated into
the polymerization medium in advance, the resulting polymer-
coated pigment is well fused with the polymer to form a homogeneous
composition.
As the pigment, a regular commercial grade is normally '
used and it is preferable to use inorganic pigments such as
chrome yellow, zinc yellow, barium yellow, white lead, prussian
blue, barium sulfate, lead sulfate, zinc flower, titanium white,
red iron oxide, chromium oxide and ultramarine. Metal-containing
organic pigments can also be employed.
Any of monomers that can be vinyl-polymerized in the
presence of a radical polymerization initiator can be used as
the vinyl monomer in this invention. As the vinyl monomer
there can be mentioned, for example, unsaturated carboxylic
acids such as acrylic acid and methacrylic acid, salts and ;
esters of these unsaturated carboxylic acids, unsaturated nitriles
such as acrylonitrile and methacrylonitriles, halogenated olefins
.
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such as vinyl chloride and vinylidene chloride, aliphatic vinyl
estess such as vinyl acetate and vinyl propionate, snd aromatic
vinyl compounds such as styrene and divinyl benzene. These
monomers are usually employed in amounts of 2 to 200 parts by
weight per 100 parts by weight of the pigment, but these amounts
can be increased depending on the intended use of the resulting
composition.
As the reaction medium, water, alcohols such as methanol
ar mixtures thereof can be used in the present invention. The
presence of acid sulfite ions (HS03 ~ in the reaction medium
is indispensable in this invention. This can be provided by
addltion of sulfur dioxide, an aqueous solution of sulfurous
acid, an acid sulfite such as ammonium acid sulfite or a combin-
ation of a su~fite and a mineral acid. The amount of acid sulfite
ions is chosen within a range of 0.01 to 100 parts by weight,
preferably 0.1 to 10 parts by weight, as calculated as sulfur
dioxide per 100 parts by weight of the mono~er.
The paint composition obtained according to this invention
can be used in the as-prepared emulsion state or various additives
can be incorporated in the composition according to need. More-
over, it is possible to separate only solid particles from the
product and utilize same for powder painting, electros~atic
painting and baking painting.
A coating film formed from the paint composition of this
invention is excellent in strength and fixing properties and
has excellent quality without uneven color concentration or pig-
ment specks.
~ This invention will now be illustrated in more detail
by reference to the following ~xamples.
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Example 1
A 300-ml volume, three-neck flask equipped with a - -
stirrer was charged with 20 g of titanium white, 100 g of a
5 % aqueous solution of polyvinyl alcohol and 50 g of methyl ` `~
acrylate and 0.5 g of a non-ionic surfactant was added to the
mixture under agitation. Then 5 ml of a 1.0 N aqueous solution
of sulfurous acid was added to the mixture and emulsion polymeri-
-æation was carried out at 60G.for 8 hours.
The so-obtained emulsion was coated as a paint on an
aluminum plate to form a coating film having a film strength of
2.5 Kg/mm . The resulting film had good adhesion to the metal
and good water resistance.
When the above procedures were repeated by employing
potassium persulfate and hydrogen peroxide instead of the aqueous ~ '
solution of sulfurous acid, the resulting emulsion gave a film
having a strength of 2.0 Kg/mm .
When the above emulsion obtained with use of the aqueous
solution of sulfurous acid was filtered and the recovered solid
was extracted with benzene for 24 hours, the polymer on the sur-
face of the titanium white was not extracted whatsoever.
The so-recovered solid was incorporated into an acrylic ,~;
lacquer of the cellulose acetate butyrate type and the resulting
composition was coated on a metal surface by spray coating.ACating
film containing tightly bonded pigment particles could be obtained.
Example2
An autoclave equipped with a stirrer was charged with
5.0 Kg of red iron oxide powder, 2.5 l~g of vinyl chloride, 20 liters
of water and 2 Kg of a 1~ aqueous solution of sulfurous acid
and these were reacted at 50C. for 8 hours. The resulting reaction
mixture was withdrawn from the autoclave and the unreacted
monomer was removed by washing. The resulting slurry was filtered
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and the residue was washed wlth water and vacuum-dried at 100 C.
to obtain 6.72 Kg of a solid having a polymer content of 25.6 %.
The so-obtained solid was freeze-pulverized to a size
of about 100 mesh and the pulverized solid was projected onto a
vinyl butyral-treated slate plate by a Elame spray gun at a powder
projection rate of 5 Kg/hr under a compressed air pressure of
3 Kg/cm and a fuel gas pressure of 0.8 Kg/c~ . Then, the slate
plate was post-treated at 200 C.for 10 minutes to obtain a water-
resistant film in which the red iron oxide powder was uniformly
1~ dispersed.
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