Note: Descriptions are shown in the official language in which they were submitted.
~09~6~
The present invention relate3 to a proce~s for form-
ing a protective coating on the surface of galvanized steel
wire.
When a zinc or zinc alloy ~urface is coated with an
aqueous solution or dispersion of a water-soluble or water-dis-
persible organic polymer resin, there will normally be for~ed
on the surface thereof oxides of zinc or zinc soaps which re-
sult, for example, from the reaction of zinc with carboxyl ra-
dicals in the resin or in the surface active agent used for
dispersing and stabilizing the resin, pigments or other bath
components. The adhesion of the resulting coating i~ very
poor. It has thus been necessary when treating galvanized
steel wire with an aqueous solution or dispersion containing
a water-soluble or water-dispersible organic polymer resin to
first treat the wire by a process of chemical conversion (e.g.,
chromic acid or zinc phosphate process).
~; When a metal surface i8 coated with an aqueouq solu-
tion or dispersion of a water-soluble or dispersible organic
polymer resin, the coating cannot be dried easily due to the
higher latent heat of vaporization and higher boiling point
of water as compared to conventional coating in organic ~ol-
vents such as thinner, toluene, xylene, etc. Further, when
applied on a material having a circular cro~s section such
as wire, aqueous coatings tend to have the disadvantage of
forming pools of the coating at the lower part of the coated
articles.
It has now been found that a protective coating
having good corrosion re~istance, adhesion and drying pro-
perties may be obtained from an aqueous solution or disper-
sion of a water-soluble or water dispersible film-forming
organic polymer resin without pretreatment by a chemical con-
version process by including tannin or tannic acid (tannin ~ -
,,
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material) in an amount ranging from 0.1 to 20% hy weight,
preferably from 1 to 5% by weight in the treating solution
or dispersion.
The water-soluble or dispersible organic polymer
resins useful in this invention include substantially all
type~ of conventionally available film-forming organic resins,
Thus one or more aqueous solutions and/or emulsions and/or
suspensions may be usable in this invention which contain one
or more water-soluble, emulsifiable or dispersible organic
resins such as, for example, vinylic polymers and copolymers
of vinyl acetate, vinyl chloride, and vinylidene chloride, -
polymers and copolymers of acrylic acid, methacrylic acid,
acrylic acid esters, methacrylic acid esters, hydroxyacrylic
acid, and hydroxymethacrylic acid, alkyd-, epoxy-, fluorine-
containing,urethane, polyester, styrene, and olefinic poly-
mers and copolymers, ~ynthetic rubber such as butadiene
rubber, and naturally occurring organic polymers. For colora-
tion, inorganic pigments such as titanium dioxide, carbon,
aluminum paste, iron oxides, molybdic acid yellow, zinc dust,
and organic dyes or pigments such as Phthalocyanine Blue,
Phthalocyanine Green, Benzidine Yellow and Naphthol Yellow,
may be included in the composition.
The concentration in the treating solution of the
polymer employed will normally be less than 40 wt. % solids
and typically between 5 and 30 wt. %.
In o~der to improve the film forming property of
the water-soluble or dispersible organic polymer resin, the
aqueous solutions or dispersions according to thi~ invention
may include, for example, a pla~ticizer such as a phthalate
ester, aliphatic dibasic acid ester, glycol ester, fatty acid
ester, phosphoric acid ester, epoxy plasticizer, trioctyl
,' "' , ~ ~ .". ,' ' '~'. ', ' ,,.' .' .'''' " ' .
109Z264
trimellitate, butylphthalyl butyl glycolate, tributyl acetyl
citrate, chlorinated paraffin, polypropylene adipate, poly-
propylene sebacate or the like and a high boiling solvent
selected from ketones, esters and glycols such as cellosolve
or butyl glycol. In addition, the aqueous solutions or dis-
persion may include, if required, surfactants such as a dis-
persing agent, wetting agent, antifungal agent, defoaming agent
or the like.
Tannins or tannic acids useful in thiq invention may
be hydrolyzable or condensed tannins or partially decomposed
products thereof and include, for example, dep~ide tannin,
gallotannin, Chinese tannic acid, Turkey tannic acid, hamameli-
tannic acid, tannic acid from Acer Ginnala, chebulinic acid,
sumac, Chinese gallotannin, ellagitannin, catechin, quebracho
and the like. m e aqueous solution or dispersion of this in-
vention may be prepared conventionally, for example, by dis-
solving tannin or tannic acid in water, adding the resulting
tannic solution to an aqueous solution or dispersion of a
water-soluble or dispersible organic polymer resin and agitat-
ing the mixture. The concentration of tannin or tannic aciddepends on the types of tannin but ranges generally from 0.1
to 20% by weight.
At a concentration of lower than 0.1% by weight of
tannin or tannic acid, the adhesion property of the coating
can be improved but the effect for improving the drying pro-
perty of coating is poor. At a concentration of higher
than 20% by weight, the coating composition is unfavorable
because of poor opera~ility and economics.
In order to improve the adhesion of the protective
coating and to stabilize the treating medium containing
tannin, when the pH of the medium is adjusted, there may be
added an inorganic acid ~uch as phosphoric acid, sulfuric
. . . . . ..
.
109Z264
acid, nitric acid, hydrofluoric acid, or the like, or a salt
thereof, or an organic acid such as oxalic acid, citric acid,
malic acid, maleic acid, phthalic acid, acetic acid, lactic
acid, tartaric acid, chloroacetic acid, acrylic acid or the
like or a salt thereof, or an alkaline compound such as ~odium
hydroxide, potassium hydroxide, lithium hydroxide or the like,
or an amine such as ammonia, ethyl amine, kiethyl amine, tri-
ethyl amine, ethanol amine or the like.
The pH value of the treating liquid according to
this invention depends on the applying procedures and types of
tannin or tannic acid, resin, pigments and the like, but ran-
ges generally from 2.5 to 9.5, preferably from 3.5 to 7Ø
The treating liquid of this invention may be applied
onto the zinc or zinc alloy surface by immersion, roll coating,
flooding, spraying, electrostatic coating, brushing or the
like.
The present invention will be now illustrated by
way of the following examples.
EXAMPLE 1
60 parts of Chinese gallotannin (available from
Fuji Chemical Industries Co., Ltd. under the name of Tannic
Acid AL) was dissolved in 440 parts of deionized water.
Separately, 500 parts of acrylic acid ester emulsion (concen-
tration of solid resin: 40% by weight, available from Toyo
Ink Co. Ltd. under the trademark Tocryl N-142) was combined
with 100 parts of Phtalocyanine Blue pigment lnonvolatile
matter: 37%, available from Toyo Ink Co. Ltd. under the name
of E.M. Blue 2G) and mixed thoroughly to prepare a homoge-
neous dispersion. m e dispersion was mixed with the previous-
ly prepared tannin solution and the mixture was di~persed
homogeneously by means of a propéller agitator. When diluted
1092Z64
with deionized water of pH 6.5 to a dilution of 10 time~, it
had a pH of 3.5. Commercially available hot galvanized steel
wire was polished by means of steel wool and then pas~ed
through cotton cloth impregnated with the treating liquid to
be coated therewith. After drying one minute at room
temperature in a horizontal position, the coating could not be
manually peeled off and was of uniform thicknes~ and color
and exhibited no evidence of dense pooling of the treating
chemicals on the bottom horizontal surface.
On the contrary, when identical galvanized steel
wire was coated with a similar solution to the above-mentioned
liquid but containing no Chinese gallotannin, the resulting
coating was still wet one minute after the application and wa~
of non-uniform thickness and coloration.
EXAMPLE 2
60 parts of the above Chinese gallotannin was dis-
solved in 440 parts of deionized water and the pH of the re-
sulting solution was adjusted to 7.0 by adding 28% aqueous
ammonia. The pH-adjusted solution was then combined with 450 -
parts of a water-soluble polyolefin resin (non-volatile mat-
ter: 25%, available from Seitetsu Chemicals Co. Ltd. under
the trade mark of Zaikthene-A) and 50 parts of carbon black
(non-volatile matter: 40%, available from Toyo Ink Co. Ltd. --
under the trade mark of EM Black-K) and dispersed homogeneously
to prepare the treating liquid. m e resin is a water ~oluble
copolymer containing 9 moles of ethylene per mole of acrylic
acid, has a molecular weight range of 100,000-150,000, and a ~-
25% aqueous solution has a vi~co~ity of 50-100 cps.
When diluted with deionized water having a pH of
6.5 to a dilution of 10 times, it had a pH of 7.3. Commer-
cially available hot galvanized steel wire having a diameter
lU5~ZZ6~
of 2.0 mm was polished by means of steel wool and then immer~-
ed in~o the preparation at room temperature (20 - 25C). The
treated wire was blown with hot air at about 80 to 120C to
remove the excess preparation and dry the surface. When the
colored galvanized steel was wound around a pipe having a
diameter of lO mm, no peeling of the coating was observed.
On the contrary, when identical galvanized steel
wire was treated with a similar treating liquid but containing
no tannin, the coating was peeled off during drying and when
the coated wire was wound around a pipe having a diameter of
10 mm, 50% of the colored coating was peeled off.
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