Coating processes – Removable protective coating applied
Reexamination Certificate
2001-02-02
2002-02-05
Szekely, Peter (Department: 1714)
Coating processes
Removable protective coating applied
C427S155000, C427S156000, C427S388400, C428S442000, C428S463000, C428S520000, C428S522000
Reexamination Certificate
active
06344236
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an aqueous dispersion of a peelable coating composition which is intended to be used for temporary protection of articles and is effective in temporary storage of articles during distribution, where articles may be temporarily stored in the open air or exposed to the open air during distribution.
2. Description of the Related Art
In more and more cases, articles such as automobiles and other vehicles, machine parts, metallic household articles and other ferrous and non-ferrous articles, wooden articles, glass articles, rubber articles, and coated rubber articles (hereinafter collectively referred to as “articles”) reach the hands of consumers after being transported from the manufacturer and stored temporarily in the open air. In such cases, during the period before these articles are in hands of consumers (generally this period is 2-12 months in duration), the surfaces of these goods are prone to becoming scratched, stained, discolored, or contaminated due to, for example, deposits such as sandy dust, iron powder, salts, alkalis, acids, soot and smoke, dead bodies or body fluids of insects, and excrement of birds and insects; sunlight; and wind and rain. Moreover, the material may come to have marks due to physical forces.
These deposits, etc. must be removed as soon as possible, as they may reduce the value of goods. However, removal of deposits requires elaborate work, which is accompanied by additional costs.
Thus, in order to temporarily protect surfaces of an article from being damaged by the aforementioned deposits, sunlight, elements, or scratches, and to eliminate the elaborate work and accompanying costs, there have been proposed a number of strippable coating compositions which areapplied to surfaces of an article when the article is shipped, and which, after a predetermined period of custody is over, can be easily stripped off.
For example, two types of strippable coating compositions are used for outer panels of automobiles: one is a so-called oily wax type in which paraffin wax is dispersed in a petroleum-based solvent, and the other is a type in which a mixture of calcium carbonate powder in paraffin wax is dispersed in a petroleum-based solvent.
These strippable coating compositions call for use of a petroleum-based solvent for removal, and in addition, they may raise the fear of environmental problems such as air pollution. Compositions of a type in which an alkali-soluble resin is the primary component are also used, and these require an alkali detergent for removal, and therefore involve the problem of environmental pollution such as water contamination.
Acccordingly, in order to eliminate the aforementioned problems, there have been proposed emulsion-type coating compositions which form a coating film capable of being peeled off by hand after they have carried out their function of protection (see, for example, Japanese Patent Publication (kokoku) Nos. 50-39685 and 44-29583).
However, the above-described conventional coating compositions of the emulsion type have the following drawbacks.
1) The coating compositions disclosed in Japanese Patent Publication (kokoku) No. 50-39685 are made from a single starting material. Therefore, their peeling property is not satisfactory under environmental conditions in which they are usually used. For example, they cannot be satisfactorily peeled off in a wide temperature range from low temperatures around 5° C. to high temperatures around 40° C. at low temperatures the formed film breaks during the peeling operation, whereas at high temperatures it stretches and thus is not quickly peeled off.
2) Japanese Patent Publication No. 44-29593 discloses a coating composition obtained through emulsion polymerization in water of acrylonitrile and an acrylic acid ester of an lower alkyl.
Aqueous dispersions of an acrylic resin which contains acrylonitrile as an essential component raise a problem that harmful nitrogen oxides are produced during incineration of waste films that have been peeled and cause environmental pollution.
In the meantime, regarding peelable coating compositions for use with automobile outer panels, there exists need for compositions capable of forming a protective film that exerts contrasting functions simultaneously in terms of adhesion; i.e., proper adhesiveness and holding power that does not permit release of the film with ease during water-resistance tests or that never permits release during transportation of vehicles under protection by the film, and ease in peeling of the film with fingers after the period of protection by the film is over.
SUMMARY OF THE INVENTION
To solve the above-described problems and meet the above-stated need, the present inventors have carried out careful studies on dispersion compositions that do not contain a nitrogen-containing vinyl monomer, and have found that an aqueous dispersion of a peelable coating composition having excellent peelability can be obtained by forming an e emulsion having the following characteristics: 1) the emulsion is an acrylic copolymer emulsion which is a mixture of two acrylic copolymer emulsions, wherein the acrylic copolymers have different predetermined glass transition temperatures, 2) the amount of ethylenically unsaturated monomers having acid value contained in the mixture is not higher than a predetermined level, and 3) the emulsion does not make use of a nitrogen-containing monomer. The present invention has been accomplished based on this finding.
Moreover, the present inventors have found that, in addition to the above-mentioned features 1) through 3), when 4) polymerization is performed under conditions in which at least one of the emulsions contains a reactive surfactant and 5) the particle size of the emulsions is controlled to fall within a predetermined range, there can be obtained an aqueous dispersion of a peelable coating composition having further improved water resistance and excellent adhesiveness, leading to completion of the present invention.
Accordingly, a first aqueous dispersion of a peelable coating composition of the present invention is characterized by comprising
(a) a mixture containing 5-40% by weight of an emulsion of an acrylic copolymer having a glass transition temperature (hereinafter referred to as “Tg”) of not lower than 40° C., and 95-60% by weight of an emulsion of another acrylic copolymer having a Tg ranging from −20° C. through 5° C.; wherein
(b) the acrylic copolymer emulsion mixture (a) contains ethylenically unsaturated vinyl monomers having acid value in a total amount of less than 2.0% by weight; and
(c) the acrylic copolymer emulsion mixture (a) contains no nitrogen-containing vinyl monomers in the form of a monomer.
A second aqueous dispersion of a peelable coating composition of the present invention is characterized by, in addition to the aforementioned requirements (a), (b), and (c),
(d) at least one of the acrylic copolymer emulsions to be incorporated into the mixture is an acrylic copolymer which has been polymerized by use of a reactive surfactant, and
(e) the particle size of the acrylic copolymer emulsions is not more than 200 nm.
MODES FOR CARRYING OUT THE INVENTION
Next will be described modes for carrying out the present invention.
A first mode of the present invention is drawn to the first aqueous dispersion of a peelable coating composition characterized by an acrylic copolymer emulsion having the below-described features (a) through (c). Synergism of these features afford, as demonstrated in Examples hereinbelow, not only excellent physicochemical properties including water resistance, adhesive strength, protective power, and weatherability during the period of protection, but also excellent peelability in a wide temperature range from low temperatures (about 5° C.) to high temperatures (about 40° C.) after the protection period is over, and in addition, when the after-use waste film is incinerated, the film does not generate nitrogen oxides and thus eliminates adverse effects of enviro
Akasaka Kensaku
Asai Hirotaka
Kurota Hisashi
Matsuki Masayuki
Matsuyama Noritsumi
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