Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
1999-11-10
2001-11-20
Yoon, Tae H. (Department: 1714)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S407100, C428S461000, C428S463000
Reexamination Certificate
active
06319557
ABSTRACT:
The present invention relates to a coating composition capable of forming a coating film which is not softened even at high temperatures of 60° C. or higher, which has excellent stain resistance, and which allows easy removal of the staining substances adhering thereto; as well as to a method for applying the coating composition.
As the top coat (clear coat, in particular) for automobile body panel, there are generally used organic solvent type coatings containing, as main components, a hydroxyl group-containing acrylic resin and a melamine resin. The coating film of such a coating is superior in weatherability, finish appearance, etc. but has a problem of insufficiency in acid rain resistance which has become an important item recently As a top coat improved in acid rain resistance, there was proposed an organic solvent type coating which contains no melamine resin and which contains, as main components, a carboxyl group-containing resin and an epoxy group-containing resin (the coating is generally called a carboxylic-epoxy type coating). The cured film of the carboxylic-epoxy type coating is superior in weatherability and finish appearance and good in acid resistance but has a problem of low stain resistance and difficulty in complete removal of staining substances adhering thereto.
The top coat film of automobile body panel undergoes adhesion, infiltration and sticking of staining substances (e.g. bird droppings, pollen and dead insects), iron dust, sand and dirt and particles in exhaust gas (e.g. carbon and paraffin) and thereby is stained easily. For example, the bird droppings on the film shrink when dried and solidified; consequently, the film surface causes shrinkage as well; the shrunk film portion is deteriorated in appearance (e.g. luster and distinctness of image gloss). Or, when pollen, dead insects, etc. on the film are wetted with rain, the proteins and amino acids contained therein dissolve in the rain and further infiltrate into the film, which may become a stain source. Further, iron dust, sand and dirt, particles in exhaust gas, etc. adhere to or stick in the film and become a stain source.
Meanwhile, the body panel of automobile, when allowed to stand outdoors, reaches even 60° C. or higher in some cases owing to the solar heat. At such high temperatures, the top coat film of body panel is softened and the above-mentioned staining easily proceeds further.
Such stains of top coat film are difficult to remove by simple wiping or use of detergent or wax, impairing the fine appearance of the film.
The main objects of the present invention are to develop a novel organic solvent type coating capable of forming a film which, as compared with the cured films formed from conventional organic solvent type coatings used as a top coat for automobile (e.g. an organic solvent type coating containing, as main components, a hydroxyl group-containing acrylic resin and a melamine resin, or a carboxylic-epoxy type coating), is at least equivalent in weatherability, finish appearance, acid resistance, etc. and good in stain resistance; and a method for applying the above coating.
The present inventors made a study in order to achieve the above objects. As a result, the present inventors found out that a cured coating film having a TUKON hardness at 20° C. of 15 or more and the minimum value of dynamic modulus E′ at a frequency of 110 Hz in the temperature range of 150-200° C., of 1×10
9
dyn/cm
2
or more is not softened even at high temperatures of 60° C. or higher, undergoes no infiltration or sticking of staining substances, allows easy removal of staining substances adhering thereto, has very high stain resistance, and is superior in weatherability, finish appearance, acid resistance, etc. The present invention has been completed based on the above finding.
According to the present invention there is provided a thermosetting organic solvent type coating capable of forming a cured coating film having a TUKON hardness at 20° C. of 15 or more and the minimum value of dynamic modulus E′ at a frequency of 110 Hz in the temperature range of 150-200° C., of 1×10
9
dyn/cm
2
or more.
The coating of the present invention is hereinafter described in detail.
The coating of the present invention is characterized in that by employing a special composition, the coating is capable of forming a cured film having a TUKON hardness of particular value at 20° C. and a dynamic modulus E′ of particular value at a frequency of 110 Hz.
The cured fi Im formed from the present coating is hard and has a TUKON hardness at 20° C. of 15 or more, preferably 17-25 and the minimum value of dynamic modulus E′ at a frequency of 110 Hz in the temperature range of 150-200° C., of 1×10
9
dyn/cm
2
or more, preferably 1.1×10
9
to 8×10
9
dyn/cm
2
, more preferably 1.2×10
9
to 5×10
9
dyn/cm
2
.
In the present specification, “TUKON hardness at 20° C.” of cured film is a value obtained when a coating is applied on a glass plate so as to give a film having a thickness of 30 &mgr;m as cured, the resulting film is heat-cured under given conditions (e.g. 140° C. and 30 minutes), and the resulting cured film is measured for hardness using a TUKON microhardness tester manufactured by American Chain & Cable Company. The larger the value, the harder is the cured film. The cured films formed from conventional thermosetting coatings, usually have TUKON hardnesses of 5-10. The present coating is capable of forming a cured film far harder than the above cured films, and the present coating has one big feature in this point.
“Dynamic modulus E′ at a frequency of 110 Hz” of cured film is a value obtained when a coating is applied on a tinplate sheet so as to give a film having a thickness of 45 &mgr;m as cured, the resulting film is heat-cured at 140° C. for 30 minutes, and the resulting cured film is peeled and measured for dynamic modulus E′ at a frequency of 110 Hz using an automatic dynamic viscoelastometer, RHEOVIBRON DDV-II-EA (a product of TOYO BALDWIN CO., LTD.). The dynamic modulus E′ is measured at 150-200° C. and its minimum value in this temperature range is determined.
The coating of the present invention has no particular restriction as to the composition as long as it can form a cured film having the above particular values. The present coating is preferred to be, in particular, a thermosetting organic solvent type coating which comprises:
(A) a compound containing at least 2 alicyclic epoxy groups in the molecule and having a number-average molecular weight of smaller than 2,000,
(B) an epoxy group-containing acrylic resin having a number-average molecular weight of 2,000-50,000, a hydroxyl value of 10-150 mg KOH/g and an epoxy equivalent of 220 or less, and
(C) a thermoinitiated cationic polymerization catalyst, wherein the molar ratio of the epoxy groups of the component (A) and the epoxy groups of the component (B) is 1:1 to 1:0.05.
Specific description is made below on this preferable coating.
Component (A) Compound containing at least 2 alicyclic epoxy groups in the molecule-and having a number-average molecular weight of smaller than 2,000
Herein, “alicyclic epoxy group” is a three-membered oxirane ring formed by two adjacent carbon atoms constituting the ring of an alicyclic hydrocarbon and one oxygen atom. The above alicyclic hydrocarbon can have usually 3-12, preferably 5-6 cyclic carbon atoms.
The component (A) is a compound containing, in the molecule, 2 or more, preferably 2 or 3 such alicyclic epoxy groups and having a number-average molecular weight of smaller than 2,000, preferably 100-1,500, more preferably 130-1,000. The component (A) preferably has epoxy equivalents of generally 50-500, particularly 100-300.
As the component, there can be mentioned, for example, dicyclopentadiene dioxide, bis((2,3-epoxycyclopentyl) ether, ethylene glycol bis(epoxycyclohexenecarboxylate), bis(3,4-epoxycyclohexylmethyl) adipate, bis(4,5-epoxy-2-methylcyclohexylmethyl) adipate, ethylene glycol bis(3,4-epoxycyclohexanecarbox
Aida Haruhiko
Hasada Ken-ichi
Ikushima Satoshi
Okumura Yasumasa
Wada Seiji
Kansai Paint Co. Ltd.
Wenderoth , Lind & Ponack, L.L.P.
Yoon Tae H.
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