Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2000-12-22
2004-03-16
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of metal
C428S327000, C428S421000, C428S500000, C106S002000, C106S014410, C427S541000, C427S544000
Reexamination Certificate
active
06706411
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a coating composition for use in lubrication of steel materials which are to be shaped by press-forming, including steel sheets (such as pickled hot-rolled steel sheets, cold-rolled steel sheets, plated steel sheets, and stainless steel sheets) and steel pipes. The present invention also pertains to lubricated steel materials having a lubricating film formed from the coating composition and exhibiting improved rust prevention, particularly when they are kept in stacked or coiled conditions.
A lubricating oil has traditionally been applied in-situ to steel materials such as steel sheets and pipes before they are subjected to press-forming. However, in view of environmental problems occurring during application of a lubricating oil, lubricated steel materials which have a previously-formed organic lubricating film on steel surfaces have recently been used widely in place of in-situ application of a lubricating oil prior to press-forming. The organic lubricating film may be formed on the surface of the steel materials either immediately after the production of the steel materials or at an appropriate subsequent stage prior to press-forming.
A coating composition which has conventionally been used to form the organic lubricating film in the production of lubricated steel materials is normally based oil a drying-type or baking-type film-forming component such as an acrylic resin, epoxy resin, melamine resin, phenolic resin, or urethane resin and it contains one or more lubricants such as fatty acids, fatty acid esters, fatty acid soaps, metallic soaps, alcohols, polyethylene fine powder, graphite, molybdenum disulfide, and fluoroplastic fine powder. See, for example, Unexamined Published Japanese Patent Application No. S60-250099 (1985).
In practical use, it is desired that a coating composition for use in the production of lubricated steel materials form a film having the following various properties required at different stages:
a) lubricity at the press-forming stage;
b) rust prevention so that the film can protect the steel material from rusting throughout the stages after the production of the lubricated steel materials (after formation of the film) and before the removal of the film performed subsequent to press-forming (namely temporary rust prevention rather than permanent rust prevention);
c) film removability so that the film can be removed by degreasing with an alkaline cleaning solution subsequent to press-forming; and
d) blocking resistance so that the film can well withstand blocking, i.e., a sticking phenomenon of contacting films, when lubricated steel materials are kept in stacked or coiled conditions.
As a coating composition which is alleged to be able to form an organic lubricating film having these requirements, Unexamined Published Japanese Patent Application No. H01-207397 (1989) discloses a composition comprising a carboxyl-containing organic polymer, polyethylene glycol, and a water-soluble anticorrosive (anti-rust) agent such as a hydroxybenzotriazole, imidazole, or amino acid. However, the presence of polyethylene glycol in the resulting lubricating film tends to cause the film to be swollen by condensed moisture when kept in a moist atmosphere, thereby leading to blocking.
Regarding a rust-preventive coating composition for use in the production of lubricated steel materials, Unexamined Published Japanese Patent Application No. H09-296132 (1997) discloses a composition comprising a rust-preventive lubricant selected from zinc, calcium, and aluminum salts of phosphoric or molybdic acid. U.S. Pat. No. 4,826,902 discloses a composition comprising a mixture of a sulfonamide-carboxylic acid and a cyclic amine as an anticorrosive agent. Unexamined Published Japanese Patent Application No. H10-1690 (1998) discloses a composition comprising an alkylenesulfonamide-carboxylic acid as an anticorrosive agent.
These coating compositions are primarily intended for improving lubricity during press-forming, and still have some problems with respect to rust prevention. For example, when lubricated steel materials produced by coating with such a composition are stored in stacked or coiled conditions in a corrosive environment, e.g., in a yard in a seaside area or along a heavily traveled road, or shipped on the ocean in the form of a coil of steel sheet, they may undergo rusting. This rusting of lubricated steel materials is particularly prominent when they are kept in stacked or coiled conditions during storage or shipping.
SUMMARY OF THE INVENTION
Thus, there is a need for a coating composition capable of forming on steel materials a lubricating film which is satisfactory with respect to all of press-formability, film removability, blocking resistance, and rust prevention.
It is an object of the present invention to provide a coating composition for use in the production of lubricated steel materials which is capable of forming a lubricating film having satisfactory press-formability, film removability, and blocking resistance and exhibiting good rust prevention even when lubricated steel materials having the coating thereon are kept in stacked or coiled conditions in a corrosive environment.
The present inventors investigated the mechanism of rusting on lubricated steel materials which takes place when the materials are kept in stacked or coiled conditions without application of oil. As a result, it was elucidated that the main mechanism of the rusting begins with condensation of water vapor contained in the atmosphere, the condensation occurring within the interstices formed between adjacent stacked or coiled lubricated steel materials. The lubricating film is injured by the action of the condensed water under a load of the stacked or coiled steel materials and the steel rusting process is accelerated by the action of an electrochemical cell created by the presence of water in the interstices, thereby leading to the formation of rust on the lubricated steel surface.
It has been found that a coating composition based on a particular acrylic resin and containing a particular water repellant and anticorrosive agent can form an organic lubricating film which is effective in preventing the formation of rust caused by the above-described mechanism and which is also satisfactory with respect to other properties such as press-formability, film removability, and blocking resistance.
In one aspect, the present invention is a coating composition for use in the production of lubricated steel materials which comprises:
(A) from 74% to 97.7% by weight of an acrylic resin having an acid number of from 30 to 150 and a glass transition temperature of from 5 to 90° C.,
(B) from 2% to 20% by weight of a water repellant, preferably one or more classes selected from the group consisting of carboxylic acid esters, metal soaps, polyethylene fine powder, and fluoroplastic fine powder, and
(C) from 0.3% to 6% by weight of an anticorrosive agent which is a mixture of an alkylamidecarboxylic acid or its salt and a nitrogen-containing basic compound, preferably an alkanolamine,
with the weight percents being based on the total weight of components (A), (B), and (C).
In another aspect, the present invention provides a lubricated steel material having an organic film formed from the coating composition. The present invention also provides a process for the production of lubricated steel materials which comprises applying the coating composition to steel materials to form a wet coating and drying the wet coating at a temperature of from 50 to 150° C.
DESCRIPTION OF PREFERRED EMBODIMENTS
The present coating composition for lubricated steel materials comprises an acrylic resin as a film-forming component, the acrylic resin having an acid number of from 30 to 150 and preferably from 40 to 120, and a glass transition temperature of from 5 to 90° C. and preferably from 10 to 85° C. An acrylic resin having an acid number of less than 30 may result in the formation of a film which cannot be readily removed by degreasing and cleaning with an aqu
Ito Hiroyuki
Kawanishi Katsuji
Matsuda Junji
Ahmed Sheeba
Burns Doane , Swecker, Mathis LLP
Sumitomo Metal Industries Ltd.
Thibodeau Paul
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