Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic -co- compound
Reexamination Certificate
2000-06-14
2003-04-15
Howard, Jacqueline V. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic -co- compound
Reexamination Certificate
active
06548460
ABSTRACT:
This application is a 371 of PCT/JP99/05606 Oct. 12, 1999.
BACKGROUND ART
The present invention relates to coating compositions and lubricated metal sheets having surfaces coated by the coating compositions. More particularly, the present invention relates to a coating composition and to a lubricated metal sheet having surface coated by the coating composition, in which press formability including galling resistance and powdering resistance can be improved while dissolution of the film in an alkaline solution, chemical processing, corrosion resistance, paint dryness, and blocking resistance are maintained when the coating composition is coated on a metal sheet, such as a hot rolled steel sheet, a cold rolled steel sheet, a plated steel sheet, a stainless steel sheet, or an aluminum sheet.
Heretofore, cold rolled steel sheets for deep-drawing were used for structural members and parts for automobiles and for home appliances, which require highly advanced press formability; however, in view of cost reduction, hot rolled steel sheets are recently in increasing demand by taking the place of cold rolled steel sheets, and are now required to have improved deep-drawing processing characteristics. However, since known hot rolled steel sheets are inferior to cold rolled steel sheets in terms of deep-drawing processing characteristics, it is important for hot rolled steel sheets to have improved press formability in order to be used for application such as those mentioned above.
In addition, galvanized steel sheets were used for structural members for automobiles and parts, which require highly advanced corrosion resistance; in view of cost reduction, alloy hot-dip galvanized steel sheets are recently in increasing demand by taking the place of galvanized steel sheets. However, known alloy hot-dip galvanized steel sheets are generally inferior to galvanized steel sheets because of their high dynamic friction coefficients and poor press formability.
Furthermore, recently high tensile strength steel sheets are increasing their share in the market for reducing the weight of automobile bodies. However, high tensile strength steel sheets are inferior to soft steel sheets in terms of press formability in view of mechanical characteristics, so that parts for which they may be used are limited in practice.
Inferior press formability causes the following problems when using the steel sheets described above.
That is, press conditions under which press forming can be conducted are narrowed. Galling and powdering at the sliding portion between a mold and a steel sheet occur, so that molds are contaminated and damaged, resulting in increase of mold repair frequency and in reduced quality of molded parts. In order to solve these problems, corrosion resistance oils having high lubricating properties or oils for pressing is used in some situations; however, the usage thereof causes working environment degradation and it is difficult to improve press formability so as to meet the required objectives.
Regarding aluminum sheets, even though potential demand thereof is anticipated to achieve weight reduction in automobile bodies, the application thereof is limited at present because of the inherently small elongation characteristics of aluminum sheets.
Stainless steel sheets are used in many cases for bathtubs, washing machine drums, and the like formed by deep-drawing. Currently, polyvinyl chloride film is adhered on a surface of a steel sheet opposing a die so as to prevent galling caused by contact with the mold. The problems associated with the above are that an additional step for stripping the polyvinyl chloride film from the molded part after press forming is required and environment pollution may occur depending on the manner of disposal of the stripped polyvinyl chloride film. Accordingly, in order to improve press formability for various types of steel sheets, lubricity improvement of metal sheets by applying organic resinous coatings thereon have been proposed.
Organic resinous coatings coated on metal sheets are stripped at customer sites by alkaline rinsing after press forming, that is, by dissolution of the film in and alkaline solution. Chemically processed films are then formed on the metal sheets by phosphoric acid treatment or the like followed by forming coatings thereon by a method such as electropainting or spray painting. Adhesion between an exterior coating and a metal sheet is constructed through the surface processing thus described. Another problem of metal sheets coated with organic resinous coating is corrosion occurring during storage thereof until they are used. In addition, from a cost reduction point of view which is emphasized recently, baking processing of the organic resinous coatings at lower temperatures and for shorter periods of time are anticipated, and good paint dryness thereof is also desired. In many cases, the metal sheets coated with organic resinous coatings are shaped in the form of bands or sheets immediately after film forming and are stored in conditions such that metal sheets contact each and are subjected to large loads. In this case, adhesion between the metal sheets not to be separated from each other has to be avoided when they are used, in other words, blocking resistance is also required.
Heretofore, many proposals for forming organic resinous coating compositions which have the property of dissoluting the film in an alkaline solution are disclosed in, for example, Japanese Patent Application Publication No. 5337817, Japanese Unexamined Patent Application Publication Nos. 6284193, 3203996, 5194984, and 9156029.
In order to solve the problems described above, Japanese Unexamined Patent Application Publication No. 5194984 discloses a coating composition of organic resins having a specified copolymer of styrene with maleic acid and two kinds of esters formed from an alcohol having an alkyl or an alkenyl group. However, this copolymer has low molecular weight, so that rupture strength thereof is low and also press formability is poor. When a mold temperature increases, in particular, a problem arises in that press formability is extremely deteriorated.
In Japanese Patent Application Publication No. 5337817 and in Japanese Unexamined Patent Application Publications Nos. 6284193 and 3203996, technologies for improving press formability by using a specific organic resin and for maintaining dissolution of the film in an alkaline solution by defining an acid value of carboxylic groups being present in the organic resin, are disclosed. For example, an organic resin disclosed in Japanese Patent Application Publication No. 5337817 is a water-soluble copolymer composed of an acrylic ester, methyl methacrylate, styrene, and a monomer having carboxylic groups, of which the mean molecular weight is 15,000 to 50,000, and the glass transition temperature (Tg) is 60 to 90° C. However, the technologies described above have drawbacks in that the crystallization of chemically processed film after alkaline rinsing is insufficient and press formability, especially at elevated temperature, is not satisfactory.
Japanese Unexamined Patent Application Publication No. 9156029 discloses a steel sheet having superior deep-drawing, galling resistance, and dissolution of the film imparted by a coating composition composed of an acrylic resin having a defined glass transition temperature and a defined acid value, a metallic soap, a phosphoric zinc, and a polyethylenic wax. However, since the technology described above maintains dissolution of the film in an. alkaline solution only by defining an acid value of the resin, dissolution of the film in an alkaline solution cannot been maintained when a resin having a high acid value is used, because of cross-linking reaction between the resin and the zinc at a zinc-plated surface of a steel sheet. In addition, even though a steel sheet has no plating layers, it is recently appreciated that primary corrosion resistance cannot be maintained, for example, when methyl methacrylate is used.
The problems of conventional technologies described
Gotou Yoshinori
Higai Kazuhiko
Mochizuki Kazuo
Mukaihara Fuminori
Ogata Hiroyuki
Howard Jacqueline V.
Kawasaki Steel Corporation
Young & Thompson
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