Coating processes – Interior of hollow article coating – Metal base
Reexamination Certificate
1997-02-25
2001-02-06
Pianalto, Bernard (Department: 1762)
Coating processes
Interior of hollow article coating
Metal base
C156S150000, C156S272200, C204S471000, C427S388100, C427S409000, C427S435000, C427S443200
Reexamination Certificate
active
06183809
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a surface-treating method of screw parts which method comprises coating beforehand a highly insulating organic resin based coating composition onto a thread of screw parts to be mounted onto an automobile body by welding.
(2) Description of the Background Art
In the field of an assembly of an automobile, for example, a fastening method by use of a combination of a nut with a welded bolt, or a bolt with a welded nut has been known in the art. That is, a normal fastening method comprises mounting the bolt or the nut by welding onto a body, chassis, suspension and the like, followed by coating and fastening with a nut or bolt respectively, and the normal fastening method has widely been used as a method having high workability, because welding of either the bolt or the nut makes the use of a detent unnecessary. After mounting the bolt or the nut by welding, however, spatters, i.e. molten metal droplets due to a welding operation carried out therearound may be scattered and adhered onto the thread of the screw parts, or a catianic electrodeposition coating film formed as an undercoating for the automobile body is thickly deposited on the thread, resulting in producing on fastening various troubles such as an abnormal increase in a screwed torque, development of an abnormal biting and the like because of resistance to fastening by the adhered spatter and the deposited electrodeposition coating film. For the purpose of preventing the above troubles, there is known in the art a method of masking the thread so that adhesion of the spatter onto, or penetration of the coating composition into the thread of the bolt or nut may be prevented. However, the above method has such drawbacks that in the actual production line, the application and removal of a mask require many manhours, resulting in reducing an assembly efficiency, and in that development of a more efficient method is demanded.
For the purpose of solving the above problems, there is also known in the art a method of coating beforehand a tetrafluoroethylene powder onto the thread of the screw parts. However, the method has such a drawback that a coated film shows poor properties in adhesion properties and wear resistance and shows difficulties in use because of easily falling off.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a surface-treating method of screw parts, which method can prevent adhesion of the spatter scattered on welding onto a thread and deposition of an electrodeposition coating film formed during a cationic electrodeposition coating step on the thread so as to provide a good screw parts-fastening workability and torque stability on screwing the screw parts in greatly reduced manhours compared with the prior art.
That is, the present invention relates to a surface-treating method of screw parts, which method consists of coating beforehand a liquid organic resin based coating composition capable of forming a film having a volume resistivity of 10
14
&OHgr;·cm or more at normal temperature onto a thread of screw parts to be mounted onto an automobile body by welding prior to a coating step of the automobile body, followed by heating and drying.
DETAILED DESCRIPTION OF THE INVENTION
The screw parts, to which the surface-treating method is applied, may include a bolt and nut, and may be in the form of an untreated iron as it is, or in such a form that the surface of the iron has been subjected to a plating treatment such as galvanization or alloying galvanization by use of an alloy containing a metal other than zinc.
The organic resin based coating composition used in the present invention is required to have such characteristics that (1) the composition is a one-pack type liquid composition having good storage properties and can form a film after drying; that (2) the composition is such that a film formed therefrom has a volume resistivity of 10
14
&OHgr;·cm or more at normal temperature and has good insulating characteristics; that (3) the composition has good adhesion properties onto the iron surface or the galvanized surface; that (4) the composition shows good chemical resistance; that (5) a film formed from the composition shows good wear resistance; and that (6) the composition shows good corrosion resistance.
Examples of the organic resin based coating composition satisfying the above characteristics may include (i) a fluoroacrylic resin based composition containing a mixture of a hydroxy group-containing fluoroacrylic resin containing, as the major components, perfluoroalkyl (meth)acrylate and hydroxy group-containing vinyl monomer and having a fluorine atom content of 10 to 40% by weight with a blocked polyisocyanate compound or an organotitanium compound; (ii) an epoxy resin-based composition containing, as a major component, a bisphenol type high molecular weight epoxy resin, or containing a mixture of a modified epoxy resin prepared by substituting a primary hydroxy group for epoxy groups at both molecular chain terminals of bisphenol type epoxy resin by use of alkanolamine or hydroxy acid with melamine resin or blocked polyisocyanate compound; (iii) a modified silicone resin based composition such as polyester resin-modified silicone polyester varnish, alkyd resin-modified silicone alkyd varnish, acrylic resin-modified silicone acrylic varnish, epoxy resin-modified silicone epoxy varnish and the like; (iv) resoil type oil-soluble phenol resin-modified alkyd resin varnish; (V) an alkyd resin based composition such as a melamine alkyd varnish prepared by mixing alkyd resin with melamine resin; (vi) a phenol resin based composition prepared by dissolving a novolac type or resol type phenol resin into an alcohol organic solvent; (vii) a polyurethane based composition prepared by mixing polyester resin with a blocked polyisocyanate compound; polyester varnish, polyimide varnish, polyimidoamide varnish, and the like. Of the above organic resin based coating compositions, (i) the fluoroacrylic resin based composition, (ii) the epoxy resin based composition and (iii) the modified silicone resin based composition are preferred. The organic resin based coating compositions are coated, followed by being heated and dried, resulting in that volatilization of the solvent and progress of the crosslinking reaction makes it possible to form a tough film having good properties in adhesion properties, electrical insulating properties, wear resistance and chemical resistance.
The hydroxy group-containing fluoroacrylic resin contained in the above composition (i) preferably used in the method of the present invention is a copolymer containing, as the major components, perfluoroalkyl (meth) acrylate and a hydroxy group-containing vinyl monomer.
Examples of the perfluoroalkyl (meth)acrylate may include 2,2-difluoroethyl (meth)acrylate, 2,2,2-trifluoroethyl (meth)acrylate, 2,2,3,3,-tetrafluoropropyl (meth)acrylate, 2,2,3,3,3-pentafluoropropyl (meth) acrylate, 2,2,3,4,4,4-hexafluorobutyl (meth)acrylate, 2,2,3,3,4,4,5,5-octafluoropentyl (meth)acrylate, and the like.
The hydroxy group-containing vinyl monomer may include ones having a double bond copolymerizable with the perfluoroalkyl (meth)acrylate, for example, 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth)acrylate and the like.
If needed, other copolymerizable monomers may additionally be used. The other copolymerizable monomers may preferably include acrylic monomers such as C
1
-C
10
lower alkyl (meth)acrylate, C
1
-C
6
lower alkoxy (meth) acrylate, cyanoethyl (meth)acrylate, acrylamide, acrylic acid, methacrylic acid and the like, and may also include styrene, alkyl-substituted styrene, acrylonitrile, methacrylonitrile and the like.
The above copolymer has a fluorine atom content of 10 to 40% by weight, preferably 12 to 30% by weight. When less than 10% by weight, chemical resistance and adhesion properties onto a substrate are reduced. When more than 40% by weight, poor solubility into the organic solvent may resul
Furuta Hikaru
Kashiwada Seiji
Minagawa Hajime
Mori Shigeto
Nakano Shinji
Nissan Motor Co,. Ltd.
Pianalto Bernard
Pillsbury Madison & Sutro LLP
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