Coated parts with film having powder-skeleton structure, and method for forming coating

Powder-content of a powder-coating is enhauced. Powder material forms a skeleton structure. The clearances are filled with resin. The coating comprises a resin layer which bonds the power-compacted layer to the parts or any underlying powder-compacted layer. The work pieces on which a resin film may be preliminarily formed, is subjected to vibration or stirring together with the powder material and means for mediating the formation of the coating, which eans is of substantially smaller size than said work pieces and greater size than said powder material, as well as with or without the resin, to vibration or stirring in a container.

BACKGROUND OF INVENTION 
1. Field of Invention 
The present invention relates to various parts, on whose surface a coating 
is formed, as well as a method for forming the film. Various parts herein 
are mechanical parts used for various machines, automobiles, other 
vehicles, ships and aircraft, electrical and electronic parts, ornamental 
parts, metal fittings, magnets, toy parts and the like. Large construction 
parts such as steel frames and bridges are excluded from the various parts 
herein. Materials of the various parts herein are metal, alloy, 
intermetallic compounds, inorganic compounds, plastics, ceramics and the 
like. In addition, the various parts may hitherto have been subjected to 
the formation of conventional films, such as resin coating or plating or 
other surface modification. 
The film herein can be applied to all of the applications, to which the 
conventional powder-film or resin-film has been applied, and is mainly 
applied to enhance corrosion-prevention, mechanical strengthening, 
formation of electro-conductive or insulating film and/or to improve 
appearance. Specific applications of the coating herein are: a conductive 
film with metallic or carbon powder; a thin magnetic film with dispersed 
magnet powder; a fluorescent film; a tool or cutter, on whose substrate a 
diamond or SiC coating is formed. 
2. Description of Related Arts 
The following prior art related to the film, which comprises powder and to 
which the present invention belongs, is heretofore known. 
(1) Resin Coating Film 
A resin coating film is provided by applying paint on the surface of parts, 
vaporizing the solvent in the paint and polymerizing the resin or the 
like. The paint is prepared by dispersing various pigments in resin or 
other vehicle, such drying oil and half-drying oil as linseed oil, 
safflower oil and soybean oil. The kind of resin and pigments used as well 
as their blending proportion affect the corrosion-proof performance, 
appearance, mechanical properties and the like. Recently, in various 
parts, such as parts related to automobiles, precision machines and 
electronics, the coating is required to be thin, and to have high 
dimensional accuracy and good corrosion-proof performance. To meet these 
requirements, the pigment amount should be increased. However, when the 
pigment amount is excessively increased, the paint loses most of its 
viscosity so that the film formation becomes virtually impossible. The 
pigment amount in the conventional coating film therefore does not exceed 
40% by volume at the most. Another problem arises when the proportion of 
pigment blending in the coating film is increased. Generally, it is 
considerably difficult to completely uniformly disperse the pigment powder 
in the resin coating film. Powder aggregates in the form of clusters may 
be occasionally formed. The thus-formed film includes portions where the 
pigments are loosely dispersed; these portions are ineffective in impeding 
corrosive media, such as water, which 1/2rp1/2ertu controls the 
corrosion-proof performance of the film. Therefore, no matter how many 
pigments are blended, not all of the pigments are effectively utilized to 
extract their properties. 
Incidentally, zinc-rich paint containing from 40 to 50% by volume of zinc 
powder is used as rust-proof paint of large constructions, such as 
bridges, but has not been used for the various parts herein. Since the 
zinc-rich paint contains an excessive amount of the pigment, it can be 
applied on an article not by spraying but by brush. This is a reason why 
this paint is not applied to the various parts herein. 
(2) Powder Film 
Flame spraying of powder, such as metal powder, is a method in which the 
powder is used as the starting material, but the powder is partially or 
totally melted. The so-formed film is therefore a continuous film. Methods 
for forming a powder film are very few One method is disclosed in Japanese 
Examined Patent Publication No. 2-71872. According to the present 
invention, the surface of parts, whose surface is preliminarily rendered 
adhesive, is brought into contact with the powder material; vibration is 
imparted to the parts so as to compress the powder adhered on the parts 
surface to the bulk density or less; subsequently, the powder not bonded 
to the parts is removed. The parts and powder specifically disclosed in 
said publication are color television screens and the fluoresecnt toner. 
The so-formed film includes numerous pores and hence is not appropriate 
for corrosion-prevention purpose. Its application is therefore limited. 
Other methods are the mechanical barrel method disclosed in U.S. Pat. Nos. 
2,640,001 and 4,849,258. Powder such as tin or aluminum powder is 
dispersed in a dispersing medium, selected from vegetable oil, grease, and 
silicone oil, and is plated on the parts by the barrel plating manner. It 
is disclosed in U.S. Pat. No. 4,849,258 that silicone resin is 
additionally used to improve the lubricating property. Flux such as acid 
is used to activate the parts surface. It is described that, when the oil 
lubricant forms a film on the parts surface, the formation of plating film 
is impeded. A large amount of emulsifier is used to prevent the oil film 
formation. The above U.S. patents describe that intended uniform metal 
film, such as Zn film, is not formed, when material other than metal, such 
as resin, is deposited on the surface of parts. Since the film consists of 
a metal layer which is directly adhered on the parts which have been 
activated by acid or the like, the parts surface seems to be very clean 
and the film adherence seems to be very sensitive to oxides and foreign 
matters. When the parts to be plated are subjected to ordinary degreasing 
but are not activated by the flux during the barrel treatment, no film 
seems to be formed, or, even if any film is formed, its adherence seems to 
be very poor. In addition, since the lubricant, emulsifying agent and flux 
are used in large amounts, there is a danger that impurities such as 
carbon and the like are incorporated in the film. 
The following methods (1)-(3) are known in the prior art of method for 
forming a film, to which the present invention belongs. 
(1) Powder Painting 
Powder paint is deposited by spraying, atomizing, flame-spraying, 
electrostatic spraying or the like on the parts, which have been 
pre-heated. The so-deposited powder melts and forms a film on the parts. 
The powder painting is disclosed, for example, in Japanese Unexamined 
Patent Publications Nos. 53-29,347 and 2258,084 and Japanese Examined 
Patent Publication Nos. 57-13,347 and 58-37,029. This method is 
pollution-free and can save natural resources because no solvent is used. 
The powder-film formation method is advantageous over the various 
film-formation method in the following points. It is advantageous over the 
electro- and electroless plating methods in the point that, since neither 
acid nor alkali is used, treatment of waste liquid is not necessary. 
Furthermore, even if the work piece is active, no corrosion problem 
arises. It is advantageous over the hot dip plating method in the point 
that exposure of the work piece to high temperature is avoided. It is 
advantageous over the PVD and CVD methods in the point that a large-scale 
plant is unnecessary and productivity is high. When the powder paint is 
applied on small parts by dispersing or spraying, the parts must be 
reversed upside down or hanged down from a hook. Powder painting is 
therefore not said to be economical. 
(2) Coating of Powder 
The above-mentioned Japanese Unexamined Patent Publication No. 2-71872 
refers to the powder coating on a work piece whose surface is adhesive. 
Japanese Unexamined Patent Publication No. 52-43731 refers to the powder 
coating on a work piece whose surface is not adhesive. In this 
publication, the metal or alloy powder and granular hard materials are 
admitted in a hollow metallic body, and the hollow metallic body is 
rotated or vibrated so that the inner surface of the metallic body is 
covered with the metal or alloy powder. The powder is pressure-bonded on 
the metallic body and is also diffusion-bonded with this body due to the 
heat energy resulting from the vibration. 
The above-mentioned U.S. Pat. Nos. 2,640,001 and 4,849,258 refers to the 
powder coating method on a work piece whose surface is not adhesive. 
According to this method, the metal parts, metal powder, lubricant and 
steel balls or glass beads are loaded in a container drum. The steel balls 
and glass beads impart the impact force onto the metallic powder which is 
then pressure-bonded on a work piece. Under the presence of the lubricant, 
the metal powder does not coagulate but is uniformly dispersed and flows, 
so that uniform film with good finishing is obtained. In addition, since 
excessive frictional force between the metal powder and parts is 
decreased, the impact force is effectively used for the pressure bonding. 
The impact force required for forming a coating in these U.S. patents is 
smaller than that required in Japanese Unexamined Patent Publication No. 
52-43,731 mentioned above. 
There is another method which refers to the powder coating on a 
non-adhesive work piece as is disclosed in Japanese Unexamined Patent 
Publication No. 56-45,372. According to the method disclosed in this 
publication, blast material is prepared in such a manner that an iron-zinc 
alloy layer is formed on the cores consisting of iron or iron alloy to 
surround the cores, zinc alloy is deposited on the iron-zinc alloy layer. 
The so-treated cores are separate from one another and form an aggregate, 
which is the blast material and is projected onto the surface of the iron 
or iron-alloy so as to form a zinc coating on said surface. Japanese 
Unexamined Patent Publication No.60-245,784 discloses formation of a 
chromate coating on the zinc coating mentioned above. The powder adhered 
directly on the adhesive surface disclosed in Japanese Unexamined Patent 
Publication No. 2-71,872 exhibits a degree of bonding force. The powder 
present on the former surface is merely compacted due to the vibrating 
force imparted to the powder particles. The latter powder is therefore 
easily removed from the coating when it is subjected to external force. 
Furthermore, considerable clearances are formed in the coating. The 
coating is therefore not appropriate for corrosion-prevention, because 
corrosive media easily pass through the clearances. In addition, the 
throwing power of the powder is poor when the work piece is concave or 
convex. 
When mechanical bonding (pressure-bonding) and diffusion-bonding are 
simultaneously carried out as is disclosed in Japanese Unexamined Patent 
Publication No. 52-43,731, considerable energy is necessary, such as 500 
kg of imparting force generated by a vibrating mill, rotation of 300 rpm 
generated by a high-speed planetary mill. The work piece must therefore 
have high strength Ceramics, plastics with low strength and the like 
cannot therefore be the work piece. In addition, oxides and other brittle 
powder are destroyed by the vibration and therefore cannot be used. 
Furthermore, the method disclosed in Japanese Unexamined Patent 
Publication No. 52-43,731 is applied only to the coating on the inner 
surface of a work piece. 
In the methods disclosed in the two U.S. patents, it is described that a 
strong emulsifying agent is necessary for preventing the formation of a 
lubricant film (oil, resin or the like) on the surface of a work piece. If 
the emulsifying agent is not added, the lubricant covers the work piece 
and forms an adhesive film, which impedes the formation of powder coating, 
as is clearly described therein. In addition, the metals which can be used 
are limited to soft powder, such as Zn, Sn or Cu. 
In the methods disclosed in Japanese Unexamined Patent Publications Nos. 
56-45,372 and 60-245,784, the projecting force of the blast steel 
particles would be as high as that of shot blasting. 
(3) Rolling of Metal Powder 
Metal powder is adhered on the surface of a rolled sheet and is then 
pressure-bonded on the rolled sheet. Subsequently, heat treatment is 
carried out to diffusion-bond the metal powder and the rolled sheet (c.f. 
Japanese Unexamined Patent Publication Nos. 47-29,232, 51-143,531, 
52-33,840, and 57-54,270). The work piece to be treated must be in sheet 
form and consist of rollable material. Powder coating cannot be formed 
directly on the mechanical parts. 
SUMMARY OF INVENTION 
As is described hereinabove, no conventional powder-coating fulfills the 
following requirements (a) the powder is in high proportion and is 
uniformly distributed and the parts have not been subjected thermal 
treatment, and/or (b) the coating can be formed on a work piece, whose 
surface is of normal cleanness. 
It is therefore an object of the present invention to provide a powder 
coating formed on the various parts and fulfilling the requirements (a) 
and/or (b). 
It is another object of the present invention to provide a method for 
forming a powder coating on various parts, which method does not suffer 
from the disadvantages described above and which can form a tight powder 
coating having improved bonding strength. 
In accordance with the objects of the present invention, there is provided 
parts having a coating thereon, which coating comprising at least one 
powder-compacted layer, said layer comprising compacted powder material 
which forms a skeleton structure, and clearances, at least a part of which 
is filled with resin, which coating further comprising a resin layer which 
bonds the powder-compacted layer to the work piece or any underlying 
powder-compacted layer. 
In accordance with the objects of the present invention, there is also 
provided a method for forming a coating on a work piece, characterized in 
that: work pieces, resin, which is at least partially uncured at least in 
the initial period of the coating forming, powder material, which may be 
resin powder harder than said resin during the coating-forming process, 
and, means for mediating the formation of the coating, which means is of 
substantially smaller size than said work pieces and greater size than 
said powder material and is subjected to vibration or stirring in a 
container, thereby forming the coating containing the powder material. 
According to another method, an uncured resin film is preliminarily formed 
on the work pieces and, then, the powder, work pieces and means for 
mediating the coating-formation are subjected to vibration or stirring. 
The present invention is described hereinafter more in detail. 
Powder Coating 
The powder coating is first described. 
In the present invention, such thermosetting resins as melamine resin, 
epoxy resin, phenol resin, furan resin, urethane resin, unsaturated 
polyester resin, polyimide resin, urea resin and the like, as well as such 
thermoplastic resins as acrylic resin, polyester resin, polyethylene 
resin, polyethylene terephthalate, polyproplylene, polyvinyl chloride, 
polyvinyl alcohol, nylon, polystyrene, polyvinyl acetate and the like can 
be used. Cellulose derivatives can also be used. Liquid prepolymer or 
monomer, an organic binder usually used for the shaping of powder, e.g., 
paraffin or camphor, can also be used. Natural resins, such as gelatin, 
glue, and Japanese lacquer can be used. Inorganic adhesive material such 
as silicate, a representative compound being water-glass, can be used 
instead of or together with the resin. The resin may contain an inorganic 
pigment(s). 
The powder is the constituent material of the powder-compacted layer. Part 
of the powder material may be incorporated in the resin layer and become 
its constituent material. Various metals, alloys and ceramics in the 
powder form as well as pigments can be used as the powder material. 
Metal powder may be the powder of Al, Cu, Fe, Cr, Co, Ni, Zn, Pb, Sn, Rh, 
Ir, Pd, Pt, Ag, Au, Mo, W or an alloy powder with the main element being 
one of these metals. All of these metals have strength higher than resins 
and do not deteriorate due to water or salt water, and hence have good 
corrosion resistance. Features of the respective metals are well known. 
Ceramics are more chemically stable than metals as well as 
electro-insulating and corrosion-proof. MgO, PbO, PbO.sub.2, Al.sub.2 
O.sub.3, SiO.sub.2, TiO.sub.2, CrO.sub.2, MnO.sub.2, Fe.sub.2 O.sub.3, 
FeO, Fe.sub.3 O.sub.4, CoO, NiO, CuO, ZnO, ZrO.sub.2, MoO, PbO, PbO.sub.2, 
and the like can be used. Composite oxides based on several of these 
compounds, various stable nitrides, such as TiN, BN, and various stable 
carbides such as SiC, WC, and TiC can also be used. 
When the coating is used to enhance appearance of the parts, various 
pigments such as carbon black, quinacridone red, permanent yellow, 
phthalocyanine blue can be used as pigments. The pigment can be mixed with 
the above-mentioned powder. 
The resin is a constituent material of the resin layer and is filled at 
least partially in the clearances and disordered portions of the skeleton 
structure described hereinafter. 
The grain size of the powder material depends on the size of the work 
pieces, thickness of coating, and material of the powder. When the powder 
is hard and difficult to deform as in the case of ceramics, small grain 
size is desirable. The grain size is usually within a range of from 0.01 
to 500 .mu.m, preferably form 0.01 to 300 .mu.m, and more preferably from 
0.01 to 100 .mu.m. Ductile powder, e.g., metal powder, may exceed this 
range. 
The structure of the coating is now described. 
In the powder-compacted layer, the particles of the powder are brought into 
surface contact with each other and are connected three-dimensionally. The 
powder therefore forms a skeleton as in a green compact produced by powder 
metallurgy. Powder particles with low ductility are compacted in the 
skeleton, while maintaining the particle size at its production. On the 
other hand, powder particles with high ductility are deformed into 
platelets under high compression force, and the platelets are stacked on 
one another and compacted. Clearances between the particles or platelets 
are completely or partially filled with the resin. If any clearances are 
left, their volume is considerably smaller than that of the skeleton, and 
the remaining clearances exert slight influence upon the strength or the 
like, practically speaking. 
The powder-compacted layer contains therefore powder in a high volume 
proportion which cannot be attained by the conventional resin coating. For 
example, when the powder is relatively hard, such as Ni powder, the powder 
proportion in the coating layer can be 55% by volume. When the powder is 
relatively soft, such as Ag powder, the powder proportion in the coating 
layer can be 65% by volume. Representative bulk density of the Ni and Ag 
powder is approximately 20% relative to the theoretical density, while the 
bulk density of such powder is from 25 to 30%. The powder proportion of 
the resin coating cannot exceed the bulk density, unless a high pressure 
is applied to the coating. Actually, the powder proportion of the resin 
coating is considerably less than the bulk density. 
The inter-connection of the powder in the powder-compacted layer is locally 
two-dimensional. Although such inter-connection is evidently 
two-dimensional at the top and bottom of the powder-compacted layer, 
two-dimensional inter-connection is formed within the coating layer and 
disorders the skeleton structure. The clearances of the ordinary skeleton 
structure with the three-dimensional inter-connection are of approximately 
the same size as that of the particles. The clearances of the disordered 
skeleton structure are considerably greater than the particle size and 
decrease the strength of the powder-compacted layer. Filling in such 
clearances with resin can effectively reinforce the powder-compacted 
layer. Fundamentally, filling in the clearances in the ordinary skeleton 
structure with resin is hereinafter described. This description is also 
applicable to the filling in of the clearances of the disordered skeleton 
structure. 
The powder particles are bonded with each other at the contact surface with 
the bonding strength which results from the pressure bonding and friction 
forces due to plastic deformation. Such bonding is similar to that in the 
green compact of powder metallurgy. In the case of a soft metal powder 
having low melting point and resin powder, thermal diffusion takes place 
partially at the contact surface of powder. The bonding force described 
above mainly determines the mechanical properties of the skeleton. 
In the conventional resin coating, the mechanical properties are mainly 
determined by the resin when the pigment amount is small. The powder in 
the conventional paint coating does not form a skeleton but is dispersed, 
and, the powder amount being small, with the result that the powder exerts 
slight influence on the mechanical properties of the resin coating. The 
aggregates in the form of clusters, which may be formed in the 
conventional resin coating with a high amount of powder, are not so strong 
as to form the skeleton. In addition, since the resin is not 
satisfactorily extended in the cluster, the cluster is very fragile and is 
likely to collapse. Since the aggregates increase with the increase in the 
pigment amount, the mechanical properties, particularly the 
wear-resistance of the coating degrades with the increase in the pigment 
amount. Furthermore, not only is the resin amount decreased, but also its 
distribution becomes non-uniform. As a result, the adhesion of coating is 
lowered drastically. 
Contrary to the resin coating, the particle density varies little in the 
skeleton according to the present invention, which therefore does not have 
fragile parts as in the case of the cluster aggregates. Notwithstanding a 
high blending proportion of powder, the coating is homogeneous and has 
improved mechanical properties, particularly wear-resistance. 
Many of the clearances in the skeleton are open pores on the coating 
surface. Resin filled in the clearances is connected with the resin layer 
through the pore openings. As a result, the resin in the clearances of the 
powder-compacted layer are like long pins or bolts and exerts strong 
bonding force. In addition, since the resin in the clearances is not 
straight but is zigzag curved, the bonding strength is further enhanced. 
The resin filled in the clearances in the skeleton structure enhances the 
adherence of the powder-compacted layer and resin layer and, further, 
reinforces the skeleton structure and hence the powder-compacted layer. 
As is described hereinabove, the ductile metal powder forms a skeleton, in 
which the metal particles are deformed flat, and the so-deformed metal 
pieces are laminated on one another. The clearances therefore communicate 
with each other mainly in a horizontal direction, i.e., between the flat 
metal platelets. The resin is filled in the flat clearances, because the 
resin is filled as soon as the skeleton and clearances are formed, or 
because the powder surrounds the resin during formation of the skeleton. 
The ceramic powder forms, on the other hand, a skeleton, in which the 
metal powder is not deformed, and the clearances communicate with each 
other equally in horizontal and vertical directions. 
The powder-compacted layer may include isolated clearances, which have 
almost the same size as the powder particles and which are isolated with 
the clearances described above The isolated clearances may be present both 
in the ordinary and disordered skeletons. The isolated clearances are 
preferably at least partially filled with resin, so as to reinforce the 
skeleton. Filling of the isolated clearances becomes possible by means of 
filling them simultaneously with their formation. Since the contiguous and 
isolated clearances are filled with resin, the film according to the 
present invention neither peels nor falls down from the substrate as 
frequently happens in the case of resin coating with many pigments. 
The resin layer is an intermediate layer between the powder-compacted layer 
and the surface of parts and strongly bonds the skeleton with the surface 
of parts. The resin layer enhances the bonding strength much more higher 
than that of direct bonding between the skeleton and the parts, where the 
powder and surface roughness of the parts mesh with one another due to 
friction force, which meshing is the main bonding force. 
It is possible to impregnate resin from outside the coating into the 
continuous clearances of the skeleton structure. 
The thickness of the powder-compacted layer is not specified at all and is 
appropriately determined depending upon the size of parts and the coating 
property required. The thickness of the powder-compacted layer is usually 
500 .mu.m at the thickest. When the thickness exceeds this value, no 
advantages are attained by the thickness increase while the thickness of 
the coating becomes non-uniform and dimensional accuracy decreases. The 
powder-compacted layer has preferably a thickness of from 50 .mu.m or less 
for the parts, which are used for precision machines and electronic parts 
which are required recently to have high dimensional accuracy. On the 
other hand, when the thickness of the coating is less than 0.1 .mu.m or 
less, such requisite properties as corrosion resistance are not obtained. 
When the volume ratio of powder material is 30% or less in the 
powder-compacted layer, the proportion of clearances in the skeleton 
increases and the contact area of the powder particles decreases. As a 
result, the requisite properties such as corrosion resistance are not 
obtained. The desirable proportion of the powder material is 40% or more. 
A more desirable proportion of the powder material is 45% by volume or 
more. The most desirable volume proportion is 50% is more. 
The resin layer, which is present between the powder-compacted layer and 
parts, may comprise in its upper part a transition region containing 
powder material the amount of which gradually decreases toward the lower 
part. The resin layer may contain powder material in such an amount as in 
the usual resin coating. Even in this case, the resin layer mainly 
contains resin and covers all or almost all of the surface of parts and 
plays the role of bonding the powder-compacted layer onto the surface of 
parts. The resin layer protrudes, on its side facing the parts, into 
minute concavities of the parts and achieves an anchoring effect. The 
adherence of the resin with the parts generates also the bonding force. 
The resin layer eliminates on the surface of parts contaminants such as 
foreign matters, oxides and the like which are detrimental factors 
impeding the bonding, so that the powder can be easily formed on the 
parts, whose surface is of normal cleanness. 
At the side facing the powder-compacted layer, the resin layer exhibits 
adherence with respect to the resin filled in the skeleton and also 
exhibits an anchoring effect, with the result that the powder-compacted 
layer is bonded to the resin layer. Usually, the resin layer has a 
thickness of from 0.1 to 20 .mu.m. When the thickness is less than this 
value, the above-described effects are not fully demonstrated and the 
bonding strength is hence low. On the other hand, when the thickness of 
the bonding layer is more than 20 .mu.m, not only are its effects not 
enhanced with the increase in the thickness, but also the resin layer has 
non-uniform thickness. Desirable thickness of the resin layer is from 0.5 
to 10 .mu.m. A more desirable thickness of the resin layer is from 0.5 to 
10 .mu.m. A further desirable thickness of the resin layer is from 1.0 to 
5 .mu.m. 
The above-described thickness values of the powder and resin layers may be 
satisfied by the average thickness-value of the layers. The layer 
thickness may vary so that it locally falls outside the above-described 
ranges. Desirably, the thickness variation is, however, as small as 
possible. The direct contact between the powder and parts decreases with 
the decrease in the powder content of the resin layer. The bonding 
strength is therefore enhanced. 
The coating according to the present invention may consist of two or more 
layers, each layer consisting of the resin and powder-compacted layers. 
The kinds of resin and/or powder may be different from one another with 
regard to these layers. Three or fewer layers are preferably used for 
constructing the coating according to the present invention because four 
or more layers are too thick to keep the process short and economical. 
The coating according to the present invention can be formed by aggregating 
and bonding the powder particles under the presence of resin in such a 
degree that the powder particles do not form a continuous body. One of 
such methods is the one in which a container with powder-forming media is 
vibrated or stirred. 
A protective resin coating may be applied on the surface of the coating 
according to the present invention described above. The protective resin 
coating is effective for enhancing the strength and corrosion resistance 
of the entire coating. When the powder-compacted layer is exposed on the 
coating surface and is subjected to impact force or strong force from 
outside during handling and mounting of the parts in a machine, the powder 
material may partly be removed or the coating may be locally damaged. The 
protective resin coating is effective for preventing these problems as 
described above. The resin smoothens and enhances the appearance of the 
coating surface. The resin pinholes are filled with resin. The kind of 
resin of the protective resin coating may be the same as or different from 
that of the resin of the coating. The protective resin coating is 
desirably from 0.5 to 300 .mu.m. When the thickness is less than 0.5 
.mu.m, the protective function is virtually lost. On the other hand, when 
the thickness is more than 300 .mu.m, the above-described problems of 
thick layers also arise. 
The protective coating may be resin coating, and, in addition, electro or 
electroless plating of any known metal or alloy and dispersion plating of 
metal and non-metallic material. When at least the top most part of the 
coating is the powder-compacted layer with metal or alloy powder, 
electro-conductivity of the coating surface is so enhanced that various 
platings can be applied on the coating surface. The plating layer and the 
metal in its underlying powder-compacted layer prevent the corrosion of 
parts. The parts according to the present invention are therefore more 
corrosion-resistant than the conventionally plated parts. 
When a plating layer is formed on the coating of the invention, the 
clearances formed in the skeleton and remaining unfilled with the resin 
may result in the formation of many more pinholes in the plating layer 
than in the usual plating layer. In order to prevent such formation, the 
plating layer of any known metal or alloy can be thickly formed on a 
substrate of any material or a thin electro-less plating layer can be 
formed beneath the plating layer. 
Preferred embodiments of the parts are hereinafter described with regard to 
the housing, box or the like with an electromagnetic interference (EMI) 
coating, as well as rareearth magnets. 
The coating according to the present invention, containing stable oxides 
such as TiO.sub.2, MgO, Fe.sub.2 O.sub.3 and the like, is formed on the 
sintered rare-earth magnets, such as Nd-Fe-B magnets. The oxide is 
dispersed in the powder-compacted layer and improves the corrosion 
resistance as compared with the conventional resin coating. Particularly, 
the corrosion resistance is improved when the content of oxide is high at 
the surface of the coating. 
A single coating according to the present invention, formed on the 
resin-bonded magnet, can attain corrosion-resistance as good as that of 
conventional multi-layer resin coating. The powder material and resin are 
forced into the pores of the resin-bonded magnet, thereby effectively 
sealing the pores. The coating according to the present invention is more 
industrially applicable than the electro- or electroless plating which is 
conventionally carried out for corrosion-resistance of the bonded Nd-Fe-B 
magnet. 
Conventionally, plating is carried out for the corrosion-prevention of the 
sintered Nd-Fe-B magnet. Before the plating, a pre-treatment is necessary. 
Since the plating coating usually has pinholes, these pinholes directly 
reach the surface of the sintered Nd-Fe-B magnet. Corrosive media intrude 
therefore through the pinholes and reach the boundary between the plating 
layer and the surface of the substrate. The plating layer is therefore 
likely to peel, particularly, when the oxide layer remains on the surface 
of parts. 
Contrary to the above described drawbacks of the plating on the sintered 
Nd-Fe-B magnet, the coating according to the present invention can be 
formed without pre-treatment of the parts. Conditions for forming the 
coating according to the present invention are less strict than those of 
the conventional plating. The powder-compacted layer according to the 
present invention stops almost all of the corrosive media which have 
passed through the overlying upper plating layer. The corrosive media does 
not therefore intrude up to the surface of substrate, and, therefore, the 
coating does not peel. Since the coating according to the present 
invention is strongly bonded on the surface of the substrate, when its 
material is appropriately selected taking into consideration the material 
of the overlying plating layer, the plating layer can be very strongly 
bonded on the sintered Nd-Fe-B magnet. 
Conventionally, an electroless plating layer is applied on the surface of 
the resin-bonded Nd-Fe-B magnet. Generally speaking, the electroless 
plating liquid is expensive and the cost of treatment of waste liquid is 
considerable. Bonding strength of the electroless plating layer with the 
underlying material is seriously lower than that of the resin coating. It 
is, therefore, difficult to make the electroless plating layer thick and 
it is generally limited to a thin one 5 um or less. Since the resin-bonded 
magnet is porous, the pinholes present on its surface are profiled in the 
electroless plating layer to a form very porous layer. The coating 
according to the present invention formed on the resin-bonded Nd-Fe-B 
magnet is advantageous over the conventional electroless plating layer 
from the points of view described for the sintered magnet. 
Method for Forming a Coating 
The features of the inventive method as compared with the conventional 
methods for forming the powder coating are first described. 
The resin layer is first formed on the work piece. Thickness of the resin 
layer depends on the charging sequence of the powder material, resin, the 
coating forming mediating means, and work pieces, and stirring method. For 
example, when the resin and powder material are simultaneously charged, 
since the contact of the powder material and resin simultaneously occurs, 
the layer of resin alone formed on the surface of work piece becomes so 
thin as to be detected by the naked eye. 
Subsequent to the formation of resin layer, the powder material is captured 
and fixed on the resin layer due to its adherence force. The powder 
material is firmly captured by the resin layer when it is cured on the 
surface of a work piece. The means for mediating the coating formation 
(hereinafter referred to as "the coating-forming means"), which are 
subjected to vibration or stirring, impart the striking force to the 
powder material which is also subjected to vibration or stirring. The 
powder material is therefore forced in between the particles of powder 
which have already been captured. The powder material is therefore further 
strongly fixed by the striking force of the coating-forming force in 
addition to the adherence force of resin. Since the work pieces collide 
with each other, the powder material is furthermore forced into the resin 
layer. The powder material mixed with the resin layer increases more and 
more, while the resin layer thickens and grows. 
The powder material is also subjected to the striking force of the 
coating-forming means and the particles collide with each other on the 
surface of the work piece. The powder material therefore plastically 
deforms, and friction between the powder particles occurs. Due to mainly 
the plastic deformation and auxiliarily the inter-atom diffusion by the 
friction heat, the bonding force is generated. Ductile metal or alloy, 
such as Al, Cu, Zn, Sn, Au, Ag, Pb and their alloys, as well as plastics 
plastically deform into the form of platelets, which are pressure-bonded. 
The materials in the coating are therefore strongly bonded. 
The coating-forming means are impinged upon the coating and squeeze the 
resin from spaces between the powder particles. The so-squeezed resin 
exudes on the coating surface. Part of such resin adheres on the 
coating-forming means. The resin adhered on the coating-forming means 
again adheres on the work piece, when such means are impinged on the 
surface of the work pieces. 
The growth of coating proceeds while the resin is squeezed out from the 
coating. While the coating grows, the proportion of powder material in the 
coating surface increases. The powder material on the surface part of the 
coating coagulates under the striking force, so that the proportion of 
resin more and more decreases, and, hence the growth speed of coating 
decreases. 
The following requirements (a)-(d) are necessary for realizing the process 
of film formation as described above. 
(a) Resin must be locally or as a whole in an uncured condition at least in 
the initial period of the film-forming process. If the resin is as a whole 
cured in the entire film-forming process, the powder material, work 
pieces, and coating-forming means, (which may be hereinafter collectively 
referred to as "the coating-forming mixture"), are merely mixed but does 
not result in the coating formation. The word "uncured" indicates that 
resin is softer than resin of the coating, after vaporization and/or 
curing of its solvent is completed, and which is prepared for use. 
(b) The coating-forming mixture must be vibrated or stirred. That is, also 
the coating-forming media must be vibrated or stirred. The work pieces can 
be stationary, provided that the other coating-forming mixture is brought 
into contact with the work pieces during mixing, and, further, the surface 
of the work pieces is subject to the impact force of the powder material 
impinging thereon. 
(c) The coating-forming means generates the striking force but essentially 
does not become the component of the coating. When the coating-forming 
means is greater than the work pieces, the striking force of such means is 
not uniform on the surface of the work pieces. When the coating-forming 
means is smaller than the powder material, the former is captured in the 
coating, The size requirement of the coating-forming means is therefore 
essential. However, several greater coating-forming means than the powder 
material may be included in the coating-forming means, less than such an 
amount that: they do not impede the function of the smaller 
coating-forming means; they do not impede formation of coating on the 
inner surface of a ring-form work piece or the corners of work pieces; 
and, their striking force is so great as to destroy the work pieces and to 
roughen the coating surface. 
The coating-forming means is usually spherical. The spherical 
coating-forming means is desirably 0.3 mm or more desirably 0.5 mm or more 
in diameter. In accordance with this rule, the size of the coating-forming 
means having another shape is determined. Smaller coating-forming means 
than the work pieces means that, when the volume of each means is 
converted to the volume of a sphere, its diameter is smaller than the 
largest diameter of the work pieces. The size of the coating-forming means 
is, however, desirably 50 mm or less, more desirably 20 mm or less, even 
in a case where the work pieces are long or large-sized. Requisite 
striking force can be produced, when the coating-forming means is greater 
in average size than the powder material. Material of the coating forming 
means should satisfy the following requirements (1) and (2): (1) Such 
great shape deformation of the coating-forming means as to be detected by 
the naked eye after the coating formation does not occur due to plastic 
deformation. In addition, elastic deformation during the coating formation 
is not excessively great. This requirement is not satisfied by soft 
rubber. (2) Neither breaking into pieces, cracking nor abrupt wear occurs. 
Some wear may occur during long use of the coating-forming means. 
The coating-forming means may consist of more than one kind of material. It 
is possible to cover alumina balls, whose specific weight is low, with 
other materials so as to adjust the hardness of the coating-forming means. 
In this regard, plating layer, cured resin layer, uncured resin layer 
and/or volatile liquid layer may be formed on the coating-forming means. 
Such resin layer and the like promotes uniform deposition of powder on the 
work pieces. The resin layer and the like also mitigate the striking force 
of the coating forming means, thereby lessening the breakage of the work 
pieces and coating-forming means, cracks and wear due to friction. It is 
preferred to form the resin layer and the like, when the coating-forming 
means are very hard, large, and/or irregularly shaped. 
(d) The powder material must be smaller than the coating-forming means so 
as to incorporate the former into the coating. The properties of the 
powder material are not at all specifically limited. However, when the 
powder material is resin, it must be harder than the resin film on the 
work pieces during the coating-forming process, so that the resin powder 
is buried under the striking force of the coating-forming means into the 
uncured resin film. The powder resin, which is completely cured, is 
preferred, because it provides the coating with excellent corrosion 
resistance. 
Preferred embodiments of the present invention are described hereinafter. 
Preferably, resin in an uncured state is liquid or semi-liquid, since the 
resin should be uniformly extended on the surface of the work pieces. It 
is possible to dissolve, dilute or disperse the liquid or solid resin in 
such dispersing means as an organic binder or water, so as to enhance 
fluidity and to uniformly spread the resin on the work pieces. Since the 
solvent or water vaporizes during mixing, the viscosity gradually 
increases, with the result that the powder adheres to the work pieces. It 
is preferred that the amount of solvent or dispersing media is adjusted to 
such a level that, as a result of their vaporization, the amount of resin 
becomes 20% by weight or more during vibration or stirring. When the 
concentration of resin is low during the vibration or stirring, the 
viscosity of resin is too low to attain the powder deposition. 
Thermoplastic resin may be heated to enhance the fluidity and viscosity and 
then used. Powder resin may be used alone without dispersing in the 
solvent. In this case, the fluidity of the resin is poor. In order to 
uniformly disperse such powder resin in the coating-forming means, no 
particle of the powder resin in the coating-forming means, no particle of 
the powder resin should exceed the size of the coating-forming means. 
The work pieces may contain resin, such as the resin-bonded magnets and 
plastic parts do. In this case, any solvent of this resin may be added to 
the coating-forming mixture so as to dissolve away the resin on the 
surface of the work pieces and to feed the resin into the coating-forming 
means. The once dissolved resin increases its viscosity during mixing or 
stirring and then adheres to the work pieces to form a resin film. 
Furthermore, the parts containing resin may be preliminarily treated with 
solvent to provide viscosity and hence to form an uncured resin layer on 
the surface of the work pieces. 
The powder material is usually in the range of from 0.05 to 500 .mu.m. The 
smaller size is preferred for a hard and difficult-to-deform powder, such 
as ceramic powder, while the greater size is preferred for ductile powder, 
such as metal powder. Known pigment such as carbon black from 0.01 to 0.05 
.mu.m in size may be used alone or in combination with the other powder 
material. The size of powder material is preferably from 0.1 to 300 .mu.m, 
preferably from 0.1 to 100 .mu.m, and ideally from 0.1 to 50 .mu.m. The 
finer the powder material is, the more likely it is to be captured by 
uncured resin, forced into the space between the powder particles 
dispersed in the resin layer, and bonded with one another and with the 
work piece due to the plastic deformation. Therefore, the finer the powder 
material is, the smaller the striking force is and the surface roughness 
is lessened. 
The coating-forming means can be made of iron, carbon steel, other alloyed 
steel, copper, copper-alloy, aluminum, aluminum-alloy, other metals and 
alloys, ceramics such as Al.sub.2 O.sub.3, SiO.sub.2, TiO.sub.2, 
ZrO.sub.2, SiC and the like, glass, and hard plastics Hard rubber may be 
used provided that it is hard enough to impart a satisfactory striking 
force. Sizes or materials of the coating-forming means may be varied in a 
particular coating-forming mixture. Occasionally, the above materials may 
be surface-treated or surface-coated and then used. Soft media, such as 
wood powder, soft rubber or plastics may be mixed with the above described 
coating-forming means in a volume ratio of 50% or less. The soft means can 
mitigate and uniformize the strking force of the coating-forming means, 
can attain uniformity of the coating and lessen the variance of the 
coating thickness. 
The coating-forming means can have such various shapes as spherical, 
elliptic, cubic, trigometric frustrum, cylindrical, conical, trigometric 
prism, pyramid, rhombohedral, and irregular. 
The components or elements of the coating-forming mixture are determined to 
provide a proportion which does not incline toward any one function of the 
elements. The amount of the powder material and resin is determined by the 
thickness of the coating and the surface area of the work pieces. It is 
preferred that the proportion of the resin and powder material as 
components of the coating-forming mixture provides 0.5% by volume or more 
of resin in terms of cured resin. 
Sequence of loading the components of the coating-forming mixture is 
preferably such that the coating-forming means are mixed in a container by 
vibrating or stirring, and, then, the work pieces, powder material and 
resin are succesively or simultaneously loaded in a container, in which 
the coating-forming means are mixed. When the coating-forming means are 
preliminarily loaded in a container and subjected to vibration or 
rotation, as soon as the other coating-forming mixture is loaded in a 
container, the resin adheres to the work pieces and the requisite striking 
force is generated. 
According to an alternative method according to the present invention, a 
resin film is preliminarily formed on the work pieces and then, the 
coating-forming means, the powder material and the work pieces are 
subjected to vibration of stirring. This method is different from the 
above described method in the fact that the work pieces have the resin 
film which is at least partially uncured at least during the initial 
period of the coating formation. The powder material is captured by this 
resin film as is described for the capturing by the resin film formed by 
the resin as one of the components of the coating-forming mixture. The 
coating film of the alternative method can be formed by various methods, 
such as spraying liquid resin, solid or liquid resin dispersed by solvent, 
or the like onto the work pieces. Alternatively, the work pieces are 
dipped in the liquid resin or the like mentioned above. Thermosetting 
resin may be dispersed on the heated work pieces. When the work pieces are 
resin-bonded magnet or plastic parts, the work pieces can be dipped into 
the solvent and then lifted, thereby dissolving the resin on the surface 
of the work pieces and simply forming the resin film mentioned above. 
Advantageously, the alternative method mentioned above enables the 
formation of a resin film on the entire surface of the work pieces, and a 
decrease to the lowest level in the amount of resin deposited on the 
coating-forming means. Powder material may be dispersed on the resin film 
which is preliminarily formed on the work pieces. 
The resin may be cured during vibration or stirring, thereby enhancing the 
fixing force of the resin which is captured in the resin film. The curing 
method may be curing at normal temperature using two-part mixing resin, 
heating a heating-curing type resin, vaporizing solvent, or irradiation of 
ultraviolet ray, gamma ray, electron ray or other radiation rays. 
Specific order of loading the coating-forming mixture is preferred in the 
following cases (1) and (2). Case (1): Resin powder is used together with 
liquid resin, solvent, or resin dissolved in solvent. When the powder 
resin is preliminarily mixed with the liquid resin and the like, and, when 
the resin powder is likely to dissolve in the liquid resin and the like, 
the resin powder so dissolves and forms the powder-compacted layer with 
difficulty. The powder resin should therefore be added to the 
coating-forming mixture at a late stage. Alternatively, when the powder 
resin is added from the beginning, the liquid resin and the like are 
subsequently added at the same time as the addition of the work pieces. 
Case (2) Any one component of the coating-forming mixture is heated. In 
this case, any one of the following methods is preferably used. The work 
pieces are heated and then loaded in a container, followed by loading the 
resin in the container. The resin and, then the heated work pieces are 
loaded. The heated work pieces and heated coating-forming means are loaded 
in the container, followed by loading resin. 
The coating-forming mixture without the powder material may be 
preliminarily mixed in a container and then the powder material may be 
mixed in a container and then the powder material may be loaded into the 
container. This method is advantageous in the following points (1)-(3). 
(1) When the resin is so diluted with solvent as to have a high fludidity, 
the resin is thoroughly and uniformly spread over the work pieces, thereby 
enabling the formation of a thoroughly uniform resin film and hence a 
uniform powder-coating. (2) The resin coating formed on the work pieces 
has such a distribution of components that the resin and powder contents 
are high at the boundary on the work pieces and the top of the coating, 
respectively. The proportion of these components varies continuously in 
the resin coating. The bonding strength of the resin coating is therefore 
high. (3) The powder material is forced onto the top of the coating at a 
proportion as high as from 40 to 80% by volume, exceedingly greater than 
the pigment proportion in the paint. When the powder material is one of 
TiO.sub.2, MgO, Fe.sub.2 O.sub. 3, and other pigments of paint, the 
coating according to the present invention exhibits excellent shielding 
performance against water and other corrosive media as compared with that 
of the resin coating. Conventionally, in order to attain heavy corrosion 
proofing for paint coating, a multi-layer painting is carried out to 
increase the pigment amount. However, not only is such painting 
complicated, but also the so-formed coating is liable to peel between the 
layers and is disadvantageously thick. The single-step method described 
above is advantageous and can form a thin coating. 
When a resin (hereinafter referred to as "the first resin") coating is 
preliminarily formed on the work pieces according to one of the methods of 
the present invention, resin (hereinafter referred to as "the second 
resin"), which is of the same kind as or a different kind from the first 
resin, may be added to the coating-forming mixture. The second coating 
flows on the resin coating, which is already formed on the work pieces, 
and forms a layer, which then grows and brings about the bonding between 
the powder material and resin. The second resin may be the one diluted 
with solvent. The amount of the second resin is preferably 0.05% or more, 
because the second resin in an amount smaller than this makes the 
deposition of powder material on the work pieces poor. 
The proportion of the volume of the coating-forming means to the work 
pieces is dependent upon the shape of the work pieces. The coating-forming 
means is preferably 20% or more, preferably 50% or more in terms of 
apparent volume ratio. Otherwise, the work pieces are not subjected to 
uniform striking force and, hence, a good coating is obtained with 
difficulty. 
It is possible to form a single layer of the coating by any one of the 
methods described above and then to form another or other layers of the 
coating by any one of the methods described above. The so-formed 
multi-layer coating can be as thick as from 10 to 300 .mu.m, thereby 
furthermore utilizing the properties of the powder material as opposed to 
those of the single-layer coating. Any defect, such as pinholes, formed in 
the first layer can be repaired by the second or subsequent layer. The 
parts exposed to brine are very corrosion-resistant, when three or more 
layers are formed. 
Other preferred embodiments, which can be found in the present invention 
are now described. 
(1) An opening hole(s) is formed in a container at its bottom or side 
portion, a work piece is passed through the opening hole(s) in such a 
manner that the part to be coated is exposed in the container. The work 
piece is displaced relative to the container so that the coating according 
to the present invention is formed on the work pieces. This method attains 
a continuous formation of the coating on long parts, wires or sheets. 
(2) After forming the single or multi-layer coating on the work pieces, the 
resin of the coating is cured. The coating is thus strengthened and the 
loss of powder is prevented. The curing is carried out by means of heating 
the coating in or outside of the container to the curing temperature of 
resin. Alternatively, the solvent may be vaporized by allowing it to be 
exposed at the ambient temperature. The curing may be carried out by 
irradiating the coating with gamma ray or electron beam, depending upon 
the kind of resin. 
(3) After forming the coating on the work pieces, free powder remaining on 
the work pieces is removed. The powder material may occasionally be loose 
and remain on the work pieces. Such powder material should be removed when 
the work pieces treated by the method according to the present invention 
are to be used for an electronic, electric or precision machine, to which 
the dust or particles are halmful. The powder material is therefore 
preferably removed by ultra-sonic cleaning or blowing air. The free powder 
can be removed either before or after curing the resin. 
The free remaining powder can be removed by subjecting the surface of the 
work pieces to friction by soft media. Soft media and the work pieces are 
mixed in a container by imparting the vibration or stirring. By this 
method shear force is generated between the soft media and the work pieces 
so that the free powder is removed and the surface of the coating is 
polished. This method is more effective for powder removal than 
ultra-sonic cleaning, and also provides a beautiful finish. This method is 
therefore appropriate for parts used as ornamental or decorative pieces. 
The soft media is preferably one that absorbs impact somewhat and hence 
does not impart such a strong striking force to the work pieces that they 
are damaged or deeply scratched. Preferred soft media are wood chips, 
shavings and sawdust, walnut shells, soft plastics and rubber. The wood 
chips may be impregnated with oil so as to enhance the surface-polishing 
effect of the soft media and rust-proofing of the work pieces. 
(5) The work pieces, on which the coating is formed, are heat treated. One 
of the objects of the heat treatment is to cure the resin. The curing 
temperature of resin is dependent on the resin but is usually in the range 
of from 30.degree. to 200.degree. C. The curing time is usually from 1 to 
500 minutes. Another object of the heat treatment is to induce diffusion 
between the work pieces and the powder material and hence to increase the 
bonding strength. Another object of the heat treatment is to lessen the 
number of pinholes and to make the coating as continuous as possible. 
Still another object is to homogenize the coating and to improve the 
corrosion resistance and mechanical properties. When the heat-treatment 
temperature is higher than the melting point of the powder material, the 
powder material melts, resulting in melt-sagging and bonding of the work 
pieces. The heat-treatment temperature is less than the melting point of 
the powder material. Since the temperature of heat treatment having the 
objectives as described above, is usually higher than the decomposition 
temperature of resin, the coating consists essentially of the powder 
material after the heat treatment. When the coating is heat treated, the 
resin is preferably one that easily decomposes and vaporizes and does not 
leave carbon and the like in the coating. Preferable resins are paraffin, 
polypropylen, and various waxes. The proportion of resin before the heat 
treatment is preferably as small as possible, for example 50% or less. 
When the powder material used has a relatively low melting point, such as 
Sn, Zn or its alloy, heat-resistant resin such as phenol fluorine or 
silicone resin, or inorganic binder may be used. Such resin or the like 
remains in the coating in a relatively high amount after the heat 
treatment. 
The heat treatment is advantageous when the powder material has a 
relatively low melting point, such as Zn, Sn or its alloys. Such metal 
prevents corrosion of almost all metals by the sacrificing 
corrosion-preventing effect. In order to fully realize this function, the 
coating is necessarily virtually continuous. Corrosion prevention under 
severe conditions such as under rain water or brine water could be 
provided by the heat treatment described above. Conventionally, the Zn or 
Sn coating is formed by electro-plating or hot-dip galvanizing. The former 
method is wet process, which incurrs the treatment of waste liquid and 
by-products. The coating by the latter method is 100 .mu.m or more, and, 
therefore, the thin coating is not obtained. The latter method is not 
appropriate for forming a coating on small parts. Contrary to this, the 
method according to the present invention is a dry method, simple, and 
enables the formation on small parts a coating as thin as from 0.1 to 100 
.mu.m. 
(6) The work pieces, on which the coating is formed, is further coated with 
resin which is the same kind as or different from that of the coating. 
Since the top of the coating formed by the method of the present invention 
contains a smaller amount of powder material than its inner part, the 
powder material may be removed from the coating or the coating may be 
locally destroyed when the coating is subjected to impact or strong force 
from outside during handling of the parts or their fitting in a machine. 
The resin which is further coated on the work pieces subjected to the 
coating process of the present invention prevents the powder removal and 
damage of parts as described above. It also fills the pinholes so that it 
enhances the corrosion resistance against water and strength of the entire 
coating. This method is advantageous for applying to the work pieces which 
are not heat treated. 
The top resin coating described above can be formed by spraying or dipping 
the work pieces in the resin. It can also be formed by modifying the 
method of the present invention; that is, the powder material is not used 
for the coating-forming mixture. A thin and uniform top resin coating is 
formed by such modified method under the function of coating-forming 
means. The top resin coating may be a conventional paint coating with 
pigment, which provides a beautiful appearance. 
In addition to the protective coating by the resin, the metal or alloy 
plating as well as dispersing plating of metal and non metallic material 
may be applied. Heretofore, when the substrate material is 
electro-insulative, such as plastics and ceramics, or when the substrate 
material has poor electro-conductivity such as resin-bonded magnets, and 
is not uniform, direct electro-plating on the substrates is difficult. A 
complicated and expensive pre-treatment, e.g., an electroless plating, is 
necessary before such electro-plating. Contrary to this, electro-plating 
on the coating according to the present invention is easy, since it is a 
metal-rich layer firmly bonded on the work pieces. 
According to the conventional plating methods, plating on some materials is 
difficult because they have a detrimental chemical reaction with the 
electrolytic liquid. One example of such materials is the one produced by 
the powder metallurgical process. Since such material has pores, the 
plating liquid penetrates even into the pores of the material and causes 
undesirable corrosion or electro-deposition in its interior. When the 
powder metallurgical material is subjected to the coating formation 
according to the present invention and then to the plating, the plating 
coating can be easily formed. This method is more advantageous than the 
known method of physical vapor deposition (PVD) followed by plating, from 
the view point of investing cost. The plating layer formed on the coating 
according to the present invention may include pinholes. In this case, the 
plating layer is thickly formed or electroless plating layer is formed on 
the coating according to the present invention, followed by plating.

Preferred embodiments are further described with reference to the drawings. 
The vibration or stirring in a container can be carried out by various 
methods as illustrated in FIGS. 1 through 9. 
An arm secured to a rotary shaft 4 installed in a container 2 (FIG. 1), 
blades 5 (FIG. 2) secured to a rotary shaft 4, and an impeller, blades or 
the like of a stirrer may be used. The coating-forming mixture is denoted 
in the drawings by reference numeral 10. In addition, a container in the 
form of a drum or pot may be rotated on a roller 6 shown in FIG. 3. As is 
shown in FIG. 4, a container in the form of a drum may be fixed to a 
rotary shaft and be rotated. The top of the container may be opened or 
closed. A container 2 may be shaken as shown in FIG. 5. During shaking, 
stirring may be carried out. Furthermore, arms 7 (FIG. 6) may be 
symmetrically secured to a rotary shaft 4, and the containers 2 fitted 
onto the front ends of the arms. The coating-forming mixture is loaded in 
the containers 2 and is subjected to centrifugal force to mix the same. 
Preferably, the containers 2 rotate around their axes. The container may 
be embodied as a holder in the form of a disc. 
A vibrator 8 may be provided in or outside of a container 2 so as to impart 
the vibration to the coating forming mixture as shown in FIG. 7. 
The force imparted to the coating-forming mixture is hereinafter described 
with reference to an example of vibrating the mixture. This force is 
hereinafter referred to as the vibrating force. The vibrating force is 
divided by the sum of weights of the container and coating-forming mixture 
(this sum being referred to as "the vibrating weight") so as to define the 
vibrating ratio in arbitrary units. This vibrating ratio is an index 
indicating the impact force which is generated by the coating-forming 
mixture and is imparted to the work pieces. According to a specific 
example, a container has a volume of 2.8 liter and weight of 1 kgf, the 
coating-forming means are steel balls 10 kgf in weight, and the work 
pieces are 1 kgf in weight. The vibrating weight is 12 kgf. Preferred 
vibrating force in this example is from 20 to 50 kgf at 40Hz period. The 
vibrating ratio is therefore from 1.67 (=20/12) to 4.17(50/12). According 
to another specific example with a greater container, a container has 20 
liter in volume and 4.5 kgf in weight, the coating-forming means are steel 
balls of 70 kgf in weight, and the work pieces are 5.5 kgf in weight. The 
vibrating weight is 80 kgf. Preferred vibrating force in this example is 
from 150 kgf at 25Hz period. The vibrating ratio is therefore 1.88 
(=150/80). 
When tough work pieces, such as steel work pieces, are treated, the 
vibration ratio may be 10 at the highest. However, when brittle work 
pieces, such as rare-earth magnets, bonded magnets, ceramics and glass, 
are treated, the vibrating ratio is preferably 5 at the highest. The 
vibrating ratio is preferably 1, more preferably 1.5 at the lowest. When 
the vibrating ratio is less than this value, the growing speed of the 
coating becomes late. On the other hand, when the vibrating ratio is more 
than the above described value, brittle work pieces are liable to be 
destroyed, and the coating-forming means are liable to deform. The 
vibrating frequency is not at all limited but is preferably in the range 
of from 2 to 200Hz. An amplitude of from 0.5 to 10 mm enables the 
provision of the above described vibrating ratio. 
In the stirring case, the rotation takes place and centrifugal force is 
generated. In calculating the vibrating ratio, the centrifugal force is 
converted to the vibrating force under the calculation described above. 
The thus calculated vibrating ratio is preferably within the ranges 
described above. 
Vibration may be carried out by using an apparatus shown In FIG. 8. A 
U-shaped trough 20 is disposed aslant preferably at an inclination of from 
1.degree. to 20.degree. and is attached to the bottom of a vibrator 8. The 
coating-forming mixture 10 is caused to slide down along the trough 20, 
while being vibrated. The cross section of the trough 20 is not limited to 
a U-shape but may be variously shaped, such as circular, V shaped or 
rectangular. The upper part of the trough 20 may not be open. A vibrating 
sieve 22 is located beneath the lower end of the trough 20. The vibrating 
sieve 22 comprises a mesh smaller than the work pieces 23 and greater than 
the coating-forming means such as steel balls 24, and a frame, to which 
the mesh is fixed. The steel balls 24 fall therefore on and then through 
the vibrating mesh 22, while the work pieces 23 fall on the vibrating mesh 
22 and are then conveyed together with the vibrating mesh 22. The steel 
balls 24 are collected by a conveyer 30 located below the vibrating mesh 
22 and are then used again for forming the coating. The work pieces 23 are 
collected by a conveyer 31 located at the lower end of the vibrating 
trough 22. The coating formation can be carried out in a continuous and 
automatic manner. The trough 20 may be arranged in a zigzag or spiral 
pattern as shown in FIG. 9. This arrangement reduces the space occupied by 
the trough. Although not shown in the drawings, the entire trough may be 
located in a container, which is vibrated. 
When relatively large parts or sheets are to be coated, the methods 
described hereinafter are preferred. 
A container 2 shown in FIG. 10 is separated by parting plates 30 to form 
the regions 31, into which the parts 33 are loaded. The container 2 is 
vibrated. When metal mesh is used instead of the parting plates shown in 
FIG. 10, the coating-forming means 7 freely pass through the mesh and move 
across the container space. The powder therefore uniformly spreads over 
the surface of the parts 33. Uniform coating can therefore be formed. In 
addition, as is shown in FIG. 11, the parts 33 may be suspended down into 
the container 2 by hangers 36. 
As is shown in FIG. 12, the parts are fixed in a container 1, and the 
container 1 and/or parts 3 are fixed to a vibrator 8, which directly or 
indirectly vibrates the parts 33. In addition, as is shown in FIG. 13, the 
parts 33 are suspended by a hanger 36 into a container 1, which is 
vibrated. Only one surface of the parts 33 is coated. Only part of the 
surface of the parts 33 can be coated when the parts 33 are put into the 
coating-forming means and powder as is shown in FIG. 14. 
Resin may be applied on a part of the surface of parts by brushing or 
spraying on the parts selectively masked by a tape or the like. The parts 
thus applied with resin are subjected to the methods described above, so 
as to form the coating of the present invention on the resin-applied 
surface. 
Hereinafter are described preferred methods for continuously forming the 
coating on a sheet, wire, rod, pipe or the like. 
A long sheet, wire, rod or pipe is passed through the aperture 28 formed at 
the bottom of a container 1 and equipped with a packing 39. The 
coating-forming means are loaded in the container 1. Resin and powder 
material are then loaded, possibly continuously little by little, into the 
container 1 being vibrated. The long sheet or the like is tightly pulled 
downwards or upwards through the packing 39. A resin layer may be 
preliminarily formed on the work pieces 33, while only the powder and 
coating-forming means are loaded in the container 1. 
Referring to FIG. 16, a part 33 is shifted to the one side of the container 
1 so as to form the coating on the one side of a sheet. The parts 33 may 
be pulled from a container horizontally as shown in FIG. 17. A plurality 
of apertures 28 may be formed so as to enable a plurality of long parts 
33, such as fine copper wires, to be pulled out continuously and 
effectively. 
Cured or uncured resin or volatile liquid may be applied on the 
coating-forming means to form a film. When the coating-forming mixture 
including the coating-forming means is subjected to the vibration or 
stirring, the powder, which is deposited once on the coating-forming 
means, then deposits on the work pieces. The powder therefore deposits 
uniformly on the work pieces. In addition, edges of the work pieces are 
difficult to crack, the powder deposited on the work pieces is difficult 
to be removed from the work pieces due to collision by the coating-forming 
means. The film mentioned above promotes therefore uniform formation of 
the coating on the work pieces. In order to more positively utilize the 
function of the cured-resin film or the like, the coating-forming mixture 
except for the work pieces is preferably subjected to the vibration or 
stirring before loading of the work pieces, because amount of powder once 
deposited on the powder-coating means can be increased. The vibration and 
stirring condition may be the same as that described above. 
According to a preferred embodiment of the present invention for forming an 
electro-conductive coating, such as a shield coating for EMI 
(electro-magnetic interference) prevention, the vibration or stirring is 
preferably carried out in a non-oxidizing atmosphere, e.g., inert-gas 
atmosphere (Ar, N.sub.2 or the like) having a residual oxygen content of 
10% or less, preferably 5% or less, ideally 3% or less. By this method, it 
is possible to provide 0.5 .OMEGA./.quadrature. or less of surface 
electro-resistance, while the surface electro-resistance of the coating 
produced in air is as high as a few K.OMEGA./.quadrature.. 
It may be difficult to form the coating on the corners of a vessel's 
interior. The coating on such corners is important for an EMI prevention, 
since leakage of electromagnetic wave through the non-coated corners is 
detrimental as well. According to a preferred method for forming the 
coating having skeleton structure as shown in FIG. 36, uncured resin or 
other adhesive media is preliminarily deposited on the coating-forming 
means, such as steel balls 42. The powder material 41 is adhered on the 
uncured resin or the like. The steel balls 42 are projected through the 
nozzle 45. An uncured-resin layer 43 is preliminarily formed on the inner 
side of a vessel 40. When the steel balls 42 are impinged on the vessel 
40, the powder material 1 is captured by and forced in the uncured-resin 
layer 43. The steel balls 42, from which the powder material 41 is 
separated, fall down. The steel balls 42 supplied from the nozzle 45 
successively impinge, so that the powder material is further forced in the 
uncured-resin layer 43. The powder material is compacted to enhance 
density of the coating, in which the skeleton structure is therefore 
produced. Although not shown in FIG. 36, the powder material 41 and the 
steel balls 42 may be projected separately toward an identical part of the 
vessel 40. The projection may be carried out mechanically or by utilizing 
gas stream. 
The present invention is hereinafter described with reference to the 
examples. 
EXAMPLE 1 
In order to facilitate the observation of a fracture surface of the coating 
according to the present invention, the coating is formed on a glass plate 
30 mm.times.20 mm.times.2 mm in size. Steel balls 3.0 mm in diameter at a 
total amount of 10 kg were first loaded in a spherical pot 2.8 liter in 
volume and 150 mm in depth. Apparent filling density was approximately 5 
kg/liter. While vibrations of 2500 cpm (cycle per minute) and 0.5 to 2 mm 
in amplitude were imparted to the pot, 20 g of TiO.sub.2 powder with an 
average diameter of 0.3 .mu.m was loaded in the pot. The vibration was 
continued for 15 minutes. 
Twenty glass pieces were preliminarily dipped in methylethyl ketone (MEK), 
in which 10% of epoxy resin (94% of resin and 6% of curing agent) was 
dissolved. The glass pieces were thus coated with resin. The glass pieces 
were loaded in the pot and the vibration was carried out for 15 minutes. 
The glass pieces were then taken out from the pot. Heat treatment was 
carried out at 120.degree. C. for 2 hours. The glass pieces were loaded in 
the container of the same size as described above together with 2.0 kg of 
walnut shells. Vibration was carried out for 5 minutes to remove the 
TiO.sub.2 powder remaining unfixed on the glass pieces. The glass pieces 
were taken out of the pot and cleaved. The fracture plane was observed by 
an SEM. The SEM images at magnification of 4000 and 13000 are shown in 
FIGS. 19 and 20, respectively. 
The resin layer and powder-compacted layer are 1.5 um and 15 um thick, 
respectively. As is shown in FIG. 19, the two layers are anchored to one 
another and an intricate border is formed between the two layers. The 
skeleton structure is clear from FIG. 20. That is, since the TiO.sub.2 is 
particles with a fine diameter, the skeleton structure can be observed 
with a microscope at magnification of 1000 or more. In FIG. 20, the 
contour of the particles appears to blur, because the particles are 
covered with resin. The resin is filled in the interior of the 
powder-compacted layer. The powder is 40% by volume or more in the 
powder-compacted layer. In addition, when the samples were cleaved for the 
observation of the cross section, the powder-compacted layer fell off. 
Such fell portions appear in the photograph and do not reproduce the 
structure of the powder-compacted layer. Virtually no difference in the 
density of particle distribution is present in the powder-compacted layer 
as is clear from the photograph. The skeleton structure is disordered at 
the top middle portion and the bottom right portion of the 
powder-compacted layer. Cavities, which appear to be isolated pores, are 
formed in the disordered skeleton structure, and are filled with resin. 
EXAMPLE 2 
Steel balls 3.0 mm in diameter in a total amount of 10 kg were first loaded 
into a spherical pot 2.8 liter in volume and 150 mm in depth. Apparent 
filling density was approximately 5 kg/liter. While vibrations of 3500 cpm 
and 0.5 to 2 mm in amplitude were imparted to the pot, 20 g of atomized Al 
powder with an average diameter of 3 .mu.m was loaded into the pot. 
Vibration was continued for 5 minutes. Twenty glass pieces were 
preliminarily dipped in methylethyl ketone (MEK), in which 10% of epoxy 
resin (94% of resin and 6% of curing agent) was dissolved. The glass 
pieces were thus coated with resin. The glass pieces were loaded into the 
pot and the vibration was carried out for 15 minutes. The glass pieces 
were then taken out from the pot. Heat treatment was carried out at 
120.degree. C. for hours. The glass pieces were loaded in a container of 
the same size as described above together with 2.0 kg of walnut shells 
with an average particle-diameter of 2 mm. Vibration was carried out for 5 
minutes to remove the Al powder remaining unfixed on the glass pieces. The 
glass pieces were taken out of the pot and cleaved. The fracture plane was 
observed by an SEM. The SEM image of the cross section is shown in FIG. 
20. The SEM image of the surface is shown in FIG. 21. 
The resin layer and powder-compacted layer are 8 um and 1 um thick, 
respectively. The powder content is 50% or more by volume and is locally 
70% or more by volume. The atomized Al powder is spherical. The Al powder 
in the powder-compacted layer is flat, and the peripheral shape is sharply 
edged. The skeleton structure is formed by the stacked flat pieces. The 
clearances between the flat pieces are partly filled with resin in the 
form of a layer. 
EXAMPLE 3 
Steel balls 3.0 mm in diameter in a total amount of 10 kg were first loaded 
into a spherical pot 2.8 liter in volume and 150 mm in depth. Apparent 
filling density was approximately 5 kg/liter. While vibrations of 3500 cpm 
and 0.5 to 3 mm in amplitude were imparted to the pot, 20 g of TiO.sub.2 
powder with an average diameter of 3 .mu.m was loaded into the pot. 
Vibration was continued for 5 minutes. Twenty magnets were preliminarily 
dipped in methylethyl ketone (MEK), in which 10% of epoxy resin (94% of 
resin and 6% of curing agent) was dissolved. The magnets were thus coated 
with resin. The magnets were loaded into the pot and the vibration was 
carried out for 15 minutes. The magnets were then taken out from the pot. 
Heat treatment was carried out at 120.degree. C. for 2 hours. The magnets 
were loaded into a container of the same size as described above together 
with 2.0 kg of walnut shells. Vibration was carried out for 5 minutes to 
remove the TiO.sub.2 powder remaining unfixed on the magnets. The magnets 
were taken out of the pot. 
The above process was repeated once. The vibrating time was however 8 
minutes. The magnets were then dipped in methylethyl ketone (MEK), in 
which 30% of epoxy resin (97% of resin and 3% of curing agent) was 
dissolved. Heat treatment was then carried out at 120.degree. C. for 2 
hours. The magnets were then cleaved. The fracture plane was observed by 
an SEM. The SEM image of the cross section is shown in FIG. 22. The SEM 
image of the surface is shown in FIG. 21. 
The first resin layer and first powder-compacted layer are 1 .mu.m and 18 
.mu.m thick, respectively. The second resin layer and second 
powder-compacted layer are 1 .mu.m and 12 .mu.m thick, respectively. The 
top resin layer is 9 .mu.m thick. The powder content is 40% by volume or 
more both in the first and second powder-layers. The skeleton structure is 
unclear from FIG. 22, because the magnification was adjusted to 2600 so as 
to be able to observe the whole layers, and, also becauser the 
powder-particles were covered with resin. The skeleton structure was 
observed at magnification of 2000. 
EXAMPLE 4 
Steel balls 3.0 mm in diameter in a total amount of 10 kg were first loaded 
into a spherical pot 2.8 liter in volume and 150 mm in depth. Apparent 
filling density was approximately 5 kg/liter. While vibrations of 2500 cpm 
and 5 mm in amplitude were imparted to the pot, 30 g of atomized Al powder 
with am average diameter of 3 .mu.m was loaded into the pot. Vibration was 
continued for 5 minutes. Twenty glass pieces were preliminarily dipped in 
methylethyl ketone (MEK), in which 15% of epoxy resin (97% of resin and 3% 
of curing agent) was dissolved. The glass pieces were thus coated with 
resin. The glass pieces were loaded into the pot and the vibration was 
carried out for 20 minutes. The glass pieces were then taken out from the 
pot. Heat treatment was carried out at 120.degree. C. for 2 hours. The 
glass pieces were loaded into a container of the same size as described 
above together with 2.0 kg of walnut shells with an average 
particle-diameter of 2 mm. Vibration was carried out for 5 minutes to 
remove the Al powder remaining unfixed on the glass pieces. The glass 
pieces were taken out of the pot. Subsequently, the work pieces were 
subjected to electrolytic plating using a conventional Ni Watt bath to 
form a 4 .mu.m thick Ni plating layer. The glass plates were then cleaved. 
The fracture plane was observed by an SEM. The SEM image of the cross 
section is shown in FIGS. 23 layer(magnification-1300) and 
24(magnification-930). 
The resin layer and powder-compacted layer are 3 .mu.m and 5 um thick, 
respectively. The powder content is 50% or more by volume. A cleavage 
formed at the cleaving appears between the Ni plating layer and the 
powder-compacted layer. 
EXAMPLE 5 
Rapidly cooled magnet powder was used. The composition was Fe.sub.81 
Nd.sub.13 B.sub.6, and the particle size was 100 .mu.m or less. 3% by 
weight of epoxy resin was mixed with the magnet powder and compacted at a 
pressure of 5 ton/cm.sup.2. One hundred forty green compacts 22 mm in 
outer diameter 20 mm in inner diameter and 10 mm in thickness were 
obtained. The green compacts were cured at 150.degree. C. for 1 hour to 
produce the resin-bonded magnets. 
Twenty magnets were subjected to each of Examples 1 through 4 so as to form 
the coating of the respective example. However, the thickness of the 
coating and respective layers is as follows. 
______________________________________ 
Thickness Thickness 
of Powder of Resin or 
Example Resin Layer 
Layer Plating Layer 
Total 
______________________________________ 
1 1 .mu.m 10 .mu.m -- 11 .mu.m 
2 1 .mu.m 9 .mu.m -- 10 .mu.m 
3 1 .mu.m .times. 2 
8 .mu.m .times. 2 
2 .mu.m 20 .mu.m 
4 1 .mu.m 5 .mu.m 10 .mu.m 16 .mu.m 
______________________________________ 
For the purpose of comparison, the following methods (5) -(7) were carried 
out. 
(5) Epoxy resin with 20% of TiO.sub.2 additive was sprayed and applied on 
the resin-bonded magnets, followed by curing at 120.degree. C. for 6 
hours. The so-formed single coating layer was 20 um thick in average 
(comparative example) 
(6) Zinc phosphate chemical conversion liquid was sprayed on the 
resin-bonded magnets and then dried. Epoxy-resin with 20% of TiO.sub.2 
additive was then spray-coated. Curing was carried out at 120.degree. C. 
for 6 hours. The so-formed single coating layer was 20 .mu.m thick in 
(comparative example). 
(7) No coating was formed on the resin-bonded magnets, which were tested as 
produced (comparative example). 
Twenty magnets treated by each of the methods as described above were 
subjected to a wet humid test under the conditions of 85.degree. C. and 
90% RH, so as to evaluate the corrosion-resistance. After the test, the 
appearance was checked. 
TABLE 1 
______________________________________ 
Method Exposure Time (hrs) 
(Example) 250 500 1000 1500 
______________________________________ 
1 A A B B 
2 A B C D 
3 A A A B 
4 A A A A 
5 B C E -- 
6 A B D E 
7 D E -- -- 
______________________________________ 
Remarks 
Judging Criterion: 
A: No rust formation on all of the samples at all. 
B: No rust formation macroscopically. However, spot rust formed on less 
than 10% of the samples, which was recognized by a microscope. 
C: Such rust as detectable with the naked eye was formed on less than 10% 
of the samples. 
D: Such rust as detectable with the naked eye was formed on from 10% to 
less than 30% of the samples. 
E: Serious rust, swelling of coating, or peeling of coating occurred on 
30% or more of the samples. 
It was proven as a result of the above tests that the inventive coating is 
superior to the conventional resin-coating with regard to the corrosion 
resistance. 
EXAMPLE 5 
Samples were cut from a rolled low-carbon steel (0.03%C) 20 mm.times.20 
mm.times.3 mm in size. Steel balls 3.0 mm in diameter of a total amount of 
10kg were first loaded into a spherical pot 2.8 liter in volume and 150 mm 
in depth. While vibrations of 1000 cpm and 5 mm in amplitude were imparted 
to the pot, 30g of various powder was loaded into the pot being vibrated. 
Vibration was continued for 5 minutes to vibrate the Al and other powder 
as well as the steel balls. Ten samples of the cut steel sheets were 
preliminarily dipped in 10% epoxy resin solution in MEK. The samples were 
thus coated with resin. The samples were loaded in the pot and the 
vibration was carried out for 15 minutes. The samples were then taken out 
from the pot. Heat treatment was carried out at 120.degree. C. for 2 
hours. The samples were loaded into a container of the same size as 
described above together with 2.0kg of walnut shells with an average 
particle-diameter of 2 mm. Vibration was carried out for 5 minutes to 
remove the powder remaining unfixed on the samples. The samples were taken 
out of the pot and cleaved. Finally, the samples were dipped in 30% 
epoxy-resin solution (epoxy resin94% of resin and 6% of curing agent). 
After drying, curing was carried out at 120.degree. C. for 2 hours. 
Materials of powder, average diameter of particles and thickness of the 
formed powder layer are as follows. 
______________________________________ 
Average Thickness of 
Material of particle- Powder-compacted 
Powder Diameter (.mu.m) 
Layer (.mu.m) 
______________________________________ 
1 Al 3 10 
2 Cu 2 10 
3 Ti 8 10 
4 Stainless 3 10 
Steel 
5 Cr 2 10 
6 Co 2 10 
7 Ni 2 10 
8 Zn 2 15 
9 Pb 1 10 
10 Sn 2 15 
11 Ag 1 5 
12 Au 1 5 
13 MgO 0.5 10 
14 Al.sub.2 O.sub.3 
0.5 10 
15 SiO.sub.2 0.7 10 
16 TiO.sub.2 0.3 10 
17 CrO.sub.2 0.6 10 
18 MnO.sub.2 0.9 10 
19 Fe.sub.2 O.sub.3 
1.0 10 
20 CoO 0.8 10 
21 NiO 0.5 10 
22 CuO 0.9 10 
23 ZnO 0.3 10 
24 ZrO.sub.2 0.3 10 
25 MoO 0.4 10 
______________________________________ 
The volume ratio of powder is 40% or more in the powder layer formed by any 
one of the methods. 
For the purpose of comparison epoxy resin with 20% by volume of TiO.sub.2 
was sprayed on a sample and cured at 120.degree. C. for 6 hours. As a 
result, a single resin coating with average thickness of 20 .mu.m was 
formed. 
The samples treated as described above were subjected to a neutral 
brine-water spraying test stipulated in the JIS corrosion test (35.degree. 
C., 5% NaCl, 16 hours). Rust formed on the edges of all of the comparative 
samples. No rust was detected for the samples produced by the methods Nos. 
1-25. 
EXAMPLE 6 
Twenty of the same steel samples as in Example 5 were prepared. Zn powder 
was used and the coating was formed under the same conditions as in 
Example 5 for ten samples. The other ten samples were subjected to shot 
blasting to clean the surface. A 40 .mu.m thick Zn layer was formed on the 
samples by flame spraying. The samples with the coating formed as 
described above were subjected to the peeling test of coating. That is, 
five grooves each in horizontal and vertical directions were scratched 
crosswise on the coating with a knife at a distance of 1 mm to such a 
depth that they penetrate the coating. An adhesive tape (cellophane tape) 
was adhered on the coating with the grooves, and then peeled. The flame 
sprayed coating totally peeled. The inventive coatings did not peel at 
all. 
EXAMPLE 7 
The powder for bonded magnet was used. The powder had composition of 
SmCo.sub.4.8 and average particle of 20 .mu.m. 3% by weight of epoxy resin 
was mixed with the magnet powder and compacted at a pressure of 5 
ton/cm.sup.2. Eighty green compacts 22 mm in outer diameter 20 mm in inner 
diameter and 10 mm in thickness were obtained. The green compacts were 
cured at 150.degree. C. for 1 hour to produce the resin-bonded magnets. 
Steel balls 3.0 mm diameter in diameter in a total amount of 10 kg were 
first loaded into a spherical pot 2.8 liter in volume and 150 mm in depth. 
While vibrations of 2500 cpm and 0.5 to 5 mm in amplitude were imparted to 
the pot, 20 g of aluminum powder with an average diameter of 5 .mu.m was 
loaded in the pot being vibrated. Vibration was continued for 5 minutes to 
vibrate the Al powder as well as the steel balls. Twenty magnets were 
preliminarily dipped in 10% epoxy resin solution in MEK. The magnets were 
thus coated with resin. The magnets were loaded in the pot and the 
vibration was carried out for 15 minutes. The magnets were then taken out 
from the pot. Heat treatment was carried out at 120.degree. C. for 2 
hours. The samples were loaded in a container of the same size as 
described above together with 2.0 kg of walnut shells with an average 
particle-diameter of 2 mm. Vibration was carried out for 5 minutes to 
remove the powder remaining unfixed on the magnets. 
The following various kinds of power were coated on the magnets by the same 
methods as described above. Twenty magnets were produced for each kind of 
powder. 
1--Coating with an average thickness of 10 .mu.m by the above described 
method. 
2--Instead of the aluminum powder, TiO.sub.2 powder with the average 
diameter of 0.3 .mu.m was used to form the coating with the thickness of 7 
.mu.m. 
3--Epoxy resin with 20% of the TiO.sub.2 additive was spray-coated on the 
resin-bonded magnets. Curing was carried out at 120.degree. C. for 6 
hours. A 10 .mu.m thick single coating was obtained (comparative coating). 
As a result of SEM observation, it turned out that, although the coatings 1 
and 2 covered the entire surface of the magnets, the coating 3 was 
extremely thin on several edges of the magnets. Such thin coating would 
not cause the corrosion of SmCo magnets but would cause dusting of the 
magnet powder. 
EXAMPLE 8 
The powder for bonded magnet was used. The powder had composition of 
Sm(Co.sub.0.72 Fe.sub.0.2 Cu.sub.0.06 Zr.sub.0.03)8.3 and average particle 
of 20 .mu.m. 3% by weight of epoxy resin was mixed with the magnet powder 
and compacted at a pressure of 5 ton/cm.sup.2. One hundred green compacts 
22 mm in outer diameter, 20 mm in inner diameter and 10 mm in thickness 
were obtained. The green compacts were cured at 150.degree. C. for 1 hour 
to produce the resin-bonded magnets. 
Steel balls 3.0 mm in diameter in a total amount of 10 kg were first loaded 
into a spherical pot 2.8 liter in volume and 50 mm in depth. While 
vibrations of 2500 cpm and 1 mm in amplitude was imparted to the pot. 20 g 
of copper powder with an average diameter of 1 .mu.m was loaded into the 
pot being vibrated. Vibration was continued for 5 minutes to vibrate the 
Cu powder as well as the steel balls. Twenty magnets were preliminarily 
dipped in 10% epoxy resin solution of MEK. The magnets were thus coated 
with resin. The magnets were loaded into the pot and the vibration was 
carried out for 15 minutes. The magnets were then taken out from the pot. 
Heat treatment was carried out at 120.degree. C. for 2 hours. The magnets 
were loaded into a container of the same size as described above together 
with 2.0 kg of walnut shells with an average particle-diameter of 2 mm. 
Vibration was carried out for 5 minutes to remove the powder remaining 
unfixed on the magnets. The resin-bonded magnets were then dipped in a 5% 
epoxy resin solution of MEK. After drying, curing was carried out at 
120.degree. C. and 2 hours. 
Twenty magnets were coated with each of following various powder by the 
same method as described above. Twenty magnets were produced for each kind 
of powder. The magnets were subjected to test of corrosion resistance 
under the condition of 85.degree. C. and 90% of relative humidity (RH). 
1--Coating with an average thickness of 10 .mu.m by the above described 
method. 
2--Instead of the aluminum powder, TiO.sub.2 powder with an average 
diameter of 0.3 .mu.m was used to form 7 .mu.m thick coating. 
3--Epoxy resin with 20% of the TiO.sub.2 additive was spray-coated on the 
resin-bonded magnets. Curing was carried out at 120.degree. C. for 6 
hours. A 10 um thick single coating was obtained (comparative coating). 
4--The resin-bonded magnets as produced without the coating were subjected 
to the test. 
TABLE 3 
______________________________________ 
Exposure Time (hours) 
Coating 250 500 1000 1500 
______________________________________ 
1 A A B C 
2 A A B B 
3 B B C E 
4 D D E -- 
______________________________________ 
The judging criterion is the same as described below Table 1. 
EXAMPLE 9 
An ingot having a composition of Nd.sub.13.8 Dy.sub.0.4 Fe.sub.78.2 
B.sub.7.6 was roughly crushed with a stamp mill to provide powder having 
average particle diameter of 20 .mu.m and then finely crushed by a jet 
mill to provide powder having an average particle diameter of 3.0 um. The 
resultant fine powder was compacted in a metal die at a pressure of 1.5 
t/cm.sup.2, while applying 12 kOe of vertical magnetic field perpendicular 
to the pressing direction. The resultant green compacts were sintered in 
vacuum at 1100.degree. C. for 2 hours and then aged at 650.degree. C. for 
1 hour. As a result, one hundred twenty sintered compacts were obtained. 
The entire surface of the sintered compacts were ground, followed by 
smoothening the corners with centrifugal barrel polishing. The sintered 
compacts were then cleaned and dried. The products were in the form of a 
disc 20 mm in diameter and 6 mm in height 
Steel balls 3.0 mm in diameter in a total amount of 10 kg were first loaded 
in a spherical pot 2.8 liter in volume and 150 mm in depth. While 
vibrations of 2500 cpm and 5 mm in amplitude were imparted to the pot, 20 
g of aluminum powder with an average diameter of 4 um was loaded into the 
pot being vibrated. Vibration was continued for 5 minutes to vibrate the 
Al powder as well as the steel balls. Twenty magnets were preliminarily 
dipped in 10% epoxy resin solution of MEK. The magnets were thus coated 
with resin. The magnets were loaded into the pot and the vibration was 
carried out for 15 minutes. The magnets were then taken out from the pot. 
Heat treatment was carried out at 120.degree. C. for 2 hours. The magnets 
were loaded into a container of the same size as described above together 
with 2.0 kg of walnut shells with an average particle-diameter of 2 mm. 
Vibration was carried out for 5 minutes to remove the powder remaining 
unfixed on the magnets. 
Twenty magnets were coated with each of the following various powder by the 
same method as described above. The magnets were subjected to test of 
corrosion resistance under the condition of 85.degree. C. and 90% of 
relative humidity (RH). 
1--Coating with an average thickness of 10 .mu.m by the above described 
method. 
2--Instead of the aluminum powder, TiO.sub.2 powder with an average 
diameter of 0.3 .mu.m was used to form a 7 .mu.m thick coating. 
3--Instead of the aluminum powder, TiO.sub.2 powder with the average 
diameter of 0.3 .mu.m was used to form a coating. Subsequently, without 
removal of the unfixed remaining powder, the magnets were dipped in 5% 
epoxy resin solution of MEK. Again, TiO.sub.2 powder with an average 
diameter of 0.3 .mu.m was used to form a coating. Subsequently, without 
removal of the unfixed remaining powder, curing was carried out at 
120.degree. C. for 2 hours. Remaining unfixed powder was removed by walnut 
shells. As a result, a coating with an average thickness of 20 .mu.m 
(maximum 27 .mu.m, minimum 18 .mu.m) was formed. 
4--Instead of the aluminum power, TiO.sub.2 powder with an average diameter 
of 1 .mu.m was used to form a coating. Subsequently, without removal of 
the unfixed remaining powder, the magnets were dipped in 5% epoxy resin 
solution of MEK. Again, TiO.sub.2 powder with an average diameter of 0.3 
.mu.m was used to form a coating. Subsequently, without removal of the 
unfixed remaining powder, curing was carried out at 120.degree. C. for 2 
hours. Remaining unfixed powder was removed by walnut shells. As a result, 
a coating with the average thickness of 22 um (maximum 29 .mu.m, minimum 
20 .mu.m) was formed. 
5--Instead of the aluminum powder, Fe.sub.2 O.sub.3 powder with an average 
diameter of 1 um was used to form a coating. 
6--Epoxy resin with 20% of TiO.sub.2 additive was spray-coated on the 
magnets. Curing was carried out at 120.degree. C. for 6 hours. A 10 .mu.m 
thick single coating was formed (comparative example). 
7--The magnets as produced were tested without coating (comparative 
example). 
The results are given in Table 4. 
TABLE 4 
______________________________________ 
Exposure Time (hours) 
Coating 250 500 1000 1500 
______________________________________ 
1 A B B C 
2 A A B C 
3 A A A B 
4 A A A A 
5 A A B B 
6 C E -- -- 
7 E -- -- -- 
______________________________________ 
EXAMPLE 10 
An ingot having a composition of Nd.sub.13.8 Dy.sub.0.4 Fe.sub.78.2 
B.sub.7.6 was roughly crushed with a stamp mill to provide powder having 
an average particle diameter of 20 .mu.m and then finely crushed with a 
jet mill to provide powder having average particle diameter of 3.0 .mu.m. 
The resultant fine powder was compacted in a metal die at a pressure of 
1.5 t/cm.sup.2, while applying 12kOe of vertical magnetic field 
perpendicular to the pressing direction. The resultant green compacts were 
sintered in vacuum at 1100.degree. C. for 2 hours and then aged at 
650.degree. C. for 1 hour. As a result, one hundred twenty sintered 
compacts were obtained. The entire surface of the sintered compacts were 
ground, followed by smoothening the corners with centrifugal barrel 
polishing. The sintered compacts were then cleaned and dried. The products 
were in the form of a disc 20 mm in diameter and 5 mm in height. 
Steel balls in 3.0 mm diameter in amount of 10 kg were first loaded into a 
spherical pot 2.8 liter in volume and 150 mm in depth. While vibrations of 
2500 cpm and 5 mm in amplitude were imparted to the pot, 20 g of aluminum 
powder with 1 .mu.m of average diameter was loaded in the pot being 
vibrated. Vibration was continued for 5 minutes to vibrate the Al powder 
as well as the steel balls. Twenty magnets were preliminarily dipped in 
10% epoxy resin solution of MEK. The magnets were thus coated with resin. 
The magnets were loaded into the pot and the vibration was carried out for 
15 minutes. The magnets were then taken out from the pot. Heat treatment 
was carried out at 120.degree. C. for 2 hours. The magnets were loaded 
into a container of the same size as described above together with 2.0 kg 
of walnut shells with an average diameter of 2 mm. Vibration was carried 
out for 5 minutes to remove the powder remaining unfixed on the magnets. 
Subsequently, the sintered compacts were dipped in 5% epoxy-resin solution 
of MEK. After drying, curing was carried out at 120.degree. C. for 2 
hours. 
The following various powder was coated on the magnets by the same methods 
as described above. 
1--Coating with an average thickness of 10 .mu.m by the above described 
method. 
2--The above coating process was repeated twice to form a coating with an 
average thickness of 20 .mu.m. 
3--Epoxy resin with 20% of TiO.sub.2 additive was spray-coated on the 
sintered magnets. Curing was carried out at 120.degree. C. for 6 hours 
(comparative example). 
It was confirmed by naked eye and an optical microscope that the coatings 1 
and 2 were smooth and free of defects. Thickness of coating 3 was not 
uniform because of liquid sagging. 
EXAMPLE 11 
An ingot having a composition of SmCo.sub.4.6 was roughly crushed with a 
stamp mill to provide powder having an average particle diameter of 25 
.mu.m and then finely crushed with a jet mill to provide powder having an 
average particle diameter of 4.0 .mu.m. The resultant fine powder was 
compacted in a metal die at a pressure of 1.5 t/cm.sup.2, while applying 
12 kOe of vertical magnetic field perpendicular to the pressing direction. 
The resultant green compacts were sintered in vacuum at 1210.degree. C. 
for 2 hours and then slowly cooled. As a result, eighty sintered compacts 
were obtained. The entire surface of the sintered compacts were ground, 
followed by smoothening the corners with centrifugal barrel polishing. The 
sintered compacts were then cleaned and dried. The products were in the 
form of a disc 20 mm in diameter and 5 mm in height. 
Steel balls in 3.0 mm diameter in amount of 10 kg were first loaded in a 
spherical pot 2.8 liter in volume and 150 mm in depth. While vibration of 
2500 cpm and 5 mm in amplitude was imparted to the pot, 20 g of TiO.sub.2 
powder with 3 .mu.m of average diameter was loaded in the pot being 
vibrated. Vibration was continued for 5 minutes to vibrate the TiO.sub.2 
powder as well as the steel balls. Twenty magnets were preliminarily 
dipped in 10% epoxy resin solution of MEK. The magnets were thus coated 
with resin. The magnets were loaded in the pot and the vibration was 
carried out for 15 minutes. The magnets were then taken out from the pot. 
Heat treatment was carried out at 120.degree. C. for 2 hours. The magnets 
were loaded in the container of the same size as described above together 
with 2.0 kg of walnut shells an average diameter of 2 mm. Vibration was 
carried out for 5 minutes to remove the powder remaining unfixed on the 
magnets. Subsequently, the sintered compacts were dipped in 5% epoxy resin 
solution of MEK. After drying, curing was carried out at 120.degree. C. 
for 2 hours. 
EXAMPLE 12 
The following powder was compacted by a die-pressing method so as to 
produce green compacts in the form of a ring 25 mm in outer diameter, 20 
mm in inner diameter and 10 mm in height. 
(A) Al-2.75 wt% Li (gas-atomized powder; average particle-diameter-20 
.mu.m; compacting pressure-2 ton/cm.sup.2) 
(B) Mg (gas-atomized powder; average particle diameter-20 .mu.m; compacting 
pressure-2 ton/cm.sup.2) 
The green compacts were sintered at 600.degree. C. for 6 hours in Ar 
atmosphere. Density of every sintered compacts was 90% relative to the 
true density. Twenty sintered compacts were coated by each of the 
following treatments. 
(1) Steel balls in 3.0 mm diameter in amount of 10 kg were first loaded in 
a spherical pot 2.8 liter in volume and 150 mm in depth. The apparent 
density was approximately 5 kg/liter. While vibrations of 2500 cpm and 5 
mm in amplitude were imparted to the pot, 20 g of TiO.sub.2 powder with an 
average diameter of 1 .mu.m was loaded in the pot being vibrated. 
Vibration was continued for 5 minutes to vibrate the TiO powder and the 
steel balls so as to uniformly distribute the TiO.sub.2 powder. Twenty 
sintered compacts were preliminarily dipped in 10% epoxy resin (97% by 
weight of resin and 3% by weight of curing agent) solution of MEK. The 
sintered compacts were thus coated with resin. The sintered compacts were 
loaded into the pot and the vibration was carried out for 15 minutes. The 
sintered compacts were then taken out from the pot. Heat treatment was 
carried out at 120.degree. C. for 2 hours. The sintered compacts were 
loaded into a container of the same size as described above together with 
2.0 kg of walnut shells with an average particle-diameter of 2 mm. 
Apparent density was 1 kg/liter. Vibration was carried out for 5 minutes 
to remove the powder remaining unfixed on the magnets. Average thickness 
of the coating was 10 .mu.m. 
(2) Approximately 5 um thick Cu coating was formed by the same method as 
(1) using 15 g of Cu powder having a particle diameter of 1 um. 
Subsequently, electro-plating was carried out to form an Ni coating with 
an average thickness of 10 .mu.m (maximum-14 .mu.m and minimum-8 um). 
(3) The sintered compacts were dipped in a commercially available 
Zn-replacement solution, which contained sodium hydroxide, zinc oxide, 
Roschel salt, and other trace additives. Subsequently, electro-plating was 
carried out using an Ni Watt bath to form an Ni coating with the average 
thickness of 10 .mu.m (comparative example). 
(4) Epoxy resin with 20% of carbon black additive was spray-coated on the 
sintered compacts to form a coating with average thickness of 10 .mu.m. 
(5) Sintered compacts as produced were tested without coating. 
Twenty sintered compacts produced by each of (1)-(5), above, were exposed 
to 85.degree. C. and 90% RH. The judging criterion is the same as in Table 
2. 
The results are given in Table 5. 
TABLE 5 
______________________________________ 
Exposure Time (hours) 
Powder Coating 250 500 1000 1500 
______________________________________ 
A 1 A A A B 
2 A A A A 
3 A E -- -- 
4 B D E -- 
5 E -- -- -- 
B 1 A A A A 
2 A A A A 
3 A E -- -- 
4 B D E -- 
5 E -- -- -- 
______________________________________ 
Numerous swelling of coating occurred for the sintered compacts A,B treated 
by 3. This seemed to be caused by remaining plating liquid. 
EXAMPLE 13 
The following powder was compacted by a die-pressing method so as to 
produce green compacts 20 mm.times.20 mm.times.5 mm in size. 
(A) Fe-0.3%C (electrolytic and annealed powder; average particle 
diameter-50 .mu.m; compacting pressure-3 ton/cm.sup.2) 
(B) Al-1%Si (gas-atomized powder; average particle diameter-25 .mu.m; 
compacting pressure-3 ton/cm.sup.2) 
The green compacts were sintered at 1300.degree. C. for 6 hours in vacuum 
for the powder (A). The green compacts were sintered at 600.degree. C. for 
6 hours for the powder (B). Densities of the sintered compacts (A) and (B) 
were 85% and 90% relative to the true density, respectively. The following 
coating treatments were applied to every twenty sintered compacts. 
(1) Steel balls 3.0 mm in diameter in a total amount of 10 kg were first 
loaded into a spherical pot 2.8 liter in volume and 150 mm in depth. The 
apparent density was approximately 5 kg/liter. While vibrations of 2500 
cpm and 5 mm in amplitude were imparted to the pot, 20 g of Fe.sub.2 
O.sub.3 powder with 1 .mu.m of average diameter was loaded in the pot 
being vibrated. Vibration was continued for 5 minutes to vibrate the 
Fe.sub.2 O.sub.3 powder and the steel balls, so as to uniformly distribute 
the Fe.sub.2 O.sub.3 powder. Twenty sintered compacts were preliminarily 
dipped in 10% epoxy resin (97% by weight of resin and 3% by weight of 
curing agent) solution of MEK. The sintered compacts were thus coated with 
resin. The sintered compacts were loaded into the pot and the vibration 
was carried out for 15 minutes. The sintered compacts were then taken out 
from the pot. Heat treatment was carried out at 120.degree. C. for 2 
hours. The sintered compacts were loaded into a container of the same size 
as described above together with 2.0 kg of walnut shells with an average 
diameter of 2 mm. Apparent density was 1 kg/liter. Vibration was carried 
out for 5 minutes to remove the powder remaining unfixed on the magnets. 
Average thickness of the coating was 10 .mu.m. 
(2) Approximately 5 .mu.m thick Cu coating was formed by the same method as 
(1) except that instead of epoxy resin a phenol resin was used, and, 
further 15 g of Cu powder having a particle diameter of 1 .mu.m was used. 
Subsequently, electro-plating was carried out to form an Ni coating with 
an average thickness of 10 .mu.m. 
(3) The sintered compacts were Zn-replacement plated by the method of 
Example 12 (3). Subsequently, electro-plating was carried out to form an 
Ni coating with an average thickness of 10 .mu.m (comparative example). 
(4) Epoxy resin with 20% of TiO.sub.2 additive was spray-coated on the 
sintered compacts to form a coating with an average thickness of 10 .mu.m. 
(5) Sintered compacts as produced were tested without coating. 
The sintered compacts treated as described above were subjected to the 
neutral brine-water spraying test stipulated under JIS corrosion test 
(35.degree. C., 5% NaCl). Appearance of the sintered compacts was then 
observed. The test results are given in Table 6. 
TABLE 6 
______________________________________ 
Exposure Time (hours) 
Powder Coating 24 48 120 240 
______________________________________ 
A 1 A A C C 
2 A A A A 
3 C D E -- 
4 C E -- -- 
5 E -- -- -- 
B 1 A A B C 
2 A A A A 
3 C D E -- 
4 B C E -- 
5 E -- -- -- 
______________________________________ 
Numerous swelling of coating occurred for the sintered compacts A, B 
treated by 3. 
EXAMPLE 14 
The following non-metal members were produced. 
A. The starting material powder was prepared by mixing NiO:Fe.sub.2 O.sub.3 
ZnO=20:50:30 (mole ratio). The starting material powder was compacted and 
sintered to produce an Ni-Zn ferrite sintered compact having 98% of 
density relative to the true density). The sintered compact was cut and 
ground to obtain a block 15 mm.times.15 mm.times.5 mm in size. 
B. The starting material powder was prepared by mixing SrCO.sub.3 :Fe.sub.2 
O.sub.3 :=1:5.9 (mole ratio). The starting material powder was compacted 
and sintered to produce an Sr ferrite sintered compact having 98% of 
density relative to the true density). The sintered compact was cut and 
ground to obtain a cylindrical body 15 mm in diameter and 4 mm in height. 
The following coating treatments were applied to the non metal members A 
and B. 
(1) TiO.sub.2 coating was formed by the method of Example 12 (FIG. 34,A-1; 
FIG. 35,B-1) 
(2) Epoxy resin coating (TiO.sub.2 content-20%) was spray coated. (FIG. 
34,A-2; FIG. 35,B-2) 
After the treatments, the members were cut and thickness distribution on 
the members was observed with a microscope. As is clear from FIG. 34 and 
35, that the inventive method (1) enables coating with more uniform 
thickness than the conventional method (2). 
EXAMPLE 15 
Twenty plastic parts in the form of a hemispherical shape 40 mm in diameter 
and 2 mm in thickness were prepared. 10 kg of steel balls 1.0 mm in 
diameter was loaded into a spherical pot 2.8 liter in volume and 150 mm in 
depth. 10 g of Cu powder with 1 .mu.m of average particle-diameter was 
also loaded into the spherical pot. Vibration was imparted to the steel 
balls and Cu powder for 15 minutes. MEK was blown on the entire surface of 
the parts to provide an adhesive surface. The parts were then loaded into 
the pot being vibrated. Vibration was continued for 15 minutes. The 
plastic parts were then taken out of the pot and were heated at 50.degree. 
C. for 2 hours. The plastic parts were then loaded, together with 2 kg of 
walnut shell (average particle diameter-2 mm) into another pot having the 
same size as the above pot. Vibration was carried out for 5 minutes so as 
to remove the free remaining Cu powder. 
An approximately 4 .mu.m thick coating was thus formed on the plastic 
parts. Surface resistance was infinite before the treatment but was 
decreased to 1.2-85 .OMEGA./.quadrature. after the treatment. An Ni 
plating could be easily formed using a conventional Watt bath. The Ni 
plating layer could not be peeled by a tape-peeling test. 
When 20 g of the Cu powder was used, an approximately 10 .mu.m thick Cu 
coating was formed and had surface resistance of from 2 to 115 
5/8/.quadrature.. Subsequently, a gold plating was carried out to form an 
approximately 2 .mu.m thick golden plating layer. 
EXAMPLE 16 
The process according to Example 9 was continued until the powder loading. 
Then, 30 g of tin powder with an average particle diameter of 1 .mu.m was 
loaded. The subsequent process was carried out as in Example 9. 
The coated magnets were heated at 300.degree. C. for 4 hours in vacuum. 
Then, the corrosion-resistance under 85.degree. C. and 90% RH was 
evaluated. The results are given in Table 7 with regard to the following 
treatments. 
1--Tin coating (as described above; an average thickness of coating-10 
.mu.m) 
2--Spray coating (epoxy resin with 20% of TiO.sub.2 ; an average thickness 
of coating-10 .mu.m) 
3--No coating 
TABLE 7 
______________________________________ 
Exposure Time (hours) 
Coating 250 500 1000 1500 
______________________________________ 
1 A A A A 
2 C E -- -- 
3 E -- -- -- 
______________________________________ 
EXAMPLE 17 
Acrylic resin parts in the form of a ring 10 mm in outer diameter, 9 mm in 
inner diameter and 5 mm in height were prepared. 10 kg of steel balls 2.0 
mm in diameter was loaded into a spherical pot 2.8 liters in volume and 
150 mm in depth. 30 g of Fe.sub.3 Nd.sub.13 B.sub.6 powder with an average 
particle-diameter of 50 .mu.m, which was rapidly quenched powder for 
bonded magnet, was also loaded into the spherical pot. Vibration was 
imparted to the steel balls and magnet powder for 5 minutes. MEK was blown 
on the entire surface of the ring parts to provide an adhesive surface. 
The ring parts were then loaded in the pot being vibrated. Vibration was 
continued for 25 minutes. The ring parts were subsequently taken out of 
the pot. 10% of epoxy resin solution of MEK was blown on the inner surface 
of the ring. Heating was then carried out at 50.degree. C. for 2 hours. An 
approximately 25 .mu.m thick magnet layer was formed on the inner surface 
of the ring. By magnetizing the ring, a stator of a small-sized motor 
could be obtained. 
EXAMPLE 18 
Twenty acrylic-resin pieces 12 mm.times.12 mm.times.4 mm in size were 
dipped in MEK to dissolve their surfaces to provide adhesive surfaces. 2 
liters of alumina balls with 1 mm in diameter, whose surface was coated 
with resin, were loaded into a pot in the form of a doughnut with a volume 
of 2.8 liters. 10 g of aluminum powder with an average diameter of 3 .mu.m 
was then loaded into the pot. Vibrations of 4000 cpm and 0.5 mm in 
amplitude were imparted to the acrylic resin pieces, aluminum powder and 
alumina balls for 20 minutes. The acrylic resin pieces were then taken out 
of the pot. Curing was carried out at 80.degree. C. for 1 hour. 
The coating on one of the sides of the acrylic-resin pieces was 10 .mu.m 
thick in average. The aluminum content in the vicinity of the coating 
surface was 80% or more. Electro-conductivity of the coating surface was 
confirmed by a conductivity checker. 
EXAMPLE 19 
The acrylic-resin pieces, which have been treated in Example 18, were 
dipped in an epoxy resin (97% of resin and 3% of curing agent) solution of 
MEK. The so-treated pieces were loaded in a pot with 5 liters of volume, 
together with 2 liter of steel balls 0.5 mm in diameter. The steel balls 
were preliminarily Ni-plated to prevent the contamination by steel. Epoxy 
resin was coated on the Ni plating. 
Four pots were preliminarily prepared. Powder loaded into the pots were: 10 
g of Ni powder with particle diameter of 1 .mu.m in the first pot; 10 g of 
Sn powder with particle diameter of 5 .mu.m in the second pot; 10 g of 
TiO.sub.2 powder with particle diameter of 0.1 .mu.m in the third pot; 
and, 10 g of Cu powder with particle diameter of 15 .mu.m in the fourth 
pot. Four pots were vibrated once by a centrifugal barrel machine for five 
minutes. Rotation number of the main axis of the centrifugal barrel 
machine was 10-160 rpm. The acrylic resin pieces were then taken out of 
the pots and cured at 80.degree. C. for 1 hour. 
Thickness of the Ni, Sn and Cu coating formed on one side of the 
acrylic-resin pieces was 6 .mu.m in average. The powder density on the Ni, 
Sn and Cu coating surface was 60% or more. Thickness of the TiO.sub.2 
coating formed on one side of the acrylic-resin pieces was 4 .mu.m in 
average. The powder density on the Ni, Sn and Cu coating surface was 50% 
or more. The acrylic resin pieces with Ni, Sn or Cu coating exhibited 
electro-conductivity, while the pieces with TiO.sub.2 coating exhibited 
electro-insulating property. 
EXAMPLE 20 
Stainless steel discs 50 mm in outer diameter, 10 mm in central aperture, 
and 0.2 mm in thickness were thoroughly cleaned and then dipped in an MEK 
solution, in which 15% of epoxy resin (97% of resin and 3% of curing 
agent) was preliminarily dissolved. Steel balls in 1 mm diameter were 
loaded into the pot of a planetary mill to provide 40% of the steel-ball 
volume. Into the other planetary mill, 40% by volume of the steel balls 
was loaded. Appropriate amount of diamond powder 1 .mu.m in particle 
diameter was in was loaded into one of the pots. Fluorescent powder 0.8 
.mu.m in particle diameter in appropriate amount was loaded in the other 
pot. The two pots were mounted on one planetary mill and stirred at 10-200 
rpm. The work pieces were taken out of the pots and cured at 100.degree. 
C. for 1 hour. 
Thickness of the diamond and fluorescent-powder coatings formed on one side 
of the stainless steel discs were 13 .mu.m and 4 .mu.m in average. The 
powder density on the surface of the both coatings was 40% or more. 
EXAMPLE 21 
Steel balls 2 mm in diameter were plated with Ni and then epoxy resin on 
the surface thereof. The steel balls in 1.5 liter of volume and 8 g of 
aluminum powder with an average particle-diameter 4 .mu.m were loaded into 
a pot A. Vibrations of 3000 cpm and 5 mm of amplitude were imparted to pot 
A for 80 minutes. 
Forty Nd-Fe-B sintered compacts 10 mm.times.10 mm.times.2 mm in size were 
dipped in epoxy resin, which was diluted with MEK, and were cleaned by 
ultra-sonic wave for 3 minutes. The sintered compacts were then taken out 
from the MEK solution, followed by drying. The sintered compacts were then 
loaded into the pot A. Vibrations of 3000 cpm and 1.5 mm of amplitude were 
imparted to the pot A for 15 minutes. Curing was carried out at 
120.degree. C. for 2 hours. 
Two liters of steel balls 1 mm in diameter, which were plated with Ni and 
then epoxy resin on the surface thereof, were loaded into a pot B. The 
steel balls, 10 g of TiO.sub.2 powder with an average particle-diameter of 
0.3 .mu.m and 3 g of thermo-setting type epoxy resin were loaded into a 
pot B. Rotation of 50-180 rpm was carried out for 10 minutes so as to 
uniformly distribute TiO.sub.2 on the surface of steel balls by break-in 
operation. The pot B was then opened. The work pieces, which were 
preliminarily coated with Al, and 2 g of TiO.sub.2 powder were loaded in 
the pot B. A centrifugal barrel machine was operated at 50-120 rpm for 10 
minutes, so as to coat the work pieces with TiO.sub.2 powder by strong 
stirring force. All of the work pieces were then taken out of the pot and 
cured at 100.degree. C. for 1.5 hours. 
Finally, the work pieces were thinly coated with commercially available 
acrylic resin to improve appearance and prevent dusting. The work pieces 
were cleaved to investigate s the fracture by an electron microscope. It 
turned out that uniform two-layer coating of 6 .mu.m thick Al layer and 4 
.mu.m thick TiO.sub.2 layer was formed. 
EXAMPLE 22 
Twenty Nd-Fe-B permanent-magnet sintered compacts 5 mm.times.5 mm.times.2 
mm size and 2 liters of steel balls 1 mm in diameter were loaded into each 
of four pots with 5 liters of volume, of a centrifugal barrel machine. 
Furthermore, 20 g of aluminum powder with an average particle diameter of 
3 .mu.m, and 5 g of paraffin binder, 10 g of polypropylene, 10 g of wax, 
and 10 g of epoxy resin were loaded into each pot. The centrifugal barrel 
machine was operated at 20-160 rpm for 5 minutes to coat the sintered 
compacts with the Al powder by strong centrifugal force. The sintered 
compacts were taken out of the pots. The work pieces were cleaved to 
investigate the fracture by an electron microscope. It turned out that 
uniform 6 .mu.m, 8 .mu.m, 15 .mu.m and 4 .mu.m thick Al layers were 
formed. 
EXAMPLE 23 
10 kg of Ni-plated steel balls 2 mm in diameter were loaded into a pot with 
2.8 liters of volume. 10 g of aluminum powder with an average particle 
diameter of 3 .mu.m was loaded into the pot. 15 cc of epoxy-resin (94% of 
epoxy resin and 6% of curing agent) solution of MEK was then loaded into 
the pot. Vibration was imparted to the steel balls, aluminum powder and 
epoxy resin for 30 minutes. The aluminum powder was uniformly captured on 
the surface of all steel balls by uncured resin. 
Seventeen magnets, which are the same as those of Example 11, were dipped 
in the epoxy-MEK solution mentioned above and then dried. The magnets were 
then loaded in the pot mentioned above. Vibration was carried out for 20 
minutes. The magnets were taken out of the pot and, then, the resin was 
cured at 120.degree. C. for 2 hours. A 12 .mu.m thick aluminum-powder 
coating was thus uniformly formed. The vibration condition was the same as 
in Example 11. 
In this example, cracking of corners of the magnets was slight as compared 
with Example 11. Thickness of the coating in this example was more uniform 
than in Example 11. 
EXAMPLE 24 
Ni-plated steel balls 2 mm and 3 mm in diameter were loaded in a total 
amount of 10 kg at a proportion of 1:1 into a pot with 2.8 liters of 
volume and 150 mm in depth. While vibrations of 2500 cpm and 5 mm in 
amplitude were imparted to the pot, 20 g of aluminum powder with an 
average particle diameter of 3 .mu.m was loaded into the pot. Vibration 
was continued for 5 minutes. 
Twenty MQ bonded magnets (20 mm in outer diameter, 16 mm in inner diameter 
and 9 mm in height) were preliminarily dipped in 10% epoxy resin (97% by 
weight of resin and 3% by weight of curing agent) solution of MEK. The 
sintered compacts were thus coated with resin. The sintered compacts were 
loaded into the pot and the vibration was carried out for 15 minutes. The 
sintered compacts were then taken out from the pot and heated at 
120.degree. C. for 2 hours. The sintered compacts were dipped in 5% 
epoxy-resin solution to cover the surface with the resin. 
The magnets were again subjected to second vibrating treatment together 
with the aluminum powder with an average particle diameter of 3 .mu.m for 
10 minutes. The magnets were taken out of the pot and dried, and, then 
cured at 120.degree. C. for 2 hours. The magnets were then dipped in 10% 
epoxy resin of MEK. Curing was then carried out at 120.degree. C. for 3 
hours. 
The double coated magnets as described above exhibited excellent corrosion 
resistance. 
One of the magnets was buried in epoxy resin, polished by Emery paper and 
finish polished with buff to observe a cross sectional structure of the 
coating with SEM. The result is shown in FIGS. 25(a) and (b). As is 
apparent from these photographs, originally spherical Al particles are 
collapsed and are bonded in the horizontal direction to form a skeleton 
structure. A resin layer is sandwiched between the first and second Al 
layers. Another resin layer is present between the first Al layer and the 
bonded magnet and is connected with the above-mentioned resin layer in the 
bonded magnet. 
EXAMPLE 25 
Resin-bonded magnets were dipped in 10% epoxy-resin solution of MEK. Ultra 
sonic vibration was imparted to this solution for 2 minutes to form a 
resin coating on the magnets. The resin-coated magnets, chromium-plated 
steel balls with a diameter of 2 mm, and 20 g of Ag powder from 0.1 to 1 
.mu.m in size were loaded in the same vibrating barrel as in Example 24 
and were vibrated for 20 minutes under the same condition as in Example 
24. The inner atmosphere of the barrel was air. The magnets were taken out 
from the barrel, dried at room temperature for 20 minutes and then cured 
at 120.degree. C. for 2 hours. 
The thus coated magnets were polished by the same method as in Example 24 
to observe the SEM image of the cross section, which is shown in FIGS. 
26(a) and (b). The SEM image of the surface of the coating is shown in 
FIG. 27. The coating formed in this example was approximately 10 .mu.m 
thick and had a skeleton structure. The surface resistance was 0.1/or 
less, which was very high notwithstanding barrel treatment in air. 
For the comparison purpose, Ag powder and epoxy resin were diluted with MEK 
and sprayed on the bonded magnets. The Ag content was made as high as 
possible but did not exceed a level that the mixture becomes 
non-sprayable. Surface resistance of the resultant Ag coating was 10/or 
more for the 10 .mu.m thick coating. 
EXAMPLE 26 
The Cu coating and Ni coating were formed by using the Cu powder with an 
average particle diameter of 10 um and the Ni powder with an average 
particle diameter of 0.8 um, respectively, under the same condition as in 
Example 25. However, nitrogen gas atmosphere was produced in the barrel in 
the case of forming the Cu coating. SEM images of the Cu coating are shown 
in FIG. 28(polished cross section) and 29(non-polished surface). SEM 
images of the Ni coating are shown in FIG. 30 (polished cross section) and 
31(non-polished surface). 
For the comparison purpose, the electro-conductive paint was prepared using 
the same Cu powder mentioned above and solvent. The so prepared paint was 
sprayed to form a coating which does not have the skeleton structure. SEM 
image of the of the comparative coating are shown in FIGS. 32 and 33, 
respectively. From comparison of FIGS. 28-31 with FIGS. 32-33, it is clear 
that the powder filing ratio is very high in the case of the skeleton 
structure. 
Surface electro-resistance of the surface of the Cu coating having the 
skeleton structure was 0.2.OMEGA./.quadrature. for a 25 .mu.m thick 
coating. Contrary to this, the sprayed Cu coating without the skeleton 
structure was approximately 0.5.OMEGA./.quadrature. for a 70 .mu.m thick 
coating. 
EXAMPLE 27 
Ni-plated steel balls 1 mm in diameter in a total amount of 10 kg were 
loaded into a pot with 2.8 liters of volume and 150 mm in depth. 3cc of 
10% epoxy-resin (97% of resin and 3% of curing agent) solution of MEK was 
sprinkled over the steel balls. Vibrations of 3600 cpm and 0.5-2 mm in 
amplitude were imparted to the pot for 10 minutes so as to thoroughly 
spread resin on the steel balls. 25 g of Ag powder with particle-diameter 
of 0.5-1 .mu.m was loaded into the pot. Vibration under the same condition 
as above was continued for 1 hour. 
Boxes with an open top, 70 mm in length, 49 mm in width and 10 mm in depth 
were prepared as work pieces. These work pieces were made of PC/ABS 
alloy-resin and masked on the outer surface. 10% epoxy-resin (94% of resin 
and 6% of curing agent) solution of MEK was sprayed on the inner surface 
of the work pieces. The work pieces were then loaded into the pot. The 
same vibrations as mentioned above were imparted to the pot so as to form 
an Ag layer on the inner surface of the work piece. The work pieces were 
then taken out of the pot and then loaded into another pot, into which 10 
kg of Ni-plated steel balls 2 mm in diameter in a total amount of 10 kg 
were preliminarily loaded. Vibrations of 5000 cpm and 0.2-1 mm in 
amplitude were imparted to the pot for 10 minutes so as to remove excess 
Ag powder deposited on the surface of the work pieces and to enhance the 
uniformity of the coating. The work pieces were then taken out of the pot 
and their resin were cured at 60.degree. C. for 2 hours. As a result, a 
uniform coating with an average thickness of 14 .mu.m was formed on the 
inner side of the work pieces. Surface resistance of the coating was 
0.1.OMEGA./.quadrature.. The inter-layer resistance of the coating was 
from 0.1 to 0.5.OMEGA./.quadrature.. 
On the inner surface of the work pieces treated as described above, 
electro-conductive polymer based on poly-aniline ("Electromagnetic Guard 
Spray", Trade Name of Sumitomo MMM) was sprayed and dried at 60.degree. C. 
for 5 minutes. An electro-conductive poly-aniline coating with an average 
thickness of 5 um was formed on the Ag coating. Surface resistance and 
inter-layer resistance of the whole coating were 0.1.OMEGA./.quadrature. 
or less. The entire coating did not peel, when subjected to a tape-peeling 
test.