U.S. patent application number 12/484746 was filed with the patent office on 2009-10-08 for mg or mg-alloy housing and method for producing the same.
This patent application is currently assigned to FUJITSU LIMITED. Invention is credited to Takayuki Fujiwara, Koichi Kimura.
Application Number | 20090250142 12/484746 |
Document ID | / |
Family ID | 36032599 |
Filed Date | 2009-10-08 |
United States Patent
Application |
20090250142 |
Kind Code |
A1 |
Kimura; Koichi ; et
al. |
October 8, 2009 |
Mg or Mg-Alloy Housing and Method for Producing the Same
Abstract
A surface of a Mg or Mg-alloy housing of the present invention
is subjected to wet blast using a mixture containing a chemical
conversion treatment agent and an abrasive, whereby a chemical
conversion film is formed on the surface of the Mg or Mg-alloy
housing. Because of this, a chemical conversion film is formed
simply on the surface of a molded product made of Mg or a Mg-alloy
to reduce the correction by puttying, whereby a Mg or Mg-alloy
housing is provided in which a decrease in yield and an increase in
cost can be prevented.
Inventors: |
Kimura; Koichi; (Kawasaki,
JP) ; Fujiwara; Takayuki; (Kawasaki, JP) |
Correspondence
Address: |
ARENT FOX LLP
1050 CONNECTICUT AVENUE, N.W., SUITE 400
WASHINGTON
DC
20036
US
|
Assignee: |
FUJITSU LIMITED
Kanagawa
JP
|
Family ID: |
36032599 |
Appl. No.: |
12/484746 |
Filed: |
June 15, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11012144 |
Dec 16, 2004 |
|
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|
12484746 |
|
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Current U.S.
Class: |
148/251 ;
148/253; 148/275 |
Current CPC
Class: |
B24C 1/083 20130101;
C23C 22/74 20130101 |
Class at
Publication: |
148/251 ;
148/275; 148/253 |
International
Class: |
C23C 22/57 20060101
C23C022/57; C23C 22/00 20060101 C23C022/00; C23C 22/07 20060101
C23C022/07; C23C 22/73 20060101 C23C022/73 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 10, 2004 |
JP |
2004-264400 |
Claims
1. A method for producing a Mg or Mg-alloy housing, comprising:
subjecting a surface of Mg or a Mg alloy to a wet blast treatment,
using a mixture containing a chemical conversion treatment agent
and an abrasive, thereby simultaneously forming unevenness due to
the blast and a chemical conversion film on the surface of the Mg
or Mg-alloy housing.
2. The method for producing a Mg or Mg-alloy housing according to
claim 1, wherein a surface roughness of the housing is in a range
of 0.5 .mu.m to 100 .mu.m in terms of a 10-point average surface
roughness.
3. The method for producing a Mg or Mg-alloy housing according to
claim 1, wherein the wet blast treatment includes injecting a
mixture containing a liquid and an abrasive under a pressure in a
range of 0.1 to 0.3 MPa.
4. The method for producing a Mg or Mg-alloy housing according to
claim 1, wherein the abrasive is at least one particulate material
selected from the group consisting of alumina, zirconia, glass, and
resin.
5. The method for producing a Mg or Mg-alloy housing according to
claim 4, wherein the resin is selected from the group consisting of
melamine resin, urea resin, polyester resin, phenol resin, epoxy
resin, and urethane resin.
6. The method for producing a Mg or Mg-alloy housing according to
claim 1, wherein an average particle diameter of the abrasive is in
a range of 10 to 300 .mu.m.
7. The method for producing a Mg or Mg-alloy housing according to
claim 1, wherein calcium used in a solution for the wet blast
treatment is at least one selected from the group consisting of
calcium nitrate, calcium nitrite, calcium thiosulfate, and
tetracalcium phosphate.
8. The method for producing a Mg or Mg-alloy housing according to
claim 1, wherein manganese used in a solution for the wet blast
treatment is at least one selected from the group consisting of
manganese carbonate, manganese nitrate, manganese hydrogen
phosphate, manganese biphosphate, and manganese fluoroborate.
9. The method for producing a Mg or Mg-alloy housing according to
claim 1, wherein phosphoric acid used in a solution for the wet
blast treatment is at least one selected from the group consisting
of orthophosphoric acid, condensed phosphoric acid, phosphorous
acid, and hypophosphorous acid.
10. The method for producing a Mg or Mg-alloy housing according to
claim 1, wherein at least one selected from sodium chlorate and
sodium hypochlorite is further added to a solution for the wet
blast treatment as an oxidation accelerator.
11. The method for producing a Mg or Mg-alloy housing according to
claim 10, wherein an added amount of the oxidation accelerator is
in a range of 0.02 to 2 g/L.
12. The method for producing a Mg or Mg-alloy housing according to
claim 1, wherein a proportion of the chemical conversion treatment
agent of a solution for the wet blast treatment is 70 to 90% by
mass, and a proportion of the abrasive of the solution for the wet
blast treatment is 10 to 30% by mass.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a Mg or Mg-alloy housing in
which a chemical conversion film is formed simply on a surface of a
molded product made of Mg or a Mg-alloy so as to improve the yield
of coating, and a method for producing the Mg or Mg-alloy
housing.
[0003] 2. Description of the Related Art
[0004] Recently there are increasing chances that mobile equipment
such as a notebook computer and a personal digital assistant (PDA)
is carried for outdoor use. Along with this, there is an increasing
demand for the miniaturization and the reduction in weight and
thickness of equipment, and hence, the reduction in thickness of a
housing occupying 30% of the entire mass of the equipment is
required. However, in the case where the equipment is reduced in
thickness, it is difficult to maintain sufficient strength with a
resin housing. Furthermore, the amount of heat generated by a
microprocessor unit (MPU) of a notebook computer is increasing. The
heat generation amount during AC driving is planned to be 13 to 16
W, so that the development of a housing having high cooling
performance is urgently necessary.
[0005] As a solution to the above-mentioned problems, light metal
such as Al, Mg, a Mg-alloy, or the like having low gravity and high
heat conduction is becoming a focus of attention as a housing
material. In particular, Mg or a Mg-alloy is light, i.e., has a
gravity of about 70% of Al, and also is excellent in recyclability.
As Mg or a Mg-alloy a Mg--Al--Zn system, a Mg--Al--Mn system, a Mg
or Mg--Al--Si system, a Mg--Al--rare earth element (RE) system, and
the like have already been put into practical use. These materials
are molded by die casting, Thixo molding, sheet metal processing,
or the like, and subjected to a chemical conversion treatment, and
the chemical conversion product thus obtained is subjected to a
coating treatment. Die casting refers to a method for injecting
molten metal into a mold under pressure to obtain a molded product.
Thixo molding refers to a method for extruding semi-molten or
molten metal into a mold at about 250.degree. C. from an extruder
at about 600.degree. C., thereby obtaining a molded product.
[0006] The chemical conversion treatment refers to a treatment of
forming a chemical conversion coating film having a corrosion
resistant function on a surface of Mg or a Mg-alloy According to
this treatment, Mg or a Mg-alloy is soaked in a chromic acid
solution mainly containing a hexavalent chromium solution, a
non-chromic acid solution containing no hexavalent chromium, or the
like, whereby a coating film of a chromium complex salt of chromic
acid (in general, xCrO.sub.3yCr.sub.2O.sub.32H.sub.2O,
Cr(OH).sub.2HCrO.sub.42H.sub.2O, etc.) is formed on the surface of
the Mg or the Mg-alloy After the chemical conversion treatment, a
coating treatment is performed. Methods for the chemical conversion
treatment are proposed by JP11(1999)-131255A and JP2000-96255A.
[0007] There are the following problems in producing a product
using Mg or a Mg-alloy as a material. A molded product obtained by
die casting, Thixo molding, or the like has burr. At present, the
burr is removed manually or mechanically by punching with a press,
cutting, or the like, any of which is a cumbersome operation. There
is also a method for removing the burr by shot blast of
air-spraying grains onto a molded product. In this case, there are
the following problems. Dust particles of Mg, a Mg-alloy or grains
are likely to be generated and scatter, resulting in poor
workability and high danger of explosion of dust particles.
[0008] Furthermore, a pretreatmnet is required for performing the
above-mentioned chemical conversion treatment. The general chemical
conversion treatment is performed as follows. The above-mentioned
molded product is degreased, and then, washed with an acid. Then,
the molded product is subjected to etching so as to remove a
releasing agent used during molding. Then, a surface adjustment
treatment is performed in which the surface of the molded product
is polished to obtain satin finish so that a coating film of a
chromium complex salt of chromic acid is likely to be formed on the
surface of the molded product. The above-mentioned treatments
correspond to a pretreatment. Then, the molded product is soaked in
the above-mentioned chromic acid solution or non-chromic acid
solution to perform a chemical conversion treatment. Then, the
resultant molded product is washed with water, and dried at about
70.degree. C., whereby a chemical conversion coating film is cured.
Thus, the pretreatment of the chemical conversion treatment needs
to have several processes such as degreasing, washing, a surface
adjustment treatment by etching, and the like, which makes the
operation cumbersome, complicates a treatment apparatus, and
increases a treatment cost.
[0009] In the molded product produced by die casting, Thixo
molding, or the like, molding defects such as a draw, a void, a hot
water flow, and the like occur. During inspection of the molding
defects (draw, void, flow, etc.), the molded product is partially
buffed up manually so as to make it easy to see the molded product,
and thereafter, a visual inspection is performed. At this time,
buffing is performed manually which makes it cumbersome to perform
the inspection, and may generate dust particles during buffing. As
the method for adjusting a surface such as buffing, JP2003-284457A
proposes a wet blast treatment. Furthermore, JP2000-263442A
proposes a method for continuously performing the wet blast as a
pretreatment of the chemical conversion treatment.
[0010] The above-mentioned conventional techniques use wet blast as
a pretreatment of the chemical conversion treatment, and the number
of processes and the like are similar to those of a treatment using
a conventional chemical treatment, so that the effect of
improvement in cost and the like is small. Furthermore, a defective
molded product needs to be corrected by puttying before the
chemical conversion treatment, decreasing a yield and increasing a
cost.
SUMMARY OF THE INVENTION
[0011] Therefore, with the foregoing in mind, it is an object of
the present invention to provide a Mg or Mg-alloy housing in which
a chemical conversion film is formed simply on a surface of a
molded product made of Mg or a Mg-alloy so as to reduce the
correction by puttying, a coating yield is enhanced, and a cost can
be reduced, and a method for producing the Mg or Mg-alloy
housing.
[0012] A Mg or Mg-alloy housing of the present invention is
characterized in that a surface of the Mg or Mg-alloy housing is
subjected to wet blast using a solution containing a chemical
conversion treatment agent and an abrasive, whereby a chemical
conversion film is formed on the surface of the Mg or Mg-alloy
housing.
[0013] A method for producing a Mg or Mg-alloy housing of the
present invention is characterized in that a surface of a Mg or
Mg-alloy is subjected to wet blast using a solution containing a
chemical conversion treatment agent and an abrasive, whereby
unevenness due to the blast and a chemical conversion film are
simultaneously formed on the surface of the Mg or Mg-alloy
housing.
[0014] These and other advantages of the present invention will
become apparent to those skilled in the art upon reading and
understanding the following detailed description with reference to
the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a diagram showing a process flow in Example 1 of
the present invention,
[0016] FIG. 2 is a diagram showing a process flow in Comparative
Example 1.
[0017] FIG. 3 is a surface observed photograph of a notebook
computer housing in Example 1 of the present invention.
[0018] FIG. 4 is a surface observed photograph of a notebook
computer housing in Comparative Example 1.
[0019] FIG. 5A to 5C are surface observed photographs showing
results of a cross-cut test in Example 1 of the present
invention.
[0020] FIG. 6A to 6C are surface observed photographs showing
results of a cross-cut test in Comparative Example 1.
[0021] FIG. 7A to 7C are surface observed photographs obtained by
evaluating the corrosion resistance by a salt spray test (SST) in
Example 1 of the present invention.
[0022] FIG. 8A to 8C are surface observed photographs obtained by
evaluating the corrosion resistance by a salt spray test (SST) in
Comparative Example 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] According to the present invention, the surface of a Mg or
Mg-alloy housing is subjected to wet blast using a mixed solution
containing a chemical conversion treatment agent and an abrasive to
form a chemical conversion film together with unevenness due to the
blast on the surface of the Mg or Mg-alloy housing, which reduces
the correction by puttying, thereby preventing a decrease in yield
and an increase in cost. More specifically when the mixed solution
containing the chemical conversion treatment agent and the abrasive
is injected onto the surface of the Mg or Mg-alloy housing by wet
blast, the surface is scraped off with the abrasive, and
simultaneously, an appropriately thick and dense calcium
phosphate-magnesium phosphate complex coating film is generated due
to the reaction between Mg and the chemical conversion treatment
agent. Thus, a film of an oxide or a hydroxide that degrades bare
corrosion resistance, rust prevention, coating adhesion, and
coating corrosion resistance is not formed on the surface of the Mg
or Mg-alloy housing; instead, a calcium phosphate-magnesium
phosphate complex coating film can be formed thereon in which
calcium and phosphorus contribute to the enhancement of bare
corrosion resistance of the chemical conversion film, and manganese
contributes to the enhancement of coating adhesion. Furthermore, a
draw, a void, a flow, and the like on the surface of a chemical
conversion product are eliminated, which makes it unnecessary to
perform correction by puttying before coating, and enables a cost
to be reduced.
[0024] The inventors of the present invention have earnestly
studied so as to solve the above-mentioned problems, and
consequently found that, for example, as a rust prevention
treatment and a pretreatment of a coating treatment of a housing
made of Mg or a Mg alloy a chemical conversion treatment and wet
blast are performed simultaneously with respect to the Mg or Mg
alloy whereby the above-mentioned problems can be solved. Herein,
wet blast refers to a treatment in which a liquid and an abrasive
are mixed, and the mixture is injected under a pressure in a range
of 0.1 to 0.3 MPa.
[0025] It is preferable that the chemical conversion treatment
agent used in the present invention contains calcium ions,
manganese ions, and phosphoric acid ions, and it is also preferable
that wet blast is performed using a solution in which an aqueous
liquid containing an oxidation accelerator and an abrasive such as
alumina are mixed. In the wet blast, surface polishing and chemical
conversion coating of a housing are performed simultaneously
Therefore, a formed coating film is also polished; however, a
sufficient coating film can be obtained by satisfying the above
conditions.
[0026] It is preferable that at least one particulate material
selected from alumina, zirconium, glass, and resin is used as the
abrasive. Furthermore, as the resin, melamine resin, urea resin,
polyester resin, phenol resin, epoxy resin, urethane resin, and the
like can be used. It is preferable that an average particle
diameter of the abrasive is in a range of 10 to 300 .mu.m.
[0027] As a calcium ion source used for a chemical conversion
treatment agent to be injected, one kind or at least two kinds of
calcium nitrate, calcium nitrite, calcium thiosulfate, tetracalcium
phosphate, and the like can be compounded. Furthermore, as the
manganese ion source, one kind or at least two kinds of manganese
carbonate, manganese nitrate, manganese hydrogen phosphate,
manganese biphosphate, manganese fluoroborate, and the like can be
compounded. Furthermore, as the phosphoric acid ion source, one
kind or at least two kinds of orthophosphoric acid, condensed
phosphoric acid, phosphorous acid, hypophosphorous acid, and the
like can be compounded.
[0028] Furthermore, as the oxidation accelerator, sodium chlorate,
sodium hypochlorite, and the like can be used. The oxidation
accelerator can enhance the reactivity between the Mg or Mg-alloy
and the above-mentioned respective component ions during the
chemical conversion treatment, whereby a chemical conversion
coating film with satisfactory bare abrasion resistance can be
formed more conveniently Furthermore, the preferable compounded
amount of the oxidation accelerator is in a range of 0.02 to 2 g/L
so as to stably obtain a chemical conversion coating film with the
above-mentioned performance.
[0029] According to the present invention, when a mixed solution of
a chemical conversion treatment agent and an abrasive is injected
onto the surface of Mg or a Mg-alloy by wet blast, the surface is
scraped off with the abrasive, and an appropriately thick and dense
calcium phosphate-manganese phosphate complex coating film is
generated due to the reaction between the Mg or Mg-alloy and the
chemical conversion treatment agent. Thus, a film of an oxide or a
hydroxide is not formed on the Mg or Mg-alloy surface, and instead,
a calcium phosphate-manganese phosphate complex coating film can be
formed. It is preferable that the adhesion amount of the complex
coating film formed by the chemical conversion treatment is 5
mg/m.sup.2 to 50 mg/m.sup.2 in terms of a Ca weight, 3 mg/m.sup.2
to 25 mg/m.sup.2 in terms of a Mn weight, and 30 mg/m.sup.2 to 100
mg/m.sup.2 in terms of a phosphorus weight.
[0030] Furthermore, it is preferable that the proportion of the
chemical conversion treatment agent is 70 to 90% by mass, and the
proportion of the abrasive is 10 to 30% by mass.
[0031] A chemical conversion coating film is formed on the Mg or
Mg-alloy surface so as to contain the above-mentioned predetermined
amount of calcium, manganese, and phosphorous, whereby a chemical
conversion coating film having predetermined bare corrosion
resistance, rust prevention, coating adhesion, and coating
corrosion resistance can be obtained. In particular, calcium and
phosphorous are considered to contribute to the enhancement of bare
corrosion resistance of a chemical conversion coating film, and
manganese is considered to contribute to the enhancement of coating
adhesion.
[0032] Furthermore, the Mg or Mg-alloy surface is polished with the
abrasive, whereby a draw, a void, a flow, and the like on the
surface of a Mg or Mg-alloy housing product are eliminated, and it
is not necessary to perform correction by puttying before coating,
whereby a cost can be reduced. It is preferable that, due to the
polishing function of the abrasive contained in the wet blast
solution, the surface roughness of the Mg or Mg-alloy housing is
set to be in a range of 0.5 .mu.m to 100 .mu.m in terms of a
10-point average surface roughness.
[0033] After the above-mentioned treatment, it is preferable that
the surface is washed with water, followed by drying. Furthermore,
if an aqueous liquid containing calcium ions, manganese ions, and
phosphoric acid ions similar to those of the chemical conversion
treatment agent used in wet blast, and an oxidation accelerator is
shower-injected onto the surface after wet blast and washing with
water, the thickness of the coating film can be increased to
enhance corrosion resistance.
[0034] Thereafter, a coating treatment can be performed. In the
coating treatment, it is possible that a coating agent such as
epoxy resin is applied by spray coating, electrodeposition, etc.,
and a coating agent such as melamine resin is applied thereto.
Alternatively a powdery coating agent of various kinds of resins
can also be applied by electrostatic coating.
EXAMPLES
[0035] Hereinafter, the present invention will be described more
specifically by way of an example and a comparative example.
Example 1
[0036] As a target member to be treated, a notebook computer
housing (length: 329 mm, width: 274 mm, height: 2 mm) produced by
subjecting Mg or a Mg-alloy of ASTM AZ91D to Thixo molding was
used. Thixo molding was performed as follows: Mg or a Mg alloy in a
semi-molten or molten state was extruded from an extruder at about
600.degree. C. to a mold at about 250.degree. C. to obtain a molded
product. FIG. 1 shows a surface treatment process.
[0037] As a chemical conversion treatment agent, a mixture
containing 80% by mass of "Grander-Finer MC1000" (produced by
Million Chemical Co., Ltd.: 15 to 25% by mass of phosphoric acid,
10 to 15% by mass of manganese compound, and 10 to 20% by mass of
calcium compound) and 20% by mass of alumina (Macorundum A#320,
produced by Macoho Co., Ltd.) with an average particle size of 40
.mu.m as an abrasive was used. Wet blast was performed using
WFB-2-2C produced by Macoho Co., Ltd. under the following
condition: a compression air pressure was 0.2 MPa, a pump pressure
was 0.12 MPa, a distance between a housing and a nozzle was 30 mm,
and the housing was fed forward at 40 mm/s. The housing was washed
with water so as to remove the chemical conversion treatment agent
and the abrasive, and further washed with deionized water, followed
by drying.
Comparative Example 1
[0038] FIG. 2 shows a process of performing a chemical conversion
treatment after etching as a comparative example. Surface
adjustments 1 and 2 in FIG. 2 represent an etching treatment.
[0039] As a degreasing agent, "GFMG15SX" (produced by Million
Chemical Co., Ltd.) was used, and the temperature thereof was kept
at 70.degree. C. Then, the above-mentioned Mg or Mg-alloy housing
was soaked in the degreasing agent for 5 minutes to degrease the
housing, followed by washing with water. As an etchant,
"Grander-Finer MG104S" (produced by Million Chemical Co., Ltd.: 30
to 40% by mass of phosphoric acid, less than 0.1% by mass of
surfactant, remaining water) was kept at a concentration of 5% and
a temperature of 60.degree. C. Then, the housing was soaked in the
etchant for 60 seconds to perform etching, followed by washing with
water. Thereafter, the member subjected to the etching treatment
was soaked in the above-mentioned "GFMG15SX" (produced by Million
Chemical Co., Ltd.) kept at a temperature of 60.degree. C. for 7
minutes, followed by washing with water. As the chemical conversion
treatment agent, "Grander-Finer MC 1000" (produced by Million
Chemical Co., Ltd.: 15 to 25% by mass of phosphoric acid, 10 to 15%
by mass of manganese compound, 10 to 20% by mass of calcium
compound) was used, and kept at 35.degree. C. Then, the Mg or
Mg-alloy housing treated as described above was soaked in the
chemical conversion treatment agent for 40 seconds, washed with
water, and further washed with deionized water, followed by
drying.
[0040] Example 1 and Comparative Example 1 were evaluated for an
outer appearance. Furthermore, the adhesion amount of elements on
the Mg or Mg-alloy housing surface was measured by quantitation
with a fluorescent X-ray Five portions on the surface of the
housing were assumed, and the variation thereof was checked. The
electric resistance was measured by "Loresta MP" (four-terminal
two-probe system) produced by Dia Instruments Co., Ltd. The results
are shown in Table 1 and FIGS. 3 and 4. FIG. 3 is a photograph
showing the outer appearance of Comparative Example 1, and FIG. 4
is a photograph showing the outer appearance of Example 1. The
outer appearance of Example 1 had a uniform surface, whereas
irregularity was observed on the outer appearance of Comparative
Example 1.
TABLE-US-00001 TABLE 1 Electric Adhesion amount of Experiment Outer
resistance elements (mg/m.sup.2) No. appearance Smut (.OMEGA.) Ca P
Example 1 FIG. 3 None 0.4 24.4 .+-. 4 59.2 .+-. 7 Comparative FIG.
4 None 0.7 70.4 .+-. 35 112.6 .+-. 27 Example 1 Note 1: Smut refers
to an outer appearance defect due to the adhesion of powder.
[0041] Furthermore, two-coat coating (baking at 150.degree. C.) of
an epoxy type was kept on a Mg or Mg-alloy housing in a
high-temperature and high-humidity environment (60.degree. C.,
relative humidity 95% RH) for 100 hours. Thereafter, a cross-cut
test was performed (a checkerboard pattern was drawn on the surface
of a sample to divide the surface into 100 portions, and the number
of remaining grids after tape-up (peeling a tape) was counted to be
determined based on the following standard: success when the number
of remaining grids is 100, and failure when the number of remaining
grids is less than 100.
[0042] FIGS. 5A to 5C are outer appearance photographs showing the
results in Example 1, and FIGS. 6A to 6C are outer appearance
photographs showing the results in Comparative Example 1. In FIGS.
5A-5C to 6A-6C, "OH" represents "before test", and "2 mm" and "1
mm" respectively represent the size of each grid.
[0043] Furthermore, a salt spray test (SST) in accordance with JIS
Z 2371 was performed for 8 hours and 24 hours, and corrosion
resistance was evaluated. FIGS. 7A to 7C are outer appearance
photographs showing the results in Example 1, and FIGS. 8A to 8C
are outer appearance photographs showing the results in Comparative
Example 1. In FIGS. 7A-7C to FIGS. 8A-8C, "OH" represents "before
test", and "8H" and "24H" respectively represent a test treatment
time.
[0044] It was confirmed from the above results that the housing in
Example 1 had a uniform color tone and was smooth, compared with
Comparative Example 1. Furthermore, in Example 1, a draw, a void, a
flow, and the like on the surface of the molded produce were
eliminated. This enhanced the yield of coating performed after a
treatment, and makes it unnecessary to perform correction by
puttying before coating, so that a cost was reduced.
[0045] In Example 1, although the adhesion amount of a coating film
was smaller than that in Comparative Example 1, the adhesion amount
was less varied compared with that in Comparative Example 1. The
other coating characteristics such as a resistance, a coating
property and corrosion resistance exhibited similar values between
Example 1 and Comparative Example 1.
[0046] Furthermore, in Example 1, since the number of processes is
small, a coating treatment can be performed easily whereby a cost
can be reduced. [0047] The invention may be embodied in other forms
without departing from the spirit or essential characteristics
thereof. The embodiments disclosed in this application are to be
considered in all respects as illustrative and not limiting. The
scope of the invention is indicated by the appended claims rather
than by the foregoing description, and all changes which come
within the meaning and range of equivalency of the claims are
intended to be embraced therein.
* * * * *