U.S. patent application number 09/794700 was filed with the patent office on 2001-07-05 for circuit-forming charging powder and multilayer wiring board using the same.
This patent application is currently assigned to Murata Manufacturing Co., Ltd.. Invention is credited to Kamada, Akihiko, Kato, Isao, Sakai, Norio.
Application Number | 20010006756 09/794700 |
Document ID | / |
Family ID | 12861965 |
Filed Date | 2001-07-05 |
United States Patent
Application |
20010006756 |
Kind Code |
A1 |
Kamada, Akihiko ; et
al. |
July 5, 2001 |
Circuit-forming charging powder and multilayer wiring board using
the same
Abstract
A circuit-forming charging powder allowing circuit patterns to
resist being peeled off a printing object when the powder is used
for printing a circuit pattern by an electrophotographic method on
the object, wherein the circuit-forming charging powder has a
conductive metal powder, a charge control agent and an adhesion
reinforcing agent combined with a heat-melt resin and a method for
producing the circuit-forming charging powder, as well as printed
objects and multilayer wiring boards are described.
Inventors: |
Kamada, Akihiko;
(Nagaokakyo-shi, JP) ; Kato, Isao;
(Nagaokakyo-shi, JP) ; Sakai, Norio;
(Nagaokakyo-shi, JP) |
Correspondence
Address: |
OSTROLENK FABER GERB & SOFFEN
1180 AVENUE OF THE AMERICAS
NEW YORK
NY
100368403
|
Assignee: |
Murata Manufacturing Co.,
Ltd.
|
Family ID: |
12861965 |
Appl. No.: |
09/794700 |
Filed: |
February 27, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09794700 |
Feb 27, 2001 |
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09260270 |
Mar 2, 1999 |
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6214508 |
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Current U.S.
Class: |
428/210 ;
428/195.1; 430/106.1; 430/108.1; 430/108.23; 430/110.2; 430/18 |
Current CPC
Class: |
Y10T 428/24802 20150115;
H05K 3/102 20130101; Y10T 428/24926 20150115 |
Class at
Publication: |
430/108.7 ;
430/106.1; 430/108.1; 430/110.2; 428/195; 430/18 |
International
Class: |
G03G 009/093; G03G
009/08 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 1998 |
JP |
10-50544 |
Claims
What is claimed is:
1. A circuit-forming charging powder for use in printing a circuit
pattern on an object by electrophotography, comprising a conductive
metal powder, a heat-melt resin, a charge control agent and an
adhesion reinforcing agent.
2. The circuit-forming charging powder according to claim 1,
wherein said conductive metal is at least one member selected from
the group consisting of copper, gold, silver, nickel, palladium or
molybdenum.
3. The circuit-forming charging powder according to claim 1,
wherein said charge control agent is at least one member selected
from the group consisting of a metallic azo dye, a chlorinated
paraffin, a chlorinated polyester, an acid-excess polyester, a
sulfonylamine naphthenic acid metal salt of copper phthalocyanine,
a metal salt of fatty acid and resinate soap.
4. The circuit-forming charging powder according to claim 1,
wherein said adhesion reinforcing agent is at least one member
selected from the group consisting of silica glass, borosilicate
glass, soda lime, lead glass, aluminosilicate glass, alumina and
ferrite.
5. The circuit-forming charging powder according to claim 1,
wherein the particle size of said circuit-forming charging powder
is in the range of about 3 to 20 .mu.m.
6. The circuit-forming charging powder according to claim 1,
wherein the content of said conductive metal powder in the
circuit-forming charging powder is more than about 90 wt % and less
than or equal to about 98 wt %.
7. The circuit-forming charging powder according to claim 1,
wherein the content of said heat-melt resin in the circuit-forming
charging powder is less than about 10 wt %.
8. The circuit-forming charging powder according to claim 7,
wherein the content of said conductive metal powder in the
circuit-forming charging powder is more than about 90 wt % and less
than or equal to about 98 wt %. and wherein the particle size of
said circuit-forming charging powder is in the range of about 3 to
20 .mu.m.
9. The circuit-forming charging powder according to claim 8,
wherein said adhesion reinforcing agent is at least one member
selected from the group consisting of silica glass, borosilicate
glass, soda lime, lead glass, aluminosilicate glass, alumina and
ferrite.
10. The circuit-forming charging powder according to claim 9,
wherein said conductive metal is at least one member selected from
the group consisting of copper, gold, silver, nickel, palladium or
molybdenum, and wherein said charge control agent is at least one
member selected from the group consisting of a metallic azo dye, a
chlorinated paraffin, a chlorinated polyester, an acid-excess
polyester, a sulfonylamine naphthenic acid metal salt of copper
phthalocyanine, a metal salt of fatty acid and resinate soap.
11. An aggregate of a plurality of circuit-forming charging powder
particles according to claim 10.
12. An aggregate of a plurality of circuit-forming charging powder
particles according to claim 1.
13. A ceramic green sheet having a circuit pattern which comprises
the circuit-forming charging powder according to claim 12
thereon.
14. A ceramic green sheet having a circuit pattern which comprises
the circuit-forming charging powder according to claim 11
thereon.
15. A ceramic green sheet having a circuit pattern which comprises
the circuit-forming charging powder according to claim 4
thereon.
16. A ceramic green sheet having a circuit pattern which comprises
the circuit-forming charging powder according to claim 1
thereon.
17. A multilayer wiring board comprising a baked laminate
comprising a plurality of ceramic green sheets of claim 16.
18. A multilayer wiring board comprising a baked laminate
comprising a plurality of ceramic green sheets of claim 15.
19. A multilayer wiring board comprising a baked laminate
comprising a plurality of ceramic green sheets of claim 14.
20. A multilayer wiring board comprising a baked laminate
comprising a plurality of ceramic green sheets of claim 13.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a circuit-forming charging
powder and a multilayer wiring board using the same, especially to
a circuit-forming charging powder (toner) to be used in printing a
circuit pattern on an object by electrophotography, and a
multilayer wiring board using the same.
[0003] 2. Description of the Related Art
[0004] Japanese Unexamined Patent Publication No. 4236484 discloses
a method for forming a desired circuit pattern on an insulating
substrate by taking advantage of the electrostatic force used in
conventional electrophotography, and a circuit-forming charging
powder to be used in this wiring method. FIG. 1 shows a cross
section of the conventional circuit-forming charging powder. The
circuit-forming charging powder 100 with a mean particle size of 10
to 15 .mu.m assumes a structure in which a conductive metal powder
101 and a charge control agent 102 are uniformly dispersed in a
heat-melt resin 103. The practical method for producing the
circuit-forming charging powder 100 comprises the steps of: mixing
a flake-shaped silver powder with a mean particle size of 0.4 .mu.m
as a conductive metal powder 101, a metallic azo dye as a charge
control agent 102 and a styrene-acrylic acid copolymer as a
heat-melt resin 103 in a weight ratio of 80:1:19, respectively; and
heat-melting the mixture followed by kneading with a kneader. Then,
the mixture is roughly crushed with a cutter mill, finely crushed
with a jet mill and classified with an air jet, thereby obtaining
the circuit-forming charging powder 100.
[0005] However, the conventional circuit-forming charging powder
involves a problem in that the circuit pattern can peel off the
baked ceramic sheet when the powder is used for printing the
circuit pattern on a ceramic green sheet by electrophotography
because the ceramic green sheet shrinks during baking.
SUMMARY OF THE INVENTION
[0006] Accordingly, the object of the present invention, carried
out for solving the problem described above, provides a
circuit-forming charging powder having little possibility for
allowing the circuit pattern to be peeled off the printing object
even when the circuit pattern is printed on the printing object by
electrophotography, and a multilayer circuit board using the
same.
[0007] According to the present invention, the circuit-forming
charging powder to be used for printing a circuit pattern on a
printing object by electrophotography comprises a conductive metal
powder, a heat-melt resin, a charge control agent and an adhesion
reinforcing agent.
[0008] The conductive metal powder is a secondary powder comprising
aggregates formed by aggregating a plurality of primary powders,
and the printing object is a ceramic green sheet.
[0009] The multilayer wiring board according to the present
invention is formed by laminating and baking the ceramic green
sheets on which the circuit pattern is printed.
[0010] The circuit-forming charging powder according to the present
invention contains the adhesion reinforcing agent, which serves for
allowing the conductive metal powder used for forming the circuit
pattern to adhere with the baked ceramic sheet when the ceramic
green sheet on which the circuit pattern has been printed is baked.
Accordingly, the adhesion strength between the baked ceramic sheet
and the circuit pattern is improved after baking, preventing the
circuit pattern from being peeled off the ceramic sheet.
[0011] Also, the conductive metal powder constituting the
circuit-forming charging powder is a secondary powder comprising an
aggregate prepared by aggregating a plurality of primary powders,
the conductive metal powder comprising the secondary powder being
dissociated into primary powders when the circuit-forming charging
powder is fixed. Accordingly, the circuit pattern formed with the
primary powders constituting the conductive metal powder is densely
packed, allowing the sheet resistance of the circuit pattern to be
further reduced along with decreasing the circuit pattern loss.
[0012] Also, the adhesion reinforcing agent contained in the
circuit-forming charging powder serves to allow the conductive
metal powder to be formed into the circuit pattern and adhered with
the baked ceramic sheet when the ceramic sheet on which the circuit
pattern has been printed. Consequently, the adhesion strength of
the baked ceramic sheet with the circuit pattern is improved after
baking, prevent the circuit pattern from being peeled off the
ceramic sheet.
[0013] Also, the multilayer wiring board according to the present
invention is produced by the steps comprising: printing the circuit
pattern on the ceramic green sheet by the electrophotographic
method using the circuit-forming charging powder containing the
adhesion reinforcing agent; and laminating the ceramic green sheets
followed by baking. Accordingly, the circuit pattern has
essentially no possibility to be peeled off the baked ceramic sheet
after baking, making it possible to improve quality and reliability
of the multilayer wiring board that can be used in high frequency
bands.
[0014] Also, the multilayer wiring board is produced by the steps
comprising: preparing the circuit-forming charging powder
containing the conductive metal powder comprising the secondary
powder of aggregates of a plurality of primary powders; and
laminating the ceramic green sheet, on which the circuit pattern is
printed by the electrophotographic method using the circuit-forming
charging powder, followed by baking. Therefore, ceramic sheet
resistance and loss of the circuit pattern is reduced along while
making it possible to use the multilayer wiring board in higher
frequency bands.
[0015] Other features and advantages of the present invention will
become apparent from the following description of the invention
which refers to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 shows a cross section of the conventional
circuit-forming charging powder;
[0017] FIG. 2 shows a cross section of the circuit-forming charging
powder according to the first preferred embodiment of the present
invention;
[0018] FIG. 3 shows a cross section of the circuit-forming charging
powder according to the second preferred embodiment of the present
invention;
[0019] FIG. 4 shows a cross section of the circuit-forming charging
powder according to the third preferred embodiment of the present
invention;
[0020] FIG. 5 illustrates the structure of the electro-photographic
system to be used in forming the circuit pattern on the printing
object;
[0021] FIG. 6 shows a cross section of the multilayer wiring board
according to the present invention; and
[0022] FIG. 7 shows one example of the cross section of the
conductive metal powder constituting the circuit-forming charging
powder shown in FIG. 2 to FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] FIG. 2 shows a cross section of the circuit-forming charging
powder in the first preferred embodiment according to the present
invention. The circuit-forming charging powder 10 assumes a
structure in which a conductive metal powder 11, a charge control
agent 12 and an adhesion reinforcing agent 13 are uniformly
dispersed in a heat-melt resin 14.
[0024] A practical method for producing the circuit-forming
charging powder 10 will be described. In the first step, spherical
copper particles with a mean particle size of 0.8 .mu.m as the
conductive metal powder 11, a metallic azo dye as a charge control
agent 12, silica as an adhesion reinforcing agent 13 and a
styrene-acrylic acid copolymer as a heat-melt resin 14 are mixed in
a weight ratio of 93:1:1:5, respectively.
[0025] In the next step, the mixture is heat-melted and kneaded in
a kneader, followed by a rough crushing with a cutter mill and a
fine crushing with a jet mill. The circuit-forming charging powder
10 with a mean particle size of 8.0 .mu.m is obtained by
classification with air jet.
[0026] According to the circuit-forming charging powder in the
first preferred embodiment, the adhesion reinforcing agent
contained therein serves for reinforcing the adhesion of the
printing object with the conductive metal powder to be formed into
a circuit pattern, preventing the circuit pattern from being peeled
off the printing object due to enhanced adhesion strength of the
printing object with the circuit pattern.
[0027] The content of the adhesion reinforcing agent contained in
the circuit-forming charging powder can be desirably adjusted since
it is kneaded with the heat-melt resin, enabling adhesion strength
of the baked ceramic green sheet with the circuit pattern to be
adjusted. A large quantity of the adhesion reinforcing agent may be
even contained in the circuit-forming charging powder in order to
obtain higher adhesion strength.
[0028] When the printing object is a ceramic green sheet, the
adhesion reinforcing agent contained in the circuit-forming
charging powder serves to allow the conductive metal powder forming
the circuit pattern to adhere to the baked ceramic sheet during
baking of the ceramic green sheet on which the circuit pattern has
been formed. Therefore, adhesion strength of the baked ceramic
sheet with the circuit pattern is enhanced to prevent the circuit
pattern from being peeled off the ceramic sheet.
[0029] FIG. 3 shows a cross section of the circuit-forming charging
powder according to the second preferred embodiment of the present
invention. An outer wall 21 comprising the adhesion reinforcing
agent 13 and heat-melt resin 14 is formed around the conductive
metal powder 11 in the circuit-forming charging powder 20, assuming
a structure in which the charge control agent 12 is adhered on the
surface of the outer wall 21.
[0030] A practical method for producing the circuit-forming
charging powder 20 will be described hereinafter. In the first
step, copper particles with a mean particle size of 5.0 .mu.m as
the conductive metal powder 11 and particles, obtained by mixing
silica as the adhesion reinforcing agent 13 and a styrene-acrylic
acid copolymer as the heat-melt resin 14 in a weight ratio of 1:5
followed by finely crushing, are mixed in a weight ratio of 93:6,
allowing the particles comprising the adhesion reinforcing agent 13
and heat-melt resin 14 to adhere on the conductive metal powder 11
by electrostatic force.
[0031] In the next step, a mechanical impact force is applied to
the product obtained by adhering the particles comprising the
adhesion reinforcing agent 13 and the heat-melt resin 14 to the
conductive metal powder 11 to form an outer wall 21 comprising the
adhesion reinforcing agent 13 and heat-melt resin 14 around the
conductive metal powder 11.
[0032] In the third step, the product prepared by forming the outer
wall comprising the adhesion reinforcing agent 13 and heat-melt
resin 14 around the conductive metal powder 11, and a azo metallic
dye as the charge control agent 12 are mixed in a weight ratio of
99:1, followed by applying a mechanical impact force to form a
circuit-forming charging powder 20 with a mean particle size of 8.0
.mu.m in which the charge control agent 12 is adhered on the
surface of the outer wall 21. In other words, the outer wall 21
comprising the adhesion reinforcing agent 13 and heat-melt resin 14
is formed around the conductive metal powder 11 to obtain the
circuit-forming charging powder 20 on the surface of which the
charge control agent 12 is adhered.
[0033] In the circuit-forming charging powder according to the
second preferred embodiment described above, a circuit-forming
charging powder that can be uniformly charged is obtained by
adhering the charge control agent on the surface of the outer wall
formed around the conductive metal powder. Accordingly, use of this
circuit-forming charging powder allows the charge to be more easily
controlled as well as improving the printing affinity for complying
with circuit patterns having narrow intervals, making it possible
to form a circuit pattern with low sheet resistance.
[0034] The conductive metal powder is prevented from being exposed
on the surface of the circuit-forming charging powder because the
outer wall comprising the adhesion reinforcing agent and heat-melt
resin is formed around the conductive metal powder. Therefore, the
charging ability of the circuit-forming charging powder is improved
by preventing deterioration of charging ability ascribed to the
conductive metal powder, consequently improving printing affinity
even more to comply with the circuit pattern having narrower
intervals.
[0035] The quantity of the adhesion reinforcing agent contained in
the circuit-forming charging powder can be adjusted to a desirable
level since it is kneaded with the heat-melt resin forming the
outer wall, thereby enabling one to adjust the adhesion strength of
the baked ceramic sheet with the circuit pattern. In order to
reinforce the adhesion strength, a large amount of the adhesion
reinforcing agent can be also included in the circuit-forming
charging powder.
[0036] FIG. 4 shows a cross section of the circuit-forming charging
powder according to the third preferred embodiment of the present
invention. The circuit-forming charging powder 30 assumes a
structure comprising the charge control agent 12, adhesion strength
reinforcing agent 13 and heat-melt resin 14 formed around the
conductive metal powder 11.
[0037] A practical method for producing the circuit-forming
charging powder 30 will be described hereinafter. In the first
step, copper particles with a mean particle size of 5.0 .mu.m as
the conductive metal powder and particles, prepared by mixing a
metallic azo dye as the charge control agent 12, silica as the
adhesion reinforcing agent 13 and a styrene-acrylic acid copolymer
as the heat-melt resin 14 in a weight ratio of 1:1:5 followed by
finely crushing, were mixed in a weight ratio of 93:7, thereby
allowing the particles comprising the charge control agent 12,
adhesion reinforcing agent 13 and heat-melt resin 14 to adhere on
the conductive metal powder 11.
[0038] In the next step, a mechanical impact force is applied to
the conductive metal powder 11 adhered with particles composed of
the charge control agent 12, adhesion reinforcing agent 13 and
heat-melt resin 14, thus obtaining the circuit-forming charging
powder 30 with a mean particle size of 8.0 .mu.m in which an outer
wall comprising the charge control agent 12, adhesion reinforcing
agent 13 and heat-melt resin 14 is formed around the conductive
metal powder 11.
[0039] In the circuit-forming charging powder according to the
third preferred embodiment, the surface of the circuit-forming
charging powder is not required to be separately adhered with the
charge control agent because the outer wall comprising the charge
control agent, adhesion reinforcing agent and heat-melt resin has
been formed around the conductive metal powder, enabling one to
simplify the production process, as well as to reduce the
production cost, of the circuit-forming charging powder.
[0040] As shown in the foregoing first to third preferred
embodiments, increasing the content of the conductive metal powder
in the circuit-forming charging powder to more than about 90 wt %,
e.g., to 93% wt, allows the film thickness of the circuit pattern
to be thicker by use of one printing process. Therefore, the sheet
resistance of the circuit pattern can be reduced as well as
diminishing the circuit pattern loss, thus allowing the multilayer
printed board obtained by using this circuit-forming charging
powder to be used in high frequency bands.
[0041] Forming a thick circuit pattern in one printing makes it
possible to simplify the production process of the circuit pattern,
reducing the production cost of the multilayer wiring board. Shift
and deformation of the printed circuit pattern may be also avoided
to further improve the quality of the multilayer wiring board
[0042] In addition, since the content of the heat-melt resin in the
circuit-forming charging powder can be reduced to less than about
10 wt %, e.g., to 5 wt %, frequency of delamination between the
circuit pattern and baked ceramic sheet that occurs due to complete
combustion of the heat-melt resin during baking can be reduced,
enabling one to form a more reliable circuit pattern.
[0043] The content of the conductive metal powder is preferably
less than about 98% by weight since when the content of the
conductive metal powder is more than about 98% by weight, it
becomes difficult to perfectly cover the conductive metal powder
with the heat-melt resin without exposing the powder surface.
[0044] FIG. 5 illustrates the construction of the
electrophotographic system to be used in forming the circuit
pattern on the printing object. Forming the circuit pattern on the
printing object comprises the steps of: charging the surface of a
photosensitive member 41 with a corona charging device 42; exposing
the surface of the photosensitive member 41 rotating along the
direction indicated by an arrow A by irradiating with a laser beam
43 to form latent images (not shown in the drawing); developing the
latent image on the surface of the photosensitive member 41 by
electrostatic adsorption of the circuit-forming charging powder 10
to 30 fed from a feed means 44; transferring the circuit-forming
charging powder 10 to 30 developed on the latent image pattern on
the printing object 45 by rotating the photosensitive member 41;
and fixing the circuit-forming charging powder 10 to 30 transferred
on the printing object 45 by irradiating with a flash lamp 46 to
form the circuit pattern (not shown in the drawing) on the printing
object 45.
[0045] FIG. 6 shows a cross section of a multilayer wiring board
according to one preferred embodiment of the present invention. The
multilayer wiring board 50 is provided with the first, second and
third green sheets represented by 51a, 51b and 51c, respectively.
Circuit patterns 52a and 52b are printed on the first green sheet
51a and second green sheet 51b using the circuit-forming charging
powder 10 to 30 (FIG. 2 to FIG. 4) in the foregoing first to third
preferred embodiments with the electro-photographic system in FIG.
4. Then, the ceramic green sheets 51a to 51c are laminated under
pressure to form a monolithic member followed by baking.
[0046] The circuit patterns 52a and 52b on the ceramic green sheets
51a and 51b are put into electrical continuity with pier holes 53,
which can be formed using currently available technologies. For
example, a pier hole is produced by injecting electric conductors
for each pier hole using a conductor drawing apparatus. It is
preferable in this method to form the pier hole 53 prior to forming
the circuit patterns 52a and 52b since the powder may possibly
damage the nozzle of the drawing apparatus when the pier hole 53 is
formed after forming the circuit patterns 52a and 52b by the
electrophotographic method.
[0047] The multilayer wiring board as described above is produced
by printing the circuit pattern by the electrophotographic method
on the ceramic green sheet, followed by laminating and baking the
green sheets. Consequently, there is essentially no possibility
that the circuit pattern is peeled off the baked ceramic sheet,
thus improving the quality and reliability of the multilayer wiring
board. Accordingly, the multilayer wiring board can be used in high
frequency bands.
[0048] Although copper was used for the circuit forming charging
powder in the first to third embodiments, the same effect as
described in these embodiments can be obtained by using a metal
such as gold, silver, nickel, palladium or molybdenum, or an alloy
comprising two or more kinds of these metals. The materials used
heretofore can also be used in this invention.
[0049] Although a styrene-acrylic acid copolymer was used for the
heat-melt resin in the foregoing embodiments, the same effect as
described in these embodiments can be obtained by using a resin
such as polymethyl methacrylate resin, cross-linked acrylic acid
resin, polystyrene resin, polyethylene resin, fluorinated resin,
fluorinated vinylidene resin and benzoguanamine resin, or a mixture
of two or more of these resins. The materials used heretofore can
also be used in this invention.
[0050] Although a metallic azo dye was used for the charge control
agent in the examples, the same effect as described in the
foregoing embodiments can be obtained by using a negatively charged
charge control agent such as a chlorinated paraffin, a chlorinated
polyester, an acid-excess polyester, a sulfonylamine naphthenic
acid metal salt of copper phthalocyanine, a metal salt of fatty
acid and resinate soap, or a mixture of two or more of these
compounds. The materials used heretofore can also be used in this
invention.
[0051] Although silica glass was used for the adhesion reinforcing
agent above, the same effect as described in the foregoing
embodiments can be obtained by using a substance such as
borolilicate glass, soda lime, lead glass and aluminosilicate
glass, or a glass comprising a mixture of two or more of these
substances, or a ceramic comprising alumina and ferrite.
[0052] As shown in FIG. 7, the conductive metal powder 11
constituting the circuit-forming charging powders 10 to 30 may be a
secondary powder comprising an aggregate in which a plurality of
primary powders 15 are aggregated. Since the conductive metal
powder 11 comprising the secondary powders is dissociated into the
primary powders 15 when the circuit-forming charging powders 10 to
30 are fixed, packing of the circuit pattern formed by the primary
powder 15 constituting the conductive metal powder is made dense,
making it possible to further reduce the sheet resistance of the
circuit pattern along with further decreasing the circuit pattern
loss. Consequently, the multilayer wiring board produced by using
this circuit-forming charging powder can be used in higher
frequency bands. It is especially preferable for obtaining a
spherical secondary powder that the particle size of the primary
powder is within the range of 1/5to {fraction (1/20)}of the
particle size of the circuit-forming charging powder.
[0053] It is preferable that the particle size of the
circuit-forming charging powder is in the range of about 3 to 20
.mu.m for enhancing the effect of the present invention.
[0054] Although the adhesion reinforcing agent contained in the
circuit-forming charging powder is kneaded with the heat-melt resin
and incorporated into the outer wall in the circuit-forming
charging powder according to the second and third preferred
embodiments, the agent may be adhered on the surface of the
circuit-forming charging powder, or on the surface of the outer
wall, without being kneaded with the heat-melt resin.
[0055] The structure in which the charge control agent is adhered
on the periphery of the circuit-forming charging powder, or the
structure in which charge control agent is adhered on the surface
of the outer wall comprising the charge control agent, adhesion
reinforcing agent and heat-melt resin can display the same effect
in the circuit-forming charging powder according to the third
preferred embodiment.
[0056] While the invention has been particularly shown and
described with reference to preferred embodiments thereof, it will
be understood by those skilled in the art that the forgoing and
other changes in form and details may be made therein without
departing from the spirit of the invention.
* * * * *