U.S. patent application number 13/988236 was filed with the patent office on 2013-11-14 for surface-treated copper foil.
This patent application is currently assigned to MITSUI MINING & SMELTING CO., LTD.. The applicant listed for this patent is Shinya Hiraoka, Fumiaki Hosokoshi, Tomoyuki Maeda, Hideaki Matsushima, Koichi Miyake, Shinichi Obata, Ayumu Tateoka, Sakiko Tomonaga. Invention is credited to Shinya Hiraoka, Fumiaki Hosokoshi, Tomoyuki Maeda, Hideaki Matsushima, Koichi Miyake, Shinichi Obata, Ayumu Tateoka, Sakiko Tomonaga.
Application Number | 20130302635 13/988236 |
Document ID | / |
Family ID | 46145930 |
Filed Date | 2013-11-14 |
United States Patent
Application |
20130302635 |
Kind Code |
A1 |
Obata; Shinichi ; et
al. |
November 14, 2013 |
SURFACE-TREATED COPPER FOIL
Abstract
An object of the present invention is to provide a copper foil
excellent in softening resistance performance which reduces
decrease in tensile strength after heat treatment at about
350.degree. C. to 400.degree. C. In order to achieve the object, a
surface-treated copper foil provided with a rust-proofing treatment
layer on both surfaces of a copper foil in which a rust-proofing
treatment layer is constituted by zinc, and the either
rust-proofing treatment layer is a zinc layer having zinc amount of
20 mg/m.sup.2 to 1,000 mg/m.sup.2; and the copper foil contains one
or two or more of small amount elements selected from carbon,
sulfur, chlorine and nitrogen, and a sum amount thereof is 100 ppm
or more is adopted.
Inventors: |
Obata; Shinichi; (Saitama,
JP) ; Hiraoka; Shinya; (Saitama, JP) ;
Hosokoshi; Fumiaki; (Kuala Lumpur, MY) ; Tateoka;
Ayumu; (Saitama, JP) ; Matsushima; Hideaki;
(Saitama, JP) ; Miyake; Koichi; (Saitama, JP)
; Tomonaga; Sakiko; (Tokyo, JP) ; Maeda;
Tomoyuki; (Saitama, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Obata; Shinichi
Hiraoka; Shinya
Hosokoshi; Fumiaki
Tateoka; Ayumu
Matsushima; Hideaki
Miyake; Koichi
Tomonaga; Sakiko
Maeda; Tomoyuki |
Saitama
Saitama
Kuala Lumpur
Saitama
Saitama
Saitama
Tokyo
Saitama |
|
JP
JP
MY
JP
JP
JP
JP
JP |
|
|
Assignee: |
MITSUI MINING & SMELTING CO.,
LTD.
Tokyo
JP
|
Family ID: |
46145930 |
Appl. No.: |
13/988236 |
Filed: |
November 22, 2011 |
PCT Filed: |
November 22, 2011 |
PCT NO: |
PCT/JP2011/076955 |
371 Date: |
July 23, 2013 |
Current U.S.
Class: |
428/612 ;
428/658 |
Current CPC
Class: |
Y10T 428/12792 20150115;
B32B 15/01 20130101; C23C 28/321 20130101; H05K 2201/0355 20130101;
C25D 7/0614 20130101; C25D 11/38 20130101; C23C 28/00 20130101;
C23C 28/324 20130101; Y10T 428/12438 20150115; C25D 5/48 20130101;
C23C 28/3455 20130101; C25D 1/04 20130101; C25D 5/10 20130101; H01B
1/026 20130101; C23C 28/30 20130101; H05K 1/09 20130101; C25D 3/565
20130101; Y10T 428/12472 20150115; C23C 2/02 20130101 |
Class at
Publication: |
428/612 ;
428/658 |
International
Class: |
B32B 15/01 20060101
B32B015/01 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 22, 2010 |
JP |
2010 260369 |
Jul 19, 2011 |
JP |
2011 158177 |
Claims
1. A surface-treated copper foil provided with a rust-proofing
treatment layer on both surfaces of a copper foil, wherein the
rust-proofing treatment layer is constituted by zinc, and the
either rust-proofing treatment layer is a zinc layer having zinc
amount of 20 mg/m.sup.2 to 1,000 mg/m.sup.2; and wherein the copper
foil contains one or two or more of small amount elements selected
from carbon, sulfur, chlorine and nitrogen, and a sum amount
thereof is 100 ppm or more.
2. The surface-treated copper foil according to claim 1, a sum
amount of zinc constituting the zinc layers provided on both
surfaces of the copper foil is 40 mg/m.sup.2 to 2,000
mg/m.sup.2.
3. The surface-treated copper foil according to claim 1, the
rust-proofing treatment layer is constituted by zinc-based
composite layer of a two-layer structure provided with a different
metal layer selected from tin layer, cadmium layer, antimony layer,
bismuth layer, indium layer and lead layer between the copper foil
and the zinc layer, or on a surface of the zinc layer.
4. The surface-treated copper foil according to claim 3, the
different metal layer is the layer containing the different metal
component of 1 mg/m.sup.2 to 200 mg/m.sup.2.
5. The surface-treated copper foil according to claim 1, the copper
foil is an electro-deposited copper foil having a grain size as
received of 1.0 .mu.m or less.
6. The surface-treated copper foil according to claim 1, the copper
foil is an electro-deposited copper foil having tensile strength as
received of 50 kgf/mm.sup.2 or more.
7. The surface-treated copper foil according to claim 1, the copper
foil is provided with a roughening treatment on one surface or both
surfaces.
8. The surface-treated copper foil according to claim 1, the
rust-proofing treatment layer is provided with one or both of a
chromate-treatment layer and an organic agent-treatment layer on a
surface.
9. The surface-treated copper foil according to claim 8, the
organic agent-treatment layer is one or both of a silane coupling
agent-treatment layer and an organic rust-proofing treatment
layer.
10. The surface-treated copper foil according to claim 1, surface
roughness (Ra) is 0.1 .mu.m to 0.7 .mu.m.
11. The surface-treated copper foil according to claim 1, tensile
strength of the surface-treated copper foil after heat treatment at
350.degree. C. for 60 min in an inert gas atmosphere is 40
kgf/mm.sup.2 or more.
12. The surface-treated copper foil according to claim 1, tensile
strength of the surface-treated copper foil after heat treatment at
400.degree. C. for 60 min in an inert gas atmosphere is 35
kgf/mm.sup.2 or more.
Description
TECHNICAL FIELD
[0001] The present invention relates to a surface-treated copper
foil, and a method for manufacturing the surface-treated copper
foil. In particular, an object of the present invention is to
provide a surface-treated copper foil which decreases less physical
strength after heat treatment at temperature exceeding 300.degree.
C.
BACKGROUND ART
[0002] Current copper foils are used not only in printed wiring
board applications but as a constituting material of various types
of electronic devices. With regard to the electronic devices in
recent years, miniaturization is required and heat resistance
against heat generation in operation of the devices is required
also. Therefore, for materials constituting the electronic devices,
heat resistance against high heats loaded in processing is required
to improve qualities of electronic devices as final products.
[0003] For example, patent document 1 discloses object in copper
foils for application in the printed wiring board technology to
provide a metal-clad laminate which ensures a sufficient strength
to form a stable flying lead and is applicable to a usage where
fine pattern formation by using an electro-deposited copper foil.
In the patent document 1, a technology in which "The metal clad
laminate is formed by laminating a copper foil layer formed by the
electro-deposited copper foil, a polyimide resin layer, and a
stainless foil layer in this order; the average of grain size in
crystal grains of copper constituting the copper layer is in the
range of 0.5 to 3.0 .mu.m, and further, difference between the
average value and the maximum value of particle diameters in
crystal grains is within a range of 2.0 .mu.m or less." is
disclosed. Further, in the descriptions in Claim 2 and the columns
0022 to 0024 of the patent document 1, the matter is disclosed that
properties including the grain size of the crystal grains of the
copper foil and physical strength as tensile strength of 400 MPa or
more are necessary when improvement of the ultrasonic resistance of
wiring (made of the copper foil) in the flying leads formed is
investigated. Furthermore, as can be understood in the descriptions
in Patent document 1, the matter is apparent that the physical
strength of flying leads formed of a copper foil is required to be
high even after loading a certain heat history.
[0004] Also in other technical fields, a copper foil after loading
a certain heat history may be required to ensure excellent physical
performance. For example, when a copper foil is used for a negative
electrode current collector of a lithium ion secondary battery, the
copper foil constituting the negative electrode current collector
is loaded repeating expansion and contraction of an active
substance provided on a negative electrode current collector.
[0005] For example, patent document 2 employs a technology to
provide a current collector having high tensile strength at low
cost regardless of its thin thickness that "The negative electrode
current collector is characterized in provided with a hard nickel
plating layer formed on at least one surface of an
electro-deposited foil composed of metal material having low
possibility in generation of lithium compounds. The hard plated
nickel layer is formed by applying electro-plating using plating
bath containing nickel, nickel salt and ammonium salt. The metal
material may be an alloy of two or more selected from copper, iron,
cobalt, nickel, zinc and silver, for example". Then patent document
2 discloses that a current collector which ensures sufficiently
high tensile strength even after heat treatment can be produced
when the electro-deposited foil is used.
[0006] Patent document 3 discloses "The composite foils provided
with a cobalt plating layer or a cobalt-nickel alloy plating layer
on a surface of a copper foil are employed as a metallic foil for
the negative electrode current collector of the nonaqueous
electrolyte secondary batteries" to provide a composite foil which
has high tensile strength even after high heat treatment and is
suitably used as a negative electrode current collector of
nonaqueous electrolyte secondary batteries.
DOCUMENTS CITED
Patent Documents
[0007] [Patent document 1] Japanese Patent Laid-Open No.
2009-289313 [0008] [Patent document 2] Japanese Patent Laid-Open
No. 2005-197205 [0009] [Patent document 3] Japanese Patent
Laid-Open No. 2005-350761
SUMMARY OF THE INVENTION
Problems to be Solved
[0010] As described above in the printed wiring board industry in
recent years, a copper foil and an insulting resin base material
are laminated using a heating temperature exceeding 300.degree. C.
in many case including manufacturings of flexible printed wiring
board by the casting method, heat-resistant substrates, and
substrates for high-frequency application. As a result, a copper
foil hardly soften after loading high heat has been required
because various problems due to decreased physical strength of the
copper foil as a result of loading of high heat on the copper foil
used in these applications has been arisen.
[0011] Also in the lithium ion secondary battery applications in
recent years, temperature of about 350.degree. C. to 400.degree. C.
is loaded in manufacturing of a negative electrode to provide a
negative electrode active substance on the surface of a copper foil
as a current collector by heating. Furthermore, the negative
electrode current collector is loaded a stresses of
expansion/contraction caused in charge/discharge operation as a
lithium ion secondary battery. Therefore, the requirement on a
copper foil which ensures a proper strength after heat treatment
has become further severe.
[0012] As can be understood from the descriptions above, an object
of the present invention is to provide a copper foil excellent in
softening resistance performance to reduce decrease in tensile
strength after heat treatment at a temperature of about 350.degree.
C. to 400.degree. C.
Means to Solve the Problem
[0013] Then, as a result of intensive studies, the inventors of the
present invention have thought out a surface-treated copper foil
which is not expensive and reduces decrease in tensile strength
after heat treatment by employing the following technical
concept.
[Surface-Treated Copper Foil According to the Present
Invention]
[0014] The surface-treated copper foil according to the present
invention is a surface-treated copper foil which is provided with a
rust-proofing treatment layer on both surfaces of a copper foil and
the rust-proofing treatment layer is constituted by zinc, the
either rust-proofing treatment layer is a zinc layer having zinc
amount of 20 mg/m.sup.2 to 1,000 mg/m.sup.2; and the copper foil
contains one or two or more of small amount elements selected from
carbon, sulfur, chlorine and nitrogen, and has a sum amount thereof
of 100 ppm or more.
[0015] In the surface-treated copper foil according to the present
invention, the sum amount of zinc constituting the zinc layers
provided on both surfaces of the copper foil is preferable to be 40
mg/m.sup.2 to 2,000 mg/m.sup.2.
[0016] In the surface-treated copper foil according to the present
invention, it is preferable to constitute the rust-proofing
treatment layer by zinc-based composite layer of a two-layer
structure provided with a different metal layer selected from tin
layer, cadmium layer, antimony layer, bismuth layer, indium layer
and lead layer between the copper foil and the zinc layer, or on a
surface of the zinc layer.
[0017] Then, it is preferable that the different metal layer is the
layer containing the different metal component of 1 mg/m.sup.2 to
200 mg/m.sup.2.
[0018] In the surface-treated copper foil according to the present
invention, it is preferable that the copper foil is an
electro-deposited copper foil having a grain size as received of
1.0 .mu.m or less.
[0019] In the surface-treated copper foil according to the present
invention, it is preferable that the copper foil is an
electro-deposited copper foil having tensile strength as received
of 50 kgf/mm.sup.2 or more.
[0020] In the surface-treated copper foil according to the present
invention, it is preferable that the copper foil is provided with a
roughening treatment on one surface or both surfaces.
[0021] In the surface-treated copper foil according to the present
invention, it is preferable that the rust-proofing treatment layer
is provided with one or both of a chromate-treatment layer and an
organic agent-treatment layer on the surface.
[0022] In the surface-treated copper foil according to the present
invention, it is preferable that the organic agent-treatment layer
is one or both of a silane coupling agent-treatment layer and an
organic rust-proofing treatment layer.
[0023] In the surface-treated copper foil according to the present
invention, surface roughness (Ra) is preferable to be 0.1 .mu.m to
0.7 .mu.m.
[0024] The surface-treated copper foil according to the present
invention is excellent in physical strength, tensile strength of 40
kgf/mm.sup.2 or more after heat treatment at 350.degree. C. for 60
min in an inert gas atmosphere.
[0025] The surface-treated copper foil according to the present
invention is excellent in physical strength, tensile strength of 35
kgf/mm.sup.2 or more after heat treatment at 400.degree. C. for 60
min in an inert gas atmosphere.
Advantages of the Invention
[0026] The surface-treated copper foil according to the present
invention employs zinc layer or zinc-based composite layer of a
two-layer structure described above as a rust-proofing treatment
layer. As a result, the surface-treated copper foil is excellent in
physical strength, tensile strength of 40 kgf/mm.sup.2 or more even
after heat treatment at 350.degree. C. for 60 min in an inert gas
atmosphere. Further, the surface-treated copper foil is excellent
in physical strength after heat treatment, tensile strength of 35
kgf/mm.sup.2 or more even after heat treatment at 400.degree. C.
for 60 min in an inert gas atmosphere. In the surface-treated
copper foils for general use, tensile strength may be 40
kgf/mm.sup.2 or less after heat treatment at 350.degree. C. for 60
min in an inert gas atmosphere, and tensile strength may be 35 kg
f/mm.sup.2 or less after heat treatment at 400.degree. C. for 60
min. In view of the fact, the surface-treated copper foil according
to the present invention has remarkably excellent softening
resistance performance against heating as a copper foil.
BRIEF DESCRIPTION OF DRAWINGS
[0027] FIG. 1 is a schematic cross-sectional diagram to grasp a
typical image of the surface-treated copper foil according to the
present invention.
[0028] FIG. 2 is cross-sectional FIB-SIM images of grain structures
in the surface-treated copper foil according to the present
invention and another surface-treated copper foil.
[0029] FIG. 3 is a cross-sectional FIB-SIM image of grain
structures in a reference specimen described in Table 2 used for
comparison with Example 2.
[0030] FIG. 4 is a cross-sectional FIB-SIM image of a grain
structure of a specimen 2-2 in Example 2.
[0031] FIG. 5 is a cross-sectional FIB-SIM image of a grain
structure of comparative specimen 2-2 in Comparative Example 2.
[0032] FIG. 6 is a cross-sectional FIB-SIM image of a grain
structure of comparative specimen 3 in Comparative Example 3.
[0033] FIG. 7 is a cross-sectional FIB-SIM image of a grain
structure of a specimen 3-1 in Example 3.
[0034] FIG. 8 is a cross-sectional FIB-SIM image of a grain
structure of a specimen 3-6 in Example 3.
DETAILED DESCRIPTION OF EMBODIMENTS
[0035] Hereinafter, embodiments of the surface-treated copper foil
and the method for manufacturing the surface-treated copper foil
according to the present invention will be described in detail.
[Embodiment of the Surface-Treated Copper Foil According to the
Present Invention]
[0036] The surface-treated copper foil according to the present
invention is a surface-treated copper foil in which a rust-proofing
treatment layer is provided on each of both surfaces of a copper
foil, as schematically shown in FIG. 1. In FIG. 1, a typical
structure is exemplified in which a surface-treatment layer of a
three-layer structure of "a rust-proofing treatment layer 3/a
chromate-treatment layer 4/an organic agent-treatment layer 5" is
provided on one surface of the copper foil 2, and a
surface-treatment layer of a four-layer structure of "a roughening
treatment layer 6/a rust-proofing treatment layer 3/a
chromate-treatment layer 4/an organic agent-treatment layer 5" is
provided on the other surface. Note that, the roughening treatment
layer shown is an aggregated fine copper particle. Next, the
roughening treatment layer 6, the chromate-treatment layer 4 and
the organic agent-treatment layer 5 in FIG. 1 are optional
surface-treatment layers provided depending on the required
performance. Therefore, many variations in the layer structures are
included in the present invention. By the way, the matter should be
clearly noted that schematically shown each layer and a roughened
state in the drawing is example for easy recognition, i.e. the
drawing do not reflect the thickness and the roughened state of an
actual product. Hereinafter, to make understanding of the
constitution of the surface-treated copper foil according to the
present invention easy, each item will be describe one by one.
[0037] Copper foil: As for a "copper foil" here, it is preferable
to use the copper foil which contains one or two or more selected
form small amount elements including carbon, sulfur, chlorine and
nitrogen, and having a sum amount thereof of 100 ppm or more. This
is because when the copper foil contains carbon, sulfur, chlorine
or nitrogen described above and has at least a sum amount thereof
is 100 ppm or more, the copper foil exhibits excellent physical
strength. Therefore, the copper foil may be a rolled copper foil or
an electro-deposited copper foil as long as contain the small
amount elements. Note that, the words "copper foil" refers to an
untreated copper foil which is not provided with surface treatment
including a roughening treatment and a rust-proofing treatment.
[0038] In addition to the specification of "a sum amount of carbon,
sulfur, chlorine and nitrogen of 100 ppm or more", the following
specification is preferably satisfied for each component. In the
copper foil used in manufacturing of a surface-treated copper foil
according to the present invention, an electro-deposited copper
foil is more preferable to contain sulfur in the range of 5 ppm to
600 ppm, carbon in the range of 20 ppm to 470 ppm, nitrogen in the
range of 5 ppm to 180 ppm, and chlorine in the range of 15 ppm to
600 ppm. Proper amounts of small amount elements contained in the
grain structure of a copper foil make a grain size of the
electro-deposited copper foil 1.0 .mu.m or less and provide
excellent tensile strength as received of 50 kgf/mm.sup.2 or more
to the copper foil. The excellent physical strength of the
electro-deposited copper foil is achieved mainly by the
miniaturization effect of crystal grain. Next, the elongation as
received of such a copper foil might be in the range of 3% to 15%.
It should be noted that the unit "ppm" indicting the content of a
component is equivalent to "mg/kg". Hereinafter, carbon, sulfur,
chlorine and nitrogen described above excluding copper contained in
a copper foil not provided with surface treatment may be referred
to simply as "small amount elements". Hereinafter, meaning in
specification of the content range for each small amount element
will be described one by one.
[0039] When sulfur content in a copper foil is less than 5 ppm,
excellent physical strength through miniaturization of crystal
grain is hardly achieved because it is hard to make the grain size
as received described later 1.0 .mu.m or less. So, it is not
preferable. In contrast, when sulfur content in an
electro-deposited copper foil exceeds 600 ppm, although tensile
strength of the electro-deposited copper foil is made high,
elongation decreases to be brittle. So, it is not preferable.
[0040] When carbon content in a copper foil is less than 20 ppm,
formation of graphite which makes the electro-deposited copper foil
texture excellent in physical strength may be made poor and an
excellent physical strength may be hardly achieved. So, it is not
preferable. In contrast, when carbon content in an
electro-deposited copper foil exceeds 470 ppm, graphite grows too
big and cracks may easily generate. So, it is not preferable.
[0041] When nitrogen content in a copper foil is less than 5 ppm,
formation of nitrogen compound which makes the electro-deposited
copper foil texture excellent in physical strength may be poor and
an excellent physical strength may be hardly achieved. So, it is
not preferable. In contrast, when nitrogen content in an
electro-deposited copper foil exceeds 180 ppm, the nitrogen
compound may be excessive and the effect of making physical
strength excellent by a deposit texture in the electro-deposited
copper foil saturates. So, it is not preferable because the
significance of increasing the nitrogen content is lost.
[0042] When chlorine content in a copper foil is less than 15 ppm,
formation of a chloride which makes the electro-deposited copper
foil texture excellent in physical strength may be poor and
chlorine cannot contribute to make physical strength excellent. So,
it is not preferable. In contrast, when chlorine content in an
electro-deposited copper foil exceeds 600 ppm, the deposit surface
of the electro-deposited copper foil is made rough and the
electro-deposited copper foil having a low profile surface cannot
be obtained. So, it is not preferable because the electro-deposited
copper foil is hardly used as a copper foil for formation of fine
pitch circuits.
[0043] The small amount elements contained in a copper foil
described above react with zinc which is a rust-proofing component
described later and diffused into the grain structure of the copper
foil. As a result, re-crystallization of the grain structure in
heat treatment of the surface-treated copper foil according to the
present invention is hindered, and the fine crystal grains are
prevented from becoming coarse.
[0044] Next, uneven deposit surface is made smooth because particle
size of crystal grains constituting the grain structure of the
electro-deposited copper foil is fine and uniform. Because of such
fine grain size, the surface roughness of the deposit surface of
the electro-deposited copper foil is very low, i.e. low profile
surface is achieved.
[0045] Thickness of a copper foil used here may be appropriately
arranged depending on applications of the surface-treated copper
foil. So, it is not especially limited. For example, in the printed
wiring board applications, the copper foil is used in the gauge
thickness range of 5 .mu.m to 120 .mu.m in many cases. In the
negative electrode current collector of lithium ion secondary
batteries, the copper foil in the gauge thickness range of 5 .mu.m
to 35 .mu.m is used in many cases.
[0046] Further, physical strength of a copper foil before providing
a rust-proofing treatment layer will be investigated. The copper
foil is preferable to have following physical strength in order to
satisfy the performance required on a surface-treated copper foil.
In order to ensure tensile strength at 40 kgf/mm.sup.2 or more
after heat treatment at 350.degree. C. for 60 min when a copper
foil is surface-treated to have a rust-proofing treatment layer,
tensile strength of the copper foil as received is preferable to be
50 kgf/mm.sup.2 or more. If further enhanced tensile strength of 40
kgf/mm.sup.2 or more after heat treatment as the surface-treated
copper foil is ensured, tensile strength of the copper foil as
received is preferable to be 60 kgf/mm.sup.2 or more.
[0047] Rust-proofing treatment layer: In the present invention,
zinc layer to be formed on the surface of a copper foil is provided
on each of both surfaces and the zinc amount of the either surface
is preferable to be 20 mg/m.sup.2 to 1,000 mg/m.sup.2. By providing
the zinc layers in such a manner, softening resistance performance
against heating of an electro-deposited copper foil is improved,
and decrease in tensile strength after heat treatment is
hindered.
[0048] When the zinc amount is less than 20 mg/m.sup.2, softening
resistance performance against heating is not enhanced and tensile
strength after heat treatment decreases. So, it is not preferable.
In contrast, when the zinc amount exceeds 1,000 mg/m.sup.2, because
the effect on enhancing of softening resistance performance against
heating may be saturated when the heating is carried out in a level
at 350.degree. C. for 60 min to 400.degree. C. for 60 min, the
resource is wasted. So, it is not preferable. Therefore, in
consideration of the zinc amounts on one surface side of the
surface-treated copper foil according to the present invention and
the zinc amount on the other surface side together, the sum amount
of zinc constituting the zinc layers provided on both surfaces of
the copper foil is preferable to be 40 mg/m.sup.2 to 2,000
mg/m.sup.2. The zinc amount here is a calculated amount per unit
area. The calculated amount is determined as a rust-proofing
component content per unit area on the assumption that the copper
foil surface is ideally flat. The words "zinc amount" used in the
present description refer to a content of zinc in the whole of a
rust-proofing treatment layer.
[0049] Further in the surface-treated copper foil according to the
present invention, the case in which zinc-based composite layer of
a two-layer structure is employed as a rust-proofing treatment
layer by providing any one different metal layer of tin layer,
cadmium layer, antimony layer, bismuth layer, indium layer, and
lead layer between the copper foil and the zinc layer or on the
surface of the zinc layer will be described. In the surface-treated
copper foil in which such zinc-based composite layer of a two-layer
structure is provided as a rust-proofing treatment layer,
decreasing ratio of tensile strength after heat treatment may be
further reduced than in a surface treated copper foil in which zinc
layer alone is provided. When a zinc-based composite layer has the
two-layer structure, amount of the different metal component
constituting different metal layer provided on either surface of
the copper foil is preferable to be in the range of 1 mg/m.sup.2 to
200 mg/m.sup.2, in addition to the specification that the zinc
amount as a rust-proofing component provided on either surface of a
copper foil is 20 mg/m.sup.2 to 1,000 mg/m.sup.2 as described
above.
[0050] A metal element used for the different metal layer is one
selected from elements satisfying any of the following
specifications. That is, the elements having larger diffusion
coefficient than zinc in copper at 300.degree. C. or more (for
example, Bi, Cd, Sn, Pb, Sb, In, Al, As, Ga, Ge), elements having
lower melting point than zinc (for example, Bi, Cd, Pb, Sn, In, Ga,
Li), or elements showing lower eutectic temperature than zinc when
alloyed with zinc (for example, Bi, Cd, Sn, Pb, Sb, Ni, Ba, Ca, In,
Al, As, Ga, Ge, Mg, Mn). This is because the coexistence of these
elements with zinc in the grain structure of a copper foil may
promote formation of compounds which contributes to excellent
physical strength.
[0051] When content of the different metal component provided is
less than 1 mg/m.sup.2, softening resistance performance against
heating is not improved and tensile strength after heat treatment
is not improved than the case of zinc layer alone. So, it is not
preferable because the significance of providing different metal
layer is lost. In contrast, when content of the different metal
component provided exceeds 200 mg/m.sup.2, the etching performance
of a copper foil when subjected to an etching processing to form
circuits is made poor, and simultaneously, the effect of improving
softening resistance performance when the copper foil is heated in
a level at 350.degree. C. for 60 min to 400.degree. C. for 60 min
saturates. So, it is not preferable because the resource is wasted.
Note that the content of the different metal component provided
indicates a calculated amount per unit area as in the case of the
zinc amount also, i.e. the calculated amount is determined as a
content of different metal component in a unit area where the
copper foil is ideally flat.
[0052] When zinc-based composite layer of a two-layer structure
described above is employed, it is preferable to arrange the
thicknesses of different metal layer and zinc layer to satisfy the
relationship of [different metal content]/[zinc amount]=1/100 to
1/2 in weight ratio between content of the different metal
component in the different metal layer and content of the zinc
component in the zinc layer constituting a rust-proofing treatment
layer. When the weight ratio is lower than 1/100, amount of the
different metal component is too small not to improve softening
resistance performance against heating. SO, it is not preferable
because the significance of providing different metal layer is
lost. When the weight ratio exceeds 1/2, the diffusion of zinc into
the grain structure of a copper foil is hindered and softening
resistance performance against heating is hardly improved because
amount of the different metal component is too excessive against
the zinc amount and the zinc amount relatively decreases in a
rust-proofing treatment layer.
[0053] When the zinc-based composite layer of a two-layer structure
is employed as a rust-proofing treatment layer, counter diffusion
of zinc and different metal component occurs between zinc layer and
different metal layer in contact by heating in press lamination of
a copper-clad laminate or by heating in a negative electrode
material manufacturing process of a lithium ion secondary battery,
and form an alloy layer of zinc-different metal. As a result, the
same effect as in the case of a rust-proofing treatment layer
originally formed of zinc-different metal alloy is achieved. The
order for stacking zinc layer and different metal layer is not
especially limited, but it is preferable that the different metal
layer is provided between a copper foil and the zinc layer. This is
because zinc and the different metal component counter diffuse when
a surface-treated copper foil is heated; the diffusion causes a
certain concentration gradient in the zinc layer and the different
metal layer to provide high zinc concentration at the utmost
surface layer; and a stable rust-proofing performance by zinc may
be achieved easily.
[0054] Next, grain structures of surface-treated copper foils after
heat treatment at 350.degree. C. for 60 min in an inert gas
atmosphere will be investigated with reference to FIG. 2. FIG. 2(A)
shows a surface-treated copper foil corresponding to the example
specimen 1-1 in Example 1 according to the present invention. In
contrast, FIG. 2(B) shows a surface-treated copper foil
corresponding to comparative specimen 1 of Comparative Example 1 in
the present application, i.e. the copper foil is not included in
the surface-treated copper foil according to the present invention.
As can be understood from FIG. 2, the grain structure in FIG. 2(A)
maintains finer crystal grains after heat treatment at 350.degree.
C. for 60 min than the grain structure in FIG. 2(B). That is, the
matter can be understood that when a "copper foil having a sum
amount of one or two or more of small amount elements selected from
carbon, sulfur, chlorine and nitrogen of 100 ppm or more" is used,
and when at least two specifications "one of zinc layer or
zinc-based composite layer of a two-layer structure is used" and
"the zinc amount is made to be in the range of 20 mg/m.sup.2 to
1,000 mg/m.sup.2" are satisfied in the rust-proofing treatment
layer, the crystal grains are not made coarse and the effect of
maintaining fine crystal grains is achieved even when high heat is
loaded.
[0055] Roughening treatment on the copper foil surface: A
roughening treatment on the copper foil surface will be described.
The roughening treatment is provided between a copper foil and the
above-mentioned rust-proofing treatment layer in general. In the
copper foil used for the surface-treated copper foil according to
the present invention, it is preferable to provide a roughening
treatment on one surface or both surfaces. Next, whether the
roughening treatment is provided on only one surface of the copper
foil or both surfaces may appropriately be judged depending on
applications of the surface-treated copper foil. When the
surface-treated copper foil is used for manufacturing of a printed
wiring board, the surface provided with roughening treatment
enhance adhesion to an insulting resin base material as a
constituting material of the printed wiring board. When the
surface-treated copper foil is used as a negative electrode current
collector of a lithium ion secondary battery, the roughening
treated surface of the negative electrode current collector
enhances adhesion to a negative electrode active substance.
[0056] As for the roughening treatment, the method for roughening
treatment, the roughening treatment condition and the like are not
especially limited. Therefore, a method of depositing and forming
fine metal particles on the copper foil surface, a method of
etching the copper foil surface to make the surface rough, a method
of depositing and forming a metal oxide, or the like can be
employed.
[0057] Other surface treatments: In the surface-treated copper foil
according to the present invention, it is preferable that one or
both of a chromate-treatment layer and an organic agent-treatment
layer is provided on the surface of the rust-proofing treatment
layer whether roughening treatment is provided or not. These
surface treatments achieve further good adhesion to "insulting
resin base material of a printed wiring board" and "negative
electrode active substance of a lithium ion secondary battery"
contact with the rust-proofing treatment layer.
[0058] The organic agent-treatment layer is a silane coupling
agent-treatment layer and an organic rust-proofing treatment layer,
and one or both of these layers may be provided. When both layers
are provided, order of providing the silane coupling
agent-treatment layer and the organic rust-proofing treatment layer
may appropriately be judged in consideration of the required
performance of a surface-treated copper foil. Components
constituting the silane coupling agent-treatment layer and the
organic rust-proofing treatment layer will be described in detail
later.
[0059] Surface roughness of the copper foil: In the surface-treated
copper foil according to the present invention, surface roughnesses
(Ra) of both surfaces measured by the procedure provided in JIS
B0601 are preferable to be 0.1 .mu.m to 0.7 .mu.m. When the surface
roughness (Ra) of a copper foil is lower than 0.1 .mu.m, adhesion
with an "insulting resin base material of a printed wiring board"
and a "negative electrode active substance of a lithium ion
secondary battery" cannot be secured in a practical use. So, it is
not preferable. When the surface roughness (Ra) of a copper foil
exceeds 0.7 .mu.m, formation of fine pitch circuits in a 50-.mu.m
pitch level is made difficult. Next, when the copper foil is used
as a negative electrode current collector of a lithium ion
secondary battery, valley portions in the irregularity of the
surface roughness may trigger off generation of microcracks in
expansion/contraction behavior of the copper foil. So, it is not
preferable.
[0060] Physical strength of the surface-treated copper foil: In the
surface-treated copper foil according to the present invention,
tensile strength after heat treatment as the physical strength is
paid attention. Hereinafter, tensile strength will be
described.
[0061] The copper foil according to the present invention has
excellent tensile strength as high as 40 kgf/mm.sup.2 or more after
heat treatment at 350.degree. C. for 60 min in an inert gas
atmosphere. Next, the reason why a temperature of 350.degree. C. is
employed will be described. In the field relating to a printed
wiring board, as many cases exist where a copper foil and an
insulting resin base material are laminated at temperature
exceeding 300.degree. C. including manufacturings of flexible
printed wiring boards produced by the casting method,
heat-resistant substrates and high-frequency substrates, softening
resistance performance of the copper foil after heat treatment is
discussed in some cases. Also in the field relating to lithium ion
secondary battery, when a negative electrode active substance is
heated and provided on the surface of a copper foil as a current
collector in manufacturing of a negative electrode, heating
temperature may be about 350.degree. C. to 400.degree. C.
[0062] As can be understood from descriptions above, in the case of
the lithium ion secondary battery, the copper foil is preferable to
have high tensile strength even after heat treatment at 400.degree.
C. for 60 min when heating temperature in manufacturing of the
negative electrode is considered. To answer the requirement, the
surface-treated copper foil according to the present invention
exhibits tensile strength of 35 kgf/mm.sup.2 or more after heat
treatment at the temperature as a physical strength. It is apparent
that the surface-treated copper foil according to the present
invention has remarkably high value of tensile strength after heat
treatment at 400.degree. C. for 60 min as compared with
conventional copper foils.
[Embodiment of Manufacturing of the Surface-Treated Copper Foil
According to the Present Invention]
[0063] A method for manufacturing the surface-treated copper foil
according to the present invention is a method for manufacturing
the above-mentioned surface-treated copper foil including a
rust-proofing treatment step for providing a "zinc layer" or a
"zinc-based composite layer of a two-layer structure" as a
rust-proofing treatment layer on the surface of a copper foil; and
the method further includes various types of surface treatments
including a roughening treatment according to needs, and a drying
step for heating in a predetermined condition. Hereinafter, each
step will be described one by one.
[0064] Preparation of a copper foil: As can be understood from the
descriptions above, it is preferable to selectively use a copper
foil which satisfies specification, "foil contains carbon, sulfur,
chlorine or nitrogen, and at least the sum amount thereof is 100
ppm or more". Further, it is more preferable to selectively use an
electro-deposited copper foil which also satisfies specification,
"a grain size as received of 1.0 .mu.m or less" and "tensile
strength as received of 50 kgf/mm.sup.2 or more" as the copper
foil. In Examples described later, an electro-deposited copper foil
without surface treatment for manufacturing of a VLP copper foil
produced by Mitsui Mining & Smelting Co., Ltd. which contains
above-mentioned small amount elements were used as a copper foil
satisfying these specifications.
[0065] Roughening treatment on the copper foil surface: It should
be clearly noted first that the roughening treatment is not an
indispensable step but an optional step. The roughening treatment
can be carried out on one surface or both surfaces of a copper foil
depending on application of the surface-treated copper foil.
Hereinafter, a method of a roughening treatment will be described.
Before the roughening treatment, it is preferable to carry out
cleaning of the copper foil surface by an acid rinsing treatment or
the like.
[0066] The roughening treatment method is not especially limited,
but one example will be described below. First, fine copper
particles are deposited and formed on a copper foil surface using a
sulfuric acid-based copper electrolytic solution having copper
concentration of 5 g/l to 25 g/l and free sulfuric acid
concentration of 50 g/l to 250 g/l, and as required, a gelatin is
added as an additive, under a burning plating condition at solution
temperature of 15.degree. C. to 30.degree. C. and cathode current
density of 20 A/dm.sup.2 to 50 A/dm.sup.2. Then, the fine copper
particles are fixed by using a sulfuric acid-based copper
electrolytic solution having copper concentration of 45 g/l to 100
g/l and free sulfuric acid concentration of 50 g/l to 150 g/l,
under a level plating condition at solution temperature of
30.degree. C. to 50.degree. C. and cathode current density of 30
A/dm.sup.2 to 60 A/dm.sup.2 to finish the roughening treatment.
[0067] Formation of a rust-proofing treatment layer: In the present
invention, a "zinc layer" or a "zinc-based composite layer of a
two-layer structure" is provided as a rust-proofing treatment layer
on both surfaces of a copper foil. In formation of the
rust-proofing treatment layer, any method for forming the
rust-proofing treatment layer can be employed as long as the zinc
amount of the either surface of the copper foil is made in the
range of 20 mg/m.sup.2 to 1,000 mg/m.sup.2 as described above. That
is, for formation of a rust-proofing treatment layer on a copper
foil surface, an electrochemical technology such as electrolytic
plating method or electroless plating method, or a physical
vapor-deposition method such as sputtering vapor-deposition or a
chemical gas-phase reaction can be used. However, it is preferable
to employ an electrochemical method in consideration of the
production cost.
[0068] When zinc layer composed of zinc is provided using an
electrolytic plating method will be described. A plating solution
including zinc pyrophosphate plating bath, zinc cyanide plating
bath and zinc sulfate plating bath can be used. In the detail of
the zinc pyrophosphate plating bath, zinc layer can be formed on a
copper foil surface by employing a bath composition, zinc
concentration of 5 g/l to 30 g/l, a potassium pyrophosphate
concentration of 50 g/l to 500 g/l, and pH 9 to pH 12, and
electrolysis is carried out in the solution cathodically polarizing
a copper foil with solution temperature of 20.degree. C. to
50.degree. C. under current density of 0.3 A/dm.sup.2 to 10
A/dm.sup.2.
[0069] Next, when a "zinc-based composite layer of a two-layer
structure" composed of zinc layer and different metal layer is
provided using an electrolytic plating method will be described. In
this case, in order to provide the different metal layer between a
copper foil and the zinc layer or on the surface of the zinc layer,
"any one layer of tin layer, cadmium layer, antimony layer, bismuth
layer, indium layer and lead layer" is first provided on the
surface of the copper foil by an electrolytic plating method. Then,
the zinc layer is provided on the different metal layer. As a
formation method of the zinc layer, the same method as described
above can be employed. Hereinafter, formation methods of different
metal layers including "tin layer", "cadmium layer", "antimony
layer", "bismuth layer", "indium layer" and "lead layer", will be
described.
[0070] When tin layer is provided as the different metal layer, any
conditions including plating solutions usable as a tin plating
solution and plating conditions can be used. For example,
conditions include "using stannous sulfate, and tin concentration
of 5 g/l to 30 g/l, solution temperature of 20.degree. C. to
50.degree. C., pH of 2 to 4, and current density of 0.3 A/dm.sup.2
to 10 A/dm.sup.2" and "using stannous sulfate, and tin
concentration of 20 g/l to 40 g/l, a sulfuric acid concentration of
70 g/l to 150 g/l, a cresol sulfonate concentration of 70 g/l to
120 g/l, a gelatin concentration of 1 g/l to 5 g/l, a
.beta.-naphthol concentration of 0.5 g/l to 2 g/l, solution
temperature of 20.degree. C. to 35.degree. C., and current density
of 0.3 A/dm.sup.2 to 3 A/dm.sup.2".
[0071] When cadmium layer is provided as the different metal layer,
any conditions including plating solutions usable as a cadmium
plating solution and plating conditions can be used. For example,
plating solutions includes cadmium cyanide bath, cadmium
borofluoride bath and cadmium sulfate bath. In the condition using
"cadmium cyanide bath", cadmium concentration of 20 g/l to 50 g/l,
solution temperature of 20.degree. C. to 30.degree. C., and current
density of 1 A/dm.sup.2 to 6 A/dm.sup.2 can be exemplified. And in
the condition using "cadmium sulfate bath", cadmium concentration
of 5 g/l to 50 g/l, solution temperature of 20.degree. C. to
50.degree. C., and current density of 0.2 A/dm.sup.2 to 5
A/dm.sup.2 can be exemplified.
[0072] When antimony layer is provided as the different metal
layer, any conditions including plating solutions usable as an
antimony plating solution and plating conditions can be used. For
example, in the condition using known potassium antimonyl tartrate
bath, conditions include antimony concentration of 10 g/l to 50
g/l, solution temperature of 30.degree. C. to 50.degree. C., and
current density of 0.2 A/dm.sup.2 to 1 A/dm.sup.2.
[0073] When bismuth layer is provided as the different metal layer,
plating solutions usable as a bismuth plating solution and plating
conditions can be used. For example, conditions include use of
bismuth sulfate, and bismuth concentration of 2 g/l to 5 g/l,
solution temperature of 30.degree. C. to 50.degree. C., and current
density of 0.05 A/dm.sup.2 to 1 A/dm.sup.2 can be exemplified.
[0074] When indium layer is provided as the different metal layer,
any conditions including plating solution usable as an indium
plating solution and plating conditions can be used. For example,
conditions include indium borofluoride bath and indium sulfate
bath, and for the "indium sulfate bath", indium concentration of 20
g/l to 35 g/l, solution temperature of 20.degree. C. to 40.degree.
C., and current density of 0.5 A/dm.sup.2 to 4 A/dm.sup.2 can be
exemplified.
[0075] When lead layer is provided as the different metal layer,
any conditions including plating solutions usable as a lead plating
solution and plating conditions can be used. For example,
conditions include lead borofluoride concentration of 250 g/l to
400 g/l, a hydrofluoroboric acid concentration of 30 g/l to 50 g/l,
a boric acid concentration of 10 g/l to 30 g/l, a glue
concentration of 0.1 g/l to 0.5 g/l, a .beta.-naphthol
concentration of 0.1 g/l to 1.0 g/l, solution temperature of
25.degree. C. to 50.degree. C., and current density of 1 A/dm.sup.2
to 5 A/dm.sup.2.
[0076] Method of a chromate treatment: Formation of the
chromate-treatment layer is not indispensable, and is a treatment
carried out suitably in consideration of the rust-proofing
performance required for the copper foil. The chromate treatment
includes an electrolytic chromate treatment and an electroless
chromate treatment, but either one may be used. However, when
deviation of the thickness in a chromate film, the stability of the
deposition amount and the like are considered, the electrolytic
chromate treatment is more preferable. The electrolysis condition
of the electrolytic chromate treatment is not especially limited,
but it is preferable to use a chromate solution having chromic acid
concentration of 2 g/l to 7 g/l, and pH of 10 to 12, with
electrolysis condition of solution temperature of 30.degree. C. to
40.degree. C. and current density of 1 to 8 A/dm.sup.2 to uniformly
coat the surface of an electro-deposited copper foil with a
chromate-treatment layer.
[0077] Method of an organic agent treatment: The organic agent
treatment includes a silane coupling agent treatment and an organic
rust-proofing treatment. Then, these treatments will be described
one by one.
[0078] In the present invention, the silane coupling agent
treatment is not indispensable, but is a treatment suitably carried
out in consideration of performances required for the copper foil
including adhesion with an insulting resin base material or a
negative electrode active substance of a lithium ion secondary
battery. A silane coupling agent is generally used as a silane
coupling agent solution in which the silane coupling agent is
dissolved in 0.3 g/l to 15 g/l in water as a solvent. Adsorption
methods of a silane coupling agent include an immersion method, a
showering method and a spraying method and are not especially
limited. Any method which can form a silane coupling
agent-treatment layer most uniformly through contact of a solution
containing a silane coupling agent with a copper foil to adsorb the
silane coupling agent in conformance to the process design may be
employed.
[0079] As a silane coupling agent, any selected from an
olefin-functional silane, an epoxy-functional silane, an
acryl-functional silane, an amino-functional silane and a
mercapto-functional silane can be used. Among these silane coupling
agents, it is important to selectively use a silane coupling agent
which ensures performances, i) no drawbacks in both an etching
process and performances of the printed wiring board in the printed
wiring board use, and ii) not spoiling the adhesion with a negative
electrode active substance of a lithium ion secondary battery.
[0080] Specifically, silane coupling agents including
vinyltrimethoxysilane, vinylphenyltrimethoxysilane,
3-methacryloxypropyltrimethoxysilane,
3-glycidoxypropyltrimethoxysilane, 4-glycidylbutyltrimethoxysilane,
3-aminopropyltriethoxysilane,
N-2-(aminoethyl)-3-aminopropyltrimethoxysilane,
N-3-(4-(3-aminopropoxy)butoxy)propyl-3-aminopropyltrimethoxysilane,
imidazolesilane, triazinesilane, 3-mercaptopropyltrimethoxysilane
can be used.
[0081] Next, an organic rust-proofing treatment will be described.
In the present invention, the organic rust-proofing treatment is
not indispensable also, but is a rust-proofing technology used
depending on the requirement in addition to a "zinc layer" or a
"zinc-based composite layer of a two-layer structure" as an
inorganic rust-proofing treatment described above. Organic agents
including benzotriazoles such as methylbenzotriazole
(tollyltriazole), aminobenzotriazole, carboxybenzotriazole, and
benzotriazole can be used for the organic rust-proofing treatment.
Also, other organic agents including aliphatic carboxylic acids,
alkylamines, benzoic acids, imidazoles, and triazinethiols can be
used. One or two or more of these organic agents are used after
dissolving or dispersing in solvents including water, an organic
solvent or a mixture thereof.
[0082] An organic rust-proofing layer is formed on the outermost
surface of a copper foil by using an organic rust-proofing agent
described above. To provide an organic rust-proofing layer on the
copper foil, methods including a step to prepare the solution in
which an organic rust-proofing agent described above is dissolved
in a solvent such as water or an organic solvent, followed by means
including, immersion, shower, spray or drop the solution on the
copper foil surface to form an organic rust-proofing layer can be
used, i.e. especially limited technology is not required as long as
the solution and the copper foil surface can thoroughly contact.
The concentration of the organic rust-proofing agent is not
especially limited and high or low in concentration is basically no
consequence.
[0083] Drying step: The purpose of the drying step is to dry a
surface-treated copper foil wet in a surface treatment step such as
a rust-proofing treatment. Next, when an organic agent-treatment
layer is provided, a drying condition should be paid attention.
That is because in the drying step, not only removing of moisture,
but also fixing of the adsorbed organic rust-proofing agent or
silane coupling agent on the surface of a rust-proofing treatment
layer should be performed without-decomposition of the organic
substances. That is, the effect of a used organic agent should be
the maximum. In view of such consideration, it is preferable to
carry out the drying step at a temperature of 100.degree. C. to
250.degree. C. for 2 sec to 10 sec. Hereinafter, the
surface-treated copper foil according to the present invention will
be described in more detail with reference to Examples and
Comparative Examples.
Example 1
[0084] Example 1 was performed to make a background of the present
invention that the zinc amount in zinc layer is preferable to be 20
mg/m.sup.2 to 1,000 mg/m.sup.2 apparent by comparing to Comparative
Example 1 described later. In Example 1, a surface-treated copper
foil was manufactured by the following procedure and properties
including tensile strength after heat treatment were measured.
Hereinafter, the procedure will be described step by step.
[Manufacturing of a Surface-Treated Copper Foil]
[0085] Copper foil: An electro-deposited copper foil of 15 .mu.m
thick manufactured by Mitsui Mining & Smelting Co., Ltd. used
for manufacturing of a VLP copper foil without surface treatment
was used. The electro-deposited copper foil has tensile strength as
received of 55.6 kgf/mm.sup.2, and having surface roughness (Ra) at
the shiny side of 0.22 .mu.m and surface roughness (Ra) at the
deposit side of 0.32 .mu.m, a low profile surface. The copper foil
used contains 19 ppm of sulfur, 55 ppm of carbon, 10 ppm of
nitrogen and 54 ppm of chlorine, and sum amount of these small
amount elements is 128 ppm.
[0086] Roughening treatment step: The copper foil was put in a
copper plating solution of free sulfuric acid concentration of 200
g/l, copper concentration of 8 g/l and solution temperature of
35.degree. C.; and fine copper particles are deposited on the shiny
side surface of the copper foil by cathodically polarizing the
copper foil to electrolyze under the burning plating condition of
current density of 25 A/dm.sup.2.
[0087] Then, roughening treatment on the shiny side was finished by
cathodically polarized the copper foil and electrolyzed in a copper
plating solution of free sulfuric acid concentration of 110 g/l,
copper concentration of 70 g/l and at solution temperature of
50.degree. C. under the level plating condition of current density
of 25 A/dm.sup.2 to prevent the copper particles from falling-off.
After finishing the roughening treatment, the surface roughness
(Ra) at the roughened surface was 0.35 .mu.m, and the surface
roughness (Ra) at the opposite surface was 0.32 .mu.m.
[0088] Rust-proofing treatment step: The rust-proofing treatment
employed in Example 1 was zinc rust-proofing treatment in which
zinc layer was provided on both surfaces of a copper foil. In the
rust-proofing treatment, as a zinc pyrophosphate plating bath, bath
composition having zinc concentration of 6 g/l, a potassium
pyrophosphate concentration of 125 g/l and pH of 10.5 was employed;
and the copper foil was cathodically polarized in the plating bath
at solution temperature of 30.degree. C., and current density and
electrolysis time were changed to prepare three kind of zinc layers
different in zinc amount shown in Table 1.
[0089] Chromate treatment step: In Example 1, a chromate-treatment
layer was formed under the following condition. As the electrolysis
condition of the electrolytic chromate treatment to form a
chromate-treatment layer on the rust-proofing treatment layer,
condition using a solution having a chromic acid concentration of 2
g/l and pH of 12 with solution temperature of 30.degree. C. and
current density of 2 A/dm.sup.2 was employed.
[0090] Silane coupling agent treatment step: After finishing the
chromate treatment, without drying of the copper foil surface after
water rinsing, a silane coupling agent aqueous solution was sprayed
on the copper foil surfaces by showering to adsorb silane coupling
agent on both surfaces of the surface-treated copper foil. The
silane coupling agent aqueous solution was prepared to make
3-aminopropyltrimethoxysilane concentration to be 5 g/l in
de-ionized water as a solvent.
[0091] Drying step: After finishing the silane coupling agent
treatment, a surface-treated copper foil was finished through
evaporating moisture and causing a condensation reaction of the
silane coupling agent by introducing the wet surface-treated copper
foil into a drying section at temperature of 150.degree. C. for 4
sec. In Example 1, surface-treated copper foils as the example
specimens 1-1 to 1-3 shown in Table 1 were prepared.
[0092] Note that, a water rinsing step was appropriately provided
between each step as required from the rust-proofing treatment step
to the silane coupling agent treatment step described above in
order to prevent carry-over of a solution in a prior treatment step
to the next step.
[Evaluation of the Surface-Treated Copper Foil]
[0093] Next, evaluation items and measurement methods will be
described. Evaluation results of the example specimens 1-1 to 1-3
in Example 1 are collectively shown in Table 1 for comparison with
the comparative specimen 1 according to Comparative Example 1
described later.
[0094] Amounts of small amount elements in a copper foil: Amounts
of carbon and sulfur in a copper foil without surface treatment was
analyzed using carbon/sulfur analyzer, EMIA-920V made by HORIBA
Ltd. Amount of nitrogen was analyzed using an oxygen/nitrogen
analyzer, EMGA-620 made by HORIBA Ltd. Amount of chlorine in a
copper foil was analyzed by a silver chloride turbidimetry using a
spectrophotometer, U-3310 made by Hitachi High-Tech Fielding
Corp.
[0095] Tensile strength: The words "tensile strength" used in the
present description means a value measured using a strip of copper
foil specimen of 10 mm.times.150 mm (gauge length: 50 mm) and at
crosshead speed of 50 mm/min according to the method provided in
IPC-TM-650. The tensile strength after heat treatment was measured
in the same manner on the copper foil specimen after heat treatment
under the condition shown in each Table followed by cooling down to
a room temperature.
[0096] Deposition amount of a rust-proofing component: One surface
of a surface-treated copper foil of 10 cm.times.10 cm opposite to
the measurement surface where zinc amount should be measured was
coated with an adhesive to dissolve only a surface-treatment layer
of the measurement surface in an aqueous solution having
hydrochloric acid concentration of 30 mg/l and a hydrogen peroxide
concentration of 20 mg/l. Then, zinc concentration in the resultant
dissolved solution was quantitatively analyzed by an ICP
(Inductively Coupled Plasma) atomic emission spectrometry which
uses radio-frequency inductively coupled plasma as a light source;
and the value obtained was converted to a deposition amount
(mg/m.sup.2) per unit area of the rust-proofing component.
[0097] Surface roughness (Ra): Surface roughness (Ra) in the
present description was measured using surface roughness/contour
measuring instrument SEF-30D made by Kosaka Lab. Ltd. according to
the method provided in JIS B0601.
[0098] Measurement of a grain size: In the measurement of a grain
size of a copper foil, FE gun-type scanning electron microscope
(SUPRA 55VP, made by Carl Zeiss AG) equipped with an EBSD
evaluation device (OIM Analysis, made by TSL Solutions Ltd.)
provided with analyzer was used. Image data of a grain distribution
pattern in a cross-section of the copper foil specimen prepared by
suitable machining was acquired by the EBSD method using the
device; and the average grain size was calculated by an analytical
menu included in an EBSD analysis program (OIM Analysis, made by
TSL Solutions Ltd.) using the image data. In the present
measurement, an orientation difference of 5.degree. or more was
assumed as a crystal grain boundary. The conditions in scanning
electron microscope observation were an acceleration voltage of 20
kV; an aperture diameter of 60 mm with high current mode and a
sample inclination angle of 70.degree.. The measurement was carried
out by appropriately changing the conditions of the observation
magnification, the measurement region and the step size depending
on the size of the crystal grains.
Comparative Example 1
[0099] In Comparative Example 1, comparative specimen 1 which has
zinc amount on both surfaces of less than 20 mg/m.sup.2 (each of
both surfaces of the surface-treated copper foil has about 10
mg/m.sup.2) as the rust-proofing component in Example 1 was
prepared. As the other manufacturing conditions were the same as in
Example 1, further descriptions are omitted.
Comparison Among Example 1 and Comparative Example 1
[0100] Example 1 and Comparative Example 1 will be compared with
reference to the following Table 1.
TABLE-US-00001 TABLE 1 Deposition Amount Tensile Strength:
kgf/mm.sup.2 (IPC Analysis): Type of Rust- After Heat Treatment
mg/mm.sup.2 Sample Proofing As Received 350.degree. C. .times. 60
min 400.degree. C. .times. 60 min Measured Surface Zn Cr Example Zn
rust-proofing 54.7 45.6 41.7 Roughening Treated Side 62.0 3.7
specimen 1-1 Deposited Side 47.4 1.6 Example 53.8 46.6 38.9
Roughening Treated Side 250.9 4.2 specimen 1-2 Deposited Side 203.3
1.8 Example 54.2 48.4 37.7 Roughening Treated Side 493.4 2.5
specimen 1-3 Deposited Side 377.2 2.5 Comparative 54.5 38.5 30.2
Roughening Treated Side 10.8 1.3 specimen 1 Deposited Side 9.6
1.0
[0101] As is apparent in Table 1, Example 1 and Comparative Example
1 are not different in surface roughness because the same copper
foil is used. Further, the rust-proofing treatment layer of the
example specimens 1-1 to 1-3 are constituted of zinc; and the zinc
amount of either surface satisfies the specification of 20
mg/m.sup.2 to 1,000 mg/m.sup.2. In contrast the rust-proofing
treatment layer of the comparative specimen 1 does not satisfy the
specification of zinc amount of either surface of 20 mg/m.sup.2 to
1,000 mg/m.sup.2.
[0102] Next, with regard to tensile strengths of the example
specimens 1-1 to 1-3 and the comparative specimen 1, tensile
strengths as received show no large difference among them. However,
in tensile strengths after heat treatment, it is apparent that
tensile strengths of the example specimens 1-1 to 1-3 show a much
higher value than that of the comparative specimen 1. According to
the result, it is apparent that the surface-treated copper foils
which satisfy the specification according to the present invention
show a good softening resistance performance of: "tensile strength
after heat treatment at 350.degree. C. for 60 min is 40
kgf/mm.sup.2 or more"; and "tensile strength after heat treatment
at 400.degree. C. for 60 min is 35 kgf/mm.sup.2 or more".
[0103] Further, the matter is also apparent in softening resistance
performance of the example specimens 1-1 to 1-3 that a sufficient
softening resistance performance is ensured when a rust-proofing
treatment layer of a surface-treated copper foil using a "copper
foil containing carbon, sulfur, chlorine or nitrogen, and having at
least a sum amount of 100 ppm or more" is constituted of zinc, and
further the zinc amount of either surface is 20 mg/m.sup.2 to 1,000
mg/m.sup.2.
Example 2
[0104] Example 2 was carried out to verify the effects of small
amount elements (carbon, sulfur, chlorine and nitrogen) in a copper
foil and the grain size of the copper foil against softening
resistance performance by comparing to Comparative Example 2.
[Preparation of a Surface-Treated Copper Foil]
[0105] Copper foil: A copper foil used in Example 2 was an
electro-deposited copper foil prepared under the following
conditions. First, a sulfuric acid-based copper electrolytic
solution was prepared by using a basic solution of a copper sulfate
solution containing copper concentration of 80 g/l and free
sulfuric acid concentration of 140 g/l, and was added with the
following additives in following concentrations. The sulfuric
acid-based copper electrolytic solution used for preparation of an
electro-deposited copper foil as the example specimen 2 contains
additives, 60.0 ppm of sodium salt of mercapto-1-propanesulfonic
acid, 70.0 ppm of diallyldimethylammonium chloride polymer (made by
Senka Corp., Unisense FPA100L), 7.0 ppm of N,N'-diethylthiourea,
and chlorine of 60 ppm. Hydrochloric acid was used to arrange the
chlorine concentration. In preparation of the electro-deposited
copper foil, electro-deposited copper foil of 15 .mu.m thick was
formed by using a titanium plate as a cathode whose surface was
polished with a #2000 emery paper and a DSA as an anode.
[0106] The copper foil prepared contains 350 ppm of carbon, 210 ppm
of sulfur, 440 ppm of chlorine and 79 ppm of nitrogen, and sum
amount of these small amount elements is 1,079 ppm. The grain size
is 0.21 .mu.m, and tensile strength as received is 80.7
kgf/mm.sup.2.
[0107] Roughening treatment step: Roughening treatment was not
subjected on the copper foil, example specimen 2.
[0108] Rust-proofing treatment step: In Example 2, on the
electro-deposited copper foils prepared as in the above, zinc
layers having two different zinc amounts were formed by changing
the zinc deposition amount as shown in Table 2.
[0109] Then, two kinds of surface-treated copper foils were
prepared by subjecting to a chromate treatment step, a silane
coupling agent treatment step and a drying step as in Example 1.
Specimens obtained from the two kinds of surface-treated copper
foils were named example specimens 2-1 and 2-2. Evaluation results
on these samples are collectively shown in Table 2 for comparison
with Comparative Example 2.
Comparative Example 2
[0110] In Comparative Example 2, an electro-deposited copper foil
having a sum amount of small amount elements in the foil of 100 ppm
or less was selected to use. And the electro-deposited copper foil
having a grain size of 1.0 .mu.m or more was selected to use.
[0111] Copper foil: As a copper foil having a sum amount of small
amount elements of less than 100 ppm, an electro-deposited copper
foil of 15 .mu.m thick used for manufacturing of an HTE copper foil
made by Mitsui Mining & Smelting Co., Ltd. without surface
treatment was used. The electro-deposited copper foil contains 34
ppm of carbon, 0 ppm of sulfur, 8 ppm of chlorine and 0 ppm of
nitrogen. The sum amount of these small amount elements is 42 ppm.
The grain size is 1.08 .mu.m, and tensile strength as received is
39.3 kgf/mm.sup.2.
[0112] Then, three kinds of surface-treated copper foils were
prepared by subjecting to a rust-proofing treatment step, a
chromate treatment step, a silane coupling agent treatment step and
a drying step as in Example 2, and were named comparative specimens
2-1, 2-2 and 2-3. As for the comparative specimen 2-1,
rust-proofing treatment step was skipped to prepare a surface
treated copper foil without a rust-proofing treatment layer.
Evaluation results on these samples are collectively shown in Table
2 for comparison with Example 2.
TABLE-US-00002 TABLE 2 Rust-Proofing Treatment Layer Zn Tensile
Strength (kgf/mm.sup.2) Amount of Small Amount Element in Foil
(ppm) Rust- Deposition After Heat Treatment Thickness Grain Sum
Proofing Amount As 350.degree. C. .times. 400.degree. C. .times.
Sample .mu.m size .mu.m Amount Carbon Sulfur Chlorine Nitrogen
Component mg/m.sup.2 Received 60 min 60 min Example 15 0.21 1079
350 210 440 79 Zn 195 80.7 64.6 60.1 specimen 2-1 Example 539 67.5
62.8 specimen 2-2 Comparative 1.08 42 34 0 8 0 -- 0 39.3 18.1 17.3
specimen 2-1 Comparative Zn 52 18.6 17.7 specimen 2-2 Comparative
481 20.4 18.7 specimen 2-3 Reference 0.21 1079 350 210 440 79 -- 0
80.7 14.9 14.5 specimen
Comparison Among Example 2 and Comparative Example 2
[0113] Comparison will be made with reference to Table 2. First,
the example specimens will be described. As can be apparently
understood, when zinc amount of the surface-treated copper foil
increases, softening resistance performance when high heats at
350.degree. C. and 400.degree. C. are loaded is improved in
proportion to the zinc amount.
[0114] When tensile strengths as received are compared, tensile
strengths after heat treatment of the example specimens may show
apparent high values because the values of the example specimens
2-1 and 2-2 are much higher than these of the comparative specimens
2-1 to 2-3.
[0115] However, the reference specimen in Table 2 is a sample
corresponding to the example specimen 2-1 and the example specimen
2-2 except that the rust-proofing treatment layer was not provided.
That is, it is apparent that even if the copper foil is the same
copper foil used in the example specimen 2-1 and the example
specimen 2-2, the reference specimen without zinc layer just
performs equal to or lower softening resistance performance than
the comparative specimens 2-1 to 2-3 when high heats at 350.degree.
C. and 400.degree. C. are loaded.
[0116] Next, the example specimens in Example 2 and the reference
specimen will be compared from the viewpoint of the grain
structure. FIG. 3 is an FIB-SIM image of the reference specimen
disclosed in Table 2. FIG. 3(A) is crystal grains as received; and
grain size is 0.21 .mu.m, and tensile strength is 80.7
kgf/mm.sup.2. FIG. 3(B) is crystal grains after heat treatment at
350.degree. C. for 60 min; and grain size is 1.83 .mu.m, and
tensile strength is 14.9 kgf/mm.sup.2. That is, the reference
specimen is low in softening resistance performance when
heated.
[0117] In contrast, tensile strength of the example specimen 2-2
having the zinc amount of 539 mg/m.sup.2 was 67.5 kgf/mm.sup.2
after heat treatment at 350.degree. C. for 60 min, and 62.8
kgf/mm.sup.2 even after heat treatment at 400.degree. C. for 60
min; i.e. decreases in tensile strength after heat treatment in the
either temperature condition are low and softening resistance
performance is high. According to FIG. 4 showing an FIB-SIM image
of the example specimen 2-2 after heat treatment at 350.degree. C.
for 60 min, the grain size is 0.31 .mu.m, and very fine crystal
grains are maintained, i.e. it can be understood that the
miniaturization effect of the crystal grain is maintained in the
surface-treated copper foil.
[0118] Then, effects on softening resistance performance of amount
of the small amount element and the grain size of a copper foil
will be investigated. In the comparative specimens 2-1 to 2-3, an
electro-deposited copper foil containing a sum amount of small
amount elements in the copper foil of 100 ppm or less and having a
grain size as received of exceeding 1.0 .mu.m is used. In the
comparative specimen 2-2 which is an electro-deposited copper foil
subjected to the rust-proofing treatment to have the zinc amount of
52 mg/m.sup.2, tensile strength after heat treatment was 18.6
kgf/mm.sup.2 at 350.degree. C. for 60 min and 17.3 kgf/mm.sup.2 at
400.degree. C. for 60 min; i.e. heat treatment in the either
temperature condition remarkably decrease the tensile strength.
FIG. 5 is an FIB-SIM image of the comparative specimen 2-2 after
heat treatment at 350.degree. C. for 60 min. The grain size is 3.48
.mu.m and it can be understood that grain size is very large.
Tensile strength of the comparative specimen 2-3 after heat
treatment having zinc amount of 481 mg/m.sup.2 was 20.4
kgf/mm.sup.2 at 350.degree. C. for 60 min and 18.7 kgf/mm.sup.2 at
400.degree. C. for 60 min; i.e. heat treatment in the either
temperature condition remarkably decrease tensile strength as in
the comparative specimen 2-2.
[0119] As described above, it can be understood that when the sum
amount of small amount elements in a copper foil used in
manufacturing of a surface-treated copper foil is 100 ppm or less,
and grain size as received is exceeding 1.0 .mu.m, even if the zinc
amount of a rust-proofing treatment layer is in the range of 20
mg/m.sup.2 to 1,000 mg/m.sup.2, tensile strength of the
surface-treated copper foil after heat treatment remarkably
decreases, i.e. softening resistance performance is poor.
Therefore, it is apparent that the grain size of a copper foil
should be in a reasonable range in addition to an appropriate zinc
amount in the rust-proofing treatment in order to improve softening
resistance performance of a surface-treated copper foil.
[0120] As is apparent in comparison among Example 2 and Comparative
Example 2, it is preferable to satisfy two specifications, "amount
of the small amount element in the copper foil is reasonable" and
"the rust-proofing layer has a reasonable zinc amount", and to
satisfy further specification "the grain size as received of the
copper foil is in a reasonable range" is more preferable in order
to secure further improvement in softening resistance performance
of an electro-deposited copper foil when high heat at 350.degree.
C. and 400.degree. C. are loaded.
Example 3
[0121] In Example 1 and Example 2 described above, improving
effects of softening resistance performance of the surface-treated
copper foil using zinc rust-proofing when high heat at 350.degree.
C. and 400.degree. C. were loaded on the copper foil are
demonstrated. Then, almost the same effect of a "zinc-based
composite layer of a two-layer structure" will be demonstrated in
Example 3. That is, samples provided with rust-proofing treatment
layers including a "zinc layer", a "zinc-based composite layer of
tin layer/zinc layer", a "zinc-based composite layer of cadmium
layer/zinc layer", a "zinc-based composite layer of antimony
layer/zinc layer", a "zinc-based composite layer of bismuth
layer/zinc layer", and a "zinc-based composite layer of lead
layer/zinc layer" were prepared in Example 3 as shown in Table 3
for comparison.
[0122] Preparation of a copper foil: In Example 3, as an
electro-deposited copper foil having a sum amount of small amount
elements in the copper foil of 100 ppm or more, an
electro-deposited copper foil of 12 .mu.m thick manufactured by
Mitsui Mining & Smelting Co., Ltd. used for manufacturing of a
VLP copper foil was used. The copper foil contains 44 ppm of
carbon, 14 ppm of sulfur, 52 ppm of chlorine, and 11 ppm of
nitrogen and the sum amount of these small amount elements is 121
ppm. The grain size is 0.60 .mu.m, and tensile strength as received
is 54.4 kgf/mm.sup.2.
[0123] Roughening treatment step: Roughening treatment was not
subjected to the copper foil used in Example 3.
[0124] Rust-proofing treatment step: In Example 3, different metal
layers were provided on each of both surfaces of a copper foil,
followed by providing zinc layer on the surface of the different
metal layer on each of both surfaces of the copper foil, as in
Example 1. So, just formation condition of different metal layer
corresponding to the kind of a rust-proofing treatment layer will
be described. The amount of the different metal of different metal
layers and the zinc deposition amounts provided on both surfaces of
the copper foil were made to be identical.
[0125] Zinc-based composite layer composed of tin layer/zinc layer
was formed on the surface of a copper foil using tin plating
solution having a composition of pH 10.0, tin pyrophosphate
concentration of 11 g/l and a potassium pyrophosphate concentration
of 100 g/l, and tin layer was formed under the condition of
solution temperature of 40.degree. C., and current density of 1.0
A/dm.sup.2 followed by providing zinc layer as in Example 1 to
finish zinc-based composite layer of a two-layer structure. In
Table 3, the present sample is named example specimen 3-3.
[0126] Zinc-based composite layer composed of cadmium layer/zinc
layer was formed on the surface of a copper foil using cadmium
plating solution having a composition of cadmium sulfate
concentration of 50 g/l and a sulfuric acid concentration of 50
g/l, and cadmium layer was formed under the condition of solution
temperature of 40.degree. C., and current density of 0.5
A/dm.sup.2, followed by providing zinc layer as in Example 1 to
finish zinc-based composite layer of a two-layer structure. In
Table 3, the present sample is named example specimen 3-4.
[0127] Zinc-based composite layer composed of antimony layer/zinc
layer was formed on the surface of a copper foil using antimony
plating solution having a composition of pH 2.1, a potassium
antimonyl tartrate concentration of 50 g/l, a formic acid
concentration of 12.5 g/l and a potassium chloride concentration of
25 g/l, and antimony layer was formed under the condition of
solution temperature of 40.degree. C. and current density of 0.5
A/dm.sup.2, followed by providing zinc layer as in Example 1 to
finish zinc-based composite layer of a two-layer structure. In
Table 3, the present sample is named example specimen 3-5.
[0128] Zinc-based composite layer composed of bismuth layer/zinc
layer was formed on the surface of a copper foil using bismuth
plating solution having a composition of pH 12.5, bismuth sulfate
concentration of 8.5 g/l, a citric acid concentration of 190 g/l
and a sodium hydroxide concentration of 140 g/l, and bismuth layer
was formed under the condition of solution temperature of
40.degree. C. and current density of 0.1 A/dm.sup.2, followed by
providing zinc layer as in Example 1 to finish zinc-based composite
layer of a two-layer structure. In Table 3, the present sample is
named example specimen 3-6.
[0129] Zinc-based composite layer composed of lead layer/zinc layer
was formed on the surface of a copper foil using lead plating
solution having a composition of lead oxide concentration of 90 g/l
and a fluorosilicic acid concentration of 120 g/l, and lead plating
layer was formed under the condition of a bath temperature of
30.degree. C., and current density of 0.5 A/dm.sup.2, followed by
providing zinc layer as in Example 1. In Table 3, the present
sample is named example specimen 3-7.
[0130] After finishing rust-proofing treatment described above, the
rust-proofing treated copper foils were subjected to a chromate
treatment step, a silane coupling agent treatment step and a drying
step as in Example 1 to prepare surface-treated copper foils
corresponding to the example specimens 3-1 to 3-7. Evaluation
results on these samples are collectively shown in Table 3 for
comparison with Comparative Example 3.
Comparative Example 3
[0131] In Comparative Example 3, a surface-treated copper foil was
prepared by the same procedure as in Example 3, using an
electro-deposited copper foil which was used for manufacturing of a
VLP copper foil used in Example 3 without subjecting to
rust-proofing treatment, and was named comparative specimen 3.
Evaluation results are collectively shown in Table 3 for comparison
with Example 3.
Comparison Among Example 3 and Comparative Example 3
[0132] Comparison will be made with reference to Table 3.
TABLE-US-00003 TABLE 3 Rust-Proofing Amount of Small Amount Element
Treatment Layer Tensile Strength (kgf/mm.sup.2) Thick- Grain in
Foil (ppm) Rust- After Heat Treatment ness Size Sum Car- Ni-
Proofing Deposition As 350.degree. C. .times. 400.degree. C.
.times. Sample .mu.m .mu.m Amount bon Sulfur Chlorine trogen
Component Amount (mg/m.sup.2) Received 60 min 60 min Example 12
0.60 121 44 14 52 11 Zn Zn: 45 54.4 47.7 43.8 specimen 3-1 Example
Zn: 457 41.4 35.0 specimen 3-2 Example Sn/Zn [Sn: 7]/[Zn: 66] 50.6
44.2 specimen 3-3 Example Cd/Zn [Cd: 37]/[Zn: 235] 50.9 41.0
specimen 3-4 Example Sb/Zn [Sb: 19]/[Zn: 260] 53.2 52.0 specimen
3-5 Example Bi/Zn [Bi: 23/][Zn: 254] 54.7 53.2 specimen 3-6 Example
Pb/Zn [Pb: 3]/[Zn: 245] 52.0 41.4 specimen 3-7 Comparative -- 0
37.5 32.5 specimen 3
[0133] The example specimens 3-3 to 3-7 in Table 3 employ a
"zinc-based composite layer of a two-layer structure" as their
rust-proofing treatment layer. The matter can be understood that
softening resistance performance of the electro-deposited copper
foil when high heat of 350.degree. C. or 400.degree. C. was loaded
is improved also in the case where the zinc-based composite layer
of a two-layer structure is used as a rust-proofing treatment
layer. Further, even if the zinc amount fluctuates in a range
exceeding 50 mg/m.sup.2, softening resistance performance after
heat treatment at both 350.degree. C. for 60 min and at 400.degree.
C. for 60 min tends to stabilize.
[0134] Next, the grain structures in Example 3 and Comparative
Example 3 will be compared. FIG. 6 is an FIB-SIM image of the
comparative specimen 3 prepared in Comparative Example 3 in which
the surface-treated copper foil was prepared without rust-proofing
treatment. The grain size as received shown in FIG. 6(A) is 0.60
.mu.m, and tensile strength is 54.4 kgf/mm.sup.2. The grain size
after heat treatment at 350.degree. C. for 60 min shown in FIG.
6(B) is 0.92 .mu.m, and tensile strength thereafter is 37.5
kgf/mm.sup.2.
[0135] In contrast, FIG. 7 shows an FIB-SIM image of the example
specimen 3-1 after heat treatment at 350.degree. C. for 60 min when
the surface-treated copper foil was prepared with the zinc amount
of 50 mg/m.sup.2. As can be understood from FIG. 7, the crystal
grains are maintained fine. The grain size is 0.74 .mu.m, and
tensile strength is 47.7 kgf/mm.sup.2. It is apparent that when a
surface-treated copper foil is prepared in such a manner with the
zinc amount being 50 mg/m.sup.2, the grain structure after heat
treatment is fine and the decrease in tensile strength can be
hindered.
[0136] That is, it is made apparent that without zinc rust-proofing
treatment layer, heat treatment at 350.degree. C. for 60 min
promotes re-crystallization to grow crystal grains. Therefore, it
can be judged that, miniaturization effect of the crystal grains is
maintained to hinder decrease in tensile strength because zinc in
the zinc rust-proofing treatment layer employed in the present
invention inhibits the re-crystallization of the copper foil grain
structure when heated.
[0137] FIG. 8 shows an FIB-SIM image of the grain structure of the
example specimen 3-6 after heat treatment at 350.degree. C. for 60
min which is provided with the zinc-based composite layer of a
two-layer structure (bismuth layer/zinc layer, bismuth deposition
amount: 23 mg/m.sup.2, zinc amount: 254 mg/m.sup.2) as a
rust-proofing treatment layer. As can be understood from FIG. 8,
the grain structure is remarkably fine. Tensile strength of the
surface-treated copper foil is 54.7 kgf/mm.sup.2, i.e. the effect
of the miniaturization of crystal grain is maintained and softening
resistance performance when high heat is loaded is excellent.
Summary of Comparisons Among Examples and Comparative Examples
[0138] From above results in comparisons, when the copper foil
which satisfies ground specification of a "copper foil containing
carbon, sulfur, chlorine or nitrogen and having at least a sum
amount thereof of 100 ppm or more" is used, satisfying the
specification of "being constituted of zinc or zinc-based composite
layer of a two-layer structure, and having zinc amount of 20
mg/m.sup.2 to 1,000 mg/m.sup.2" is indispensable for a
rust-proofing treatment layer provided on each of both surfaces of
the copper foil in order to improve softening resistance
performance when high heat is loaded on a surface-treated copper
foil. The deposition amount of different metal component when
zinc-based composite layer of a two-layer structure is employed is
preferable to be 1 mg/m.sup.2 to 200 mg/m.sup.2. It can be
understood that when the above-mentioned specifications are
satisfied, a good softening resistance performances, "tensile
strength of 40 kgf/mm.sup.2 or more after heat treatment at
350.degree. C. for 60 min" and "tensile strength of 35 kgf/mm.sup.2
or more after heat treatment at 400.degree. C. for 60 min" can be
provided in the surface-treated copper foil.
INDUSTRIAL APPLICABILITY
[0139] The surface-treated copper foil according to the present
invention shows a good softening resistance performance even if
high heat is loaded on the surface treated copper foil. Therefore,
the surface treated copper foil is suitable in applications such as
printed wiring boards and negative electrode current collectors of
lithium ion secondary batteries. The reason is that the life of
products can be elongated and the quality is stabilized because the
decrease of tensile strength of the surface-treated copper foil
according to the present invention after heat treatment is low even
though the surface-treated copper foil used in the manufacturing
processes of these products may be exposed to high heat. In
addition, as the manufacturing of the surface-treated copper foil
according to the present invention can utilize existing copper
foil-manufacturing facilities and does not require new facility
investments, the effective utilization of copper foil manufacture
facilities as a social capital is made possible.
SYMBOL LIST
[0140] 1 SURFACE-TREATED COPPER FOIL [0141] 2 COPPER FOIL LAYER
[0142] 3 RUST-PROOFING TREATMENT LAYER [0143] 4 CHROMATE-TREATMENT
LAYER [0144] 5 ORGANIC AGENT-TREATMENT LAYER [0145] 6 ROUGHENING
TREATMENT LAYER (FINE COPPER PARTICLE)
* * * * *