U.S. patent application number 14/582989 was filed with the patent office on 2015-04-30 for polyimide film and process for producing the same.
This patent application is currently assigned to KANEKA CORPORATION. The applicant listed for this patent is Kiyokazu Akahori, Toshihisa Itoh, Hisayasu Kaneshiro, Katsunori Yabuta. Invention is credited to Kiyokazu Akahori, Toshihisa Itoh, Hisayasu Kaneshiro, Katsunori Yabuta.
Application Number | 20150118472 14/582989 |
Document ID | / |
Family ID | 27567024 |
Filed Date | 2015-04-30 |
United States Patent
Application |
20150118472 |
Kind Code |
A1 |
Kaneshiro; Hisayasu ; et
al. |
April 30, 2015 |
POLYIMIDE FILM AND PROCESS FOR PRODUCING THE SAME
Abstract
A process includes the steps of: casting or coating a polyamic
acid organic solvent solution on a support and drying the polyamic
acid organic solvent solution thereon, so as to form a partially
cured and/or partially dried polyamic acid film; dipping the
polyamic acid film in tertiary amine or a solution of tertiary
amine, or coating tertiary amine or a solution of tertiary amine on
the polyamic acid film; and drying the film while imidizing the
polyamic acid. In another process, a chemical converting agent and
a catalyst are mixed in an organic solvent solution of polyamic
acid. After casting and heating the mixture on a support, a
partially cured and/or partially dried polyamic acid film is
detached from the support. The film contains, with respect to the
remaining volatile component, not less than 50 parts of catalyst,
not more than 30 parts of solvent, and not more than 20 parts of
chemical converting agent and/or a chemical converting agent
derived component. The remaining amic acid is imidized and the film
is dried.
Inventors: |
Kaneshiro; Hisayasu; (Kyoto,
JP) ; Itoh; Toshihisa; (Shiga, JP) ; Yabuta;
Katsunori; (Shiga, JP) ; Akahori; Kiyokazu;
(Shiga, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kaneshiro; Hisayasu
Itoh; Toshihisa
Yabuta; Katsunori
Akahori; Kiyokazu |
Kyoto
Shiga
Shiga
Shiga |
|
JP
JP
JP
JP |
|
|
Assignee: |
KANEKA CORPORATION
Osaka
JP
|
Family ID: |
27567024 |
Appl. No.: |
14/582989 |
Filed: |
December 24, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11674620 |
Feb 13, 2007 |
8962790 |
|
|
14582989 |
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10468524 |
Aug 18, 2003 |
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PCT/JP2002/001727 |
Feb 26, 2002 |
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11674620 |
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Current U.S.
Class: |
428/220 ;
264/216; 264/331.19; 427/385.5; 524/879; 528/353 |
Current CPC
Class: |
B29C 41/46 20130101;
Y10T 428/31721 20150401; H05K 2201/0154 20130101; C08J 5/18
20130101; C09D 179/08 20130101; B29D 7/01 20130101; B29K 2105/0014
20130101; B29K 2079/08 20130101; B29C 41/003 20130101; B29L
2007/008 20130101; C08J 2379/08 20130101; B29C 41/28 20130101; B29K
2105/0005 20130101; B29C 41/24 20130101 |
Class at
Publication: |
428/220 ;
528/353; 524/879; 264/216; 264/331.19; 427/385.5 |
International
Class: |
C08J 5/18 20060101
C08J005/18; B29C 41/46 20060101 B29C041/46; B29C 41/00 20060101
B29C041/00; C09D 179/08 20060101 C09D179/08; B29C 41/24 20060101
B29C041/24 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2001 |
JP |
2001-052235 |
Mar 23, 2001 |
JP |
2001-086452 |
Mar 30, 2001 |
JP |
2001-099369 |
May 31, 2001 |
JP |
2001-165791 |
Jun 7, 2001 |
JP |
2001-172893 |
Nov 30, 2001 |
JP |
2001-367440 |
Feb 15, 2002 |
JP |
2002-038287 |
Claims
1. A process for producing a polyimide film by deposition of a
polyamic acid containing composition by casting and/or coating,
said process comprising the step of: adding, to the polyamic acid
containing composition, a curing agent that contains not less than
1 mole equivalent of a dehydrating agent with respect to the
polyamic acid and not less than 0.2 mole equivalent of an imidizing
catalyst with respect to the polyamic acid, wherein a mole ratio of
the dehydrating agent and the imidizing catalyst is in a range of
1:0.15 to 1:0.75.
2. The process as set forth in claim 1, wherein the dehydrating
agent is contained in 1 to 5 mole equivalent with respect to the
amic acid unit, and the imidizing catalyst is contained in 0.2 to
1.5 mole equivalent with respect to the amic acid unit.
3. A process for producing a polyimide film whose tensile strength
is equal to or more than 265 kg/mm.sup.2 by deposition of a
polyamic acid containing composition by casting and/or coating,
said process comprising the step of: adding, to the polvamic acid
containing composition, a curing agent that contains not less than
1 mole equivalent of a dehydrating agent with respect to the
polyamic acid and not less than 0.2 mole equivalent of an imidizing
catalyst with respect to the polyamic acid, wherein the curing
agent is added in 30 parts by weight to 70 parts by weight with
respect to 100 parts by weight of the polyamic acid solution.
4. A process for producing a polyimide film whose tensile strength
is equal to or more than 265 kg/mm.sup.2 by deposition of a
polyamic acid containing composition by casting and/or coating,
said process comprising the step of: adding, to the polyamic acid
containing composition, a curing agent that contains not less than
1 mole equivalent of a dehydrating agent with respect to the
polyamic acid and not less than 0.2 mole equivalent of an imidizing
catalyst with respect to the polyamic acid, wherein the curing
agent is added to an organic solvent solution of the polyamic acid
to obtain a resin solution composition whose viscosity at 0.degree.
C. is not more than 600 poise.
5. A process for producing a polyimide film whose tensile strength
is equal to or more than 265 kg/mm.sup.2 by deposition of a
polyamic acid containing composition by casting and/or coating,
said process comprising the step of: adding, to the polyamic acid
containing composition, a curing agent that contains not less than
1 mole equivalent of a dehydrating agent with respect to the
polyamic acid and not less than 0.2 mole equivalent of an imidizing
catalyst with respect to the polyamic acid, wherein the curing
agent is added to an organic solvent solution of the polyamic acid
to obtain a resin solution composition whose viscosity at 0.degree.
C. is not more than 400 poise.
6. The process as set forth in claim 1, wherein the imidizing
catalyst is a tertiary amine.
7. A process for producing a polyimide film whose tensile strength
is equal to or more than 265 kg/mm.sup.2 by deposition of a
polyamic acid containing composition by casting and/or coating,
said process comprising the step of: adding, to the polyamic acid
containing composition, a curing agent that contains not less than
1 mole equivalent of a dehydrating agent with respect to the
polyamic acid and not less than 0.2 mole equivalent of an imidizing
catalyst with respect to the polyamic acid, wherein the polyimide
film has a thickness unevenness of not more than 2.0 .mu.m in a
machine direction.
8. The process as set forth in claim 3, wherein the dehydrating
agent is contained in 1.0 to 3.0 mole equivalent with respect to
the amic acid unit, and the imidizing catalyst is contained in not
less than 0.3 mole equivalent with respect to the amic acid
unit.
9. The process as set forth in claim 8, wherein the imidizing
catalyst is a tertiary amine.
10. The process as set forth in claim 9, further comprising the
step of: continuously casting an organic solvent solution of the
polyamic acid on a support to cover a width of not less than 1 m,
wherein the resulting polyimide film has 0.7 or greater ratio of
maximum value to minimum value of tear propagation strength
measured across an entire width, and 0.6 g or smaller R value of
tear propagation strength measured at an outermost portion.
11. A polyimide film, produced by continuously casting an organic
solvent solution of the polyamic acid on a support to cover a width
of not less than 1 m, having 0.7 or greater ratio of maximum value
to minimum value of tear propagation strength measured across an
entire width, and 0.6 g or smaller R value of tear propagation
strength measured at an outermost portion.
12. A process for producing a polyimide film by deposition of a
polyamic acid containing composition by casting and/or coating,
said process comprising the step of: adding, to the polyamic acid
containing composition, a curing agent that contains not less than
1 mole equivalent of a dehydrating agent with respect to the
polyamic acid and not less than 0.2 mole equivalent of an imidizing
catalyst with respect to the polyamic acid, forming a gel film that
has been partially cured and/or partially dried to be
self-supporting in the casting and/or coating of the polyamic acid
containing composition on a support; and passing the gel film
through a heating furnace with both ends of the gel film being
fastened, wherein: (1) the dehydrating agent is contained in 1.0 to
5.0 mole equivalent with respect to an amic acid unit, and the
imidizing catalyst is contained in 0.2 to 2.0 mole equivalent with
respect to the amic acid unit, and (2) an initial temperature of
heating in the heating furnace is controlled to be no more than
+100.degree. C. of a temperature of the support and within a range
of 150.degree. C. to 250.degree. C.
13. The process as set forth in claim 12, wherein the gel film
contains a remaining volatile component within 15% to 150%.
14. The process as set forth in claim 13, wherein the polyamic acid
is obtained by polycondensation of monomers which contain a diamine
component and an acid dianhydride component as a raw material, and
the diamine component contains not less than 20 mole % of
paraphenylene diamine with respect to the entire diamine
component.
15. The process as set forth in claim 14, wherein the resulting
polyimide film has a film width of 1250 mm or greater, a molecular
orientation MOR-c of not more than 1.30 at any point of the film,
and a tensile modulus of not less than 2.5 GPa and not more than
5.0 GPa.
16. A polyimide film, having a film width of 1250 mm or greater, a
molecular orientation MOR-c of not more than 1.30 at any point of
the film, and a tensile modulus of not less than 2.5 GPa and not
more than 5.0 GPa.
17. A process for producing a polyimide film by deposition of a
polyamic acid containing composition by casting and/or coating,
said process comprising the step of: adding, to the polyamic acid
containing composition, a curing agent that contains not less than
1 mole equivalent of a dehydrating agent with respect to the
polyamic acid and not less than 0.2 mole equivalent of an imidizing
catalyst with respect to the polyamic acid, wherein the curing
agent is added in 30 parts by weight to 70 parts by weight with
respect to 100 parts by weight of the polyamic acid solution,
wherein the polyamic acid is obtained by polycondensation of
monomers which contain a diamine component and an acid dianhydride,
and the diamine component is a mixture of 4,4'-diaminodiphenylether
and p-phenylenediamine.
18. A process for producing a polyimide film by deposition of a
polyamic acid containing composition by casting and/or coating,
said process comprising the step of: adding, to the polyamic acid
containing composition, a curing agent that contains not less than
1 mole equivalent of a dehydrating agent with respect to the
polyamic acid and not less than 0.2 mole equivalent of an imidizing
catalyst with respect to the polyamic acid, wherein the curing
agent is added to an organic solvent solution of the polyamic acid
to obtain a resin solution composition whose viscosity at 0.degree.
C. is not more than 600 poise, wherein the polyamic acid is
obtained by polycondensation of monomers which contain a diamine
component and an acid dianhydride, and the diamine component is a
mixture of 4,4'-diaminodiphenylether and p-phenylenediamine.
19. A process for producing a polyimide film by deposition of a
polyamic acid containing composition by casting and/or coating,
said process comprising the step of: adding, to the polyamic acid
containing composition, a curing agent that contains not less than
1 mole equivalent of a dehydrating agent with respect to the
polyamic acid and not less than 0.2 mole equivalent of an imidizing
catalyst with respect to the polyamic acid, wherein the curing
agent is added in 30 parts by weight to 70 parts by weight with
respect to 100 parts by weight of the polyamic acid solution,
wherein the process includes the step of forming a gel film that
has been partially cured and/or partially dried to be
self-supporting in the casting and/or coating of the polyamic acid
containing composition on the support, and the gel film contains a
remaining volatile component within 10% to 80%.
20. A process for producing a polyimide film by deposition of a
polyamic acid containing composition by casting and/or coating,
said process comprising the step of: adding, to the polyamic acid
containing composition, a curing agent that contains not less than
1 mole equivalent of a dehydrating agent with respect to the
polyamic acid and not less than 0.2 mole equivalent of an imidizing
catalyst with respect to the polyamic acid, wherein the curing
agent is added to an organic solvent solution of the polyamic acid
to obtain a resin solution composition whose viscosity at 0.degree.
C. is not more than 600 poise, wherein the process includes the
step of forming a gel film that has been partially cured and/or
partially dried to be self-supporting in the casting and/or coating
of the polyamic acid containing composition on the support, and the
gel film contains a remaining volatile component within 10% to
80%.
21. The process as set forth in claim 3, further comprising the
steps of: subsequently drying an organic solvent solution of
polyamic acid on a support, so as to produce a gel film, which is a
partially cured and/or partially dried polyamic acid film; and
detaching a polyamic acid composition on the support with a
remaining volatile component, so that the gel film contains not
less than 50 parts by weight of an imidizing catalyst and not more
than 30 parts by weight of a solvent, and not more than 20 parts by
weight of a dehydrating agent, with respect to 100 parts by weight
of the remaining volatile component.
22. The process as set forth in claim 4, further comprising the
steps of: subsequently drying an organic solvent solution of
polyamic acid on a support, so as to produce a gel film, which is a
partially cured and/or partially dried polyamic acid film; and
detaching a polyamic acid composition on the support with a
remaining volatile component, so that the gel film contains not
less than 50 parts by weight of an imidizing catalyst and not more
than 30 parts by weight of a solvent, and not more than 20 parts by
weight of a dehydrating agent, with respect to 100 parts by weight
of the remaining volatile component.
23. The process as set forth in claim 5, further comprising the
steps of: subsequently drying an organic solvent solution of
polyamic acid on a support, so as to produce a gel film, which is a
partially cured and/or partially dried polyamic acid film; and
detaching a polyamic acid composition on the support with a
remaining volatile component, so that the gel film contains not
less than 50 parts by weight of an imidizing catalyst and not more
than 30 parts by weight of a solvent, and not more than 20 parts by
weight of a dehydrating agent, with respect to 100 parts by weight
of the remaining volatile component.
24. The process as set forth in claim 7, further comprising the
steps of: subsequently drying an organic solvent solution of
polyamic acid on a support, so as to produce a gel film, which is a
partially cured and/or partially dried polyamic acid film; and
detaching a polyamic acid composition on the support with a
remaining volatile component, so that the gel film contains not
less than 50 parts by weight of an imidizing catalyst and not more
than 30 parts by weight of a solvent, and not more than 20 parts by
weight of a dehydrating agent, with respect to 100 parts by weight
of the remaining volatile component.
Description
CROSS-REFERENCE TO THE RELATED APPLICATIONS
[0001] This is a divisional of application Ser. No. 11/674,620
filed Feb. 13, 2007, which is a continuation of application Ser.
No. 10/468,524 filed Aug. 18, 2003, which is a national phase of
international application No. PCT/JP2002/01727 filed Feb. 26, 2002,
the entire contents of which are incorporated by reference. This
application also claims benefit of priority under U.S.C. .sctn.119
to Japanese Patent Application No. 2001-052235 filed Feb. 27, 2001,
Japanese Patent Application No. 2001-086452 filed Mar. 23, 2001,
Japanese Patent Application No. 2001-099369 filed Mar. 30, 2001,
Japanese Patent Application No. 2001-165791 filed May 31, 2001,
Japanese Patent Application No. 2001-172893 filed Jun. 7, 2001,
Japanese Patent Application No. 2001-367440 filed Nov. 30, 2001 and
Japanese Patent Application No. 2002-038287 filed Feb. 15, 2002,
the entire contents of all of which are incorporated by
reference.
TECHNICAL FIELD
[0002] The present invention relates to high-quality polyimide
films and producing processes for suitably producing such polyimide
films.
[0003] The invention also relates to producing processes for
producing highly strong polyimide films with good productivity.
[0004] The invention also relates to polyimide films with
mechanical strengths and with small unevenness of mechanical
properties in a transverse direction, and producing processes of
such polyimide films.
[0005] The invention also relates to polyimide films with superior
in-plane isotropy and with improved dimensional stability, and
producing processes of such polyimide films.
[0006] The invention also relates to polyimide films with high
modulus and with low coefficient of thermal expansion, and
producing processes of such polyimide films.
BACKGROUND ART
[0007] Polyimide films are heat resistant, insulative, solvent
resistant, and low-temperature resistant, and it is for this reason
that polyimide films have been widely used as a material of
electronic and electrical components of computers and IC controls,
for example, such as flexible printed circuit boards, base films of
TAB carrier tapes, electronic cable coverings for air craft and the
like, base films of magnetic recording tapes, and wire rod
coverings for superconductive coils. Various types of polyimide
films are suitably selected depending on their use.
[0008] Therefore, there has been increasing demand for polyimide
films and there is a present need to develop a producing process
for producing polyimide films with higher productivity.
[0009] It has also become common over the last years to use
polyimide films in small general devices such as portable phones.
The smaller and thinner electronic and electrical components have
caused the wiring of the circuits to fine. This change in dimension
of parts used in these components may cause the circuit structure
of fine wiring to malfunction by wire breakage or shorting, etc.
Therefore, those parts used in such electronic and electrical
components are required to have highly accurate dimensional
stability.
[0010] Incidentally, a common producing process of a polyimide film
involves casting or coating an organic solvent solution of polyamic
acid, which is the precursor, onto a support, followed by
solidification and heat treatment. The polyimide film produced in
this manner and its producing process had the following
problems.
[0011] In the foregoing producing process, the process employs
either thermal curing or chemical curing. In the case of thermal
curing, a solvent is removed from the polyamic acid varnish, which
is the polyimide precursor, to form a polyamic acid film, and the
polyamic acid film is then converted to a polyimide film by
heating. However, in this process, when heating time is reduced,
the film fails to show sufficient levels of properties or the film
may crack. In chemical curing, a polyamic acid varnish is mixed
with a chemical imidizing agent to obtain a gel film, which is
cured and dried to obtain the product polyimide film. However, when
the polyamic acid film (gel film) which is partially cured and/or
partially dried is to be prepared in a shorter period of time to
improve productivity, the chemical imidization of the gel film
becomes insufficient and as a result basic mechanical strengths of
the product polyimide film, such as tear propagation strength,
tensile strength, and adhesion strength suffer.
[0012] Common procedures of producing the polyimide film proceed as
follows. As shown in FIG. 4, a polyamic acid solution composition,
which is the polyimide precursor, is mixed with a chemical
imidizing agent in an extruder 102. The mixture is spread in a
direction of width by the extruder 102 and continuously extruded
through a narrow slit opening of a slit die 104 onto an endless
belt, on which the mixture forms a flat thin film. The film is
imidized while it is dried and cooled to solidify to the extent
where the film becomes self-supporting. The film is then subjected
to a heat treatment.
[0013] Where the polyamic acid composition as the polyimide
precursor is used to form the polyimide film by casting using a T
die, which involves casting, heating, and drying of the film for
the completion of imidization, a sudden onset of the imidization
reaction in the process of casting may cause a resin film to
partially undergo imidization. This might cause gel defects on the
film or the problem of coating stripe which is caused by clogging
of the slit die by a partially imidized gel product. While these
problems can be effectively solved by controlling the imidization
reaction by cooling the polyamic acid solution composition to
0.degree. C. or below, it tends to increase the viscosity, in
particular, of the polyamic acid solution composition.
[0014] With such a viscosity range, i.e., with the use of a resin
solution composition with such a relatively high viscosity, the
resin solution composition becomes resilient. In this case, as
shown in FIG. 5, a curtain 122 of the fluidic resin solution
composition extruded from the slit die 120 is pulled in the machine
direction as the speed of the belt becomes faster. Pulling of the
curtain 122 in the machine direction makes the landing sheet angle
.theta. between the curtain 122 and the belt 124 of a reel smaller,
which may cause the curtain 122 to trap surrounding air when it
lands on a surface of the belt 124.
[0015] As a result, air is sealed between a surface of the resin
film 126 and the belt 124 to leave large and small bubbles of
protrusions on the surface of the resin film 126. This air trapping
phenomenon has a detrimental effect on the surface of the resin
film in the drying step of the resin film, as it causes the resin
film to thin or breaks and fluctuates the resin film by expansion
of the trapped air.
[0016] Further, the high viscosity curtain, because it is more
elastic than the curtain of a lower viscosity and has stronger
adhesion for the belt, is pulled in the machine direction by the
movement of the belt. The curtain pulled by the belt to move over a
certain distance in the machine direction is opposed by the force
of the opposite direction exerted by the elasticity of the resin
film. This opposing force periodically changes the landing site of
the curtain, which in turn changes the thickness of the product
resin film, with the result that the thickness periodically becomes
uneven in the machine direction. Such an uneven thickness appears
as a striped pattern on the product film.
[0017] As a counter-measure to this problem, Japanese Publication
for Unexamined Patent Application No. 198157/1999 (Tokukaihei
11-198157; published on Jul. 27, 1999) discloses a film producing
method by casting, in which the viscosity in a die is lowered to
prevent air trapping during casting of the resin film and to
improve uneven thickness. A lower viscosity in the die is attained
by lowering a degree of polymerization of the resin solution
composition or by increasing the solvent proportion of the resin
solution composition.
[0018] However, the mechanical properties of the polyimide film
obtained by the method of lowering the degree of polymerization as
disclosed in the foregoing publication 11-198157 are significantly
poorer than those of the polyimide film obtained from equimolar
amounts of diamine component and tetracarboxylic dianhydride
component. Further, in the method in which a solvent proportion of
the resin solution composition is increased as disclosed in the
foregoing publication 11-198157, the temperature of the belt needs
to be increased by a large margin to dry the film on the endless
belt until the film becomes self-supporting. As a result, the
product polyimide film has poor mechanical properties.
[0019] As described, in the film producing method by casting as
disclosed in the foregoing publication 11-198157 in which air
trapping during casting of the resin film is prevented to improve
evenness of the film, the mechanical properties of the product
polyimide film are considerably poor. Such poor mechanical
properties prevent stable production of flexible printed circuit
boards, base films of TAB carrier tapes, electronic cable coverings
of air craft and the like, base films of magnetic recording tapes,
and wire rod coverings for super conductive coils and the like,
because the film stretches to generate a slack during their
production. The products, as a result, have poor mechanical
resistance and poor reliability.
[0020] In the foregoing step of solidifying the film before the
heat treatment until the film becomes self-supporting, the heat
treatment often involves grasping end portions of the film using
clips or pins (known as a tenter frame method).
[0021] However, in this case, curing of the film cannot be carried
out evenly in the transverse direction, and particularly the end
portions cannot be cured sufficiently. This is because a grasping
jig such as clips or pins prevents a temperature increase at the
end portions of the film, or high temperatures of the heat
treatment in a heating furnace become uneven when the width of the
product polyimide film is wide. Attempts to compensate for the
insufficiently cured end portions have resulted in over curing of
the central portion, which degrades properties.
[0022] The tenter frame method, while it is a suitable conventional
technique to maintain or stretch the width of the gel film against
cure shrinkage of the gel film in the drying and curing step of the
heat treatment in the heating furnace, the held end portions and
the unheld central portion often shrink differently. Thus, for the
last many years, a solution has been sought for a phenomenon in
which the molecular chains of polyimide are oriented in an oblique
direction by a 45.degree. angle particularly at the end portions.
This anisotropy of molecular orientation is closely associated with
properties which relate to dimensional stability, and therefore
causes a direction-dependent difference of properties. Such a
molecular orientation therefore fails to meet the demand for a
material of a flexible printed circuit board and the like of ever
increasing precision.
[0023] Methods for obtaining isotropic films are disclosed in
Japanese Publication for Unexamined Patent Application Nos.
190314/1985 (Tokukaisho 60-190314; published on Sep. 27, 1985),
237928/1993 (Tokukaihei 5-237928; published on Sep. 17, 1993), and
81571/1996 (Tokukaihei 8-81571; published Mar. 26, 1996).
[0024] Commonly, a mother roll of the product film is suitably
provided with a slit of a predetermined width. It has also become
common to produce a wide film so that more products could be made
from a single mother roll to increase yield.
[0025] Dimensional stability is one property that is required for
electronic and electrical components. It is well-known that tensile
modulus, which is one of the important parameters of dimensional
stability, can be improved with use of monomers having a rigid
structure, namely, diamines with high linearity such as
paraphenylenediamine, for the diamine component. For example,
Japanese Publication for Unexamined Patent Application No.
13242/1989 (Tokukaisho 64-13242; published on Jan. 18, 1989)
discloses a three-component polyimide of pyromellitic anhydride,
4,4'-diaminodiphenylether, and paraphenylenediamine. However, a
large amount use of rigid and highly linear monomers causes too low
coefficient of thermal expansion to be applicable to the laminates
with a metal foil like a copper foil. Further, generally, the use
of rigid and highly monomers lowers flexibility of the film to
cause a problem in bendability which is one of the advantages of
the flexible printed circuit board. Further, in order to improve
tensile modulus, Japanese Publication for Unexamined Patent
Application No. 111359/1986 (Tokukaisho 61-111359; published on May
29, 1986) discloses a four-component polyimide which contains
3,3'-4,4'-biphenyltetracarboxylic dianhydride. However, this
technique poses the problem of productivity because it increases
the number of monomer components and complicates the polymerization
step of polyamic acid, which is the precursor of polyimide.
Further, since the technique uses a special type of monomer, it is
disadvantageous in terms of cost. Further, Japanese Publication for
Unexamined Patent Application No. 20238/1989 (Tokukaisho 64-20238;
published on Jan. 24, 1989) discloses improving properties by
stretching. However, this technique introduces a complex stretching
device in the production process and has a problem that, depending
on the type of polyimide, the film may be broken during the
stretching process.
DISCLOSURE OF INVENTION
[0026] In order to achieve the foregoing objects, a process for
producing a polyimide film according to the present invention
includes the steps of: casting or coating and subsequently drying
an organic solvent solution of polyamic acid on a support, so as to
produce a partially cured and/or partially dried polyamic acid
film; dipping the polyamic acid film in tertiary amine or in a
solution of tertiary amine, or applying tertiary amine or a
solution of tertiary amine onto the polyamic acid film; and drying
the film while imidizing the polyamic acid to polyimide.
[0027] A polyimide film according to the present invention may be
produced by any of the foregoing processes.
[0028] Further, in order to achieve the foregoing objects, another
process for producing a polyimide film includes the steps of:
mixing a chemical converting agent and a catalyst in a polyamic
acid organic solvent solution and casting the resulting polyamic
acid composition on a support; heating the polyamic acid
composition on the support at temperatures of at least two levels;
detaching the polyamic acid film from the support so as to obtain a
partially cured and/or partially dried polyamic acid film; and
imidizing remaining amic acid in the polyamic acid film and drying
the film.
[0029] A polyimide film according to the present invention may be
produced by the foregoing process.
[0030] Further, in order to achieve the foregoing objects, another
process for producing a polyimide film according to the present
invention includes the steps of: mixing a chemical converting agent
and a catalyst in a polyamic acid organic solvent solution and
casting and heating the mixture on a support; detaching the resin
film from the support with a remaining volatile component, so as to
obtain a partially cured and/or partially dried polyamic acid film
in which not less than 50 parts by weight is the catalyst, not more
than 30 parts by weight is the solvent, and not more than 20 parts
by weight is the chemical converting agent and/or a component
derived from the chemical converting agent, with respect to 100
parts by weight of the remaining volatile component; and imidizing
remaining amic acid and drying the film.
[0031] A polyimide film according to the present invention may be
produced by the foregoing process.
[0032] Further, in order to achieve the foregoing objects, a
process for producing a polyimide film according to the present
invention, which produces the polyimide film by casting and/or
coating a polyamic acid containing composition, includes the step
of adding, to an organic solvent solution of the polyamic acid, a
curing agent that contains a 1:0.15 to 1:0.75 mole ratio of not
less than 1 mole equivalent of a dehydrating agent with respect to
the amic acid and not less than 0.2 mole equivalent of an imidizing
catalyst with respect to the amic acid.
[0033] The producing process of a polyimide film according to the
present invention produces the polyimide film that is produced by
the foregoing process.
[0034] Further, in order to achieve the foregoing objects, in a
polyimide film according to the present invention, a width during
production is 1 m or greater, a ratio of maximum value to minimum
value of tear propagation strength measured across the entire width
is 0.7 or greater, and an R value of measured tear propagation
strength of not more than 0.6 g.
[0035] Further, the inventors of the present invention achieved
producing the polyimide film with superior in-plane isotoropy by
(I) preventing the shrinkage of the gel film on the support in the
process of casting the mixture of polyamic acid, dehydrating agent,
ring-closure catalyst, and organic solvents onto a rotating
support, and partially heating and/or partially drying the cast
mixture to a self-supporting film, (II) using the mixture of
dehydrating agent and the ring-closure catalyst in a specific
proportion to prevent the shrinkage of the gel film by suitable
adhesion between the gel film and the support, (III) heating the
gel film under specific temperature condition in the process of
removing the gel film with a controlled amount of volatiles from
the support and carrying the gel film, whose ends are restrained in
the transverse direction, to the heating furnace.
[0036] The present invention also provides a novel polyimide film
and novel producing processes of the following configurations to
achieve the foregoing objects.
[0037] 1) A polyimide film having a film width of 1250 mm or
greater, a degree of molecular orientation MOR-c of not more than
1.30 at any point of the film, and a tensile modulus of not less
than 2.5 GPa and not more than 5.0 GPa.
[0038] 2) A process for producing a polyimide film, which includes
the steps of: casting a mixture solution of polyamic acid,
dehydrating agent, ring-closure catalyst, and organic solvent on a
support so as to obtain a film ("gel film" hereinafter) that is
partially cured and/or partially dried to be self-supporting; and
passing the gel film through a heating furnace with both ends of
the gel film fastened, wherein
[0039] (1) the polyamic acid mixture solution is mixed with 1.0 to
5.0 equivalent of a dehydrating agent with respect to an amic acid
unit and 0.2 to 2.0 equivalent of a ring-closure catalyst with
respect to the amic acid unit, and
[0040] (2) an initial temperature of heating in the heating furnace
is controlled to be no more than +100.degree. C. of a temperature
of the support and within 150.degree. C. to 250.degree. C.
[0041] 3) A process of producing a polyimide film as defined in 2),
wherein the gel film contains the remaining volatile component in a
range of 15% to 150%.
[0042] 4) A process of producing a polyimide film as defined in 2)
or 3), wherein the polyamic acid is obtained by polycondensation of
monomers which contain a diamine component and an acid dianhydride,
and the diamine component contains not less than 20 mole % of
paraphenylenediamine with respect to the total diamine
component.
[0043] Further, in order to achieve the foregoing objects, a
process for producing a polyimide film according to the present
invention provides controlled modulus and coefficient of thermal
expansion of the polyimide film (1) by partially curing and/or
partially drying the polyamic acid until the content of volatile
component takes a specific value, and (2) by starting heating under
specific temperature conditions in the subsequent heat treatment in
the producing process of the self-supporting gel film which is
prepared by partially curing and/or partially drying the
precursor.
[0044] Further, in order to achieve the foregoing objects, a
process for producing a polyimide film according to the present
invention includes the steps of: casting a mixture solution of
polyamic acid, dehydrating agent, ring-closure catalyst, and
organic solvent on a support so as to obtain a film ("gel film"
hereinafter) that is partially cured and/or partially dried to be
self-supporting; and heating the gel film by tenter frame in which
a heat treatment is carried out on the gel film with restrained
both ends, wherein a content of remaining volatile component of the
gel film and an initial temperature of heating in the tenter frame
are controlled to control modulus and coefficient of thermal
expansion.
[0045] Further, a process for producing a polyimide film according
to the present invention includes the steps of: casting a mixture
solution of polyamic acid, dehydrating agent, ring-closure
catalyst, and organic solvent on a support so as to obtain a film
("gel film" hereinafter) that is partially cured and/or partially
dried to be self-supporting; and heating the gel film by tenter
frame in which heat treatment is carried out on the gel film with
restrained both ends, wherein a content of remaining volatile
component of the gel film and an initial temperature of heating in
the tenter frame are controlled to increase modulus within a range
of 1.0 GPa or to lower coefficient of thermal expansion within a
range of 4 ppm.
[0046] A polyimide film according to the present invention is
produced by the foregoing producing process of the polyimide film
to have a birefringence of not less than 0.15.
[0047] For a fuller understanding of other objects and the nature
and advantages of the invention, reference should be made to the
ensuing detailed description taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0048] FIG. 1 is a drawing showing how tear propagation strength R
is obtained.
[0049] FIG. 2 is a drawing showing a microwave transmission curve
and a principal axis of orientation, which are obtained by a
molecular orientation measurement instrument.
[0050] FIG. 3 is a conceptual view of measuring birefringence.
[0051] FIG. 4 is a drawing showing a producing process of a
polyimide film.
[0052] FIG. 5 is a drawing showing how a curtain is extruded from a
die lip in a casting method.
BEST MODE FOR CARRYING OUT THE INVENTION
[0053] Producing processes of polyimide films of the present
invention are in principle applicable to the production of any
polyimide films.
[0054] Note that, "parts" means percent by weight.
[0055] The polyamic acid, as used in the present invention, is the
precursor of polyimide, and, in principle, any known polyamic acid
can be used. The polyamic acid of the present invention can be
polymerized by any known methods. Particularly, the following
polymerization methods are preferable.
[0056] (1) A method in which aromatic diamine is dissolved in an
organic polar solvent and reacted therein with essentially an
equimolar amount of aromatic tetracarboxylic dianhydride for
polymerization.
[0057] (2) A method in which aromatic tetracarboxylic dianhydride
is reacted in excess mole with an aromatic diamine compound in an
organic polar solvent so as to obtain a pre-polymer having acid
anhydride groups at the both ends. Subsequent polymerization is
carried out using the aromatic diamine compound such that the
aromatic tetracarboxylic dianhydride becomes essentially equimolar
with the aromatic diamine compound in all steps of production.
[0058] (3) A method in which aromatic tetracarboxylic dianhydride
is reacted with excess mole of an aromatic diamine compound in an
organic polar solvent so as to obtain a pre-polymer having amino
groups at the both ends. Subsequent polymerization is carried out
by adding an aromatic diamine compound in the pre-polymer and using
the aromatic tetracarboxylic dianhydride so that the aromatic
tetracarboxylic dianhydride becomes essentially equimolar with the
aromatic diamine compound.
[0059] (4) A method in which aromatic tetracarboxylic dianhydride
is dissolved and/or dispersed in an organic polar solvent and is
polymerized using an aromatic diamine compound of an equimolar
amount.
[0060] (5) A method in which polymerization is carried out by a
reaction of a mixture of equimolar amounts of aromatic
tetracarboxylic acid dianhydride and an aromatic diamine compound
in an organic polar solvent.
[0061] The following describes materials used to produce the
precursor of polyimide, i.e., the polyamic acid of the present
invention.
[0062] Examples of acid anhydrides used to produce the polyamic
acid include: pyromellitic dianhydride; 2,3,6,7-naphthalene
tetracarboxylic dianhydride; 3,3',4,4'-biphenyl tetracarboxylic
dianhydride; 1,2,5,6-naphthalene tetracarboxylic dianhydride;
2,2',3,3'-biphenyl tetracarboxylic dianhydride;
3,3',4,4'-benzophenone tetracarboxylic dianhydride;
2,2-bis(3,4-dicarboxyphenyl)propane dianhydride; 3,4,9,10-perylene
tetracarboxylic dianhydride; bis(3,4-dicarboxyphenyl)propane
dianhydride; 1,1-bis(2,3-dicarboxypheyl)ethane dianhydride;
1,1-bis(3, 4-dicarboxyphenyl)ethane dianhydride;
bis(2,3-dicarboxyphenyl)methane dianhydride;
bis(3,4-dicarboxyphenyl)ethane dianhydride; oxydiphthalic
dianhydride; bis(3,4-dicarboxyphenyl)sulfone dianhydride;
p-phenylenebis(trimellitic acid monoester anhydride; ethylene
bis(trimellitic acid monoester anhydride; bisphenol A
bis(trimellitic acid monoester anhydride; and their analogues.
These compounds can be suitably used either individually or in a
mixture of any proportions.
[0063] Among these compounds, the acid dianhydrides that are most
suitable for the precursor of polyimide, i.e., the polyamic acid of
the present invention are pyromellitic dianhydride;
3,3',4,4'-benzophenone tetracarboxylic dianhydride;
3,3',4,4'-biphenyl tetracarboxylic dianhydride; p-phenylene
bis(trimellitic monoester anhydride. These compounds can be
suitably used either individually or in a mixture of any
proportions.
[0064] Examples of diamines that can be suitably used to produce
the precursor of polyimide, i.e., the polyamic acid of the present
invention, include: 4,4'-diaminophenylpropane;
4,4'-diaminophenylmethane; benzidine; 3,3'-dichlorobenzidine;
4,4'-diaminodiphenyl sulfide; 3,3'-diaminodiphenylsulfone;
4,4'-diaminodiphenylsulfone; 4,4'-diaminodiphenylether;
3,3'-diaminodiphenylether; 3,4'-diaminodiphenylether;
1,5-diaminonaphthalene; 4,4'-diaminodiphenyldiethylsilane;
4,4'-diaminodiphenylsilane; 4,4'-diaminodiphenyl ethylphosphine
oxide; 4,4'-diaminodiphenyl N-methylamine; 4,4'-diaminodiphenyl
N-phenylamine; 1,4-diaminobenzene(p-phenylenediamine);
1,3-diaminobenzene; 1,2-diaminobenzene, and their analogues. These
compounds can be suitably used either individually or in a mixture
of any proportions.
[0065] Among these diamines, 4,4'-diaminodiphenylether and
p-phenylenediamine are particularly preferable. Further, these
compounds can be suitably used in a mixture with a mole ratio of
100:0 to 0:100, or more preferably 100:0 to 10:90.
[0066] The solvents that can be suitably used for the synthesis of
the polyamic acid are amide-family solvents, examples of which
include N,N-dimethylformamide; N,N-dimethylacetoamide; and
N-methyl-2-pyrrolidone. Among these compounds, it is preferable to
use N,N-dimethylformamide and N,N-dimethylacetoamide either
individually or in a mixture of any proportions.
[0067] A polyamic acid solution is usually obtained in a
concentration of 5 wt % to 35 wt %, or more preferably 10 wt % to
30 wt %. With a concentration of polyamic acid solution in these
ranges, a suitable molecular weight and a suitable solution
viscosity can be obtained.
[0068] The polyimide is obtained by imidizing its precursor
polyamic acid, which is carried out either by thermal curing or
chemical curing. The thermal curing is a method in which the
imidization reaction proceeds only by heating, without any action
of a dehydrating agent or an imidizing catalyst, etc. The chemical
curing is a method in which an organic solvent solution of polyamic
acid is acted upon by a dehydrating agent as represented by acid
anhydrides such as acetic acid anhydride, and by an imidizing
catalyst as represented by tertiary amines such as isoquinoline,
.beta.-picoline, and pyridine. The chemical curing may be performed
with the thermal curing. Reaction conditions of imidization vary
depending on the type of polyamic acid, the thickness of the film,
or the selected method of curing, which may be thermal curing
and/or chemical curing.
[0069] Where imidization is carried out by chemical curing,
examples of dehydrating agents that are added to the polyamic acid
solution in the production of the polyimide film according to the
present invention include: aliphatic acid anhydrides; aromatic acid
anhydrides; N,N'-dialkylcarbodiimide; lower aliphatic halides;
halogenated lower aliphatic halides; haloganated lower aliphatic
anhydrides; arylphosphoric acid dihalides; thionyl halides; and a
mixture of two or more of these compounds. Among these compounds,
aliphatic anhydrides such as acetic acid anhydride, propionic
anhydride, lactic anhydride, and the like, or a mixture of two or
more of these compounds can be suitably used.
[0070] For effective imidization, it is preferable that the
dehydrating agent be used simultaneously with the imidizing
catalyst. The imidizing catalyst may be aliphatic tertiary amines,
aromatic tertiary amines, or heterocyclic tertiary amines, among
which compounds selected from heterocyclic tertiary amines are
particularly preferable. Specifically, quinoline, isoquinoline,
.beta.-picoline, pyridine, and the like can preferably be used.
[0071] In a producing process of the polyimide film of the present
invention, a step of producing a partially cured and/or partially
dried polyamic acid film (gel film) is carried out by a known
method. Namely, the organic solvent solution of polyamic acid
adjusted in the foregoing manner is cast or coated on a support
such as a glass plate, an endless stainless-steel belt, or a
stainless-steel drum, so as to carry out imidization by heating.
Alternatively, the dehydrating agent and the catalyst are mixed in
a polyamic acid solution at a low temperature and the polyamic acid
solution is cast in the form of a film on a support and heated to
activate the dehydrating agent and the imidizing catalyst. By this
thermal imidization or chemical imidization, a partially cured
self-supporting polyamic acid film (gel film) is produced. Note
that, as the term is used herein, "partially cured" or "partially
dried" means partial imidization of the amide bonds initially
present in the polyamic acid solution, or partial evaporation or
drying of a volatile component initially present in the initial
polyamic acid solution. These terms do not mean partial curing or
partial drying with respect to the entire surface of the film.
[0072] The gel film is in an intermediate stage of curing from the
polyamic acid to the polyimide and is self-supporting. A state of
the gel film can be expressed by the remaining content of the
volatile component and the percentage of imidization, which are
calculated as follows.
[0073] The remaining content of the volatile component is
calculated from
(A-B).times.100/B (1)
where A is the mass of the gel film, and B is the mass of the gel
film after it was heated at 450.degree. for 20 minutes.
[0074] The percentage of imidization is calculated by IR absorption
spectrometry from
(C/D).times.100/(E/F) (2)
where C is the height of the absorption peak of the gel film at
1370 cm.sup.-1, D is the height of the absorption peak of the gel
film at 1500 cm.sup.-1, E is the height of the absorption peak of
the polyimide film at 1370 cm.sup.-1, and F is the height of the
absorption peak of the polyimide film at 1500 cm.sup.-1.
[0075] Thereafter, the both ends in the transverse direction of the
gel film are grasped using pins or clips, etc., before the gel film
is carried to a heating furnace, where the gel film is dried to
remove a volatile component such as an organic solvent and then
subjected to a heat treatment to obtain the polyimide film.
[0076] The following describes one example of the producing process
of the polyimide film according to the present invention.
[0077] As the term is used herein, "curtain" refers to a particular
shape of the fluidic resin solution composition that was extruded
from the slit die in the form of a curtain, which exists in the air
gap before it lands on the belt.
[0078] A producing process of the polyimide film according to the
present invention is adapted to form the film by casting of a resin
solution composition which is prepared by adding to an organic
solvent of polyamic acid a curing agent that contains a 1:0.15 to
1:0.75 mole ratio of not less than 1 mole equivalent of a
dehydrating agent with respect to the amic acid and not less than
0.2 mole equivalent of an imidizing catalyst with respect to the
amic acid. With this process, it is possible to obtain the
polyimide film without decrease of mechanical properties, without
air trapping during the casting of the resin film, and with
improved thickness uniformity.
[0079] The gel film is prepared that is formed by mixing the
polyamic acid varnish and the curing agent of the foregoing process
and then continuously extruding the mixture in the form of a thin
flat curtain from the slit die so as to cast it on the endless
belt. The gel film is dried thereon and cooled to be
self-supporting and further heated to obtain the polyimide film
with desired mechanical properties.
[0080] The amount of dehydrating agent used is 1 mole to 5 mole
equivalent, preferably 1.2 mole to 4 mole equivalent, or more
preferably 1.5 mole to 3 mole equivalent with respect to the amic
acid. Outside these ranges, the percentage of imidization may fall
below its suitable range, or it may be hard to peel the gel film
from the support.
[0081] The amount of catalyst used is 0.2 mole equivalent to 1.5
mole equivalent, preferably 0.25 mole equivalent to 1.2 mole
equivalent, or more preferably 0.3 mole equivalent to 1 mole
equivalent with respect to the amic acid. Outside these ranges,
percent imidization may fall below its suitable range, or it may be
hard to peel the gel film from the support.
[0082] It is preferable that the dehydrating agent and the
imidizing catalyst be used in an amount in their foregoing
preferable ranges and at a mole ratio of 1:0.15 to 1:0.75, or
preferably 1:0.2 to 1:0.7. An amount of imidizing catalyst below
0.15 mole with respect to 1 mole of dehydrating agent prevents the
chemical imidization from being carried out sufficiently, which may
result in weaker strengths or difficulty in peeling from the
support. On the other hand, an amount of imidizing catalyst above
0.75 mole with respect to 1 mole of dehydrating catalyst often
increases the rate of curing, which may cause partial imidization
of the resin film to cause gel defects on the film, or may cause
coating stripes to occur when the slit die is clogged by the
partially imidized gel.
[0083] The curing agent should be added to 100 parts of the
polyamic acid solution in an amount of 30 parts to 80 parts,
preferably 35 parts to 75 parts, or more preferably 35 parts to 70
parts. When the amount of curing agent added is less than 30 parts,
the viscosity of the resin solution composition containing the
curing agent may be high, which often causes air trapping and
aggravates thickness unevenness. On the other hand, when the amount
of curing agent exceeds 80 parts, drying takes more time, which
means lower productivity, and the amount of solvent used is
increased, which means higher cost.
[0084] The viscosity of the resin solution composition containing
the curing agent, as given by a rotation viscosity measured by a
B-type viscometer at 0.degree. C., is preferably not more than 600
poise, or more preferably not more than 400 poise. When the
viscosity of the resin solution composition containing the curing
agent is greater than 600 poise, attempts to maintain a high level
of productivity often fails by aggravated thickness unevenness and
increased air trapping.
[0085] In another example of the producing process of the polyimide
film of the present invention, the polyamic acid film (gel film) is
immersed in tertiary amine or a solution of tertiary amine, or
alternatively tertiary amine or a solution of tertiary amine is
applied onto the polyamic acid film. That is, the process includes
the steps of:
[0086] casting or coating an organic solvent solution of polyamic
acid on a support and drying it to produce a partially cured and/or
partially dried polyamic acid film;
[0087] immersing the polyamic acid film in tertiary amine or a
solution of tertiary amine, or alternatively applying tertiary
amine or a solution of tertiary amine onto the polyamic acid film;
and
[0088] converting the polyamic acid into polyimide by imidization
and drying the film.
[0089] Imidization of the polyamic acid may be carried out by
chemical curing also in this process. In this case, the amount of
dehydrating agent is 0.5 to 5 times, preferably 1 to 4 times, or
more preferably 1.5 to 3 times the amount in mole of the amic acid
in the polyamic acid solution.
[0090] The amount of imidizing catalyst is 0.1 to 2 times, or more
preferably 0.2 to 1 times the amount in mole of the amic acid in
the polyamic acid solution. When the amount of imidizing catalyst
is too low, the percentage of imidization may fall below its
suitable range. On the other hand, when the amount of imidizing
catalyst is too high, the curing rate is increased, which makes it
difficult to carry out casting on the support.
[0091] The content of remaining volatile component in the gel film
is in the range of 5% to 500%, preferably 5% to 100%, more
preferably 10% to 80%, and most preferably 30% to 60%. It is
preferable that the film satisfy these ranges; otherwise, the film
may fail to exhibit its predetermined effects. The percentage of
imidization of the gel film is not less than 50%, preferably not
less than 80%, more preferably not less than 85%, and most
preferably not less than 90%. It is preferable that the film
satisfy these ranges; otherwise, the film may fail to exhibit its
predetermined effects.
[0092] With the producing process of the polyimide film of the
present invention, when the content of remaining volatile component
and the percentage of imidization of the gel film are in the
foregoing ranges, the time for preparing the gel film can be
reduced by 10% to 70%, or 20% to 70% of that of conventional gel
films.
[0093] The partially cured and/or partially dried polyamic acid
film obtained by thermal curing or chemical curing is fed to a step
in which the partially cured and/or partially dried polyamic acid
film is coated with or immersed in tertiary amine or a solution of
tertiary amine.
[0094] Examples of tertiary amines that are used to coat or immerse
the partially cured and/or partially dried polyamic acid film (gel
film) include aliphatic tertiary amines, aromatic tertiary amines,
and heterocyclic tertiary amines, among which those selected from
the heterocyclic tertiary amines are particularly preferable.
Specifically, quinoline, isoquinoline, .beta.-picoline, pyridine,
and the like are preferable. These tertiary amines may be used
individually or in a mixture of two or more kinds. Further, the
tertiary amines may be used as the organic solvent solution, in
which case the tertiary amines may be diluted with any solvent. The
solvents are preferably amide-family solvents such as
N,N-dimethylformamide, N,N-dimethylacetoamide,
N-methyl-2-pyrrolidone, among which N,N-dimethylformamide and
N,N-dimethylacetoamide can be preferably used either individually
or in a mixture of any proportions. The solution may be diluted to
any concentration but the solution should preferably be adjusted to
have a concentration of tertiary amine in the range of 100 wt % to
5 wt %. A solution of an excessively weak concentration fails to
achieve an object of the present invention satisfactorily, i.e., to
prevent decrease of strengths.
[0095] The method by which the gel film is coated with tertiary
amine or a solution of tertiary amine may be of any conventional
methods known to a person skilled in the art. For example, methods
using a gravure coat, a spray coat, or a knife coater can be used,
among which a gravure coater can be preferably used in view of ease
of control of the amount of tertiary amine or a solution of
tertiary amine used to coat the gel film, or evenness of coating.
The amount of coating is preferably 1 g/m.sup.2 to 40 g/m.sup.2, or
more preferably 5 g/m.sup.2 to 30 g/m.sup.2. With an amount below
these ranges, it becomes difficult to prevent decrease of
strengths. Above these ranges, appearance of the film becomes
poor.
[0096] The method by which the gel film is immersed in tertiary
amine or a solution of tertiary amine is not particularly limited
and a common dip coating method is applicable. Specifically, the
gel film is immersed in the solution in a tank either continuously
or in a batch. The immerse time ranges from 1 to 100 seconds, or
preferably 1 to 20 seconds. An immerse time longer than this range
results in poor appearance of the film and below this range brings
about difficulty in preventing decrease of strengths.
[0097] It is preferable that the gel film coated with or immersed
in tertiary amine or a solution of tertiary amine is subjected to a
step of removing unnecessary droplets on a film surface. In this
way, a polyimide film with superior appearance and with no
disturbance on a film surface can be obtained. The droplets can be
removed by conventionally known methods, including squeezing by a
nip roll, an air knife method, a doctor blade method, wiping, and
sucking, among which the nip roll method is preferable in view of
film appearance, ease of wiping, and workability, etc.
[0098] The gel film coated with or immersed in tertiary amine or a
solution of tertiary amine is subjected to a heating step with its
end portions fastened to avoid shrinkage during thermal treatment.
The polyimide film is obtained by removing the moisture, residual
solvent, residual converting agent and the catalyst in the gel
film, and then by completing imidization of remaining amic acid.
Preferably, the temperature conditions of the drying step are such
that the final temperature reaches 500.degree. C. to 580.degree. C.
and heating is carried out in this temperature range for 1 to 400
seconds. Heating at a higher temperature and/or for a longer period
of time causes heat decomposition of the film. On the other hand,
heating at a lower temperature and/or for a shorter period of time
fails to exhibit predetermined effects.
[0099] With the producing process of the polyimide film of the
present invention, the polyimide film can be obtained without
decrease of mechanical strengths even when the gel film is prepared
in a shorter period of time. The shorter time to prepare the gel
film improves productivity and prevents decrease of tear
propagation strength and adhesion strength. As a result, the
polyimide film with improved tensile strength can be obtained.
[0100] The polyimide film according to the present invention can be
suitably used in flexible printed substrates, magnetic tapes and
magnetic disks for general magnetic recording, and passivation
films of semiconductor elements of solar cells and the like.
[0101] The following describes yet another example of the producing
process of the polyimide film of the present invention.
[0102] In this example, the gel film is peeled from the support
while controlling the remaining volatile component, and the film is
subsequently imidized.
[0103] That is, the producing process of the polyimide film of the
present invention has the following sequence. The dehydrating agent
and imidizing catalyst are mixed in an organic solvent solution of
polyamic acid. The mixture is then cast on a support and heated to
peel a polyamic acid film from the support while leaving a volatile
component in the film. The polyamic acid film is partially cured
and/or partially dried so that it contains 50 parts by weight or
more of catalyst, 30 parts by weight or less of solvent, and 20
parts by weight or less of dehydrating agent and/or dehydrating
agent derived component, with respect to 100 parts by weight of the
remaining volatile component. Thereafter, a remaining portion of
the amic acid is imidized and the film is dried.
[0104] The amount of dehydrating agent added with respect to the
polyamic acid solution is suitably selected, taking into
consideration concentration of the polyamic acid in the solution or
density of amic acid bonding sites in the polyamic acid molecules.
For example, in an 18.5 wt % polyamic acid containing pyromellitic
anhydride and 4,4'-diaminodiphenylether, the dehydrating agent is
used in a proportion of 1 part to 80 parts, preferably 5 parts to
70 parts, and more preferably 10 parts to 50 parts with respect to
100 parts of the polyamic acid solution. When the amount of
dehydrating agent is excessive, a mixing failure is likely to
occur, and when deficient the rate of chemical imidization (curing)
tends to be slow.
[0105] The amount of imidizing catalyst added with respect to the
polyamic acid solution is suitably selected, taking into
consideration concentration of the polyamic acid in the solution or
density of amic acid bonding sites in the polyamic acid molecules.
For example, in an 18.5 wt % polyamic acid containing pyromellitic
anhydride and 4,4'-diaminodiphenylether, the dehydrating agent is
used in a proportion of 0.1 to 30 parts, preferably 0.5 to 20
parts, and more preferably 1 to 15 parts with respect to 100 parts
of the polyamic acid solution. When the amount of imidizing
catalyst is deficient, the chemical imidization (curing) becomes
sluggish, and when excessive the rate of chemical imidization
(curing) is increased and casting on the support becomes
difficult.
[0106] The dehydrating agent and the imidizing catalyst are mixed
at a low temperature in the polyamic acid solution, and the mixture
of the polyamic acid solution is cast in the form of a film on the
support such as a glass plate, an aluminum foil, an endless
stainless-steel belt, or a stainless-steel drum. The film on the
support is heated in a temperature range of 80.degree. C. to
200.degree. C., or preferably 100.degree. C. to 180.degree. C. so
as to activate the dehydrating agent and the catalyst and peel the
partially cured and/or partially dried film from the support and
thereby obtain the gel film.
[0107] The content of remaining volatile component is in the range
of from 5 wt % to 500 wt %, preferably 10 wt % to 200 wt %, more
preferably 10 wt % to 80 wt %, or most preferably 30 wt % to 60 wt
%. It is preferable that the film satisfies these ranges. In
practice, the film is preferably produced with the content of
remaining volatile component not more than 100 wt %. With a content
outside of this range, predetermined effects may not be
obtained.
[0108] The gel film is heated under such heating conditions that
the gel film contains the catalyst in an amount of 50 wt % or
greater, preferably 60 wt % or greater, and more preferably 70 wt %
or greater, and contains a remaining chief solvent in an amount of
30 wt % or less, preferably 25 wt % or less, and more preferably 20
wt % or less, and contains the dehydrating agent and/or the
dehydrating derived component in an amount of 20 wt % or less,
preferably 15 wt % or less, and more preferably 10 wt % or less,
all with respect to 100 wt % of the total remaining volatile
component in the gel film (disregarding water content), as
quantified by gas chromatography, after extracting the catalyst
from the gel film in N-methyl-2-pyrolidone for 48 hours with
concussion. Specific examples of heating conditions include a
change in weight ratio of the chief solvent and the catalyst, a
change of drying temperature, a change in volume of hot air, a
change in wind speed of hot air, a change of heating time, and a
change in temperature of the support. These conditions vary
depending on such factors as the boiling points of the catalyst and
the chief solvent, the amount of catalyst added, the thickness of
the film, the type of polyamic acid, and the production rate.
[0109] When the content of the catalyst, solvent, and dehydrating
agent and/or dehydrating agent component fall out of the foregoing
ranges, it becomes difficult to achieve objects of the present
invention, i.e., to improve productivity and to prevent decrease of
strengths at the same time.
[0110] By heating the gel film with its end portions fastened and
by completely imidizing the amic acid, the producing process of the
present invention can produce the polyimide film with improved
productivity and without decrease of tear propagation strength,
adhesion strength, and tensile strength.
[0111] Here, it is preferable that the final temperature and time
of heating be 500.degree. C. to 580.degree. C. and for 15 to 400
seconds. A higher temperature and/or a longer time cause heat
decomposition, which may lead to problems. Conversely, with a lower
temperature and/or a shorter time, it becomes difficult to obtain
predetermined effects.
[0112] It is desirable that heating temperatures and heating times
in all stages of heating in the present producing process be so
adjusted that the percentage of weight loss by heating of the
polyimide film, which is determined from
(The percentage of weight loss by heating)=(X-Y)/Y (3)
where X is the mass of the film after 10 minute heating at
150.degree. C., and Y is the mass of the film after 20 minute
heating at 450.degree. C., is 0.2 wt % to 2.5 wt %, preferably 0.3
wt % to 2.0 wt %, more preferably 0.3 wt % to 1.5 wt %, and most
preferably 0.5 wt % to 1.5 wt %. It is also desirable that, with
respect to the total weight of the film, the catalyst makes up 0.01
wt % or greater, preferably 0.05 wt % or greater, or more
preferably 0.1 wt % or greater of the percentage of weight loss by
heating. When the percentage of weight loss by heating and the
content of the lost weight by heating fall outside of the foregoing
ranges, predetermined effects may not be obtained.
[0113] The lost weight by heating is measured as follows. The film
is wrapped with a tared aluminum foil and heated at 150.degree. C.
for 10 minutes. Out of the oven after 10 minutes, the film is
immediately transferred to a descicater. After cooling for 2
minutes, the weight of the film including the aluminum foil is
measured and the tare in the aluminum foil is subtracted to give
initial weight X. After measuring initial weight X, the film is
heated again at 450.degree. C. for 20 minutes. Out of the oven
after 20 minutes, the film is immediately transferred to a
descicater. After cooling for 2 minutes, the weight of the film
including the aluminum foil is measured and the tare in the
aluminum foil is subtracted to give weight Y after heating. The
film is highly moisture absorptive and the operations of the
measurement must be carried out quickly.
[0114] The following describes still another example of the
producing process of the polyimide film of the present invention.
The producing process includes a step of casting a polyamic acid
composition on a support and continuously heating the polyamic acid
composition on the support at at least two levels of
temperatures.
[0115] That is, the producing process of the polyimide film
according to the present invention has the following sequence. The
dehydrating agent and the imidizing catalyst are mixed in an
organic solvent solution of polyamic acid. The resulting polyamic
acid composition is then cast on the support and heated on the
support at temperatures of two or more levels. Then, the film is
detached from the support to obtain a partially cured and/or
partially dried polyamic acid film. Finally, remaining amic acid is
imidized and the film is dried.
[0116] The amount of dehydrating agent is 1 to 80 parts, preferably
5 to 70 parts, and more preferably 10 to 50 parts, with respect to
100 parts of the polyamic acid solution. When the amount of
dehydrating agent is too low, the percentage of imidization may
fall below the preferable range. On the other hand, when the amount
of imidizing catalyst is too high, the curing rate becomes faster,
which makes it difficult to carry out casting on the support.
[0117] The amount of imidizing catalyst is 0.1 to 30 parts,
preferably 0.5 to 20 parts, and more preferably 1 to 15 parts, with
respect to 100 parts of the polyamic acid solution. When the amount
of imidizing catalyst is too low, percent imidization may fall
below the preferable range. On the other hand, when the amount of
imidizing catalyst is too high, the curing rate becomes faster,
which makes it difficult to carry out casting on the support.
[0118] The dehydrating agent and the imidizing catalyst are mixed
at a low temperature in the polyamic acid solution, and the mixture
of the polyamic acid solution is cast in the form of a film on the
support such as a glass plate, an aluminum foil, an endless
stainless-steel belt, or a stainless-steel drum. The film on the
support is heated stepwise at temperatures of at least two levels
in a temperature range of 80.degree. C. to 200.degree. C., or
preferably 100.degree. C. to 180.degree. C. so as to activate the
dehydrating agent and the catalyst and detach the partially cured
and/or partially dried film from the support and thereby obtain the
gel film.
[0119] The content of remaining volatile component is in the range
of from 5 wt % to 500 wt %, preferably 5 wt % to 100 wt %, more
preferably 10 wt % to 80 wt %, or most preferably 30 wt % to 60 wt
%. It is preferable that the film satisfies these ranges. With the
content outside of these ranges, predetermined effects may not be
obtained.
[0120] In the stepwise heating at temperatures of at least two
levels, it is preferable that the first heating be carried out at a
temperature of 80.degree. C. to 160.degree. C., or more preferably
100.degree. C. to 140.degree. C. Here, when temperature T1 of the
first heating is too low, the content of volatile component in the
gel film tends to be high, whereas when too high the rate of
volatilization of the dehydrating agent and the catalyst becomes
faster and the chemical imidization becomes sluggish.
[0121] Further, in the stepwise heating at temperatures of at least
two levels, it is preferable that the last heating be carried out
at a temperature of 120.degree. C. to 200.degree. C., or more
preferably 140.degree. C. to 180.degree. C. Here, when the
temperature T2 is too low, the content of volatile component in the
gel film tends to be high. Controlling the content of volatile
component in the gel film within a suitable range requires a longer
heating time. That is, productivity suffers. On the other hand,
when temperature T2 is too high, the content of volatile component
in the gel film tends to fall below the suitable range and
predetermined effects may not be obtained.
[0122] When the stepwise heating is to be carried out at
temperatures of three or more levels, intermediary heating other
than the first and last heating should preferably be carried out at
80.degree. C. to 200.degree. C., or preferably 100.degree. C. to
180.degree. C.
[0123] Further, in the stepwise heating at temperatures of at least
two levels, it is required in an early stage of heating to activate
the dehydrating agent and the catalyst to allow curing while
suppressing volatilization of the dehydrating agent and the
catalyst, while drying needs to be promoted in a late stage of
heating. It is therefore preferable that the heating temperature be
increased as the heating stage proceeds.
[0124] A range of temperature fluctuations of temperature T1 in the
first stage should preferably be within -10.degree. C. to
+10.degree. C., or more preferably -5.degree. C. to +5.degree. C.
Similarly, a range of temperature fluctuations of temperature T2 in
the last stage should preferably be within -10.degree. C. to
+10.degree. C., or more preferably -5.degree. C. to +5.degree. C. A
similar range of temperature fluctuations is optionally employed at
heating temperatures of the third and subsequent stages.
[0125] For a shorter production time, a transition of heating from
temperature T1 to temperature T2 should be completed in a short
period of time.
[0126] By heating the gel film with its end portions fastened to
avoid shrinkage, followed by removal of water, the remaining
solvent, and the residual converting agent and the catalyst, and
finally by completely imidizing the amic acid, the producing
process of the present invention can produce the polyimide film
with improved productivity and without decrease of tear propagation
strength, adhesion strength, and tensile strength.
[0127] Here, it is preferable that the final temperature and time
of heating be 500.degree. C. to 580.degree. C. and for 5 to 400
seconds. A higher temperature and/or a longer time cause heat
decomposition, which may lead to problems. Conversely, with a lower
temperature and a shorter time, it becomes difficult to obtain
predetermined effects.
[0128] It is desirable that heating temperatures and heating times
in all stages of heating in the present producing process be so
adjusted that percent weight loss by heating of the polyimide film,
which is determined from the foregoing equation (3), is 0.2 wt % to
2.5 wt %, preferably 0.3 wt % to 2.0 wt %, more preferably 0.3 wt %
to 1.5 wt %, and most preferably 0.5 wt % to 1.5 wt %. It is also
desirable that, with respect to the total weight of the film, the
catalyst makes up 0.01 wt % or greater, preferably 0.05 wt % or
greater, or more preferably 0.1 wt % or greater of the percent
weight loss by heating. When the percent weight loss by heating and
the content of the lost weight by heating fall outside of the
foregoing ranges, predetermined effects may not be obtained.
[0129] Further, the polyimide film of the present invention has a
width of not less than 1 m during production, wherein a ratio of
maximum value to minimum value of tear propagation strength
measured across the entire width is 0.7 or greater, and an R value,
which is obtained when measuring the tear propagation strength of
an outermost portion, is 0.6 g or smaller. That is, curing of the
outermost portion is sufficient and unevenness of curing from the
central portion is small.
[0130] Here, the ratio of maximum value to minimum value of tear
propagation strength is preferably 0.7 or greater, more preferably
0.75 or greater, or even more preferably 0.80 or greater. The
optimum curing temperature, which varies depending on the type of
polyimide, is suitably set. The tear propagation strength generally
becomes larger when curing is insufficient and becomes smaller when
there is over-curing. Thus, where a ratio of maximum value to
minimum value of tear propagation strength is below 0.7, physical
properties in one location of the film in the transverse direction
often become profoundly different from physical properties in
another location of the film in the transverse direction. The ratio
of maximum value to minimum value of tear propagation strength
measured across the entire width is a value that is obtained by
calculating (minimum value)/(maximum value) of tear propagation
strength that was measured according to ASTM D-1938 on samples
collected in the transverse direction of the film at 10 cm
intervals.
[0131] It is preferable that the R value when measuring tear
propagation strength of the outermost portion is 0.6 g or less,
preferably 0.4 g or less, and more preferably 0.3 g or less. An R
value above 0.6 g often results in extreme under-curing or extreme
over-curing. The R value when measuring tear propagation strength
of the outermost portion is the difference between a measured
maximum value and a measured minimum value of a sample of 2.5 cm
(width).times.7.5 cm, which is collected out of the film, using a
reference point 10 mm inside the fastened point of the film where
pins or clips are used.
[0132] The polyimide film of the present invention is obtained, for
example, by a process of casting a resin solution which is prepared
by addition of a curing agent containing 1.0 to 3.0 mole equivalent
of dehydrating agent and not less than 0.3 mole equivalent of
imidizing catalyst with respect to the amic acid in an organic
solvent solution of polyamic acid.
[0133] The dehydrating agent is used in 1.0 to 3.0 mole equivalent,
or preferably 1.5 to 2.5 mole equivalent with respect to the amic
acid, and the imidizing catalyst is used in a not less than 0.3
mole equivalent, or more preferably not less than 0.4 mole
equivalent with respect to the amic acid. When the amount of
dehydrating agent falls outside of the preferable ranges, the
properties of the polyimide film may decrease. When the amount of
imidizing catalyst is too low, the chemical imidization becomes
insufficient and the properties of the polyimide film often
decrease.
[0134] The polyimide film is prepared as a gel film that is formed
by mixing the polyamic acid varnish and the curing agent of the
foregoing process and then continuously extruding the mixture in
the form of a thin flat curtain from the slit die so as to cast it
on a support such as a stainless-steel drum or an endless belt. The
gel film is heated on the support in the temperature range of from
80.degree. C. to 200.degree. C., or preferably 100.degree. C. to
180.degree. C., so as to activate the dehydrating agent and the
imidizing catalyst. The resulting gel film, partially cured and/or
partially dried, is detached from the support.
[0135] The content of volatile component of the gel film is 5% to
500%, preferably 5% to 100%, more preferably 10% to 80%, and most
preferably 30% to 60%. The film preferably should satisfy these
ranges; otherwise the film may fail to exhibit superior mechanical
strengths.
[0136] By heating the gel film with its end portions fastened to
avoid shrinkage, followed by removal of water, the remaining
solvent, and the residual converting agent and the catalyst, and
finally by completely imidizing the amic acid, the producing
process of the present invention can produce the polyimide film
with small unevenness of mechanical properties across the entire
width.
[0137] Here, it is preferable that the final temperature and time
of heating be 500.degree. C. to 580.degree. C. and for 5 to 400
seconds. A higher temperature and/or a longer time often cause heat
decomposition, which may result in uneven curing in the transverse
direction.
[0138] The following describes another example of the polyimide
film of the present invention.
[0139] The polyimide film of the present invention is produced with
a film width of not less than 1250 mm, wherein the molecular
orientation MOR-c is 1.30 or less at any point of the film, and the
tensile modulus is not less than 2.5 GPa and not more than 5.0
GPa.
[0140] Such a polyimide film is produced, for example, by a process
in which a polyamic acid mixed solution containing polyamic acid, a
dehydrating agent, an imidizing catalyst, and an organic solvent is
cast on a support to form a film that is partially cured and/or
partially dried until it becomes self-supporting, and the gel film,
with its both ends fastened, is passed a heating furnace,
wherein
[0141] (1) the polyamic acid mixture solution is a mixture of
dehydrating agent, 1.0 to 5.0 equivalent, and imidizing catalyst,
0.2 to 2.0 equivalent, with respect to the amic acid unit, and
[0142] (2) the initial heating temperature in the heating furnace
is controlled to be no more than +100.degree. C. of a temperature
of the support and within 150.degree. C. to 250.degree. C.
[0143] In order to minimize shrinkage of the film during heating
and/or partially drying of the film on the support, the amount of
dehydrating agent should be adjusted to preferably 1.0 to 5.0
equivalent, more preferably 2.0 to 4.0 equivalent, and most
preferably 1.5 to 3.0 equivalent, with respect to the amic acid
unit of the polyamic acid. Outside these ranges, a film with good
isotropy may not be obtained. Below 1.0, imidization becomes
insufficient and the gel film with sufficient strengths cannot be
obtained. In addition, it becomes difficult to remove the gel film
from the support. Above 5.0, the rate of imidization of polyamic
acid becomes faster and proper adhesion of the gel film with the
support cannot be obtained, causing the gel film to shrink on the
support.
[0144] The amount of imidizing catalyst added should be adjusted to
preferably 0.1 to 2.0 equivalent, more preferably 0.3 to 1.5
equivalent, and most preferably 0.5 to 1.0 equivalent, with respect
to the amic acid unit of the polyamic acid.
[0145] When the amount of imidizing catalyst exceeds 2.0, the rate
of imidization of polyamic acid becomes faster and partial
imidization occurs on the support or in the mixing process with the
polyamic acid, causing gel defects on the film. In other cases, the
slit die is clogged with the defect gel to cause stripe defects.
Below 0.1, curing and/or drying on the support often become
insufficient and mechanical properties suffer.
[0146] The polyamic acid mixed solution containing a mixture of
dehydrating agent and imidizing catalyst in the suitable range is
cast in the form of a film through the slit die on the support such
as a rotary metal drum or an endless belt. The film is partially
cured and/or partially dried on the support by heating to obtain a
self-supporting gel film. The polyamic acid mixed solution cast on
the support may be heated by hot air or by the heat of far IR
radiation. Alternatively, the support itself may be heated.
Further, the method employing hot air or far IR radiation and the
method of heating the support itself may be carried out
together.
[0147] Percent imidization is not less than 50%, preferably not
less than 80%, or most preferably not less than 90%. It is
preferable that "partial imidization" falls in these ranges.
Outside these ranges, predetermined effects may not be
obtained.
[0148] The content of remaining volatile component is in the range
of 15% to 300%, preferably 15% to 150%, more preferably 30% to 80%,
and most preferably 30% to 60%. It is preferable that the content
of remaining volatile component of the gel film falls in these
ranges. Heating the gel film on the support below these ranges not
only imidizes and dries the film but promotes heat decomposition,
with the result that sufficient strengths may not be obtained for
the polyimide film. Above these ranges, the film may be broken in a
later heating step and productivity suffers.
[0149] The gel film, with its both ends fastened with pins or
clips, is transported to a heating furnace, where the gel film is
dried to remove the volatile component of the organic solvent,
etc., and then subjected to a heat treatment to obtain the
polyimide film. The heating furnace may be adapted to continuously
apply heat in response to transport of the film, or apply heat
stepwise. The two structures are essentially the same, and it is
preferable in either case that the initial heating temperature is
not more than an ambient temperature +100.degree. C. of a
temperature of the support, or more preferably an ambient
temperature +80.degree. C. of a temperature of the support. It is
also important that the ambient temperature be controlled within
the range of 150.degree. C. to 250.degree. C., or more preferably
180.degree. C. to 200.degree. C. When the temperature difference
between the support and the heating furnace falls outside these
ranges, the film with desirable isotropy may not be obtained.
Further, when the initial heating temperature falls outside the
foregoing ranges, the volatile component contained in the gel film
may boil to cause bubble defects on a film surface, in which case
smoothness of the film may be lost.
[0150] The final step of the producing process of the polyimide
film of the present invention is the heating step of 450.degree. C.
to 580.degree. C. for 15 to 400 seconds, or preferably 500.degree.
C. to 580.degree. C. for 15 to 400 seconds.
[0151] The film of the present invention with a 1250 mm or greater
thickness is produced with this thickness through the heating
furnace. Thus, the present invention is particularly effective in a
producing step of producing a film of such a wide width. The
product film may be cut into a predetermined width.
[0152] The isotropic polyimide film so produced has small
anisotropy of molecular orientation at any point of the film in the
direction of width. That is, by a molecular orientation MOR-c of
not more than 1.3, or preferably not more than 1.2 at any point of
the film in the transverse direction, it is possible to minimize
changes in properties of the film, such as modulus, tensile
strength, and coefficient of thermal expansion, which vary
depending on the direction of measurement. That is, the polyimide
film can be suitably applied to those materials for which
particularly high dimensional stability is needed, for example,
such as flexible printed circuit boards on which a metal foil or a
metal thin film is laminated, TAB carrier tapes, or cover lay films
for flexible printed circuit boards.
[0153] The following describes another example of the polyimide
film of the present invention.
[0154] The polyamic acid used in the present invention is usually
produced by dissolving essentially equimolar amounts of at least
one kind of aromatic acid dianhydrides and at least one kind of
aromatic diamines in an organic solvent, and by stirring the
resultant polyamic acid organic solvent solution under controlled
temperature conditions until polymerization of the acid
dianhydrides and diamines proceeds to completion. The polyamic acid
solution is usually used in a concentration of 15 wt % to 25 wt %.
With a concentration in this range, a suitable molecular weight and
a suitable solution viscosity can be obtained.
[0155] The imidization in the present invention can be suitably
carried out by chemical curing.
[0156] In this example, 4,4'-diaminodiphenylether and
p-phenylenediamine should preferably be used in combination as the
diamine. Particularly, in order to improve modulus and realize low
coefficient of thermal expansion that compares to that of metals,
the proportion of p-phenylenediamine component with respect to the
diamine should preferably be not less than 20 mole % and not more
than 65 mole %, or more preferably not less than 25 mole % and not
more than 50 mole %. Below this range, the effects of the present
invention may not be obtained. Above this range, the coefficient of
thermal expansion often becomes too low to be used in such flexible
printed circuit boards in which the metal layer is laminated either
directly or via an adhesive agent.
[0157] In this example, the proportion of dehydrating agent is 1 to
80 parts, preferably 5 to 70 parts, or more preferably 10 to 50
parts, with respect to 100 parts of polyamic acid organic solvent
solution.
[0158] In this example, the proportion of imidizing catalyst is 0.1
to 30 parts, preferably 0.5 to 20 parts, or more preferably 1 to 15
parts, with respect to 100 parts of polyamic acid organic solution.
When the proportion of imidizing agent is too low, percent
imidization may fall below its suitable ranges. When too high, the
curing rate increases and it becomes difficult to carry out casting
on the support.
[0159] In this example, percent imidization as given by the
foregoing equation (2) is not less than 50%, preferably not less
than 70%, or more preferably not less than 80%. The "partial
imidization" should preferably be percent imidization in these
ranges. Below these ranges, it becomes difficult to remove the gel
film from the support or the ease of self-supporting may
suffer.
[0160] Further, in this example, the content of remaining volatile
component in the gel film as given by the foregoing equation (1) is
in the range of from 50% to 300%, preferably 80% to 250%, or more
preferably 100% to 200%. It is preferable that the film satisfies
these ranges. With a gel film whose content of remaining volatile
component exceeds these ranges, the gel film may not become
self-supporting sufficiently, or may be stretched or broken during
transport to the heating furnace, with the result that production
becomes unstable. With a gel film whose content of remaining
volatile component falls below the foregoing ranges, predetermined
effects may not be obtained.
[0161] The gel film is subsequently heated to remove (dry) the
remaining solvent and to finish curing (imidization). Here, in
order to avoid the gel film from shrinkage during drying and
curing, it is required that the gel film be transported to the
heating furnace by being held on a tenter frame with pins or tenter
clips, etc., at its end portions. The initial temperature of the
heating furnace is preferably 200.degree. C. to 400.degree. C., or
more preferably 250.degree. C. to 350.degree. C. to obtain the
predetermined effect more effectively. With a temperature above
these ranges, the film may break in the heating furnace in response
to sudden heat. In other cases, foaming defects may occur on a
surface of the film by boiling of the remaining volatile component
such as the solvent. In a lower temperature range, predetermined
effects may not be obtained.
[0162] As described, the inventors of the present invention have
found that controlling the content of remaining volatile component
in the gel film and the initial temperature of the tenter heating
furnace within a specific range has direct effect on modulus and
coefficient of thermal expansion of the product polyimide film.
Specifically, such an effect can be obtained most effectively under
the following conditions, without causing breakage of the gel film
or foaming on a surface of the film and thus with good
productivity.
[0163] In a relatively lower range of the foregoing suitable ranges
of the remaining volatile component, i.e., in the range of 50 wt %
to 150 wt %, preferably 80 wt % to 150 wt %, and more preferably
100 wt % to 150 wt %, the initial temperature in the tenter heating
furnace should be set in the range of 250.degree. C. to 400.degree.
C., more preferably 300.degree. C. to 400.degree. C., or most
preferably 350.degree. C. to 400.degree. C. Here, a high
temperature can be set for the initial temperature of the tenter
heating furnace because the gel film, with the low volatile
component content, is highly self-supporting and rarely causes
breakage of the film or boiling of the remaining volatile
component.
[0164] On the other hand, in a relatively higher range of the
foregoing suitable ranges of the remaining volatile component,
i.e., in the range of 150 wt % to 300%, preferably 150 wt % to 250
wt %, and more preferably 150 wt % to 200 wt %, the initial
temperature in the tenter heating furnace should be set in the
range of 200.degree. C. to 350.degree. C., more preferably
200.degree. C. to 300.degree. C., or most preferably 200.degree. C.
to 250.degree. C. The gel film, with a high volatile component
content, is less self-supporting. Thus, in order to obtain the
effects of the present invention without lowering productivity, the
initial temperature of the tenter heating furnace is set in a
relatively lower range of the suitable range.
[0165] The content of remaining volatile component in the gel film
is restricted in some way by the type and thickness of polyimide
resin, the type of solvent used, and the time and capacity of
heating on the support. In any case, the content of remaining
volatile component is controlled in the foregoing suitable ranges
to set the initial temperature in the tenter heating furnace.
[0166] The producing process of the polyimide film according to the
present invention is finished by a heating step at 450.degree. C.
to 600.degree. C., or preferably at 500.degree. C. to 600.degree.
C., for 15 to 400 seconds. The heating furnace may be adapted to
apply heat continuously (stepless) until the temperature reaches a
temperature, known as the highest curing temperature, in the
foregoing preferable ranges, or apply heat stepwise. The two
structures are essentially the same, and it is important in either
case that the initial heating temperature is in the foregoing
suitable ranges.
[0167] The polyimide film so produced has a larger birefringence, a
higher modulus, and a lower coefficient of thermal expansion than
those of a polyimide film that is obtained by a deposition method
using the same material (the precursor is the same polyamic acid).
For example, a polyimide film with a birefringence of 0.15 or
greater can be obtained. More specifically, with the process of the
present invention, modulus can be increased within 1.0 GPa and
coefficient of thermal expansion can be increased within 4 ppm.
That is, the present invention can produce the polyimide film that
can be suitably used in ever more precise base films of flexible
printed circuit boards, cover lay films, or base films for TAB
carrier tapes.
[0168] Referring to Examples, the following specifically describes
effects of the present invention. The present invention however is
not limited by any ways by the following Examples and various
changes, corrections, and modifications are possible by a person
ordinary skill in the art within the scope of the present
invention.
[0169] The tear propagation strength and tensile strength of the
polyimide films were measured according to ASTM D-1938 and JIS
C-2318, respectively.
[0170] The adhesion strength was evaluated using a trilayer
copper-clad laminate, which was prepared by laminating an
electrolytic copper foil (Mitsui Mining & Smelting Co., Ltd.;
product name 3ECVLP; thickness 35 .mu.m) and the polyimide film,
wherein the evaluation was carried out at a 90.degree. peel and a
copper pattern width of 3 mm, according to JIS C-6481.
[0171] The temperature conditions in the heating step of the gel
film were the same in Comparative Examples and Examples.
Comparative Example 1
[0172] Polyamic acid was synthesized from a 4:3:1 mole ratio of
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. 100 g of a DMF solution containing 18.5 wt % of
the polyamic acid was prepared and then mixed with a converting
agent containing 35 g of acetic anhydride and 5 g of .beta.
picoline. The mixture was stirred, defoamed by centrifugation, and
coated by casting on an aluminum foil to a thickness of 400 .mu.m.
The processes of stirring to defoaming were carried out while
cooling to 0.degree. C. The laminate of aluminum foil and polyamic
acid solution was then heated at 120.degree. C. for 150 seconds to
obtain a self-supporting gel film. The content of remaining
volatile component of the gel film was 41 wt % and percent
imidization was 81%. The gel film was then detached from the
aluminum foil and anchored on a frame. The gel film was heated at
300.degree. C., 400.degree. C., and 500.degree. C. for 30 seconds
at each temperature, so as to produce a polyimide film with a
thickness of 25 .mu.m. Table 1 shows basic mechanical properties of
this polyimide film.
Comparative Example 2
[0173] A polyimide film with a thickness of 25 .mu.m was produced
in exactly the same manner as in the Comparative Example 1, except
that the laminate of aluminum foil and polyamic acid solution was
heated at 160.degree. C. for 75 seconds. The content of remaining
volatile component in the gel film in an intermediate stage was 36
wt % and percent imidization was 78%. Table 1 shows basic
mechanical properties of this polyimide film.
Comparative Example 3
[0174] A polyimide film with a thickness of 25 .mu.m was produced
in exactly the same manner as in the Comparative Example 1, except
that a 1:1 mole ratio of pyromellitic dianhydride and
4,4'-diaminodiphenylether were used. The content of remaining
volatile component in the gel film in an intermediate stage was 40
wt % and percent imidization was 89%. Table 1 shows tear
propagation strength of this polyimide film.
Comparative Example 4
[0175] A polyimide film with a thickness of 25 .mu.m was produced
in exactly the same manner as in the Comparative Example 3, except
that the laminate of aluminum foil and polyamic acid solution was
heated at 160.degree. C. for 75 seconds. The content of remaining
volatile component in the gel film in an intermediate stage was 38
wt % and percent imidization was 87%. Table 1 shows basic
mechanical properties of this polyimide film.
[0176] It can be seen from the comparison of Comparative Examples 1
and 2 and Comparative Examples 3 and 4 that the mechanical
strengths, including tear propagation strength, tensile strength,
and adhesion strength, become weaker as the fabrication time of the
gel film becomes shorter.
Example 1
[0177] As in Comparative Example 2, a gel film with a 48 wt %
content of remaining volatile component and 78% percent imidization
was obtained. The gel film was dipped in isoquinoline and
unnecessary droplets were removed through a nip roll. The gel film
was then heated at 300.degree. C., 400.degree. C., and 500.degree.
C. for 30 seconds at each temperature, so as to produce a polyimide
film with a thickness of 25 .mu.m. Table 1 shows basic mechanical
properties of this polyimide film.
Example 2
[0178] As in Comparative Example 2, a gel film with a 53 wt %
content of remaining volatile component and 78% percent imidization
was obtained. The gel film was dipped in a 35 wt % DMF solution of
isoquinoline and unnecessary droplets were removed by spraying
compressed air. The gel film was then heated under the same heating
conditions as in Comparative Example 2 to obtain a polyimide film
with a thickness of 25 .mu.m. Table 1 shows basic mechanical
properties of this polyimide film.
Example 3
[0179] As in Comparative Example 4, a gel film with a 49 wt %
content of remaining volatile component and 87% percent imidization
was obtained. The gel film was dipped in isoquinoline and
unnecessary droplets were removed by spraying compressed air. The
gel film was then heated under the same heating conditions as in
Comparative Example 4 to obtain a polyimide film with a thickness
of 25 .mu.m. Table 1 shows basic mechanical properties of this
polyimide film.
Example 4
[0180] As in Comparative Example 4, a gel film with a 52 wt %
content of remaining volatile component and 87% percent imidization
was obtained. The gel film was dipped in a 35 wt % DMF solution of
isoquinoline and unnecessary droplets were removed by spraying
compressed air. The gel film was then heated under the same heating
conditions as in Comparative Example 2 to obtain a polyimide film
with a thickness of 25 .mu.m. Table 1 shows basic mechanical
properties of this polyimide film.
Example 5
[0181] As in Comparative Example 4, a gel film with a 51 wt %
content of remaining volatile component and 85% percent imidization
was obtained. The gel film was dipped in .beta. picoline and
unnecessary droplets were removed by spraying compressed air. The
gel film was then heated under the same heating conditions as in
Comparative Example 2 to obtain a polyimide film with a thickness
of 25 .mu.m. Table 1 shows basic mechanical properties of this
polyimide film.
Example 6
[0182] Polyamic acid was synthesized from a 1:1 mole ratio of
pyromellitic dianhydride and 4,4'-diaminodiphenylether. 100 g of a
DMF solution containing 18.5 wt % of the polyamic acid was prepared
and then mixed with a converting agent containing 35 g of acetic
anhydride and 5 g of .beta. picoline. The mixture was stirred,
defoamed by centrifugation, and coated by casting on an aluminum
foil to a thickness of 400 .mu.m. The processes of stirring to
defoaming were carried out while cooling to 0.degree. C. The
laminate of aluminum foil and polyamic acid solution was then
heated at 140.degree. C. for 110 seconds to obtain a
self-supporting gel film. The content of remaining volatile
component of the gel film was 46 wt % and percent imidization was
82%. The gel film was dipped in isoquinoline and unnecessary
droplets were removed through a nip roll. The gel film was then
heated at 300.degree. C., 400.degree. C., and 500.degree. C. for 30
seconds each, so as to produce a polyimide film with a thickness of
25 .mu.m. Table 1 shows basic mechanical properties of this
polyimide film.
Example 7
[0183] Polyamic acid was synthesized from a 1:1 mole ratio of
pyromellitic dianhydride and 4,4'-diaminodiphenylether. 100 g of a
DMF solution containing 18.5 wt % of the polyamic acid was prepared
and then mixed with a converting agent containing 35 g of acetic
anhydride and 5 g of .beta. picoline. The mixture was stirred,
defoamed by centrifugation, and coated by casting on an aluminum
foil to a thickness of 400 .mu.m. The processes of stirring to
defoaming were carried out while cooling to 0.degree. C. The
laminate of aluminum foil and polyamic acid solution was then
heated at 170.degree. C. for 60 seconds to obtain a self-supporting
gel film. The content of remaining volatile component of the gel
film was 42 wt % and percent imidization was 88%. The gel film was
dipped in isoquinoline and unnecessary droplets were removed
through a nip roll. The gel film was then heated at 300.degree. C.,
400.degree. C., and 500.degree. C. for 30 seconds each, so as to
produce a polyimide film with a thickness of 25 .mu.m. Table 1
shows basic mechanical properties of this polyimide film.
TABLE-US-00001 TABLE 1 PRODUCTION TEAR HEATING TIME OF GEL
PROPAGATION TENSILE ADHESION POLYIMIDE TERTIARY TEMP. FILM STRENGTH
STRENGTH ELONGATION STRENGTH STRUCTURE AMINE (.degree. C.) (SEC.)
(g/mm) (kg/mm.sup.2) (%) (N/cm) COMPARATIVE PMDA/4,4' NONE 120 150
267 285 70 11.0 EXAMPLE 1 ODA/p-PDA COMPARATIVE 160 75 220 263 71
8.9 EXAMPLE 2 COMPARATIVE PMDA/4,4' 120 150 325 240 99 11.1 EXAMPLE
3 ODA COMPARATIVE 160 75 253 222 101 9.2 EXAMPLE 4 EXAMPLE 1
PMDA/4,4' ISOQUINOLINE 160 75 265 310 71 10.9 EXAMPLE 2 ODA/p-PDA
ISOQUINOLINE/ 263 307 72 11.3 35 WT % DMF EXAMPLE 3 PMDA/4,4'
ISOQUINOLINE 331 258 103 10.9 EXAMPLE 4 ODA/p-PDA ISOQUINOLINE/ 323
265 98 11.2 35 WT % DMF EXAMPLE 5 .beta. PICOLINE 160 75 320 263
100 11.0 EXAMPLE 6 ISOQUINOLINE 140 110 318 256 100 11.0 EXAMPLE 7
ISOQUINOLINE 170 60 315 260 98 10.8
[0184] In the Table, PMDA indicates pyromellitic dianhydride,
4,4'ODA the 4,4'-diaminodiphenylether, and p-PDA the
p-phenylenediamine.
[0185] Examples 1 through 7 despite their shorter production time
have values of mechanical strengths that compare to those of
polyimide films of Comparative Examples 1 and 3 with longer
production time.
[0186] It is therefore possible by the present invention to produce
polyimide films with superior mechanical properties and with good
productivity.
[0187] In the following Examples and Comparative Examples,
evaluations of tear propagation strength and tensile strength of
the polyimide films were carried out according to ASTM D-1938 and
JIS C-2318, respectively. The adhesion strength was evaluated using
a trilayer copper-clad laminate, which was prepared by laminating
an electrolytic copper foil (Mitsui Mining & Smelting Co.,
Ltd.; product name 3ECVLP; thickness 35 .mu.m) and the polyimide
film, wherein the evaluation was carried out at a 90.degree. peel
and a copper pattern width of 3 mm, according to JIS C-6481.
[0188] The amount of catalyst in a weight loss on heating was
decided by pyrolysis gas chromatography (using the Hewlett-Packard
Co. product HP5890-II; pyrolysis conditions: 445.degree. C., 20
seconds).
Comparative Example 5
[0189] Polyamic acid was synthesized from a 4:3:1 mole ratio of
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. 100 g of a DMF solution containing 18.5 wt % of
the polyamic acid was prepared and then mixed with a converting
agent containing 35 g of acetic anhydride and 5 g of .beta.
picoline. The mixture was stirred, defoamed by centrifugation, and
coated by casting on an aluminum foil to a thickness of 400 .mu.m.
The processes of stirring to defoaming were carried out while
cooling to 0.degree. C. The laminate of aluminum foil and polyamic
acid solution was then heated at 120.degree. C. for 150 seconds to
obtain a self-supporting gel film. The content of remaining
volatile component of the gel film was 38 wt %. The gel film was
then detached from the aluminum foil and anchored on a frame. The
gel film was heated at 300.degree. C., 400.degree. C., and
500.degree. C. for 30 seconds each, so as to produce a polyimide
film with a thickness of 25 .mu.m. Table 2 shows basic mechanical
properties of this polyimide film.
Comparative Example 6
[0190] A polyimide film with a thickness of 25 .mu.m was produced
in exactly the same manner as in the Comparative Example 5, except
that the laminate of aluminum foil and polyamic acid solution was
heated at 160.degree. C. for 75 seconds. The content of remaining
volatile component in the gel film in an intermediate stage was 39
wt %. Table 2 shows basic mechanical properties of this polyimide
film.
Example 8
[0191] Polyamic acid was coated by casting on an aluminum foil as
in the Comparative Example 5. A laminate of the aluminum foil and
the polyamic acid solution was heated at 120.degree. C. for 10
seconds, 140.degree. C. for 10 seconds, and 160.degree. C. for 55
seconds, so as to obtain a self-supporting gel film. The content of
remaining volatile component of the gel film was 56 wt %. The gel
film was then heated at 300.degree. C., 400.degree. C., and
500.degree. C. for 30 seconds at each temperature to produce a
polyimide film with a thickness of 25 .mu.m. Table 2 shows basic
mechanical properties of the polyimide film.
Comparative Example 7
[0192] A polyimide film with a thickness of 25 .mu.m was produced
in exactly the same manner as in the Comparative Example 5, except
that a 1:1 mole ratio of pyromellitic dianhydride and
4,4'-diaminodiphenylether were used. The content of remaining
volatile component in the gel film in an intermediate stage was 35
wt %. Table 2 shows basic mechanical properties of the polyimide
film.
Comparative Example 8
[0193] A polyimide film with a thickness of 25 .mu.m was produced
in exactly the same manner as in the Comparative Example 7, except
that the laminate of aluminum foil and polyamic acid solution was
heated at 160.degree. C. for 75 seconds. The content of remaining
volatile component in the gel film in an intermediate stage was 37
wt %. Table 2 shows basic mechanical properties of the polyimide
film.
Comparative Example 9
[0194] Polyamic acid was coated by casting on an aluminum foil as
in the Comparative Example 2. A laminate of the aluminum foil and
the polyamic acid solution was heated at 120.degree. C. for 10
seconds, 140.degree. C. for 10 seconds, and 160.degree. C. for 55
seconds, so as to obtain a self-supporting gel film. The content of
remaining volatile component of the gel film was 54 wt %. The gel
film was then heated at 300.degree. C., 400.degree. C., and
500.degree. C. for 30 seconds at each temperature to produce a
polyimide film with a thickness of 25 .mu.m. Table 2 shows basic
mechanical properties of the polyimide film.
TABLE-US-00002 TABLE 2 PRODUCTION TEAR AMOUNT OF TIME OF GEL
PROPAGATION TENSILE ADHESION WEIGHT REMAINING POLYIMIDE FILM
STRENGTH STRENGTH ELONGATION STRENGTH LOSS CATALYST STRUCTURE
(SEC.) (g/mm) (kg/mm.sup.2) (%) (N/cm) (wt %) (wt %) COMPARATIVE
PMDA/4,4' 150 267 285 70 11.0 0.76 N.D. EXAMPLE 5 ODA/p-PDA
COMPARATIVE 75 220 263 71 8.9 0.68 N.D. EXAMPLE 6 EXAMPLE 8 75 255
312 68 12.1 0.82 0.005 COMPARATIVE PMDA/4,4' 150 325 240 99 11.1
0.78 N.D. EXAMPLE 7 ODA/p-PDA COMPARATIVE 75 253 222 101 9.2 0.80
N.D. EXAMPLE 8 EXAMPLE 9 75 318 268 100 12.9 0.83 0.008 N.D.: NOT
DETECTED
[0195] It can be seen that the present invention can produce
polyimide films with superior mechanical properties and with good
productivity.
[0196] In the following Examples and Comparative Examples,
evaluations of tear propagation strength and tensile strength of
the polyimide films were carried out according to ASTM D-1938 and
JIS C-2318, respectively. The adhesion strength was evaluated using
a trilayer copper-clad laminate which was prepared by laminating an
electrolytic copper foil (Mitsui Mining & Smelting Co.; product
name 3ECVLP; thickness 35 .mu.m) and the polyimide film, wherein
the evaluation was carried out at a 90.degree. peel and a copper
pattern width of 3 mm, according to JIS C-6481.
[0197] The amount of remaining catalyst and the amount of main
solvent in the gel film were decided by gas chromatography analysis
of a liquid that was prepared by dipping the gel film in
N-methyl-2-pyrrolidone for 48 hours. The calculation did not take
into account the moisture content of the remaining volatile
component and the calculation quantified the acetic acid anhydride
as the quantity of acetic acid that was generated by hydrolysis of
the gel film dipped in the N-methyl-2-pyrrolidone.
Comparative Example 9
[0198] Polyamic acid was synthesized from a 4:3:1 mole ratio of
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. 100 g of a DMF solution containing 18.5 wt % of
the polyamic acid was prepared and then mixed with a converting
agent containing 38 g of acetic anhydride, 4.5 g of isoquinoline,
and 15 g of DMF. The mixture was stirred, defoamed by
centrifugation, and coated by casting on an aluminum foil. The
laminate of aluminum foil and polyamic acid solution was then
heated at 120.degree. C. for 150 seconds to obtain a
self-supporting gel film. The content of remaining volatile
component of the gel film was 40 wt %. The remaining volatile
component contained 39 wt % DMF, 51 wt % isoquinoline, and 10 wt %
acetic acid. The gel film was then detached from the aluminum foil
and anchored on a frame. The gel film was heated at 300.degree. C.,
400.degree. C., and 500.degree. C. for 30 seconds each, so as to
produce a polyimide film with a thickness of 25 .mu.m. Table 3
shows basic mechanical properties of this polyimide film.
Comparative Example 10
[0199] A polyimide film with a thickness of 25 .mu.m was produced
in exactly the same manner as in the Comparative Example 9, except
that the laminate of aluminum foil and polyamic acid solution was
heated at 160.degree. C. for 75 seconds. The content of remaining
volatile component in the gel film in an intermediate stage was 39
wt % and the remaining volatile component contained 38 wt % DMF, 45
wt % isoquinoline, and 17 wt % acetic acid. Table 3 shows basic
mechanical properties of this polyimide film.
Example 10
[0200] A polyimide film with a thickness of 25 .mu.m was produced
in exactly the same manner as in the Comparative Example 9, except
that a converting agent containing 20 g acetic anhydride, 10 g
isoquinoline, and 30 g DMF were used and the laminate of aluminum
foil and polyamic acid solution was heated at 160.degree. C. for 75
seconds. The content of remaining volatile component in the gel
film in an intermediate stage was 44 wt % and the remaining
volatile component contained 17 wt % DMF, 75 wt % isoquinoline, and
8 wt % acetic acid. Table 3 shows basic mechanical properties of
this polyimide film.
Comparative Example 11
[0201] A polyimide film with a thickness of 25 .mu.m was produced
in exactly the same manner as in the Comparative Example 9, except
that a 1:1 mole ratio of pyromellitic dianhydride and
4,4'-diaminodiphenylether were used. The content of remaining
volatile component in the gel film in an intermediate stage was 35
wt %. The remaining volatile component contained 37 wt % DMF, 56 wt
% isoquinoline, and 7 wt % acetic acid. Table 3 shows basic
mechanical properties of the polyimide film.
Comparative Example 12
[0202] A polyimide film with a thickness of 25 .mu.m was produced
in exactly the same manner as in the Comparative Example 9, except
that the laminate of aluminum foil and polyamic acid solution was
heated at 160.degree. C. for 75 seconds. The content of remaining
volatile component in the gel film in the intermediate stage was 38
wt % and the remaining volatile component contained 36 wt % DMF, 43
wt % isoquinoline, and 21 wt % acetic acid. Table 3 shows basic
mechanical properties of this polyimide film.
Example 11
[0203] A polyimide film with a thickness of 25 .mu.m was produced
in exactly the same manner as in the Comparative Example 3, except
that an additive containing 20 g acetic anhydride, 10 g
isoquinoline, and 30 g DMF were used and the laminate of aluminum
foil and polyamic acid solution was heated at 160.degree. C. for 75
seconds. The content of remaining volatile component in the gel
film in the intermediate stage was 50 wt % and the remaining
volatile component contained 18 wt % DMF, 72 wt % isoquinoline, and
10 wt % acetic acid. Table 3 shows basic mechanical properties of
this polyimide film.
TABLE-US-00003 TABLE 3 PRODUCTION TEAR AMOUNT OF TIME OF
PROPAGATION TENSILE ADHESION WEIGHT REMAINING POLYIMIDE GEL FILM
STRENGTH STRENGTH ELONGATION STRENGTH LOSS CATALYST STRUCTURE
(SEC.) (g/mm) (kg/mm.sup.2) (%) (N/cm) (wt %) (wt %) COMPARATIVE
PMDA/4,4' 150 265 283 71 11.3 0.75 N.D. EXAMPLE 9 ODA/p-PDA
COMPARATIVE 75 235 263 71 8.9 0.68 N.D. EXAMPLE 10 EXAMPLE 10 75
268 307 69 11.8 0.83 0.11 COMPARATIVE PMDA/4,4' 150 325 240 99 11.1
0.79 N.D. EXAMPLE 11 ODA/p-PDA COMPARATIVE 75 265 225 100 9.2 0.81
N.D. EXAMPLE 12 EXAMPLE 11 75 318 268 102 12.1 0.82 0.12 N.D.: NOT
DETECTED
[0204] It can be seen that the present invention can produce
polyimide films with superior mechanical properties and with good
productivity.
[0205] In the following Examples and Comparative Examples, "parts"
are "parts by weight", and "%" is percent by weight.
[0206] (Method of Evaluation)
[0207] 1) Measurements of Tensile Strength
[0208] Measurements were carried out according to ASTM D882.
[0209] 2) Measurements of R Value in MD Direction
[0210] A central portion of the product polyimide film was sampled
for 5 m in the MD direction. A continuous pachymeter of a contact
type was used to continuously measure thickness. A maximum
thickness and a minimum thickness were taken out of a chart.
[0211] R value was determined as follows (the unit is in
microns):
R value=[maximum thickness]-[minimum thickness]
Comparative Example 13
[0212] Polyamic acid was synthesized from a 4:3:1 mole ratio of
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. A DMF solution containing 18.5 wt % of the
polyamic acid was prepared and mixed with 40 wt % of a curing agent
containing 573 g of acetic anhydride, 73 g of isoquinoline, and 154
g of DMF. The mixture was quickly stirred in a mixer and extruded
from a T die to be cast on a stainless-steel endless belt traveling
25 mm below the die at a speed of 12 m/minute. The viscosity of a
resin solution in the T die was 750 poise at 0.degree. C. The
acetic anhydride as the dehydrating agent and the isoquinoline as
the catalyst were used in mole ratios of 3 and 0.3, respectively,
with respect to 1 mole of amic acid in the polyamic acid varnish.
The resin film was dried and imidized for 130.degree. C..times.100
seconds, 300.degree. C..times.20 seconds, 450.degree. C..times.20
seconds, and 500.degree. C..times.20 seconds, so as to obtain a
polyimide film with a thickness of 25 .mu.m. Table 4 shows
properties of this polyimide film. Examining the film showed
trapping of countless bubbles of about a 5 mm diameter at the both
ends of the film.
Comparative Example 14
[0213] Polyamic acid was synthesized from a 4:3:1 mole ratio of
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. A DMF solution containing 18.5 wt % of the
polyamic acid was prepared and mixed with 60 wt % of a curing agent
containing 764 g of acetic anhydride, 97 g of isoquinoline, and 336
g of DMF. The mixture was quickly stirred in a mixer and extruded
from a T die to be cast on a stainless-steel endless belt traveling
25 mm below the die at a speed of 16 m/minute. The viscosity of a
resin solution in the T die was 460 poise at 0.degree. C. The
acetic anhydride as the dehydrating agent and the isoquinoline as
the catalyst were used in mole ratios of 4 and 0.4, respectively,
with respect to 1 mole of amic acid in the polyamic acid varnish.
The resin film was dried and imidized for 140.degree. C..times.100
seconds, 300.degree. C..times.20 seconds, 450.degree. C..times.20
seconds, and 500.degree. C..times.20 seconds, so as to obtain a
polyimide film with a thickness of 25 .mu.m. Table 4 shows
properties of this polyimide film. Examining the film showed
trapping of countless bubbles of about a 5 mm diameter at the both
ends of the film.
Comparative Example 15
[0214] Polyamic acid was synthesized from a 1:1 mole ratio of
pyromellitic dianhydride and 4,4'-diaminodiphenylether. A DMF
solution containing 18.5 wt % of the polyamic acid was prepared and
mixed with 40 wt % of a curing agent containing 632 g of acetic
anhydride, 80 g of isoquinoline, and 88 g of DMF. The mixture was
quickly stirred in a mixer and extruded from a T die to be cast on
a stainless-steel endless belt traveling 25 mm below the die at a
speed of 12 m/minute. The viscosity of a resin solution in the T
die was 790 poise at 0.degree. C. The acetic anhydride as the
dehydrating agent and the isoquinoline as the catalyst were used in
mole ratios of 3.5 and 0.35, respectively, with respect to 1 mole
amic acid in the polyamic acid varnish. The resin film was dried
and imidized for 130.degree. C..times.100 seconds, 300.degree.
C..times.20 seconds, 450.degree. C..times.20 seconds, and
500.degree. C..times.20 seconds, so as to obtain a polyimide film
with a thickness of 25 .mu.m. Table 4 shows properties of this
polyimide film. Examining the film showed trapping of countless
bubbles of about a 5 mm diameter at the both ends of the film.
Comparative Example 16
[0215] Polyamic acid was synthesized from a 1:1 mole ratio of
pyromellitic dianhydride and 4,4'-diaminodiphenylether. A DMF
solution containing 18.5 wt % of the polyamic acid was prepared and
mixed with 60 wt % of a curing agent containing 813 g of acetic
anhydride, 103 g of isoquinoline, and 285 g of DMF. The mixture was
quickly stirred in a mixer and extruded from a T die to be cast on
a stainless-steel endless belt traveling 25 mm below the die at a
speed of 16 m/minute. The viscosity of a resin solution in the T
die was 480 poise at 0.degree. C. The acetic anhydride as the
dehydrating agent and the isoquinoline as the catalyst were used in
mole ratios of 4.5 and 0.45, respectively, with respect to 1 mole
of amic acid in the polyamic acid varnish. The resin film was dried
and imidized for 140.degree. C..times.100 seconds, 300.degree.
C..times.20 seconds, 450.degree. C..times.20 seconds, and
500.degree. C..times.20 seconds, so as to obtain a polyimide film
with a thickness of 25 .mu.m. Table 4 shows properties of this
polyimide film. Examining the film showed trapping of countless
bubbles of about a 5 mm diameter at the both ends of the film.
Example 12
[0216] Polyamic acid was synthesized from a 4:3:1 mole ratio of
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. A DMF solution containing 18.5 wt % of the
polyamic acid was prepared and mixed with 40 wt % of a curing agent
containing 382 g of acetic anhydride, 97 g of isoquinoline, and 318
g of DMF. The mixture was quickly stirred in a mixer and extruded
from a T die to be cast on a stainless-steel endless belt traveling
25 mm below the die at a speed of 12 m/minute. The viscosity of a
resin solution in the T die was 520 poise at 0.degree. C. The
acetic anhydride as the dehydrating agent and the isoquinoline as
the catalyst were used in mole ratios of 2.0 and 0.4, respectively,
with respect to 1 mole amic acid in the polyamic acid varnish. The
resin film was dried and imidized for 130.degree. C..times.100
seconds, 300.degree. C..times.20 seconds, 450.degree. C..times.20
seconds, and 500.degree. C..times.20 seconds, so as to obtain a
polyimide film with a thickness of 25 .mu.m. Table 4 shows
properties of this polyimide film.
Example 13
[0217] Polyamic acid was synthesized from a 4:3:1 mole ratio of
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. A DMF solution containing 18.5 wt % of the
polyamic acid was prepared and mixed with 60 wt % of a curing agent
containing 382 g of acetic acid anhydride, 169 g of isoquinoline,
and 249 g of DMF. The mixture was quickly stirred in a mixer and
extruded from a T die to be cast on a stainless-steel endless belt
traveling 25 mm below the die at a speed of 16 m/minute. The
viscosity of a resin solution in the T die was 320 poise at
0.degree. C. The acetic anhydride as the dehydrating agent and the
isoquinoline as the catalyst were used in mole ratios of 2.0 and
0.7, respectively, with respect to 1 mole amic acid in the polyamic
acid varnish. The resin film was dried and imidized for 140.degree.
C..times.100 seconds, 300.degree. C..times.20 seconds, 450.degree.
C..times.20 seconds, and 500.degree. C..times.20 seconds, so as to
obtain a polyimide film with a thickness of 25 .mu.m. Table 4 shows
properties of this polyimide film.
Example 14
[0218] Polyamic acid was synthesized from a 1:1 mole ratio of
pyromellitic dianhydride and 4,4'-diaminodiphenylether. A DMF
solution containing 18.5 wt % of the polyamic acid was prepared and
mixed with 40 wt % of a curing agent containing 361 g of acetic
anhydride, 103 g of isoquinoline, and 336 g of DMF. The mixture was
quickly stirred in a mixer and extruded from a T die to be cast on
a stainless-steel endless belt traveling 25 mm below the die at a
speed of 12 m/minute. The viscosity of a resin solution in the T
die was 580 poise at 0.degree. C. The acetic anhydride as the
dehydrating agent and the isoquinoline as the catalyst were used in
mole ratios of 2.0 and 0.45, respectively, with respect to 1 mole
of amic acid in the polyamic acid varnish. The resin film was dried
and imidized for 130.degree. C..times.100 seconds, 300.degree.
C..times.20 seconds, 450.degree. C..times.20 seconds, and
500.degree. C..times.20 seconds, so as to obtain a polyimide film
with a thickness of 25 .mu.m. Table 4 shows properties of this
polyimide film.
Example 15
[0219] Polyamic acid was synthesized from a 1:1 mole ratio of
pyromellitic dianhydride and 4,4'-diaminodiphenylether. A DMF
solution containing 18.5 wt % of the polyamic acid was prepared and
mixed with 60 wt % of a curing agent containing 271 g of acetic
anhydride, 228 g of isoquinoline, and 301 g of DMF. The mixture was
quickly stirred in a mixer and extruded from a T die to be cast on
a stainless-steel endless belt traveling 25 mm below the die at a
speed of 16 m/minute. The viscosity of a resin solution in the T
die was 360 poise at 0.degree. C. The acetic anhydride as the
dehydrating agent and the isoquinoline as the catalyst were used in
mole ratios of 1.5 and 1.0 with respect to 1 mole of amic acid in
the polyamic acid varnish. The resin film was dried and imidized
for 140.degree. C..times.100 seconds, 300.degree. C..times.20
seconds, 450.degree. C..times.20 seconds, and 500.degree.
C..times.20 seconds, so as to obtain a polyimide film with a
thickness of 25 .mu.m. Table 4 shows properties of this polyimide
film.
TABLE-US-00004 TABLE 4 DEHYDRATING TENSILE THICKNESS POLYIMIDE
AGENT/CATALYST STRENGTH ELONGATION UNEVENNESS AIR STRUCTURE (MOLE
RATIO) (kg/mm.sup.2) (%) (.mu.m) TRAPPING COMPARATIVE PMDA/4,4'
1/0.1 307 70 2.8 PRESENT EXAMPLE 13 ODA/p-PDA COMPARATIVE 285 71
3.3 PRESENT EXAMPLE 14 COMPARATIVE PMDA/4,4' 260 105 3.0 PRESENT
EXAMPLE 15 ODA/p-PDA COMPARATIVE 223 106 3.5 PRESENT EXAMPLE 16
EXAMPLE 12 PMDA/4,4' 1/0.2 310 72 1.5 ABSENT EXAMPLE 13 ODA/ p-PDA
1/0.35 313 75 1.8 ABSENT EXAMPLE 14 PMDA/4,4' 1/0.23 265 110 1.6
ABSENT EXAMPLE 15 ODA/ p-PDA 1/0.67 270 108 1.9 ABSENT
[0220] According to the present invention, the composition of the
curing agent is adjusted so as to lower viscosity of the solution
in the extruding die. This prevents trapping of bubbles during the
high-speed deposition process. In addition, the thickness does not
become uneven in the MD direction. As a result, the polyimide film
with superior mechanical properties can be produced.
[0221] In the following Examples and Comparative Examples,
measurements were carried out as follows.
[0222] (Method of Evaluation)
[0223] 1) Measurement of Tensile Strength
[0224] The measurements were carried out according to ASTM
D882.
[0225] 2) Measurement of Tear Propagation Strength
[0226] The measurements were carried out according to ASTM
D-1938.
[0227] 3) Measurement of a Ratio of Maximum Value to Minimum Value
of Tear Propagation Strength
[0228] Samples were collected at 10 cm intervals in the transverse
direction of the film. The samples were measured to obtain the
maximum value and minimum value of tear propagation strength. The
maximum value and minimum value were used to calculate a ratio
(maximum value/minimum value).
[0229] 4) R Value of Tear Propagation Strength
[0230] The difference of maximum value and minimum value of the
measured samples was used for the evaluation (FIG. 1).
[0231] Note that, a location of the film 10 mm inside the portion
of the film fastened with pins or clips will be called an outermost
portion of the film.
[0232] 5) Adhesion Strength
[0233] The adhesion strength was evaluated using a trilayer
copper-clad laminate, which was prepared by laminating an
electrolytic copper foil (Mitsui Mining & Smelting Co., Ltd.;
product name 3ECVLP; thickness 35 .mu.m) and the polyimide film
using a nylon-epoxy adhesive, wherein the evaluation was carried
out at a 90.degree. peel and a copper pattern width of 3 mm,
according to JIS C-6481.
[0234] The heating conditions of the film were the same throughout
the Examples and Comparative Examples.
Example 16
[0235] Polyamic acid was synthesized from a 4:3:1 mole ratio of
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. 100 parts of a DMF solution containing 18.5 wt
% of the polyamic acid was prepared and mixed with 50 parts of a
curing agent containing 38 parts of acetic anhydride, 10 parts of
isoquinoline, and 52 parts of DMF. The mixture was quickly stirred
in a mixer and extruded from a T die to be cast on a
stainless-steel endless belt traveling 20 mm below the die. The
acetic anhydride as the dehydrating agent and the isoquinoline as
the catalyst were used in mole ratios of 2.0 and 0.4, respectively,
with respect to 1 mole of amic acid in the polyamic acid varnish.
The resin film, after heated for 130.degree. C..times.100 seconds,
was separated from the support and dried and imidized with its end
portions fastened with pins for 300.degree. C..times.20 seconds,
450.degree. C..times.20 seconds, and 500.degree. C..times.20
seconds, so as to obtain a polyimide film with a thickness of 25
.mu.m and a width of 1500 mm. Table 5 shows properties of this
polyimide film.
Example 17
[0236] Polyamic acid was synthesized from a 4:3:1 mole ratio of
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. 100 parts of a DMF solution containing 18.5 wt
% of the polyamic acid was prepared and mixed with 50 parts of a
curing agent containing 38 parts of acetic anhydride, 19 parts of
isoquinoline, and 43 parts of DMF. The mixture was quickly stirred
in a mixer and extruded from a T die to be cast on a
stainless-steel endless belt traveling 20 mm below the die. The
acetic anhydride as the dehydrating agent and the isoquinoline as
the catalyst were used in mole ratios of 2.0 and 0.8, respectively,
with respect to 1 mole of amic acid in the polyamic acid varnish.
The resin film, after heated for 130.degree. C..times.100 seconds,
was separated from the support and dried and imidized with its end
portions fastened for 300.degree. C..times.20 seconds, 450.degree.
C..times.20 seconds, and 500.degree. C..times.20 seconds, so as to
obtain a polyimide film with a thickness of 25 .mu.m and a width of
1500 mm. Table 5 shows properties of this polyimide film.
Example 18
[0237] Polyamic acid was synthesized from a 1:1 mole ratio of
pyromellitic dianhydride and 4,4'-diaminodiphenylether. 100 parts
of a DMF solution containing 18.5 wt % of the polyamic acid was
prepared and mixed with 65 parts of a curing agent containing 28
parts of acetic anhydride, 14 parts of isoquinoline, and 58 parts
of DMF. The mixture was quickly stirred in a mixer and extruded
from a T die to be cast on a stainless-steel endless belt traveling
20 mm below the die. The acetic anhydride as the dehydrating agent
and the isoquinoline as the catalyst were used in mole ratios of
2.0 and 0.8, respectively, with respect to 1 mole of amic acid in
the polyamic acid varnish. The resin film, after heated for
130.degree. C..times.100 seconds, was separated from the support
and dried and imidized with its end portions fastened with pins for
300.degree. C..times.20 seconds, 450.degree. C..times.20 seconds,
and 500.degree. C..times.20 seconds, so as to obtain a polyimide
film with a thickness of 25 .mu.m and a width of 1500 mm. Table 5
shows properties of this polyimide film.
Comparative Example 17
[0238] Polyamic acid was synthesized from a 4:3:1 mole ratio of
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. 100 parts of a DMF solution containing 18.5 wt
% of the polyamic acid was prepared and mixed with 50 parts of a
curing agent containing 67 parts of acetic anhydride, 8 parts of
isoquinoline, and 25 parts of DMF. The mixture was quickly stirred
in a mixer and extruded from a T die to be cast on a
stainless-steel endless belt traveling 20 mm below the die. The
acetic anhydride as the dehydrating agent and the isoquinoline as
the catalyst were used in mole ratios of 3.5 and 0.35,
respectively, with respect to 1 mole of amic acid in the polyamic
acid varnish. The resin film, after heated for 130.degree.
C..times.100 seconds, was separated from the support and dried and
imidized with its end portions fastened with pins for 300.degree.
C..times.20 seconds, 450.degree. C..times.20 seconds, and
500.degree. C..times.20 seconds, so as to obtain a polyimide film
with a thickness of 25 .mu.m and a width of 1500 mm. Table 5 shows
properties of this polyimide film.
Comparative Example 18
[0239] Polyamic acid was synthesized from a 1:1 mole ratio of
pyromellitic dianhydride and 4,4'-diaminodiphenylether. 100 parts
of a DMF solution containing 18.5 wt % of the polyamic acid was
prepared and mixed with 50 parts of a curing agent containing 36
parts of acetic acid anhydride, 5 parts of isoquinoline, and 59
parts of DMF. The mixture was quickly stirred in a mixer and
extruded from a T die to be cast on a stainless-steel endless belt
traveling 20 mm below the die. The acetic anhydride as the
dehydrating agent and the isoquinoline as the catalyst were used in
mole ratios of 2.0 and 0.2, respectively, with respect to 1 mole of
amic acid in the polyamic acid varnish. The resin film was then
heated for 130.degree. C..times.100 seconds. After the heating, an
attempt to separate the resin film from the support failed.
TABLE-US-00005 TABLE 5 TEAR PROPAGATION STRENGTH (g) R VALUE OF
TENSILE CHARACTERISTICS ADHESION MAXIMUM MINIMUM OUTERMOST MODULUS
ELONGATION STRENGTH VALUE VALUE PORTION (GPa) (%) (N/cm) EXAMPLE 16
7.15 6.47 0.21 CENTRAL 4.22 80 11.3 PORTION OUTERMOST 4.16 89 11.5
PORTION EXAMPLE 17 7.31 6.53 0.15 CENTRAL 4.21 78 11.8 PORTION
OUTERMOST 4.18 84 11.5 PORTION EXAMPLE 18 8.21 7.74 0.22 CENTRAL
3.31 129 10.5 PORTION OUTERMOST 3.20 136 10.8 PORTION COMPARATIVE
8.80 6.53 1.33 CENTRAL 4.13 82 12.2 EXAMPLE 17 PORTION OUTERMOST
4.38 99 8.36 PORTION
[0240] According to the present invention, the composition of the
curing agent is adjusted. In this way, the mechanical strengths and
adhesion strength in the direction of width become less variant
during the continuous deposition process.
Example 19
[0241] Polyamic acid was synthesized from a 4:3:1 mole ratio of
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. A DMF solution containing 18.5 wt % of the
polyamic acid was prepared and mixed and stirred with 50 wt % of a
curing agent containing acetic anhydride, isoquinoline, and DMF.
The mixture was adjusted so that the acetic anhydride and
isoquinoline were 2.0 mole equivalent and 0.4 mole equivalent,
respectively, with respect to the amic acid group of the polyamic
acid. The mixture was then cast through a T slit die onto a rotary
stainless-steel endless belt, and the resin film so cast was heated
in hot air at 150.degree. C. As a result, a self-supporting gel
film with a 55 wt % remaining volatile component and a thickness of
about 0.20 mm was obtained. The gel film was then detached from the
endless belt and, with its end portions fastened on a tenter frame,
conveyed to a heating furnace maintained at 220.degree. C.,
370.degree. C., and 550.degree. C. Slitting the end portions
produced a polyimide film with a width of 1500 mm and a thickness
of 25 .mu.m. The polyimide film was evaluated for molecular
orientation MOR-c, modulus, and tensile strength as follows. The
results are shown in Table 6.
[0242] (Molecular Orientation MOR-c) Portions of the product film,
1500 mm wide, were cut out to obtain samples of 40 mm.times.40 mm
each. Namely, samples were obtained from the central portion, from
portions 375 mm from the central portion, and from the end
portions, i.e., 750 mm from the central portion. The molecular
orientation MOR-c was measured using the microwave molecular
orientation measurement instrument MOA2012A of KS Systems Inc. Note
that, the MOR value given by this measurement instrument is a
measure of anisotropy of molecular orientation in a film plane. The
MOR value, however, is proportional to the thickness and therefore
was converted to a value at a thickness of 75 .mu.m according to
the equation below. The film becomes more isotropic as the MOR-c
approaches 1.0.
MOR-c=1+(MOR-1).times.t/75
where MOR is the molecular orientation before conversion, and t is
the thickness of a target (.mu.m).
[0243] The measurement device used herein measures microwave
transmission intensity by rotating a sample that has been inserted
into a microwave resonance waveguide with its measured film plane
being perpendicular to the machine direction of the microwave. FIG.
2 conceptually shows a resulting transmission intensity curve,
where a direction which gives the minimum transmission intensity is
the principal axis of orientation. The modulus and coefficient of
thermal expansion were measured as follows with respect to
directions parallel to and perpendicular to the principal axis of
orientation. Note that, indicated by the reference sign 1 is the
principal axis of molecular orientation, 2 the microwave
transmission intensity curve, and 3 the orientation angle.
[0244] (Modulus)
[0245] The modulus and tensile strength were measured according to
JIS C-2318 with respect to a total of 5 locations on the 1500 mm
wide film, at the central portion, portions 375 mm from the central
portion, and the end portions, i.e., portions 750 mm from the
central portion. Note that, the measurement was taken by cutting
out the samples in directions parallel to and perpendicular to the
principal axes of orientation that was obtained from the molecular
orientation measurement instrument.
[0246] (Coefficient of Thermal Expansion)
[0247] The coefficient of thermal expansion was measured with
respect to a total of 5 locations on the 1500 mm wide film, at the
central portion, portion 375 mm from the central portion, and the
end portion, i.e., portions 750 mm from the central portion, using
the thermophysical testing instrument TMA-8140 of Rigaku. The film
at room temperature was heated to 400.degree. C. at 10.degree.
C./minute and then cooled back to room temperature. The same
heating was carried out again to obtain coefficient of thermal
expansion in a temperature range of 100.degree. C. to 200.degree.
C.
Comparative Example 19
[0248] A gel film with a 45 wt % remaining volatile component and a
thickness of about 0.20 mm was obtained as in Example 19, except
that the mixture was adjusted to have 5.5 mole equivalent and 2.0
mole equivalent of acetic anhydride and isoquinoline, respectively,
with respect to the amic acid group of the polyamic acid. Then, the
gel film was detached from the endless belt and, with its end
portions fastened on a tenter frame, conveyed to a heating furnace
maintained at 200.degree. C., 350.degree. C., and 550.degree. C.
Slitting the end portions produced a polyimide film with a width of
1500 mm and a thickness of 25 .mu.m. Table 6 shows the molecular
orientation MOR-c, modulus, tensile strength, and coefficient of
thermal expansion of the polyimide film.
Comparative Example 20
[0249] A polyimide film with a width of 1500 mm and a thickness of
25 .mu.m was obtained as in Example 19, except that the gel film
was conveyed to a heating furnace maintained at 300.degree. C.,
450.degree. C., and 550.degree. C. for heating. Table shows the
molecular orientation MOR-c, modulus, tensile strength, and
coefficient of thermal expansion of the polyimide film.
Example 20
[0250] Polyamic acid was synthesized from a 4:3:1 mole ratio of
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. A DMF solution containing 18.5 wt % of the
polyamic acid was prepared and mixed and stirred with 50 wt % of a
converting agent containing acetic anhydride, isoquinoline, and
DMF. The mixture was adjusted so that the acetic anhydride and
isoquinoline were 2.0 mole equivalent and 0.4 mole equivalent,
respectively, with respect to the amic acid unit of the polyamic
acid. The mixture was then cast through a T slit die onto a rotary
stainless-steel endless belt, and the resin film so cast was heated
in hot air at 150.degree. C. As a result, a self-supporting gel
film with a 50 wt % remaining volatile component and a thickness of
about 0.10 mm was obtained. The gel film was then detached from the
endless belt and, with its end portions fastened on a tenter frame,
conveyed to a heating furnace maintained at 200.degree. C.,
350.degree. C., and 550.degree. C. Slitting the end portions
produced a polyimide film with a width of 1500 mm and a thickness
of 12.5 .mu.m. Table 7 shows the molecular orientation MOR-c,
modulus, tensile strength, and coefficient of thermal expansion of
the polyimide film.
Comparative Example 21
[0251] A gel film with a 45 wt % remaining volatile component and a
thickness of about 0.10 mm was obtained as in Example 19, except
that the mixture was adjusted to have 5.5 mole equivalent and 2.0
mole equivalent of acetic anhydride and isoquinoline, respectively,
with respect to the amic acid group of the polyamic acid. Then, the
gel film was detached from the endless belt and, with its end
portions fastened on a tenter frame, conveyed to a heating furnace
maintained at 200.degree. C., 350.degree. C., and 550.degree. C.
Slitting the end portions produced a polyimide film with a width of
1500 mm and a thickness of 25 .mu.m. Table 7 shows the molecular
orientation MOR-c, modulus, tensile strength, and coefficient of
thermal expansion of the polyimide film.
Comparative Example 22
[0252] A polyimide film with a width of 1500 mm and a thickness of
12.5 .mu.m was obtained as in Example 19, except that the gel film
was conveyed to a heating furnace maintained at 300.degree. C.,
450.degree. C., and 550.degree. C. for heating. Table shows the
molecular orientation MOR-c, modulus, tensile strength, and
coefficient of thermal expansion of the polyimide film.
[0253] It can be seen from Table 6 and Table 7 that an isotropic
film with an extremely small variance of properties in the
direction of the principal axis of orientation and the direction
perpendicular to the principal axis can be obtained when the
molecular orientation MOR-c is not more than 1.30 or not more than
1.20 in any part of the film in the transverse direction.
TABLE-US-00006 TABLE 6 POSITIONS FROM THE CENTER 750 mm 375 mm 0 mm
375 mm 750 mm EXAMPLE 19 MOR-c VALUE 1.20 1.12 1.05 1.13 1.13
MODULUS (GPa) 4.2 4.1 4.2 4.2 4.2 4.2 4.1 4.0 4.2 4.1 TENSILE 311
308 304 300 305 301 300 298 310 290 STRENGTH (MPa) COEFFICIENT OF
15 16 15 16 16 16 15 16 15 16 THERMAL EXPANSION (ppm) COMPARATIVE
MOR-c VALUE 1.40 1.20 1.03 1.22 1.35 EXAMPLE 19 MODULUS (GPa) 4.7
3.6 4.3 3.9 4.1 4.0 4.3 3.9 4.6 3.7 TENSILE 343 281 315 298 305 301
310 290 340 275 STRENGTH (MPa) COEFFICIENT OF 13 18 15 18 16 16 15
17 13 19 THERMAL EXPANSION (ppm) COMPARATIVE MOR-c VALUE 1.48 1.29
1.11 1.28 1.43 EXAMPLE MODULUS (GPa) 4.6 3.5 4.4 3.8 4.1 3.9 4.2
3.8 4.5 3.6 20 TENSILE 351 288 318 295 310 300 309 289 340 271
STRENGTH (MPa) COEFFICIENT OF 13 20 15 18 16 17 14 18 13 19 THERMAL
EXPANSION (ppm) (LEFT COLUMN: DIRECTION OF PRINCIPLE AXIS OF
ORIENTATION; RIGHT COLUMN: DIRECTION PERPENDICULAR TO PRINCIPLE
AXIS OF ORIENTATION)
TABLE-US-00007 TABLE 7 POSITIONS FROM THE CENTER 750 mm 375 mm 0 mm
375 mm 750 mm EXAMPLE 20 MOR-c VALUE 1.18 1.15 1.10 1.13 1.15
MODULUS (GPa) 4.3 4.2 4.2 4.2 4.3 4.2 4.2 4.2 4.3 4.2 TENSILE 320
305 315 311 307 305 309 306 316 304 STRENGTH (MPa) COEFFICIENT 15
16 16 16 16 16 15 16 15 16 OF THERMAL EXPANSION (ppm) COMPARATIVE
MOR-c VALUE 1.46 1.19 1.02 1.15 1.40 EXAMPLE 21 MODULUS (GPa) 4.8
3.5 4.4 4.0 4.3 4.3 4.3 4.1 4.7 3.7 TENSILE 350 293 327 300 310 310
312 310 344 299 STRENGTH (MPa) COEFFICIENT 12 19 13 17 16 16 13 17
13 19 OF THERMAL EXPANSION (ppm) COMPARATIVE MOR-c VALUE 1.50 1.25
1.15 1.28 1.43 EXAMPLE MODULUS (GPa) 4.6 3.5 4.4 3.8 4.1 3.9 4.2
3.8 4.5 3.6 22 TENSILE 351 288 318 295 310 300 309 289 340 271
STRENGTH (MPa) COEFFICIENT 13 20 15 18 16 17 14 18 13 19 OF THERMAL
EXPANSION (ppm) (LEFT COLUMN: DIRECTION OF PRINCIPLE AXIS OF
ORIENTATION; RIGHT COLUMN: DIRECTION PERPENDICULAR TO PRINCIPLE
AXIS OF ORIENTATION)
[0254] With the present invention, an isotropic film with extremely
small differences of mechanical properties between any points of
the film can be obtained. The film can be obtained with an improved
in-plane isotropy particularly at the end portions. The film can be
suitably put to applications where precise dimension accuracy is
required, such as in flexible printed circuit boards, TAB carrier
tapes, or cover lay films for flexible printed circuit boards.
[0255] In the following Examples and Comparative Examples, the
modulus and tensile strength of polyimide films were measured
according to JIS C-2318.
[0256] The coefficient of thermal expansion was measured using the
thermophysical testing instrument TMA-8140 of Rigaku. The film at
room temperature was heated to 400.degree. C. at 10.degree.
C./minute and then cooled back to room temperature. The same
heating was carried out again to obtain coefficient of thermal
expansion in a temperature range of 100.degree. C. to 200.degree.
C.
[0257] As the term is used herein, "birefringence" is the
difference of refractive indices between an arbitrary direction in
the film plane and the direction of thickness, which is given as
follows.
Birefringence .DELTA.n=(refractive index Nx in an in-plane
direction)-(refractive index Nz in the direction of thickness)
[0258] FIG. 3 briefly shows a specific example of the measurement
method. A portion of a film sample 21 is cut out in the form of a
wedge 22. Projecting sodium light 24 in parallel onto the bottom of
the wedge, i.e., the film plane, produces interference fringes 25,
which can be seen under a polarizing microscope. When the number of
interference fringes is n, the birefringence .DELTA.n can be
expressed as follows.
.DELTA.n=n.times..lamda./d
where .lamda. is the wavelength of sodium D light at 589 nm, and d
is the width (nm) of the sample. Details are explained in New
Lecture on Experimental Chemistry, Vol. 19 (published by Maruzen
Co., Ltd.)
Comparative Example 23
[0259] Polyamic acid was synthesized from a 4:3:1 mole ratio of
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. 100 g of a 18.5 wt % N,N-dimethylformamide
solution of the polyamic acid was mixed and stirred with 35 g of
acetic anhydride and 5 g of isoquinoline. After defoamed by
centrifugation, the mixture was cast on an aluminum foil to form a
resin film of 400 .mu.m. The mixture was stirred and defoamed while
cooling to 0.degree. C. The resin film was then heated at
100.degree. C. for 120 seconds and detached from the aluminum foil
to obtain a self-supporting gel film. The content of remaining
volatile component and percent imidization of the gel film were
160% and 81%, respectively. Thereafter, the gel film, with its end
portions fastened on a pin frame, was heated at 150.degree. C.,
250.degree. C., 450.degree. C., and 500.degree. C. for 30 seconds
at each temperature, so as to produce a polyimide film with a
thickness of 25 .mu.m. Table 8 shows properties of the polyimide
film.
Comparative Example 24
[0260] Polyamic acid was synthesized from a 4:3:1 mole ratio of
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. 100 g of a 18.5 wt % N,N-dimethylformamide
solution of the polyamic acid was mixed and stirred with 40 g of
acetic acid anhydride and 8 g of isoquinoline. After defoaming by
centrifugation, the mixture was cast on an aluminum foil to form a
resin film of 400 .mu.m. The mixture was stirred and defoamed while
cooling to 0.degree. C. The resin film was then heated at
140.degree. C. for 150 seconds and detached from the aluminum foil
to obtain a self-supporting gel film. The content of remaining
volatile component and percent imidization of the gel film were 35%
and 92%, respectively. Thereafter, the gel film, with its end
portions fastened on a pin frame, was heated at 350.degree. C.,
400.degree. C., 450.degree. C., and 500.degree. C. for 30 seconds
at each temperature, so as to produce a polyimide film with a
thickness of 25 .mu.m. Table 8 shows properties of the polyimide
film.
Example 21
[0261] A gel film with a content of remaining volatile component
160% and percent imidization 81% was obtained in the exactly the
same manner as in Comparative Example 23. The gel film, with its
end portions fastened on a pin frame, was heated at 350.degree. C.,
400.degree. C., 450.degree. C., and 500.degree. C. for 30 seconds
at each temperature, so as to produce a polyimide film with a
thickness of 25 .mu.m. Table 8 shows properties of the polyimide
film.
Comparative Example 25
[0262] Polyamic acid was synthesized from a 3:1:3:1 mole ratio of
p-phenylene bis (trimellitic acid monoester anhydride),
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. 100 g of a 18.5 wt % N,N-dimethylformamide
solution of the polyamic acid was mixed and stirred with 35 g of
acetic anhydride and 3.5 g of .beta.-picoline. After defoamed by
centrifugation, the mixture was cast on an aluminum foil to form a
resin film of 400 .mu.m. The mixture was stirred and defoamed while
cooling to 0.degree. C. The resin film was then heated at
90.degree. C. for 120 seconds and detached from the aluminum foil
to obtain a self-supporting gel film. The content of remaining
volatile component and percent imidization of the gel film were
140% and 80%, respectively. Thereafter, the gel film, with its end
portions fastened on a pin frame, was heated at 180.degree. C.,
370.degree. C., and 520.degree. C. for 45 seconds at each
temperature, so as to produce a polyimide film with a thickness of
25 .mu.m. Table 8 shows properties of the polyimide film.
Comparative Example 26
[0263] Polyamic acid was synthesized from a 3:1:3:1 mole ratio of
p-phenylene bis (trimellitic acid monoester anhydride),
pyromellitic dianhydride, 4,4'-diaminodiphenylether, and
p-phenylenediamine. 100 g of a 18.5 wt % N,N-dimethylformamide
solution of the polyamic acid was mixed and stirred with 35 g of
acetic anhydride and 4.2 g of .beta.-picoline. After defoamed by
centrifugation, the mixture was cast on an aluminum foil to form a
resin film of 400 .mu.m. The mixture was stirred and defoamed while
cooling to 0.degree. C. The resin film was then heated at
90.degree. C. for 120 seconds and detached from the aluminum foil
to obtain a self-supporting gel film. The content of remaining
volatile component and percent imidization of the gel film were 33%
and 95%, respectively. Thereafter, the gel film, with its end
portions fastened on a pin frame, was heated at 350.degree. C.,
450.degree. C., and 520.degree. C. for 45 seconds at each
temperature, so as to produce a polyimide film with a thickness of
25 .mu.m. Table 8 shows properties of the polyimide film.
Example 22
[0264] A gel film with a content of remaining volatile component
140% and percent imidization 80% was obtained in the exactly the
same manner as in Comparative Example 25. The gel film, with its
end portions fastened on a pin frame, was heated at 350.degree. C.,
400.degree. C., 450.degree. C., and 520.degree. C. for 45 seconds
at each temperature, so as to produce a polyimide film with a
thickness of 25 .mu.m. Table 8 shows properties of the polyimide
film.
TABLE-US-00008 TABLE 8 COMPARATIVE COMPARATIVE EXAMPLE COMPARATIVE
COMPARATIVE EXAMPLE EXAMPLE 23 EXAMPLE 24 21 EXAMPLE 25 EXAMPLE 26
22 CONTENT OF REMAINING 160 35 160 140 33 140 VOLATILE COMPONENT
(%) INITIAL TEMPERATURE 150 350 350 180 350 350 OF HEATING
(.degree. C.) BIREFRINGENCE (.DELTA.n) 0.12 0.13 0.15 0.13 0.13
0.16 MODULUS (GPa) 4.0 4.1 4.5 4.6 4.9 5.4 TENSILE STRENGTH (MPa)
270 277 328 300 304 319 COEFFICIENT OF THERMAL 16.8 15.9 14.0 15.0
14.5 13.3 EXPANSION (ppm)
[0265] With the present invention, a polyimide film with high
modulus and low coefficient of thermal expansion can be provided
both inexpensively and stably by a process not found
conventionally, without increasing the number of monomer
components, or without introducing expensive rigid monomers or a
complex stretching device. The present invention can be suitably
put to applications where precise dimension accuracy is required,
such as in flexible printed circuit boards, TAB carrier tapes, or
cover lay films for flexible printed circuit boards.
[0266] A process for producing a polyimide film according to the
present invention may be adapted to include the steps of: casting
or coating and subsequently drying an organic solvent solution of
polyamic acid on a support, so as to produce a partially cured
and/or partially dried polyamic acid film; dipping the polyamic
acid film in tertiary amine or in a solution of tertiary amine, or
applying tertiary amine or a solution of tertiary amine onto the
polyamic acid film; and drying the film while imidizing the
polyamic acid to polyimide.
[0267] A process for producing a polyimide film according to the
present invention may include the step of removing waste droplets
from a surface of the film.
[0268] A process for producing a polyimide film according to the
present invention may be adapted so that the partially cured and/or
partially dried polyamic acid film contains not more than 5 wt % to
100 wt % of remaining volatile component and has not less than 50%
percent imidization.
[0269] In a process for producing a polyimide film according to the
present invention, the tertiary amine may be selected from the
group consisting of quinoline, isoquinoline, .beta.-picoline, and
pyridine.
[0270] A polyimide film according to the present invention may be
produced by any of the foregoing processes.
[0271] Further, in order to achieve the foregoing objects, another
process for producing a polyimide film may be adapted to include
the steps of: mixing a chemical converting agent and a catalyst in
a polyamic acid organic solvent solution and casting the resulting
polyamic acid composition on a support; heating the polyamic acid
composition on the support at temperatures of at least two levels;
detaching the polyamic acid film from the support so as to obtain a
partially cured and/or partially dried polyamic acid film; and
imidizing remaining amic acid in the polyamic acid film and drying
the film.
[0272] A polyimide film according to the present invention may be
produced by the foregoing process.
[0273] A polyimide film according to the present invention may be
produced by the steps of: mixing a chemical converting agent and a
catalyst in a polyamic acid organic solvent solution and casting
the resulting polyamic acid composition on a support; heating the
polyamic acid composition on the support at temperatures of at
least two levels; detaching the polyamic acid film from the support
so as to obtain a partially cured and/or partially dried polyamic
acid film; and imidizing remaining amic acid in the polyamic acid
film and drying the film, wherein percent loss on heating of the
polyimide film is 0.2 wt % to 2.5 wt %, of which a 0.01 wt % or
greater portion with respect to a total weight of the film is from
the catalyst.
[0274] Further, in order to achieve the foregoing objects, another
process for producing a polyimide film according to the present
invention may be adapted to include the steps of: mixing a chemical
converting agent and a catalyst in a polyamic acid organic solvent
solution and casting and heating the mixture on a support;
detaching the mixture from the support with a remaining volatile
component, so as to obtain a partially cured and/or partially dried
polyamic acid film in which not less than 50 parts by weight is the
catalyst, not more than 30 parts by weight is the solvent, and not
more than 20 parts by weight is the chemical converting agent
and/or a component derived from the chemical converting agent, with
respect to 100 parts by weight of the remaining volatile component;
and imidizing remaining amic acid and drying the film.
[0275] A process for producing a polyamic acid according to the
present invention may be adapted so that the content of remaining
volatile component of the partially cured and/or partially dried
polyamic acid film is not more than 100 wt % when a weight of the
polyamic acid film after 450.degree. C. heating for 20 minutes is
used as a reference.
[0276] A process for producing a polyimide film according to the
present invention may be adapted so that the catalyst is a tertiary
amine.
[0277] A polyimide film according to the present invention may be
produced by the foregoing process.
[0278] A polyimide film according to the present invention has
percent weight loss by heating of 0.2 wt % to 2.5 wt %, which is
determined from
(percent weight loss by heating)=(X-Y)/Y,
where X is a film mass after 150.degree. C. heating for 10 minutes
and Y is a film mass after 450.degree. C. heating for 20 minutes,
the percent weight loss by heating containing a 0.01 wt % or
greater portion from a catalyst with respect to a total weight of
the film.
[0279] Further, in order to achieve the foregoing objects, a
process for producing a polyimide film according to the present
invention, which produces the polyimide film by deposition of a
polyamic acid containing composition by casting and/or coating, may
be adapted to include the step of adding, to an organic solvent
solution of the polyamic acid, a curing agent that contains a
1:0.15 to 1:0.75 mole ratio of not less than 1 mole equivalent of a
dehydrating agent with respect to the amic acid and not less than
0.2 mole equivalent of an imidizing catalyst with respect to the
amic acid.
[0280] Further, a process for producing a polyimide film according
to the present invention, in the foregoing producing process of the
polyimide film, may be adapted so that 30 to 70 parts of the curing
agent is added to an organic solvent solution of 100 parts polyamic
acid.
[0281] Further, a process for producing a polyimide film according
to the present invention, in the foregoing producing process of the
polyimide film, may be adapted so that a resin solution
composition, which is prepared by adding the curing agent in the
organic solvent solution of the polyamic acid, has a viscosity of
600 poise at 0.degree. C.
[0282] Further, a process for producing a polyimide film according
to the present invention, in the foregoing producing process of the
polyimide film, may be adapted so that a resin solution
composition, which is prepared by adding the curing agent in the
organic solvent solution of the polyamic acid, has a viscosity of
400 poise at 0.degree. C.
[0283] A process for producing a polyimide film according to the
present invention may be adapted so that the imidizing catalyst is
a tertiary amine.
[0284] The producing process of a polyimide film according to the
present invention produces the polyimide film that is produced by
the foregoing process.
[0285] Further, in order to achieve the foregoing objects, a
polyimide film according to the present invention may be adapted so
that a width during production is 1 m or greater, a ratio of
maximum value to minimum value of tear propagation strength
measured across the entire width is 0.7 or greater, and an R value
of measured tear propagation strength of 0.6 g.
[0286] A process for producing a polyimide film according to the
present invention may be adapted to deposit the film by casting a
resin solution which is prepared by adding to an organic solvent
solution of polyamic acid a curing agent containing not less than
1.0 to 3.0 mole equivalent of a dehydrating agent with respect to
amic acid and not less than 0.3 mole equivalent of an imidizing
catalyst with respect to the amic acid.
[0287] Further, a process for producing a polyimide film according
to the present invention may be adapted so that the imidizing
catalyst is a tertiary amine.
[0288] The present invention also provides a novel polyimide film
and novel producing processes of the following configurations.
[0289] 1) A polyimide film having a film width of 1250 mm or
greater, a molecular orientation MOR-c of not more than 1.30 at any
point of the film, and a tensile modulus of not less than 2.5 GPa
and not more than 5.0 GPa.
[0290] 2) A process for producing a polyimide film, which includes
the steps of: casting a polyamic acid mixture solution of polyamic
acid, dehydrating agent, ring-closure catalyst, and organic solvent
on a support so as to obtain a film ("gel film" hereinafter) that
is partially cured and/or partially dried to be self-supporting;
and passing the gel film through a heating furnace with both ends
of the gel film fastened, wherein
[0291] (1) the polyamic acid mixture solution is mixed with 1.0 to
5.0 equivalent of a dehydrating agent with respect to an amic acid
unit and 0.2 to 2.0 equivalent of a ring-closure catalyst with
respect to the amic acid unit, and
[0292] (2) an initial temperature of heating in the heating furnace
is controlled to be no more than +100.degree. C. of a temperature
of the support and within 150.degree. C. to 250.degree. C.
[0293] 3) A process of producing a polyimide film as defined in 2),
wherein the gel film contains the remaining volatile component in a
range of 15% to 150%.
[0294] 4) A process of producing a polyimide film as defined in 2)
or 3), wherein the polyamic acid is obtained by polycondensation of
monomers which contain a diamine component and an acid dianhydride
as a raw material, and the diamine component contains not less than
20 mole % of paraphenylenediamine with respect to the total diamine
component.
[0295] Further, a process for producing a polyimide film according
to the present invention may be adapted to include the steps of:
casting a polyamic acid mixture solution of polyamic acid,
dehydrating agent, ring-closure catalyst, and organic solvent on a
support so as to obtain a film ("gel film" hereinafter) that is
partially cured and/or partially dried to be self-supporting; and
heating the gel film by tenter heating in which a heat treatment is
carried out on the gel film with fastened both ends, wherein a
content of remaining volatile component of the gel film and an
initial temperature of heating in the tenter heating are controlled
to control modulus and coefficient of thermal expansion.
[0296] Further, a process for producing a polyimide film according
to the present invention may be adapted to include the steps of:
casting a polyamic acid mixture solution of polyamic acid,
dehydrating agent, ring-closure catalyst, and organic solvent on a
support so as to obtain a film ("gel film" hereinafter) that is
partially cured and/or partially dried to be self-supporting; and
heating the gel film by tenter heating in which heat treatment is
carried out on the gel film with fastened both ends, wherein a
content of remaining volatile component of the gel film and an
initial temperature of heating in the tenter heating are controlled
to increase modulus within a range of 1.0 GPa or to lower
coefficient of thermal expansion within a range of 4 ppm.
[0297] Further, the producing process of the polyimide film may be
adapted so that the content of remaining volatile component of the
gel film is set within 50 wt % to 300 wt %, and the initial
temperature in the tenter heating step is set within 200.degree. C.
to 400.degree. C.
[0298] Further, the producing process of the polyimide film may be
adapted so that the initial temperature of the tenter heating is
set within 250.degree. C. to 400.degree. C. when the content of
remaining volatile component of the gel film is 50 wt % to 150 wt
%, or within 200.degree. C. to 350.degree. C. when the content of
remaining volatile component of the gel film is 150 wt % to 300 wt
%.
[0299] Further, the producing process of the polyamic acid may be
adapted so that the polyamic acid, which is the precursor of the
polyimide, is obtained by polycondensation of monomers which mainly
contain aromatic tetracarboxylic dianhydride and aromatic diamine
as a raw material, and the proportion of paraphenylene contained is
not less than 20 mole % and not more than 65 mole % with respect to
the total aromatic diamine component.
[0300] A polyimide film according to the present invention may be
produced by the foregoing producing process of the polyimide film
to have a birefringence of not less than 0.15.
[0301] The invention being thus described by way of specific
embodiments and examples in the foregoing best mode for carrying
out the invention section, it will be obvious that the same way may
be varied in many ways. Such variations are not to be regarded as a
departure from the spirit and scope of the invention, and all such
modifications as would be obvious to one skilled in the art are
intended to be included within the scope of the following
claims.
INDUSTRIAL APPLICABILITY
[0302] The present invention relates to polyimide films with high
mechanical strengths and producing processes of such polyimide
films. The invention is applicable, for example, in the fields of
electronic and electrical component materials of computers and IC
controls.
* * * * *