U.S. patent application number 12/278885 was filed with the patent office on 2010-07-01 for biaxially oriented polyester film and magnetic recording tape.
This patent application is currently assigned to TEIJIN DUPONT FILMS JAPAN LIMITED. Invention is credited to Takeshi Ishida, Ieyasu Kobayashi, Shinji Muro.
Application Number | 20100167092 12/278885 |
Document ID | / |
Family ID | 38344988 |
Filed Date | 2010-07-01 |
United States Patent
Application |
20100167092 |
Kind Code |
A1 |
Kobayashi; Ieyasu ; et
al. |
July 1, 2010 |
BIAXIALLY ORIENTED POLYESTER FILM AND MAGNETIC RECORDING TAPE
Abstract
A biaxially oriented polyester film which has a Young's modulus
(YMD) in the film machine direction (YMD) of 6.5 GPa or more and a
Young's modulus in the width direction (YTD) of 8.2 to 9.8 GPa and
is used as a base film for magnetic recording tapes of linear
recording system, and a magnetic recording tape of linear recording
system comprising the same as a base film. There are provided a
biaxially oriented polyester film which has excellent dimensional
stability, especially dimensional stability in the width direction
and is suitable for use as a base film for magnetic recording tapes
of linear recording system and a magnetic recording tape comprising
the same.
Inventors: |
Kobayashi; Ieyasu; (Gifu,
JP) ; Muro; Shinji; (Gifu, JP) ; Ishida;
Takeshi; (Gifu, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW, SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
TEIJIN DUPONT FILMS JAPAN
LIMITED
Chiyoda-ku, Tokyo
JP
|
Family ID: |
38344988 |
Appl. No.: |
12/278885 |
Filed: |
December 27, 2006 |
PCT Filed: |
December 27, 2006 |
PCT NO: |
PCT/JP2006/326369 |
371 Date: |
August 8, 2008 |
Current U.S.
Class: |
428/832 ;
428/847.2; 428/847.6; 528/271 |
Current CPC
Class: |
G11B 5/73929 20190501;
B29K 2067/00 20130101; C08J 2367/02 20130101; G11B 5/73931
20190501; C08J 5/18 20130101; B29C 55/143 20130101; G11B 5/7305
20130101; G11B 5/73927 20190501; G11B 5/733 20130101; G11B 5/73935
20190501; B29C 55/12 20130101 |
Class at
Publication: |
428/832 ;
428/847.2; 428/847.6; 528/271 |
International
Class: |
G11B 5/66 20060101
G11B005/66; G11B 5/73 20060101 G11B005/73; C08G 63/00 20060101
C08G063/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 9, 2006 |
JP |
2006-032343 |
Claims
1. A biaxially oriented polyester film which has a Young's modulus
in the film machine direction (YMD) of 6.5 GPa or more and a
Young's modulus in the width direction (YTD) of 8.2 to 9.8 GPa and
is used as a base film for magnetic recording tapes of linear
recording system.
2. The biaxially oriented polyester film according to claim 1,
wherein the polyester is polyethylene-2,6-naphthalene
dicarboxylate.
3. The biaxially oriented polyester film according to claim 1,
which has a thickness of 3 to 6 .mu.m.
4. The biaxially oriented polyester film according to claim 1,
wherein the total of YMD and YTD is 15 to 18 GPa.
5. The biaxially oriented polyester film according to claim 1,
wherein YTD is equal to or lager than YMD.
6. The biaxially oriented polyester film according to claim 1,
which has a temperature expansion coefficient in the film width
direction of -8 to +1 ppm/.degree. C.
7. The biaxially oriented polyester film according to claim 1,
which has a humidity expansion coefficient in the film width
direction of 5 to 10 ppm % RH.
8. The biaxially oriented polyester film according to claim 1,
which has a heat shrinkage factor (105.degree. C..times.30 minutes)
in the film width direction of 0.8% or less.
9. The biaxially oriented polyester film according to claim 1,
which has a rupture elongation in the film width direction of 45%
or more.
10. The biaxially oriented polyester film according to claim 1,
which has a crystallinity of 28 to 33%.
11. The biaxially oriented polyester film according to claim 1,
which has a dimensional change in the film width direction of more
than 0.3% and 1% or less when a load of 32 MPa is applied thereto
in the film machine direction in a 40.degree. C. and 90% RH
atmosphere.
12. The biaxially oriented polyester film according to claim 1,
wherein the surface roughness (WRa) of at least one surface is 1 to
10 nm.
13. The biaxially oriented polyester film according to claim 1,
which is a single-layer film and has a surface roughness (WRa) of 1
to 10 nm.
14. The biaxially oriented polyester film according to claim 1,
which is a laminate film consisting of two polyester film layers A
and B.
15. The biaxially oriented polyester film according to claim 14,
wherein the layer A is formed on the side on which a magnetic layer
is to be formed and has a surface roughness (WRa(A)) of 0.5 to 4 nm
and the layer B is formed on the side on which no magnetic layer is
to be formed and has a surface roughness (WRa(B)) of 5 to 10
nm.
16. The biaxially oriented polyester film according to claim 14,
wherein the layer A contains inert particles A having an average
particle diameter of 0.01 to 0.20 .mu.m in an amount of 0.01 to
0.15 wt % based on the weight of the layer A and the layer B
contains inert particles B2 having an average particle diameter of
0.2 to 0.4 .mu.m in an amount of 0.01 to 0.2 wt % based on the
weight of the layer B.
17. The biaxially oriented polyester film according to claim 16,
wherein the layer B contains inert particles B1 having an average
particle diameter of 0.01 to 0.20 .mu.m in an amount of 0.01 to 0.3
wt % based on the weight of the layer B besides the inert particles
B2.
18. The biaxially oriented polyester film according to claim 16,
wherein the average particle diameter of the inert particles A is
0.01 to 0.18 .mu.m, the thickness (t) of the entire film is 3 to 6
.mu.m, and the thickness (tB) of the layer B accounts for 50 to 90%
of the thickness (t) of the entire film.
19. The biaxially oriented polyester film according to claim 16,
wherein the thickness (t) of the entire film is 3 to 6 .mu.m, the
thickness (tB) of the layer B accounts for more than 20% and less
than 50% of the thickness (t) of the entire film, and the value
(tB/dB) obtained by dividing tB by the average particle diameter
(dB) of all the inert particles contained in the layer B is 2 to
30.
20. The biaxially oriented polyester film according to claim 16,
wherein the thickness (t) of the entire film is 3 to 6 .mu.m, the
thickness (tB) of the layer B accounts for 10 to 20% of the
thickness (t) of the entire film, and the value (tB/dB) obtained by
dividing tB by the average particle diameter (dB) of all the inert
particles contained in the layer B is 0.5 to 15.
21. The biaxially oriented polyester film according to claim 16,
wherein the inert particles A are spherical silica particles or
heat-resistant polymer particles.
22. The biaxially oriented polyester film according to claim 17,
wherein the inert particles B1 have an average particle diameter
0.1 .mu.m or more smaller than that of the inert particles B2.
23. The biaxially oriented polyester film according to claim 17,
wherein the inert particles A and the inert particles B1 are of the
same chemical species.
24. The biaxially oriented polyester film according to claim 16,
wherein the inert particles B2 are crosslinked organic
particles.
25. A magnetic recording tape of linear recording system comprising
a biaxially oriented polyester film having a Young's modulus in the
film machine direction (TMD) of 6.5 GPa or more and a Young's
modulus in the width direction (YTD) of 8.2 to 9.8 GPa and a
non-magnetic layer and a magnetic layer formed on one side of the
film and a back coat layer formed on the other side.
26. The magnetic recording tape according to claim 24, wherein the
total thickness of the non-magnetic layer, magnetic layer and back
coat layer is 0.2 to 0.8 based on the thickness of the biaxially
oriented polyester film.
Description
TECHNICAL FIELD
[0001] The present invention relates to a biaxially oriented
polyester film which is suitable for use as a base film for
magnetic recording tapes of linear recording system and a magnetic
recording tape of linear recording system, comprising the same.
BACKGROUND OF THE ART
[0002] A polyester film is used in a magnetic recording tape
because it has excellent thermal and mechanical properties.
Magnetic recording tapes, especially data storage magnetic
recording tapes require a larger storage capacity and a higher
recording density as the size of data to be recorded is growing,
and the requirements for the characteristic properties of base
films constituting the magnetic recording tapes are becoming more
severe.
[0003] Out of the magnetic recording tapes, magnetic recording
tapes for data storage such as QIC, DLT, large-capacity super-DLT
and LTO employ linear recording system (also called "linear track
system"), and the track pitch is becoming very narrow to realize a
large capacity and a high density for the magnetic recording tapes.
The dimensional changes rate in the width direction of the magnetic
recording tape changes, track dislocation occurs even if the
dimensional changes rate in the width direction is so small that it
does not cause a problem in the prior art, whereby an error
occurs.
[0004] The dimensional changes rate in the width direction of the
magnetic recording tape are caused by temperature and humidity
variations and tension variations. To solve these the dimensional
changes rate in the width direction dimensional changes rate in the
width direction, the pamphlet of WO99/29488 proposes a biaxially
oriented polyester film whose temperature expansion coefficient
.alpha.t in the width direction (.times.10.sup.-6/.degree. C.),
humidity expansion coefficient .alpha.h in the width direction
(.times.10.sup.-6/% RH) and shrinkage factor P (ppm/g) in the width
direction for a load which is applied in the longitudinal direction
are set to specific ranges. The pamphlet of WO00/76749 and the
pamphlet of WO02/45959 also propose a biaxially oriented polyester
film whose dimensional changes rate in the width direction when it
is left under load in the longitudinal direction, temperature
expansion coefficient .alpha.t in the width direction
(.times.10.sup.-6/.degree. C.), humidity expansion coefficient
.alpha.h in the width direction (.times.10.sup.-6/% RH) and
dimensional changes rate in the width direction (%) for a load
which is applied in the longitudinal direction are set to specific
ranges.
[0005] However, the requirements for large storage capacity and
high recording density from magnetic recording tapes are becoming
more severe nowadays and the biaxially oriented polyester films
proposed by these patent documents cannot meet the requirements
fully.
DISCLOSURE OF THE INVENTION
[0006] It is a first object of the present invention to provide a
biaxially oriented polyester film which has excellent dimensional
stability, especially dimensional stability in the width direction,
and is suitable for use as a base film for magnetic recording tapes
of linear recording system, especially linear tape-open (LTO), and
a magnetic recording tape comprising the biaxially oriented
polyester film.
[0007] It is a second object of the present invention to provide a
biaxially oriented polyester film which has excellent dimensional
stability, especially dimensional stability in the width direction,
and film forming properties and is suitable for use as a base film
for magnetic recording tapes of linear recording system, especially
linear tape-open (LTO), and a magnetic recording tape comprising
the biaxially oriented polyester film.
[0008] It is a third object of the present invention to provide a
biaxially oriented polyester film which has excellent dimensional
stability, especially dimensional stability in the width direction,
and excellent electromagnetic conversion characteristics and is
suitable for use as a base film for magnetic recording tapes of
linear recording system, especially linear tape-open (LTO), and a
magnetic recording tape comprising the biaxially oriented polyester
film.
[0009] It is a fourth object of the present invention to provide a
biaxially oriented polyester film which has excellent dimensional
stability, especially dimensional stability in the width direction,
and excellent electromagnetic conversion characteristics and
recyclability and is suitable for use as a base film for magnetic
recording tapes of linear recording system, especially linear
tape-open (LTO), and a magnetic recording tape comprising the
biaxially oriented polyester film.
[0010] It is a fifth object of the present invention to provide a
biaxially oriented polyester film which has excellent dimensional
stability, especially dimensional stability in the width direction,
excellent electromagnetic conversion characteristics and
recyclability and also film forming properties and is suitable for
use as a base film for magnetic recording tapes of linear recording
system, especially linear tape-open (LTO), and a magnetic recording
tape comprising the biaxially oriented polyester film.
[0011] When a magnetic recording tape of linear recording system
and a magnetic recording tape of helical system are compared with
each other, as damage to the edge of the tape does not become
problematic in the magnetic recording tape of linear recording
system unlike the magnetic recording tape of helical system, a high
Young's modulus in the transverse direction of the tape is not
required. Since tension applied in the traveling direction of the
tape is larger in the tape of linear recording system than that of
the tape of helical system, a high Young's modulus in the
longitudinal direction is required, and a tape having a higher
Young's modulus in the film machine direction than that in the
transverse direction is proposed in the above patent documents.
Since a high-density magnetic recording tape is becoming extremely
thin in order to increase its recording capacity, it is considered
that this tendency becomes stronger and stronger.
[0012] However, when the inventors of the present invention have
conducted intensive studies to solve the above problem, they have
found that it is important to enhance the dimensional stability in
the width direction where temperature and humidity variations are
received more than in the film machine direction because a
high-density magnetic recording tape having a storage capacity of
more than 500 GB is thin and tension applied during the traveling
of the tape is suppressed. As the thickness of the tape is becoming
smaller due to the recent demand for high density, the thickness of
a base film is becoming smaller but the total thickness of a back
coat layer, a magnetic layer and a non-magnetic layer cannot be
made very small to achieve surface flatness. Therefore, the
proportion of the base film to the magnetic tape is decreasing.
Although it has been considered that the temperature expansion
coefficient .alpha.t in the width direction of the film should be
about the same as the temperature expansion coefficient .alpha.t of
a magnetic head for reading it (about 7 ppm/.degree. C. in the case
of a MR head), the temperature expansions of the back coat layer,
magnetic layer and non-magnetic layer are large and their
influences are large. Therefore, to provide higher dimensional
stability, they have found that it is necessary to ease the
temperature expansions of these layers with the base film, that is,
it is important to provide an extremely low temperature expansion
coefficient to the base film.
[0013] According to the present invention, there is provided a
biaxially oriented polyester film which has a Young's modulus (YMD)
in the film machine direction of 6.5 GPa or more and a Young's
modulus (YTD) in the width direction of 8.2 to 9.8 GPa and is used
as a base film for magnetic recording tapes of linear recording
system.
[0014] According to the present invention, there is further
provided a biaxially oriented polyester film having at least one of
features that the polyester is polyethylene-2,6-naphtahlene
dicarboxylate, the thickness of the film is 3 to 6 .mu.m, the total
of YMD and YTD is 15 to 18 GPa, YTD is equal to or larger than YMD,
the temperature expansion coefficient in the width direction of the
film is -8 to +1 ppm/.degree. C., the humidity expansion
coefficient in the width direction of the film is 5 to 10 ppm % RH,
the heat shrinkage factor (105.degree. C..times.30 minutes) in the
width direction of the film is 0.8% or less, the rupture elongation
in the width direction of the film is 45% or more, the
crystallinity of the film is 28 to 33%, the dimensional change rate
in the width direction when a load of 32 MPa is applied in the film
machine direction in a 40.degree. C. and 90% RH atmosphere is more
than 0.3% and 1% or less, the surface roughness (WRa) of at least
one surface is 1 to 10 nm, the roughness (WRa) of at least one
surface of the film is 1 to 10 nm, the biaxially oriented polyester
film is a single-layer film having a surface roughness (WRa) of 1
to 10 nm, the polyester film is a laminate film consisting of two
polyester film layers (layers A and B), the layer A is formed on
the side on which a magnetic layer is to be formed and has a
surface roughness (WRa(A)) of 0.5 to 4 nm, the layer B is formed on
the side on which no magnetic layer is to be formed and has a
surface roughness (WRa(B)) of 5 to 10 nm, the layer A contains
inert particles A having an average particle diameter of 0.01 to
0.18 .mu.m in an amount of 0.01 to 0.15 wt % based on the weight of
the layer A, the layer B contains inert particles B1 having an
average particle diameter of 0.01 to 0.18 .mu.m in an amount of
0.01 to 0.3 wt % and inert particles B2 having an average particle
diameter of 0.2 to 0.4 .mu.m in an amount of 0.01 to 0.2 wt % based
on the weight of the layer B, the thickness (t) of the whole film
is 3 to 6 .mu.m, the thickness of the layer B accounts for 50 to
90% of the thickness of the whole biaxially oriented polyester
laminate film, the layer A contains inert particles A having an
average particle diameter of 0.01 to 0.20 .mu.m in an amount of
0.01 to 0.15 wt % based on the weight of the layer A, the total
thickness of the film is 3 to 6 .mu.m, the (tB/t) ratio of the
thickness (tB) of the layer B to the thickness (t) of the whole
film is 10% or more and less than 50%, the layer B contains the
inert particles B2 having an average particle diameter of 0.2 to
0.4 .mu.m in an amount of 0.01 to 0.20 wt % based on the weight of
the layer B, the (tB/dB) ratio of the thickness (tB) of the layer B
to the average particle diameter (dB) of all the inert particles
contained in the polyester layer B is 0.5 to 25, the inert
particles A are spherical silica particles or heat-resistant
polymer particles, the layer B further contains inert particles B1
having an average particles diameter 0.1 .mu.m or more smaller than
that of the inert particles B2, the inert particles A and the inert
particles B1 are the same inert particles, tB/t is more than 20%
and less than 50%, tB/dB is 5 to 25, tB/t is 10 to 20%, tB/dB is
0.5 to 10, and the inert particles B2 are crosslinked organic
particles.
[0015] According to the present invention, there are further
provided a magnetic recording tape of linear recording system which
comprises the above biaxially oriented polyester film of the
present invention, a non-magnetic layer and a magnetic layer formed
on one side of the film, and a back coat layer formed on the other
side, and a magnetic recording tape in which the ratio of the total
thickness of the non-magnetic layer, magnetic layer and back coat
layer to the thickness of the biaxially oriented polyester film is
0.2 to 0.8.
BRIEF DESCRIPTION OF THE DRAWING
[0016] FIG. 1(A) is a diagram of an apparatus for measuring the
chipping resistance of a film, and FIG. 1(B) is an enlarged view of
the blade of the apparatus and guide rollers located on the right
and left sides of the blade.
BEST MODE FOR CARRYING OUT THE INVENTION
[0017] The present invention will be described in detail
hereinunder. For the convenience of explanation, the film machine
direction of the biaxially oriented polyester film is called
"vertical direction, longitudinal direction or MD direction" and
the direction orthogonal to the film machine direction is called
"width direction, transverse direction or TD direction". The
vertical direction, longitudinal direction, transverse direction
and width direction of a magnetic recording tape mean the same as
the vertical direction, longitudinal direction, transverse
direction and width direction of the biaxially oriented polyester
film, respectively.
<Polyester>
[0018] The biaxially oriented polyester film of the present
invention is made from an aromatic polyester. The term "aromatic
polyester" as used herein denotes a polymer obtained by
polycondensing a diol and an aromatic dicarboxylic acid. Examples
of the aromatic dicarboxylic acid include terephthalic acid,
isophthalic acid, 2,6-naphthalenedicarboxylic acid and
4,4'-diphenyldicarboxylic acid. Examples of the diol include
ethylene glycol, 1,4-butanediol, 1,4-cyclohexandimethanol and
1,6-hexanediol. Out of these, polyethylene terephthalate and
polyethylene-2,6-naphthalene dicarboxylate are preferred from the
viewpoint of mechanical properties, and
polyethylene-2,6-naphthalene dicarboxylate is particularly
preferred because it has high mechanical properties and dimensional
stability.
[0019] The aromatic polyester in the present invention is not
limited to a homopolymer but may be a copolymer or a mixture as far
as it does not impair the effect of the present invention. The
amount of another component to be copolymerized or mixed is
preferably 10 mol % or less, more preferably 5 mol % or less based
on the number of mols of the recurring unit. Comonomers known per
se may be used, such as a diol component exemplified by diethylene
glycol, neopentyl glycol and polyalkylene glycol and a dicarboxylic
acid component exemplified by adipic acid, sebacic acid, phthalic
acid, isophthalic acid, terephthalic acid and 5-sodium
sulfoisophthalic acid. It is preferred that syndiotactic
polystyrene should be copolymerized or mixed to reduce the humidity
expansion coefficient of the obtained biaxially oriented polyester
film and that polyimide should be copolymerized or mixed to improve
the mechanical properties or thermal properties of the film.
[0020] The intrinsic viscosity of the polyester resin in the
present invention is preferably 0.40 or more, more preferably 0.40
to 0.80, particularly preferably 0.5 to 0.7 in o-chlorophenol at
35.degree. C. When the intrinsic viscosity is less than 0.4,
breakage may often occur during film formation or the strength of a
molded product may become unsatisfactory. When the intrinsic
viscosity is higher than 0.8, productivity at the time of
polymerization tends to lower.
<Young's Modulus>
[0021] The biaxially oriented polyester film of the present
invention has a Young's modulus in the film machine direction (YMD)
of 6.5 GPa or more, preferably 6.7 GPa or more, more preferably 7.0
GPa or more, particularly preferably 7.5 GPa or more, most
preferably 8 GPa or more. When the Young's modulus in the film
machine direction (YMD) falls below the lower limit, the film is
stretched in the running direction of the magnetic tape, that is,
the film machine direction of the film and the width of the film is
narrowed while it is caused to run repeatedly as a magnetic tape
with the result of the occurrence of track dislocation. This is due
to a dimensional change with time (creep) in the width direction of
the film caused by applying a load in the film machine direction of
the film for a long time. When YMD exceeds the upper limit, it is
difficult to set the Young's modulus in the width direction of the
film to the above range from the viewpoint of film forming
properties. Therefore, YMD is preferably 9 GPa or less.
[0022] The Young's modulus in the width direction (YTD) of the
biaxially oriented polyester film of the present invention must be
8.2 to 9.8 GPa, preferably 8.5 to 9.5 GPa, more preferably 8.7 to
9.3 GPa. When YTD is outside the above range, the difference
between the dimensional changes rate in the width direction of the
magnetic head and the tape by temperature variations becomes large
with the result of the occurrence of track dislocation. The total
of YMD and YTD is 15 to 18 GPa, preferably 16 to 18 GPa. When the
total of YMD and YTD falls below the lower limit, the Young's
modulus in the film machine direction (YMD) or the Young's modulus
in the width direction (YTD) does not become the above value and
the dimensional changes rate in the width direction of the film
becomes large with the result of the occurrence of track
dislocation. When the total of YMD and YTD exceeds the upper limit,
it is extremely difficult to form a film (film breakage often
occurs), which is not preferred from the viewpoint of
productivity.
[0023] It is preferred that YTD of the biaxially oriented polyester
film of the present invention should be equal to or larger than YMD
because a biaxially oriented polyester film having little track
dislocation of interest is stably obtained and the surface
properties of the obtained biaxially oriented polyester film can be
easily made excellent. From this point of view, YTD is preferably
0.5 GPa or more larger than YMD. Meanwhile, the difference between
YTD and YMD is preferably 2.5 GPa or less, more preferably 2.0 GPa
or less because the dimensional changes rate in the width direction
caused by the above creep and temperature and humidity variations
can be easily made small.
<Temperature Expansion Coefficient in Width Direction of
Film>
[0024] Preferably, the biaxially oriented polyester film of the
present invention has a temperature expansion coefficient .alpha.t
in the width direction of the film of -8 to +1 ppm/.degree. C. It
is more preferably -6 to 0 ppm/.degree. C., particularly preferably
-5 to -1 ppm/.degree. C. When at is outside the above range, the
temperature expansion of a layer other than the base film of the
obtained magnetic recording tape cannot be fully suppressed and the
dimensional changes rate in the width direction of the film by
temperature variations becomes large, whereby track dislocation
readily occurs. The temperature expansion coefficient can be
adjusted by the above Young's modulus in the width direction.
<Humidity Expansion Coefficient in Width Direction of
Film>
[0025] Preferably, the biaxially oriented polyester film of the
present invention has a humidity expansion coefficient .alpha.h in
the width direction of the film of 5 to 10 ppm/% RH. It is more
preferably 6 to 9 ppm % RH. When .alpha.h exceeds the upper limit,
the dimensional changes rate in the width direction of the film by
humidity variations becomes large, whereby track dislocation
readily occurs. When .alpha.h falls below the lower limit, at
becomes large in the negative direction and the dimensional changes
rate in the width direction by temperature variations becomes
large, whereby track dislocation readily occurs. The humidity
expansion coefficient can be also adjusted by the above Young's
modulus in the width direction.
<Film Thickness>
[0026] The thickness of the whole biaxially oriented polyester film
of the present invention is preferably 3.0 to 6.0 .mu.m, more
preferably 3.5 to 5.5 .mu.m, particularly preferably 4.0 to 5.0
.mu.m. When the thickness exceeds the upper limit, the thickness of
the tape becomes large and the length of the tape to be stored in a
cassette becomes small, whereby a sufficiently large magnetic
recording capacity, especially a recording capacity of more than
500 GB is not obtained or the proportion of the base film to the
magnetic recording tape becomes large. Therefore, the magnetic
layer and the non-magnetic layer become thin and the magnetic
surface becomes roughened by the influence of the surface
properties of the base film with the result that output
characteristics deteriorate, thereby increasing the error rate.
When the thickness falls below the lower limit, the thickness of
the film is very small, whereby the film is often broken at the
time of film formation, the winding of the film fails, and the
suppression of the temperature expansion of a layer other than the
base film by the base film of the present invention becomes
difficult.
<Heat Shrinkage Factor in Width Direction of Film>
[0027] The biaxially oriented polyester film of the present
invention has a heat shrinkage factor in the width direction of the
film of 0.8% or less, preferably 0.7% or less, particularly
preferably 0.6% or less when it is heated at 105.degree. C. under
no load for 30 minutes because the dimensional stability of the
film can be easily improved. To reduce the heat shrinkage factor,
the draw ratio in the width direction of the film is reduced, the
drawing temperature in the width direction of the film is
increased, the heat setting temperature is increased, or the film
is relaxed in the width direction during heat setting. Although the
lower limit of heat shrinkage factor is not particularly limited,
to carry out relaxation excessively in order to reduce the heat
shrinkage factor as much as possible, a higher draw ratio is
required to maintain the same Young's modulus, whereby film forming
properties are readily impaired. From this point of view, the lower
limit of heat shrinkage factor in the width direction of the film
is 0.1% or more, more preferably 0.3% or more.
<Rupture Elongation in Width Direction of Film>
[0028] The biaxially oriented polyester film of the present
invention has a rupture elongation in the width direction of the
film of preferably 45% or more, more preferably 47% or more,
particularly preferably 50% or more from the viewpoint of film
forming properties. When the elongation in the width direction of
the film falls below the lower limit, stretching conditions in the
width direction become very severe and film forming properties may
be impaired. To increase the elongation, the draw ratio in the
width direction of the film is reduced, the stretching temperature
in the width direction of the film is increased, the heat setting
temperature is increased, or the film is relaxed in the width
direction during heat setting. Although the upper limit of rupture
elongation is not particularly limited as long as the above Young's
modulus is obtained, the upper limit is determined naturally from
the Young's modulus.
<Crystallinity of Film>
[0029] The crystallinity of the biaxially oriented polyester film
of the present invention is preferably 28 to 33%, more preferably
29 to 32% when the polyester is polyethylene-2,6-naphthalene
dicarboxylate, whereby the surface of the film can be made very
flat and high electromagnetic conversion characteristics can be
obtained for a magnetic recording tape. The crystallinity is
greatly influenced by heat setting temperature and can be made high
by increasing the heat setting temperature or extending the heat
setting time. For instance, the above crystallinity can be obtained
by carrying out heat setting at a temperature of preferably 202 to
210.degree. C., particularly preferably 203 to 208.degree. C. for
preferably 1 to 20 seconds. To make the crystallinity higher than
the above lower limit, the heat setting temperature must be made
high, whereby the surface flatness of even a film having a large
Young's modulus in the width direction specified by the present
invention can be improved by heat setting with the result that a
high-density magnetic recording tape provided by the present
invention easily exhibits excellent electromagnetic conversion
characteristics. When the crystallinity is made higher than the
upper limit, the effect of improving the surface flatness of the
film by increasing the heat setting temperature becomes
unsatisfactory, thereby causing a reduction in Young's modulus, the
deterioration of film forming properties by increasing the draw
ratio to eliminate the reduction in Young's modulus, or
nonuniformity in the thickness of the film due to the reception of
an excessive heat history with the result of impaired surface
flatness.
<Dimensional Changes Rate in the Width Direction of Film when a
Load is Applied in Film Forming Direction of Film>
[0030] When a load of 32 MPa is applied to the biaxially oriented
polyester film of the present invention in the film machine
direction of the film in a 40.degree. C. and 90% RH atmosphere, the
dimensional changes rate in the width direction is preferably more
than 0.3% and 1.0% or less, more preferably 0.4 to 0.9% from the
viewpoints of film forming properties and track dislocation. The
dimensional changes rate in the width direction rate at the time of
applying the above load can be reduced by increasing the Young's
modulus in the film machine direction or reducing the heat
shrinkage factor in the width direction of the film. When the
dimensional changes rate in the width direction at the time of
applying the above load falls below the lower limit, the Young's
modulus in the film machine direction must be increased excessively
or the heat shrinkage factor in the width direction of the film
must be reduced, whereby a high draw ratio is required, thereby
impairing the film forming properties. The reason that the
dimensional changes rate in the width direction at the time of
applying the above load may be made high is that tension applied to
the magnetic recording tape becomes smaller as the recording
density of the magnetic recording medium becomes higher, which is
totally unexpected from a magnetic recording tape having a low
recording density in the prior art. When the dimensional changes
rate in the width direction of the film at the time of applying the
above load exceeds the upper limit, even if tension applied to the
magnetic tape becomes small, the size in the width direction of the
film changes while it is used repeatedly, thereby causing track
dislocation.
<Surface Roughness and Inert Particles>
[0031] The biaxially oriented polyester film of the present
invention has a surface roughness WRa(center plane average
roughness) of at least one exposed surface of preferably 1 to 10
nm, more preferably 2 to 6 nm, particularly preferably 3 to 5 nm.
When this surface roughness WRa is higher than the upper limit, the
surface of the magnetic layer becomes rough, thereby deteriorating
the electromagnetic conversion characteristics. When the surface
roughness WRa is lower than the lower limit, the surface becomes
too flat, whereby slippage over a pass roll or a calender becomes
worse, the film is wrinkled, the magnetic layer cannot be formed
well, or the calendering step becomes unstable.
[0032] The biaxially oriented polyester film is not limited to a
single-layer film but may be a laminate film consisting of two or
more layers which differ from each other in the composition of
inert particles contained therein.
[0033] When the polyester film of the present invention is a
single-layer film, the surface roughness of the both sides of the
film is preferably 1 to 10 nm. It is more preferably 2 to 10 nm
from the viewpoint of film forming and winding properties and 1 to
7 nm from the viewpoint of electromagnetic conversion
characteristics. It is particularly preferably 2 to 7 nm to achieve
both film forming and winding properties and electromagnetic
conversion characteristics.
[0034] In the case of a laminate film, a polyester film layer which
contains substantially no inert particles or a small amount of
relatively small inert particles if it contains, that is, a layer
forming a flat surface is formed on the side on which a magnetic
layer is to be formed, and a polyester film layer which contains a
large amount of relatively large inert particles, that is, a
surface having excellent running properties is formed on the other
running surface, that is, a non-magnetic layer side. Since this
laminate film provides both electromagnetic conversion
characteristics and film winding properties to a magnetic recording
tape more easily than the single-layer film, it can be said that
the laminate film is a preferred embodiment of the present
invention. Preferably, the layer A on the side on which a magnetic
layer is to be formed has a surface roughness (WRa(A)) of 0.5 to 4
nm and the layer B on the side on which no magnetic layer is to be
formed has a surface roughness (WRa(B)) of 5 to 10 nm, whereby both
film forming and winding properties and electromagnetic conversion
characteristics can be obtained.
[0035] The above surface roughness WRa can be adjusted by
containing inert particles, for example, inorganic fine particles
containing the element of group IIA, IIB, IVA or IVB of the
periodic table (such as kaolin, alumina, titanium oxide, calcium
carbonate or silicon dioxide) or organic particles of a polymer
having high heat resistance such as crosslinked silicone resin,
crosslinked polystyrene or crosslinked acrylic resin particles in
the film, or carrying out a surface treatment for forming fine
irregularities, for example, coating a lubricant coating.
[0036] To contain the inert particles in the film, the average
particle diameter of the inert particles is preferably 0.01 to 0.8
.mu.m, more preferably 0.05 to 0.6 .mu.m, particularly preferably
0.1 to 0.4 .mu.m. The content of the inert particles is preferably
0.01 to 0.8 wt %, more preferably 0.03 to 0.6 wt %, particularly
preferably 0.05 to 0.4 wt % based on the weight of the entire film
in the case of a single-layer film or the weight of the film layer
containing the inert particles in the case of a laminate film. As a
matter of course, the inert particles contained in the film are not
limited to a single component but may be composed of two or more
components. It is preferred that inert particles composed of two
components or three or more components should be contained in the
film layer on the non-magnetic layer side of the laminate film
because both tape electromagnetic conversion characteristics and
film winding properties can be obtained at the same time.
[0037] The surface roughness WRa can be adjusted by suitably
selecting the average particle diameter and amount of the inert
particles from the above ranges. For instance, the surface
roughness WRa can be made large by increasing the average particle
diameter or content of the inert particles. As a matter of course,
the biaxially oriented polyester film of the present invention may
have a coating layer which is formed by coating a lubricant
coating. In this case, the lubricant coating may be applied not
only to one side but also to both sides. Coating layers known per
se may be advantageously used. For example, those enumerated in the
pamphlet of WO00/76749 may be used as the coating layer. It is
possible to form a coating layer by coating a lubricant coating
without containing inert particles in the film.
<Layer Constitution of Film>
[0038] As described above, the biaxially oriented polyester film of
the present invention may be a single-layer film or a laminate film
consisting of a plurality of layers which differ in the type,
particle diameter and amount of inert particles contained
therein.
[0039] It is particularly preferably a double-layer laminate film
consisting of layer A and layer B because high film running
properties such as winding properties and high surface flatness on
the side on which a magnetic layer is to be formed can be easily
obtained at the same time.
[0040] As for the preferred double-layer laminate film, it is
preferred that the layer A should contain inert particles A having
an average particle diameter of 0.01 to 0.20 .mu.M in an amount of
0.01 to 0.15 wt % based on the weight of the layer A and that the
layer B should contain inert particles B2 having an average
particle diameter of 0.2 to 0.4 .mu.m in an amount of 0.01 to 0.2
wt % based on the weight of the layer B. When the average particle
diameter of the inert particles A is smaller than 0.01 .mu.m or the
content of the inert particles A is lower than 0.01 wt %, winding
becomes difficult, chipping occurs or chipping powders are produced
by a pass roll, or a scratch is formed at the time of forming a
film, thereby causing an error. When the average particle diameter
is larger than 0.20 .mu.m or the content is higher than 0.15 wt %,
if high dimensional stability is to be provided to a high-density
recording medium which the present invention is aimed to attain,
the surface of the layer A becomes rough and an error readily
occurs. To suppress the error rate significantly, the content of
the inert particles A is preferably 0.09 wt % or less.
[0041] The layer B preferably contains the above inert particles
B2. When the average particle diameter or content of the inert
particles B2 falls below the lower limit, air squeezability and
friction coefficient become high, whereby it may be difficult to
wind the film. When the average particle diameter or content of the
inert particles B2 exceeds the above upper limit, the surface of
the layer A is greatly tossed by the inert particles B2, thereby
impairing the surface properties of the layer A and making it
difficult to increase the recording density.
[0042] The layer B may be composed of a single component, that is,
the inert particles 32 alone but preferably contains inert
particles B1 having an average particle diameter of 0.01 to 0.2
.mu.m in an amount of 0.01 to 0.3 wt % based on the weight of the
layer B from the viewpoints of the influence upon the surface
properties of the magnetic surface of the polyester layer B
(improvement of electromagnetic conversion characteristics) and
film winding properties. When the average particle diameter or
content of the inert particles B1 falls below the lower limit, the
friction coefficient becomes high, thereby making it difficult to
wind the film, or the surface is shaved and foreign matter produced
by shaving is transferred to the surface of the layer A, thereby
causing an error. When the average particle diameter or content of
the inert particles B1 exceeds the upper limit, the inert particles
B1 or agglomerates of the inert particles B1 form large projections
which toss the surface, thereby impairing surface flatness. The
inert particles B1 preferably have an average particle diameter 0.1
.mu.m or more smaller than that of the inert particles B2 because a
combination of the inert particles B1 and B2 provides the effect of
improving electromagnetic conversion characteristics and film
winding properties more easily. The average particle diameter of
the inert particles B1 is preferably 0.05 to 0.2 .mu.m, more
preferably 0.10 to 0.15 .mu.m.
[0043] Preferred examples of the inert particles A and the inert
particles B1 and B2 are those listed for the above inert particles.
Spherical silica particles and spherical heat-resistant polymer
particles are preferred as the inert particles A and B1 because
they provide the effect of the present invention easily. As the
inert particle B, heat-resistant polymer particles having low
hardness, for example, a Mohs hardness of less than 3 are
particularly preferred because the transfer of the rough surface of
the layer B to the surface of the layer A can be suppressed.
[0044] When a film is to be formed, all the charged polymer does
not become a film used as a product. For example, the edge portions
of the molten and extruded film are held by clips to stretch the
film, remain thick without being stretched and therefore, cannot be
used as part of a product. When the width of the formed film is,
for example, 4 m and the film is cut to a width of 1 m and divided
into three, at least a 1 m portion is not used as part of a product
and may be broken during film formation, and the broken film cannot
become a product as well. Portions which are not used as part of a
product account for several tens of wt % including ear portions at
both ends in the width direction of the film. It is desired that
these portions should be self-recovered so that they can be
collected and re-used in the manufacture of a film, particularly
the same film can be used in the film forming process as it is.
[0045] To enable the above self-recyclability, the inert particles
B1 contained in the layer B are preferably identical to the inert
particles A. When the layer B contains the inert particles B1, the
recovered polymer can be used as the polymer of the layer B. When
the recovered polymer is used in the layer A, the inert particles
B2 are existent in the layer A, which may impair the surface
flatness of the layer A on which a magnetic layer is to be
formed.
[0046] To provide excellent recyclability that enables all the
amount of the polymer which is not used in a product and is
generated during film formation to be recycled while the surface
flatness on the side on which a magnetic layer is to be formed is
maintained at a practical level, it is preferred that the average
particle diameter of the inert particles A should be set to 0.01 to
0.18 .mu.m and the thickness (tB) of the layer B should account for
50 to 90%, specifically 60 to 80% of the thickness of the entire
biaxially oriented polyester film. When the (tB/t) ratio falls
below the lower limit, the amount of the recovered polymer to be
used in the layer B becomes small and it is difficult to recycle
all the amount of the recovered polymer. When (tB/t) exceeds the
upper limit, the particles of the layer B greatly toss the surface
of the layer A, whereby the surface properties of the layer A may
be impaired and it may be difficult to increase the recording
density.
[0047] To provide excellent recyclability that enables half or more
of the polymer which does not become a product and is generated
during film formation to be recycled while the surface flatness on
the side on which a magnetic layer is to be formed is maintained at
a level higher than the practical level, the thickness (tB) of the
layer B accounts for preferably more than 20% and less than 50% of
the thickness (t) of the entire biaxially oriented polyester
laminate film, and the ratio (tB/dB) of tB to the average particle
diameter (dB) of all the inert particles contained in the layer B
is preferably 2 to 30, more preferably 4 to 25. When (tB/t) falls
below the lower limit, the amount of the recovered polymer which
can be used in the layer B becomes extremely small, and almost all
the recovered polymer cannot be used. When (tB/t) exceeds the upper
limit, the effect of suppressing the tossing of the surface of the
polyester layer A by the inert particles of the polyester layer B
lowers and the effect of improving the surface flatness of the
polyester layer A becomes small. When the (tB/dB) ratio of the
thickness (tB) of the layer B to the average particle diameter (dB)
of all the inert particles contained in the polyester layer B falls
below the lower limit, the particle diameter of the inert particles
contained in the polyester layer B becomes large, the influence on
the surface properties of the polyester layer A of tossing becomes
large, the effect of suppressing the tossing of the surface of the
polyester layer A by the particles of the polyester layer B lowers,
and the effect of improving the surface flatness of the polyester
layer A becomes small. When the ratio (tB/dB) exceeds the upper
limit, the contained inert particles become extremely small and the
running and winding properties may be impaired.
[0048] Further, tB/dB is preferably 0.5 to 15, more preferably 2 to
10, and tB/t is preferably 10 to 20%, more preferably 12 to 18% to
provide extremely excellent surface flatness to the biaxially
oriented polyester film of the present invention so as to improve
the error rate, thereby making it possible to increase the
recording density and to use the recovered polymer in another film.
When (tB/t) falls below the lower limit, the particles contained in
the layer B may falloff, or chipping occurs in a die coater or the
calendering step, thereby causing an error. When (tB/t) exceeds the
upper limit, the thickness of the polyester layer B becomes large
and the effect of improving the surface flatness of the film
becomes unsatisfactory. When the (tB/dB) ratio of the thickness
(tB) of the layer B to the average particle diameter (dB) of all
the inert particles contained in the polyester layer B falls below
the lower limit, the particles contained in the layer B may fall
off, or chipping occurs in the die coater or the calendering step,
thereby causing an error. When (tB/dB) exceeds the upper limit, the
effect of making projections formed by the particles contained in
the layer B uniform in height lowers, and the effect of improving
the surface flatness becomes unsatisfactory.
<Film Forming Method>
[0049] The biaxially oriented polyester film of the present
invention whose Young's moduli in the film machine direction and
the width direction are set to extremely high specific ranges is
preferably manufactured, for example, by the following method
because the above Young's moduli can be obtained while the film
forming properties are retained.
[0050] The above aromatic polyester as a raw material is dried and
supplied into an extruder heated at a temperature of the melting
point (Tm: .degree. C.) of the aromatic polyester to
(Tm+50).degree. C. to be extruded into a sheet form from a die such
as a T die. This extruded sheet form is solidified by quenching to
obtain an unstretched film which is then stretched biaxially.
Biaxial stretching may be sequential biaxial stretching or
simultaneous biaxial stretching. At least transverse stretching is
preferably carried out in two or more stages because this makes it
easy to set the Young's modulus in the width direction to the range
of the present invention and to stabilize the film forming
properties. To increase the Young's modulus in the film machine
direction, longitudinal stretching is preferably carried out in two
or more stages, that is, longitudinal stretching is carried out
again after transverse stretching because this makes it easy to
increase the Young's modulus in the film machine direction and to
stabilize the film forming properties.
[0051] Sequential biaxial stretching in which longitudinal
stretching, transverse stretching, transverse re-stretching and
heat setting are carried out in this order will be explained herein
as an example. Preferably, the aromatic polyester is first
stretched to 4.5 to 6.5 times in the longitudinal direction at a
temperature of its glass transition temperature (Tg: .degree. C.)
to (Tg+40).degree. C., to 3.5 to 5.5 times in the transverse
direction at (Tg+10) to (Tg+50).degree. C. which is higher than the
above temperature for longitudinal stretching and then at a total
transverse draw ratio of 5.5 to 7.0 times which is obtained by
multiplying by the previous transverse draw ratio at (Tg+20) to
(Tg+110).degree. C. which is higher than the temperature for
transverse stretching, and heat set at (Tg+70) to (Tg+110).degree.
C. for 1 to 20 seconds and further for 1 to 15 seconds.
[0052] When the area draw ratio becomes 30 times or more to obtain
high Young's moduli in the longitudinal direction and the
transverse direction, the surface flatness of the film is easily
impaired. In order to further improve the surface flatness of the
film in the above situation, it is preferred that the first
transverse stretching should be divided into two or more
temperature zones, the temperature of the former half stretching
zone should be set to (Tg+5) to (Tg+20).degree. C., the temperature
of the latter half stretching zone should be set to (Tg+25) to
(Tg+40).degree. C., the transverse re-stretching should be divided
into two or more temperature zones, the temperature of the former
half stretching zone should be set to (Tg+45) to (Tg+65).degree.
C., the temperature of the latter half stretching zone should be
set to (Tg+80) to (Tg+90).degree. C., and the heat setting
temperature should be set to (Tg+80) to (Tg+90).degree. C. Heat
setting may be carried out simultaneous with transverse
re-stretching. In this case, the highest temperature for transverse
re-stretching is the heat setting temperature, and heat setting is
preferably carried out for 1 to 20 seconds.
[0053] When the polyester is polyethylene-2,6-naphthalene
dicarboxylate, heat setting is particularly preferably carried out
at 202 to 210.degree. C., specifically 203 to 208.degree. C. for 1
to 20 seconds because both surface flatness and film forming
properties can be obtained at the same time.
[0054] When the draw ratio in the longitudinal direction is high,
the Young's modulus in the film machine direction improves but the
Young's modulus in the width direction lowers whereas when the draw
ratio in the transverse direction is high, the Young's modulus in
the film machine direction lowers but the Young's modulus in the
width direction improves. Therefore, the draw ratios must be
further adjusted according to the target Young's moduli. The
sequential biaxial stretching in which longitudinal stretching,
transverse stretching, transverse re-stretching and heat setting
are carried out in this order can apply to the same manufacturing
method in which longitudinal stretching, transverse stretching,
longitudinal re-stretching, transverse re-stretching and heat
setting are carried out in this order except that the draw ratio of
the first longitudinal stretching is 2.0 to 3.5 times, the draw
ratio of the first transverse stretching is 3.5 to 5.5 times, and
longitudinal re-stretching is carried out at a total longitudinal
draw ratio of 4.5 to 6.5 times obtained by multiplying the raw
ratio of the previous longitudinal stretching and a total
transverse draw ratio of 5.5 to 7.0 times at a temperature between
the temperature of transverse stretching and the temperature of
transverse re-stretching. Longitudinal stretching is preferably
carried out by preheating the film at a temperature of (Tg-20) to
(Tg+10).degree. C. before longitudinal stretching and using an IR
heater as a heater to adjust the surface temperature of the film to
the above range because the effect of the present invention is
easily obtained.
[0055] The above description has been given of sequential biaxial
stretching. The biaxially oriented polyester film of the present
invention can be manufactured by simultaneous biaxial stretching in
which longitudinal stretching and transverse stretching are carried
out simultaneously. Refer to the draw ratios and the stretching
temperatures explained in the foregoing.
[0056] When the biaxially oriented polyester film of the present
invention is a laminate film, two or more molten polyesters are
joined together in the die and extruded into a film form preferably
at a temperature of the melting point of the polyester (Tm:
.degree. C.) to (Tm+70).degree. C., or two or more molten
polyesters are extruded from the die, joined together and
solidified by quenching to obtain an unstretched laminate film
which is then biaxially stretched and heat set like the above
single-layer film. To form the above coating layer, it is preferred
that a desired coating solution should be applied to one side or
both sides of the above unstretched film or monoaxially stretched
film and then the obtained film should be biaxially stretched and
heat set like the above single-layer film.
<Magnetic Recording Tape>
[0057] According to the present invention, a non-magnetic layer and
a magnetic layer are formed in this order on one side of the above
biaxially oriented polyester film of the present invention as a
base film, and a back coat layer is formed on the other side.
Although the composition of the non-magnetic layer is not
particularly limited, a thermosetting resin or a high-energy ray
curable resin containing inorganic fine powders such as silica,
alumina or titanium dioxide powders is used. The thickness of the
non-magnetic layer is preferably 0.5 to 3.0 .mu.m, more preferably
0.5 to 2.5 .mu.m, particularly preferably 1.0 to 2.0 .mu.m. The
above range is preferred because the effect of the present
invention is easily obtained.
[0058] As for the type of the magnetic layer formed on the
non-magnetic layer, a so-called "coating" type magnetic layer
formed by applying magnetic powders together with a binder is
preferred. The type of the magnetic powders constituting the
magnetic layer is not particularly limited, and iron oxide,
chromium oxide, cobalt coated iron oxide, and metals and alloys
thereof such as iron, cobalt, iron-cobalt, iron-cobalt-nickel and
cobalt-nickel are preferably used. Metals and alloys thereof are
more preferred than oxides. Although the binder constituting the
magnetic layer is not particularly limited, a thermosetting
resin-based binder and a high energy ray curable binder are
preferred, and the magnetic layer may further contain additives
such as a dispersant, lubricant and antistatic agent. For example,
a copolymer of vinyl chloride, vinyl acetate and vinyl alcohol,
polyurethane, polyisocyanate or a mixture thereof is preferably
used. The thickness of the magnetic layer is preferably 0.05 to 0.5
.mu.m, more preferably 0.05 to 0.3 .mu.m, particularly preferably
0.05 to 0.2 .mu.m. The above range is preferred because the effect
of the present invention is easily obtained.
[0059] Although the back coat layer is not limited to particular
composition, a back coat layer containing carbon black and a
thermosetting resin-based or high energy ray curable binder is
preferred, and the back coat layer may further contain additives
such as a dispersant, lubricant and antistatic agent. For example,
a copolymer of vinyl chloride, vinyl acetate and vinyl alcohol,
polyurethane, polyisocyanate or a mixture thereof is preferably
used. The thickness of the back coat layer is preferably 0.1 to 1.0
.mu.m, more preferably 0.3 to 0.8 .mu.m. The above range is
preferred because the effect of the present invention is easily
obtained.
[0060] As for the magnetic recording tape of the present invention,
the thickness obtained by subtracting the thickness of the base
film from the thickness of the magnetic recording tape is
preferably 0.2 to 0.8 time, more preferably 0.2 to 0.6 time,
particularly preferably 0.3 to 0.5 time the thickness of the base
film. When the above thickness ratio falls below the lower limit,
the magnetic layer, the non-magnetic layer and the back coat layer
become thin, coating becomes difficult, the surface properties of
the base film exert a great influence upon the surface properties
of the magnetic layer and the back coat layer, thereby causing an
error, and the effect of suppressing temperature expansion with the
base film becomes excessive, thereby causing track dislocation.
When the thickness ratio exceeds the upper limit, the tape becomes
too thick, whereby the length of the tape stored in a cassette
becomes short, thereby making it impossible to obtain a
sufficiently large magnetic recording capacity and making it
difficult to obtain the effect of suppressing temperature expansion
with the base film.
[0061] As described above, according to the present invention, a
biaxially oriented polyester film which has excellent dimensional
stability in the width direction when a magnetic recording tape of
linear recording system is formed from the biaxially oriented
polyester film can be provided, and a magnetic recording tape of
linear recording system which rarely sees track dislocation and has
excellent dimensional stability can be obtained as a high-density
magnetic recording tape having a recording capacity of more than
500 GB by using this biaxially oriented polyester film as a base
film. Therefore, the prevent invention is of extremely great
industrial value.
EXAMPLES
[0062] The following examples are provided to further illustrate
the present invention. Various physical property values and
characteristic properties in the present invention were measured as
follows and defined.
(1) Young's Modulus
[0063] The film is cut into a sample having a width of 10 mm and a
length of 15 cm, and this sample is pulled with an Instron type
universal tensile tester at a chuck interval of 100 mm, a pull
speed of 10 mm/min and a chart speed of 500 mm/min to calculate the
Young's modulus from the tangent line of a rising portion of the
obtained load-elongation curve. The measurement direction is the
longitudinal direction of the sample, the Young's modulus is
measured 10 times, and the average value of the measurement data is
used.
(2) Surface Roughness (WRa)
[0064] The center plane average roughness (WRa) is obtained from
the following equation by surface analyzing software incorporated
in the non-contact 3-D roughness meter (NT-2000) of WYKO Co., Ltd.
at a measurement magnification of 25 times and a measurement area
of 246.6 .mu.m in the film machine direction.times.187.5 .mu.m in
the width direction (0.0462 mm.sup.2). The measurement is repeated
10 times and the average value of the measurement data is used.
WR a = k = 1 M j = 1 N Z jk - Z _ / ( M N ) ##EQU00001## wherein
##EQU00001.2## Z _ = k = 1 M j = 1 N Z jk / ( M N )
##EQU00001.3##
[0065] Z.sub.jk is the height of a 3-D roughness chart at a j-th
position and a k-th position in the measurement direction (246.6
.mu.m) and a direction (187.5 .mu.m) orthogonal to the measurement
direction when these directions are divided into M and N sections,
respectively.
(3) Average Particle Diameter of Inert Particles
[0066] This is measured with the CP-50 Centrifugal Particle Size
Analyzer of Shimadzu Corporation. A particle diameter corresponding
to 50 mass percent is read from a cumulative curve showing the
particle diameter of each particle and the amount of the particle
calculated based on the obtained centrifugal sedimentation curve
and taken as the above average particle diameter.
[0067] The average particle diameter of the inert particles
contained in the film can be measured as follows.
[0068] First, the polyester of the surface layer of the film is
removed by a low-temperature plasma ashing method (for example,
PR-503 of Yamato Kagaku Co., Ltd.) to expose particles. The
treating conditions are selected to ensure that the polyester is
ashed but the particles are not damaged. The exposed particles are
observed through SEM (scanning electron microscope) at a
magnification of 10,000 times, an image (light shade formed by the
particles) of the particles is linked to an image analyzer (for
example, QTM900 of Cambridge Instrument Co., Ltd.), and the area
circle equivalent diameters (Di) of at least 5,000 (n) particles
are obtained by changing the observation site. The particle size
distribution curve is formed from the obtained results to calculate
the proportion of the number of particles at each peak (the area of
each peak is determined with the boundary as a valley portion of
the distribution curve). The number average value represented by
the following equation is obtained from the measurement results of
the particle diameter and the number of particles in each peak area
and taken as the average particle diameter (DA) of the particles.
In the case of particles which are agglomerated in the film (for
example, alumina particles), the particle diameters (secondary
particle diameter) of the agglomerates are measured to obtain the
average particle diameter (DA). The identification of the type of
the particles can be made by using the quantity analysis of each
metal element by SEM-XMA or ICP.
[0069] The content of the inert particles in the film can be
measured as follows.
[0070] First, the total content of the inert particles can be
measured from the weight ratio (wt %) of the particles to the
sample by shaving off 100 g of the single-layer film or 100 g of
each layer in the case of the polyester laminate film as a sample,
selecting a solvent which dissolves the polyester but not the
particles to dissolve the sample and centrifugally separating the
particles from the polyester.
[0071] When inorganic particles are existent in the film, a sample
obtained in the same manner as described above is combusted in a
platinum crucible in a furnace at 1,000.degree. C. for 3 hours or
more, and the combusted product in the crucible is mixed with
terephthalic acid (powdery) to prepare a 50 g lock-like plate. The
total content of the inorganic particles in each layer of this
plate can be determined from the calibration curve of each element
prepared from the count value of the element with wavelength
dispersion type fluorescent X-rays. The X-ray tube for measuring
fluorescent X-rays is preferably a Cr tube and may be an Rh tube.
The X-ray output is set to 4 kW and the analyzing crystal is
changed for each element to be measured. When different types of
inorganic particles are existent, the content of each type of
inorganic particles can be determined by this measurement.
[0072] Further, as for organic particles, the proportion of
particles existent in each peak area is calculated from the ratio
of the number and the average particle diameter of particles
constituting the peak obtained by the measurement of the average
particle diameter of the inert particles contained in the film and
the density of the particles, and the content (wt %) of particles
existent in each peak area is obtained from this proportion of the
particles and the total content of inert particles obtained by the
measurement of the total amount of the inert particles. When
organic particles and inorganic particles are existent, the content
of the organic particles and the content of the inorganic particles
in each layer can be calculated from the total content of the
particles in each layer and the above total content of the
inorganic particles.
[0073] The densities of typical heat-resistant polymer particles
are given below.
Density of crosslinked silicone resin: 1.35 g/cm.sup.3 Density of
crosslinked polystyrene resin: 1.05 g/cm.sup.3 Density of
crosslinked acrylic resin: 1.20 g/cm.sup.3
[0074] The density of the resin constituting the organic particles
can be measured with a picnometer in accordance with the method
described in "Fine Particle Handbook", Asakura Shoten, 1991, p. 150
by further classifying particles centrifugally separated from the
polyester by the above method.
(4) Temperature Expansion Coefficient (.alpha.t)
[0075] Samples of the film and the magnetic recording tape are cut
into pieces having a length of 15 mm and a width of 5 mm in the
width direction which is the measurement direction, and these test
specimens are set in the TMA3000 of Shinku Riko Co., Ltd. to be
pretreated in a nitrogen atmosphere (0% RH) at 60.degree. C. for 30
minutes and cooled to room temperature. Thereafter, the temperature
is raised from 25.degree. C. to 70.degree. C. at a rate of
2.degree. C./min to measure the lengths of the specimens at each
temperature in order to calculate their temperature expansion
coefficients (at) from the following equation. The measurement
direction is the longitudinal direction of the specimen, the
measurement is made 5 times, and the average value of the
measurement data is used.
.alpha.t={(L.sub.60-L.sub.40)/(L.sub.40.times..alpha.T)}+0.5
wherein, L.sub.40: sample length at 40.degree. C. (mm) L.sub.60:
sample length at 60.degree. C. (mm)
.DELTA.T: 20 (=60-40).degree. C.
[0076] 0.5: temperature expansion coefficient (ppm/.degree. C.) of
quartz glass
(5) Humidity Expansion Coefficient (.alpha.h)
[0077] Samples of the film and the magnetic recording tape are cut
into pieces having a length of 15 mm and a width of 5 mm in the
width direction which is the measurement direction, and these test
specimens are set in the TMA3000 of Shinku Riko Co., Ltd. and kept
in a nitrogen atmosphere at 30.degree. C. by maintaining 30% RH and
70% RH to measure the lengths of the samples so as to calculate
their humidity expansion coefficients from the following equation.
The measurement direction is the longitudinal direction of the
specimen, the measurement is made 5 times, and the average value
(.alpha.h) of the measurement data is used.
.alpha.h=(L.sub.70-L.sub.30)/(L.sub.30.times..alpha.H)
wherein, L.sub.30: sample length at 30% RH (mm) L.sub.70: sample
length at 70% RH (mm)
.alpha.H: 40 (=70-30) % RH
(6) Amount of Off-Track Between Magnetic Recording Tape and
Head
[0078] The dimensional change rates (ppm) in the width direction
under the following conditions 1 and 2 are calculated from the
temperature expansion coefficient and the humidity expansion
coefficient measured in (4) and (5) above. The dimensional change
rates (ppm) in the width direction of the magnetic head under the
following conditions 1 and 2 are calculated from the temperature
expansion coefficient (7 ppm/.degree. C.) and the humidity
expansion coefficient (0 ppm % RH). The difference (ppm) in
dimensional change rate between the magnetic recording tape and the
magnetic head under the following conditions 1 and 2 is taken as
the amount of off-track between the magnetic recording tape and the
head, and the larger change rate out of the change rates under the
following conditions 1 and 2 is taken as the maximum amount of
off-track.
Condition 1: 10.degree. C./10% RH->29.degree. C./80% RH
Condition 2: 45.degree. C./10% RH->10.degree. C./80% RH
(7) Amount of Creep Compliance
[0079] After the film sample is set in the TMA/6000 of Seiko
Instruments Co., Ltd. in the MD direction at a film width of 4 mm
and a sample chuck interval of 200 mm and kept in a 30.degree. C.
atmosphere under a load of 1 g for 30 minutes, the length of the
sample is measured and taken as L0. Then, after the film sample is
kept under a load of 0.022 GPa for 60 minutes, the length of the
sample is measured and taken as L1. The creep compliance is
calculated from the following equation. Creep compliance
(GPa.sup.-1)={(L1-L0)/L0}/0.022
(8) Overall Evaluation
[0080] The overall evaluation of the sample is .largecircle. when
the maximum amount of off-track measured in (6) is less than 700
ppm and the amount of creep measured in (7) is less than 0.20 and X
when any one of the above evaluation items is outside the above
range.
(9) Error Rate
[0081] The error rate is obtained by recording (recording
wavelength of 0.37.mu.) and reproducing data with an LTO drive. The
error rate is obtained from the following equation based on error
information (number of error bits) output from the drive and judged
by the following criteria based on the error rate of Example 1
(100).
Error rate=(number of error bits/number of write bits)
Criteria
[0082] .circleincircle.: less than 50 .largecircle.: 50 or more and
less than 200 .DELTA.: 200 or more and less than 400 X: 400 or
more
(10) Chipping Resistance
[0083] The chipping resistance is evaluated based on the deposition
of powders on the edge of a blade for testing an industrial razor
manufactured by GKI of the U.S. under the following running
conditions by using the apparatus shown in FIG. 1 and applying the
edge of the blade to the film at an angle of 174.degree.. In the
case of a laminate film, the layer B is in contact with the blade.
In FIG. 1, reference numeral 1 denotes a feed roll, 2 a tension
controller, 3 a tension detector 1 (inlet), 4, 5, 7 and 8 guide
rollers (free rollers), 6 a blade, 9 a tension detector 1 (outlet),
10 a speed controller and 11 a wind-up roll.
Running conditions: speed of 60 m/min, tension of 60 g, running
length of 50 m
Criteria
[0084] .circleincircle.: the deposition of powders on the edge of
the blade is less than 1.0 mm .largecircle.): the deposition of
powders on the edge of the blade is 1.0 mm or more and less than
2.0 mm X: the deposition of powders on the edge of the blade is
more than 2.0 mm
(11) Recyclability
[0085] When edge waste produced in the manufacturing process of the
biaxially oriented polyester film is ground and used in the layer B
as a recovered polymer, recyclability is evaluated from the ratio
of the usable recovered polymer to the weight of the polymer of the
entire film based on the following criteria.
.circleincircle.: 60 wt % or more of recovered polymer is usable
.largecircle.): 50 wt % or more and less than 60 wt % of recovered
polymer is usable .DELTA.: 20 wt % or more and less than 50 wt % of
recovered polymer is usable X: less than 20 wt % of recovered
polymer is usable
(12) Heat Shrinkage Factor
[0086] After a film having a length of about 30 cm and a width of 1
cm whose length has been accurately measured is put into an oven
set to 105.degree. C. under no load, heated for 30 minutes, taken
out from the oven and cooled to room temperature, its dimensional
change is read. The heat shrinkage factor [(.DELTA.L/L0).times.100]
is obtained from the length (L0) before the heat treatment and the
dimensional change (.DELTA.L) by the heat treatment.
(13) Rupture Elongation
[0087] The rupture elongation (%) is obtained from the equation
(extended length/original length of sample).times.100 when the film
is measured at 25.degree. C. and 65% RH with an Instron type
tensile tester in accordance with the method specified in JIS
K-7127.
(14) Winding Properties
[0088] After winding conditions at the time of slitting are
optimized, 50 rolls are slit to a size of 1,000 mm
(width).times.8,000 m at a rate of 50 m/min and the winding
properties of the slit films are evaluated based on the following
criteria on the condition that a roll without bumps, projections or
wrinkles on the surface of the film is accepted.
.circleincircle.: 40 or more accepted rolls .largecircle.): 35 or
more and 39 or less accepted rolls .DELTA.: 30 or more and 34 or
less accepted rolls X: 29 or less accepted rolls
(15) Film Forming Properties
[0089] The film forming state is observed and evaluated based on
the following criteria.
.circleincircle.: no problem such as breakage during film formation
and 16 hours or longer continuous film formation possible
.largecircle.: no problem such as breakage during film formation
and 8 hours or longer continuous film formation possible .DELTA.:
narrow and limited film formable conditions and possible to make a
roll as long as 8,000 m or more X: poor continuous film forming
properties and difficult to make a roll as long as 8,000 m or
more
(16) Dimensional Change Rate in Width Direction Under No Load
[0090] A film (30 cm long) slit to a width of 12.65 mm (1/2 inch)
is set as shown in FIGS. 1(A) and 1(B) in a 23.degree. C. and 50%
RH atmosphere. Gold is deposited on the surface of the sample slit
to a width of 12.65 mm by sputtering in advance to enable the
measurement of the size in the width direction with the detector.
In this state, a dead weight of 32 MPa is attached to one end (the
other end is fixed) of the film to measure the width (L1) of the
film with the laser outer-diameter measuring instrument of Keyence
Co., Ltd. (body: Model 3100, sensor: Model 3060).
[0091] After a dead weight of 32 MPa is attached to one end (the
other side is fixed) in a 49.degree. C. (120.degree. F.) and 90% RH
atmosphere and kept in this state for 72 hours (3 days), the dead
weight is removed, and the sample is kept in a 23.degree. C. and
50% RH atmosphere for 24 hours, and a dead weight of 32 MPa is
attached to one end (the other side is fixed) of the film again to
measure the width (L2) of the film with the laser outer-diameter
measuring instrument of Keyence Co., Ltd. (body: Model 3100,
sensor: Model 3060).
[0092] The dimensional changes rate in the width direction
(.alpha.W) before and after the temperature and humidity treatment
under no load is calculated from the measured sizes before and
after the above temperature and humidity treatment based on the
following equation.
.alpha.W={|L2-L1|/L1}.times.100(%)
(17) Thickness (Entire Film and Each Layer)
[0093] As for the thickness of the entire film, the film is
measured at 10 points selected at random with a micrometer and the
average value of the measurement data is used. As for the thickness
of the polyester layer B, the (M+/C+) concentration ratio of the
metal element (M+) derived from highest concentration particles out
of the particles contained in the film in an area of 5,000 nm from
the surface layer excluding the coating layer to the hydrocarbon
(C+) of the polyester is taken as a particle concentration, and a
portion from the surface to a depth of 5,000 nm in the thickness
direction is analyzed. The concentration of the particles is low in
the surface layer due to the boundary of the surface and becomes
higher as the distance from the surface increases. In the case of
the present invention, the concentration of the particles becomes a
stable value of 1 and rises to a stable value of 2, or decreases
monotonously. Based on this distribution curve, a depth which
provides a particle concentration of (stable value of 1+stable
value of 2)/2 in the former case or a depth at which the
concentration of the particles becomes 1/2 of the stable value of 1
in the latter case (this depth is larger than the depth which
provides a stable value of 1) is taken as the thickness (.mu.m) of
the polyester layer B.
[0094] The measurement of the polyester layer B is carried out with
a secondary ion mass spectroscope (SIMS) (6300 of PERKINELMER INC.)
under the following conditions.
type of primary ion: O.sub.2.sup.+ primary ion acceleration
voltage: 12 KV primary ion current: 200 nA luster area: 400 .mu.m
analyzing area: 30% of a gate measurement vacuum degree:
6.0.times.10.sup.-9 Torr E-GUNN: 0.5 kV-3.0 A.
[0095] When particles existent in an area of 5,000 nm from the
surface in largest quantity are organic polymer particles other
than silicone resin, as it is difficult to measure the particles by
SIMS, the concentration distribution curve is measured with FT-IR
(Fourier transform infrared spectroscopy) while etching from the
surface or XPS (X-ray photoelectric spectroscopy) depending on the
type of particles to obtain the thickness of each layer
(.mu.m).
[0096] The thickness of the other polyester layer is obtained by
subtracting the thickness of the polyester layer B from the above
total thickness.
(18) Crystallinity
[0097] The density of the polyester film is measured by a density
gradient tube to obtain crystallinity from the following
equation.
crystallinity = .rho. c ( .rho. - .rho. a ) .rho. ( .rho. c - .rho.
a ) .times. 100 [ % ] ##EQU00002##
wherein, .rho.: density of polyester film sample .rho.a: 1.325
(perfect non-crystal density of polyethylene naphthalate) .rho.c:
1.407 (perfect crystal density of polyethylene naphthalate) The
unit is g/cm.sup.3.
Example 1
[0098] A PEN resin composition 1 containing 0.1 wt % of spherical
silica particles with an average particle diameter of 0.1 .mu.m and
having an intrinsic viscosity (orthochlorophenol, 35.degree. C.) of
0.60 dl/g and a PEN resin composition 2 containing 0.15 wt % of
spherical silica particles with an average particle diameter of 0.3
.mu.m and 0.10 wt % of spherical silica particles with an average
particle diameter of 0.14 .mu.m and having an intrinsic viscosity
(orthochlorophenol, 35.degree. C.) of 0.60 dl/g were each dried at
180.degree. C. for 5 hours, supplied into the hopper of an
extruder, molten at 300.degree. C. in the extruder, joined together
in a ratio of 1:2 in such a manner that the molten resin
composition 1 was positioned on the surface A and the resin
composition 2 was positioned on the surface B, extruded onto a
casting drum whose surface temperature was kept at 60.degree. C.
from a T-shaped extrusion die at a surface finish of 0.3 S while
they were kept joined together and solidified by quenching to
obtain an unstretched laminate film.
[0099] The unstretched film obtained as described above was
preheated at 120.degree. C., further heated with an infrared heater
having a surface temperature of 830.degree. C. 14 mm from above to
be stretched to 5.1 times between low-speed and high-speed rolls,
quenched, supplied to a stenter to be stretched to 5.2 times at
150.degree. C. in the transverse direction and then to 1.2 times at
180.degree. C. in the transverse direction and then heat set at
205.degree. C. for 3 seconds to obtain a biaxially oriented
polyester film having a thickness of 5.0 .mu.m. The Young's modulus
of the obtained film was 6.7 GPa in the longitudinal direction and
9 GPa in the transverse direction.
[0100] After a back coating having the following composition was
applied to the side A of the film with a die coater and dried, a
non-magnetic coating and a magnetic coating having the following
compositions were applied to the side B of the film with a die
coater at the same time to different thicknesses, magnetically
oriented and dried. Further, the film was calendered with a
small-sized test calender (5 sets of steel rolls/nylon rolls) at a
temperature of 70.degree. C. and a line pressure of 200 kg/cm and
cured at 70.degree. C. for 48 hours. The above tape was slit to a
width of 12.65 mm and set in a cassette to obtain a magnetic
recording tape. The thicknesses of the back coat layer,
non-magnetic layer and magnetic layer after drying were 0.5 .mu.m,
1.2 .mu.m and 0.1 .mu.m, respectively.
Composition of Non-Magnetic Coating
[0101] Titanium dioxide fine particles: 100 parts by weight Eslec A
(vinyl chloride-vinyl acetate copolymer of Sekisui Chemical Co.,
Ltd.): 10 parts by weight Nipporan 2304 (polyurethane elastomer of
Nippon Polyurethane Industry Co., Ltd.): 10 parts by weight
Colonate L (polyisocyanate of Nippon Polyurethane Industry Co.,
Ltd.): 5 parts by weight Lecithin: 1 part by weight Methyl ethyl
ketone: 75 parts by weight Methyl isobutyl ketone: 75 parts by
weight Toluene: 75 parts by weight Carbon black: 2 parts by weight
Lauric acid: 1.5 parts by weight
Composition of Magnetic Coating
[0102] Iron (length: 0.3 .mu.m, needle ratio: 10/1, 1800 Oersted):
100 parts by weight Eslec A (vinyl chloride-vinyl acetate copolymer
of Sekisui Chemical Co., Ltd.): 10 parts by weight Nipporan 2304
(polyurethane elastomer of Nippon Polyurethane Industry Co., Ltd.):
10 parts by weight Colonate L (polyisocyanate of Nippon
Polyurethane Industry Co., Ltd.): 5 parts by weight Lecithin: 1
part by weight Methyl ethyl ketone: 75 parts by weight Methyl
isobutyl ketone: 75 parts by weight Toluene: 75 parts by weight
Carbon black: 2 parts by weight Lauric acid: 1.5 parts by
weight
Composition of Back Coating
[0103] Carbon black: 100 parts by weight Thermoplastic polyurethane
resin: 60 parts by weight Isocyanate compound (Colonate L of Nippon
Polyurethane Industry Co., Ltd.): 18 parts by weight Silicone oil:
0.5 part by weight Methyl ethyl ketone: 250 parts by weight
Toluene: 50 parts by weight
[0104] The characteristic properties of the obtained biaxially
oriented polyester laminate film and the magnetic recording tape
are shown in Table 1.
Example 2
[0105] A PEN resin composition 3 containing 0.02 wt % of
crosslinked silicone resin particles with an average particle
diameter of 0.5 .mu.m and 0.30 wt % of spherical silica particles
with an average particle diameter of 0.1 .mu.m and having an
intrinsic viscosity (orthochlorophenol, 35.degree. C.) of 0.60 dl/g
was dried at 180.degree. C. for 5 hours, supplied into the hopper
of an extruder, molten at 300.degree. C. in the extruder, extruded
onto a casting drum whose surface temperature was kept at
60.degree. C. from a T-shaped extrusion die at a surface finish of
0.3 S and solidified by quenching to obtain an unstretched laminate
film.
[0106] The unstretched film obtained as described above was
preheated at 120.degree. C., further heated with an infrared heater
having a surface temperature of 830.degree. C. 14 mm from above to
be stretched to 5.5 times between low-speed and high-speed rolls,
quenched, supplied to a stentor to be stretched to 4.8 times at
150.degree. C. in the transverse direction and then to 1.2 times at
180.degree. C. in the transverse direction and then heat set at
205.degree. C. for 3 seconds to obtain a biaxially oriented
polyester film having a thickness of 5.0 .mu.m. The Young's modulus
of the obtained film was 7.5 GPa in the longitudinal direction and
8.5 GPa in the transverse direction.
[0107] A non-magnetic coating and a magnetic coating were applied
to this film with a die coater at the same time to different
thicknesses, magnetically oriented, dry calendered and cured at
70.degree. C. for 48 hours in the same manner as in Example 1. The
above tape was slit to a width of 12.65 mm and set in a cassette to
obtain a magnetic recording tape.
[0108] The characteristic properties of the obtained biaxially
oriented polyester laminate film and the magnetic recording tape
are shown in Table 1.
Example 3
[0109] An unstretched laminate film was obtained in the same manner
as in Example 1. The unstretched laminate film obtained as
described above was preheated at 120.degree. C., further heated
with an infrared heater having a surface temperature of 830.degree.
C. 14 mm from above to be stretched to 3.0 times between low-speed
and high-speed rolls, quenched, supplied to a stentor to be
stretched to 4.0 times at 135.degree. C. in the transverse
direction and then heat set at 160.degree. C. for 3 seconds.
Subsequently, the film was stretched to 1.9 times at 155.degree. C.
in the longitudinal direction, supplied to the stenter to be
stretched to 1.7 times at 160.degree. C. in the transverse
direction and heat set at 205.degree. C. for 3 seconds to obtain a
biaxially oriented polyester film having a thickness of 5.0 .mu.m.
The Young's modulus of the obtained film was 8.0 GPa in the
longitudinal direction and 9.5 GPa in the transverse direction.
[0110] A non-magnetic coating and a magnetic coating were applied
to this film with a die coater at the same time to different
thicknesses, magnetically oriented, dry calendered and cured at
70.degree. C. for 48 hours in the same manner as in Example 1. The
above tape was slit to a width of 12.65 mm and set in a cassette to
obtain a magnetic recording tape.
[0111] The characteristic properties of the obtained biaxially
oriented polyester laminate film and the magnetic recording tape
are shown in Table 1.
Comparative Example 1
[0112] An unstretched laminate film was obtained in the same manner
as in Example 1. The unstretched laminate film obtained as
described above was preheated at 120.degree. C., further heated
with an infrared heater having a surface temperature of 830.degree.
C. 14 mm from above to be stretched to 5.1 times between low-speed
and high-speed rolls, quenched, supplied to the stenter to be
stretched to 4.6 times at 150.degree. C. in the transverse
direction and then heat set at 205.degree. C. for 3 seconds to
obtain a biaxially oriented polyester film having a thickness of
5.0 .mu.m. The Young's modulus of the obtained film was 8.0 GPa in
the longitudinal direction and 6.5 GPa in the transverse
direction.
[0113] A non-magnetic coating and a magnetic coating were applied
to this film with a die coater at the same time to different
thicknesses, magnetically oriented, dry calendered and cured at
70.degree. C. for 48 hours in the same manner as in Example 1. The
above tape was slit to a width of 12.65 mm and set in a cassette to
obtain a magnetic recording tape.
[0114] The characteristic properties of the obtained biaxially
oriented polyester laminate film and the magnetic recording tape
are shown in Table 1.
Comparative Example 2
[0115] An unstretched laminate film was obtained in the same manner
as in Example 1. The unstretched laminate film obtained as
described above was preheated at 120.degree. C., further heated
with an infrared heater having a surface temperature of 830.degree.
C. 14 mm from above to be stretched to 4.3 times between low-speed
and high-speed rolls, quenched, supplied to the stenter to be
stretched to 4.7 times at 150.degree. C. in the transverse
direction and then to 1.1 times at 180.degree. C. in the transverse
direction, and heat set at 205.degree. C. for 3 seconds to obtain a
biaxially oriented polyester film having a thickness of 5.0 .mu.m.
The Young's modulus of the obtained film was 6.0 GPa in the
longitudinal direction and 9.0 GPa in the transverse direction.
[0116] A non-magnetic coating and a magnetic coating were applied
to this film with a die coater at the same time to different
thicknesses, magnetically oriented, dry calendered and cured at
70.degree. C. for 48 hours in the same manner as in Example 1. The
above tape was slit to a width of 12.65 mm and set in a cassette to
obtain a magnetic recording tape.
[0117] The characteristic properties of the obtained biaxially
oriented polyester laminate film and the magnetic recording tape
are shown in Table 1.
Comparative Example 3
[0118] An unstretched laminate film was obtained in the same manner
as in Example 1. The unstretched laminate film obtained as
described above was preheated at 120.degree. C., further heated
with an infrared heater having a surface temperature of 830.degree.
C. 14 mm from above to be stretched to 3.5 times between low-speed
and high-speed rolls, quenched, supplied to the stenter to be
stretched to 5.4 times at 150.degree. C. in the transverse
direction and then to 1.2 times at 180.degree. C. in the transverse
direction, and heat set at 205.degree. C. for 3 seconds to obtain a
biaxially oriented polyester film having a thickness of 5.0 .mu.m.
The Young's modulus of the obtained film was 5.5 GPa in the
longitudinal direction and 12.0 GPa in the transverse
direction.
[0119] A non-magnetic coating and a magnetic coating were applied
to this film with a die coater at the same time to different
thicknesses, magnetically oriented, dry calendered and cured at
70.degree. C. for 48 hours in the same manner as in Example 1. The
above tape was slit to a width of 12.65 mm and set in a cassette to
obtain a magnetic recording tape.
[0120] The characteristic properties of the obtained biaxially
oriented polyester laminate film and the magnetic recording tape
are shown in Table 1.
Comparative Example 4
[0121] An unstretched laminate film was obtained in the same manner
as in Example 1. The unstretched laminate film obtained as
described above was preheated at 120.degree. C., further heated
with an infrared heater having a surface temperature of 830.degree.
C. 14 mm from above to be stretched to 4.9 times between low-speed
and high-speed rolls, quenched, supplied to the stenter to be
stretched to 4.7 times at 150.degree. C. in the transverse
direction and then to 1.1 times at 180.degree. C. in the transverse
direction, and heat set at 205.degree. C. for 3 seconds to obtain a
biaxially oriented polyester film having a thickness of 5.0 .mu.m.
The Young's modulus of the obtained film was 7.0 GPa in the
longitudinal direction and 7.3 GPa in the transverse direction.
[0122] A non-magnetic coating and a magnetic coating were applied
to this film with a die coater at the same time to different
thicknesses, magnetically oriented, dry calendered and cured at
70.degree. C. for 48 hours in the same manner as in Example 1. The
above tape was slit to a width of 12.65 mm and set in a cassette to
obtain a magnetic recording tape.
[0123] The characteristic properties of the obtained biaxially
oriented polyester laminate film and the magnetic recording tape
are shown in Table 1.
Comparative Example 5
[0124] A PEN resin composition containing 0.38 wt % of spherical
silica particles with an average particle diameter of 0.3 .mu.m and
having an intrinsic viscosity (orthochlorophenol, 35.degree. C.) of
0.60 dl/g and a PEN resin composition containing 0.1 wt % of
crosslinked polystyrene particles with an average particle diameter
of 0.8 .mu.m and 0.9 wt. % of crosslinked polystyrene particles
with an average particle diameter of 0.3 .mu.m and having an
intrinsic viscosity (orthochlorophenol, 35.degree. C.) of 0.60 dl/g
were each dried at 180.degree. C. for 5 hours, supplied into the
hopper of an extruder, molten at 300.degree. C. in the extruder,
joined together in a ratio of 40:3 in such a manner that the molten
resin composition containing spherical silica particles was
positioned on the surface A and the resin composition containing
crosslinked polystyrene particles was positioned on the surface B,
extruded onto a casting drum whose surface temperature was kept at
60.degree. C. from a T-shaped extrusion die at a surface finish of
0.3 S while they were kept joined together and solidified by
quenching to obtain an unstretched laminate film.
[0125] The unstretched film obtained as described above was
preheated at 120.degree. C., further heated up to 140.degree. C.
with a heating metal roll to be stretched to 4.6 times between
low-speed and high-speed rolls, quenched, supplied to the stenter
to be stretched to 4.0 times at 145.degree. C. in the transverse
direction and then to 1.4 times at 170.degree. C. in the transverse
direction, heat set at 215.degree. C. for 3 seconds, relaxed at a
relaxation rate of 4.0% in the transverse direction in a
160.degree. C. cooling zone, further 1.2% in the transverse
direction in a 120.degree. C. zone, cooled to room temperature and
wound up as a film having a thickness of 4.3 .mu.m.
[0126] The characteristic properties of the obtained biaxially
oriented polyester laminate film and the magnetic recording tape
are shown in Table 1.
Example 4
[0127] The operation of Example 1 was repeated except that the draw
ratio in the longitudinal direction was changed from 5.1 times to
4.7 times, the draw ratio of re-stretching in the transverse
direction was changed from 1.2 times to 1.1 times, the heat setting
temperature was changed to 200.degree. C., and the thickness was
controlled as shown in Table 1.
[0128] The characteristic properties of the obtained biaxially
oriented polyester laminate film and the magnetic recording tape
are shown in Table 1.
Example 5
[0129] The operation of Example 1 was repeated except that the draw
ratio in the longitudinal direction was changed from 5.1 times to
5.5 times, the draw ratio of re-stretching in the transverse
direction was changed from 1.2 times to 1.3 times, the heat setting
temperature was changed to 215.degree. C., and the thickness was
controlled as shown in Table 1.
[0130] The characteristic properties of the obtained biaxially
oriented polyester laminate film and the magnetic recording tape
are shown in Table 1.
TABLE-US-00001 TABLE 1 Unit Ex. 1 Ex. 2 Ex. 3 C. Ex. 1 C. Ex. 2
Film thickness Layer A .mu.m 1.7 0 3.3 1.7 1.7 Layer B .mu.m 3.3 5
1.7 3.3 3.3 All layers .mu.m 5 5 5 5 5 Ratio of layer B 66 100 34
66 66 Inert particles Particles A Type of lubricant Spherical --
Spherical Spherical Spherical silica silica silica silica Average
particle diameter .mu.m 0.1 -- 0.1 0.1 0.1 Content wt % 0.1 -- 0.1
0.1 0.1 Particles B2 Type of lubricant Spherical Crosslinked
Spherical Spherical Spherical silica silicon silica silica silica
Average particle diameter .mu.m 0.3 0.5 0.3 0.3 0.3 Content wt %
0.15 0.02 0.15 0.15 0.15 Particles B1 Type of lubricant Spherical
Spherical Spherical Spherical Spherical silica silica silica silica
silica Average particle diameter .mu.m 0.14 0.1 0.14 0.14 0.14
Content wt % 0.1 0.3 0.1 0.1 0.1 Average particle diameter of .mu.m
0.16 0.1 0.16 0.16 0.16 all particles in layer B (dB) tB/dB -- 20
50 11 20 20 Surface roughness (WRa) Layer A nm 3.5 6.5 3 3.5 3.5
Layer B nm 7.5 6.5 6.5 7.5 7.5 Young's modulus Film forming
direction GPa 6.7 7.5 8 8 6 Width direction GPa 9 8.5 9.5 6.5 9
Film forming direction + GPa 15.7 17 17.5 14.5 15 width direction
Crystallinity % 30 30 30 30 30 Heat shrinkage factor (width
direction) % 0.6 0.5 0.7 0.3 0.4 Rupture elongation (width
direction) % 52 60 48 85 54 Dimensional change rate under load %
0.67 0.51 0.65 0.31 0.53 Base film (width direction) Temperature
expansion coefficient ppm/.degree. C. -2 -1 -4 7 -2 Humidity
expansion coefficient ppm/% RH 7.5 8 7 12 7.5 Magnetic tape (width
direction) Temperature expansion coefficient ppm/.degree. C. 6 7.5
5 12 6 Humidity expansion coefficient ppm/% RH 8.5 9 8 10.5 8.5
Amount of off-track with head Conditions 1 ppm 580 640 520 830 580
Conditions 2 ppm 630 610 630 560 630 Maximum (bigger one of the
conditions ppm 630 640 630 830 630 1 and 2.) Amount of creep
compliance ppm 0.19 0.18 0.17 0.17 0.2 Overall evaluation --
.largecircle. .largecircle. .largecircle. X X Film forming
properties -- .largecircle. .DELTA. .DELTA. .circleincircle.
.circleincircle. Winding properties -- .largecircle.
.circleincircle. .largecircle. .largecircle. .largecircle. Error
rate -- .largecircle. .DELTA. .largecircle. .largecircle.
.largecircle. Chipping resistance -- .circleincircle.
.circleincircle. .circleincircle. .circleincircle. .circleincircle.
Unit C. Ex. 3 C. Ex. 4 C. Ex. 5 Ex. 4 Ex. 5 Film thickness Layer A
.mu.m 1.7 1.7 4 1.7 1.7 Layer B .mu.m 3.3 3.3 0.3 3.3 3.3 All
layers .mu.m 5 5 4.3 5 5 Ratio of layer B 66 66 6 66 66 Inert
particles Particles A Type of lubricant Spherical Spherical
Spherical Spherical Spherical silica silica silica silica silica
Average particle diameter .mu.m 0.1 0.1 0.3 0.1 0.1 Content wt %
0.1 0.1 0.38 0.1 0.1 Particles B2 Type of lubricant Spherical
Spherical Cross- Spherical Spherical silica silica linked silica
silica polystylene Average particle diameter .mu.m 0.3 0.3 0.8 0.3
0.3 Content wt % 0.15 0.15 0.1 0.15 0.15 Particles B1 Type of
lubricant Spherical Spherical Cross- Spherical Spherical silica
silica linked silica silica polystylene Average particle diameter
.mu.m 0.14 0.14 0.3 0.14 0.14 Content wt % 0.1 0.1 0.9 0.1 0.1
Average particle diameter .mu.m 0.16 0.16 0.3 0.16 0.16 of all
particles in layer B (dB) tB/dB -- 20 20 1 20 20 Surface roughness
(WRa) Layer A nm 3.5 3.5 14 4.7 3 Layer B nm 7.5 7.5 20 9.8 7
Young's modulus Film forming direction GPa 5.5 7 6.2 6.7 6.7 Width
direction GPa 12 7.3 8.3 9 9 Film forming direction + width
direction GPa 17.5 14.3 14.5 15.7 15.7 Crystallinity % 30 30 35 27
35 Heat shrinkage factor (width direction) % 0.5 0.3 0.1 0.8 0.4
Rupture elongation (width direction) % 45 64 62 52 52 Dimensional
change rate under load % 0.7 0.36 0.18 0.87 0.47 Base film (width
direction) Temperature expansion coefficient ppm/.degree. C. -10
2.5 0 -2 -2 Humidity expansion coefficient ppm/% RH 6 10 8.5 7.5
7.5 Magnetic tape (width direction) Temperature expansion
coefficient ppm/.degree. C. 1 9 8 6 6 Humidity expansion
coefficient ppm/% RH 7 10 9 8.5 8.5 Amount of off-track with head
Conditions 1 ppm 380 740 650 580 580 Conditions 2 ppm 700 630 600
630 630 Maximum ppm 700 740 650 630 630 (bigger one of the
conditions 1 and 2.) Amount of creep compliance ppm 0.21 0.19 0.20
0.19 0.19 Overall evaluation -- X X X .largecircle. .largecircle.
Film forming properties -- .circleincircle. .circleincircle.
.circleincircle. .largecircle. .DELTA. Winding properties --
.largecircle. .largecircle. .circleincircle. .largecircle.
.largecircle. Error rate -- .largecircle. .largecircle. X .DELTA.
.largecircle. Chipping resistance -- .circleincircle.
.circleincircle. X .circleincircle. .circleincircle. Ex.: Example
C. Ex.: Comparative Example
Example 6
[0131] A PEN resin composition 4 containing 0.03 wt % of spherical
silica particles with an average particle diameter of 0.14 .mu.m
and having an intrinsic viscosity (orthochlorophenol, 35.degree.
C.) of 0.60 dl/g and a PEN resin composition 5 containing 0.07 wt %
of crosslinked silicone resin particles with an average particle
diameter of 0.3 .mu.m and 0.10 wt % of spherical silica particles
with an average particle diameter of 0.14 .mu.m and having an
intrinsic viscosity (orthochlorophenol, 35.degree. C.) of 0.60 dl/g
were each dried at 180.degree. C. for 5 hours, supplied into the
hopper of an extruder, molten at 300.degree. C. in the extruder,
joined together in a ratio of 17:33 in such a manner that the
molten resin composition 4 was positioned on the surface A and the
resin composition 5 was positioned on the surface B, extruded onto
a casting drum whose surface temperature was kept at 60.degree. C.
from a T-shaped extrusion die at a surface finish of 0.3 S while
they were kept joined together and solidified by quenching to
obtain an unstretched laminate film.
[0132] The unstretched film obtained as described above was
preheated at 120.degree. C., further heated with an infrared heater
having a surface temperature of 830.degree. C. 14 mm from above to
be stretched to 5.1 times between low-speed and high-speed rolls,
quenched, supplied to the stenter to be stretched to 5.2 times in
the transverse direction at 130.degree. C. in the first half and at
150.degree. C. in the latter half and then to 1.2 times in the
transverse direction at 175.degree. C. in the first half and at
205.degree. C. in the latter half. The film was heat set at
205.degree. C. for 3 seconds while it was stretched in the latter
half and cooled at 190.degree. C. for 3 seconds to obtain a
biaxially oriented polyester film having a thickness of 5.0 .mu.m.
The Young's modulus of the obtained film was 6.7 GPa in the
longitudinal direction and 9 GPa in the transverse direction.
[0133] The operation of Example 1 was repeated to manufacture a
magnetic recording tape from the obtained film.
Example 7
[0134] A PEN resin composition 6 containing 0.09 wt % of spherical
silica particles with an average particle diameter of 0.05 .mu.m
and having an intrinsic viscosity (orthochlorophenol, 35.degree.
C.) of 0.60 dl/g and a PEN resin composition 7 containing 0.15 wt %
of crosslinked silicone resin particles with an average particle
diameter of 0.2 .mu.m and 0.20 wt % of spherical silica particles
with an average particle diameter of 0.05 .mu.m and having an
intrinsic viscosity (orthochlorophenol, 35.degree. C.) of 0.60 dl/g
were each dried at 180.degree. C. for 5 hours, supplied into the
hopper of an extruder, molten at 300.degree. C. in the extruder,
joined together in a ratio of 10:40 in such a manner that the
molten resin composition 6 was positioned on the surface A and the
resin composition 7 was positioned on the surface B, extruded onto
a casting drum whose surface temperature was kept at 60.degree. C.
from a T-shaped extrusion die at a surface finish of 0.3 S while
they were kept joined together and solidified by quenching to
obtain an unstretched laminate film.
[0135] A biaxially oriented polyester film having a thickness of
5.0 .mu.m was obtained from the unstretched film obtained as
described above in the same manner as in Example 6. The Young's
modulus of the obtained film was 6.7 GPa in the longitudinal
direction and 9 GPa in the transverse direction.
[0136] The operation of Example 1 was repeated to manufacture a
magnetic recording tape from the obtained film.
Example 8
[0137] A PEN resin composition 8 containing 0.01 wt % of spherical
silica particles with an average particle diameter of 0.18 .mu.m
and having an intrinsic viscosity (orthochlorophenol, 35.degree.
C.) of 0.60 dl/g and a PEN resin composition 9 containing 0.02 wt.
% of crosslinked silicone resin particles with an average particle
diameter of 0.4 .mu.m and 0.05 wt % of spherical silica particles
with an average particle diameter of 0.18 .mu.m and having an
intrinsic viscosity (orthochlorophenol, 35.degree. C.) of 0.60 dl/g
were each dried at 180.degree. C. for 5 hours, supplied into the
hopper of an extruder, molten at 300.degree. C. in the extruder,
joined together in a ratio of 24:26 in such a manner that the
molten resin composition 8 was positioned on the surface A and the
resin composition 9 was positioned on the surface B, extruded onto
a casting drum whose surface temperature was kept at 60.degree. C.
from a T-shaped extrusion die at a surface finish of 0.3 S while
they were kept joined together and solidified by quenching to
obtain an unstretched laminate film.
[0138] A biaxially oriented polyester film having a thickness of
5.0 .mu.m was obtained from the unstretched film obtained as
described above in the same manner as in Example 6. The Young's
modulus of the obtained film was 6.7 GPa in the longitudinal
direction and 9 GPa in the transverse direction.
[0139] The operation of Example 1 was repeated to manufacture a
magnetic recording tape from the obtained film.
Example 9
[0140] A PEN resin composition 10 containing 0.10 wt % of spherical
silica particles with an average particle diameter of 0.14 .mu.m
and having an intrinsic viscosity (orthochlorophenol, 35.degree.
C.) of 0.60 dl/g and a PEN resin composition 11 containing 0.10 wt
% of spherical silica particles with an average particle diameter
of 0.3 .mu.m and 0.30 wt % of spherical silica particles with an
average particle diameter of 0.14 .mu.M and having an intrinsic
viscosity (orthochlorophenol, 35.degree. C.) of 0.60 dl/g were each
dried at 180.degree. C. for 5 hours, supplied into the hopper of an
extruder, molten at 300.degree. C. in the extruder, joined together
in a ratio of 17:33 in such a manner that the molten resin
composition 10 was positioned on the surface A and the resin
composition 11 was positioned on the surface B, extruded onto a
casting drum whose surface temperature was kept at 60.degree. C.
from a T-shaped extrusion die at a surface finish of 0.3 S while
they were kept joined together and solidified by quenching to
obtain an unstretched laminate film.
[0141] A biaxially oriented polyester film having a thickness of
5.0 .mu.m was obtained from the unstretched film obtained as
described above in the same manner as in Example 6. The Young's
modulus of the obtained film was 6.7 GPa in the longitudinal
direction and 9 GPa in the transverse direction.
[0142] The operation of Example 1 was repeated to manufacture a
magnetic recording tape from the obtained film.
Example 10
[0143] A PEN resin composition 12 containing 0.05 wt % of spherical
silica particles with an average particle diameter of 0.20 .mu.m
and having an intrinsic viscosity (orthochlorophenol, 35.degree.
C.) of 0.60 dl/g and a PEN resin composition 13 containing 0.06 wt
% of crosslinked silicone resin particles with an average particle
diameter of 0.5 .mu.m and 0.35 wt % of spherical silica particles
with an average particle diameter of 0.2 .mu.m and having an
intrinsic viscosity (orthochlorophenol, 35.degree. C.) of 0.60 dl/g
were each dried at 180.degree. C. for 5 hours, supplied into the
hopper of an extruder, molten at 300.degree. C. in the extruder,
joined together in a ratio of 17:33 in such a manner that the
molten resin composition 12 was positioned on the surface A and the
resin composition 13 was positioned on the surface B, extruded onto
a casting drum whose surface temperature was kept at 60.degree. C.
from a T-shaped extrusion die at a surface finish of 0.3 S while
they were kept joined together and solidified by quenching to
obtain an unstretched laminate film.
[0144] A biaxially oriented polyester film having a thickness of
5.0 .mu.m was obtained from the unstretched film obtained as
described above in the same manner as in Example 6. The Young's
modulus of the obtained film was 6.7 GPa in the longitudinal
direction and 9 GPa in the transverse direction.
[0145] The operation of Example 1 was repeated to manufacture a
magnetic recording tape from the obtained film.
Example 11
[0146] An unstretched laminate film was obtained in the same manner
as in Example 1.
[0147] The unstretched film obtained as described above was
preheated at 120.degree. C., further heated with an infrared heater
having a surface temperature of 830.degree. C. 14 mm from above to
be stretched to 5.5 times between low-speed and high-speed rolls,
quenched, supplied to the stenter to be stretched to 4.8 times in
the transverse direction at 130.degree. C. in the first half and at
150.degree. C. in the latter half and then to 1.2 times in the
transverse direction at 175.degree. C. in the first half and at
205.degree. C. in the latter half and heat set at 190.degree. C.
for 3 seconds to obtain a biaxially oriented polyester film having
a thickness of 5.0 .mu.m. The Young's modulus of the obtained film
was 7.5 GPa in the longitudinal direction and 8.5 GPa in the
transverse direction.
[0148] The operation of Example 6 was repeated to manufacture a
magnetic recording tape from the obtained film.
Example 12
[0149] An unstretched laminate film was obtained in the same manner
as in Example 6. The unstretched laminate film obtained as
described above was preheated at 120.degree. C., further heated
with an infrared heater having a surface temperature of 830.degree.
C. 14 mm from above to be stretched to 3.0 times between low-speed
and high-speed rolls, quenched, supplied to the stenter to be
stretched to 4.0 times in the transverse direction at 135.degree.
C., heat set at 160.degree. C. for 3 seconds, stretched to 1.9
times in the longitudinal direction at 155.degree. C., supplied to
the stenter to be stretched to 1.7 times in the transverse
direction at 160.degree. C. and heat set at 205.degree. C. for 3
seconds to obtain a biaxially oriented polyester film having a
thickness of 5.0 .mu.m. The Young's modulus of the obtained film
was 8.0 GPa in the longitudinal direction and 9.5 GPa in the
transverse direction.
[0150] The operation of Example 1 was repeated to manufacture a
magnetic recording tape from the obtained film.
TABLE-US-00002 TABLE 2 Unit Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11
Ex. 12 Film thickness Layer A .mu.m 1.7 1 2.4 1.7 1.7 1.7 1.7 Layer
B .mu.m 3.3 4 2.6 3.3 3.3 3.3 3.3 All layers .mu.m 5 5 5 5 5 5 5
Ratio of layer B 66 80 52 66 66 66 66 Inert particles Particles A
Type of lubricant Spherical Spherical Spherical Spherical Spherical
Spherical Spherical silica silica silica silica silica silica
silica Average particle .mu.m 0.14 0.05 0.18 0.14 0.2 0.14 0.14
diameter Content wt % 0.03 0.09 0.01 0.1 0.05 0.03 0.03 Particles
B2 Type of lubricant Cross- Cross- Cross- Spherical Cross- Cross-
Cross- linked linked linked silica linked linked linked silicon
silicon silicon silicon silicon silicon Average particle .mu.m 0.3
0.2 0.4 0.3 0.5 0.3 0.3 diameter Content wt % 0.07 0.15 0.02 0.1
0.06 0.07 0.07 Particles B1 Type of lubricant Spherical Spherical
Spherical Spherical Spherical Spherical Spherical silica silica
silica silica silica silica silica Average particle .mu.m 0.14 0.05
0.18 0.14 0.2 0.14 0.14 diameter Content wt % 0.1 0.2 0.05 0.3 0.35
0.1 0.1 Average particle .mu.m 0.16 0.05 0.21 0.15 0.21 0.16 0.16
diameter of all particles in layer B (dB) tB/dB -- 21 76 12 23 16
21 21 Surface roughness (WRa) Layer A nm 2.5 2.5 2.5 3.5 4 2.5 2.5
Layer B nm 6.5 6.5 6.5 7.5 10 6.5 6.5 Young's modulus Film forming
direction GPa 6.7 6.7 6.7 6.7 6.7 7.5 8 Width direction GPa 9 9 9 9
9 8.5 9.5 Film forming direction + GPa 15.7 15.7 15.7 15.7 15.7 17
17.5 width direction Crystallinity % 30 30 30 30 30 30 30 Heat
shrinkage factor (width direction) % 0.6 0.6 0.6 0.6 0.6 0.5 0.7
Rupture elongation (width direction % 52 52 52 52 52 60 48
Dimensional change rate under load % 0.67 0.67 0.67 0.67 0.67 0.51
0.65 Base film (width direction) Temperature expansion coefficient
ppm/.degree. C. -2 -2 -2 -2 -2 -1 -4 Humidity expansion coefficient
ppm/% RH 7.5 7.5 7.5 7.5 7.5 8 7 Magnetic tape (width direction)
Temperature expansion coefficient ppm/.degree. C. 6 6 6 6 6 7.5 5
Humidity expansion coefficient ppm/% RH 8.5 8.5 8.5 8.5 8.5 9 8
Amount of off-track with head Condition 1 ppm 580 580 580 580 580
640 520 Condition 2 ppm 630 630 630 630 630 610 630 Maximum (bigger
one of the ppm 630 630 630 630 630 640 630 conditions 1 and 2.)
Amount of creep compliance ppm 0.19 0.19 0.19 0.19 0.19 0.18 0.17
Overall evaluation -- .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. Film
forming properties -- .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .DELTA. .DELTA. Winding properties --
.DELTA. .DELTA. .DELTA. .circleincircle. .circleincircle. .DELTA.
.DELTA. Error rate -- .circleincircle. .circleincircle.
.circleincircle. .largecircle. .DELTA. .circleincircle.
.circleincircle. Recyclability -- .circleincircle. .circleincircle.
.largecircle. .circleincircle. .circleincircle. .circleincircle.
.circleincircle. Chipping resistance -- .circleincircle.
.circleincircle. .circleincircle. .circleincircle. .circleincircle.
.circleincircle. .circleincircle. Ex.: Example
Example 13
[0151] A PEN resin composition 14 containing 0.05 wt % of spherical
silica particles with an average particle diameter of 0.14 .mu.m
and having an intrinsic viscosity (orthochlorophenol, 35.degree.
C.) of 0.60 dl/g and a PEN resin composition 15 containing 0.07 wt
% of crosslinked silicone resin particles with an average particle
diameter of 0.3 .mu.m and 0.10 wt % of spherical silica particles
with an average particle diameter of 0.14 .mu.m and having an
intrinsic viscosity (orthochlorophenol, 35.degree. C.) of 0.60 dl/g
were each dried at 180.degree. C. for 5 hours, supplied into the
hopper of an extruder, molten at 300.degree. C. in the extruder,
joined together in a ratio of 33:17 in such a manner that the
molten resin composition 14 was positioned on the surface A and the
resin composition 15 was positioned on the surface B, extruded onto
a casting drum whose surface temperature was kept at 60.degree. C.
from a T-shaped extrusion die at a surface finish of 0.3 S while
they were kept joined together and solidified by quenching to
obtain an unstretched laminate film.
[0152] The unstretched film obtained as described above was
preheated at 120.degree. C., further heated with an infrared heater
having a surface temperature of 830.degree. C. 14 mm from above to
be stretched to 5.1 times between low-speed and high-speed rolls,
quenched, supplied to the stenter to be stretched to 5.2 times in
the transverse direction at 130.degree. C. in the first half and at
150.degree. C. in the latter half and then to 1.2 times in the
transverse direction at 175.degree. C. in the first half and at
205.degree. C. in the latter half. The film was heat set at
205.degree. C. for 3 seconds while stretching at 205.degree. C. in
the latter half and then cooled to 190.degree. C. for 3 seconds to
obtain a biaxially oriented polyester film having a thickness of
5.0 .mu.m. The Young's modulus of the obtained film was 6.7 GPa in
the longitudinal direction and 9 GPa in the transverse
direction.
[0153] The operation of Example 1 was repeated to manufacture a
magnetic recording tape from the obtained film.
Example 14
[0154] A PEN resin composition 16 containing 0.01 wt % of spherical
silica particles with an average particle diameter of 0.18 .mu.m
and having an intrinsic viscosity (orthochlorophenol, 35.degree.
C.) of 0.60 dl/g and a PEN resin composition 17 containing 0.02 wt
% of crosslinked silicone resin particles with an average particle
diameter of 0.4 .mu.m and 0.05 wt % of spherical silica particles
with an average particle diameter of 0.18 .mu.m and having an
intrinsic viscosity (orthochlorophenol, 35.degree. C.) of 0.60 dl/g
were each dried at 180.degree. C. for 5 hours, supplied into the
hopper of an extruder, molten at 300.degree. C. in the extruder,
joined together in a ratio of 44:6 in such a manner that the molten
resin composition 16 was positioned on the surface A and the resin
composition 17 was positioned on the surface B, extruded onto a
casting drum whose surface temperature was kept at 60.degree. C.
from a T-shaped extrusion die at a surface finish of 0.3 S while
they were kept joined together and solidified by quenching to
obtain an unstretched laminate film.
[0155] A biaxially oriented polyester film having a thickness of
5.0 .mu.m was obtained from the unstretched film obtained as
described above in the same manner as in Example 10. The Young's
modulus of the obtained film was 6.7 GPa in the longitudinal
direction and 9 GPa in the transverse direction.
[0156] The operation of Example 1 was repeated to manufacture a
magnetic recording tape from the obtained film.
Example 15
[0157] A PEN resin composition 18 containing 0.15 wt % of spherical
silica particles with an average particle diameter of 0.05 .mu.m
and having an intrinsic viscosity (orthochlorophenol, 35.degree.
C.) of 0.60 dl/g and a PEN resin composition 19 containing 0.15 wt
% of crosslinked silicone resin particles with an average particle
diameter of 0.2 .mu.m and 0.30 wt % of spherical silica particles
with an average particle diameter of 0.05 .mu.m and having an
intrinsic viscosity (orthochlorophenol, 35.degree. C.) of 0.60 dl/g
were each dried at 180.degree. C. for 5 hours, supplied into the
hopper of an extruder, molten at 300.degree. C. in the extruder,
joined together in a ratio of 26:24 in such a manner that the
molten resin composition 18 was positioned on the surface A and the
resin composition 19 was positioned on the surface B, extruded onto
a casting drum whose surface temperature was kept at 60.degree. C.
from a T-shaped extrusion die at a surface finish of 0.3 S while
they were kept joined together and solidified by quenching to
obtain an unstretched laminate film.
[0158] A biaxially oriented polyester film having a thickness of
5.0 .mu.m was obtained from the unstretched film obtained as
described above in the same manner as in Example 13. The Young's
modulus of the obtained film was 6.7 GPa in the longitudinal
direction and 9 GPa in the transverse direction.
[0159] The operation of Example 1 was repeated to manufacture a
magnetic recording tape from the obtained film.
Example 16
[0160] A PEN resin composition 24 containing 0.05 wt % of spherical
silica particles with an average particle diameter of 0.14 .mu.m
and having an intrinsic viscosity (orthochlorophenol, 35.degree.
C.) of 0.60 dl/g and a PEN resin composition 25 containing 0.07 wt
% of crosslinked silicone resin particles with an average particle
diameter of 0.3 .mu.m and 0.10 wt % of spherical silica particles
with an average particle diameter of 0.14 .mu.m and having an
intrinsic viscosity (orthochlorophenol, 35.degree. C.) of 0.60 dl/g
were each dried at 180.degree. C. for 5 hours, supplied into the
hopper of an extruder, molten at 300.degree. C. in the extruder,
joined together in a ratio of 47:3 in such a manner that the molten
resin composition 24 was positioned on the surface A and the resin
composition 25 was positioned on the surface B, extruded onto a
casting drum whose surface temperature was kept at 60.degree. C.
from a T-shaped extrusion die at a surface finish of 0.3 S while
they were kept joined together and solidified by quenching to
obtain an unstretched laminate film.
[0161] A biaxially oriented polyester film having a thickness of
5.0 .mu.m was obtained from the unstretched film obtained as
described above in the same manner as in Example 13. The Young's
modulus of the obtained film was 6.7 GPa in the longitudinal
direction and 9 GPa in the transverse direction.
[0162] The operation of Example 1 was repeated to manufacture a
magnetic recording tape from the obtained film.
Example 17
[0163] An unstretched laminate film was obtained in the same manner
as in Example 13.
[0164] The unstretched film obtained as described above was
preheated at 120.degree. C., further heated with an infrared heater
having a surface temperature of 830.degree. C. 14 mm from above to
be stretched to 5.5 times between low-speed and high-speed rolls,
quenched, supplied to the stenter to be stretched to 4.8 times in
the transverse direction at 150.degree. C. and then to 1.2 times in
the transverse direction at 180.degree. C., and heat set at
205.degree. C. for 3 seconds to obtain a biaxially oriented
polyester film having a thickness of 5.0 .mu.m. The Young's modulus
of the obtained film was 7.5 GPa in the longitudinal direction and
8.5 GPa in the transverse direction.
[0165] The operation of Example 1 was repeated to manufacture a
magnetic recording tape from the obtained film.
Example 18
[0166] An unstretched laminate film was obtained in the same manner
as in Example 13.
[0167] The unstretched film obtained as described above was
preheated at 120.degree. C., further heated with an infrared heater
having a surface temperature of 830.degree. C. 14 mm from above to
be stretched to 3.0 times between low-speed and high-speed rolls,
quenched, supplied to the stenter to be stretched to 4.0 times in
the transverse direction at 135.degree. C., heat set at 160.degree.
C. for 3 seconds, stretched to 1.9 times in the longitudinal
direction at 155.degree. C., supplied to the stenter to be
stretched to 1.7 times in the transverse direction at 160.degree.
C., and heat set at 205.degree. C. for 3 seconds to obtain a
biaxially oriented polyester film having a thickness of 5.0 .mu.m.
The Young's modulus of the obtained film was 8.0 GPa in the
longitudinal direction and 9.5 GPa in the transverse direction.
[0168] The operation of Example 1 was repeated to manufacture a
magnetic recording tape from the obtained film.
TABLE-US-00003 TABLE 3 Unit Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex.
18 Film thickness Layer A .mu.m 3.3 4.4 2.6 4.7 3.3 3.3 Layer B
.mu.m 1.7 0.6 2.4 0.3 1.7 1.7 All layers .mu.m 5 5 5 5 5 5 Ratio of
layer B 34 12 48 6 34 34 Inert particles Particles A Type of
lubricant Spherical Spherical Spherical Spherical Spherical
Spherical silica silica silica silica silica silica Average
particle diameter .mu.m 0.14 0.18 0.05 0.14 0.14 0.14 Content wt %
0.05 0.01 0.15 0.05 0.05 0.05 Particles B2 Type of lubricant Cross-
Cross- Cross- Cross- Cross- Cross- linked linked linked linked
linked linked silicon silicon silicon silicon silicon silicon
Average particle diameter .mu.m 0.3 0.4 0.2 0.3 0.3 0.3 Content wt
% 0.07 0.02 0.15 0.07 0.07 0.07 Particles B1 Type of lubricant
Spherical Spherical Spherical Spherical Spherical Spherical silica
silica silica silica silica silica Average particle diameter .mu.m
0.14 0.18 0.05 0.14 0.14 0.14 Content wt % 0.1 0.05 0.3 0.1 0.1 0.1
Average particle diameter of .mu.m 0.16 0.21 0.11 0.16 0.16 0.16
all particles in layer B (dB) tB/dB -- 11 3 22 2 11 11 Surface
roughness (WRa) Layer A nm 2.5 2.5 2.5 2 2.5 2.5 Layer B nm 5.5 5.5
5.5 4.5 5.5 5.5 Young's modulus Film forming direction GPa 6.7 6.7
6.7 6.7 7.5 8 Width direction GPa 9 9 9 9 8.5 9.5 Film forming
direction + GPa 15.7 15.7 15.7 15.7 17 17.5 width direction
Crystallinity % 30 30 30 30 30 30 Heat shrinkage factor (width
direction) % 0.6 0.6 0.6 0.6 0.5 0.7 Rupture elongation (width
direction % 52 52 52 52 60 48 Dimensional change rate under load %
0.67 0.67 0.67 0.67 0.51 0.65 Base film (width direction)
Temperature expansion coefficient ppm/.degree. C. -2 -2 -2 -2 -1 -4
Humidity expansion coefficient ppm/% RH 7.5 7.5 7.5 7.5 8 7
Magnetic tape (width direction) Temperature expansion coefficient
ppm/.degree. C. 6 6 6 6 7.5 5 Humidity expansion coefficient ppm/%
RH 8.5 8.5 8.5 8.5 9 8 Amount of off-track with head Condition 1
ppm 580 580 580 580 640 520 Condition 2 ppm 630 630 630 630 610 630
Maximum (bigger one of the conditions ppm 630 630 630 630 640 630 1
and 2.) Amount of creep compliance ppm 0.19 0.19 0.19 0.19 0.18
0.17 Overall evaluation -- .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. Film
forming properties -- .largecircle. .largecircle. .largecircle.
.largecircle. .DELTA. .DELTA. Winding properties -- .DELTA. .DELTA.
.DELTA. .DELTA. .DELTA. .DELTA. Error rate -- .circleincircle.
.circleincircle. .circleincircle. .circleincircle. .circleincircle.
.circleincircle. Recyclability -- .DELTA. X .DELTA. X .DELTA.
.DELTA. Chipping resistance -- .circleincircle. .largecircle.
.circleincircle. X .circleincircle. .circleincircle. Ex.:
Example
[0169] The biaxially oriented polyester film of the present
invention can be advantageously used as a base film for magnetic
recording tapes of linear recording system and data storage tapes
for the back-up of computers, especially linear tape-open (LTO)
tapes.
* * * * *