U.S. patent application number 08/978613 was filed with the patent office on 2002-06-06 for laminate film with organic particulate for magnetic recording medium.
Invention is credited to HANDA, MAKOTO, OSAWA, TOSHIFUMI, TOJO, MITSUO.
Application Number | 20020068196 08/978613 |
Document ID | / |
Family ID | 18113138 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020068196 |
Kind Code |
A1 |
HANDA, MAKOTO ; et
al. |
June 6, 2002 |
LAMINATE FILM WITH ORGANIC PARTICULATE FOR MAGNETIC RECORDING
MEDIUM
Abstract
A laminate film has a coated film layer containing a binder
resin and an organic filler. The laminate film satisfies the
following expressions (1) and (2) when it is heated at 200.degree.
C. for 120 minutes: 0.ltoreq.(Ra.sup.1-Ra.sup.2)/Ra.sup.1<0.4
(1) 0.1<Ra.sup.2<7 (2) wherein Ra.sup.1 is an average
roughness of root mean square (nm) of an exposed surface of the
coated film layer before the heat treatment, and Ra.sup.2 is an
average roughness of root mean square (nm) of the exposed surface
of the coated film layer after the heat treatment. The film has
protrusions with two or more interference fringes on the surface at
a density of 100 per 100 cm.sup.2 at the most. The present laminate
film is useful as a base film for a magnetic recording medium.
Inventors: |
HANDA, MAKOTO;
(SAGAMIHARA-SHI, JP) ; TOJO, MITSUO;
(SAGAMIHARA-SHI, JP) ; OSAWA, TOSHIFUMI;
(SAGAMIHARA-SHI, JP) |
Correspondence
Address: |
SUGHRUE MION ZINN
MACPEAK & SEAS
2100 PENNSYLVANIA AVENUE N W
WASHINGTON
DC
20037
|
Family ID: |
18113138 |
Appl. No.: |
08/978613 |
Filed: |
November 26, 1997 |
Current U.S.
Class: |
428/848.2 ;
G9B/5.286; G9B/5.288 |
Current CPC
Class: |
Y10T 428/254 20150115;
C08J 7/043 20200101; G11B 5/73931 20190501; C08J 7/046 20200101;
Y10T 428/2998 20150115; Y10T 428/2991 20150115; C08J 2467/00
20130101; C08J 2433/00 20130101; G11B 5/73925 20190501; C08J 7/0427
20200101; B82Y 15/00 20130101; Y10T 428/31786 20150401 |
Class at
Publication: |
428/694.0SL |
International
Class: |
G11B 005/78 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 29, 1996 |
JP |
8-319,693 |
Claims
What is claimed is:
1. A laminate film: (A) which comprises a film consisting of a
single layer or a plurality of layers of a thermoplastic resin and
a first coated film layer present on at least one surface of the
film, the first coated film layer containing a binder resin and an
organic filler, (B) which satisfies the following expressions (1)
and (2) at the same time when it is heated at 200.degree. C. for
120 minutes:0.ltoreq.(Ra.sup.1-Ra- .sup.2)/Ra.sup.1<0.4
(1)0.1<Ra.sup.2<7 (2)wherein Ra.sup.1 is an average roughness
of root mean square (nm), measured by an atomic force microscope,
of an exposed surface of the first coated film layer before the
heat treatment, and Ra.sup.2 is an average roughness of root mean
square (nm), measured by the atomic force microscope, of the
exposed surface of the first coated film layer after the heat
treatment, and (C) in which protrusions with two or more
interference fringes which can be observed when two films are
superposed in such a manner that their first coated film layers
come in contact with each other and exposed to light from a sodium
lamp are present on the surface of each film at a density of 100
per 100 cm.sup.2 at the most.
2. The laminate film of claim 1, wherein the thermoplastic resin
has a melting point of at least 210.degree. C.
3. The laminate film of claim 1, wherein the organic filler present
in the first coated film layer has a deformation retention rate at
200.degree. C. of 60% or more.
4. The laminate film of claim 1, wherein the organic filler is made
from a material selected from the group consisting of a
styrene/divinylbenzene copolymer, a methyl methacrylate crosslinked
copolymer, polytetrafluoroethylene, polyvinylidene fluoride,
polyacrylonitrile and benzoguanamine.
5. The laminate film of claim 1, wherein the organic filler
contained in the first coated film layer has an average particle
diameter of 5 to 100 nm.
6. The laminate film of claim 1, wherein the following relationship
is established between the thickness t.sub.1 (nm) of the first
coated film layer and the average particle diameter d.sub.1 (nm) of
the organic filler contained in the first coated film
layer:0.05.ltoreq.t.sub.1/d.sub- .1<1.
7. The laminate film of claim 1, wherein the organic filler is
contained in an amount of 0.1 to 25% by weight in the first coated
film layer.
8. The laminate film of claim 1, wherein the binder resin is at
least one aqueous resin selected from the group consisting of acryl
resins, polyester resins and acryl/polyester resins.
9. The laminate film of claim 1, wherein a second coated film layer
containing inert particles is further present on the surface not in
contact with the first coated film layer, of the thermoplastic
resin film.
10. The laminate film of claim 1, wherein the single layer or a
layer in contact with the first coated film layer out of the
plurality of layers of the thermoplastic resin contains
substantially no inert particles.
11. The laminate film of claim 1, wherein the single layer or a
layer in contact with the first coated film layer out of the
plurality of layers of the thermoplastic resin contains 0.005 to
0.1% by weight of inert fine particles having an average particle
diameter of 20 to 400 nm and a volume shape factor of 0.1 to
.pi./6.
12. The laminate film of claim 1 having a thickness of 2.5 to 80
.mu.m.
13. Use of the laminate film of claim 1 as a base film for a
magnetic recording medium.
14. Use of claim 13, wherein the magnetic recording medium is a
metal thin film magnetic recording medium.
15. A magnetic recording medium comprising the laminate film of
claim 1 and a magnetic layer present on the first coated film layer
of the laminate film.
16. The magnetic recording medium of claim 15 which is a metal thin
film magnetic recording medium.
17. The magnetic recording medium of claim 15, wherein a magnetic
layer has a thickness of 1 .mu.m or less.
18. The magnetic recording medium of claim 15 for use in Hi8 for
analog signal recording and a digital video cassette recorder, data
8 mm and DDSIV for digital signal recording.
Description
[0001] This invention relates to a laminate film and, more
specifically, to a laminate film suitable for use as a magnetic
recording medium, particularly a high-density magnetic recording
medium, having excellent electromagnetic conversion characteristics
and durability and few drop-outs.
[0002] In recent years, remarkable progress has been made in
high-density magnetic recording, as exemplified by the development
and implementation of a ferromagnetic metal thin film magnetic
recording medium in which a ferromagnetic metal thin film is formed
on a non-magnetic base film by a physical deposition method such as
vacuum vapor deposition or sputtering, or a plating method, and a
thin layer coated magnetic recording medium in which a
needle-shaped magnetic powder such as a metal powder or iron oxide
powder is coated on a film to a thickness of not larger than 2
.mu.m.
[0003] Known examples of the former include a Co deposited tape
(see JP-A 54-147010) (the term "JP-A" as used herein means an
"unexamined published Japanese patent application") and a vertical
magnetic recording medium composed of Co--Cr alloy (see JP-A
52-134706). Known examples of the latter include an extremely thin
layer coated medium for high-density magnetic recording (see
"Technical Report MR 94-78" (1995-02) issued by the Institute of
Electronics and Communication Engineering of Japan).
[0004] Since a coated magnetic recording medium of the prior art,
i.e. a magnetic recording medium, in which a mixture of magnetic
powders and an organic polymer binder is coated on a non-magnetic
base film, has a low recording density and a long recording
wavelength, the thickness of its magnetic layer is as large as
about 2 .mu.m or more. On the other hand, a metal thin film formed
by thin film forming means such as vacuum vapor deposition,
sputtering or ion plating has a thickness as extremely small as 0.2
.mu.m or less. In the case of an extremely thin layer coated
medium, a coated magnetic layer is as extremely thin as 0.13 .mu.m
though a non-magnetic primary coat layer is provided.
[0005] In the above high-density magnetic recording media, the
surface condition of the non-magnetic base film has a great
influence on the surface characteristics of the magnetic recording
layer. Particularly, in the case of a metal thin film magnetic
recording medium, the surface condition of the non-magnetic base
film appears directly as an uneven surface of the magnetic
recording layer, which causes noise in a reproduction signal.
Therefore, it is desirable that the surface of the non-magnetic
base film be as smooth as possible.
[0006] Further, in the case of a deposited metal thin film magnetic
recording medium, the durability of a metal thin film surface is an
important factor when the medium is actually used. In the case of a
coated magnetic recording medium in which magnetic powders are
mixed into an organic polymer binder and the resulting mixture is
coated onto the base film, the durability of the magnetic surface
can be improved by mixing hard fine particles such as aluminum
oxide into the binder. However, in the case of a deposited metal
thin film magnetic recording medium, this measure cannot be taken,
and it is extremely difficult to maintain stable durability.
[0007] As means for solving this problem, there have been proposed
(1) a method for forming a discontinuous surface film by applying a
specific coating to the surface of a film (see JP-B 3-80410 (the
term "JP-B" as used herein means an "examined patent publication"),
JP-A 60-180839, JP-A 60-180838, JP-A 60-180837, JP-A 56-16937 and
JP-A 58-68223) and (2) a method for forming a continuous surface
film having fine protrusions (see JP-A 5-194772 and JP-A
5-210833).
[0008] However, it is difficult to maintain sufficient durability
with a discontinuous surface film alone. Also when a continuous
surface film having fine protrusions is to be formed by inert fine
particles, it is difficult to uniformly disperse the inert fine
particles into a surface film and coarse protrusions are liable to
produce by agglomerated particles, thereby deteriorating
electromagnetic conversion characteristics. Thus, films produced by
the above proposals still have a problem in that the quality of a
magnetic tape is unstable. Further, the agglomerated particles are
scraped off by their contact with a guide roll in the film
formation step more easily than monodisperse particles, adhered to
and accumulated on the base film thereby to produce protrusions,
which causes a drop out when a magnetic tape is formed
therefrom.
[0009] Generally speaking, inorganic particles are excellent in the
cleaning properties of a magnetic head because they are hard and
difficult to be deformed, are rarely changed in shape by heat in
the tape processing step due to its high heat resistance and hence,
provide excellent durability to a tape. However, they have poor
affinity with a polymer and are apt to fall off. On the other hand,
organic particles have lower hardness than inorganic particles
though they have excellent affinity with a polymer, and the
electromagnetic conversion characteristics of a tape degrade along
with repeated running of the tape because all the particles undergo
deformation by heat and mechanical friction.
[0010] It is an object of the present invention to provide a
laminate film which eliminates the above defects of the prior art,
has excellent abrasion resistance in the film formation step and
excellent electromagnetic conversion characteristics, resistance to
drop-out and running durability when it is used as a base film for
a deposited metal thin film magnetic recording medium or an
extremely thin layer coated magnetic recording medium, for
example.
[0011] It is another object of the present invention to provide a
magnetic recording medium which comprises the above laminate film
of the present invention as a base film and is excellent in
electromagnetic conversion characteristics, resistance to drop out
and running durability.
[0012] Other objects and advantages of the present invention are
apparent from the following description.
[0013] According to the present invention, firstly, the above
objects and advantages of the present invention can be attained by
a laminate film:
[0014] (A) which comprises a film consisting of a single layer or a
plurality of layers of a thermoplastic resin, and a first coated
film layer present on at least one surface of the film, the first
coated film layer containing a binder resin and an organic
filler,
[0015] (B) which satisfies the following expressions (1) and (2) at
the same time when it is heated at 200.degree. C. for 120
minutes:
0.ltoreq.(Ra.sup.1-Ra.sup.2)/Ra.sup.1<0.4 (1)
0.1<Ra.sup.2<7 (2)
[0016] wherein Ra.sup.1 is an average roughness of root mean square
(nm), measured by an atomic force microscope, of an exposed surface
of the first coated film layer before the heat treatment and
Ra.sup.2 is an average roughness of root mean square (nm), measured
by the atomic force microscope, of the exposed surface of the first
coated film layer after the heat treatment, and
[0017] (C) in which protrusions with two or more interference
fringes which can be observed when two films are superposed in such
a manner that their first coated film layers come in contact with
each other and exposed to light from a sodium lamp are present on
the surface of each film at a density of 100 per 100 cm.sup.2 at
the most.
[0018] In the laminate film of the present invention, the
thermoplastic resin for the single layer or the plurality of layers
of the film is, for example, a polyester resin, polyamide resin,
polyimide resin, polyether resin, polycarbonate resin, polyvinyl
resin, polyolefin resin or the like. Out of these, the
thermoplastic resin is preferably a polyester resin, more
preferably an aromatic polyester. The thermoplastic resin
preferably has a melting point of at least 210.degree. C.
[0019] Preferred examples of the aromatic polyester include
polyethylene terephthalate, polyethylene isophthalate,
polytetramethylene terephthalate, poly-1,4-cyclohexylene
dimethylene terephthalate, polyethylene-2,6-naphthalene
dicarboxylate and the like. Out of these, polyethylene
terephthalate and polyethylene-2,6-naphthalene dicarboxylate are
particularly preferred.
[0020] These polyesters may be either a homopolyester or
copolyester. In the case of a copolyester, the copolymerizable
component of polyethylene terephthalate or
polyethylene-2,6-naphthalene dicarboxylate, for example, is a diol
component such as diethylene glycol, propylene glycol, neopentyl
glycol, polyethylene glycol, p-xylene glycol or 1,4-cyclohexane
dimethanol; a dicarboxylic acid component such as adipic acid,
sebacic acid, phthalic acid, isophthalic acid, terephthalic acid
(in the case of polyethylene-2,6-naphthalene dicarboxylate),
2,6-naphthalenedicarboxylic acid (in the case of polyethylene
terephthalate) or 5-sodium sulfoisophthalic acid; or an
oxycarboxylic acid component such as p-oxyethoxybenzoic acid. The
amount of the copolymerizable component is not more than 20 mol %,
preferably not more than 10 mol %. Further, a polyfunctional
compound having 3 or more functional groups, such as trimellitic
acid or pyromellitic acid, may be copolymerized. In this case, the
polyfunctional compound may be copolymerized in such an amount that
the polymer is substantially linear, for example, in an amount of
not more than 2 mol %.
[0021] The laminate film of the present invention has a first
coated film layer on at least one surface of the film consisting of
a single layer or a plurality of layers of the above thermoplastic
resin.
[0022] The first coated film layer contains a binder resin and
organic filler. The binder resin is preferably a water-soluble
resin, that is, a water-soluble organic resin or water-dispersible
organic resin. Illustrative examples of the water-soluble resin
include aqueous alkyd resins, phenol resins, epoxy resins, amino
resins, polyurethane resins, vinyl acetate resins, vinyl
chloride-vinyl acetate copolymers, acryl resins, polyester resins
and acryl/polyester resins. Out of these, aqueous acrylic resins,
polyester resins and acryl/polyester resins are preferred from
viewpoints of adhesion to the above film, protrusion retention
properties and slipperiness. These aqueous resins may be a
homopolymer, copolymer or mixture.
[0023] The aqueous acryl resins include polymers formed of a
combination of two or more members selected from acrylic esters
(alcohol residues include methyl, ethyl, n-propyl, isopropyl,
n-butyl, isobutyl, t-butyl, 2-ethylhexyl, cyclohexyl, phenyl,
benzyl, phenylethyl and the like); methacrylic esters (alcohol
residues are the same as above); hydroxy-containing monomers such
as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate,
2-hydroxypropyl acrylate and 2-hydroxypropyl methacrylate; amide
group-containing monomers such as acrylamide, methacrylamide,
N-methylmethacrylamide, N-methylacrylamide, N-methylolacrylamide,
N-methylolmethacrylamide, N,N-dimethylolacrylamide,
N-methoxymethylacrylamide, N-methoxymethylmethacrylamide and
N-phenylacrylamide; amino group-containing monomers such as
N,N-diethylaminoethyl acrylate and N,N-diethylaminoethyl
methacrylate; epoxy group-containing monomers such as glycidyl
acrylate, glycidyl methacrylate and allyl glycidyl ether; monomers
containing a sulfonic acid group or a salt thereof such as
styrenesulfonic acid, vinylsulfonic acid and salts thereof (such as
sodium salt, potassium salt and ammonium salt); monomers containing
a carboxyl group such as crotonic acid, itaconic acid, acrylic
acid, maleic acid and fumaric acid, and salts thereof (such as
sodium salt, potassium salt and ammonium salt); monomers containing
an anhydride such as maleic anhydride and itaconic anhydride; and
vinyl isocyanate, allyl isocyanate, styrene, vinylmethylether,
vinylethylether, vinyltrisalkoxysilane, alkyl maleic monoester,
alkyl fumaric monoester, acrylonitrile, methacrylonitrile, alkyl
itaconic monoester, vinylidene chloride, vinyl acetate and vinyl
chloride. Out of these, an acryl resin comprising 50 mol % or more
of a (meth)acrylic monomer such as an acrylic acid derivative or
methacrylic acid derivative, particularly methyl methacrylate, is
preferred.
[0024] The aqueous acryl resin can be self-crosslinked with a
functional group in the molecule or crosslinked using a
crosslinking agent such as a melamine resin, epoxy compound or the
like.
[0025] The aqueous polyester resins include polymers comprising, as
an acid component, a polyvalent carboxylic acid such as
terephthalic acid, isophthalic acid, phthalic acid,
1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid,
4,4'-diphenyldicarboxylic acid, adipic acid, sebacic acid,
dodecanedicarboxylic acid, succinic acid, 5-sodium sulfoisophthalic
acid, 2-potassium sulfoterephthalic acid, trimellitic acid,
trimesic acid, trimellitic anhydride, phthalic anhydride,
p-hydroxybenzoic acid or monopotassium salt of trimellitic acid
and, as a hydroxy compound component, a polyvalent hydroxy compound
such as ethylene glycol, propylene glycol, 1,3-propanediol,
1,4-butanediol, 1,6-hexanediol, neopentyl glycol,
1,4-cyclohexanedimethanol, p-xylyleneglycol, addition product of
bisphenol A with ethylene oxide, diethylene glycol, triethylene
glycol, polyethylene oxide glycol, polytetramethylene oxide glycol,
dimethylolpropionic acid, glycerin, trimethylolpropane,
dimethylolethyl sodium sulfonate and dimethylol potassium
propanate. The polyester resins can be produced from these
compounds by a conventional method. An aqueous polyester resin
containing a 5-sodium sulfoisophthalic acid component or a
carboxylate salt group is preferably used from a viewpoint of
preparing an aqueous coating. The polyester resin may be
self-crosslinked with a functional group in the molecule or
crosslinked using a curing agent such as a melamine resin or epoxy
resin.
[0026] Further, the term "aqueous acryl-polyester resin" is used to
imply acryl modified polyester resins and polyester modified acryl
resins, and for example, both graft and block type polymers in
which an acryl resin component and a polyester resin component are
bonded together. The acryl-polyestser resin can be produced, for
example, by adding a radical initiator to both terminals of a
polyester resin to polymerize acryl monomers, or adding a radical
initiator to a side chain of a polyester resin to polymerize acryl
monomers, or adding a hydroxyl group to a side chain of an acryl
resin and reacting it with a polyester having an isocyanate group
or carboxyl group at a terminal to produce a comb-like polymer, or
the like.
[0027] The first coated film layer contains an organic filler in
addition to the above binder resin. The organic filler preferably
is ones having a deformation retention rate at 200.degree. C. of
60% or more. The organic filler is formed of a material selected
from the group consisting of styrene/divinylbenzene copolymer,
methyl methacrylate crosslinked copolymer, polytetrafluoroethylene,
polyvinylidene fluoride, polyacrylonitrile and benzoguanamine.
[0028] In addition to the above organic fillers, there may be used
particles formed by coating inorganic particles, as the core, such
as silica, alumina, titanium dioxide, kaolin, talc, graphite,
calcium carbonate, feldspar, molybdenum disulfide, carbon black and
barium sulfate with an organic polymer. The same substances as
described above can be listed as the organic polymer.
[0029] The average particle diameter of the organic filler is
preferably 5 to 100 nm, more preferably 10 to 80 nm, particularly
preferably 12 to 55 nm. If the average particle diameter is smaller
than 5 nm, the durability of the first coated film will be
insufficient, while if the average particle diameter is larger than
100 nm, the electromagnetic conversion characteristics of the
magnetic recording medium will be affected adversely.
[0030] The content of the organic filler in the first coated film
is preferably 0.1 to 25% by weight, more preferably 0.5 to 20% by
weight, particularly preferably 1 to 15% by weight. If the content
is smaller than 0.1% by weight, durability will be insufficient due
to a too small number of protrusions formed by the organic filler,
whereas if the content is larger than 25% by weight, it will be
difficult to retain the organic filler in the coated film layer
stably, whereby the organic filler will fall off to form an adhered
foreign matter. Contrarily, when the organic filler is retained in
the coated film, the number of protrusions is liable to become too
large with the result of making a too rough surface, thereby
degrading the electromagnetic conversion characteristics of a
magnetic recording medium.
[0031] The following relationship is preferably established between
the thickness t.sub.1 (nm) of the first coated film layer and the
average particle diameter d.sub.1 (nm) of the organic filler
contained in the first coated film layer.
0.05.ltoreq.t.sub.1/d.sub.1<1
[0032] When the above relationship is established, the effect of
the present invention becomes further marked.
[0033] When the ratio (t.sub.1/d.sub.1) is more than 1, the effect
of adding the organic filler is extremely small, while when the
ratio is less than 0.05, the organic filler is apt to fall off,
resulting in an increase in the number of adhered foreign matters.
The ratio is preferably in the range of 0.08 to 0.80, more
preferably 0.10 to 0.70, particularly preferably 0.12 to 0.50.
[0034] In the laminate film of the present invention, the first
coated film layer satisfies the following equations (1) and (2) at
the same time when it is heated at 200.degree. C. for 120
minutes.
0.ltoreq.(Ra.sup.1-Ra.sup.2)/Ra.sup.1<0.4 (1)
0.1<Ra.sup.2<7 (2)
[0035] wherein Ra.sup.1 is an average roughness of root mean square
(nm), measured by an atomic force microscope, of an exposed surface
of the first coated film layer before the heat treatment and
Ra.sup.2 is an average roughness of root mean square (nm), measured
by the atomic force microscope, of the exposed surface of the first
coated film layer after the heat treatment.
[0036] When the value (Ra.sup.1-Ra.sup.2)/Ra.sup.1 is larger than
0.4, the surface of the first coated film layer becomes too flat by
heat applied in the film processing step with the result that the
film cannot exhibit sufficient durability. On the other hand, when
the value is smaller than 0, the surface of the film is roughened
by the heat treatment, thereby degrading electromagnetic conversion
characteristics. The value is more preferably in the range of 0 to
0.35, more preferably 0 to 0.3, particularly preferably 0 to
0.25.
[0037] When the surface roughness (Ra.sup.2) of the first coated
film layer after the heat treatment is 7 nm or more,
electromagnetic conversion characteristics deteriorate. On the
other hand, when the value is 0.1 nm or less, the surface becomes
too flat with the result of insufficient durability. The value is
preferably in the range of 0.4 nm or more and less than 6 nm, more
preferably 0.7 nm or more and less than 5 nm.
[0038] The laminate film of the present invention is further
characterized in that protrusions showing two or more interference
fringes which can be observed when two films are superposed in such
a manner that their first coated film layers come in contact with
each other and exposed to light from a sodium lamp are present on
the surface of each film at a density of 100 per 100 cm.sup.2 at
the most. When the density of the protrusions is more than 100 per
100 cm.sup.2, they cause drop-outs when a tape is formed therefrom.
Although they are present on the side opposite to the magnetic
layer side of the film, they thrust the film up from a cooling roll
in the processing step, particularly in the deposition step,
thereby causing the film to be broken by heat or insufficient
durability due to surface flattening. The number of protrusions is
preferably 80 or less, more preferably 60 or less, particularly
preferably 50 or less, per 100 cm.sup.2.
[0039] The first coated film layer in the present invention can be
formed by applying a coating solution containing the
above-described organic filler and aqueous resin, preferably an
aqueous coating solution, to at least one side of a single layer or
a plurality of layers of a thermoplastic resin, and drying the
coating. The solid content of the coating solution is preferably
0.2 to 10% by weight, more preferably 0.5 to 5% by weight,
particularly preferably 0.7 to 3% by weight. This coating solution,
preferably an aqueous coating solution, may contain other
components such as a surfactant, stabilizer, dispersant, UV
absorber and thickener as required in limits not prejudicial to the
effect of the present invention.
[0040] Preferably, coating is carried out onto a thermoplastic
resin film before it is subjected to final stretching and the film
is stretched in at least a uniaxial direction after coating. The
coated film is dried before or during this stretching. Particularly
preferably, coating is carried out onto an unstretched
thermoplastic resin film or longitudinally (uniaxially) stretched
thermoplastic resin film. Means of coating is not particularly
limited but it is preferably roll coating, die coating or the
like.
[0041] To provide excellent winding properties to the film in the
present invention, a surface layer containing inert particles is
preferably formed on the surface, of the thermoplastic resin film,
not in contact with the first coated film layer.
[0042] The surface layer may be formed by coating or co-extrusion
which will be described hereinafter. When the surface layer is
formed by coating, the inert particles contained in the surface
layer can be a single type of particles or two or more different
types of particles which differ in size. The average particle
diameter of the largest particles out of the single type or two or
more types of particles is preferably 20 to 200 nm, more preferably
30 to 100 nm. The content of the inert particles in the surface
layer is preferably 3 to 50% by weight, more preferably 5 to 30% by
weight. When the average particle diameter of the inert particles
is smaller than 20 nm or the content thereof is less than 3% by
weight, the resulting film is unsatisfactory in terms of winding
properties and transportability during the film formation step, and
blocking readily occurs. On the other hand, when the average
particle diameter is larger than 200 nm, the particles readily fall
off from the coated film. When the content of the inert particles
in the surface layer is larger than 50% by weight, the surface
layer is readily scraped off due to a reduction in its
strength.
[0043] Preferred examples of the inert particles contained in the
surface layer include particles of organic materials such as
polystyrene, polystyrene/divinylbenzene, polymethyl methacrylate,
methyl methacrylate copolymer, methyl methacrylate crosslinked
copolymer, polytetrafluoroethylene, polyvinylidene fluoride,
polyacrylonitrile and benzoguanamine resins; particles of inorganic
materials such as silica, alumina, titanium dioxide, kaolin, talc,
graphite, calcium carbonate, feldspar, molybdenum disulfide, carbon
black and barium sulfate; and particles formed by coating these
inorganic particles as a core with an organic polymer.
[0044] Illustrative examples of the resin forming the coated film
layer (second coated film layer) containing the above particles are
the same as those listed for the aqueous resin used for the
formation of the first coated film layer. The resin may further
contain a cellulose resin.
[0045] When the surface layer is formed by coextrusion, the inert
particles contained in the surface layer can be a single type or
two or more different types of particles. The average particle
diameter of the largest particles out of the single type or two or
more different types of particles is preferably 100 to 1,000 nm,
more preferably 100 to 500 nm. The content of the inert particles
contained in the surface layer is preferably 0.001 to 5.0% by
weight, more preferably 0.005 to 1.0% by weight. When the average
particle diameter of the inert particles is smaller than 100 nm or
the content thereof is smaller than 0.001% by weight, the resulting
film is unsatisfactory in terms of winding properties and
transportability in the film formation step, and blocking readily
occurs. When the average particle diameter is larger than 1,000 nm
or the content is larger than 5.0% by weight, the particles' effect
of thrusting up into the coated film layer becomes marked with the
result of deterioration in electromagnetic conversion
characteristics.
[0046] Illustrative examples of the inert particles are the same as
those listed for the particles used when the surface film is formed
by coating.
[0047] The laminate film of the present invention can be produced
by a conventionally known method or a method accumulated in the
industry.
[0048] For example, in the case of a biaxially oriented polyester
film of which the surface layer is formed by coating, a polyester
as the thermoplastic resin is extruded into a film from a slit at a
temperature of Tm to (Tm+70).degree. C. (Tm: melting point) and
solidified by quenching at 40 to 90.degree. C. to obtain an
unstretched film. Thereafter, the unstretched film is stretched in
a uniaxial direction (longitudinal or transverse direction) to 2.5
to 8.0 times, preferably 3.0 to 7.5 times, at a temperature of
(Tg-10) to (Tg+70).degree. C. (Tg: glass transition temperature of
the polyester) by a commonly used method. Thereafter, coating
solutions for forming the first coated film layer and further the
surface layer as the case may be are applied to both sides of the
film and stretched in a direction perpendicular to the above
direction to 2.5 to 8.0 times, preferably 3.0 to 7.5 times, at a
temperature of Tg to (Tg+70).degree. C. It may be re-stretched in a
longitudinal direction and/or a transverse direction as required.
That is, two-, three-, four- or multi-stage stretching may be
carried out. The total stretch ratio is generally 9 times or more,
preferably 12 to 35 times, more preferably 15 to 32 times in terms
of area stretch ratio. Subsequently, the biaxially oriented film is
heat-set and crystallized at a temperature of (Tg+70) to
(Tm-10).degree. C., e.g., at 180 to 250 .degree. C.,to achieve
excellent dimensional stability. The heat-set time is preferably 1
to 60 sec.
[0049] When the surface layer of the laminate film is formed by
coextrusion, the surface layer is formed in the same manner as in
the above case where the surface layer of the film is formed by
coating except that two different polyesters for the single layer
or the plurality of layers of a thermoplastic resin and for the
surface layer are laminated together in a molten state within or
before an extrusion slit generally called "multi-manifold system"
for the former case and "feed block system" for the latter),
adjusted to an appropriate thickness ratio, and coextruded into a
double-layer unstretched laminate film, and a coating solution for
forming the first coated film layer is applied to the film after it
is stretched in a uniaxial direction. Thus, a biaxially oriented
laminate polyester film having excellent interlaminar adhesion is
obtained by the above method.
[0050] When the laminate film of the present invention comprises a
single layer of a thermoplastic resin, this layer contains
substantially no inert particles or can contain inert particles.
When it contains inert particles, it preferably contains 0.005 to
0.1% by weight of inert fine particles having an average particle
diameter of 20 to 400 nm and a volume shape factor of 0.1 to
.pi./6.
[0051] When the laminate film of the present invention comprises a
plurality of layers of a thermoplastic resin, a layer in contact
with the first coated film layer out of the plurality of layers
contains substantially no inert particles or can contain inert
particles. When it contains inert particles, it preferably contains
the same inert fine particles in the same proportion as described
above. The inert particles are preferably inorganic particles
listed above.
[0052] The layer of the thermoplastic resin can further contain
other additives such as a stabilizer, colorant, resistivity control
agent for a molten polymer and the like, as required.
[0053] The laminate film of the present invention generally has a
thickness of 2.5 to 80 nm.
[0054] The laminate film of the present invention is advantageously
used as a base film for a magnetic recording medium, preferably
metal thin film magnetic recording medium.
[0055] Therefore, according to the present invention, there is
further provided a magnetic recording medium comprising the
laminate film of the present invention and a magnetic layer present
on the first coated film layer of this laminate film.
[0056] The magnetic recording medium is preferably produced as
follows. A metal thin film magnetic recording medium for
high-density recording having excellent output at a
short-wavelength range and electromagnetic conversion
characteristics such as S/N and C/N, few drop-outs and a small
error rate can be obtained from the laminate film of the present
invention by forming a ferromagnetic metal thin film layer composed
of iron, cobalt, chromium, an alloy or oxide mainly comprising
these on the surface of the first coated film layer by means of
vacuum vapor deposition, sputtering, ion plating or the like, and
according to the purpose and application or as required, forming a
protective layer of diamond-like carbon (DLC) or the like and a
fluorine-containing carboxylic acid-based lubricant layer
sequentially on the surface of the ferromagnetic metal thin film
layer, and further a known back coat layer on the surface of the
thermoplastic resin layer or the surface layer. This metal thin
film magnetic recording medium is extremely useful as a tape medium
for Hi8 for analog signal recording and digital video cassette
recorders, data 8 mm and DDSIV for digital signal recording.
[0057] It is advantageous that the magnetic layer or the
ferromagnetic metal thin layer should have a thickness of 1 .mu.m
or less.
[0058] A metal coated magnetic recording medium for high-density
recording having excellent output at a short wavelength range and
electromagnetic conversion characteristics such as S/N and C/N, few
drop-outs and a small error rate can be obtained from the laminate
film of the present invention by uniformly dispersing needle-shaped
fine magnetic powders of iron or containing iron as a main
ingredient into a binder such as vinyl chloride or vinyl
chloride-vinyl acetate copolymer, and by applying the binder so as
to make the thickness of a magnetic layer not larger than 1 .mu.m,
preferably 0.1 to 1 .mu.m, and further forming a back coat layer on
the surface of the thermoplastic resin layer or the surface layer
by a known method. If required, titanium oxide fine particles may
be dispersed into the same organic binder as that for the magnetic
layer and this binder may be applied to the surface of the first
coated film layer to form a non-magnetic layer as a layer
underlying the metal powder-containing magnetic layer. This metal
coated magnetic recording medium is extremely useful as a tape
medium for 8 mm video, Hi8, .beta.-cam SP and W-VHS for analog
signal recording and digital video cassette recorders (DVC), data 8
mm, DDSIV, digital .beta.-cam, D2, D3 and SX for digital signal
recording.
[0059] A coated magnetic recording medium for high-density
recording having excellent output at a short wavelength range and
electromagnetic conversion characteristics such as S/N and C/N, few
drop-outs and a small error rate can be obtained from the laminate
film of the present invention by uniformly dispersing needle-shaped
fine magnetic powders such as iron oxide or chromium oxide, or
lamellar fine magnetic powders such as barium ferrite into a binder
such as vinyl chloride or vinyl chloride-vinyl acetate copolymer,
applying the binder so as to make the thickness of a magnetic layer
not larger than 1 .mu.m, preferably 0.1 to 1 .mu.m, and further
forming a back coat layer on the surface of the thermoplastic resin
layer or the surface layer by a known method. If required, titanium
oxide fine particles may be dispersed into the same organic binder
as that for the magnetic layer and this binder may be applied to
the surface of the coated film layer to form a non-magnetic layer
as a layer underlying the metal powder-containing magnetic layer.
This oxide coated magnetic recording medium is useful as a
high-density oxide coated magnetic recording medium for QIC for
data streamers for digital signal recording, and the like.
[0060] The above-described W-VHS is a VTR for analog HTDV signal
recording and DVC can be used for digital HDTV signal recording. It
can be said that the laminate film of the present invention is a
base film extremely useful for a magnetic recording medium for
these VTRs applicable to HDTV signals.
[0061] The following examples are given to further illustrate the
present invention. Measurement methods used in the present
invention are as follows.
[0062] (1) Average Particle Diameter I of Particles (Average
Particle Diameter: Not Smaller Than 0.06 .mu.m)
[0063] This is measured using the CP-50 Centrifugal Particle Size
Analyzer of Shimadzu Corporation. A particle diameter, "equivalent
spherical diameter" equivalent to 50 mass percent, is read from a
cumulative curve of the particles of each diameter and the amount
thereof calculated based on the obtained centrifugal sedimentation
curve, and taken as the average particle diameter (refer to "Book
of Particle Size Measurement Technology" issued by Nikkan Kogyo
Press, pp. 242-247, 1975).
[0064] (2) Average Particle Diameter II of Particles (Average
Particle Diameter: Smaller Than 0.06 .mu.m)
[0065] Particles having an average particle diameter smaller than
0.06 .mu.m which form small protrusions are measured by a light
scattering method. That is, it is expressed by the "equivalent
spherical diameter" of the particles which account for 50% by
weight of the total of all particles obtained by the NICOMP Model
270 Submicron Particle Sizer of Nicomp Instruments Inc.
[0066] (3) Volume Shape Factor f
[0067] A photo of each particle is taken at a magnification
corresponding to its size using a scanning electron microscope and
the maximum diameter of a projection plane and the volume of the
particle are calculated from the photo using a Luzex 500 Image
Analyzer (a product of Nippon Regulator Co., Ltd) and a volume
shape factor is calculated from the following equation.
f=V/d.sup.3
[0068] wherein f is a volume shape factor, V is a volume
(.mu.m.sup.3) of the particle and d is the maximum diameter (.mu.m)
of the projection plane.
[0069] (4) Layer Thickness
[0070] The thickness of a film is measured at 10 locations selected
at random by a micrometer and the average of the measurement values
is taken as the total thickness of the film. As for the thickness
of each layer, the thickness of a thin layer is measured by the
following method, while the thickness of a thick layer is obtained
by subtracting the thickness of the thin layer from the total
thickness. That is, using a secondary ion mass spectrometer (SIMS),
the concentration ratio (M.sup.+/C.sup.+) of an element (M.sup.+)
derived from particles having the highest concentration out of the
particles contained in the film in the area range from the surface
layer to a depth of 5,000 nm to the carbon element (C.sup.+) of a
polyester is taken as a particle concentration, and a portion from
the surface up to a depth of 5,000 nm is analyzed in the thickness
direction. In the surface layer which is interfacial, the particle
concentration is measured to be low but becomes higher as the
distance of the measured point from the surface increases. In the
above laminate film, there are two cases: one where after the
particle concentration becomes a stable value 1, it increases or
decreases to a stable value 2, and the other where after the
particle concentration becomes a stable value 1, it decreases
continuously. Based on this distribution curve, in the former case,
a depth which provides a particle concentration of (stable value
1+stable value 2)/2 is taken as the thickness of the layer whereas,
in the latter case, a depth that provides a particle concentration
of one-half of the stable value 1 (deeper than the depth that gives
a stable value 1) is taken as the thickness of the layer.
[0071] Measurement conditions are as follows.
[0072] (i) measuring instrument
[0073] secondary ion mass spectrometer (SIMS): 6300 of PERKIN ELMER
Co., Ltd.
[0074] (ii) measurement conditions
[0075] species of primary ion: O.sup.2+
[0076] primary ion acceleration voltage: 12 kV
[0077] amount of primary ion current: 200 nA
[0078] luster area: 400 .mu.m.quadrature.
[0079] analysis area: gate 30%
[0080] measured degree of vacuum: 6.0.times.10.sup.-9 Torr
[0081] E-GUNN: 0.5 kV-3.0 A
[0082] In the case where most of particles contained in an area of
from the surface layer to a depth of 5,000 nm are organic polymer
particles other than a silicone resin, it is difficult to measure
them with SIMS. Therefore, a concentration distribution curve
similar to the above is measured by FT-IR (Fourier transform
infrared spectrometry) or XPS (X-ray photo-electron spectrometry)
to obtain a thickness of the layer while the film is etched little
by little from the surface.
[0083] The above method is effective for a coextrusion layer. In
the case of a coated film layer, a film piece is overlaid with an
epoxy resin and fixed, and then, an ultrathin piece having a
thickness of about 60 nm is prepared by cutting the film piece in
the direction parallel to the machine direction of the film, using
a microtome. This sample is observed through a transmission
electron microscope (H-800 supplied by Hitachi Ltd.) to obtain the
layer thickness from the interface of the layer. The particle
diameter of the inert particle is obtained by observing the profile
of this ultrathin piece.
[0084] (5) Particle Diameter of Inert Particle (Including Organic
Filler)
[0085] 100 particles B present on the surface of the coated film
layer B are observed through a transmission electron microscope
(H-800 of Hitachi Ltd.) to obtain the particle diameter of each of
the particles B, and the average of the obtained values is taken as
the particle diameter of the particles B. Here, the particle
diameter of each particle is the average of a minor diameter and a
major diameter thereof.
[0086] (6) Average Roughness of Root Mean Square of Surface
Measured by Atomic Force Microscope
[0087] Using the J scanner of the Nano Scope III AFM atomic force
microscope of Digital Instruments Co., Ltd, Ra (average roughness
of root mean square) calculated under the following conditions is
measured.
[0088] probe: single bond silicon sensor
[0089] scanning mode: tapping mode
[0090] scanning range: 5 .mu.m.times.5 .mu.m
[0091] number of pixels: 256.times.256 data points
[0092] scanning speed: 2.0 Hz
[0093] measurement environment: room temperature, in the air
[0094] The heat treatment of the film is carried out in a gear oven
at 200.degree. C. for 120 minutes.
[0095] (7) Number of Protrusions
[0096] Two films are superposed each other and exposed to light
from a sodium lamp (wavelength of 589 nm) to observe an area of 100
cm.sup.2 through an optical microscope.
[0097] The number of protrusions showing two or more interference
fringes which can be observed is counted, and the protrusions are
photographed and marked. The two films are then separated from each
other, pressurized air is blown against their contact surfaces,
marked protrusions are observed through an optical microscope
again, and the number of remaining marked protrusions is counted.
The number of the object protrusions is obtained by subtracting the
count value after pressurized air is blown from the first count
value.
[0098] (8) Production of Magnetic Tape and Evaluation of Its
Characteristic Properties
[0099] Two 100% cobalt ferromagnetic thin film layers are formed on
the surface of the coated film layer of a laminate film so as to
have a total thickness of 0.02 .mu.m (each layer has a thickness of
about 0.1 .mu.m) by vacuum vapor deposition. A diamond-like carbon
(DLC) film layer and a fluorine-containing carboxylic acid-based
lubricant layer are formed sequentially on the surface of the thin
film layers, and a back coat layer is further formed on the surface
of the thermoplastic resin or the surface layer by a known method.
Thereafter, the resulting laminate is slit into an 8 mm wide tape
which is then loaded into a commercially available 8 mm video
cassette. Then, the characteristic properties of this tape are
measured using the following trade measuring instruments.
[0100] Instruments used:
[0101] 8 mm video tape recorder: EDV-6000 of Sony Corporation
[0102] C/N measurement: noise meter of Shibasoku Co., Ltd.
[0103] (i) C/N measurement
[0104] A signal having a recording wavelength of 0.5 .mu.m
(frequency of about 7.4 MHz) is recorded, the ratio of values of
its reproduced signal at 6.4 MHz and 7.4 MHz is taken as the C/N of
a tape, and the C/N is expressed as a relative value of when the
C/N of a deposited tape for a commercial 8 mm video is 0 dB, and is
evaluated based on the following criteria.
[0105] .circleincircle.: +2 dB or more
[0106] .largecircle.: -1 to +2 dB
[0107] X: less than -2 dB
[0108] (ii) drop-out (D/O) measurement
[0109] Using a drop-out counter, the number of drop-outs per minute
at 12 .mu.s/15 dB is measured.
[0110] .circleincircle.: 0 to 19 drop-outs per minute
[0111] .largecircle.: 20 to 39 drop-outs per minute
[0112] X: 40 or more drop-outs per minute
[0113] (3) still durability
[0114] C/N is measured after recording and reproduction are
repeated 500 times at a running speed of 85 cm/min at 23.degree. C.
and 20% RH and a difference from the initial value is evaluated
based on the following criteria.
[0115] .circleincircle.: above +0.0 dB based on the initial
value
[0116] .largecircle.: -2.0 to +0.0 dB based on the initial
value
[0117] X: less than -2.0 dB based on the initial value
[0118] 9) Deformation Retention Rate (%)
[0119] This is the rate (%) of the height of the particle B on the
surface of a film after a heat treatment in a gear oven at
200.degree. C. for 120 minutes to the height of the particle B
before the heat treatment.
[0120] The height of the particle B is measured as follows. A film
piece is overlaid with an epoxy resin and fixed, and then, an
ultrathin sample having a thickness of about 60 nm is prepared by
cutting the film piece in the direction parallel to the machine
direction of the film and the thickness direction of the film,
using a microtome. This sample is observed through a transmission
electron microscope (H-800 of Hitachi Ltd.) to measure the particle
diameters of 100 particles B in the direction perpendicular to the
surface of the film, and the average of the measurement values is
taken as the height of the particle B.
EXAMPLE 1
[0121] Dimethyl 2,6-naphthalene dicarboxylate and ethylene glycol
were polymerized in accordance with a commonly used method by
adding manganese acetate as an ester exchange catalyst, titanium
trimellitate as a polymerization catalyst, phosphorous acid as a
stabilizer, and inert particles shown in Table 1 as a lubricant to
obtain polyethylene-2,6-naphthalate (PEN) having an intrinsic
viscosity of 0.60 for a thermoplastic resin film layer and a
surface layer (designated as layer A and layer C,
respectively).
[0122] The resin A and the resin C were dried at 170.degree. C. for
6 hours, supplied to two extruders, molten at 290 to 310.degree. C.
and laminated together using a multimanifold extrusion die in such
a manner that the layer C was laminated on one side of the layer A.
The resulting laminate was quenched to obtain a 94 .mu.m-thick
unstretched laminate film.
[0123] The obtained unstretched film was preheated, stretched to
3.8 times between high-speed and low-speed rolls at a film
temperature of 130.degree. C. and quenched, and an aqueous coating
solution (total solid content of 1.0% by weight) having a
composition shown in Table 1 was applied to the surface of the
layer A of the longitudinally stretched film by kiss-roll coating.
The coated film was supplied to a stenter and stretched to 5.5
times in a transverse direction at 150.degree. C. The obtained
biaxially oriented film was heat set with hot air heated at
200.degree. C. for 4 seconds to obtain a 4.5 .mu.m-thick biaxially
oriented laminate polyester film having the first coated film layer
(layer B). The thickness of each of the layers A and C was adjusted
by controlling the discharge to the two extruders. The film had a
Young's modulus of 580 kg/mm.sup.2 in a longitudinal direction and
1,050 kg/mm.sup.2 in a transverse direction.
[0124] The surface properties of this laminate film and the
characteristic properties of a ferromagnetic thin film deposited
magnetic tape comprising this film are shown in Table 2.
EXAMPLE 2 AND COMPARATIVE EXAMPLES 1 TO 4
[0125] Laminate films were obtained in the same manner as in
Example 1 except that the inert particles contained in the layers A
and C and the thickness of each layer were changed as shown in
Table 1 and the composition of the first coated film layer (layer
B) was changed as shown in Table 1. The characteristic properties
of the obtained films and the characteristic properties of
ferromagnetic thin film deposited magnetic tapes comprising these
films are shown in Table 2.
EXAMPLES 3 AND 4
[0126] Polyethylene-2,6-naphthalate (PEN) for the layer A was
obtained in the same manner as in Example 1 by adding inert
particles shown in Table 1 to the layer A and supplied to one
extruder to obtain unstretched single-layer films.
[0127] The thus obtained unstretched films were preheated,
stretched to 3.5 times between high-speed and low-speed rolls at a
film temperature of 135.degree. C. and quenched, and an aqueous
coating solution having a composition shown in Table 1 for the
coated film layer B was applied to both sides of the film by
kiss-roll coating. The coated films were supplied to a stenter and
stretched to 3.5 times in a transverse direction at 150.degree. C.
The obtained biaxially oriented films were heat set with hot air
heated at 220.degree. C. for 5 seconds to obtain laminate
films.
EXAMPLES 5 AND 6 AND COMPARATIVE EXAMPLE 5
[0128] Polyethylene terephthalate (PET) for the layers A and C
(layer A and layer C) was obtained in the same manner as in Example
1 except that the same molar amount of dimethyl terephthalate was
used in place of 2,6-naphthalene dimethyl dicarboxylate and
particles shown in Table 1 were used as the inert particles.
[0129] The resins for layers A and C were dried at 170.degree. C.
for 3 hours and thickness thereof were adjusted in the same manner
as in Example 1 to obtain unstretched laminate films.
[0130] The thus obtained unstretched laminate films were preheated,
stretched to 3.3 times between high-speed and low-speed rolls at a
film temperature of 100.degree. C. and quenched, and an aqueous
coating solution having a composition shown in Table 1 for the
coated film layer B was applied to the surface of the layer A. The
coated films were then supplied to a stenter and stretched to 4.2
times in a transverse direction at 110.degree. C. The obtained
biaxially oriented films were heat set with hot air heated at
220.degree. C. for 3 seconds to obtain biaxially oriented laminate
polyester films.
[0131] The characteristic properties of the thus obtained films and
the characteristic properties of ferromagnetic thin film deposited
magnetic tapes comprising these films are shown in Table 2.
1 TABLE 1-a Thermoplastic resin film layer A Coated film layer B
Inert particles A Inert particles B Average Average particle Volume
Material particle diameter shape Content Core Cover diameter
Content Kind Material (nm) factor (wt %) Kind portion portion (nm)
(wt %) Ex. 1 PEN Silica 80 0.5 0.02 A Pst-DVB PMMA 32 5 copolymer
Ex. 2 PEN -- -- -- -- A Silica PMMA 18 10 Ex. 3 PEN -- -- -- -- B
Pst-DVB PMMA 24 8 copolymer Ex. 4 PEN Silicone 40 0.4 0.04 C
PMMA-DVB -- 45 3 copolymer Ex. 5 PET Silica 120 0.5 0.05 B Pst-DVS
PMMA 43 5 copolymer Ex. 6 PET Silica 60 0.5 0.03 A PMMA-DVB Pst 28
12 copolymer Comp. PEN Silica 80 0.5 0.02 A Pst PMMA 32 5 Ex. 1
Comp. PEN Silica 80 0.5 0.02 A Silica PMMA 40 30 Ex .2 Comp. PEN --
-- -- -- -- -- -- -- -- Ex. 3 Comp. PEN -- -- -- -- A Silica -- 18
10 Ex. 4 Comp. PET -- -- -- -- A Pst-DVB PMMA 43 10 Ex. 5
copolymer
[0132]
2 TABLE 1-b Surface film layer C Inert particles C Other particles
Average Average particle particle Composition of thickness diameter
Content diameter Content Layer A Layer B Layer C Kind Material (Nm)
(wt %) Kind (Nm) (wt %) (.mu.m) (nm) (nm) Ex. 1 PEN Silicone 500
0.02 silica 100 0.4 4 4 500 Ex. 2 PEN Silica 400 0.02
.theta.-alumina 50 0.3 3 3 1000 Ex. 3 B same with 24 8 -- -- -- 63
8 8 inert particle B Ex. 4 C same with 45 3 -- -- -- 32 10 10 inert
particle B Ex. 5 PET Silicone 500 0.2 .theta.-alumina 70 0.2 8 8
2000 Ex. 6 PET Silicone 700 0.1 titanium 200 0.3 6 5 500 oxide
Comp. PEN Silicone 500 0.02 silica 100 0.3 4 4 500 Ex. 1 Comp. PEN
Silicone 500 0.02 silica 60 0.5 4 10 500 Ex. 2 Comp. PEN Silicone
500 0.2 silica 160 0.2 4 -- 500 Ex. 3 Comp. PEN Silicone 500 0.02
.theta.-alumina 90 0.3 3 3 1000 Ex. 4 Comp. PET Silicone 500 0.2
silica 45 0.3 8 1 2000 Ex.5
[0133]
3 TABLE 2 Film strength Surface roughness of coated Young's Number
of film layer B (AFB) modulus foreign Before heat After heat Rate
Electromagnetic (MD/TD) matters treatment treatment of conversion
Drop- Still (kg/mm.sup.2) per 100 cm.sup.2 tB/dB (nm) (nm) change
characteristics out durability Ex. 1 580/1050 21 0.13 2.5 1.7 0.32
.largecircle. .largecircle. .largecircle. Ex. 2 580/1050 15 0.17
1.6 1.5 0.06 .circleincircle. .largecircle. .circleincircle. Ex. 3
650/650 8 0.33 1.9 1.3 0.32 .circleincircle. .circleincircle.
.circleincircle. Ex. 4 650/650 32 0.22 3.1 3.0 0.03 .largecircle.
.largecircle. .largecircle. Ex. 5 500/700 45 0.19 2.3 1.8 0.22
.largecircle. .largecircle. .circleincircle. Ex. 6 500/700 26 0.18
1.8 1.6 0.11 .circleincircle. .largecircle. .largecircle. Comp.
580/1050 14 0.13 2.5 1.2 0.52 .circleincircle. .largecircle.
.times. Ex. 1 Comp. 580/1050 28 0.25 7.8 7.2 0.08 .times.
.largecircle. .largecircle. Ex. 2 Comp. 580/1050 10 -- 1.2 1.2 0.00
.circleincircle. .circleincircle. .times. Ex. 3 Comp. 580/1050 460
0.17 1.7 1.6 0.06 .largecircle. .times. .largecircle. Ex. 4 Comp.
500/700 165 0.02 2.1 1.7 0.19 .largecircle. .times. .largecircle.
Ex. 5
[0134] In the above Tables, "Ex." stands for Example and "Comp.
Ex." for Comparative Example.
[0135] Notes
[0136] Kind of Resins of Coated Film Layer B and Surface Layer
C
[0137] A: acryl modified polyester (IN-170-6 of Takamatsu Yushi
K.K.)
[0138] B: water-soluble polyester (RZ-530 of Goh Kagaku K.K.)
[0139] C: water-dispersible polyester (2,6-naphthalenedicarboxylic
acid/isophthalic acid/5-sodium sulfoisophthalic acid/ethylene
glycol/addition product of bisphenol A with 2-mols of propylene
oxide)
[0140] Material of inert particle B
[0141] Pst: polystyrene
[0142] Pst-DVB: polystyrene-divinylbenzene copolymer
[0143] PMMA: polymethylmethacrylate
[0144] PMMA-DVB: polymethylmethacrylate-divinylbenzene
copolymer
[0145] As is evident from Table 2, the laminate film of the present
invention is extremely excellent in electromagnetic conversion
characteristics, resistance to drop out and still durability when
it is used as a magnetic recording medium. On the other hand, a
laminate film which does not satisfy the requirements of the
present invention cannot achieve these excellent properties at the
same time.
[0146] According to the present invention, there can be provided a
laminate film which is useful as a base film for a magnetic
recording medium having excellent electromagnetic conversion
characteristics, resistance to drop out and still durability.
* * * * *