Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2~3~26~
Magnetic recording medium
[Field of Industrial Application]
The present invention relates to a magneticrecording medium. In particular, the present
invention is concerned with a magnetic recording
medium wherein use is made of a binder having an
excellent dispersibility.
[Prior Art]
A magnetic recording medium is prepared by
coating the surface of a non-magnetic substrate, such
as polyester film, with a magnetic coating material
comprising a magnetic powder, a binder-, an organic
solvent and, if necessary, other additives, and drying
it.
In order to attain such electrical character-
istics as high xeproduction output and high ~ ratio,
the magnetic recording medium should have such various
properties that the magnetic powder is homogeneously
dispersed in the above-described coating material, the
surface of the magnetic coating film is smooth and the
resultant magnetic recording medium has excellent
durability. For this reason, various binders have
been studied for the purpose of satisfying the above-
required properties.
~3~2~
A magnetic recording medium wherein a
polyurethane resin having, introduced thereinto, a
component containing a metal sulfonate group is used
as a binder has been proposed for the purpose of
increasing the ratio of the residual magnetism, Br, to
the saturation magnetization, Bm, i.e., Br/Bm
(squareness ratio), in the direction of orientation o
a magnetic tape, and lowering the void fraction (see
Japanese Patent Publication No. 41565/1983).
The magnetic recording medium proposed in the
Japanese Patent Publication No. 41565!1983, however,
is unsatisfactory in the durability because it has a
problem with the hydrolysis resistance. Further, it
has a drawback that the thixotropy of the magnetic
coating material is enhanced.
In order to solve this problem, a proposal has
been made on the use of a polyurethane resin prepared
by the ring-opening polymerization of s-capro]actone
(see Japanese Patent Laid-Open No. 115920/1989).
However, also the magnetic recording medium prepared
by this method is unsatisfactory in the performance.
21~3~2~
An object of the present invention is to provide
a polyurethane resin for a magnetic recording medium
having such various properties that it is a coating
material for a magnetic recording medium wherein a
novel polyurethane resin is used as a binder, a
magnetic powder is homogeneously dispersed in the
coating material, the surface of the magnetic coating
film is smooth, the resultant magnetic recording
medium has an excellent durability and the coating
material has a low thixotropy.
( Summary oi the:invention )
The present inventors have made intensive studies
with a view to solving the above-described problem
and, as a result, have found that a polyurethane resin
prepared by reacting a polyisocyanate with a starting
polyol comprlsing polymethylvalerolactonediol prepared
by subjecting ~-methyl-~-valerolactone to ring-opening
polymerization in the presence of a polymerization
initiator comprising a dihydroxy compound having a
metal sulfonate group in its molecule instead of a
polyurethane resin prepared by the ring-opening
polymerization of ~-caprolactone can serve as a binder
having an excellent dispersibility, which has led to
the completion of the present invention.
21~3~2~
The magnetic recording medium of the invention
comprises a non-magnetic substrate and a magnetic
layer, provided on the substrate, comprising
ferromagnetic powder and a binder comprising
polyurethane resin which is obtained by reacting
polyisocyanate with polymethylvalerolactonediol
prepared by polymerizing ~-methyl- ~-valerolactone
in the presence of a dihydroxy compound having a
metal sulfonate group as a polymerization
initiator. It is improved in view of
dispersibility of magnetic power in the layer.
Specifically, according to the present invention,
there is provided a magnetic recording medium
comprising a non-magnetic substrate and a magnetic
layer provided thereon through coating with a
ferromagnetic powder, characterized in that said
magnetic layer comprises a polyurethane resin prepared
by reacti.ng a polyisocyanate with polymethylvalero-
lactonedi.ol prepared by polymerizing ~-methyl-~-
valerolactone in the presence of a dihydroxy compound
having a metal sulfonate group as a polymerization
initiator.
The polyurethane resin used in the present
invention has a low viscosity and therefore an
2'~3~
improved handleability. This is because the viscosity
of the polyester of ~-methyl-o-valerolactone is much
lower than that of the polyester of E-caprolactone.
In the polymerization of ~-methyl-~-valerolactone
in the present invention, a dihydroxy compound having
a metal sulfonate group is used as a polymerization
initiator. The proportion of ~-methyl-~-
valerolactone to the polymerization initiator in terms
of the molar ratio is preferably 3-methyl-~-
valerolactone : polymerization initiator = (50 : 1) to
(2 : 1), preferably (3 : 1) to (20 : 1). When this
value exceeds 2 : 1, there is a possibility of
bringing ahout an unfavorable phenomenon such as a
lowering in the solubility of the synthesized
polymethylvalerolactonediol in the solvent.
Examples of the dihydroxy compound having a metal
sulfonate group used as a polymerization initiator
include dihydroxy compounds represented by the
following general formula and comprising a benzene
ring as a skeleton and one or two metal sulfonate
groups.
(MO~S ~ R ~ X ' CH z )e - OH] z
(110~S~ R ~X ~CHzCH20~H] z
(MO~S~ R~X ~CH2CHO~H] 2
wherein a is 1 or 2, Q is an integer of 1 to 8, m and
n are each an integer of 1 to 5, R is
CH,
S ~ or
O ,.. .
X is -O- or -COO-, and M is Li, Na or K.
Preferred examples of the dihydroxy compound
include those represented by the following formulae
(I) to (V):
HOCH2CHzOOC ~ COOCHzCHzOH
SO3M
COOCHzCHzOH OCH7.CHzOH
S 0 3 M ~ SO~M
COOCHzCHzOH OCHzCHzOH
(II) (m)
~ir~3$2~
OCHzCHzOH
MO 3S ~ SO ~M
OCHzCH20H
( ~ )
CH 3
HOCHzCHzO ~ C ~ OCHzCH20H
S O I ~ S O
( V )
In the above-described formulae (I) to (V), M is Na or
K.
Among the compounds represented by the above-
described formulae (I) to (V), the compounds
represented by the formulae (I) and (II) are
particularly preferred. It is also possible to use an
ethylene glycol solution thereof.
Polymethylvalerolactonediol is prepared according
to a conventional process, i.e., by subjecting ~-
methyl-~-valerolactone to ring-opening polymerization
through the use of the above-described dihydroxy
compound as a polymerization initiator, and contains a
metal sulfonate group.
In the reaction, a catalyst may be used according
3 ~3 2 ~
65702-381
to need. The reaction temperature is 50 to 300C,
preferably 130 to 230C.
Examples of the catalyst include al~ali metals
and organometallic compounds. Examples of the alkali
metal include lithium, sodium and potassium, while
examples of the organometallic compound include
organotitanium compounds such as tetrabutyl titanate
and tetrapropyl titanate, organotin compounds, such as
dibutyltin oxide, and stannous chloride.
Among them, the organotitanium compounds are most
desirable because they have a high catalytic activity
and enables a less colored product to be produced in a
short period of time.
The content of the metal sulfonate group in the
polyurethane resin used in the present invention
depends upon the content of the metal sulfonate group
in the above-described polymethylvalerolactonediol
and, in the case of its use in combination with other
polyester polyol not containing a metal sulfonate
group, the proportion of mixing of polymethylvalero-
lactonediol with other polyester polyol and the
concentration of the metal sulfonate group in
polymethylvalerolactonediol. The content of the metal
sulfonate group in the resultant polyurethane resin is
0.1 to 300 ~eq/g, preferably 1 to 200 ~eq/g, more pre-
ferably about 9 to about 120 ~ueq/g.
g
When the content of the metal sulfonate group in
the polyurethane is less than 0.1 ~eq/g, no effect of
improving the dispersibility of the magnetic powder
can be expected. On the other hand, when the content
exceeds 300 ~eq/g, the thixotropy of the resultant
magnetic coating material increases, which raises a
possibility of giving an adverse effect on the
dispersion of the magnetic powder. Fuxther, there is
a possibility that an increase in the hydrophilicity
lowers the hydrolysis resistance of the polymer, which
raises a possibility of giving an adverse effect on
the durability, environmental resistance, etc. of the
magnetic recording medium per se.
In the present invention, it is n-ecessary to
incorporate the above-described polymethylvalero-
lactonediol as a polyhydroxy compound having two or
more active hydrogen atoms in its molecule. It may be
used in combination with other polyhydroxy compound.
Examples of the other polyhydroxy compound
include known polyhydroxy compounds usually having a
molecular weight of 50 to 10,000 and commonly used for
the production of polyurethane, for example, low-
molecular glycols, polyethers, polyesters,
polythioethers, polybutadiene glycols, silicon-
containing polyols and phosphorus-containing polyols.
~3~
Examples of the low-molecular glycols include
ethylene glycol, propylene glycol, 1,3-propanediol,
1,4-butanediol, 1,5-pentanediol, 1,5-hexanediol,
neopentyl glycol, diethylene glycol, dipropylene
glycol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-
cyclohexanedimethanol, ethylene oxide adduct and
propylene oxide adduct of bisphenol A, ethylene oxide
adduct and propylene oxide adduct of hydrogenated
bisphenol A, polyethylene glycol, polypropylene glycol
and polytetramethylene glycol. They may be used in
combination with tri- and tetraols such as
trimethylolethane, trimethylolpropane, glycerin and
pentaerythritol.
Examples of the polyethers include polymers and
copolymers of ethylene oxide, propylene oxide and
tetrahydrofuran. Further, it is also possible to use
polyethers prepared by the condensation of the above-
described low-molecular glycols, or mixed ethers, and
further products of addition polymerization of the
above-described polyethers and the above-described
low-molecular glycols with ethylene oxide and
propylene oxide.
A thioglycol alone or a product of condensation
thereof with other glycol is particularly suitable as
the polythioethers.
2 ~
Examples of the polyesters include those prepared
by the dehydration condensation of low-molecular
glycols with a dibasic acid, and lactone polyols
prepared by the ring-opening polymerization of a
lactone, such as ~-caprolactone, in the presence of
the above-described low-molecular glycol or the like.
It is also possible to use a trifunctional or
higher polyol in the form of a mixture as part of the
above-described polyhydroxy compound.
The use of a (monofunctional or higher) hydroxy
compound having metal sulfonate group, such as 2-
sodium sulfo-1,4-butanediol or 2-potassium sulfo-1,4-
butanediol, in part of the glycol moiety enables the
metal sulfonate group to be introduced into a hard
segment portion of the polyurethane resin.
Examples of the polyisocyanate compound used for
preparing a polyurethane resin through the reaction
with a polyhydroxy compound in the present invention
include 2,4-tolylene diisocyanate, 2,6-tolylene
diisocyanate, p-phenylene diisocyanate, diphenyl-
methane diisocyanate, m-phenylene diisocyanate,
hexamethylene diisocyanate, tetramethylene
diisocyanate, 3,3-dimethoxy-4,4'-biphenylene
diisocyanate, 2,4-naphthalene diisocyanate, 3,3'-
dimethyl-4,4'-biphenylene diisocyanate, 4,4'-
~d ~ 2 ~ ~
diphenylene diisocyanate, 4,4'-diisocyanatodiphenyl
ether, 1,5-naphthalene diisocyanate, p-xylylene
diisocyanate, m-xylylene diisocyanate, 1,3-
diisocyanatomethylcyclohexane, 1,4-diisocyanato-
methylcyclohexane, 4,4'-diisocyanatodicyclohexane,
4,4,-diisocyanatodicyclohexylmethane and isophorone
diisocyanate. If necessary, minor amounts of 2,4,4'-
triisocyanatodiphenyl, benzene triisocyanate, etc. may
also be used.
Among the above-described organic diisocyanates,
urethane resins wherein use is made of an organic
diisocyanate containing a diisocyanate having a
cyclohexyl group provide particularly good results.
Especially, urethane resins wherein us-e is made of a
diisocyanate containing isophorone diisocyanate are
excellent particularly in the dispersibility of the
magnetic powder as well as in the surface smoothness
of the magnetic layer.
Examples of the chain extender used for the
production of the polyurethane resin include glycols
such as ethylene glycol, propylene glycol, 1,4-
butanediol, 1,6-hexanediol, neopentyl glycol, 3-
methyl-1,5-pentanediol and 1,5-pentanediol, low-
molecular polyols such as trimethylolpropane and
glycerin, and diamines such as ethylenediamine,
~ 3
t 3
propylenediamine, hydrazine, piperazine and
isophoronediamine.
It is also possible to use the above-described
polyhydroxy compound as the chain extender.
Examples of the solvent used for the production
of the polyurethane resin in the present invention
include compounds usually inert to an isocyanate
group, such as ketones such as methyl ethyl ketone,
methyl isobutyl ketone and cyclohexanone, esters such
as ethyl acetate and butyl acetate, aromatic
hydrocarbon solvents such as toluene and benzene, and
tetrahydrofuran.
The polyurethane resin is prepared according to
the conventional process. Examples of the catalyst
used in this case include usual urethanization
catalysts, i.e., those based on tin, iron and tertiary
amine. Examples of the tin-based catalyst include
dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin
dioctoate and stannous octoate. Examples of the iron-
based catalyst include acetylacetonatoiron and ferric
chloride. Examples of the tertiary amine-based
catalyst include triethylamine and trlethylenediamine.
In the present invention, the process for
preparing the polyurethane resin is properly selected
from conventional processes taking into consideration
~J ~ P3~ ~
1~
the degree of polymerization of the intended
polyurethane resin, the kind of starting material
used, etc. Examples of the process for preparing the
polyurethane resin include one which comprises
reacting a polyhydroxy compound having an active
hydrogen atom with a stoichiometrically excess
polyisocyanate compound, if necessary, in the presence
of a solvent usually inert to the isocyanate group and
further, if necessary, a usual urethanization
catalyst, at a temperature of 10 to 150C, preferably
20 to 130C to prepare a prepolymer having an
isocyanate group at its terminal, and reacting the
prepolymer with a chain extender such as a diol,
diamine or triol to prepare a polyurethane having a
hydroxyl group at its terminal, and one wherein a
polyhydroxy compound, a chain extender and a
polyisocyanate compound are simultaneously reacted
with each other in such a feed ratio that the hydroxyl
group is stoichiometrically excess. Further, it is
also possible to use a method wherein a polyisocyanate
compound is reacted with a polyhydroxy compound
without use of a chain extender to prepare a
hydroxy-terminated polyurethane resin, a method which
comprises reacting a polyhydroxy compound with a
polyisocyanate compound to prepare a hydroxy-
terminated compound and further reacting the hydroxy-
terminated compound with the polyisocyanate compound
to prepare a hydroxy-terminated polyurethane resin,
and other methods.
The number-average molecular weight of the
polyurethane resin of the present invention thus
prepared is 5,000 to 200,000, preferably 7000 to
70,000. The weight-average molecular weight thereof
is about 5,000 to 500,000, preferably 8,000 to
150,000.
No additivity exists between the number-average
molecular weight and the weight-average molecular
weight because polymers synthesized so as to have the
same number-average molecular weight do not always
have the same weight-average molecular weight. The
ratio of the weight-average molecular weight to the
number-average molecular weight is generally about 1
to 5.
The magnet:ic layer of the magnetic recording
medium of the present invention is formed by kneading
a binder, a magnetic powder and optional additives
with a suitable solvent to prepare a magnetic coating
material, coating the surface of a non-magnetic
substrate with the magnetic coating material, and
drying the coated substrate.
Examples of the binder include the polyurethane
resin prepared in the present invention and further
mixtures of the polyurethane with compounds commonly
employed as a binder component, such as vinyl
chloride-vinyl acetate copolymer, vinyl chloride-
vinylidene chloride copolymer, vinyl chloride-
acrylonitrile copolymer, acrylic ester-vinylidene
chloride copolymer, acrylic ester-styrene copolymer,
methacrylic acid-acrylonitrile copolymer, methacrylic
ester-vinylidene chloride copolymer, methacrylic
ester-styrene copolymer, urethane resin, polyvinyl
fluoride, vinylidene chloride-acrylonitrile copolymer,
butadiene-acrylonitrile copolymer, polyamide resin,
polyvinyl butyral, cellulose derivative (cellulose
acetate butyrate, cellulose propionate,
nitrocellulose, etc.), styrene-butadiene copolymer,
polyester resin, chlorovinyl ether-acrylic ester
copolymer, amino resin, phenolic resin, epoxy resin,
phenoxy resin, alkyd resin, silicone resin, etc.
Among the above-described resins, binders having
a metal sulfonate group, a metal carboxylate group, an
amino group, etc. may also be used in combination with
the polyurethane.
Further, it is also possible to add a
polyisocyanate compound in the preparation of a
~ ~3 S~
1~, 65702-381
magnetic layer of the magnetic recording medium of the
present invention. Examples of the polyisocyanate
compound include Desmodur*L and Desmodu~ N
manufactured by Bayer, Coronate L and Coronate*HL
manufactured by Nippon Polyurethane Industry Co.,
Ltd., and Takenate*D102 manufactured by Takeda
Chemical Industries, Ltd. These polyisocyanate
compounds are used in a proportion of 1 to 50% by
weight based on the total amount of the binder.
Examples of the magnetic powder used in the
magnetic recording medium of the present invention
include known magnetic powders commonly used in the
art, for example, y-iron oxide, cobalt-coated y-iron
oxide, cobalt-doped Y-iron oxide, CrO2, barium
ferrite, magnetic alloy powder and magnetic metal
powder.
There is no particular llmitation on the form of
the ferromagnetic powder, and acicular, granular,
dice-like, rice-like granular and flaky powders may
usually be employed. The specific surface area of the
ferromagnetic powder is preferably 45 m2/g or more
from the viewpoint of electromagnetic transduction.
The total content of the binder in the magnetic
layer of the magnetic recording medium according to
the present invention is generally 5 to 100 parts by
*Trade-mark
~3~
1~
weight, preferably 10 to 40 arts by weight based on
100 parts by weight of the ferromagnetic powder.
It is preferred that the magnetic layer of the
magnetic recording medium according to the present
invention additionally comprise an inorganic particle
having a Mohs hardness of 5 or more.
There is no particular limitation on the
inorganic particle used as far as it has a Mohs
hardness of 5 or more. Examples of the inorganic
particle having a Mohs hardness of 5 or more include
A1203 (Mohs hardness: 9), Tio (Mohs hardness: 6), TiO2
(Mohs hardness: 6.5), SiO2 (Mohs hardness: 7), SnO2
(Mohs hardness: 6.5), Cr203 (Mohs hardness: 9) and
~-Fe203 (Mohs hardness: 5.5). They may be used alone
or in the form of a mixture thereof.
An inorganic particle having a Mohs hardness of 8
or more is particularly preferred. The use of a
relatively soft inorganic particle having a Mohs
hardness lower than 5 brings about drawbacks that the
inorganic particle tends to fall off from the magnetic
layer, the clogging of the head tends to occur due to
a sub~tantial absence of any polishing action of the
head and the travelling durability becomes poor.
The content of the inorganic particle is usually
0.1 to 30 parts by weight, preferably 1 to 15 parts by
~ s.t$~
weight based on 100 parts by weight of the
ferxomagnetic powder.
It is desirable to incorporate carbon black
(particularly one having a mean particle diameter of
10 to 300 nm), etc., besides the above-described
inorganic particle.
In the preparation of the magnetic coating
material, the above-described materials may be used in
combination with known additives such as dispersants,
antistatic agents and lubricants.
Examples of the dispersant include known one such
as lecithin.
The amount of the dispersant, when used, is
usually 0.1 to 10 parts by weight based on 100 parts
by weight of the ferromagnetic powder used.
Examples of the antistatic agent include
electrically conductive impalpable powders such as
carbon black and carbon black graft polymer; natural
surfactants such as saponin; cationic surfactants such
as higher alkylamines, quaternary ammonium salts,
salts of pyridine and other heterocyclic compounds,
phosphoniums and sulfoniums; anionic surfactants
containing a polar group, such as salts of phosphonic
acid, salts of phosphoric acid, salts of phosphoric
ester, salts of sulfonic acid, salts of sulfuric acid
and salts of sulfuric ester; and amphoteric
surfactants such as amino acids, aminosulfonic acids,
and sulfuric or phosphoric esters of amino alcohols
When the above-described electrically conductive
impalpable powder is used as the antistatic agent, for
example, the amount thereof is 0.1 to 50 parts by
weight based on 100 parts by weight of the
ferromagnetic powder, while when the surfactant is
used, the amount thereof is 0.10 to 10 parts by
weight.
Examples of the lubricant include the above-
described fatty acids, higher alcohols, esters of
monobasic fatty acids having 12 to 20 carbon atoms
with monohydric or polyhydric alcohols having 3 to 20
carbon atoms, such as butyl stearate and sorbitan
oleate, known lubricants and lubricants for plastics,
such as mineral oils, vegetable and animal oils,
oligomers of olefins, fatty acid amides, silicone oil
and modified silicone oil, and further impalpable
powder of graphite, impalpable powder of molybdenum
disulfide and impalpable powder of tetrafluoroethylene
polymer.
The function and effect of the above-described
additives, such as dispersants, antistatic agents and
lubricants, are not strictly limited to the above-
~ r
2~
described function and effect only. For example,there is a possibility that the dispersant might
function as a lubricant or an antistatic agent.
Therefore, it is a matter of course that the function
and effect of the compounds recited above according to
the above-described classification are not limited to
the matters described in the above classified items.
When a substance having a plurality of functions and
effects is used, the amount of addition thereof is
preferably determined by taking into consideration the
function and effect thereof.
The process for preparing the magnetic recording
medium of the present invention will now be described.
At the outset, a ferromagnetic powder, a binder
containing a polyurethane resin which is one of the
features of the present invention, and other optional
fillers and additives are kneaded together with a
solvent to prepare a magnetic coating material.
Examples of the solvent used in the kneading include
cyclohexanone, methyl ethyl ketone, tetrahydrofuran,
dioxane and dimethylformamide. They may he used alone
or in the form of a mixture thereof. Alternatively,
use may be made of mixed solvents comprising a mixture
of the above-described solvents with methyl isobutyl
ketone, toluene or the like.
~ 3~ J ~ ~y_
2~
There is no particular limitation on the method
of kneading, and the order of addition of individual
components may be properly determined.
The preparation of the magnetic coating material
may be conducted by means of usual kneaders, for
example, twin-rol~ mill, triple-roll mill, ball mill,
pebble mill, trommel, sand grinder, Szegvari,attritor,
high-speed impeller disperser, high-speed stone mill,
high-speed impact mill, disper, kneader, high-speed
mixer, homogenizer, ultrasonic disperser, etc.
A non-magnetic substrate is coated with the
magnetic coating material thus prepared. The coating
may be conducted directly on the non-magnetic
substrate. ~lternatively, the coating may be
conducted on the non-magnetic substrate through an
adhesive layer.
Examples of the method of coating the
non-magnetic substrate with the magnetic coating
material include air doctor coating, blade coating,
rod coating, extrusion coating, air knife coating,
squeeze coating, impregnation coating, reverse roll
coating, transfer roll coating, gravure coating, kiss
coating, cast coating, spray coating and spin coati.ng.
Further, it is also possible to use methods other than
those described above.
~f,jf3~,?J~ff
23
Examples of the non-magnetic substrate include
polyesters (for example, polyethylene terephthalate
and polyethylene naphthalate), polyamides,
polyolefins, cellulose derivatives, non-magnetic
metals and paper. They may be in the form of film,
tape, sheet, card, disk, etc.
The magnetic layer is provided by coating so that
the thickness after drying is generally about 0.1 to
10 ~m, usually 0.1 to 7.0 ~m.
The magnetic layer applied on the non-magnetic
substrate, when the magnetic recording medium is used
in a tape form, is usually subjected to a treatment
for orienting the ferromagnetic powder in the magnetic
layer, i.e., magnetic orientation tre-atment, and then
dried~ If necessary, a surface smoothing treatment is
applied. The magnetic recording medium subjected to
the surface smoothing treatment is then cut into a
desired shape.
Since the polyurethane resin prepared by a method
characteristic of the present invention is
incorporated in a binder for a magnetic recording
medium, the magnetic recording medium of the present
invention thus prepared has a much higher capability
of dispersing the magnetic powder, a better surface
smoothness of the magnetic coating and better moist
~,~
2 ~
heat resistance and durability than those of he
conventional magnetic recording medium wherein use is
made of a conventional thermoplastic polyurethane
resin.
As compared with the conventional polyurethane
resin prepared through the use of a polycondensation
type polyester glycol containing a metal sulfonate
group, the binder containing the polyurethane resin of
the present invention, by virtue of the ease of
introducing a metal sulfonate group, selective
introduction of one or two metal sulfonate groups per
molecule of polymethylvalerolactonediol and
homogeneous distribution of polar groups in the
resultant polyurethane resin, has advantages such as
less increase in the thixotropy of the magnetic
coating material caused by the interaction between the
metal sulfonates themselves not participating in the
adsorption on the magnetic powder, possible
minimization of the amount of introduction of the
metal sulfonate group by virtue of its high
effectiveness, and possible suppression of a lowering
in the moist heat deterioration due to an increase in
the hydrophilicity by virtue of the superiority in the
hydrolysis resistance to the polyurethane resin
prepared by making use of a conventional usual
~ ~ ~ 'f 3 ~
2;)
aromatic or aliphatic polycondensed polyester glycol.
[Examples]
The present invention will now be described in
more detail by way of the following Examples, though
it is not limited to these Examples only.
Preparation of polvmethvlvalerolactonediol:
Preparation Examples A to D
The inside of a separable flask equipped with a
thermometer, an agitator, a nitrogen gas inlet tube
and a dropping funnel was sufficiently purged with a
nitrogen gas and then charged with 91.8 parts by
weight of sodium di-2-hydroxyethyl 5-sulfoisophthalate
and 0.65 part by weight of metallic sodium. The
mixture was heated while agitating for effecting
dissolution. 1000 parts by weight of ~-methyl-
~-valerolactone was dropwise added thereto, and the
mixture was maintained at a reaction temperature of
40C for about 1 hr to prepare polymethylvalero-
lactonediol (A).
The polymethylvalerolactonediol (A) thus prepared
had a hydroxyl value of 113 and a content of a sodium
sulfonate group of 260 ~eq/g.
Polymethylvalerolactonediols B to D were prepared
in the same manner as that described above, except
that the amounts of the sodium di-2-hydroxyethyl 5-
2~
sulfoi.sophthalate and ethylene glycol were varied asspecified in Table 1.
Preparation Example E
Polycaprolactonediol (E) was prepared in the same
manner as that described in Japanese Patent Laid-Open
No. 115920/1989, except that ~-caprolactone was used
instead of ~-methyl-~-valerolactone.
Preparation Example F
An isophthalate type condensation polyester (F)
was prepared through the use of starting materials
listed in the column of Preparation Example F in Table
1.
~ ~ o ~ ~ 0
__ U~. _ _ _1~. _~ ~1
~ ; ~ - ~ ~ - ~ : : -~ ~
V h X O N t9 O O ~1 0
c ~ m _ ~r _ __ ~r u~ _ _ _
v x o _--1--r o _I ~ o
R ~
~ v o ~u o
~ ~ ~ ~n~ ~C~ O' O ~ ~
v c v c e o v c ~ v v--O :~: v
_ V O O ~ O O r O V v V
1~ J - ~ ~__ ~
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Preparation of polyurethane resin:
Preparation Example 1
A four-necked flask equipped with an agitator, a
thermometer, a condenser and a nitrogen gas inlet tube
was charged with 323 parts by weight of methyl ethyl
ketone and 100 parts by weight of polymethylvalero-
lactonediol (A) (OHV: 113) prepared in the Preparation
~xample A, and the mixture was heated and agitated to
prepare a homogeneous solution. 89.3 parts by weight
of 4,4'-diphenylmethane diisocyanate was poured into
the homogene~us solution, and they were mixed at a
solution temperature of 80C while agitating and
allowed to react it that temperature for 2 to 3 hr to
synthesize an isocyanate-terminated prepolymer.
Then, 11.9 parts by weight of 1,4-butanediol as a
chain extender and 13.8 parts by weight of neopentyl
glycol were added to the prepolymer, and the chain
extension reaction was conducted at 70 to 85C for 10
to 15 hr to prepare a polyurethane resin.
Dibutyltin dilaurate was added as a
urethanization catalyst in an amount of 0.11 part by
weight based on the solid content to promote the
reaction.
The above-described reactlon was regarded as
completed when the concentration of the residual
~ ~,J~
2'~
isocyanate group in the reaction system is 0.01% by
weight or less based on the solid content of the
system.
Preparation Examples 2 to 7
Polyurethanes were prepared in the same manner as
that of Preparation Example 1, except that individual
starting materials were used in amounts specified in
Table 2 and diols ~ to E and polyester F prepared in
the above-described Preparation Examples B to F were
used.
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Examples 1 to 4 and Comparatlve Examples 1 to 3
Preparation of magnetic coatinq material:
A mixture having the following mixing proportions
was kneaded by means of a sand mill at 1200 rpm for 3
hr to prepare a magnetic coating material.
. metallic powder 100 parts by weight
(specific surface area: 50 m2/g
coerclve force (Hc): 1450 Oe
saturation/magnetization (as): 122 emu/g)
. polyurethane resin prepared
in Preparation Examples 1
to 7 10 parts by weight
. vinyl chloride/vinyl acetate/
vinyl alcohol copolymer 10- parts by weight
. carbon black2 parts by weight
. alumina5 parts by weight
. tridecyl stearate1 part by weight
. palmitic acid1 part by weight
. methyl ethyl ketone200 parts by weight
. cyclohexanone155 parts by weight
Preparation of maqnetic tape-
S parts by weight of a polyisocyanate compound
(Coronate*L; a product of Nippon Polyurethane Industry
Co., Ltd.) was added as a curing agent to 100 parts by
weight of the magnetic coating material prepared by
*Trade-mark
r l~
the above-described method. They were mixed and
agitated, and the mixture was applied to a 10 ~m-thick
polyethylene terephthalate film by means of an
applicator of 40 ~m, subjected to orientation
treatment, dried, calendered for planishing, and slit
to a width of 8 mm, thereby preparing a magnetic tape
for video.
Evaluation of ma~netic tape:
The magnetic tape prepared above was subjected to
the following evaluation.
(1) Reflectance (at 60C)
(~) Residual magnetic flux density (Br)
(3) Squareness ratio (Sq)
(4) S/N ratio ~
(5) Durability: The magnetic tape was stored at
40C and 80 %RH for 30 days, set in a tape-
driving unit and subjected to measurement of the
number of runs necessary for lowering the output
by 10% from the initial output. This value was
used as a measure of the durability.
The results of evaluation are given in Table 3.
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