JP3254476B2 - Binder for magnetic recording medium and magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder for a magnetic recording medium and a magnetic recording medium containing the binder.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, floppy disks and the like. In a magnetic recording medium, a magnetic layer in which ferromagnetic powder is dispersed in a binder is laminated on a nonmagnetic support. The magnetic recording medium is required to be at a high level in various characteristics such as electromagnetic conversion characteristics, running durability and running performance. That is, audio tapes for recording and reproducing music are required to have higher original sound reproduction capabilities. Also, video tapes are required to have excellent electromagnetic conversion characteristics such as excellent original image reproduction capability. At the same time as having such excellent electromagnetic conversion characteristics, the magnetic recording medium is required to have good running durability as described above. In order to obtain good running durability, an abrasive and a lubricant are usually added to the magnetic layer.

However, in order to obtain excellent running durability by using an abrasive, it is necessary to increase the addition amount to some extent, and therefore, the content of the ferromagnetic powder decreases.
If an abrasive having a large particle diameter is used to obtain excellent running durability, the abrasive tends to excessively protrude from the surface of the magnetic layer. Therefore, the improvement of the running durability by the abrasive often causes the deterioration of the above-mentioned electromagnetic conversion characteristics, which is a problem. When the above-mentioned running durability is improved by a lubricant, it is necessary to increase the amount of addition, and therefore, the binder is easily plasticized, and the durability of the magnetic layer tends to decrease.

[0004] In order to improve the durability and the electromagnetic conversion characteristics, the binder, which is one of the main components of the magnetic layer, naturally plays an important role. Conventionally used vinyl chloride resins, cellulosic resins, urethane resins, acrylic resins and the like have a problem that the wear resistance of the magnetic layer is inferior and the running members of the magnetic tape are contaminated. As a method of solving such a problem, a method of increasing the hardness of the magnetic layer using a hard binder has been used. However, when the hardness of the magnetic layer is increased, the brittleness of the magnetic layer becomes remarkable, and there is a problem that contact with a magnetic head causes dropout or deterioration of still characteristics.

[0005] As still another method, a vinyl chloride copolymer having a hydroxyl group (via an alkyl group or an alkyl ester group) and a polar group which is not directly bonded to the main chain, and vinyl alcohol is used as a copolymer component. A magnetic recording medium having a configuration that does not include it is disclosed in Japanese Patent Application Laid-Open Nos. 62-134819 and 62-208423. Since the vinyl alcohol as the copolymer component is produced through a saponification process, the polymer containing the same is hardly changed with time, and the magnetic recording medium has little change with time and has excellent durability. In addition, it has a hydroxyl group and a polar group, so that the ferromagnetic powder has excellent dispersibility and excellent electromagnetic conversion characteristics.

However, in the above magnetic recording medium, since the strength of the magnetic layer is not high and the smoothness of the surface of the magnetic layer is not sufficient, sufficiently excellent durability and electromagnetic conversion characteristics cannot be obtained. Therefore, extremely high smoothness and excellent electromagnetic conversion characteristics are required. For example, for S-VHS or 8 m
It cannot be said that a tape for m-video is a sufficiently excellent magnetic recording medium.

In order to improve the durability of the coating film, Japanese Patent Publication No. 63-55549 discloses a polyvalent OH group and SO3M (M
Describes that a modified polyurethane resin containing an alkali metal or a quaternary ammonium ion) is used as a magnetic coating composition. By using such a binder, the surface glossiness, blocking property, adhesion and the like are improved.

As a binder made of polyurethane, -SO using polyester polyol as polyol is used.
About polyurethane binder having 3M
JP-A-59565 / 1985 describes a polyurethane binder obtained from a hydroxy terminal group-containing polycarbonate and a diisocyanate.
And a polyurethane binder using carboxyl group-containing polycaprolactone as a raw material is disclosed in
-201918. Further, a polyurethane binder using a carboxyl group-containing polyether as a raw material is described in JP-A-61-190717. However, although the binders made of these polyurethanes exhibit the excellent properties of polyurethanes, the dispersibility of ferromagnetic powders and the long-term storage properties are insufficient, and the durability under a wide range of temperature and humidity conditions is insufficient. There was a problem.

The present inventors have conducted intensive studies on the structure of these polyurethanes. As a result, the polyol components of conventional polyurethanes all have hydrophilic segments such as ester bonds, ether bonds, and carbonate bonds. The polarity is not as strong as the COOH group, and there is no function of adsorbing on the surface of the ferromagnetic powder. However, in a solution, a weak hydrogen bond may be formed, and the spread of the polyurethane molecular chain adsorbed on the surface of the magnetic material is reduced. Therefore, the adsorption volume of the binder around the ferromagnetic powder is small, the dispersibility and dispersion stability are reduced, and the hydrophilic segment in the polyol increases the temperature and humidity dependence of the mechanical properties of the magnetic coating film. Thus, it was found that the temperature and humidity dependence of running durability was increased and the long-term storage property was reduced. He found that the point was how to increase the extent of this molecular chain, and led to the invention.

[0010]

DISCLOSURE OF THE INVENTION The present invention provides a PET (polyethylene terephthalate) having extremely high dispersibility, excellent long-term storage properties, excellent durability under a wide range of temperature and humidity conditions.
G), a binder for a magnetic recording medium and a magnetic recording medium which have excellent adhesion to a non-magnetic support such as PEN (polyethylene naphthalate).

[0011]

SUMMARY OF THE INVENTION The object of the present invention is to provide a binder for a magnetic recording medium comprising a polyurethane which is a reaction product of a polyol and a polyisocyanate as main raw materials, wherein the polyol has a molecular weight of 500 to 5,000. br /> magnetic recording medium which is a mixture or port <br/> Li polyether polyol of molecular weight 800 to 3000 which is derived from a polyolefin polyol <br/> polyether polyols of the polyolefin polyol having a molecular weight of 500 to 3000 Can be achieved by a binder. Preferably in the above purpose is the polyurethane molecules of the present invention, -SO ₃ M,
_{-OSO 3 M, -COOM, -PO 3} M 2, -OPO 3
^{_{M 2, -NR 2, -N +}} R 3 X -, -N + R 2 R'SO 3 -,
—N ⁺ R ₂ R′COO ⁻ (where M is hydrogen, alkali metal, alkaline earth metal, ammonium salt, M ′ is hydrogen, alkali metal, alkaline earth metal, ammonium salt, alkyl group, R and R ′ are alkyl groups;
X represents a halogen) and a binder for a magnetic recording medium, comprising a polyurethane containing at least one polar group selected from the group consisting of:

It is another object of the present invention to provide a magnetic recording medium wherein a magnetic layer containing a ferromagnetic powder and a binder is formed on at least one surface of a non-magnetic support, wherein the binder comprises a polyol and a polyisocyanate as main raw materials. And a polyol having a molecular weight of 500.
-5000 polyolefin polyol and molecular weight 500
A mixture of polyether polyols having a molecular weight of 3,000 or a molecular weight derived from a polyolefin polyol of 800-
3,000 polyether polyol, a magnetic recording medium provided with a lower magnetic layer or a lower non-magnetic layer on at least one surface of a non-magnetic support, and an upper magnetic layer provided thereon. In at least one of the magnetic layer or the non-magnetic layer, the binder for binding the ferromagnetic powder or the non-magnetic powder contains a polyurethane which is a reaction product of a polyol and a polyisocyanate as main raw materials, and the polyol has a molecular weight of 500 ~ 500
0 of polyolefin polyol and a molecular weight from 500 to 300
0 or a molecular weight of 800 to 3000 derived from a mixture of polyether polyols or polyolefin polyols.
It can be achieved by a magnetic recording medium which is a polyether polyol.

Polyurethanes using polyolefin polyols as polyols have a larger molecular spread in organic solvents and a higher degree of dispersion than conventional polyurethanes having polar bonds, such as polyesters and polycarbonates. Is significantly improved. This is thought to be because polyolefin polyols are fatty chains and have low polarity, that is, high lipophilicity, so that the molecular chains are widened, and as a result, good dispersion of individual ferromagnetic powders and non-magnetic powders is performed. . According to the present invention, it is difficult to substantially disperse a substance containing a polar bond, such as a conventional polyester or polycarbonate, at that portion, and the individual ferromagnetic powders are close to each other and cannot be substantially dispersed. Unexpectedly, such a problem was solved.

However, this polyolefin polio
However, in order to improve this, the present invention includes a polyurethane which is a reaction product containing a polyol and a polyisocyanate as main raw materials. The polyol can be improved by using a mixture of a polyolefin polyol and a polyether polyol, or a polyether polyol derived from a polyolefin polyol. That is, the polyether polyol does not hydrolyze, is a component having extremely excellent storage stability, and is useful for increasing the Tg of the polyurethane. The polyether polyol can also solve the problem that polyurethane containing polyolefin polyol has poor compatibility with other binder components.
Polyether bonds are not hydrolyzed and are extremely excellent in storability, for example, -COO such as polyester polyol.
-The bond is easily hydrolyzed by water to form -COOH and-
This is because such a reaction is unlikely to occur in a polyether polyol having an —O— bond, although it is likely to be in the form of OH. Such an effect is not only a mixture of a polyolefin polyol and a polyether polyol as a polyol, but also a form in which a polyolefin polyol is contained in a molecular chain of the polyether polyol.

The binder for a magnetic recording medium of the present invention is a binder for a magnetic recording medium comprising a polyurethane, which is a reaction product of a polyol and a polyisocyanate as main raw materials, wherein the polyol is a mixture of a polyolefin polyol and a polyether polyol. A magnetic recording medium using a polyether polyol derived from a polyolefin polyol, and having a magnetic layer containing a ferromagnetic powder and a binder on at least one surface of a nonmagnetic support; Is a polyurethane which is a reaction product using an aliphatic polyol and a polyisocyanate as main raw materials.

That is, the present invention relates to a binder for a magnetic recording medium comprising a polyurethane produced from a raw material containing a polyol and a polyisocyanate as main raw materials and containing various additives such as a chain extender. Preferably, it is a polyol having a molecular weight of 500 to 5000 and having an OH group at the terminal of a hydrocarbon chain, and the OH group may be located at a position other than the terminal of the carbon chain. Further, the more preferable range of the molecular weight is 800 to 3000. If the molecular weight is too small, the dispersibility is not preferable. If the molecular weight is too large, the solubility in a solvent is reduced and the dispersibility is reduced. The carbon chain may have any of a straight-chain structure and a branched structure, and a saturated carbon chain may be used.

Specifically, polyolefins obtained from ethylene, propylene, butene-1, 4-methylpentene-1 and the like, in which an OH group is introduced into a terminal, are used.

Specific examples of these compounds include those obtained by introducing an OH group into the terminal of a polyolefin obtained from ethylene, propylene, 1-butene, 4-methyl-1-pentene or the like.

The polyether polyol used together with the polyolefin polyol includes not only aliphatic polyethers such as polyethylene oxide, polypropylene oxide and polytetramethylene glycol, but also aromatic oxides such as bisphenol A, ethylene oxide and propylene oxide. There is an aromatic-containing polyether obtained by addition. The preferred range of the molecular weight of the polyether polyol is from 500 to 3000. If it is smaller than this range, the adhesion to the non-magnetic support decreases, and if it is larger, the dispersibility decreases. By adding polyether polyol to polyolefin polyol, P
Since the affinity with a non-magnetic support such as ET and PEN is increased, the adhesion is improved. The mixing ratio of the polyolefin polyol and the polyether polyol is from 80/20 to 20/80.
(Weight ratio) is preferred. If the amount of polyolefin is less than this range, the dispersibility decreases, and if the amount of polyether is less, the adhesion to the non-magnetic support decreases.

In the present invention, a polyether polyol derived from a polyolefin polyol can be used in addition to a method in which a mixture of a polyolefin polyol and a polyether polyol is used as a raw material of a polyurethane polyol. That is, a polyolefin polyol is incorporated into a part of the polyether polyol. This can be obtained by adding an alkylene oxide such as ethylene oxide or propylene oxide to the above-mentioned polyolefin polyol.

In a solvent such as toluene or xylene,
The polyolefin polyol is obtained by heating to about 110 ° C. in the presence of 1-10% sodium hydroxide to the above-mentioned polyolefin polyol and adding an aerated alkylene oxide such as ethylene oxide or propylene oxide.

The preferred molecular weight of the polyether derived from this polyolefin polyol is from 800 to 300
0. Outside this range, the dispersibility decreases. The preferred weight ratio of the polyolefin polyol to the alkylene oxide is from 80/20 to 20/80. When the amount of the polyolefin is small, the dispersibility decreases, and when the amount of the alkylene oxide is small, the adhesion to the nonmagnetic support decreases. The alkylene oxide is preferably propylene oxide.

The content of the mixture of the polyolefin polyol and the polyether polyol in the polyurethane or the content of the polyolefin-derived polyether is preferably 20 to 90% by weight. . On the other hand, if it is too large, the glass transition temperature (Tg) decreases, and it is difficult to adjust the physical properties of the obtained composition. The molecular weight of the polyurethane is from 1 to
It is preferable to be 150,000. If it is larger than 150,000, the viscosity is high and the dispersibility is reduced. If it is smaller than 150,000, the mechanical strength is low and the durability is deteriorated.

The polyisocyanate includes MDI
(4,4'-diphenylmethane diisocyanate), 2,
4-TDI (tolylene diisocyanate), 2,6-TDI,
1,4-XDI (xylylene diisocyanate), 1,3-XD
I, 4,4'-diphenylether-diisocyanate, 2-nitrodiphenyl-
4,4′-diisocyanate, 2,2′-diphenylpropane diisocyanate, 3,3′-dimethyldiphenylmethane-4,4′-diisocyanate, 4,4′-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, Naphthalene-1,4-diisocyanate, naphthalene-1,
Aromatic polyisocyanate such as 5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, aliphatic diisocyanate such as tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate (IPDI), hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate and the like are used. Since the segment of the polyolefin polyol is soft, the physical properties of the aromatic diisocyanate are more easily adjusted. Preferred are MDI, TDI, IPDI and the like.

In addition to the polyol and the polyisocyanate, additives such as a chain extender can be added. Examples of the chain extender include ethylene glycol, 1,4-butanediol,
Glycols such as 2,3-butanediol, neopentyl glycol, dihydroxyethyl ether of bisphenol A and hydroquinone dihydroxyethyl ether, and diamines such as diphenylmethanediamine and m-phenylenediamine can be used. The terminal of the polyurethane molecule is preferably an OH group terminal. The OH group reacts and crosslinks with the isocyanate curing agent in the magnetic layer to increase the strength of the magnetic layer coating film. Further, the glass transition temperature (Tg) of the polyurethane is preferably from -20 to + 50C. If the glass transition temperature is low, the magnetic coating film before curing has low blocking properties, and if it is high, it becomes brittle, which is not preferable in terms of durability.

The binder comprising the polyurethane of the present invention includes -SO3M, -OSO3M, -COOM, -PO3M '.
2, -OPO3 M'2, -NR2, -N + R3 X-, -N +
R2R'SO3-, -N + R2R'COO- (however,
M is hydrogen, an alkali metal, an alkaline earth metal, or an ammonium salt; M ′ is hydrogen, an alkali metal, an alkaline earth metal, an ammonium salt, or an alkyl group;
Is an alkyl group, and X represents a halogen), and preferably contains at least one polar group selected from the group consisting of 1 × 10 −6 to 2 ×
It is preferred to contain 10-4 equivalents. If it is more than 2 × 10 −4 equivalents, the viscosity increases, and the dispersibility tends to decrease. If it is less than 1 × 10 −6 equivalents, the dispersibility tends to decrease.

The polyurethane compound used in the present invention includes a polyol component (a mixture of a polyolefin polyol and a polyether polyol), a chain extender (for example, neopentyl glycol, 1,4-butanediol, etc.), sulfonic acid Containing diol compound (for example, 5-sodium sulfoisophthalsandi (β-hydroxyethyl) and the like)
Is dissolved in a solvent such as toluene, cyclohexanone, dimethylacetamide, or a mixture thereof, and
Heat and dissolve at 90 ° C, and add catalyst (eg di-
n-butyltin dilaurate), and then the isocyanate
The compound can be synthesized by adding a solution in which a catalyst component (for example, MDI, TDI, or the like) is dissolved in the above-described catalyst and performing a urethanation reaction.

When the binder of the present invention is used in a magnetic layer, a vinyl chloride synthetic resin or a synthetic resin described below may be used in combination with the polyurethane of the present invention. The polymerization degree of the vinyl chloride resin that can be used in combination is 200 to 6
00 is preferable, and 250 to 450 is particularly preferable. Vinyl chloride resin is a vinyl monomer such as vinyl acetate,
Those obtained by copolymerizing vinyl alcohol, vinylidene chloride, acrylonitrile and the like may be used.

In the polyurethane of the present invention, various synthetic resins can be used in combination with the vinyl chloride resin for forming each magnetic layer. For example, ethylene-vinyl acetate copolymer, cellulose derivatives such as nitrocellulose resin, acrylic resin, polyvinyl acetal resin, polyvinyl butyral resin, epoxy resin, and phenoxy resin.
These can be used alone or in combination. It is preferable that the above-mentioned polar group is also introduced into the above-mentioned resin used in combination with the polyurethane of the present invention.

When another synthetic resin is used in combination, the amount of urethane contained in the magnetic layer is preferably at least 10% by weight, more preferably at least 20% by weight in the binder. . Further, the vinyl chloride resin is preferably contained in the binder in an amount of 80% by weight or less, more preferably 70% by weight or less.

In addition, a curing agent such as a polyisocyanate compound can be used together with the binder of the present invention.
Examples of the polyisocyanate compound include a reaction product of 3 mol of tolylene diisocyanate and 1 mol of trimethylolpropane (eg, Desmodur L-75 (manufactured by Bayer)), diisocyanate 3 such as xylylene diisocyanate or hexamethylene diisocyanate. Reaction product of 1 mol of trimethylolpropane, burette addition compound with 3 mol of hexamethylene diisocyanate, isocyanurate compound of 5 mol of tolylene diisocyanate, isocyanurate addition of 3 mol of tolylene diisocyanate and 2 mol of hexamethylene diisocyanate Mention may be made of compounds, polymers of isophorone diisocyanate and diphenylmethane diisocyanate. The polyisocyanate compound contained in the magnetic layer is preferably contained in the binder in the range of 10 to 50% by weight, more preferably in the range of 20 to 40% by weight.

In the case of performing a curing treatment by electron beam irradiation, a compound having a reactive double bond (eg, urethane acrylate) can be used. The total weight of the resin component and the curing agent (that is, the binder) is usually preferably in the range of 15 to 40 parts by weight, more preferably 20 to 30 parts by weight, based on 100 parts by weight of the ferromagnetic powder. It is.

The ferromagnetic powder used in the magnetic recording medium of the present invention is a ferromagnetic chromium dioxide, barium ferrite, ferromagnetic iron oxide, cobalt-containing ferromagnetic iron oxide or ferromagnetic alloy powder having an SBET specific surface area of 40 m 2 / g. (Preferably at least 50 m @ 2 / g), and the crystallite size is at most 35 nm, preferably at most 25 nm. As ferromagnetic powder, F
e, Ni, Fe-Co, Fe-Ni, Co-Ni, Co
-Ni-Fe and the like, and aluminum, silicon, sulfur, scandium, titanium, vanadium, chromium, manganese, copper, zinc, yttrium, molybdenum, rhodium, palladium, gold within a range of not more than 20% by weight of the metal component. , Tin, antimony, boron, barium, tantalum, tungsten, rhenium, gold, mercury, lead, phosphorus, lanthanum, cerium, praseodymium, neodymium, tellurium,
An alloy containing bismuth can be given. Further, the ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide.

The method for producing these ferromagnetic powders is already known, and the ferromagnetic powder used in the present invention can be produced according to a known method. The shape of the ferromagnetic powder is not particularly limited, but usually a needle shape, a granular shape, a dice shape, a rice grain shape, a plate shape or the like is used. It is particularly preferable to use acicular ferromagnetic powder.

The above resin component, curing agent and ferromagnetic powder are kneaded and dispersed together with a solvent such as methyl ethyl ketone, dioxane, cyclohexanone and ethyl acetate which are usually used in the preparation of a magnetic paint to obtain a magnetic paint. The kneading and dispersion can be performed according to a usual method. In the magnetic paint, in addition to the above components, α-Al2 O3, Cr2
Abrasives such as O3, antistatic agents such as carbon black, lubricants such as fatty acids, fatty acid esters, silicone oils,
It may contain a commonly used additive or filler such as a dispersant. A magnetic coating prepared from the above materials is applied on a non-magnetic support to form a magnetic layer.
For magnetic recording media with multiple layers consisting of an upper magnetic layer and a lower magnetic layer or a lower non-magnetic layer, the structure of each layer, materials such as ferromagnetic powder, binder, abrasive, lubricant, antistatic agent, etc. About JP-A-63-146210,
Those described in JP-A-63-187418 can be used.

In the method for producing a magnetic recording medium of the present invention, for example, a coating solution of a magnetic layer is preferably applied to the surface of a running non-magnetic support, preferably in a thickness of 0.05 to 10 μm after drying the magnetic layer.
, More preferably 0.2 to 5.0 μm. Here, a plurality of magnetic paints may be sequentially or simultaneously applied in a multilayer manner. Examples of the coating machine for applying the magnetic paint include an air doctor coat, a blade coat,
Rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure cord, kiss coat, cast coat, spray coat, spin coat and the like can be used. These can be referred to, for example, “Latest Coating Technology” (May 31, 1983) issued by “Tokyo Gijutsu Center”.

When the present invention is applied to a magnetic recording medium having two or more layers, the following can be proposed as an example of a coating apparatus and method. (1) The lower layer is first applied by a gravure coating, a roll coating, a blade coating, an extrusion coating device, etc., which are generally applied in the application of a magnetic paint, and the lower layer is formed in a wet state. JP-A-1-46186, JP-A-60-160
The upper layer is applied by a support pressure type extrusion coating apparatus disclosed in JP-A-238179 and JP-A-2-265672. (2) JP-A-63-88080, JP-A-2-17
No. 971 and Japanese Unexamined Patent Publication No. 2-265672 disclose the upper and lower layers almost simultaneously from one coating head 2 having two built-in coating liquid passage slits. (3) The upper and lower layers are coated almost simultaneously by an extrusion coating device with a backup roll disclosed in Japanese Patent Application Laid-Open No. 2-174965.

A back layer (backing layer) may be provided on the surface of the non-magnetic support used in the present invention on which the magnetic paint is not applied. Normally, the back layer is provided by applying a back layer forming paint in which a particulate component such as an abrasive and an antistatic agent and a binder are dispersed in an organic solvent on a surface of the non-magnetic support on which the magnetic paint is not applied. Layer. An adhesive layer may be provided on the surface of the non-magnetic support on which the magnetic paint and the back layer forming paint are applied.

The applied layer of the applied magnetic paint is dried after subjecting the ferromagnetic powder contained in the applied layer of the magnetic paint to a magnetic field orientation treatment. After being dried in this manner, the coating layer is subjected to a surface smoothing treatment. For the surface smoothing treatment, for example, a super calender roll or the like is used. By performing the surface smoothing treatment, voids generated by the removal of the solvent during drying disappear, and the filling rate of the ferromagnetic powder in the magnetic layer is improved, so that a magnetic recording medium having high electromagnetic conversion characteristics can be obtained. it can.

The magnetic recording medium of the present invention has an extremely smooth surface having a center line average roughness of 4 nm or less (preferably in the range of 3 to 1 nm) at a cutoff value of 0.25 mm. Is preferred. As a method of this, for example, as described above, the recording layer formed by selecting a specific ferromagnetic powder and a binder is subjected to the above calendering treatment. The calendering conditions were as follows.
It is preferable to perform the operation by operating under the condition of 00 to 500 kg / cm. The laminate thus cured is then formed into a desired shape. Cutting can be performed under normal conditions using a normal cutting machine such as a slitter.

The binder for a magnetic recording medium of the present invention uses a mixture of an aliphatic polyol and a polyether polyol or a polyether polyol derived from an aliphatic polyol as the polyol obtained by the reaction between the polyol and the polyisocyanate. The resulting polyurethane has a high dispersibility, and the magnetic layer obtained from the coating composition containing the ferromagnetic powder using the binder of the present invention has an extremely high dispersibility of the ferromagnetic powder, It has excellent storage properties and durability under a wide range of temperature and humidity conditions, and also has excellent adhesion to a nonmagnetic support. Hereinafter, examples of the present invention will be described, and the present invention will be described in more detail.

[0042]

EXAMPLES Synthesis Examples 1 to 7 100 equipped with a condenser and a stirrer, and previously purged with nitrogen.
The following monomer composition A was added to a 0 ml three-necked flask, and a mixed solvent 226 of toluene / cyclohexanone = 1/1 was added.
g. The following monomer composition B was added thereto, and di-n-butyltin dilaurate 0.03 was further used as a catalyst.
lg (0.049 mol) and 90 ° C. under a nitrogen stream.
For 6 hours to obtain the following polyurethane solution.

[0043]

[0044]

[0045]

Synthesis Example 4 Monomer Composition A Propylene oxide adduct of polyolefin polyol (molecular weight 3000) 120 g (polyolefin / fluoropropylene oxide = 2/1 wt) neopentyl glycol 6.4 g 5-sodium sulfoisophthalic acid dihydroxyethyl 3.2 g monomer composition B1 MDI 25g

Synthesis Example 5 Monomer composition A Polycaprolactone polyol (molecular weight: 2,000, OH value: 52.4) 120 g Neopentyl glycol 4.4 g Dihydroxyethyl 5-sodium sulfoisophthalate 3.2 g Monomer composition B1 25 g MDI

Synthesis Example 6 Monomer composition A Polybutylene adipate polyol (molecular weight: 2,000, OH value: 52.4) 120 g Neopentyl glycol 4.4 g Dihydroxyethyl 5-sodium sulfoisophthalate 3.2 g Monomer composition B1 MDI 25 g

Synthesis Example 7 Monomer composition A Polytetramethylene glycol (molecular weight: 2,000, OH value: 52.4) 120 g Neopentyl glycol 4.4 g Dihydroxyethyl 5-sodium sulfoisophthalate 3.2 g Monomer composition B1 MDI 25 g Characteristics of the obtained polyurethane Is shown in Table 1.

[0050]

[Table 1]

Example 4 Ferromagnetic alloy powder (composition: iron 94% by weight, zinc 4% by weight,
100 parts by weight of nickel 2% by weight, coercive force (Hc) 1500 Oe, crystallite size 20 nm) were pulverized by an open kneader for 10 minutes, and then the copolymer of vinyl chloride / vinyl acetate / glycidyl methacrylate = 86/9/5 was converted to hydroxy. Compound to which ethylsulfonate sodium salt is added (SO ₃ Na 6 × 10 ⁻⁵ eq / g, epoxy group =
10 ⁻³ eq / g, weight average molecular weight = 30,000)
0 parts and 60 parts of methyl ethyl ketone are kneaded for 60 minutes, and then 10 parts by weight of polyurethane (sample obtained in Synthesis Example 4 ) (solid content) abrasive (Al ₂ O ₃ particle size 0.3 μm) 2 parts by weight carbon black ( (Particle size: 400 nm) 2 parts by weight methyl ethyl ketone / toluene = 1/200 parts by weight were added and dispersed by a sand mill for 120 minutes. 5 parts by weight of polyisocyanate (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.) (solid content) sec. 1 part by weight of butyl stearate 1 part by weight of butoxyethyl stearate 1 part by weight of stearic acid 50 parts by weight of methyl ethyl ketone are added, and the mixture is further stirred and mixed for 20 minutes, and then filtered using a filter having an average pore diameter of 1 μm to prepare a magnetic paint. did. The thickness of the obtained magnetic paint after drying is 2.5μ.
m was applied to the surface of a 10 μm thick polyethylene naphthalate support using a reverse roll.

The non-magnetic support coated with the magnetic paint is magnetically oriented with a 3000 Gauss magnet while the magnetic paint is not dried, and after drying, the metal roll-metal roll-metal roll-metal roll-metal A calendar process using a roll-metal roll-metal roll combination (speed 10
After applying a pressure of 0 m / min, a linear pressure of 300 kg / cm, and a temperature of 90 ° C.), the resultant was slit into a width of 8 mm to produce an 8 mm video tape.

Comparative Examples 1-3 An 8-mm video tape was produced in the same manner as in Example 4 except that the polyurethanes of Example 4 were replaced with those of Synthesis Examples 5-7.

[0054] except for the use of polybutadiene polyol instead of the polyurethane of Comparative Example 4 Example 4 (Nippon曹逹Co. NISSO PB "G2000"), creates a 8mm video tape in the same manner as in Example 4 did.

Comparative Example 5 The addition amount of the polyurethane of Comparative Example 3 was reduced from 10 parts by weight to 5 parts by weight, and instead, polybutadiene polyol was used.
An 8 mm video tape was prepared in the same manner as in Comparative Example 3 except that 5 parts by weight of "G2000" was added. Next, the characteristics of the video tape of the example and the video tape of the comparative example were measured by the following measurement methods. The results are shown in Tables 2 and 3.

Measurement method Electromagnetic conversion characteristics: A Hi8-VTR (So
The signal was recorded and reproduced by using the product (ny Corporation: TR-705). The S / N ratio at this time was measured with a noise meter, and the value of the tape of Comparative Example 4 was expressed as a relative value assuming 0 dB.

Runnability: The obtained video tape and stainless steel rod were wound with a tension (T1) of 50 g and a winding angle of 180.
° under this condition, the tape was 3.3 cm /
The tension (T2) required to run at a speed of seconds was measured. Based on the measured values, the friction coefficient μ of the tape was determined by the following formula. The measurement condition of the coefficient of friction was 25 ° C 7
0% RH. μ = 1 / π · ln (T2 / T1)

Durability: The time until the reproduction output becomes 50% of the recording signal in the still state without operating the still limiting mechanism using the same VTR used for the measurement of the electromagnetic conversion characteristics is defined as the still durability time. It was measured.

Repeatability: 0 ° C., 10% RH, 0
A 90-minute length tape was continuously and repeatedly run 100 times using the same VTR used for the measurement of the electromagnetic conversion characteristics under each environment of 70% RH at 40 ° C. and 70% RH at 40 ° C., and the stain on the video head was observed. The video output was recorded continuously and the output drop was measured. Video head dirt ○: No dirt was observed △: Dirt was observed after wiping × ×: Dirt was visually observed

Surface roughness Ra: Optical interferometry using a digital optical profilometer (manufactured by WYKO)
The center line average roughness Ra was determined under the condition of a cutoff of 0.25 mm.

Repeatability after High Temperature and High Humidity Storage The sample tape was exposed to an environment of 60 ° C. and 90% RH for 2 weeks, and then evaluated repeatedly in the same manner as in an environment of 23 ° C. and 30% RH.

Dirt on a calender roll Tape length 300
When the stain on the roll surface after calendering of m was visually observed, it was evaluated as x, and when it was not observed, it was evaluated as ○. Tables 2 and 3 show the measurement results.

Adhesion to Non-Magnetic Support The magnetic layer of the tape was fixed to a glass plate with an adhesive tape.
The peel strength at the time of peeling was measured.

[0064]

[Table 2]

[0065]

[Table 3]

Examples 9 to 12 Undercoating solutions were prepared by stirring with a disperser stirrer for 12 hours according to the following formulation. Polyester resin (-SO ₃ Na group-containing) 100 parts by weight Tg: 65 ° C. Na content: 4600 ppm Cyclohexanone 9900 parts by weight Using the obtained undercoat liquid, polyethylene terephthalate (thickness 10 μm, F5 value: MD direction 20 kg / mm)
² , TD direction 14 kg / mm ² , Young's modulus: MD direction 750 kg / mm ² , TD direction 470 kg / mm ² )
Was applied with a bar coat at a dry thickness of 0.1 μm.

On the other hand, a coating solution for the upper magnetic layer and a coating solution for the lower non-magnetic layer were prepared according to the following formulations.

Formulation of Coating Solution for Upper Magnetic Layer Ferromagnetic powder: 100 parts by weight of Fe alloy powder (Fe—Co—Ni) Composition: Fe: Co: Ni = 92: 6: 2 Al 2 O 3 used as sintering inhibitor Hc 1600 Oe, σs: 119 emu / g Long axis length: 0.13 μm, needle ratio: 7 Crystallite size: 17.2 nm Water content: 0.6% by weight Vinyl chloride copolymer 13 parts by weight -SO3 Na: 8 × 10-5 eq / g-OH, epoxy group-containing Tg: 71 ° C., degree of polymerization: 300 Number average molecular weight (Mn): 12,000 Weight average molecular weight (Mw): 38000 Polyurethane resin (Table 4) 5 parts by weight α-alumina (average particle Diameter: 0.15 μm) 12 parts by weight SBET: 8.7 m 2 / g, pH: 8.2 Water content: 0.06% by weight Cyclohexanone 150 parts by weight Methyl ethyl ketone 150 parts by weight After mixing and dispersing in a sand mill for 6 hours,
Polyisocyanate (Coronate L) and oleic acid 5
Parts by weight, 7 parts by weight of stearic acid, butyl stearate 1
By adding 5 parts by weight, a coating solution for an upper magnetic layer was obtained.

Formulation of Coating Solution for Lower Nonmagnetic Layer 85 parts by weight of TiO2 Average particle size: 0.035 μm Crystal form: rutile TiO2 content: 90% or more Surface treatment layer: Al 2 O 3 SBET: 35 to 45 m 2 / g True specific gravity: 4 PH: 6.5 to 8.0 Carbon black 5 parts by weight Average particle diameter: 160 nm DBP oil absorption: 80 ml / 100 g pH: 8.0 SBET: 250 m 2 / g Coloring power: 143% Vinyl chloride copolymer 13 weight Part: SO3 Na: 8 * 10 <-5> eq / g-OH, epoxy group-containing Tg: 71 [deg.] C., degree of polymerization: 300 Number average molecular weight (Mn): 12000 Weight average molecular weight (Mw): 38000 Polyurethane resin (Table 4) 5 Parts by weight cyclohexane 100 parts by weight methyl ethyl ketone 100 parts by weight After the above composition was mixed and dispersed in a sand mill for 4 hours,
5 parts by weight of polyisocyanate (Coronate L), 5 parts by weight of oleic acid, 5 parts by weight of stearic acid, and 15 parts by weight of butyl stearate were added to obtain a coating solution for a lower nonmagnetic layer.

The above-mentioned coating solution was applied in a wet state using two doctors having different gaps, and then subjected to an orientation treatment using a permanent magnet of 3500 gauss and then an electromagnet of 1600 gauss and then dried. After that, a super calender treatment using a metal roll and a metal roll was performed at a temperature of 80 ° C.
The coating thickness was 0.3 μm for the magnetic layer and 3.0 μm for the non-magnetic layer. Next, a coating solution for the back coat layer was prepared according to the following formulation.

Backcoat layer formulation Carbon black 100 parts by weight SBET: 220 m 2 / g Average particle size: 170 nm DBP oil absorption: 75 ml / 100 g Volatile content: 1.5% pH: 8.0 Bulk density: 240.2 kg / m 3 nitro Cellulose RSI / 2 100 parts by weight Polyurethane (Table 4) 30 parts by weight Dispersant Copper oleate 10 parts by weight Copper phthalocyanine 10 parts by weight Barium sulfate (precipitating) 5 parts by weight Methyl ethyl ketone 500 parts by weight Toluene 500 parts by weight Reserve the above composition The mixture was kneaded and kneaded by a roll mill, and 100 parts by weight of the obtained composition was used. 100 parts by weight of carbon black SBET: 200 m 2 / g Average particle size: 0.2 μm DBP oil absorption: 36 ml / 100 g pH: 8.5 α -Al2O3 (average particle size: 0.2 µm) in a composition containing 0.1 parts by weight Disperse with a sand grinder,
After filtration, the following composition was added to 100 parts by weight of the above composition to prepare a coating solution.

120 parts by weight of methyl ethyl ketone 5 parts by weight of polyisocyanate The obtained coating solution was applied by a bar coater to the non-magnetic support on the side opposite to the side on which the magnetic layer was provided so as to have a dry thickness of 0.5 μm. The raw material thus obtained was cut into an 8 mm width to prepare an 8 mm video tape, and the results measured by the same method as in Example 4 are shown in Tables 4 and 5.

Comparative Example 6 A video tape similar to that of Example 9 was prepared except that the polyester polyurethane of Synthesis Example 5 was used as the polyurethane for both the upper magnetic layer and the lower nonmagnetic layer.
Tables 4 and 5 show the results of measuring the characteristics in the same manner as in No. 9 .

[0074]

[Table 4]

[0075]

[Table 5]

Examples 16 to 18 Coating solutions for the upper magnetic layer and for the lower magnetic layer having the following compositions were prepared. Upper layer liquid CO-γ-FeOx 100 parts by weight (x = 1.45, major axis length 0.20 μm Hc950Oe, Br 1600 gauss) Polyvinyl chloride copolymer 10 parts by weight (containing sulfonic acid group 0.25% by weight) Polyurethane (synthesis) Examples 4, 5 ) 5 parts by weight Polyisocyanate (Coronate L) 6 parts by weight Stearic acid (for industrial use) 1 part by weight Butyl stearate (for industrial use) 1 part by weight α-alumina (particle size 0.2 μm) 10 parts by weight Carbon black (particle size 70 nm) 1 part by weight Methyl ethyl ketone / cyclohexanone = 7/3 solvent 200 parts by weight

Lower layer solution (solution B) 100 parts by weight of CO-γ-FeOx (x = 1.45, major axis length 0.25 μm Hc850Oe, Br1400 gauss) 11 parts by weight of vinyl chloride copolymer (sulfonic acid group 0.25 Polyurethane (Synthesis Examples 4 and 5 ) 4 parts by weight Polyisocyanate (Coronate L) 6 parts by weight Stearic acid (for industrial use) 1 part by weight Butyl stearate (for industrial use) 1 part by weight Conductive carbon black (particle size) 20 nm) 5 parts by weight Methyl ethyl ketone / cyclohexanone = 7/3 solvent 200 parts by weight

Adjustment of the coating solution was performed using a kneader, a sand grinder, or the like, and simultaneous multilayer coating was performed. The non-magnetic support has a center line average surface roughness (Ra) of 4 nm and 14 μm.
An m-thick polyethylene terephthalate film was used. After the application, it was oriented in the longitudinal direction and dried to obtain a bulk roll. The obtained bulk roll was further subjected to a calender roll treatment. Calendar roll treatment is Shore A hardness 80
Temperature, Ra has a metal roll of 0.5 nm stacked on 7 stages, temperature 8
The treatment was performed at 0 ° C. and a linear pressure of 300 kg / cm ² . After performing the calender roll treatment, bulk magnetic treatment was performed at 60 ° C. for 24 hours to cure the magnetic layer, and then slit to a 1/2 inch width to obtain a video tape. When the surface roughness of the obtained video tape was measured, it was 5 to 6 nm in all cases. The obtained video tape was incorporated into an S-VHS type cassette to prepare a video cassette tape, and the results measured by the same method as in Example 4 except that the VTR was changed to "S9000" manufactured by Victor Company of Japan, were shown in Tables 6 and 7. FIG.

Comparative Example 7 A video tape similar to that of Example 16 was prepared except that the polyester polyurethane of Synthesis Example 5 was used as the polyurethane for both the upper magnetic layer and the lower magnetic layer.
Tables 6 and 7 show the results of measuring the characteristics in the same manner as in Table 16 .

[0080]

[Table 6]

[0081]

[Table 7]

The polyurethane-containing binder of the present invention (Example 1)
In Nos. 6 to 18), the dispersibility was high, the roll contamination in the calendering step was improved, the squareness ratio and the surface roughness were also improved, and as a result, the electromagnetic conversion characteristics were improved. In addition, 0 ° C to 40 ° C, 10
% To 70% RH, the running performance was improved, and the running performance was also improved in a long-term storage acceleration test at 60 ° C., 90% for 4 weeks.

[0083]

According to the present invention, there is provided a binder for a magnetic recording medium comprising a polyurethane which is a reaction product of a polyol and a polyisocyanate as main raw materials, wherein the polyol is derived from a mixture of a polyolefin polyol and a polyether polyol or a polyolefin polyol. A binder for a magnetic recording medium, characterized in that the binder is a polyether polyol prepared as a binder for a magnetic layer containing a ferromagnetic powder and a binder on at least one surface of a nonmagnetic support. Very high durability, excellent long-term storage, excellent durability under a wide range of temperature and humidity conditions, adhesion to non-magnetic supports such as PET (polyethylene terephthalate) and PEN (polyethylene naphthalate) A magnetic recording medium excellent in the above is obtained.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tsukasa Okita 2-2-1-1, Ogimachi, Odawara-shi, Kanagawa Prefecture Inside Fuji Photo Film Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) C09D 5 / twenty three

Claims (4)

(57) [Claims] 1. A binder for a magnetic recording medium comprising a polyurethane which is a reaction product of a polyol and a polyisocyanate as main raw materials, wherein the polyol has a molecular weight of 1.
500-5000 polyolefin polyol and molecular weight
A molecular weight of 8 derived from a mixture of polyether polyols having a molecular weight of 500 to 3000 or a polyolefin polyol.
A binder for a magnetic recording medium, which is a polyether polyol having a molecular weight of 00 to 3000 . 2. The polyurethane according to claim 1, wherein the molecule has —SO _{3
M, -OSO 3 M, -COOM,} -PO 3 M 2, -OPO 3
^{_{M 2, -NR 2, -N +}} R 3 X -, -N + R 2 R'SO 3 -, -N
⁺ R ₂ R'COO ^- (however, M is hydrogen, alkali metal, alkaline earth metal, ammonium salts, M 'is hydrogen,
An alkali metal, an alkaline earth metal, an ammonium salt, an alkyl group, R and R ′ are alkyl groups and X represents a halogen). The binder for a magnetic recording medium according to claim 1, wherein 3. A magnetic recording medium in which a magnetic layer containing a ferromagnetic powder and a binder is formed on at least one surface of a nonmagnetic support, wherein the binder is a reaction product containing a polyol and a polyisocyanate as main raw materials. include certain polyurethanes, said polyol is a polio <br/> les fins polyol and a mixture or polyether polyol derived molecular weight 800 to 3000 from a polyolefin polyol polyether polyol having a molecular weight 500 to 3000 of molecular weight 500 to 5000 Characteristic magnetic recording medium. 4. The method according to claim 1, wherein at least one surface of the nonmagnetic support has
In a magnetic recording medium in which a lower magnetic layer or a lower non-magnetic layer is provided and an upper magnetic layer is provided thereon, at least one of the magnetic layer and the non-magnetic layer has a binder binding the ferromagnetic powder or the non-magnetic powder to a polyol. and a polyisocyanate comprises a polyurethane that is the reaction product as the main raw material, wherein the polyol is derived from a mixture or polyolefin polyol polyether polyol poly <br/> olefin polyols with molecular weight 500 to 3000 of molecular weight 500 to 5000 And a polyether polyol having a molecular weight of 800 to 3000 .