JPH0682455B2 - Magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium having a magnetic layer coated on a base fabric, and more specifically, fine magnetic powder is well dispersed and oriented. The present invention relates to a coating type magnetic recording medium having a magnetic layer and having excellent magnetic properties and running properties.

(Prior Art) To date, in response to high-density recording and high S / N of magnetic recording media, magnetic powders that have been miniaturized and have high coercive force are highly dispersed to form a magnetic layer with a smooth surface. In order to obtain the same, improvements have been made such as improvement of magnetic powder dispersion method and surface forming condition, improvement of dispersant, and addition of dispersion performance to binder. On the other hand, the magnetic tape having a magnetic layer with a smooth surface thus obtained increases the frictional resistance between the head guide and the tape,
It causes a problem that the tape runs poorly.

In order to solve these problems, it has been conventionally practiced to incorporate fine particles of silicon oil, lubricants represented by fatty acids or esters thereof, and fine particles of carbon black, alumina and the like into the magnetic layer. However, the former lubricant is
Problems such as bleeding after being left for a long time, instability of magnetic coating dispersion, and non-uniformity of the magnetic layer after coating are likely to occur, leading to risk of deterioration of tape storage stability and electromagnetic conversion characteristics. There is. On the other hand, the latter fine particles, as a result, reduce the filling property of the magnetic powder in the magnetic layer, so that the use of a large amount is naturally limited.

(Problems to be Solved by the Invention) As a result of earnest research aimed at solving the drawbacks of the conventional methods as described above, the present inventor has found that a long-chain alkyl group is added to a specific resin or rubber containing an epoxy group. By using as a binder a modified resin obtained by heating and adding a secondary amine having a magnetic field, a magnetic layer having excellent surface properties in which magnetic powder is well dispersed can be obtained. The present invention has been completed by discovering that there is no change in bleeding or the like even when it is left standing and that it has excellent electromagnetic conversion characteristics, running properties and durability as a magnetic tape.

(Means for Solving Problems) Thus, according to the present invention, at least one epoxy group-containing resin selected from polyvinyl chloride resins having 1 to 8% by weight of epoxy groups, polyester resins and acrylonitrile-butadiene rubber. Or rubber has 9 to 9 carbon atoms
There is provided a magnetic recording medium characterized by using an amine-modified resin or rubber obtained by reacting a secondary amine having 18 alkyl groups as a binder component.

The epoxy group-containing polyvinyl chloride resin used in the present invention is a vinyl chloride homo- or copolymer resin having a polymerization degree of 200 to 900 and a chlorinated polyvinyl chloride resin. Polymerization degree is 20
When it is less than 0, the durability of the magnetic tape is insufficient, and when it exceeds 900, the viscosity of the magnetic paint is high and the dispersibility of the magnetic powder is deteriorated. These polyvinyl chloride resins are (1) vinyl chloride, a radical polymerizable monomer having an epoxy group that is copolymerizable with vinyl chloride, and other monomers that can be copolymerized with these monomers if necessary. Is obtained in the presence of a radical generator, or (2) by partially dehydrochlorinating polyvinyl chloride or a copolymer whose main component is vinyl chloride by heating or contact with a dehydrochlorinating agent. It can be obtained by a method of epoxidizing a resin with an epoxidizing agent such as percarboxylic acid. The chlorinated polyvinyl chloride resin having an epoxy group can be obtained exclusively by the method (2) using a chlorinated polyvinyl chloride resin or a chlorinated polyvinyl chloride copolymer resin as a starting material.

Examples of the epoxy group-containing monomer copolymerizable with vinyl chloride by the method (1) include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methallyl glycidyl ether, glycidyl acrylate,
Glycidyl methacrylate, glycidyl-P-vinyl benzoate, methyl glycidyl itaconate, glycidyl ethyl malate, glycidyl vinyl sulfonate, glycidyl esters of unsaturated acids such as glycidyl (meth) allyl sulfonate, butadiene monooxide, vinylcyclohexene monooxide, 2 Examples include epoxide olefins such as -methyl-5,6-epoxyhexene. Further, examples of the monomer having an epoxy group and a monomer other than vinyl chloride which is optionally used include carboxylic acid vinyl esters such as vinyl acetate and vinyl propionate; methyl vinyl ether, isobutyl vinyl ether, cetyl vinyl ether, etc. Vinylidene chloride; vinylidene chloride, vinylidene fluoride, etc .: maleic acid, maleic anhydride, monomethyl maleate, diethyl maleate, butylbenzyl maleate, di-2-hydroxyethyl maleate, itaconic acid, dimethyl itaconate, Unsaturated carboxylic acids such as (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, lauryl (meth) acrylate, and 2-hydroxypropyl (meth) acrylate, and their anhydrides or esters; Ethylene, propylene And olefins; unsaturated nitriles such as (meth) acrylonitrile; aromatic vinyls such as styrene, α-methylstyrene and P-methylstyrene. These monomers are used for the purpose of improving the solubility of the resin while controlling the compatibility and softening point of the resin of the present invention and the other resin when mixed, and the characteristics of the coating film and the coating. It can be appropriately selected depending on needs such as process improvement.

Further, as an acrylonitrile-butadiene rubber containing an epoxy group, generally, an acrylonitrile content of 12 to 50
Weight% and molecular weight of 5,000 to 500,000 are used. If the acrylonitrile content is less than 12%, the compatibility with other binders generally used for magnetic recording media such as polyvinyl chloride and nitrocellulose is poor, and if it exceeds 50% by weight, the solvent solubility decreases and the magnetic powder Greatly disperses the dispersibility of. When the molecular weight is less than 5,000, the durability of the coating film is low, and when it is more than 500,000, the viscosity of the coating is too high to be practical. Acrylonitrile-butadiene rubber containing an epoxy group, as in the case of the polyvinyl chloride resin described above, with acrylonitrile, butadiene, a radical copolymerizable monomer containing an epoxy group, if necessary, other copolymerizable, While obtained by copolymerizing with a monomer in the presence of a radical generator,
It can also be obtained by partially epoxidizing a double bond in the rubber of an acrylonitrile-butadiene rubber using an epoxidizing agent such as a percarboxylic acid.

Polyester resin containing epoxy group has a molecular weight of 4000 ~
200,000 are used. If the molecular weight is less than 4000,
The durability of the coating film is insufficient, and if it exceeds 200,000, the viscosity of the coating material becomes too high, which causes practical problems. Polyester resin containing epoxy group, maleic acid, fumaric acid,
Unsaturated dibasic acids such as itaconic acid or saturated dibasic acids such as phthalic acid, adipic acid, terephthalic acid and 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10- It is obtained by epoxidizing an unsaturated polyester resin obtained by heat condensation with a diol such as decanediol or a butadiene oligomer having hydroxyl groups at both ends, by an epoxidizing agent such as percarboxylic acid. In addition, in order to improve the dispersibility of the magnetic powder, it is possible to use one containing a sulfonate as an acid or diol component. Further, a modified unsaturated polyester resin obtained by melt-mixing the unsaturated polyester resin obtained as described above with a polycarbonate resin or a saturated polyester resin in the presence of a catalyst and carrying out a transesterification reaction is also used in the present invention. It can be used as a starting material for an epoxidized polyester resin.

These polyvinyl chloride-based resins, polyester resins and acrylonitrile-butadiene rubber have an epoxy group of 1 to
It is necessary to contain 8% by weight. Otherwise, it is not possible to add a sufficient amount of secondary alkylamine to achieve the object of the invention.

The resin used in the present invention is selected from polyvinyl chloride resins, polyester resins, and acrylonitrile-butadiene rubber, because these resins have good properties such as poly, which meet the requirements as a binder for magnetic tapes. Vinyl chloride resin has low paint viscosity, good magnetic powder dispersibility, and appropriate hardness. Polyester resin is
It has good adhesion to the base film, and
Acrylonitrile-butadiene rubber imparts flexibility to the coating film, has excellent use characteristics of the magnetic tape particularly at low temperatures, and has good compatibility with other resins.

The long-chain secondary alkylamine used in the present invention requires that the alkyl group has 9 to 18 carbon atoms. When the number of carbon atoms is less than 9, the function of improving the slip of the magnetic layer is insufficient, and the dispersibility of the magnetic powder is insufficient. Further, the alkyl group is preferably a straight-chain alkyl group, and preferably has 12 or more carbon atoms. Examples of such long-chain alkylamines include methyllaurylamine, dilaurylamine, distearylamine and the like.

For a magnetic recording medium by mixing and dispersing an amine-modified product obtained by previously subjecting a specific resin or rubber containing an epoxy group and a secondary alkylamine to a magnetic powder and other materials in a solvent. A paint is obtained. 2 here
The amount of the primary amine used is preferably within the equivalent of the epoxy groups in the resin and the rubber, and if it is used in excess of this, not only the prevention of bleeding and the good dispersibility of the magnetic powder are impaired, but also crosslinking is performed. The strength of the subsequent magnetic coating decreases,
The durability of the medium is reduced.

The addition reaction between the secondary amine and the epoxy group-containing resin or rubber is usually performed in a mixed state under heating and melting conditions of 80 to 150 ° C. using a mixer such as a kneader. Whether or not the reaction is proceeding can be easily judged because the incompatible secondary amine is absorbed and integrated into the resin or rubber. The amount of amine added can be confirmed by elemental analysis after removing unreacted amine with methanol.
The addition amount depends on the length of the alkyl group of the amine, but is preferably 5 parts by weight or more per 100 parts by weight of the modified resin.

The amine-modified resin or rubber thus obtained has abundant hydroxyl groups as well as long-chain alkyl groups due to the reaction with amines. It is presumed that this is because hydration by water existing during the reaction occurs as a parallel reaction in addition to the addition of the hydroxyl group by the amine addition. Therefore, the amine-modified resin or rubber thus obtained has a high reactivity with the polyisocyanate compound which is usually used as a crosslinking agent, highly crosslinks the magnetic coating film, and has a good durability. Is useful for giving.

The amine-modified resin and rubber may be combined with each other in the present invention or may be other commonly used binder resins, for example, nitrocellulose, cellulose acetate or other fibrin resin, polyvinyl butyral resin, phenoxy resin. It may be used in combination with a hard binder such as vinyl chloride resin or a soft binder such as polyester resin, polyurethane resin, acrylonitrile butadiene rubber or epichlorohydrin rubber.

The magnetic powder used in the magnetic recording medium of the present invention includes Fe
Γ-Fe including metallic magnetic powders such as powder and Co powder
₂ O ₃ , Fe ₃ O ₄ , Co-containing γ-Fe ₂ O ₃ , Co-containing Fe ₃ O ₄ , iron oxide powders such as barium ferrite, and CrO ₂ powders.

The magnetic powder, the binder, the abrasive, the antistatic agent, and optionally a dispersant are mixed and dispersed in a solvent by a sand mill or the like, and then a cross-linking agent typified by a polyisocyanate compound is mixed to form a polyester film. It is coated on a representative base film. Next, the coating film which has been subjected to orientation treatment and dried and formed on the surface is subjected to cross-linking aging and cut to be used as a magnetic tape or disk.

(Effect of the Invention) The binder for a magnetic recording medium of the present invention provides excellent magnetic powder dispersibility, and the obtained magnetic coating film has a smooth surface, yet exhibits low friction resistance, and for a long period of time. This makes it possible to manufacture magnetic tapes and floppy disks that do not cause phenomena such as bleeding and can maintain excellent electromagnetic conversion characteristics and running performance in a stable manner even after long-term use. In addition,
Although the number of cases where a back coat is applied for the purpose of improving the running property of the magnetic tape has recently been increasing, the amine-modified epoxidized resin used in the present invention is also effective as a binder for this back coat layer. I knew it was.

(Example) Hereinafter, the present invention will be described more specifically with reference to Examples. Parts and% in the examples are based on weight unless otherwise specified. It was confirmed by elemental analysis that the modified product had an amino group.

(Synthesis Example 1) 50 parts of polyvinyl chloride resin (a) having an average degree of polymerization of 360 and an epoxy group content of 4%, obtained by copolymerizing vinyl chloride, vinylcyclohexene monooxide and vinyl acetate, and 50 parts of distearyl. When 6 parts of the amine was melt-kneaded in a plastomill having an internal volume of 60 cc at 130 ° C., the kneading torque of the plastomill began to rise after 30 minutes, so after 45 minutes, the contents were taken out to obtain a modified product (A). After unreacted distearylamine in the modified product was extracted and removed with methanol in a Soxhlet extractor, it was confirmed by elemental analysis that 10.4 parts of distearylamine were added per 100 parts of the resin.

(Synthesis Example 2) Polyvinyl chloride having an average degree of polymerization of 380 was obtained by post-chlorination,
Chlorinated polyvinyl chloride resin with a chlorine content of 68% at 160 ° C
After dehydrochlorination treatment in nitrogen stream, epoxidized with perbenzoic acid in benzene and the amount of epoxy groups was 3%
A chlorinated polyvinyl chloride resin (b) was obtained. 50 parts of this epoxidized chlorinated polyvinyl chloride resin and 4 parts of dilaurylamine were melt-kneaded in a 60 cc plastomill at 160 ° C. for 20 minutes to obtain a modified product (B). As a result of the analysis, the amine addition amount was 7.6 parts per 100 parts of the resin.

(Synthesis example 3) Acrylonitrile content is 30%, average molecular weight is 30,000
The acrylonitrile-butadiene rubber of was partially epoxidized with peracetic acid to obtain an epoxidized acrylonitrile-butadiene rubber having an epoxy group content of 8% (c), which contained 400 parts of this epoxidized rubber and 70 parts of distearylamine. The modified product (C) was obtained by heating and concentrating for 2 hours at 80 ° C. in the pressure kneader of product 1. As a result of analysis, the amount of amine added is rubber
It was 12.2 per 100 copies.

(Synthesis Example 4) An unsaturated polyester resin obtained by heat-condensing maleic anhydride, mixed phthalic acid, and 1,4-butanediol as raw materials was epoxidized with peracetic acid in toluene to have a molecular weight of 9,00.
0, an epoxidized polyester resin having an epoxy group content of 6% was obtained (d). The epoxidized polyester resin 40 and 6 parts of distearylamine were heated and mixed under high vacuum at 120 ° C. for 1 hour to obtain a modified product (D). Amine addition amount is resin
It was 12.5 parts per 100 parts.

(Synthesis Example 5) A modified product (A ') was obtained by the same experiment as in Synthesis Example 1 except that 6 parts of di-n-butylamine was used instead of 6 parts of distearylamine used in Synthesis Example 1. The addition amount of amine was 8.5 parts per 100 parts of the resin.

(Synthesis example 6) Synthesis example 3 except that the epoxy group content of the epoxidized acrylonitrile-butadiene rubber used in synthesis example 3 is 0.5%
The same experiment as above was carried out to obtain a modified product (E). As a result of the analysis, the amount of added amine was 3.2 parts per 100 parts of rubber.

(Preparation of magnetic paint) Magnetic paints were prepared according to Tables 1 and 2 using the amine-modified products obtained in Synthesis Examples 1 to 6. This is coated on a 20μ thick polyester film with a blade coater to a dry thickness of 5μ, magnetic field orientation is performed, and the glossiness of the coated surface is measured after drying. After carrying out a crosslinking treatment for 48 hours in an atmosphere of 65 ° C. and a relative humidity of 90%, it was cut into a 12.65 mm width to prepare a magnetic tape test piece.

Next, Table 3 shows the results of evaluating the characteristics of the obtained magnetic tape.
It was shown to. The evaluation method was as follows.

(1) Glossiness The reflectance at 60 ° reflection angle of the coating film before surface forming treatment was measured with a gloss meter.

(2) Crosslinking property A part of the sample was taken, and the degree of removal of the rubbing coating film was rubbed with absorbent cotton soaked with methyl ethyl ketone.

◯: No dropout or almost no dropout Δ: Slight dropout x: Large dropout (3) Orientation The sample was cut into 50 mm lengths and measured with a magnetic property measuring machine (Br / Bm).

(4) Durability A sample with a length of 50 cm is loaded on a rotating drum with abrasive paper attached.
100 g of them were brought into contact with each other, rotated at 150 rpm, and the degree of dirt adhering to the abrasive paper was visually observed and displayed in the following three stages.

○: No stain △: Slightly stain ×: Severe stain (5) Runability-1 The force generated between the sample and the rotating drum was measured by the U gauge in the atmosphere of 65 ° C and 80% relative humidity in the same manner as the durability evaluation. The running resistance was measured and displayed in the following three stages.

○: Small resistance △: Medium resistance ×: Large resistance (6) Runability-2 The sample is brought into contact with a hard chrome-plated mirror surface rotating drum, and the force generated between the drum and the sample is the same as in Runability-1. It was measured and displayed by the method.

(7) Bleed The sample was allowed to stand at 60 ° C. for 2 months, passed through a super calendar used for surface formation 10 times, and the degree of stain on the surface of the calender roll was visually observed and displayed in the following three stages.

○: No stain △: Slightly stain ×: Severe stain

Claims (1)

[Claims] 1. At least one epoxy group-containing resin or rubber selected from polyvinyl chloride resins having 1 to 8% by weight of epoxy groups, polyester resins and acrylonitrile-butadiene rubber, and an alkyl group having 9 to 18 carbon atoms. A magnetic recording medium comprising an amine-modified resin or rubber obtained by reacting a secondary amine having a group as a binder component.