JPH05182174A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve stability by using a vinyl polymers comprising 25-70wt.% acrylate unit having >8.5 homopolymer, SP, 20-55wt.% vinyl chloride unit, and 3-20wt.% acryl glycidylether unit as the principal agent of a binder resin. CONSTITUTION:If acrylate monomers having <8.5 homopolymer SP are used, a uniform coating film is not obtd. If the amt. of vinyl chloride unit exceeds 55%, solubility decreases, and if the vinyl chloride unit is <20%, mechanical properties of the coating film decrease. The weight proportion of acryl glycidylether unit is specified to 3-20wt.%, and if its amt. is too small, thermal stability is lost, and if it exceeds, coating film strength decreases. If the average polymn. degree of vinyl copolymers is too low, physical strength of the film decreases, and if the degree is too high, the viscosity of the coating material increases to decrease workability. The average polymn. degree is specified in a range from 200 to 800. Thereby, the binder shows excellent dispersibility for a ferromagnetic finer powder and good solubility as a medium for a coating material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel magnetic recording medium having excellent coating film characteristics and magnetic characteristics.

[0002]

2. Description of the Related Art Magnetic recording media such as magnetic tapes and magnetic cards are generally prepared by providing a coating film (magnetic layer) comprising a magnetic powder and a binder (synthetic resin) on the surface of a support such as a polyester film. ing. In recent years, magnetic powders have become finer and have higher coercive force in response to the demands for improvement of recording density and improvement of S / N and C / N ratio of magnetic recording media. Therefore, in order to form a smooth and highly filled magnetic layer to improve the performance as a magnetic recording medium, the dispersion performance of the binder is a crucial factor.

The material of such a ferromagnetic fine powder is transitioned from iron oxide to iron oxide in which cobalt ions are adsorbed or doped, and further, a ferromagnetic metal such as iron, nickel or cobalt, or these metals are used. Including alloys have come into use.

On the other hand, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, etc. are known as synthetic resin binders for improving the dispersibility of ferromagnetic powders. The molecule is -OH, -COOH, -S
_{O 3 M, -OSO 3 M,} -PO 3 M 2, -OPO 3 M
It is advantageous to disperse magnetic powder by having one or two or more hydrophilic functional groups such as ₂ , -N <, -CON <(where M is a hydrogen atom or an alkali metal). Is disclosed in.

However, even if these good binders are selected, the finer the particle size of the ferromagnetic powder for high density recording, the more difficult the dispersion becomes, and the kneading at the time of preparing the magnetic coating material. The dispersion process requires a long time. In this kneading and dispersion process, the ferromagnetic powder and the synthetic resin binder are subjected to high shearing force and exposed to harsh conditions for a long time, so the properties of the ferromagnetic powder may be impaired. In a product, especially in a vinyl chloride-based copolymer, hydrochloric acid produced by dehydrochlorination causes deterioration of the magnetic powder. Further, a copolymer having a high vinyl chloride unit content has a drawback in that it has a poor solubility in a solvent used when preparing a magnetic coating material, resulting in a high coating material viscosity. However, if the vinyl chloride units are reduced to solve these problems, the compatibility with the polyurethane elastomer added during the preparation of the coating composition is reduced.

[0006]

SUMMARY OF THE INVENTION From the above-mentioned circumstances, the present invention provides: It exhibits excellent dispersibility in ferromagnetic fine powder. 2. Excellent stability. 3. Good solubility in organic solvents used as paint media. 4. Excellent compatibility with polyurethane elastomers. We have developed a copolymer for binders that has the characteristics of
Thus, the present invention has been made to provide a new magnetic recording medium having excellent characteristics.

[0007]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that the SP value of homopolymer
It was found that a vinyl copolymer obtained by copolymerizing (meth) acrylic acid ester having a (solubility parameter) of 8.5 or more with vinyl chloride and allyl glycidyl ether has a possibility of solving problems as a binder, and further, The present invention has been completed by examining the ratio of each monomer unit and the like.

That is, the present invention provides a magnetic recording medium comprising a magnetic layer having ferromagnetic fine powder dispersed in a binder on a non-magnetic support, wherein the binder is a) the homopolymer has an SP value of 8 .5 or more (meta)
Acrylic ester unit 25-70% by weight b) Vinyl chloride unit
20 to 55% by weight c) Allyl glycidyl ether unit
A magnetic recording medium characterized by comprising a vinyl copolymer having an average degree of polymerization of 200 to 800 and comprising 3 to 20% by weight as a main component.

The present invention will be described in detail below. Examples of the (meth) acrylic acid ester monomer having a homopolymer SP value of 8.5 or more used in the present invention include methyl methacrylate, ethyl methacrylate, and n.
-Propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, benzyl methacrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, and other methacrylates, methyl acrylate, ethyl acrylate,
Examples thereof include acrylates such as n-propyl acrylate and n-butyl acrylate. The selection based on the SP value is based on the Chemical Society of Japan, revised 2nd edition, page 831 and Encyclopedia of Polymer Science and Engineering.
Second Edition Vol.1 p257〜258 (John Willy & Son)
This can be done based on the description in s).

Such a (meth) acrylic acid ester monomer may be used alone or in combination of two or more kinds, but the ratio of the (meth) acrylic acid ester unit in the vinyl copolymer is 25. If it is less than wt%, the solubility in the solvent during the preparation of the magnetic paint will decrease and the paint viscosity will increase.
The compatibility with the polyurethane elastomer is lowered to impair the uniformity of the magnetic film, and if it exceeds 70% by weight, the coating strength and blocking resistance are lowered. Therefore, the ratio of the (meth) acrylic acid ester unit is 25 in the vinyl copolymer.
To 70% by weight.

The SP value of the homopolymer is 8.5.
Even when a (meth) acrylic acid ester monomer that is less than the above is used, the coating viscosity is increased due to the decrease in the solubility of the vinyl copolymer in the solvent and the compatibility with the polyurethane elastomer is decreased, resulting in non-uniformity of the coating film. Will occur.

The vinyl chloride unit is 55 in the vinyl copolymer.
Solubility in an industrially advantageous solvent decreases when the content exceeds 10% by weight, and when the magnetic powder is mixed with an organic solvent solution of this copolymer, the viscosity of the coating increases, which makes application difficult. The thermal stability, aging resistance and discoloration resistance of this copolymer are reduced. If it is less than 20% by weight, the mechanical properties of the coating film formed are deteriorated and blocking is likely to occur.
Therefore, the proportion of vinyl chloride units in the vinyl copolymer is 20 to 55% by weight.

The weight ratio of the allyl glycidyl ether unit in the vinyl copolymer is in the range of 3 to 20% by weight, but if this amount is too small, dehydrochlorination during heating will be remarkable and thermal stability will be impaired. If too much, it becomes difficult to dissolve in various organic solvents used as a coating medium, or the strength of the coating film decreases.

The vinyl copolymer, which is the main component, may contain a monomer unit other than the above, if necessary, and examples of the radical-polymerizable monomer that can be used for that purpose include: Styrene, α-methylstyrene, acrylonitrile, vinyl acetate, vinyl propionate,
Examples thereof include (meth) acrylic acid, maleic anhydride, crotonic acid, and itaconic acid. These monomers can be used within a range of up to about 10% by weight unless the effects of the present invention are impaired.

If the average degree of polymerization of the vinyl copolymer composed of a combination of the above-mentioned monomers is too low, the physical strength of the magnetic coating is lowered such that the magnetic coating film becomes brittle, and conversely the average degree of polymerization is decreased. If it is too high, the viscosity of the coating material at a predetermined concentration becomes high, the workability becomes poor, and the handling becomes difficult. Therefore, the average degree of polymerization is set in the range of 200 to 800.

For the production of the vinyl copolymer, it is preferable to use a persulfate polymerization initiator, and examples thereof include potassium persulfate, sodium persulfate, ammonium persulfate and the like.
The amount of the polymerization initiator used is usually 0.1 with respect to the monomer.
~ 10.0 wt%, but the preferred range is 0.5 ~
It is 5.0% by weight. By using a copolymer having sulfate radicals derived from these polymerization initiators as the main component of the binder, the dispersion of the ferromagnetic fine powder is improved and the characteristics are improved.

This vinyl copolymer can be produced by a known emulsion polymerization method. It is economically advantageous to obtain a copolymer by a known salting-out method after the polymerization. Examples of the emulsifier include anionic emulsifiers such as alkyl or alkylallyl sulfate, alkyl or alkylallyl sulfonate, alkylallyl succinate, polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene carboxylic acid ester, etc. Examples of nonionic emulsifiers include At the time of polymerization, the above-mentioned monomers, polymerization initiator, emulsifier and the like may be added to the polymerization system all at once at the start of polymerization, or may be dividedly added during the polymerization. Polymerization is usually 35
It may be carried out at a temperature of -80 ° C with stirring. After polymerization, according to a known salting-out method, after adding an aqueous solution of an inorganic salt such as sodium sulfate or calcium chloride or adding a water-soluble organic solvent to agglomerate the particles, filtration, washing with water and drying do it.

When the above-mentioned copolymer is used as a binder resin in the production of a magnetic coating liquid, other resins may be used in an amount equal to or less than an equal amount, if necessary. Examples thereof include various polymers such as polyurethane, nitrocellulose, polyester resin, epoxy resin, polyamide resin, phenol resin, alkyd resin, polyvinyl butyral resin, and other polymers or copolymers.
Of these, polyurethane resin is particularly preferable.

In addition to this, it is desirable to use a polyisocyanate curing agent in combination, and as this curing agent, Coronate L [trade name of Nippon Polyurethane Industry Co., Ltd.] and Dismodur L (trade name of Bayer Co.) are used. ) And other trifunctional isocyanates, urethane prepolymers having isocyanate groups at both ends, and the like. In addition,
The amount of these curing agents used is preferably 5 to 40 parts by weight per 100 parts by weight of the binder resin, that is, the above vinyl copolymer or a combination thereof with the resins used in combination.

As the ferromagnetic powder used in the present invention,
γ-Fe ₂ O ₃ , Fe ₃ O ₄ and adsorbed or doped cobalt ions on these, CrO ₂ , and needle-like fine particles of metal or alloy containing Fe, Co, Fe-Co, Ni, etc. First, various other conventionally known magnetic powders are exemplified. The mixing ratio of the ferromagnetic fine powder and the binder resin is preferably 8 to 50 parts by weight of the binder resin per 100 parts by weight of the ferromagnetic fine powder.

In order to uniformly disperse the ferromagnetic fine powder and the binder resin, etc., a lubricant, an abrasive, an antistatic agent, a dispersion aid, an anticorrosive, etc., which have been conventionally used, are added. Furthermore, it is possible to use various organic solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and toluene as the coating medium in the same manner as in the past, and there is no particular limitation in these points. Further, as the dispersing means, a known method can be used.

As the support, synthetic resins such as polyester, polyolefin, cellulose acetate and polycarbonate, non-magnetic metals, ceramics and the like are used, and the form is used as a film, tape, sheet, plate or the like. As a coating means for forming the magnetic layer on the support, a conventionally known method may be used. By appropriately performing a smoothing treatment such as calendering treatment, a high-performance magnetic recording medium aimed at by the present invention can be obtained. can get.

[0023]

EXAMPLES Next, synthetic examples of vinyl copolymers and specific examples and comparative examples using a binder containing this copolymer will be given, but the present invention is limited to the scope of these examples. Not a thing. In addition, part and% in an example show a weight part and weight%, respectively.

Synthesis Example 1 (Synthesis of Polymer 1) A polymerization vessel equipped with a stirrer, a condenser, a thermometer and a nitrogen gas inlet was replaced with nitrogen, and then 870 parts of deionized water,
306 parts of methyl methacrylate, 160 parts of vinyl chloride,
55 parts allyl glycidyl ether, 1 potassium persulfate
3.6 parts, sodium carbonate 5.3 parts, and polyoxyethylene nonylphenyl ether 13.6 parts were charged, the temperature was raised to 55 ° C. with stirring to start the reaction, and vinyl chloride 1 was added.
60 parts was continuously added for 8 hours to carry out a polymerization reaction. After continuous addition, the reaction was further continued at 55 ° C. for 4 hours to complete the polymerization.

After the completion of the polymerization, 170 parts of sodium chloride, 5
% 68% hydrochloric acid and 1700 parts of hot deionized water were added to precipitate a polymer. The precipitated polymer is treated with deionized water 500
The washing-filtration operation was repeated 5 times at 0 part / time, and 510 parts of polymer 1 was obtained by drying. This polymer has 45% methyl methacrylate units and 5 vinyl chloride units.
0%, allyl glycidyl ether unit 5%, average degree of polymerization 380.

Synthetic Examples 2 to 8 (Synthesis of Polymers 2 to 8) In the same manner as in Synthetic Example 1, copolymerization was performed with the types and amounts of the monomers shown in Table 1, and salting out was carried out in the same manner as in Table 2. Polymers 2 to 8 having the respective compositions and degrees of polymerization as shown in (1) were obtained.

[0027]

[Table 1]

[0028]

[Table 2]

Synthesis Example 9 (Synthesis of Polymer 9) A polymerization vessel equipped with a stirrer, a condenser, a thermometer and a nitrogen gas inlet was charged with 750 parts of deionized water, 5 parts of potassium persulfate and 1.6 parts of sodium carbonate. , After nitrogen substitution 57
The temperature was raised to ° C. Meanwhile, 500 parts of deionized water in advance,
Methyl methacrylate 290 parts, n-butyl methacrylate 125 parts, hydroxyethyl methacrylate 25
Parts, 60 parts of allyl glycidyl ether, 10 parts of sodium lauryl sulfate, and 1.25 parts of n-dodecyl mercaptan were mixed and emulsified with a homomixer, and the mixture was uniformly added dropwise to the polymerization container under stirring for 9 hours. After further reacting at 57 ° C for 2 hours to complete the polymerization, methanol 500
And 10 parts of sodium sulfate were added to precipitate a polymer. The precipitated polymer was twice added with 5000 parts of methanol,
Then, wash 4 times with 5000 parts of deionized water, filter,
It was dried to obtain Polymer 9. This polymer had a methyl methacrylate unit of 60%, an n-butyl methacrylate unit of 25%, a hydroxyethyl methacrylate unit of 5%, an allyl glycidyl ether unit of 5%, and an average degree of polymerization of 320.

Synthesis Example 10 (Synthesis of Polymer 10) Polymer 10 was obtained in the same manner as in Synthesis Example 9 except that 400 parts of methyl methacrylate, 75 parts of ethyl acrylate, and 25 parts of hydroxyethyl vinyl ether were used as monomers for polymerization. .. This polymer had a methyl methacrylate unit of 80%, an ethyl acrylate unit of 15%, a hydroxyethyl vinyl ether unit of 5%, and an average degree of polymerization of 430.

Examples 1-5, Comparative Examples 1-5 The vinyl copolymers (Polymer 1
The thermal stability of 10 to 10), the solubility in a solvent, the compatibility with a polyurethane resin, and the dispersion stability are investigated, and a magnetic tape is prepared by using these vinyl copolymers. The characteristics were investigated. The results were as shown in Tables 3 and 4. In addition, the measurement of each characteristic was performed as follows.

A. Thermal stability of vinyl copolymer 1.0g of vinyl copolymer was placed in a 15ml test tube, the opening was plugged with absorbent cotton sandwiched with Congo red test paper, and placed in an oil bath at 150 ° C. The time until the color of the Congo red paper changed due to hydrochloric acid was measured.

B. Solubility of vinyl copolymer in solvent Vinyl copolymer 4 in 160 parts of mixed solvent of methyl ethyl ketone / methyl isobutyl ketone / toluene = 1/1/1
When 0 part was added and the mixture was stirred at 50 ° C. for 1 hour, the degree of dissolution was visually evaluated in four grades. ◎: Excellent ○: Good △: Acceptable ×: Impossible

C. Compatibility of vinyl copolymer with polyurethane resin 2 of vinyl copolymer using mixed solvent of methyl ethyl ketone / methyl isobutyl ketone / toluene = 1/1/1
100 parts of 0% solution and polyurethane resin (N-2304:
50 parts of the above) were mixed, stirred for 1 hour with a stirrer, and then coated and dried on a glass plate, and the compatibility was visually evaluated on a four-point scale from the presence or absence of surface coating and the degree of cloudiness. ◎: Excellent ○: Good △: Acceptable ×: Impossible

D. Dispersion stability Vinyl copolymer (polymer 1 to 10) 18 parts Metal iron magnetic powder (BET value 55 m ² / g) 100 parts Polyurethane resin (N-2304: trade name of Nippon Polyurethane Industry Co., Ltd.) 7 parts Methyl ethyl ketone / Methyl isobutyl ketone / toluene = 1/1/1 mixed solvent 225 parts After mixing and dispersing the above components with a sand grinder for 2 hours, the resulting mixture was put in a sample bottle and kept at 25 ° C for 48 hours.
After standing for a while, methyl ethyl ketone / methyl isobutyl ketone / toluene = 1/1/1 mixed solvent 225
Parts were added and stirred on a glass plate for 30 minutes with a lab mixer, and the dispersion stability was visually evaluated in four grades from the gel generation state. ◎: Excellent ○: Good △: Acceptable ×: Impossible

E. A 60-degree reflectance of the coated surface of the magnetic tape before calendering was compared with that of a standard glass plate using a gloss gloss meter (manufactured by Murakami Color Research Institute).

F. Residual magnetic flux density (Br) and square ratio It was measured using a vibration sample type magnetometer (manufactured by Toei Industry Co., Ltd.).

G. Durability The created magnetic tape was left in a constant temperature and humidity room at 65 ° C and a relative humidity of 90% for 168 hours, then a load of 100 g was applied, and the magnetic tape was brought into contact with a rotary drum to which it was attached at 2 rpm at 150 rpm.
It was rotated 000 times, and the degree to which the magnetic coating film adhered to the abrasive paper was visually evaluated in four levels. ⊚: No stain on the abrasive paper ○: Very slight stain △:
There is a little dirt x: A lot of dirt

The magnetic tape was prepared as follows. Liquid A Vinyl copolymer (polymer 1 to 10) 18 parts Metal magnetic powder 100 parts Polyurethane resin (N-2304: trade name of Nippon Polyurethane Industry Co., Ltd.) 7 parts Carbon black 5 parts Lecithin 2 parts Methyl ethyl ketone 75 parts Methyl isobutyl Ketone 75 parts Toluene 75 parts The above components were mixed with a lab mixer for 90 minutes and further kneaded with an Eiger mill containing glass beads for 3 hours to obtain a coating liquid A. Liquid B Liquid A 355 parts Polyisocyanate (Coronate L: above) 5 parts Methyl ethyl ketone / methyl isobutyl ketone = 1/1 mixed solvent 30 parts The above components are mixed and dispersed for 90 minutes with a lab mixer, and paint B
A liquid was obtained. On the polyester film, add the above paint B liquid 6
A magnetic tape was prepared by applying a coating having a thickness of μm, subjecting it to magnetic field orientation treatment and drying, and then subjecting it to surface treatment with a super calendar.

[0040]

[Table 3]

[0041]

[Table 4]

[0042]

According to the present invention, a novel magnetic recording medium having coating film properties and magnetic properties superior to those of conventional magnetic recording media is provided. This is because the vinyl copolymer used in the present invention has excellent dispersibility in ferromagnetic fine powder, excellent stability, good solubility in an organic solvent used as a coating medium, and compatibility with a polyurethane elastomer. It is due to the fact that it is superior to the conventional copolymers in that it also has various properties such as excellent properties.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeji Yanagisawa No. 1 Towada, Kamisu Town, Kashima-gun, Ibaraki Prefecture Shin-Etsu Chemical Co., Ltd.

Claims (2)

[Claims] 1. A magnetic recording medium comprising a magnetic layer having a ferromagnetic fine powder dispersed in a binder on a non-magnetic support, wherein the binder a) has a SP value of homopolymer of 8.5 or more. Is (meta)
Acrylic ester unit 25-70% by weight b) Vinyl chloride unit
20 to 55% by weight c) Allyl glycidyl ether unit
A magnetic recording medium comprising a vinyl copolymer having an average degree of polymerization of 200 to 800 of 3 to 20% by weight as a main component. 2. The magnetic recording medium according to claim 1, wherein the vinyl copolymer is obtained by polymerization in the presence of a persulfate polymerization initiator.