JPH06131650A - Production of binder for magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the adequate binder by producing the binder having high dispersibility in magnetic powder in such a manner that a large amt. of scale is not generated during polymn. at the time of forming the binder for magnetic recording media. CONSTITUTION:A vinyl chloride monomer and a hydroxyl groupcontg. vinyle monomer are subjected to aq. suspension polymn. in the presence of an oil soluble radical initiator. Namely, at least >=1 kinds among the reaction emulsifiers expressed by general formulas (I), (III) are used. In the formulas, R<1>, R<2> denote 1 to 22C alkyl group; R<3>, R<4> are H, Na, K; m and n are an integer from 1 to 30. More specifically, water, the reactive emulsifiers and the oil soluble radical initiator are supplied into a polymn. device and after the pressure in the device is reduced, the vinyl chloride monomer is forcibly fed into the polymn. device and heated while these materials are kept stirred. The temp. at the time of the suspension polymn. is preferably 40 to 85 deg.C and the polymn. time is specified to two to 20 hours. The unreacted vinyl chloride monomer is removed from the polymn. device after the end of the polymn. reaction. The polymer slurry is then taken out and is subjected to treatments, such as washing, dehydrating and drying, by which the granular vinyl chloride binder is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a binder for a vinyl chloride magnetic recording medium.

[0002]

2. Description of the Related Art Generally, a magnetic recording material used for a magnetic tape or a magnetic disk is prepared by applying a magnetic coating material containing a magnetic powder and a binder onto a base material and applying a magnetic field to orient the magnetic powder. The magnetic powder is prepared by forming a magnetic layer by heat-crosslinking and drying, but it is necessary to uniformly disperse the magnetic powder in the binder in order to obtain a magnetic recording material having excellent magnetic properties.

Conventionally, as the above-mentioned binder, vinyl chloride-
A vinyl acetate-polyvinyl alcohol copolymer and a vinyl chloride-2-hydroxypropyl acrylate copolymer (Japanese Patent Publication No. 52-50204) have been proposed.

However, recently, the magnetic powder tends to be atomized as the density of the magnetic recording medium is increased, and the above-mentioned binder has a problem that the atomized magnetic powder is not sufficiently dispersed. It was

Further, the above-mentioned binder is produced by a solution polymerization method or an emulsion polymerization method, but since the solvent polymerization method uses a large amount of a solvent such as methanol, ethyl acetate, toluene, etc., the cost becomes high and the safety is high. There was also a problem in terms of. In addition, the emulsion polymerization method requires complicated treatments such as salting out and filtration, and the obtained polymer has a problem that it is difficult to handle because it is an ultrafine powder. Therefore, the suspension polymerization method using water as a dispersion medium is preferable from the viewpoints of productivity and safety and the reason that the particle size of the obtained polymer is appropriate.

However, in the case of the suspension polymerization method,
Usually, a polymer dispersant such as partially saponified polyvinyl alcohol or a cellulose derivative is generally used as the dispersant. When these polymer dispersants are used, the particle surface of the polymer is a polymer dispersant. It was confirmed with a scanning transmission microscope that it was covered with a strong film mainly composed of. Such a film has a problem that the solubility is lowered when the polymer is dissolved in an organic solvent.

As a method for solving the above-mentioned problem of the film, it has been proposed to use an emulsifier instead of the polymer dispersant in the suspension polymerization method. However, the use of an emulsifier causes a large amount of scale to be generated during the polymerization and adheres to the inner wall surface of the polymerization vessel, which causes a problem that scale removal work is required.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and an object thereof is to provide a magnetic material having excellent solubility in an organic solvent and high dispersibility in magnetic powder. It is an object of the present invention to provide a method for producing a binder for a recording medium without producing a large amount of scale during polymerization.

[0009]

The method for producing a binder for a magnetic recording medium according to the present invention is an aqueous suspension polymerization of a vinyl chloride monomer and a hydroxyl group-containing vinyl monomer in the presence of an oil-soluble radical initiator. , At least one of the reactive emulsifiers represented by the general formulas (I) and (II) is used, whereby the above object is achieved.

The present invention will be described in detail below. The hydroxyl group-containing monomer used in the present invention is a vinyl monomer having a reactive double bond and a hydroxyl group, and examples thereof include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 2-hydroxybutyl ( (Meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 3-chloro-2-hydroxypropyl (meth) acrylate, 2-acryloyloxy Reaction products of (meth) acrylic acid such as ethyl-2-hydroxyphthalate and polyhydric alcohol; (meth) acrylic acid amides such as N-methylol (meth) acrylamide.

In the present invention, when the amount of the above-mentioned hydroxyl group-containing vinyl monomer added is small, the coating performance of the obtained binder decreases, and when it is large, the crosslinking performance becomes high and the coating becomes hard, and it is resistant to organic solvents. Since the solubility is lowered, 40 to 1 is added to 60 to 99 wt% of vinyl chloride monomer.
The amount is preferably 5% by weight, and more preferably 30 to 5% by weight based on 70 to 95% by weight of the vinyl chloride monomer.

In the present invention, in addition to the hydroxyl group-containing vinyl monomer, other monomer copolymerizable with the vinyl chloride monomer may be added. As the other monomer, any of those having a functional group and those not having a functional group can be used.

Among the above-mentioned other monomers, those not having a functional group include, for example, ethylene, propylene, 1
-Α-olefins such as hexene; vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as butyl vinyl ether, cetyl vinyl ether and phenyl vinyl ether; methyl (meth) acrylate,
(Meth) acrylic acid esters such as ethyl (meth) acrylate; aromatic vinyls such as styrene and α-methylstyrene; vinyl cyanides such as (meth) acrylonitrile; vinyl halides such as vinylidene chloride and vinyl fluoride And unsaturated dicarboxylic acid esters such as dimethyl maleate and dimethyl fumarate; unsaturated dicarboxylic acid anhydrides such as maleic anhydride; N-substituted maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide. it can.

Examples of the other monomer having a functional group include (meth) acrylic acid, succinic acid mono (meth) acryloyloxyethyl ester, phthalic acid mono (meth) acryloyloxyethyl ester,
Carboxyl group-containing monomers such as maleic acid n-butyl monoester, maleic acid and fumaric acid; 2-acrylamido-2-methylpropane sulfonic acid,
Sulfonic acid group- or sulfonate-containing monomers such as sodium methallyl sulfonate; (meth) acryloyloxyethyl acid phosphate, (meth) acryloyloxypropyl acid phosphate, (meth) acryloyloxypropyl-3-chloro-2-acid phosphate Phosphoric acid group-containing monomers such as; 3-methacryloyloxypropyl trimethyl ammonium chloride, methacryloyloxyethyl trimethyl ammonium chloride, quaternary ammonium chloride-containing monomers such as trimethyl-3-methacrylamido-propyl ammonium chloride; dimethylaminoethyl (meth) Acrylate, diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, t- Amino group-containing monomers such as chill aminoethyl (meth) acrylate.

The above-mentioned other monomers may be used alone or in combination of two or more kinds.

In the present invention, if the amount of addition of the above-mentioned other monomer increases, the physical properties of the copolymer of vinyl chloride monomer and hydroxyl group-containing vinyl monomer deteriorates. Therefore, when other monomer having a functional group is used, It is preferably 5% by weight or less in the above copolymer, and when other monomer having no functional group is used, it is 20 in the above copolymer.
It is preferably less than or equal to weight%.

The oil-soluble radical initiator used in the present invention is not particularly limited, and those used in the conventional polymerization of vinyl chloride resin can be used. For example, azobisisobutyro Azobis compounds such as nitrile and dimethylazobisvaleronitrile; lauroyl peroxide, benzoyl peroxide, di-t
-Butyl peroxide, di-t-butyl peroxy-
Examples thereof include organic peroxides such as 2-ethylhexanate, t-butylperoxyisobutyrate and di-2-ethylhexylperoxydicarbonate.

The above oil-soluble radical initiators may be used alone or in combination of two or more kinds.

In the present invention, the addition amount of the oil-soluble radical initiator is appropriately determined according to the polymerization conditions. When the addition amount is small, the yield of the copolymer decreases, and when it is large, the heat of reaction per unit time is reduced. Generally, the monomer used (vinyl chloride monomer, hydroxyl group-containing vinyl monomer, and others) will increase as the temperature rises beyond the heat removal capacity of the polymerization vessel and the temperature inside the reaction vessel rises, resulting in a dangerous state. 0.05 to 3 parts by weight, more preferably 0.1 to 100 parts by weight,
~ 3 parts by weight.

The reactive emulsifier used in the present invention is at least one of those represented by the general formulas (I) and (II).
It consists of more than one seed.

[0021]

[Chemical 3]

[0022]

[Chemical 4]

In the general formula, R ¹ and R ² are alkyl groups, and as the number of carbon atoms increases, the hydrophobicity increases, so that 1 to 22.
Limited to R ³ and R ⁴ are H, Na, K or NH ₄
Is. Further, when m and n are large, the emulsifying effect is lowered, so that it is limited to an integer of 1 to 30.

In the present invention, when the amount of the reactive emulsifier added is reduced, not only the dispersibility is reduced but also a large amount of scale is attached, and when the amount is increased, the particles of the copolymer become fine particles and the handling becomes difficult. The amount is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the monomer.

In the present invention, other emulsifiers may be used in combination with the above reactive emulsifiers, if necessary. As such emulsifiers, nonionic emulsifiers and anionic emulsifiers generally used in emulsion polymerization are preferable.

Examples of the nonionic emulsifiers include:
Polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene alkyl allyl ether, polyoxyethylene lauryl ether, polyoxyethylene alkylene alkyl ether, polyoxyethylene-polyoxypropylene block polymer, polyoxyethylene fatty acid ester, Examples thereof include sorbitan monolaurate, polyoxyethylene lanolin alcohol ether, polyoxyethylene lanolin fatty acid ester, polyoxyethylene alkylamine ether, and fatty acid diethanolamide.

Examples of the above-mentioned anionic emulsifiers include higher alcohol sulfate ester sodium, sodium alkylbenzene sulfonate, sodium β-naphthalene sulfonate, dialkyl sulfosuccinate sodium salt,
Examples thereof include polyoxyethylene alkyl ether phosphate ester and polyoxyethylene alkyl ether sulfate ester.

Of the above-mentioned emulsifiers, polypropylene oxide is the main component and has an HLB of 9 or less and a molecular weight of 1000.
The above nonionic type is more preferable. Examples of such nonionic emulsifiers include polypropylene oxide alkyl ether, polypropylene oxide alkyl ester, polypropylene oxide alkyl allyl ether, and propylene oxide polyethyleneimine block copolymer.

In the present invention, the scale tends to adhere when the amount of the emulsifier added is large. Therefore, the amount is preferably less than 100 parts by weight, more preferably less than 30 parts by weight, based on 100 parts by weight of the reactive emulsifier.

The suspension polymerization used in the present invention may be any method conventionally used for aqueous suspension polymerization of vinyl chloride monomers. For example, in a polymerization vessel, water,
Examples thereof include a method in which a reactive emulsifier, an oil-soluble radical initiator, and if necessary an emulsifier are supplied, the pressure is reduced, and then a vinyl chloride monomer is pressure-inserted while stirring and heating is performed. In the suspension polymerization, the hydroxyl group-containing monomer may be initially supplied together with water, or the vinyl chloride monomer may be dissolved in the hydroxyl group-containing monomer and then injected together with the vinyl chloride monomer.

When the polymerization rate of the hydroxyl group-containing monomer is higher than that of the vinyl chloride monomer in terms of the copolymerizability ratio with the vinyl chloride monomer, it is possible to add the monomers in a divided manner or continuously from the initial stage to the latter stage of the polymerization. It is preferable because a uniform copolymer can be obtained. Such an addition method is also preferably adopted when adding another monomer which can be copolymerized with the vinyl chloride monomer.

The temperature during the suspension polymerization is generally 40 to 85.
C. is preferred and the polymerization time is generally preferred from 2 to 20 hours. After the completion of the polymerization reaction, unreacted vinyl chloride monomer is removed from the polymerization vessel, and the polymer slurry is taken out, washed, dehydrated, dried, etc. to obtain a granular vinyl chloride-based binder. During suspension polymerization, a chain transfer agent such as mercaptoethanol may be used if necessary.

The obtained binder is used as a magnetic recording medium after being made into a magnetic coating material, coated on a substrate and dried.
Examples of the method for forming a magnetic coating include a method in which a binder dissolved in a solvent is uniformly kneaded and dispersed together with magnetic powder.

Examples of the base material include polyester resins such as polyethylene terephthalate and polyethylene naphthalate; polyolefin resins; cellulose derivatives;
Films or sheets of vinyl resins, polyimide resins, polyamide resins and the like, and non-magnetic metal foils of aluminum, copper and the like can be mentioned.

Examples of the magnetic powder include γ-iron oxide, Co-γ-iron oxide, iron oxide, chromium oxide and Co-N.
Known materials such as i-P alloy, Fe-Co-Ni alloy, and Co ferrite can be used.

Examples of the solvent include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl isobutyl ketone and cyclohexanone; esters such as methyl acetate, ethyl acetate and butyl acetate; glycols such as ether, glycol dimethyl ether and dioxane. Ethers; aromatic hydrocarbons such as benzene, toluene, xylene and the like, and one or two of these
More than one species are commonly used. Among these solvents, polar solvents such as ketones or solvents containing polar solvents are more preferable.

When a curing agent is used in the above magnetic paint,
Generally, a polyisocyanate compound is used. The polyisocyanate compound is selected from those generally used as a curing agent for polyurethane resins and the like.

If necessary, additives such as abrasives, lubricants, dispersants, antistatic agents, etc. may be added to the above magnetic paint according to known techniques.

[0039]

【Example】

(Examples 1 to 7 and Comparative Examples 1 to 5) 1) Preparation of Vinyl Chloride Copolymer A jacketed 25 liter pressure resistant polymerizer equipped with a stirrer was added to 133 parts by weight of ion-exchanged water and an oil-soluble radical initiator. 0.3 parts by weight of t-butylperoxy-2-ethylhexanate and a predetermined amount of reactive emulsifier shown in Table 1 [represented by the general formula (I)], an emulsifier and a polymer dispersant are supplied. After sealing and eliminating air, 65 parts by weight of vinyl chloride monomer was press-fitted. 35 parts by weight of vinyl chloride monomer, 2-hydroxypropyl acrylate 1
After 10% by weight of 0 parts by weight of the post-addition composition was injected under pressure, immediately after the temperature inside the polymerization reactor reached 74 ° C. while stirring, the rest of the post-addition composition was divided into 120 parts, and 2 Suspension polymerization was carried out by adding every minute. After 5 minutes from the completion of the addition of the post-addition composition, cooling was completed, and then unreacted vinyl chloride monomer was taken out, washed with ion-exchanged water and dried to obtain a vinyl chloride-based copolymer.

2) Measurement of Physical Properties of Vinyl Chloride Copolymer The vinyl chloride copolymer obtained in 1) was measured for the following items, and the results are shown in Table 1. (1) Degree of polymerization Measured according to JIS K6721. (2) Scale Adhesion Rate After the polymerization was completed, the copolymer slurry was taken out, the polymerization vessel was opened, the scale attached inside was taken out, dried and weighed. From this weight and the weight of the copolymer previously taken out as a slurry after drying, the scale adhesion rate was calculated by the following formula. Scale adhesion rate (%) = [(scale dry weight) / (slurry dry weight + scale dry weight)] × 100 (3) Vinyl chloride component The chlorine content was measured by the oxygen flask combustion method to determine the amount of vinyl chloride component. . (4) Hydroxyl group-containing vinyl component The amount of hydroxyl group-containing vinyl component was determined by a method using acetic anhydride and pyridine (Analysis Chemistry Handbook). (5) Number of insoluble foreign matters 1 g of a vinyl chloride-based copolymer was dissolved in 99 g of a mixed solvent of methyl ethyl ketone and toluene at a ratio of 1: 1 (weight ratio) to prepare a 1 wt% solution, and then a fine particle measuring device (“particles manufactured by Rion Co., Ltd.” Solution 10 using a counter KL-01 ")
The number of particles of insoluble foreign matter having a size of 20 μm or more in milliliters was measured and defined as the number of insoluble foreign matters.

3) Production of magnetic recording medium The vinyl chloride-based copolymer prepared in 1) was dissolved in a mixed solvent of toluene and methyl ethyl ketone in a ratio of 1: 1 (weight ratio) to prepare a 15% by weight copolymer solution. The Co-γ-iron oxide (BET value: 35 m ² ) 4 times as much as the total weight of the solution and the copolymer prepared and a stainless steel ball (1/8 inch) 20 times as much as the copolymer. A magnetic paint was prepared by mixing with the paint and dispersing for 4 hours with a paint conditioner. The magnetic coating material obtained was applied to a polyethylene terephthalate film having a thickness of 25 μm to give a magnetic flux density of 2000.
A magnetic field was applied with a strength of Gs to orient the magnetic powder and then dried to obtain a magnetic recording medium on which a magnetic layer having a thickness of 6 μm was formed.

4) Measurement of physical properties of magnetic recording medium The magnetic paint obtained in 3) was measured for the following items, and the results are shown in Table 1. (1) Gloss level Digital variable angle gloss meter ("VG-1" manufactured by Nippon Denshoku Industries Co., Ltd.)
G ”) was used to measure the glossiness at an incident angle and a reflection angle of 60 degrees. (2) Squareness ratio DC magnetization characteristic recording device ("T / 3256-" manufactured by Yokogawa Electric Corporation)
30 ").

[0043]

[Table 1]

(Examples 8 to 14 and Comparative Examples 6 to 10) A vinyl chloride copolymer and a magnetic material were prepared in the same manner as in Example 1 except that the reactive emulsifier represented by the general formula (II) was used. A recording medium was obtained. Physical properties of the vinyl chloride copolymer and the magnetic recording medium were measured in the same manner as in Example 1, and the results are shown in Table 2.

[0045]

[Table 2]

[0046]

The method for producing the binder for a magnetic recording material of the present invention is as described above, and when the vinyl chloride monomer, the hydroxyl group-containing monomer and the other monomer are copolymerized in the suspension polymerization method, Since it is polymerized using a reactive emulsifier, the scale generation in the polymerization vessel during polymerization is small, the obtained vinyl chloride-based copolymer is easily dissolved in an organic solvent, and the dispersibility of magnetic powder is Are better. Therefore, the obtained vinyl chloride-based copolymer is suitable for use as a binder for magnetic recording materials.

Continuation of the front page (51) Int.Cl. ⁵ Identification code Reference number within the agency FI Technical display location C09D 5/23 PQV 7211-4J 127/06 PFD 9166-4J // C08F 216/14 MKZ 6904-4J 299/02 MSR 7442-4J (C08F 214/06 212: 14 216: 14 220: 20)

Claims (1)

[Claims] 1. A reactive emulsifier represented by the general formula (I) or (II) for aqueous suspension polymerization of a vinyl chloride monomer and a hydroxyl group-containing vinyl monomer in the presence of an oil-soluble radical initiator. A method for producing a binder for a magnetic recording medium, which comprises using at least one kind. [Chemical 1] [Chemical 2] [In the general formula, R ¹ and R ² are alkyl groups having 1 to 22 carbon atoms, R ³ and R ⁴ are H, Na, K or NH ₄ , m and n.
Represents an integer of 1 to 30, respectively. ]