JPH0689057B2 - Method for producing vinyl chloride resin - Google Patents

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 vinyl chloride resin, particularly a vinyl chloride resin which is suitably used as a binder for a magnetic recording medium and can be crosslinked and cured by electron beam irradiation.

[0002]

2. Description of the Related Art Magnetic recording media such as magnetic tapes and magnetic cards are usually manufactured by applying a magnetic coating material containing a magnetic powder and a binder thereof as a magnetic layer on a substrate such as a polyester film. In recent years, in order to increase the coercive force and the maximum saturation magnetization amount and to improve the SN ratio and the recording density, fine magnetic powder having a large specific surface area has been used as the above magnetic powder. However, fine magnetic powders are usually used binders such as vinyl chloride-vinyl acetate-vinyl alcohol terpolymer, vinyl chloride-vinyl acetate-maleic acid terpolymer and nitrocellulose. In addition, there is a drawback that the dispersibility is still insufficient because the viscosity of the paint increases. In addition, a low molecular weight surfactant is used as a dispersant for improving dispersibility, but if a large amount of these dispersants is used,
Since the durability of the magnetic recording medium is deteriorated and the head is stained, the amount of the surfactant used is naturally limited.
On the other hand, in order to improve the durability, running characteristics and reliability of the magnetic recording medium, a thermosetting cross-linking agent typified by a polyisocyanate compound is used together with a flexible material such as polyurethane resin, polyester resin, acrylonitrile-butadiene rubber. Hydroxyl group in the binder added to the magnetic paint
Crosslinking the magnetic layer into a coating film by a chemical reaction with a group having active hydrogen such as a carboxyl group or an amino group is generally performed especially in a magnetic recording medium for recording. However, such a thermosetting binder basically causes the curing reaction to start at the moment when the crosslinking agent is added, which causes a problem of the pot life of the coating material. Further, the curing speed varies depending on the material in the magnetic coating material and the environment, and its control is difficult, which causes problems such as storage stability of the coating material and variation in the effect of surface treatment of the coating film. Furthermore, complete curing requires a long time, and during curing and aging, the surface roughness of the surface of the base material that is in contact with the coating surface is easily transferred, which is an important characteristic for high-density recording media. It is easy to cause deterioration of sex. In view of the above points, the thermosetting binder has hitherto been limited in the conventional resin in order to cope with extremely high density recording of the magnetic recording medium and stabilization, rationalization and automation of the production process.

[0003]

DISCLOSURE OF THE INVENTION The inventors of the present invention have earnestly studied to develop a binder resin capable of improving the performance of such a magnetic recording medium and rationalizing and stabilizing the production process. The copolymer retains high dispersibility, can prevent thickening, and is suitable as a magnetic paint that is instantly crosslinked and cured by an electron beam, and a magnetic recording medium obtained by using the paint is a coating film. It was found that the surface smoothness and the durability of the product are good, and the running property, the magnetic property, and the electromagnetic conversion property are excellent, and the manufacturing method of the present invention was completed in order to achieve this object.

[0004]

That is, the present invention provides the substituents COOM, SO ₃ M, SO ₄ M, PO ₃ M ₂ and PO ₄
A vinyl chloride polymer having at least one hydrophilic group and an epoxy group selected from M ₂ (M is hydrogen, alkali metal or ammonium), and acryloyl having an acid strength of 3.5 or less represented by PKa. A double bond equivalent of an acryloyl group or a methacryloyl group by reacting a monobasic acid having a group or a methacryloyl group,
The method for producing a vinyl chloride resin is characterized by introducing an amount of 500 to 10,000. The manufacturing method of the present invention includes COOM, SO ₃ M, SO ₄ M,
A vinyl chloride polymer having at least one hydrophilic group and an epoxy group selected from PO ₃ M ₂ and PO ₄ M ₂ ,
A vinyl chloride resin is obtained by reacting a monobasic acid having an acryloyl group or a methacryloyl group having an acid strength represented by PKa of 3.5 or less. Further, COOM, SO ₃ M, S used as raw materials in the production method of the present invention
The vinyl chloride polymer having at least one hydrophilic group selected from O ₄ M, PO ₃ M ₂ and PO ₄ M ₂ and an epoxy group is the following methods (1) to (3) or a combination thereof. Can be manufactured. (1) A method in which a radical-polymerizable monomer having a corresponding hydrophilic group and a monomer having an epoxy group are obtained by copolymerizing a vinyl chloride monomer and, if desired, vinyl chloride with another monomer. (2) A monomer mixture containing an epoxy group-containing monomer, a vinyl chloride monomer, and optionally another copolymerizable monomer is used as a radical generator having the above-mentioned specific hydrophilic group. Method of copolymerization using. (3) Epoxy group-containing vinyl chloride-based polymer or vinyl chloride-based polymer obtained by copolymerizing a monomer having an epoxy group, a vinyl chloride monomer and another monomer used as necessary Is dehydrochlorinated and then epoxidized with an epoxidizing agent such as percarboxylic acid to partially add the epoxy group-containing vinyl chloride polymer with the compound having the specific hydrophilic group.

Examples of the epoxy group-containing monomer commonly used in the production of vinyl chloride-based polymers having both a hydrophilic group and an epoxy group used as raw materials in the present invention include allyl glycidyl ether and meta. Unsaturated glycidyl ethers of unsaturated alcohols such as lyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, glycidyl-p-vinyl benzoate, methyl glycidyl itaconate, glycidyl ethyl malate, glycidyl vinyl sulfonate, glycidyl (meth) allyl sulfonate, etc. Glycidyl esters of acids,
Examples thereof include epoxide olefins such as butadiene monooxide, vinylcyclohexene monooxide, and 2-methyl-5,6-epoxyhexene. Among the production methods of the vinyl chloride polymer which is the raw material of the production method of the present invention, examples of the monomer having a hydrophilic group in the above method (1) include COOM in the example of COOM such as acrylic acid and methacrylic acid. Examples thereof include unsaturated monocarboxylic acids, unsaturated dicarboxylic acids such as fumaric acid and itaconic acid, and monoesters thereof. Examples of SO ₃ M include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, ethyl (meth) acrylic acid-2-sulfonate, 2-acrylamido-2-methylpropane sulfonic acid. , Acids such as 3-allyloxy-2-hydroxypropanesulfonic acid, and alkali metal salts and ammonium salts of these acids. Examples of SO ₄ M include (meth) acrylic acid-2-ethyl sulfate, 3-
There are acids such as allyloxy-2-hydroxypropanesulfate, and alkali metal salts or ammonium salts of these acids. Examples of PO ₄ M ₂ include acids such as (meth) acrylic acid-3-propyl-2-chloro-2-phosphate, ethyl (meth) acrylate-2-phosphate, and 3-allyloxy-2-hydroxypropanephosphoric acid. , And these acid alkali metal salts or ammonium salts. PO ₃ M ₂
Examples of the acid include vinylphosphonic acid, acrylamidomethanephosphonic acid, ethyl 2-phosphonate- (meth) acrylate, and 3-allyloxy-2-hydroxypropanephosphonic acid, and alkali metal salts or ammonium salts of these acids. Is mentioned. Examples of the radical generator having a hydrophilic group in the above method (2) include:
COOM includes 4,4′-azobis-4-cyanovaleric acid and the like, SO ₄ M includes potassium persulfate and ammonium persulfate, and PO ₄ M _{2 includes} potassium perphosphate and sodium perphosphate.

Furthermore, in the method (3), an example of a compound used for introducing a hydrophilic group into a resin by polymer-reacting with a copolymer of a monomer having an epoxy group and vinyl chloride As for COOM, malonic acid,
Phthalic acid and the like are SO ₃ M, sodium sulfite, ammonium sulfite, sodium bisulfite, potassium bisulfite, ammonium thiosulfate, sodium aminoethanesulfonate, sodium sulfanilate, sodium sulfamate, and the like, and SO ₄ M is bisulfite. sodium, ammonium bisulfate and 2-aminoethyl sodium sulfate, the PO ₃ M _2, sodium hydrogen phosphite,
Examples of ammonium hydrogen phosphite include PO ₄ M ₂ , and dipotassium hydrogen phosphate and disodium hydrogen phosphate. Further, examples of the monomer other than the monomer having an epoxy group, the vinyl chloride and the monomer having a hydrophilic group, which is used as necessary, include vinyl acetate and vinyl propionate. Acid vinyl ester; vinyl ether such as methyl vinyl ether, isobutyl vinyl ether and cetyl vinyl ether; vinylidene such as vinylidene chloride and vinylidene fluoride; diethyl maleate, butylbenzyl maleate, di-2-hydroxyethyl maleate, dimethyl itaconate,
Unsaturated carboxylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, lauryl (meth) acrylate, and 2-hydroxypropyl (meth) acrylate; olefins such as ethylene and propylene; (meth) acrylonitrile Unsaturated nitriles such as styrene; aromatic vinyl such as styrene, α-methylstyrene, p-methylstyrene, and the like. These monomers are for the purpose of improving the solubility of the resin while adjusting 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 process. Is appropriately selected according to the need for improvement of The copolymerization of a monomer having an epoxy group and a vinyl chloride monomer, or the copolymerization of a monomer having an epoxy group, a monomer having a hydrophilic group and a vinyl chloride monomer is Known ordinary polymerization methods can be used, including the case of further copolymerizing the monomers. In addition, a partial polymer reaction between a copolymer of a monomer having an epoxy group, vinyl chloride, and another monomer used as necessary, and a compound having a hydrophilic group is also a property of a raw material or Known methods can be widely used due to process convenience such as product separation.

COOM and SO ₃ obtained as described above
A vinyl chloride polymer having at least one hydrophilic group selected from M, SO ₄ M, PO ₃ M ₂ and PO ₄ M ₂ and an epoxy group has 0.5% by weight or more of an epoxy group. Need to be. If the amount is less than 0.5% by weight, the amount of the acryloyl group or methacryloyl group bonded to the resin due to the reaction with the monobasic acid having an acryloyl group or methacryloyl group is small, and the crosslinking reaction by electron beam is likely to be insufficient, resulting in insufficient irradiation after electron beam irradiation The durability of the magnetic layer is insufficient. Further, the monobasic acid having an acryloyl group or a methacryloyl group, which is reacted with a vinyl chloride polymer having a hydrophilic group and an epoxy group, has an acid strength of PKa of 3.
It must be a strong acid of 5 or less. With a weak acid having a PKa of more than 3.5, the addition reaction with the epoxy group is difficult to proceed under mild conditions, so that it is necessary to use a higher temperature for a longer time or to use a quaternary ammonium salt together. However, since vinyl chloride-based polymers are susceptible to dehydrochlorination due to heat, the dehydrochlorination of the polymer and the addition reaction of hydrogen chloride to the epoxy group precede the targeted acryloyl modification reaction, and the target modified product is In addition to being effectively obtained, the vinyl chloride polymer is deteriorated during the reaction, and the thermal stability of the produced resin is significantly lowered. The monobasic acid having an acryloyl group or methacryloyl group and having a PKa of 3.5 or less used in the present invention is defined to include those in which the hydrogen atom of the group is substituted with another element. As a specific example, halogen-substituted (meth) acrylic acids such as chloroacrylic acid, (meth) 2
-Acrylamido-2-methylpropanesulfonic acid,
Sulfonic acid-containing (meth) acrylates such as ethyl (meth) acrylate-2-sulfonate, sulfuric acid-containing (meth) acrylates such as ethyl (meth) acrylate-2-ethyl sulfate, di-2- (meth) acrylate Examples include phosphoric acid-containing di (meth) acrylates such as roxyethyl acid phosphate. The reaction of the vinyl chloride-based polymer containing a hydrophilic group and an epoxy group in the present invention with a monobasic acid having a PKa of 3.5 or less is carried out at room temperature to 80 ° C. in a solvent in which both are dissolved. It progresses easily under mild conditions. Alternatively, the vinyl chloride polymer can be reacted in the form of an aqueous dispersion. Further, as long as the monobasic acid can be dissolved in the polymer, it is also possible to directly knead the both on a Banbury roll or a roll to react them. In any case, it is desirable that the amount of the monobasic acid used be equal to or less than the equimolar amount of the epoxy group in the vinyl chloride polymer. If you use too much,
The unreacted monobasic acid remains not only increases the hygroscopicity of the produced resin and the risk of developing metal corrosiveness, but also increases the hydrophilic group and epoxy group in the vinyl chloride polymer. There is a risk of inducing the reaction and causing the produced resin to become insoluble. During the reaction, a polymerization inhibitor such as hydroquinone, hydroquinone monomethyl ether or t-butyl catechol is added within a common sense.

The resin of the present invention thus obtained is
Average degree of polymerization is 100-900, preferably 200-50
0, the content of vinyl chloride is 60% by weight or more. If the degree of polymerization is less than 100, the abrasion resistance of the magnetic layer will be insufficient no matter how electron beam crosslinking is carried out, and if it exceeds 900, the viscosity of the coating will be high and the dispersion of the magnetic powder will tend to be insufficient. When the vinyl chloride content is less than 60% by weight,
The compatibility with the flexible material is reduced, and the solvent separation of the coating film is significantly reduced, which causes inconvenience. The amount of the hydrophilic group bonded to the resin is -COO _2, -SO _3, -SO
It is necessary that the content of ₄ , -PO ₄ and -PO ₃ be 0.1 to 4.0% by weight. When the amount of the hydrophilic group is less than 0.1% by weight, the dispersibility of the magnetic powder is insufficient, and when it exceeds 4.0% by weight, the hydrophilicity of the resin becomes strong and the solubility in the solvent becomes insufficient. However, the moisture resistance of the coating film decreases, and the magnetic powder agglomerates to rather deteriorate the dispersibility. Due to the reaction with the monobasic acid, vic
An electron beam curable double bond in the form of a glycol monoester is introduced, which also enables crosslinking with an isocyanate compound together with the chlorohydrin formed during the reaction.
The amount of double bonds contributing to electron beam curing needs to be 500 to 10,000 as double bond equivalent.
When the double bond equivalent is less than 10,000, the running property and durability of the magnetic layer after electron beam irradiation are insufficient. If it is less than 500, the resin surface becomes too hard due to the electron beam curing reaction. In the present invention, the double bond equivalent is represented by the molecular weight of the polymer per double bond in the polymer chain. The resin obtained by the production method of the present invention constitutes a binder system together with a flexible material such as a polyurethane resin, a polyester resin, and an acrylonitrile-butadiene copolymer, in the same manner as a usual vinyl chloride resin binder for magnetic paints. In addition, some or all of these flexible materials are replaced with other resins, oligomers or monomers having one or more electron beam-reactive unsaturated bonds, and magnetic powder, and if necessary, lubricant, It is mixed with a known material such as a dispersant, an antistatic agent, and an abrasive, and used as an arbitrary solvent dispersion. Further, if necessary, together with the resin of the present invention, vinyl chloride-vinyl acetate-maleic acid copolymer resin, vinyl chloride-vinyl alcohol-vinyl acetate copolymer resin, fiber resin,
Ordinary resin binders for magnetic paints such as phenoxy resin, amino resin, epoxy resin, butyral resin and acrylic resin can be used together within the range where the object of the present invention is achieved. The magnetic powder to be dispersed in the vinyl chloride resin obtained by the production method of the present invention includes metallic magnetic powder such as Fe powder and Co powder, γ-Fe ₂ O ₃ , and Fe.
₃ O ₄ , Co-containing γ-Fe ₂ O ₃ , Co-containing Fe ₂ O ₄ , iron oxide powder such as barium ferrite, and CrO ₂ powder can be used. The active energy ray used for crosslinking the magnetic coating film using the resin of the production method of the present invention,
An electron beam from an electron beam accelerator is used because of the control of absorbed dose and the ease of introduction into the manufacturing process line. The electron beam used for curing the magnetic coating film has an accelerating voltage of 100 to 750 KV, preferably 150 to 300, from the viewpoint of penetrating power.
Irradiation can be performed using an electron beam accelerator of KV so that the absorbed dose becomes 0.5-20 megarads.

[0009]

EXAMPLES The present invention will be specifically described below with reference to examples. The vinyl chloride content was determined by quantification of chlorine content by combustion, the double bond content was determined by titration, the epoxy group content was determined by titration, and the hydrophilic group content was determined by combined elemental analysis, titration and infrared absorption analysis. It was (Example of Resin Synthesis) Example 1 Epoxy groups are converted into 4 by emulsion polymerization of allyl glycidyl ether and vinyl chloride with potassium persulfate.
% By weight, SO ₄ group is 0.5% by weight, vinyl chloride unit is 82%
A weight percent vinyl chloride copolymer was obtained. This copolymer 1
Dissolve 00 parts by weight, 7 parts by weight of 2-acrylamido-2-methylpropane sulfonic acid (PKa20) and 0.01 parts by weight of hydroquinone monoethyl ether in 200 parts by weight of dimethylformamide, and stir and mix at 65 ° C. for 3 hours. After that, the reaction solution was dropped into a large amount of water, the resin was recovered, and the resin was thoroughly washed by washing with water and hot water under strong agitation to thoroughly wash the resin, and then dried to obtain a resin A. Example 2 A resin B was obtained in the same manner as in Example 1 except that α-chloroacrylic acid (PKa2.5) was used instead of 2-acrylamido-2-methylpropanesulfonic acid. Example 3 Glycidyl methacrylate, sodium styrene sulfonate, vinyl acetate and vinyl chloride are polymerized with azobisisobutyronitrile in methanol to give an epoxy group content of 3% by weight and an SO ₃ group content of 0.5% by weight. A vinyl chloride copolymer having a vinyl chloride unit content of 72% by weight was obtained.
100 parts by weight of this copolymer and 10 parts by weight of di-2-acryloxyethyl-acid phosphate (PKa2.3) were mixed in a high speed mixer with 0.015 parts by weight of hydroquinone monomethyl ether, and then mixed at 90 ° C. A sheet-like material obtained by kneading with a kneading roll for 10 minutes was crushed with water in a high-speed stirrer, washed with hot water repeatedly, and then dried to obtain a resin C. Example 4 Butadiene monooxide, glycidyl methacrylate,
The copolymer obtained by suspension polymerization of vinyl acetate and vinyl chloride with lauroyl peroxide is carboxy-modified with malonic acid to give 3.5% by weight of epoxy groups, 0.9% by weight of COO groups, and vinyl chloride units. To obtain 78% by weight of vinyl chloride copolymer. A resin D was obtained by the same operation as in Example 1 using 100 parts by weight of this resin.

Comparative Example 1 Resin E was obtained in the same manner as in Example 1 except that acrylic acid (PKa4.2) was used instead of 2-acrylamido-2-methylpropanesulfonic acid. Comparative Example 2 A vinyl chloride copolymer containing an epoxy group was prepared in the same manner as in Example 3 without using sodium styrenesulfonate. The amount of the epoxy group was 3.7% by weight and the vinyl chloride was 7%.
It was 7% by weight. Using this copolymer, a resin F was obtained in the same manner as in Example 3. Comparative Example 3 A vinyl chloride copolymer containing an epoxy group was prepared in the same manner as in Example 3 while reducing the amount of glycidyl methacrylate used. The epoxy group was 0.4% by weight and the SO ₃ group was 0.5% by weight. The vinyl chloride unit was 84% by weight. This copolymer was treated in the same manner as in Example 3 to obtain Resin G. Comparative Example 4 100 parts by weight of a commercially available vinyl chloride-vinyl acetate-vinyl alcohol terpolymer, 150 parts by weight of toluene and 80 parts by weight of cyclohexanone were charged into a 3 L four-necked flask and dissolved by heating. After heating to 80 ° C. Add 2-hydroxyethyl methacrylate adduct of tolylene diisocyanate to 8
In addition to 0.005 parts by weight of tin octoate,
0.0015 parts by weight of hydroquinone was added, and the mixture was reacted at 80 ° C. in an N ₂ gas stream until the NCO reaction rate was 90% or more.
After completion of the reaction, the mixture was cooled, and 100 parts by weight of methyl ethyl ketone was added to dilute to obtain a resin solution H. The properties of these resins are shown in Table 1 together with commercially available vinyl chloride-vinyl acetate-maleic acid terpolymer (I) and vinyl chloride-vinyl acetate-vinyl alcohol terpolymer (J). (Evaluation of Resin Properties) Next, each resin was evaluated by the following test methods for magnetic paints and magnetic recording media, and the results are shown in Table 1.

[0011]

[Table 1]

[0012]

[Table 2]

1) Solubility 100 parts by weight of vinyl chloride resin, 20 methyl ethyl ketone
A solution consisting of 0 parts by weight and 200 parts by weight of toluene was prepared, and the degree of transparency of this solution was visually inspected and judged by three grades of ◯ Δx. 2) Thermal stability 1.0 g of vinyl chloride resin is placed in a 15 ml test tube, the opening is capped with absorbent cotton sandwiched with Congo red test paper, and placed in an oil bath at 150 ° C. The time until the red test paper changed color was measured. 3) Dispersion stability A mixture of 400 parts by weight of metallic iron magnetic powder, 100 parts by weight of vinyl chloride resin, 300 parts by weight of methyl ethyl ketone, 300 parts by weight of methyl isobutyl ketone, and 300 parts by weight of toluene was subjected to high speed shear dispersion for 90 minutes. The dispersion paint was sampled in a sample bottle and stored in a thermostat at 25 ° C. to observe the gel generation state. Whether or not the gel was generated was determined by taking out a part of the dispersion paint on a glass plate, diluting it with about 5 times the amount of methyl ethyl ketone, mixing it with a glass rod, and visually observing. The order of less gel generation is indicated by ○ △ ×. 4) Gloss 400 parts by weight of magnetic iron oxide powder coated with cobalt, 70 parts by weight of vinyl chloride resin, 30 parts by weight of polyurethane resin [Nitporan 2304 manufactured by Nippon Polyurethane Industry Co., Ltd.], 300 parts by weight of methyl ethyl ketone, 300 parts of methyl isobutyl ketone.
A mixture of 1 part by weight, 300 parts by weight of toluene, and 2 parts by weight of silicone oil was subjected to high-speed shear dispersion for 90 minutes, and the resulting magnetic paint was applied onto a polyester film to give a film thickness of 5 μm.
It was applied so that the coating film had a thickness of m, was subjected to magnetic field orientation treatment, and was then dried. The reflectance at 60 ° C. reflection angle of the magnetic coating film was measured using a gloss meter. However, for resin J, after 90 minutes of dispersion and mixing, 20 parts by weight of polyisocyanate [Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.] was added, and the mixture was further mixed and dispersed for 10 minutes, and the same test was performed as a magnetic paint. 5) Pot life The magnetic coating used for gloss evaluation was passed through a calendar roll at a normal linear pressure of 1/2, and the reflectance at a reflection angle of 60 ° C. was measured using a gloss meter, followed by 23 weeks for another week. The coating film left under the conditions of ° C and 50% relative humidity was subjected to calendering treatment under the same conditions as above to measure gloss, and the pot life was judged from the difference. 6) Squareness Ratio (Br / Bm) The magnetic coating film used for evaluation of glossiness was cut out into 125 mm × 50 mm and measured by a magnetic property measuring machine. 7) Durability and cross-linking property The magnetic coating film used for glossiness evaluation was smoothed with a calendar roll, and then using an ESI electron curtain type electron beam accelerator, accelerating voltage of 168 KV and irradiation dose of 10 M.
After irradiating electron beam in N ₃ atmosphere under rad condition to cure the coating film, load 100 g, contact the rotary drum with abrasive paper and rotate at 150 rpm, magnetic paint adheres to abrasive paper The degree to which it was done was visually inspected, and it was judged in three grades of ◯ Δ ×. Further, a part of the cured coating film was taken and rubbed with absorbent cotton soaked with methyl ethyl ketone to determine the degree of falling of the coating film in three grades of ◯ Δ ×. However, for the coating film using resin J, instead of electron beam irradiation, 65 ° C. at 65 ° C.
Heat treatment was performed for an hour. 8) Running property The force generated between the coating film and the rotary drum was measured with a U gauge in an atmosphere of 65 ° C and 80% relative humidity in the same manner as in the durability evaluation, and the running resistance was reduced in three steps of ○ △ ×. It was judged.

[0014]

INDUSTRIAL APPLICABILITY The vinyl chloride resin produced by the production method of the present invention is used as a magnetic coating resin, because it has very good dispersibility of the magnetic material, excellent surface smoothness and durability, and is used as a magnetic recording medium. In this case, there is an advantage that the running property, magnetic property, and electromagnetic conversion property are excellent.

Claims (1)

[Claims] 1. Substituents COOM, SO ₃ M, SO ₄ M, PO
_A vinyl chloride polymer having at least one hydrophilic group selected from ₃ M ₂ and PO ₄ M ₂ (M is hydrogen, an alkali metal or ammonium) and an epoxy group has an acid strength of PKa. Vinyl chloride characterized by introducing an acryloyl group or a methacryloyl group in an amount of 500 to 10,000 as a double bond equivalent by reacting a monobasic acid having an acryloyl group or a methacryloyl group of 3.5 or less. Method for producing a base resin.