JPH0363123B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a magnetic recording medium, and in particular an improvement using a special ternary copolymer mainly composed of vinyl chloride, which exhibits excellent performance as a binder for ferromagnetic powder. The present invention relates to magnetic recording media. (Prior Art) Magnetic recording media are generally made by applying magnetic powder to the surface of a support such as polyester using a binder such as synthetic resin. Examples of magnetic powders include γ-Fe ₂ O ₃ , Fe ₃ O ₄ and those obtained by adsorbing or doping cobalt ions, or Cr ₂ O, as well as Fe, Co, Fe, etc.
-Acicular fine particles containing Co or Ni in some cases are used, but in recent years household use
With the spread of VTRs and the improved performance of audio cassette tapes, high signal density and high playback output for short wavelength recording are required. In order to cope with these trends, magnetic powder has become finer than ever before, and has an extremely large magnetic moment, which causes the particles to coagulate with each other, making it possible to disperse them more uniformly in the binder resin than before. It's becoming difficult. To solve this technical problem, from the viewpoint of improving the affinity of the binder resin for magnetic powder, it is necessary to impart to the binder resin the hydrophilic properties of the particle surface of metal oxide and alloy fine particles, which are magnetic fine particles. It is being widely studied. For example, hydrophilic functional groups such as carboxyl groups and hydroxyl groups have been introduced into the vinyl chloride-vinyl acetate copolymer, which has been used practically as a binder. , No. 4 (1981), pp. 155-162, "Magnetic Tape and Polymers," contains a research report on introducing various hydrophilic functional groups into polymeric materials used as binders for magnetic paints. According to this document, the types of anchor segments in the binder and the order of functional group effects are described as follows. JP-A No. 58-108032 also describes the introduction of sulfonic acid groups into binder resins. , vinylsulfonic acid, vinylbenzenesulfonic acid, 2-acrylamide-2-
It has been disclosed that a polymer obtained by copolymerizing a polymerizable unsaturated sulfonic acid such as methylpropanesulfonic acid is used as a binder for magnetic powder. However, although the introduction of sulfonic acid groups does have an excellent effect on improving the dispersibility of magnetic powder when examined, for example, in the case of vinyl chloride-vinyl fatty acid copolymers, the introduction of sulfonic acid groups is still effective in improving the dispersibility of magnetic powders. It appears to be insufficient, and also has the disadvantage that the amount of saturation magnetization decreases significantly over time. Note that the introduction of carboxyl groups or hydroxyl groups has a small effect on improving dispersibility, and the purpose is not achieved. On the other hand, for copolymers into which vinyl alcohol units have been introduced, such as vinyl chloride-vinyl acetate-vinyl alcohol copolymers, -SO ₃ M, -COOM, -OSO ₃ M, etc. are added for the purpose of improving the dispersibility of the OH groups. It has been proposed to use a polymer formed by introducing a hydrophilic group containing a group (M is a metal atom) as a binder resin for magnetic powder. However, this binder resin is manufactured through a complicated three-step reaction process: copolymerization of vinyl chloride and vinyl acetate, saponification of the copolymer, and sulfonation of the saponified product, so it is not suitable for industrial use. Not only is the cost high, but because each molecule contains an OH group, a Cl atom, and a metal base such as an SO ₃ M group, a de-HCl reaction occurs, which deteriorates the magnetic properties over time and reduces the saturation magnetization. There is a drawback that it decreases significantly. (Structure of the Invention) The present inventors have solved the above-mentioned drawbacks, and have created a bond that has better dispersibility for various magnetic powders and has excellent durability without causing deterioration of magnetic properties over time. The present invention was achieved as a result of extensive research aimed at developing a magnetic recording medium and using it to obtain a magnetic recording medium with high performance and reliability. That is, the present invention provides a copolymer obtained by copolymerizing vinyl chloride, a fatty acid vinyl ester having 8 to 16 carbon atoms, and a polymerizable unsaturated sulfonic acid on a support, and then neutralizing it with a basic substance. The present invention relates to a magnetic recording medium in which a magnetic layer in which fine ferromagnetic powder is dispersed is formed. The binder resin used in the present invention has excellent dispersibility and filling properties of the ferromagnetic fine powder, has sufficient compatibility with the polyurethane resin etc. used in combination, and also has vinyl acetate in the molecule. Since it does not contain units such as vinyl propionate, it has various performance advantages such as thermal decomposition reactions and dehydrochlorination reactions are extremely difficult to occur, so by using it, high performance magnetic recording with improved long-term durability can be achieved. medium can be obtained. The present invention will be explained in detail below. The binder resin used in the present invention is a copolymer of each of the monomers described above neutralized with a basic substance, and this copolymer is particularly suitable for vinyl chloride units.
65 to 90% by weight, 8 to 25% by weight of fatty acid vinyl ester units having 8 to 16 carbon atoms, and 0.1 to 10% by weight of polymerizable unsaturated sulfonic acid units, and having an average degree of polymerization of 200 to 800. It is desirable to do so. If the vinyl chloride unit is too small, the physical strength will be reduced, and if it is too large, the solubility will be reduced, which is disadvantageous in use. Regarding fatty acid vinyl ester units, those with a small number of carbon atoms, such as vinyl acetate, vinyl propionate, vinyl lactate, etc., will not only have poor dispersibility, but also cause thermal decomposition of these units, resulting in the elimination of vinyl chloride. Hydrochloric acid is accelerated and the durability of magnetic recording media (magnetic tape, etc.) decreases. On the other hand, if this fatty acid vinyl ester is a polymer with a total number of carbon atoms of 17 or more in the molecule, such as vinyl stearate, the dispersibility will decrease, so if the total number of carbon atoms in the molecule is in the range of 8 to 16, the dispersibility will decrease. It is desirable to use certain fatty acid vinyl esters. This fatty acid moiety can be both linear and branched, but for the purposes of the present invention, branched fatty acids are preferred, specifically birtissuccinic acid (trade name manufactured by Ciel Chemical Co., Ltd., carbon number 9, 10 or 11 tertiary monocarboxylic acids) is preferred. In addition, if the amount of fatty acid vinyl ester units in the copolymer is too small, the solubility will decrease, and if it is too large, the dispersibility of the ferromagnetic powder will decrease, and the thermal stability will also decrease, causing magnetic deterioration over time. The content is preferably in the range of 8 to 25% by weight. As polymerizable unsaturated sulfonic acids, CH ₂ = CH-SO ₃ H, CH ₂ = CH-C ₆ H ₄ -
_SO3H , _CH2 =CH-CO-NH-C( _CH3 ) _{2
( CH2SO3H} ), (However, R' in the formula is an alkyl group having 12 to 14 carbon atoms) _CH2 =CH( _CH3 )-CO-O- _{C4O8 - SO3H} , _CH2 =CH( _CH3 )-CO- Examples include O _{- C2H4} - _SO3H . If the amount of polymerizable unsaturated sulfonic acid is too large, the solubility will be poor and gelation will easily occur, while if the amount is too small, the dispersibility of the magnetic powder will be poor. Therefore, it is desirable that the amount of this polymerizable unsaturated sulfonic acid be within the range described above, particularly within the range of 0.5 to 7% by weight. Regarding the degree of polymerization of the copolymer, if it is too low, its strength as a binder will be reduced and powder will easily fall off, reducing durability. If it is too high, the viscosity will become high, resulting in poor workability and reduced dispersibility. Therefore, it is desirable that the average degree of polymerization is in the range of 200 to 800 (particularly 250 to 500). In addition, if a polymerizable unsaturated sulfonic acid salt is used in the copolymerization instead of the above polymerizable unsaturated sulfonic acid,
This sulfonate has poor solubility in other monomers such as vinyl chloride, fatty acid vinyl ester, and organic solvents, so it is difficult to uniformly copolymerize, and the resulting copolymer is difficult to dissolve in organic solvents. Therefore, the objects and effects of the present invention cannot be achieved. Polymerization methods for obtaining copolymers include bulk polymerization, solution polymerization, and
Emulsion polymerization, suspension polymerization, etc. may be used, and the polymerization method itself is not limited. In the present invention, the copolymer obtained by copolymerization must not be used as it is, but must be neutralized with a basic substance. This neutralization is carried out by adding a basic substance after the copolymerization reaction is completed. Specifically, it may be carried out in a manner desired by each polymerization method. For example, in the solution polymerization method, after the polymerization reaction is completed, neutralization is performed by adding an alcoholic solution of sodium hydroxide, and then alcohol, which is a non-solvent for the copolymer, is added to neutralize the polymerization reaction. The desired copolymer can be obtained by reprecipitating with a solvent or a hydrocarbon solvent such as n-hexane, washing with the same solvent, and removing liquid and drying. In addition, in the suspension polymerization method, the polymer slurry after the polymerization reaction is neutralized by adding an aqueous solution of alkali metal hydroxide, aqueous ammonia, etc., and the copolymer is obtained by washing, removing liquid, and drying. In the emulsion polymerization method, a copolymer is obtained by neutralizing in substantially the same manner, followed by salting out, washing, excessive dehydration, and drying in accordance with conventional methods. When using the above-mentioned copolymer as a binder resin, other resins may be used in equal or less amounts as necessary, and resins that can be used in combination include polyurethane resins, nitrocellulose, epoxy resins,
Polyamide resin, phenolic resin, acrylic ester, methacrylic ester, styrene, acrylonitrile, butadiene, ethylene,
Examples include various polymers such as propylene, vinylidene chloride, acrylamide, vinyl ethers, and copolymers. Among these, polyurethane resins and nitrocellulose are particularly preferred. In addition, it is desirable to use a polyisocyanate-based curing agent in combination, and examples of this curing agent include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, and Coronate L (trade name, manufactured by Nippon Polyurethane Industries). , Days module L
Examples include trifunctional isocyanates such as (trade name, manufactured by Bayer AG), and urethane polymers containing isocyanate groups at both ends. The amount of these curing agents used is 40% per 100 parts by weight of binder resin.
It should be less than parts by weight. The ferromagnetic fine powder used in the present invention includes γ
- Fe ₂ O ₃ , Fe ₃ O ₄ and these adsorbed or doped with cobalt ions, CrO ₃ etc., and acicular fine particle materials containing Fe, Co, Fe-Co or in some cases Ni etc. , and various other conventionally known magnetic powders. The mixing ratio of ferromagnetic fine powder and binder resin is
Preferably, the amount of binder resin is 8 to 30 parts by weight per 100 parts by weight. In addition, in order to uniformly disperse the ferromagnetic powder and the binder resin, it is necessary to add commonly used lubricants, abrasives, antistatic agents, dispersion aids, rust preventives, etc., as well as coating media. Various other organic solvents such as methyl ethyl ketone, methyl isobutyl ketone, and toluene may be used as in the past, and there are no particular restrictions on these points. As the support, synthetic resins such as polyester, polyolefin, cellulose acetate, and polycarbonate, other nonmagnetic metals, and ceramics are used, and the support is in the form of a film, tape, sheet, plate, etc. The coating means for forming the magnetic layer on the support may be any conventionally known method, and by appropriately performing a smoothing treatment such as calendaring treatment,
A high-performance magnetic recording medium, which is the object of the present invention, can be obtained. Next, examples of synthesis of binder resins and specific examples using the binder resins will be given. Synthesis Example 1 (Synthesis of Polymer A) In an autoclave equipped with a stirring device, 400 parts by weight of methanol, 86 parts by weight of vinyl chloride, 20 parts by weight of Beoba #10 (trade name manufactured by Ciel Chemical Co., Ltd.), and 8 parts by weight of allyldodecyl sulfosuccinate. part, di(2-
6 parts by weight of (ethylhexyl) peroxydicarbonate and 2 parts by weight of partially saponified polyvinyl alcohol were charged, and the temperature was raised to 50°C while stirring in a nitrogen gas atmosphere to start the reaction, and then 86 parts by weight of vinyl chloride was added for 8 hours. In short, continuous pressure injection was carried out to cause a copolymerization reaction. Autoclave internal pressure reaches 0 after 12 hours
Kg/ ^cm2 . Cool the resulting slurry to 10%
The mixture was neutralized with an aqueous potassium hydroxide solution, washed three times with 1000 parts by weight of methanol, and filtered and dried to obtain 160 parts by weight of a copolymer powder. This is called Polymer A. Synthesis Example 2 (Synthesis of Polymer B) The following composition was charged into an autoclave equipped with a stirring device: Deionized water 400 parts by weight Vinyl chloride 79 Beopa #9 (vinyl versatility, trade name manufactured by Ciel Chemical Co., Ltd.) 24 〃 2-ethylhexyl acrylate 10 〃 2-acrylamido-2-methylpropanesulfonic acid 14 〃 Ammonium persulfate 1 part by weight polyoxyethylene nonyl phenyl ether
4. The reaction was started by heating to 55°C while stirring. Further, 80 parts by weight of vinyl chloride was continuously added over a period of 8 hours to cause a copolymerization reaction, and a thermal reaction was further carried out for 1 hour to obtain an emulsion. This emulsion was neutralized with a 28% ammonia aqueous solution, 50 parts by weight of sodium chloride and 500 parts by weight of hot water were added, and the slurry was filtered to obtain a cake. This product was dispersed in 1200 parts by weight of water, washed five times, and then dried to obtain 125 parts by weight of copolymer powder. This will be referred to as Polymer B. Comparative Synthesis Example 1 (Synthesis of Polymer C) A copolymer was obtained in exactly the same manner as Synthesis Example 1 except that neutralization with a 10% aqueous potassium hydroxide solution was omitted. This will be referred to as Polymer C. Comparative Synthesis Example 2 (Synthesis of Polymer D) A copolymer was obtained in exactly the same manner as in Synthesis Example 1 except that 20 parts by weight of vinyl acetate was used instead of Beoba #10. This will be referred to as Polymer D. Comparative Synthesis Example 3 (Synthesis of Polymer E) In a reactor equipped with a cooling tube and a stirrer, 100 parts by weight of vinyl chloride-vinyl acetate-vinyl alcohol copolymer (vinyl alcohol 12% by weight), 400 parts by weight of dimethylformamide, 21.5 parts by weight of pyridine and 45 parts by weight of monochloroethylsulfonate Na salt (Cl-C ₂ H ₄ OSO ₃ Na) were charged and heated at 80℃.
The reaction was allowed to proceed for 10 hours, and after cooling, the solid matter was filtered and added to 1000 parts by weight of methanol to precipitate a polymer. Furthermore, the operation of dispersing and washing using 1000 parts by weight of methanol was repeated three times, followed by drying to obtain 88 parts by weight of copolymer powder. This is called Polymer E. Examples 1 and 2 Co-γ-Fe ₂ O ₃ as ferromagnetic powder (coercive force 640 oersted, saturation magnetization 74 emu/g, specific surface area 23
m ² /g) 300 parts by weight, 30 parts by weight of polymer A or B, 20 parts by weight of polyurethane Nituporan N-5032 (trade name manufactured by Nippon Polyurethane Industries), 0.5 parts by weight of silicone oil KF-96 (trade name manufactured by Shin-Etsu Chemical Industries). A composition consisting of 300 parts by weight of methyl ethyl ketone, 300 parts by weight of methyl isobutyl ketone and 300 parts by weight of toluene was kneaded and dispersed in a ball mill for 10 hours, and then 25 parts by weight of Coronate L (trade name, manufactured by Nippon Polyurethane Industries, Ltd., a low molecular weight isocyanate compound) was added. of the mixture was added and kneaded and dispersed again in a ball mill for 1 hour. The magnetic paint thus obtained was applied onto a polyester film to a dry film thickness of 5 μm.
It was subjected to magnetic field orientation treatment and dried. The surface gloss and magnetic properties of the magnetic recording medium thus obtained were measured. The surface gloss was measured by comparing the light reflectance at Gs60° with a standard glass plate using a gloss meter GM-3D (Murakami Color Giken). The magnetic properties were measured using a VSM-3 model (manufactured by Toei Kogyo) in an external magnetic field of 3000 oersteds. The result is the first
It was as shown in the table. Comparative Example 1 A magnetic recording medium was produced in the same manner as in Example 1 except that Polymer C was used instead of Polymer A or B, and the surface gloss and magnetic properties were measured. The results were as shown in Table 1.

[Table] Examples 3 and 4, Comparative Examples 2 to 4 Ferromagnetic powder Fe-Co-Ni 300 parts by weight Retention force 1500 Oersted saturation magnetization 135 emu/g Specific surface area 50/g Binder resin (Polymer A, B, C, D or E) 30 parts by weight Polyurethane Nitsuporan N-3022 (trade name manufactured by Nippon Polyurethane Industries) 20 parts by weight Silicone oil KF-96 3 parts by weight Methyl ethyl ketone 300 parts by weight Methyl isobutyl ketone 300 parts by weight Toluene 300 parts by weight The above composition Kneaded and dispersed in a ball mill for 10 hours,
Furthermore, 2 parts by weight of Coronate L (described above) was added and kneaded and dispersed again in a ball mill for 1 hour. The magnetic paint thus obtained was applied onto a polyester film to a dry film thickness of 5 μm, subjected to magnetic field orientation treatment, and after drying, calendering treatment was performed. For each tape thus obtained, the surface gloss and magnetic properties were measured in the same manner as in the previous example, and in order to evaluate the oxidation resistance of the ferromagnetic powder to the binder resin, each tape was heated in air at 60℃ and 90℃. %
The rate of decrease in saturation magnetization was determined after being left at RH and accelerated over time. The results were as shown in Table 2. Decrease rate of saturation magnetization = σ _SO −σ _ST /σ _SO ×100 σ _SO : Initial saturation magnetization (emu/g) σ _ST : Saturation magnetization after accelerated test (emu/g)

[Table] As can be seen from the above examples and comparative examples,
The magnetic recording medium according to the present invention has excellent dispersibility of ferromagnetic fine powder, small change in saturation magnetization over time, and excellent oxidation resistance.

Claims (1)

[Claims] 1. A copolymer obtained by copolymerizing vinyl chloride, a fatty acid vinyl ester having 8 to 16 carbon atoms, and a polymerizable unsaturated sulfonic acid on a support, and then neutralizing it with a basic substance. A magnetic recording medium formed by forming a magnetic layer in which fine ferromagnetic powder is dispersed during coalescence. 2 The copolymer contains 65 to 90% by weight of vinyl chloride,
8-25% by weight of fatty acid vinyl ester having 8-16 carbon atoms and 0.1-10% by weight of polymerizable unsaturated sulfonic acid
2. The magnetic recording medium according to claim 1, which has an average degree of polymerization of 200 to 800 obtained by copolymerizing at a ratio of .