JPH0256730B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a magnetic recording medium, and in particular to an improved magnetic recording medium made using a special copolymer mainly composed of vinyl chloride, which exhibits excellent performance as a binder for ferromagnetic fine powder. Related to magnetic recording media. (Prior Art) Magnetic recording media such as magnetic tapes are generally made by providing a coating (magnetic layer) made of magnetic powder and a binder on the surface of a support such as a polyester film. As magnetic powder, γ-
Fe ₂ O ₃ , Fe ₃ O ₄ and these adsorbed or doped with cobalt ions, or CrO ₂ , etc.
Furthermore, Fe, Co, Fe−Co or depending on the case
Acicular fine particle materials containing Ni or the like have been used, but in recent years, as the performance of video tapes and audio tapes has improved, high signal density and high playback output in short wavelength recording are required. To address these trends, magnetic powders have become finer particles than ever before, and because they have a very large magnetic moment, the particles tend to agglomerate with each other, resulting in uniform dispersion in the binder resin. is becoming more difficult than ever before. In order to address these technical issues, extensive studies are currently being conducted from the viewpoint of improving the affinity of binder resins for magnetic powder. Although it has been put into practical use, the dispersibility of the ferromagnetic powder is still insufficient, resulting in poor surface properties of the magnetic coating, unsatisfactory residual magnetic flux density and squareness ratio, and moreover, it is prone to powder falling and has poor durability. There are drawbacks. On the other hand, surfactants are also added to improve the dispersibility of the ferromagnetic powder and smoothen the coating surface.
Attempts have been made to treat ferromagnetic powder with silicone oil or add a silane coupling agent that is reactive with the binder resin.
In both cases, sufficient effects have not been obtained,
It is desired to develop a binder that exhibits even better dispersibility for ferromagnetic powders used for high-density recording. (Structure of the Invention) The present inventors have conducted extensive research in order to overcome these conventional drawbacks, develop a binder resin with improved dispersibility and surface properties of magnetic coatings, and obtain a high-performance magnetic recording medium. As a result, we have arrived at the present invention. That is, the present invention forms a magnetic layer on a support in which ferromagnetic powder is dispersed in a copolymer consisting of (a) vinyl chloride units, (d) vinyl alcohol units, and (c) amine-modified vinyl units. The present invention relates to a magnetic recording medium formed by: Regarding the dispersibility of ferromagnetic powder in a system that uses a conventional main binder of vinyl chloride-vinyl acetate copolymer and a polyurethane resin binder in combination with a surfactant, the dispersibility of ferromagnetic powder can be improved by dissolving the surfactant in an organic solvent. When fine magnetic powder is added and kneaded, it appears to have excellent dispersion, but when vinyl chloride-vinyl acetate copolymer and polyurethane resin are added to form a paint system, the dispersibility deteriorates. When the binder according to the present invention is used, the dispersibility in the coating system is very good, and the ferromagnetic powder does not agglomerate economically. Further, the binder according to the present invention has excellent adhesion ability to a substrate and various physical properties as a tape. The present invention will be explained in detail below. The binder resin used in the present invention is as described in (a) to
It is characterized in that it is a copolymer comprising each unit of (c) as an essential component, and this copolymer is particularly characterized by (a) 60 to 95% by weight of vinyl chloride units,
(b) 2 to 16% by weight of vinyl alcohol units, (c) 0.05 to 5% by weight of amine-modified vinyl units, and a small amount of other vinyl units as necessary, with an average degree of polymerization.
It is desirable to use one with a value of 200-800. (a) If the amount of vinyl chloride units is too small, the physical strength will decrease, and if it is too large, the solubility will decrease, which is disadvantageous in use. (b) If the amount of vinyl alcohol units is too small, the dispersibility of the ferromagnetic powder will decrease,
In addition, the compatibility with polyurethane resins and the like that are appropriately used in combination decreases. On the other hand, if it is too large, physical strength and thermal stability will decrease. (c) If the amine-modified vinyl unit is too small, the dispersibility will be reduced and the smoothness of the coating film will be reduced. If the amount is too large, the dispersibility and smoothness will decrease, and the solubility will also decrease, making it impossible to use it as a binder. If the average degree of polymerization of a copolymer composed of such unit components is too low, the magnetic coating film will become brittle, resulting in a decrease in physical strength, and the durability of magnetic tapes etc. will also decrease, and vice versa. If the average degree of polymerization is too high, the viscosity of the paint at a given concentration will increase, resulting in significantly poor workability and difficulty in handling, so it is desirable that the average degree of polymerization is in the range of 200 to 800. This copolymer is produced by general suspension polymerization, emulsion polymerization, solution polymerization, bulk polymerization, etc., but for the introduction of vinyl alcohol units, lower fatty acid vinyl such as vinyl acetate and vinyl propionate are used. The resulting copolymer is saponified in an appropriate solvent using an alkali such as KOH, NaOH, or sodium alcoholate, or an acid such as hydrochloric acid or sulfuric acid as a catalyst, and then purified by a conventional method. Vinyl acetate, vinyl propionate, etc. may be present in small amounts as unsaponified moieties, or vinyl versatate, alkyl esters of acrylic acid or methacrylic acid, esters of areic acid or itaconic acid, maleic acid or Some amount of itaconic acid ester, vinylidene chloride, various vinyl ethers, etc. may be copolymerized. The introduction of vinyl alcohol units is described in 2 to 16 above.
Since the amount is within a range of % by weight, the lower fatty acid vinyl copolymer and saponification rate (mol %) must be adjusted so as to maintain the range. On the other hand, the introduction of amine-modified vinyl units can be carried out simultaneously with the saponification reaction. That is, various amine compounds described later are added to the saponification reaction system.
Vinyl alcohol units are obtained by heating and stirring at 10 to 80°C for a certain period of time until the desired degree of saponification is obtained, and at the same time, amines are introduced into the side chains by reaction between the chlorine atoms of the vinyl chloride units and the amine compound. . In this amine modification, it is necessary to determine the amount of the amine compound used so that the amine-modified vinyl units in the copolymer are in the range of 0.05 to 5% by weight. The amine compounds used are:
Includes primary, secondary or tertiary amines such as aliphatic amines, alicyclic amines and aromatic amines, specifically ethylamine, propylamine,
Butylamine, cyclohexylamine, ethanolamine, naphthylamine, aniline, O-toluidine, diethylamine, dioctylamine, diisobutylamine, diethanolamine, N-methylaniline, trimethylamine, triethylamine, triisobutylamine, tridecylamine, N-methyldiphenylamine, hexa Examples include methylenetetramine, triethanolamine, tributylamine, pyridine, α-picoline, β-picoline, γ-picoline, 2,4-lutidine, quinoline, and morpholine. Note that even if the amine compound is added directly to a magnetic coating system consisting of ferromagnetic powder and a conventional binder resin and kneaded to create a magnetic coating film without reacting as in the present invention, the magnetic powder will not react. Although some effects are seen in terms of dispersion and smoothing, the dispersibility deteriorates over time and the desired effects cannot be achieved. When using the above-mentioned copolymer as a binder resin, other resins may be used in equal or less amounts as necessary, and examples of resins that can be used in combination include polyurethane resins, nitrocellulose, polyester resins,
Examples include various polymers such as epoxy resins, polyamide resins, phenolic resins, alkyd resins, polyvinyl butyral resins, and polymers or copolymers of acrylic esters, methacrylic esters, styrene, acrylonitrile, butadiene, ethylene, propylene, vinylidene chloride, etc. be done. Among these, especially polyurethane resin,
Nitrocellulose is preferred. In addition to this, it is desirable to use a polyisocyanate-based curing agent, such as Coronate L (trade name manufactured by Nippon Polyurethane Industries) and Dismodule L (trade name manufactured by Bayer).
Examples include trifunctional isocyanates such as , and urethane prepolymers containing isocyanate groups at both ends. The amount of these curing agents used should be 5 to 40 parts by weight per 100 parts by weight of binder resin. The ferromagnetic powder used in the present invention includes γ-
Fe ₂ O ₃ , Fe ₃ O ₄ and these adsorbed or doped with cobalt ions, or CrO ₂ , etc.
Further examples include acicular fine particle materials containing Fe, Co, Fe-Co, Ni, etc., and various other conventionally known magnetic powders. 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 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, cyclohexanone, 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 applying smoothing treatment such as calendaring treatment, the high-performance magnetic recording medium that is the object of the present invention can be obtained. is obtained. Next, examples of synthesis of the binder resin and specific examples using the binder resin will be given. However, in the following description, all parts are by weight. Synthesis Example (Polymer Synthesis) In an autoclave equipped with a stirring device, after purging with nitrogen, add 400 parts of deionized water, 72 parts of vinyl chloride, 56 parts of vinyl acetate, 6 parts of trichlorethylene,
-ethylhexyl) peroxydicarbonate 6
1 part and 2 parts of partially saponified polyvinyl alcohol were charged, and the reaction was started by raising the temperature to 60°C while stirring, and then 72 parts of vinyl chloride was continuously pressurized over a period of 8 hours to cause a polymerization reaction. Autoclave internal pressure is 0.5Kg/cm ² G after 12 hours
The residual pressure was released, the mixture was cooled, washed three times with 1000 parts of deionized water, filtered, and dried at 50°C.
As a result, the copolymer contained 75.3% by weight of vinyl chloride units, 24.7% by weight of vinyl acetate units, and an average degree of polymerization of 380.
Part was obtained. 160 parts of the copolymer thus obtained were mixed with 432 parts of methanol, 48 parts of triene, and 16 parts of sodium hydroxide.
1 part and 8 parts of morpholine in a reactor (with a stirring device and jacket), reacted at 40°C for 6 hours, and washed 3 times with 1000 parts of methanol.
Furthermore, it was washed twice with 1000 parts of deionized water, filtered and dried. The obtained polymer is further dissolved in 800 parts of methyl ethyl ketone, 3000 parts of methanol is added with stirring to cause reprecipitation, and the polymer is filtered off.
This dissolution and reprecipitation was repeated twice, and the mixture was further washed twice with 1000 parts of deionized water, filtered and dried to obtain 128 g of copolymer powder (polymer). As a result, vinyl chloride units are 85.8% by weight and vinyl alcohol units are 11.5%.
A copolymer having a weight of 2.2% by weight of vinyl acetate units, 0.5% by weight of morpholine-modified vinyl units, and an average degree of polymerization of 320 was obtained. Synthesis example (polymer) After replacing nitrogen in an autoclave equipped with a stirring device, 400 parts of deionized water, 72 parts of vinyl chloride, 56 parts of vinyl acetate, 1 part of ammonium persulfate, and 4 parts of polyoxyethylene nonyl phenyl ether were charged. While stirring, 72 parts of vinyl was continuously added over a period of 8 hours to cause a copolymerization reaction. Subsequently, an aging reaction was performed for 6 hours to obtain an emulsion. To this emulsion, add 50 parts of sodium chloride and 5% dilute hydrochloric acid.
20 parts and 500 parts of hot water were added, and the resulting slurry was filtered to form a cake. This cake was dispersed and washed in 1200 parts of deionized water and filtered. This water washing and filtration operation was repeated five times and then dried to obtain 150 parts of a copolymer.
As a result, 73.8% by weight of vinyl chloride, vinyl acetate unit
A copolymer with an average polymerization degree of 26.2% by weight and 400 was obtained. 150 parts of the copolymer thus obtained were mixed with 400 parts of methanol, 50 parts of xylene, and 15 parts of sodium hydroxide.
1 part and 40 parts of morpholine in a reactor equipped with a stirrer and jacket, and reacted at 40°C for 6 hours.
Washed twice with deionized water, filtered and dried. The obtained polymer is further dissolved in methyl ethyl ketone and reprecipitated with methanol. The dissolution and reprecipitation process was repeated twice, followed by washing twice with deionized water, filtering and drying to obtain 125 parts of copolymer powder (polymer). Synthesis Example (Polymer ~) Polymer ~ having each composition and degree of polymerization as shown in [Table 1] was produced according to Synthesis Example (Polymer). In addition, the above-mentioned polymers and are listed again in [Table 1]. Synthesis Example (Polymer ~) Polymers having each composition and degree of polymerization as shown in "Table 1" according to Synthesis Example (Polymer),
, was manufactured. However, the raw materials should be prepared to have the composition ratio shown in "Table 1", and the saponification and amination reaction conditions should be adjusted to 60%.
A polymer was obtained by treating in the same manner as the polymer except that the temperature was kept at ℃ for 4 hours. Comparative synthesis examples 1, 3, 4, 5, 6 (polymer,
) On the other hand, for comparison, as shown in [Table 2], polymerization was carried out according to Synthesis Example 1, and for the obtained polymer, each copolymer was mixed with methanol, toluene, and sodium hydroxide, and the amine compound was A saponification reaction was carried out at 40°C for 6 hours in the absence of additives to obtain a polymer. Comparative Synthesis Example 2 (Polymer) Emulsion polymerization was carried out according to Synthesis Example 2, salting out,
Regarding the polymer obtained by washing and purification,
A saponification reaction was carried out in the same manner as in the above comparative synthesis example, and a polymer was obtained by the same operation.

【table】

【table】

[Table] Examples 1 to 9, Comparative Examples 1 to 6 A Liquid γ-Fe ₂ O ₃ (major axis average particle diameter 0.3 μm, axial ratio 1/10)
100 parts Lecithin 2 parts Nonion #NS-230 3 parts Methyl isobutyl ketone 60 parts Methyl ethyl ketone 60 parts Cyclohexane 60 parts Mix the above formulation in an Eiger mill for 30 minutes Solution B Binder resin (polymer ~) 25 parts Polyurethane resin (N-2304: (manufactured by Nippon Polyurethane Co., Ltd.) 7 parts Methyl isobutyl ketone 65 parts Methyl ethyl ketone 65 parts Cyclohexanone 65 parts The above formulation was dissolved and mixed in a lab mixer for 30 minutes. Solution B was added to solution A in the Eiger mill and kneaded for 1 hour. Furthermore, 6 parts of Coronate L was added and kneaded for 30 minutes, followed by suction filtration through a 20 micron filter to obtain a magnetic paint. The above magnetic paint was applied to a thickness of 6 μm on a polyester film having a thickness of 16 μm, subjected to magnetic field orientation treatment, dried, and then surface treated using a super calender. Regarding the magnetic tape made in this way,
The coating properties and magnetic properties were investigated. The results were as shown in Table 3. However, in the same table, the column ``Magnetic paint not left unused'' indicates magnetic tape made by preparing magnetic paint and continuing the application process without leaving it for 24 hours, and the column ``Magnetic paint left 24 hours'' means the prepared magnetic paint was left for 24 hours. This table shows data for magnetic tapes produced by coating the tapes. However, in Comparative Examples 2 and 3 marked with an asterisk, an amine compound was added to the paint as described below. Comparative Example 2: Two parts of morpholine were added to a lab mixer when preparing Solution B. Comparative Example 3: Two parts of pyridine was added to a lab mixer when preparing liquid B. [Measurement conditions for gloss and magnetic properties] Gloss: The 60°C reflectance before calendering was compared with a standard glass plate using a gloss meter (manufactured by Murakami Color Giken). Magnetic properties: Measured using a vibrating sample magnetometer (manufactured by Toei Kogyo).

【table】

Claims (1)

[Scope of Claims] 1. On a support, ferromagnetic fine powder is dispersed in a copolymer whose essential components are (a) vinyl chloride units, (b) vinyl alcohol units, and (c) amine-modified vinyl units. A magnetic recording medium is formed by forming a magnetic layer. 2. The copolymer contains (a) 60 to 95% by weight of vinyl chloride, (b) 2 to 16% by weight of vinyl alcohol units, (c) 0.05 to 5% by weight of amine-modified vinyl units, and other vinyl units as necessary. The average degree of polymerization consists of a certain amount
200 to 800
Magnetic recording medium described in Section 1.