JPH0137424B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a magnetic coating composition for magnetic recording media containing nitrocellulose. Currently, magnetic coating compositions for magnetic recording media include magnetic powders such as Fe ₂ O ₃ , binders, dispersants,
Consists of a mixture of lubricants, solvents, etc. Among these binders, vinyl chloride/vinyl acetate copolymer resin, epoxy resin, polyurethane resin,
Phenoxy resin, isocyanate group-containing resin, 30
% of nitrocellulose moistened with a lower alcohol such as isopropyl alcohol or ethyl alcohol. Among these, a combination of polyurethane resin/isocyanate group-containing resin/lower alcohol-wetted nitrocellulose has been mainly used. However, the lower alcohol contained in lower alcohol-wetted nitrocellulose reacts with isocyanate groups to produce a low molecular weight polymer, resulting in a problem of deteriorating the performance of the magnetic recording medium. In order to correct this problem, nitrocellulose obtained by volatilizing the alcohol content in the lower alcohol-wetted nitrocellulose is used, nitrocellulose moistened with a solvent inert to isocyanate groups such as toluene is used, or Using nitrocellulose chips with alcohol substituted by plasticity such as dibasic acid esters, e.g. dibutyl phthalate, or nitrocellulose with alcohol substituted by resins such as salt vinyl acetate copolymer resins 142756) has been proposed. However, the use of dry nitrocellulose tends to cause spontaneous decomposition of nitrocellulose, and the use of toluene-wetted nitrocellulose significantly increases the chargeability of the nitrocellulose, both of which cause nitrocellulose to be easily decomposed during handling. This has the problem of increasing the risk of ignition. Furthermore, the use of nitrocellulose containing a plasticizer has the drawback of increasing friction of the magnetic recording medium, resulting in poor running and generation of squeaking noise. Additionally, nitrocellulose in which the alcohol has been substituted with a resin can be substituted with other known substituted nitrocelluloses, such as those in which the isocyanate group is substituted with an inert organic solvent that does not dissolve nitrocellulose, such as toluene, or with a plastic substituted material such as dibutyl phthalate. Compared to the former, the danger of electrostatic charge and the latter's negative effects from plasticity bleed-out can be avoided, but
It has the following essential drawbacks. (a) For the safety of nitrocellulose, there is a lower limit to the amount of resin used to replace water and/or alcohol; for example, in the case of a salt-vinyl acetate copolymer, it cannot be less than 20% of the nitrocellulose. Therefore, once the amount of nitrocellulose relative to the urethane resin is determined, the lower limit of the amount of salt-vinyl acetate copolymer mixed is fixed, and it is virtually impossible to design a magnetic coating composition with a lower amount. (b) Even in the range where the amount of substituted resin exceeds the lower limit, the ratio of the amount of resin to nitrocellulose is fixed during water and/or alcohol substitution, so for example, polyurethane resin, salt-vinyl acetate copolymer, and nitrocellulose The ratio cannot be arbitrarily adjusted at the paint manufacturing stage. (c) Not only is the substituted resin component specified at the time of substitution, but it is also necessary to design the final coating composition according to the selected resin component, making production complicated. The present inventors have conducted various studies regarding magnetic coating compositions for obtaining magnetic recording media free from the above-mentioned problems. As a result, the present inventors have discovered that an organic solvent that dissolves nitrocellulose and is inert to isocyanate groups and nitrocellulose. The problem described above can be solved by using solid nitrocellulose as part of the binder, which contains a mixed solvent in which isocyanate groups are mixed with an inert organic solvent without dissolving the isocyanate groups, and does not substantially contain water and/or alcohol. The present invention was completed by discovering that a magnetic coating composition for magnetic recording media without dots can be obtained. That is, the present invention comprises (a) nitrocellulose, (b) an organic solvent that is inert to isocyanate groups and dissolves nitrocellulose, and (c) an organic solvent that is inert to isocyanate groups and does not dissolve nitrocellulose. A non-adhesive nitrocellulose composition (hereinafter referred to as solid nitrocellulose) consisting of a solvent and these three components forming a uniform solid phase is added to the binder in an amount of 10 to 50% by weight in terms of pure nitrocellulose. This is a method for producing a magnetic coating composition for a magnetic recording medium, characterized in that a magnetic coating composition for a magnetic recording medium is added. The solid nitrocellulose used in the present invention is
This will be explained with reference to FIG. Figure 1 shows the three compositions of (a) nitrocellulose, (b) an organic solvent that is inert to isocyanates and dissolves nitrocellulose, and (c) an organic solvent that is inert to isocyanates and does not dissolve nitrocellulose. It is a triangular diagram showing the composition range of solid nitrocellulose used in the present invention,
The nitrocellulose composition comprising the three components within this range has no tackiness and maintains its shape even when molded into an arbitrary shape. B is the range in which the nitrocellulose composition consisting of the three components in this range has adhesive properties, so even if it is molded into an arbitrary shape, it will begin to fuse over time and eventually become unable to maintain the molded shape. show. C indicates a range in which nitrocellulose undergoes phase separation and nitrocellulose and both organic solvents do not separate to form a homogeneous phase in a nitrocellulose composition consisting of three components within this range. For example, to explain the behavior when 20 g of nitrocellulose is dissolved in 80 g of ethyl acetate (a solvent that dissolves nitrocellulose), this composition is shown as a in Figure 1, and it is extremely sticky and does not form into a molded product. It is in liquid form. If this is concentrated as it is, ethyl acetate will be removed by evaporation, and b
Even if it were to be molded in a liquid or paste form that passes through point and point c, both of which have adhesive properties,
The molded products immediately coalesce and cannot actually become a molded product. If the concentration continues, substantially all of the ethyl acetate is removed, leaving only nitrocellulose, which poses a risk of ignition. Further, the behavior when 20 g of nitrocellulose is dissolved in a mixed solvent of 50 g of ethyl acetate (a solvent that dissolves nitrocellulose) and 30 g of xylene (a solvent that does not dissolve nitrocellulose) is also explained with reference to FIG. This composition is shown by d in the same figure, and is in a liquid state that is extremely sticky and cannot be formed into a molded product. When this is distilled, both solvents are removed by evaporation, but ethyl acetate is removed first due to its vapor pressure, so it is concentrated through points e and f. Point e is in the form of a sticky paste, and even if molded at this point, the molded products will immediately coalesce and cannot actually become a molded product. At point f, nitrocellulose precipitates and the nitrocellulose and both organic solvents separate into two layers. In this respect, the three materials do not exhibit a uniform solid phase and, of course, cannot be formed into a molded product. Even with such a limited composition of the three components, it is possible to obtain a shaped nitrocellulose composition in the form of non-adhesive granules, chips or pellets, and in which the three components exhibit a uniform solid phase. The solid nitrocellulose used in the present invention is
It consists of nitrocellulose moistened with alcohols and/or water, and a mixture of an organic solvent that is inert to isocyanate groups and dissolves nitrocellulose, and an organic solvent that is inert to isocyanate groups and does not dissolve nitrocellulose. After adding a mixed solvent in an amount such that the nitrocellulose is at least partially dissolved and the resulting mixture does not flow easily at room temperature without applying mechanical force, and kneading or sintering, A process of mechanically forming into granules, chips, or pellets, and applying an organic solvent that is inert to isocyanate groups and does not dissolve nitrocellulose alone or together with the organic solvent that is inert to isocyanate groups and does not dissolve nitrocellulose. The alcohol and/or water can be obtained by a distillation step in which a mixture with an organic solvent that dissolves the alcohol is added, and the alcohol and/or water is substantially removed together with a part of the organic solvent used by heating and/or reduced pressure. The solid nitrocellulose used in the present invention is not particularly limited in nitrogen content (N%) and viscosity (average degree of polymerization) of nitrocellulose, and any can be used, but preferably JIS-K-6703 Industrial nitrocellulose described in , N% of nitrocellulose is 10.7~
12.2%, viscosity symbol is L1/8~1/2 and H1/16~
120 and is moistened with alcohols such as ethyl alcohol, isopropyl alcohol, or butyl alcohol, and/or water. The organic solvent that dissolves inert nitrocellulose in the isocyanate groups of the solid nitrocellulose used in the present invention is one of the known organic solvents that dissolve nitrocellulose that have active properties with isocyanate groups such as OH groups, COOH groups, and _NH2 groups. It is an organic solvent that does not have a functional group, and typical examples include acetate esters such as ethyl acetate, propyl acetate, butyl acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, methyl ethyl ketone, and methyl isobutyl ketone. , isophorone, cyclohexanone and other ketones; and nitroparaffins such as nitromethane, nitroethane and nitropropane. Among these, considering the solubility of nitrocellulose, odor during handling, economic efficiency, etc., ethyl acetate, propyl acetate, butyl acetate,
Methyl ethyl ketone and methyl isobutyl ketone are preferred. Typical organic solvents that do not dissolve inert nitrocellulose in the isocyanate groups of solid nitrocellulose used in the present invention include hexane, heptane, octane, cyclohexane, methylcyclohexane, solvent naphtha, petroleum spirits, kerosene, benzene, and toluene. , aliphatic, alicyclic and aromatic hydrocarbons such as xylene, and halogenated hydrocarbons such as trichloroethylene and carbon tetrachloride. Among these, toluene, xylene and hexane are preferred in consideration of odor during handling, economic efficiency, etc. The solid nitrocellulose needs to be substantially free of water and/or alcohol. "Substantially free" means that it is contained only to the extent that it does not adversely affect the coating performance of the intended magnetic coating composition for magnetic recording media, and does not affect the required level of coating performance or the magnetic coating composition. Naturally, the amount of solid nitrocellulose added will vary. Therefore, although it is difficult to set a difference, it is necessary to keep water at 1% by weight or less and alcohol at 0.5% by weight or less. The magnetic coating composition for magnetic recording media of the present invention is:
Consists of magnetic powder, binder, dispersant, wetting agent, solvent, etc. The magnetic powder may be anything that is normally used in magnetic recording media, such as γ-Fe ₂ O ₃ ,
Examples include Fe ₃ O ₄ , CrO ₂ , CoO-Fe ₂ O ₃ , Co-γ-Fe ₂ O ₃ and mixtures thereof, and a needle-like shape with a long axis of 1 to 0.2 μ and a short axis of 0.2 to 0.05 μ is preferable. . Examples of the binder include, in addition to solid nitrocellulose, a combination of two or more selected from vinyl chloride/vinyl acetate copolymer resins, epoxy resins, polyurethane resins, phenoxy resins, isocyanate group-containing resins, polyester resins, etc. It is particularly effective to add the solid nitrocellulose into a binder containing an isocyanate group-containing resin. The isocyanate group-containing resins mentioned here include tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, metaxylylene diisocyanate, hexamethylene diisocyanate, methylene bis(cyclohexyl isocyanate), methylcyclohexane diisocyanate, isocyanate methylcyclohexane, and isophorone. Refers to diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate and its prepolymers with dihydric and trihydric alcohols, water adducts, allophanates, and isocyanurates. Further, the solid nitrocellulose needs to be contained in the binder in an amount of 10 to 50% by weight as a solid content (nitrocellulose pure content). Ten
If it is less than % by weight, the coefficient of friction of the surface of the coating film obtained from the magnetic coating composition of the present invention will increase, which is undesirable. Moreover, if it exceeds 50% by weight, the adhesive strength between the magnetic paint and the support (base) deteriorates. Solid nitrocellulose formed into granules, chips, or pellets has good fluidity and is easy to take out from a container during dissolution and preparation. Also, granular,
Chips or pellets are easier to fill into containers than large irregularly shaped chunks, and shipping costs are lower. In addition, as with conventional nitrocellulose moistened with alcohol and/or water, the moist content evaporates during handling operations and the nitrocellulose approaches a dry state, causing nitrocellulose dust such as short fibers to scatter. Solid nitrocellulose accumulates in places that are difficult to clean, and if left untreated, it can cause safety problems due to natural decomposition. No problems occur and it is safe and easy to handle. Furthermore, solid nitrocellulose is surprisingly relatively unchargeable. This is a major feature in the case of nitrocellulose, which has a risk of fire and the like and safety in handling is important. Furthermore, compared to those with large irregularly shaped lumps,
Granules, chips, or pellets are well-shaped and have good dispersion and solubility when dissolved in the lacquer, so the dissolution process can be completed in a short time.
Highly preferred by consumers. In the present invention, solid nitrocellulose is used during the manufacturing process of conventional magnetic coating compositions. For example, along with magnetic powder, other binders, dispersants, lubricants, solvents, etc., kneaders, ball mills, etc.
A magnetic coating composition can be produced by adding a predetermined amount into a sand mill, attritor, etc. and mixing. This will be explained in detail in Examples below. Example 1 γ-Fe ₂ O ₃ (long axis 0.8 μ, short axis 0.1 μ) 400 parts by weight Lecithin 5 Carbon black 12 Methyl ethyl ketone 300 Methyl isobutyl ketone 300 Toluene 300 Tetrahydrofuran 100 Solid nitrocellulose ^* 25 Polyurethane resin (solid content 35%) ) (Product name: Nipporan 3022, manufactured by Nippon Polyurethane) 60 Isocyanate group-containing resin (solid content 75%) (Coronate U, manufactured by Nippon Polyurethane) 15 (Note) * Nitrocellulose/Methyl isobutyl ketone/Toluene = 70/9/21 (weight) (ratio) Alcohol content = 0% Moisture content = 0.2%, this solid nitrocellulose could be taken out from the container very smoothly without dust being thrown up. The above components were mixed in a sand mill for 3 hours to obtain a magnetic coating composition. This magnetic coating composition was applied to a polyester film to a thickness of 6μ, and then heated at 80°C.
Dry for 48 hours. Further, this was cut into 1/2 inch width to obtain a video magnetic recording tape. The adhesive strength and friction coefficient of the video magnetic recording tape thus obtained were measured. The results are A in Table 1.
Shown in the column. In addition, the adhesive strength is 180% between the magnetic surface and the base film.
The friction coefficient was measured by friction between the brass and the magnetic surface at low speed. Example 2 The same method as in Example 1 was carried out by changing the amount of the solid nitrocellulose composition in the components of Example 1 to 56 parts by weight, 40 parts by weight, 6.3 parts by weight, and 4 parts by weight, respectively.
A magnetic tape was obtained by coating, coating, drying, and cutting.
The adhesive strength and friction coefficient of this magnetic tape were measured, and the results are shown in columns B, C, D, and E of Table 1, respectively. Example 3 The solid nitrocellulose in the ingredients of Example 1 was replaced with the following, and the same method as in Example 1 was used to make a paint.
Coating, drying, and cutting were performed to obtain a magnetic tape. Nitrocellulose/n-butyl acetate/toluene = 70/7/23 (weight ratio) Alcohol content = 0% Water content = 0.4% The adhesive strength and friction coefficient of this magnetic tape were measured.
The results are shown in column F of Table 1. Comparative Example 1 In place of the solid nitrocellulose in the components of Example 1, nitrocellulose HIG1/2 manufactured by Asahi Kasei Industries, Ltd.
(containing 27.5% alcohol and 2.5% water) was used in an amount of 25 parts by weight. The nitrocellulose was cotton-like and had to be pulled out with great force when taken out of the container, creating a lot of dust. This was made into a paint, coated, dried, and cut in the same manner as in Example 1 to obtain a magnetic tape. We measured the adhesive force and friction coefficient of this magnetic tape,
The results are shown in column G of Table 1. Comparative Example 2 In place of the solid nitrocellulose in Example 1, 20 parts by weight of Clearchip H1/2 (alcohol content = 0%, water content = 1.0%, dibutyl phthalate content = 12%) manufactured by Asahi Kasei Kogyo Co., Ltd. A magnetic tape was obtained by coating, coating, drying, and cutting in the same manner as in Example 1. We measured the adhesive force and friction coefficient of this magnetic tape,
The results are shown in column H of Table 1.

[Table] * Comparative example of nitrocellulose purity conversion 3 H1/ moistened with 30% isopropyl alcohol
2 seconds Add 60 g of salt-vinyl acetate copolymer resin (Vinylite VAGH manufactured by UCC) and 60 g of methyl ethyl ketone to 200 g of nitrocellulose, knead with a kneader for 1 hour, then knead several times with two rolls kept at 40°C to form a sheet. A mixture of This sheet-like mixture was dried with hot air at 50° C. for 6 hours and then ground into chips. The product obtained in this manner is hereinafter referred to as salt vinyl acetate/nitrification chips. In place of the solid nitrocellulose used in Example 1, salt vinyl acetate/nitrified cotton chips were used to form a coating, coated, dried and cut in the same manner as in Example 1 to obtain a magnetic tape. The adhesive force of this magnetic tape was 140 g/1/2 inch, and the coefficient of friction was 0.48. Comparative Example 4 Since it is necessary to further reduce the coefficient of friction, the amount of the salt-vinyl acetate/nitrified cotton chips of Comparative Example 3 was changed to 90 parts by weight, and the same method as in Example 1 was used to form a coating, apply it, dry it, cut it, and then apply it to a magnetic tape. I got it. The coefficient of friction of this magnetic tape was 0.22, but the adhesive strength was 45 g/1/2 inch. As shown in the examples, a mixed solvent containing an organic solvent that dissolves nitrocellulose and is inert to isocyanate groups and an organic solvent that does not dissolve nitrocellulose and is inert to isocyanate groups is used, and water and/or alcohol are used. 10 to 10% of nitrocellulose in the binder of the magnetic paint
By adding 50% by weight, a good magnetic recording medium can be obtained by exhibiting an excellent balance between the adhesion to the support and the coefficient of friction of the magnetic surface. Additionally, the use of vinyl acetate/nitrate cotton chips may offset or worsen the desirable performance of nitrocellulose in this application due to the vinyl acetate copolymer resin; however, according to the present invention, the performance of nitrocellulose is Therefore, a good magnetic recording medium can be obtained.

[Brief explanation of drawings]

FIG. 1 is a triangular diagram showing the three compositions of nitrocellulose, an organic solvent that is inert to isocyanates and dissolves nitrocellulose, and an organic solvent that is inert to isocyanates and does not dissolve nitrocellulose. In the figure, A is the range of the nitrocellulose composition of the present invention, B is the range where the nitrocellulose composition has adhesiveness and begins to fuse with the passage of time and can no longer maintain its molded shape, and C is the range of the nitrocellulose and organic Indicates the range in which the solvent undergoes phase separation. In addition, in the figure, a, b, and c represent the behavior of a composition consisting of 20 g of nitrocellulose and 80 g of ethyl acetate, and d, e, and f represent the behavior of a composition in which 20 g of nitrocellulose was dissolved in a mixed solvent of 50 g of ethyl acetate and 30 g of xylene. Show the behavior of things.

Claims (1)

[Scope of Claims] 1. (a) nitrocellulose prepared in advance, (b) an organic solvent that is inert to isocyanate groups and dissolves nitrocellulose, and (c) an organic solvent that is inert to isocyanate groups and does not dissolve nitrocellulose. A non-adhesive nitrocellulose composition consisting of an organic solvent and in which these three components form a uniform solid phase is added to the binder in terms of pure nitrocellulose,
1. A method for producing a magnetic coating composition for a magnetic recording medium, characterized by adding 10 to 50% by weight.