JPH0576093B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium with high packing density. Introducing a polar group such as a sodium sulfonate group into the binder of a magnetic recording medium has the effect of reinforcing the interface between the magnetic powder and the binder, and also improves the dispersion and orientation of the magnetic powder, wear resistance, and durability. However, with such a binder, even if a technique such as kneading is used, it is not effective in densely packing the magnetic layer, and therefore sensitivity, especially in the low frequency region, cannot be improved. In order to achieve high-density packing, materials that alleviate the intermolecular forces of the binder, such as dispersants, have been added, but this has resulted in serious drawbacks in powder shedding and durability. The present invention overcomes these drawbacks and provides a highly densely packed magnetic recording medium. That is, the present invention is directed to a polyester resin containing a sulfonic acid metal base and a monovalent aliphatic hydrocarbon group having 8 to 20 carbon atoms in one molecule, a polyurethane resin, and a vinyl chloride copolymer resin. It is characterized by using a binder which is any one type of resin material and has a monovalent aliphatic hydrocarbon group equivalent of 1,000 to 20,000. In this invention, the sulfonic acid metal base contained in the binder is preferably one or more kinds represented by the general formula: -SO ₃ M (wherein M represents a hydrogen atom, lithium, sodium or potassium). be. This metal sulfonate base adsorbs to the magnetic powder in the magnetic coating material used in manufacturing the magnetic recording medium to prevent agglomeration and promote dispersion. If the amount of the sulfonic acid metal base is too small, such a dispersion effect cannot be sufficiently expected, and if it is too large, the solubility in general-purpose solvents decreases, which is disadvantageous for preparing magnetic paints. For this reason, the sulfonate metal base equivalent (molecular weight per sulfonate metal base) of the binder of the present invention is advantageously within the range of 3,000 to 20,000. The binders of this invention also contain monovalent aliphatic hydrocarbon groups having 8 to 20 carbon atoms. This hydrocarbon group may be linear or branched and may be saturated or unsaturated. The number of unsaturated bonds (double bonds and triple bonds) is also not limited to one, and may be two or more. This hydrocarbon group is effective in relaxing the intermolecular forces of the binder and achieving high density packing. In order to fully obtain this effect, the hydrocarbon group equivalent (molecular weight of the binder per hydrocarbon group) is
It is better to be less than 20000. However, if there are too many hydrocarbon groups, plasticity increases within or between molecules of the binder, which may reduce the mechanical strength of the binder. Therefore, this hydrocarbon group equivalent is
It is better if it is 1000 or more. Further, the number average molecular weight of the binder is preferably in the range of 5,000 to 60,000. This is because if the molecular weight is too small, the physical properties of the coating film formed will deteriorate, and if the molecular weight is too large, the viscosity of the coating will become too high. Further, the ratio Mw/Mn of the weight average molecular weight to number average molecular weight of the binder is preferably 1.5 to 3.5. The binder used in this invention can be obtained by introducing a sulfonic acid metal base and a monovalent aliphatic hydrocarbon group as described above into a resin such as a polyester resin, a polyurethane resin, or a vinyl chloride copolymer resin. Methods for introducing it include (1) a method in which a monomer containing the sulfonic acid metal base or the hydrocarbon group is partially used as a starting material monomer for polyester resin or polyurethane resin; (2) active hydrogen A compound containing a halogen atom and the sulfonic acid metal base, and a compound containing a halogen atom and the hydrocarbon group are added to a polyester resin, a polyurethane resin, a vinyl chloride resin, etc. containing a dehydrohalogenating agent. A method such as reacting each in the presence of the two is applicable. In this invention, the carboxylic acid component of the polyester resin used as the binder includes terephthalic acid, isophthalic acid, orthophthalic acid, 1,5-
Aromatic dicarboxylic acids such as naphthalic acid, aromatic oxycarboxylic acids such as p-oxybenzoic acid and p-(hydroxyethoxy)benzoic acid, aliphatic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. Mention may be made of dicarboxylic acids, tri- and tetracarboxylic acids such as trimellitic acid, trimesic acid, and pyromellitic acid. Particularly preferred are terephthalic acid, isophthalic acid, adipic acid, and sebacic acid. The polyhydric alcohol component of the polyester resin includes ethylene glycol, propene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-
hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol,
2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, ethylene oxide adduct of bisphenol A, ethylene oxide adduct and propylene oxide adduct of hydrogenated bisphenol A, polyethylene glycol, Examples include polypropylene glycol and polytetramethylene glycol. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol may be used in combination. Among the carboxylic acid components containing the sulfonic acid metal base that can be used to introduce the sulfonic acid metal base into the polyester resin, -SO ₃ -containing carboxylic acids include 5-sodium sulfoisophthalic acid and 5-potassium sulfoisophthalic acid. , 5-sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, 2-potassium sulfoterephthalic acid, 2-sulfoterephthalic acid, and mixtures thereof. In addition to these typical compounds, any of the organic acids exemplified above as the carboxylic acid component and having the sulfonic acid metal base can be used. It is also possible to use a polyhydric alcohol component in which a sulfonic acid metal base is introduced. Furthermore, the monovalent aliphatic hydrocarbon group can also be synthesized by using a carboxylic acid or polyhydric alcohol containing this monovalent aliphatic hydrocarbon group as a part of the carboxylic acid component or polyhydric alcohol component. As a result, they can be incorporated into polyester resins.
As such hydrocarbon group-containing carboxylic acids,
Esters of a dicarboxylic acid containing a hydroxyl group such as malic acid or tartaric acid and a fatty acid having 9 to 21 carbon atoms or a halide thereof can be used. In addition, as the hydrocarbon group-containing polyhydric alcohol, triols such as glycerin, trimethylolpropane, and trimethylolethane, and carbon atoms of 9 to
21 fatty acids or monoesters with their halides, etc. can be used. Fatty acids with 9 to 21 carbon atoms include saturated fatty acids such as nonanoic acid, capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid, as well as oleic acid, linoleic acid, linoleic acid, elaidic acid, stearolic acid, and taliline. Examples include unsaturated fatty acids such as acids, and halides of these include chlorides and bromides. The polyurethane resin containing the sulfonic acid metal base and the monovalent aliphatic hydrocarbon group that can be used as a binder in the present invention can be synthesized by further using a diisocyanate together with the compounds of each component of the polyester resin as described above. It can be obtained by Examples of the diisocyanate include aliphatic diisocyanates such as tetramethylene diisocyanate and hexamethylene diisocyanate, m-phenylene diisocyanate,
p-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-xylylene diisocyanate,
p-xylylene diisocyanate, diphenylmethane diisocyanate, 3,3'-dimethoxy-4,
4'-biphenylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 4,4'-diisocyanate diphenyl ether, 1,5-naphthalene isocyanate, 2,4
Examples include aromatic diisocyanates such as -naphthalene diisocyanate, alicyclic diisocyanates such as 1,3-diisocyanatemethylcyclohexane, 1,4-diisocyanatemethylcyclohexane, 4,4'-diisocyanatedicyclohexylmethane, and isophorone diisocyanate. Polyester resins and polyurethane resins made of such components may be of electron beam curing type.
Electron beam-curable polyurethane resin is made by introducing double bonds by reacting the isocyanate groups at both ends with a (meth)acrylic monomer having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate. You can get it by twisting it. Furthermore, it is also possible to obtain electron beam-curable polyester resins or polyurethane resins by using diols having double bonds such as glycerin mono(meth)acrylate as part of the polyhydric alcohol component of polyester resins and polyurethane resins. can. When modifying a vinyl chloride resin to introduce the sulfonic acid metal base, the vinyl chloride resin that can be used must contain at least vinyl alcohol as a copolymerization component, and further contain vinyl acetate, vinyl propionate, etc. Unsaturated fatty acids such as fatty acid vinyl, acrylic acid, methacrylic acid, and maleic acid may be included in the copolymerization component. This vinyl chloride resin specifically includes vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer,
These include vinyl chloride-vinyl acetate-maleic acid-vinyl alcohol copolymer. Examples of the compound to be reacted to introduce the sulfonic acid metal base into these vinyl _chloride resins include the general formula: ,A
represents a lower alkylene group) Compounds containing a halogen atom and a polar group in one molecule can be used. In addition, in order to introduce a monovalent aliphatic hydrocarbon group with 8 to 20 carbon atoms into a vinyl chloride resin, the aforementioned halides of fatty acids with 9 to 21 carbon atoms are added to the vinyl chloride resin to be modified. All you have to do is react. All of these reactions can be carried out in a solvent such as dimethylformamide or dimethyl sulfoxide in the presence of an amine such as pyridine, picoline or triethylamine, or a dehydrohalogenating agent such as ethylene oxide or propylene oxide. This method of modifying a resin can be applied to any resin having active hydrogen, such as polyester resins and polyurethane resins, in addition to vinyl chloride resins. In this invention, it is preferable that the binder made of the resin containing the sulfonic acid metal base and the monovalent aliphatic hydrocarbon group having 8 to 20 carbon atoms is used in an amount of 30% by weight or more of the total binder component. A sufficient effect on dispersing the powder and relaxing intermolecular forces cannot be expected. Other binders that can be used in combination include vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-acrylonitrile copolymers, and acrylic ester copolymers.
Acrylonitrile copolymer; thermoplastic resin such as thermoplastic polythane elastomer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative, polyester resin, polybutadiene, and phenol Resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, methacrylate Thermosetting materials such as mixtures of acid salt copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight diols, high molecular weight diols, and triphenylmethane triisocyanate, and polyamine resins. resins and mixtures thereof. It is also possible to further improve the abrasion resistance of the magnetic layer by using polyisocyanate as a crosslinking agent in the binder. Furthermore, ferromagnetic iron oxide particles, ferromagnetic chromium dioxide, ferromagnetic alloy powder, etc. can be used as the magnetic powder that constitutes the magnetic layer together with the binder as described above.
Ferromagnetic iron oxide particles have the general formula FeOx (1.33≦V≦
1.50), that is, maghemite (γ
−Fe ₂ O ₃ X=1.50), magnetite (Fe ₃ O ₄ X=
1.33), and their solid solutions (FeOx 1.33<X<
1.50) can be used. These ferromagnetic iron oxides may be doped with or coated with cobalt for the purpose of increasing coercive force. As the ferromagnetic chromium dioxide, CrO 2 or CrO ₂ to which at least one of Ru, Sn, Te, Sb, Fe, Ti, V, Mn, etc. is added for the purpose of improving coercive force can be used.
Ferromagnetic alloy powders include Fe, Co, Ni, Fe-Co,
Fe-Ni or Fe-Co-Ni, etc. can be used, and in order to improve various properties, Al, Si, Ti, Cr,
It may also contain metal components such as Mn, Cu, and Zn. The magnetic layer further contains abrasives such as aluminum oxide, chromium oxide, and silicon oxide, antistatic agents such as carbon black, lubricants such as molybdenum disulfide, graphite, silicone oil, olive oil, and fatty acid esters, and lecithin as a dispersant. , a fatty acid having 12 to 18 carbon atoms (eg, palmitic acid, stearic acid), etc. may be added. The constituent materials of these magnetic layers are dissolved in an organic solvent during manufacture of the magnetic recording medium. Examples of this organic solvent include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; methyl acetate, ethyl acetate, butyl acetate;
Ester systems such as ethyl lactate and acetic acid glycol monoethyl ether; Glycol ether systems such as ether, glycol dimethyl ether, glycol monoethyl ether, and dioxane; Tar systems (aromatic hydrocarbons) such as benzene, toluene, and xylene; Methylene chloride, ethylene chloride,
Chlorinated hydrocarbons such as carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene can be selected and used. A magnetic paint made of these materials is applied to a non-magnetic carrier according to a conventional method. Materials for this non-magnetic carrier include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polyethylene and polypropylene; cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate, etc. Cellulose derivatives; vinyl resins such as polyvinyl chloride and polyvinylidene chloride; polycarbonate,
In addition to plastics such as polyimide and polyamide-imide, non-magnetic metals such as aluminum, copper, tin, zinc, or non-magnetic alloys containing these; ceramics such as glass, earthenware, and porcelain;
Paper, baryta, or polyethylene, polypropylene, ethylene-butene copolymer, etc. with 2 or more carbon atoms
Paper such as paper coated or laminated with α-polyolefins of 10 can also be used. These non-magnetic carriers may be transparent or opaque depending on the intended use. In addition, the form of the non-magnetic carrier is a film,
It may be a tape, sheet, disk, card, drum, etc., and various materials are selected as necessary depending on the form. The thickness of these non-magnetic carriers is approximately 1 to 50μ in the case of films, tapes, and sheets.
m, preferably 1 to 30 μm. In addition, in the case of disks and cards, it is about 0.5 to 10 mm,
If it is drum-shaped, it is cylindrical, and its shape is determined depending on the recorder used. Examples of this invention will be described below. Synthesis Example 1 A polyester resin (A) having the following composition () was synthesized by melt polycondensation according to a conventional method. The number average molecular weight (Mn) of this polyester resin was 40,000 (measured by vapor pressure osmosis method), and the ratio of weight average molecular weight to number average molecular weight (Mw/Mn) was 2.1. Composition () Dibasic acid components: Terephthalic acid 20 mol% Isophthalic acid 20 mol% 5-sodium sulfoisophthalic acid 2.5 mol% Adipic acid 57.5 mol% Diol components: Ethylene glycol 47.5 mol% Neopentyl glycol 50 mol% Trimethylol propane monooleate
2.5 mol% Synthesis Example 2 A polyester resin (B) having the following composition () was synthesized under the same conditions as Synthesis Example 1. This polyester resin had Mn of 37,000 and Mw/Mn of 2.1. Composition () Dibasic acid components: Terephthalic acid 20 mol% Isophthalic acid 20 mol% 5-sodium sulfoisophthalic acid 2.5 mol% Adipic acid 57.5 mol% Diol components: Ethylene glycol 50 mol% Propylene glycol 50 mol% Synthesis example 3 A polyester diol having the following composition () was synthesized. The Mn of this polyester diol is
2000, and the hydroxyl number was 900 equivalents/10 ⁶ g. Composition () Dibasic acid components: Terephthalic acid 20 mol% Isophthalic acid 20 mol% 5-sodium sulfoisophthalic acid 2.5 mol% Adipic acid 57.5 mol% Diol components: Ethylene glycol 50 mol% Neopentyl glycol 50 mol% Next 100 parts by weight of this polyester diol, 4.47 parts by weight of neopentyl glycol, 1.04 parts by weight of glycerin monooleate, 23.0 parts by weight of diphenylmethane diisocyanate and 0.58 parts by weight of dibutyltin dilaurate were mixed in a 1:1 mixed solvent of methyl ethyl ketone and toluene. After dissolving to a concentration of about 30%, the polyurethane resin (A) was synthesized by reacting at 80° C. for 6 to 8 hours under a nitrogen stream in a reaction vessel equipped with a reflux condenser. The reduced viscosity ηsp/c of this polyurethane resin is 0.60 dl/g, and the Mn is
It was 25,000. Synthesis Example 4 100 parts by weight of the polyester diol of Synthesis Example 3,
A polyurethane resin (B) was synthesized in the same manner as in Synthesis Example 3 using 4.78 parts by weight of neopentyl glycol, 23.0 parts by weight of diphenylmethane diisocyanate, and 0.58 parts by weight of dibutyltin dilaurate. The ηsp/c of this polyurethane resin is 0.60dl/g, and the Mn is
It was 24,000. Synthesis Examples 5 and 6 Some of the hydroxyl groups of the vinyl alcohol component are -
Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (B) modified to OSO ₃ Na has Mn=24000, -
The OSO ₃ Na equivalent was 5000 (Synthesis Example 5). Next, 100 g of this vinyl chloride-vinyl acetate-vinyl alcohol copolymer (B) was dissolved in 300 g of a 1:1 mixed solvent of methyl ethyl ketone and toluene, and 1.64 g
of pyridine was mixed. Meanwhile, 6.3 g of oleic acid chloride was dissolved in 10 g of a 1:1 mixed solvent of methyl ethyl ketone and toluene, and the solution was gradually added to the previously prepared mixture while stirring under a nitrogen stream. After the addition, the reaction was carried out under reflux for 4 hours, and the generated pyridine hydrochloride was removed by filtration. In this way, a vinyl chloride-vinyl acetate-vinyl alcohol copolymer (A) was synthesized in which the remaining hydroxyl groups of the copolymer (B) were replaced with oleic ester acid groups. Comparative Example 1 Vinyl chloride as a binder in composition ()
Vinyl acetate-vinyl alcohol copolymer (trade name)
An audio tape was produced using VAGH/USA (manufactured by Union Carbye Co., Ltd.) and in a similar manner. The Br, Rs and S ₃₁₅ of this tape are shown in Table 2. Comparative Example 2 An audio tape was produced using a thermoplastic polyurethane resin (trade name N-2304/manufactured by Nippon Polyurethane Kogyo Co., Ltd.) as the binder in composition () and in the same manner as above. of this tape
Br, Rs and S ₃₁₅ are shown in Table 2. Examples 1 to 3 and Comparative Examples 3 to 5 Using the resins of synthetic agents 1 to 6 and a binder, a magnetic paint having the following composition () was prepared through kneading, dissolving, and mixing steps, and then a 10 μm polyethylene terephthalate film was prepared. The tape was coated on top, the surface was mirror-finished, and the tape was cut to make an audio tape. Composition () γ-Fe ₂ O ₃ 100 parts by weight Binder 20 parts by weight Olive oil 1 part by weight Cr ₂ O ₃ 3 parts by weight Methyl ethyl ketone 180 parts by weight Toluene 180 parts by weight Residual magnetic velocity density of the audio tape thus obtained
Tables 1 and 2 show the results of measuring Br, squareness ratio Rs, and sensitivity S ₃₁₅ at 315 Hz. Note that Br and Rs are measured values when a magnetic field of 2000 Oe is applied.

【table】

【table】

[Table] From the above results, the audio tape of the present invention using polyester resin (A), polyurethane resin (A), and vinyl chloride-vinyl acetate-vinyl alcohol copolymer (A) as binders has a low frequency range. It can be seen that the sensitivity has improved and the packing density has increased.

Claims (1)

[Claims] 1. In a magnetic recording medium in which a magnetic layer mainly composed of magnetic powder and a binder is provided on a non-magnetic support, the binder contains a sulfonic acid metal base and a monovalent fat having 8 to 20 carbon atoms in one molecule. Any one resin material selected from the group consisting of polyester resins, polyurethane resins, and vinyl chloride copolymer resins having group hydrocarbon groups, and the monovalent aliphatic hydrocarbon group equivalent is 1000- 20,000 magnetic recording medium.