JPH0619821B2 - Magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium such as a magnetic tape, and more particularly to improvement of a binder contained in a magnetic layer formed on a non-magnetic support.

Conventionally, vinyl chloride-vinyl acetate copolymers, cellulose derivatives, polyester resins, etc. have been widely used as binders in magnetic recording media. Further, in order to improve the wear resistance of the magnetic layer, or in the coating of the magnetic layer. A thermoplastic polyurethane resin is used to adjust the physical properties.

On the other hand, high density recording is required for the magnetic recording medium, and as a result, the surface of the magnetic layer of the magnetic recording medium is smoothed more and more.

However, when the smoothness of the surface of the magnetic layer is improved as described above, the contact area increases, which not only adversely affects the running property and durability of the magnetic recording medium but also significantly deteriorates the blocking resistance. In particular, conventionally used binders are poor in heat resistance such as low softening point and high glass transition point, so that adhesion or peeling of the magnetic layer to the non-magnetic support occurs and the performance as a magnetic recording medium is sufficient. There is a problem that you can not exert it.

Therefore, in order to improve the heat resistance of the thermoplastic polyurethane resin and improve the blocking resistance of the magnetic recording medium, the proportion of the low molecular weight diol, which is a component of the thermoplastic polyurethane resin, is increased to increase the concentration of urethane groups in the molecule. It has been considered to use a thermoplastic polyurethane resin having increased content as a binder for a magnetic recording medium.

Generally, increasing the urethane group concentration can modify the thermal properties of the thermoplastic polyurethane resin. That is, a thermoplastic polyurethane resin having a high softening point and a low glass transition point can be obtained as the concentration of urethane groups in the molecule increases. However, when the urethane group concentration of the thermoplastic polyurethane resin increases, it becomes insoluble in a general-purpose solvent system used for manufacturing a ketone-based, alcohol-based, ester-based, aromatic hydrocarbon-based, aliphatic hydrocarbon-based magnetic recording medium, It has a drawback that it is soluble only in a slightly toxic solvent such as dimethylformamide or tetrahydrofuran. Solvents such as dimethylformamide and tetrahydrofuran attack the base film, coating surface, adherend surface, and other parts of the material that are exposed to the solvent, causing wrinkles and unevenness in some areas, and in some cases dissolving them. Occurs,
There is a limit to the improvement by increasing the urethane group concentration of the thermoplastic polyurethane resin.

The present inventors have conducted extensive studies to solve the above-mentioned problems, and as a result, as a binder for the magnetic layer, thermoplastic polyurethane-
By using a urea resin or a cured product obtained by reacting the thermoplastic polyurethane resin with a polyisocyanate curing agent, blocking resistance and durability can be significantly improved, and the thermoplastic polyurethane-urea resin is a general-purpose solvent system. The present invention has been completed by finding that it is easily dissolved in a magnetic recording medium in which a coating layer mainly composed of a ferromagnetic powder and a binder is formed on a non-magnetic support. In a magnetic recording medium in which a coating layer composed mainly of a ferromagnetic powder and a binder is formed on a non-magnetic support, the upper coating layer has a molecular weight of 500 or more, 5
It is obtained by reacting a long-chain diol of 000 or less, a short-chain diol having a molecular weight of 50 or more and less than 500, an organic diamine, and an organic diisocyanate, and the total amount of the urethane group concentration and the urea group concentration is 1.8 mmol / g ~
It contains a thermoplastic polyurethane-urea resin having a concentration of 3.0 mmol / g and a urea group concentration / urethane group concentration of 0.3 to 1.6 as a binder, and further contains the above thermoplastic polyurethane-urea resin and poly It contains a cured product obtained by a reaction with an isocyanate curing agent.

The thermoplastic polyurethane-urea resin used in the present invention is characterized by having a urethane bond and a urea bond (urea bond) in its molecule, and the urethane bond and the urea bond are the thermal bond of the binder resin. It plays an important role in improving the properties, can increase the softening point, which is a measure of heat resistance, and lower the glass transition point, maintain stable physical properties of the magnetic layer over a wide temperature range, and have blocking resistance. Exerts a remarkable effect on the improvement of.

The thermoplastic polyurethane-urea resin used in the present invention contains both a urethane group and a urea group, and the introduction of the urea group has a remarkable effect of improving the thermal properties of the resin like the urethane group, and is more important. This means that a soluble resin can be obtained by using a combination of the above-mentioned ketone-based, alcohol-based, ester-based, aromatic hydrocarbon-based, and aliphatic hydrocarbon-based solvents by introducing the urea group.
Further, since the concentration of the polar group (urethane group, urea group) in the molecule of the thermoplastic polyurethane-urea resin can be made larger than that of a general thermoplastic polyurethane resin, the interaction between the molecule and the molecule is strengthened, and the magnetic layer obtained is The physical properties of the coating film are improved and the durability is also effective. That is, by using the thermoplastic polyurethane-urea resin as a binder for a magnetic recording medium, it is possible to provide a magnetic recording medium excellent in blocking resistance and durability.

The total concentration of urethane groups and urea groups of the thermoplastic polyurethane-urea resin is 1.8 mmol / g to 3.
It is preferably 0 mmol / g. The concentration is 1.8 mmol
If it is less than / g, the softening point of the resin will be lowered and the blocking resistance will not be improved, and if it exceeds 3.0 mmol / g, it will be insoluble in a general-purpose solvent and only dissolved in dimethylformamide and the like. The ratio of urea group concentration / urethane group concentration is preferably 0.3 to 1.6. If the urea group concentration / urethane group concentration ratio is less than 0.3, it becomes insoluble in a general-purpose solvent, and if the urea group / urethane group concentration ratio exceeds 1.6, the glass transition point of the resin becomes high.

The thermoplastic polyurethane-urea resin has a number average molecular weight of 10,000 to 10,000, more preferably 1
It is preferably in the range of 0000 to 60,000. When the number average molecular weight is less than 10,000, the resin film-forming ability becomes insufficient, and the number average molecular weight is 60,000.
If it exceeds the above range, problems may occur in the steps of mixing, coating, etc. in the production of paint.

Further, the softening point of the thermoplastic polyurethane-urea resin is preferably 80 ° C or higher, more preferably 100 ° C or higher. If the softening point is lower than this, the properties approach those of conventional thermoplastic polyurethane resins, and it becomes impossible to improve the blocking resistance and physical properties.

The thermoplastic polyurethane-urea resin preferably has a glass transition point of 0 ° C or lower, more preferably -10 ° C or lower. If the glass transition point is higher than this, the transition region of physical properties approaches room temperature, which is not preferable.

The long-chain diol used for producing the thermoplastic polyurethane-urea resin has a molecular weight of 500 or more and 5000 or less, and is roughly classified into polyester diol, polyether diol, polyether ester glycol and the like. Specific examples of the polyester diol include aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid and azelaic acid, aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid or lower alcohol esters thereof, and ethylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 1,6
-Polyester diols obtained by reacting hexane glycol, diethylene glycol, neopentyl glycol, ethylene oxide adduct of bisphenol A, etc., or a mixture thereof, or a lactone system obtained by ring-opening polymerization of a lactone such as ε-caprolactone The polyester diols of Examples of the polyether diol include polyalkylene ether glycols such as polyethylene glycol, polypropylene ether glycol, polytetramethylene ether glycol, and copolymerized polyether glycols thereof. Examples of the polyether ester glycol include polyester glycols obtained by reacting the above polyalkylene ether glycol as a polyol component with an aliphatic or aromatic dicarboxylic acid. If the molecular weight of this long-chain diol is too small, the concentration of urethane groups in the resulting thermoplastic polyurethane-urea resin will be too high and the flexibility of the resin will be poor, and the solubility in the solvent will be poor, and the magnetic recording medium Less preferred for use as a binder. Also,
When the molecular weight of the long-chain diol is too large, the content of the long-chain diol in the resin becomes too large and the urethane group concentration becomes relatively small, so that the abrasion resistance and heat resistance of the resin deteriorate.

The short chain diol used for producing the thermoplastic polyurethane-urea resin has a molecular weight of 50 or more and 50 or more.
Is less than 0, for example, ethylene glycol, propylene glycol, 1,4-butylene glycol, 1,6
-Aromatic diols such as aliphatic glycols such as hexane glycol and neopentyl glycol, bisphenol A ethylene oxide adducts or propylene oxide adducts, hydroquinone ethylene oxide adducts, etc. These may be used alone or as a mixture in various quantitative ratios.

Examples of the organic diamine used for producing the thermoplastic polyurethane-urea resin used in the present invention include aliphatic diamines such as tetramethylenediamine and hexamethylenediamine, m-phenylenediamine, p-phenylenediamine and 2,4-tridiamine. Diamine, 2,6-tolylenediamine, m-xylylenediamine, p-xylylenediamine, diphenylmethanediamine, 3,3'-dimethoxy-4,4'-biphenylenediamine, 3,3'-dimethyl-4, Aromatic diamines such as 4'-biphenylenediamine, 4,4'-diaminodiphenyl ether, 1,5-naphthalenediamine and 2,4-naphthalenediamine, 1,3-diaminomethylcyclohexane, 1,4-
Examples thereof include alicyclic diamines such as diaminomethylchlorohexane, 4,4'-diaminodicyclohexylmethane and isophoronediamine.

Examples of the organic diisocyanate used for producing the thermoplastic polyurethane-urea resin used in the present invention include aliphatic diisocyanates such as tetramethylene diisocyanate and hexamethylene diisocyanate, m-phenylene diisocyanate, p- Phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 3,3'- Aromatic diisocyanates such as dimethyl-4,4'-biphenylene diisocyanate, 4,4'-diisocyanate diphenyl ether, 1,5-naphthalene diisocyanate and 2,4-naphthalene diisocyanate, 1,3 -Diisocyanatomethyl cyclohexa , 1,4-diisocyanate methylcyclohexane, 4,4'-diisocyanate dicyclohexylmethane, and alicyclic diisocyanates such as isophorone diisocyanate.

Further, when the above-mentioned thermoplastic polyurethane-urea resin is used in combination with a polyisocyanate curing agent, a magnetic recording medium having excellent wear resistance can be obtained. As the polyisocyanate used as the curing agent, any polyisocyanate conventionally usable as the curing agent such as Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) and Desmodur L (manufactured by Bayer Co.) can be used. Can also be used. Also, the polyisocyanate curing agent may be used in an amount that is normally used.

Next, a method for producing the thermoplastic polyurethane-urea resin used in the magnetic recording medium of the present invention will be described.

The thermoplastic polyurethane-urea resin used in the present invention is
It is obtained by polyaddition reaction of a long-chain diol having a molecular weight of 500 or more and 5000 or less, a short-chain diol having a molecular weight of 50 or more and less than 500, an organic diamine and an organic diisocyanate.

In the polyaddition reaction, a mixture of a long-chain diol and a short-chain diol is previously reacted with an organic diisocyanate to prepare a prepolymer having an isocyanate group terminal, and then an organic diamine is added to perform chain extension and introduction of a urea group. There is a prepolymer method to do.

In the above reaction, the molar ratio of the short chain diol to the long chain diol is preferably 3 or less. If this molar ratio is too large, the urethane group concentration becomes too high, and the produced polyurethane-urea resin cannot be dissolved in the above-mentioned general-purpose solvent used when preparing a magnetic coating, which is not suitable. When a straight chain diol such as ethylene glycol, 1,4-butylene glycol or 1,6-hexane glycol is used as the short chain diol, the above molar ratio is preferably 1 or less, preferably 0.5 or less, and neopentyl glycol. If a branched short-chain diol such as bisphenol A or an ethylene oxide or propylene oxide adduct of bisphenol A is used, the solubility of the resin is good, so that the above-mentioned molar ratio can be increased as compared with the linear diol. But,
Even in this case, if the above-mentioned molar ratio exceeds 3 and is too large, the solubility is deteriorated, which is not preferable.

In the production of the thermoplastic polyurethane-urea resin used in the present invention, the long-chain diol having a molecular weight of 500 or more and 5000 or less is a polyester diol among the above-mentioned examples, particularly polybutylene adipate, polyhexamethylene adipate, polycaprolactone. It is preferable to use a diol. Also, the molecular weight is 50 or more, 500
As the short-chain diol of less than 1, it is preferable to use a branched short-chain diol among the above-mentioned examples, especially neopentyl glycol. Further, as the organic diamine, it is particularly preferable to use isophoronediamine in the above-mentioned examples. As the organic diisocyanate, among the above-mentioned examples, 4,4'-diphenylmethane diisocyanate,
Preference is given to using isophorone diisocyanate.

Further, as the method of the polyaddition reaction employed in the production of the thermoplastic polyurethane-urea resin used in the present invention, melt polymerization in which the reaction is carried out in a molten state, ethyl acetate, methyl ethyl ketone, acetone, toluene alone or a mixed solvent such as Although there is solution polymerization or the like which is carried out by dissolving the above-mentioned raw materials in an inert solvent, solution polymerization is preferable for the production of a resin often used by being dissolved in a solvent such as a binder of a magnetic recording medium, and particularly It is more preferable that melt polymerization is carried out during preparation of the prepolymer, and solution polymerization is carried out by adding the above-mentioned inert solvent before carrying out the chain extension reaction.

During the reaction, an organometallic compound such as stannous octylate or an organotin compound such as dibutyltin dilaurate, or a tertiary amine such as N-methylmolarurine or triethylamine may be added as a catalyst. Also, to increase the stability of the product, antioxidants, UV absorbers,
A hydrolysis inhibitor or the like may be added.

The above-mentioned thermoplastic polyurethane-urea resin can be used in combination with other thermoplastic resin, thermosetting resin or reactive resin. In this case, the blending ratio of the thermoplastic polyurethane-urea resin to all the binders in the magnetic layer is preferably 5% by weight or more. The blending ratio of thermoplastic polyurethane-urea resin to all binders is 5
If it is less than wt%, improvement in blocking resistance of the magnetic recording medium can hardly be expected. The above-mentioned thermoplastic resin has a softening temperature of 150 ° C. or lower and an average molecular weight of 1,000.
0 to 200000 and a degree of polymerization of about 200 to 2000, for example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer Polymer, thermoplastic polyurethane elastomer,
Examples thereof include synthetic rubber thermoplastic resins such as polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative, polyester resin and polybutadiene. Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin, polyurethane curable resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose-melamine resin, and high resin. Mixture of molecular weight polyester resin and isocyanate prepolymer, mixture of methacrylate copolymer and diisocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, low molecular weight glycol / high molecular weight diol / triphenylmethane Examples include mixtures of triisocyanates, polyamine resins, and mixtures thereof.

Particularly vinyl chloride in the above resin - vinyl acetate copolymer, a polyurethane resin, a polyester resin, -SO ₃ M ₁ group in cellulose derivative, -OSO ₃ M ₁ group, -COOM
₁ unit, (However, M ₁ represents hydrogen or an alkali metal,
₂ represents hydrogen, an alkali metal or a hydrocarbon group. )
By using a resin containing a hydrophilic polar group such as the above in the molecule and the above thermoplastic polyurethane-urea resin in combination, a magnetic recording medium having improved magnetic properties and improved dispersibility of the magnetic powder in the magnetic layer can be obtained.

The magnetic layer is formed by dispersing the ferromagnetic powder in the above-mentioned binder, dissolving it in an organic solvent and coating it on a non-magnetic support.

Examples of the ferromagnetic powder used in the present invention include ferromagnetic iron oxide particles, ferromagnetic chromium dioxide, and ferromagnetic alloy powder.

As the ferromagnetic iron oxide particles, when represented by the general formula FeOx, those having an X value in the range of 1.33 ≦ X ≦ 1.50, that is, maghemite (γ-Fe ₂ O ₃ , X = 1. 50),
Magnetite (Fe ₃ O ₄ , X = 1.33) and solid solutions thereof (FeOx, 1.33 <X <1.50). These γ-Fe ₂ O ₃ and Fe ₃ O ₄ are usually obtained by the following production method.
That is, an alkali is added to a ferrous salt solution to produce ferrous hydroxide, and air is blown at a predetermined temperature and pH to oxidize to obtain acicular hydrous iron oxide, which is used as a starting material in the air. It is heated and dehydrated at 250 to 400 ° C., and then heat reduced at 300 to 450 ° C. in a reducing atmosphere to obtain needle-shaped magnetite particles. Further, if necessary, the magnetite may be added to 200-
Needle-shaped maghemite (γ-Fe ₂ O ₃ ) reoxidized at 350 ℃
And Further, cobalt may be added to these ferromagnetic iron oxides for the purpose of increasing coercive force. Cobalt-containing magnetic iron oxide is roughly classified into two types: a doped type and an adhered type.
CO-doped iron oxide particles are produced by the following methods: (1) hydrothermal treatment of ferric hydroxide containing cobalt hydroxide in an alkaline atmosphere to reduce and oxidize the produced powder (2) synthesis of goethite At this time, a solution of cobalt salt is added in advance and the pH is adjusted to synthesize cobalt-containing goethite, which is then reduced and oxidized. (3) Goethite containing no Co To
The same reaction as in (2) is performed to grow Goethite containing Co, and then reduction / oxidation is performed. (4) The surface of acicular goethite or maghemite is treated with an alkaline aqueous solution containing a Co salt. Then, there is a method of adsorbing a Co compound and then reducing / oxidizing or heat treating at a relatively high temperature. In addition, Co-adhered iron oxide magnetic particles are prepared by mixing acicular magnetic iron oxide and cobalt iron in an alkaline aqueous solution and heating them to adsorb cobalt compounds such as cobalt hydroxide on the iron oxide particles and washing them with water.・ Dry out and then remove
It can be obtained by heat treatment in a non-reducing atmosphere such as N ₂ gas in air.

The Co-adhered particles have a characteristic of being excellent in transfer characteristics and demagnetization characteristics when formed into a tape, as compared with Co-doped particles.

The ferromagnetic chromium dioxide may be CrO ₂ or Ru, Sn, Te, Sb, Fe, for the purpose of improving coercive force.
It is possible to use a material to which at least one of Ti, V, Mn and the like is added. CrO ₂ is basically obtained by pyrolyzing chromium trioxide (CrO ₃ ) in the presence of water at 400 to 525 ° C. at 500 atm. In addition, as a synthetic method under atmospheric pressure, CrO ₃ is used in the presence of nitric oxide (NO) in addition to oxygen.
There is also a method of decomposing at ˜375 ° C. As the ferromagnetic alloy powder, Fe, Co, Ni, Fe-Co, Fe-Ni or Fe-Co-Ni
Etc. can be used, and for the purpose of improving various characteristics of these
Metal components such as Al, Si, Ti, Cr, Mn, Cu and Zn may be added. These ferromagnetic alloy powders can be produced by (1) pyrolyzing the organic acid salt (mainly acid salt) of ferromagnetic metal or alloy and reducing it with a reducing gas (2) needle-shaped iron oxyhydroxide or A method of reducing those containing Co or acicular magnetic iron oxide in a reducing gas (3) A method of evaporating a ferromagnetic metal or alloy in an inert gas (4) A method of decomposing a metal carbonyl compound ( 5) Method to separate and remove mercury after depositing ferromagnetic metal powder by mercury electrolysis (6) In solution, add salt of ferromagnetic metal in sodium hypophosphite or sodium borohydride There is a method of wet reduction with.

Further, in addition to the binder and the ferromagnetic fine powder, a dispersant, a lubricant, an abrasive, an antistatic agent, an anticorrosive agent, etc. may be added to the magnetic layer.

Examples of the dispersant (pigment wetting agent) include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid,
Fatty acids having 12 to 18 carbon atoms such as linolenic acid and stearolic acid (R ₁ COOH, R ₁ is an alkyl or alkenyl group having 11 to 17 carbon atoms), alkali metals of the above fatty acids (Li, Na, K, etc.) ) Or alkaline earth metal (Mg,
Ca, Ba) metal soap, fluorine-containing compound of the above fatty acid ester, amide of the above fatty acid, polyalkylene oxide alkyl phosphate ester, trialkylpolyolefinoxy quaternary ammonium salt (where alkyl is 1 to 5 carbon atoms) And olefins such as ethylene and propylene) are used. In addition to these, higher alcohols having 12 or more carbon atoms, and other than these, sulfuric acid esters and the like can also be used. These dispersants are added in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of the binder.

Examples of the lubricant include dialkyl polysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxy polysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkyl monoalkoxy polysiloxane (alkyl has 1 to 5 carbon atoms). ,
Alkoxy has 1 to 4 carbons), phenyl polysiloxane, fluoroalkyl polysiloxane (alkyl has 1 to 5 carbons), etc. Silicon oil, conductive fine powder such as graphite, molybdenum disulfide, inorganic such as tungsten dioxide Fine powder, polyethylene, polypropylene, polyethylene vinyl chloride copolymer, plastic fine powder such as polytetrafluoroethylene, α-olefin polymer, unsaturated aliphatic hydrocarbon liquid at room temperature (n-olefin double bond is a terminal Compound bound to carbon, carbon number about 2
0), monobasic fatty acids having 12 to 20 carbon atoms and 3 carbon atoms
Fatty acid esters, fluorocarbons and the like composed of 12 monohydric alcohols can be used. These lubricants are added in the range of 0.2 to 20 parts by weight with respect to 100 parts by weight of the binder.

The above-mentioned abrasives are commonly used materials such as fused alumina, silicon carbide, chromium oxide (Cr ₂ O ₃ ), corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main components: corundum and magnetite), etc. Is used. These abrasives have a Mohs hardness of 5
The above is used, and those having an average particle diameter of 0.05 to 5 µ are used, and particularly preferably 0.1 to 2 µ. These abrasives are used in an amount of 0.5-2 with respect to 100 parts by weight of the binder.
It is added in the range of 0 parts by weight.

Examples of the antistatic agent include conductive fine powders such as carbon black and carbon black graft polymer, natural surfactants such as saponin, alkylene oxides,
Nonionic surfactants such as glycerin type and glycidol type, higher alkyl amines, quaternary ammonium salts,
Pyridine and other heterocyclics, cationic surfactants such as phosphoniums, carboxylic acids, sulfonic acids, phosphoric acids, anionic surfactants containing acidic groups such as sulfate ester groups and phosphate ester groups, amino acids, aminosulfonic acids An amphoteric activator such as sulfuric acid or phosphoric acid ester of amino alcohol is used. The conductive fine powder is added in an amount of 0.2 to 20 parts by weight, and the surfactant is added in an amount of 0.1 to 10 parts by weight, based on 100 parts by weight of the binder. You may add these surfactant individually or in mixture. Although these are used as antistatic agents, they are sometimes used for other purposes such as dispersion, improvement of magnetic properties, improvement of lubricity, and coating aid.

As the rust inhibitor, phosphoric acid, sulfamide, guanidine, pyridine, amine, urea, zinc chromate, calcium chromate, strontium chromate and the like can be used, but especially dicyclohexylamine kitelite, cyclohexylamine chromate, diisopropylamine nitrite, diethanolamine. Evaporative rust inhibitors such as phosphate, cyclohexyl ammonium carbonate, hexamethylene diamine carbonate, propylene diamine stearate, granidine carbonate, triethanolamine nitrite, morpholine stearate (amine, amide or imide inorganic acid salt or organic acid The use of (salt) improves the rust prevention effect. These rust preventives were added in an amount of 0.
It is used in the range of 01 to 20 parts by weight.

Further, the constituent material of the magnetic layer is dissolved in an organic solvent to prepare a magnetic paint, which is applied on a non-magnetic support. The solvent of the magnetic paint is a ketone-based solvent such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone. , Ester type such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol monoethyl ether acetate, glycol dimethyl ether, glycol monoethyl ether, glycol ether type such as dioxane, aromatic hydrocarbon such as benzene, toluene, xylene, Hexane, heptane and other aliphatic hydrocarbons, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform,
Examples thereof include chlorinated hydrocarbons such as ethylene chlorohydrin and dichlorobenzene. The material of the non-magnetic support is polyethylene terephthalate, polyethylene-2,
Polyesters such as 6-naphthalate, polyethylene,
Polyolefins such as polypropylene, cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate such as cellulose acetate propionate, polyvinyl resins such as polyvinyl chloride and polyvinylidene chloride, plastics such as polycarbonate, polyimide and polyamideimide. In addition, non-magnetic metals such as aluminum, copper, tin, zinc or non-magnetic alloys containing them, ceramics such as glass, pottery and porcelain, paper, baryta or polyethylene, polypropylene, ethylene-butene Papers such as papers coated or laminated with α-polyolefins having 2 to 10 carbon atoms such as polymers can also be used. The form of the non-magnetic support may be any of film, tape, sheet, disk, card, drum and the like.

Hereinafter, the present invention will be described with reference to examples. Needless to say, the present invention is not limited to these examples.

Resin synthesis example In a reaction vessel equipped with a heating and cooling device equipped with a stirring propeller, a thermometer and a condenser, a molecular weight of 1
000 polybutylene adipate (manufactured by Nippon Polyurethanes Co., Ltd., trade name Nipporan 4009, structural formula -CH (CH ₃ ) -CH (CH ₃ ) -O
OC (CH ₂ ) ₄ COO-) 1000 g (1.0 mol), neopentyl glycol 26 g (0.25 mol), 4,4'-diphenylmethane diisocyanate 500 g (2.0 mol)
And charged with methyl ethyl ketone 700g 75-80
After reacting for 4 hours at ℃, methyl ethyl ketone 90
0 g was added and cooled to around room temperature. Then, a diamine solution in which 122.4 g (0.72 mol) of isophoronediamine was dissolved in 1345 g of methyl ethyl ketone and 2000 g of cyclohexanone was added. Since the solution viscosity rapidly increases as the diamine solution is added, when the predetermined viscosity is reached, residual glycol is added to meet the NCO group concentration and the end is
Modified to OH group. The obtained polyurethane-urea resin solution was a transparent viscous liquid having a solid content of 25% and a viscosity of 10000 CP / 25 ° C., and did not thicken or thixotropic even after long-term storage, and had good liquidity. .

According to the above synthesis method, Samples A to K were synthesized as shown in Table 1 by arbitrarily changing the mole numbers of polybutylene adipate, neopentyl glycol, 4,4-diphenylmethane diisocyanate and isophoronediamine. The properties of the resulting resin are shown in Table 1.

Sample A in Table 1 is polybutylene adipate 100.
0 g (1.0 mol), 18 g of 1,4-butanediol
(0.2 mol) and 300 g (1.2 mol) of 4,4-diphenylmethane diisocyanate were synthesized, and the concentration of urethane group containing no urea group was 1.8 mm.
It is a polyester polyurethane resin with an ol / g level.

In addition, in Table 1, the glass transition temperature was measured by the TBA method using a torsion blade analysis (manufactured by Rigaku Denki Co., Ltd.), and the softening point was cut with a JIS No. 2 tumbler to cut the sample.
The temperature was raised at a rate of 5 ° C. per minute while applying a load equivalent to g / 100 μm, and the temperature was set to a temperature at which the amount of deformation rapidly increased.

A magnetic recording medium is prepared using the resin shown in Table 1.

Example 1 100 parts by weight of γ-Fe ₂ O _{3 for} Co deposition Vinyl chloride-vinyl acetate copolymer 17.5 〃 (UCGH VAGH) Thermoplastic polyurethane-urea resin 7.5 〃 (Sample F) Dispersant (lecithin) 1 〃 Lubricant (silicon oil) 1 〃 Abrasive (Cr ₂ O ₃ ) 2 〃 Methyl ethyl ketone 100 〃 Methyl isobutyl ketone 50 〃 Toluene 50 〃 The above composition was mixed in a ball mill for 48 hours and filtered with a 3μ filter L (Made by Bayer)
Was added as a curing agent in an amount of 2.5 parts by weight, and the mixture was further mixed for 30 minutes, and this was coated on a polyethylene terephthalate film having a thickness of 16 μm so that the thickness after drying would be 6 μm. I wound it up. This was calendered and then cut into a 1/2 inch width to prepare a sample tape.

Example 2 Co Coated γ-Fe ₂ O ₃ 100 parts by weight Vinyl chloride-vinyl acetate copolymer 12.5 〃 (VAGH) Thermoplastic polyurethane-urea resin 12.5 〃 (Sample F) Dispersant (lecithin) 1 〃 Lubricant ( Silicon oil) 1 〃 Abrasive (Cr ₂ O ₃ ) 2 〃 Methyl ethyl ketone 100 〃 Methyl isobutyl ketone 50 〃 Toluene 50 〃 Using the above composition, a sample tape was prepared in the same manner as in Example 1.

Example 3 Co Coated γ-Fe ₂ O ₃ 100 parts by weight Vinyl chloride-vinyl acetate copolymer 7.5 〃 Thermoplastic polyurethane-urea resin 17.5 〃 (Sample F) Dispersant (lecithin) 1 part by weight Lubricant (silicon oil) 1) Abrasive (Cr ₂ O ₃ ) 2 〃 Methyl ethyl ketone 100 〃 Methyl isobutyl ketone 50 〃 Toluene 50 〃 Using the above composition, a sample tape was prepared in the same manner as in Example 1.

Example 4 A sample tape was prepared in the same manner as in Example 1, except that the thermoplastic polyurethane-urea resin (Sample F) was replaced with the thermoplastic polyurethane-urea resin (Sample B) in the composition of Example 2. .

Example 5 A sample tape was prepared in the same manner as in Example 1 except that in the composition of Example 2, the thermoplastic polyurethane-urea resin (Sample F) was used in place of the thermoplastic polyurethane-urea resin (Sample F). .

Example 6 A sample tape was prepared in the same manner as in Example 1 except that in the composition of Example 2, the thermoplastic polyurethane-urea resin (Sample F) was used in place of the thermoplastic polyurethane-urea resin (Sample D). .

Example 7 A sample tape was prepared in the same manner as in Example 1, except that the thermoplastic polyurethane-urea resin (Sample E) was used in place of the thermoplastic polyurethane-urea resin (Sample F) in the composition of Example 2. .

Example 8 A sample tape was prepared in the same manner as in Example 1 except that the thermoplastic polyurethane-urea resin (Sample F) was replaced with the thermoplastic polyurethane-urea resin (Sample G) in the composition of Example 2. .

Comparative Example 1 A sample tape was prepared by the same method as in Example 1 except that the polyester polyurethane resin (Sample A) was used in place of the thermoplastic polyurethane-urea resin (Sample F) in the composition of Example 1.

Comparative Example 2 A sample tape was prepared in the same manner as in Example 1 except that the polyester polyurethane resin (Sample A) was used in place of the thermoplastic polyurethane-urea resin (Sample F) in the composition of Example 3.

Comparative Examples 3 to 6 In the composition of Example 3, thermoplastic polyurethane-urea resin (Sample H) to thermoplastic polyurethane-Silea resin (Sample K) were used in place of the thermoplastic polyurethane-urea resin (Sample F). Otherwise, a sample tape was prepared by the same method as in Example 1. However, in Comparative Example 4 and Comparative Example 6 in which the thermoplastic polyurethane-urea resin (Sample I) and the thermoplastic polyurethane-urea resin (Sample K) were used, these thermoplastic polyurethane-urea resins were not well dissolved in the solvent, It was not possible to make sample tapes whose properties could be evaluated.

The following table shows the measurement results of the tackiness and the still property of the above sample tape.

The adhesive property was determined by winding the sample tape on a reel and leaving it for 24 hours at a temperature of 40 ° C. and a humidity of 80%, visually observing the degree of peeling of the sample tape, and scoring with a 10-point method. The better the adhesive property, the lower the score.

For the still characteristic, a 4.5 MHz video signal was recorded on a sample tape, and the time until the reproduction output was attenuated to 50% was measured.

As described above, by using the thermoplastic polyurethane-urea resin as the binder of the magnetic layer of the magnetic recording medium,
A magnetic recording medium with greatly improved thermal properties, blocking resistance, and durability can be obtained, and by incorporating both a urethane group and a urea group into the resin molecule, a binder soluble in a general-purpose solvent can be obtained. can get.

However, when the urethane group concentration and the urea group concentration are out of the range of the present invention, various disadvantages occur. For example, in Comparative Example 3 using the sample H in which the total amount of the urethane group concentration and the urea group concentration is too small, the mechanical low strength is insufficient, the adhesive property is poor, and the still property is insufficient. Further, in Example 4 using Sample I in which the total amount was too large, the binder was not dissolved in a general-purpose solvent so much, and a proper magnetic recording medium could not be prepared.

On the other hand, in Example 5 using Sample J having a high urea group concentration, the Young's modulus is high, but the breaking strength is low, so the still characteristics are remarkably deteriorated.

Further, in Comparative Example 6 in which the sample K having a low urea group concentration ratio was used, the improvement of the solubility due to the introduction of the urea group was insufficient, and thus an appropriate magnetic recording medium could not be prepared.

Claims (2)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and a coating layer mainly composed of a ferromagnetic powder and a binder, wherein the coating layer is a long-chain diol having a molecular weight of 500 or more and 5000 or less, and a molecular weight. It is obtained by reacting 50 or more and less than 500 short chain diols, organic diamines and organic diisocyanates, and the total amount of urethane group concentration and urea group concentration is 1.8 mmol / g to 3.0 mmol /
A magnetic recording medium containing g, a thermoplastic polyurethane-urea resin having a urea group concentration / urethane group concentration of 0.3 to 1.6 as a binder. 2. A magnetic recording medium comprising a non-magnetic support and a coating layer mainly composed of a ferromagnetic powder and a binder, wherein the coating layer is a long-chain diol having a molecular weight of 500 or more and 5000 or less, and a molecular weight. It is obtained by reacting 50 or more and less than 500 short chain diols, organic diamines and organic diisocyanates, and the total amount of urethane group concentration and urea group concentration is 1.8 mmol / g to 3.0 mmol /
g, a cured product obtained by reacting a thermoplastic polyurethane-urea resin having a urea group concentration / urethane group concentration of 0.3 to 1.6 with a polyisocyanate curing agent is contained as a binder. Magnetic recording medium.