JPS6262428A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve a thermal characteristic, blocking resistance, durability, running stability, magnetic characteristics, electromagnetic conversion characteristic, etc. by using a thermoplastic polyurethane/urea resin contg. a siloxane bond in the molecular chain for a binder constituting a magnetic layer. CONSTITUTION:The magnetic layer contains the thermoplastic polyurethane/urea resin having the siloxan bond in the molecular chain. The thermoplastic polyurethane/urea rsin has the urethane bond and urea bond in the molecular chain and further the siloxane bond is incorporated into the molecular chain. The totaled concn. of the urethane group and urea group of the thermoplastic polyurethane/urea resin is preferably 1.8-3.0mmol/g. The concn. siloxane group of the thermoplastic polyurethane/urea resin is preferably 0.03-3mmol/g.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks, and more specifically relates to magnetic recording media such as magnetic tapes and magnetic disks. The present invention relates to improvements in binders used in the manufacturing process.

[Summary of the invention]

The present invention provides a magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic powder and a binder is formed on a non-magnetic support, in which the binder constituting the magnetic layer contains siloxane bonds in the molecular chain. Thermal properties and blocking resistance of the obtained Am magnetic recording medium are determined by using a thermoplastic polyurethane-urea resin or a cured product obtained by the reaction of the thermoplastic polyurethane-urea resin and a polyisocyanate curing agent. This aims to improve durability, running stability, magnetic properties, electromagnetic conversion properties, etc.

[Conventional technology]

Vinyl chloride-vinyl acetate copolymers, cellulose derivatives, polyester resins, etc. have been widely used as binders for conventional magnetic recording media. Thermoplastic polyurethane resins are used to adjust the film properties.

On the other hand, there is a demand for high-density recording in magnetic recording media, and as a result, the surface of the magnetic layer of magnetic recording media is becoming increasingly smooth.

However, as described above, when the surface smoothness of the magnetic layer is improved, the contact area increases, which not only adversely affects the runnability and durability of the magnetic recording medium, but also significantly deteriorates the blocking resistance. In particular, conventionally used hard binders have a low softening point and a high glass transition point, which means they have poor heat resistance, so they tend to stick to or peel off from the magnetic layer (DJP magnetic support), impairing its performance as a magnetic recording medium. The problem has arisen that they are unable to perform to their full potential.

Therefore, in order to improve the heat resistance of the thermoplastic polyurethane resin and the blocking resistance of the magnetic recording medium, we increased the proportion of low molecular weight diol, which is a component of the thermoplastic polyurethane resin, and increased the concentration of urethane groups in the molecule. It has been proposed to use specific thermoplastic polyurethane resins as binders for magnetic recording media.

Generally, the thermal properties of thermoplastic polyurethane resins can be modified by increasing the urethane group concentration. That is, as the concentration of urethane groups in the molecule increases, a thermoplastic polyurethane resin having a high softening point and a very low glass transition point can be obtained. However, as the urethane group concentration of thermoplastic polyurethane resin increases, it becomes insoluble in general-purpose solvent systems used for manufacturing ketone-based, alcohol-based, ester-based, aromatic hydrocarbon-based, and aliphatic hydrocarbon-based magnetic recording media. It has the disadvantage of being soluble only in slightly toxic solvents such as dimethylformamide and tetrahydrofuran. Solvents such as dimethylformamide and tetrahydrofuran attack the parts of the material that are exposed to the solvent, such as the base film, coated surface, and adhered surface; There is a limit to the improvement by increasing the urethane group concentration of thermoplastic polyurethane resins because of the problem of dissolving them.

Furthermore, when the above-mentioned resin is used as a binder for the magnetic layer, there is a problem in running stability because the resin itself lacks lubricity.

[Problem that the invention seeks to solve]

The present invention has been proposed to solve the above problems, and provides a magnetic recording medium with excellent thermal properties, anti-blocking properties, durability, running stability, n1 magnetic properties, and electromagnetic conversion properties. The purpose is to

[Elaborate means to solve problems]

As a result of intensive research, the present inventors have determined that the above object can be achieved by combining a thermoplastic polyurethane/urea resin containing a siloxane bond in the molecular chain or the thermoplastic polyurethane/urea resin with a polyisocyanate curing agent. It was discovered that the cured product obtained by the reaction is useful for improving the blocking resistance of the magnetic layer of magnetic recording media and for improving running stability, and that it is easily dissolved in general-purpose solvent systems and is easy to handle. The present invention has been completed in a magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic powder and a binder is formed on a non-magnetic support, the magnetic layer having siloxane in its molecular chains. It is characterized by containing a thermoplastic polyurethane/urea resin containing a bond as a binder, and further comprises a cured product obtained by the reaction of the thermoplastic polyurethane/urea resin and a polyisocyanate curing agent. It is characterized by containing it as a binder.

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 molecular chain, and further has a siloxane bond introduced into its molecular chain. It is characterized by

In addition, the urethane bond and urea bond described above play an important role in improving the thermal properties of the binder resin, and can increase the softening point temperature, which is a measure of heat resistance, and lower the glass transition point temperature, allowing a wide range of Stable physical properties of the magnetic layer are maintained over a temperature range.

In other words, the introduction of urea groups can significantly improve the thermal properties of the resin, similar to urethane groups.

More importantly, the introduction of this urea group makes it possible to obtain resins that are soluble when used in combination with the aforementioned ketone, alcohol, ester, aromatic hydrocarbon, and aliphatic hydrocarbon solvents. Is Rukoto. In addition, since the concentration of urethane groups and urea groups in the thermoplastic polyurethane/urea resin molecules can be higher than that of general thermoplastic polyurethane resins, the interaction between molecules becomes stronger, resulting in a magnetic layer coating film. Physical properties are improved and durability is also improved. 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 with excellent blocking resistance and durability.

The siloxane bond introduced into the chain of the above-mentioned thermoplastic polyurethane flare resin imparts lubricity to the resin itself, making it possible to provide a magnetic recording medium with excellent running stability.

The total concentration of urethane groups and urea groups in the thermoplastic polyurethane-urea resin is 1.8 mnol/p.
It is preferable that it is 3.0 mmol/#. If the concentration is less than 1 m 8 mmol/P, the softening point of the resin will be lowered and the blocking magnetism will not be improved, and if the concentration exceeds 3.0 mmol/lt, it will become insoluble in general-purpose solvents, such as dimethylformamide. It will no longer dissolve. Further, the ratio of urea group concentration/urethane group concentration is preferably 0.3 to 1.6. If the ratio of urea group concentration/urethane group concentration is less than 0.3, it will become insoluble in general-purpose solvents, and if the ratio of urea group/urethane group concentration exceeds 1.6'i, the glass transition point of the resin will become high. Put it away.

In addition, the above thermoplastic polyurethane/urea resin nosiloxane group concentration is 0.03 oL/g to 3rIrIno
Luno is preferred at 1/y, O,1 mmo 1/
It is more preferable that the value is o1/7 in the y to 0.7 column. If the siloxane group concentration is less than 0.03 mol/f, lubricity cannot be imparted, and if the siloxane group concentration exceeds 3 m +++ ol/Ii', the solubility with the solvent and other binder resins may be reduced. In addition, the physical properties such as the breaking strength and Young's modulus of the magnetic coating film are deteriorated.The number average molecular weight of the thermoplastic polyurethane/urea resin is 10,000-100,000. More preferably 1
The range is preferably from 0,000 to 60,000. If the number average molecular weight is less than 10,000, the coating film forming ability of the resin will be insufficient;
If the amount exceeds this amount, there is a risk that problems may occur in paint production, mixing, coating, and other processes.

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

Further, it is desirable that the glass transition point of the thermoplastic polyurethane/urea resin is 0° C. or lower, more preferably -10'C or lower. If the glass transition point is 9 or higher, the transition region of physical properties approaches room temperature, which is not preferable.

The thermoplastic polyurethane urea resin according to the present invention is obtained by polyaddition reaction of long chain diols, short chain diols, organic diamines and organic diincyanates. In this polyaddition reaction, a mixture of a long-chain diol and a short-chain diol is reacted with an organic diincyanate in advance to prepare a polymer with an incyanate group terminal, and then an organic diamine is added to extend the chain and introduce a urea group. It is carried out by the greborimer method.

The long-chain diol used in the expansion of the thermoplastic polyurethane-urea resin has a molecular weight of about 500 to about 5,000, and is broadly classified into, for example, polyester diol, polyether diol, polyether ester glycol, etc. . Examples of polyester diols include, for example, aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, and azelaic acid; aromatic dicarboxylic acids such as terephthalic acid and inphthalic acid; and lower alcohol nisterates thereof, and ethylene f IJ. Coal, 1,3-propylene glycol, 1,4-7" ethylene glycol,
Polyester diols or ε obtained by reacting 1, 6-hexyl glycol, diethylene glycol, neopentyl glycol, ethylene oxide adduct of bisphenol A, etc., or a mixture thereof.
Examples include lactone-based polyester diols obtained by ring-opening polymerization of lactones such as caprolactone. Examples of the polyether diol include polyalkylene ether glycols such as polyethylene glycol, polypropylene ether glycol, and polytetramethylene ether glycol, and copolymerized polyether glycols such as these.

Examples of polyether ester glycols include polyester glycols obtained by reacting the polyalkylene ether glyco-kfrpo')ol component with aliphatic or aromatic dicarboxylic acids. If the molecular weight of this long-chain diol is too small, the urethane group concentration of the resulting thermoplastic polyurethane/urea resin will become too large, resulting in poor flexibility of the resin and poor solubility in cold solvents. It is not very preferred for use as a binder in magnetic recording media. Additionally, if the molecular weight of the long-chain diol is too large, the content of the long-chain diol in the resin will be too large and the urethane group concentration will be relatively very low, resulting in a decrease in the abrasion resistance and heat resistance of the resin. do.

The short-chain diol used in the production of the thermoplastic polyurethane/urea resin has a molecular weight of about 50 to about 500, and includes, for example, ethylene glycol, propylene glycol, 1,4-butylene glycol, 6-diol, These include aliphatic glycols such as chitin glycol and neopentyl glycol, aromatic diols such as ethylene oxide or propylene oxide adducts of bisphenol A, and ethylene oxide adducts of hydroquinone, depending on the desired properties of the polyurethane/urea resin. The levers can be used alone or in combination in various ratios.

In addition, examples of the organic diamine include aliphatic diamines such as tetramethylene diamine and hexamethylene diamine;
m-7 22 diamine, p-phenylene diamine, 2
．． 4-tolylene diamine, 2,6-tolylene diamine,
m-xylylene diamine, p-xylylene diamine, diphenylmetabiphenylene diamine, 4,4-diaminodiphenyl ether, l,5-naphthalenecyamine,
Aromatic diamines such as 2゜4-s7talediamine, 1
．． Examples include alicyclic diamines such as 3-diaminomethylcyclohexane, 1,4-diaminomethylcyclohexane, +, i-diaminodicyclohexylmethane, and inphorondiamine.

Examples of the organic diisocyanate include aliphatic diincyanates such as tetramethylene diinocyanate and hextemethylene diinocyanate, m-7 22 diisocyanate, p-ph22 diisocyanate, 2.4-)
lylene diisocyanate), 2,6-lylene diisocyanate, diphenylmethane diisocyanate, 3,3-
dimethoxy-4,4-biphenylene diinocyanate,
(cyaner), 4.4-diincyanatodiphenyl ether, 5-naphthalene diisocyaner), 2.4-
Aromatic diincyanates such as 7tale diisocyanate, 1,3-diincyanatomethylcyclohexane, 4-diisocyanatomethylcyclohexane, 4-diisocyanatomethylcyclohexane,
, 4-diincyanate, dicyclohexylmethane, and alicyclic diincyanate such as inphorone diisocyanate.

Furthermore, when a polyisoryanate curing agent is used in combination with the above-mentioned thermoplastic polyurethane/urea resin, a magnetic recording medium with excellent wear resistance can be obtained. In addition, examples of the polyisocyanate curing agent include polyisocyanate curing agents that can be conventionally used as curing agents, such as the product name Coronate L (manufactured by Nippon Polyurethane Kogyo Co., Ltd.) and the product name Desmodur L (manufactured by Bayer Co., Ltd.). It is also possible to use the polyisocyanate curing agent in an amount that is normally used.

Further, in the above reaction, the molar ratio of the short chain diol to the long chain diol is desirably 3 or less.

If this molar ratio is too large, the urethane group concentration becomes too high, and the manufactured polyurethane/urea resin cannot be dissolved in the above-mentioned general-purpose solvents used in making magnetic paints, making it less suitable. When using a straight chain diol such as ethylene glycol, 1.4-butylene glycol, 1,6-hexane glycol as the short chain diol, the above-mentioned molar ratio is desirably 1 or less, preferably 0.5 or less.
When branched short chain diols such as neopentyl glycol are used, ethylene oxide or propylene oxide adducts of bisphenol A have good solubility in the resin, so the above-mentioned molar ratio can be increased compared to straight chain diols. However, even in this case, the molar ratio mentioned above is 3f! : If it is too thick, the solubility will deteriorate, which is not preferable.

In producing the thermoplastic polyurethane/urea resin used in the present invention, among the nine long-chain diols with a molecular weight of about 500 to about 50,000, polyester diols, especially polybutylene adipate, poly, hexamethylene adipate, etc. , it is preferable to use polycaprolactone diol. Further, as the short chain diol having a molecular weight of about 50 to about 500, among the above-mentioned examples, it is particularly preferable to use a branched short chain diol, especially neopentyl glycol. Further, as the organic diamine, it is particularly preferable to use inphorone diamine among the examples mentioned above. Yes
Among the above-mentioned examples, particularly 4 is used as the organic diincyanate.
, 4-diphenylmethane diincyanate, and inphorone diincyanate are preferably used.

In addition, the polyaddition reaction method employed in the production of the thermoplastic polyurethane/urea resin used in the present invention includes melt polymerization in which the reaction is carried out in a molten state, and single or mixed solvents such as ethyl acetate, methyl ethyl ketone, acetone, and toluene. There is solution polymerization, which is carried out by dissolving the above-mentioned raw materials in an inert solvent such as Especially when preparing a polymer, it is preferable to carry out melt polymerization and carry out solution polymerization by adding the above-mentioned inert solvent to carry out a chain extension reaction.

During the reaction, a metal compound such as an organic tin compound such as stannous octylate or diptyltin dilaurate, or a tertiary amine such as N-methylmolorin or triethylamine may be added as a catalyst. Also, to increase the stability of the product, antioxidants, ultraviolet absorbers,
A hydrolysis inhibitor or the like may be added.

Furthermore, a siloxane bond is introduced into the main chain of the thermoplastic polyurethane/urea resin, and the method for introducing it is as follows:
There are many methods of mixing a compound having a siloxane bond. Specifically, a diol having a siloxane bond or a diamine having a siloxane bond is used as the compound having a siloxane bond, and the diol having a siloxane bond is mixed into a portion of the long chain diol. The above-mentioned diamine having a siloxane bond is mixed into a portion of the siloxane bond.

Examples of the diol having a siloxane bond include compounds represented by the following general formula.

(However, R represents a divalent hydrocarbon group.) Examples of the diamine having a siloxane bond include compounds represented by the following general formula.

The molecular weight of the above compound can be from 300 to 10,000.Also, long-chain diols with siloxane bonds introduced in advance can also be used.For example, polyester diol, polyether ester glycol, etc. When synthesizing long-chain diols such as siloxane bond-containing diols, the siloxane bond-containing diols described above can be used.

The thermoplastic polyurethane-urea resin synthesized as described above can be used in combination with other thermoplastic resins, thermosetting resins, or reactive resins. In this case, it is preferable that the blending ratio of the thermoplastic polyurethane-urea resin to the total binder of the binder is 10% by weight or more. If the blending ratio of the thermoplastic polyurethane/urea resin to the total binder is less than 10% by weight, hardly any improvement in the blocking resistance of the magnetic recording medium can be expected.

It is preferably 40% by weight or more. The above-mentioned thermoplastic resin has a softening temperature of 150°C or less, an average molecular weight of 10,000 to 200,000, and a polymerization degree of about 200 to 20.
For example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-7crylonitrile copolymer, thermoplastic polyurethane elastomer, Examples include synthetic rubber thermoplastic resins such as polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives, polyester resin, and polybutadiene. Examples of thermosetting resins or reactive resins include phenolic resins, epoxy resins, polyurethane curable resins, melamine resins, alkyd resins, silicone resins, acrylic reactive resins, epoxy-polyamide resins, nitrocellulose-melamine resins, and polymer resins. Mixtures of molecular weight polyester resins and isocyanate prepolymers, mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, low molecular weight glycols/high molecular weight diols/triphenylmethane Examples include mixtures of triisocyanates, polyamine resins, and mixtures thereof. Among these, it is desirable to use in combination those with good dispersibility in ferromagnetic powder.

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

Examples of the ferromagnetic powder used in the present invention include ferromagnetic iron oxide particles, ferromagnetic chromium dioxide, ferromagnetic alloy powder, hexagonal barium ferrite particles, iron nitride, and the like.

As the above-mentioned ferromagnetic iron oxide particles, when expressed by the general formula FeOx, the value of X is in the range of 1.33≦X≦1.50, that is, maghemite (γ-1;
．． 50), magnetite (Fes 04 y
= 1.33) and Hikore et al.'s solid solution (, FeOx, 1.3
3(X(1,50)).Furthermore, cobalt may be added to these ferromagnetic iron oxides for the purpose of increasing coercive force.Cobalt-containing iron oxides are broadly classified into doped type and coated type. There are two types.

The above-mentioned ferromagnetic chromium dioxide may include CrO2 or Ru for the purpose of improving the coercive force thereof.

A material to which at least one of Sn, Te, Sb, Fe, Ti, v2Mn, etc. is added can be used.

Ferromagnetic alloy powders include Fe, Co, and Ni.

Fe-Co, Fe-Ni, Fe-Co-Ni, Co-
Ni, Fe-Co-8, Fe-Co-Cr-B, Mn
-B i , Mn -A , z , Fe-Co-V
etc., and for the purpose of improving various properties, Aj, S i , Ti, Cr, Mn, Cu
, Zn, and other metal components may be added.

Furthermore, in addition to the binder and ferromagnetic fine powder, additives such as a dispersant, a lubricant, an abrasive, an antistatic agent, and a rust preventive may be added to the magnetic layer.

The above dispersants (pigment wetting agents) include cabrylic 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 (RC00I-1°R is an alkyl or frucnyl group having 11 to 17 carbon atoms) such as lyrinnic acid and stearolic acid, and alkali metals (Li) of the above-mentioned fatty acids.

Na, etc.) and alkaline earth metals (M g t
Ca, Ba), fluorine-containing compounds of the above fatty acid esters, amides of the above fatty acids, polyalkylene oxide alkyl phosphate esters, trialkyl polyolefin oxy quaternary ammonium salts (alkyl has 1 to 5 carbon atoms) The olefins used are ethylene, propylene, etc. In addition, higher alcohols having 12 or more carbon atoms and sulfuric esters thereof can also be used. These dispersants are added in an amount of 0.5 to 20 parts by weight per 100 parts by weight of the binder.

The above-mentioned lubricants include dialkylpolysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxypolysiloxane (alkoxy carbon number 1 to 4), monoalkylmonoalkoxypolysiloxane (alkyl has 1 to 5 carbon atoms, Silicone oil such as alkoxy (carbon number 1 to 4), phenyl polysiloxane, fluoroalkyl polysiloxane (alkyl has 1 to 5 carbon atoms), conductive fine powder such as graphite, molybdenum disulfide, tungsten disulfide, etc. fine inorganic powders, fine plastic powders such as polyethylene, polypropylene, polyethylene vinyl chloride copolymers, polytetrafluoroethylene, α-olefin polymers, unsaturated aliphatic hydrocarbons that are liquid at room temperature (g-olefin double bonds are Compound bonded to terminal carbon, approximately 2 carbons
0), monobasic fatty acids with 12 to 20 carbon atoms and 3 carbon atoms
Fatty acid esters consisting of ~12 monohydric alcohols, fluorocarbons, etc. can be used. These lubricants are added in an amount of 0.2 to 20 parts by weight per 100 parts by weight of the binder.

As the abrasive, commonly used materials such as fused alumina, silicon carbide, chromium oxide (CR20S), corundum, artificial corundum, diamond, artificial diamond, garnet, and emery (main components: corundum and magnetite) are used. Ru. These abrasives have a Mohs hardness of 5 or more and an average particle size of 0.05 to 5 μm, particularly preferably 1 to 2 μm. These abrasives are added in an amount of 0.5 to 20 parts by weight per 100 parts by weight of the binder.

Examples of the antistatic agent include conductive fine powder such as carbon black and carbon black graft polymer, natural surfactants such as saponin, nonionic surfactants such as alkylene oxide, glycerin, and glycidol, higher alkyl amines, Cationic surfactants such as quaternary ammonium salts, pyridine and other heterocycles, phosphoniums, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric acid ester groups; Ampholytic active agents such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used. The above conductive fine powder is binder 1
The surfactant is added in an amount of 0.1 to 10 parts by weight to 0.00 parts by weight. These surfactants may be added alone or in combination. Although these are used as antistatic agents, they are sometimes used for other purposes, such as dispersion, improving magnetic properties, improving lubricity, and as coating aids.

As the above rust preventive agent, phosphoric acid, sulfamide, guanidine, pyridine, amine, urea, zinc chromate, calcium chromate, strontium chromate, etc. can be used, but in particular, dicyclohexylamine nitrite, cyclohexylamine chromate, diisopropylamine nitrite, diethanolamine Hoscet,
Volatile rust inhibitors (inorganic or organic acid salts of amines, amides or imides) such as cyclohexylammonium carbonate, hexamethylene diamine carbonate, propylene diamine stearate, guanidine carbonate, triethanolamine nitrite, and morpholine stearate. Rust prevention effectiveness improves when used. These rust inhibitors are 0.01 parts by weight per 100 parts by weight of ferromagnetic fine powder.
It is used in a range of 20 parts by weight.

In addition, the constituent materials of the magnetic layer are dissolved in an organic solvent to prepare a magnetic paint, which is coated on a non-magnetic support.The solvent for the magnetic paint is a ketone type such as acetone, methyl ethyl ketone, methyl isobutyl ketone, or cyclohexanone. , methyl acetate, ethyl acetate, butyl acetate, ethyl lactate,
Ester types such as acetic acid glycol monoethyl ether, glycol ether types such as glycol dimethyl ether, glycol monoethyl ether, and dioxane, aromatic hydrocarbons such as benzene, toluene, and xylene, hexane,
Examples include aliphatic hydrocarbons such as heptane, chlorine hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene. Materials for non-magnetic supports 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 gropionate, etc. Cellulose derivatives, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate, polyimide,
In addition to plastics such as polyamide-imide, non-magnetic metals such as aluminum, copper, tin, zinc or non-magnetic alloys containing these, ceramics such as glass, earthenware, and porcelain, lighters, lighters, or polyethylene Papers coated or laminated with α-polyolefins having 2 to 10 carbon atoms, such as polypropylene, ethylene-butene copolymer, etc., can also be used. The nonmagnetic support may be in any form such as a film, tape, sheet, disk, card, or drum.

[Effect]

The urethane groups, urea groups, and siloxane bonds in the thermoplastic polyurethane/urea resin greatly improve its affinity for magnetic powder. Therefore, by using this as a binder, even ultra-fine magnetic powders and magnetic powders with a large amount of magnetization can be dispersed well.

At the same time, the siloxane bonds have a lubricating effect, which provides good running properties.

However, thermoplastic polyurethane/urea resins are not soluble in general-purpose solvent systems and are easy to handle.

〔Example〕

Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to these examples.

Resin Synthesis Example A thermoplastic polyurethane urea resin containing +1-X% sun bonds in the molecule was synthesized according to the synthesis method described above. Table 1 shows the properties of the synthesized resin.

Table 1 Example I Co-coated r-Fe203 100 weighted vinyl/vinyl acetate copolymer 10 parts by weight (U, C
, C, manufactured by V A G, H) Siloxane bonded metal thermoplastic polyurethane/urea resin (resin A)
15 parts by weight Dispersant (lecithin) 0
．． 5 parts by weight Lubricant (silicone oil) L
Weight part abrasive CCr20s) 2
Parts by weight Methyl ethyl ketone 100 parts Methyl ingutyl ketone 50 parts Toluene 50 parts The above composition was mixed in a ball mill for 48 hours, filtered through a 3μ filter, and then mixed with a curing agent (Desmodur L, manufactured by Bayer AG).
) was added in an amount of 2.5 parts by weight, mixed for an additional 30 minutes, and coated on a polyethylene terephthalate film with a thickness of 16 μm so that the thickness after drying would be 6 μm. After performing magnetic field orientation treatment, it was dried and rolled. I took it. After calendering the tape, it was cut into 1/2 inch width to prepare sample tapes.

Example 2 In the composition of Example 1, a thermoplastic polyurethane/urea resin containing a siloxane bond (resin B) was used instead of a thermoplastic polyurethane/urea resin containing a siloxane bond (resin A).
A sample tape was prepared using the same method as in Example 1 above.

Example 3 In the composition of Actual Example 1, a thermoplastic polyurethane/urea resin containing a siloxane bond (resin C) was used instead of a thermoplastic polyurethane/urea resin containing a siloxane bond (resin A).
A sample tape was prepared using the same method as in Example 1 above.

Example 4 In the composition of Example 1, a siloxane bond-containing thermoplastic polyurethane-urea resin (resin D) was used in place of 71λ of the siloxane bond-containing thermoplastic polyurethane-urea resin (resin A), and the same procedure as in Example 1 was carried out. Create a sample tape using Lyc.

Example 5 In the composition of Example 1, a thermoplastic polyurethane/urea resin containing a siloxane bond (resin E) was used instead of a thermoplastic polyurethane/urea resin containing a siloxane bond (resin A).
A sample tape was prepared using the same method as in Example 1 above.

Comparative Example 1 A sample tape was prepared in the same manner as in Example 1 using a thermoplastic polyurethane resin (resin F) instead of the siloxane bond-containing thermoplastic polyurethane/urea resin (resin A) in the composition of example 1. Create t.

Comparative Example 2 In the composition of Example 1, a thermoplastic polyurethane/urea resin (resin G) was used instead of the siloxane bond-containing thermoplastic polyurethane/urea resin (resin A), and the same method as in Example 1 was carried out. A sample tape was created.

Comparative Example 3 In the composition of Example 1, a siloxane bond-containing polyurethane resin (resin H) was used in place of 71\ of the siloxane bond thermoplastic polyurethane/urea resin (resin A), and the same procedure as in Example 1 was carried out. A sample tape was prepared by the method.

Table 2 shows the measurement results of the coefficient of dynamic friction, amount of falling powder, adhesive properties, and still properties of the above sample tape.

Note that the coefficient of dynamic friction is determined by the low tape speed (0,4y+a/
It was measured as the coefficient of friction between the magnetic layer surface and IS stainless steel (load: 50 t) at 50 t (sec). The powder is
After running the shuttle 100 times for 60 minutes, the amount of powder falling on the hemlock drum, guide, etc. was visually observed, and the highest score was 0 points and the lowest score was 15 points.

Adhesive properties were determined by winding the sample tape onto a reel and heating it at a temperature of 40°C.
After being left for 24 hours at 80% humidity, the sample tape was visually evaluated for peeling and scored on a 10-point scale, with the better the adhesive properties, the lower the score. Still characteristics were determined by recording a 4.2 MHz video signal on a sample tape and measuring the time until the playback output attenuated to 50%.

It is clear from the results in Table 2 that by using thermoplastic polyurethane/urea resin containing siloxane bonds as the binder for the magnetic layer, the thermal properties and resistance to corrosion of the magnetic recording medium can be improved. Kingability, durability, dispersibility of magnetic powder, etc. are significantly improved.

〔Effect of the invention〕

As is clear from the above description, in the present invention,
Since the binder for the magnetic layer is a thermoplastic polyurethane/urea resin having siloxane bonds in its molecules, or a cured product obtained by reacting this resin with a polyisocyanate curing agent, it has high affinity for magnetic powder. Therefore, even if the magnetic powder is made into ultra-fine particles or has a large amount of magnetization, the dispersibility is good. Therefore, the durability and surface properties of the obtained magnetic recording medium are improved, and the electromagnetic conversion characteristics are also extremely excellent.

-! In addition, the inclusion of siloxane bonds provides lubricity, reduces the coefficient of friction, and improves running properties.

Furthermore, the thermoplastic polyurethane/urea resin used in the present invention is soluble in general-purpose solvent systems and easy to handle.
It is also advantageous in terms of productivity and workability.

Claims (1)

[Claims] 1) A magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic powder and a binder is formed on a non-magnetic support, wherein the magnetic layer contains siloxane bonds in its molecular chains. A magnetic recording medium characterized by containing a thermoplastic polyurethane/urea resin as a binder. 2) In a magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic powder and a binder is formed on a non-magnetic support, the magnetic layer is a thermoplastic polyurethane/urea resin containing siloxane bonds in its molecular chains. 1. A magnetic recording medium comprising, as a binder, a cured product obtained by a reaction between a polyisocyanate curing agent and a polyisocyanate curing agent.