JPS6292117A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve durability, running stability, magnetic characteristics, electromagnetic conversion characteristic, etc. by using a polyurethane resin having a siloxane bond in the molecular chain and having a ternary amine salt of a sulfonic acid as a polar group in the molecular side chain for a binder constituting a magnetic layer. CONSTITUTION:The magnetic layer contains the polyurethane resin having the siloxane bond in the molecular chain and having the ternary amine salt of the sulfonic acid as the polar group in the molecular side chain as the binder. The polyurethane resin is obtd. by the reaction of a polyhydroxy compd. and polyisocyanate. A long chain diol having about 500-5,000mol.wt. and short chain diol having about 50-500mol.wt. are preferably used for the polyhydroxy compd. An org. diisocyanate is preferably used for the polyisocyanate. Such polyurethane resin exhibits high affinity to magnetic powder and lubricity and has excellent running stability.

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, the present invention relates to magnetic recording media such as magnetic tapes and magnetic disks, and more specifically, the present invention relates to magnetic recording media such as magnetic tapes and magnetic disks. This invention relates to improvements in binders.

[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 has a siloxane bond in its molecular chain. By using a polyurethane resin having a sulfonic acid tertiary amine salt as a dominant group in the molecular side chain, we aim to improve the dispersibility of the magnetic powder and the surface properties of the magnetic layer, thereby improving the durability and running performance of the resulting magnetic recording medium. The aim is to improve stability, magnetic properties, electromagnetic conversion properties, etc.

[Conventional technology]

In recent years, magnetic recording media, especially VTJ video tape recorders)
There is a demand for improved magnetic properties and electromagnetic conversion properties in magnetic recording media for use in order to obtain high reproduction output even when recording at short wavelengths.

As a measure to this end, efforts have been made to make the magnetic powder particles finer and to increase the magnetic force, and there is a growing tendency to increase the packing density of the magnetically injected powder in the magnetic layer, the so-called backing density.

On the other hand, conventionally used binders for magnetic recording media include nitrocellulose, polyester resin, polyurethane resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, etc. can be mentioned.

However, as mentioned above, as the specific surface area increases due to finer particles of magnetic powder and the cohesive force increases due to higher magnetic force,
However, it is difficult to obtain satisfactory dispersibility and surface properties with the above-mentioned binders, and it is also difficult to increase the backing density of the magnetic powder.

Therefore, the durability, magnetic properties, and electromagnetic conversion properties were also insufficient. Or (well, for example, surface activity 1" = i
; Methods such as using No. 11 as a dispersant have been considered, but in this case, since the surfactant is a low molecular weight, the presence of this surfactant in the magnetic layer causes powder drop and aging. Problems have arisen in mechanical strength, durability, etc. due to blooming.

Under these circumstances, there is a need for a binder that can further improve these properties, and attempts have been made to introduce hydrophilic polar groups into the side chains of various binder resins. Examples of the above-mentioned binders include polyester resins containing sulfonic acid metal bases (Japanese Patent Publication No. 57-313-1), polyurethane resins containing sulfonic acid metal bases (Japanese Patent Publication No. 58-4156).
5), -8O3Ni, -0803M, -CO
Binder resins containing OM, -P(OM)2 (where N is I, a hydrogen atom or an alkali metal) as a hydrophilic polar group (JP-A-59-79427) are known.

However, although the above-mentioned binders show some effect in improving dispersibility compared to conventional binders that do not have polar groups introduced, they do not work well with ultra-fine magnetic powders or magnetic powders with high magnetization. The performance for this cannot be said to be sufficient.

Furthermore, when the various binder resins mentioned above are used as binders for the magnetic layer, the resins themselves lack lubricity and have problems in running stability.

[Apex while trying to invent or solve]

As described above, there is no known binder that exhibits sufficient dispersibility even for ultrafine magnetic powder, and therefore magnetic recording media using this ultrafine ffRff powder do not have the desired durability and magnetic properties. , it was difficult to ensure electromagnetic conversion characteristics.

Furthermore, since the binder itself lacks lubricity, there is a problem in running stability of the magnetic recording medium.

Therefore, the present invention was proposed in order to eliminate the above-mentioned drawbacks in the technical field, and it greatly improves the dispersibility of magnetic powder and the surface properties of the magnetic layer, and improves the durability and running stability of the magnetic layer. The object of the present invention is to provide a magnetic recording medium with good characteristics and electromagnetic conversion characteristics.

[Means for solving problems]

As a result of intensive research, the present inventors have found that a polyurethane resin having a siloxane bond in the molecular chain and a sulfonic acid tertiary amine salt on the molecular side chain; The present invention was completed by discovering that it has a high affinity for magnetic powder, exhibits lubricity, and has excellent running stability. In a magnetic recording medium formed with a magnetic layer mainly composed of siloxane bonds, the magnetic layer has siloxane bonds in the molecular chain, and sulfonic acid 3 as a polar group in the molecular side chain.
It is characterized by containing a polyurethane resin having a grade amine salt as a binder.

The polyurethane resin according to the present invention is obtained by reacting poly, a droxy compound, and a polyisocyanate, and the polyhydroxy compound has a molecular weight of about 500 to about 5,000.
It is preferable to use long chain diols and short chain diols having a molecular weight of about 50 to about 500, and it is preferable to use organic inocyanates as the polyisocyanate.

The above-mentioned long-chain diols are roughly classified into, for example, polyether diols, polyether ester glycols, and the like. Specific examples of polyester diols 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 their lower alcohol nysterates, ethylene glycol, l, 3-7
'0 pyrene glycol, l, 4-butylene glycol,
1,6-hexane glycol, diethylene glycol,
Examples include polyester diols obtained by reacting neopentyl glycol, ethylene oxide adducts of bisphenol A, etc., or mixtures thereof, and lactone-based polyester diols obtained by ring-opening polymerization of lactones such as ε-caprolactone. It will be done. Examples of the polyester diol include polyalkylene ether glycols such as polyethylene glycol, polypropylene ether glycol, and polytetramethylene ether glycol, or copolymerized polyether glycols thereof. Examples of polyether ester glycols 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 urethane group concentration of the resulting polyurethane resin will be too high, resulting in poor flexibility of the resin and poor solubility in solvents, making it difficult to use as a binder for magnetic recording media. I don't like it very much. Furthermore, when the molecular weight of the long-chain diol is too large, the long-chain diol content in the resin becomes too large and the urethane group concentration becomes relatively low, resulting in a decrease in the abrasion resistance and heat resistance of the resin.

Examples of the short chain diols include ethylene glycol, propylene glycol, 1,4-butylene glycol, 1,
6-hexane glycol, aliphatic glycol such as neopentyl glycol, or ethylene oxide adduct or propylene oxide adduct of bisphenol A;
There are aromatic diols such as ethylene oxide adducts of hydroquinone, and these can be used alone or in mixtures in various ratios depending on the desired properties of the polyurethane resin.

Furthermore, glycerin, glycerin ethylene oxide adduct, 2-methylpropane-1,2,3-triol,
4-[Bis(2-hydroxyethyl)]-]2-hydroxypentane 3-methylpentane-1,3,5-triol, 1.2.6-hexane glycol, 1-bis(2
It is also possible to use triols such as -hydroxyethyl)amino-2-propanol and a propylene oxide adduct of jetanolamine.

Examples of the organic diisocyanate include aliphatic diisocyanates such as tetramethylene diisocyanate and hexamethylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, and 2,4-tolylene diisocyanate. ~． 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, 3,3
-dimethoxy-4,4-biphenylene diisocyanate, cyanate, 4,4-diincyanato diphenyl ether, 1,5-naphthalene diisocyanate, 2,4
- Aromatic diisocyanates such as naphthalene diisocyanate - 1-11,3-diisocyanatomethylcyclohexane, 1,4-diincyanatomethylcyclohexane, 4,4-diincyanatodicyclohexylmethane,
Examples include alicyclic diisocyanates such as inphorone diisocyanate.

In addition, the reaction method adopted in the production of the polyurethane resin according to the present invention includes melt polymerization in which the reaction is carried out in a molten state, and the above-mentioned raw materials are added to an inert solvent such as a single or mixed solvent of ethyl acetate, methyl ethyl ketone, acetone, toluene, etc. There is solution polymerization, which is carried out by dissolving the
Solution polymerization is preferred for the production of polyurethane resins, which are often dissolved in solvents and used as binders for magnetic recording media.In particular, when preparing a prepolymer, melt polymerization is performed, and the above-mentioned non-containing substances are removed before chain extension reaction. It is more preferable to perform solution polymerization by adding an active solvent.

During the reaction, an organometallic compound such as an organotin compound such as stannous octylate or dibutyltin dilaurate, or a tertiary amine such as N-methylmorpholine or triethylamine may be added as a catalyst. Further, in order to increase the stability of the product, antioxidants, ultraviolet absorbers, hydrolysis inhibitors, etc. may be added in an amount of up to about 596% based on the solid content.

Furthermore, a sulfonic acid tertiary amine salt is introduced as a polar group into the above polyurethane resin.
A method in which a compound containing a class amine salt is mixed.

(11) A method of modifying a hydroxyl group remaining at the terminal or side chain of a polyurethane resin with a compound containing a tertiary amine sulfonic acid salt.

etc.

In method (1), the sulfonic acid tertiary amine salt-containing compound is polymerized with other raw materials to form part of the polymer molecular chain of the polyurethane resin, and as a result, the sulfonic acid 3 A class amine salt is introduced as a polar group.

Here, as the sulfonic acid tertiary amine salt-containing compound,
For example, a diol containing a tertiary amine salt of sulfonic acid may be mentioned, and a carboxylic acid component having no tertiary amine salt of sulfonic acid;
It is obtained by reacting a glycol component and a dicarboxylic acid component having a sulfonic acid tertiary amine salt.

Examples of the carboxylic acid component not having a sulfonic acid tertiary amine salt include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and 1,5-naphthalic acid;
- Aromatic oxycarboxylic acids such as oxybenzoic acid and p-(hydroxyethoxy)benzoic acid, aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid, trimellitic acid, and pyromellitic acid. and tri- and tetracarboxylic acids such as.

The above-mentioned glycol components include ethylene glycol, propylene gellicol, 1,3-propanediol, 1.
4-butanediol, 1,5-bentanediol, 1,
6-hexanediol, neopentyl glycol, diethylene glycol, diethylene glycol, 2,2,4
-1-dimethyl-1,3-pentanediono 1,4
- cyclohexane dimetatool, ethylene oxide adduct and propylene oxide adduct of bisphenol A,
polyethylene glycol, polypropylene glycol,
Examples include polytetramethylene glycol. In addition, tri- and tetraols such as trimethylolethane, trimethylalpropane, glycerin, and pentaerythritol may be used in combination (,MO). Can be mentioned.

(However, Ri, Rz, and R3 each have 1 to 6 carbon atoms.
Represents an alkyl group up to. ) On the other hand, the method (*++) involves reacting a tertiary amine with a compound containing a sulfonic acid group to the OH group present at the end or side chain of a polyurethane resin whose chain has been extended to a predetermined molecular weight by a polymerization reaction. The reaction formula is as follows.

(Ii) a Rs-N f-Rs (In the formula, Rpυ represents polyurethane resin,
, s and 几6 each represent a hydrocarbon group having 1 to 6 carbon atoms. ) +++++-b O (In the formula, RPU represents a polyurethane resin.) In this case, the sulfonic acid tertiary amine salt to be introduced may specifically include the following.

(2) O Furthermore, a siloxane bond is introduced into the molecular chain (main chain) of the polyurethane resin, and an example of an introduction method is to mix a compound having a siloxane bond into the starting material of the polyurethane resin. Specifically, a diol 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 polyhydroxy compound.

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

(However, R represents a divalent hydrocarbon group.) The molecular weight of the above compound can be from 300 to 10,000.

It is also possible to use a polyhydroxy compound with a siloxane bond introduced into the purse string in advance.

For example, when synthesizing polyhydroxy compounds such as polyester diols and polyether ester diols, the diols having the aforementioned siloxane bonds may be used.

The amount of polar groups introduced into the polyurethane resin according to the present invention is:
It is preferably in the range of 0.01 to 1.0 mmol/g, more preferably in the range of 0.1 to 0.5 mmol/g. The amount of the above polar group introduced is 0.01 mmol/g
If it is less than this, sufficient effect on the dispersibility of the ferromagnetic powder will not be recognized. In addition, the amount of the polar group introduced is 1.0 mmol.
If it exceeds /g, intermolecular or intramolecular aggregation tends to occur, which not only adversely affects dispersibility, but also causes selectivity to the solvent, which may make it impossible to use ordinary general-purpose solvents.

Further, the siloxane group concentration of the polyurethane resin according to the present invention is Q, Q 3 mmol/g to 3 mmol/
g, preferably 0.1 mmol/, j9~0
．． More preferably, it is 7 mmol/g. If the siloxane group concentration is less than 0.03 mmol/g, lubricity cannot be imparted, and if the siloxane group concentration exceeds 3 mmol/g, solubility with the solvent and other bonds may be impaired. Not only does the compatibility with the magnetic agent deteriorate, but also the physical properties of the magnetic coating, such as breaking strength and Young's modulus, deteriorate.

Further, the number average molecular weight of the polyurethane resin according to the present invention is 1
0000 to 100000, more preferably 10000 to
The range is preferably 60,000. If the number average molecular weight is less than 10,000, the coating film-forming ability of the resin will be insufficient, and if the number average molecular weight exceeds 60,000, there is a risk that problems will occur in the steps of paint manufacturing such as mixing, transport, and coating. be.

The polyurethane resins according to the invention can be used in combination with other thermoplastics, thermosets or reactive resins. The above-mentioned thermoplastic resin has a softening temperature of 150°C or less and an average molecular weight of 10,000 to 20,000.
0 and the degree of polymerization is about 200 to 2000, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonyl-IJ
Acrylic acid ester-acrylonitrile copolymer, thermoplastic polyurethane elastomer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative, polyester resin, Examples include synthetic rubber-based thermoplastic resins such as 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, di-sefoxy polyamide resins, and 0-arcylulose melamine. Resin, mixture of high 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/ Examples include mixtures of triphenylmethane triincyanate, 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, magnetite (γ-Feze3°
0), magnetite (Fe3O4,
0). Furthermore, cobalt may be added to these ferromagnetic iron oxides for the purpose of increasing coercive force. There are two types of cobalt-containing iron oxide: doped type and deposited type.

The above-mentioned ferromagnetic dioxide may be CrCh or Ru or Sn for the purpose of improving coercive force.

A material containing at least one of Te, Sb, Fe, Ti, V, Mn, etc. can be used.

As the ferromagnetic alloy powder, Fe, Co, Nj
.

Fe-Co, Fe-Ni, Fe-Co-N
i-,C.

-Ni, Fe-Co-B, Fe-Co-Cr-
B.

Mn-Bi, Mn-AJ, Fe-Co
-V, etc. can be used, and in order to improve various properties of these, Aj, Si, Ti, Cr, Mn,
Metal components such as Cu and Zn 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 caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid,
Fatty acids with 12 to 18 carbon atoms (RC0OH) such as lyrinic acid and stearolic acid.

R is an alkyl or alkenyl group having 11 to 17 carbon atoms), an alkali metal of the above-mentioned fatty acid (Li.

(Na, etc.) or alkaline earth metals (Mg, Ca, etc.).

Metal soaps consisting of 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 include ethylene, propylene, etc. In addition to these, higher alcohols having 12 or more carbon atoms and sulfuric esters 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 lubricants include dialkylpolysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxypolysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkylmonoalkoxypolysiloxane (alkyl has 1 to 5 carbon atoms) ,
Alkoxy has 1 to 4 carbon atoms), silicone oil such as 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, and polytetrafluoroethylene, α-olefin polymers, unsaturated aliphatic hydrocarbons that are liquid at room temperature (n-olefin double bonds end A compound with approximately 2 carbon atoms bonded to the carbon of
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 (Cr203), 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 0.1 to 2 μm. These abrasives have a ratio of 0.5 to 20 to 100 parts of the binder.
It is added in a range of parts by weight.

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, and 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 0.2 to 20 parts by weight per 0.00 parts by weight, and a surfactant is added in an amount of 0.1 to 10 parts by weight. These surfactants may be added alone or in combination. Although these are used as antistatic agents, they are sometimes applied for other purposes, such as dispersion, improving magnetic properties, improving lubricity, and as coating aids.

As the above-mentioned rust preventive agent, phosphoric acid, sulfamide, guanidine, pyridine, amine, urea, zinc oxide mate, calcium chromate, strontium chromate, etc. can be used, but in particular, dicyclohexylamine nitrite, cyclohexylamine chromate, diisopropylamine night light, jetanolamine phosphate,
Volatile rust inhibitors such as cyclohexylammonium carbonate, hexamethylene diamine carbonate, propylene diamine stearate, quanidine carbonate, triethanolamine nitrite, morpholine stearate (inorganic or organic acid salts of amines, amides or imides) ) will improve the rust prevention effect. 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 ethylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene. Materials for the nonmagnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polyethylene and polypropylene, cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, and cellulose acetate. Cellulose derivatives such as DOB0 bionate, 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, pottery and porcelain, paper, baryta, polyethylene, polypropylene, etc. , carbon number 2 such as ethylene-butene copolymer
Papers such as those coated or laminated with ~10 α-polyolefins can also be used. The nonmagnetic support may be in any form such as a film, tape, sheet, disk, card, or drum.

[Function] Due to the action of the sulfonic acid tertiary amine salt in the polyurethane resin, the affinity for magnetic powder is greatly improved. Therefore, by using this as a binder, even ultrafine magnetic powder or magnetic powder 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.

Furthermore, polyurethane resins are soluble in general-purpose solvent systems, are easy to handle, and have excellent coating film properties.

〔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 polyurethane resin containing a sulfonic acid tertiary amine salt and a siloxane bond in the molecule was synthesized according to the synthesis method described above. Table 1 shows the properties of the synthesized resin.

(Varnish under construction) Example I Co coating - Fe2031oo Weight parts Vinyl chloride - Vinyl acetate copolymer 10 (U, C, C
, VAGH) Polyurethane resin (Resin A) 15" Dispersant (
Lecithin) 05 Lubricant (silicone oil) 1 Abrasive (CrzCh)
2 〃Methyl ethyl ketone
100 〃Methyl isobutyl ketone 5
0〃Toluene 50'' The above composition was mixed in a ball mill for 48 hours, filtered through a 3 μm filter, 2.5 parts by weight of a hardening agent (Desmodur L, manufactured by Bayer AG) was added, and further mixed for 30 minutes.
This was applied onto a polyethylene terephthalate film having a thickness of 16 μm so that the thickness after drying would be 6 μm, subjected to magnetic field orientation treatment, dried, and wound up. After calendering this, it was cut into a % inch width to create a sample tape.

Example 2 A sample tape was prepared in the same manner as in Example 1 except that polyurethane resin (Resin B) was used in place of the polyurethane resin (Resin A) in the composition of Example 1.

Example 3 A sample tape was prepared in the same manner as in Example 1 except that polyurethane resin (Resin C) was used in place of the polyurethane resin (Resin A) in the composition of Example 1.

Example 4 A sample tape was prepared in the same manner as in Example 1 except that polyurethane resin (Resin D) was used in place of the polyurethane resin (Resin A) in the composition of Example 1.

Example 5 A sample tape was prepared in the same manner as in Example 1 except that polyurethane resin (Resin E) was used in place of the polyurethane resin (Resin A) in the composition of Example 1.

Example 6 A sample tape was prepared in the same manner as in Example 1 except that polyurethane resin (Resin F) was used in place of the polyurethane resin (Resin A) in the composition of Example 1.

Example 7 A sample tape was prepared in the same manner as in Example 1 except that polyurethane resin (Resin G) was used instead of polyurethane resin (Resin A) in the composition of Example 1.

Comparative Example 1 A sample tape was prepared in the same manner as in Example 1 except that polyurethane resin (Resin H) was used instead of polyurethane resin (Resin A) in the composition of Example 1.

Comparative Example 2 A sample tape was prepared in the same manner as in Example 1 except that polyurethane resin (Resinko) was used in place of the polyurethane resin (Resin A) in the composition of Example 1.

Comparative Example 3 A sample tape was prepared in the same manner as in Example 1, using a polyurethane resin (Resin J) instead of the polyurethane resin (Resin A) in the composition of Example 1.

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

Note that the coefficient of dynamic friction is calculated at low tape speed (0,47+1/
It was measured as the coefficient of friction (load: 50 g) between the magnetic layer surface and IS stainless steel at 50 g. The surface gloss was determined by measuring the reflectance at an incident angle of 75° and a reflection angle of 75° using a gloss meter. The amount of falling powder was evaluated by visually observing the amount of falling powder on the head drum, guide, etc. after running the shuttle 100 times for 60 minutes, and scoring the highest as 0 points and the lowest as 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 under conditions of 80% humidity for 24 hours, the degree of peeling of the sample tape was visually evaluated and scored on a 10-point scale, with the better the adhesive properties, the lower the score.

Still characteristics were measured by placing a 4°2 MHz video signal on a sample tape and measuring the time until the playback output attenuated to 50%.

(1 Kushita Yuiro) As is clear from the results in Table 2, by using a polyurethane resin containing a tertiary sulfonic acid amine salt and a siloxane bond as a binder for the magnetic layer, the coefficient of dynamic friction, Surface gloss and amount of powder falling off are improved, and adhesive properties and still properties are significantly improved. Therefore, the thermal characteristics, running stability, blocking resistance, and durability of the magnetic recording medium are as follows: 1. The dispersibility of the magnetic powder is greatly improved.

〔Effect of the invention〕

As is clear from the above description, in the present invention,
Since the binder of the magnetic layer is a polyurethane resin having a tertiary sulfonic acid amine salt and a siloxane bond in the molecule, it has a high affinity for magnetic powder, even if it is a finely divided magnetic powder or a magnetic material with a large amount of magnetization. Even if it is a powder, it has good dispersibility. Therefore, the durability and surface properties of the obtained magnetic recording medium are improved, and the electromagnetic conversion characteristics are also extremely deteriorated.

In addition, the lubricity provided by the inclusion of siloxane bonds reduces the coefficient of friction and improves running properties.

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

Claims (1)

[Claims] 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 has siloxane bonds in its molecular chains, and A magnetic recording medium comprising a polyurethane resin having a sulfonic acid tertiary amine salt as a polar group in a side chain as a binder.