JPH11175955A - Binder and magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder for a magnetic recording medium which shows excellent dispersibility for a magnetic powder compared to a conventional binder and which has low viscosity of a coating material and excellent durability. SOLUTION: This binder for a magnetic recording medium consists of a polyurethane resin (C) derived from a polyol component (A) and an org. polyisocyanate (B). The polyol component (A) consists of a high mol.wt. polyol (A1) having 500 to 8000 number average mol.wt., or (A1) and a low mol.wt. polyol (A2). In the high mol.wt. polyol (A1), at least 10 wt.% of the polyol consists of castor oil (A11) partially dehydrated in the molecule and having 1.8 to 2.4 hydroxyl groups in average and/or partially acylated castor oil (A12).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder used for manufacturing a magnetic recording medium such as a magnetic tape, a magnetic card, and a magnetic disk, and a magnetic recording medium using the binder.

[0002]

2. Description of the Related Art Conventionally, as a binder for magnetic recording,
Polyurethane resins (for example, Japanese Patent Publication No. 41-16894) made from a polyester polyol obtained from 1,4 butanediol and adipic acid and an organic polyisocyanate are used. However, in recent years, as the performance of magnetic recording media has become higher, the magnetic powder has been made finer and higher in magnetic force, and the above-mentioned binders cannot provide sufficient magnetic powder dispersibility, magnetic layer surface smoothness and durability. In order to solve such problems, polycaprolactone-based polyurethane resins (Japanese Patent Publication No. 63-10457) and polycarbonate-based polyurethane resins (Japanese Patent Publication No. 2-8369)
It has been proposed to use such as a binder.

[0003]

However, although the polycaprolactone-based polyurethane resin and the polycarbonate-based polyurethane resin have improved durability such as hydrolysis resistance as compared with the conventional polyester-based polyurethane resin, the magnetic powders have a disadvantage. As a matter of fact, a substance which is sufficiently satisfactory in terms of dispersibility has not yet been obtained.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies on a binder for a magnetic recording medium having excellent dispersibility of magnetic powder, low paint viscosity, and excellent durability. It has been found that these problems can be solved by using a specific modified castor oil at least in part, and the present invention has been achieved.

That is, the present invention provides a number average molecular weight of 500 to
8,000 high molecular polyols (A1) or (A1)
1) and a binder for a magnetic recording medium comprising a polyurethane resin (C) derived from a polyol component (A) comprising a low molecular polyol (A2) and an organic polyisocyanate (B). At least 10% by weight of intramolecular partially dehydrated castor oil (A11) having an average of 1.8 to 2.4 hydroxyl groups and / or
A binder for a magnetic recording medium, which is a partially acylated castor oil (A12); and a magnetic recording medium having a magnetic layer containing the binder.

The partially dehydrated castor oil having an average of 1.8 to 2.4 hydroxyl groups in the present invention (A11) can be used in the presence of an acidic catalyst such as sulfuric acid, phosphoric acid or p-toluenesulfonic acid in the presence of hydroxyl groups. It is obtained by heating castor oil to partially dehydrate intramolecularly so that the average number is in the above range. The dehydration reaction is usually performed by heating to a temperature of 80 to 180 ° C. Dehydration may be performed under reduced pressure to promote the reaction. Here, the intramolecular partial dehydration reaction is a dehydration reaction between a part of the hydroxyl group in castor oil and a hydrogen atom bonded to a carbon atom adjacent to the carbon atom to which the hydroxyl group is bonded, and the hydroxyl group is formed. The reaction that is pulled out. The average number of hydroxyl groups in (A11) is determined from the hydroxyl value.

[0007] The castor oil is a naturally occurring substance, and is mainly composed of a mixture of fatty acid glycerides such as ricinoleic acid, oleic acid and linoleic acid.
３3, preferably about 2.7 on average.

The partially acylated castor oil (A12) having an average of 1.8 to 2.4 hydroxyl groups in the present invention can be obtained by partially acylating the castor oil so that the hydroxyl groups thereof are in the above range. The partial acylation is performed by adding an acylating agent [for example, an aliphatic or aromatic monocarboxylic acid having 2 to 8 carbon atoms or a derivative thereof (anhydride, acid halide, etc.), 2 carbon atoms] to a part of the hydroxyl group of castor oil. ~ 8 ketene, aromatic sulfonic acid halides (such as p-toluenesulfonic acid chloride)], preferably acetylation. Examples of the acetylation method include, for example, a method of reacting aldoketene with a part of the hydroxyl group of castor oil, a method of reacting acetic anhydride,
Examples thereof include a method of reacting acetic chloride, and a method of reacting acetic anhydride is preferable. The acetylation reaction with acetic anhydride is usually performed by heating to a temperature of 80 to 180 ° C, and (A12) is obtained by removing by-produced acetic acid by a method such as distillation or washing with water. The average number of hydroxyl groups in (A12) is determined from the hydroxyl value.

The average number of hydroxyl groups of the above (A11) or (A12) is usually 1.8 to 2.4, preferably 1.9 to 2.3, more preferably 2 to 2.1. It is. If the average number of hydroxyl groups is less than 1.8, the monool content will increase and the physical properties of the binder will decrease. If it exceeds 2.4, the viscosity during the urethanization reaction will increase and the workability will deteriorate.

The amount of (A11) and / or (A12) used in the present invention depends on the amount of the polymer polyol (A
1) Usually 10% by weight or more, preferably 3% by weight based on the total amount
0% by weight or more, more preferably 50% by weight, particularly preferably 70% by weight or more. If it is less than 10% by weight, the resulting polyurethane resin will have insufficient dispersibility in magnetic powder.

The polymer polyol (A1) in the present invention
As required, other polymer polyols can be used in combination with (A11) and / or (A12). Examples of other polymer polyols that can be used in combination include polyester polyols, polyether polyols, polycarbonate polyols, polydiene polyols, and polymer polyols. Preferred among these are polyester polyols.

Examples of the polyester polyol include a condensed polyester polyol from a low molecular polyol and a dicarboxylic acid or an ester-forming derivative thereof, and a polylactone polyol obtained by ring-opening polymerization of lactone using the low molecular polyol as an initiator. It is. Examples of the low molecular polyol include alkylene glycols (ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4
-Butanediol, 1,3-butanediol, neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,10 -Decanediol, etc.); low molecular weight diols having a cyclic group [cyclohexanediol, cyclohexanedimethanol, xylylene glycol, 1,4-bis (hydroxyethyl)
Benzene, 1,4-bis (2-hydroxyethoxy) benzene, 4,4'-bis (2-hydroxyethoxy)-
Diphenylpropane, etc.]; low molecular weight triols (trimethylolpropane, glycerin, hexanetriol, etc.); their alkylene oxides (alkylene oxides having 2 to 4 carbon atoms, for example, ethylene oxide, propylene oxide, 1,2-, 2,3-, 1,3- or 1,4-butylene oxide) adducts (molecular weight less than 500); and mixtures of two or more thereof.

The condensation polyester polyol is, for example,
One or more of the above low-molecular polyols and dicarboxylic acids [aliphatic dicarboxylic acids (succinic acid, adipic acid, sebacic acid, glutaric acid, azelaic acid, maleic acid, fumaric acid, etc.), aromatic dicarboxylic acids (terephthalic acid, isophthalic acid) Etc.) and one or more of these ester-forming derivatives (acid anhydrides, acid halides, lower alkyl esters of an alkyl group having 1 to 4 carbon atoms, etc.)] and the like. . Polylactone polyols include, for example, lactones (γ-butyrolactone, ε-caprolactone,
γ-valerolactone) in the usual manner by ring-opening polyaddition.

Specific examples of these polyester polyols include polyethylene terephthalate diol, polybutylene terephthalate diol, polyhexamethylene isophthalate diol, polyneopenthylene terephthalate diol, polyethylene adipate diol, polybutylene adipate diol, and polyhexamethylene adipate diol. , Polyneopenthylene adipate diol, polyethylene propylene adipate diol, polyethylene butylene adipate diol, polybutylene hexamethylene adipate diol, polyoxydiethylene adipate diol, poly (polytetramethylene ether) adipate diol, polyethylene azelate diol, polyethylene sebacate diol , Polybutylene azelate di Lumpur, polybutylene sebacate diol, polycaprolactone diol or triol, poly-valerolactone diol or triol, and mixtures of two or more thereof. In addition to the above, for example, phthalic acid-modified polycaprolactone polyol described in JP-A-62-202324 can be used.

As the above polyether polyol, one or more of the above-mentioned low molecular polyols include an alkylene oxide (alkylene oxide having 2 to 4 carbon atoms, for example, ethylene oxide, propylene oxide, 1,2-, 1,3-,
And a compound obtained by (co) adding one or more of 2,3- or 1,4-butylene oxide (in the case of co-addition, the addition form may be either block or random). Specific examples of the polyether polyol include polyethylene glycol, polypropylene glycol, polyethylene-polypropylene (block or random) glycol, polytetramethylene ether glycol, polytetramethylene-ethylene (block random) ether glycol, polytetramethylene-propylene ( Block or random) ether glycol, polyhexamethylene ether glycol, polypropylene triol, polyethylene-polypropylene (block or random) triol and mixtures of two or more thereof.

As the above-mentioned polycarbonate polyols, low molecular weight polyols (1,4-butanediol, 1,1
5-pentanediol, 1,6-hexanediol, etc.)
And a carbonate (eg, dimethyl carbonate, ethylene carbonate, trimethylene carbonate, tetramethylene carbonate, etc.).

Examples of the polydiene polyol include polybutadiene polyol, polyisoprene polyol, a partially or completely hydrogenated product thereof. Further, as the polymer polyol, a polyol obtained by polymerizing a vinyl monomer (for example, acrylonitrile, styrene or the like) in one or more of the above-mentioned polymer polyols in the presence of a radical polymerization initiator to stabilize the dispersion ( For example, a polymer content of 5 to 30% by weight).

The polymer polyol (A1) in the present invention
Has a number average molecular weight of usually 500 to 8,000, preferably 700 to 6,000, more preferably 800 to 4,
000. If the number average molecular weight is less than 500, the obtained polyurethane resin becomes brittle and the scratch resistance tends to decrease. If the number average molecular weight exceeds 8,000, the resin strength of the obtained polyurethane resin becomes insufficient, and the abrasion resistance, scratch resistance and the like become poor. It tends to decrease.

In the present invention, the polymer polyol (A1)
Low molecular polyol (A)
As 2), for example, low molecular polyols exemplified as the starting material of the polyester polyol (alkylene glycols, low molecular diols having a cyclic group, low molecular triol, alkylene oxide adducts thereof and the like);
4- to 8-hydric alcohols such as pentaerythritol, diglycerin, α-methylglucoside, sorbitol, xylitol, mannitol, glucose, fructose, sucrose; alkylene oxide adducts thereof (molecular weight 50
0); amine-based polyol [alkylene oxide adduct of an amine having two or more active hydrogens such as primary monoamine, primary and / or secondary polyamine (molecular weight 5
And a mixture of two or more of these. Of these, preferred are alkylene glycols and low molecular weight diols having a cyclic group. (A
Polyol component (A) when 1) and (A2) are used in combination
Number average molecular weight is usually 200 to 5,000, preferably 300 to 4,000, more preferably 300 to 3,
000. Further, when used in combination, (A) in (A)
The weight ratio of 2) is usually 50% by weight or less, preferably 40% by weight.
% By weight, more preferably 30% by weight or less.

Further, a carboxylic acid (salt) group, a sulfonic acid (salt) group, a sulfamic acid (salt) group, a phosphoric ester (salt) group or a phosphonic acid (salt) or the like is added to the molecular side chain of the polyurethane resin (C). By introducing at least one or more selected organic acid (salt) groups, the dispersibility of the magnetic powder when used in a binder can be further improved. Examples of the salt of the organic acid include metal salts (potassium,
Sodium, lithium, etc.) and amine salts (for example, mono-, di- or trialkylamine salts having 1 to 4 carbon atoms of an alkyl group, mono-, di- or trialkanolamine salts having 2 to 4 carbon atoms of a hydroxyalkyl group) Etc.). Preferred as the organic acid (salt) group are a sulfonate group and a sulfamate group, and particularly preferred are a metal sulfonate group and a metal sulfamate group. As a method for introducing an organic acid (salt) group into the molecular side chain of (C), for example, a low molecular polyol having the organic acid (salt) group as a part of the low molecular polyol (A2) used in the present invention Is used.

Examples of the low molecular polyol having a carboxylic acid (salt) group include, for example, And salts thereof (metal salts, organic amine salts, etc.).

Examples of the low molecular polyol having a sulfonic acid (salt) group include, for example, And salts thereof (metal salts, organic amine salts, etc.).

Examples of the low molecular polyol having a sulfamic acid (salt) group include, for example, And salts thereof (metal salts, organic amine salts, etc.).

Examples of the low molecular polyol having a phosphate (salt) group or a phosphonic acid (salt) group include, for example, And salts thereof (metal salts, organic amine salts, etc.).

In addition to the above, as a method for introducing an organic acid (salt) group into the molecular side chain of (C), a polyester polyol using the above-mentioned low molecular weight polyol containing an organic acid (salt) group as a starting material; A method in which a polyol obtained by addition-polymerizing an alkylene oxide or a lactone using a (salt) group-containing low-molecular-weight polyol as an initiator is used as a part of (A1) or (A2).

When an organic acid (salt) group is introduced into the molecular side chain of (C), the content of the organic acid (salt) group in (C) is usually 1,6 per 10 ⁶ g of (C). 000 equivalent or less, preferably 5 to 500 equivalent, more preferably 10 to 300 equivalent
Is equivalent. When the content of the organic acid (salt) group exceeds 1,000 equivalents, the viscosity of the magnetic coating material becomes high, and the workability deteriorates.

The organic polyisocyanate (B) used in the present invention is, for example, an aromatic diisocyanate having 6 to 20 carbon atoms (excluding carbon in the NCO group) (1,3-
Or 1,4-phenylene diisocyanate, 2,4
-Or 2,6-tolylene diisocyanate, 2,
4'- or 4,4'-diphenylmethane diisocyanate); aliphatic or araliphatic diisocyanates having 2 to 18 carbon atoms (excluding carbon in the NCO group) (tetramethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, α , Α,
α ′, α′-tetramethylxylylene diisocyanate); an alicyclic diisocyanate having 4 to 18 carbon atoms (excluding carbon in the NCO group) (isophorone diisocyanate,
4,4′-dicyclohexylmethane diisocyanate,
2,5-bicyclo [2,2,1] heptanebisisocyanate, 2,6-bicyclo [2,2,1] heptanebisisocyanate, etc.); modified polyisocyanates (buret modified form of hexamethylene diisocyanate, isocyanate of isophorone diisocyanate) Nurate modified, 2,
Trimethylolpropane adducts of 4- and / or 2,6-tolylene diisocyanate); and mixtures of two or more thereof. Of these, preferred are aromatic diisocyanates, and particularly preferred is 4,4'-diphenylmethane diisocyanate.

In producing (C) by reacting (A) and (B), the equivalent ratio (OH / NCO) of (A) and (B) is used.
Ratio) is usually 0.6 to 1.5, preferably 0.8 to 1.2.
It is. By setting the equivalent ratio within the above range, (C) having good dispersibility, sufficient resin strength and excellent abrasion resistance, scratch resistance and hydrolysis resistance can be obtained. The polyurethane conversion reaction can be performed in the presence or absence of a solvent inert to isocyanate groups.
As the solvent, ester solvents (ethyl acetate, acetic acid-n
-Butyl), ether solvents (dioxane, tetrahydrofuran, etc.), ketone solvents (cyclohexanone,
Methyl ethyl ketone, methyl isobutyl ketone, etc.), aromatic hydrocarbon solvents (toluene, xylene, etc.) and mixed solvents of two or more thereof.

As a reaction method, (A) and (B) are charged into a reaction vessel at once and reacted. (A) and (B)
(A method of forming an isocyanate group-terminated prepolymer or a hydroxyl group-terminated prepolymer and reacting them); (A) and (B) previously mixed
Is passed through a heated multi-screw extruder to cause a reaction. The reaction temperature is usually 30 to 180 ° C, preferably 60 to 120 ° C. Catalysts used in ordinary urethane reactions to promote the reaction, such as tin catalysts (trimethyltin laurate, trimethyltin hydroxide, dimethyltin dilaurate, dibutyltin dilaurate, stannas octoate, etc.), lead catalysts ( Red oleate, red 2-ethylhexoate, etc.), amine catalysts (triethylene diamine, etc.) may be used.

The polyurethane resin (C) thus obtained
Usually has a number average molecular weight of 5,000 to 200,000,
It is preferably from 7,000 to 150,000, more preferably from 8,000 to 50,000. If the number average molecular weight is less than 5,000, the physical properties of the obtained polyurethane resin are reduced, and the durability of the magnetic tape tends to be inferior.
If it exceeds 000, the viscosity of the coating material increases and the dispersibility of the magnetic powder tends to decrease.

The (C) used in the binder of the present invention
May be used in combination with another resin if necessary. Examples of the other resin include polyvinyl chloride [vinyl chloride-vinyl acetate copolymer ("VYHH", manufactured by UCC, "Slec C", manufactured by Sekisui Chemical Co., Ltd.)), vinyl chloride-vinyl acetate-
Vinyl alcohol copolymer resin ("VAGH", manufactured by UCC, "Slec A", manufactured by Sekisui Chemical, etc.), vinyl chloride
Polyvinylidene chloride-acrylonitrile copolymer resin (“Saran”, manufactured by Asahi Dow, etc.)]; polyurethane [polyurethane resin (“Esten”, manufactured by Goodrich Co., Ltd.)]; polybutadiene-based [acrylonitrile-butadiene copolymer resin (“Hiker 1482”) ", Nippon Zeon Co., Ltd., etc.); polyacrylic (acrylate copolymer resin, etc.); nitrocellulose; phenoxy resin; epoxy resin; and a mixture of two or more of these.

These other resins may have a functional group such as a carboxyl group, a metal sulfonate group, a sulfobetaine, a phosphoric ester group, an amino group, a quaternary ammonium base, and a hydroxyl group in the resin. When used in combination with the other resin, the content of (C) is usually at least 30% by weight, preferably at least 40% by weight, more preferably at least 50% by weight.

The magnetic recording medium of the present invention is obtained by mixing and dispersing the binder, magnetic powder, solvent and additives of the present invention, and applying the obtained magnetic paint on a non-magnetic support to form a magnetic layer. can get. Further, the binder of the present invention can also be used as a binder for the back coat layer on the side opposite to the magnetic layer.

The magnetic powder used in the magnetic paint includes iron oxide (eg, γ-Fe ₂ O ₃ (γ-hematite)), CrO ₂ (chromium dioxide), and an alloy-based magnetic material (eg, Co-γ- Fe ₂ O ₃ (cobalt ferrite or cobalt-doped γ-iron oxide), Fe—Co—Cr],
Pure iron Fe (metal powder), iron nitride, iron carbide and the like can be mentioned.

Solvents used in the magnetic paint include ester solvents (ethyl acetate, butyl acetate, etc.), ether solvents (dioxane, tetrahydrofuran, etc.), ketone solvents (cyclohexanone, methyl ethyl ketone, methyl isobutyl luketone, etc.), Aromatic hydrocarbon solvents (toluene, xylene, etc.) and mixed solvents of two or more thereof are exemplified. Of these, preferred is a mixed solvent of a ketone solvent and an aromatic hydrocarbon solvent. The amount of the solvent used is such that the solid content in the magnetic paint is usually 20 to 8%.
The range is 0% by weight.

Further, in addition to the binder and the magnetic powder, well-known additives such as dispersants, lubricants, abrasives, antistatic agents, rust preventives, and crosslinking agents may be added to the magnetic paint. .

As the dispersant, fatty acids having 12 to 18 carbon atoms (caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearolic acid) And the like; metal soaps (the alkali metal (potassium, sodium, etc.) salts and alkaline earth metal (magnesium, calcium, barium, etc.) salts of the above-mentioned fatty acids) and the like.

Examples of the lubricant include dialkyl polysiloxane (alkyl group having 1 to 5 carbon atoms), dialkoxy polysiloxane (alkoxy group having 1 to 4 carbon atoms) and monoalkyl monoalkoxy polysiloxane (alkyl group having 1 carbon atom. -5, carbon number of alkoxy group 1-4), phenylpolysiloxane, fluoroalkylpolysiloxane, silicon oil, conductive fine powder (graphite etc.), inorganic powder (molybdenum disulfide, tungsten disulfide etc.), plastic fine powder , Fatty acid esters, fluorocarbons and the like.

Examples of the abrasive include alumina, silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial diamond and the like.

Examples of the antistatic agent include conductive powders (carbon black, carbon black graft polymer, etc.),
Natural surfactants (such as saponins), nonionic surfactants (such as alkylene oxides, glycerins, and glycidols), and cationic surfactants (higher alkylamines, quaternary ammonium salts, pyridine, and other heterocycles) , Phosphoniums, etc.), anionic surfactants (carboxylic acid type, sulfonic acid type, phosphoric acid type, sulfate ester type, phosphate ester type, etc.), amphoteric surfactants (amino acids, aminosulfonic acids, amino acids) Sulfuric acid or phosphoric acid esters of alcohols).

As rust preventives, phosphoric acid, sulfide, guanidine, pyridine, amine, urea, zinc chromate,
Examples thereof include calcium chromate and strontium chromate. Further, in particular, volatile rust preventives such as dicyclohexylamine nitrite, cyclohexylamine chromate, diisopropylamine nitrite, diethanolamine phosphate, cyclohexylammonium carbonate, propylenediamine stearate, guanidine carbonate, triethanolamine nitrite, morpholine stearate and the like ( Use of an inorganic or organic acid salt of an amine, amide or imide) improves the rust prevention effect.

In order to improve the strength of the magnetic layer of the magnetic recording medium, a polyfunctional polyisocyanate can be blended as a crosslinking agent in the magnetic paint. Preferred polyfunctional polyisocyanates include, for example, NCO-terminated prepolymers of organic polyisocyanates (TDI, MDI, etc.) and active hydrogen compounds (low molecular weight polyols, polyamines, polyether polyols, polyester polyols, etc.) [for example, “Coronate” L "(manufactured by Nippon Polyurethane Industry)," Coronate HL "(manufactured by Nippon Polyurethane Industry) and the like].

The mixing ratio of the binder and the crosslinking agent is not particularly limited, but the crosslinking agent is usually 3 to 80 parts by weight based on 100 parts by weight of the binder. Further, in order to accelerate the crosslinking reaction, the same catalyst as that used in producing the above-mentioned polyurethane resin may be appropriately blended.

As the material of the nonmagnetic support constituting the magnetic recording medium, polyesters (polyethylene terephthalate, polyethylene-2,6-naphthalate, etc.); polyolefins (polyethylene, polypropylene, etc.); cellulose derivatives (cellulose triacetate, cellulose) Diacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate, etc .; vinyl resins (polyvinyl chloride, polyvinylidene chloride, etc.); other plastics (polycarbonate, polyimide, polyamideimide, etc.); non-magnetic metals (Aluminum, copper, tin, zinc or non-magnetic alloys containing them, etc.); ceramics (glass, pottery, porcelain, etc.); olefins (baryta, polyethylene, ethylene-butene copolymer) Such as paper coated or laminated body, etc.). Further, the form of the nonmagnetic support may be any of a film, a tape, a sheet, a disk, a card, a drum, and the like. The thickness of a magnetic layer formed by applying a magnetic paint on a non-magnetic support is usually 0.1 to 50 as a dry film thickness.
μm.

As a method for producing a magnetic recording medium (magnetic tape or the like), for example, a binder, a magnetic powder, a solvent, and additives as necessary are mixed in advance by a premixer or the like, and then mixed and dispersed by a mixer (ball mill, paint conditioner, sand conditioner, etc.). Magnetic powder is dispersed with a grinder, sand mill, plast mill, etc.) to prepare a magnetic paint, and then this magnetic paint is applied to a non-magnetic support by a doctor blade method, a transfer printing method (gravure method, reverse roll method, etc.). After the application, a method of forming a magnetic recording medium through various steps such as orientation, drying, surface processing, cutting, and winding can be exemplified.

The magnetic recording medium generally comprises a non-magnetic support and a magnetic layer (magnetic powder and binder, etc.), but an intermediate layer (undercoat layer, undercoat layer) between the non-magnetic support and the magnetic layer.
Undercoat layer), a magnetic layer on both sides of a non-magnetic support, a stack of magnetic layers having different magnetic properties, a protective layer on a magnetic layer, a non-magnetic support May be provided with a back coat layer.

[0047]

EXAMPLES The present invention will be further described with reference to examples below, but the present invention is not limited to these examples. In the following, "parts" indicates parts by weight.

Production Example 1 [Production of dehydrated castor oil (D-1)] Castor oil (average number of hydroxyl groups: 2.7) was added to a four-necked kolben equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet pipe. Charge 600 parts and 77 parts of sulfuric acid,
The mixture was heated to 50 ° C. and reacted for about 2 hours. Then, these reactants are washed with water to separate and recover unreacted sulfuric acid.
The solution was dehydrated under reduced pressure at 10 ° C. and a reduced pressure of 10 mmHg. The hydroxyl group (mgKOH / g) of the obtained compound was 114. Thus, intramolecular partially dehydrated castor oil (D-1) having an average of 2.1 hydroxyl groups in the molecule was obtained.

Production Example 2 [Acetylated castor oil (D-2)
Production of a castor oil (average number of hydroxyl groups: 2.7) 600 parts and acetic anhydride 80 parts were charged into a four-necked kolben equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas introduction pipe, and 120
The mixture was heated to about 150 ° C. and reacted for about 1.5 hours. Then, these reactants were washed with water to separate and collect acetic acid produced as a by-product and unreacted acetic anhydride.
g and dehydrated under reduced pressure. The hydroxyl value of the obtained compound (mgK
OH / g) was 114. Thus, acetylated castor oil having an average of 2.1 hydroxyl groups in the molecule (D-
2) was obtained.

Example 1 In a four-necked kolben equipped with a stirrer, thermometer, reflux condenser and nitrogen gas inlet pipe, 0.6 mol of (D-1) was obtained from adipic acid and 1,4-butanediol. 0.4 mol of a polyester diol having a number average molecular weight of 1,000,
0.42 mol of an adduct of 8 mol of propylene oxide of OCH2CH2) 2NSO3Na and 1.38 mol of diphenylmethane diisocyanate were charged and reacted at about 70 ° C.
This was mixed with a MEK / cyclohexanone mixture (weight ratio 1:
1), and a polyurethane resin solution (C
-1) was obtained. The viscosity of the (C-1) is 800 cP / 25.
C., the solid content concentration was 30%, the number average molecular weight (in terms of polystyrene) by GPC method was 12,000, and the content of sulfamate group in the polyurethane resin was 270 equivalents per 10 ⁶ g of the resin. Using (C-1) as a binder, the following composition was mixed and dispersed with a paint conditioner to prepare a magnetic paint (E-1). Co-γ-Fe2O3 fine powder 100 parts Polyurethane resin (C-1) 10 parts (in terms of solid content) Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (trade name "VAGH"; manufactured by UCC) 10 parts Lecithin 1 part 75 parts of methyl ethyl ketone 75 parts of toluene 5 parts of a curing agent [“Coronate L” (manufactured by Nippon Polyurethane Industry Co., Ltd., adduct of 3 mol of tolylene diisocyanate of trimethylolpropane)] are added to the obtained magnetic paint, and 10 parts of
Mix for minutes. The magnetic paint was applied to a polyester film (dry film thickness: 5 μm), and a magnetic field of 1,000 Oe was applied to orient the tape to obtain a tape. Further, this tape was processed by a calender roll to obtain a magnetic tape (F-1).

Example 2 A 4-port kolben equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas introduction tube was charged with (D-2) 0.6 mol, obtained from adipic acid and 1,4-butanediol. 0.4 mol of a polyester diol having a number average molecular weight of 1,000,
0.42 mol of an adduct of 8 mol of propylene oxide of OCH2CH2) 2NSO3Na and 1.38 mol of diphenylmethane diisocyanate were charged and reacted at about 70 ° C.
This was mixed with a MEK / cyclohexanone mixture (weight ratio 1:
1), and a polyurethane resin solution (C
-2) was obtained. The viscosity of (C-2) is 700 cP / 25.
C., the solid content concentration was 30%, the number average molecular weight (in terms of polystyrene) by GPC method was 10,000, and the content of sulfamate group in the polyurethane resin was 268 equivalents per 10 ⁶ g of the resin. Using the obtained polyurethane resin solution (C-2), a magnetic paint (E-
2) was prepared, and a magnetic tape (F-2) was obtained.

Example 3 A 4-necked kolben equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas introduction pipe was charged with (D-1) 0.5 mol, neopentylglycol 0.5 mol, (HOCH 2 CH 2) Two
8 mol of propylene oxide adduct of NSO3Na
17 mol and diphenylmethane diisocyanate
14 mol was charged and reacted at about 70 ° C. This is MEK
/ Cyclohexanone mixture (weight ratio 1: 1) was added to obtain a polyurethane resin solution (C-3) having a solid content of 30%.
The viscosity of the (C-3) is 900 cP / 25 ° C., the solid content concentration is 30%, the number average molecular weight (in terms of polystyrene) by GPC method is 11,000, and the sulfonic acid group content in the polyurethane resin is 10 ⁶ g of the resin. It was 185 equivalents. Using the obtained polyurethane resin solution (C-3), a magnetic paint (E-3) was prepared in the same manner as in Example 1 to obtain a magnetic tape (F-3).

Example 4 A 4-necked kolben equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas inlet was charged with (D-2) 0.5 mol, neopentyl glycol 0.5 mol, (HOCH 2 CH 2) 2 N
0.12 mol of SO3Na and 1 mol of diphenylmethane diisocyanate were charged and reacted at about 70 ° C. A MEK / cyclohexanone mixture (weight ratio 1: 1) was added thereto, and a polyurethane resin solution (C-4) having a solid content of 30% was added.
I got The viscosity of the (C-4) is 1,100 cP / 25
° C, the solid content concentration is 30%, the number average molecular weight (in terms of polystyrene) by GPC method is 12,000, and the sulfonic acid group content in the polyurethane resin is 13 per 10 ⁶ g of the resin.
It was 7 equivalents. The obtained polyurethane resin solution (C-
Using 4), a magnetic paint (E-4) was prepared in the same manner as in Example 1 to obtain a magnetic tape (F-4).

COMPARATIVE EXAMPLE 1 A four-necked kolben equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas inlet was charged with a number average molecular weight of 1,000 obtained from 1,6-hexanediol and dimethyl carbonate.
0 mol of polycarbonate diol, 1 mol of neopentyl glycol and 1.9 mol of diphenylmethane diisocyanate were charged and reacted at about 70 ° C. M
An EK / cyclohexanone mixture (weight ratio 1: 1) was added to obtain a polyurethane resin solution (C-5) having a solid content of 30%. The viscosity of (C-5) is 1,500 cP / 25 ° C.
The solid concentration was 30%, and the number average molecular weight (polystyrene conversion) by GPC was 15,000. Using the obtained polyurethane resin solution (C-5), a magnetic paint (E-5) was prepared in the same manner as in Example 1 to obtain a comparative magnetic tape (F-5).

Test Example 1 The magnetic tape (F) obtained in Examples 1 to 4 and Comparative Example 1
The surface glossiness was measured to see the dispersibility of the magnetic powders of -1) to (F-5). Table 1 shows the results. The surface gloss was measured at a regular reflectance of 75 ° using a digital variable angle gloss meter manufactured by Nippon Denshoku Industries Co., Ltd. Numerical values were expressed as relative values (%) as compared with the case where the reflectance of the standard plate was 95. The higher the gloss, the better the dispersibility.

[0056]

[Table 1]

Test Example 2 The magnetic paints (E-E) obtained in Examples 1 to 4 and Comparative Example 1
The viscosities of 1) to (E-5) were measured. Table 2 shows the results. The viscosity was measured using a BL type viscometer (manufactured by Tokyo Keiki).
It was measured at 5 ° C.

[0058]

[Table 2]

Test Example 3 The magnetic tape (F) obtained in Examples 1 to 4 and Comparative Example 1
-1) to (F-5) were measured for durability. Table 3 shows the results. The durability was represented by the amount of powder falling off (mg) after 30 times of rubbing with a load of 100 g using a Gakushin friction fastness tester (manufactured by Daiei Chemical Seiki Seisakusho). The smaller the value, the better the durability of the magnetic tape.

[0060]

[Table 3]

[0061]

The binder for a magnetic recording medium of the present invention comprises:
The following effects are obtained as compared with the conventional one. (1) The binder for a magnetic recording medium of the present invention has excellent dispersibility in magnetic powder and improves the magnetic properties of a magnetic tape. (2) Further, since the viscosity of the magnetic paint obtained by using the binder for a magnetic recording medium of the present invention is low, the speed of the application line can be increased, and the magnetic powder can easily move at the time of orientation to improve the magnetic properties. I do. (3) The magnetic recording medium obtained using the magnetic recording medium binder of the present invention has excellent durability. Because of the above effects, the binder of the present invention is useful as a binder for a magnetic recording medium such as an audio tape, a video tape, a computer tape, a data recorder tape, a metal tape, a floppy disk, and a magnetic card. It is also useful as a binder for dispersing metal (oxide) fine particles such as nickel and aluminum.

Claims (4)

[Claims] An organic polyisocyanate (B) derived from a high molecular polyol (A1) having a number average molecular weight of 500 to 8,000 or a polyol component (A) comprising the (A1) and a low molecular polyol (A2). In a binder for a magnetic recording medium comprising a polyurethane resin (C), at least 10% by weight of the polymer polyol (A1) has an intramolecular partially dehydrated castor oil (A11) having an average of 1.8 to 2.4 hydroxyl groups. And / or a partially acylated castor oil (A12). (C) is a carboxylic acid (salt) in the molecular side chain.
And at least one organic acid (salt) group selected from the group consisting of a group, a sulfonic acid (salt) group, a sulfamic acid (salt) group, and a phosphate (salt) group or a phosphonic acid (salt) group, and When the content of the organic acid (salt) group is (C) 10 ⁶
2. The binder for a magnetic recording medium according to claim 1, wherein the amount is from 1 to 1,000 equivalents per g. 3. The number average molecular weight of (C) is from 5,000 to 2
3. The binder for a magnetic recording medium according to claim 1, wherein the binder is 0.00000. 4. A magnetic recording medium having a magnetic layer containing the binder according to claim 1.