JP2000322728A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium which is excellent in blocking resistance, curling resistance and the like and environment-friendly without utilizing polyvinyl chloride based resin. SOLUTION: Relating to a magnetic recording medium having a magnetic layer formed by applying a magnetic coating material consisting essentially of ferromagnetic powder and a bonding agent, on a non magnetic supporting body, the bonding agent contains polyurethane resin and has a <=50 ppm chlorine content and an absolute value of the difference of the coefficient of linear expansion of the bonding agent and an average coefficient of linear expansion of the non magnetic supporting body at 0-40 deg.C is equal to 7.00×10-5/ deg.C or less and a probe tuck of the bonding agent is 15 kPa or less. And the bonding agent preferably consists of a polyurethane resin having a glass transition temperature of <50 deg.C and a polyurethane resin having a glass transition temperature of >=50 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a magnetic recording medium. More specifically, the present invention relates to an environment-friendly magnetic recording medium which is excellent in blocking resistance and curling resistance after applying a magnetic paint on a non-magnetic support, and does not use a vinyl chloride resin.

[0002]

2. Description of the Related Art Generally, audio equipment, video equipment,
Magnetic recording media used for computers, magnetic cards, etc. (specifically, audio tapes, video tapes, proppy disks, computer data tapes, prepaid cards, magnetic tickets, etc.) are supported by non-magnetic supports such as polyester film and paper. It is obtained by applying a magnetic paint having a ferromagnetic powder, a binder and the like on a body and drying it to form a magnetic layer. As a binder for forming such a magnetic recording medium, a combination of a polyurethane resin and a vinyl chloride resin is widely used.

[0003] When the magnetic paint is applied, dried, or used, the coating film shrinks due to internal stress, which may cause a problem of curling. When the curl occurs, the contact between the obtained magnetic recording medium and the magnetic head is impaired, so that inconvenience tends to occur during recording / reproducing, and the winding is likely to be disturbed.

Various studies have been made to prevent curling. For example, JP-A-2-287919 discloses that two or more types of polyester polyurethane resins having a glass transition point of 30 ° C. or more are used, and one of these polyester polyurethane resins has a weight average molecular weight of 80,000 or more. The magnetic recording medium used is shown.

[0005] In recent years, the problem of dioxin generated during incineration of waste has become remarkable, and as a result, the use of resins containing a large amount of chlorine, such as vinyl chloride resins, has become less preferred. The technique described in Japanese Patent Application Laid-Open No. 2-287919 can solve the problem of curling, but does not suggest any means for solving the problem of so-called dehalogenation.

[0006]

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above-mentioned problems, and has excellent blocking resistance, curling resistance, etc., and can be used in an environment where a vinyl chloride resin is not used. An object is to provide a gentle magnetic recording medium.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve such conventional problems, and as a result, a binder for a magnetic recording medium made of a specific polyurethane resin has been described. Have been found to be able to solve, and the present invention has been completed.

That is, the present invention provides the following (1) to (3)
It is shown in. (1) In a magnetic recording medium in which a magnetic coating mainly composed of a ferromagnetic powder and a binder is applied on a non-magnetic support to form a magnetic layer, the binder contains a polyurethane resin; The chlorine content of the binder is 50 ppm or less,
The absolute value of the difference between the coefficient of linear expansion of the binder and the average coefficient of linear expansion of the nonmagnetic support at 0 to 40 ° C. is 7.00 × 10 ⁻⁵ ° C.- ¹ or less, and the probe tack of the binder is Is 15 kPa or less.

(2) In the magnetic recording medium of (1), the binder contains a polyurethane resin having a glass transition temperature of less than 50 ° C. and a polyurethane resin having a glass transition temperature of 50 ° C. or more. And a magnetic recording medium.

(3) The magnetic recording medium according to (1) or (2), wherein a polyisocyanate curing agent is added to the magnetic paint.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The binder used in the magnetic paint of the magnetic recording medium of the present invention is mainly composed of a polyurethane resin. Examples of resins that can be used in combination with the binder include polyester resins, polyamide resins, phenol resins, melamine resins, urea resins, silicone resins, acrylic resins, and cellulose resins such as nitrocellulose. Vinyl chloride resins such as vinyl chloride resin, vinyl chloride-vinyl acetate resin, ethylene-vinyl chloride resin, and acryl-vinyl chloride resin are not particularly problematic in terms of magnetic properties of the magnetic recording medium, but may be discarded. Considering the environmental load during incineration, its use is not preferred.

The chlorine content of the binder used in the magnetic paint of the magnetic recording medium of the present invention is 50 ppm or less, preferably 45 ppm or less. If the chlorine content exceeds the upper limit, the polyurethane resin has self-extinguishing properties at the time of disposal, particularly in incineration treatment, and it is difficult to completely burn the polyurethane resin.

Since isocyanate, which is a raw material of a polyurethane resin, is usually obtained by reacting an amine with phosgene, a small amount of chlorine is present in the polyurethane resin. In addition, in a normal binder for a magnetic recording medium, a vinyl chloride resin is used in combination as a sub-binder in addition to a polyurethane resin, so that the chlorine content of the entire binder for a magnetic recording medium is about several tens mass%.

The absolute value of the difference between the average linear expansion coefficient of the binder in the practical temperature range of 0 to 40 ° C. and the average linear expansion coefficient of the non-magnetic support is 7.00 × 10 ⁻⁵ ° C.- ¹ or less. And preferably 6.70 × 10 ⁻⁵ ° C.- ¹ or less. If the absolute value of the difference between the average linear expansion coefficients exceeds the upper limit, the obtained magnetic recording medium tends to curl.

The average linear expansion coefficient is JIS K7197.
(1991). The test piece is measured by cutting the non-magnetic support as it is. The binder is measured after forming a cast film and then cutting. Measurement conditions Measurement temperature: 0 to 40 ° C Specimen size: 10 × 4 × 0.1 mm Heating rate: 5 ° C / min Weight: 4 kPa

The probe tack of the binder of the present invention is 15 k.
Pa or less, preferably 10 kPa or less. If the probe tack exceeds the upper limit, blocking tends to occur in winding after coating and drying. In addition, the probe tack is an index indicating the surface tackiness.

The probe tack is JIS Z02.
37 (1991) and is measured according to the “probe tack test”. The measurement conditions for the probe tack of the present invention are as follows: a test specimen was subjected to a load of 10 MPa for 1 second with a probe having a diameter of 5 mm in an atmosphere of 23 ± 2 ° C. and 50 ± 5% RH, and then released at a speed of 1 cm / sec. It is the value at the time of doing.

The content of the polyurethane resin in the binder is as follows:
It is preferably at least 60% by mass, and more preferably at least 80% by mass. When the content of the polyurethane resin in the binder is less than the lower limit, the abrasion resistance tends to be insufficient.

The polyurethane resin used for the magnetic recording medium of the present invention has a glass transition temperature of less than 50 ° C., preferably 40 ° C. or less (low Tg polyurethane resin).
A high Tg polyurethane resin having a glass transition temperature of 50 ° C. or higher, preferably 60 ° C. or higher.

The mixing ratio of the low Tg polyurethane resin and the high Tg polyurethane resin is from 30:70 to 70:30 by mass.
It is. If the amount of the low Tg polyurethane resin is too large, the blocking resistance tends to decrease. In addition, when the high Tg polyurethane resin is too large, curling is likely to occur.

The glass transition temperature of these polyurethane resins is the temperature at which E ″ (loss modulus) in dynamic viscoelasticity is maximized, and the measurement conditions are as follows: frequency: 35
Hz, heating rate: 2 ° C. per minute.

The low Tg polyurethane resin and the high Tg polyurethane resin are obtained by reacting an organic diisocyanate with an active hydrogen group-containing compound. As the organic diisocyanate, 2,4-tolylene diisocyanate, 2,6
-Tolylene diisocyanate, xylene-1,4-diisocyanate, xylene-1,3-diisocyanate,
4,4'-diphenylmethane diisocyanate, 2,
4'-diphenylmethane diisocyanate, 2,2'-
Diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane-4,4 ' -Diisocyanate, 4,4'-diphenylpropane diisocyanate,
m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3 '
Aromatic diisocyanates such as -dimethoxydiphenyl-4,4'-diisocyanate, aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, hydrogenated Diphenylmethane diisocyanate, an alicyclic diisocyanate such as tetramethylxylene diisocyanate, and a biuret, dimer, trimer, dimer / trimer, carbodiimide, uretonimine, bifunctional or higher functional bifunctional polyol or the like of the isocyanate and the isocyanate An adduct obtained by the reaction is suitable. These can be used as one kind or as a mixture of two or more kinds. In consideration of the mechanical strength and the like of the obtained polyurethane resin, the organic diisocyanate preferred in the present invention is an aromatic diisocyanate, more preferably 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylene-1,4. -Diisocyanate, xylene-1,3-diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate.

The active hydrogen group-containing compound includes a high molecular polyol having a number average molecular weight of 500 or more, preferably 500 to 10,000, a (number average) chain extender having a molecular weight of less than 500,
And a reaction terminator. Examples of the high molecular polyol include polyester polyol, polyamide ester polyol, polyether polyol, polyether ester polyol, polycarbonate polyol, polyolefin polyol, animal and plant-based polyol, and the like. These can be used as one kind or as a mixture of two or more kinds.

Examples of the polyester polyol include known phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, succinic acid, tartaric acid, oxalic acid, malonic acid,
Glutaric acid, adipic acid, pimelic acid, suberic acid, curtaconic acid, azelaic acid, sebacic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, 1,4-cyclohexyldicarboxylic acid, α-hydromuconic acid, β-hydro Muconic acid, α-butyl-α-ethylglutaric acid,
α, β-diethyl succinic acid, maleic acid, fumaric acid, and other dicarboxylic acids or one or more of anhydrides, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol , 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 3-methyl-
1,5-pentanediol, 3,3-dimethylolheptane, diethylene glycol, dipropylene glycol, neopentyl glycol, diethylene glycol,
Dipropylene glycol, cyclohexane-1,4-diol, cyclohexane-1,4-dimethanol, dimer acid diol, ethylene oxide or propylene oxide adduct of bisphenol A, bis (β-hydroxyethyl) benzene, xylylene glycol, glycerin , Trimethylolpropane, pentaerythritol, and other low molecular polyols. Further, ε-caprolactone, alkyl-substituted ε
Lactone-based polyester polyols obtained from ring-opening polymerization of cyclic ester (so-called lactone) monomers such as -caprolactone, δ-valerolactone, and alkyl-substituted δ-valerolactone. Further, part of the low molecular polyol hexamethylene diamine, isophorone diamine,
A low molecular weight polyamine such as monoethanolamine or a low molecular weight amino alcohol may be used. In this case, a polyester-amide polyol is obtained. Also,
Polycarbonate polyols, polyolefin polyols, and plant and animal polyols described below can also be used as raw materials for polyester polyols.

Examples of the polyether polyol include homopolymers and copolymers of epoxides such as ethylene oxide, propylene oxide, and tetrahydrofuran, and cyclic ethers.

The polycarbonate polyol is obtained by a dealcoholation reaction or a dephenolization reaction of at least one of the above-mentioned low molecular weight diols and low molecular weight triols of the polyester polyol with ethylene carbonate, diethyl carbonate and diphenyl carbonate.

As the polyetherester polyol, there is a copolyol obtained from the above-mentioned polyether polyol and the above-mentioned dicarboxylic acid. In addition, there are those obtained by the reaction of the above-mentioned polyester or polycarbonate with epoxide or cyclic ether.

Examples of the polyolefin polyol include polybutadiene having two or more hydroxyl groups, hydrogenated polybutadiene, polyisoprene, and hydrogenated polyisoprene.

Examples of animal and plant-based polyols include castor oil-based polyols and silk fibroin.

Further, as long as the number average molecular weight is 500 or more, preferably 500 to 10,000 and has at least one active hydrogen group in one molecule, a dimer acid polyol or hydrogenated dimer acid can be used. Active hydrogen group-containing resins such as epoxy resin, polyamide resin, polyester resin, acrylic resin, rosin resin, urea resin, melamine resin, phenol resin, coumarone resin, and polyvinyl alcohol can be used in addition to the system polyol.

Examples of the chain extender include low-molecular polyol, low-molecular polyamine, low-molecular amino alcohol, and the like used in the above-mentioned polyester polyol. These can be used as one kind or as a mixture of two or more kinds.

Further, a reaction terminator can be used if necessary. Examples of the reaction terminator include amino alcohols, monoalcohols such as methanol and ethanol, primary monoamines such as ethylamine and butylamine, and secondary monoamines such as diethylamine and dibutylamine.

The number average molecular weight of the low Tg polyurethane resin and the high Tg polyurethane resin is measured by a gel permeation chromatography (GPC) method using a polystyrene calibration curve.
0 to 50,000 and 10,000 to 40,000
Is more preferable, and 12,000 to 38,000 is most preferable. When the number average molecular weight is less than 8,000, durability and blocking resistance are reduced. Number average molecular weight is 5
When it exceeds 000, the dispersibility, the adhesion and the like are liable to decrease.

It is preferable to introduce a polar group into at least one of the low Tg polyurethane resin and the high Tg polyurethane resin because the dispersibility of the ferromagnetic powder is improved. Examples of the polar group include those represented by the following chemical formula.

[0035]

Embedded image (M represents a hydrogen atom or an alkali metal)

[0036]

Embedded image (M represents a hydrogen atom or an alkali metal)

[0037]

Embedded image (M represents a hydrogen atom or an alkali metal)

[0038]

Embedded image (M represents a hydrogen atom, an alkali metal, or an alkyl group)

[0039]

Embedded image (N represents an integer of 1 or more)

[0040]

Embedded image (R represents an alkyl group)

[0041]

Embedded image (R ₁ and R ₂ are alkyl groups, and X ⁻ is a monovalent anion.)

[0042]

Embedded image

As a method for synthesizing the polyurethane resin used in the present invention, a known method is used. That is, (1) a method in which an active hydrogen group-containing compound and an organic diisocyanate are reacted under a condition of an excess of active hydrogen groups until a predetermined molecular weight is reached (one-shot method); Under such conditions, a prepolymer containing an isocyanate group is obtained, and then the prepolymer is chain-extended with a low molecular weight glycol or a low molecular weight diamine and reacted until a predetermined molecular weight is reached (prepolymer method).

An organic solvent can be used if necessary. This organic solvent is an aromatic hydrocarbon-based solvent such as toluene, xylene, pentane, hexane, an aliphatic hydrocarbon-based solvent such as octane, cyclopentane, cyclohexane, an alicyclic hydrocarbon-based solvent such as methylcyclohexane, acetone, Ketone solvents such as methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, methyl cyclohexanone, ether solvents such as diethyl ether, 1,4-dioxane, tetrahydrofuran, ethylene glycol dimethyl ether, ethylene glycol monomethyl ether acetate, propylene Cellosolve solvents such as glycol dimethyl ether and propylene glycol monomethyl ether acetate; monobasic ester solvents such as ethyl acetate and butyl acetate; Phosphate, dimethyl succinate, dibasic esters such as dioctyl phthalate, dimethyl formamide, dimethyl acetamide, N
There is no particular limitation as long as it is inert to isocyanate groups such as -methylpyrrolidone. Depending on the conditions, an alcoholic solvent such as isopropanol can be used.

As a reaction apparatus for obtaining the polyurethane resin in the present invention, any apparatus can be used as long as the above-mentioned reaction can be achieved. A kneading device may be used.

The magnetic recording medium of the present invention is characterized in that a polyisocyanate curing agent is added to a magnetic paint. Examples of the polyisocyanate curing agent are products of Nippon Polyurethane Industry Co., Ltd., such as hexamethylene diisocyanate-modified type Coronate (registered trademark) HX, coronate HL, tolylene diisocyanate-modified type coronate L, coronate 2030, coronate 2031 and the like. These may be used alone or as a mixture. The amount of the polyisocyanate curing agent to be added is 1 to 30 parts by mass in terms of solids based on 100 parts by mass of the solids of the magnetic paint.

As the ferromagnetic powder that can be used in the magnetic recording medium of the present invention, any of oxidized magnetic powder, metal magnetic powder, hexagonal barium ferrite fine particles, and a mixture thereof can be used.

As the oxidized magnetic powder, γ-Fe ₂ O ₃ , γ
-Fe ₂ O ₃ and Fe ₃ O ₄ crystals, Co-γ-Fe ₂ O ₃ , C
o-Fe ₃ O ₄ , CrO ₂ , and the like.
Average major axis is 0.1-1.0 μm, average minor axis is 0.01-
0.10 μm, coercive force 20-80 kA / m, specific surface area 1
0 to 50 m ² / g.

Examples of the metal magnetic powder include Fe, Ni, Co,
Fe-Ni-Co alloys, Fe-Mn-Zn alloys and the like are listed, and their properties are as follows.
Coercive force 50-200 kA / m, specific surface area 20-70 m ²
/ G. It is.

In order to obtain the magnetic recording medium of the present invention, the magnetic recording medium is prepared by using the binder and the magnetic powder described above.
In addition, an organic solvent is used, and if necessary, additives such as an abrasive, a filler, an antistatic agent, a rust inhibitor, a fungicide, and a lubricant can be appropriately used. The ratio of the binder, the magnetic powder, and the organic solvent is 5 to 1 with respect to 100 parts by mass of the magnetic powder.
00 parts by mass and 100 to 1,000 parts by mass of an organic solvent are preferred.

A known method is used for preparing the magnetic paint. For example, the components to be used are kneaded and dispersed in a sand grind mill, a ball mill or the like using glass beads, metal beads or the like. Alternatively, the magnetic powder and additives can be made into a paste in advance and then dispersed in a binder.

The magnetic paint thus obtained is applied to a non-magnetic support such as plastic or paper, and dried. The application method includes doctor blade, reverse roll, gravure roll, spinner coat, and the like. A known method such as an extruder is used. After applying the magnetic paint,
Depending on the application, it is oriented, dried and calendered to obtain a magnetic recording medium.

The polyurethane resin according to the present invention may be used in addition to a binder for a magnetic recording medium, a paint other than a magnetic paint, an adhesive, a sealing agent, a coating agent, various primers, artificial leather, a fiber treatment agent, an elastic fiber, It can be used for films, sheets and the like.

[0054]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples, “part” and “%” are
Unless otherwise specified, "parts by mass" and "% by mass" are indicated.

[Synthesis of Polyol for Polyurethane Resin] Synthesis Example 1 582 parts of isophthalic acid as an acid component and 542 parts of 1,6-hexanediol as a polyol component were placed in a reactor equipped with a stirrer, a nitrogen introducing pipe, and a cooling pipe. Charge, 140 ° C
Heated. When the distilling of water gradually disappeared, 0.01 part of tetrabutyl titanate was charged as a catalyst,
The temperature was gradually heated to 220C. When the temperature reached 220 ° C., the pressure was gradually reduced to 0.4 kPa to obtain a polyol A which was a polyester polyol. Table 1 shows the synthesis results.

Synthetic Examples 2 to 6 Polyols B to G, which are polyester polyols, were obtained in the same manner as in Synthetic Example 1 with the preparations shown in Table 1. Table 1 shows the results.

Synthesis Example 7 A reactor similar to that of Synthesis Example 1 was charged with 752 parts of diethyl carbonate as an acid component and 859 parts of 1,6-hexanediol as a polyol component, and heated to 140 ° C. When the distillation of ethanol gradually disappeared, 0.01 part of tetrabutyl titanate was charged as a catalyst,
The temperature was gradually heated to 220C. When the temperature reached 220 ° C., the pressure was gradually reduced to 0.4 kPa to obtain a polyol G which was a polycarbonate polyol. Table 1 shows the synthesis results.

[0058]

[Table 1]

In Table 1, i-PhA: isophthalic acid AA: adipic acid t-PhA: terephthalic acid DEC: diethyl carbonate HD: 1,6-hexanediol BD: 1,4-butanediol MPD: 3-methyl-1, 5-pentanediol EG: ethylene glycol NPG: neopentyl glycol CHDM: 1,4-cyclohexanedimethanol DMH: 3,3-dimethylolheptane TBT: tetrabutyl titanate

[Synthesis of Polyurethane Resin Solution] Synthesis Example 8 In a reactor equipped with a stirrer, a nitrogen inlet tube, and a cooling tube, 229 parts of polyol A, 2.84 parts of ethylene glycol,
After charging 200 parts of methyl ethyl ketone and mixing and dissolving at 50 ° C., 0.06 parts of dibutyltin dilaurate was added.
4,4'-diphenylmethane diisocyanate
One part was charged and urethanization reaction was carried out at 75 ° C. Since the viscosity increased as the reaction progressed, it was diluted with methyl ethyl ketone and toluene as appropriate. The reaction was terminated at the time when the absorption of the isocyanate group in the infrared absorption spectrum was extinguished, to obtain a hydroxyl-terminated polyurethane resin solution PU-1 having a glass transition temperature of less than 50 ° C. In addition, the final solvent composition is methyl ethyl ketone / toluene = 1/1. The solid content of the obtained polyurethane resin solution is 30.
%, Number average molecular weight (GPC method, polystyrene calibration curve) is 50,000, glass transition temperature is 40 ° C. (dynamic viscoelasticity,
Loss elastic modulus maximum temperature). Table 2 shows the results.

Synthesis Examples 9-17 Polyurethane resin solutions PU-1-6 having a glass transition temperature of less than 50 ° C.
Polyurethane resin solution PU with glass transition temperature of 50 ° C or higher
-7 to 10 were obtained. The results are shown in Tables 2 and 3.

[0062]

[Table 2]

[0063]

[Table 3]

In Tables 2 and 3, polyol H: hydrogenated polybutadiene diol number average molecular weight = 1,000 Tg: glass transition temperature EG: ethylene glycol BD: 1,4-butanediol NPG: neopentyl glycol MDI: 4,4 ' -Diphenylmethane diisocyanate DBTDL: dibutyltin dilaurate MEK: methyl ethyl ketone

[Preparation and Evaluation of Binder for Magnetic Recording Medium] Example 1 PU-1 having a glass transition temperature of less than 50 ° C. and PU-6 having a glass transition temperature of 50 ° C. or more were converted into PU-1 / PU
After mixing at −6 = 50/50, an adduct type coronate (registered trademark) 3041 of tolylene diisocyanate (solvent composition: methyl ethyl ketone / toluene = 1/1, solid content = 50%) as a curing agent was converted to solid content. By adding 10 parts, a cast film having a dry film thickness of about 100 μm was prepared. The chlorine content of the film, the difference in the absolute value of the average linear expansion coefficient with a nonmagnetic support (polyethylene coated paper) at 0 to 40 ° C, and the probe tack were measured. Table 4 shows the results.

Conditions for preparing cast film: 60 ° C. × 30 minutes + 120 ° C. × 60 minutes

Examples 2 to 10 and Comparative Examples 1 to 11 Cast films were prepared with the formulations shown in Tables 4 to 7,
Evaluation was performed in the same manner as in Example 1. The results are shown in Tables 4 to 7. Examples 1 to 8 and Comparative Examples 1 to 8 were compared with polyethylene coated paper, and Examples 9 to 10 and Comparative Examples 9 to 1 were compared.
1 is a comparison with a polyethylene terephthalate film.

[0068]

[Table 4]

[0069]

[Table 5]

[0070]

[Table 6]

[0071]

[Table 7]

The average linear expansion coefficient of the polyethylene-coated paper used as the nonmagnetic support at 0 to 40 ° C. was 1.66 × 1.
0 ⁻⁵ ° C. ⁻¹ , 2.83 × 1 for polyethylene terephthalate
It was 0 ^-5 ° C ^-1 . The vinyl chloride resin in Tables 6 and 7 has a solvent composition of methyl ethyl ketone / toluene = 1.
/ 1, solid content = 30% before use. The values in the table are
It is a solid content conversion value.

Method for measuring chlorine content: Comparative Examples 1, 2, 8,
9 was measured according to JIS K7229 (1995).
Other than that, it measured according to JISK7243 (1996). Linear expansion coefficient measuring method: JIS K7197 (1
991). Measurement conditions Specimen size: 10 × 4 × about 0.1 (mm) Heating rate: 5 ° C./min Weight: 4 kPa Probe tack measurement method: Other than that, JIS Z02
37 (1991), and was measured according to the “probe tack test”. Measurement conditions Test atmosphere: 23 ± 2 ° C., 50 ± 5% RH Probe diameter: 5 mm Load condition: 10 MPa Contact time: 1 second Release speed: 1 cm / second

Example 11 The following raw materials were mixed and dispersed in a sand grind mill for 3 hours to prepare a magnetic paint. This magnetic paint was applied on a polyethylene coated paper by a gravure coater so as to have a dry film thickness of 5 μm, dried, cut into a width of 25 mm, and wound up to obtain a sample. The presence or absence of curling of this sample was visually determined. Also, the presence or absence of resistance when rewinding the wound magnetic tape was determined. Further, the state of the inside of the can after the sample was incinerated in a tin can was observed. Table 8 shows the results. 33 parts of PU-1 (as a resin solution) 33 parts of PU-6 (as a resin solution) 100 parts of Co-γ-Fe ₂ O _{3 2} parts of α-Al ₂ O ₃ 2 parts of coronate 3041 2 parts (as a resin solution) ) Myristic acid 2 parts Methyl ethyl ketone 77 parts Toluene 77 parts

Examples 12 to 18, Comparative Examples 12 to 22 Except for PU-1 and PU-6 in Example 11, the preparation was performed in the same manner as in Example 11, except that the binder was added to the composition shown in Tables 8 and 9. A magnetic coating material was prepared, applied, dried, cut, wound up, and similarly tested. The results are shown in Tables 8 and 9. In addition,
Examples 11 to 16 and Comparative Examples 12 to 19 were applied to a polyethylene coated paper, and Examples 17 to 18 and Comparative Examples 20 to 22 were applied to a polyethylene terephthalate film.

[0076]

[Table 8]

[0077]

[Table 9]

In Tables 8 and 9, curlability: no curl ×: curl Resistance during rewind ○: no resistance ×: resistance Inside of can ○: no corrosion ×: corrosive

[0079]

As described above, according to the present invention, it is possible to provide an environmentally friendly magnetic recording medium which is excellent in blocking resistance, curling resistance, etc. and does not use a vinyl chloride resin.

Continued on the front page F-term (reference) 4J034 CA02 CA03 CA04 CA05 CA13 CA15 CA17 CB01 CB03 CB04 CB05 CB07 CB08 CC03 CC08 CC12 CC23 CC26 CC45 CC52 CC61 CC62 CC65 CC67 CD04 DA01 DB03 DB07 DF02 DF11 DF12 DF22 DF21 DF21 DF20 DF20 DF20 DG06 DG08 DG09 DH02 DH06 DH07 DH10 DJ08 DJ09 DK00 DL01 DL09 DP17 DP18 EA11 EA12 EA14 FA01 FB01 FC03 FD01 FD05 GA05 GA06 GA23 GA33 GA55 HA01 HA02 HA07 HB05 HB06 HB07 HB08 HB11 HCB HC HC2 HC HC HC HC HC HC HC HC HC HC HC HC HC HC HC HC HC HC HC64 HC67 HC70 HC71 HC73 JA14 JA42 QB03 QC08 RA03 RA07 RA08 RA09 RA16 4J038 DG101 DG111 DG121 DG131 DG171 DG191 DG271 DG281 DG291 KA03 KA07 MA13 NA10 NA27 PB09 PB11 PC08 PC10 5D006 BA15

Claims (3)

[Claims] 1. A magnetic recording medium having a magnetic layer formed by applying a magnetic paint mainly composed of a ferromagnetic powder and a binder on a non-magnetic support, wherein the binder contains a polyurethane resin. The chlorine content of the binder is 50 ppm or less, and the absolute value of the difference between the coefficient of linear expansion of the binder and the average coefficient of linear expansion of the nonmagnetic support at 0 to 40 ° C. is 7.00 × 10 5 ^-5 ° C.- ¹ or less, and the probe tack of the binder is 15 kPa or less. 2. The magnetic recording medium according to claim 1, wherein the binder contains a polyurethane resin having a glass transition temperature of less than 50 ° C. and a polyurethane resin having a glass transition temperature of 50 ° C. or more. And a magnetic recording medium. 3. The magnetic recording medium according to claim 1, wherein a polyisocyanate curing agent is added to the magnetic paint.