JPH03248319A - Magnetic coating material and magnetic recording medium - Google Patents

Abstract

PURPOSE:To form a magnetic layer of high dispersibility and high durability and to obtain good electromagnetic conversion characteristics and stable high output for a long time by using such a polyurethane resin having urethane couplings by the amt. of 1.8 - 2.5 mmol/g and polar groups such as carboxyl group as a binder for the magnetic layer. CONSTITUTION:The binder contains such a polyurethane resin into which at least one group selected from carboxyl groups, sulfo groups, phospho groups, amino groups or polar groups obtained by substituting metal or alkyl group for these groups is incoporated. The amt. of urethane couplings of this polyure thane resin is specified to 1.8 - 2.5 mmol/g. It is preferable that the polyurethane resin is prepared by the reaction of polycarbonate and isocyanate compd. There by, a magnetic layer of high dispersibility and high durability can be formed even with using a magnetic powder of fine particles, and the obtd. medium has excellent electromagnetic conversion characteristics and stable high output even if repeatedly used for a long time. By introducing polar groups such as carboxyl groups, adsorption property to the magnetic powder can be increased.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a magnetic recording medium having a magnetic layer on a non-magnetic support, in which the dispersibility of breakable powder and the durability of the magnetic layer are improved. .

[Prior art]

Magnetic recording media such as magnetic tapes and magnetic disks are widely used in the video field, audio field, computer field, etc. Such magnetic recording media are produced by applying a magnetic coating consisting of a breakable powder, a binder, a solvent, a dispersant, and other additives to a base material such as a polyester film and drying it to form a magnetic coating. Magnetic recording media are also used.

Particularly in recent years, as the recording density of magnetic recording media has improved, there has been a demand for higher output by improving electromagnetic conversion characteristics, and as a result, breakable powders have been made into fine particles and are required to have high dispersibility. On the other hand, a magnetic layer that is rubbed by a magnetic head or the like is required to have high durability. from these things,
It is attempted to obtain high dispersion and high durability by selecting the mixing ratio and types of the magnetic powder, binder, additives, etc. that constitute the magnetic layer.

The function of the binder in a magnetic recording medium is to adhere the magnetic powder etc. to the base material, hold the magnetic powder homogeneously and firmly, and play a major part in the mechanical performance of the magnetic coating film.

Conventionally, polycarbofoot group or polyester urethane resins, vinyl chloride-vinyl acetate resins, etc. have been used alone or in combination as binders for magnetic recording media.
When high durability is required for the magnetic layer coating, thermosetting polyester urethane resin etc. are used, and the hardness is improved by further accelerating the curing of the coating and adding VR polishing agent. In this way, damage to the surface of the magnetic recording medium is prevented as much as possible.

In addition, in order to achieve high dispersion of magnetic powder, various functional groups such as carboxyl groups, sulfonic acid groups, and phosphate ester groups are added to the polyurethane resin to improve the adsorption of the binder resin to the magnetic powder. Is the method adopted?
Alternatively, a method has been adopted to increase the dispersibility by increasing the amount of distributed work.

[Problems to be Solved by the Invention] However, simply by highly dispersing magnetic powder using a polyurethane resin having a polar group such as a carboxyl group, the electromagnetic conversion characteristics cannot be sufficiently improved; If the amount of dispersion work is increased, there is a risk that the magnetic powder will be over-pulverized and the thermal stability will be reduced, and a significant improvement in output cannot be expected. Further, there is a limit to promoting hardening of the magnetic layer in order to increase durability, and addition of abrasives is accompanied by deterioration of characteristics. For these reasons, at present, the dispersibility is not sufficient to improve electromagnetic conversion characteristics and significantly increase output, and the durability is not sufficient to maintain these properties stably for a long time. Improvement is desired.

An object of the present invention is to provide a magnetic recording medium in which a highly dispersible and highly durable magnetic layer is formed, thereby having good electromagnetic conversion characteristics and capable of stably obtaining high output over a long period of time.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a magnetic paint containing ferromagnetic powder and a binder, in which the binder contains a polyurethane resin, and the polyurethane resin has a carboxyl group, a sulfonic acid group, a phosphoric acid group, It has at least one of the group consisting of an amine group, each of these metal-substituted and alkyl-substituted polar groups, and the number of urethane bonds is 1.8
su+. The present invention provides a magnetic paint having a concentration of 1/g to 2.5 mmol/g. In this case, it is also preferable that the polyurethane resin is a resin obtained by a reaction between polyester, polycarbonate, and an isocyanate compound, and the above polar group-based polyurethane resin is added in an amount of 5 to 8 parts by weight per 100 parts by weight of the ferromagnetic powder. Resin other than this 12~
It is also preferable that the magnetic paint contains 15 parts by weight.

The present invention also provides a magnetic recording medium obtained using the above magnetic coating material.

Next, the present invention will be explained in detail.

The polyurethane resin used in the present invention is obtained by reacting a base polymer such as polyester or polycarbonate, which forms a polyurethane skeleton, with an isocyanate compound. -HCO-) number to 1.8 txmo
l/g to 2.5 mmol/g to make the polyurethane skeleton rigid (heart).

If the number of urethane bonds is less than 1.8 mmof/g, the hardening of the urethane skeleton will be insufficient, and the effect of improving the durability of the magnetic layer using this will be small;
If the amount is more than u + mol/g, the plasticity of the resin will be poor, resulting in powder drop-off of the magnetic layer using it (a phenomenon in which magnetic powder flakes off when the magnetic layer is rubbed by a magnetic head, etc.) This causes phenomena such as surface damage.

In addition, the polyurethane resin used in the present invention has carboxyl groups (-COOH), sulfonic acid groups (SO3
H) At least one of phosphoric acid groups, amino groups, and those substituted with alkyl groups or metals.
Has seeds. As those having a substituent, -COOM
, -503M , -N(+?)2, -PO(OM')
(OR”) (However, M and M' are, for example, alkali gold N
Representing an atom, R,! ? ' represents a substituent such as an alkyl group, and A and R may be the same),
It is preferable to use at least one type of polyurethane resin having these polar groups, since high adsorption to the magnetic powder can result in high dispersibility.

Examples of the polyurethane resin used in the present invention include polyester urethane resin, which has a molecular weight of 500
Examples include those obtained by using the above polyester diol with a polyisocyanate and, if necessary, a chain extender having a molecular weight of less than 500, by a general manufacturing method for polyurethane resins such as a prepolymer method and a one-shot method.

The above polyester diol consists of a polycondensation of a carboxylic acid component and a glycol component, and the carboxylic acid component includes aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and 1,5-naphthalic acid, p-oxybenzoic acid,
Examples include aromatic oxycarboxylic acids such as benzoic acid (p-<hydroxyethoxy), aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. Particularly preferred are terephthalic acid, isophthalic acid, adipic acid, and sebacic acid.

In addition, glycol components include ethylene glycol,
Propylene glycol, 1,3-propanediol, 1
, 4-butanediol, 1,5-bentanediol, 1
, 6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2.2
．． 4-trimethyl-1,3-bentanediol, cyclohexane dimethanol, ethylene oxide adducts and propylene oxide adducts to bisphenol, ethylene oxide adducts and propylene oxide adducts to hydrogenated bisphenol, polyethylene glycol, polypropylene glycol, Examples include polytetramethylene glycol.

Examples of polyisocyanates include hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, xylylene diisocyanate, cyclohexane diisocyanate, toluidine diisocyanate, 2,4-tolylene diisocyanate, 2,6-)
lylene diisocyanate, 4.4″-diphenylmethane diisocyanate, p-phenylene diisocyanate,
(1)-phenylene diisocyanate, 185-naphthylene diisocyanate, and the like.

Moreover, polycarbonate polyurethane resin is also used as the polyurethane resin used in the present invention. This is obtained by reacting a polyol, a polyisocyanate, and, if necessary, a chain extender.

Here, polyol means, for example, the general formula % formula % (1) [wherein R is, for example, -fco2i (n=3 to 14]
, polyhydric alcohols and phosgene, chloroacetic esters,
A polycarbonate polyol with a molecular weight of 300 to 20,000 and a hydroxyl value of 20 to 300 obtained by condensation with dialkyl carbonate or diallyl carbonate, or the above polycarbonate polyol with the general formula [1-HOOCR'C0OH(ff) (wherein R1+ is, for example, -(CH24 (n'=3~6
), with a polyhydric carboxylic acid, the molecular weight is 300 to 2.
0.000, and a polycarbonate polyester polyol having a hydroxyl value of 5 to 300. It can also be used in combination with other polyols, such as polyether polyols, polyester ether polyols, and polyesters.

Examples of polyisocyanates include those mentioned in the production of the polyester urethane.

In order to introduce a polar group into the above-mentioned resin, there are two methods: (1) a method in which the above-mentioned polar group is introduced in advance into a part of the polyisono-2-ate or polyol, which is the raw material of the polyurethane resin, (2)
Examples include a method in which one (0) group is left at the terminal or side chain of the polyurethane resin, and this OH group is modified with the above-mentioned compound having a polar group.

For example, the following method can be used to introduce a polar group using the method (2).

(2) A diol having 1-COOM (M also includes hydrogen, the same applies hereinafter), such as dimethylolpropionic acid or a salt thereof neutralized with a methanol solution of NaOH, )[OH, is used as the polyol component.

(2) A diol having 2-503M is used as a polyol component. That is, a diol obtained by reacting a carboxylic acid component not having -303M, a glycol component, and a dicarboxylic acid component having -5o3M is used. -303M
Examples of the dicarboxylic acid component having the above include 5-sodium sulfoisophthalic acid, 5-potassium isophthalic acid, 2-sodium sulfoterephthalic acid, and 2-potassium sulfoterephthalic acid.

As the other glycol components and carboxylic acid components, those used in ordinary urethane resins can be used.

■-COOM for isocyanate compounds with more than 33 functional groups
and one of the compounds used as the diisocyanate component.
-React with two NGOs.

(2) SO3M is introduced into an isocyanate compound having 43 or more functionalities and used as a diisocyanate component. Examples of the method (2) above include the following method.

■-I CICH2CO0M, ctctt2cH2s
o3M, a compound having chlorine and a polyurethane resin having polyfunctional -OH are dissolved in a solvent such as dimethylformamide or dimethyl sulfoxide, and in the presence of a dehydrochlorination agent such as an amine such as pyridine or an epoxy compound such as ethylene oxide. How to react to.

■-2HOCH2COOM, I(OCH2CH2S
A method in which O3M is reacted with an equimolar amount of a diisocyanate compound, that is, one of them, -NGO, and the remaining -NGO is reacted with -OH of the polyurethane resin.

Further, in order to introduce -N(R)2 (R represents an alkyl group or the like and also includes hydrogen), the following method of introducing a diol having a tertiary amino group into the main chain of the polyurethane resin can be mentioned.

H C-Si t13 H In addition, in order to introduce a phosphoric acid group and a phosphoric acid ester group (-PO(OM')(OR') having a substituent thereof into a polyurethane resin, a trifunctional or higher functional polyisocyanate compound and a phosphoric acid ester group having a substituent thereof are introduced into the polyurethane resin. An acid or its mono- or diester is reacted, and an isocyanate group is left behind, which is used as a polyisocyanate component which is a raw material for polyurethane resin.

After this, it may be used as an alkali metal salt. For example, it is shown by the following formula.

(R"'-NGO is trifunctional or higher functional polyisocyanate)
The amount of polar groups introduced into the polyurethane resin used as a binder is, for example, when -COOM and other polar groups are used together, the sum is 0.01 to 1.0 mmol.
/g, more preferably in the range of 0.01 to 0.5 mmol/H. -The amount of introduced C00M is 0.01 to 0.
．． 5 mmol, the amount of other polar groups introduced is 0.01 mmol
/g or more. The amount of the above polar group introduced is 0.01 mmo
If it is less than 1/g, sufficient effects on polishing and dispersibility of magnetic powder will not be observed, and the amount of polar group introduced will be 1.0+■
If it exceeds ol/g, intermolecular or intramolecular aggregation of the resin tends to occur (which not only is bad for the dispersibility of abrasives and magnetic powders, but also may not dissolve in ordinary solvents).

The molecular weight of the polyurethane resin having the polar group and the alicyclic hydrocarbon group is 20,000-1000.000.
is preferable; if it is less than 20,000, the elastic modulus is small and the strength of the magnetic layer is reduced, and if it is less than 10,000
If the number is more than 00,000, the viscosity of the magnetic paint becomes too high, and magnetic powder, etc., may not be uniformly dispersed.

Details of the above-mentioned polyurethane resin into which polar groups have been introduced are described in JP-A-63-138523.
Those described here are also preferably used according to the above.

In the present invention, the polar base resin described above and other resins can be used in combination, and examples of other resins used in combination include polyester urethane resins and polycarbonate polyurethane resins, but in addition to these, polyvinyl chloride resins Thermoplastic resins and thermosetting resins may be used in combination. Those with the above-mentioned polar groups introduced can also be used, for example, by saponifying vinyl chloride-vinyl acetate copolymer,
A polar group, such as introducing -OH, is introduced into the resin having 100 in the side chain by method (2). Moreover, -N(R)2 can be introduced by copolymerizing a heptamer such as dialkylamine ethyl acrylate with another monomer.

Thermoplastic resins such as polyvinyl chloride resins that can be used in combination with the above have a softening temperature of 150°C or less and an average molecular weight of 10
000 to 200,000 and the degree of polymerization is about 200 to 20,000
For example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride -Acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic ester-vinylidene chloride copolymer, methacrylic ester-styrene copolymer, thermoplastic polyurethane resin, polyfluoride vinyl chloride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-
Examples include resins such as methacrylic acid copolymers, polyamide resins, polyvinyl butyral, cellulose derivatives, styrene-butadiene copolymers, polyester resins, and synthetic rubbers such as polybutadiene.

In addition, examples of the thermosetting resin include phenol resin,
Epoxy resin, thermosetting polyurethane resin (excluding those listed above), urea resin, melamine resin, alkyd resin,
Urea-formaldehyde resin, silicone resin, acrylic reactive resin, epoxy-polyamide resin, nitrocellulose-melamine resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea-formaldehyde resin, low molecular weight Glycol/High molecular weight diol/
Examples include mixtures of triphenylmethane triisocyanate, polyamine resins, and mixtures thereof. Among these, it is preferable to use a combination of those that have good dispersibility in the ferromagnetic powder.

The ratio of the above polar group-based resin to other resins is preferably 5 to 8 and 12 to 15.

The magnetic powder used in the present invention can be either oxidized magnetic powder, metal magnetic powder, or both. Examples of the metal magnetic powder include iron, iron alloy, iron nitride, and iron carbide magnetic powder, and the average long axis thereof is preferably 0.1 to 1.0 μm, particularly preferably 0.2 to 0.5 μm. Furthermore, as a specific surface area, a BET value of 25 to 60nr/g can be used, especially 35 to 50nr+? /g is preferred.

Moreover, as a coercive force, 650-17000e can be used, and 100-13000e is preferable.

As the oxidized magnetic powder, T-Fe20B, T-Fe2
Examples of γFe203X coated with 0B and Fe3O4 crystals, CrO2, and cobalt include Fe3O4. Also,
Major axis 0.3-0.5 pta, minor axis 0.03-0.0
7 p a+, specific surface area 12-45 m/g, H
Oxidized magnetic powder of c 300 to 8000e is also preferably used.

In order to obtain the magnetic recording medium of the present invention, a magnetic paint is prepared, and this magnetic paint contains an organic solvent in addition to the above-mentioned magnetic powder and binder, and if necessary, an abrasive, a filler, and a charging agent. Components such as inhibitors, rust preventives, and fungicides are appropriately selected and mixed. The ratio of each of these components is the binder (total of polar base resin and other resins) to 100 parts by weight of magnetic powder.
20 to 25 parts by weight and 300 to 350 parts by weight of the solvent are preferred.

To produce the above paint, the components used may be mixed together using a glass bead or the like, for example, in a sand mill or ball mill, but the magnetic powder and the A-layer agent may be mixed together or separately in some resin solution. It is also preferred to process and then add the remaining resin before mixing the other ingredients.

Applying the above magnetic paint to a non-magnetic support such as plastic,
A magnetic recording medium is produced by drying, and known coating methods such as a doctor blade, reverse roll, gravure roll, and spinner coat can be used to coat the support. Depending on the purpose, magnetic powder may be oriented or The magnetic recording medium is then dried and subjected to surface smoothing treatment to form a magnetic recording medium.

[Effect]

Increasing the number of urethane bonds in polyurethane resin makes the polymer skeleton harder and improves durability. If the number of urethane bonds is too large, the plasticity will decrease, so 1.8 to 2.5 m
mol/g is preferred. Furthermore, when a polar group such as a carboxyl group is introduced, the adsorption to the magnetic powder can be increased and the magnetic powder can be made highly dispersible.

〔Example〕

Next, the present invention will be explained in detail.

Example I Co adhesion r Fe2O3 100 fi amount parts (BET value 3
s=7g) Polyurethane resin containing sulfonic acid groups (70 ppm/per molecule of polyurethane) 10 parts by weight Vinyl chloride-vinyl acetate copolymer resin 10 parts by weight Al2032 parts by weight Polyisocyanate 3 parts by weight Fatty acid ester 3 parts by weight Methyl ethyl ketone ioo weight part toluene
50 parts by weight cyclohexanone 50 parts by weight The above polyurethane resin was polyester based to obtain a magnetic paint.

This magnetic paint was applied onto a polyester film, oriented in a magnetic field, dried, calendered, and cut to a width of 3.81 m to produce a video magnetic tape.

This is applied to an actual video recording and playback machine, and immediately after that and 4
The output deterioration was measured when the device was left at 0° C. and 80% relative humidity. Br/Bs was used as the output characteristic.

The deterioration of the a-function was expressed as a dB value indicating the decrease in output after running the tape a certain number of times. The results are shown in the table.

Examples 2 to 5 Magnetic tapes were produced in the same manner as in Example 1, except that the polyurethane resin was used in place of the resins shown in the table, and these were also measured in the same manner as in Example 1. The results are shown in the table. .

Comparative Examples 1 to 3 Magnetic tapes were produced in the same manner as in Example 1, except that polyurethane resin was used instead of the resin shown in the table, and these were also measured in the same manner as in Example 1. The results are shown in the table. .

(Margins below this page) The results in the above table indicate the dispersibility of the magnetic powder from the squareness ratio and the durability from the output deterioration, and it can be seen that the examples are better than the comparative examples in all items.

〔Effect of the invention〕

According to the present invention, the number of urethane bonds in the polyurethane resin is set to 1.8 to 2.5 mmol/g, and a polyurethane resin having polar groups such as carboxyl groups is used as the binder for the magnetic layer. Durability can be improved by making the molecular skeleton hard, and the latter can improve bondability with magnetic powder and improve its dispersibility. This makes it possible to provide a magnetic recording medium having a highly dispersible and highly durable magnetic layer even when using fine magnetic powder particles. In this way, it is possible to provide a stable magnetic recording medium with excellent electromagnetic conversion characteristics and high output even after repeated long-term use.

February 27, 1990

Claims (4)

[Claims] (1) A magnetic paint containing a ferromagnetic powder and a binder, wherein the binder contains a polyurethane resin, and the polyurethane resin has a carboxyl group, a sulfonic acid group, a phosphoric acid group,
It has at least one of the group consisting of an amino group, each of these metal-substituted and alkyl-substituted polar groups, and the number of urethane bonds is 1.8 mmol/g to 2.5 mmol/g.
magnetic paint. (2) The magnetic paint according to claim 1, wherein the polyurethane resin is a resin obtained by reacting polyester, polycarbonate, and an isocyanate compound. (3) Claim 1 or 2 for 100 parts by weight of ferromagnetic powder
5 to 8 parts by weight of the polyurethane resin described above, and 12 to 15 parts by weight of other resins other than the polyurethane resin described in claim 1 or 2.
Magnetic paint contained in parts by weight. (4) A magnetic recording medium in which a magnetic layer is formed on a non-magnetic support using the magnetic paint according to any one of claims 1 to 3.