JPH01302526A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To prevent the increase in the viscosity by stagnation of a magnetic coating compd. and to improve the dispersibility of ferromagnetic powder as well as to improve the traveling property of the recording medium by specifying a binder to be used together with the ferromagnetic powder at the time of forming a magnetic layer. CONSTITUTION:Two kinds of the binders which vary in the presence or absence of polar groups are used in combination in the binder used for the magnetic layer. A 1st binder is the urethane resin into which at least one kind selected from the polar group expressed by formula I (where M is a hydrogen atom, lithium, sodium or potassium; M1, M2 add an alkyl group to respective M) and the ratio thereof is <50wt.% of the total binder. The 2nd binder is a resin such as vinyl chloride/vinyl acetate copolymer which does not have the above- mentioned polar groups and has >=-25 deg.C glass transition temp. Tg. A hardener, dispersant, lubricant, antistatic agent, polishing agent, etc., are added thereto at need to prepare a magnetic coating compd. which is coated on a base and is dried to finish the recording medium.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to magnetic recording media such as magnetic tapes, magnetic disks, and magnetic floppy disks used for magnetic recording and reproduction.
Regarding this.

[Prior art]

Magnetic recording media in information processing equipment are extremely useful as recording and reproducing elements, and there is a large demand for them, but at the same time, as recording media, they must have advanced and precise electromagnetic conversion characteristics, rich storage capacity, and high density. It is required that the composition be suitable for ensuring runnability, durability, and durability, that it be inexpensive, and that there be no troubles in production technology from a production standpoint. technological efforts have been undermined.

However, the ultimate goal of these technological efforts is to create a high-performance magnetic material, that is, a magnetic material with good electromagnetic performance, fine dispersibility and dispersion stability in which the powder particles are individually independent, and a product that is trouble-free and durable. This results in good layer structure conditions.

Specifically, coercive force (Hc) and residual magnetic flux density (Br)
A search has been made for magnetic materials that have a high magnetic flux and are suitable for high-density recording, and ferromagnetic materials containing iron, nickel, cobalt, etc. as main components have been developed from conventional magnetic materials. Particularly in video tapes, the above-mentioned ferromagnetic alloy powder has come to be used in place of the conventional iron oxide powder due to the need to shorten the recording wavelength and narrow the track width.

However, if the fine ferromagnetic alloy powder with a large specific surface area and good S/N performance is used, problems such as poor dispersion in the binder and thickening of the magnetic paint may occur, and these phenomena may affect the surface properties of the magnetic layer. , impairs durability and magnetic properties, and becomes an obstacle to high-performance recording media.

Regarding the dispersion of magnetic powder, studies have been conducted from the viewpoint of dispersants and binders.

- First, lecithin has been known for a long time as a dispersant, and furthermore, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinic acid esters, surfactants, etc., and their salts. Negative organic groups (e.g. -COOH, -P
Salts of polymeric dispersants with O3H) have been developed. These dispersants may be used alone or in combination of two or more. These dispersants are sometimes used to pre-treat magnetic powder.

Furthermore, for binders, various curable resins such as polyurethane, cellulose, vinyl chloride resin, phenoxy resin, various modified resins whose properties have been modified by introducing polar groups, and thermoplastic resins with characteristic behavior have been investigated. They are combined with good compatibility, significantly improving the physical properties of the media constituent layer, and magnetic powder,
Improved dispersibility and retention of fillers.

However, the level of dispersion and stable dispersion of ultrafine ferromagnetic alloy powder has not reached a satisfactory level, and the physical properties of the magnetic layer, especially mechanical strength or retention (powder falling, film peeling, etc.), have not reached a satisfactory level. This often leads to disadvantages in wear resistance, etc.

In other words, the technological effects examined individually do not necessarily produce favorable results mutually or synergistically; on the contrary, they may be mutually contradictory or cause autotoxic symptoms outside of the intended performance. Therefore, it is necessary to seek a solution through comprehensively balanced technical measures and a specific range of materials and their usage amounts.

[Purpose of the invention]

The object of the present invention is to achieve (1) no increase in the viscosity of the magnetic coating material due to stagnation, (2) a good dispersion state of the ferromagnetic powder in the magnetic layer, and (3) an excellent An object of the present invention is to provide a magnetic recording medium having running properties.

[Structure of the invention]

The object of the present invention is to provide a magnetic recording medium comprising a magnetic layer containing ferromagnetic powder and a binder on a non-magnetic support, the binder comprising a urethane resin having a polar group;
Does not have polar groups Tg (glass transition temperature) is -25℃
It consists of a resin composition containing the above resins, and the amount of the resin having the polar group is OM.

-503M, -0SO□M, -P-OM2 (wherein, M is a hydrogen atom, lithium, sodium, or potassium, and M, , M are each a hydrogen atom, lithium, sodium, potassium, or an alkyl group) This is achieved by a magnetic recording medium characterized by being at least one type selected from the group shown in (.).

In the present invention, the term "polar group" refers to the groups of the above-mentioned group.

The present invention is characterized by the combined use of two types of binders that differ in the presence or absence of polar groups in the binder used in the magnetic layer.

The first binder among the two types of binders is a urethane resin into which a polar group is introduced, and the polar group is a group represented by. The above M is a hydrogen atom, lithium, sodium or potassium, and M + and M 2 are each a hydrogen atom, lithium, sodium, potassium or an alkyl group. The alkyl group is preferably a straight chain or branched alkyl group having 23 or less carbon atoms.

Further, the amount of the polar group-modified resin used is less than 5 Qwt% of the total binder.

Next, the sulfo group, sulfinoxy/group according to the present invention,
At least one phospho group or a group forming a salt thereof
Methods for introducing species into side chains are described in JP-A Nos. 57-44227, 58-108032, 59-8127, and 6
The method described in No. 0-101161 and the like is used.

For example, polyurethane resins containing sulfonic acid metal groups can be obtained by condensation and addition reactions using three starting materials of polyesters containing sulfonic acid metal groups together with diisocyanates. Furthermore, a method of modifying the polyurethane resin to introduce polar groups can be considered.

Diisocyanate components used to obtain the polyurethane resin include 2.4-tolylene diisocyanate, 2.6-tolylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, and tetramethylene diisocyanate. ,3
．． 3'-dimethoxy-4,4'-biphenylene diisocyanate, 2.4-naphthalene diisocyanate, 3.
3'-dimethyl-4,4'-biphenylene diisocyanate, 4,4'-diisocyanate-diphenyl ether diisocyanate, p-xylylene diisocyanate,
Examples include m-quinrylene diisocyanate, 1,3-diisocyanate, methylcyclohexane, 1,4-diisocyanatemethylcyclohexane, 4,4'-diisocyanate dicyclohexane, 4,4'-diisocyanate dicyclohexylmethane, inphorone diisocyanate, etc. .

In this invention, a resin having a molecular weight of 50,000 or less is used as the resin having a polar group.

This is because if the molecular weight exceeds 50,000, the viscosity of the paint becomes too large beyond the allowable range when the specific surface area of the magnetic powder measured by the BET method becomes large as described later. The molecular weight of the resin is preferably 2,00
It is 0 or more. This is because if the above molecular weight is less than 2.000, unreacted portions will be removed when the magnetic paint is formed on the support and then cured using a curing agent, and if low molecular weight components remain, the paint will be coated. This is because it deteriorates the physical properties of the film. Furthermore, it is more preferable that the molecular weight of the resin containing this polar group is 10,000 or more. Therefore, a more preferable range of this molecular weight is 10,000 to 50,000. The amount of polar groups contained in this resin is preferably such that the molecular weight per polar group is in the range of 2,000 to 50,000. This is because if it is more than 50,000, no sufficient improvement in dispersibility can be expected, and if it is less than 2,000, it tends to be difficult to dissolve in non-polar solvents.

In this invention, it is preferable that the above-mentioned resin having a polar group is contained in the binder in an amount of 1 Owt% or more and less than 50% of the total binder components; if it is less than this, a sufficient dispersion effect cannot be generated, and if it is more than this, a sufficient dispersion effect cannot be generated. If the tape is allowed to stagnate in the paint state, the viscosity increases rapidly, resulting in poor workability and further deterioration in durability as a tape.

The second binder according to the present invention is a binder that does not have a polar group and has a glass transition point of 125°C or higher.

The binder used as the second binder does not have any polar groups (polar groups of the first binder) that are particularly easily adsorbed to the surface of the magnetic particles in its molecules, or even if it does have it, it has substantially no polar groups (polar groups of the first binder). It is a non-magnetic polymer or oligomer that has a trace amount of polar groups that are not adsorbed to magnetic materials. For example, thermosetting resins, thermoplastic resins, reactive resins, or mixtures thereof, which are conventionally known for use in magnetic recording media, can be used.

Examples include vinyl chloride-vinyl acetate copolymer, acrylic resin, epoxy resin, polyamide resin, butadiene resin, urethane elastomer, and isocyanate-curable resin. The degree of polymerization is preferably 100 to 10,000.

The above binders may be used alone or in combination.

In this invention, the glass transition point is preferably -25°C or higher, more preferably 10'0 or higher.

If the temperature is below -25°C, the strength of the magnetic layer will be extremely reduced, resulting in poor running (edge breakage, head clogging, etc.).

The purpose is achieved by using the binders described above.

In the present invention, other conventional binder resins may be used in combination as long as the effects of the present invention are not adversely affected.

In the present invention, equipment and material technology conventionally used for manufacturing magnetic recording media are used.

Examples of the magnetic material used in the present invention include γ-Fe
203. Co-containing γ-Fe203. Co deposited - Fe2
03, Fe50. .

Co-containing Fe3O4, Co-coated Fend4. Oxide magnetic materials such as Cry□, e.g. Fe, Ni, Fe-Ni alloy,
Fe-Co alloy, Fe-N1-P alloy, Fe-A(1 alloy, Fe-Mn-Zn alloy, Fe-Ni-Zn alloy, F
Examples include various ferromagnetic materials such as e-Co-Ni-Cr alloy, Fe-Co-N1-P alloy, Co-P alloy, Co-Cr alloy, and metal magnetic powder containing Fe, Ni, and Co as main components. Additives to these metal magnetic materials include Si,
Cu, Zn, A12. Elements such as P, Mn, and Cr or compounds thereof may be included. Hexagonal ferrite such as barium ferrite and iron nitride are also used.

In addition, the granularity is 30m2/9 or more in BET value, and further 40m
'/g or more is preferable, and such fine particles significantly improve electromagnetic conversion characteristics.

In order to improve the durability of the constituent layers such as the magnetic layer of the magnetic tape of the present invention, various hardening agents can be contained, for example, incyanate can be contained.

Aromatic isocyanates that can be used include, for example, tolylene diisocyanate (TDI) and adducts of these incyanates and active hydrogen compounds, and those having an average molecular weight of 100 to 3,000 are preferred.

Examples of aliphatic incyanates include hexamethylene diisocyanate (HMDI) and adducts of these incyanates and active hydrogen compounds. Among these aliphatic incyanates and adducts of these incyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Among the aliphatic isocyanates, non-alicyclic incyanates and adducts of these compounds with active hydrogen compounds are preferred.

The magnetic paint used to form the magnetic layer may contain additives other than those mentioned above, such as a dispersant, a lubricant, an antistatic agent, and an abrasive, if necessary.

Dispersants used in combination with the present invention include amine compounds, alkyl sulfates, fatty acid amides, higher alcohols,
Examples include polyethylene oxide, sulfosuccinic acid, sulfosuccinic acid ester, known surfactants, and salts thereof.

These dispersants may be used alone or in combination of two or more. These dispersants are added in an amount of 1 to 20 parts by weight per 100 parts by weight of the magnetic powder. These dispersants may be used to pre-treat the magnetic powder in advance.

In addition, as lubricants, silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid,
Fatty acid esters consisting of a monobasic fatty acid having 12 to 22 carbon atoms and a monohydric alcohol having 13 to 40 carbon atoms in total can also be used. These lubricants are used in an amount of 0.2 to 2 parts by weight per 100 parts by weight of magnetic powder.
It is added in an amount of 0 parts by weight.

As the abrasive, commonly used materials such as fused alumina, silicon carbide, chromium oxide, corundum, and artificial corundum are used. These abrasives have an average particle size of 0.0
A size of 5 to 5 μm is used, particularly preferably 0.1 to 2 μm. These abrasives are magnetic powder 100%
It is added in an amount of 1 to 20 parts by weight.

Antistatic agents include carbon black, graphite, conductive powders such as tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds; natural surfactants such as saponin; alkylene oxides, and glycerin. Cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, phosphoniums or sulfoniums; Carboxylic acids, sulfonic acids, phosphoric acids, sulfuric acids Examples include anionic surfactants containing acidic groups such as ester groups, diamino acids, aminosulfonic acids, and amphoteric surfactants such as sulfuric acid of amino alcohols.

Solvents added to the above paint or diluting solvents during application of this paint include Kents such as acetone, methyl ethyl ketone, and methyl isobutyl ketonon; Alcohols such as metalol, ethanol, propatool, and butanol; Methyl acetate;
Esters such as ethyl acetate, butyl acetate, ethyl lactate, and ethylene glycol monoacetate; Ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, and tetrahydro-7rane; Aromatic hydrocarbons such as benzene, toluene, and quintylene: methylene chloride , ethylene chloride, carbon tetrachloride, chloroform, halogenated hydrocarbons such as nitrolhenzene, etc. can be used.

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. Metals, glass, ceramics such as BNS Si carbide, etc. can also be used.

The thickness of these supports is about 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm,
In the case of a disk or card, it is about 30 μm to 10 ram, and in the case of a drum, it is cylindrical, and its shape is determined depending on the recorder used.

An intermediate layer for improving adhesiveness may be provided between the support and the constituent layers such as the magnetic 18E layer.

Coating methods for forming the magnetic layer on the support include air knife coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, trans7 roll coating, gravure coating, kiss coating, and cast coating. , spray coat, etc. can be used, but are not limited thereto.

〔Example〕

The present invention will be specifically explained using examples.

<Example-■>: Magnetic paint formulation: Co-γ-Fe20x (BET 40m'/g
) 100 parts by weight Sodium sulfonate group-containing polyurethane resin 2AIOll Vinyl chloride, vinyl acetate copolymer 2B (polar group L
, VACH: manufactured by UCC) 15 ttα-A
JO3 7 tt stearic acid 2 tt butyl stearate 2 〃, methyl ethyl ketone
300 tt toluene
100 tt After preparing a magnetic paint by mixing and dispersing the above prescription composition in a ball mill for 48 hours, an isocyanate compound (Coronate L; manufactured by Nippon Polyurethane Co., Ltd.) was added.
Add 5 parts by weight of and mix. The obtained magnetic paint was coated with a thickness of 14 μl so that the thickness of the magnetic layer after drying was 4 μm.
on a polyethylene terephthalate support. After drying, the tape was supercalendered and slit into 1/2 inch width to produce a VHS tape.

<Example-2> The formulation was the same as Example-1 except that A was 12 parts and B was 13 parts in Example-1.

<Example-3> Co-γ-Fe20 of Example-1 was mixed with Fe-A12-based ferromagnetic metal powder (BET 551M2/g) 100
A tape sample was prepared by changing the parts by weight. Other changes are:
The magnetic layer was set to 3 μm, the thickness of the support was set to 10 μm, and the tape was slit to a width of 8 mm to obtain an 8 ml 1M video tape.

<Example 4> In Example 2, tapes were produced by changing the magnetic powder to Fe-AQ gold metal powder.

Comparative example-(1)> In Example-1, A was changed to 15 parts and B was changed to 10 parts.

<Comparative Example-(2)> A of Example-1 was replaced with polyurethane resin (no polar group) 10
Changed to Department.

The characteristics shown in the following table were measured for each of the above samples, and the results are listed in the same table.

The viscosity of the paint was measured with a B-type rotational viscometer using a No. 4 rotor at 30 revolutions.

As is clear from the above table, the samples of the present invention exhibit superior performance than the comparative examples.

Claims (1)

[Scope of Claims] A magnetic recording medium comprising a magnetic layer containing ferromagnetic powder and a binder provided on a non-magnetic support, wherein the binder comprises a urethane resin having a polar group and a urethane resin having no polar group. Tg(
It consists of a resin composition containing a resin having a glass transition temperature) of -25°C or higher, and the amount of the resin having the polar group is 5% of the total binder.
0wt%, and its polar groups are -SO_3M, -OSO_2M, ▲Mathematical formulas, chemical formulas, tables, etc.▼ (In the formula, M is a hydrogen atom, lithium, sodium, or potassium, and M_1 and M_2 are each a hydrogen atom. , lithium, sodium, potassium or an alkyl group).
A magnetic recording medium characterized by being at least one type selected from a group of groups represented by: