JPH02189713A - Magnetic recording medium having improved electromagnetic conversion characteristic - Google Patents

Abstract

PURPOSE:To improve the bonding strength of a binder to a magnetic material and the dispersibility of a magnetic coating by incorporating polyurethane polymers respectively having specific weight average mol.wts. into the 1st magnetic layer and the 2nd magnetic layer. CONSTITUTION:The polyurethane polymer having 50,000 to 150,000 weight average mol. wt. is incorporated into the 1st magnetic layer of the magnetic recording medium constituted by providing the 1st magnetic layer (lower layer) and the 2nd magnetic layer (upper layer) and the polyurethane polymer having <50,000 weight average mol. wt. is incorporated into the 2nd magnetic layer. Since the dispersibility of the respective components in the 2nd magnetic layer is improved in this way, the electromagnetic conversion characteristics are improved; in addition, drop-outs are decreased by the improvement in the bondability of the magnetic powder in the 1st magnetic layer to the binder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic tapes, magnetic disks, and magnetic floppy disks.

[Background of the Invention] Magnetic recording media usually contain ferromagnetic powder and binder resin.
Add curing agents, dispersants, abrasives, lubricants, matting agents, antistatic agents, and other various additives, and if necessary, add an appropriate solvent to disperse them in the liquid. It is manufactured by applying the resulting magnetic paint onto a support and then drying it.

In this case, various binder resins have been proposed in the past, but among them, polyurethane resins, derivatives thereof, or polymer blends and copolymers (hereinafter referred to as In the present invention, polyurethane polymers (collectively referred to as polyurethane polymers) have strong adhesion to other materials, can withstand repeated stress or bending, and are mechanically strong due to the properties of polyurethane. and wear resistant,
It is usually preferred in this type of recording medium because of its good weather resistance.

By the way, when this polyurethane polymer is used as a binder for a magnetic recording medium, conventionally, when the magnetic recording medium consists of a single layer, a polymer having a certain average molecular weight is used, and when the magnetic recording medium has a When it consists of layers, each layer uses a polymer with the same average molecular sac.

In these cases, when a polyurethane polymer with a weight average molecular weight of so or so is used as a binder, the binding force of the binder to the magnetic material is weak, resulting in an increase in deposit-type dropouts; When a polyurethane polymer having a weight average molecular weight of 50,000 or more was used, the dispersibility of the magnetic paint was reduced.

Such a decrease in the dispersibility of the magnetic coating material causes deterioration or deterioration of the electromagnetic conversion characteristics of the magnetic recording medium.

[Object of the Invention] In view of the above-mentioned circumstances, the present inventors have conducted various studies in an attempt to provide a multilayer magnetic recording medium, especially a two-layer magnetic recording medium, in which the above-mentioned drawbacks have been corrected.
We have arrived at the invention described below.

[Structure of the Invention] That is, the present invention provides a first magnetic layer (lower layer) on a non-magnetic material.
and a second magnetic layer (upper layer), the first magnetic layer has a weight average molecular weight of 50.000 to 1.
50,000, and the second magnetic layer contains a polyurethane polymer having a weight average molecular weight of less than 50,000. It is.

Examples of the magnetic material used in the present invention include γ-Fe
, 03, Co-containing -Fe, 03 or Co-adhered -F
Co-γ-Fe2O3 like e20°, Fe50iC
o-containing Fe3O4 or CO-coated Fe50. C like
o-γ-Fe2O3; oxide magnetic materials such as CrO2, others such as Fe, Ni, Fe-Ni alloy, Fe-C.

alloy, Fe-N1-P alloy, Fe-Ni-Co alloy, F
e-Mn-Zn alloy, Fe-Ni-Zn alloy, Fe-C
o-Ni-Cr alloy, Fe-Co-N1-P alloy, co
Examples include various ferromagnetic materials (powders) such as metal magnetic powders containing Fe, Ni, and Co as main components, such as -P alloy and Co-Cr alloy. Additives to these metal magnetic materials include Si, Cu, Zn, AI2. P,
Elements such as Mn and Cr or compounds thereof may be included. Hexagonal ferrite such as barium ferrite, iron nitride, etc. are also used.

In the present invention, it is essential to use a polyurethane polymer as a binder.

As already mentioned, the polyurethane-based polymer in the present invention refers to a urethane homopolymer, its derivative, a copolymer of urethane and other polymerizable monomers, and a so-called polymer of polyurethane or its derivative and other polymers. Refers to polymer blends (polymer mixtures), etc.

Therefore, for example, in the present invention, in addition to polyurethane, a cellulose resin and a vinyl chloride (co)polymer can be used in combination. In this case, it is expected that the dispersibility of the magnetic powder in the magnetic layer will further improve and its mechanical strength will increase. However, if only the cellulose resin and vinyl chloride copolymer are used, the layer becomes too hard, but this can be prevented by the presence of polyurethane.

Usable cellulose resins include cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester, and the like. The above polyurethane and vinyl chloride copolymers may be partially hydrolyzed. Preferable examples of the vinyl chloride copolymer include a copolymer containing vinyl chloride-vinyl acetate or a copolymer containing vinyl chloride-vinyl acetate-vinyl alcohol.

Phenoxy resins can also be used.

Phenoxy resin has advantages such as high mechanical strength, excellent dimensional stability, good heat resistance, water resistance, chemical resistance, and good adhesiveness.

These advantages are complementary to those of the polyurethane described above, and the stability of the physical properties of the magnetic recording medium over time can be significantly improved. .

In addition, as long as the characteristics of the present invention are not lost, the polyurethane polymer and other polymers can be used together in the form of copolymerization or polymer blend.

That is, in addition to the resins mentioned above, various thermoplastic resins,
- A copolymer or polymer blend with a thermosetting resin, a reactive resin, or an electron beam curable resin may be used.

If the weight average molecular weight of the polyurethane polymer used for the first magnetic layer (lower layer) is too small, it is preferable because dropouts due to deposits such as broken debris of the magnetic layer will increase, whereas if it is too high, , which is undesirable because it makes it difficult to improve the dispersibility of the magnetic paint.

For this reason, in the first magnetic layer of the present invention, a polyurethane polymer having a weight average molecular weight of usually about 50,000 to 150,000 is preferably used.

Furthermore, if the weight average molecular weight of the polyurethane polymer used for the second III layer (upper layer) is too high, it is undesirable in that it deteriorates the dispersibility of the magnetic coating material and reduces the electromagnetic conversion characteristics. Usually, a polyurethane polymer having a weight average molecular weight of less than 50,000 is preferably used for this layer.

The amount of polyurethane polymer used in the magnetic recording medium of the present invention is usually 3 to 15 parts by weight based on the magnetic material in the first magnetic layer, and the amount used in the second magnetic layer is also usually 3 to 15 parts by weight based on the magnetic material. , 3 to 15 weight relative to the magnetic material.

In order to improve the durability of the magnetic layer of the magnetic recording medium of the present invention, the magnetic paint can contain various curing agents, such as incyanate. Examples of aromatic incyanates include tolylene diisocyaner 1- (TDI) and adducts of these incyanates with active hydrogen compounds, and the average molecular weight is 1.
A value in the range of 00 to 3.000 is suitable.

Examples of aliphatic isocyanates 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 isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

A dispersant is usually used in the magnetic paint used to form the magnetic layer, and additives such as a lubricant, abrasive, a matting agent, and an antistatic agent may be included as necessary.

Dispersants used in the present invention include phosphoric acid esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxides, sulfosuccinic acids, sulfosuccinic esters, known surfactants, and salts thereof. , and also a negative organic group (e.g. -〇〇OH)
It is also possible to use salts of polymeric dispersants having . These dispersants may be used alone or in combination of two or more. Furthermore, as shown in the examples below, there are cases where it is not necessary to use a dispersant.

In addition, as lubricants, silicone oil, graphite, carbon black graft polymer molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid,
Fatty acid esters (so-called waxes) consisting of a monobasic fatty acid having 12 to 16 carbon atoms and a monohydric alcohol having 21 to 23 carbon atoms in total can also be used. These lubricants are added in an amount of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

As the abrasive, commonly used materials such as fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, artificial diamond, garnet, and emery (main components: corundum and magnetite) are used. These abrasives have an average particle size of 0.05 to 5 μm,
Particularly preferably, it is 0.1 to 2 μm. These abrasives are added in an amount of 1 to 20 parts by weight based on 100 parts by weight of the binder.

As the matting agent, organic powder or inorganic powder may be used individually or in combination.

As the organic powder used in the present invention, acrylic styrene resin, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment are preferable, but polyolefin resin powder, polyester resin powder, polyamide resin powder, and polyimide resin are preferred. Powder, polyfluoroethylene resin powder, etc. can also be used, and inorganic powders include silicon oxide, titanium oxide, aluminum oxide, calcium carbonate,
barium sulfate, zinc oxide, tin oxide, aluminum oxide,
Chromium oxide, silicon carbide, calcium carbide.

σ-Fez03. Talc, kaolin, calcium sulfate,
Examples include boron nitride, zinc fluoride, and molybdenum dioxide.

Antistatic agents include carbon black, conductive powders such as graphite, 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 anionic surfactant diamino acids containing acidic groups such as ester groups and phosphate ester groups;
Examples include amphoteric activators such as aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like.

Solvents to be added to the above paint or diluting solvents during application of this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propatool, and butanol; 116 methyl vinegar , esters such as ethyl acetate, butyl acetate, ethyl lactate, and ethylene glycol monoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, and xylene; methylene chloride , ethylene chloride, carbon tetrachloride, chloroform, dichlorobenzene, and other halogenated hydrocarbons.

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, plastics such as polyamide and polycarbonate, metals such as Cu, kQ, and Zn, and glass. , boron nitride, and ceramics such as Si carbide can also be used.

The thickness of these supports is approximately 3 to 100μm in the case of a film or sheet, preferably 5 to 50μm, approximately 30ura to 10mm in the case of a disk or card, and cylindrical in the case of a drum. The type is determined depending on the recorder used.

An intermediate layer for improving adhesion may be provided between the support and the magnetic layer.

Furthermore, other magnetic layers or nonmagnetic layers may be provided above and below each of the first magnetic layer and the second magnetic layer, or between them, without impairing the effects of the present invention.

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, transfer roll coating, gravure coating, kiss coating, cast coating, A tin ray coat, an extrusion coat, etc. can be used, but are not limited to these.

When constructing a magnetic layer on a support using these coating methods, there are two methods: one method involves stacking the coating and drying steps layer by layer (the so-called wet-on-dry coating method); There is a method of coating layers simultaneously or sequentially (so-called wet-on-wet method), but either method can be used in manufacturing the magnetic recording medium of the present invention.

By such a method, the magnetic layer coated on the support is optionally treated to orient the ferromagnetic metal oxide powder in the layer, and then the formed magnetic layer is dried.

In this case, the orientation magnetic field is approximately 500 to 50
The drying temperature is approximately 40~120℃.
The drying time is approximately 0.01 to 10 minutes.

Further, the magnetic recording medium of the present invention is manufactured by subjecting it to surface smoothing treatment or cutting it into a desired shape, if necessary.

Next, the present invention will be explained with reference to examples, but it goes without saying that the present invention is not limited to these examples.

[Example] After kneading magnetic paints with the compositions shown in Tables 1 and 2 to disperse each component well, the viscosity of the paint was adjusted to 1 to 20 centivoise using a solvent (male ethyl ketone, toluene). do. Thereafter, 5 parts by weight of polyisocyanate was added to prepare the magnetic paint for coating of Example 1.

Hereinafter, each magnetic paint for the upper layer and the lower layer (Example 2 and Comparative Examples 1 to 4 After preparing the magnetic paint used on each side, a magnetic paint for the lower layer and a magnetic paint for the upper layer on each side were coated in multiple layers according to a conventional method, and dried to produce a magnetic recording medium.

Next, the electromagnetic conversion characteristics and other characteristics of the obtained magnetic recording medium were measured.

The weight average molecular weight of the polyurethane used on each side is shown in Table 3, and the properties obtained are shown in Table 4. First magnetic layer (lower layer) Table 1: Magnetic layer (lower layer) Values before calendering #lOμ■, - As is clear from the number table 4 at 14 dB, Example 1 according to the present invention
and 2, the electromagnetic conversion characteristics (RF ratio output Lumi S/N
), and dropout is low, resulting in well-balanced characteristics.

On the other hand, in the case of Comparative Example L2, the weight average molecular weight of the upper layer polyurethane was 50,000 or more, so the dispersibility was poor;
Large surface roughness and poor electromagnetic conversion characteristics. Furthermore, since the molecular weight of the polyurethane in the lower layer is less than 50,000, dropouts increase.

In Comparative Example 3, the electromagnetic conversion characteristics were relatively good, but the dropout was large. Comparative Example 4 had good dropout but poor electromagnetic conversion characteristics. Therefore, both Comparative Examples 3 and 4 are magnetic recording media with poorly balanced characteristics.

■Measurement method in Examples and Comparative Examples Surface roughness R
a (μm)> Three-dimensional roughness measuring instrument 5E for the sample before calendering
It was determined by measuring the length of the sample surface by 2.5 mm using a -3FK (Koita Research Institute) with a cutoff of 0.25 mm and a stylus force of 30 mg.

<Example 1: Output during playback with 100% RF ratio output white signal
It was determined in comparison with the tape of Example 1 using the tape of Example 1 as a reference.

<Lumi S/N> Using a noise meter (manufactured by Shibatsu Co., Ltd.), in comparing the reference tape (from Example 1) and the sample tape, 1.
The difference in S/N of the sample in the 00% white signal was determined.

<Dropout> VTR dropout counter (VHO manufactured by Shibatsuku)
IBZ) for a long time of 10 μs or more, and R
An output that is 14 dB or more lower than the output of the F envelope is defined as one dropout, and measured across the entire length of the tape.
The average value per minute was determined.

[Effects of the Invention] In the magnetic recording medium of the present invention, the dispersibility of each component in the second magnetic layer (upper layer) is improved, so the electromagnetic conversion characteristics are significantly improved compared to the conventional one. By improving the binding properties of the magnetic powder (lower layer) to the binder, it has become possible to reduce dropouts compared to conventional methods.

Applicant: Konica Corporation

Claims (1)

[Claims] In a magnetic recording medium comprising a first magnetic layer (lower layer) and a second magnetic layer (upper layer) on a non-magnetic material, the first magnetic layer contains a polyurethane-based material having a weight average molecular weight of 50,000 to 150,000. 1. A magnetic recording medium comprising a second magnetic layer containing a polyurethane polymer having a weight average molecular weight of less than 50,000.