JPS6120221A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having substantial mechanical strength, durability and low-friction characteristic together with adequate resilience and having excellent runnability and a less tendency to powder dislodging by incorporating an urethane resin having yield point, fatty acid, fatty acid ester and conductive carbon black into the magnetic layer of said medium. CONSTITUTION:The yield point of the urethane resin exists preferably in the stress range of 50-600kg/cm<2>, more preferably 100-560kg/cm<2>. The urethane resin having a residual cyclic hydrocarbon group in the molecule is preferable, which group includes a bivalent or monovalent cyclopentyl group, cyclohexyl group, etc. or the deriv. thereof. The compounding ratio of the fatty acid and fatty acid ester is made (1:3)-(3:1) (by weight), more preferably (1:2)-(2:1). The conductive carbon black is further incorporated into the magnetic layer and therefore the generation of electricity is prevented and the electrostatic charge of the medium is effectively prevented, by which the runnability is additionally improved.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks.

2. Prior Art Generally, magnetic recording media are manufactured by applying a magnetic paint containing magnetic powder, binder resin, etc. onto a support and drying it.

It is well known to use urethane resin as a binder resin for the magnetic layer of such magnetic recording media.
Conventionally known urethane resins are synthesized from polymeric diols, diisocyanates, chain extenders, and crosslinking agents (used as necessary). Examples of polymeric diols include polyester diols obtained from adipic acid, butanediol, etc., polyether diols, and polycarbonate diols, diisocyanates include butanediol, etc., and crosslinking agents include polyols, polyamines, etc. It's good.

However, even though these general urethane resins have excellent flexibility, they lack hardness, which results in poor mechanical strength of the magnetic recording medium in sliding contact with guide pins, magnetic heads, etc. Moreover, there are problems in terms of runnability and powder shedding.

On the other hand, various lubricants are added to the magnetic layer to lower its coefficient of friction, thereby improving the running properties of the medium. However, the known lubricants are still insufficiently effective and tend to cause sagging and blooming.

3. Purpose of the Invention The purpose of the present invention is to provide a magnetic recording medium that has appropriate flexibility, sufficient mechanical strength, durability, and low friction characteristics, has excellent running properties, and has little powder falling off. .

4. Structure of the invention and its effects: In the magnetic recording medium according to the invention, the magnetic layer contains a urethane resin having a yield point, a fatty acid, a fatty acid ester, and conductive carbon black. This is a characteristic feature.

According to the present invention, as a binder resin component of the magnetic layer,
A urethane resin having a yield point is used, but this urethane resin has a yield point Y, as shown in the curve exemplified above, compared to the characteristics of the conventional urethane resin shown by the curve a in Fig. 1.
A urethane resin containing P exhibits very little elongation even when stress is applied until it reaches its yield point YP.For this reason, the urethane resin is given appropriate hardness, and the yield point YP is
After that, it exhibits the property of elongating with stress without breaking.

Therefore, the mechanical strength of the magnetic recording medium is improved, damage such as abrasion during sliding contact, powder falling, etc. is significantly reduced, and the running performance is also significantly improved. In particular, for magnetic tapes for VTRs, There is no edge folding, etc., and the control track near the edge can be maintained to perform its function well. The above yield point YP is important for the performance of the urethane resin of the present invention, and is 50 to 600 kg/c.
II? , preferably 100-560kl! It is desirable that a yield point exist in the stress range of /al (approximately 290 to 97 cl? in the example of FIG. 1). The range where the yield point exists is
If the stress is less than 9/d at 50, the resin will be soft and easy to peel;
If the value exceeds 0 to 9/cR, the resin will not be hard and will easily become brittle.

In order to exhibit the above-mentioned excellent performance, the urethane resin used in the present invention preferably has a cyclic hydrocarbon residue in the molecule. The cyclic hydrocarbon residue is preferably a saturated cyclic hydrocarbon residue, such as a divalent or monovalent cyclopentyl group, a cyclohexyl group, etc., or a derivative thereof (for example, an alkyl group substituted product such as a methyl group, Examples include those consisting of a halogen substituted product such as a chlorine atom. These saturated cyclic hydrocarbon residues are desirable from the viewpoint of imparting appropriate hardness to the urethane resin and availability of raw materials. In addition, the bonding position of this cyclic hydrocarbon residue is
It is preferable that it be in the main chain of the urethane resin molecule, but it may also be bonded to its side chain.

In addition, by changing the amount of the component having a cyclic hydrocarbon residue in the urethane resin, it is possible to obtain a urethane resin with an arbitrary glass transition point (1), and η is between -508C and 100C. , preferably 0°C to 90°C. If T1 is lower than -30°C, the film becomes soft and it is difficult to obtain sufficient film strength, and if T2 is higher than 100'C, the film tends to become brittle.

Further, according to the present invention, since the magnetic layer contains both a fatty acid and a fatty acid ester as a lubricant, the frictional force is reduced and the running properties of the medium are significantly improved. That is, fatty acids have the property of lowering the static friction coefficient of the magnetic layer, and many have melting points of 50° C. or higher, making it difficult for blooming to occur. Furthermore, fatty acid esters have the property of lowering the dynamic friction coefficient of the magnetic layer. Therefore, by using fatty acids and fatty acid esters in combination, in addition to their inherent friction-reducing effects, by determining the blending ratio, the friction of the medium can be sufficiently reduced under any friction condition, and its running properties can be maintained well. be able to.

For this purpose, it is desirable that the above-mentioned blending ratio is fat M:fatty acid ester=1:3 to 3:1 (weight ratio), more preferably 1:2 to 2:1. If the amount of fatty acid is too small outside this range, the static friction properties will deteriorate and the lubricant will tend to bloom. Furthermore, if there is too much fatty acid, the proportion of ester decreases, which tends to reduce the dynamic friction properties.

Furthermore, the magnetic layer is likely to be charged with static electricity due to sliding contact with a magnetic head, etc., and this may adversely affect the running properties of the medium. Therefore, as described above, the use of a urethane resin or a lubricant improves the runnability of the medium, but the runnability can be further improved by preventing the adverse effects of static electricity.

According to the present invention, since the magnetic layer further contains conductive carbon black, it is possible to prevent the generation of static electricity, effectively prevent charging of the medium, and improve running properties. can.

The urethane resin used in the present invention can be synthesized by reacting a polyol and a polyisocyanate. At this time, in order to introduce all of the above cyclic hydrocarbon residues, follow the steps (1) to
Method (4) can be adopted.

(11. A method in which a polyhydric alcohol having a cyclic hydrocarbon residue in advance is used as a polyhydric alcohol that is a raw material for a polyol (for example, a polymeric diol).

(2) A method in which a dicarboxylic acid having a cyclic hydrocarbon residue in advance is used as an organic dibasic acid (dicarboxylic acid) serving as a raw material for the polyol.

(3) A method in which the polyhydric alcohol and dicarboxylic acid of (1) and (2) above are used as raw materials for polyol.

(4) A method of using a polyhydric alcohol having a cyclic hydrocarbon residue in advance as a chain extender, in combination with any of the above (1) to (3), or alone.

For example, as a synthesis method for obtaining the above urethane resin, 1,
4-di-hydroxymethylcyclohexa(CH-4-C
A method of converting a polyester polyol obtained from (OoH) into methylene-bis-phenylisocyanate is mentioned. In this case, the chain extender can be the above-mentioned 1,4-di-hydroxymethylcyclohexane or other diols (for example butane-1,4-diol).

As the polyhydric alcohol which may have a cyclic hydrocarbon residue in advance, those having a cyclohexyl group in the molecular chain of the ethylene glycol structure can be used, as described above, but there are also propylene glycol, hydroxyl groups, etc. Glycols such as lengelicol and diethylene glycol, or trimethylpropane, hexanetriol, glycerin, trimethylolpropane, '/'l1l
)I')j'-/End $11/Da If/) Polyhydric alcohols such as limethylolethane and pentaerythritol, or their glycols, or those having a cyclic hydrocarbon residue in their structure can be used. . In addition, usable dibasic acids include phthalic acid, dimerized sulfuric acid, maleic acid, etc., and those having a cyclic hydrocarbon residue in their molecules.

In place of the above polyol, S-caprolactam, α-
Lactone-based polyester polyols synthesized from lactams such as methyl-1-caprolactam, S-methyl-5-caprolactam, and γ-butyrolactam; or polyether polyols synthesized from ethylene oxide, propylene oxide, butylene oxide, etc. are also used. You may do so.

In these books, urethanized polyester polyurethanes and polyether polyurethanes are synthesized by reacting these polyols with incyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, and metaxylylene diisocyanate. The urethane resins according to the invention are usually produced primarily by the reaction of polyisocyanates and polyols and are also in the form of urethane resins or urethane prepolymers containing free incyanate groups and/or hydroxyl groups, or reactive terminals thereof. It may also be one that does not contain groups (for example in the form of a urethane elastomer).

Further, usable chain extenders may be the polyhydric alcohols exemplified above (which may or may not contain a cyclic hydrocarbon residue in the molecule).

On the other hand, as the above-mentioned fatty acids that can be used in the present invention, those with a melting point higher than 50°C include myristic acid, palmitic acid, stearic acid, etc., and those with a melting point of 50°C or lower include caproic acid, caprylic acid, etc. , capric acid, lauric acid, lyric acid, oleic acid, etc. Fatty acids with melting points higher than 50°C have the advantage of being difficult to cause leaching.
On the other hand, if it is 50°C or lower, it is compatible with the binder resin etc., but it is easy to migrate to the surface, so this point needs to be kept in mind.

In addition, the above-mentioned fatty acid esters that can be used in the present invention include inpropyl stearate, butyl stearate,
Examples include inbutyl stearate, butyl palmitate, cetyl caprate, isocetyl stearate, butyl oleate, octyl myristate, hexyl stearate, nonyl laurate, and the like.

Further, as the above-mentioned conductive carbon black that can be used in the present invention, for example, Conductex 975 (specific surface area 250 m"/gs, particle size 24 mμ) manufactured by Columbia Carbon, Conductex 900 (specific surface area 125 m" 7 g, particle size 27mμ)
, Cabot Vulc
an ) XC-72 (specific surface area 254 mSg, particle size 3
0mμ), Raven 1040.420, Mitsubishi Kasei Corporation
There are #44 etc. made by the manufacturer.

Light-shielding carbon black may also be used in combination, and as such fc light-shielding carbon black, for example, Laben 2000 (specific surface area: 19Q m") manufactured by Columbia Carbon Co., Ltd.
7g, particle size 18mμ), 2100.1170.100
0, #100, #75, #40 manufactured by Mitsubishi Kasei Corporation
, #35, $30, etc. are available. Carbon black is 20-30 mμ, preferably 21-29 mI
It is preferable to have a particle size of t, but the oil absorption amount is 90a.
/(DBP)/100 g or more is desirable because it is easy to form a structured structure and exhibits high conductivity.

In addition, since the binder resin contains a phenoxy resin and/or a vinyl chloride copolymer together with the above-mentioned urethane resin, the dispersibility of the magnetic powder is improved and its mechanical strength is increased. However, if the phenoxy resin and/or vinyl chloride copolymer is used alone, the layer becomes hard, but this can be prevented by containing polyurethane, and the adhesion to the support or base layer is improved.

The phenoxy resin that can be used is a polymer obtained by the polymerization of hisphenol A and ethylhydrin, and is expressed by the following general formula.

(However, nsen 82-13) An example is PKHC manufactured by Union Carbide.

There are PKHH, PKHT, etc.

Further, as the above-mentioned vinyl chloride copolymers that can be used, there are those represented by the general formula: In this case, ! The molar ratio derived from and m is 1i95-50 molar for the punisher unit. Fi 5-50 molar for the latter unit.

Further, X represents a monomer residue copolymerizable with vinyl chloride, and represents at least one member selected from the group consisting of vinyl acetate, vinyl alcohol, maleic anhydride, and the like.
The degree of polymerization expressed as (10m) is preferably 100
-600, and if the degree of polymerization is less than 100, the magnetic layer etc. tend to become sticky, and if it exceeds 600, the dispersibility becomes poor. The vinyl chloride copolymer described above may be partially hydrolyzed. As a vinyl chloride copolymer,
Preferably a vinyl chloride-vinyl acetate copolymer (
Hereinafter, it will be referred to as "vinyl chloride-vinyl acetate copolymer."

). Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride copolymers, etc. Among the polymers, partially hydrolyzed t'Lfc copolymers are preferred. Specific examples of the vinyl chloride-vinyl acetate copolymer include (7) rVAG manufactured by Union Carbide;
HJ, l'-VYHHJ, "VMcHJ, "S-LEC A", "S-LEC A-5", "S-LEC C", "S-LEC M" manufactured by Block Chemical Co., Ltd., Denki Kagaku Kogyo Co., Ltd.
[Denkabinir 1000 G J, "Denkabinir 100 OWJ," etc. manufactured by Manufacturer Co., Ltd. can be used.

In addition to the above, cellulose resins can be used as the binder resin, such as cellulose ethers, cellulose inorganic acid esters, cellulose organic acid esters, and the like. As the cellulose ether, methyl cellulose, ethyl cellulose, etc. can be used.
As cellulose inorganic acid esters, nitrocellulose, cellulose sulfate, cellulose phosphate, etc. can be used to kill the cellulose.

Further, as the cellulose organic acid ester, acetyl cellulose, propionyl cellulose, phthyryl cellulose, etc. can be used. Among these cellulose resins, nitrocellulose is preferred.

In addition to the binder resins mentioned above, thermoplastic resins, thermosetting resins, reactive resins, and electron beam curable resins may be used as binder resins for the layers constituting the magnetic recording medium of the present invention.

The thermoplastic resin has a softening temperature of 150°C or less, an average molecular weight of 10,000 to 200,000, and a polymerization degree of about 200 to 2,000, such as acrylic ester-acrylonitrile copolymer, acrylic acid Ester-vinylidene chloride copolymers, acrylic ester-styrene copolymers, etc. are used.

As a thermosetting resin or a reactive resin, it has a molecular weight of 200,000 or less in the state of a coating liquid, and has a molecular weight of 200,000 or less after coating and drying.
The molecular weight becomes infinite due to reactions such as t'i condensation and addition. Moreover, among these resins, those which do not soften or melt before the resin is thermally decomposed are preferable.
Specifically, for example, phenol resin, epoxy resin, urea resin 1. These include melamine resin, alkyd resin, etc.

Examples of electron beam irradiation-curable resins include unsaturated prepolymers,
For example, there are maleic anhydride type, urethane acrylic type, polyester acrylic type, etc.

The layer containing the above-mentioned urethane resin having a cyclic hydrocarbon residue as a binder resin is, for example, the magnetic layer 2 of the support 1, as shown in FIG.

An 80 layer 3 is provided on the surface opposite to the magnetic layer 2 (B
The C layer may or may not be provided. ).

The magnetic powder, especially the ferromagnetic powder, used for the magnetic layer 2 includes r-FelOs, Co-containing r-pe! O
x, Fe, 0 Co-containing iron oxide magnetic powder such as Fe3O4;
Fe, Ni, Co, Fe-Ni-Co alloy, F
e-Mn-Zn alloy, Fe-Ni-Zn alloy,
Fe-Co-Ni-Cr alloy, Fe-Co-Nj
-p alloy, Co-Ni alloy, etc. Fe.

Examples include metal magnetic powders containing Ni, Co, etc. as main components.

If the specific surface area of the magnetic powder of the magnetic layer 2 is set to 30rn1/* or more (preferably by reducing the particle size), the reciprocating power and S/N ratio of the medium can be significantly improved.

If the specific surface area of the magnetic powder is increased more than necessary, poor dispersion will occur, so it is desirable that the upper limit is 100 mfr.

Furthermore, known dispersants (for example, powdered lecithin), abrasives (for example, fused alumina), etc. may be added to the magnetic layer 2.

Examples of abrasives that can be added include α-AltO, (corundum), artificial corundum, fused alumina, silicon carbide,
Chromium oxide, diamond, artificial diamond, garnet, emery (main ingredients: corundum and magnetite), etc. are used.

These abrasives have an average particle size of 0.05 to 5 .mu.m, particularly preferably 0.1 to 2 .mu.m.

In addition, the non-magnetic powder contained in the 80 layer 3 is as follows:
Carbon black, silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, zinc oxide, α-Fe, Os, curcum, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbonate, etc. (preferably carbon black (especially conductive carbon black)) and/or titanium oxide. If these non-magnetic powders are included in the BC layer, the surface of the BC layer can be appropriately roughened (matted) to improve its surface properties, and in the case of carbon black, it can be used to impart conductivity to the BC layer. Provides antistatic effect. It is advantageous to use carbon black and other non-magnetic powders in combination, since the effects of improving surface properties (stabilizing runnability) and improving conductivity cannot be obtained.

Further, the magnetic recording medium shown in FIG. 2 may be provided with an undercoat layer (not shown) between the magnetic layer 2 and the support 1, or may not be provided with an undercoat layer (not shown). Same below).

In addition, the material of the support body 1 may be plastics such as polyethylene terephthalate or polypropylene, Aj! ,Z
Metals such as n, glass, BN, Si carbide, porcelain,
Ceramics such as pottery are used.

Incidentally, when forming the magnetic layer and BC layer by coating, it is desirable to add a predetermined amount of polyfunctional isocyanate as a crosslinking agent to each coating material. Examples of such crosslinking agents include triphenylmethane triisocyanate, tris-(p-incyanate phenyl) neophosphite, polymethylene polyphenylisocyanate, and the like, in addition to the polyfunctional polyisocyanates mentioned above.

FIG. 3 shows another magnetic recording medium.
A 00 layer 4 is provided on the magnetic layer 2 of the illustrated medium.

This 00 layer 4 is provided to protect the magnetic layer 2 from damage, etc., and for this purpose, it needs to have sufficient slipperiness. The surface roughness of the 00 layer 40 is preferably Ra≦0.01 μm and 1 (max≦0.13 μm, especially in relation to the color S/N. In this case, the surface roughness of the support 1 is Ra≦
0.01 μm, Rmax≦0.13 μm, and it is desirable to use a smooth support 1.

FIG. 4 shows a magnetic recording medium configured as a magnetic disk, with magnetic layers 2.00 similar to those described above on both sides of the support 1.
A layer 4 is provided respectively.

5. Examples Hereinafter, the present invention will be explained with reference to specific examples.

The components shown in Table 1 were placed in a ball mill and dispersed. After filtering the magnetic paint through a 1 μm filter, 5 parts of polyfunctional incyanate was added, and the mixture was coated onto a support to a thickness of 5 μm using a reverse roll coater. The tape was supercalendered and slit into 14-inch widths to make video tapes (corresponding to the numbers of each Example and Comparative Example). However, table-
The numbers after the second column of 1 indicate parts by weight, and "actual" after the second column indicates examples, and "ratio" indicates comparative examples.

The following measurements were made on videotapes from each side described above.

Chroma S/N: Color video noise meter [Sh 1basoku9
Measurement was performed using 25D/IJ.

Lumi S/N S Same as above RF output RF at 4MHz using VTR deck for RF output measurement
The output was measured, and after 100 playbacks, it showed a value that was lower than the initial output.

(Unit: dB).

Skew value: A parameter that expresses the size of the timing deviation during image playback. After 100 @ playback, the deviation from the reference signal (a signal that scans the CRT screen at approximately 64 μsec) K is measured, and the value is determined. The smaller the difference, the smaller the deviation and the less disordered the image.

Jitter value: Using a VTR jitter meter [MK-612AJ manufactured by Meguchi Electronics Co., Ltd.], the jitter was measured after 0 and 100 runs at 30° C. and 80% RH under high temperature and humidity.

Table 2 shows the videotape performance of each example. However, the chroma S/N of the ratio -1, Lumi S/N, RF output, and audio output fluctuation after 100 passes are shown in Table 2, where actual -1 is OdB. was measured.

Chroma S/N of ratio -2 with actual -2 as OdB.

Lumi S/N, RF output, and audio output fluctuation after 100 passes were measured.

From the above results, it can be seen that in the examples in which the magnetic layer was formed according to the present invention, the tape performance was significantly improved.

[Brief explanation of drawings]

The drawings show examples of the present invention, and FIG. 1 is a curve diagram showing the relationship between the stress elongation rate of urethane resin, and FIGS. FIG. 3 is an enlarged cross-sectional view of a portion. In addition, in the symbols used in the drawings, 2...
・Magnetic layer 3... Barafco layer (BCJln) 4...
...covered with an overcoat layer (00 layer).

Claims (1)

[Claims] 1. A magnetic recording medium characterized in that a magnetic layer contains a urethane resin having a yield point, a fatty acid, a fatty acid ester, and conductive carbon black.