JPS6117221A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To form a magnetic recording medium having proper softness, substantial mechanical strength and durability and good reproduced output characteristic by in corporating an urethane resin having a yield point and magnetic particles contg. bivalent iron into a magnetic layer. CONSTITUTION:The urethane resin having a yield point is used as a binder resin component for a magnetic layer, by which the mechanical strength of the magnetic recording medium is improved, the injury, dust dislodgment, etc. as a result of wear during sliding contact are considerably decreased and runnability is remarkably improved. The yield point exists preferably in a 100-560kg/cm<2> stress range. The magnetic particles contg. 4-6atomic% (more preferably 4.5- 5.5atomic%) bivalent iron (Fe<2+>) are used. The hiding power (i.e., light shieldability) by the magnetic powder is thus increased and the amt. of the light shielding material such as carbon black to be added is decreased. The hiding power of the magnetic layer is thoroughly obtd. and the durability thereof is 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 the polymer diol include polyester diol obtained from adipic acid, butane diol, etc., polyether diol, and polycarbonate diol, and diphenylmethane diisocyanate and the like can be used as the diisocyanate.
Further, the chain extender may be ethylene glycol, butanediol, etc., and the crosslinking agent may be polyols, polyamines, etc.

However, even though common urethane resins have excellent flexibility, they lack hardness, which reduces the mechanical strength of magnetic recording media against sliding contact with guide pins, magnetic heads, etc. There are also problems in terms of runnability and powder shedding.

On the other hand, γ-Fe2rm is generally used as magnetic powder for the magnetic layer. This 7-Fezes powder is usually 3
It consists of a coexistence of valent iron (Fe) and divalent iron < Pe2+), and the proportion of Fe"+ is 2 to 3 atoms, and most of it is Fe"+. There is. It is said that the magnetic properties are better as the amount of Fe''+ increases, so Fe''+ is minimized as much as possible.

In addition, in certain types of magnetic recording media, such as video magnetic tapes, the light transmittance of the magnetic layer is reduced (the hiding power is increased).
Detects the difference in light transmittance with the leader tape part,
There is a method to adjust the running of the tape. In this case, carbon black particles are added to the magnetic layer to increase the hiding power and suppress the light transmittance to 0.05 inches or less. However, when carbon black is added to increase the hiding power, the magnetic layer tends to be weak in strength and has poor durability.

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 and durability, has excellent running properties, has little powder falling off, and has good reproduction output characteristics. It is in.

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 and magnetic particles containing 4 to 6 atoms of divalent iron. It is characterized by:

According to the present invention, as the 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.
P-containing urethane resin has very little elongation even when stress is applied until it reaches the yield point YP, and 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. are significantly reduced, and running properties are also significantly improved. In particular, magnetic tapes for VTRs have no edge bending, and can hold control tracks near the edges and perform their functions well. The above yield point YP is important for the performance of the urethane resin of the present invention. 50 to 600 ky/q
Desirably, the yield point exists in a stress range of "100 to 560 kt/1M" (approximately 29 o1 kr/l♂ in the example of Figure 1). If the stress within the range where the yield point exists is less than 5°ky/cm, the resin tends to be soft and 60%
If it exceeds 0ky/Cm, the resin will not be hard and will easily become brittle.

Moreover, according to the present invention, divalent iron (p
Since the magnetic powder contains 4 to 6 atoms (preferably 4.5 to 5.5 atoms) of e-power, the magnetic powder has a large hiding power (i.e., light-shielding ability). The amount of light-shielding material added, such as the carbon black mentioned above, can be reduced. Therefore, the hiding power of the magnetic layer can be made sufficient, and at the same time, its durability can also be improved. As a result, as shown in Figs. 2 and 3, variations in audio output,
The RF specific output characteristics are significantly improved. Moreover, in the above content range, the original magnetic properties of trivalent iron (Fe''+) are well exhibited.
If + is less than 4 atoms, as shown in Figure 2 (however, carbon black is contained in the magnetic layer so that the light transmittance is 0.05%), the problem as described above (carbon black, etc.) It is not possible to eliminate the decrease in strength and durability due to the addition of ions), and the audio output fluctuates greatly.Moreover, if it exceeds 6 atoms, it is too much, and as shown in Figure 3, the magnetic properties as magnetic powder (
(coercive force, magnetic flux density, etc.) will deteriorate, and RF output will drop.

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 feeding 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 constituents having cyclic hydrocarbon residues in the urethane resin, it is possible to obtain a urethane resin with an arbitrary glass transition point (Tg), and the Tg is between -30°C. ~100'C, preferably o Oc
~90°C. If the Tg is lower than -30°C, the film will be too soft to obtain sufficient strength, and if the Tg is higher than 1000C, the film will become brittle.

In the present invention, it has been confirmed that the combination of the above-mentioned urethane resin and magnetic powder also improves the dispersibility of the magnetic powder.

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 the above-mentioned cyclic hydrocarbon residue, the following (1) to
Method (4) can be adopted.

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

(2) A method of using a dicarboxylic acid containing a cyclic hydrocarbon residue in advance as an organic dibasic acid (dicarboxylic acid) that is 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-cyhydroxymethylcyclohexa(CH2)a
A method of methylene-bis-7enyl isocyanation of a polyester polyol obtained from C0OH) can be 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 above-mentioned 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 in addition to such a structure, propylene glycol, butylene Glycols, glycols such as diethylene glycol, trifluorol, hexanetriol, glycerin, -Ill-ff〆[shifhYX/,,
y) Polyhydric alcohols such as limethylolethane and pentaerythritol, or glycols thereof, or those having a cyclic hydrocarbon residue in their structure can be used. Further, usable dibasic acids include phthalic acid, trimerized lyluic acid, maleic acid, etc., or those having a cyclic hydrocarbon residue in their molecules. In place of the above polyol, S-caprolactam, α-methyl-1
- caprolactam, S-methyl-8-caprolactam,
Lactone polyester polyols synthesized from lactams such as γ-butyrolactam; or polyether polyols synthesized from ethylene oxide, propylene oxide, butylene oxide, etc. may also be used.

These polyols are reacted with isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, and metaxylylene diisocyanate, thereby synthesizing urethanized polyester polyurethanes and polyether polyurethanes.

These urethane resins according to the present invention usually mainly include:
Produced by the reaction of polyisocyanate and polyol,
They may also be in the form of urethane resins or urethane prepolymers containing free incyanate groups and/or hydroxyl groups, or in the form of urethane elastomers that do not contain these reactive end groups.

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

Since the binder resin contains a phenoxy resin and/or a vinyl chloride copolymer in addition to 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 will not be too hard.
This can be prevented by containing polyurethane, resulting in good adhesion to the support or base layer.

The phenoxy resin that can be used is a polymer obtained by superimposing bisphenol A and epichlorohydrin, and is expressed by the following general formula.

(However, n82-13) For example, 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 following. In this case, the molar ratio derived from J and m is 95 to 50 molar for the former unit and 5 to 50 molar for the latter unit.

Further, X represents a monomer residue copolymerizable with vinyl chloride, and represents at least one selected from the group consisting of vinyl acetate, vinyl alcohol, maleic anhydride, and the like. (
The degree of polymerization expressed as A+m) is preferably from 100 to
If the degree of polymerization is less than 100, the magnetic layer etc. tend to become sticky, and if it exceeds 600, the sheet 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 copolymers, partially hydrolyzed copolymers are preferred.

Specific examples of the above-mentioned vinyl chloride-vinyl acetate copolymers include rVAGHJ, r manufactured by Union Carbide Co., Ltd.
VYHHJ, rVMCHJ, "S-LEC A", [S-LEC A-5J, "S-LEC C" manufactured by Tanezu Kagaku Co., Ltd.
, "S-LEC M j," Denkabinir 1000 G J, r Denkabini/I/10 manufactured by Denki Kagaku Kogyo Co., Ltd.
00W" etc. 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. Cellulose ether, methylcellulose, ethylcellulose, etc. can be used.
As the cellulose inorganic acid ester, nitrocellulose, cellulose sulfate, cellulose phosphate, etc. can be used.As the cellulose organic acid ester, acetyl cellulose, propionyl cellulose, butyryl cellulose, etc. can be used. 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 io, oao to 200,000, and a polymerization degree of about 200 to 2,000, such as acrylic acid ester-acrylonitrile copolymer, acrylic Acid ester-vinylidene chloride copolymers, acrylic ester-styrene copolymers, etc. are used.

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating solution, but after coating and drying, the molecular weight becomes infinite due to reactions such as 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, melamine resin, alkyd resin, etc. are used. Examples of the electron beam irradiation-curable resin include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, and polyester acrylic type.

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.

A 30 layer 3 is provided on the opposite side of the magnetic layer 2.
(The Be layer may or may not be provided.

). Examples of the magnetic powder, particularly the ferromagnetic powder, used in the magnetic layer 2 include iron oxide magnetic powders such as γ-FezOa and Co-containing -Fears.

In such magnetic powder, Fe2+ is added to 4 based on the present invention.
~6 atoms, which can be achieved by adjusting the ratio of the amounts of starting materials in addition to conventional magnetic powder manufacturing methods.

In addition, a known lubricant (for example, palmitic acid), a known dispersant (for example, powdered lecithin), an abrasive (for example, fused alumina), an antistatic agent (for example, graphite), etc. are added to the magnetic layer 2. good. Furthermore, carbon black may be added.

It is desirable that the carbon black has electrical conductivity, but a light-shielding carbon black may also be added. Examples of such conductive carbon black include Conductex 9 manufactured by Columbia Carbon Co., Ltd.
75 (specific surface area zsom"/g1 particle size 24 mμ),
Conductex 900 (specific surface area 125rn”/g
% particle size 27 mμ), Cabot Omega Palcan (Cabo
t Vulcan) XC-72 (specific surface area 254 m
"/L coarse particle size omμ), Raben 1040.420, 4-44 manufactured by Mitsubishi Kasei Corporation, etc. Examples of light-shielding carbon black include Raben 2000 (specific surface area x 9 om"/gs) manufactured by Columbia Carbon Co., Ltd. Particle size Particle size 1
8冫μ2100.1170.1000, Mitsubishi Kasei Corporation
#! Nosu 1001+75, +40, +35.4p30, etc. can be used.

Carbon black has a particle diameter of 20 to 30 mμ, preferably 21 to 30 mμ.
It is preferable that the particles have a particle size of 29 mμ, but it is desirable that the oil absorption amount be 9 oW1t (DBP) /1 oOg1 or more, since the structure can be easily removed and a high conductivity can be exhibited.

The non-magnetic powder contained in the 30 layer 3 is as follows:
Carbon black, silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, zinc oxide, α-Feign, talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide,
Examples include those made of calcium carbonate and the like, preferably carbon black (especially conductive carbon black) and/or titanium oxide. If these non-magnetic powders are included in the 30 layers, the surface of the 30 layers can be appropriately roughened (matted) to improve the surface properties, and in the case of carbon black, the 30 layers can be made conductive. Provides antistatic effect. It is advantageous to use carbon black and other non-magnetic powders in combination, as it can improve surface properties (stabilize runnability) and improve conductivity.

Furthermore, the magnetic recording medium shown in FIG. 4 may be one in which an undercoat layer (not shown) is provided between the magnetic layer 2 and the support 1, or may be one in which no undercoat layer is provided. Good (the same applies hereafter)0 In addition, the material of the support 1 may be plastics such as polyethylene terephthalate or polypropylene, AJ, Z
Metals such as n, glass, BN, Si carbide, ceramics such as porcelain and earthenware are used.In addition, when coating and forming the above magnetic layer, 30 layers, a polyfunctional isocyanate as a crosslinking agent is added to each coating material. It is desirable to add a predetermined amount. Examples of such crosslinking agents include triphenylmethane triisocyanate, tris-(p-incyanate phenyl)thiophosphite, polymethylene polyphenyl isocyanate, and the like, in addition to the polyfunctional polyinsyanate described above.

FIG. 5 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. Therefore, as the binder resin for the 00 layer 4, the urethane resin used for the magnetic layer 2 described above may be used (preferably in combination with a phenoxy resin and /l or a vinyl chloride copolymer). The surface roughness of 00 layer 4 is &≦0.01 μm, Rmax≦0.1, especially in relation to color S/N.
It is best to set it at 3 pm. In this case, the surface roughness of the support 1 is Ra≦0.01 pm, Rmax≦0.13
/Jm, and it is desirable to use a flat support 1.

FIG. 6 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 l.
A layer 4 is provided respectively.

5. Example 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 mixture was supercalendered and slit into A-inch width to obtain tape (corresponding to the number of each Example and Comparative Example). However, Table-1
The numbers in the second and subsequent columns represent parts by weight, and in the second and subsequent columns, "actual" indicates an example, and "ratio" indicates a comparative example.

(See margin below, continued on next page) The following measurements were performed on the videotapes from each side described above.

Chroma S/N: Color video noise meter [5hibasoku92
It was measured by 5D/IJ.

Lumi S/N: RF output at 4MHz using the same VTR deck for measuring RF output.
The output was measured, and after 100 playbacks, the value that was lower than the initial output was shown (unit: dB).

Table 2 shows the performance of each example videotape.

Table-2 However, the chroma S/N ratio is -1, with actual -1 being OdB.

Measure Lumi S/NXRF output. Measure the chroma S/N, Lumi S/N, and RF output of the ratio-2 with the real-2 set as OdB.

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

[Brief explanation of the drawing]

The drawings show examples of the present invention, in which Fig. 1 is a curve diagram showing the relationship between the stress elongation rate of urethane resin, and Figs. 2 and 3 show the characteristics depending on the amount of Fe''+ in the magnetic powder. Graphs showing changes, Figures 4, 5, and 6 are enlarged cross-sectional views of a portion of the magnetic recording medium from each side.In addition, in the symbols used in the drawings, 2. Bottom...
...Magnetic layer 3...--Back coat layer (BC layer)
4・・・・・・・・・・・・Overcoat layer (OC layer)
It is. Agent Patent Attorney Hiroshi Aisaka Figure 2 Figure 3 LTC Tokino (Breath (1st P) aS Temple) (Self-procedural amendment August q, 1985 1, Indication of case 1988 Patent application No. 131487 No. 2, Name of the invention Magnetic recording medium ° 3. Relationship with the case of the person making the amendment Patent applicant address 1-26-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Name
(127) Roku Konishi Photo Industry Co., Ltd. 4, Agent 6, Number of inventions increased by amendment 8, Contents of amendment (1), 1 or more in the 5th line of Table 2 on page 21 of the specification −

Claims (1)

[Claims] 1. Urethane resin with a yield point and divalent iron of 4 to 6
1. A magnetic recording medium characterized in that a magnetic layer contains magnetic particles containing atomic %.