JPH04356724A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To impart sufficient mechanical strength and durability together with adequate resilience by incorporating an urethane resin having a yield point, metallic magnetic powder and carbon black into a magnetic layer. CONSTITUTION:Since this magnetic recording medium is formed by using the urethane resin having the yield point YP, this medium elongates extremely little even if a stress is applied to the medium up to the yield point YP and, therefore, adequate hardness is imparted to the urethane resin. The traveling of the medium is smoothed and the generation of jitters is drastically decreased by adding the carbon black into the magnetic layer. The medium formed by providing an under coat layer between the magnetic layer 2 and a base 1 is equally good or the under coat layer may not be provided. Plastics, metals, ceramics, etc., are used as the blank material of the base 1.

Description

Description: [0001] The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks. 2. Description of the Related Art Magnetic recording media are generally manufactured by applying a magnetic paint containing magnetic powder, binder resin, etc. onto a support and drying it. In such magnetic recording media, urethane resin is generally used as a binder resin for magnetic layers and the like. Conventionally known urethane resins are synthesized from polymeric diols, diisocyanates, chain extenders, and crosslinking agents (used as necessary). [0004] Polyester diols include polyester diols obtained from adipic acid, butanediol, etc.
Examples include 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, although such general urethane resin has excellent flexibility, it lacks hardness, so it is difficult for the magnetic recording medium to mechanically contact sliding contact with guide pins, magnetic heads, etc. The strength is poor, and there are also problems in runnability and powder shedding. On the other hand, in the field of magnetic recording media, metal magnetic powders that exhibit high output are attracting attention. Metal magnetic powder is an advantageous material in terms of improving RF output, etc., compared to other magnetic powders when packed at high density. However, magnetic recording media using metal magnetic powders have problems such as insufficient mechanical strength and relatively poor dispersibility of metal magnetic powders, and no media has yet fully overcome these problems. The reality is that it has not been proposed. With the development of recent magnetic recording media, when a simply soft urethane resin is included in the magnetic layer along with magnetic powder, the durability during running of the medium,
Still image stability, dispersibility of finely divided magnetic powder, etc. are insufficient. OBJECTS OF THE INVENTION The object of the present invention is to provide a magnetic layer with adequate flexibility as well as sufficient mechanical strength and durability, to provide high output and excellent runnability, and to improve surface properties and static images of the magnetic layer. An object of the present invention is to provide a magnetic recording medium with improved durability. [Configuration of the Invention and Its Effects] That is, the magnetic recording medium according to the present invention is a magnetic recording medium in which a urethane resin having a yield point, a metal magnetic powder, and carbon black are contained in a magnetic layer. This is related. According to the present invention, a urethane resin having a yield point YP as illustrated by curve b in FIG. 1 is used, compared to the characteristics of conventional urethane resin shown by curve a in FIG. , until the yield point YP, the elongation is very small even when stress is applied, which gives the urethane resin appropriate hardness, and after the yield point YP it shows the property of elongating with stress without breaking, It also has appropriate flexibility and binding strength as a binder resin. As a result, 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, V
The magnetic tape for TR has no edge folds, and can maintain control tracks near the edges and exhibit its functions effectively. [0013] As described above, the urethane resin having a yield point makes the magnetic layer strong and strong, so even if metal magnetic powder is used, this magnetic powder is well retained in the magnetic layer, and as a result, The RF output etc. are improved and the original high output characteristics of metal magnetic powder can be fully demonstrated. On the other hand, if an attempt is made to supplement the strength of a magnetic recording medium using metal magnetic powder by adding an abrasive agent without using a urethane resin having a yield point, the surface of the magnetic layer will be easily roughened. This may lead to a decrease in output, etc. According to the present invention, the strength of the magnetic layer can be obtained by using a urethane resin having a yield point, without relying on the addition of such an abrasive, and the surface properties can be maintained well. Regarding this surface property, if a urethane resin with a yield point is used, compared to a normal urethane resin,
The dispersibility of the metal magnetic powder improves, promoting the dispersion of the metal magnetic powder, which originally does not have very good dispersibility, and this contributes to reducing the surface roughness of the magnetic layer and improving the surface properties. Generally, when the surface properties are increased, jitter tends to increase when a medium runs on the surface of the magnetic layer when a normal urethane resin is used. However, by using a urethane resin having the above-mentioned yield point, the medium can run smoothly and the occurrence of jitter can be significantly reduced. According to the present invention, this can be further improved by adding carbon black to the magnetic layer. That is, carbon black acts as a filler in the magnetic layer to fill in the roughness of the surface of the magnetic layer to improve its surface properties, and also to improve the rubbing and running properties of the magnetic layer with the medium. The metal magnetic powder used in the magnetic layer of the present invention generally exhibits a color (for example, blackish brown) that does not easily transmit light.
Since it is also electrically conductive, it has been recognized that it is unnecessary to add carbon black to the magnetic layer. but,
Apart from such recognition, the inventor of the present invention has discovered that by actively adding carbon black when using metal magnetic powder,
Effectively demonstrates the performance as a filler as described above,
It has been discovered that the surface properties and runnability can be greatly improved and the advantages of using metal magnetic powder can be further promoted. In the present invention, the above-mentioned yield point YP is important for the performance of the urethane resin.
/cm2, preferably 100 to 560kg/c
m2 stress range (approximately 290 kg/cm in the example of Figure 1)
It is desirable that a yield point exists at 2). If the stress in the range where the yield point exists is 50 kg/cm2 or more, the resin will be prevented from becoming too soft, and the stress will be 600 kg/cm2.
The following can prevent the resin from becoming hard and brittle. [0020] Here, the conditions for measuring the yield point are, for example, JIS
K-6301 describes this in detail. To explain the measurement method, a 100 μm thick urethane resin film was heated at 80°C for 10 minutes, then at 120°C for 1 hour.
Heat treated for 0 minutes, then left in an atmosphere of 25°C and 55% RH (relative humidity) for 3 days, and then JISK-
According to 6301, using No. 2 dumbbells, pulling speed 2
Measure at 00 mm/min. [0021] In order to exhibit the above-mentioned excellent performance, the above-mentioned urethane resin having a yield point preferably has a cyclic hydrocarbon residue in the molecule. This cyclic hydrocarbon group 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, a substituted alkyl group such as a methyl group). , 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. [0023] The bonding position of this cyclic hydrocarbon residue is preferably within the main chain of the urethane resin molecule, but it may be bonded to a side chain thereof. [0024] Furthermore, by changing the amount of the component having a cyclic hydrocarbon residue in the urethane resin, it is possible to obtain a urethane resin having an arbitrary glass transition point (Tg), and the Tg is -30. ℃~100℃, preferably 0℃~90℃. Setting Tg to -30°C or higher prevents the film strength from decreasing due to softening of the resin (Tg<-30°C), and setting Tg to below 100°C prevents the film from becoming unnecessarily hard and brittle. It can be prevented. The urethane resin used in the present invention can be synthesized by reacting a polyol and a polyisocyanate. At this time, the following methods (1) to (4) can be employed to introduce the above-mentioned cyclic hydrocarbon residue. (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 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 of using the polyhydric alcohol and dicarboxylic acid of (1) and (2) above 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 (1) to (3) above, or alone. For example, as a synthetic method for obtaining the above-mentioned urethane resin, 1,4-di-hydroxymethylcyclohexane [Formula 1] and adipic acid (HOOC-(CH2)4-COOH
) and the polyester polyol obtained from methylene-
A method of urethanizing with bis-phenylisocyanate [Chemical formula 2] can be mentioned. In this case, the chain extender is the above-mentioned 1,4-di-hydroxymethylcyclohexane or other diol (e.g. butane-1,4-diol).
It may be. 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 in addition to such a structure, propylene Glycols such as glycol, butylene glycol, diethylene glycol, polyhydric alcohols such as trimethylolpropane, hexanetriol, glycerin, hexanetriol, trimethylolethane, pentaerythritol, or these glycols, or those containing cyclic hydrocarbon residues in their structure. Those having groups can be used. Further, usable dibasic acids include phthalic acid, dimerized linoleic acid, maleic acid, etc., and those having a cyclic hydrocarbon residue in their molecules. In place of the above polyol, a lactone polyester polyol synthesized from lactams such as s-caprolactam, α-methyl-1-caprolactam, s-methyl-s-caprolactam, and γ-butyrolactam; or ethylene oxide; Polyether polyols synthesized from butylene oxide and the like 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 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 isocyanate groups and/or hydroxyl groups, or It may also be in the form of a urethane elastomer, which does not contain these reactive end groups. Further, usable chain extenders may be the polyhydric alcohols listed above (which may or may not have a cyclic hydrocarbon group in the molecule). . If a phenoxy resin and/or a vinyl chloride copolymer is also contained as a binder resin in addition to the above-mentioned urethane resin, the dispersibility of the magnetic powder will be improved when applied to the magnetic layer, and its mechanical properties will be improved. Strength increases. However, if only the phenoxy resin and/or the vinyl chloride copolymer is used, the layer becomes too 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 polymerizing bisphenol A and epichlorohydrin, and is represented by the following general formula. [Chemical 3] For example, PKHC, PKHH manufactured by Union Carbide
, PKHT, etc. Further, as the above vinyl chloride copolymers that can be used, there are those represented by the general formula: In this case, the molar ratio derived from l and m in is from 95 to 50 mol % for the former units and from 5 to 50 mol % for the latter units. 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 (l+m) is preferably from 100 to 600; if the degree of polymerization is less than 100, the magnetic layer etc. will tend to become sticky, and if it exceeds 600, the dispersibility will deteriorate. 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,
Examples include vinyl chloride-vinyl acetate-maleic anhydride copolymers, and among vinyl chloride-vinyl acetate copolymers, partially hydrolyzed copolymers are preferred. Specific examples of the above-mentioned vinyl chloride-vinyl acetate copolymers include "VAGH" and "VYHH" manufactured by Union Carbide;
"VMCH", "S-LEC A" manufactured by Sekisui Chemical Co., Ltd.,
"S-LEC A-5", "S-LEC C", "S-LEC M", "Denkabinyl 100" manufactured by Denki Kagaku Kogyo Co., Ltd.
0G", "Denkabinir 1000W", etc. can be used. In addition to the above, cellulose resins can be used as the binder resin, such as cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester, etc. [0045] As the cellulose ether, methyl cellulose, ethyl cellulose, etc. can be used. As the cellulose inorganic acid ester, nitrocellulose, cellulose sulfate, cellulose phosphate, etc. can be used. Further, as the cellulose organic acid ester, acetyl cellulose, propionyl cellulose, butyryl cellulose, etc. can be used. Among these cellulose resins, nitrocellulose is preferred. Regarding the entire binder composition, the ratio of the above-mentioned urethane resin to other resins (total amount of phenoxy resin, vinyl chloride copolymer, etc.) is 90/10 to 40/4 by weight. 60 is desirable, 85
It has been confirmed that a range of /15 to 45/55 is more desirable. Outside this range, if the amount of urethane resin is too large, dispersion tends to be poor, and if the amount of other resins is too large, the surface properties tend to be poor, and especially if it exceeds 60% by weight, the physical properties of the coating film become unfavorable overall. In the case of vinyl chloride-vinyl acetate, it can be mixed with the urethane resin with a considerable degree of freedom, and preferably the urethane resin is 15 to 75% by weight. As the binder resin for the layer constituting the magnetic recording medium of the present invention, in addition to those mentioned above, thermoplastic resins, thermosetting resins, reactive resins, and electron beam curable resins may be used. The thermoplastic resin has a softening temperature of 150
℃ or less, average molecular weight 10,000 to 200,000
, with a degree of polymerization of about 200 to 2,000,
For example, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, etc. are used. [0049] As the thermosetting resin or reactive resin,
In the state of a coating liquid, the molecular weight is 200,000 or less, and 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 curable resin include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, and polyester acrylic type. In the magnetic recording medium of the present invention, the metal magnetic powder used as the magnetic powder includes Fe, Ni, Co
, Fe-Al, Fe-Ni-Co alloy, Fe-Mn-Z
n alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-C
Examples include metal magnetic powders containing Fe, Ni, Co, etc. as main components, such as r alloy, Fe-Co-Ni-P alloy, Co-Ni alloy. [0052] In the present invention, the carbon black added to the magnetic layer is preferably one having electrical conductivity, but carbon black having light-shielding properties may also be added. [0053] As such conductive carbon black, for example, Conductex (manufactured by Columbia Carbon Co., Ltd.) is used.
Conductex)975 (specific surface area 250m2
/g, particle size 24 mμ), Conductex 900
(specific surface area 125 m2/g, particle size 27 mμ), Cabot Vulcan XC
-72 (specific surface area 254m2/g, particle size 30mμ)
, Raven 1040, 420, # manufactured by Mitsubishi Kasei Corporation
There is a 44th mag. Examples of light-shielding carbon blacks include Raven 2000 (specific surface area 190 m2/g, particle size 18 mμ), 2100, and 11 manufactured by Columbia Carbon Co., Ltd.
70, 1000, #100, #7 manufactured by Mitsubishi Kasei Corporation
5, #40, #35, #30, etc. can be used. The carbon black preferably has a particle size of 20 to 30 mμ, preferably 21 to 29 mμ,
It is desirable that the oil absorption amount is 90 ml (DBP)/100 g or more because it is easy to form a structured structure and exhibits higher conductivity. The layer containing the above-mentioned urethane resin or the like having a cyclic hydrocarbon residue as a binder resin is, for example, a magnetic layer 2 on a support 1, as shown in FIG. Also, magnetic layer 2
A back coat (BC) layer 3 is provided on the opposite side. Although this BC layer may be provided, it is not necessary to provide it. The magnetic layer 2 also contains a lubricant such as silicone oil, graphite, molybdenum disulfide, tungsten disulfide, a monobasic fatty acid having 12 to 20 carbon atoms (such as stearic acid), and a lubricant having 12 to 20 carbon atoms. Monobasic fatty acids (e.g. stearic acid) with 4 to 2 carbon atoms
fatty acid ester consisting of six monohydric alcohols, etc.),
Abrasives (eg alumina), antistatic agents (eg graphite), etc. may be added. As a dispersant that can be added to the magnetic layer 2, etc., at least one type of phosphoric ester represented by the following general formula (A-1) or (A-2) can be used. General formula (A-1): General formula (A-2): [Formula 4] (However, in each of the above general formulas, R is an alkyl group or alkylaryl group having 8 to 30 carbon atoms, and n is 1 (This is a real number of ~20.) [0059] By using the phosphoric acid ester of the above general formula (A-1) or (A-2), magnetic powder etc. can be well dispersed while maintaining the stability of the magnetic paint over time. , and the surface properties of the magnetic layer etc. can be improved. In the general formula of the above phosphoric acid ester, R
should have a carbon atom number of 8 to 30, but it is desirable to have a carbon atom number of 8 or more in order to improve compatibility with the binder and prevent movement in the layer. This is because it is preferable to set the following value in terms of preventing poor dispersion of the magnetic paint etc. and maintaining appropriate hydrophilicity of the phosphoric acid residue. The number of carbon atoms is preferably 10 to 24. In particular, R is an alkylaryl group,
More preferably, it is an alkylphenyl group. In addition, n in the above general formula is preferably 1 to 20 (preferably 2 to 15, more preferably 6 to 12); This is desirable because it appropriately separates the hydrophilic groups from the [0062] The above phosphoric acid ester has 10 to 14
HLB (Hydrophilic-Lipophi)
lic Balance (hydrophilic-lipophilic balance) is desirable. That is, if the HLB is smaller than 10, the lipophilic property becomes strong, and if the HLB is larger than 14, the hydrophilic property becomes strong. be. Note that the above-mentioned phosphoric acid ester may contain a trace amount of triester. The above-mentioned phosphoric esters are specifically exemplified compound (1) [Formula 5] and/or this monophosphoric ester exemplified compound (2) [Formula 6] and/or this diphosphoric ester exemplified compound (3) ) [Chemical 7] and/or this diphosphoric ester exemplified compound (4) [Chemical 8] and/or this diphosphoric ester exemplified compound (5) [Chemical 9] and/or this diphosphoric ester exemplified compound (6) [ Chemical formula 10] and/or this monophosphate ester exemplary compound (7) [Chemical formula 11] and/or this diphosphoric acid ester exemplary compound (8) [Chemical formula 12] and/or this diphosphoric acid ester exemplary compound (9) [Chemical formula 13] and/or this diphosphoric ester exemplified compound (10) [Image Omitted] and/or this monophosphoric ester exemplified compound (11) [Image Omitted] and/or this diphosphoric ester. [0064] Furthermore, there is an appropriate range for the amount of the phosphoric acid ester added to the layer, and in the case of a magnetic layer, the amount of magnetic powder 10
It is preferably 1 to 10 parts by weight, and even more preferably 2 to 7 parts by weight. When the amount added is 1 part by weight or more, sufficient dispersion can be achieved and the surface properties of the layer are improved, and when the amount is 10 parts by weight or less, the viscosity of the coating material is sufficient and the film thickness can be easily controlled. The non-magnetic powder contained in the BC layer 3 includes carbon black, silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, zinc oxide, α-Fe2O3, talc, kaolin,
Calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbonate, etc., preferably carbon black (especially conductive carbon black) and/or
Or one made of titanium oxide can be mentioned. [0066] Further, as the non-magnetic powder, organic powder,
For example, benzoguanamine resin, melamine resin, phthalocyanine pigment, etc. may be added. 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 be provided with no undercoat layer. Good (the same applies hereafter). Further, the BC layer 3 may also contain the urethane resin according to the present invention. As the material for the support 1, plastics such as polyethylene terephthalate and polypropylene, metals such as Al and Zn, glass, BN, Si carbide, and ceramics such as porcelain and earthenware are used. [0069] When coating and forming the above-mentioned magnetic layer, etc.,
It is desirable to add a predetermined amount of polyfunctional isocyanate as a crosslinking agent to the paint. Such crosslinking agents include
In addition to the polyfunctional polyisocyanates mentioned above, examples include triphenylmethane triisocyanate, tris-(p-isocyanate phenyl) thiophosphite, polymethylene polyphenylisocyanate, and methylene diisocyanate type and tolylene diisocyanate type are preferable. FIG. 3 shows another magnetic recording medium in which an overcoat (OCC) is applied on the magnetic layer 2 of the medium in FIG.
) layer 4 is provided. This OC layer 4 is provided to protect the magnetic layer 2 from damage, etc., and for this purpose, it needs to have sufficient lubricity. Therefore, as the binder resin for the OC layer 4, the urethane resin used for the magnetic layer 2 described above is used (preferably in combination with a phenoxy resin and/or a vinyl chloride copolymer). The surface roughness of the OC layer 4 is Ra≦0.01 μm, Rmax≦0.13 μm, especially in relation to color S/N.
It is better to In this case, the surface roughness of the support 1 is Ra
It is desirable that the support 1 be ≦0.01 μm, Rmax≦0.13 μm, and be smooth. FIG. 4 shows a magnetic recording medium configured as a magnetic disk, in which a magnetic layer 2 and an OC layer 4 similar to those described above are provided on both sides of a support 1, respectively, and the OC layer 4 has a magnetic layer 2 and an OC layer 4 similar to those described above. A binder resin containing urethane resin as a main component may be included. [Examples] The present invention will be explained below with reference to specific examples. The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. [0075] Charge the ingredients shown in Table 1 into a ball mill,
After dispersion, this magnetic paint was filtered through a 1 μm filter, 5 parts of polyfunctional isocyanate was added, and coated on a support to a thickness of 5 μm using a reverse roll coater, supercalendered, and coated to a width of 1/2 inch. It was slit to make a videotape (corresponding to the numbers of each Example and Comparative Example). However, the numbers after the second column of Table 1 represent parts by weight, and "actual" after the second column represents an example, and "ratio" represents a comparative example. [0076]
Table-1A Magnetic paint components
Fruit-1 Fruit-
2 Fruit-3 Fruit-4──────────
──────────────────────────
Fe-based metal magnetic powder
100 100 100
100 Co-containing γ-Fe2O3 polyurethane (of the present invention: 11
11 11 11
Yield point approximately 290kg/cm2, cyclohe
xyl group-containing) PVC-vinyl acetate copolymer (VAGH) PVC-vinyl acetate-maleic anhydride copolymer
11 11 Polymer Phenoxy resin (PKHH)
11 11 Monoester of Exemplified Compound (1) 3
Mixture of 3 3 and diester Polyurethane (Estan 5701)
3 Myristic acid
0.5 0.5 0
．． 5 0.5 Palmitic acid
0.5 0
．． 5 0.5 0.5 Butyl stearate 0.5
0.5 0.5 0.5
lecithin

3 Alumina
2
2 2 2 Carbon Black (Conducte 5
5 5 5 x975) Cyclohexanone
160 160 160
160 Tetrahydrofuran
50 50
50 50 Toluene
70
70 70 70 0077]
Table-1B Magnetic paint components
Ratio-1 Ratio-2
Ratio-3 Ratio-4 Ratio-5──────
──────────────────────────
────── Fe-based metal magnetic powder
100 100 1
00 Co-containing γ-Fe2O3

100 100 Polyurethane (of the present invention:
11 11 Yield point approx. 29
0kg/cm2, containing cyclohexyl group) PVC-vinyl acetate copolymer (VAGH)

11 11 PVC-vinyl acetate-maleic anhydride 11 11
Polymer phenoxy resin (PKHH)
11 Monoester of Exemplified Compound (1)

3 Mixture of diester and polyurethane (estane 5701) 11
11 3
11 Myristic acid
0.5 0.5
0.5 0.5 0.5 Palmitic acid
0.5 0.5 0.5 0
．． 5 0.5 Butyl stearate
0.5 0.5
0.5 0.5 0.5 Lecithin
3 3 3
3 Alumina
2
2 2 2
2 Carbon black (conducte)
5 5
5 5 x975) Cyclohexanone
160 160 160
160 160 Tetrahydrofuran
50 50
50 50 50
toluene
70 70 70
The following measurements were performed on the videotapes according to each of the above examples. Chroma S/N: Measured using a color video noise meter "Shibasoku 925 D/1". RF output: The RF output at 4 MHz was measured using a VTR deck for RF output measurement, and after 100 playbacks, the value showed a decrease compared to the initial output. (
Unit: dB) Jitter value: Using a VTR jitter meter "MK-612A" manufactured by Meguro Electronics, the initial value (
0th time: value at normal temperature and humidity), and jitter after running 100 times was measured. Glossiness: Measured at an angle of 60° using a variable angle photometer, and expressed with the value of Comparative Example 1 as 100% (the larger the value, the better the surface smoothness). The performance of each example videotape is shown below.
Shown in 2. [0084]
Table-2
Fruit-1 Fruit-2 Fruit-3 Fruit-4 Ratio-
1 Ratio-2 Ratio-3 Ratio-4 Ratio-5────
──────────────────────────
───────Chroma S/N (dB) 0
+1.0 +0.9 -0.2 -2.6 -
2.7 -0.3 0 -2.2RF output (dB) 0 +0.8 +0.
7 -0.3 -2.7 -3.0 -0.4
0 -1.8 Jitters at the beginning of the run 0.1
10 0.108 0.109 0.109 0.13
0 0.150 0.140 0.105 0.123
ter value (μsec) after 100 runs 0.110 0.108 0
．． 110 0.119 0.370 0.380 0.
290 0.105 0.220 Jitter value (μsec
) Glossiness (%) 165 170 1
70 160 120 120 15
0 140 100 [0085] However, the chroma S/N and RF output of the ratio -1 were determined by setting the actual -1 to 0 dB. The chroma S/N and RF output of the ratio -5 were determined by setting the ratio -4 to 0 dB. Jitter is each value. From the above results, it can be seen that the tape performance is significantly improved by adding urethane resin having a yield point, metal magnetic powder, and carbon black to the magnetic layer according to the present invention. In particular, in the case of metal magnetic powder, the ratio
As seen in Example 1, the performance tends to be worse than when iron oxide magnetic powder with a ratio of -5 is used, but based on the present invention, by adding a urethane resin with a yield point, it can be The results are markedly improved in the case of metal magnetic powder. In addition, compared to the ratio of -3 without adding carbon black, the actual ratio of -4
As shown in the figure, the effect of adding carbon black is remarkable.

[Brief explanation of drawings]

FIG. 1 is a curve diagram showing the stress-elongation relationship of urethane resin.

FIG. 2 is an enlarged cross-sectional view of an example of a magnetic recording medium.

FIG. 3 is an enlarged cross-sectional view of another example of a magnetic recording medium.

FIG. 4 is an enlarged cross-sectional view of still another example of a magnetic recording medium.

[Explanation of symbols]

2 Magnetic layer 3 Back coat layer (BC layer)

Claims (1)

[Claims] 1. A magnetic recording medium in which a magnetic layer contains a urethane resin having a yield point, metal magnetic powder, and carbon black.