JPH0576691B2 - - Google Patents

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 examples of the diisocyanate include diphenylmethane diisocyanate. Further, the chain extender may be ethylene glycol, butanediol, etc., and the crosslinking agent may be polyols, polyamines, etc. However, such general urethane resin,
Although it has excellent flexibility, the lack of hardness results in poor mechanical strength of the magnetic recording medium against sliding contact with guide pins, magnetic heads, etc., and there are also problems in terms of runnability and powder shedding. There is. On the other hand, γ-
Fe ₂ O ₃ is used. This γ-Fe ₂ O ₃ powder usually consists of trivalent iron (Fe ³⁺ ) and divalent iron (Fe ²⁺ ) coexisting, and the proportion of Fe ²⁺ is 2.
~3 atomic percent, mostly consisting of Fe ³⁺ . It is said that the magnetic properties are better when there is more Fe ³⁺ , so Fe ²⁺ is kept as low as possible. In addition, in some types of magnetic recording media, such as video magnetic tapes, the light transmittance of the magnetic layer is reduced (the hiding power is increased), and the difference in light transmittance with the leader tape portion is detected to detect the tape. There is a method to adjust the running. In this case, carbon black particles are added to the magnetic layer to increase the hiding power and reduce the light transmittance by 0.05%.
Efforts are being made to keep it below. However, when carbon black is added to increase the hiding power, the strength of the magnetic layer tends to weaken, resulting in poor durability. 3. Purpose of the Invention The purpose of the present invention is to provide a magnetic recording medium that has adequate flexibility, sufficient mechanical strength and durability, has excellent runnability, has little powder falling off, and has good reproduction output characteristics. be. 4 Structure of the invention and its effects That is, the present invention provides a magnetic recording medium containing magnetic particles containing 4 to 6 at% of Fe ²⁺ in a coating film, which contains 50 to 600 kg as a binder resin of the coating film. /
a urethane resin having a yield point in the stress range of cm ² ;
The present invention relates to a magnetic recording medium characterized in that at least a phenoxy resin and/or a vinyl chloride copolymer is used. According to the present invention, as the binder resin component of the magnetic layer, a urethane resin having a yield point is used. As shown in the example in b, urethane resin has a yield point YP, and until the yield point YP is reached, the elongation is very small even when stress is applied, and for this reason, the urethane resin is given appropriate hardness. , and yield point YP
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 do not have edges bent, and can retain 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, and is in the stress range of 50 to 600 Kg/cm ² , preferably 100 to 560 Kg/cm ² (approximately 290 Kg/cm ² in the example shown in Figure 1). It is important that there is a yield point at ). If the stress in the range where the yield point exists is less than 50 kg/cm ² , the resin tends to become soft, and if it exceeds 600 kg/cm ² , the resin tends to become hard and brittle. Moreover, according to the present invention, divalent iron (Fe ²⁺ ) is contained as magnetic particles in an amount of 4 to 6 atomic percent (preferably 4.5 to 6 atomic percent).
5.5 atomic%) is used, so
The magnetic powder has a greater hiding power (i.e., light-shielding ability), and therefore 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, the characteristics of audio output fluctuation and RF output are significantly improved. Moreover, within the above content range, the original magnetic properties of trivalent iron (Fe ³⁺ ) are well exhibited. If Fe ²⁺ is less than 4 atomic %, the problems described above (carbon black, etc.) will occur as shown in Figure 2 (however, carbon black is included in the magnetic layer so that the light transmittance is 0.05%). If it exceeds 6 atomic %, the magnetic properties (coercive force, magnetic flux) as shown in Figure 3 will deteriorate. (density, etc.) deteriorates, and RF output, etc. decreases. 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. Further, the bonding position of this cyclic hydrocarbon residue is preferably in the main chain of the urethane resin molecule, but it may be bonded to the side chain thereof. In addition, by changing the amount of components 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 ranges from -30℃ to 100℃. °C, preferably 0 °C to 90 °C. If the Tg is lower than -30°C, the film is too soft and it is difficult to obtain sufficient film strength, and if the Tg is higher than 100°C, the film tends to 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, 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 that already has a cyclic hydrocarbon residue 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) that is a raw material for the polyol. (3) A method using the polyhydric alcohols and dicarboxylic acids of (1) and (2) above as raw materials for polyols. (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 synthesis method for obtaining the above urethane resin, 1,4-di-hydroxymethylcyclohexane

The polyester polyol obtained from [Formula] and adipic acid (HOOC-(CH ₂ ) ₄ -COOH) is converted into methylene-bis-phenyl isocyanate.

An example of this method is to convert it into urethane using [chemical formula]. In this case, the chain extender is the above-mentioned 1,4-di-hydroxymethylcyclohexane or other diols (e.g. 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 having an ethylene glycol structure can be used as described above, but in addition to such a structure, propylene glycol, Glycols such as butylene glycol, diethylene glycol, trimethylolpropane, hexanetriol,
Polyhydric alcohols such as glycerin, trimethylolethane, 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 linoleic acid,
Examples include maleic acid, etc., or those having a cyclic hydrocarbon residue in the molecule. Instead of the above polyols, lactone polyester polyols synthesized from lactams such as s-caprolactam, α-methyl-1-caprolactam, s-methyl-s-caprolactam, and γ-butyrolactam; or ethylene oxide, propylene 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, metaxylylene diisocyanate, etc.
In this way, urethanized polyester polyurethane and polyether polyurethane are synthesized. These urethane resins according to the invention are usually produced primarily by the reaction of polyisocyanates with polyols and also in the form of urethane resins or urethane prepolymers containing free isocyanate groups and/or hydroxyl groups, or by the reaction of these. It may also be in the form of a urethane elastomer, which does not contain any terminal groups. In addition, usable chain extenders include the polyhydric alcohols listed above (which may or may not have a cyclic hydrocarbon residue in the molecule).
That's fine. 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 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.

[C] (However, n82-13) For example, PKHC manufactured by Union Carbide,
There are PKHH, PKHT, etc. In addition, the above-mentioned vinyl chloride copolymers that can be used have the general formula:

[ka] There is something expressed as in this case,

The molar ratio derived from l and m in the formula is 95 to 50 mol % for the former unit and 5 to 50 mol % 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 (l+m) is preferably 100 to 600, and the degree of polymerization is 100 to 600.
If it is less than that, the magnetic layer etc. tends to become sticky,
If it exceeds 600, the dispersibility becomes poor. The vinyl chloride copolymer described above may be partially hydrolyzed. The vinyl chloride copolymer is preferably a copolymer containing vinyl chloride-vinyl acetate (hereinafter 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-
Examples include copolymers of maleic anhydride, and among vinyl chloride-vinyl acetate copolymers, partially hydrolyzed copolymers are preferred. Specific examples of the above vinyl chloride-vinyl acetate copolymer include:
"VAGH" manufactured by Union Carbide,
"VYHH", "VMCH", "Eslec A", "Eslec A-5", "Eslec C" manufactured by Sekisui Chemical Co., Ltd.
"Esuretsuku M", "Denkabinir 1000G", "Denkabinir 1000W" manufactured by Denki Kagaku Kogyo Co., Ltd., 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. 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. Also,
As the cellulose organic acid ester, acetyl cellulose, propionyl cellulose, butyryl 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. As a thermoplastic resin, the softening temperature is 150℃ or less,
Average molecular weight is 10000~200000, degree of polymerization is about 200~
About 2000, for example, acrylic ester.
Acrylonitrile copolymers, acrylic 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 liquid, and after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Moreover, among these resins, those that do not soften or melt before the resin is heated are preferred. Specifically, for example, phenolic 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 above-mentioned layer containing a urethane resin having a cyclic hydrocarbon residue as a binder resin is, for example, a fourth layer.
As shown in the figure, this is a magnetic layer 2 of a support 1. A BC layer 3 is provided on the surface opposite to the magnetic layer 2 (the BC layer may or may not be provided). The magnetic powder used for the magnetic layer 2, especially the ferromagnetic powder, is γ-Fe ₂ O ₃ , Co-containing γ-
Examples include iron oxide magnetic powder such as Fe ₂ O ₃ . In such magnetic powder, based on the present invention,
The content of Fe ²⁺ is 4 to 6 at %, which can be achieved by adjusting the ratio of the amounts of starting materials in a conventional method for producing magnetic powder. 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. It's fine. Furthermore, carbon black may be added. This carbon black is preferably electrically conductive, but a light-shielding material may also be added. Examples of such conductive carbon black include Conductex 975 (specific surface area 250 m ² /g, particle size
24 mμ), Conductex 900 (specific surface area 125 m ² /
g, particle size 27 mμ), Cabot Vulcan XC-72 (specific surface area 254 m ² /g,
(particle size: 30 mμ), Raven 1040, 420, #44 manufactured by Mitsubishi Kasei Corporation, etc. As a light-shielding carbon black, for example, Raven manufactured by Columbia Carbon Co., Ltd.
2000 (specific surface area 190m ² /g, particle size 18mμ), 2100,
1170, 1000, Mitsubishi Kasei Corporation's #100, #75, #40,
#35, #30 etc. can be used. Carbon black is 20-30mμ, preferably 21
It is preferable that the particles have a particle size of ~29 mμ, but it is preferable 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 non-magnetic powders that can also be contained in the BC layer 3 include carbon black, silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, zinc oxide, α-Fe ₂ O ₃ , talc, and kaolin. , calcium sulfate, boron nitride,
Examples include those made of 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 made to have electrical conductivity. Provides antistatic effect. It is advantageous to use carbon black and other non-magnetic powders in combination, since both the effects of improving surface properties (stabilizing runnability) and improving conductivity can be obtained. Further, the magnetic recording medium shown in FIG. 4 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). As the material for the support 1, plastics such as polyethylene terephthalate and polypropylene, metals such as Al and Zn, glass, BN, Si carbide, ceramics such as porcelain and earthenware, etc. are used. In addition, when coating and forming the above magnetic layer and BC layer,
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-isocyanate phenyl) thiophosphite, polymethylene polyphenyl isocyanate, and the like, in addition to the polyfunctional polyisocyanates mentioned above. FIG. 5 shows another magnetic recording medium in which an OC layer 4 is provided on the magnetic layer 2 of the medium in FIG. This OC 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 OC layer 4, the urethane resin used for the magnetic layer 2 described above may be used (preferably in combination with a phenoxy resin and/or a vinyl chloride copolymer). The surface roughness of the OC layer 4 is preferably Ra≦0.01 μm and Rmax≦0.13 μm, especially in relation to color S/N. In this case, the surface roughness of the support 1 is Ra≦
0.01μm, Rmax≦0.13μm, smooth support 1
It is preferable to use FIG. 6 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. EXAMPLES The present invention will be described below with reference to specific examples. After charging the components shown in Table 1 in a ball mill and dispersing them, this magnetic paint was filtered through a 1 μm filter, 5 parts of polyfunctional isocyanate was added, and the mixture was coated on a support to a thickness of 5 μm using a reverse roll coater. It was calendered and slit into 1/2 inch width to make video tapes (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 examples, and "ratio" represents comparative examples.

[Table] The following measurements were performed on the videotapes according to each of the above examples. Chroma S/N: Color video noise meter “Shibasoku
925D/1". Lumi S/N: Same as above RF output: At 4MHz using a VTR deck for RF output measurement
We measured the RF output, and after 100 playbacks, we showed a value that was lower than the original output (unit: dB). Table 2 shows the performance of each example videotape.

[Table] 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 embodiments of the present invention, and the first
The figure is a curve diagram showing the stress-elongation relationship of urethane resin, Figures 2 and 3 are graphs showing changes in characteristics depending on the amount of Fe ²⁺ in magnetic powder, and Figures 4, 5, and 6.
Each figure is an enlarged sectional view of a portion of a magnetic recording medium according to each example. In addition, in the symbols used in the drawings, 2
...Magnetic layer, 3...Back coat layer (BC layer), 4
...It is an overcoat layer (OC layer).

Claims (1)

[Scope of Claims] 1. A magnetic recording medium containing magnetic particles containing 4 to 6 at% Fe ²⁺ in a coating film, which is used as a binder resin in the coating film to a stress range of 50 to 600 Kg/cm ² . A magnetic recording medium comprising at least a urethane resin having a yield point, a phenoxy resin and/or a vinyl chloride copolymer.