JPS6252718A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide high output and high S/N ratio and to improve durability by incorporating cobalt-contg. iron oxide magnetic powder of which the specific surface area is >=50m<2>/g BET value, specific phosphate and fatty acid into a magnetic layer and specifying the total content of the phosphate and fatty acid to >=5wt% of the magnetic powder. CONSTITUTION:The cobalt-contg. iron oxide magnetic powder of which the specific surface area is >=50m<2>/g BET value, the phosphate expressed by the formula and the fatty acid are incorporated into the magnetic layer. The total content of the phosphate and fatty acid is specified to >=5wt% of the magnetic powder. The phosphate expressed by the formula satisfactorily disperses even the magnetic powder having >=50m<2>/g BET value and improves the surface characteristic of the magnetic layer, etc. while maintaining the stability of a magnetic coating compd. with age. The deterioration of the thermal and mechanical characteristics is additionally prevented if the ester contains the arom. ring substd. by the residual fatty acid group particularly as R. The durability (still image durability), heat resistance, etc. of the magnetic layer are further improved while the substantial dispersibility is maintained. The high output and high S/N ratio are thus obtd.

Description

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

BACKGROUND OF THE INVENTION Generally, magnetic recording media such as magnetic tapes are manufactured by applying a magnetic paint made of magnetic powder, binder resin, etc. onto a support and drying it.

In such magnetic recording media, the BET value of cobalt-containing magnetic powder used in video tapes and the like is becoming larger and larger due to the demand for higher density media. However, videotapes using magnetic powder with a high BET value of 50rd/g have now appeared, but apart from some improvements in S/N compared to conventional high-quality videotapes, the output is It cannot be said that the performance of powder with a high BET value is fully brought out, as the chroma performance is inferior to that of conventional products. Furthermore, media using magnetic powder with a high BET value have not had sufficient durability.

OBJECT OF THE INVENTION An object of the present invention is to provide a magnetic recording medium that uses Co-containing iron oxide magnetic powder with a high BET value and has high output, high S/N ratio, and durability.

20 Structure of the invention and its effects, that is, the present invention comprises cobalt-containing iron oxide magnetic powder having a specific surface area of 50 d/g or more in BET value, a phosphoric acid ester of the following general formula, and a fatty acid contained in a magnetic layer. and the total amount of the phosphoric acid ester and the fatty acid is 5% of the magnetic powder.
% by weight or more.

General formula: (A, A' is a hydroxyl group, a group represented by -0M (M is an alkaline alkaline earth metal) to form a ring together with a phosphorus atom, or R-0→CH2CHz O uniform "- A and A' may be the same or different. n and m are real numbers of 1.5 or more. R
is a hydrocarbon residue. ) According to the present invention, a phosphoric ester of the above general formula (hereinafter,
Referred to as "ester of the invention". ) allows magnetic powder with a BET value of 50rd/g or more to be dispersed well, while maintaining the stability of the magnetic paint over time, and can improve the surface properties of the magnetic layer, etc. In particular, when this ester contains an aromatic ring substituted with a fatty residue as R, it is possible to further prevent deterioration of the thermal and mechanical properties of the magnetic layer, and the magnetic layer can be formed while maintaining sufficient dispersibility. It is possible to further improve durability (still image stability), heat resistance, etc., and obtain high output and high S/N ratio.

Regarding the ester of the present invention, n and m in the above general formula should be 1.5 or more, preferably 2 to 80, so that the effects of the present invention can be fully exhibited.

Further, R may be a hydrocarbon residue having a total number of carbon atoms of 4 to 30, but it is preferable to include an aromatic ring. Preferred are phenyl groups introduced into an aromatic ring, unsubstituted phenyl groups, and phenyl groups substituted with an alkyl group having 1 to 9 carbon atoms. It is desirable that the total number of carbon atoms in the hydrocarbon residue be 4 or more to improve compatibility with the binder and prevent movement in the layer, and 30 or less is preferable for magnetic paints, etc. This is because it is desirable in terms of preventing poor dispersion and maintaining appropriate hydrophilicity of phosphoric acid residues. In this case, R is a hydrocarbon residue and exhibits lipophilicity, and the ethylene oxide residue (÷CHz CHt O+) exhibits hydrophilicity, so the ratio of these two groups (especially the types of n and R) By adjusting the appropriate HL B (Hydrop
hilic-L 1pophilic-Ba1anc
e hydrophilicity-lipophilicity balance).

In the ester of the present invention, A in the above general formula is R-0-
When ←CHt cH,O, it becomes a diester, but when used in combination with a monoester in which A is a hydroxyl group, a medium with preferable characteristics can be obtained. Of course,
Monoesters and diesters may be used alone. Furthermore, -0Na, -OK, barium salt, etc. may be used as A and/or A' in the above general formula. Alternatively, the magnetic powder can be pretreated with the ester of the present invention and then added to the paint.

In addition, in the compound of the present invention, n%m in the above general formula
By selecting HLB of the compound from 8 to 1
It is desirable to set it to 4. That is, if the HLB is smaller than 8, the lipophilic property becomes strong, and if the HLB is larger than 14, the hydrophilic property becomes strong (in either case, it may be undesirable as a dispersant for magnetic paints, etc. in terms of poor dispersion or dispersion stability over time). be.

The amount of the ester of the present invention added to the magnetic layer has an appropriate range. That is, the total amount of the fatty acid (lubricant) used in combination should be 5% by weight or more based on 100 parts by weight of the magnetic powder. By setting the total addition amount to 5% by weight or more, the dispersibility, lubricity, durability, etc. can be made sufficient, and the surface properties of the layer can be improved. If the amount is 20% or less, the viscosity of the paint will be sufficient and the film thickness will be easily controlled.

In addition, the blending ratio of the phosphoric acid ester and fatty acid is as follows by weight: phosphoric acid ester: fatty acid - (1:0.01) to (1:
100 is desirable. Outside this range, if the amount of phosphoric acid ester increases, it may be difficult to obtain a good S/N ratio, and if the amount of phosphoric acid ester decreases, the effect on durability may become insufficient.

Specific examples of esters of the present invention include, but are not limited to, the synthesis methods of these compounds may be as follows, i.e. compounds with terminal OH, e.g. Polyoxyethylenized phenyl ether and After producing an alkylphenyl ether or an alkyl ether, this is reacted with phosphorus pentoxide or phosphorus oxychloride to obtain the phosphoric acid ester of the present invention.

Exemplary compound ■ Exemplary compound ■ Exemplary compound ■ Exemplary compound ■ Exemplary compound■ Exemplary compound■ Exemplary compound■ Exemplary compound [phase] Exemplary compound ■ Exemplary compound O Exemplary compound 0 Exemplary compound 0 Exemplary compound■ In the above, A is -OH or R-0→cH, cHt may be O elliptical.

That is, for example, in exemplified compound (■), and mixtures of monoesters and diesters.

Moreover, -OH may be an alkali metal salt such as 10Na or -OK, or may be an alkaline earth metal salt such as.

The esters of the present invention may of course be used in combination with other dispersants such as lecithin. Further, the layer containing the ester of the present invention may be not only the magnetic layer but also a back coat layer and an overcoat layer. In the case of a magnetic layer, the compound of the present invention may be added at the time of preparing the magnetic paint, or it may be applied to the surface of the magnetic powder in advance by dipping, etc., and the surface-treated magnetic powder may be added to the paint. It's okay.

Furthermore, the compound of Exemplary Compound (1), when used as a dispersant in the magnetic layer, showed the unexpected advantage of significantly improving the adhesion of the magnetic layer to the support (eg, polyester base).

Examples of fatty acids used in the present invention are as follows.

(1) Caproic acid (2) Caprylic acid (3) Capric acid (4) Lauric acid (5) Myristic acid (6) Valmitic acid (7) Stearic acid (8) Isostearic acid (9) Rilunic acid (10) Linoleic acid (11) Oleic acid (12) Elaidic acid (13) Behenic acid (14) Malonic acid (15) Succinic acid (16) Maleic acid (17) Glutaric acid (18) Adipic acid (19) Pimelic acid (20) Azelaic acid In the magnetic recording medium of the present invention, at least polyurethane can be used as the binder resin for the magnetic layer, which can be synthesized by reacting polyol and polyisocyanate. Usable polyols include organic dibasic acids such as phthalic acid, adipic acid, azelaic acid, dimerized sulfuric acid, and maleic acid, and glycols such as ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol, or trimethylolpropane. , polyester polyols synthesized by reaction with polyhydric alcohols such as hexanetriol, glycerin, trimethylolethane, and pentaerythritol, or any two or more polyols selected from these glycols and polyhydric alcohols. or lactone polyester polyols synthesized from lactams such as S-caprolactam, α-methyl-1-caprolactam, and γ-butyrolactam; or polyether polyols synthesized from ethylene oxide, propylene oxide, butylene oxide, etc. Can be mentioned.

These polyols are reacted with isocyanate compounds such as tolylene diisocyanate, hexamelene diisocyanate, methylene diisocyanate, metaxylylene diisocyanate, etc., and thereby urethanized polyester polyurethane, polyether polyunitane, phosgene, and prime numbers 2 to 6. A polycarbonate polyurethane carbonated with an alkylene carbonate represented by an alkylene group) is synthesized.

These polyurethanes are usually produced primarily by the reaction of polyisocyanates with polyols and are also in the form of urethane resins or urethane prepolymers containing free isocyanate groups and/or hydroxyl groups, or containing reactive end groups of these. It may also be in the form of a urethane elastomer, for example.

Since the methods for producing polyurethane, urethane prepolymers, urethane elastomers, curing and crosslinking methods, etc. are well known, detailed explanation thereof will be omitted.

In addition, in the present invention, if a phenoxy resin and/or a vinyl chloride copolymer is contained in addition to the above-mentioned polyurethane as a binder 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.

(However, n 82 to 13 each) 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 general formula: In this case, the molar ratio derived from l and m in is 95-50 mol% for the former unit and 5-50 mol% 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, etc.
The degree of polymerization expressed as +m) is preferably from 100 to 6
When the degree of polymerization is less than 100, the magnetic layer etc. tend to become sticky, and when it exceeds 600, the dispersibility becomes poor. The vinyl chloride copolymer described above may be partially hydrolyzed. The vinyl chloride copolymer is preferably a vinyl chloride-vinyl acetate copolymer (hereinafter referred to as
It is called "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, and vinyl chloride-vinyl acetate copolymers. Among these, partially hydrolyzed copolymers are preferred. Specific examples of the above-mentioned vinyl chloride-vinyl acetate copolymers include rVAGHJ, rVYHHJ, and "
vMCH", "S-LEC A", "S-LEC A-5", "S-LEC C", "S-LEC M" manufactured by Building Block Chemical ■,
"Denkabinir 100OGJ" and "Denkabinir 100OWJ" manufactured by Denki Kagaku Kogyo ■ can be used.

In addition to the above, cellulose resins can be used as binder resins, such as cellulose ethers, cellulose inorganic acid esters, cellulose organic acid esters, and the like. As cellulose ethyl, 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.

In addition, 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 90/1 by weight.
Desirably 0 to 40/60, 85/15 to 45
155 has been found to be even more desirable. If the amount of urethane resin is outside this range, dispersion tends to be poor.
Also, if there is a large amount of other resins, the surface quality will likely be poor,
In particular, if it exceeds 60% by weight, the physical properties of the coating film become less favorable 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.

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 degree of polymerization of about 200 to 2,000, such as acrylic acid ester-acrylonitrile copolymer, acrylic Acid ester - vinylidene chloride copolymer, acrylic ester -
Styrene copolymers and the like 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 thermally decomposed are preferable. Specifically, for example, phenol resin, epoxy resin, urea resin, melamine resin, alkyd resin, etc. are used.

Examples of electron beam irradiation-curable resins include unsaturated prepolymers,
Examples include maleic anhydride type, urethane acrylic type, and polyester acrylic type.

In the magnetic recording medium of the present invention, a carbon blank may be further added to the magnetic layer. This carbon black preferably has tetraelectricity, but carbon black with light-shielding properties may also be added. Examples of such conductive carbon black include Conductefx (manufactured by Columbia Carbon Co., Ltd.).
Conductex) 975 (specific surface area 250 i/g
, particle size 24 mμ), Conductex 900 (specific surface area 125 n (/g, particle size 27 mμ), Cabot Vulcan XC-72 (specific surface area 254 m2/g, particle size 30 mμ), Raven 10
40.420, #44 manufactured by Mitsubishi Kasei ■, etc. As a light-shielding carbon blank, for example, Raben 2000 manufactured by Columbia Carbon Co., Ltd. (specific surface area 190 rrr/g
, particle size 18m μ), 2100.1170.1000
, #100, #75, #40, #35 manufactured by Mitsubishi Kasei ■
, #30, etc. can be used. The carbon blank has an oil absorption capacity of 90ml! (DBP), / 100 g or more is desirable because it tends to form a struttle structure and exhibits higher conductivity.

The magnetic recording medium of the present invention has, for example, as shown in FIG.
A magnetic layer 2 is provided on a support 1.

Further, a BC layer 3 is provided on the opposite side of the magnetic layer 2. Although this BC layer may be provided, it is not necessary to provide it. Examples of the magnetic powder used in the magnetic layer 2 include iron oxide magnetic powders such as Ca-containing γ-F'3z Ch and Go-containing Fe, O, and the like.

The magnetic layer 2 also contains a lubricant (e.g. silicone oil,
Graphite, molybdenum disulfide, tungsten disulfide, organic carboxylic acid with a melting point of 85°C or less, organic carboxylic acid (
(e.g. stearic acid) and a fatty acid ester consisting of a monohydric alcohol having 1 to 26 carbon atoms), an abrasive (e.g. α-alumina), an antistatic agent (e.g. graphite or a surfactant), etc. good.

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-Fe, O, talc, kaolin, calcium sulfate,
Examples include those made of nitrogen boron, zinc fluoride, molybdenum dioxide, calcium carbonate, etc., preferably carbon black and/or titanium oxide.

Further, as the non-magnetic powder, organic powder such as benzoguanamine resin, melamine resin 1, phthalocyanine pigment, etc. may be added.

Further, the magnetic recording medium shown in FIG. 1 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). The same applies below), the support may be subjected to corona discharge treatment, and
The 80 layer 3 may also contain the compound according to the present invention.

The material of the support body 1 may be plastics such as polyethylene terephthalate or polypropylene, A1. ,Z
Metals such as n, glass, BN, St carbide, ceramics such as porcelain, earthenware, etc. are used.

Incidentally, when forming the magnetic layer by coating, a predetermined amount of polyfunctional isocyanate as a crosslinking agent is added to the coating material.

FIG. 2 shows other magnetic recording media.
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 is used (preferably in combination with a phenoxy resin and/or a vinyl chloride copolymer). The surface roughness of the 00 layer 4 is Ra: 50, especially in relation to the color S/N. OLcrm, Rmax≦0.13μm
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. 3 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.
Layers 4 are provided, and the 00 layer 4 may contain a binder resin containing the above-mentioned urethane resin as a main component.

E, Example Hereinafter, the present invention will be explained 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.

After dispersing the ingredients shown in Table 1, apply 1μ of this magnetic paint.
After filtration with M filter, 5 parts of polyfunctional isocyanate was added, coated on a support to a thickness of 5 μm, supercalendered, 1 part was sifted to a width of 2 inches, and a videotape (corresponding to each example and comparative number) ). however,
The numbers after the second column in Table 1 represent parts by weight, and
After the column, "actual" indicates an example, and "ratio" indicates a comparative example.

(The following margins are continued on the next page.) This compound is polyoxyethylene-tert- which is obtained by reacting tert-butylphenol with ethylene oxide in an autoclave under pressure in the presence of KOH at 110 to 150°C. It is a viscous pale yellowish brown liquid obtained by reacting butyl phenyl ether with phosphorus pentoxide, and its pH is 1.5 as a 10% aqueous solution (25°C).

*2) *3) The following measurements were performed on the videotapes according to each of the above columns.

Chroma S/N: Color video noise meter r S h 1basok
Measured by u925D/IJ.

Lumi S/N: Same as above.

RF output A small RF output at 4 MHz was measured using a VTR deck for measuring RF output, and after 100 playbacks, a value that was lower than the initial output was shown.

(Unit: dB) Still image lifespan: Shows the time in minutes for a still image to degrade by 2 dB.

The larger the value, the higher the durability and wear resistance of the magnetic recording medium.

The performance of each example videotape is shown in Table 2.

Table 2 However, for Actual 1 and Actual 2, the chroma S/N, Lumi S/N, and RF output were determined using the value of ratio -1 as OdB.

The above results show that the tape performance is significantly improved by configuring the magnetic layer according to the present invention.

[Brief explanation of drawings]

The drawings illustrate embodiments of the invention, and FIGS. 1, 2, and 3 are enlarged cross-sectional views of a portion of a magnetic recording medium from each side. In addition, in the symbols used in the drawings, 2...
Magnetic layer 3... Back coat layer (BC layer) 4... Overcoat I'1i (QC layer).

Claims (1)

[Claims] 1. A magnetic layer contains cobalt-containing iron oxide magnetic powder having a specific surface area of 50 m^2/g or more in BET value, a phosphoric acid ester of the following general formula, and a fatty acid, and The total amount of the phosphoric acid ester and the fatty acid is 5% by weight of the magnetic powder.
A magnetic recording medium that is the above. General formula: ▲There are mathematical formulas, chemical formulas, tables, etc.▼ {However, A and A' are hydroxyl groups, -OM (M is an alkali metal)
There is a group represented by ▲, a mathematical formula, a chemical formula, a table, etc. ▼ (M' is an alkaline earth metal), a group that forms a ring with a phosphorus atom, or R-O-(CH_2CH_2O)- It is a group represented by _m, and A and A' may be the same or different. n and m are real numbers of 1.5 or more. R
is a hydrocarbon residue. }