JPS61180922A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the title magnetic recording medium capable of obtaining a high output and a high S/N ratio and having excellent heat resistance, durability and traveling stability by using a specified compd. and an aromatic isocyanate and an aliphatic isocyanate as curing agents in the magnetic layer. CONSTITUTION:A compd. expressed by the general formula (I) and an aromatic isocyanate and an aliphatic isocyanate as curing agents are used in a magnetic layer. In the formula, A is a hydroxyl group or a group expressed by -OM (M is an alkali metal) or a group represented by formula (II), and (n) and (m) are 1-30 real numbers. Since the aromatic isocyanate and the aliphatic isocyanate are jointly used, the curing reaction proceeds rapidly, and the advantages of both substances to promote the curing uniformly and fully can be synergistically exhibited. Since any substituents are not introduced into the phenyl group existing in the molecule of the compd. (I), the durability, heat resistance, etc. of the magnetic layer are improved by the compd. while keeping the dispersibility of the compd., and a high output and a high S/N ratio can be obtained.

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, Bassinder resin, etc. onto a support and drying it.

In such magnetic recording media, it is widely practiced to add a polyfunctional isocyanate as a curing agent or crosslinking agent when applying a magnetic paint to a support to form a magnetic layer. For example, Special Publication No. 57-44967, No. 57-56
No. 128 and the like also disclose the addition of polyfunctional isocyanates.

However, simply adding a polyfunctional isocyanate does not sufficiently harden or crosslink the magnetic layer, and may conversely cause deterioration in the strength of the magnetic layer. For example, in systems where curing or crosslinking reactions do not occur effectively, polyfunctional isocyanates act as plasticizers and may prevent the natural hardening of the magnetic layer.

From this point of view, highly reactive aromatic isocyanates are preferably used as polyfunctional isocyanates, but these are also not sufficiently effective.

On the other hand, it is known to use phosphoric acid ester as an additive to the magnetic layer. For example, Tokuko Sho 47-26882
The publication discloses the use of a phosphate ester surfactant as one of the additives. Among phosphoric esters, those well known in the field of magnetic recording media include phosphoric esters of compounds in which ethylene oxide is added to aliphatic alcohols or alkylphenols.
This is often used as a dispersant and is represented by the following formula N.

(However, X is a hydrogen group or a group represented by RO+CHz CH201-, and R is an alkyl group, alkenyl group, or alkylphenyl group.) A magnetic recording medium using a phosphate ester represented by this formula (1) is , for example, in Japanese Patent Application Laid-Open No. 54-21806, Japanese Patent Publication No. 59-21087, Japanese Patent Application Publication No. 15803-1983, and Japanese Patent Publication No. 57-44970.

The present inventor conducted various studies on such known phosphoric acid esters, and as a result, discovered that they had the following problems. That is, in recent years, as the demand for high-density recording has increased and magnetic powder has become finer, the phosphoric acid esters of formula (1) and the like used in conventional magnetic recording media have poor still image durability. It was found that the output and S/N ratio could not be sufficiently improved. That is, especially video formats such as VH3 and Beta formats, higher density 8mm video, high definition video,
For electronic still recording, high-density sheet recording, etc., even if conventional phosphate esters are added to the magnetic layer, only insufficient magnetic recording and reproducing characteristics can be obtained.

C1 Purpose of the Invention The purpose of the present invention is to provide a magnetic material with electromagnetic conversion characteristics (high output, high S/N ratio) that meets the demands for high density, and with excellent heat resistance, durability, running stability, etc. The goal is to provide recording media.

20 Structure of the invention and its effects, that is, the magnetic recording medium according to the invention has a magnetic recording medium in which a compound represented by the following general formula and an aromatic isocyanate and an aliphatic incyanate as a hardening agent are used in the magnetic layer. This relates to recording media.

(However, A is a hydrogen group or a group represented by -ON (M is an alkali metal), or according to the present invention, aromatic isocyanate and aliphatic isocyanate are used together as a curing agent (or crosslinking agent). The former allows the curing reaction to proceed rapidly, while the latter allows the curing to proceed sufficiently and uniformly, synergistically exhibiting the advantages of both.

For this purpose, the proportion of aliphatic isocyanates in the total isocyanates used is less than 50% by weight,
It is more effective to use more than 0.5% by weight.

On the other hand, in the process of arriving at the present invention, the inventors obtained the following new knowledge. Conventional phosphoric acid esters, especially the aromatic phosphoric acid esters of the above-mentioned formula H), are used exclusively as dispersants to improve the dispersibility of magnetic powder. Substitution is introduced to form an alkylphenyl group. Therefore, there has been a strong preconception that the phenyl group has poor dispersibility unless it has a substituent such as an alkyl group. however,
Upon investigation by the present inventor, we found that the above-mentioned dispersibility is determined only by the physical properties of the phosphoric acid ester itself, and that when it is actually added to the magnetic layer, it is not compatible with the various components of the magnetic layer. No consideration has been given to the behavior of phosphate ester molecules in magnetic paints, etc. In this regard, the conventional phosphoric acid esters described above have difficulty in compatibility with other components in the magnetic layer because the substituted alkyl group of the alkylphenyl group present in the molecule causes steric hindrance or moves in a certain manner. It is considered that the durability of the magnetic layer is deteriorated.

On the other hand, the compound of the present invention having the above general formula (hereinafter referred to as the "compound of the present invention") has no substituents introduced into the phenyl group present in the molecule, so the above-mentioned phenomenon occurs. It is possible to improve the durability (especially still durability), heat resistance, etc. of the magnetic layer while sufficiently maintaining its own dispersibility, and to obtain high output and high S/N ratio. In this case, the phenyl group in the molecule has lipophilicity and rigidity (r
igid) and exhibits hydrophobicity, while the ethylene glycol residue in the molecule exhibits hydrophilicity, so by adjusting the ratio of these side groups, appropriate HL B ( Hydrophilic
-Lipophilic-Balance: Hydrophilicity-
lipophilic balance).

In the compound of the present invention, in the above general formula, n and m should be real numbers of 1 to 30 in order to maintain the dispersibility of the magnetic powder in the magnetic layer, and n and m should be real numbers of 2 to 20. In some cases, it becomes a diester, but if this diester and a monoester in which A is a hydroxyl group are used together, a medium with preferable characteristics can be obtained. Of course, the monoester and the diester may be used alone. In addition, -0Na, -OK, etc. may be used as A in the above general formula, but in this case, it is preferable to pre-treat the magnetic powder with the compound of the present invention before adding it to the paint.

Furthermore, 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, and in either case, it may be undesirable as a dispersant for magnetic paints etc. in terms of poor dispersion and stability over time of dispersion. .

The amount of the compound of the present invention added to the magnetic layer has an appropriate range, and is preferably 1 to 10 parts by weight, more preferably 2 to 7 parts by weight, based on 100 parts by weight of the magnetic powder. By adding 1 part by weight or more, the dispersibility, durability, etc. are sufficient and the surface properties of the layer are improved, and by adding 10 parts by weight or less, the viscosity of the paint is sufficient and the film thickness can be controlled. It becomes easy.

Next, the aromatic isocyanate used as the above-mentioned curing agent includes, for example, tolylene diisocyanate (TDI).
, (2,4-TDI, 2.6-TD
I), 2.4-) dimer of lylene diisocyanate,
4,4'-diphenylmethane diisocyanate (MDI
), xylylene diisocyanate (MDI), metaxylylene diisocyanate (MXD■), naphthylene-1
, 5-diisocyanate (ND(), o-tolylene diisocyanate (TODI), and adducts of these isocyanates with active hydrogen compounds, etc., and the average molecular weight thereof is preferably in the range of 100 to 3,000. Specifically, the product names are Sumiseal T80, Sumiseal 44s1 PF, and Sumiseal L1 manufactured by Beyer Urethane Co., Ltd.
Desmodille T65, 15, R1 RF.

Same IL, same SL; Takenate 30 manufactured by Takeda Pharmaceutical Company Limited
0S, 500; Product rNDIJ manufactured by Mitsui Nisso Urethane Co., Ltd.
, rTODI includes Nippon Polyurethane products Desmodur T1oo, Millionate MR1 MT, Coronate L
; Kasei Upjohn product PAP I-135, T
DI 65, 80, 100, Isonate 12
Examples include 5M and 143L.

Preferred aromatic isocyanates are illustrated below.

Examples include adducts of methylene diisocyanate (HMDI), lysine isocyanate, trimethylhexylylene diisocyanate and active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Among the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

Specifically, for example, products Sumidur N and Desmodur Z 4273 manufactured by Bayer Urethane Co., Ltd., Duranate 50M, 24A-100, and 24A manufactured by Asahi Kasei Co., Ltd.
-90CX, Coronate HL manufactured by Nippon Polyurethane Co., Ltd., and TMDI manufactured by Schuls Co., Ltd., etc.

Furthermore, examples of alicyclic isocyanates among aliphatic isocyanates include methylcyclohexane-2,4-
Examples include diisocyanate, 4,4-methylenebis(cyclohexyl isocyanate), isophorone diisocyanate, and adducts of active hydrogen compounds thereof. Specifically, products rrPDIJ and r manufactured by Huls Chemical Co., Ltd.
lPDI-T18990, J-H2921, IPDI-B
1065 etc.

Other polyvalent isocyanates include adducts of diisocyanates and trivalent polyols, pentamers of diisocyanates, and decarbonized compounds of 3 moles of diisocyanates and water. Examples of these include an adduct of 3 moles of tolylene diisocyanate and 1 mole of trimethylolpropane, an adduct of 3 moles of metaxylylene diisocyanate, an adduct of 3 moles of metaxylylene diisocyanate and 1 mole of trimethylolpropane, and an adduct of tolylene diisocyanate and 1 mole of trimethylolpropane. There is a pentamer consisting of 2 moles, and these are easily obtained by engineering.

Preferred aliphatic isocyanates are as follows.

(1) OCN (CH2)6 N COGO Further, specific examples of the compounds of the present invention are as follows,
It is not limited to these.

Exemplary Compound ■ and/or this monophosphoric acid ester Exemplary Compound ■ Exemplary Compound ■ Exemplary Compound ■ Exemplary Compound ■ At least polyurethane can be used as the binder resin of the magnetic layer in the magnetic recording medium of the present invention, but this is a combination of polyol and polyisocyanate. It can be synthesized by the following reaction. Polyols that can be used include phthalic acid,
Dibasic acids such as adipic acid, azelaic acid, trimerized lyluic acid, and maleic acid, glycols such as ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol, or trimethylolpropane, hexanetriol, glycerin, trimethylolethane, Polyester polyol synthesized by reaction with polyhydric alcohols such as pentaerythritol or any two or more polyols selected from these glycols and polyhydric alcohols; or S-cabrolactam, α-methyl - Lactone polyester polyols synthesized from lactams such as -1-caprolactam, S-methyl-3-caprolactam, and T-butyrolactam; or polyether polyols synthesized from ethylene oxide, propylene oxide, butylene oxide, etc. .

These polyols are reacted with isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, metaxylylene diisocyanate, etc., resulting in urethanized polyester polyurethanes, polyether polyurethanes, and polycarbonates carbonated with phosgene or diphenyl carbonate. Polyurethane 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. (for example, in the form of a urethane elastomer).

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=82-13) For example, PK HC manufactured by Union Carbide.

There are PKHH, PKHT, etc.

Moreover, 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 l and m in 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 (1+m) is preferably 100 to 600, and when the degree of polymerization is less than 100, the magnetic layer etc. tend to become sticky.
, 600, the dispersibility deteriorates. The vinyl chloride copolymer described above may be partially hydrolyzed.

As the vinyl chloride copolymer, preferably vinyl chloride-
Examples include copolymers containing vinyl acetate (hereinafter referred to as "vinyl chloride-vinyl acetate copolymers"). 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, l'-VYHHJ, and rVMCHJ manufactured by Union Carbide.
, "S-LEC A" manufactured by Building Block Chemical ■.

In addition to the above, cellulose resins can also be used as binder resins, including cellulose ether,
Cellulose inorganic acid esters, cellulose organic acid esters, etc. can be used. 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.

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.
Furthermore, if the amount of other resins increases, surface properties tend to be poor.

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 has a
The ratio is 85%.

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°C or less, an average molecular weight of 10.000 to 200,000, and a polymerization degree of about 200 to 2,000, such as acrylic ester-acrylonitrile copolymer, acrylic acid Ester-vinylidene chloride copolymers, acrylic ester-styrene copolymers, etc. are used.

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 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 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, carbon black may be further added to the magnetic layer. It is desirable that this carbon black has electrical conductivity, but carbon black with light-shielding properties may also be added. As such conductive carbon black, for example, Conductex 975 (specific surface area 250 m") manufactured by Columbia Carbon Co., Ltd.
/g, particle size 24 mμ), Conductex 900 (specific surface area 125 m” /g, particle size 27 mμ), Cabot Vulcan XC-72
(Specific surface area: 254 m"/g, particle size: 30 mu), Raven 1040.420, #44 manufactured by Mitsubishi Kasei ■, etc. Examples of light-shielding carbon black include Raben 2000 manufactured by Columbia Carbon (specific surface area: 190 m").
/g, particle size 18 mu), 2100.1170.10
00, Mitsubishi Kasei #100, #75, #40, #
35, #30, etc. can be used. Carbon black has an oil absorption of 90mj! (DBP)/100 g or more is desirable because it facilitates formation of a stracture 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 BCC 84 is provided on the surface opposite to the magnetic layer 2. These 80 layers may be provided, but may not be provided. The magnetic powder used for the magnetic layer 2, especially the ferromagnetic powder, is γ-Fez.
o3, CO-containing r F e2cl+ , F ezoa
,, Iron oxide magnetic powder such as CO-containing Fe3O4; Fe,
Ni, Co, Fe-N1-Co alloy, Fe-Mn
-Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni
-Cr alloy, Fe-Co-N1-P alloy, Co-Ni alloy, etc. Fe.

Examples include various ferromagnetic powders such as metal magnetic powders containing Ni, Co, etc. as main components. Among these, Co-containing iron oxide and metal magnetic powder are preferable. Also, the BET value of magnetic powder is 25
m"/g or more, preferably 30 m"/g or more. The magnetic layer 2 also contains lubricants such as silicone oil, graphite, molybdenum disulfide, tungsten disulfide, monobasic fatty acids having 12 to 26 carbon atoms (such as stearic acid), and monobasic fatty acids having 13 to 26 carbon atoms. A fatty acid ester consisting of a monohydric alcohol, an abrasive (for example, fused alumina), an antistatic agent (for example, graphite), etc. may be added.

The non-magnetic powder contained in the 80 layer 3 includes carbon black, silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, zinc oxide,
α-Fe203, talc, kaolin, calcium sulfate,
Composed of nitrogen boron, zinc fluoride, molybdenum dioxide, calcium carbonate, etc., preferably carbon black (
In particular, those made of conductive carbon black) and/or titanium oxide may be mentioned.

Further, as the non-magnetic powder, organic powder such as benzoguanamine resin, melamine resin, 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). Same below). The support may also be subjected to corona discharge treatment. Also,
The 80 layer 3 may also contain the compound according to the present invention.

In addition, the material of the support 1 includes plastics such as polyethylene terephthalate and polypropylene, and AI! ,,
Metals such as Zn, glass, BN, Si carbide, porcelain,
Ceramics such as pottery 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 particularly related to color S/N: Ra≦0.01 μm, Rmax≦0.13. cr
It is better to set it to m. In this case, the surface roughness of the support 1 is R
a≦0.01μmSRmax≦0.13. um and
It is desirable to use a smooth support 1.

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, the following polyfunctional isocyanate 5
The mixture was coated onto a support to a thickness of 5 μm, supercalendered, and each portion was slit to a width of 2 inches to make a videotape (corresponding to each example and comparative number). However, the numbers after No. 2a in Table 1 represent parts by weight, and "actual" after the second column represents examples, and "ratio" represents comparative examples.

(The following is a blank space, continued on the next page) Table 1 The following measurements were performed on the videotapes from each side described above.

Chroma S/N: Color Video Noise Meter
Measured using 925D/IJ.

Lumi S/N: Same as above.

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

(Unit: dB) Jitter value: Using a VTR jitter meter rMK-612AJ manufactured by Meguchi Electronics, 30°C, 180%RH
Each jitter was measured after 0 and 100 runs under high temperature and high humidity conditions.

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.

(Margins below, continued on next page) Table 2 Shi1gu1 "1 gate l" However, for Real-1 and Real-2, the value of ratio -1 is QdB, and chroma S/N, Lumi S/N, The RF output was determined.The smaller the jitter value, the more stable the running.

From the above results, it can be seen that tape performance is significantly improved by configuring the magnetic layer according to the present invention.

[Brief explanation of the drawing]

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----
----111 Magnetic layer 3-1--------Back coat layer (BC layer) 4
-・--------Overcoat layer (OC layer). Agent Patent Attorney Hiroshi Aisaka Figure 1 Figure 2 Figure 3 (Voluntary) Proceedings Ne M Official Book February 1985 β 1, Display of the Case 1988 Patent Application No. 281406 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 7, Subject of amendment (1), “13” on page 23, line 15 of the specification was corrected to “3” Masu. (2), 4th column from the left in Table 1 on page 27 of the same
Add "3" to the 6th line of "Ratio - 1". -That's all-

Claims (1)

[Claims] 1. A magnetic recording medium in which a compound represented by the following general formula and an aromatic isocyanate and an aliphatic isocyanate as a curing agent are used in a magnetic layer. General formula: ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (However, A is a hydroxyl group or a group represented by -OM (M is an alkali metal), or ▲There are mathematical formulas, chemical formulas, tables, etc.▼ A group represented by n, , m is a real number from 1 to 30.)