JPS619827A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the titled recording medium having proper flexibility, sufficient mechanical strength, durability, and resistance to abrasion, excellent traveling property and surface property and with less release of powder and dropouts by incorporating a urethane resin having a yield point and aromatic isocyanate and aliphatic isocyanate as a hardener into the specific layer on a supporting body. CONSTITUTION:A urethane resin having a yield point of used as the component of a resinous binder of a magnetic layer, etc. The elongation of the resin when stressed is extremely small below the yield point, and the resin elongates without being broken above the yield point. The yield point important to the performance of the urethane resin is in the stress range 50-600kg/cm<2>, or preferably 100-560kg/cm<2>. The resin is easy to soften at <50kg/cm<2> stress, and the resin hardens and is fragile at >600kg/cm<2>. Since both aromatic isocyanate and aliphatic isocyanate are incorporated into the layer as a hardener, high durability and resistance to abrasion and excellent surface property and traveling property can be sufficiently prevented.

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 polymeric diols include polyester diols obtained from adipic acid, butanediol, etc., polyether diols, and polycarbonate diols, and diphenylmethane diisocyanate and the like can be used as diisocyanates. 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, resulting in poor mechanical strength of magnetic recording media against sliding contact with guide pins, magnetic heads, etc. Moreover, there are problems in terms of runnability and powder shedding.

In addition, ferromagnetic powder is generally used as magnetic powder,
Since it has a large magnetic moment, interactions between particles tend to occur, resulting in particle aggregation and dispersion uniformly in the binder resin. As a result, the magnetic recording medium obtained is not only significantly inferior in magnetic properties such as squareness ratio, but also inferior in properties such as surface properties, runnability, and abrasion resistance. out, etc., resulting in a decrease in playback output and still characteristics.

For the purpose of eliminating such drawbacks,
No. 67 proposes the use of a magnetic paint containing polyvinyl butyral resin and a polyfunctional isocyanate compound as a binder component of magnetic powder. Also, ■,
In Japanese Patent Publication No. 57-56128, the binder resin for the magnetic layer has a molecular weight distribution of 1.80 to 2.40.
It is proposed that the main components be a vinyl chloride-vinyl acetate-vinyl alcohol copolymer and a urethane polymer, to which a low molecular weight polyisocyanate is added.

However, the dispersibility of the magnetic paint obtained by the above-mentioned known techniques (1) and (2) is not necessarily sufficient;
Since the viscosity of the paint is high and the durability and abrasion resistance of the paint film (magnetic layer) are low, it is not possible to reduce the occurrence of head clogging and dropouts due to falling powder.

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, durability, and abrasion resistance, has excellent runnability and surface properties, and has little dust or dropout. Our goal is to provide the following. Rei 4. Structure of the invention and its effects, that is, the magnetic recording medium according to the invention contains a urethane resin having a yield point and an aromatic isocyanate and an aliphatic isocyanate as a curing agent in a predetermined layer on a support. It is characterized by the fact that

According to the present invention, a urethane resin having a yield point is used as the binder resin component of the magnetic layer, etc., but this urethane resin has characteristics that are different from those of the conventional urethane resin shown by curve a in FIG. As shown in the example of the curve, this is a urethane resin that has a yield point YP, and until the yield point YP is reached, the elongation is very small even when stress is applied, and this gives the urethane resin appropriate hardness. and yield point y
After p, it shows the property of elongating with stress without breaking. Therefore, the mechanical strength of the magnetic recording medium is improved, damage such as abrasion during sliding contact, powder falling, etc. are significantly reduced, and running properties are also significantly improved. In particular, magnetic tapes for VTRs have no edge bending, and can maintain control tracks near the edges to perform their functions well. The above yield point YP is important for the performance of the urethane resin of the present invention, and is 4 to 50 to 600.
It is desirable that the yield point exists in the stress range of 7cs4s, preferably from 100 to 560 kp/- (approximately 290 kf/a/l in the example of FIG. 1). If the stress within the range where the yield point exists is less than 50 kf/cJ, the resin tends to become soft, and if it exceeds 600 kp/-, the resin tends to become hard and brittle.

In order to exhibit the above-mentioned excellent performance, the urethane resin used in the present invention preferably has a cyclic hydrocarbon residue in its 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 herogen-substituted chlorine atom, etc.). These saturated cyclic hydrocarbon residues are desirable from the viewpoint of imparting appropriate hardness to the urethane resin and availability of raw materials. In addition, the bonding position of this cyclic hydrocarbon residue is
It is preferable that it be in the main chain of the urethane resin molecule, but it may also be bonded to its side chain.

In addition, by changing the amount of the constituent components such as cyclic hydrocarbon residues in the urethane resin, it is possible to obtain a urethane resin having an arbitrary glass transition point (T1), and T2 is between -30°C and 100°C. °C, preferably 0 °C to 90 °C. If Tf is lower than -(9)°C, the film is too soft to obtain sufficient film strength.If Tt is higher than 100°C, the film tends to become brittle.

In addition, according to the present invention, since both aromatic isocyanate and aliphatic isocyanate are contained as hardening agents in the layer, durability and abrasion resistance are high, surface properties and runnability are excellent, and powder removal is prevented. , dropout, etc. can be sufficiently prevented. That is, aromatic isocyanates and aliphatic isocyanates (which may be cycloaliphatic isocyanates) are not only compatible with each other, but also have the property of reacting with a paint containing a binder component and curing it appropriately. The reaction of aromatic isocyanates in the paint is fast-acting, but the reaction of aliphatic isocyanates is slow-acting.
When both are mixed in an appropriate ratio and added to the paint,
A layer with appropriate hardness, no stickiness, and good surface properties can be formed.

For example, the running stability and recording and reproducing performance of the medium are improved. Moreover, if only aromatic isocyanate is used,
Curing by itself is too fast and tends to harden unevenly, and the solvent used during synthesis may also mix into the paint, so the presence of this solvent limits the type of solvent that should originally be added to the paint. receive. However, by using an aliphatic isocyanate together with an aromatic isocyanate, the amount of the former can be relatively reduced and the above-mentioned problems can be alleviated, and at the same time, the latter can cause sufficient and uniform curing.

Further, urethane resins having the above-mentioned yield point especially have cyclic hydrocarbon residues in their molecules and are harder than ordinary urethane resins, and therefore tend to have weak molecular motion and slow curing. However, by using both of the above isocyanates in combination, the urethane resin will be cured sufficiently and at an appropriate speed.

The urethane resin used in the present invention can be synthesized by reacting a polyol and a polyisocyanate. At this time, in order to introduce the above-mentioned cyclic hydrocarbon residue, the following (1) to
Method (4) can be adopted.

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

(2) A method of using a dicarboxylic acid having a cyclic hydrocarbon residue in advance as an organic dibasic acid (dicarboxylic acid) which is a raw material for the polyol.

(3) A method in which the polyhydric alcohol and dicarboxylic acid of (1) and (2) above are used as raw materials for polyol.

(4) A method of using a polyhydric alcohol having a cyclic hydrocarbon residue in advance as a chain extender, in combination with any of the above (1) to (3), or alone.

For example, as a synthesis method for obtaining the above urethane resin, 1,
4-di-hydroxymethylcyclohexane (HO) I,
C3C1 (,OH) and adipic acid (HOOC-(CH,
) 4-COOH) and a method of converting methylene-bis-phenylisocyanate into a polyester polyol obtained from 4-COOH). In this case, the chain extender can be the above-mentioned 1,4-di-hydroxymethylcyclohexane or other diols (for example butane-1,4-diol).

The above-mentioned polyhydric alcohol which may have a cyclic hydrocarbon residue in advance can be one having an ethylene glycol structure (=cyclohexyl group) in the molecular chain as described above, but in addition to such a structure, propylene glycol, Glycols such as butylene glycol, diethylene glycol, polyhydric alcohols such as trimethylolpropane, hexanetriol, glycerin, trimethylolethane, pentaerythritol, or these glycols, or those having cyclic hydrocarbon residues in their structure In addition, dibasic acids that can be used include phthalic acid, trimerized lyluic acid, maleic acid, etc., or those having cyclic hydrocarbon residues in their molecules.In place of the above polyol, S - caprolactam,
Lactone polyester polyols synthesized from lactams such as α-methyl-1-caprolactam, 8-methyl-8-caprolactam, and r-butyrolactam; or polyether polyols synthesized from ethylene oxide, propylene oxide, butylene oxide, etc. may also be used.

These polyols are reacted with isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, and metaxylylene diisocyanate, thereby synthesizing urethanized polyester polyurethane and polyether polyurethane. Urethane resins are usually produced primarily by the reaction of polyisocyanates and polyols, and are also produced in the form of urethane resins or polyurethane prepolymers containing free isocyanate groups and/or hydroxyl groups, or with reactive end groups of these. It may also be in the form of a urethane elastomer (for example, in the form of a urethane elastomer).

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

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 phenoxy resin and/or vinyl chloride copolymer is used, the layer will be too hard;
This can be prevented by containing polyurethane, resulting in good adhesion to the support or base layer.

The usable phenoquine resin is a polymer obtained by polymerizing bisphenol A and epichlorohydrin, and is expressed by the following general formula.

(However, n82-13) For example, PKHC manufactured by Union Carbide.

, 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 t 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 member selected from the group consisting of vinyl acetate, vinyl alcohol, maleic anhydride, and the like.
The degree of polymerization expressed as (t+m) is preferably 10
If the polymerization degree is less than 100, the magnetic layer etc. tend to become sticky, and if it exceeds 600, the dispersibility becomes poor. The above vinyl chloride copolymer 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-maleic anhydride copolymers, etc. Among the copolymers, partially hydrolyzed copolymers are preferred. Specific examples of the vinyl chloride-vinyl acetate copolymers include rVAGHJ and rVAGHJ manufactured by Union Carbide.
VYHHJ, rVMcHJ, “S-LEC A”, “S-LEC A-5”, “S-LEC C”, “
"S-LEC M", "Denkabinir 1" manufactured by Denki Kagaku Kogyo ■
000 G J, "Denkabinir 1000W", 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.

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 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 and an average molecular weight of 10,000 to 200. The polymer has a degree of polymerization of about 200 to 2,000, such as acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, etc.

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 the electron beam irradiation-curable resin include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, and polyester acrylic type.

Aromatic isocyanates used in the present invention are, for example, thorine diisocyanate (TDI), 4,4'-diphenylmethane diisonanate (MDI), xylylene diisocyanate (XDI), methaquine lylene diisocyanate (XDI), ) (MXDI), and adducts of these isocyanates with active hydrogen compounds, etc., and those having an average molecular weight of 100 to 3,000 are suitable. Specifically, Sumitomo Bayer Urethane ■ product name Sumigier T80, 44S1 PF1 L1
Desmodille T65, 15, R1 RF, IL
, Same SL: Takenate aoos, a product manufactured by Takeda Pharmaceutical Co., Ltd.
Same 500: Mitsui Nisso Urethane Co., Ltd. products rNDIJ, rT
ODIJ: Desmosier T manufactured by Nippon Polyurethane Co., Ltd.
100, Millionate MR, Same MT, Coronate L
: Kasei Upjohn product PAPI-135, TDI
65, 80, 100, Isonate 125M, 14
Examples include 3L.

On the other hand, examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDI), lysine isocyanate, and trimethylhexamethylene diisocyanate (TMD).
I) and adducts of these isocyanates and active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those with a molecular weight of 100 are preferred.
~3,000. Among the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

Specifically, for example, Sumidur N1 Desmodur Z4273 manufactured by Sumitomo Bayer Urethane Co., Ltd., Durane 50M, 24A-100, and 24 manufactured by Mukasei Co., Ltd.
A-90CX, product corone manufactured by Nippon Polyurethane Co., Ltd.
)HL, TMDI manufactured by Heels, etc.

Among the aliphatic isocyanates, examples of alicyclic isocyanates include methylcyclohexane-2,4-
Diisocyanate 4.4'-methylenebis(cyclohexyl isocyanate) Isophorone diisocyanate and its adduct of an active hydrogen compound can be mentioned. Specifically, the product "rIPD" manufactured by Hiels Kagaku Co., Ltd., IPDI-T18
90, H2921, B1065, etc.

In the magnetic recording medium of the present invention, for example, a magnetic coating material is prepared by mixing and dispersing magnetic powder, a binder resin, and various additives with an organic solvent, and after adding the above-mentioned aromatic isocyanate and aliphatic isocyanate, this is applied to a support ( For example, it is coated onto a polyester film and dried if necessary.

Isocyanates (both aromatic isocyanates and aliphatic isocyanates are simply referred to as isocyanates.

) is added in an amount of 1 to 100% by weight based on the binder resin.
Add. If it is less than 1% by weight, the hardening of the magnetic layer tends to be insufficient, and if it is more than 100% by weight, even if the magnetic layer is hardened, it tends to become "sticky". In order to obtain a more preferable magnetic layer, the amount of isocyanate added is preferably 5 to 40% by weight based on the binder.

Further, the proportion of aromatic isocyanate in the isocyanate [weight of aromatic isocyanate/(weight of aromatic isocyanate + weight of aliphatic isocyanate)] is preferably 20 to 80%. That is, as shown in FIG. 2, if the aromatic isocyanate content is less than 20%, the curing reaction may be too slow, and if it is more than 80%, the curing reaction may be too fast. In either case, the surface condition of the magnetic layer may become unfavorable (“stickiness”).
It may be easy to clean or the surface may become rough. ) For example, the small RF output of the magnetic recording medium may be reduced.

The above-mentioned layer containing a urethane resin having a cyclic hydrocarbon residue is, for example, as shown in FIG.
It is. An 80 layer 3 is provided on the opposite side of 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, includes r-Fe203, Co-containing 1-F
Iron oxide magnetic powder such as elOl, Fe3O4, Co-containing Fa304; Fe, Ni, Co.

Fe-Ni-Co alloy, Fe-Mn-Zn 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, and the like.

In addition, the magnetic layer 2 may contain other known lubricants (for example, palmitic acid) and other known dispersants (for example, powdered lecithin).
, an antistatic agent (eg, graphite), etc. may be added. Abrasives that can be added include α-ht, o, (corundum), artificial corundum, fused alumina, silicon carbide, chromium oxide, diamond, artificial diamond, garnet, emery (main components: corundum and magnetite), etc. be done. These abrasives have an average particle size of 0.05~
A size of 5μ is used, particularly preferably a size of 0.
It is 1 to 2μ. These abrasives are added in an amount of 1 to 20 parts by weight per 100 parts by weight of the magnetic powder.

Furthermore, carbon black may be added. It is desirable that this carbon black has electrical conductivity, but carbon black with light-shielding properties may also be added. Examples of such conductive carbon black include Conductex 975 (specific surface area zso-/g, particle size 24#1μ) manufactured by Columbia Carbon Co., Ltd., and Conductex 975 manufactured by Columbia Carbon Co., Ltd.
00 (specific surface area 125 i/g, particle size 27 sμ), Cabot Vulcan
XC-72 (specific surface area zs4W?/g, particle size 30m1
μ), Raven 1040.420, + manufactured by Mitsubishi Kasei ■,
There is a 44th mag. Examples of light-shielding carbon black include Laben 2000 (specific surface area 190W?/g, particle size 18 μm) and 2100.1 manufactured by Columbia Carbon Co., Ltd.
170.1000, Mitsubishi Kasei ■≠100.41=
75.41-40, $35, ≠30, etc. can be used. Carbon black is 20 to 39 sμ, preferably 2
It is preferable that the particles have a particle size of 1 to 29 layers μ, but it is preferable that the oil absorption amount is 9o-(DBp)/loo or more because it is easy to form a struttered structure and exhibits higher conductivity.

Note that the 80 layer 3 may contain the urethane resin described above and both of the above isocyanates. 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-Fs203, talc, kaolin, calcium sulfate, boron nitride, 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 the surface properties, and in the case of carbon black, it can also impart conductivity to the BC layer. Provides antistatic effect. It is advantageous to use carbon black and other non-magnetic powders in combination, as it can improve surface properties (stabilize runnability) and improve conductivity.

Further, the magnetic recording medium shown in FIG. 3 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. (Same below).

In addition, the material of the support 1 includes plastics such as polyethylene terephthalate and polypropylene, At, and Z.
Metals such as n, glass, BN, Si carbide, porcelain,
Ceramics such as pottery are used.

Figure 4 shows another magnetic recording medium.
A 00 layer 4 is provided on the magnetic layer 2 of the illustrated medium.

This 00 layer 4 is provided to protect the magnetic layer 2 from damage, etc., and for this purpose, it needs to have sufficient slipperiness. Therefore, as the binder resin for the 00 layer 4, the urethane resin used for the magnetic layer 2 described above may be used (preferably in combination with a phenoquine resin and/or a vinyl chloride copolymer), and both of the isocyanates described above may be used. May be included.

The surface roughness of the 00 layer 4 is Ra, especially in relation to the color S/N.
It is preferable that ≦0.01 μs and Rmax≦0.13, 11111. In this case, the surface roughness of the support 1 is Ra≦
It is desirable to set Q, Ql, 4s, Rmax≦0.13#lI, and to use a smooth support 1.

FIG. 5 shows a magnetic recording medium configured as a magnetic disk, in which magnetic layers 2.0 as described above are coated on both sides of a support 1.
A layer 4 is provided respectively.

5. Examples Hereinafter, the present invention will be explained with reference to specific examples.

After charging the components shown in Table 1 into a ball mill and dispersing them, the magnetic paint was filtered through a 1 μm filter, the polyfunctional isocyanate shown in Table 1 was added, and a 5 μm thickness was coated on the support using a reverse roll coater. The film was coated on a film, supercalendered, slit to a pseudo-inch width, and videotape (in each Example and Comparative Example, ``Actual'' indicates the Example, and ``Ratio'' indicates the Comparative Example).

Table 1 The following measurements were performed on the videotapes from each of the above sides.

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).

Skinny value: A parameter that represents the size of the timing deviation during image playback. After 100 playbacks, the amount of deviation from the reference signal (a signal that scans the CRT screen at approximately 64 μBee) is measured, and the value is calculated. The smaller the difference, the smaller the deviation and the less disturbed the image.

Jitter value: Using a VTR jitter meter rMK-612AJ manufactured by Meguchi Electronics Co., Ltd., each jitter was measured after 0 and 100 runs at 30° C. and 80% RH under high temperature and humidity.

Table 2 shows the performance of each example videotape.

Table 2 However, the audio output fluctuation after 100 passes of low RF output of ratio -1 was measured with actual -1 as OdB.

The audio output fluctuation after 100 passes of the low RF output of -2 was measured with the actual -2 as OdB.

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

[Brief explanation of drawings]

The drawings show examples of the present invention, in which Fig. 1 is a curve diagram showing the relationship between the stress elongation rate of urethane resin, and Fig. 2 is a graph showing the change in paint viscosity depending on the blending amount of both isocyanates. FIGS. 3, 4, and 5 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・・・・・・・・・Paraco) 1m (BCJi)
4・・・・・・・・・Overcoat l1G (OCI
It is. Weight part: 11t4V Tour 72rD71% 41wanate Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. A magnetic recording medium characterized in that a urethane resin having a yield point and an aromatic isocyanate and an aliphatic isocyanate as a curing agent are contained in a predetermined layer on a support.