JPH02199625A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve dispersibility of magnetic powder and traveling durability of the medium by using such polyurethane for the binder resin of the magnetic layer that contains a specific polyether component as a part of the main chain thereof and incorporating the specific amt. of silicon into the magnetic powder. CONSTITUTION:At least either silicon or aluminum is incorporated into the magnetic powder and the total amt. of silicon and aluminum in the magnetic powder is specified to >=0.002wt.%. The binder resin contains the polyurethane having a structural unit expressed by formula I as a part of the main chain thereof. In the formula I, R represents an alkyl group and (m) and (n) are 1 or 2. By this method, dispersibility of the magnetic powder becomes excellent and the binder resin has good physical properties. Thus, the obtd. medium is excellent in both of electromagnetic conversion characteristics and traveling durability.

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 recent years, magnetic recording media, especially video magnetic recording media that require short wavelength recording, have become more fine-grained than ever before.
There is a growing tendency to use magnetic powder with high magnetic force. However, as magnetic powder becomes finer and has higher magnetic force,
The cohesive force of individual particles becomes stronger, and as a result, the dispersibility and surface smoothness required for obtaining high reproduction output and good S/N ratio for short wavelength recording are no longer fully satisfied. In addition, since such recording media come into violent sliding contact with the magnetic head during recording and reproduction, repeated use causes the magnetic coating to wear out and the magnetic powder contained in the coating to easily fall off, resulting in undesirable effects such as clogging of the magnetic head. bring forth.

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 made of a high molecular weight polyol, a diisocyanate, a chain extender (used as necessary), and
It is synthesized from a crosslinking agent.

However, with conventional urethane resins, it is difficult to solve the above-mentioned problems associated with the use of finely divided magnetic powder and to achieve both high levels of electrical properties and running durability.

An object of the present invention is to provide a magnetic recording medium that has excellent dispersibility of magnetic powder, good physical properties of the binder of the magnetic layer, and that can achieve both high-level electromagnetic conversion characteristics and running durability. It is to provide a medium.

20 Structure of the Invention and Its Effects The present invention provides a magnetic recording medium having a magnetic layer containing magnetic powder and a binder, wherein at least one of silicon and aluminum is contained in the magnetic powder, and the magnetic powder contains at least one of silicon and aluminum. The sum of the silicon content and aluminum content of is 0.002
The present invention relates to a magnetic recording medium characterized in that polyurethane having a structural unit represented by the following general formula (1) in a part of the main chain is contained as the binder in an amount of % by weight or more. .

General formula (1) [R represents an alkyl group.

m and n each represent l or 2. ] According to the magnetic recording medium of the present invention, the polyurethane used as the binder resin of the magnetic layer has a polyether component represented by the above general formula (1) in a part of its main chain. It is a remarkable feature. That is, since the above structure contains both the bisphenol A component and the alkylene oxide adduct component, the characteristics of each of these components are effectively exhibited, and the drawbacks of each of these components are mutually compensated for. can do. This results in
The physical properties of polyurethane have been improved, and the running durability of the media has been improved. Moreover, since the magnetic powder contains a predetermined amount of silicon and/or aluminum, its dispersibility is improved and the amount of lubricant in the magnetic layer adsorbed to the magnetic powder is reduced, further improving running durability. did. Furthermore, the present inventor has discovered that the above-mentioned specific polyurethane magnetic powder has excellent dispersibility, and in combination with the effects of silicon and aluminum in the above-mentioned magnetic powder, the dispersibility of the magnetic powder is further improved. This improved the falling off of the magnetic powder and further improved the running durability of the medium.

Next, a polyurethane containing the structural unit represented by the above general formula as part of the main chain will be described.

Similar to the usual polyurethane synthesis method, it is synthesized by reacting a high molecular weight polyol (molecular weight 500 to 3000) such as a polycarbonate polyol, polyester polyol, polylactone polyol, or polyether polyol with a polyfunctional aromatic or aliphatic isocyanate. As a result, polyester polyurethane, polyether polyurethane, and polycarbonate polyurethane carbonated with phosgene or diphenyl carbonate are synthesized.

These polyurethanes are primarily produced by the reaction of polyisocyanates with polyols and optionally other copolymers, and may also be in the form of urethane resins or urethane prepolymers containing free isocyanate groups and/or hydroxyl groups; The isocyanate component may be of various diisocyanate compounds, such as hexamethylene diisocyanate (HMDI), diphenylmethane diisocyanate (
MDI), hydrogenated MDI (H, □MDI), toluene diisocyanate (TDI), 1,5-naphthalene diisocyanate (NDI), tolidine diisocyanate (T
ODT), lysine diisocyanate methyl ester (L
DI), isophorone diisocyanate [IPDI], etc. can be used.

Polyester polyol can be synthesized by polycondensing a dicarboxylic acid component and a polyhydric alcohol component.

Polycarbonate polyols are generally synthesized by transesterification of polyhydric alcohols with dialkyl carbonates or diallyl carbonates, or can be obtained by condensation of polyhydric alcohols with phosgene.

In order to introduce the structural unit represented by the above structural formula into the main chain, when producing polyester polyols, polycarbonate polyols, etc., when reacting the following polyols, polycarbonate polyols, etc. with polyisocyanates, the following polyvalent Use alcohol.

General formula [II] In addition to the above, polyhydric alcohol components that can be used in polyol production include glycols such as ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol, or trimethylolpropane, hexanetriol, glycerin, trimethylolpropane, Examples include polyhydric alcohols such as trimethylolethane, pentaerythritol, polytetramethylene glycol, and neopentyl glycol, or any two or more types selected from these glycols and polyhydric alcohols.

Polyhydric carboxylic acid components such as dicarboxylic acids that can be used in polyol production include terephthalic acid, isophthalic acid,
Examples include sebacic acid, adipic acid, secondary luic acid, and maleic acid.

When reacting a polyester polyol or the like with a polyisocyanate, in addition to the diol of the above general formula, if necessary, a low-molecular polyester such as 1,4-butanediol, 1゜6-hexanediol, 1,3-butanediol, etc. Functional alcohols can also be used to adjust molecular weight, resin physical properties, and the like.

Furthermore, it is also possible to use the following aromatic diols in combination.

[R represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R' represents a hydrogen atom, an alkyl group having 1 to 7 carbon atoms, or an aryl group. ] [n represents an integer of 1 to 10. ] [n represents 1 or 2. ] [n represents 1 or 2. ] [n represents 1 or 2. ] [n represents 1 or 2. ] The amount of the structural unit represented by the general formula (1) introduced into the polyurethane of the present invention is preferably 1 to 30a+o 1%, more preferably 5 to 15a+o 42%. If the amount introduced is smaller than the above, it will be difficult to notice a sufficient effect on the dispersibility of the magnetic powder. If the amount of this structural unit introduced is larger than the above, the degree of improvement in electrical properties by calendering will be reduced.

Further, the number average molecular weight of the polyurethane resin according to the present invention is 5
ooo~100000, more preferably 1oooo~5
Preferably, it is in the range of 0000. If the number average molecular weight is less than 5,000, the coating film-forming ability of the resin is likely to be insufficient, and if the number average molecular weight exceeds 100,000, problems may occur in paint manufacturing processes such as mixing, transport, and coating. There is.

In the structural unit represented by general formula (1), R [n is 1
or 2. ] is more preferably a methyl group.

The bisphenol A alkylene oxide adduct represented by general formula [II] can be synthesized by reacting bisphenol A alkylene oxide.

Next, the magnetic powder contained in the magnetic layer of the magnetic recording medium of the present invention will be described.

At least one of silicon and aluminum is contained in the magnetic powder, and the term "contained" herein also includes the case where it is attached to the surface of the core by surface treatment.

When silicon is contained in the magnetic powder, the silicon content in the magnetic powder is preferably 0.01 to 2.0% by weight, and O
, OS to 1.0% by weight is more preferable.

When the silicon content in the magnetic powder is 0.01% by weight or more, the surface activity of the magnetic powder can be increased, and the adsorption of the magnetic powder to the polyurethane of the present invention is promoted.

On the other hand, even if it exceeds 2.0% by weight, the effect commensurate with the increase in content may not be achieved, and the magnetic properties may deteriorate on the contrary.

The silicon can be attached to the magnetic powder by, for example, adding a soluble silicon compound to a dispersion prepared by dispersing the magnetic powder in an alkaline aqueous solution.

As the silicon compound, for example, orthosilicic acid (F!4
SiO, ), metasilicic acid (l(zslos) %metanige 4M (FltSizO) metatrisilicate (HaSi
30x), silicate di-silicon oxide such as metatetrasilicic acid (HiSi4oz), silicon dioxide: sodium orthosilicate (Na4Si(la)).

Sodium metasilicate (NaSiOz), potassium metasilicate (KzSi(h), calcium orthosilicate (
Ca4Si04), calcium metasilicate (CazSi
O:+), barium metasilicate (BazStOs)
, cobalt metasilicate (Ca4Si04), and other silicate metal salts.

These silicon compounds may be used alone or in combination.
You may use a combination of more than one species.

When aluminum is contained in the magnetic powder, the content of aluminum in the magnetic powder is preferably 0.002 to 1.0% by weight, more preferably 0.01 to 1.0% by weight. The aluminum content in the magnetic powder is 0.
When the content is 0.02% by weight or more, the surface activity of the magnetic powder can be increased, and the adsorption of the magnetic powder to the polyurethane of the present invention is promoted. On the other hand, even if it exceeds 1.0% by weight, the effect commensurate with the increase in content may not be achieved, and the magnetic properties may deteriorate on the contrary.

In order to attach the aluminum to the magnetic powder, for example,
It can also be carried out by adding a soluble aluminum compound to a dispersion prepared by dispersing magnetic powder in an alkaline aqueous solution.

Examples of such aluminum compounds include aluminum oxide (^2□03).

When both silicon and aluminum are contained in the magnetic powder, the total content of both in the magnetic powder is 0.01~
The content is preferably 2.0% by weight. When the total content of both in the magnetic powder is 0.01% by weight or more, the surface activity of the magnetic powder can be increased, and the adsorption of the magnetic powder to the polyurethane of the present invention tends to be promoted. On the other hand, even if it exceeds 2.0% by weight, the effect commensurate with the increase in content may not be achieved, and the magnetic properties may deteriorate on the contrary.

When using the silicon (Si) and aluminum (A1) together, the silicon (St) and aluminum (A1)
The ratio with i) is the weight ratio of (Si):CAl), which is 30
: Preferably within the range of 1 to 1:30, preferably 20:1 to 1:30.
More preferably, it is within the range of 1:1O.

Magnetic powder containing aluminum and/or silicon can also be produced by bringing the magnetic powder into contact with a gas containing aluminum and/or silicon. Further, in the case of a metal magnetic powder obtained by thermal reduction of goethite, the above-mentioned /l (and/or) St treatment may be performed at the generation or treatment stage of the raw goethite and then reduced.

It is preferable that aluminum and/or silicon exist in the form of an oxide or a hydrous oxide in the surface region of the magnetic powder.

When forming a double layer of a compound containing aluminum and a compound containing silicon on the surface of the magnetic powder particles, the upper and lower layers of both coatings may be used. When provided on the upper layer side, durability is further improved. This is because the silicon-containing compound coating has excellent bonding strength with both the surface of the magnetic powder and the aluminum-containing compound coating, so the double coating layer and the magnetic powder are strongly bonded together. The surface hardness of the magnetic powder can be increased because the aluminum is bound and the compound containing aluminum has a higher hardness.

When magnetic powder contains both aluminum and silicon,
Each magnetic powder particle may contain both aluminum and silicon, or may be a mixture of magnetic particles containing only aluminum and magnetic particles containing only silicon.

In the former case where both aluminum and silicon are present on the surface of each magnetic powder, there is less local non-uniformity in durability on the surface of the magnetic layer.

The content of polyurethane according to the present invention is preferably 100 to 1 part by weight per 100 parts by weight of magnetic powder, and 5 parts by weight.
It is more preferable to use 0 to 2 parts by weight.

Examples of "magnetic powder" include T-FetO3, Fe3O4, intermediate oxides thereof, cobalt-containing iron oxide magnetic powder obtained by doping or depositing cobalt atoms on these iron oxide magnetic powders, ferromagnetic chromium dioxide powder, and iron nitride powder. , iron carbide, alloy metal magnetic powder, barium ferrite, or those modified with metals such as titanium and cobalt.

In the cobalt-containing iron oxide magnetic powder, the content of cobalt is preferably 1.0 to 5.0% by weight based on the total magnetic powder.

The coercive force (Hc) of the magnetic powder is preferably 600 to 1200 oersted, and the specific surface area of the magnetic powder is preferably within the range of lO to 70rrf/g in terms of BET value, more than 35rrf/g, and more preferably 40rrf. /g or more is more preferable.

The above specific surface area is expressed as a BET value, which refers to the surface area per unit weight, and is a physical quantity that is completely different from the average particle diameter.For example, even if the average particle diameter is the same, there are Some have a small surface area. To measure the specific surface area, for example, first heat the powder at around 250'C for 30 minutes.
The powder is degassed while being heated for ~60 minutes to remove what is adsorbed on the powder, and then introduced into the measuring device, the initial pressure of nitrogen is set to 0.5 kg/nf, and the liquid is heated with nitrogen. Adsorption measurement is carried out at nitrogen temperature (-195°C) (Specific surface area measurement method generally referred to as B, E, T method. For details, see J, As+e, Chew, Soc, 60
309 (1938)).

This specific surface area (BET value) measuring device uses a digestion battery.
It is also possible to use the "powder measuring device (Canterthorpe)" manufactured jointly by Digestion Ionics (1). For a general explanation of the specific surface area and its measurement method, see "Measurement of Granules" by J. M. DALLAVALLE.
, co-authored by CLYDEORR Jr., translated by Benguchi and others; published by Sangyo Toshosha), and ``Chemistry Handbook''.
(Application Edition, pp. 1170-1171, published by Nippon Kagaku Gosen, Maruzen, April 30, 1966).
/gr), which is the same as the specific surface area in this specification. ).

Next, the overall structure of the magnetic recording medium of the present invention will be further described.

In addition to the polyurethane of the present invention, known binders for magnetic layers can be used.

The binder that can be used in combination has an average molecular weight of about 10,000.
~200,000, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various synthetic rubbers, phenolic resin, epoxy resin, urea resin, melamine resin, phenoxy Resin, silicone resin, acrylic reactive resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, mixture of low molecular weight glycol/high molecular weight diol/isocyanate, and mixtures thereof, etc. is exemplified.

The polyurethane of the present invention is preferably used in combination with vinyl chloride fat or a vinyl chloride copolymer (vinyl chloride-vinyl acetate copolymer, etc.). In this case, the ratio of the polyurethane of the present invention to the vinyl chloride resin and the vinyl chloride copolymer is preferably (18) to (8:2) by weight, and (3 near) to (7:3). ) is more preferable.

The vinyl chloride resin may contain an epoxy group-containing monomer and/or a hydroxyl group-containing monomer. This hydroxyl group may be supplied as a monomer from the beginning, or may be generated by partial hydrolysis of a copolymer using another copolymerizable monomer (for example, fatty acid vinyl such as vinyl acetate).

Examples of monomers having an epoxy group include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methallyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, glycidyl-p-vinyl benzoate, methylglycidyl itaconate, and glycidyl ethyl maleate. , glycidyl vinyl sulfonate, glycidyl esters of unsaturated acids such as glycidyl (meth)allylsulfonate, butadiene monooxide, vinylcyclohexene monooxide, 2
Examples include epoxide olefins such as -methyl-5,6-nipoxyhexene. This monomer is generally used in such a range that the amount of epoxy groups in the copolymer is 0.5% by weight or more.

In other words, as the monomer containing the above hydroxyl group, as X in the monomer having -X-OH group, C
nH,n, C00CnH,n and C0NHCnH,n
(n is an integer of 1 to 4). Examples of monomers having this -X-OH group include carbon atoms of α,β-unsaturated acids such as (meth)acrylic acid-2-hydroxyethyl ester and (meth)acrylic acid-2-hydroxypropyl ester. Alkanol esters of unsaturated dicarboxylic acids such as number 2 to 4 alkanol esters, maleic acid mono-2-hydroxypropyl ester, maleic acid di-2-hydroxypropyl ester, itaconic acid mono-2-hydroxybutyl ester, 3-butene- Examples include olefin alcohols such as 1-ol and 5-hexen-1-ol, alkanol vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether, and acrylamides such as N-methylol acrylamide and N-methylol methacrylamide. .

In addition, the amount of hydroxyl groups based on the 1X-OH group bonded to the resin is preferably 0.1 to 2.0% by weight; if it is less than 0.1% by weight, the incyanate compound will not exhibit the crosslinking effect of the coating film. If the amount is more than 2.0% by weight, the pot life of the paint will be too short to be useful. Although the amount of this hydroxyl group is much smaller than that of vinyl chloride-vinyl alcohol-vinyl acetate copolymer, which has been known for use in magnetic paints, the crosslinking reaction with isocyanate compounds is difficult. fully achieved. The reason for this is not clear, but it is thought to be due to the fact that the hydroxyl groups that participate in the reaction are farther away from the main chain of the copolymer, increasing the degree of freedom, and that the distribution of the hydroxyl groups in the polymer is more uniform. .

Other copolymerizable monomers that can be copolymerized as necessary include known polymerizable monomers, such as various vinyl esters such as vinyl acetate and vinyl propionate, vinylidene chloride, acrylonitrile, methacrylate, styrene, and various other copolymerizable monomers. Examples include acrylic ester, methacrylic ester, ethylene, propylene, isobutyne, butadiene, isoprene, vinyl ether, aryl ether, aryl ester, acrylamide, methacrylamide, and maleic ester.

As the vinyl chloride copolymer, preferably vinyl chloride-
A copolymer containing vinyl acetate is hereinafter referred to as a "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, vinyl chloride-vinyl acetate-vinyl alcohol-maleic anhydride, and vinyl chloride-acetic acid. Examples include vinyl-vinyl alcohol-maleic anhydride-maleic acid copolymers, and among vinyl chloride-vinyl acetate copolymers, partially hydrolyzed copolymers can be used.

By the way, conventional vinyl chloride copolymer resins (for example, U
, VAGH manufactured by C1C) consisted of the following copolymerized components.

: Indicates a copolymerization unit.

However, it is thought that the CH and Co-0- groups here do not easily contribute to the crosslinking reaction with the curing agent and the like. So c
It is preferable to contain an epoxy group such as these instead of H or co. For example, a copolymer having the following units may be mentioned.

The degree of polymerization of the vinyl chloride resin is preferably 100 to 600.
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.

In addition, as a method for measuring the degree of polymerization described above, the vinyl chloride resin of the present invention is heated and dissolved in cyclohexanone, and 3
The specific viscosity of the solution was measured at 0°C according to JIS K6721, and the specific viscosity was measured according to JIS K6721 using nitrobenzene.
Convert to specific viscosity to determine the degree of polymerization.

The above-mentioned vinyl chloride resin is polymerized by a polymerization method such as emulsion polymerization, solution polymerization, suspension polymerization, or bulk polymerization.

In either method, known techniques such as divisional addition or continuous addition of molecular weight regulators, polymerization initiators, and monomers can be applied as necessary.

As the vinyl chloride resin used in the present invention, it is more preferable to use one containing a polar group and having improved dispersibility.

The polyurethane of the present invention may be used in combination with an epoxy resin (particularly a phenoxy resin), a polyester resin, or a nitrocellulose resin (hereinafter referred to as other resins). In this case, the blending ratio of the urethane resin and other resin is 90 to 10 parts by weight, more preferably 80 to 10 parts by weight.
It is desirable to have a weight of 20 layers. If the above-mentioned blending ratio exceeds 90 parts by weight, the coating film becomes too brittle and the durability of the coating film is significantly deteriorated, and the adhesion to the support also deteriorates. Moreover, if the above-mentioned blending ratio is less than 10 parts by weight, the magnetic powder tends to fall off.

Incorporating carbon black in the magnetic layer is further advantageous in terms of improving runnability and electromagnetic conversion characteristics, and also slightly improves dispersibility and reduces the amount of residual solvent in the magnetic layer.

If a light shielding carbon black is used as such carbon black, the degree of light shielding can be further increased. As the light-shielding carbon black, for example, Raben 2000 manufactured by Columbia Carbon Co., Ltd. (specific surface area: 190
i/g, particle size 18 layers μ), 2100.1170.10
00, Mitsubishi Kasei #100, #75, #40, #3
5, #30, etc. can be used.

Further, as the conductive carbon black, for example, Conductex (Columbia Carbon Co., Ltd.) is used.
x) 975 (BET value (hereinafter abbreviated as BET) 2
50n? /g, DBP oil absorption (hereinafter abbreviated as DBP) 170
Id/100gr, particle size 24mμ), Conductex 900 (BE T125rrf/g, particle size 27
mμ), Conductex 40-220 (particle size 20m
um), Conductex SC (B ET 220r
rf/gr, D B P 115m/10Qgr, particle size 20mμ), Palcan manufactured by Cabot (Cabot
Vulcan) X C-72C specific surface area 254n? /
g, particle size 30μ), Palcan P (BET 143n
(/gr, DBP118 d/I00gr, particle size 2
0+nμ), Raven 1040.420, Black Pearls 2000 (particle size 15a+μ), # manufactured by Mitsubishi Kasei ■
There is a 44th mag.

Other carbon blacks that can be used in the present invention include Conductex (manufactured by Columbia Carbon) (
Conductex) S C, (B E T220
rrf/g, D B P 115d/100
g, particle size 20 mμ), Palcan (V
ulcan) 9 (BE T140rd/g, D
B P 114-/100 g, particle size 19 mμ), #80 manufactured by Asahi Carbon Co., Ltd. (B ET 117 bo/g, DBP
113 ll11/100 g, particle size 23 reμ),
H3100 manufactured by Denki Kagakusha (BET32 bo/g,
D B P 180d/100 g, particle size 53 cmμ
), 422B manufactured by Mitsubishi Kasei (BET55rd/gS
DBP 131d/100g, particle size 40mμ), 42
0B (BET56 bo/g, DBP115 mg/10
0g.

Particle size 40 tau), #3500 (B ET47
nf/g, D B P187 d/100 g, particle size 40 mμ), and in addition, C
F-9, #4000, MA-600, Cabot Black Pearls L-
, Monarch 800, Black Burls 700, Black Burls 1000, Black Burls 8801 Black Burls 900, Black Burls 1300, Black Pearls 2000° Sterling Vs Raven made by Columbia Carbon Co. (Raven) 410,
Raven 3200, Raven 430, Sieben 450.
Raven 825, Raven 1255, Raven 1035
, Raven 1000, Sieben 5000. Examples include Ketschen Black FC.

Furthermore, in the present invention, durability can be improved by further adding a polyisocyanate curing agent to the magnetic paint containing a binder.

Examples of such polyisocyanate curing agents include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, as well as coronate and Nippon Polyurethane Industries.
Trifunctional isocyanates such as Desmodul (manufactured by Bayer AG), desmodulite (manufactured by Bayer AG), or urethane prepolymers containing isocyanate groups at both ends, which are conventionally used as curing agents, can also be used as curing agents. Any polyisocyanate can be used. The polyisocyanate curing agent is used in an amount of 5 to 80 parts by weight based on the total amount of binder.

The magnetic recording medium of the present invention has, for example, as shown in FIG.
It has a magnetic layer 2 on a non-magnetic support 1 such as polyethylene terephthalate, and if necessary, a BCC 3A is provided on the opposite side of the magnetic layer 2. Also,
As shown in FIG. 2, an overcoat layer (OC layer) 4 may be provided on the magnetic layer 2 of the magnetic recording medium shown in FIG.

Further, the magnetic recording media shown in FIGS. 1 and 2 may be provided with an undercoat layer (not shown) between the magnetic layer 2 and the support 1, or may be provided with no undercoat layer. It's okay. The support may also be subjected to corona discharge treatment.

The magnetic layer 2 can contain a fatty acid and/or a fatty acid ester as a lubricant.

Thereby, while exhibiting the respective features of both, it is possible to offset the defects that occur when used alone, improve the lubrication effect, and improve still image durability, running stability, S/N ratio, etc. In this case, the amount of fatty acid added is preferably 0.2 to 10 parts by weight, preferably 0.5 to 8 parts by weight, per 100 parts by weight of the magnetic powder.
Even better is 0 parts by weight. If the fatty acid content falls outside of this range, the dispersibility of the magnetic powder decreases, and the runnability of the medium tends to decrease, and if the fatty acid content exceeds this range, the fatty acid tends to seep out and output decreases. In addition, the amount of fatty acid ester added is preferably 0.1 to 10 parts by weight per 100 parts by weight of magnetic powder.
Even better is 0.2 to 8.5 parts by weight. If the amount of ester decreases outside of this range, the effect of improving still durability will be poor, and if it increases, the ester will easily seep out and the output will decrease.

In addition, in order to better achieve the above effects, the weight ratio of fatty acids and fatty acid esters should be set as fatty acid/fatty acid ester =
10/90 to 90/10 is preferred. Note that fatty acids also have a dispersing effect, and it is thought that by using fatty acids, the amount of other low molecular weight dispersants used can be reduced, and the Young's modulus of the magnetic recording medium can be improved by that amount.

Fatty acids may be monobasic or dibasic.

Fatty acids having 6 to 30 carbon atoms, more preferably 12 to 22 carbon atoms, are preferred. Examples of fatty acids are as follows.

(1) Caproic acid (2) Caprylic acid [6] capric acid Lauric acid myristic acid Valmitic acid stearic acid isostearic acid lyrinic acid linoleic acid oleic acid Elaidic acid Behenic acid malonic acid Succinic acid maleic acid glutaric acid Adipic acid pimelic acid azelaic acid Sebacic acid 1.12-dodecanedicarboxylic acid (23) Octane dicarboxylic acid Examples of the above fatty acid esters are as follows.

(1) Oleyl oleate (2) Oleyl stearate (3) Isocetyl stearate (4) Dioleyl maleate (5) Butyl stearate (6) Butyl palmitate (7) Butyl myristate (8) Octyl myristate ( 9) Octyl palmitate (10) Amyl stearate (11) Amyl palmitate (12) Isobutyl oleate (13) Stearyl stearate (14) Lauryl oleate (15) Octyl oleate (16) Isobutyl oleate (17) Ethyl oleate ( 18) Isotridecyl oleate (19) 2-ethylhexyl stearate (20)
2-ethylhexyl myristate (21) ethyl stearate (22) 2-ethylhexyl palmitate (23) isopropyl palmitate (24) isopropyl myristate (25) butyl laurate (26) cetyl-2-ethyl hexalate ( 27) Dioleyl adipate (28) Diethyl adipate (29) Diisobutyl adipate (30) Diisodecyl adipate In addition to the fatty acids and fatty acid esters mentioned above, other lubricants (such as silicone oil, carboxylic acid modified, ester modified, etc.) may be added to the magnetic layer.

Non-magnetic abrasive particles can also be added to the magnetic layer. For example, α-alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, silicon carbide, zirconium oxide, zinc oxide, cerium oxide, magnesium oxide, boron nitride, etc. are used. The average particle diameter of this abrasive is preferably 0.6 μm or less. Moreover, it is preferable that the Mohs hardness is 5 or more.

In addition, the magnetic layer further contains an antistatic agent such as graphite.
A dispersing agent such as powdered lecithin or phosphate ester can be added. Furthermore, carbon black can also be used in combination.

In addition, the non-magnetic particles contained in the back coat layer are
It is more preferable that the average particle size is within the range of 10 mμ to 1000 mμ. If it is within the above range, the non-magnetic particles will not become too fine (this is because the addition effect is good).

Non-magnetic particles include silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide,
Examples include zinc oxide, α-F e t 01 , talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbide, barium sulfate, and the like. In addition, organic powders such as benzoguanamine resins, melamine resins, phthalocyanine pigments, etc. can also be used, and organic powders and the above-mentioned inorganic powders can also be used in combination.

Furthermore, it is more preferable to use carbon black together with the above-mentioned non-magnetic particles. This further stabilizes the running properties of the medium, and in combination with the effect of the non-magnetic particles described above, it is possible to further improve the durability of the medium.

The thickness of the magnetic layer is preferably thin in order to achieve a high S/N ratio, and thicker in terms of running performance and still durability. Therefore, 6.0 to 1.0 μm is preferable,
It is more preferable to set it to 5.0 to 2.9 gm.

Examples of the material forming the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; plastics such as polycarbonate, etc. can be mentioned. Furthermore, Cu
, metals such as Al, Zn, glass, and various ceramics such as so-called new ceramics (for example, boron nitride, silicon carbide, etc.) can also be used.

The form of the non-magnetic support is not particularly limited, and may include tape,
It may be a sheet, card, disk, drum, etc., and various materials can be selected and used depending on the form and as necessary.

When the non-magnetic support is in the form of a tape or sheet, the thickness is usually within the range of 3 to 100 μm, preferably within the range of 5 to 50 μm. Furthermore, in the case of a disk or card shape, the thickness can usually be within the range of 30 to 100 μm. Furthermore, in the case of a drum shape, it can be made into a cylindrical shape, etc., depending on the recorder used.

E, Example The present invention will be explained in detail below.

The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. In addition, in the following examples, all "parts" are parts by weight.

(Preparation of videotape) First, a magnetic layer was formed on a polyethylene terephthalate base film having a thickness of 14 μm as a support in the following manner.

That is, using the specified magnetic powder shown in Table 1 below, Table 1
A magnetic paint is prepared by dispersing each resin and various additives shown in the following, and this magnetic paint is filtered through a 1 μm filter, 6 parts of trifunctional isocyanate is added, and a 4.0μ-
It was coated thickly and supercalendered to produce magnetic layers having various compositions shown in Table 1.

Thereafter, a paint for the BC layer having the following composition was applied to the opposite surface of the magnetic layer to a dry thickness of 0.4 μm.

Carbon black 40 parts (
Conductefx-975 (manufactured by Columbian Bonn)) Barium sulfate (average particle size 0.1 μ-) 10 parts Nitrocellulose 25 parts N-2301 (
Made by Nippon Polyurethane) 25 parts Coronate L ()
10 parts Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene 250 parts In this way, a wide magnetic film having a magnetic layer and a BC layer of a predetermined thickness was obtained, and this was wound up.

This film was cut to a width of 3 inches to produce each videotape shown in Table 1. However, the numerical values shown in Table 1 represent parts by weight.

(Margin below) Each component shown in Table-1 is as follows.

■Commercial untreated CO-containing yFexOtffi powder (Co
(content 2.5% by weight) was suspended in an NaOH aqueous solution, a Na<SiO4 aqueous solution and an Affit (SO2)3 aqueous solution were added thereto, and while stirring thoroughly, carbon dioxide gas was blown into the suspension. A film made of a silicon compound and an aluminum compound was formed on the surface of the magnetic particles. After washing this magnetic powder with water, it was dried under reduced pressure at 60°C.

Here, the concentrations and amounts of the NaaSi04 aqueous solution and Alt(SO2)i aqueous solution were variously changed, and the Si, le
Each magnetic powder having a certain content was obtained.

However, in an example where Si is not included in the magnetic powder, Aj! Using only the z(SO2)i aqueous solution, Al
In an example in which l is not contained in the magnetic powder, Na,
Only the SiO4 aqueous solution was used.

Furthermore, in Example 8, Na
Co-1-Fe, O using 4s i 04 aqueous solution.

After forming the Si film on the magnetic powder, A l! is applied again as described above. An A2 film was formed on the Si film using a (S O4) s aqueous solution.

Boteuren of the day This polyurethane has the following composition.

1.4-butanediol) (0-(CHz) 4-OH Adipic acid HOOC (CHri) 4COOH 42.9 moffi% 36.1 moffi% (rrI'+n'=2~3, main components are m', n=1
)Evaluation of Videotape Performance> Each videotape shown in Table 1 was evaluated for the characteristics shown in Table 2 below.

The measurement method for each evaluation data is as follows.

Electromagnetic conversion characteristics Lumi S/N, Rf output: Measured using HR-37000 (manufactured by Victor).

In RH, using a deck of NV-6200 (manufactured by Kenshi Denki), the tape was repeatedly run for 100 passes (100 pass tape). Regarding this, Rf output fluctuation and dropout were measured.

Dropout: Japan Victor dropout counter VD-5M
The entire length was measured using a dropout that was longer than 15 g sec and had an output that was 20 dB or more lower than the R envelope output, and the average value per minute was determined.

Tape Damage> The tape was run for 100 hours at a temperature of 40°C and 180% humidity for 100 hours, and damage to the tape was observed.

O: No edge bending or wakame state of the tape.

△D Some parts have bent edges and seaweed appearance.

×: Edges were bent over the entire length, and a seaweed condition occurred.

As shown in Table 2, the sample constructed based on the present invention was
Superior to the comparative sample. It is also understood that it is important to limit the total content of St and Af in the magnetic powder.

[Brief explanation of the drawing]

FIGS. 1 and 2 are partially enlarged sectional views showing examples of magnetic recording media. In addition, in the symbols shown in the drawings, 1...Nonmagnetic support 2...Magnetic layer 3...Back coat layer (BC layer) )4...
...... Overcoat layer (QC layer). Agent Patent Attorney Hiroshi Tsuita

Claims (1)

[Claims] 1. In a magnetic recording medium having a magnetic layer containing magnetic powder and a binder, at least one of silicon and aluminum is contained in the magnetic powder, and the content of silicon in the magnetic powder is and the aluminum content is 0.002% by weight
A magnetic recording medium having the above structure and containing a polyurethane having a structural unit represented by the following general formula [I] as a part of the main chain as the binder. General formula [I] ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [R represents an alkyl group. m and n each represent 1 or 2. ]