JPS6022734A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium having a layer such as a magnetic layer which has excellent tackiness, wear resistance, durability and surface characteristic and is substantially low in both surface electric resistance and light transmittance by forming a layer incorporated therein with soft polyurethane and hard polyurethane having tensile strength and breaking elongation within a specific range and carbon black having a specific surface area within a specific range. CONSTITUTION:Soft polyurethane and hard polyurethane can be synthesized by the reaction between polyol and polyisocyanate. Both polyurethanes may be used in combination at an optional ratio and it is verified that there is a specified preferable range in the respective contents thereof. The ratio of the soft polyurethane to the hard polyurethane by weight is preferably 80:20-20:80 in terms of still durability and more preferably 70:30-30:70. A magnetic recording medium is formed by laminating an undercoating layer 2 and a magnetic layer 3 on a non-magnetic base 1. The soft polyurethane, the hard polyurethane, light shieldable carbon black CB1 having 40m<2>/g<B1< 200m<2>/g specific surface area (BET value) B1 and conductive carbon black CB2 having 200m<2>/g<=B2<500m<2>/g specific surface area (BET value) B2 are incorporated respectively by prescribed contents in the layer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to magnetic recording media such as magnetic tapes and magnetic sheets.

2. Prior Art Generally, magnetic recording media are manufactured by applying a magnetic paint containing magnetic powder, a binder, etc. onto a support and drying it. In the magnetic recording medium created in this way,
During recording and reproduction, the magnetic layer comes into violent sliding contact with the magnetic head, which tends to cause abrasion and powder fall, which tends to reduce reproduction output, cause output fluctuations, dropouts, increase noise, and the like.

In order to overcome these drawbacks, various studies have been made on binders for binding magnetic powder. For example, it has been proposed to use a binder made by kneading a urethane resin with a cellulose resin that has excellent dispersibility for magnetic powder.

However, in this binder, the urethane component is made of polyurethane produced by curing reaction of polyol such as polyester or polyether and polyisocyanate in the magnetic layer after coating on the support.
The polyisocyanate reacts gradually during the process. As a result, not only can the coating film change over time, but the coating film using such a binder is relatively hard.
For example, soft polyurethane is well compatible with hard polyurethane and cellulose resin, and plays the role of a plasticizer for both of the latter hard resins, thereby creating a strong coating film based on the interaction between the two. Based on the recognition that it is possible to form It has been proposed to use a magnetic coating film made by bonding magnetic powder.

For each of the above polyurethanes in this known binder composition, load (kg/cJ) and elongation rate (%)
From the relationship, as shown in Figure 1, the b1 line (load 10
0 kg/ciO line) and b2 line (load 30 kg/ciO line)
The hard thermoplastic polyurethane belongs to the area B1 surrounded by the load O line and the b5 line (load 20k).
The soft thermoplastic polyurethane belongs to the region A surrounded by the g/d line). However, since the difference in hardness and softness of each polyurethane having properties belonging to regions Bl and A1 is not so large, there is a limit to the range in which the properties of the magnetic coating film can be adjusted even if the mixing ratio of the two is changed. Yes, but the curing power is not sufficient.

Therefore, the adhesiveness of the magnetic coating film is high, and the dispersibility of the resins is not sufficient, so the abrasion resistance, durability, and surface properties of the magnetic recording medium obtained are insufficient, resulting in problems such as powder falling, dropouts, and video S. S/N ratio and chroma S/N ratio were not satisfactory.

On the other hand, in magnetic recording media, when static electricity is accumulated, discharge occurs between the media and the magnetic head, which tends to generate noise, and dust and the like can be attracted, causing dropouts. Furthermore, for video tapes, a method is known in which the running of the tape is adjusted by detecting the difference in light transmittance between a tape portion having a magnetic layer and a leader tape portion.

For these reasons, the surface electrical resistance 103 of the magnetic layer is generally
It is required that the optical transmittance of the tape portion where the magnetic layer is located be 0.05% or less for light of 900 nm. For this purpose, carbon black particles are usually added to the magnetic layer.

For example, according to Japanese Patent Publication No. 57-4968, a conductive carbon blank with a surface area of 500 n/g or more and a particle size of 30 mμ or less, a conductive carbon blank with a surface area of 500 d/g or less and a particle size of 4
Light-shielding carbon black of 0 mμ or more is added to each magnetic layer. However, with this magnetic tape,
Conductive carbon black has a surface area of 500 rrf/g
Since the above amount is too large, the amount of oil absorbed becomes large, making it difficult to disperse in the magnetic layer, resulting in poor dispersion stability and poor surface properties of the tape.

In addition, Japanese Patent Application Laid-Open No. 51-200934 discloses that the specific surface area (BET value) is 140 d, 'g or more and the particle size is 20 m.
, cr or less, carbon black having a specific surface area (BET value) of 40rd/g or less and a particle size of 50 mμ or more, and a higher fatty acid are shown in the magnetic layer.

However, in this magnetic tape, carbon blanks with a specific surface area of 40n/g or less and a particle size of 50mμ or more have poor coloring power and electrical conductivity, so it is necessary to increase the amount of carbon blanks added.
This has the disadvantage that the mechanical properties of the magnetic layer deteriorate.

3. Purpose of the Invention The purpose of the present invention is to provide a magnetic recording medium having layers such as a magnetic layer that have excellent adhesiveness, abrasion resistance, durability, and surface properties, and have sufficiently low surface electrical resistance and light transmittance. It's about doing.

4. Structure and effect of the invention, that is, the magnetic recording medium according to the invention has a tensile strength of 200
kg/al1 and elongation at break is 900%
Soft polyurethane with a tensile strength of 200K or more
Rigid polyurethane with g/d or more and an elongation at break of less than 900%, and a specific surface area (BET value) B+ of 40
%/g < Bi < 200 rrr/g (hereinafter sometimes referred to as CB1), and specific surface area (BP, T value) B2 is 200 i/g ≦ B2 <
Carbon black (hereinafter referred to as C
It is sometimes called Bz. ) The present invention relates to a magnetic recording medium characterized by having a layer containing the following.

According to the present invention, the presence of the above-mentioned soft polyurethane facilitates calendering and improves the adhesion of the layer, and the presence of the above-mentioned hard polyurethane prevents the disadvantages of using soft polyurethane alone, such as stickiness and rigidity. (Stiffness) can be prevented from decreasing, tackiness can be suppressed, and the stiffness of the medium can be strengthened. The present invention has extremely important significance in that the mechanical properties of each polyurethane are specified within the above range in order to effectively exhibit the respective characteristics of these soft and hard polyurethanes. In other words, in order to fully utilize the above-mentioned effects of soft polyurethane, its tensile strength and elongation at break should be less than 200 kg/cJ and 900% or more, and at the same time, the tensile strength and elongation at break should be lower than that of hard polyurethane. 200 kg/cnT or more each, 90
If the content is less than 0% and the mechanical property values are sufficiently different between the two polyurethanes, the properties of the constituent layers of the magnetic recording medium, especially the magnetic layer, can be adjusted over a wide range. As a result, it is possible to obtain abrasion resistance and durability of the medium while suppressing tackiness, and also to obtain good surface properties due to improved dispersibility of the binder component. Figure 2 shows the tensile strength of 200 k.
Elongation rate (elongation at break) of soft polyurethane less than g/crA and abrasion resistance of the magnetic layer (ease of scratching, resistance to powder falling off)
It can be seen that when the elongation rate is increased to 900% or more, the properties are significantly improved. Further, FIG. 3 shows the relationship between the elongation rate of a rigid polyurethane having a tensile strength of 200 kg/cn1 or more and the ease with which the medium is calendered, and when the elongation rate is less than 900%, the properties are significantly improved.

The preferable range of physical properties of both polyurethanes used in the present invention is tensile strength of 10 to 100 for soft polyurethane.
kg/cf, elongation at break 1000-1200%, and tensile strength 300-600 k for rigid polyurethane.
g/c+A.

The elongation at break is 400 to 750%.

To illustrate the mechanical properties of the above-mentioned polyurethane according to the present invention, in FIG. Polyurethane belongs to this area, and soft polyurethane belongs to the other area AZ.

In addition, the mechanical properties of the polyurethane according to the present invention (
Tensile strength, elongation at break) are based on Japanese Industrial Standards (JIS)
It is specified in K2SO3-1975, and elongation at break corresponds to "elongation at break" in the same standard.

In addition to the above-mentioned polyurethanes, the important composition of the present invention is that each of the above-mentioned carbon blacks (C&, C
B2) is also included.

That is, carbon black CBi is added mainly for light shielding, but its specific surface area Bt is 40rrr/g〈B
It is extremely important to be specific in the range +, < 200 rrf/g. With the specific surface area within this range, the layer can have sufficient light-shielding properties, and at the same time, the dispersibility of CB+ in the layer can be improved. Outside this range,
If the specific surface area of CB+ is less than 40 rtr/g, the particle size will be too large and the light shielding properties will be poor, and the amount added will need to be increased more than necessary, and if it is more than 200 rtr/g, the particle size will be too small. This results in poor dispersion into the layer. On the other hand, in order to obtain sufficient conductivity, both CBs
2 is added, but its specific surface area is 200 I/g≦B2
The specification of <500 i/g is also very important. That is, if the specific surface area B2 of CBg is less than 200 rd/g, the particle size will be too large and the conductivity will be extremely insufficient even with the addition of carbon black;
This is because if the particle size is more than g, the particle size will be too small and the dispersibility of CB will deteriorate.

Therefore, according to the present invention, light shielding CB and conductive C
Only by limiting the specific surface areas of & to the above-mentioned specific ranges can the surface electrical resistance and optical transmittance of the magnetic layer etc. be sufficiently reduced, and the surface smoothness of the layer (i.e. the dispersibility of carbon black) be improved. This makes it possible to improve the durability of the layer by reducing the amount of carbon black added. This has been experimentally confirmed as shown in FIG. The specific surface area range of each carbon black is fundamentally different from the range shown in the prior art, and is a new and original condition discovered by the present inventor. In order to more fully achieve the object of the present invention, the specific surface area of each of the above should be 100≦Bt<200.200≦
It is desirable that B2≦300.

Further, regarding the particle size of each carbon blank, it is desirable that CBL is 20 μm or less and CBt is 40 to 50 mμ, which correspond to the above range of specific surface area according to the present invention.

In the present invention, the above-mentioned "specific surface area" refers to the surface area per unit weight, and is a physical quantity that is completely different from the average particle size. For example, even if the average particle size is the same, the specific surface area is larger. There are those with a small specific surface area and those with a small specific surface area. To measure the specific surface area, carbon black powder is first heat-treated at around 250°C for 30 to 60 minutes, then degassed to remove what is adsorbed to the powder, and then introduced into a measuring device. and the initial pressure of nitrogen is 0.5kgγ.
/ A, and lower the liquid nitrogen temperature (-195℃) using nitrogen.
(Specific surface area measurement method generally referred to as the B, E, T method. For details, see J, Ame, C-
see hem, Soc, i 309 (193B))
. As a device for measuring the specific surface area (BET value), it is possible to use a "powder measuring device (Cantersoap)" jointly manufactured by Yusen Battery Co., Ltd. and Yusen Ionics Co., Ltd. A general explanation of the specific surface area and its measurement method can be found in ``Measurement of Powders'' (J.

Co-authored by M. DALLAVALLE and CLYDE 0RR Jr., Translated by Benyo and others; Published by Sangyo Toshosha).
It is also described in Section 1, Nippon Kagaku Complete Edition, published by Maruzen Co., Ltd., April 30, 1960). (Note that in the above-mentioned "Chemistry Handbook," the specific surface area is simply described as surface area (, 1/gγ), which is the same as the specific surface area in this specification.

) 5. Examples Hereinafter, the present invention will be explained in more detail with reference to Examples.

The soft polyurethane and hard polyurethane used in the magnetic recording medium of the present invention can be synthesized by reacting a polyol and a polyisocyanate. Polyols that can be used include organic dibasic acids such as phthalic acid, adipic acid, trimerized lyluic acid, and maleic acid, and ethylene glycol, propylene glycol, butylene glycol,
Glycols such as diethylene glycol, trimethylpropane, hexanetriol, glycerin,
Synthesized by reaction with polyhydric alcohols such as trimethylolpropane, hexanetriol, glycerin, trimethylolethane, and pentaerythritol, or any two or more polyols selected from these glycols and polyhydric alcohols. or lactone polyester polyols synthesized from lactams such as S-caprolactam, α-methyl-■-caprolactam, S-methyl-3-caprolactam, and γ-butyrolactum; or ethylene oxide, propylene oxide, etc. Examples include polyether polyols synthesized from oxide, butylene oxide, and the like.

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. Polyurethanes are usually produced primarily by the reaction of polyisocyanates and polyols and can also be in the form of urethane resins or urethane prepolymers containing free isocyanate groups and/or hydroxyl groups, or without these reactive end groups. (For example, in the form of urethane elastomer)
It may be.

Since these methods are well known, detailed explanation thereof will be omitted.

The above-mentioned polyurethanes are soft depending on their ingredients,
Hard ones can be obtained respectively. For example, flexible polyurethane can be obtained by making multiple types of polyester polyol components exist randomly in the molecule, or by using as an isocyanate an isocyanate whose molecular chain between isocyanate groups consists of chain aliphatic hydrocarbon groups. I can do it.

Rigid polyurethane can be produced by using the same type of polyol, by increasing the amount of isocyanate added, by using isocyanate that easily crystallizes, or by using isocyanate that has a benzene ring in the molecule. It has been confirmed that there is a range of favorable stories. As shown in FIG. 5, the weight ratio of soft polyurethane to hard polyurethane is 80:20 to 20:80 in terms of still durability, and 70:30 to 30:70 is even better.

Next, to explain in more detail the effect of adding the above-mentioned carbon blank in the present invention, as mentioned above, carbon blank is added to lower the surface electrical resistance and light transmittance. Since it significantly deteriorates mechanical properties, it is usually necessary to add carbon blank in an amount of 5 to 35% by weight (preferably 10 to 25% by weight) to the binder. In the present invention, due to the specific surface area within the above range, there is no need to increase the amount of carbon black added, and it can be set within the above range of 5 to 35% by weight, and the mechanical properties of the layer (for example, the magnetic layer Not only can powder fall-off be maintained well, but the desired surface electrical resistance (1
0.01 Ω·cm or less) and light transmittance (0.05% or less).

In addition, carbon black with a small particle size (large surface area) is advantageous because it improves the surface resistivity and light transmittance of the coating film when it contains carbon blanks of the same weight, but This makes dispersion difficult, resulting in surface roughness and pinhole formation due to poor dispersion, which increases the surface resistivity and light transmittance, and causes deterioration of electromagnetic conversion characteristics.

Acicular magnetic materials tend to break during dispersion, and if they become over-fractionated, they will break and the electromagnetic conversion characteristics will drop significantly. Therefore, when applied to a magnetic layer, dispersion is usually stopped when the dispersion of the magnetic powder reaches its maximum. Stop. In this case, if a carbon blank with poor dispersibility is used, it is often not dispersed sufficiently, resulting in separation of the carbon blank in the paint, roughening of the surface of the paint film, generation of pinholes, etc. Can be effectively prevented by using

In the present invention, conductive CB2 is used in order to reduce the surface resistivity of the magnetic layer, etc. to a sufficient range, but it is preferable that such a carbon blank has particles connected to each other in the shape of a bunch of grapes. It is desirable to have a porous material with a large specific surface area, ie, a material with a high stracture level. Examples of such carbon black include, for example, Conduat Sox manufactured by Columbia Carbon Company.
ex ) 975 (specific surface area 270 rd/g, particle size 46 mμ), :+y Dactesox 950 (specific surface area 2
45 rd/g, particle size 46 m, c+), Cabot Vulcan X C-7
2 (specific surface area 257 M/g, particle size 1 Bmμ), etc. can be used. Although these carbon blacks have a large specific surface area, when applied to a magnetic layer, they can be sufficiently dispersed before the dispersion of magnetic powder is completed. Outside the scope of the invention, CB2
If the specific surface area of CB2 is 500 rrF/g or more, the conductivity and light shielding properties are good in a completely dispersed state, but the dispersion of CB2 is not completed even after the dispersion of the magnetic powder is completed, and the surface roughness of the coating film may occur. , which causes pinholes. 20 On? /
If the specific surface area is less than g, the effect of adding carbon black cannot be expected.

On the other hand, in order to reduce the light transmittance of the magnetic layer etc., it is possible to use the above-mentioned carbon black CB2, but in the present invention, although the electrical conductivity is poor, the light shielding property is good (the original conductive carbon By adding a small amount of carbon CBs, which has a smaller surface area than the conductive carbon and has excellent dispersibility, a more significant synergistic effect can be obtained than when using conductive carbon alone. That is, by adding the light-shielding carbon CB1 together with the conductive carbon CB2, the light transmittance can be sufficiently reduced, and the amount of conductive carbon added can be significantly reduced, so the overall amount of carbon black added can be reduced. The mechanical properties and surface smoothness of the layer are significantly improved. Such light-shielding carbon black CB1 has a small particle size, a relatively low stracture level, and a relatively low specific surface area, such as Rave manufactured by Columbia Carbon Co., Ltd.
n) 2000 (specific surface area 180 g/g, grain size 19
mμ), 2100.1170.10 (10, #100, #75, #44, #40, #3 manufactured by Mitsubishi Kasei Corporation
5, #30, etc. can be used.

There is a certain preferable range for the mixing ratio (weight ratio) of each of the above carbon blacks, and CB2/CB! =90/
10-50150 is better, 80/20-60/40 is even better.

If this mixing ratio is greater than 90/10, the proportion of conductive carbon black CB2 will increase, resulting in insufficient light-shielding properties, and if it is less than 50/150, the surface resistivity will increase due to less conductive carbon blank CBt. I end up.

In the present invention, in addition to the above-mentioned soft polyurethane and hard polyurethane, the binder also contains a cellulose resin and a vinyl chloride copolymer to improve the dispersibility of the magnetic powder when applied to the magnetic layer. and its mechanical strength increases. However, if the cellulose resin and vinyl chloride copolymer are used alone, the layer becomes too hard, but this can be prevented by containing the above-mentioned polyurethane.

Usable cellulose resins include cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester, and the like. Examples of cellulose ether include methylcellulose, ethylcellulose, propylcellulose, isopropylcellulose, butylcellulose, methylethylcellulose, methylhydro, xyethylcellulose,
Ethylhydroxyethylcellulose, carboxymethylcellulose, carboxymethylcellulose sodium salt, hydroxyethylcellulose, benzylcellulose, cyanoethylcellulose, vinylcellulose, nitrocarboxymethylcellulose, diethylaminoethylcellulose, aminoethylcellulose, and the like can be used. Examples of cellulose inorganic acid esters include nitrocellulose,
Cellulose sulfate, cellulose phosphate, etc. can be used. In addition, cellulose organic acid esters include acetyl cellulose, propionyl cellulose, butyryl cellulose,
Methacryloylcellulose, chloroacetylcellulose, 'β-oxypropionylcellulose, benzoylcellulose, cellulose p-)luenesulfonate, acetylpropionylcellulose, acetylbutyrylcellulose, etc. can be used.

Among these cellulose resins, nitrocellulose is preferred. Specific examples of nitrocellulose include Seltsuba BTH1/2, Nitrocellulose 5L-1, manufactured by Asahi Kasei Co., Ltd.
Examples include Nitrocellulose R31/2 and Cell Line L-200 manufactured by Daicel Corporation. The viscosity of nitrocellulose (as specified in JIS, K-6703 (1975)) is preferably 2 to 1/64 seconds,
In particular, 1 to 1/2 seconds is excellent. Anything outside this range is
The film adhesion and film strength of the magnetic layer are insufficient. 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 β and m in is 95-50 mol% for the former unit and 5-50 mol% for the latter unit. In addition, X represents a monomer residue that can be copolymerized with vinyl chloride, vinyl acetate, vinyl alcohol, maleic anhydride, maleic anhydride, maleic acid, maleic ester, vinylidene chloride, acrylonitrile, acrylic acid, It represents at least one member selected from the group consisting of acrylic ester, methacrylic acid, methacrylic ester, vinyl propionate, glycidyl methacrylate, and glycidyl acrylate. The degree of polymerization expressed as (j!+m) is preferably from 100 to 600; if the degree of polymerization is less than 100, the magnetic layer etc. tend to become sticky, and if it exceeds 600, the dispersibility deteriorates. The vinyl chloride copolymer described above may be partially hydrolyzed. The vinyl chloride copolymer is preferably a copolymer containing vinyl chloride-vinyl acetate (hereinafter referred to as "vinyl chloride-vinyl acetate copolymer"). Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-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 are preferred. Specific examples of the above-mentioned vinyl chloride-vinyl acetate copolymers include rVAGHJ, rVYHHJ, and rVM manufactured by Union Carbide.
CHJ, "S-Resoku A", "S-Resoku A-5", "S-Lec C", "S-Lec M" manufactured by Tanezu Kagaku Co., Ltd.
”, “Denkabinyl 1000G” manufactured by Denki Kagaku Kogyo Co., Ltd.
", "Denkabinir 1ooow", etc. can be used.

The above vinyl chloride copolymer and cellulose resin may be used in any blending ratio, but as shown in Figure 6, the weight ratio of vinyl chloride copolymer and cellulose resin is 90'/ 10~
Preferably 5/95, 8o/20 to 10/90
has been confirmed to be even more desirable.

Outside of this range, if the amount of cellulose resin increases (the above weight ratio is less than 5/95), stickiness tends to occur, the surface properties deteriorate, and drop-out easily occurs.Also, vinyl chloride As the amount of copolymer increases, the above weight ratio becomes 9.
If it exceeds 0/10), poor dispersion tends to occur, for example, the squareness ratio tends to deteriorate.

However, in FIG. 6, C shows a tendency toward stickiness (adhesiveness), and the stickiness decreases toward the top of the vertical axis, resulting in a good coating film. d shows the change in squareness ratio.

It is desirable that the ratio of the other resins (total amount of cellulose resin and vinyl chloride copolymer) be 90/10 to 50,150 by weight as shown in FIG.
It has been confirmed that 85/15 to 60/40 is more desirable. Outside this range, if the amount of polyurethane is too high, poor dispersion tends to occur and the still properties tend to deteriorate, and if other resins increase too much, the surface properties tend to be poor and the still properties deteriorate, especially if it exceeds 60% by weight. The physical properties of the coating film become less favorable overall.

FIG. 8 shows a magnetic recording medium, for example a magnetic tape, according to the present invention, in which a sub-layer N2,
Magnetic layers 3 are laminated.

Based on the present invention, magnetic N3 contains soft polyurethane having the above-mentioned mechanical properties, hard polyurethane, and a specific surface area (BET value) of Bl of 4°/g<BX
<200 i/g light-shielding carbon blank CB1 and specific surface area (B'ET value) B2 of 200 rd/g≦B2
<50On(/g conductive carbon black CB
2 are contained in predetermined amounts, respectively.

The magnetic powder used in the present invention, particularly the ferromagnetic powder, includes γ-Fezes, Co-containing r-Fe203, F
Iron oxide magnetic powder such as c404, Co-containing Fe50+; Fe
, Ni XCo SFe - Ni-Co alloy, Fe -
Mn-Zn alloy, Fe-Ni-Zn alloy, Fe-C
.

-Ni-Cr alloy, Fe-Co-Ni-P alloy,
Examples include various ferromagnetic powders such as metal magnetic powders containing Fe, Ni% Co, etc. as main components.

The magnetic paint according to the present invention is prepared by kneading and dispersing magnetic powder, binder, dispersant, each of the above carbon blacks CB1, CB2, etc. with a coating solvent, and coats this magnetic paint on a non-magnetic support to make it magnetic. A magnetic recording medium according to the present invention.

As the binder for the magnetic layer, etc. of the present invention, in addition to the binder according to the present invention described above, a mixture of this binder and a thermoplastic resin, a thermosetting resin, a reactive resin, or an electron beam curable resin is used. Good too.

As a thermoplastic resin, the softening temperature is 150"c or less,
The average molecular weight is io, o'oo~200,000 and the degree of polymerization is about 200~2.000, such as acrylic ester/L/-7/y')O nitrile copolymer, acrylic ester/ L/-hynylidene chloride copolymer, acrylic acid ester-styrene copolymer, methacrylic acid ester-acrylonitrile copolymer, metallic acid ester-vinylidene chloride copolymer, meccrylic acid ester-styrene copolymer, polyvinyl fluoride, Vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butylene copolymer, polyamide resin, polyvinyl butyral, styrene-butadiene copolymer, polyester resin, chlorovinyl ether-acrylic acid ester copolymer, amino resin, various synthetic rubber systems Thermoplastic resins and mixtures thereof are used.

These resins are disclosed in Japanese Patent Publications Nos. 37-6877 and 39-1.
No. 2528, No. 39-19282, No. 40-5349
No. 40-20907, No. 41-9463, No. 4
No. 1-14059, No. 41-16985, No. 42-6
No. 428, No. 42-11621, No. 43-4623, No. 43-15206, No. 44-2889, No. 44
-17947, 44-18232, 45-14
No. 020, No. 45-14500, No. 47-18573
No. 47-22063, No. 47-22064, No. 47-22068, No. 47-22069, No. 47-
No. 22070, US Patent No. 48-27886, US Patent No. 3,144,352, US Patent No. 3,419,420, US Patent No. 3. No. '499.789 and No. 3,713,887.

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, silicone resin, acrylic reaction resin, mixture of methacrylate copolymer and diisocyanate prepolymer, urea formaldehyde resin, polyamine resin, and mixtures thereof.

These resins are disclosed in Japanese Patent Publications Nos. 39-8103 and 40-97.
No. 79, No. 41-7192, No. 41-8016, No. 41-'14275, No. 42-18179, No. 43
-12081, 44-28023, 45-14
No. 501, No. 45-24902, No. 46-13103
No. 47-22067, No. 47-22072, No. 47-22073, No. 47-28045, No. 47-
No. 28048, US Pat. No. 47-28922, US Pat. No. 3,144,353, US Pat. No. 3.320,090, US Pat.
No. 3,781.210 and No. 3,781,211, described in the specification.

Examples of electron beam irradiation-curable resins include unsaturated prepolymers,
For example, maleic anhydride type, urethane acrylic type, polyester acrylic type, polyether acrylic type, polyurethane acrylic type, polyamide acrylic type, etc., or as a polyfunctional monomer, ether acrylic type, urethane acrylic type, phosphate ester acrylic type, aryl type , hydrocarbon type, etc.

The total amount of the binder used in the present invention is 5 to 50 parts by weight, more preferably 10 parts by weight per 100 parts by weight of magnetic powder.
From the viewpoint of recording density, strength, etc., it is desirable that the amount be 30 parts by weight.

Furthermore, in order to improve the durability of the magnetic recording medium according to the present invention, various hardening agents can be contained in the magnetic layer etc., for example, isocyanate can be contained. Aromatic isocyanates that can be used include, for example, tolylene diisocyanate (TD■), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), metaxylylene diisocyanate (
MXDr) and adducts of these isocyanates with active hydrogen compounds.

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.

nate) [Structural formula: 0CN-■-CH2-■-N CO
], isophorone diisocyanate and its adduct of an active hydrogen compound, and the like.

The magnetic recording medium of the present invention is prepared by mixing and dispersing the magnetic powder, the binder, and various additives in an organic solvent to prepare a magnetic coating material, and adding the aromatic isocyanate-1 and aliphatic isocyanate. is coated onto a support (for example, a polyester film) and dried if necessary.

The amount of isocyanate added is 1 to 10 to the binder.
0% by weight is preferred. If it is less than 1%, the magnetic layer tends to be insufficiently hardened, and if it is more than 100%, the magnetic layer is hardened but tends to become sticky. In order to obtain a more preferable magnetic layer, the amount of isocyanate added is preferably 3 to 30% by weight based on the binder.

Examples of the isocyanate include an adduct of diisocyanate and a trivalent polyol, a pentamer of diisocyanate, and a decarboxylation compound of 3 moles of diisocyanate 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 and 1 mole of trimethylolpropane, a pentamer of tolylene diisocyanate,
There are a 5M form consisting of 3 moles of tolylene diisocyanate and 2 moles of hexamethylene diisocyanate, and a decarbonized form obtained by reacting 3 moles of hexamethylene diisocyanate with 1 mole of water, and these are easily obtained industrially.

The coating material used to form the magnetic layer and the like may contain additives such as dispersants, lubricants, abrasives, and other antistatic agents, if necessary.

Dispersants that may be used include lecithin; caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linuric acid, etc. having 8 to 18 carbon atoms; fatty acids (
R-COOH (R is a saturated or unsaturated alkyl group having 7 to 17 carbon atoms); an alkali metal (Li) of the above-mentioned fatty acid;

) or alkaline earth metals (Mg, Ca, etc.) or alkaline earth metals (Mg, Ca, etc.)
.

Examples include metal soaps made of Ba, etc.). In addition, higher alcohols having 12 or more carbon atoms and other sulfuric esters thereof can also be used. Moreover, commercially available general surfactants can also be used.

These dispersants may be used alone or in combination of two or more. In addition, as lubricants, silicone oil, graphite, carbon blank graft polymer, molybdenum disulfide, tungsten disulfide, monobasic fatty acids with 12 to 16 carbon atoms, and the total number of carbon atoms of the fatty acids are used. Fatty acid esters (so-called waxes) consisting of 21 to 23 monohydric alcohols can also be used.

These lubricants are used in amounts of 0.2 to 100 parts by weight of the binder.
It is added in an amount of 20 parts by weight.

Abrasive materials that may be used include commonly used materials such as fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial diamond,
Garnet, emery (main ingredients: corundum and magnetite), etc. are used. These abrasives have an average particle size of 0.05~
A size of 5μ is used, particularly preferably 0.1
~2μ.

These abrasives are used in an amount of 0.2 to 100 parts by weight of the binder.
It is added in an amount of 20 parts by weight.

Other antistatic agents that may be used include conductive powders such as graphite, tin oxide-anticene oxide compounds, titanium oxide-tin oxide-antimony oxide compounds; natural surfactants such as saponin; and alkylene oxide compounds. ,
Nonionic surfactants such as glycerin and glycidol; cationic surfactants such as higher alkyl amines, quaternary ammonium salts, pyridine, other heterocycles, phosphonium or sulfonium; carboxylic acids, sulfonic acids, phosphoric acids, Examples include anionic surfactants containing acidic groups such as sulfuric acid ester groups and phosphoric acid ester groups; amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric acid or phosphoric acid esters of amino alcohols.

Examples of solvents for magnetic paints or solvents used when applying magnetic paints include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone:
Alcohols such as methanol, ethanol, propatool, butanol; Esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol monoacetate; ethylene glycol dimethyl ether, diethylene glycol monoethyl ether, dioxane,
Ethers such as tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, and xylene; and halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene can be used.

In addition, materials for the 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, 8β, and Zn. Metals such as, glass, so-called new ceramics (for example, boron nitride, silicon carbide), and ceramics such as porcelain and earthenware are used.

The thickness of these non-magnetic supports is approximately 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm, and 30 μm to 1Qm in the case of a disk or card.
m, and if it is drum-shaped, it is cylindrical, and its shape is determined depending on the leyoder used.

The above-mentioned non-magnetic support has a so-called back coat (
Backcoat) may be used.

Coating methods for forming a magnetic layer by coating the magnetic paint etc. on the support include air doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, and gravure coating. Coat, kiss coat, cast coat, spray coat, etc. can be used, and other methods are also possible.

The magnetic layer coated on the support by such a method is optionally treated to orient the ferromagnetic powder in the layer, and then the formed magnetic layer is dried.

Further, if necessary, the magnetic recording body of the present invention is manufactured by subjecting it to surface smoothing processing or cutting it into a desired shape.

In this case, the orientation magnetic field is approximately 500 to 35
00 Gauss, the drying temperature is preferably about 50 to 100°C, and the drying time is preferably about 3 to 10 minutes.

The magnetic recording medium according to the present invention produced as described above has lower stickiness and extremely good abrasion resistance than conventionally known magnetic recording media, and has excellent surface properties.
There is less dropout. Furthermore, the magnetic recording medium according to the present invention has a significantly improved S/N ratio compared to conventional magnetic recording media, and can obtain higher reproduction output than conventional magnetic recording media.

Furthermore, it is possible to provide a layer with sufficiently low surface electrical resistance and light transmittance.

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

The components, roles, 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".
represents.

Souse top First, the following composition was prepared.

CO-containing r Fe40a 100 parts Soft polyurethane (Pandesox T-5610 manufactured by Dainippon Ink and Chemicals Co., Ltd.: Tensile strength 155 kg/ctA, elongation at break 1000%) 3 parts Hard polyurethane (Rispon 4216 manufactured by Dainippon Ink and Chemicals Co., Ltd.: Tensile Strength 680 kg/cJ, elongation at break 530%) 3 parts Nitrocellulose 5 parts (Seltsuba BTHI/2 manufactured by Asahi Chemical Co.) Vinyl chloride-vinyl acetate copolymer 1 part (VAGH manufactured by Union Carbide) Conductex 975 (BET value 270 i/g.

Particle size 46 mμ) 2.5 parts Raven 2000 (BET value 180 n (/g, particle size 19 mμ)) 2.5 parts Lecithin 5 parts Myristic acid 2 parts Valmitic acid butyl ester 1 part Alumina 4 parts Methyl ethyl ketone 50 parts Cyclohexanone 100 parts After stirring and mixing the composition in a ball mill for 72 hours, 5 parts of polyfunctional incyanate (curing agent) was added and filtered through a filter with an average pore size of 1 μm.
After coating on a 4 μm thick polyester film using a reverse roll coater and drying, the magnetic layer was surface treated using a super calendar roll to obtain a wide magnetic film having a 5 μm thick magnetic layer. One copy of this film was cut into a 2-inch width to produce a magnetic tape for video.

In the paint composition of Example 1, soft polyurethane was added to 1.
A magnetic tape was prepared in the same manner as in Example 1, using 5 parts of hard polyurethane and 4.5 parts of hard polyurethane.

Disaster Treatment 1 In the paint composition of Example 1, 3 parts of soft polyurethane, 7 parts of hard polyurethane, 3 parts of nitrocellulose,
Example 1: 1 part of vinyl chloride-vinyl acetate copolymer
A magnetic tape was made in the same way.

Large flow m↓ In the paint composition of Example 1, softened polyurethane was 0.
A magnetic tape was prepared in the same manner as in Example 1 using 7 parts of hard polyurethane, 1.3 parts of nitrotrocellulose, and 4 parts of vinyl chloride-vinyl acetate copolymer.

In the paint composition of Sharp Paint Example 1, the soft polyurethane was added to 3.
5 parts, 6.5 parts of rigid polyurethane, 1.5 parts of nitrocellulose, 0.5 parts of vinyl chloride-vinyl acetate copolymer.
A magnetic tape was prepared in the same manner as in Example 1.

A magnetic tape was prepared in the same manner as in Example 1 except that in the coating composition of Example 1, the soft polyurethane was not used and the total amount of polyurethane was changed to hard polyurethane (6 parts).

Comparison N1 A magnetic tape was prepared in the same manner as in Example 1 except that the hard polyurethane was not used in the coating composition of Example 1, and the total amount of polyurethane was changed to soft polyurethane (6 parts).

A magnetic tape was prepared in the same manner as in Example 1 except that Conductexox 975 was not used as the carbon blank and only 5 parts of Laben 200o was used as the carbon blank.

In the paint composition of Comparison Example 1, Lahen 2000 was not used as the carbon blank, and Conductexox 975 was used as the carbon blank.
A magnetic tape was prepared in the same manner as in Example 1, except that 5 parts of chloride was added.

In Example 1, Conductex 975 and Raven 2000 were not used (i.e., without carbon blank).
A magnetic tape was prepared in the same manner as in Example I.

For each of the above magnetic tapes, gloss (surface gloss) surface electrical resistance, light transmittance, video characteristics, dust removal, adhesive layer, and coefficient of friction were measured, and the results are shown in the table below. The method for these measurements was as follows.

Gloss: Measured with a variable angle photometer at an angle of 60° C., and expressed with the value of Example 1 as 100% (the larger the value, the better the surface smoothness).

Light transmittance: A certain part of the tape's magnetic layer is irradiated with white light and the ratio of transmitted light to incident light is measured.

Surface electrical resistance: Measured according to the usual method.

Video characteristics: The 4MHz playback output is a small RF output, and the video S/N and color S/N are measured using a Shibaku Color Video Noise Meter 9250 (the measured value of Example 1 is assumed to be 0, and the relative values are shown). Powder removal: VCR (HR-3
After running 400 times at 300), collect the magnetic powder adhering to the head cylinder and guide pole with adhesive tape.
Judging by visual inspection.

Attach adhesive tape to the magnetic layer, peel it off, and visually judge the degree of peeling of the magnetic layer.

The following is clear from the above results. That is, Examples 1 to 3 completely satisfy the conditions according to the present invention, so all properties are good, and in Examples 4 and 5, the amount of polyurethane is close to the limit of the desired range or within the range. The gloss, video characteristics, and frictional resistance are somewhat poor due to the outsideness, but the values are sufficient for practical use. On the other hand, Comparative Example 1
Comparative Example 2 has a magnetic layer that is too hard and has poor surface gloss, Comparative Example 2 has a magnetic layer that is too soft and has high frictional resistance, and Comparative Example 3 has a high surface electrical resistance because it does not contain conductive carbon black. It can be seen that Comparative Example 4 has too high light transmittance because it does not contain carbon black for light shielding, and Comparative Example 5 has too high surface electrical resistance and light transmittance because it does not contain carbon black.

[Brief explanation of drawings]

The drawings show examples of the present invention, in which Figure 1 is a graph showing the relationship between load (tensile strength) and elongation rate (elongation at break) of polyurethane, and Figure 2 is a graph showing the characteristics of soft polyurethane depending on its elongation rate. Figure 3 is a diagram of changes in properties depending on the elongation rate of hard polyurethane, Figure 4 is a diagram of changes in properties depending on the specific surface area of carbon blank, Figure 5 is a diagram of changes in still durability depending on the blending ratio of soft and hard polyurethane. Figure 6 is a graph showing the change in stickiness and squareness ratio depending on the blending ratio of other resins, and Figure 7 is a graph showing the change in still durability depending on the blending ratio of polyurethane and other resins. The graph shown in FIG. 8 is an enlarged cross-sectional view of a portion of the magnetic tape. In addition, in the reference numerals shown in the drawings, 1.-----Nonmagnetic support 2--1 Subbing layer 3--1 Magnetic layer A, 1. Soft layer of the present invention Polyurethane area B2
-...One area of the hard polyurethane of the present invention. Agent: Hiroshi Aisaka, patent attorney (and other figure 1, figure 2, figure 3, figure 4, surface area (m21g) figure 5, figure 6) #
δd intellectual property ttTJ fact (self-handling - Nei city official book 1. Indication of the case 1982 Patent Application No. 86888 2, Name of the invention Magnetic recording medium 3, Person making the amendment Relationship to the case 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 il+, “(so-called low)” on page 33, line 5 of the specification
Delete. (2), "Binder" in line 6 on page 33 is corrected to "magnetic powder." (3) "Binding material" on page 33, line 15 is "magnetic powder"
I will correct it. 1 or more - (Voluntary) Procedure Nefusho 1. Indication of the case 1982 Patent Application No. 86888 2, Name of the invention Magnetic recording medium 3, Person making the amendment Relationship to the case Patent applicant address 1-26-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Name Name
(127) Roku Konishi Photo Industry Co., Ltd. 4, Agent (11 "Area A" in the fourth line from the bottom of page 3 of the specification is corrected to "Area A1J." (2) Page 4, line 4 of the same) First, "dispersibility" is corrected to "compatibility". (3) "Shima." in the third line from the bottom of page 9 of the same page is corrected to "put away." (4) Bottom of page 9 of the same page. 3rd line from ``r CB to'' to 1CB
I corrected it to ``with 1''. (5) “S-caprolactam” on page 133, line 9 of the same page [
ε-caprolactam” is corrected. (6) Delete "α-methyl-1-caprolactam," from lines 9 to 10 on page 13. (7) “S-methyl-3-
Correct ``prolactam'' to ``δ-caprolactam.'' (8) “Methacrylic acid” in the fourth line from the bottom of page 26 of the same page is “
methacrylic acid”. (9) On page 33, line 3 from the bottom, "anticene oxide" is corrected to "antimony oxide." αψ [Soft polyurethane] in lines 2 to 1 from the bottom of page 39 will be corrected to "soft polyurethane." (11) On page 400, line 1, “trocellulose” is replaced with “
Cellulose,” I corrected. (12) "Made with adhesive" in the fourth line from the bottom of page 41 is corrected to "adhesive." One or more -

Claims (1)

[Claims] 1. A soft polyurethane with a tensile strength of less than 200 kg/ci and an elongation at break of 900% or more, and a tensile strength of 200 kg/a? + or more and elongation at break is 9
The soft polyurethane is less than 00% and the specific surface area (BE
T value) Bl is 4 On (/g < Bt < 200
rrr/g and a carbon blank with specific surface area (
BET value) Bs is 200M/g IB, <500 resistance/
1. A magnetic recording medium comprising a layer containing carbon black.