JPH059844B2 - - Google Patents

Description

[Detailed description of the invention]

1. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes and magnetic sheets. 2. Prior Art In general, magnetic recording media are manufactured by applying a magnetic paint containing magnetic powder, a binder, etc. onto a support and drying it. In magnetic recording media 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, resulting in decreased reproduction output, output fluctuations, dropouts, increased noise, etc. It happens easily. In order to overcome these drawbacks, traditionally,
Various studies have been attempted regarding binders that bind 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 composed of polyurethane produced by a curing reaction between a polyol such as polyester or polyether and polyisocyanate in the magnetic layer after coating on the support. Reactions occur gradually during the process. As a result, not only can the coating film become brittle, but also the coating film may not have sufficient abrasion resistance using such a binder. On the other hand, according to the specification of Japanese Patent Publication No. 53-1641, 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. However, based on the recognition that this allows the formation of a strong coating film based on the interaction of the three, we developed a 100% modulus of 30 to 100 kg/cm ^2.
hard thermoplastic polyurethane, cellulose resin,
It has been proposed to use a magnetic coating film made by binding magnetic powder with a binder made of a soft thermoplastic polyurethane resin with a 100% modulus of 20 kg/cm ² or less. For each of the above polyurethanes with this known binder composition, from the relationship between load (Kg/cm ² ) and elongation rate (%), as shown in Figure 1, line b ₁ (line with load 100Kg/cm ² ) The hard thermoplastic polyurethane belongs to the area B ₁ surrounded by the line B ₁ and the line b 2 (the line with a load of 30 kg/cm ² ), and the line with a load of 0 and the b ₃ line (the line with a load of 20
The soft thermoplastic polyurethane belongs to the area _A1 surrounded by the Kg/cm ² line). However, the difference in hardness and softness of polyurethanes with properties belonging to regions B ₁ and A ₁ is not so large, so even if the mixing ratio of the two is changed, the properties of the magnetic coating film can be adjusted. There are limitations, and the curing power is not sufficient. Therefore, the adhesiveness of the magnetic coating is high,
In addition, because the dispersibility of the resins is not sufficient, the resulting magnetic recording medium has insufficient abrasion resistance, durability, and surface properties, resulting in problems such as powder falling, dropouts, and video S/S/
A satisfactory N ratio and chroma S/N ratio could not be obtained. On the other hand, in magnetic recording media, the dispersibility of magnetic powder tends to be poor even when a binder is used alone or in combination with various binders.
For this reason, surface properties and abrasion resistance were not fully satisfied. Particularly in video tapes that require short wavelength recording, poor dispersion of the support in the magnetic layer leads to deterioration of the S/N ratio and decrease in sensitivity.
In addition, since such a recording medium comes into violent sliding contact with a magnetic head during recording and reproduction, the magnetic coating is worn out by repeated use, and the magnetic material contained in the coating is likely to fall off, resulting in a deterioration in wear resistance. . The reason for this is that the magnetic powder such as γ-Fe ₂ O ₃ powder used as the recording element of the magnetic recording medium has a hydrophilic surface, so when it is kneaded with the binder, it has a weak affinity with the binder. This is thought to be because it is difficult to uniformly disperse it in the binder. For this reason, various additives are used to improve the dispersion of magnetic powder and improve wear resistance. Examples include higher fatty acids, fatty acid amides, fatty acid esters, higher alcohols, metal soaps, and polyethylene oxide. However, even with the addition of these additives, it has been difficult to obtain a magnetic recording layer having desirable characteristics. for example,
If these additives are used in large amounts, the mechanical strength of the magnetic recording layer may decrease, and a blooming phenomenon in which the additives gradually ooze out after the magnetic recording layer is formed may be observed. Ta. For this reason, the characteristics and dispersion of the magnetic recording layer were never satisfactory. Generally, in order to improve recording density and short wavelength recording, it is necessary to improve the surface smoothness of magnetic powder and make it finer to improve its dispersibility. However, if the particle size of the magnetic powder is reduced (in other words, the specific surface area is increased) to meet these requirements, the dispersibility of the magnetic powder deteriorates, making it impossible to obtain desired electromagnetic properties. 3. Purpose of the invention The purpose of the present invention is to improve adhesiveness, abrasion resistance, durability,
The object of the present invention is to provide a magnetic recording medium having a magnetic layer having excellent surface properties and improved dispersibility of magnetic powder. 4. Structure and Effects of the Invention That is, the magnetic recording medium according to the present invention comprises a soft polyurethane having a tensile strength of less than 200 Kg/cm ² and an elongation at break of 900% or more, and a tensile strength of 200 Kg/cm 2 or more.
cm ² or more and has an elongation at break of less than 900%, and at least one monomer unit having a negative organic group as a copolymerization component, and the negative organic group is an ammonium and/or alkali metal salt (hereinafter referred to as , sometimes referred to as a salt of a negative organic group). According to the present invention, the presence of the above-mentioned soft polyurethane in the magnetic layer facilitates calendering and improves the adhesion of the layer.
The presence of the above-mentioned hard polyurethane prevents the disadvantages of using soft polyurethane alone, such as stickiness and a decrease in stiffness, thereby suppressing stickiness and increasing the stiffness of the medium. 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 for the soft polyurethane to fully produce the above-mentioned effects, its tensile strength and elongation at break should each be 200%.
Kg/cm ² less than 900%, and at the same time the tensile strength and elongation at break of the rigid polyurethane, respectively.
By setting the amount to be 200 Kg/cm ² or more and less than 900%, and ensuring a sufficient difference in these mechanical properties between the two polyurethanes, the properties of the magnetic layer of the magnetic recording medium 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 relationship between the elongation rate (elongation at break) of a soft polyurethane with a tensile strength of less than 200 Kg/cm ² and the abrasion resistance (ease of scratching, resistance to powder falling off) of the magnetic layer. It can be seen that the characteristics are significantly improved when the ratio is increased to 900% or more. Also, Figure 3 shows
The relationship between the elongation rate of a rigid polyurethane with a tensile strength of 200 Kg/cm ² or more and the ease with which the medium is calendered is shown, and when the elongation rate is less than 900%, the properties are significantly improved. Preferred ranges of physical properties of both of the polyurethanes used in the present invention are tensile strength of 10 to 100 Kg/cm ² and elongation at break of 1000 to 1200% for soft polyurethane.
Hard polyurethane has a tensile strength of 300 to 600 Kg/cm ² ,
The elongation at break is 400-750%. To illustrate the mechanical properties of the polyurethane according to the present invention, in Fig. 1, line b ₄ (load 200
The hard polyurethane belongs to one region B ₂ surrounded by the Kg/cm ² line) and the a ₁ line (900% elongation), and the soft polyurethane belongs to the other region A ₂ . The mechanical properties (tensile strength, elongation at break) of the polyurethane according to the present invention are those specified by Japanese Industrial Standards (JIS) K6301-1975, and the elongation at break is defined by the "elongation at break" in the same standard. ”. An important feature of the present invention is that, in addition to using both of the polyurethanes described above as binders for the magnetic layer, the magnetic powder is (pre)treated with the copolymer described above. In other words, since the above copolymer has a salt of a negative organic group formed in the monomer, the hydrocarbon residue portion of the copolymer is well compatible with the binder, and the above salt portion is simply It has a moderately large dissociation constant compared to organic groups (free, not forming salts), and is sufficient for the hydrophilic surface of magnetic powder when it is treated with the above copolymer, especially in an aqueous system. be combined with In addition, since it is more hydrophilic than free organic groups, when surface-treated magnetic powder is dispersed in a binder or solvent, there is less tendency for it to be desorbed and transferred to the binder or solvent phase. As a result, the above-mentioned copolymer, on the one hand, sufficiently binds to the surface of the magnetic powder, and on the other hand, it adapts well to the binder of the magnetic layer without being desorbed, so that the magnetic powder treated with this copolymer The dispersibility of the powder is greatly improved, and various properties such as squareness ratio, output, and surface seepage are significantly improved. 5 Examples Hereinafter, the present invention will be described in more detail with reference to Examples. The soft polyurethane and hard polyurethane used as the binder of the magnetic layer in the magnetic recording medium of the present invention can be synthesized by reacting a polyol and a polyisocyanate. Usable polyols include organic dibasic acids such as phthalic acid, adipic acid, dimerized linoleic acid, and maleic acid, and glycols such as ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol, or trimethylpropane, hexanetriol, For reaction with polyhydric alcohols such as glycerin, trimethylolpropane, hexanetriol, glycerin, trimethylolethane, pentaerythritol, or any two or more polyols selected from these glycols and polyhydric alcohols. polyester polyol synthesized by this method; or s
- Lactone polyester polyol synthesized from lactams such as caprolactam, α-methyl-1-caprolactam, s-methyl-s-caprolactam, and γ-butyrolactam; or synthesized from ethylene oxide, propylene oxide, butylene oxide, etc. Examples include polyether polyols. These polyols are reacted with isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, metaxylylene diisocyanate, etc.
In this way, urethanized polyester polyurethane and polyether polyurethane are synthesized. These polyurethanes according to the invention are usually produced primarily by the reaction of polyisocyanates with polyols and also in the form of urethane resins or urethane prepolymers containing free isocyanate groups and/or hydroxyl groups, or in the form of urethane prepolymers containing free isocyanate groups and/or hydroxyl groups. It may also be one that does not contain end groups (for example in the form of a urethane elastomer). Since the methods for producing polyurethane, urethane prepolymers, urethane elastomers, curing and crosslinking methods, etc. are well known, detailed explanation thereof will be omitted. The polyurethane described above can be either soft or hard depending on its components. For example, flexible polyurethane is produced by having multiple types of polyester polyol components randomly present in the molecule, or by using an isocyanate in which the molecular chain between the isocyanate groups consists of chain aliphatic hydrocarbon groups. Obtainable. Rigid polyurethane can be synthesized by using the same type of polyol, by increasing the amount of isocyanate added, by using isocyanate that is easily crystallized, by using isocyanate having a benzene ring in the molecule, etc. Although both polyurethanes may be used together in any proportion, it has been confirmed that there is a certain preferable range for their respective contents. As shown in FIG. 4, the weight ratio of soft polyurethane to hard polyurethane is 80:20 to 20:80, which may be a disadvantage in still durability, and 70:30 to 30:70 is even better. Next, the above-mentioned copolymer used for pretreating the surface of magnetic powder in the present invention will be explained in detail. A negative organic group-containing monomer (hereinafter referred to as monomer unit A) constituting this copolymer.
Examples of the negative organic groups include carboxyl groups, phosphoric acid residues, sulfonic acid residues, etc.
Among these, carboxyl groups and phosphoric acid residues are preferred, and their salts include ammonium salts, alkali metal salts, and the like, with ammonium salts being preferred. Examples of the monomer unit A include acrylic acid, methacrylic acid, maleic anhydride, and 2-hydroxyethyl acryloyl phosphate, with acrylic acid and maleic anhydride being preferred. The negative organic group is preferably a carboxyl group or a phosphoric acid residue, and the salt is preferably an ammonium salt. Acrylic acid and maleic anhydride are preferred as monomer unit A because they have particularly excellent storage stability and dispersibility. In the case of additives conventionally used to improve the blooming phenomenon, the blooming phenomenon can be improved to some extent, but the storage stability is poor, pecking is likely to occur, and agglomeration is likely to occur during dispersion. However, the copolymer used in the present invention is excellent in these points. In this copolymerization component, to explain the effect of the salt of a negative organic group, the dissociation constant of a simple negative organic group (e.g., free -COOH) and its salt (e.g., ammonium salt, Na salt) is as follows. It's different. [Dissociation constant K] -COOH<-COO ^- N ⁺ H ₄ <-COONa and,
Squareness ratio of a magnetic recording medium comprising a magnetic layer prepared by the method described in detail later using magnetic powder surface-treated with each copolymer containing monomer unit A having each of these groups. It was confirmed that (Bm/Br) is as shown in FIG. 5, for example. That is, it can be seen that the use of a copolymer in which -COOH is a salt according to the present invention improves the squareness ratio, compared to the case where a copolymer having just -COOH is used. This is because when -COOH is made into a salt, it has a large dissociation constant and is therefore more hydrophilic.
This is because the copolymer easily binds sufficiently to the hydrophilic surface of the magnetic powder during surface treatment of the magnetic powder, and there is little tendency for the adsorbed material to be desorbed during dispersion (that is, the hydrophilicity is good). it is conceivable that. On the other hand, -COOH has the property of easily adhering to or bonding to the surface of magnetic powder. That is, it is easy to attach or bind, but it has higher lipophilicity than salts,
Easily desorbed during dispersion in organic solvents. Furthermore, among the above-mentioned organic groups according to the present invention, from FIG. 5, ammonium salts have better magnetic properties than alkali metal salts, and the use of ammonium salts is the highest, and before and after that, the dissociation constant decreases or increases. It can be seen that the squareness ratio tends to decrease as
The reason for this is that alkali metal salts have greater hydrophilicity (possibly due to a considerably larger dissociation constant), which makes them easier to bond to the magnetic powder surface during surface treatment in aqueous systems, as well as being more likely to detach. This is thought to be because ammonium salts preferentially bond to the magnetic powder surface due to their moderate dissociation constants. In addition, desorption in organic solvents is low. Note that when the magnetic powder is not subjected to any surface treatment, the characteristics of the medium become even worse (see FIG. 3). As the ammonium salt, the above −COO ⁻ N ⁺ H ₄
General formula containing: −COO ⁻ N ⁺ (R ¹ ) (R ² ) (R ³ ) (R ⁴ ) (However, R ¹ , R ² , R ³ , and R ⁴ are each a hydrogen atom, or are the same or (different lower alkyl groups) are applicable. Here, when the above R ¹ , R ² , R ³ , and R ⁴ are lower alkyl groups, the total number of carbon atoms of R ¹ to ^{R 4} is 6 or less because of steric hindrance. This is desirable because it does not impair the sex. The above-mentioned copolymer used in the present invention is expressed as [-A] using the above-mentioned monomer unit A (also written as - [A-]) and monomer unit B (also written as - [B-]). It can be expressed as _n --- [B] _o --. However, m and n are each positive real numbers. The average value of (m+n) is 100 or less, preferably 50 or less. If it exceeds 100, it becomes difficult to disperse uniformly in the magnetic layer of the magnetic recording medium, and the performance (for example, output, etc.) of the recording medium tends to become partially non-uniform, which is not preferable. Further, (m+n) is particularly preferably 30 or less, and the dispersion effect in this case is particularly excellent, and the performance of the magnetic recording medium according to the present invention is particularly significantly improved. Note that the average value of (m+n) is, for example, from the viewpoint of preventing the blooming phenomenon.
It is preferable that it is 4 or more. Here, by selecting the values of m and n and the type of salt of the organic group in unit A, the copolymer can have both hydrophilic and hydrophobic properties.
Appropriate control of HLB (Hydrophile Lipophile Balance) is possible. In addition, monomer units other than monomer unit A (hereinafter referred to as monomer unit B) of this copolymer are
It is called. ) Examples include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-n-butylstyrene, p-tert-
Butylstyrene, p-n-hexylstyrene, p
-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene Examples include styrene and styrene derivatives such as styrene and styrene derivatives. Examples of vinyl monomers other than these include ethylenically unsaturated monoolefins such as ethylene, propylene, butylene, and isobutylene; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide, and vinyl fluoride. ;
Vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, acrylic acid n
-butyl, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate,
Phenyl acrylate, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n methacrylate
-butyl, n-isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate,
α-methylene aliphatic monocarboxylic acid esters such as dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; derivatives of acrylic acid or methacrylic acid such as acrylonitrile, methacrylonitrile, and acrylamide;
vinyl methyl ether, vinyl ethyl ether,
Vinyl ethers such as vinyl isobutyl ether; Vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and methyl isopropenyl ketone; N-vinyl compounds such as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole, and N-vinylpyrrolidone. ; Examples include vinylnaphthalenes. In order to surface-treat the magnetic powder with the above-mentioned copolymer, an aqueous solution of the copolymer may be added to the magnetic powder, kneaded with a kneader or the like for a predetermined period of time, and further water may be removed by filtration and/or drying. The treated magnetic powder after filtration and/or drying can be pulverized to a desired particle size and classified. Alternatively, the above copolymer is dissolved in a solvent such as toluene, methyl ethyl ketone, ethyl cellosolve, acetone, methanol, etc.
Magnetic powder is immersed in the solution at a predetermined ratio, stirred and mixed, and then filtered or the solvent is evaporated, and if necessary, it can be further dried. It has also been found that when the specific surface area of the magnetic powder to be treated is set to 30 m ² /g or more, the surface treatment effect of the above-mentioned copolymer is well exhibited. That is, if the specific surface area is 30 m ² /g or more, the particle size is small and the magnetic properties are improved to some extent in terms of high-density recording, but the dispersibility of the magnetic powder tends to be poor. As shown in Figure 6, when the magnetic powder is not subjected to any surface treatment, its properties improve to some extent as the specific surface area increases, and the copolymer in which the organic group in the monomer unit A is simply -COOH Although the properties of the magnetic powder treated with (treated magnetic powder) are improved, the improvement is only approximately linear with the specific surface area of the magnetic powder. On the other hand, magnetic powder surface-treated with a copolymer according to the present invention (treated magnetic powder)
It has been confirmed that when the specific surface area is 30 m ² /g or more, the properties are dramatically improved compared to treated magnetic powder. This clearly shows that not only the deterioration of the dispersibility of magnetic powder can be effectively prevented by the surface treatment with the copolymer according to the present invention, but also the dispersibility can be significantly improved. Note that if the specific surface area of the magnetic powder used is increased more than necessary, poor dispersion will occur, so it is desirable that the upper limit is 100 m ² /g. In addition, "specific surface area" in the above refers to the surface area per unit weight, and is a physical quantity that is completely different from the average particle diameter. Some have small surface areas. To measure the specific surface area, for example, first, magnetic powder is degassed while being heat-treated at around 250°C for 30 to 60 minutes to remove what is adsorbed to the powder, and then introduced into a measuring device. Set the initial pressure of nitrogen to 0.5Kg/m ² and perform adsorption measurement using nitrogen at liquid nitrogen temperature (-195℃) (Specific surface area measurement method generally referred to as BET method. For details, see J.Ame. Chem.Soc, 60 309 (1938)
). As a measuring device for this specific surface area (BET value), it is possible to use a "fine powder measuring device (Canterthorpe)" jointly manufactured by Yuasa Battery Co., Ltd. and Yuasa Ionics Co., Ltd. A general explanation of the specific surface area and how to measure it can be found in ``Measurement of Powders'' (JMDALLAVALLE, CLYDE).
Co-authored by ORR Jr., translated by Benta and others; published by Sangyo Toshosha), and also in ``Chemistry Handbook'' (Application Edition, Sections 1170-1171, edited by the Chemical Society of Japan, published by Maruzen Co., Ltd. in 1968).
(published on April 30, 2015). (In addition,
In the above-mentioned "Chemistry Handbook", the specific surface area is simply described as surface area (m ² /g), which is the same as the specific surface area in this specification. ) 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. improves its mechanical strength. 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 ethers include methylcellulose, ethylcellulose, propylcellulose, isopropylcellulose, butylcellulose, methylethylcellulose, methylhydroxyethylcellulose, ethylhydroxyethylcellulose, carboxymethylcellulose, carboxymethylcellulose sodium salt, hydroxyethylcellulose, benzylcellulose, cyanoethylcellulose, vinylcellulose, Nitrocarboxymethylcellulose, diethylaminoethylcellulose, aminoethylcellulose, etc. can be used. As the cellulose inorganic acid ester, nitrocellulose, cellulose sulfate, cellulose phosphate, etc. can be used. In addition, cellulose organic acid esters include acetylcellulose, propionylcellulose, butyrylcellulose, methacryloylcellulose, chloroacetylcellulose, β-oxypropionylcellulose, benzoylcellulose, p-toluenesulfonate cellulose, acetylpropionylcellulose, acetylbutyrylcellulose. etc. can be used. Among these cellulose resins, nitrocellulose is preferred. Specific examples of nitrocellulose include Cellnova BTH1/2 and Nitrocellulose SL-1 manufactured by Asahi Kasei Corporation, Nitrocellulose RS1/2 and Cell Line L-200 manufactured by Daicel Corporation.
Viscosity of nitrocellulose (JIS, K-6703 (1975)
2 to 1/64 seconds, particularly preferably 1 to 1/4 seconds. If it is outside this range, the film thickness and film strength of the magnetic layer will be insufficient. In addition, the above-mentioned vinyl chloride copolymers that can be used have the general formula: There is something expressed as in this case,

The molar ratio derived from l and m in the formula and [-X] _n -- units is 95 to 50 mol % for the former unit and 5 to 50 mol % for the latter unit. In addition, X represents a monomer residue copolymerizable with vinyl chloride, including vinyl acetate, vinyl alcohol, maleic anhydride, maleic anhydride ester,
Represents at least one member selected from the group consisting of maleic acid, maleic ester, vinylidene chloride, acrylonitrile, acrylic acid, acrylic ester, methacrylic acid, methacrylic ester, vinyl propionate, glycidyl methacrylate, and glycidyl acrylate. The degree of polymerization expressed as (l+m) is preferably from 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, 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"). Vinyl chloride
Examples of vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, and vinyl chloride-vinyl acetate-vinyl alcohol.
Examples include copolymers of vinyl acetate-maleic anhydride, vinyl chloride-vinyl acetate-vinyl alcohol-maleic anhydride, vinyl chloride-vinyl acetate-vinyl alcohol-maleic anhydride-maleic acid, and vinyl chloride-vinyl acetate. Among the copolymers, partially hydrolyzed copolymers are preferred. Specific examples of the above-mentioned vinyl chloride-vinyl acetate copolymers include "VAGH", "VYHH", and "VMCH" manufactured by Union Carbide Co., Ltd., and Sekisui Chemical Co., Ltd.
"Eslec A", "Eslec A-5", "Eslec C", "Eslec M" manufactured by Denki Kagaku Kogyo Co., Ltd.
"Denkabinir 1000G", "Denkabinir
1000W" etc. can be used. The above-mentioned vinyl chloride copolymer and cellulose resin may be used in any blending ratio, but as shown in Figure 7, the weight ratio of vinyl chloride resin to cellulose resin is 90/10 to 90/10. Preferably 5/95, 80/20~
It has been confirmed that 10/90 is even more desirable. Outside 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 dropouts tend to occur. Furthermore, if the amount of the vinyl chloride copolymer increases (if the above weight ratio exceeds 90/10), poor dispersion tends to occur, for example, the squareness ratio tends to deteriorate. However, in FIG. 7, c indicates a tendency toward stickiness (adhesiveness), and as it goes up the vertical axis, stickiness decreases, resulting in a good coating film. d shows the change in squareness ratio. Regarding the entire binder composition, the ratio of the above-mentioned polyurethane (total amount of both hard and soft polyurethane) and other resins (total amount of cellulose resin and vinyl chloride copolymer) is as follows. It has been confirmed that the weight ratio shown in Figure 8 is preferably 90/10 to 50/50, and more preferably 85/15 to 60/40. 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 the amount of other resins increases, 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. The magnetic layer of the magnetic recording medium according to the present invention further has a specific surface area (BET value) B ₁ of 40 m ² /g<B ₁ <
Carbon black ( ^hereinafter referred to as CB ₁
It is sometimes called. ) and specific surface area (BET value)
It is preferable to contain carbon black (hereinafter sometimes referred to as CB ₂ ) in which B ₂ satisfies 200 m ² /g≦B ₂ <500 m ² /g. Generally, when static electricity is accumulated during use of a magnetic recording medium, discharge occurs between the medium and the magnetic head, which tends to generate noise, and dust and the like may be attracted, causing dropouts. Furthermore, for video, 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, it is generally required that the surface electrical resistance of the magnetic layer be 10 ⁹ Ω·cm or less, and that the light transmittance of the tape portion where the magnetic layer is located be 0.05% or less. For this purpose, carbon black particles are usually added to the magnetic layer. In this case, the carbon black CB ₁ mentioned above,
It is effective to use CB ₂ . That is, carbon black CB ₁ is added mainly for light shielding, but its specific surface area B ₁ is 40 m ² /g<B ₁ <200 m ² /
It is extremely important to specify the range of g. By having a specific surface area within this range, the light-shielding property of the layer can be sufficiently achieved, and at the same time, the dispersibility of CB ₁ in the layer can be improved. Outside this range, CB ₁
If the specific surface area is less than 40 m ² /g, the particle size will be too large and the light-shielding properties will tend to deteriorate, making it necessary to increase the amount added more than necessary.If the specific surface area is more than 200 m ² /g, the particle size If it is too small, dispersibility into the layer tends to be poor. On the other hand, CB 2 is added to both CB ₁ and CB ₂ to provide sufficient conductivity, but its specific surface area
It is also important to specify that 200m ² /g≦B ₂ <500m ² /g. That is, the specific surface area B ₂ of CB ₂ is 200
If the particle size is less than m ² /g, the particle size will be too large and the conductivity will be insufficient even when carbon black is added.If it is more than 500 m ² /g, the particle size will be too small and the dispersibility of CB ₂ will be affected. becomes susceptible to deterioration. Therefore, by limiting the specific surface areas of the light-shielding CB ₁ and the conductive CB ₂ to the above-mentioned specific ranges, the surface electrical resistance and light transmittance of the magnetic layer etc. can be sufficiently reduced, and the layer It is possible to improve the surface smoothness of the layer (that is, the dispersibility of carbon black), suppress the amount of carbon black added, and improve the durability of the layer. The range of the specific surface area of each carbon black is determined by the conventional technology
88307)) (specific surface area is 700
m ² /g or more). In addition,
Each specific surface area above is 100m ² /g≦B ₁ <200m ² /g,
It is desirable that 200m ² /g≦B ₂ <300m ² /g.
In addition, regarding the particle size of each carbon black,
It is desirable that CB ₁ be 20 mμ or less and CB ₂ be 40 to 50 mμ, which correspond to the above specific surface area range according to the present invention. The amount of carbon black to be added is determined within a range that maintains the mechanical strength of the magnetic layer, but it is usually necessary to add 5 to 35% by weight (preferably 10 to 25% by weight) of carbon black to the binder. 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 magnetic layer (for example, powder falling off of the magnetic layer) can be improved. ) and also maintain the desired surface electrical resistance (10 ⁹ 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 black of the same weight, but on the contrary, it As a result, surface roughness and pinhole formation due to poor dispersion result in increased surface resistivity and light transmittance, which in turn causes deterioration of electromagnetic conversion characteristics. Acicular magnetic materials tend to break during dispersion, and if they become overdispersed, they will break and the electromagnetic conversion characteristics will decrease significantly.
When applied to a magnetic layer, the dispersion is usually stopped when the dispersion of the magnetic powder reaches its maximum. in this case,
When using carbon black that is difficult to disperse, it is often not dispersed sufficiently, resulting in separation of the carbon black in the paint, roughening of the surface of the paint film, generation of pinholes, etc., but this can be solved by using the carbon black of the present invention. It can be effectively prevented. In the present invention, it is preferable to use conductive _CB2 in order to reduce the surface resistivity of the magnetic layer, etc. to a sufficient range, but such carbon black has particles connected to each other like a bunch of grapes. A material with a high structure level, which is porous and has a large specific surface area, is preferable. Examples of such carbon black include Conductex 975 (specific surface area 270 m ² /g, particle size
46 mμ), Conductex 950 (specific surface area 245 m ² /
g, particle size 46 mμ), Cabot Vulcan XC-72 (specific surface area 257 m ² /gγ,
Particle size 18mμ) 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 above range, if the specific surface area of CB ₂ is 500 m ² /g or more, conductivity and light shielding properties are good in a completely dispersed state, but even after the dispersion of magnetic powder is completed, CB ₂ is not dispersed. is not completed, which tends to cause surface roughness and pinholes on the coating film.
If the specific surface area is less than 200 m ² /g, the effect of carbon black addition becomes weak. On the other hand, in order to reduce the light transmittance of the magnetic layer, it is possible to use the carbon black CB ₂ mentioned above, but although it has poor electrical conductivity, it has good light shielding properties (it has a larger surface area than the original conductive carbon). small),
By adding a small amount of carbon CB ₁ , which has excellent dispersibility, a synergistic effect can be obtained more significantly than when using conductive carbon alone. That is,
By adding light shielding carbon CB ₁ together with conductive carbon CB ₂ , the light transmittance can be made sufficiently small, and the amount of conductive carbon added can be significantly reduced, so the overall amount of carbon black added can be reduced. This results in improved mechanical properties and surface smoothness of the layer. Such light-shielding carbon black CB ₁ has a small particle size, a relatively low structure level, and a relatively low specific surface area, such as Raven 2000 manufactured by Columbia Carbon Co., Ltd. (specific surface area 180 m ^{2 )} . /gγ, particle size 19 mμ), 2100, 1170, 1000, #100, #75, #44, #35, #30 manufactured by Mitsubishi Kasei Corporation, etc. can be used. There is a certain preferable range for the mixing ratio (weight ratio) of each of the above carbon blacks, and CB ₂ /CB ₁
=90/10 to 50/50 is good, and 80/20 to 60/40 is even better. If this mixing ratio is larger than 90/10, the proportion of conductive carbon black CB ₂ will be large, resulting in insufficient light shielding properties, and if it is smaller than 50/50, the surface resistivity will be low due to the small amount of conductive carbon black CB ₂ . It will increase. FIG. 9 shows a magnetic recording medium, for example a magnetic tape, according to the present invention, in which a subbing layer 2 (this layer may not be provided if necessary) and a magnetic layer 3 are provided on a support 1. are laminated. Based on the present invention, the magnetic layer 3 contains soft polyurethane having the above-mentioned mechanical properties, hard polyurethane, and the above-mentioned treated magnetic powder, respectively. The magnetic powder used in the present invention, particularly the ferromagnetic powder, includes γ-Fe ₂ O ₃ and Co-containing γ-
Iron oxide magnetic powder such as Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ ; Fe, Ni, Co, Fe-Ni-Co alloy, Fe-Mn-
Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-Co-Ni-P alloy, Co-Ni alloy, etc. Fe,
Examples include various ferromagnetic powders such as metal magnetic powders containing Ni, Co, etc. as main components. The magnetic paint according to the present invention includes magnetic powder (preferably treated with the above copolymer in advance), a binder, and each of the above carbon blacks.
CB ₁ , CB ₂ , the above copolymer (if the magnetic powder has already been treated with this copolymer, it is not necessary to add it again, or it may be added further), etc. in a coating solvent. Prepared by kneading and dispersing with
This magnetic paint is applied onto a support to form a magnetic layer.
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℃ or less,
Average molecular weight is 10000~200000, degree of polymerization is about 200~
About 2000, for example, acrylic ester.
Acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, methacrylic ester-acrylonitrile copolymer, methacrylic ester-vinylidene chloride copolymer, methacrylic ester-styrene copolymer Coalescence, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, styrene-butadiene copolymer, polyester resin, chlorovinyl ether-acrylic acid ester copolymer, amino resin , various synthetic rubber-based thermoplastic resins, and mixtures thereof. These resins are disclosed in Japanese Patent Publications No. 37-6877 and No. 39-
No. 12528, No. 39-19282, No. 40-5349, No. 40-
No. 20907, No. 41-9463, No. 41-14059, No. 41-
No. 16985, No. 42-6428, No. 42-11621, No. 43-
No. 4623, No. 43-15206, No. 44-2889, No. 44-
No. 17947, No. 44-18232, No. 45-14020, No. 45
-14500, 47-18573, 47-22063, 47-22063, 47-18573, 47-22063,
No. 47-22064, No. 47-22068, No. 47-22069,
No. 47-22070, No. 48-27886, U.S. Patent No.
It is described in the specifications of No. 3144352, No. 3419420, No. 3499789, and No. 3713887. 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, phenolic resin, epoxy resin, urea resin, melamine resin,
These include alkyd resins, silicone resins, acrylic reactive resins, mixtures of methacrylate copolymers and diisocyanate prepolymers, urea formaldehyde resins, polyamine resins, and mixtures thereof. These resins are listed in Special Publication No. 39-8103 and No. 40-9779.
No. 41-7192, No. 41-8016, No. 41-14275
No. 42-18179, No. 43-12081, No. 44-
No. 28023, No. 45-14501, No. 45-24902, No. 46
−13103, No. 47-22067, No. 47-22072, No.
No. 47-22073, No. 47-28045, No. 47-28048,
Publication No. 47-28922, U.S. Patent No. 3144353, U.S. Pat.
3320090, 3437510, 3597273, 3437510, 3597273, 3437510, 3597273,
No. 3781210 and No. 3781211, described in the specifications. Examples of electron beam irradiation-curable resins include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, polyester acrylic type,
Polyether acrylic type, polyurethane acrylic type, polyamide acrylic type, etc., and polyfunctional monomers include ether acrylic type, urethane acrylic type, phosphate ester acrylic type, aryl type, hydrocarbon type, etc. From the viewpoint of recording density and strength, it is desirable that the total amount of the binder used in the present invention be 5 to 50 parts by weight per 100 parts by weight of magnetic powder. 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 (TDI), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), metaxylylene diisocyanate (MXDI) and these isocyanates together with active hydrogen compounds. and adducts with the average molecular weight of 100 to 3000. Specifically, Sumitomo Bayer Urethane Co., Ltd. products Sumidyur T80, Sumidyur 44S, Sumidyur PF, Sumidyur L, Desmodyur T65, Sumidyur 15, Sumidyur R, Sumidyur RF, Sumidyur IL,
Same SL; Takenate 300S manufactured by Takeda Pharmaceutical Company,
500: Mitsui Nisso Urethane Co., Ltd. product “NDI”,
"TODI": Desmodille T100 manufactured by Nippon Polyurethane Co., Ltd., Millionate MR, MT, Coronatore, PAPI-135 manufactured by Kasei Upjiyon Co., Ltd.
TDI65, TDI80, TDI100, Isonate 125M, TDI1431
etc. can be mentioned. On the other hand, examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDI), lysine isocyanate, trimethylhexamethylene diisocyanate (TMDI), and adducts of these isocyanates with active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. On the other hand, among the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred. Specifically, for example, Sumidyur N and Desmodyur Z4273 manufactured by Sumitomo Bayer Urethane Co., Ltd., Dulanate 50M and Dulanate 24A-100 manufactured by Asahi Kasei Co., Ltd.
24A-90CX, Coronate HL manufactured by Nippon Polyurethane Co., Ltd., and TMDI manufactured by Hyurus Co., Ltd. Furthermore, examples of alicyclic isocyanates among aliphatic isocyanates include methylcyclohexane-2,4-diisocyanate [structural formula:

[Formula]] 4,4-methylenebis(cyclohexyl isocyanate) [Structural formula: ] Examples include isophorone diisocyanate and adducts of its active hydrogen compounds. Specifically, the product “IPDI” manufactured by Hyurus Chemical Co., Ltd.
"PDI-T1890, PDI H-2921, PDI B1065, etc." The magnetic recording medium of the present invention is prepared by mixing and dispersing the magnetic powder, the binder, and various additives with an organic solvent to prepare a magnetic paint. After adding aromatic isocyanate and aliphatic isocyanate, this is coated on a support (for example, a polyester film), and dried as necessary to produce the product.The amount of isocyanate added is 1 to 100% by weight based on the binder. Preferably. If it is less than 1%, the hardening of the magnetic layer tends to be insufficient, and if it is more than 100%, 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 30% by weight based on the binder. Examples of the adducts of isocyanates and active hydrogen compounds and polyisocyanates include adducts of diisocyanates and trivalent polyols, pentamers of diisocyanates, and decarboxylation compounds of 3 moles of diisocyanates and water. Examples of these include an adduct of 3 moles of tolylene diisocyanate and 1 mole of trimethylolpropane, an adduct of 3 moles of metaxylylene diisocyanate and 1 mole of trimethylolpropane, a pentamer of tolylene diisocyanate, and 3 moles of tolylene diisocyanate. There are pentamers consisting of 2 moles of hexamethylene diisocyanate and 2 moles of hexamethylene diisocyanate, and decarboxylated products 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 may contain other additives such as dispersants, lubricants, abrasives, and other antistatic agents, if necessary. Other 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, linolenic acid, etc. having 8 or more carbon atoms; 18 fatty acids (represented by R-COOH, where R is a saturated or unsaturated alkyl group having 7 to 17 carbon atoms); alkali metals (Li, Na, K, etc.) or alkaline earth metals of the above fatty acids Examples include metal soaps made of (Mg, Ca, Ba, etc.). In addition to these, higher alcohols having 12 or more carbon atoms and sulfuric esters 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. Examples of lubricants include silicone oil, graphite, molybdenum disulfide, tungsten disulfide, monobasic fatty acids with 12 to 16 carbon atoms, and monobasic fatty acids with a total number of carbon atoms of 21 to 23 carbon atoms. Fatty acid esters consisting of alcohols of different types can also be used.
These lubricants are 0.2 to 100 parts by weight of magnetic powder.
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, and emery (main components: columnundum and magnetite). used.
These abrasives have an average particle diameter of 0.05 to 5 μm, particularly preferably 0.1 to 2 μm.
These abrasives are used in amounts of 1 to 100 parts by weight of magnetic powder.
It is added in an amount of 20 parts by weight. Other antistatic agents that may be used include graphite, tin oxide-antimony oxide compounds,
Conductive powders such as titanium oxide-tin oxide-antimony oxide compounds; natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin, and glycidol; higher alkylamines, quaternary ammonium salts , pyridine, other heterocycles, phosphonium or sulfonium; anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester groups, phosphate ester groups;
Examples include amphoteric activators such as amino acids, aminosulfonic acids, and sulfuric acid or phosphoric acid esters of amino alcohols. Solvents for magnetic paints or solvents used when applying magnetic paints include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; methanol, ethanol,
Alcohols such as propanol and butanol; Esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and ethylene glycol monoacetate; ethylene glycol dimethyl ether,
Ethers such as diethylene glycol monoethyl ether, dioxane, and tetrahydrofuran; Aromatic hydrocarbons such as benzene, toluene, and xylene; Methylene chloride, ethylene chloride,
Halogenated hydrocarbons such as 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, metals such as Al and Zn, glass, BN, Si carbide, ceramics such as porcelain, and ceramics are used. The thickness of these supports is approximately 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm.
In the case of disks and cards, it is 30 μm ~
It is about 10mm, and if it is drum-shaped, it should be cylindrical.
The type is determined depending on the recorder used. The surface of the support opposite to the side on which the magnetic layer is provided may be coated with a so-called backcoat, as shown by the dashed line 4 in FIG. 9, for the purpose of preventing static electricity, preventing transfer, and the like. Coating methods for forming a magnetic layer by coating the magnetic coating material on the support include air doctor coating, blade coating, air knife coating,
Squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure 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 magnetic powder in the layer, and then the formed magnetic layer is dried. Furthermore, the magnetic recording medium of the present invention is manufactured by subjecting it to surface smoothing processing or cutting it into a desired shape, if necessary. The magnetic recording medium according to the present invention produced as described above has lower tackiness than conventionally known magnetic recording media, has extremely good abrasion resistance, and has excellent dispersibility and 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, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. In addition, all "parts" in the following examples represent "parts by weight." Examples First, cobalt-containing γ-Fe ₂ O ₃ was surface-treated with each of the following copolymers (a) to (i) to obtain correspondingly treated magnetic powders. In other words, for 100 parts of iron oxide, the solid content is
An aqueous solution of each copolymer was added at a concentration of 2.5 parts, and kneaded for 2 hours using a kneader (manufactured by Inoue Seisakusho). Each treated magnetic powder that has been surface-treated in this way is transferred to a rotary vibration dryer to evaporate the moisture contained therein.
Furthermore, the magnetic powder was loosened in a colloid mill and classified through a mesh sieve to obtain treated magnetic powder with a desired particle size. (a) Ammonium salt of a copolymer of acrylic acid and butyl acrylate (b) Ammonium salt of a copolymer of acrylic acid and N-octylacrylamide (c) Sodium salt of a copolymer of acrylic acid and butyl acrylate (d) Ammonium salt of copolymer of maleic anhydride and styrene (e) Octylamine salt (ammonium salt) of copolymer of methacrylic acid and methyl methacrylate (f) 2-hydroxyethyl acryloyl phosphate and lauryl Ammonium salt of a copolymer with acrylate (g) Ammonium salt of a copolymer of acrylic acid with propylene (h) Butylamine salt (ammonium salt) of a copolymer with methacrylic acid and butylene (i) With acrylic acid Ammonium salt of ethylene copolymer The following composition was prepared using these treated magnetic powders. Treated Co-containing γ-Fe ₂ O ₃ (above) (BET value 40
^m2 /g) 100 parts soft polyurethane (Pandex T-5610 manufactured by Dainippon Ink & Chemicals Co., Ltd.: tensile strength 120Kg/cm2 ^,
7 parts hard polyurethane (Nituporan N-2304 manufactured by Nippon Polyurethane Co., Ltd.: tensile strength 400 Kg/cm ² , elongation at break 700%) 7 parts nitrocellulose 5 parts (Cellnova BTH1/2 manufactured by Asahi Kasei Co., Ltd.) Vinyl chloride-acetic acid Vinyl copolymer 1 part (VAGH manufactured by Union Carbide) Conductex 975 (BET value 270 m ² /g, particle size 46 mμ)
2.5 parts Raven 2000 (BET value 180m ² /g, particle size 19mμ)
2.5 parts lecithin 5 parts myristic acid 2 parts butyl palmitate 1 part alumina 4 parts methyl ethyl ketone 50 parts cyclohexanone 100 parts This composition was thoroughly stirred and mixed in a ball mill. At this time, samples were taken at regular intervals and applied onto a glass plate, and the degree of dispersion was compared with a standard plate under a 100x microscope to determine the end point of dispersion. This composition is then added with a polyfunctional isocyanate (curing agent).
5 parts of were added and filtered through a filter with an average pore size of 1 μm. The obtained magnetic paint was applied onto a 14 μm thick polyester film using a reverse roll coater while applying a magnetic field, and dried (dry film thickness: 6 μm).
Thereafter, the surface of the magnetic layer was treated using a super calender roll to obtain a wide magnetic film having a magnetic layer of a predetermined thickness. This film was cut to 12.7 mm width to create magnetic tape for video. Comparative Example 1 A magnetic tape was prepared in the same manner as in the Example except that the coating composition of the Example was treated with a magnetic powder that had been surface-treated with a copolymer of acrylic acid and butyryl acrylate. Comparative Example 2 A magnetic tape was prepared in the same manner as in the example except that magnetic powder whose surface was not treated was used in the coating composition of the example. Comparative Example 3 In the coating composition of the example, magnetic powder that had been surface-treated with the above-mentioned copolymer (a) was used, and the binder was soft polyurethane (Pandex T).
-5610) was replaced with Paraprene 22S (manufactured by Nippon Polyurethane Co., Ltd.: tensile strength 500 Kg/cm ² , elongation at break 600%), and otherwise a magnetic tape was prepared in the same manner as in the example. Comparative Example 4 In the coating composition of the example, magnetic powder surface-treated with the copolymer (a) above was used, and the binder was hard polyurethane (Nitsuporan N-
2304) to Pandex T-5610 (manufactured by Dainippon Ink and Chemicals, tensile strength 155Kg/cm ² , elongation at break 1000)
%), and otherwise a magnetic tape was produced in the same manner as in the example. Comparative Example 5 In the coating composition of the example, magnetic powder that had been surface-treated with the above-mentioned copolymer (a) was used, and the binder was soft polyurethane (Pandex T).
-5610) was replaced with Nipporan N-2304 (manufactured by Nippon Polyurethane Co., Ltd., tensile strength 400 Kg/cm ² , elongation at break 700%), and otherwise a magnetic tape was produced in the same manner as in the example. Regarding each of the above magnetic tapes, the squareness ratio, gloss,
The viscosity dispersion time and video characteristics were measured, and the results are shown in the table below. The method of these measurements was as follows. Gloss: Measured at an angle of 60° using variable angle luminosity, and expressed with the value of Comparative Example 1 as 100% (the larger the value, the better the surface smoothness). Dispersion time: Measures the time required for magnetic paint to reach a certain degree of dispersion under microscope observation. Video characteristics: Video deck HR-3300 (Victor Corporation) with 4MHz playback output as RF output
(Comparative Example 1), and the measured value of Comparative Example 1 is set as 0, and the relative value is displayed. The same applies to video S/N and color S/N.

[Table] As is clear from this result, when magnetic powder pretreated with the above copolymers a to i (especially ammonium salt) is used, the magnetic powder treated with a copolymer consisting of a simple free organic acid is Compared to powder (Comparative Example 1), untreated magnetic powder (Comparative Example 2), and those whose binder composition was outside the range of the present invention (Comparative Examples 3, 4, and 5), the squareness ratio was higher and the gloss was lower. Excellent and low viscosity magnetic paint can be prepared. Further, since the dispersion time is significantly shortened, productivity is greatly improved, and the cost increase due to pretreatment can be more than offset, or the cost can be reduced. The low viscosity means that
This means that the solids concentration can be further increased by reducing the amount of solvent used, and that the load on production equipment during drying can be reduced.

[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 the elongation rate. Change chart, 3rd
The figure is a graph showing changes in properties depending on the elongation rate of soft polyurethane, Figure 4 is a graph showing changes in still durability depending on the blending ratio of soft and hard polyurethane, and Figure 5 is a graph showing changes in the durability of stills depending on the type of magnetic powder surface treatment agent. A graph showing the mold ratio, Figure 6 is a graph showing changes in output S/N of various magnetic powders depending on the specific surface area of the magnetic powder, and Figure 7 is a graph showing changes in stickiness and squareness ratio depending on the blending ratio of other resins. FIG. 8 is a graph showing changes in still durability depending on the blending ratio of polyurethane and other resins, and FIG. 9 is an enlarged sectional view of a portion of the magnetic tape. In addition, in the symbols shown in the drawings, 1...nonmagnetic support, 2...subbing layer, 3...magnetic layer, _A2
...A region of the soft polyurethane of the present invention, B ₂ ...
This is the area of rigid polyurethane of the present invention.

Claims (1)

[Claims] 1 A soft polyurethane with a tensile strength of less than 200 Kg/cm ² and an elongation at break of 900% or more, and a soft polyurethane with a tensile strength of 200 Kg/cm ² or more and an elongation at break of 900%.
treated with a copolymer containing as a copolymerization component at least one monomer unit having a negative organic group and in which the negative organic group forms an ammonium and/or alkali metal salt. 1. A magnetic recording medium comprising a magnetic layer containing magnetic powder.