JPS59218627A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To suppress adhesion and to improve wear resistance, surface characteristics and dispersiblility of magnetic powder by forming a magnetic layer contg. soft and rigid polyurethanes having specific tensile strength and breaking elongation and magnetic powder treated with a specific copolymer. CONSTITUTION:Soft and rigid polyurethanes have respectively tensile strength and breaking elongation of <200kg/cm<2> and >=900% as well as >=200kg/cm<2> and <900% and are used as a binder for a magnetic layer. A carboxyl group and residual phosphoric acid group are preferable as a negative org. group in a monomer contg. a negative org. group constituting a copolymer and the salt thereof is preferably ammonium salt. An aq. soln. of a copolymer is added to the magnetic powder and the mixture is kneaded, filtered and dried to treat the surface of the magnetic powder. The magnetic powder, the binder and various additives are mixed and dispersed with an org. solvent to prepare a magnetic coating. A curing agent is added to such coating which is then applied on a base.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Industrial Application Field 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 the coating film may become brittle, but also the coating film using such a binder cannot obtain sufficient abrasion resistance.

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 a strong coating film can be formed based on the interaction of these three components, a hard thermoplastic polyurethane with a 100% modulus of 30 to 100 kg/Ca, a cellulose resin, and a 100% modulus of 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 of 20 kg/cTa or less.

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/cJ line) and b2 line (load 30 kg
The hard thermoplastic polyurethane belongs to the region B+ surrounded by the line of 0 load and the line of 20 load.
The soft thermoplastic polyurethane belongs to the area surrounded by the line (kg/cmlO line). However, since the difference in hardness and softness of each polyurethane having properties belonging to regions B1 and AI is not so large, there is a limit to the range in which the properties of the magnetic coating 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, the dispersibility of magnetic powder tends to be poor even when a binder is used alone or in combination with various binders, and for this reason, surface properties and abrasion resistance are not fully satisfied. Ta. 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, and such a recording medium is subject to intense contact with the magnetic head during recording and reproduction. Due to the sliding contact, the magnetic coating is worn out by repeated use, and the magnetic material contained in the coating is likely to fall off, resulting in poor wear resistance. The reason for this is that the magnetic powder such as γ-Fe2O5 powder used as the recording element of the magnetic recording medium has a hydrophilic (0) surface, so when it is kneaded with the binder, it has poor affinity with the binder. This is thought to be because it is weak and difficult to disperse uniformly 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 a large amount of these additives is used, 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. There was also. 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, in order to meet these demands, the particle size of the magnetic powder must be reduced (in other words, the specific surface area must be increased).
4) If <), the dispersibility of the magnetic powder becomes even worse, making it impossible to obtain the desired electromagnetic properties.

3. Object of the invention An object of the invention is to provide a magnetic recording medium having a magnetic layer with excellent adhesiveness, abrasion resistance, durability, and surface properties, and with improved dispersibility of magnetic powder.

4. Structure and effect of the invention, that is, the magnetic recording medium according to the invention has a tensile strength of 200
Soft polyurethane with less than kg/cJ and elongation at break of 900% or more and tensile strength of 200 kg
/cJ or more and an elongation at break of less than 900%, and a copolymer containing at least one monomer unit having a negative organic group as a copolymer component, and the negative organic group forming a salt. It is characterized by having a magnetic layer containing treated magnetic powder.

According to the present invention, the presence of the soft polyurethane in the magnetic layer facilitates calendering and improves the adhesion of the layer, and the presence of the hard polyurethane eliminates the disadvantages of using soft polyurethane alone. That is, it is possible to prevent 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 to fully produce the above-mentioned effects of soft polyurethane, its tensile strength and elongation at break should be less than 200 kg/cta and 900% or more, and at the same time, the tensile strength and elongation at break of hard polyurethane should be Each elongation is 200 kg/
By setting c1 or more and less than 900% and making 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, the media's abrasion resistance, durability, and
In turn, it is possible to obtain good surface properties due to improved dispersibility of the binder component. Figure 2 shows tensile strength of 200
kg / ca less than 7) This shows the relationship between the elongation rate (elongation at break) of soft polyurethane and the abrasion resistance (scratchability, dust-off resistance) of the magnetic layer. It can be seen that the characteristics are significantly improved when the amount is above. In addition, Fig. 3 shows the tensile strength of 200 k.
The relationship between the elongation rate of rigid polyurethane of g/cIM or more and the ease with which the medium is calendered is 900%.
If the elongation rate is less than 100%, the properties will be 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/cry, elongation at break is 100-1200%, and tensile strength is 300-600 kg for rigid polyurethane.
/C111° elongation at break is 400 to 750%.

To illustrate the mechanical properties of the polyurethane according to the present invention, in FIG.
Rigid polyurethane belongs to one area B2 surrounded by the line (l line) and the al line (elongation rate 900%), and the other area A2
Soft polyurethane belongs to this category.

In addition, the mechanical properties of the polyurethane according to the present invention (
Tensile strength, elongation at break) are specified in Japanese Industrial Standards/Q'1 (JTS) K6301-1975, and elongation at break corresponds to "elongation at break" in the same standard.

Furthermore, an important feature of the present invention is that in addition to using both of the above-mentioned polyurethanes as binders for the magnetic layer, the magnetic powder is (pre)treated with the above-mentioned copolymer. In other words, the copolymer described above has a salt of a negative organic group formed in the monomer, so that the hydrocarbon residue portion of the copolymer is well compatible with the binder, and the salt portion is has a moderately large dissociation constant compared to the free organic groups that do not form salts. It is fully bonded to the surface.

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 binds well to the surface of the magnetic powder on the one hand, and on the other hand, it blends well with the binder of the magnetic layer without being desorbed. The dispersibility of the magnetic powder is greatly improved, and the properties such as squareness ratio, output, and surface seepage are significantly improved.

5. Examples Hereinafter, the present invention will be explained 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. Polyols that can be used include phthalic acid,
Organic dibasic acids such as adipic acid, dimerized sulfuric acid, maleic acid, glycols such as ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, or trimethylpropane, hexanetriol, glycerin, trimethylolpropane, hexanetriol, A polyester polyol synthesized by reaction with polyhydric alcohols such as glycerin, trimethylolethane, and pentaerythritol, or any two or more polyols selected from these glycols and polyhydric alcohols; or, S -Caprolactam, α-methyl-1-caprolactam, S-
Examples include lactone polyester polyols synthesized from lactams such as methyl-8-caprolactam and γ-butyrolactam; and polyether polyols synthesized from ethylene oxide, propylene 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. Such polyurethanes are usually produced primarily by the reaction of polyisocyanates and polyols, and the urethane resins containing free isocyanate groups and/or hydroxyl groups or /11 It may also be one that does not contain groups (for example in the form of a urethane elastomer).

Since the methods for producing polyurethane, urethane prepolymers, urethane elastomers, effective crosslinking methods, etc. 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 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 Figure 4, the weight ratio of soft polyurethane to hard polyurethane is 80:20-20.
: 80 is better in terms of still durability, 70:30-30
: 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. In the negative organic group-containing monomer (hereinafter referred to as monomer unit A) constituting this copolymer, the negative organic group includes, for example, a carboxyl group, a phosphoric acid residue, a sulfonic acid residue, etc. A group or a phosphoric acid residue is preferable, and its salts include ammonium salts, alkali metal salts, etc., and ammonium salts are preferable. Examples of the monomer unit 8 include acrylic acid, methacrylic acid, maleic anhydride, and 2-hydroxyethyl acryloyl phosphate, among which acrylic acid and maleic anhydride are preferred.

The negative organic group is preferably a carboxyl group or a phosphoric acid (12) residue, and the salt is preferably an ammonium salt I. Acrylic acid and maleic anhydride are preferred as monomer unit 8 because they have particularly excellent storage stability and dispersibility. In the case of additives conventionally used to improve the blooming phenomenon, they can improve the blooming phenomenon to some extent, but they have poor storage stability, tend to stick together, and tend to agglomerate during dispersion. The copolymer used in the present invention is excellent in these points.

In this copolymer, to explain the effect of the salt of the negative organic group, it is as follows: a simple negative organic group (e.g. free 100OH) and its salt (e.g. ammonium salt, Na
F) has different dissociation constants.

[Dissociation constant K]

A corner of a magnetic recording medium is provided with a magnetic layer prepared by a method described in detail later using magnetic powder surface-treated with each copolymer containing monomer units 8 having each of these groups. It was confirmed that the mold ratio (Bm/Br) was as shown in FIG. 5, for example. That is, just one COOH
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 -COOH is used as a salt. In this case, when -COOH is used as a salt, the dissociation constant is large, so it is more hydrophilic, and the copolymer is easily bonded to the hydrophilic surface of the magnetic powder during surface treatment of the magnetic powder. And there is little tendency for adsorbed substances to be desorbed during dispersion (i.e., good hydrophilicity)
It is thought that this is because On the other hand, -COOH has the property of being easily attached or bonded to the surface of magnetic powder. That is, although it is easy to adhere or bond, it has higher lipophilicity than salt and is easily desorbed during dispersion in an organic solvent.

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 there are some species whose squareness ratio decreases with increasing speed (15). 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. have, but
This seems to be because ammonium salt preferentially binds to the magnetic powder surface due to its appropriate dissociation constant. In addition, desorption in organic solvents is low. Note that if the magnetic powder is not subjected to any surface treatment, the characteristics of the medium will deteriorate further (
(See Figure 3).

As an ammonium salt, the general formula containing bipartite -CO6N+electrode: %Formula % (4) is a lower alkyl group which is the same or different from each other.

) is applicable. Here, the above R1
, R2, R', R+ are lower alkyl groups, R1
It is desirable that the total number of carbon atoms in -R1 is 6 or less, since the basicity of the ammonium salt will not be impaired due to steric hindrance116).

The above-mentioned copolymer used in the present invention can be expressed using the above-mentioned monomer unit A (-(also written as -A→-)) and monomer unit !-A (-(also written as -B+)). −(Can be expressed as a 7B rectangle. However, m, , n are each positive real numbers. The average value of (m+n) is 100 or less, preferably 50 or less. If it exceeds +00, magnetic recording It becomes difficult to disperse uniformly in the magnetic layer of the medium,
In the recording medium, performance (for example, output, etc.) is likely to become partially non-uniform, which is undesirable. Also, (m +
n) is particularly preferably 30 or less, in which case the dispersion effect is particularly excellent, and the performance of the magnetic recording medium according to the present invention is particularly significantly improved. In addition, (m+n)
The average value of is preferably 4 or more, for example, from the viewpoint of preventing the blooming phenomenon.

Here, by selecting the values of m and n and the type of salt of the organic group in unit A, (10) both the hydrophilic and hydrophobic properties of the copolymer, that is, HLB
(T(hydrophile Lipophile B
a1ance) can be appropriately controlled.

In addition, monomer units other than monomer unit A (hereinafter referred to as monomer unit B) of this copolymer include, for example, styrene, 0-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2 .4-dimethylstyrene, p-n-butylstyrene, p-t'ert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, Examples include styrene and styrene derivatives such as p-n-dodecylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, and 3,4-dichlorostyrene. Examples of vinyl monomers other than these include ethylene,
1lff of ethylenically unsaturated monoolefins such as propylene, butylene, and isobutylene; vinyl halides such as vinyl fluoride, vinylidene chloride, vinyl bromide, and vinyl fluoride; vinyl acetate, vinyl propionate, vinyl benzoate, i[vinyl Vinyl esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, acrylic acid 2-
Chlorethyl, phenyl acrylate, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, n-isobutyl methacrylate, n-octyl methacrylate, methacrylate α such as dodecyl acrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, etc.
-Methylene aliphatic monocarboxylic acid esters; derivatives of acrylic acid or methacrylic acid such as acrylonitrile, methacrylonitrile, acrylamide, etc.: vinyl methyl ether, vinyl ethyl ether, vinyl compound 1
10) Vinyl ethers such as thyl ether; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and methyl isopropyl ketone; N-vinyl such as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole, and N-vinylpyrrolidone Compounds; examples include vinylnaphthalenes.

In order to surface-treat the magnetic powder with the above-mentioned copolymer, an aqueous solution of the copolymer is added to the magnetic powder, kneaded with a kneader or the like for a predetermined period of time, and water is 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. , If necessary, further drying treatment can be performed.

In addition, it was found that the surface treatment effect of the above-mentioned co-electric (9nS) coalescence can be exhibited well if the specific surface area of the magnetic powder to be treated is 3Onf/gr or more.In other words, the specific surface area If it is 30n?/gγ 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 organic group in the monomer unit A is
It is only improved when treated with a copolymer that is OOH. On the other hand, when magnetic powder surface-treated with a copolymer according to the present invention (treated magnetic powder I) is used, the specific surface area is 30rrr/g.
It has been confirmed that at γ or higher, the properties are significantly improved compared to treated magnetic powder (2). 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. It should be noted that if the specific surface area of the magnetic powder used is made larger than necessary, it is preferable that the specific surface area of the magnetic powder be increased.

Note that "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 size. The surface area is large and candy exists. To measure the specific surface area, for example, magnetic 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. , the initial pressure of nitrogen is set to 0.5 kg r/g, and the adsorption measurement is carried out using nitrogen at liquid nitrogen temperature (-195 °C) (a specific surface area measurement method generally referred to as the B, E, T method). .For details, see J, Ame, Chem, S.
oc, 60309 (1938)). As the device for measuring the specific surface area (BET value), it is possible to use the "powder measuring device (Cantersoap)" jointly manufactured by Yuasa Battery Co., Ltd. and Yuasa Ionics Co., Ltd.

A general explanation of the specific surface area and its measurement method can be found in [Powder Measurement J (J, M, DALLAV-A L
Co-authored by L E, CI-Y D EORR, 1r,
It is described in detail in the ``Chemistry Handbook'' (Application Edition, Sections 1170-1171, Nippon Kagaku Complete Edition, published by Maruzen Co., Ltd. on April 30, 1966). Are listed. (In addition, in the above-mentioned "Chemistry Handbook," the specific surface area is simply described as surface area (rd/gγ), but it is the same as the specific surface area in this specification.) In addition, in the present invention, the above-mentioned binders are used as binders. In addition to the soft polyurethane and hard polyurethane, if cellulose resin and vinyl chloride copolymer are also included, the dispersibility of the magnetic powder will improve when applied to the magnetic layer, increasing its mechanical strength. . However, if only the cellulose resin and the vinyl chloride copolymer are used, 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, edylcellulose (23), propylcellulose, isopropylcellulose, butylcellulose, methylethylcellulose, methylhydroxyethylcellulose, ethylhydroxyethylcellulose, carboxymethylcellulose, carboxymethylcellulose sodium salt, hydroxyethylcellulose, benzylcellulose, and cyanoethylcellulose. ,
vinyl cellulose, nitrocarboxymethylcellulose, diethylaminoethylcellulose, aminoethylcellulose)
Li loin 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 Seltsuba BTHI/2 and nitrocellulose SL- manufactured by Asahi Kasei Corporation.
1. Nitrocellulose R81/2 manufactured by Daicel Corporation,
Examples include ceBv-)inT and -2oO. The viscosity of nitrocellulose (specified in JTS, 6703 (1975)) is preferably 2 to 1/64 seconds, particularly preferably 1 to 1/4 seconds. If it is outside this range, the film adhesion and film strength of the magnetic layer will be 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 l and m in is 95-50 mol% for the former unit and the latter ('t4
) is 5 to 50 mol%. Also,
X represents a monomer residue copolymerizable with vinyl chloride, including vinyl acetate, vinyl alcohol, maleic anhydride, maleic anhydride ester, maleic acid, maleic ester,
Represents at least one member selected from the group consisting of vinylidene chloride, acrylonitrile, acrylic acid, acrylic ester, methacrylic acid, methacrylic ester, vinyl propionate, glycidyl methacrylate, and glycidyl acrylate. The degree of polymerization expressed as (4+m) is preferably from 100 to 600; if the degree of polymerization is less than 100, the magnetic layer etc. will become sticky, and if it exceeds 600, the dispersibility will deteriorate. The vinyl chloride copolymer described above may be partially hydrolyzed. As the vinyl chloride copolymer, preferably a copolymer containing vinyl chloride-vinyl acetate is hereinafter referred to as a "vinyl chloride-vinyl acetate copolymer". ). Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate-
Vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride, vinyl chloride-vinyl acetate-vinyl alcohol-
Examples include copolymers of maleic anhydride, vinyl chloride-vinyl acetate-vinyl alcohol-maleic anhydride-maleic acid, and among vinyl chloride-vinyl acetate copolymers, partially hydrolyzed copolymers are preferable. Specific examples of the above-mentioned vinyl chloride-vinyl acetate copolymers include r V A G HJ and r V manufactured by Union Carbide.
Y HHJ, “VMCH”, 1 Esretsu A”, “Esuresoku A-5”, “Esuresoku C” manufactured by Building Block Chemical Co., Ltd.
, "Sresoku M", Denki Kagaku Kogyo Co., Ltd.! v [Denkabinir 100OGJ, [Denkabinir 1000W, J
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 4, the weight ratio of vinyl chloride resin to cellulose resin is 90/10 to 90/10. 5
It has been confirmed that a ratio of /95 is desirable, and a ratio of 80/20 to 10/90 is even more desirable.

If the weight ratio exceeds this range and the amount of cellulose resin increases (less than 5/95), stickiness tends to occur (t97), resulting in poor surface properties and dropouts. Furthermore, if the amount of the vinyl chloride copolymer increases (←L written weight ratio exceeds 90/10), poor dispersion tends to occur, for example, the squareness ratio tends to deteriorate.

However, in FIG. 7, C shows a tendency toward stickiness (adhesiveness), and the stickiness decreases toward 1 on the vertical axis, resulting in a good coating film. d shows the change in squareness ratio.

It is preferable that the ratio of the weight ratio of the polymer (measured) and other resins (total amount of cellulose resin and vinyl chloride copolymer) is 90/10 to 50,150 as shown in FIG. 8.
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.

(99) The magnetic layer of the magnetic recording medium according to the present invention further has a specific surface area (BET value) Bl of 4 (Jrrr/gr < B,
<200rd/gγ carbon blank (hereinafter referred to as C
It is sometimes called B. ) and specific surface area (BET value)
B2 is 200m/gr≦B2<500rd/g
It is preferable to contain carbon black (hereinafter sometimes referred to as CB2) which is r.

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. For video applications, 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 1 (/'Ω·cm or less) and the light transmittance of the tape portion where the magnetic layer is located be 0.05% or less. Therefore, carbon blank particles are usually added to the magnetic layer.

In this case, it is effective to use the carbon blacks CBL and CB2 described above. That is, carbon black C
B+ is added mainly for light shielding, or its specific surface area B1 is 40 rrr / gr < Bt < 2
It is extremely important to be specific in the range of 00 rl/gr. With the 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 in the layer can be improved. If the specific surface area of CB+ is outside this range and is less than 40rd/gγ, the particle size will be too large and the light-shielding property will tend to deteriorate, and the amount added will need to be increased more than necessary. If so, the particle size is too small and the dispersibility in the layer tends to be poor. on the other hand,
CB2 is added to both CB1 and CB2 to provide sufficient conductivity, but the specific surface area is 200i/gγ≦B2<5
It is also important to specify 00 rd/gγ. That is, the specific surface area B2 of CB2 is 20On? If the particle size is less than /gγ, the particle size is too large and the conductivity is insufficient even when carbon blank is added, and if it is more than 500rrr/gγ, the particle size is too small and the dispersibility of CB2 tends to deteriorate.

Therefore, by limiting the specific surface areas of the light-shielding CBI and the conductive C&, respectively, to the above-mentioned specific ranges, the surface electrical resistance and light transmittance of the magnetic layer, etc. can be sufficiently reduced, and the surface smoothness of the layer can be improved. In other words, it improves the dispersibility of the carbon blank.
This makes it possible to reduce the amount of carbon blank added and improve the durability of the layer. The specific surface area range of each of these carbon blacks is fundamentally different from the range shown in the prior art. In addition, it is preferable that the above specific surface areas are 100≦B+<200.200≦82<300. In addition, regarding the particle size of each carbon blank, CB+ is 20 IIm or less, CB2 is 40 to 5
0 m, 17 is desirable, and corresponds to the range of surface area arranged on - according to the present invention.

The amount of carbon blank to be added is determined within a range that can maintain 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. With the specific surface area in the range described above, there is no need to increase the amount of carbon blank added, and it can be set in the range of 5 to 35% by market weight,
Mechanical properties of the magnetic layer (31) Obtain the desired surface electrical resistance (109 Ω cm or more) and light transmittance (0.05% or less) while maintaining good physical properties (e.g., dust removal of the magnetic layer). be able to.

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, it is preferable to use conductive CB in order to reduce the surface resistivity of the magnetic layer, etc. to a sufficient range. It is preferable to have a continuous structure, and it is preferable to use a material that is porous and has a large specific surface area, that is, has a high stracture level. As such carbon black, for example, Cond++ctex 975 (specific surface area 210 g/
gr, particle size 46 mμ), Conductesox 950 (specific surface area 245 n (/gγ, particle size 46 mμ), Cabot Vulcan X C-7
2 (specific surface area 251rd/gr, particle size 18 mμ), etc. can be used. These carbon blanks have a large specific surface area, but when applied to a magnetic layer, they can be sufficiently dispersed before the magnetic powder is completely dispersed. Outside the above range, CB
If the specific surface area of CB2 is 500rd/gr 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 of the coating film becomes rough. , which can easily cause pinholes. 20 On
? When the specific surface area is less than /gγ, 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 above-mentioned carbon black CB2.
By adding a small amount of carbon CB1, which has poor electrical conductivity but good light shielding properties (smaller surface area than original conductive carbon) and excellent dispersibility, a more significant synergistic effect is achieved than when using conductive carbon alone. effect can be obtained. That is, by adding the light-shielding carbon C& together with the conductive carbon CB2, 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 blank added can be reduced. The mechanical properties and surface smoothness of the layer will be improved. As such a carbon blank CBI for light shielding,
Those with a small particle size, a relatively low stracture level, and a relatively low specific surface area, such as Raven 2000 (specific surface area 180 ++?/g r, particle size 19 m μ) manufactured by Columbia Carbon Co., Ltd. 2
100.1170.1000, B1 manufactured by Mitsubishi Kasei Corporation
00, B75, B44, B40, B35, B30, 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/CBI=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 CBp will increase, resulting in insufficient light-shielding properties, and if it is less than 50/50, the surface resistivity will increase due to less conductive carbon black CB2. I end up.

FIG. 9 shows a magnetic recording medium, for example a magnetic tape, according to the present invention, which comprises a support 1, a subbing layer 2 (this layer may not be provided if necessary), and a magnetic layer 3. 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 7 Fe2O8, Co-containing rFe2O3
, Fe50+CO-containing iron oxide magnetic powder HF such as Fetsu04
e, (35) NiXCo, Fe-Ni-Co alloy, Fe-M
n-Zn alloy, Fe-Ni-Zn alloy, Fe'-C0-
Ni-Cr alloy, Fe-Co-Ni-P alloy, C
Examples include various ferromagnetic powders such as o-Ni alloys and metal magnetic powders containing Fe, Ni, Co, etc. as main components.

The magnetic paint according to the present invention includes a magnetic powder (preferably treated with the above copolymer), a binder, each of the above carbon blacks CBL and CB2, and the above copolymer (the magnetic powder is preferably treated with the copolymer in advance). If the magnetic coating material has been treated with This is used as a magnetic layer, and is used as 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, /Q
G) Those with an average molecular weight of 10,000 to 200,000 and a degree of polymerization of about 200 to 2,000, such as acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester -Styrene copolymer, methacrylic acid ester-acrylonitrile copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer,
Polyamide resins, polyvinyl butyral, styrene-butadiene copolymer L polyester resins, chlorovinyl ether-acrylic acid ester copolymers, amino resins, various synthetic resins, 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. 40-5
No. 349, No. 40-20907, No. 41-9463, No. 41=14059, No. 41-16985, No. 42-6428, No. 42-11621, No. 43-4
No. 623, No. 43-15206, No. 44-2889, No. 10-44-17947, No. 44-18232, No. 45-
No. 14020, No. 45-14500, No. 47-185
No. 73, No. 47-22063, No. 47-22064, No. 47-22068, No. 47-22069, No. 4
7-22070, 48-27886, U.S. Patent No. 3,144,352, 3,419,420, 3,499,789, 3,713,887
It is stated in the specification of the No.

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,
These include melamine resins, 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 disclosed in Japanese Patent Publication No. 39-8103 and 4o-9.
No. 779, No. 41-7192, No. 41-8016,
41-14275, 42-18i79, 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. 41-28922, US Pat. No. 3,144.353, US Pat. No. 3,320,090, US Pat.
No. 3,781,210, No. 3,78L2], No. 1, and 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.

From the viewpoint of recording density, strength, etc., the total amount of the binder used in the present invention is desirably 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 (M
XDI) and adducts of these isocyanates with active hydrogen compounds, etc., and have an average molecular weight of 100 to
A range of 3,000 is preferred.

Specifically, Sumidur T80, Sumidur 44S1 PF, Desmodur L1 Desmodur T65, Sumidur 15, R1 RF, and L1 S are manufactured by Sumidur Bayer Urethane Co., Ltd.
L: Takenate 300S1 50 manufactured by Takeda Pharmaceutical Co., Ltd.
0; Mitsui Nisso Urethane Co., Ltd. product [ND[l, rTODI
Nippon Polyurethane Co., Ltd. product Desmodule T100,
Millionate MR, MT, Co (5υ Noronate ■7, Kasei Upjohn products PA, PT-
135, TD Te3, TD Te3, TD Te3, TD Te 80, TD Te 100, Isonate 125M, and TD Te 1431.

On the other hand, examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDT), lysine isocyanate, and trimethylhexamethylene diisocyanate (TMD).
T) and adducts of these isocyanates and active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those with a molecular weight of 100 to 3 are preferable.
,000.

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, products Sumidur N and Desmodur Z4273 manufactured by Bayer Urethane Co., Ltd., Duranate 50M, 24A-100, and 241- manufactured by Asahi Kasei Co., Ltd.
90CX, Coronate HL manufactured by Nippon Polyurethane Co., Ltd.
There are products such as TMD I manufactured by Hüls (40).

In addition, examples of alicyclic isocyanates among aliphatic isocyanates include methylcyclohexaCH+ 4,4-methylenebis(cyclohexyl isocyanate) [structural formula: 0CN-■-CH,7-CH-NCO] isophorone diisocyanate and its activity. Examples include adducts of hydrogen compounds.

Specifically, products manufactured by Huls Chemical Co., Ltd. [PDIJ, rPD
There are T-T1890, T-T1921, T-T B1065, etc.

In the magnetic recording medium of the present invention, a magnetic coating is prepared by mixing and dispersing the magnetic powder, the binder, and various additives in an organic solvent, and after adding the aromatic isocyanate and aliphatic isocyanate, this is coated on a support ( For example, it is coated onto 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 hardening of the magnetic layer tends to be insufficient, and if it is more than 100%, the magnetic layer tends to become "sticky" even though it is hardened.

In order to obtain a more preferable magnetic layer, the amount of isocyanate to be added is preferably 5 to 5 to the binder.
It is 30% by weight.

As for the 1 adduct of isocyanate and an active hydrogen compound, and the polyisocyanate, 1 adduct of diisocyanate and trivalent polyol, or 5 adduct of diisocyanate is used.
There is a decarboxylation compound of 1 to 3 moles of diisocyanate and water.

Examples of these include an adduct of 1.3 mol of tolylene diisocyanate and 1 mol of trimethylolpropane, an adduct of 3 mol of metaxylylene diisocyanate and 1 mol of trimethylolpropane, a pentamer of tolylene diisocyanate, and There are a pentamer consisting of 3 moles of diisocyanate and 2 moles of hexamethylene diisocyanate, and a decarboxylated product obtained by reacting 3 moles of hexamethylene diisocyanate with 1 mole of water, and these can be 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, linuric acid, etc. with carbon atoms of 8 to 18111i
l fatty acid (represented by R-COOH, where R is 7 carbon atoms)
~17 saturated or unsaturated alkyl groups); metal soaps made of alkali metals (1-++Na+, etc.) or alkaline earth metals (Mg, Ca, Ba, etc.) of the fatty acids mentioned above. In addition to these, higher alcohols having 12 or more carbon atoms and sulfuric esters may 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.

These 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 (solid). (43) Fatty acid esters (so-called waxes) consisting of -valent alcohols can also be used.These lubricants have a binding agent of 100%
It is added in an amount of 0.2 to 20 parts by weight based on the market 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 1 to 20 parts by weight per 100 parts by weight of the binder.
It is added in a range of parts by weight.

Other antistatic agents that may be used include conductive powders such as graphite, tin oxide-antimony 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; higher alkyl amines, quaternary ammonium salts, pyridine, (44) cationic surfactants such as other heterocycles, phosphonium or sulfonium: carboxylic acid, sulfonic acid ,
Examples include anionic surfactants containing acidic groups such as phosphoric acid, sulfuric acid ester groups, and phosphoric ester groups; amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric or phosphoric 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, xylene; and halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, dichlorobenzene, etc. can be used.

Support materials 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, A6. Metals such as Zn, glass, BN, Si carbide, and ceramics such as porcelain and earthenware are used.

The thickness of these supports is about 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm,
In the case of a disk or card shape, it is approximately 30 μm to 10 mm, and in the case of a drum shape, it is cylindrical, and the shape is determined depending on the recorder used.

May be coated.

Coating methods for forming a magnetic layer by coating the magnetic paint etc. on the support include air doctor coating, plate coating 1-1, air knife coating, squeeze coating, impregnation coating, and reverse roll coating 1-1). Transfer roll coating, gravure coating, kiss coating, cast coating, spray coating, 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 stickiness and extremely good side abrasion resistance than conventionally known magnetic recording media, and also has excellent dispersibility and surface properties, and has excellent drop resistance. There are few outs. Furthermore, the magnetic recording medium according to the present invention has a significantly improved 5(47)/N ratio compared to conventional magnetic recording media, and can obtain higher reproduction output than conventional magnetic recording media. can. 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 variously changed without departing from the spirit of the present invention.

In addition, in the following examples, all "parts" are "parts by weight".
represents.

Actual difference■ First, the following (a) to (+
) were surface-treated with each copolymer to obtain correspondingly treated magnetic powders. That is, the solid content is 2.5 parts per 100 parts of iron oxide.
Aqueous solutions of each copolymer were added thereto in such a manner that the resulting mixture was mixed with a kneader (manufactured by Bengami Seisakusho Co., Ltd.) for 2 hours. The surface-treated magnetic powders are transferred to a rotary vibration dryer to evaporate the water content, and the magnetic powders are further loosened in a colloid mill, passed through a mesh sieve, and classified to obtain the desired particle size (48). A treated magnetic powder was obtained.

(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 Salt (d) Ammonium salt of a copolymer of maleic anhydride and styrene (e) Octylamine salt (ammonium salt) of a copolymer of methacrylic acid and methyl methacrylate-1 (f) 2-hydroxy Ammonium salt of a copolymer of ethyl acryloyl phosphate and lauryl acrylate (g) Ammonium salt of a copolymer of acrylic acid and propylene (h) Butylamine salt (ammonium salt) of a copolymer of methacrylic acid and butylene ) (+) Ammonium salt of copolymer of acrylic acid and ethylene.The following compositions were prepared using these treated magnetic powders.

Treated Co-containing r Fe2e5 (above>(BET value 40 rrr/g r) 100
fa soft polyurethane (Pandesox T-5610 manufactured by Dainippon Ink and Chemicals Co., Ltd.: tensile strength 120 kg/cl
, elongation at break 1050%) 7 parts hard polyurethane (Nipporan N-2 manufactured by Dainippon Polyurethane Co., Ltd.)
304: Tensile strength 400 kg/cJ, elongation at break 7
00%) 7 parts Nitrocellulose 5 parts (Seltsuba BTH1 manufactured by Asahi Kasei Co., Ltd.
/2) Vinyl chloride-vinyl acetate copolymer 1 part (VAGH manufactured by Union Carbide) Conductor, 2.975 (BET value 210rd
/gr, particle size 46mμ) 2.5 parts Rahe: /2000 (BET value 180rrr/gr,
1ft, diameter 19m1i>2.5 parts Lecithin 5 parts Myristic acid 2 parts Palmidic acid phthyl ester 1 part Alumina 4
50 parts methyl ethyl ketone 100 parts cyclohexanone 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. Then, 5 parts of polyfunctional isocyanate (curing agent) was added to this composition, and the average pore size was 1 μm.
It was filtered with a filter of m. The obtained magnetic paint was 14μ
It was applied onto a polyester film of m thickness using a reverse roll coater while applying a magnetic field and dried (dry film thickness: 6
μm).

Thereafter, the magnetic layer was surface-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 a width of 12.7 mm to produce a magnetic tape for video.

A magnetic tape was prepared in the same manner as in the example except that in the paint composition of the example, a magnetic powder treated with ac(51), a copolymer of lyric acid and butyryl acrylate, was used. did.

Comparison Example 1 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.

The squareness ratio, gloss, viscosity dispersion time, and video characteristics of each of the above magnetic tapes were measured, and the results are shown in the table below. The method for these measurements was as follows.

Gloss: Measured at an angle of 60' with a variable angle photometer, Comparative Example 1
The value is expressed 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: Measured with a Video Deck HR-4aoo (manufactured by Victor Corporation) using 4MHz playback output as RF output, and displaying relative values, assuming the measured value of Comparative Example 1 as 0, video S/N, color S/N. The same goes for N.

(52) (54) As is clear from these results, when magnetic powder pretreated with the above a% i copolymer (especially ammonium salt) is used, the copolymer consisting of a mere free organic acid is Treated magnetic powder (Comparative Example 1) and untreated magnetic powder (Comparative Example 2)
), it is possible to prepare a magnetic paint with a high squareness ratio, excellent gloss, and low viscosity. 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 the solids concentration can be further increased with less solvent and that the load on production equipment during drying can be reduced.

[Brief explanation of the drawing]

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 graph showing changes in properties depending on the elongation rate of hard polyurethane. Figure 4 is a graph showing changes in still durability depending on the blending ratio of soft and hard polyurethane. Figure 5 is a graph showing changes in still durability depending on the type of magnetic powder surface treatment agent. A graph showing the squareness ratio of magnetic recording media. Figure 6 shows the output S/of various magnetic powders depending on the specific surface area of the magnetic powder.
A graph showing changes in N. Figure 7 is a graph showing changes in stickiness and squareness ratio depending on the blending ratio of other resins. Figure 8 is a graph showing still durability depending on the blending ratio of polyurethane and other resins. FIG. 9 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 polyurethane region of the present invention B2--
----One area of the rigid polyurethane of the present invention. Agent: Patent attorney Hiroshi Aisaka (and 1 other person)
) b Ruden 1 豐 9 A boat ~ Migo Δ =>-1;
-ノzcOφ2f'='Ad 7Ugot;mine/dinya. ku q banquet v tochi dispute 0〕 ■ i) -ka) d 0 0 0 0? Hn Kiku vl-→Hanapo Ekiyo (self-procedure amendment document January 1980) 1st 1st, Indication of the case 1988 Patent Application No. 93054 2, Name of invention Magnetic recording medium 3, Make amendment Relationship with the patent 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 the amendment 7, Detailed description of the invention in the specification subject to the amendment, column a corner 8, Contents of the amendment (11, Specification No. "Elongation at break 100" on page 8, line 11 is corrected to "elongation at break 100 OJ. (2)""Before" on page 43, line 5 is corrected to "above" - First. 3), same. First, delete "these" in the fourth line from the bottom of page 44. (4), “(so-called low)” in the 1st and 2nd lines of page 45.
Delete. (5), page 45, line 3, "1 binder" is corrected to "magnetic powder." (6), page 45, line 12, “1 binder” is “magnetic powder”
I will correct it. One - He (2)

Claims (1)

[Claims] 1. A soft polyurethane with a tensile strength of less than 200 kg/cJ and an elongation at break of 900% or more, and a hard polyurethane with a tensile strength of 200 kg/cJ or more and an elongation at break of less than 900%, negative. A magnetic layer comprising a magnetic powder treated with a copolymer containing at least one monomer unit having an organic group as a copolymer component and in which the negative organic group forms a salt. recoding media.