JPH0772936B2 - Magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium, and an object thereof is to provide a magnetic layer having excellent wear resistance and durability, smoothness of the magnetic layer surface, and reduction of frictional resistance. Another object of the present invention is to provide a magnetic recording medium containing a specific fluorocopolymer having improved dispersibility and orientation of magnetic powder.

<Prior Art> A magnetic recording medium such as a magnetic tape or a magnetic disk is in sliding contact with a magnetic head at a high relative velocity during recording and reproduction, and therefore the magnetic layer is required to have wear resistance, and the magnetic surface is smooth and Low frictional resistance is desired. However, the magnetic powder has good dispersibility and is a general-purpose magnetic binder resin having excellent adhesion to the base, for example, poly (vinyl chloride-vinylidene chloride), poly (vinyl chloride-vinyl acetate), polyurethane, polyester, phenoxy resin, And these mixed resin etc. are generally poor in lubricity and non-adhesiveness. For this reason, the frictional force increases during sliding contact with the magnetic head, which deteriorates the running property of the magnetic recording medium and significantly impairs the durability of the magnetic layer.

On the other hand, when a magnetic coating composed of magnetic powder and a binder resin is applied on the base film, the leveling property is poor due to the large surface tension, resulting in uneven coating or uneven thickness, and fluctuations in output as a magnetic recording medium. It had the drawback of becoming large.

To solve these problems, conventionally, a surfactant such as lecithin or liquid paraffin or stearic acid is added to the magnetic paint.
A method of improving the activity of the surface of the magnetic layer by adding various lubricants such as silicone oil (these are hereinafter referred to as non-fluorine-based additives).

A method of improving the sliding characteristics by containing a fluororesin powder that does not contain a perfluoroalkyl group on the surface of the magnetic layer (JP-A-59-162644), and a surfactant containing a perfluoroalkyl group in the magnetic layer. , A method for improving the smoothness and durability of the surface of the magnetic layer and the dispersibility of the magnetic powder (JP-A-59-167837 and JP-A-
59-167838, JP-A-59-167839, JP-A-59-167840
No. 59, No. 59-167841, No. 59-172140, etc.), and by improving the leveling property when applying a magnetic coating on a base film, and obtaining a smooth coated surface There is a proposal for a method of lowering it (JP-A-58-159232).

<Problems to be Solved by the Invention> However, since the above-mentioned non-fluorine-based additives and fluorine-based surfactants that have been conventionally used are easily slipped off during sliding contact with the magnetic head, they have a slipping effect. There was a problem that it disappeared in a relatively short time and the running stability and the like were impaired. When a large amount of the above-mentioned non-fluorine-based additive and fluorine-based surfactant is used for the purpose of improving the durability of the lubricity effect, the dispersibility of the magnetic powder is deteriorated and the magnetic properties are lowered, or the magnetic layer is deteriorated. There was a problem that the mechanical properties of the product itself were deteriorated and the durability was impaired. Generally, conventional fluorosurfactants have a high foaming property even in an organic solvent system, and when agitated and mixed in a magnetic paint, the bubbles are easily entangled in the paint, resulting in workability and a smooth magnetic coating surface. There was a problem in getting.

Furthermore, when a lubricant having poor compatibility with the magnetic layer, such as silicone oil, is added, excessive surface leakage occurs, which causes leakage of the dispersant in the magnetic layer. For this reason, there is a problem that output fluctuations and tape squeal etc. occur due to powder falling.

On the other hand, when an additive or a surfactant having excellent compatibility with the magnetic layer is added, the desired lubrication effect may not be obtained because the surface leaching amount of these lubricants is small. There were many.

As described above, a non-fluorine-based additive and a fluorine that exhibit sufficient surface lubricity with a small amount of addition, do not fall off during sliding contact with a magnetic head, have excellent lubricity, and have a low foaming property. At present, no systematic surfactant has been found.

<Means for Solving Problems> The inventors of the present invention have conducted earnest research to solve the above problems, and as a result, a monomer having two perfluoroalkyl groups having 3 to 20 carbon atoms in a molecule. And a non-fluorine-containing monomer, which is a fluorine-containing copolymer, especially when it is composed of two or more of the above-mentioned non-fluorine-containing monomers, it contains a polysiloxane chain-containing monomer as one component thereof. If the fluorine-based copolymer is used, the inclusion of bubbles in the magnetic paint is extremely small,
The leveling property when applied on a magnetic paint base can be significantly improved to obtain a smooth coated surface, and the dispersibility and orientation of the magnetic powder are improved compared to conventional ones, and surface lubricity, lubricity continuity, Further, they have found that a magnetic recording medium excellent in durability and the like, excellent in running stability, and capable of producing a magnetic recording medium in which output fluctuation and tape squeal are significantly reduced can be obtained.

Furthermore, a fluorine-based copolymer having a perfluoroalkyl group having 3 to 20 carbon atoms and a polysiloxane chain at the same time in a molecule has a conventional fluorine-based surface active agent having only one of the perfluoroalkyl group and the polysiloxane chain. Agent or fluorine-based surface modifier, or silicon-based surfactant or silicon-based surface modifier alone or in combination, the synergistic effect of significantly improving the lubricity and durability of the magnetic surface Was discovered, and the present invention was completed.

That is, the present invention relates to a fluorine-based monomer having two perfluoroalkyl groups having 3 to 20 carbon atoms in the magnetic layer and having an acryloyl group or a methacryloyl group in the magnetic layer, and an acryloyl group or methacryloyl group in the molecule. A magnetic recording medium characterized by containing a fluorine-based copolymer obtained by copolymerizing a non-fluorine-containing monomer having a group; The present invention provides a magnetic recording medium characterized in that the seed contains a fluorine-based copolymer containing a polysiloxane chain-containing monomer.

A monomer having two perfluoroalkyl groups having 3 to 20 carbon atoms in the molecule, which is a constitutional unit of the fluorocopolymer according to the present invention, means two perfluoroalkyl groups having 3 to 20 carbon atoms. Is not particularly limited as long as it is a monomer that is bonded to an acryloyl group or a methacryloyl group with a trivalent linking group. The surface characteristics of the magnetic recording medium according to the present invention are difficult to obtain if the magnetic recording medium contains only one perfluoroalkyl group or the perfluoroalkyl group has less than 3 carbon atoms. or,
When the carbon number of the perfluoroalkyl group exceeds 20, the compatibility with the magnetic paint becomes poor and a smooth surface cannot be obtained.

Specific examples of the monomer having two perfluoroalkyl groups having 3 to 20 carbon atoms in the molecule according to the present invention include general formula (I
-1) [In the formula, Rf is a perfluoroalkyl group having 3 to 20 carbon atoms, and Z ₁ is (However, R ₁ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.) Or CH _{2 n} (where n is 1 to 6)
Is an integer. ) And Z ₂ is CH _{2 m} (where m is an integer of 2 to 6) or And R is a hydrogen atom, a methyl group, or a halogen atom, for example,
Cl and Br, and X is (However, Y is a divalent linking group having 15 or less carbon atoms and having a weight ratio in the X group of 35 to 65%.) Is (However, R ₂ is a hydrogen atom, a methyl group, an ethyl group, or a nitro group.) Or Is a trivalent linking group represented by. ] The compound represented by And the general formula [In the formula, Rf and R′f are perfluoroalkyl groups having 3 to 20 carbon atoms, and ▲ Z ^′ ₁ ▼ and ▲ Z ^′ ₂ ▼ are (However, ▲ R ^' ₁ ▼ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms) or CH _{2 n} (however, n is an integer of 1 to 6). It is a linking group, and Z ₃ is CH _{2 m} (provided that m is an integer of 2 to 6).
Or And R is a hydrogen atom, a methyl group, or a halogen atom, and X ₁ , X ₂ , and X ₃ are (However, R ₂ is a hydrogen atom, or an alkyl group or an alkenyl group having 1 to 36 carbon atoms.) Or Is a divalent linking group selected from (However, R ₃ is a hydrogen atom, a hydroxymethyl group, a methyl group, an ethyl group, or a nitro group.), Is a trivalent linking group represented by. ] It is a compound represented by.

Specific examples of the monomer having two perfluoroalkyl groups having 3 to 20 carbon atoms in the molecule include the following, but the present invention is not limited to these specific examples. Is.

Among the non-fluorine-containing monomers according to the present invention, specific examples of those not containing a polysiloxane chain include acrylic acid, methacrylic acid, and derivatives thereof, in which the alkyl group has 1 to 18 carbon atoms, (meth). Acrylic acid alkyl ester (hereinafter, this expression generically refers to both acrylic acid alkyl ester and methacrylic acid alkyl ester), that is, (meth) acrylic acid methyl, ethyl, propyl, butyl, octyl, 2-ethylhexyl, Decyl, dodecyl, stearyl ester, etc., and (meth) acrylic acid C1-C18 hydroxyalkyl esters, that is, hydroxyethyl, ethyl ester, hydroxypropyl ester, hydroxybutyl ester, etc., and (meth) acrylic acid carbon number. 1-18 aminoalkyl esters, ie dimethylamino Ester, diethylaminoethyl ester, diethylaminopropyl ester and the like, and ether oxygen-containing alkyl ester of (meth) acrylic acid having 3 to 18 carbon atoms, such as methoxyethyl ester, ethoxyethyl ester, methoxypropyl ester, methylcarbyl ester, ethyl ester. Carbyl ester, butyl carbyl ester, etc., and alkyl vinyl ethers having an alkyl carbon number of 1 to 18, such as methyl vinyl ether, propyl vinyl ether, dodecyl vinyl ether, etc., glycidyl ester of (meth) acrylic acid,
That is, glycidyl methacrylate, glycidyl acrylate, etc., and Stermer macromonomer 450 manufactured by Sartomer Co., Ltd.
0, macromonomers such as NK Ester M-230G manufactured by Shin-Nakamura Chemical Co., Ltd., etc., and one or two or more of them are selected, and the monomer (I-1) or (I-2 ),
It is used for copolymerization with (I-3).

Further, among the non-fluorine-containing monomers according to the present invention, polysiloxane
As a monomer containing a sun chain, a polysiloxane chain
Acrylo via a divalent linking group at one or both ends
Group or methacryloyl group
The compound represented by the general formula (II-1) can be used.[Wherein R ′_ThreeAnd R_FourIs an alkyl group having 1 to 20 carbon atoms or
Phenyl groups, which may be the same or different,
It may be the same or different for each siloxy unit, p is an integer of 3 to 520, q is 0 or 1, and Y'is a divalent linking group, And R_FiveIs a hydrogen atom or a methyl group, Z₃Is a methyl group, a phenyl group, orIs. ] Or a compound represented by the general formula[In the formula, ▲ R^′ _Three▼, ▲ R^″ _Three▼, ▲ R _Three▼, ▲ R^′
_Four▼, ▲ R^″ _Four▼, ▲ R _Four▼ is an alky with 1 to 20 carbon atoms
Group or phenyl group, which may be the same or different
May be the same or different for each siloxane unit
Well, r, s, t are integers from 1 to 200, which may be the same or different.
May be Y ', q, R_FiveIs as defined above. ]
The compound represented by

The following are examples of more specific monomers containing a polysiloxane chain.

However, Me and Ph represent a methyl group and a phenyl group, respectively.

Nothing is required for producing a fluorine-based copolymer obtained by copolymerizing a monomer having two perfluoroalkyl groups having 3 to 20 carbon atoms in the molecule with a non-fluorine-based monomer according to the present invention. There is no limitation, and a known method, that is, a radical polymerization method, a cationic polymerization method, an anionic polymerization method, or the like is used, but the radical polymerization method is particularly convenient and industrially preferable. In this case, as the polymerization initiator, those known in the art can be used, for example, benzoyl peroxide, peroxides such as diacyl peroxide, azo compounds such as azobisisobutyronitrile and phenylazotriphenylmethane. , A metal chelate compound such as Mn (acac) _{3 and the} like, and a chain transfer agent such as lauryl mercaptan can be used together if necessary. The fluorine-based random or block copolymer according to the present invention can also be obtained by photopolymerization in the presence of a photosensitizer or a photoinitiator, or polymerization using radiation or heat as an energy source.

The polymerization can be carried out in the presence or absence of a solvent, but it is more preferable in the presence of a solvent from the viewpoint of workability. Examples of the solvent include ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, esters such as methyl acetate, ethyl acetate and butyl acetate, polar solvents such as dimethylformamide and dimethyl sulfoxide, 1,1,1-trichloroethane and chloroform. Any of halogenated solvents, ethers such as tetrahydrofuran and dioxane, aromatics such as benzene, toluene and xylene can be used.

The copolymerization composition ratio of the monomer having two perfluoroalkyl groups having 3 to 20 carbon atoms in the molecule and the non-fluorine-containing monomer is 4: 1 to 1: 100 by weight, and 1 A range of: 1 to 1:50 is particularly preferred. When the ratio of the monomer having two perfluoroalkyl groups having 3 to 20 carbon atoms is less than the above range, sufficient magnetic surface antifriction, smoothness, durability, etc. according to the present invention cannot be obtained. . On the other hand, when the ratio of the monomer having two perfluoroalkyl groups having 3 to 20 carbon atoms exceeds the above range or when the carbon number of the perfluoroalkyl group exceeds 20, the magnetic coating composition or The compatibility with the binder resin is lowered, and the properties of the magnetic surface are deteriorated.

When a polysiloxane chain-containing monomer is used as one component of the non-fluorine-based monomer, the upper limit of the polysiloxane chain-containing monomer in the non-fluorine-based monomer is 90% by weight. , And more preferably up to 85%. If the content of the polysiloxane chain-containing monomer exceeds this upper limit, the compatibility with the magnetic coating material or the binder resin decreases, and the lubricity persistence and durability of the magnetic surface decrease.

The molecular weight of the fluorine-based copolymer according to the present invention is ▲
▼ ＝ 3,000 to 500,000 is preferable, ▲ ▼ ＝ 3,000 to 1
00,000 is particularly preferred.

The amount of the fluorine-based copolymer used in the present invention is 100 times the magnetic powder in the magnetic layer, which is composed of the magnetic powder, a binder (polyurethane resin, vinyl chloride resin, vinyl acetate resin, etc.) and an additive.
0.0001 to 30 parts by weight, preferably 0.001
Particularly preferred is -20 parts by weight. Further, as means for containing the fluorine-based copolymer in the magnetic layer, for example, aromatic solvents such as benzene and toluene, halogen-based solvents such as Freon-113, 1,1,1-trichloroethane, methyl ethyl ketone and methyl isobutyl ketone. Such as a ketone-based solvent, ethyl acetate, an ester-based solvent such as isobutyl acetate, or a fluorine-based copolymer is appropriately dissolved in a mixed system of these solvents,
A method of applying or spraying this solution onto the surface of a magnetic layer formed in advance, a method of immersing the magnetic layer in the solution, or a method of mixing a fluorine-based copolymer in a magnetic paint such as the organic solvent system. Method for forming magnetic layer, and further, resin for magnetic binder such as vinyl chloride-vinyl acetate copolymer, polyamide resin, vinyl chloride-vinyl propionate copolymer, polyvinyl butyral resin, polyester resin, epoxy resin , A phenoxy resin, a nitrocellulose resin, a polyurethane resin, and the like, which are mixed with known resins that are normally used.
The magnetic powder used together with the binder resin in the magnetic layer is, for example, reduced iron powder, γ-Fe ₂ O ₃ powder, Fe ₃ O ₄ powder, Co-containing γ-Fe ₂ O ₃ powder, Co-containing Fe. ₃ O ₄ , CrO ₂ powder, various alloy powders and the like can be mentioned, and various conventionally known magnetic powders can be used.

Further, various additives such as a reinforcing agent (eg, aluminum oxide and silicon oxide), a reinforcing material (eg, graphite, molybdenum disulfide), a lubricant (eg, higher fatty acid and The ester, silicone oils, olive oil, polyethylene oxides) may be added to such an extent that the effect of the present invention is not impaired.

<Function> The fluorine-based copolymer according to the present invention has less frictional resistance than the previously disclosed non-fluorine-based additives and fluorine-based surfactants, and has long-lasting lubricity and durability. It is not sufficiently clear whether a magnetic layer having excellent properties is provided. However, according to the findings of the present inventors to date, in the conventional high molecular weight fluorine-based surfactant,
Since the perfluoroalkyl groups exhibiting the slipping effect were randomly arranged in the molecule, the slippery portion and the good portion of the resin component of the magnetic layer could not form distinct domains, respectively. In addition, since the anchoring effect on the resin portion in the magnetic layer is insufficient, the fluorosurfactant near the surface easily fell off during sliding contact, and it was not possible to obtain sufficient lubricity effect and lubricity sustainability. It is considered. It is also presumed that the low-molecular-weight fluorosurfactant did not have sufficient lubricity and long-lasting lubricity because the anchor effect and the concentration effect of the perfluoroalkyl group on the magnetic layer surface were insufficient. To be done.

On the other hand, recently, a comb-type polymer or AB type copolymer containing a perfluoroalkyl group having a structure in which perfluoroalkyl groups are densely aggregated and non-fluorine-based moieties are also aggregated has been developed. It is expected to be applied as an additive type surface modifier. According to the knowledge of the present inventors, these surface modifiers can obtain a certain degree of surface lubricity and smoothness, but from the viewpoint of improving the lubricity of the magnetic surface, their effect is not significant. It is enough. Further, these surface modifiers have a high foaming property, and when they are added to and mixed with a resin or a resin solution or a magnetic paint, bubbles are liable to be included, and defoaming is difficult. However, there is a defect that a smooth surface cannot be obtained. It is considered that this is due to the structure of the surface modifier. That is, in these surface modifiers, a perfluoroalkyl group portion having low lipophilicity and a non-fluorine-based portion having high lipophilicity form distinct aggregates, respectively, and easily behave as a surfactant even in an organic system. Therefore, it is estimated that the foaming property is high.

On the other hand, the fluorine-based copolymer according to the present invention is a random copolymer of a monomer containing two perfluoroalkyl groups in the molecule and a non-fluorine-based monomer, and therefore, the perfluoroalkyl group Of the non-fluorine-based and non-polysiloxane chain-based portion having a good affinity with the resin component of the magnetic layer, that is, the anchor component is adequately present. It is considered that the foaming property is low as well as the smoothness effect and the long-lasting smoothness are exhibited.

One of the features of the present invention is that the molecule has 3 to 20 carbon atoms.
The fluorine-based copolymer having both the perfluoroalkyl group and the polysiloxane chain at the same time synergistically improves the lubricity of the surface of the magnetic medium. This is because the perfluoroalkyl group and the polysiloxane chain are microscopically It is presumed that this is due to the formation of dense hybrid aggregates.

It is needless to say that these considerations are helpful in understanding the content of the present invention and do not limit the present invention in any way.

<Effects of the Invention> The fluorine-based copolymer according to the present invention improves the leveling property of the magnetic coating material, and thus contributes greatly to the improvement of the productivity of the magnetic tape and the magnetic disk, and also provides a coated surface having a high degree of homogeneity. Since the magnetic tape is provided, it is possible to make the magnetic layer thin, which has been particularly required in recent years as the tape becomes longer.

Further, since the magnetic recording medium according to the present invention is excellent in slipperiness and slipperiness sustainability, it improves running stability and durability of a magnetic tape, a floppy disk, a magnetic disk or the like as compared with the conventional one, and In addition to enabling playback with little output fluctuation, it also enables still playback of video tapes for a long time.

Next, in order to explain the present invention in more detail, reference examples, examples and comparative examples will be given.

Reference Example 1. (Fluorine-based Copolymer 1) In a glass flask equipped with a stirrer, a condenser, and a temperature property, 30 parts by weight of a fluorine-based monomer shown in I-1-2 in the text, methyl methacrylate (hereinafter referred to as MMA) 10 parts by weight, β-hydroxyethyl methacrylate (hereinafter β-HE
15 parts by weight of MA, i-butyl methacrylate (hereinafter referred to as MA)
iBMA) 10 parts by weight, and methyl isobutyl ketone
Charge 150 parts by weight, add 0.4 parts by weight of azobisisobutyronitrile (hereinafter referred to as AIBN) as a polymerization initiator and 0.3 parts by weight of lauryl mercaptan as a chain transfer agent under reflux with introducing nitrogen gas, and then reflux for 7 hours. Then, the polymerization was completed.

The polystyrene conversion molecular weight by gel permeation chromatograph (hereinafter referred to as GPC) is ▲ ▼ ＝ 10,200
Met.

Reference Examples 2 to 6 In the same manner as in Reference Example 1, using a monomer containing two perfluoroalkyl groups in the molecule and a non-fluorine-based non-polysiloxane-based monomer, A polymer was obtained.
The properties are shown in Table 1.

Reference Example 7 (Fluoropolymer 7) 40 parts by weight of a fluorine-based monomer shown in I-1-2 in the text, II- 1 in the text, in a glass flask equipped with a stirrer, a condenser, and a thermometer. 10 parts by weight of polysiloxane chain-containing monomer (▲ ▼ = 5,000) shown in 10, M-230 manufactured by Shin Nakamura Chemical Co., Ltd.
G 10 parts by weight, MMA 50 parts by weight, iBMA 38 parts by weight, β-HEMA 2
0 parts by weight and 392 parts by weight of methyl isobutyl ketone were charged, and AIBN was used as a polymerization initiator under a nitrogen gas and under reflux.
1.6 parts by weight and lauryl mercaptan as chain transfer agent 1.
After adding 1 part by weight, the mixture was refluxed for 7 hours to complete the polymerization. G
The styrene-equivalent molecular weight measured by PC was ▲ ▼ ＝ 9,900.

Reference Examples 8 to 12 Using the above-described monomer containing two perfluoroalkyl groups in the molecule and a non-fluorine-based monomer, a fluorine-based copolymer was obtained in the same manner as in Reference Example 7. . Their properties are shown in Table 2.

Example 1 [Formulation] The above blended composition was mixed in a ball mill for 60 hours, passed through a 3μ filter, and then applied onto a polyester film having a thickness of 11 μm so that the dry thickness was 5 μm. The surface was treated with a super calendar and cut into 1/2 inch width to obtain a magnetic tape.

The fluorine-based copolymer means the compound of Reference Example 1.

Examples 2 to 12 Magnetic tapes were obtained in the same manner by substituting the following compounds for the fluorine-based copolymer in the compounded composition described in Example 1.

The fluorocopolymer means the compounds shown in Tables 1 and 2.

Comparative Examples 1 to 3 Magnetic tapes were obtained in the same manner by substituting the following compounds for the fluorine-based copolymer in the compounded composition described in Example 1.

Comparative Example 1 Fluorine-based surfactant 〃 2 Fluorosurfactant 〃 3 Fluorosurfactant (C ₈ F ₁₇ CH ₂ CH ₂ OH) 〃 4 II-1-10 polysiloxane chain-containing monomer 20
Parts by weight MMA / nBMA / β-HEMA (45/35/20 parts by weight) copolymer n = 10,000 〃 5 MMA / nBMA / β-HEMA / polysiloxane chain-containing monomer II-1-10 (45 / 35/20/3 parts by weight) copolymer n
= 10,000 〃 6 A graft copolymer having a composition of 22 parts by weight and MMA 78 parts by weight, the former monomer constituting the backbone and the latter monomer constituting the graft chain n = 8,000 Comparative Example 7 20 parts by weight, MMA / nBMA / β-HEMA / II-1-10 (45/35/20/3
(Part by weight) copolymer n = 10,000 〃 8 40 parts by weight of A component, MMA / nBMA / β-HEMA (45 /
AB type block polymer (35/20 parts by weight) is a constituent component of B part n = 10,000 〃 9 dimethyl silicone oil n = about 4,000 〃 10 stearic acid 〃 11 lecithin 〃 12 liquid paraffin 〃 13 Comparative Examples 4 and 5 Mixture containing 50 wt% of each compound of the magnetic tape of each example obtained as described above,
The squareness ratio (that is, the dispersion orientation of the magnetic powder), the coefficient of kinetic friction (that is, the lubricity and the durability of the lubricity), the running stability, and the durability (that is, the output fluctuation) were measured. The results are shown in Table-3.

The squareness ratio was measured with a Vibrating Sample Magnetmeter. The coefficient of kinetic friction is the coefficient of kinetic friction with the magnetic head during the first run μ _K1 and the coefficient of kinetic friction after 600 runs μ
I asked about _K600 . The running stability is judged from the image of running unevenness when it is applied to a VCR, and it is classified into 5 levels (5; there is no running unevenness, 4; there is only slight running unevenness, 3; there is slight running unevenness, 2; There is uneven running, 1; uneven running is remarkable). The endurance test was evaluated by measuring the output fluctuation value with respect to the initial output after running each magnetic tape 600 times at a head load of 10 g and a running speed of 4.8 cm / sec under the conditions of 40 ° C and 85% RH. did.

Immediately after kneading with a ball mill, the degree of inclusion of air bubbles in the magnetic paint was visually observed and evaluated in three levels.

◯: No inclusion of bubbles is observed.

Δ: The inclusion of bubbles is slightly recognized.

X: Dissolution of bubbles is noticeable.

As is clear from the results of Table 3, by incorporating the fluorine-based copolymer according to the present invention in the magnetic layer, the squareness ratio, the dynamic frictional resistance reduction property, and the running stability as compared with the conventional additives were obtained. Is excellent, and the difference between μ _K1 and μ _{K600 and} the output fluctuation value are small, the magnetic recording medium of the present invention has a magnetic powder dispersion orientation, surface lubricity, surface smoothness, running stability,
And it was confirmed that it was excellent in durability.

Claims (2)

[Claims] 1. A fluorine-containing monomer having two perfluoroalkyl groups having 3 to 20 carbon atoms in the molecule and an acryloyl group or a methacryloyl group in the magnetic layer, and an acryloyl group or a methacryloyl group in the molecule. A magnetic recording medium comprising a fluorine-based copolymer obtained by copolymerizing a non-fluorine-containing monomer having 2. A non-fluorine-containing monomer having an acryloyl group or a methacryloyl group in the molecule, which is composed of two or more kinds, one of which is a polysiloxane chain-containing monomer. The magnetic recording medium according to item 1.