JPH04146521A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve still property in a low humidity environment with small reduction in S/N and small head wearing by using a combination of alumina powder almost spherical having 2 - 4m<2>/g specific surface area and a squarish alumina powder of 5 - 14m<2>/g specific surface area by specified amts. in the magnetic layer. CONSTITUTION:On a nonmagnetic supporting body, a magnetic layer containing ferromagnetic powder, an abrasive and a binder are provided. The abrasive consists of alumina powder almost spherical having 2 - 4m<2>/g specific surface area (SBET) and a squarish alumina power of 5 - 14m<2>/g specific surface area (SBET). To 100g of the ferromagnetic powder, 4 - 18g of almost spherical alumina powder and 2 - 15g of squarish alumina is used. By this method, still property in a low humidity environment can be improved, which results in small reduction in S/N and small head wearing.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a magnetic recording medium comprising a non-magnetic support and a magnetic layer, and more specifically to a magnetic recording medium having at least two magnetic layers. It is related to.

(Background of the Invention) Magnetic recording media are widely used as recording tapes, video tapes, floppy disks, and the like. A magnetic recording medium basically consists of a magnetic layer in which ferromagnetic powder is dispersed in a binder, which is laminated on a non-magnetic support.

Magnetic recording media are required to have high levels of performance characteristics such as tm conversion characteristics, running durability, and running performance. That is, audio tapes for music recording and playback are required to have higher original sound playback capabilities. Furthermore, video tapes are required to have excellent tF61 conversion characteristics, such as excellent original picture playback ability.

In addition to having such excellent electromagnetic conversion characteristics, magnetic recording media are required to have good running durability as described above. And in order to obtain running durability,
Normally, the function of abrasives plays an important role. In other words, the abrasive contained in the magnetic layer is distributed throughout the magnetic layer, but this part is present on the surface of the magnetic layer, and the magnetic recording medium runs while contacting a running member such as a hen. At this time, the abrasive material present on the surface of the magnetic layer exhibits a polishing effect at the contact surface between the surface of the magnetic layer and the hennode or the like. Therefore, by incorporating an abrasive into a magnetic recording medium, it is possible to improve running durability. However, the amount of abrasive present on the surface of the magnetic layer is only a small portion of the amount actually added to the magnetic layer, making it difficult to obtain sufficiently excellent running durability. For example, if the amount of abrasive added is increased to improve running durability, the content of ferromagnetic powder will decrease, and if abrasive +1 with a large particle size is used, the surface of the magnetic layer will be The abrasive material protrudes excessively,
As a result, the above-mentioned electromagnetic conversion characteristics deteriorate (7 problems).In addition, it is also common practice to use abrasives with large particle diameters and small abrasives, etc., but if the above-mentioned electromagnetic conversion characteristics are sufficient. Not obtained (Unexamined Japanese Patent Publication No. 57-16
No. 2129, Japanese Unexamined Patent Publication No. 58-85931).

For example, in JP-A No. 58-85931, two types of polishing 7pj with different average grain sizes are used.Example 1 has an average grain size of 0.05 to 0.05.
It is disclosed that the magnetic layer contains an abrasive of 3 μm and an abrasive with an average particle size of 0.5 to 15 μm. However, the shape of the abrasive has not been studied, and such With this combination, it was not possible to improve the still performance, especially at low temperatures.Also, it was not possible to sufficiently improve the S/N reduction and head wear.

(Object of the invention) The object of the present invention is to improve stills in low humidity environments, S/N
It is an object of the present invention to provide a magnetic recording medium that exhibits less deterioration and less head wear.

(Structure of the Invention) That is, the above object of the present invention is to provide a magnetic recording medium in which a magnetic layer including a ferromagnetic powder, an abrasive, and a bonding side is provided on a nonmagnetic support, in which the abrasive has a specific surface area (S□, ). The ferromagnetic powder 1 is made of spherical granular alumina with a specific surface area (SIFT) of 2 to 4 nf/H and angular granular alumina with a specific surface area (SIFT) of 5 to 14 nr/g.
4 to 18 granular alumina similar to the above method Q per 00g
g. A magnetic recording medium comprising 2 to 15 g of the angular granular alumina.

This can be achieved by using the magnetic recording medium Q in which the average particle size of granular alumina measured by a light scattering method similar to the method described above is 0.5 to 0.7 μm.

Further, the above object of the present invention can be achieved by a magnetic recording medium characterized in that the magnetic layer contains 0.3 to 2 g of a fatty acid having a melting point of 7.degree. C. or less per 100 g of ferromagnetic powder.

In other words, the present invention uses a relatively large amount of spherical granular alumina with a relatively small specific surface area, and a relatively small amount of spherical granular alumina with a relatively large specific surface area, thereby significantly improving still performance at low humidity. and S/N
It was previously unanticipated that deterioration and wear and tear would be improved at the same time. The reason for this is not clear, but because there is moisture in a high QFA state, the μ value does not increase even if the magnetic tape slides on the magnetic field. However, when the humidity is low, the μ value increases, heat is generated by sliding, and in extreme cases, the magnetic tape may become deformed.

In the case of the present invention, the shape (7) is such that it is easy to ensure a decrease in the μ value due to the granular shape that is almost spherical in places (7), so the μ value decreases even under very harsh conditions such as low humidity. It seems that the still has been improved.Also, by using a granular abrasive with a rather large specific surface area and many corners, it is possible to keep the surface of the magnetic layer excessively smooth and not damage the hend. The estimated relationship between humidity and μ value will be further explained as follows.

At high humidity, the moisture present on the surface of the material is thought to be responsible for reducing the μ value of the mirror state material.

Of course, this is also related to the interaction between the liquid/solid lubricant used in the case of magnetic recording media and the surface moisture.

In the case of magnetic recording media, this lubrication effect due to minute surface moisture is estimated from the fact that the μ value of mirror-like materials increases at low temperatures. mode), the lubrication effect is insufficient due to the lack of surface moisture, and the μ value between the VTR head and the magnetic recording medium increases, causing the magnetic layer of the magnetic recording medium to adhere to the head. The magnetic layer is destroyed.In other words, still images cannot be reproduced due to the destruction of the magnetic layer.

Regarding these phenomena, relatively small alumina and chromium oxide have no effect on suppressing the increase in μ value under low humidity conditions, whereas relatively large alumina is effective. This is thought to be because only a relatively large abrasive agent is interposed between the VTR head and the magnetic recording medium to compensate for the lack of water lubrication effect in low humidity conditions and can save the magnetic layer from destruction. It can be done. In particular, only alumina can supplement the effect of water lubrication, although the reason is unclear.

In addition, in the present invention, the still and head wear amount are improved by combining a fatty acid with a melting point of 70°C or less, particularly myristic acid or palmitic acid, with these aluminas. It is thought that it has high compatibility with alumina and alumina, and enters into the magnetic phase coating film, making the surface layer a little soft and exerting the Kunjon effect.On the other hand, stearic acid, which has a melting point higher than 70°C and has a long carbon chain, It is surmised that this has a relatively low affinity with the binder and alumina, and is likely to be adsorbed to the ferromagnetic powder or appear on the surface of the magnetic layer, which is why there is a large difference in the effects of the present invention.

Preferred embodiments of the present invention are as follows.

m The average particle size of the angular granular alumina contained in the m-layer is 0. A magnetic recording medium characterized in that it has a diameter of lO to 0.30 μm (according to a light scattering method).

(2) A magnetic recording medium characterized in that 60% or more of the saturated fatty acids contained in the magnetic layer are myristic acid and/or palmitic acid.

(3) In a magnetic recording medium consisting of a magnetic layer containing ferromagnetic powder, a back layer, and a nonmagnetic support, the ferromagnetic fine powder is a metal powder, the SQ of the magnetic tape is 0°85 or more, and the Bm of the magnetic tape is is 3000 Gauss or more, the average particle + xb<o, 5 to 0.7 as an abrasive for the magnetic layer.
1. A magnetic recording medium comprising 4 to 18 g of alumina particles in the form of particles close to spheres of μm (according to a light scattering method) per 100 g of ferromagnetic fine powder.

The alumina of the present invention has a granular shape close to a sphere with a specific surface area (Sst
r) is 2-4 rrf/g. The average particle size is 0.5-0.7 μm. Bulk density is 0. 7-1
．． 1 g/d is preferred. Density is 1.2~l, 6g/cd
is preferable, pH is preferably 3.0 to 9.5, and moisture is 0. It is preferably 4% or less. α-alumina is 80wt%
It is preferable that it is above.

More preferably, the content is 95 wt% or more, such as AKP 12 manufactured by Sumitomo Chemical Co., Ltd.

Another type of alumina is granular with many corners.

The specific surface area (S□a) is 5 to 14 rrf/g. The average particle size is 0.1-0. It is 3 μm. Bulk density is 0
．． 9 to 1.3 g/cd is preferable, and the density is 1.2 to 1.2 g/cd.
6 g/cj is preferable, and the pH is preferably 3.0 to 9.5. The water content is preferably 0.6% or less.

The content of α-alumina is preferably 80 wt% or more, preferably 95 wt% or more, and a specific example thereof includes Juminaka-type Hit55.

Light scattering method The average particle size is determined by dynamic light scattering on microparticles undergoing Brownian motion in solution using a particle size analysis system using laser light, and by natural sedimentation method to determine the particle size and particle size distribution. It can be measured and determined. Commercially available measuring instruments include CULTER's DELSA440 and Tenba Denshi's LPA3000 and LPA3100. The angular granular alumina is defined from the average particle size and nitrogen adsorption specific surface area. Granular alumina that is close to spherical has a smaller specific surface area than granular alumina that has many corners because it has fewer irregularities on its surface.The relationship between the average particle size of granular alumina that is close to zero sphere and the specific surface area for nitrogen adsorption is given by the following equation.

Alumina Hit55 (manufactured by Sumitomo Chemical) L o g (
The nitrogen adsorption specific surface area) is 0.929, which is clearly a larger value than that of granular alumina, which is closer to spheres, and it can be said that the surface is uneven and has a granular shape with many corners.

The magnetic recording medium of the present invention basically has a structure in which at least two magnetic layers containing ferromagnetic powder dispersed in a binder are provided on a nonmagnetic support.

Non-magnetic supports that can be used in the present invention include:
Polyesters such as polyethylene naphthalate (CPET), polyethylene naphthalate (CPET), polyolefins such as polypropylene caps, cellulose derivatives such as cellulose triacetate and cellulose acetate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride. Films or sheets made of synthetic resins such as polyamide, polyamideimide, polyimide, etc.; Non-magnetic metal foils such as aluminum and copper; Gold N foils such as stainless steel foils; selected from.

The thickness of these supports is in the range of 2.5 to 100 μm, preferably in the range of 3=80 ImLy).

There are no particular restrictions on the binder resin used to form each magnetic layer of the present invention. Examples of binder resins include vinyl chloride copolymers (e.g., vinyl chloride/vinyl acetate copolymers, vinyl chloride/vinyl acetate copolymers, vinyl chloride/vinyl acetate copolymers,・Vinyl alcohol copolymer, vinyl chloride/vinyl acetate/acrylic acid copolymer, vinyl chloride/vinylidene chloride copolymer, vinyl chloride/acrylonitrile copolymer, ethylene/vinyl acetate copolymer), nitrocellulose resin, etc. Cellulose derivatives, acrylic resins, polyvinyl acetal resins, polyvinyl butyral resins,
Epoxy resin, phenoxy resin, polyurethane resin (
Examples include polyester polyurethane resins, polyether polyurethane resins, polycarbonate polyurethane resins, and the like. These resins may contain polar groups such as hydroxyl groups, carboxyl groups, epoxy groups, sulfonic acid metal bases, phosphoric acid groups, and phosphoric ester groups.

These can be used alone or in combination.

Furthermore, when a curing agent is used, a polyisocyanate compound is usually used. The polyisocyanate compound is selected from those commonly used as curing agent components for polyurethane resins and the like. Examples of polyisocyanun-1 compounds include the reaction product of tolylene diisonoanate and 1 mole of trimethylolpropane (e.g.
Death module! ,,-75 (Bayer GmbH %u)), reaction product of 3 moles of diisocyanate such as quinolyl diisocyanate or hexamethylene diisocyanate and 1 mole of trimethylolpropane, hexamethylene diisocyanate-1-3 mol of bij2-ret adduct, 1.5 mol of tolylene diisocyanate and 1.5 mol of isocyanurate, 3 mol of tolylene diisocyanate and 1.2 mol of hexamethylene diisocyanate, isophorone diiso Mention may be made of polymers of sodium chloride and diphenylmethane diisocyanate.

Further, when performing curing treatment by electron beam irradiation, a compound having a reactive double bond (eg, urethane acrylate) can be used.

The total weight of the resin component and curing agent is 100% of the ferromagnetic powder.
It is usually preferably in the range of 5 to 40 parts by weight, more preferably 10 to 20 parts by weight.

Examples of ferromagnetic powders used in the present invention include γ-Fe, Q
Metal oxide-based ferromagnetic powder such as □, dissimilar metal/metal oxide-based ferromagnetic powder such as γ-FezO3 containing other components such as cobalt, and ferromagnetic powder such as iron, cobalt or nickel. Examples include ferromagnetic metal fine powder containing metal.

When using a ferromagnetic metal fine powder, it is a ferromagnetic metal fine powder containing iron, cobalt, or nickel, and has a specific surface area of 42rrr/g or more (particularly preferably 45rrr/g or more). Preferably, it is a fine powder.

As an example of this ferromagnetic metal fine powder, the metal content in the ferromagnetic metal fine powder is 75% by weight or more, and the metal content is 8% by weight.
0% by weight or more of at least one ferromagnetic metal or alloy (e.g., Fe, Co, N1, Fe-Co, Fe-Ni)
, Co-Ni, Co-N1-Fe), and other components (e.g., Ai, Si,
S, Sc, Ti, ■, Cr, Mn, Cu, Zn, Y, M
o, R'h, Pd, Ag, Sn, Sb, B, Ba.

Ta, W, Re, Au, Hg, Pb, P, La.

Mention may be made of alloys that may contain (Ce, Pr, Nd, Te, Bi). Further, the ferromagnetic metal may contain a small amount of water, hydroxide, or oxide.

Methods for producing these ferromagnetic powders are already known, and the ferromagnetic powder used in the present invention can also be produced according to known methods.

There are no particular restrictions on the shape of the ferromagnetic powder, but needle-like, granular, dice-like, rice-grain-like, and plate-like shapes are usually used. In particular, it is preferable to use acicular ferromagnetic powder.

The above resin component, curing agent, and ferromagnetic powder are mixed and dispersed together with a solvent (e.g., methyl ethyl ketone, dioxane, cyclohexanone, ethyl acetate) that is normally used in the preparation of magnetic paint to obtain a magnetic paint. Crosstalk dispersion can be performed according to conventional methods.

In addition to the above components, magnetic paints contain commonly used additives or fillers such as antistatic agents (e.g. carbon black), lubricants (e.g. fatty acids, fatty acid esters, silicone oil), dispersants, etc. It goes without saying that it may also contain agents.

Next, a method for manufacturing the magnetic recording medium of the present invention will be described. For coating, a magnetic paint prepared from the above materials is applied onto a non-magnetic support by the following method. First, a coating solution for the magnetic layer is prepared by cross-dispersing magnetic layer forming components such as a resin component for the magnetic layer, a ferromagnetic powder, and a curing agent blended if desired with a solvent.

Applicators for applying the above magnetic paint include air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat,
reverse roll coat, transfer roll coat,
Gravure coat, kiss coat, cast coat, spray coat, spin cord, etc. can be used.

A backing layer may be provided on the surface of the nonmagnetic support used in the present invention that is not coated with the magnetic paint. Normally, the bank layer is formed by applying a back layer forming paint consisting of particulate components such as abrasives and antistatic agents and a binder dispersed in an organic solvent to the side of the non-magnetic support that is not coated with the magnetic paint. It is a layer provided.

Note that an adhesive layer may be attached to the surface of the nonmagnetic support on which the magnetic paint and the bank layer forming paint are applied.

Usually, the coated layer of magnetic paint is dried after being subjected to a treatment for orienting the ferromagnetic powder contained in the coated layer of magnetic paint, that is, a magnetic field orientation treatment.

After being dried in this manner, the coated layer is subjected to surface smoothing treatment. For the surface smoothing process, for example, a super calender roll is used. By performing the surface smoothing treatment, the pores generated by the removal of the solvent during drying disappear and the filling rate of the ferromagnetic powder in the magnetic layer is improved, so that a magnetic recording medium with high electromagnetic conversion characteristics can be obtained. I can do it.

The thus cured laminate is then cut into a desired shape.

The cutting can be carried out under normal conditions using a normal cutting machine such as a slitter. (Effects of the Invention) The present invention uses granular alumina particles with a specific surface area of 2 to 4 m2/g that are close to spheres in the magnetic layer. By using a predetermined amount of angular granular alumina with a specific surface area of 5 to 14 m2/g in combination, the still performance in low humidity environments is improved, and magnetic recording media with less S/N reduction and less wear and tear. was gotten.

By further using a fatty acid having a melting point of 70° C. or lower in combination with these two types of polishing agents, the above-mentioned effects can be further improved.

(Example) The present invention will be specifically described according to an example. In the examples, "part j" indicates "part by weight."

[Example 1] The following magnetic layer composition (CI) was put into a Ni-Goo and thoroughly kneaded, then (n) was added and mixed and dispersed ([[] was added and dispersed to prepare a magnetic coating liquid.

/ / / Summer 8 Easy 8 Easy Easy 8 Graduation Journal Ji Rough Kneel VCO of the sustenance mouth ~ ×〉 to ~ Lotto 0 0-, ev) -〇 〇More u) A's. CsP+x +jt.

~L5F-RO's RO "-X ・-,,: To 1ku=Tomifu Δ
After adjusting the viscosity of this magnetic coating solution, it was coated onto a 18 um non-magnetic support of polyethylene naphthalate to a thickness of 4.5 mm.
It is coated with a thickness of μm and dried while being oriented in the direction of coating progress using opposing magnets of 3000 gauss.

After that, the magnetic layer was continuously calendered, and the following pack layer was applied to the back side of the non-magnetic support with the magnetic layer to a thickness of 1.5 μm. After slitting the magnetic layer into 1 inch width, the magnetic layer was surface treated with a diamond blade. I made a tape.

, 1jjl■ Moxibustion (1) Carbon black (Cabonoto■, BP800)
100 parts carbon flake (Cancafleaf ■, Thermanox MT) 25 parts polyurethane polycarbonate (Dainippon Seika ■, FJ2) 35 parts phenoxy resin (Union Carbide ■, PKHH) 25 parts methyl ethyl ketone 300 parts (n) Polyisocyanate (Japan Polyurethane ■, C3040) Abrasive (Sumiman Chemical ■, )1itlOO) Abrasive (Sakai Chemical ■, BF-LL) Lubricant (Shin-Etsu Chemical ■, KF69) Olein #Copper methyl ethyl ketone 15 parts 1 part 1 part 1 part 700 parts Table 1 As is clear from the results, all the samples of Examples 1 to 6 of the present invention had a still temperature of 3 at low humidity (30% RH).
It was confirmed that the magnetic recording medium was good for less than 0 minutes and did not cause any problems when the Y S/N head wore out. All comparative samples are stills, head wear amount,
At least one of Y S/H was defective, and three characteristics could not be satisfied at the same time.

Claims (3)

[Claims] (1) In a magnetic recording medium in which a magnetic layer containing ferromagnetic powder, an abrasive agent, and a binder is provided on a nonmagnetic support, the abrasive agent is similar to a sphere with a specific surface area (S_B_E_T) of 2 to 4 m^2/g. Granular alumina and specific surface area (S_B_E_T) 5~
14 m^2/g of granular alumina with many corners, and per 100 g of the ferromagnetic powder, 4 to 18 g of the granular alumina that is close to a sphere, and 2 to 2 g of the granular alumina with many corners.
A magnetic recording medium characterized in that it contains 15g. (2) The magnetic recording medium according to claim (1), wherein the average particle size of the nearly spherical alumina particles measured by a light scattering method is 0.5 to 0.7 μm. (3) The magnetic recording medium according to claim (1), wherein the magnetic layer contains 0.3 to 2 g of a fatty acid having a melting point of 70° C. or less per 100 g of ferromagnetic powder.