JPH04153912A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve compatibility with a resin binder, to enhance the dispersibility of magnetic powder and to further improve electromagnetic transducing characteristics by incorporating acrylic resin having one or more carboxyl groups at one terminal into a magnetic layer. CONSTITUTION:Acrylic resin having one or more carboxyl groups at one terminal is incorporated into a magnetic layer. The carboxyl groups are adsorbed on the surfaces of particles of magnetic powder and the adsorbed acrylic resin produces a three-dimensional repulsing effect. Compatibility with a resin binder generally used in a magnetic recording medium is improved, the dispersibility of the magnetic powder in the magnetic layer is satisfactorily enhanced and electromagnetic transducing characteristics are further improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium in which magnetic powder has good dispersibility and excellent electromagnetic conversion characteristics.

[Conventional technology]

Magnetic recording media are usually made by applying a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components onto a substrate such as a polyester film, and drying the coating.
With the increase in recording density, further improvements in electromagnetic conversion characteristics such as output and S/N ratio are required.

For this reason, in recent years, magnetic powders with extremely fine particle diameters have been used to improve the electromagnetic characteristics as described above. It is difficult to uniformly disperse them in a magnetic paint using an organic solvent, and it is not possible to sufficiently improve electromagnetic conversion characteristics such as the S/N ratio.

Therefore, in order to improve the dispersibility of such magnetic powder,
For example, this magnetic powder may be surface-treated with fatty acids or various surfactants (Japanese Unexamined Patent Publication No. 102504/1983),
Alternatively, the surface may be treated with a silane coupling agent or a titanium coupling agent (JP-A-55-125539,
No. 56-58135) to improve dispersibility.

[Problem to be solved by the invention]

However, methods such as surface treatment of magnetic powder using fatty acids, surfactants, silane coupling agents, or titanium coupling agents, or methods of adding these dispersants to magnetic paints, still do not have sufficient dispersion effects. However, if a large amount of these dispersants is used in an attempt to obtain a sufficient dispersion effect, the strength of the coating film of the magnetic layer etc. decreases significantly, making it impossible to obtain sufficient durability. In addition, magnetic powder surface-treated with a silane coupling agent or titanium coupling agent has a hydrophobic treatment on the particle surface of the magnetic powder, which improves the dispersibility in the magnetic paint, but it has poor meltability. On the contrary, the solubility of the binder resin, which has both hydrophilicity and hydrophilicity, decreases, and ultimately the dispersibility of the magnetic powder in the magnetic layer may not be sufficiently improved.

[Means to solve the problem]

This invention was made as a result of various studies in view of the current situation, and by incorporating an acrylic resin having one or more carboxyl groups at one end into the magnetic layer,
It improves the compatibility with the binder resin that conventional dispersants have, sufficiently improves the dispersibility of magnetic powder, and further improves electromagnetic conversion characteristics.

The acrylic resin used in this invention preferably has one or more carboxyl groups at one end, and when it has one or more carboxyl groups at one end,
The carboxyl group at the end of the molecule is adsorbed to the particle surface of the magnetic powder, producing a steric repulsion effect of the adsorbed acrylic resin, thereby significantly improving the dispersibility of the magnetic powder. In addition, conventional fatty acids, low molecular weight surfactants, silane coupling agents,
Compared to titanium coupling agents, since it has a carbonyl group in the hydrophobic group, it has a certain degree of compatibility with binder resins such as vinyl chloride-vinyl acetate copolymers and urethane resins. Therefore, it has good compatibility with binder resins commonly used in magnetic recording media, and the dispersibility of the magnetic powder in the final magnetic layer is sufficiently improved, further improving electromagnetic conversion characteristics.

The production method of such acrylic resins having one or more carboxyl groups at one end is not particularly limited, and any method may be used. ,4.
It is produced by vinyl polymerization using 4-azobis (4-cyanopentanoic acid) or the like, or by a macromonomer method using a chain transfer agent having a carboxyl group.

In the case of the macromonomer method, the polymerization initiators include α, α
'-Azobisisobutylnitrile, benzoyl peroxide, etc. can be used, and as the chain transfer agent, thiomalic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, orthomercaptobenzoic acid, etc. can be used.

Examples of the seven polymers used in polymerization include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, and acrylic ester, and these may be used alone or in combination of two or more. Also,
Styrene derivatives other than acrylic monomers may be added as monomers to be copolymerized.

The acrylic resin produced in this manner preferably has a number average molecular weight of 500 or more and 20,000 or less, and preferably has 1 to 3 carboxyl groups.

When using such an acrylic resin having one or more carboxyl groups at one end, a magnetic paint is prepared by mixing and dispersing it with other additives such as magnetic powder, binder resin, organic solvent, and abrasive. It is used by applying a paint onto a substrate by any means such as spraying or roll coating and drying to form a magnetic layer, and
Other methods include surface-treating magnetic powder with this acrylic resin, preparing a magnetic paint using the surface-treated magnetic powder, and forming a magnetic layer in the same manner as described above. When surface-treating the magnetic powder, an acrylic resin is dissolved in an organic solvent such as tetrahydrofuran, ethanol, cyclohexanone, toluene, etc., and the magnetic powder is immersed in this solution. In order to sufficiently improve the dispersibility of the magnetic powder, the amount used is preferably 0.1 to 20% by weight based on the magnetic powder, and 0.5 to 5% by weight. It is more preferable to adhere within this range.

Examples of the magnetic powder used in the magnetic layer include 7-
Fe, O, powder, Fe, O<powder, Co-containing 7-Fez
In addition to O3 powder, CO-containing Fe50 powder, Cr0z powder, Fe powder, Co powder, Fe-Ni alloy powder, Fe-C
Various conventionally known magnetic powders are widely included, such as metal powders such as O alloy powder, Co-Ni alloy powder, and Fe-Ni-Cr alloy powder, and barium ferrite powder.

In addition, as the binder resin, conventionally known thermoplastic resins,
Thermosetting resins are used, and thermoplastic resins include, for example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and vinyl chloride-acetic acid and nyl-maleic acid copolymer. Polymers, polyvinyl butyral, acrylic esters, acrylonitrile copolymers, cellulose derivatives such as cellulose acetate butyrate and nitrocellulose, polyurethane resins, etc. are preferably used. In addition, thermoplastic resins include phenolic resin, epoxy resin, urea resin,
Alkyd resins are used.

As the organic solvent, those commonly used in magnetic recording media, such as methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dioxane, and dimethyl formamide, are used alone or in combination.

Furthermore, as the nonmagnetic support, various synthetic resin films such as polyethylene terephthalate, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, polyimide, and metal foils such as aluminum foil and stainless steel foil are used.

In addition, magnetic paint contains myristic acid, stearic acid,
Lubricants such as n-butyl stearate, octyl stearate, isoamyl stearate, silicone oil, paraffin, alumina, Cr.

03, an abrasive such as red iron oxide, an antistatic agent such as carbon black, and a dispersant such as lecithin may be appropriately added and used.

Further, the magnetic layer may be provided on at least one side of the nonmagnetic support, and a hack coat layer may be provided on the side where the magnetic layer is not provided.

〔Example〕

Next, embodiments of the invention will be described.

Example 1 Methyl methacrylate 50 parts by weight α, α′-
Azobisisobu 0.8〃Tylnitrile 3-mercaptopropionic acid 3゜2〃 Tetrahydrofuran 60〃This composition,
The mixture was placed in a flask equipped with a condenser, and after sufficient nitrogen purging, the mixture was reacted at 60° C. for 3 hours with stirring.

Next, the obtained reaction product was purified by reprecipitation in petroleum ether and water, and dried under reduced pressure at 60° C. for 48 hours to obtain a one-end carboxylic acid acrylic resin.

The single-end carboxylic acid acrylic resin thus obtained had a number average molecular weight of 3.0×10 3 as determined by the smoke pressure osmosis method. In addition, the content of carboxylic acid groups is 0.3++u+o
It was l/g.

Next, using the thus obtained one-end carboxylic acid acrylic resin, Co-containing 7 FezOz 100 parts by weight one-end carboxylic acid acrylic resin 3
Vinyl acetate-vinyl alcohol copolymer (T1.C, manufactured by C company; VAGH) Polyurethane resin (Nippon Boliu 8, manufactured by Retan Kogyo Co., Ltd.; M-5033) Carbon black 7 #Alumina
5 Myristic acid
1 #n-butyl stearate 1
〃Cyclohexanone 130〃Toluene 130〃 in a ball mill to 10
After mixing and dispersing for 0 hours, a trifunctional low molecular weight isocyanate compound (manufactured by Nippon Polyurethane Industries Co., Ltd.: Coronate L) was added.
) was added thereto and mixed and dispersed for 0.5 hours to prepare a magnetic paint. This magnetic paint is applied onto a polyester film with a thickness of 14 μm so that the thickness after drying is 4.5 μm, the magnetic powder is oriented through a magnetic field, and after drying, the surface is smoothed and 1/ A magnetic tape was produced by cutting it into a 2-inch width.

Example 2 In the synthesis of the one-end carboxylic acid acrylic resin in Example 1, the amount of 3-mercaptopropionic acid used was 3.
Example 1 except that the amount was changed from 2 parts by weight to 1.6 parts by weight.
Similarly, the number average molecular weight was determined by vapor pressure osmosis to 6. OX
10', the content of carboxylic acid group is 0.17 smol
/g of one-end carboxylic acid acrylic resin was obtained.

Example 1 except that the single-end carboxylic acid acrylic resin thus obtained was used in the same amount in place of the single-end carboxylic acid acrylic resin used in Example 1 in the composition of the magnetic paint in Example 1. A magnetic tape was produced in the same manner.

Example 3 In the synthesis of the one-terminally carboxylic acid acrylic resin in Example 1, the number average molecular weight was 3. by f pressure osmosis method. lX103
Thus, a one-end carboxylic acid acrylic resin having a carboxylic acid group content of 0.65 mmol/g was obtained.

Example 1 except that the single-end carboxylic acid acrylic resin thus obtained was used in the same amount in place of the single-end carboxylic acid acrylic resin used in Example 1 in the composition of the magnetic paint in Example 1. A magnetic tape was produced in the same manner.

Example 4 In the synthesis of the one-terminally carboxylic acid acrylic resin in Example 1, the number average molecular weight was 5.8X10" by vapor pressure osmosis method
Thus, a one-end carboxylic acid acrylic resin having a carboxylic acid group content of 0.32 mmol/g was obtained.

Example 1 except that the single-end carboxylic acid acrylic resin thus obtained was used in the same amount in place of the single-end carboxylic acid acrylic resin used in Example 1 in the composition of the magnetic paint in Example 1. A magnetic tape was produced in the same manner.

Example 5 A magnetic tape was produced in the same manner as in Example 1, except that in the composition of the magnetic paint in Example 1, the amount of one-end carboxylic acid acrylic resin used was changed from 3 parts by weight to 0.3 parts by weight. .

Comparative Example 1 A magnetic tape was produced in the same manner as in Example 1 except that the one-end carboxylic acid acrylic resin was omitted from the composition of the magnetic coating material in Example 1.

The chroma S/N ratio was measured for each magnetic tape obtained in each Example and Comparative Example. Measurement of chroma S/N ratio is
The obtained magnetic tape is inserted into a video cassette and VH
A chroma signal was recorded on a magnetic tape using three types of VTR, and a chroma noise measuring device measured the noise portion of the reproduced signal to determine the chroma S/N ratio. Note that the chroma S/N ratio is expressed as a relative value with the magnetic tape of Comparative Example 1 as a reference (OdB).

Table 1 below shows the results.

Table 1 [Effects of the Invention] As is clear from Table 1 above, the magnetic tapes obtained in Examples Works to 5 had a higher chroma S/N than the magnetic tape obtained in Comparative Example 1. Therefore, the magnetic recording medium obtained using the acrylic resin having one or more carboxyl groups at one end of the present invention has good dispersibility of magnetic powder and excellent electromagnetic conversion characteristics. I understand.

Claims (1)

[Scope of Claims] 1. A magnetic recording medium having a magnetic layer comprising an acrylic resin having one or more carboxyl groups at one end; 2. The acrylic resin has a number average molecular weight of 500 or more and 2,000 or more.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is an acrylic resin having a molecular weight of 0 or less.