JP2993092B2 - Magnetic recording media - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a magnetic recording medium such as a magnetic tape and a magnetic disk, and more particularly to an improvement in a binder contained in a magnetic layer.

[Summary of the Invention]

The present invention relates to a magnetic recording medium in which a magnetic layer mainly composed of a magnetic powder and a binder is formed on a non-magnetic support, and a vinyl chloride having a primary hydroxyl group via an alkylene oxide chain in a side chain as a binder. It is an object of the present invention to improve the crosslinkability of a binder by using a system resin and to provide a magnetic recording medium having excellent running properties and durability.

[Conventional technology]

In a so-called coating type magnetic recording medium, a magnetic coating material obtained by dispersing and kneading a ferromagnetic powder, a binder, a dispersant, a lubricant and the like in an organic solvent is applied to a non-magnetic support such as a polyester film. A layer is formed.

The binder contained in the magnetic layer is excellent in dispersibility of the magnetic powder, can provide a good electromagnetic conversion property to the magnetic recording medium, and can form a magnetic layer excellent in abrasion resistance and heat resistance. Is required.

Examples of binders having relatively excellent properties include vinyl chloride resins such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-propionic acid copolymer, and vinyl chloride-vinyl acetate-vinyl alcohol copolymer. Is widely used.

A commonly used vinyl chloride resin is represented, for example, by the following general formula.

That is, the conventional vinyl chloride resin is a hydrophilic group (polar group) such as vinyl chloride, vinyl alcohol, and SO ₃ Na group.
Of monosubstituted ethylene. In such a vinyl chloride resin, the adsorptivity to magnetic powder is improved by the polar group, and a good dispersion effect can be expected.

[Problems to be solved by the invention]

However, when the above-mentioned vinyl chloride resin is used as a binder, for example, the hydroxyl group introduced by using vinyl alcohol as a component is a secondary hydroxyl group, so that the crosslinking property is poor, and the durability at high temperatures is particularly poor. There is a problem.

As a remedy for this problem, a method of adding a curing agent to the binder is known. As the above curing agent,
Hexamethyleneidisocyanate (HDI) -based isocyanates having a relatively low glass transition point Tg are considered.

However, in the method of adding an isocyanate having a relatively low glass transition point Tg as described above, although the durability can be improved, the magnetic surface sticks inside the roll during winding, for example.

Therefore, the present invention has been proposed in view of such circumstances, and aims at improving the crosslinkability of the binder to improve the running property,
An object of the present invention is to provide a magnetic recording medium having excellent durability.

[Means for solving the problem]

The inventor of the present invention has intensively studied that the above-mentioned object has been achieved, and as a result of using the vinyl chloride resin having a primary hydroxyl group via an ethylene oxide chain or a propylene oxide chain as a binder, the crosslinkability is reduced. It has been found that the present invention is improved, and the present invention has been completed.

That is, the present invention relates to a magnetic recording medium in which a magnetic layer mainly composed of a magnetic powder and a binder is formed on a nonmagnetic support, wherein the binder has the following general formula: (However, the above l, m, n represent the ratio of each constituent unit in% by weight, and the above j, k each represent an integer.) Wherein the vinyl chloride resin is crosslinked via at least a part of the primary hydroxyl groups.

In the present invention, a vinyl chloride resin represented by the above formula (1) is used as a binder for forming a magnetic layer together with the magnetic powder.

The vinyl chloride resin is structurally composed of vinyl chloride (in some cases, it may contain another monomer such as vinyl acetate), a mono-substituted ethylene having a polar group X introduced, and an alkylene in the side chain. It can be regarded as a copolymer of a monomer having a primary hydroxyl group via an oxide chain.
The two types of units, the above-mentioned vinyl chloride and the above-mentioned mono-substituted product of ethylene into which the polar group X has been introduced, are constituent components contained in a general vinyl chloride-based resin. A monomer having a hydroxyl group is a third unit newly introduced according to the present invention.

The proportions of vinyl chloride, the third unit, and the monosubstituted product of ethylene into which the polar group X has been introduced in the vinyl chloride resin are represented by l, m, and n, respectively.
Is preferably 1 + m + n = 100% by weight 10% by weight ≦ m ≦ 25% by weight 0.1% by weight ≦ n ≦ 3% by weight When the proportion m of the third unit is below the above range, that is, less than 10% by weight, the concentration of the primary hydroxyl group serving as a crosslinking point is insufficient, and the crosslinking property cannot be sufficiently improved. Conversely, if it exceeds the above range, that is, if it is more than 25% by weight, primary hydroxyl groups are excessively present and the viscosity increases, which adversely affects the physical properties of the coating film. On the other hand, when the proportion n of the ethylene mono-substituted substance into which the polar group X has been introduced is less than the above range, that is, less than 0.1% by weight, the effect of the polar group is insufficient and good dispersibility cannot be obtained. If it exceeds the above range, that is, if it exceeds 3% by weight, the water resistance will decrease.

The type of the polar group X is appropriately selected according to the properties such as the degree of acid dissociation of the hydroxyl group present on the surface of the magnetic powder to be used so that the resin component is adsorbed to the interface of the magnetic powder as much as possible. Is preferred. Examples of the polar group X, -SO ₃ M (M is hydrogen, an alkali metal), - COOM (M is hydrogen, an alkali metal), - OSO ₃ M (M is hydrogen, an alkali metal), (M ₁ and M ₂ are each hydrogen, an alkali metal or an alkyl group) and the like, and a plurality of these functional groups may be combined. However, quaternary ammonium bases and tertiary ammonium bases cannot be used because they interact with the alkylene oxide chain.

On the other hand, in the third unit, the alkylene oxide chain to be introduced into the side chain, -CH ₂ -CH ₂ -O-, or -
It has a repeating unit of CH ₂ —CH ₂ —CH ₂ —O—, and the degree of freedom of the terminal hydroxyl group is increased through the alkylene oxide chain. The number k of the repeating unit in the alkylene oxide chain is preferably 2 to 10. When the number k of the repeating units exceeds the above range, a problem of solubility in the dispersion medium occurs. On the other hand, when the number k is below the above range, the effect of introducing the alkylene oxide chain becomes insufficient. Further, if the length of the alkylene oxide is too long, the viscosity increases, and it becomes difficult to control the length of the chain. Therefore, ethylene oxide or propylene oxide is preferable, and an ethylene oxide chain is preferable.

Therefore, in the vinyl chloride resin, by introducing a primary hydroxyl group into the side chain via an alkylene oxide chain, the degree of freedom at a crosslinking point is increased, and the crosslinkability can be improved. Here, the concentration of the primary hydroxyl group is a value determined by the ratio m of the third unit in the vinyl chloride resin.
Sufficient effects can be obtained if the content is in the range of 10% by weight to 25% by weight.

As a method for introducing the primary hydroxyl group, polyoxyethylene glycol is previously esterified with acrylic acid,
A method of coexisting at the time of forming the main chain is conceivable. The reaction formula of the above esterification is as follows.

In the present invention, in addition to the vinyl chloride resin as the binder, other resins may be selected and mixed according to the required physical properties and the like. In this case, the type of the resin used is not particularly limited as long as it is a resin material usually used in the field of this type of medium, but for example, a resin having a relatively low glass transition point such as a urethane resin or a polyester resin. The component (soft resin component) is preferred. Excellent durability can be expected when used in combination with such a soft resin component. At this time, the mixing ratio of the vinyl chloride resin is preferably 30% by weight to 80% by weight based on the total binder. If it is below the above range, that is, if it is less than 30% by weight, the magnetic layer is liable to fall off or peel off, which causes dropout.

It is preferable to add a curing agent to such a binder in order to further improve durability. As the curing agent, a polyfunctional isocyanate can be used, and tolylene diisocyanate (TDI) is particularly preferable. The addition amount of the curing agent is 5 to the total binder amount.
30% by weight is preferred.

In the magnetic recording medium of the present invention, the magnetic layer is formed, for example, by dispersing magnetic powder in a binder, and depending on the type of the binder, ethers, esters, ketones, aromatic hydrocarbons, aliphatic hydrocarbons, chlorinated hydrocarbons, and the like. It is formed by applying a magnetic paint prepared by kneading with an organic solvent selected from hydrocarbons and the like to the surface of a non-magnetic support.

As the magnetic powder used in the present invention, any conventionally known magnetic powder can be used, and may be an oxide magnetic powder or a metal magnetic powder. Examples of the oxide magnetic powder include γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Co-coated γ-Fe ₂ O ₃ , Fe ₃ O ₄ , and Co-containing γ-Fe ₃ O ₄ , Co Γ-Fe ₃ O ₄ , Cr
O _{2 and the} like. As the metal magnetic powder, for example, F
e, Co, Ni, Fe-Co, Fe-Ni, Fe-Co-Ni, Co-Ni, Fe-Co-B,
Fe-Co-Cr-B, Mn-Bi, Mn-Al, Fe-Co-V and the like, and further, for the purpose of improving these various properties, Al, Si,
Metals such as Ti, Cr, Mn, Cu, and Zn may be added. Also, hexagonal ferrites such as barium ferrite, iron nitride, and the like can be used.

In the magnetic recording medium of the present invention, in addition to the binder and the magnetic powder, various dispersants, lubricants,
An antistatic agent, a rust inhibitor and the like may be added. As the dispersant, lubricant, antistatic agent, rust inhibitor and the nonmagnetic support, any of conventionally known materials can be used, and there is no particular limitation.

[Action]

By introducing a primary hydroxyl group into the side chain via an alkylene oxide chain, the degree of freedom of the hydroxyl group at the terminal of the alkylene oxide chain, which is a crosslinking point, is increased, and excellent crosslinkability is obtained. Therefore, if the vinyl chloride resin having a primary hydroxyl group is used as a binder, a magnetic recording medium having excellent durability can be provided.

〔Example〕

Hereinafter, the present invention will be described with reference to specific examples, but it goes without saying that the present invention is not limited to these examples.

Examples 1 to 6 Magnetic tapes were prepared using a vinyl chloride resin having a primary hydroxyl group in a side chain via an ethylene oxide chain as a binder. In addition, SO ₃ Na group was introduced as a polar group into the vinyl-based resin, and the introduction amount was 2 parts by weight based on the addition amount of the mono-substituted ethylene.

In these vinyl chloride resins, the length of the ethylene oxide chain and the concentration of the primary hydroxyl group are as shown in Table 1. In addition, the length of the ethylene oxide chain was represented by the number k of the repeating units —CH ₂ —CH ₂ —O— of the ethylene oxide chain. The concentration of the primary hydroxyl group was represented by the ratio (% by weight) of the monomer (third unit) having the primary hydroxyl group introduced into the side chain via the ethylene oxide chain in the vinyl chloride resin.

 The method for producing each magnetic tape is as follows.

First, a magnetic paint was prepared using each of the vinyl chloride resins shown in Table 1 according to the composition shown below.

Composition of magnetic paint Co-containing γ-Fe ₂ O ₃ magnetic powder 100 parts by weight Primary hydroxyl group-containing vinyl chloride resin 15 parts by weight Polyurethane resin 5 parts by weight Lubricant 2 parts by weight Abrasive 3 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 70 parts by weight Cyclohexanone 60 parts by weight The above materials were placed in a container, dispersed and mixed in a ball mill for 24 hours, 2 parts by weight of a curing agent (trade name: Coronate L) was added, and the mixture was further kneaded for 30 minutes to prepare a magnetic paint. .

Then, the magnetic paint was applied on polyethylene terephthalate having a thickness of 14 μm so that the dried coating film had a thickness of 4 μm. After that, it is calendered at 100 ° C,
After holding at 20 ° C. for 20 hours to perform a hardening treatment, each magnetic tape was cut by cutting to a 1/2 inch width.

Comparative Example 1 In preparing a magnetic paint, vinyl chloride, a monosubstituted ethylene substituted with SO ₃ Na group, and a vinyl chloride resin containing vinyl alcohol as a constituent were used instead of the primary hydroxyl group-containing vinyl chloride resin. Other than that, a magnetic tape was produced in the same manner as in Examples 1 to 6.

Comparative Examples 2 to 6 In Comparative Examples 2 to 6, Example 1 was repeated except that “number k of repeating units” and “concentration of primary hydroxyl group” were as shown in Table 1.
A magnetic tape was produced in the same manner as described above.

The glossiness, running property at high temperature, and durability of each magnetic tape produced as described above were examined. Table 1 shows the results.

 The gloss was measured with a gloss meter.

The running performance at high temperature is as follows.
%, Stored at 50 ° C for 2 days, run on a general-purpose VHS deck in playback mode in this environment, check the expansion of the magnetic tape, and determine if the drum sticks immediately after running. , ▲ for sticking, Δ for increased magnetic tape extension, ○ for no particular problem
And

The durability is as follows: After each magnetic tape is stored for 2 days at a relative humidity of 80% and a temperature of 50 ° C, reproduction and rewinding are repeated 10 times in this environment on a general-purpose VHS deck. Examine the amount of powder fall,
The case where the number is small is indicated by “，”, and the case where they are intermediate is indicated by “△”.

As shown in Examples 1 to 6 to which the present invention is applied, by using a vinyl chloride-based resin having a primary hydroxyl group via an ethylene oxide chain in a side chain as a binder, running properties at high temperatures are improved. It was also found that the durability was improved.

Also, from Comparative Examples 2 to 6, when the length of the ethylene oxide chain or the concentration of the primary hydroxyl group is too small, the degree of freedom of the hydroxyl group at the end of the ethylene oxide chain is insufficient, and good crosslinkability cannot be obtained. In addition, it was found that running performance and durability could not be improved.

〔The invention's effect〕

As described above, in the present invention, since a vinyl chloride resin having a primary hydroxyl group in the side chain via an alkylene oxide chain is used as a binder, crosslinkability is improved, and there is no problem such as adhesion, and It is possible to provide a magnetic recording medium having excellent running properties and durability.

──────────────────────────────────────────────────続 き Continued on the front page (72) Keiko Nihei Inventor, Sony Magne Products Co., Ltd. 6-5-6 Kita Shinagawa, Shinagawa-ku, Tokyo (56) References JP-A-5-189745 (JP, A JP-A-56-77930 (JP, A) JP-A-62-181310 (JP, A) JP-A-63-117055 (JP, A) JP-A-62-149763 (JP, A) JP-A-57-1979 44227 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 5/702 C09D 5 / 23,127 / 06 C08F 214/06 CA (STN) CAOLD (STN) REGISTRY (STN)

Claims (1)

(57) [Claims] 1. A magnetic recording medium comprising a nonmagnetic support and a magnetic layer mainly composed of a magnetic powder and a binder formed on a nonmagnetic support, wherein the binder has the following general formula: [However, the above l, m, n indicate the ratio of each constituent unit in% by weight, and l + m + n = 100, 10 ≦ m ≦ 25, 0.1 ≦ n ≦ 3
It is. The above j and k each represent an integer, j is 2 to 3, and k is 2 to 10. Further, the X is -SO ₃ M (M is hydrogen, an alkali metal), - COOM (M is hydrogen, an alkali metal), - OS
O ₃ M (M is hydrogen, alkali metal), (M ₁ and M ₂ are each hydrogen, an alkali metal or an alkyl group). A magnetic recording medium comprising a vinyl chloride resin represented by the formula: wherein the vinyl chloride resin is crosslinked via at least a part of the primary hydroxyl groups in the above general formula.