JPH0444622A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility and electrical characteristics of magnetic powder by using a comb-type polar group-contg. acrylic resin formed by bonding a polar group-contg. acrylic resin with a specific bond as a binder component. CONSTITUTION:The degree of freedom near the polar group increases and the polar group-contg. acrylic resin adsorbs well on the surfaces of magnetic powder if this resin is bonded by either of the urethane bond or urea bond or both bonds. The dispersibility and electrical characteristics of the magnetic powder are improved in this way. The acrylic resin having 5,000 to 100,000 number average mol. wt. is used in terms of mechanical characteristics and formation of a magnetic coating material. The polar group-contg. acrylic resin before bonding to the comb shape having 500 to 50,000 number average mol. wt. is preferable and further, a carboxyl group, sulfonic acid group, phosphoric acid group, tertiary amino group or the salts thereof and a hydroxyl group, etc., are adequate as the polar group to be introduced into the comb-type polar group-contg. acrylic resin.

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 electrical properties.

[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. As the binder component used in this case, it is desired that the binder component has excellent dispersibility of the magnetic powder, can impart excellent electrical properties to the magnetic recording medium, and has excellent durability.

For this reason, polyurethane resins have traditionally been widely used as binder components with excellent properties. However, although conventional polyurethane resins have excellent mechanical properties, they have a low ability to disperse magnetic powders, making it difficult to disperse magnetic powders. cannot be dispersed well.

Therefore, bonding resins having polar groups such as hydroxyl groups are used together with polyurethane resins, and polar groups such as carboxyl groups, sulfonic acid groups, phosphoric acid groups or salts thereof, and tertiary amino groups are used in the main chain of polyurethane resins. The dispersibility of magnetic powders has been improved by using powders into which groups have been introduced. (JP-A-55-'38693, JP-A-57-92422, JP-A-59-30235) [Problems to be Solved by the Invention] However, when a binder resin having a polar group such as a hydroxyl group is used as a polyurethane resin, Dispersion of magnetic powder can meet the recent demands for high density and high reliability, even when used in combination with polyurethane resin or polyurethane resin with various polar groups introduced into the main chain of polyurethane resin. However, the properties are still insufficient, and the electrical characteristics cannot be sufficiently improved.

(Means for Solving the Problems) The present invention has been made as a result of various studies in view of the current situation, and is a combination of combs in which polar group-containing acrylic resins are bonded by either or both of urethane bonds and urea bonds. By using an acrylic resin containing polar groups as a binder component, the dispersibility of the magnetic powder is sufficiently improved, and the electrical properties are further improved, meeting the recent demands for high density and 4 high reliability rhyming properties. This is what I responded to.

In this invention, the comb-shaped polar group-containing acrylic resin used as a binder component, in which the polar group-containing acrylic resin is bonded by either or both of urethane bonds and urea bonds, has polar group-containing acrylic chains in a comb shape. Therefore, compared to polyurethane resins in which the polar groups are in the main chain, the degree of freedom in the vicinity of the polar groups is increased, and the affinity with the magnetic powder is further improved, resulting in extremely good adsorption to the surface of the magnetic powder. Therefore, when this type of acrylic resin containing comb-shaped polar groups is used as a binder component, the dispersibility of the magnetic powder is sufficiently improved and the electrical properties are sufficiently improved.

A comb-shaped polar group-containing acrylic resin in which such a polar group-containing acrylic resin is bonded by either or both of a urethane bond and a urea bond can be produced by any method, but for example, (a) Diol at one end Acrylic resin containing a polar group (b) Organic diisocyanate (c) Chain extender (cl) At least (a) and (b) of polyols having hydroxyl groups at both ends, such as polyester and polyether, are reacted, and the necessary Depending on the situation, those obtained by further reacting (C) or (d) are preferably used. Here, the ratio of each component (a), (b), (c), and (d) is adjusted as necessary, and as each of these components, for example, the following are preferably used.

(a) As the acrylic resin containing a diol polar group at one end, one manufactured by any method can be used. For example, one manufactured by a typical manufacturing method such as radical polymerization of an acrylic monomer with a chain transfer agent can be used. It will be done. Then, a polar group-containing acrylic monomer is added to the acrylic monomer so that the polar group is introduced into the acrylic resin obtained at this time.

Here, examples of the acrylic monomer include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, lauryl methacrylate, and stearyl methacrylate, which may be used alone or in combination of two or more. In addition, examples of the polar group-containing acrylic monomer added to the acrylic monomer include acrylic acid, methacrylic acid, dimethylaminoethyl methacrylate, 2-acrylamido-2-methyl-neepropanesulfonic acid, methacryloxyethylsulfonic acid, and 2-methacrylic acid. Examples include oxyethyl acid phosphate, etc. Furthermore, new polar groups can also be introduced by copolymerizing monomers with reactive functional groups such as glycidyl methacrylate and reacting these reactive functional groups with other compounds. It is possible. As the initiator, α,α'-azobisisobutyronitrile and benzoyl peroxide are used, and as the chain transfer agent, thioglycerin and the like are used.

(b) As the organic diisocyanate, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethane diisocyanate, etc. are preferably used.

(C)I extenders include ethylene glycol, 1,3
- Diols such as propanediol, 1,4-butanediol, neopentyl glycol, diamines such as ethylenediamine and tolylene diamine, those without polar groups such as water, 2,2-dimethylolpropionic acid, bis(4-
Those having polar groups such as sodium hydroxybutyl-5-sulfoisophthalate, sodium β-glycerophosphate, N-methyljetanolamine, and potassium 2,3-dihydroxy-1-propanesulfonate are used.

(d) As the polyol, polyethylene glycol,
Preferably used are polyether diols such as polypropylene glycol, polyester diols such as polybutylene adipate and polybutylene phthalate, polylactone diols such as poly ε-caprolactone, and polycarbonate diols such as poly 1,6-hexane carbonate.

The comb-shaped polar group-containing acrylic resin obtained by reacting these components has an acrylic resin content of 10% by weight.
If it is less than 90%, the properties of acrylic resin cannot be expressed.
If the amount exceeds 20% by weight, the resin becomes brittle and the durability decreases, so the content of acrylic resin is preferably within the range of 10 to 90% by weight, and preferably within the range of 20 to 80% by weight. More preferred. In addition, the number average molecular weight is 5000
If it is smaller, the mechanical properties will deteriorate, 1oooo.

If the number average molecular weight is 500, the viscosity will be high when dissolved in an organic solvent etc., making it difficult to make magnetic paint.
Those having a number average molecular weight of 0 to 100,000 are preferably used, and those having a number average molecular weight of 20,000 to 60,000 are more preferably used. Furthermore, if the number average molecular weight of the polar group-containing acrylic resin before being bonded into a comb shape by urethane bond or urea bond is smaller than 500, it will not be able to exhibit the properties of acrylic resin, and if it is larger than 50,000, the degree of freedom of the acrylic resin will be reduced. number average molecular weight of 500 to 50.
000 is preferably used, and the number average molecular weight is 100.
0 to 1oooo is more preferably used.

Further, as the polar group to be introduced into the comb-shaped polar group-containing acrylic resin, a carboxyl group, a sulfonic acid group, a phosphoric acid group, a tertiary amino group or a salt thereof, a hydroxyl group, etc. are introduced as suitable polar groups, These polar groups may be included in the main chain. If the amount introduced is less than 0.05 mmol/g, the dispersibility of the magnetic powder cannot be sufficiently improved, and if the amount is more than 10 mmol/g. Then, due to aggregation of polar groups, the viscosity increases when dissolved in an organic solvent etc., making it difficult to make a magnetic paint.
It is preferably within the range of mmol/g, 0.2 to 5
More preferably, it is within the range of mmol/g.

Such comb-shaped polar group-containing acrylic resins may be used in combination with other binder resins, such as polyurethane resins, vinyl chloride-vinyl acetate copolymers, cellulose resins, polyvinyl butyral resins, and polyester resins. based resin,
It is used in combination with commonly used binder resins such as polyacrylic resins, epoxy resins, phenolic resins, and polyisocyanates with good compatibility.

The bonding component using such a comb-shaped polar group-containing acrylic resin sufficiently improves the dispersibility of the magnetic powder.
It is preferably used in an amount of 10 to 35% by weight, more preferably 15 to 30% by weight, based on the magnetic powder.

The magnetic recording medium of the present invention may be manufactured according to a conventional method. For example, the above-mentioned acrylic resin containing a comb-shaped polar group may be used with or without other binder resin, magnetic powder, organic A magnetic paint is prepared by mixing and dispersing it with a solvent and other additives, and this magnetic paint is applied onto a substrate such as a polyester film by any means such as spraying or roll coating, and then dried. , a magnetic layer may be provided on the surface of the substrate and a back coat layer may be provided on the opposite surface, or a magnetic layer may be provided on both sides of the substrate. When providing the back coat layer in this way, this comb-shaped polarity The group-containing acrylic resin is also suitably used as a binder resin for the backcoat layer.

Here, as the magnetic powder used, for example, 7-
Fe, 02 powder, Fe5Oa powder, T-Fezes and F
Iron oxide powder in intermediate oxidation state with e, O, Co-containing 7-
In addition to Fez03 powder, CO-containing Fe, O, powder, Cry powder, metal powder such as Fe powder, Co powder, Fe-Ni-Cr alloy powder, barium ferrite powder, nitride magnetic powder such as iron nitride, etc. A wide variety of conventionally known magnetic powders are included. In the case of acicular magnetic powder, the average particle diameter (long axis) of these magnetic powders is usually 0.2 to 1.
．． It is preferable that the average axial ratio (average major axis diameter/average minor axis diameter) is usually about 5 to 10, and in the case of a plate, the average major axis diameter is usually about 0.07 to 0.0 μm. It is desirable that the thickness be about 3 μm.

In addition, organic solvents that are generally used in magnetic recording media, such as methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dioxane, and dimethylformamide F, may be used singly or in combination of two or more. used.

Incidentally, various commonly used additives such as lubricants, abrasives, antistatic agents, dispersants, etc. may be optionally added to the magnetic paint.

〔Example〕

Next, embodiments of the invention will be described.

Example 1 Methyl methacrylate 90 parts by weight 2-methacryloxyethyl acetate 11 diphosphate α, α'-azobisisobutyro 1.7 I nitrile thioglycerin 2.31 tetrahydrofuran 100A This composition was mixed with a cooler. After the flask was sufficiently purged with nitrogen, the mixture was reacted at 60° C. for 2 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 an acrylic resin.

The acrylic resin thus obtained had a molecular weight of 6.0×10'' as measured by vapor pressure osmosis, and a phosphoric acid group content of 0.6 mmol/g.

Next, using the acrylic resin obtained in this way, 150 parts by weight of acrylic resin 1.4-
Butanediol 6.7Jf Poly 1,6-hexane carbonate 100〃Todiol (number average molecular weight 4.4'-diphenylmethane 50〃Socyanate tin octylate 0.05# Tetrahydrofuran 100# Toluene
100〃 composition at 80℃ under nitrogen atmosphere
After the reaction, dilute with tetrahydrofuran for 10 hours.
A comb-shaped acrylic resin solution was obtained by diluting it to 0% by weight.

The comb-shaped acrylic resin thus obtained has an acrylic resin content of 49% by weight and a number average molecular weight of 49% by weight.
The measured value was 3.0 x 10' in terms of polystyrene.

Using the comb-shaped acrylic resin obtained in this way, α-Fe magnetic powder (coercive force 1500 300 parts by weight Oersted, saturation magnetization 120 e■u/g) comb-shaped acrylic resin 65 polyfunctional isocyanate 10 carbon black
10〃α-AIyo08 powder 3
〃Myristic acid 61 n-butyl stearate 8 〃Cyclohexanone
395/r toluene 3
A magnetic coating material was prepared by mixing and dispersing the composition No. 95 in a ball mill for 72 hours. This magnetic paint was applied onto a polyester film with a thickness of 20〃m so that the thickness after drying would be 5μm, and dried to form a magnetic layer. After calendering, it was cut into 1 x 2 inch width and magnetic tape was applied. was created.

Example 2 Example 1 except that in the synthesis of the acrylic resin in Example 1, the amount of 2-methacryloxyethyl acid phosphate used was changed from 11 parts by weight to 20 parts by weight.
Similarly, the molecular weight was determined to be 5.5XlO' by vapor pressure osmosis.
Thus, an acrylic resin having a phosphoric acid group content of 1.0 mmol/g was obtained.

Next, in the synthesis of the comb-shaped acrylic resin in Example 1, the same amount of the acrylic resin obtained in Example 2 was used in place of the acrylic resin obtained in Example 1, and 1.4-
The procedure was the same as in Example 1 except that the amount of butanediol used was changed from 6.7 parts by weight to 6.5 parts by weight, and the content of acrylic resin was 49% by weight, and the number average molecular weight was calculated as polystyrene by GPC measurement. A 2.8×10′ comb-shaped acrylic resin was obtained.

A magnetic tape was produced in the same manner as in Example 1, except that the same amount of the comb-shaped acrylic resin thus obtained was used in place of the comb-shaped acrylic resin used in the composition of the magnetic paint in Example 1.

Example 3 In the synthesis of the acrylic resin in Example 1, the molecular weight was determined by vapor pressure osmosis method in the same manner as in Example 1, except that the amount of thioglycerin used was changed from 2.3 parts by weight to 4.9 parts by weight. So 3. OX 10'' and the content of phosphate groups is 0.
6 mmol/g of acrylic resin was obtained.

Next, in the synthesis of the comb-shaped acrylic resin in Example 1, the same amount of the acrylic resin obtained in Example 3 was used in place of the acrylic resin obtained in Example 1, and 1.4-
The procedure was the same as in Example 1 except that the amount of butanediol used was changed from 6.7 parts by weight to 4.5 parts by weight, and the content of acrylic resin was 49% by weight, and the number average molecular weight was calculated as polystyrene by GPC measurement. A 3.5×10′ comb-shaped acrylic resin was obtained.

A magnetic tape was produced in the same manner as in Example 1, except that the same amount of the comb-shaped acrylic resin thus obtained was used in place of the comb-shaped acrylic resin used in the composition of the magnetic paint in Example 1.

Example 4 In the synthesis of acrylic resin in Example 1, instead of 2-methacryloxyethyl acid phosphate,
An acrylic resin with a molecular weight of 5.8 x 10'' and an amino group content of 0.5 mmol/g was obtained by vapor pressure osmosis in the same manner as in Example 1, except that 19 parts by weight of diethylaminoethyl methacrylate was used. Ta.

Next, in the synthesis of the comb-shaped acrylic resin in Example 1, the same procedure as in Example 1 was carried out except that the same amount of the acrylic resin obtained in Example 4 was used instead of the acrylic resin obtained in Example 1. A comb-shaped acrylic resin having an acrylic resin content of 49% by weight and a number average molecular weight of 3.2×104 in terms of polystyrene measured by GPC was obtained.

A magnetic tape was produced in the same manner as in Example 1, except that the same amount of the comb-shaped acrylic resin thus obtained was used in place of the comb-shaped acrylic resin used in the composition of the magnetic paint in Example 1.

Example 5 In the synthesis of acrylic resin in Example 1, instead of 2-methacryloxyethyl acid phosphate,
The same procedure as in Example 1 was carried out, except that 19 parts by weight of methacryloxyethyl sulfonic acid was used, and a 7. Acrylic resin was obtained.

Next, in the synthesis of the comb-shaped acrylic resin in Example 1, the same amount of the acrylic resin obtained in Example 5 was used in place of the acrylic resin obtained in Example 1, and 1.4-
The procedure was the same as in Example 1 except that 5.2 parts by weight of tolylene diamine was used instead of butanediol, the content of the acrylic resin was 49% by weight, and the number average molecular weight was 2.5% by weight in terms of polystyrene by GPC measurement. A 9×10′ comb-shaped acrylic resin was obtained.

A magnetic tape was produced in the same manner as in Example 1, except that the same amount of the comb-shaped acrylic resin thus obtained was used in place of the comb-shaped acrylic resin used in the composition of the magnetic paint in Example 1.

Comparative Example 1 In the synthesis of comb-shaped acrylic resin in Example 1,
A polyurethane having a number average molecular weight of 3.0 x 10' in terms of polystyrene by GPC measurement was prepared in the same manner as in Example 1 except that 1.9 parts by weight of tolylene diamine was used instead of the acrylic resin obtained in Example 1. A urea resin was obtained.

A magnetic tape was produced in the same manner as in Example 1, except that the polyurethane urea resin thus obtained was used in the same amount in place of the comb-shaped acrylic resin used in the composition of the magnetic paint in Example 1.

Regarding the magnetic tapes obtained in each example and comparative example,
Chroma S/N ratio, C/N ratio and RF specific output were measured by the following methods.

<Chroma S/N ratio> Using a VH3 system VTR, a 3.58 MHz chroma signal was applied to each obtained magnetic tape at 0.714 V p-p.
The signal was recorded on a brightness modulated signal, and the noise portion of the reproduced signal was measured using a chroma noise measuring device 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).

<C/N ratio> Using a VH3 system VTR, the obtained magnetic tape was
5± when recording a MHz signal and reproducing this signal.
Measure the noise generated within the IMHz range, and calculate the ratio of the reproduced signal to this noise using the NV-8 manufactured by Matsushita Electric Industrial Co., Ltd.
Measurements were made using a 70HD output level measuring device. In addition,
The C/N ratio is expressed as a relative value with the magnetic tape of Comparative Example 1 as a reference (OdB).

<RF specific output Using a VTR for measuring RF output, the obtained magnetic tape was
After recording a MHz signal at a certain level, the output when played back was measured, and the magnetic tape of the comparative example was used as a reference (OdB).
) is expressed as a relative value.

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 N to 5 had a higher chroma S/N than the magnetic tape obtained in Comparative Example 1. These results show that the magnetic recording medium obtained by the present invention has good dispersibility of magnetic powder and further improved electromagnetic conversion characteristics.

Patent applicant: Hitachi Maxell, Ltd.

Claims (1)

[Claims] 1. A magnetic layer containing, as a binder component, a comb-shaped polar group-containing acrylic resin in which a polar group-containing acrylic resin is bonded by either or both of a urethane bond and a urea bond. Magnetic recording medium 2, the comb-shaped polar group-containing acrylic resin contains a polar group selected from a carboxyl group, a sulfonic acid group, a phosphoric acid group, a tertiary amino group or a salt thereof, and a hydroxyl group. The magnetic recording medium 3 according to claim 1, which is a resin, wherein the polar group-containing acrylic resin has a number average molecular weight of 500 to 500.
50,000, the magnetic recording medium 4 according to claim 1, wherein the comb-shaped polar group-containing acrylic resin has a number average molecular weight of 5.
3. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is an acrylic resin containing a comb-shaped polar group of 000 to 100,000.