JPH04159611A - Magnetic recoridng medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility and durability by using both comb-shaped resin, which includes acrylic resin with urethane-linkages and containing a polar group, and acrylic resin having carboxylic acid at one end and an active hydrogen group in a molecular chain. CONSTITUTION:A comb-shaped acrylic resin is obtained from an acrylic resin with urethaneor urea-linkages and containing a polar group. In this resin, the acrylic chain containing the polar group has the comb-shape. Therefore, the freedom in the vicinity of the polar group is high. The affinity for polar powder is improved, and excellent adsorption is achieved. The acrylic chain has one or more carboxylic acids at one end. The compatibility with the acrylic resin having an active hydrogen group within a molecular chain is excellent. When the material is used as a bonding agent, the carboxyl group at the end of the molecule is adsorbed with the surface of the magnetic power, and the steric repulsioon effect of the acrylic resin is generated. Thus, the dispersibility of the magnetic powder is improved, and the durability is also 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 electrical properties and durability.

[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 resin has traditionally been widely used as a binder component with excellent properties, but conventional polyurethane resins have a low ability to disperse magnetic powder, so it is difficult to disperse magnetic powder well. I can't do it, and
Although polyurethane resin has relatively excellent mechanical properties,
The improvement in durability is still not completely satisfactory.

Therefore, binder 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 the polyurethane resin. The dispersibility of magnetic powders has been improved by using powders into which groups have been introduced (Japanese Unexamined Patent Publications No. 55-38693, No. 57).
~92422, JP-A-59-30235), and
It is widely practiced to improve durability by using polyisocyanate as a crosslinking agent together with polyurethane resin.

[Problem to be solved by the invention]

However, even if binder resins having polar groups such as hydroxyl groups are used together with polyurethane resins, or polyurethane resins with various polar groups introduced into the main chain of polyurethane resins are used, recent advances in densification, The dispersibility of magnetic powder is still insufficient to meet the requirement for high magnetization, and the electrical properties cannot be sufficiently improved.

In addition, polyurethane resin cannot introduce a large amount of active hydrogen groups into its molecules, so the polyisocyanate used in combination with polyurethane resin reacts faster with moisture in the air than with the polyurethane resin. As a result, the crosslinking reaction of the polyurethane resin is no longer sufficient, and durability cannot 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 includes a comb-shaped polar group-containing acrylic resin that is bonded with a polar group-containing acrylic resin as a binder component by either or both of a urethane bond and a urea bond. By using an acrylic resin together with an acrylic resin that has at least one carboxylic acid at one end and an active hydrogen group in its molecular chain, the dispersibility of the magnetic powder can be sufficiently improved and the electrical properties can be improved. This is a further improvement. In addition, when used in combination with polyisocyanate, the active hydrogen groups within the molecular chain fully react with the polyisocyanate, further improving durability and meeting the recent demands for higher density and higher reliability. It is.

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 comb-shaped polar group-containing acrylic chains. As a result, compared to polyurethane resins in which the polar groups are in the main chain, the degree of freedom near the polar groups is higher, and the affinity with the magnetic powder is further improved, resulting in extremely good adsorption to the surface of the magnetic powder. In addition, it is used in combination with an acrylic resin that has one or more carboxylic acids at one end and an active hydrogen group in the molecular chain, and the acrylic resin used in combination has a carboxylic acid only at one end. Therefore, the carboxyl group at the end of the molecule is adsorbed to the surface of the magnetic powder, creating a steric repulsion effect of the adsorbed acrylic resin. Therefore, the dispersibility of the magnetic powder is significantly improved, and the viscosity does not increase after the magnetic powder is dispersed.

Furthermore, since this type of acrylic resin has active hydrogen groups in its molecules, it reacts sufficiently with polyisocyanate, forming a magnetic layer having a strong three-dimensional mesh structure.

Therefore, a polar group-containing acrylic resin was bonded with either or both of a urethane bond and a urea bond. When an acrylic resin having active hydrogen groups is used in combination as a binder component, the dispersibility of the magnetic powder is sufficiently improved, the electrical properties are further improved, and the durability is further 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 (d) At least (a) and (b) of polyols having hydroxyl groups at both ends such as polyester, polyether, polycarbonate, etc. are reacted. , and those obtained by further reacting (c) and (d) as necessary 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, an acrylic monomer containing a polar group is added together with 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, stearyl methacrylate, and acrylic ester, which may be used alone or in combination.
Used in combination with more than one species. In addition, as polar group-containing acrylic monomers, acrylic acid, methacrylic acid, dimethylaminoethyl methacrylate, 2-acrylamide-
2-methyl-1-propanesulfonic acid and 2-methacryloxyethyl acindophosphate, etc.
Furthermore, it is also possible to copolymerize monomers having reactive functional groups such as glycidyl methacrylate, and to react these reactive functional groups with other compounds to introduce new polar groups. Furthermore, styrene derivatives and the like other than acrylic monomers can be added as monomers to be copolymerized. As the initiator, an azo compound such as α,α-azobisisobutyronitrile or a peroxide such as benzoyl peroxide is used, and as a chain transfer agent, thioglycerin or the like is used.

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

(C) As a chain extender, ethylene glycol, 1,3
- Diols such as propanediol, 1,4-butanediol, neopentyl glycol, diamines such as ethylene diamine and tolylene diamine, those without polar groups such as water, 2,2-dimethylolpropionic acid, bis(hydroxybutyl )-5-sodium sulfoisofucrate,
Examples include those having polar groups such as sodium β-glycerophosphate, N-methyljetanolamine, and potassium 2,3-dihydroxy-neepropanesulfonate.

(d) Polyols include polyether diols such as polypropylene glycol and polytetramethylene glycol, polyester diols such as polybutylene adipate and polybutylene phthalate, polylactone diols such as polyε-caprolactone, poly 1,6-hexane carbonate, etc. Polycarbonate diols and the like are preferably used.

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 70% by weight, the properties of acrylic resin cannot be expressed, and if it is more than 70% by weight, the resin becomes brittle. Therefore, it is preferable to keep the content of acrylic resin within the range of 10 to 70% by weight, and 20 to 50% by weight. It is more preferable to keep it within this range. Also, if the number average molecular weight is less than 5,000, the mechanical properties will deteriorate, and if it is larger than 100,000, the viscosity will be high when dissolved in an organic solvent etc., making it difficult to make magnetic paint. It is preferably used, and those having a number average molecular weight of 10,000 to 50,000 are more preferably used. In addition, if the number average molecular weight of the polar group-containing acrylic resin before being bonded into a comb shape by urethane bonds or urea bonds is smaller than 1,000, it will not be able to exhibit the properties of acrylic resin, and if it is larger than 20,000, the degree of freedom of the acrylic resin will decrease. The dispersibility of the magnetic powder when made into a magnetic paint is therefore preferably used, and those with a number average molecular weight of 1,000 to 20,000 are preferably used, and those with a number average molecular weight of 1,000 to 5,000 are more preferably used. Suitable polar groups to be introduced into the polar group-containing acrylic resin include carboxyl groups, sulfonic acid groups, phosphoric acid groups, tertiary amino groups or salts thereof, and betaine. may be included in the main chain. The amount introduced is 0
．． If it is less than 1 mmol/g, the dispersibility of the magnetic powder cannot be sufficiently improved, and if it is more than 1 mmol/g, the viscosity when dissolved in an organic solvent etc. increases due to agglomeration of polar groups, and the magnetic powder becomes Because it becomes difficult to make into paint,
It is preferably within the range of 0.01 to 1 mmol/g, and more preferably within the range of 0.03 to 0.5 mmol/g.

In addition, such a polar group-containing acrylic resin is used in combination with a comb-shaped polar group-containing acrylic resin bonded by either or both of urethane bonds and urea bonds, and has one or more carboxylic acids at one end, and Acrylic resins having active hydrogen groups in their molecular chains can be produced using any method other than the carboxyl group-containing monomer, such as radical polymerization of a monomer other than the carboxyl group-containing monomer together with a chain transfer agent. Those manufactured by a typical manufacturing method are used.

Here, monomers other than the carboxyl group-containing monomer are classified into neutral monomers and monomers having active hydrogen groups, and both are preferably used. Examples of neutral additives include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, lauryl methacrylate, stearyl methacrylate, and acrylic ester, which may be used alone or in combination of two or more. Examples of monomers having active hydrogen groups include 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, methacrylamide, and acrylamide, which can be used alone or in combination of two or more. It will be done. Furthermore, styrene derivatives and the like other than acrylic monomers can be added as monomers to be copolymerized. As the initiator, an azo compound such as α,α-azobisisobutyronitrile or a peroxide such as benzoyl peroxide is used, and as a chain transfer agent, a compound containing a carboxyl group, such as mercaptoacetic acid. , 2-mercaptopropionic acid, 3-mercaptopropionic acid, 0
-mercaptobenzoic acid, thiomalic acid, etc.

In addition, carboxyl group-containing starting side, for example, 4.4
- Even if monomers other than carboxyl group-containing monomers are polymerized using azobis (4-cyanopentanoic acid), diglutaric peroxide, etc., the molecule has one or more carboxylic acids at one end and Acrylic resins having active hydrogen groups in their chains can be produced, and acrylic resins produced in this way that have one or more carboxylic acids at one end and have active hydrogen groups in their molecular chains are also suitable. used for.

Acrylic resins that have one or more carboxylic acids at one end and active hydrogen groups in their molecular chains cannot exhibit the properties of acrylic resins if their number average molecular weight is smaller than 1,000, and if it is larger than 20,000. If this happens, the degree of freedom of the acrylic resin will decrease, and the dispersibility of the magnetic powder will decrease when it is made into a magnetic coating.
0 is preferably used, and the number average molecular weight is 2000 to 1.
oooo is more preferably used.

In addition, the number of carboxylic acids at one end of this acrylic resin is preferably within the range of 1 to 2, and the amount of active hydrogen groups contained in the molecular chain is 0.2 mmol/g.
If it is less than 5 mmol/g, it will not be able to sufficiently react with the polyisocyanate to form a magnetic layer with a strong three-dimensional mesh structure, and if it is more than 5 mmol/g, when dissolved in an organic solvent generally used for magnetic paints. Since the viscosity of the compound becomes high and it becomes difficult to make it into a magnetic paint, it is preferably used within the range of 0.2 to 5 mmol/g, and more preferably within the range of 0.5 to 2 mmol/g. used.

Such an acrylic resin having one or more carboxylic acids at one end and an active hydrogen group in the molecular chain is combined with the above polar group-containing acrylic resin by bonding with either or both of a urethane bond and a urea bond. When used in combination with a bonded comb-shaped polar group-containing acrylic resin, the blending ratio is such that the comb-shaped polar group-containing acrylic resin has at least one carboxylic acid at one end, and has an active hydrogen group in its molecular chain. If the amount of the acrylic resin is less than 5% by weight, the dispersibility of the magnetic powder cannot be sufficiently improved, and if it is more than 50% by weight, the durability of the magnetic layer will be poor.
It is preferable that the amount of the acrylic resin having one or more carboxylic acids at one end and an active hydrogen group in the molecular chain is in the range of 5 to 50% by weight based on the comb-shaped polar group-containing acrylic resin. , 10-30! It is more preferable to keep the amount within the range of %. In addition, in order to sufficiently improve the dispersibility of the magnetic powder when blending in such a ratio, the total amount of both should be within the range of 10 to 35% based on the magnetic powder. It is preferably in the range of 15 to 30% by weight.

Such an acrylic resin having one or more carboxylic acids at one end and an active hydrogen group in the molecular chain, and the above-mentioned polar group-containing acrylic resin are bonded by either or both of a urethane bond and a urea bond. The bonded comb-shaped polar group-containing acrylic resin may be used in combination with other binder resins, such as polyurethane resins, vinyl chloride-vinyl acetate copolymers, cellulose resins, polyvinyl butyral resins, and polyesters. It is compatible with and used in combination with commonly used binder resins such as polyacrylic resins, polyacrylic resins, epoxy resins, phenolic resins, and polyisocyanates.

The magnetic recording medium of the present invention may be manufactured according to a conventional method. For example, the polar group-containing acrylic resin described above may be bonded with either or both of a urethane bond and a urea bond. Containing acrylic resin,
An acrylic resin having one or more carboxylic acids at one end and an active hydrogen group in its molecular chain, with or without other binder resins, magnetic powder, organic solvents, and other additives. A magnetic paint is prepared by mixing and dispersing the magnetic paint, and the magnetic paint is applied onto a substrate such as a polyester film by any means such as spraying or roll coating, and then dried. At this time, 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 magnetic layers may be provided on both surfaces of the substrate. When providing a back coat layer in this way, 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, and a carboxylic acid at one end are combined. An acrylic resin having active hydrogen groups in its molecular chain is also suitably used as a binder resin for the bank coat layer.

Here, as the magnetic powder used, for example, 7-
Fe, 0. Powder, Fe=04 powder, T-FetO, and F
Iron oxide powder in intermediate oxidation state with e, O, Co-containing T
F'eZo:l powder, Co-containing Fe3O4 powder, Cry
In addition to powder, metal powder such as Fe powder, Co powder, Fe-Ni-Cr alloy powder, and barium ferrite powder,
Conventionally known am
A wide range of powders are included. In the case of acicular magnetic powder, the average particle diameter (long axis) of these magnetic powders is usually 0.2.
It is preferable that the average axis ratio (average major axis diameter/average minor axis diameter) is usually about 5 to 10, and in the case of a plate shape, the average major axis diameter is usually 0.07. ~0.3μm
It is preferable that the amount is within a certain range.

Further, as the organic solvent, those commonly used in magnetic recording media, such as methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, ethyl acetate, tetrahydrofuran, dioxane, and dimethyl formamide, are used alone or in a mixture of two or more.

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 72 parts by weight α, α-Abbisisobutyroni 1 Tolylthioglycerin 9 Tetrahydrofuran 100 This composition was placed in a flask equipped with a condenser, and after being sufficiently purged with nitrogen, the flask was stirred. The reaction was carried out at 60°C for 8 hours.

Next, the obtained reaction product was separated in a toluene-water system, and 6
It was dried under reduced pressure at 0°C for 48 hours to obtain one-end diol acrylic resin A.

One-end diol acrylic resin A obtained in this way
had a molecular weight of 1.5X IO2 by vapor pressure osmosis.

On the other hand, 66 parts by weight of methyl methacrylate α, α-azobisisobutyroni 1 Tolylthioglycerin 9 ” Acrylic acid
9 Tetrahydrofuran
100% of the composition was put into a flask equipped with a condenser, and after thoroughly purging with nitrogen, the composition was heated to 60% while stirring.
The reaction was allowed to proceed for 8 hours at °C.

Next, the obtained reaction product was separated in a toluene-water system, and 6
It was dried under reduced pressure at 0°C for 48 hours to obtain one-end diol acrylic resin B.

One-end diol acrylic resin B obtained in this way
has a molecular weight of 1.5×10″ by vapor pressure osmosis,
The content of carboxylic acid groups is 0. It was millimoles/g.

Next, using the thus obtained one-end diol acrylic resin A and one-end diol acrylic resin B, one-end diol acrylic resin A 30 parts by weight one-end diol acrylic resin B 30 neopentyl glycol 5 poly 1,6-hexane carbonate
90〃-Todiol (number average molecular weight 4.4-diphenylmethane 45〃Socyanate tin octylate 0.05〃Cyclohexanone 400〃Toluene
A comb-shaped carboxylic acid-containing acrylic resin was obtained by reacting the composition No. 100 at 80° C. in a nitrogen atmosphere for 10 hours.

The comb-shaped carboxylic acid-containing acrylic resin thus obtained has an acrylic resin content of 30% by weight, and a number average molecular weight of 2.0X in terms of polystyrene by GPC measurement.
It was 10'.

In addition, a cooler was attached to a composition of 50 parts by weight of methyl methacrylate, 8.4 parts by weight of 2-hydroxyethyl methacrylate, 0.8 parts by weight of α,α-azobisisobutyroni, 3.2 parts by weight of tolylmercaptopropionic acid, and 60 parts by weight of tetrahydrofuran. The mixture was placed in a flask, and after the atmosphere was sufficiently purged with nitrogen, the mixture was reacted at 60°C for 3 hours with stirring.

The resulting reaction product was then purified by reprecipitation in petroleum ether and water, dried under reduced pressure at 60°C for 48 hours,
A one-end carboxylic acid acrylic resin was obtained.

The single-end carboxylic acid acrylic resin thus obtained has a molecular weight of 3.0×103 as measured by vapor pressure osmosis method,
The content of hydroxyl groups was 1.3 mmol/g, and the content of carboxylic acid groups was 0.30 mmol/g.

Next, α-Fe magnetic powder (coercive force 1500, 300 parts by weight Oersted, saturated Magnetization 12
0 emu/g) Comb-shaped carboxylic acid-containing acrylic 55〃Resin end carboxylic acid acrylic resin 10〃Trifunctional low molecular weight isocyanate 10〃To compound (manufactured by Nippon Polyurethane Industries, Ltd.; Coronate L) Carbon black 10〃α-A1zC
h powder 3 Myristic acid
6 n-butyl stearate 8
〃Cyclohexanone 395〃Toluene
A magnetic coating material was prepared by mixing and dispersing the composition No. 395 in a ball mill for 72 hours. This magnetic paint was coated on a 20 μm polyester film to a dry thickness of 5 μm, dried to form a magnetic layer, calendered, and cut into 1×2 inch width to produce a magnetic tape.

Example 2 In the synthesis of the one-terminally carboxylic acid acrylic resin in Example 1, the molecular weight was changed in the same manner as in Example 1, except that the amount of mercaptopropionic acid used was changed from 3.2 parts by weight to 1.6 parts by weight. 6.0×10” by vapor pressure osmosis method,
A one-end carboxylic acid acrylic resin having a hydroxyl group content of 1.2 mmol/g and a carboxylic acid group content of 0.17 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 3 In the synthesis of the one-terminal carboxylic acid acrylic resin in Example 1, 2.3 parts by weight of thiomalic acid was used instead of mercaptopropionic acid, and 4.5 parts by weight of acrylamide was used instead of 2-hydroxyethyl methacrylate. The same procedure as in Example 1 was carried out except that the molecular weight was determined to be 3.5% by vapor pressure osmosis method. lX103, amide group content is 1.0
An acrylic resin with dicarboxylic acid at one end and having a carboxylic acid group content of 0.65 mmol/g was obtained.

Example 1 except that the single-end dicarboxylic acid acrylic resin thus obtained was used in the same amount in place of the single-terminal 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-terminal carboxylic acid acrylic resin in Example 1, the molecular weight was determined by the vapor pressure osmosis method in the same manner as in Example 1, except that 1.2 parts by weight of thiomalic acid was used instead of mercaptopropionic acid. 5.8×10′, one-end dicarboxylic acid acrylic resin with a hydroxyl group content of 1.1 mmol/g and a carboxylic acid group content of 0.32 mmol/g was obtained.

Example I, except that the same amount of the one-terminal dicarboxylic acid acrylic resin thus obtained was used in the composition of the magnetic paint in Example 1 in place of the one-terminal carboxylic acid acrylic resin used in Example 1. A magnetic tape was produced in the same manner as in Example 1.

Example 5 In the synthesis of single-terminated diol acrylic resin B in Example 1, the same procedure as in Example 1 was performed except that 3.1 parts by weight of 2-methacryloxyethyl acid phosphate was used instead of acrylic acid. By pressure osmosis method 1.
A single-terminated diol acrylic resin C having a size of 5×10” and a phosphoric acid group content of 0.65 mmol/g was obtained.

Next, in the synthesis of the comb-shaped carboxylic acid-containing acrylic resin in Example 1, an acrylic resin was prepared in the same manner as in Example 1, except that the same amount of one-end diol acrylic resin C was used in place of the one-end diol acrylic resin. A comb-shaped phosphoric acid-containing acrylic resin was obtained in which the content was 30% by weight and the number average molecular weight was 2.0×10′ in terms of polystyrene measured by GPC.

Example 1 Except that the thus obtained comb-shaped phosphoric acid-containing acrylic resin was used in the same amount in place of the comb-shaped carboxylic acid-containing 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 as in Example 1.

Example 6 In the composition of the magnetic paint in Example 5, the same amount of the one-end carboxylic acid acrylic resin used in Example 2 was used in place of the one-end carboxylic acid acrylic resin used in Example 5. A magnetic tape was produced in the same manner as in Example 5.

Example 7 In the composition of the magnetic paint in Example 5, the same amount of the one-end dicarboxylic acid acrylic resin used in Example 3 was used in place of the one-end carboxylic acid acrylic resin used in Example 5. A magnetic tape was produced in the same manner as in Example 5.

Example 8 In the composition of the magnetic paint in Example 5, the same amount of the one-end dicarboxylic acid acrylic resin used in Example 4 was used in place of the one-end carboxylic acid acrylic resin used in Example 5. A magnetic tape was produced in the same manner as in Example 5.

Example 9 In the synthesis of single-terminated diol acrylic resin B in Example 1, 2.6 parts by weight of 3-sulfopropyl methacrylate potassium salt was used in place of acrylic acid, and the amount of tetrahydrofuran was varied from 100 parts by weight to 50 parts by weight. In the same manner as in Example 1, except that 50 parts by weight of methanol was added, the molecular weight was determined to be 1.5X by vapor pressure osmosis.
103, the content of potassium sulfonate group is 0. A one-end diol acrylic resin having a loamyl mole/g was obtained.

Next, in the synthesis of the comb-shaped carboxylic acid-containing acrylic resin in Example 1, one-terminal diol acrylic resin B
The same procedure as in Example 1 was carried out except that the same amount of one-terminated diol acrylic resin was used instead, and the content of the acrylic resin was 30% by weight, and the number average molecular weight was 2, l x 10' in terms of polystyrene by GPC measurement. A comb-shaped potassium sulfonate group-containing acrylic resin was obtained.

The same amount of the comb-shaped potassium sulfonate group-containing acrylic resin obtained in Example 2 was used in place of the comb-shaped carboxylic acid-containing 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 as in Example 1.

Example 10 In the composition of the magnetic paint in Example 9, the same amount of the one-end carboxylic acid acrylic resin used in Example 2 was used in place of the one-end carboxylic acid acrylic resin used in Example 9. A magnetic tape was produced in the same manner as in Example 9.

Example 11 In the composition of the magnetic paint in Example 9, the same amount of the one-end dicarboxylic acid acrylic resin used in Example 3 was used in place of the one-end carboxylic acid acrylic resin used in Example 9. A magnetic tape was produced in the same manner as in Example 9.

Example 12 In the composition of the magnetic paint in Example 9, the same amount of the one-end dicarboxylic acid acrylic resin used in Example 4 was used in place of the one-end carboxylic acid acrylic resin used in Example 9. A magnetic tape was produced in the same manner as in Example 9. 'Example 13 Example 1 except that 4.1 parts by weight of dimethylaminoethyl methacrylate was used instead of acrylic acid in the synthesis of one-terminated diol acrylic resin B in Example 1.
Synthesis was carried out in the same manner as above, and then 1 equivalent of propane sultone was added to the amino group, and the reaction was carried out at 80°C for 5 hours. The resin was dried under reduced pressure for 48 hours to obtain one-end diol acrylic resin E.

One-end diol acrylic resin E obtained in this way
has a molecular weight of 1.5X 103 by vapor pressure osmosis, and a potassium sulfonate group content of 0. It was loamyl mole/g.

Next, in the synthesis of the comb-shaped carboxylic acid-containing acrylic resin in Example 1, the same amount of one-end diol acrylic resin E was used in place of the one-end diol acrylic resin E,
The same procedure was used as in Example 1, except that 3.6 parts by weight of tolylene diamine was used instead of 5 parts by weight of neopentyl glycol.The content of the acrylic resin was 30% by weight, and the number average molecular weight was calculated as polystyrene by GPC measurement. So 2. lX10
'<C type sulfobetaine-containing acrylic resin was obtained.

Example 1 Except that the comb-shaped sulfobetaine-containing acrylic resin thus obtained was used in the same amount in place of the comb-shaped carboxylic acid-containing 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 as in Example 1.

Example 14 In the composition of the magnetic paint in Example 13, Example 1
Instead of the one-end carboxylic acid acrylic resin used in 3,
A magnetic tape was produced in the same manner as in Example 13, except that the same amount of the one-end carboxylic acid acrylic resin used in Example 2 was used.

Example 15 In the composition of the magnetic paint in Example 13, Example 1
Instead of the one-end carboxylic acid acrylic resin used in 3,
A magnetic tape was produced in the same manner as in Example 13, except that the same amount of the one-end dicarboxylic acid acrylic resin used in Example 3 was used.

Example 16 In the composition of the magnetic paint in Example 13, Example 1
Instead of the one-end carboxylic acid acrylic resin used in 3,
A magnetic tape was produced in the same manner as in Example 13, except that the same amount of the one-end dicarboxylic acid acrylic resin used in Example 4 was used.

Comparative Example 1 In the synthesis of the comb-shaped carboxylic acid-containing acrylic resin in Example 1, 8.4 parts by weight of neopentyl glycol was used in place of the one-end diol acrylic resin A, and the one-end diol acrylic resin B was omitted. The procedure was repeated in the same manner as in Example 1 except that 1 part by weight of dimethylolpropionic acid was used instead of pentyl glycol.
A polyurethane resin of 2.2×10′ in terms of polystyrene was obtained by PC measurement.

The procedure was the same as in Example 1, except that the polyurethane resin thus obtained was used in the same amount as in the composition of the magnetic paint in place of the one-terminal carboxylic acid acrylic resin used in Example 1. A magnetic tape was made.

Regarding the magnetic tapes obtained in each example and comparative example,
The C/N ratio and RF output were measured by the following method, and the durability was tested by the following method.

<C/N ratio> When a 7MHz signal is recorded on each obtained magnetic tape using an 8mm VTR, and this signal is played back, the
Measure the noise generated within the range of ±IMHz, and calculate the ratio of the reproduced signal to this noise using the Sony 1ED-V90.
Measurements were made using a Model 0 output level measuring device. In addition, C/N
The ratio is expressed as a relative value using the magnetic tape of Comparative Example 1 as a reference (OdB).

<RF output> Using a VTR for RF output measurement, an IMHz signal was recorded at a constant level on each of the obtained magnetic tapes, and the output when played back was measured, and the magnetic tape of Comparative Example 1 was used as a reference (Oc
It is expressed as a relative value of 1B).

(Durability test) Durability was determined by testing each obtained magnetic tape at 20°C, 140% R.
Under the conditions of H and 40°C 160%RH, V
When playing in TR's still mode, the playback RF output level is
The time required for the output level to drop to 1/2 of the initial output level was measured.

Table 1 below shows the results.

Table 1 [Effects of the Invention] As is clear from Table 1 above, Examples 1 to 16
The magnetic tape obtained in Comparative Example 1 has a higher C/N ratio and RF output, and is more durable. Therefore, the magnetic recording medium obtained by the present invention has It can be seen that the magnetic powder has good dispersibility, excellent electromagnetic conversion characteristics, and excellent durability.

Patent applicant: Hitachi Maxell, Ltd.

Claims (1)

[Claims] 1. As a binder component, a comb-shaped polar-containing acrylic resin in which a polar-containing acrylic resin is bonded by either or both of a urethane bond and a urea bond, and one or more carboxylic acids at one end. and an acrylic resin having an active hydrogen group in its molecular chain. Claim 1: The acrylic resin is a comb-shaped polar group-containing acrylic resin containing a polar group selected from a tertiary amino group or a salt thereof, and betaine.
In the magnetic recording medium 3 described above, the comb-shaped polar group-containing acrylic resin has a number average molecular weight of 5.
000 to 100,000, the magnetic recording medium 4 according to claims 1 and 2, wherein the acrylic resin has one or more carboxylic acids at one end and an active hydrogen group in the molecular chain. , number average molecular weight 10
2. The magnetic recording medium according to claim 1, which is an acrylic resin having one or more carboxylic acids at one end of 00 to 20,000 and having an active hydrogen group in its molecular chain.