JPH0432016A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve thermal stability and reliability by using an acryl/urethane graft copolymer, acryl/urea graft copolymer or acryl/urethane/urea graft copolymer formed by bonding an acrylic resin by either or both of an urethane bond and urea bond as a binder component. CONSTITUTION:The acryl/urethane graft copolymer, acryl/urea graft copolymer or acryl/urethane/urea graft copolymer formed by bonding the acrylic resin by either or both of the urethane bond and urea bond is used as the binder component. The thermal stability is, therefore, improved by the acrylic resin component having the excellent stability particularly to heat, light, chemicals, etc., and since the intramolecular flocculating force is simultaneously insufficient in the acrylic resin alone, the mechanical characteristics insufficient as the binder resin are made up by the urethane resin component. The thermal stability and reliability are improved in this way.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a magnetic recording medium, and more specifically, to a magnetic recording medium that does not emit corrosive gas, has good thermal stability, and has excellent reliability. Regarding the medium.

[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, vinyl chloride resins, cellulose resins, and the like have been widely used as binder components with excellent properties.

[Problem to be solved by the invention]

However, although these vinyl chloride resins and cellulose resins have excellent dispersibility of magnetic powder and excellent durability, they have poor thermal stability and decompose when exposed to energy such as light and heat, producing HCI, HNO, There is a problem that HC
When I or HNO3 is produced, the vinyl chloride resin or cellulose resin changes in quality, deteriorating the mechanical properties, decreasing durability, or causing dropout. In addition, HCf2 and H
NO3 and the like cause oxidation and denaturation of the magnetic powder particles in the magnetic layer, reducing the amount of saturation magnetization and further corroding the recording/reproducing head.

[Means to solve the problem]

The present invention was made as a result of various studies in view of the current situation, and is based on an acrylic-urethane graft copolymer or an acrylic-urea graft copolymer in which an acrylic resin is bonded with either or both of a urethane bond and a urea bond. By using a polymer or an acrylic-urethane-urea graft copolymer as a binder component, corrosive gases such as HCf and HNO3 generated from the binder resin are eliminated, and thermal stability is sufficiently improved. Suppresses the decrease in saturation magnetization and deterioration of mechanical properties,
This further improves reliability.

In this invention, the acrylic-urethane graft copolymer, the acrylic-urea graft copolymer, and the acrylic-urethane-urea graft copolymer used as the binder component have either a tan bond or a urea bond in the acrylic resin. Or, by graft copolymerizing acrylic resin, which cannot be used together due to their inherent lack of compatibility, and urethane resin or urea resin, these two resin components can be graft copolymerized by bonding them together. This is a binder resin that has both properties, and is designed to bring out the characteristics of each. However,
In particular, the acrylic resin component has excellent thermal stability against heat, light, chemicals, etc., improving thermal stability, and at the same time, acrylic resin alone has insufficient mechanical properties as a binder resin due to lack of intramolecular cohesive force. is supplemented by the urethane resin component.

Therefore, in a magnetic recording medium obtained by using these graft copolymers as a binder resin, these graft copolymers do not decompose even when energy such as light or heat is applied, and they do not contain HCf2 or HN03. It does not generate corrosive gases such as Further, as a result, these graft copolymers are not altered in quality and mechanical properties are not deteriorated, and the magnetic powder particles in the magnetic layer are not adversely affected and the saturation magnetization amount is not reduced. Furthermore, the recording/reproducing head will not be corroded.

Acrylic-urethane graft copolymers, acrylic-urea graft copolymers, and acrylic urethane-urea graft copolymers in which such acrylic resins are bonded by either or both of urethane bonds and urea bonds can be produced by any method. Although manufactured products can also be used, for example, (a) one-end diol acrylic resin (b) organic diisocyanate (C) chain extender (d) polyols having hydroxyl groups at both ends such as polyester and polyether, at least ( Those obtained by reacting a) and (b) and 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) One-end diol The acrylic resin may be produced by any method, for example, one produced by a typical production method such as radical polymerization of an acrylic monomer together with a chain transfer agent.

At this time, a polar group-containing acrylic monomer may be added to the acrylic monomer so that a polar group is introduced into the resulting acrylic resin, and adding a polar group-containing acrylic monomer can easily introduce a polar group. I can do it.

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. Further, as the polar group-containing acrylic monomer added to the acrylic monomer, acrylic acid, methacrylic acid, dimethylaminoethyl methacrylate, 2-acrylamido-2-methyl-1-propanesulfonic acid, methacryloxyethylsulfonic acid, and 2- Examples include methacryloxyethyl acid phosphate, etc., and further, copolymerizing monomers with reactive functional groups such as glycidyl methacrylate, and reacting these reactive functional groups with other compounds to introduce new polar groups. is also 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) As a chain extender, 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) Polyols include polycarbonate diols such as poly 1,6-hexane carbonate diol, polyolefin diols such as polybutadiene diol and hydrogenated butadiene diol, 1°6-hexamethylene lactone diol, and poly ε-caprolactone. Polycaprolactone diol such as diol, polyether diol such as polyethylene glycol, polypropylene glycol,
Polyester diols such as polyphthylene adibate and polybutylene phthalate are preferably used.

The acrylic-urethane graft copolymer, acrylic-urea graft copolymer, and acrylic-urethane-urea graft copolymer obtained by reacting each of these components have an acrylic resin component content of less than 10% by weight. If the amount exceeds 90% by weight, the resin becomes brittle and the durability decreases, so it is preferable to keep the content of the acrylic resin component within the range of 10 to 90% by weight. More preferably, the content is within the range of 70% by weight. In addition, if the number average molecular weight is less than 3000, the mechanical properties will deteriorate, and if it is larger than 100000, the viscosity will be high when dissolved in an organic solvent etc., making it difficult to make magnetic paint.
00 is preferably used, and the number average molecular weight is 1000.
Those with a molecular weight of 0 to 50,000 are more preferably used.

Furthermore, when introducing a polar group into an acrylic-urethane graft copolymer, an acrylic-urea graft copolymer, and an acrylic-urethane-urea graft copolymer,
Preferred polar groups to be introduced include carboxyl groups, sulfonic acid groups, phosphoric acid groups, tertiary amino groups or salts thereof, and hydroxyl groups, and these polar groups are not included in the main chain. You can leave it there. The amount introduced is 0.0
If it is less than 0.05 mmol/g, the dispersibility of the magnetic powder cannot be sufficiently improved, and if it is more than 5 mmol/g, the viscosity when dissolved in an organic solvent etc. increases due to the aggregation of polar groups, and the magnetic powder becomes 0.0 because it becomes difficult to make into paint.
It is preferably within the range of 0.005 to 5 mmol/g,
More preferably, it is within the range of 0.05 to 1 mmol/g.

Such acrylic-urethane graft copolymers, acrylic-urea graft copolymers, and acrylic-urethane-urea graft copolymers may be used in combination with other binder resins, such as polyurethane resins, vinyl chloride resins, etc. It is compatible with commonly used binder resins such as resins, cellulose resins, polyvinyl butyral resins, polyester resins, polyacrylic resins, epoxy resins, phenolic resins, and polyisocyanates. In addition, in order to suppress the generation of HCl and HNO3 as much as possible,
It is preferable to avoid co-use with vinyl chloride resins and cellulose resins as much as possible.

A binder component using such an acrylic-urethane graft copolymer, an acrylic-urea graft copolymer, an acrylic-urethane-urea graft copolymer, or the like can sufficiently improve the dispersibility of the magnetic powder. It is preferably used within the range of 5 to 35% by weight, more preferably within the range of 15 to 30% by weight.

The magnetic recording medium of the present invention may be manufactured according to conventional methods. , magnetic powder, with or without other binder resins,
A magnetic paint may be prepared by mixing and dispersing the magnetic paint with an organic solvent and other additives, and this magnetic paint may be applied onto a substrate such as a polyester film by any method 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, the acrylic-urethane graft copolymer, acrylic-urea graft copolymer, and acrylic-urethane-urea graft copolymer are preferably used as binder resins for the back coat layer. be done.

Here, the magnetic powder used is, for example, 7
Fe2O3 powder, Fez-04 powder, T-FezO:
Iron oxide powder in intermediate oxidation state between + and Fe30m, Co-containing 7-Fe, O, powder, Co-containing Fe3eg powder, Cr
In addition to C, powder, Fe powder, Co powder, Fe-Ni-Cr
A wide variety of conventionally known magnetic powders are included, such as metal powders such as alloy powders, barium ferrite powders, and nitride-based magnetic powders such as iron nitride. In the case of acicular magnetic powder, the average particle diameter (long axis) of these magnetic powders is usually 0.
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 plate-shaped magnetic powder, the average major axis diameter is about 2 to 1.0 μm. Usually 0.07
It is desirable that the thickness is about 0.3 μm.

In addition, organic solvents used in magnetic recording media such as methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dioxane, and dimethyl formamide can be used alone or in combination of two or more. Ru.

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 100 parts by weight α α'
-Azobisisobutyro 1.7〃Nitrilethioglycerin 2.3N Tetrahydrofuran 1OO〃This composition was placed in a flask equipped with a condenser, and after being sufficiently purged with nitrogen, it was heated at 60°C with stirring for 2 hours. Allowed time to react.

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 x 10' as determined by the smoke pressure osmosis method.

Next, using the acrylic resin obtained in this way, acrylic resin 180 parts by weight polyolefin polyol 80 (number average molecular weight 2000
, hydroxyl value 1000) 4.4'-diphenylmethane 18 Socyanate 1.4-butanediol 9 Tin octylate 0.03 Tetrahydrofuran 200 Toluene
200〃 composition at 70°C under nitrogen atmosphere for 10
After the reaction, the mixture was diluted to 20% by weight with tetrahydrofuran to obtain an acrylic-urethane graft copolymer.

The acrylic-urethane graft copolymer thus obtained had an acrylic resin component content of 64% by weight,
The number average molecular weight is 2 in terms of polystyrene by GPC measurement.
．． It was 8x10'.

Using the acrylic-urethane graft copolymer thus obtained, α-Fe powder 100 parts by weight Acrylic-urethane graft 25 Copolymer carbon black 10 Alumina
5 Hydrogenated butadiene (number average molecule 15, amount 4
200〃 composition was mixed and dispersed for 2 hours using a high-speed disper, and further mixed and dispersed for 6 hours using a sand grinder mill, and then 10 parts by weight of a trifunctional low molecular weight incyanate compound (manufactured by Nippon Polyurethane Co., Ltd., Coronat) was mixed and dispersed for 2 hours. The mixture was added and further mixed and dispersed for 30 minutes using a sand grinder mill. After that, add a predetermined amount of tetrahydrofuran/toluene mixed solvent to make the solid concentration 2.
A magnetic paint was prepared by adjusting the amount to 0%. This magnetic paint
A magnetic layer was formed by coating and drying on a polyester film with a thickness of 7.5 μm so that the thickness after drying was 3.0 μm, and after calendering, the magnetic tape was cut into 5IXIII1 widths. .

Example 2 In the synthesis of the acrylic resin in Example 1, the amount of methyl methacrylate used was changed from 100 parts by weight to 90 parts by weight, and 10 parts by weight of 2-methacryloxyethyl acid phosphate was newly added. In the same manner as in 1, the molecular weight is 4.5 x 10' by vapor pressure osmosis,
An acrylic resin having a phosphoric acid group content of 0.5 mmol/g was obtained.

Next, in the synthesis of the acrylic-urethane graft copolymer in Example 1, the acrylic resin obtained in Example 2 was replaced with 13
Using 5 parts by weight, instead of polyolefin polyol,
Using 100 parts by weight of poly 1,6-hexane carbonate diol (number average molecular weight 1000), using 24 parts by weight of toluene diisocyanate in place of 4,4'-diphenylmethane diisocyanate, and using the amount of 1,4-butanediol. The procedure was the same as in Example 1 except that the content of the acrylic resin component was changed from 9 parts by weight to 6.3 parts by weight. An acrylic-urethane graft copolymer was obtained.

The acrylic-urethane graft copolymer thus obtained was used in place of the acrylic-urethane graft copolymer used in the composition of the magnetic paint in Example 1.
Using 0 parts by weight, hydrogenated butadiene and Garfac R
A magnetic tape was produced in the same manner as in Example 1 except that 3-610 was omitted.

Example 3 In the synthesis of acrylic resin in Example 2, instead of 2-methacryloxyethyl acid phosphate,
The same procedure as in Example 2 was carried out except that the same amount of acrylic acid was used and the amount of thioglycerin used was changed from 2.3 parts by weight to 1.2 parts by weight.
0', carboxyl group content is 0.2 mmol/g
of acrylic resin was obtained.

Next, in the synthesis of the acrylic-urethane graft copolymer in Example 1, the acrylic resin obtained in Example 3 was replaced with 15% of the acrylic resin obtained in Example 1.
0 parts by weight was used in place of the polyolefin polyol,
90 parts by weight of polytetramethylene ether glycol (number average molecular weight 2000) was used, and the amount of 4,4'-diphenylmethane diisocyanate was varied from 18 parts by weight to 50 parts by weight.
Change the amount of 1,4-butanediol to 9 parts by weight.
The content of the acrylic resin component was 51% by weight in the same manner as in Example 1, except that parts by weight were changed to 2 parts by weight, and the number average molecular weight was 4.5% in terms of polystyrene by GPC measurement.
A 0x10' acrylic-urethane graft copolymer was obtained.

The acrylic-urethane graft copolymer thus obtained was used in place of the acrylic-urethane graft copolymer used in the composition of the magnetic paint in Example 1.
Using 0 parts by weight, hydrogenated butadiene and Garfac R
A magnetic tape was produced in the same manner as in Example 1, except that 3-610 was omitted and 0.1 part by weight of tetraglycidylaminoethylphenylene, an epoxy crosslinking agent, was newly added.

Comparative Example 1 In the composition of the magnetic paint in Example 1, 25% of MR-110 (manufactured by Nippon Zeon Co., Ltd., vinyl chloride-acrylic resin copolymer) was used instead of the acrylic-urethane graft copolymer used in Example 1. N-2304 (manufactured by Nippon Polyurethane Industries, Ltd.) was used in place of hydrogenated butadiene.
A magnetic tape was produced in the same manner as in Example 1, except that 15 parts by weight of polyester polyurethane) was used and hydrogenated butadiene and Garfunk R3-610 were omitted.

Comparative Example 2 In the composition of the magnetic paint in Example 1, in place of the acrylic-urethane graft copolymer used in Example 1, 1 part by weight of 1/2 nitrocellulose (manufactured by Daicel Corporation, nitrocellulose) was used. , Garfunk R3-61
A magnetic tape was produced in the same manner as in Example 1 except that 0 was omitted.

Comparative Example 3 In the composition of the magnetic paint in Example 1, 25 parts by weight of polymethyl methacrylate (manufactured by Mitsubishi Rayon Co., Ltd., Acrypet VH) was used in place of the acrylic-urethane graft copolymer used in Example 1. However, the magnetic powder in the magnetic paint separated, making it impossible to coat it onto a polyester film, making it impossible to manufacture a magnetic tape.

Regarding the magnetic tapes obtained in each example and comparative example,
The thermal stability was tested and the saturation magnetization was measured. In the thermal stability test, each of the obtained magnetic tapes was cut into 5 m length samples, and these were stored for 3 weeks under the conditions of (1) 60°C, 990% RH, and (2) 5°C Cl2O%RH. Storage under the conditions of 1 and 45°C 280%RH
Repeat every hour and store for 3 weeks. was irradiated for 30 minutes to extract ions from the magnetic tape. Then, the ions of the extract were collected using an ion chromatograph model 20201 (column AS-
4A type). The saturation magnetization amount was measured when the sample was stored under the same conditions as those for the thermal stability described above.

Table 1 below shows the results.

〔Effect of the invention〕

As is clear from Table 1 above, the magnetic tape obtained in Comparative Example 1 decomposes under high temperature and high humidity and generates a large amount of CI-, and the magnetic tape obtained in Comparative Example 2 It decomposes under high humidity and generates large amounts of NO2 and NO4-, but
The magnetic tapes obtained in Examples T to 3 had extremely low generation of these ions, and compared to the magnetic tapes obtained in Comparative Example 1, All of them had a large amount of saturation magnetization, which indicates that the magnetic recording medium obtained by the present invention has further improved thermal stability and excellent reliability.

Patent applicant: Hitachi Maxell, Ltd. IS-4

Claims (1)

[Claims] 1. As a binder component, an acrylic-urethane graft copolymer, an acrylic-urea graft copolymer, or an acrylic-urethane in which an acrylic resin is bonded by either or both of a urethane bond and a urea bond. -Magnetic recording medium 2 having a magnetic layer containing a urea graft copolymer, an acrylic-urethane graft copolymer, an acrylic-
An acrylic-urethane graft copolymer, an acrylic-urea graft copolymer, and an acrylic-urethane-urea graft copolymer, each of which contains an acrylic resin component of 10% by weight or more. The magnetic recording medium 3 according to claim 1, which is a graft copolymer, an acrylic-urethane graft copolymer, an acrylic-
Both the urea graft copolymer and the acrylic-urethane-urea graft copolymer have a number average molecular weight of 300.
0 to 100,000, the magnetic recording medium is an acrylic-urethane graft copolymer, an acrylic-urea graft copolymer, or an acrylic-urethane-urea graft copolymer.