JPS6226628A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve wear resistance, durability and surface smoothness by selectively combining a specific binder, specific lubricating agent and specific crosslinking agent so that mechanical properties and coefft. of friction are maintained with less changes in a wide temp. range. CONSTITUTION:The magnetic coating compd. prepd. by mixing uniformly pulverous ferromagnetic particles in a liquid contg. a binder A consisting of a polyurethane resin having 10-100equiv./10<6>g metallic salt group of a sulfonic acid per polymer and nitrocellulose, a cyclic trimmer B of hexamethylene diisocyanate as the crosslinking agent and a single substance selected from butyl cellosolve palmitate and butyl cellosolve stearate or a mixture C composed thereof is coated on a nonmagnetic substrate to form the magnetic layer. The high packability of the magnetic particles is not obtainable if the metallic salt group of the sulfonic acid group is <10equiv./10<6>g. The solvent sollubility of the polyurethane resin is poor if said group exceeds 1,000equip./10<6>g.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention has excellent surface smoothness of the coating film (magnetic layer), and particularly improves the strength, elongation, elastic modulus, and compressibility of the magnetic layer over a wide temperature and humidity range. The present invention relates to a magnetic recording medium that exhibits extremely little change in mechanical properties such as friction coefficients, etc., and has excellent wear resistance and durability.

(Prior art) Conventionally, in order to improve the abrasion resistance and durability of magnetic recording media, thermosetting binders and various lubricants have been used to strengthen the coating film (magnetic layer) and make the surface slippery. A combination of these has been proposed.

For example, as a binder, polyurethane resin, epoxy! It is known to use resins, polyester resins, nitrocellulose, vinyl chloride-vinyl acetate copolymers, etc., and to crosslink them with polyfunctional incyanate compounds.

On the other hand, solid lubricants such as graphite and molybdenum disulfide and liquid lubricants such as silicone oil, fluorine oil, and higher fatty acids and their ester compounds are used as lubricants to reduce the coefficient of friction on the paint surface. Many proposals have been made for mixing and dispersing in the liquid preparation process, or, if necessary, adding externally by impregnation, spraying, coating, etc. after forming the magnetic layer.

(Problems to be Solved by the Invention) However, in the above-mentioned prior art, the surface of the magnetic layer, which is the object of the present invention, is smooth, has little change in mechanical properties and coefficient of friction over a wide temperature and humidity range, and It has been difficult to provide a magnetic recording medium having a magnetic layer with excellent wear resistance and durability. For example, when polyurethane resin or polyester resin is used as a binder, it is difficult to disperse magnetic powder such as ferromagnetic fine particles, so a dispersant such as a surfactant is required. When using nitrocellulose, vinyl chloride-vinyl acetate copolymer, etc., the coating film lacks flexibility and requires a plasticizer. Addition of these surfactants and plasticizers leads to a decrease in the adhesive strength between the magnetic layer and the non-magnetic base material.
Furthermore, when a magnetic recording medium in the form of a tape or disk is run or rotated for a long time, the coating film may peel off. In addition, polyfunctional incyanate is generally used as a crosslinking agent used to cure each resin used as a binder and improve the strength of the coating film. Group polyisocyanates, such as tolylene diisocyanate adducts of L()rimethylpropane (manufactured by Nippon Polyurethane Co., Ltd.) and Millionate MR (initial condensate of diphenylmethane diisonanate: manufactured by Nippon Polyurethane Co., Ltd.) are preferred. However, when using these materials, it is difficult to control the viscoelasticity of the magnetic coating film, and it is difficult to control the viscoelasticity of the magnetic coating film. However, it is not possible to obtain a magnetic recording medium having a magnetic layer with excellent wear resistance and durability.

Similarly to surfactants and plasticizers, if lubricants are selected too easily based on their compatibility with the binder, they may reduce the adhesion between the magnetic layer and the non-magnetic base material or cause problems at high temperatures. This will cause blooming.

(Means for Solving the Problems) In order to solve the above problems, the present applicant has invented a binder that is excellent in dispersing magnetic powder and has excellent adhesive strength to non-magnetic substrates, and has already filed an application ( Patent application 1973-E3645
9) did not fully satisfy the purpose of the present invention. As a result of further research, the present inventors found that sulfonic acid metal bases were used as a binder at 10 to 10% per polymer.
A polyurethane resin having a weight of 1000 ffi/108 g is used in combination with nitrocellulose, and a lubricant selected from butyl cellosolve palmitate and butyl cellosolve stearate, singly or as a mixture, is further added as a crosslinking agent, hexamethylene diisocyanate. The object of the present invention was achieved by selecting a circular trimmer, dispersing magnetic powder therein, and applying the dispersion to a non-magnetic substrate to form a magnetic layer. By selecting and combining the above-mentioned specific binder, specific lubricant, and specific cross-linking agent, it is possible to maintain small changes in mechanical properties and coefficient of friction over a wide temperature and humidity range, and has excellent wear resistance and durability. We succeeded in obtaining a magnetic recording medium with excellent surface smoothness.

That is, the present invention uses a binder [A] consisting of a polyurethane resin having 10 to 1000 equivalents/10"g of sulfonic acid metal base per polymer and nitrocellulose, and a cyclic trimer 1"B) of hexamethylene diisocyanate as a crosslinking agent. A magnetic coating in which ferromagnetic fine particles are uniformly dispersed in a liquid containing [C] selected from butyl cellosolve palmitate and butyl cellosolve stearate as a lubricant is applied onto a non-magnetic substrate to form a magnetic layer. The present invention is a magnetic recording medium characterized by having a magnetic layer containing [A], [B], and [c] made of ferromagnetic particles.

The nonmagnetic base material used in the present invention is appropriately selected from uniaxially stretched, biaxially stretched, or unstretched tapes, films, and sheets made of polyester, polyphenylene sulfite, etc., as specific examples.

Furthermore, tapes, films, and sheet-like products made from polymers such as the above-mentioned polyesters and polyphenylene sulfites to which fibrous reinforcing materials, fine powder fillers, etc. are added may also be used, if necessary.

The polyurethane resin used in the present invention has a sulfonic acid metal base content of 10 to 1000 equivalents ffi/10 per polymer.
It is sufficient to contain 6 g. When the sulfonic acid metal base per polymer is less than 10 equivalents ffi/10''g, Br/B
Not only is it not possible to increase the m value, but at the same time it is not possible to obtain high packing properties of the magnetic particles. Furthermore, if the amount of sulfonic acid metal base per polymer exceeds 1000 equivalent ffi/108 g, the solvent solubility of the polyurethane resin will be poor and it will be impractical.

The polyurethane resin of the present invention is obtained by the reaction of a polyhydroxy compound and a polyisocyanate,
Part or all of the polyhydroxy compound contains a sulfonic acid metal base.

As the polyhydroxy compound having a sulfonic acid metal group, a polyester polyol containing a sulfonic acid metal group is particularly desirable. A polyester polyol containing a sulfonic acid metal group consists of a carboxylic acid component free of a sulfonic acid metal group, a glycol component, and a dicarboxylic acid component containing a sulfonic acid metal group.

Examples of carboxylic acid components that do not contain sulfonic acid metal bases include terephthalic acid, isophthalic acid, orthophthalic acid, 1,
Aromatic dicarboxylic acids such as 5-naphthalic acid, aromatic oxycarboxylic acids such as P-oxybenzoic acid and P-(hydroxyethoxy)benzoic acid, resins such as succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. Examples include tri- and tetracarboxylic acids such as group dicarboxylic acids, trimellitic acid, trimesic acid, and pyromellitic acid.

Glycol components include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-bentanediol, 1. E3-
Hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2.4-
Trimethyl-1,3-bentanediol, 1,4-cyclohexane dimetatool, ethylene oxide and propylene oxide adducts of bisphenol A, ethylene oxide and propylene oxide adducts of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, Examples include polytetramethylene glycol. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol may be used in combination.

Examples of the dicarboxylic acid component containing a sulfonic acid metal group include 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, and 2-potassium sulfoterephthalic acid. The copolymerization amount of the dicarboxylic acid component containing these sulfonic acid metal bases is 0.5 mol% or more, preferably 1 to 50 mol%, based on the total carboxylic acid components.

There may be one or more types of polyhydroxy compounds having the above-mentioned sulfonic acid metal base.

It may also be used in combination with polyhydroquine compounds that do not have sulfonic acid metal groups, such as ordinary polyester polyols, polyether polyols, acrylic polyols, castor oil derivatives, tall oil derivatives, and their Sendai hydroxyl group compounds.

The polyisocyanates used in the polyurethane resin of the present invention include 2.4-) lylene diisocyanate, 2.
．． 8-) lylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate,
m-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate), 3
．． 3'-dimethoxy 4,4'-biphenylene diisocyanate and 2,4-naphthalene diisocyanate), 3
．． 3'-dimethyl-4,4'-biphenylene diisocyanate), 4,4'-diphenylene diisocyanate, and 4
．． 4'-Diisocyanate-diphenyl ether, 1.
5-naphthalene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,
3-diisocyanatomethylcyclohexane, 1,4-
Examples include diisocyanate methylcyclohexane, 4,4'-diisocyanate dicyclohexane, 4,4''-diisocyanate cyclohexylmethane, isophorone diisocyanate, etc., and if necessary, 2,4°4'
-Triisocyanate-Diphenyl, benzene triisocyanate, etc. can also be used in small amounts.

A polyurethane resin can be obtained by reacting a polyhydroxy compound and a polyisocyanate in a solvent or in the absence of a solvent by a known method, but the desirable blending ratio is 0.5 of the NCO group of the polyisocyanate/OH group of the polyhydroxy compound. ~2/1. The molecular weight of the resulting polyurethane resin is preferably 8,000 to 100,000.

In the present invention, when nitrocellulose is used in combination as part of the binder, the surface smoothness of the coating film (magnetic layer) is further improved, and the hardness of the coating film is prevented from decreasing, especially at high temperatures.
It has been found that this method is extremely effective in preventing an increase in the coefficient of dynamic friction. This effect could not be obtained either when the binder was a polyurethane resin having a sulfonic acid group alone or when this resin was used in combination with other resins other than nitrocellulose.

The nitrocellulose used in the present invention is not particularly limited, but has a degree of nitrification of 10 to 12% and a degree of polymerization of 50 to 12%.
200 is preferable, and examples include Cell Line manufactured by Daicel Chemical Industries, Ltd.

If the degree of polymerization is too low, the coating film will become brittle, and if it is too high, the viscosity of the paint will be too high and coating will become difficult, so the above range is preferable. In the present invention, the appropriate mixing ratio of polyurethane resin and nitrocellulose is 3 to 200 parts by weight, preferably 5 to 100 parts by weight, and more preferably 5 to 50 parts by weight of nitrocellulose per 100 parts by weight of polyurethane resin. Department.

° In the present invention, one or a mixture of butyl cellosolve palmitate and butyl cellosolve stearate is used as a lubricant.

The amount of the lubricant added alone or in combination is preferably 1 to 20% by weight, more preferably 3 to 15% by weight, based on the binder made of the polyurethane resin and nitrocellulose. The amount of the lubricant added is preferably within the above range from the viewpoint of reducing the coefficient of friction on the surface of the coating film and preventing head contamination due to blooming. The reason why this lubricant exhibits particularly excellent effects not seen with other lubricants when combined with the binder of the present invention is unknown, but because the two have appropriate interaction and compatibility, However, it is relatively resistant to blooming, and a strong oil film is formed on the surface of the paint film, which reduces the friction coefficient of the paint film over a wide temperature and humidity range without impairing its adhesion to the base material. This is thought to be due to the effect of reducing the amount of water.

The crosslinking agent used in the present invention is a cyclic trimer of hexamethylene diisocyanate, specifically Coronate E
Examples include H (manufactured by Nippon Polyurethane Co., Ltd.). The reason why this crosslinking agent contributes to improvement of abrasion resistance and durability over a wide temperature and humidity range is that the crosslinking agent itself is flexible and has a trifunctional incyanate group, so it is difficult to combine with the binder used in the present invention. When a flexible network structure with high crosslinking density is formed, the temperature dependence of mechanical properties such as strength and elongation of the coating film and elasticity is very small, and especially the elastic recovery and flexibility at low temperatures are improved. It turned out that this was to prevent damage to the The amount of the crosslinking agent added is 5 to 100% by weight, preferably 5 to 60% by weight, based on the binder used in the present invention, so that the coating film does not become brittle and an effective crosslinking density can be obtained. More preferably, it is 10 to 40% by weight. Furthermore, the magnetic layer of the present invention may include, if necessary,
In order to improve the conductivity, carbon fine particles or other non-magnetic inorganic fine particles as an abrasive or the like may be added.

The ferromagnetic fine particles (magnetic powder) used in the present invention include γ-FetusCr On, which has a spinel structure;
'Balto ferrite (Coo, F exO5), cobalt adsorbed iron oxide, ferromagnetic Fe-G.

-Ni alloy, hexagonal ferrite, etc. can be mentioned.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the Examples in any way. "Example Middle" indicates parts by weight.

(Example) Examples 1 to 9. Comparative Examples 1 to 7 [Manufacture of polyester polyol] In a reaction vessel equipped with a thermometer, a stirrer, and a partial reflux condenser, 582 parts of dimethyl terephthalate, 298 parts of dimethyl 5-sodium sulfoisophthalate, 434 parts of ethylene glycol, and Add 728 parts of pentyl glycol, 0.66 parts of zinc acetate, and 0.08 parts of sodium acetate to 1
Transesterification reaction was carried out at 40-2.20°C for 3 hours.

Next, 1212 parts of sebacic acid was added and reacted at 120 to 250°C for 2 hours, and then the reaction system was heated to 20 m
Reduce pressure to m Hg and further reduce pressure to 5-20 ++ m Hg
s A polycondensation reaction was carried out at 250°C for 50 minutes. The obtained polyester polyol (a) has η5PIC=0.1
82 and a hydroxyl number of 38. According to NMR analysis, etc., the composition was as follows. Terephthalic acid 3
0 mol%, 5-sodium sulfoisophthalic acid 10 mol%, sebacic acid 60 mol%, ethylene glycol 44 mol%,
Neopeptyl glycol 56 mol%.

Polynispolyol (b) was obtained in the same manner.

It had η5PIC=0.302 and a hydroxyl number of 22, and its composition was as follows from NMR analysis. Terephthalic acid 30 mol%, isophthalic acid 20 mol%
, adipic acid 50 mol%, ethylene glycol 65 mol%, 1.5-bentanediol 35 mol%.

[Production of polyurethane resin]

Into a reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser, 1280 parts of toluene, 850 parts of methyl isobutyl ketone, 1000 parts of polyester polyol (a), 71 parts of diphenylmethane diisocyanate, and 1.2 parts of dibutyltin silaurylate were added. , and reacted at 70 to 90°C for 8 hours. The sulfonic acid metal base of the obtained polyurethane resin (I) was 378 equivalent ffi/108 g, and the molecular weight was 1.
It was 8000. By the same method, 10 parts of polyester polyol (a) and 10 parts of polyester polyol (b) were added.
) to obtain a polyurethane resin (n). The sulfonic acid metal salt/group of the obtained polyurethane resin (II) was 30 g equivalent/108 g, and the molecular weight was 30
It was 000.

[Manufacture of magnetic recording media]

After mixing and dispersing for 60 hours, add 2 parts of Coronate E) (manufactured by IC Nippon Polyurethane Co., Ltd.) (listed in Table 1) and W parts of lubricant (listed in Table 1), and stir to homogenize. − was mixed. Each adjusted magnetic paint was passed through the mouth, defoamed, and applied onto a 75μ thick polyethylene terephthalate film using a doctor blade with a 25μ gap, and left in a hot air dryer at approximately 80°C to remove the solvent. After removing it, apply the same coating on the back side again and dry it at 60℃, 65%
The magnetic layer was left in an RH constant temperature bath to sufficiently harden the magnetic layer. The thickness of the resulting coating film was approximately 2.5 μm. Thereafter, punched discs were made in the shape of discs with a diameter of 3 to 4 inches. Table 1 shows the composition of the components used in the magnetic layer and the performance of the disk, along with the following comparative examples.

The following margin Comparative Example Na 1 is the polyurethane resin (I) of Example Nα1.
) A disc was made using polyurethane resin (II) instead of polyurethane resin (II).

Comparative example Nα2 uses Coronate instead of Coronate EH)
A disk was prepared in the same manner as in Example N1L1, except that 4090 (urethane prepolymer manufactured by Nippon Polyurethane Co., Ltd.) was used as a crosslinking agent.

In Comparative Examples Nα3 to Nα5, disks were prepared in the same manner as in Example Na1, except that η-butyl myristate, dimethylpolysiloxane, or liquid paraffin was used as the lubricant.

In Comparative Example Na6, a disk was prepared in the same manner as in Example Nα7, except that η-butyl myristate was used as the lubricant.

The method for measuring each performance is described below.

・Surface roughness: Measured with a surfcom manufactured by Tokyo Seimitsu ■.

- Coefficient of dynamic friction: The friction force when the disk was rotated at 300 r, p, m and contacted with a head load of 2 g was detected and measured using a strain gauge.

・Compressive modulus: Lo on a sample area of 5 φ using TMA
The instantaneous double load was measured after applying a load of up to 50 g at a speed of g/min.

・Durability: A continuous running test was conducted using a disk drive in a constant temperature bath, and the output drop (%) after 3 million passes was measured.

(Effect of the invention) From the results in Table 1, the magnetic layer containing [A], [B], and [C] of the present invention has a smooth surface and a large dynamic friction coefficient between 5°C and 45°C. There is no change and the value is small, and the compressive elastic recovery rate also shows a large value without much difference between 5°C and 45°C. Furthermore, it can be seen that it has excellent performance in terms of durability.

In comparison, if even one of the components [A], [B], and [C] is missing, the comparative example satisfies all the requirements as a magnetic recording medium aimed at by the present invention as a disk. It clearly states that something cannot be obtained, [A], [B],
It is clear that certain selected combinations of [C] are essential for superior magnetic recording media.

Claims (1)

[Scope of Claims] A polyurethane resin having 10 to 1000 equivalents/10^8 g of sulfonic acid metal base per polymer, a binder [A] made of nitrocellulose, and a cyclic trimer [B] of hexamethylene diisocyanate as a crosslinking agent. As a lubricant, one or a mixture selected from butyl cellosolve palmitate and butyl cellosolve stearate [C]
A magnetic layer is formed by applying a magnetic paint containing ferromagnetic particles uniformly dispersed in a liquid containing
], [B], [C] and a magnetic layer containing fine ferromagnetic particles.