JPH0361249B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention has an excellent coating film (magnetic layer) surface smoothness,
In particular, the present invention relates to a magnetic recording medium that exhibits very little change in mechanical properties such as strength, elongation, elastic modulus, and compressibility of the magnetic layer and coefficient of friction over a wide temperature and humidity range, 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, it is known to use polyurethane resins, epoxy resins, polyester resins, nitrocellulose, vinyl chloride-vinyl acetate copolymers, etc. as binders, and to crosslink these with polyfunctional isocyanate compounds. On the other hand, solid lubricants such as graphite and molybdenum disulfide, silicone oil, fluorine-based oil,
Many proposals have been made to mix and disperse liquid lubricants such as higher fatty acids and their ester compounds in the paint preparation process, or to externally add them, if necessary, by impregnation, spraying, coating, etc. after the magnetic layer is formed. (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 minimal changes in mechanical properties and coefficient of friction over a wide temperature and humidity range, and is resistant. It has been difficult to provide a magnetic recording medium having a magnetic layer with excellent abrasion 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. Also, nitrocellulose and vinyl chloride
When a vinyl acetate copolymer or the like is used, a plasticizer is required because the coating film lacks flexibility. Addition of these surfactants and plasticizers leads to a decrease in the adhesive strength between the magnetic layer and the non-magnetic base material, and also causes the coating film to peel off when a tape or disk-shaped magnetic recording medium is run or rotated for a long time. This will cause problems. In addition, polyfunctional isocyanates are generally used as crosslinking agents used to cure each resin used as a binder and improve the strength of the coating film. Polyisocyanate, for example Coronate L (tolylene diisocyanate adduct of trimethylpropane: manufactured by Nippon Polyurethane Co., Ltd.)
Ya Millionate MR (initial condensate of diphenylmethane diisocyanate: manufactured by Nippon Polyurethane Co., Ltd.)
etc. are preferably used, but when using these,
It is difficult to control the viscoelasticity of magnetic coatings,
It is not possible to obtain a magnetic recording medium that has a magnetic layer that reduces changes in mechanical properties and coefficient of friction over a wide temperature range from low to high temperatures, and has 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 ( Japanese Patent Application No. 53-66459) did not fully satisfy the object of the present invention. As a result of further research, the present inventors found that sulfonic acid metal base was used as a binder in an amount of 10 to 1000 equivalents/10 ⁶ g per polymer.
A combination of polyurethane resin and nitrocellulose, a lubricant selected from butyl cellosolve palmitate and butyl cellosolve stearate, singly or a mixture thereof, and a cyclic trimer of hexamethylene diisocyanate as a crosslinking agent, magnetic The object of the present invention was achieved by dispersing the powder and applying it 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, we can maintain small changes in mechanical properties and coefficient of friction over a wide temperature and humidity range, and have 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 a sulfonic acid metal base in an amount of 10 to 1000 equivalents/10 ⁶ g per polymer and nitrocellulose, a cyclic trimer of hexamethylene diisocyanate as a crosslinking agent [B], and a lubricant as a cyclic trimer [B]. 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 is applied onto a non-magnetic substrate to form a magnetic layer. This is a magnetic recording medium characterized by having a magnetic layer containing [A], [B], and [C] and ferromagnetic fine 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 sulfide, and the like.
Furthermore, tapes, films, and sheet-like products made of polymers such as the above-mentioned polyesters and polyphenylene sulfides to which fibrous reinforcing materials, unfilled fine particles, etc. are added may also be used, if necessary. The polyurethane resin used in the present invention contains 10 to 1000 equivalents of sulfonic acid metal base per polymer.
It is sufficient to contain 10 ⁶ g. less than 10 equivalents/10 ⁶ g of sulfonic acid metal base per polymer;
Not only cannot an increase in the Br/Bm value be expected, but at the same time it is not possible to obtain high packing properties of the magnetic particles. In addition, the amount of sulfonic acid metal base per polymer is 1000 equivalents/
If it exceeds 10 ⁶ 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, and part or all of the polyhydroxy compound contains a sulfonic acid metal base. As the polyhydroxy compound having a sulfonic acid metal base, a polyester polyol having a sulfonic acid metal base is particularly desirable. A polyester polyol having a sulfonic acid metal base consists of a carboxylic acid component without a sulfonic acid metal base, a glycol component, and a dicarboxylic acid component having a sulfonic acid metal base. Examples of carboxylic acid components that do not have a sulfonic acid metal base include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and 1,5-naphthalic acid, P-oxybenzoic acid, P-(hydroxyethoxy)benzoic acid, etc. aromatic oxycarboxylic acids, resinous dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid; and tri- and tetracarboxylic acids such as trimellitic acid, trimesic acid, and pyromellitic acid. Glycol components include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4 butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2, 2,4-trimethyl-
1,3-pentanediol, 1,4-cyclohexanedimethanol, 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, any tri- and tetraol 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 copolymerized 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 polyhydroxy 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 other hydrous acid group compounds. The polyisocyanates used in the polyurethane resin of the present invention include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate,
p-phenylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate,
2,4-naphthalene diisocyanate, 3,3'-
Dimethyl-4,4'-biphenylene diisocyanate, 4,4'-diphenylene diisocyanate,
4,4'-diisocyanate-diphenyl ether, 1,5-naphthalene diisocyanate, p-
Examples include xylylene diisocyanate, m-xylylene diisocyanate, 1,3-diisocyanatemethylcyclohexane, 1,4-diisocyanatemethylcyclohexane, 4,4'-diisocyanate dicyclohexane, 4,4'-diisocyanate dicyclohexylmethane, isophorone diisocyanate, etc. However, if necessary, 2, 4,
Small amounts of 4'-triisocyanate-diphenyl, benzene triisocyanate, etc. can also be used. 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 desired blending ratio is
NCO group / 0.5 to OH group of polyhydroxy compound
It is 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 it also prevents a decrease in the hardness of the coating film, especially at high temperatures, and prevents an increase in the coefficient of dynamic friction. It was found that it has a significant effect on This effect could not be obtained either when the binder was a polyurethane resin having a sulfonic acid group alone or when the resin was used in combination with other resins other than nitrocellulose. The nitrocellulose used in the present invention is not particularly limited, but preferably has a degree of nitrification of 10 to 12% and a degree of polymerization of 50 to 200, such as Cell Line manufactured by Daicel Chemical Industries, Ltd., and the like. 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 200 parts by weight of nitrocellulose per 100 parts by weight of polyurethane resin.
The amount is 100 parts by weight, more preferably 5 to 50 parts by weight. 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 since the two have appropriate interaction and compatibility, it is effective even at high temperatures. It is relatively difficult to bloom, and strong oil film bonding and formation of a tough oil film occur on the coating film surface, and the effect of the friction coefficient of the coating film over a wide temperature and humidity range without impairing the adhesion to the base material. This is thought to be due to a decrease in performance. The crosslinking agent used in the present invention is a cyclic trimer of hexamethylene diisocyanate, and specific examples include Coronate EH (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 isocyanate group. When a flexible network structure with high crosslinking density is formed, the temperature dependence of the mechanical properties such as strength and elongation and elasticity of the coating film is very small, and especially the elastic recovery and flexibility at low temperatures are improved. It turned out that this was to prevent damage. 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. Preferably it is 10 to 40% by weight. Furthermore, fine carbon particles or other nonmagnetic inorganic fine particles as an abrasive or the like may be added to the magnetic layer of the present invention, if necessary, in order to improve conductivity. Ferromagnetic fine particles (magnetic powder) used in the present invention
As, γ- with spinel structure
Fe ₂ O ₃ CrO ₂ , cobalt ferrite (CoO.Fe ₂ O ₃ ),
Examples include cobalt-adsorbed iron oxide, ferromagnetic Fe-Co-Ni alloy, hexagonal ferrite, and the like. 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] 582 parts of dimethyl terephthalate,
Dimethyl 5-sodium sulfoisophthalate 296
1 part, 434 parts of ethylene glycol, 728 parts of neopentyl glycol, 0.66 part of zinc acetate, and 0.08 part of sodium acetate were added, and transesterification reaction was carried out at 140 to 220°C for 3 hours. Then add 1212 parts of sebacic acid.
After reacting at 120 to 250℃ for 2 hours, the reaction system was depressurized to 20 mmHg over 30 minutes, and further heated to 5 to 20 mmHg.
Polycondensation reaction was carried out under Hg at 250°C for 50 minutes. The obtained polyester polyol (a) has ηSP/C=
0.182, and had a hydroxyl number of 38. From NMR analysis, etc., its composition was as follows. Terephthalic acid 30 mol%, 5-sodium sulfoisophthalic acid 10 mol%, sebacic acid 60 mol%, ethylene glycol 44 mol%, neopedetyl glycol 56 mol%. Polyester polyol (b) was obtained in the same manner.
It had ηSP/C=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-pentanediol 35 mol%. [Manufacture of polyurethane resin] In a reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser, add 1280 parts of toluene, 850 parts of methyl isobutyl ketone, and 1000 parts of polyester polyol (a).
Add 71 parts of diphenylmethane diisocyanate and 1.2 parts of dibutyltin dilaurylate, and heat at 70 to 90°C.
Allowed time to react. The sulfonic acid metal base of the obtained polyurethane resin (2) was 378 equivalents/10 ⁶ g, and the molecular weight was 18,000. A polyurethane resin () was obtained in the same manner using 10 parts of polyester polyol (a) and 990 parts of polyester polyol (b). The sulfonic acid metal base of the obtained polyurethane resin () is 3.9 equivalent/10 ⁶ g
and the molecular weight was 30,000. [Manufacture of magnetic recording media] {Co-coated γ-Fe ₂ O ₃ (manufactured by Toda Kogyo Co., Ltd.) 50 parts Cr ₂ O ₃ (manufactured by Bayer) 4 parts carbon (manufactured by Lion Akzo: Ketsutien Black) 2 parts polyurethane Resin (30%)
Part X (listed in Table 1) Nitrocellulose (16%) (Cell line: manufactured by Daicel) Part Y (〃) Methyl ethyl ketone 40 parts Toluene 40 parts Shikuihexanone 40 parts were placed in a ball mill and mixed and dispersed for 60 hours. rear,
Coronate EH (manufactured by Nippon Polyurethane Co., Ltd.) Z part (listed in Table-1) and lubricant W part (listed in Table-1)
was added and mixed uniformly under stirring. 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, the same coating and drying was performed on the back side again, and the magnetic layer was left in a constant temperature bath at 60° C. and 65% RH to sufficiently harden the magnetic layer.
The thickness of the resulting coating film was approximately 2.5μ. He then punched out a disc with a diameter of 3.4 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.

【table】

[Table] *: Measurement is not possible.
**: The paint film was damaged during driving and the drive stopped.
***; The drive stopped due to large rotational torque.
In Comparative Example No. 1, a disk was made using polyurethane resin (2) instead of the polyurethane resin (2) in Example No. 1. Comparative Example No. 2 is the same as Example No. 2, except that Coronate 4090 (manufactured by Nippon Polyurethane Co., Ltd.: urethane prepolymer) was used as a crosslinking agent instead of Coronate EH.
A disk was created in the same way as 1. In Comparative Examples No. 3 to No. 5, disks were prepared in the same manner as in Example No. 1, except that η-butyl myristate, dimethylpolysiloxane, or liquid paraffin was used as the lubricant. In Comparative Example No. 6, a disk was prepared in the same manner as in Example No. 7 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. ●Dynamic friction coefficient: The friction force was detected and measured using a strain gauge when the disk was rotated at 300 rpm and a head load of 2 g was applied. ●Compressive elastic modulus: using TMA for a sample area of 5 mmφ
The instantaneous recovery rate was measured after applying a load of up to 50 g at a rate of 10 g/min. ●Durability: Continuous running tests were conducted using a disk drive in a constant temperature chamber, and the output drop (%) after 3 million passes was measured. (Effects of the invention) From the results in Table 1, it can be seen that [A], [B],
The magnetic layer containing [C] has a smooth surface, the coefficient of dynamic friction does not change significantly between 5°C and 45°C, and
The value is small, and the compressive elastic recovery rate is also 5℃ and 45℃.
shows a large value without much difference. 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 is clear that a particular selected combination of [A], [B], and [C] is essential for an excellent magnetic recording medium.

Claims (1)

[Claims] 1. 10 to 10 sulfonic acid metal bases per polymer
A polyurethane resin having a weight of 1000 equivalents/10 ⁶ g, a binder made of nitrocellulose [A], a cyclic trimer of hexamethylene diisocyanate [B] as a crosslinking agent, and a lubricant selected from butyl cellosolve palmitate and butyl cellosolve stearate, singly or as a mixture. [A], [B], [C] and ferromagnetic coatings are formed by coating a magnetic paint containing ferromagnetic particles uniformly dispersed in a liquid containing [C] on a non-magnetic base material to form a magnetic layer. 1. A magnetic recording medium comprising a magnetic layer containing fine particles.