JPH0212506B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks. The present invention relates to a high-performance magnetic recording medium with excellent performance. (Prior Art) Conventionally, magnetic recording media used in audio equipment, video equipment, computers, etc. are obtained by forming a magnetic layer consisting of magnetic particles and a binder resin on a non-magnetic support such as a polyester film. . Such a magnetic layer is formed by coating or transferring a dispersion of magnetic particles in a medium containing a binder resin onto a non-magnetic support. Conventionally, binder resins include polyester resins, cellulose resins, polyurethane resins, phenol resins, epoxy resins, polyamide resins, acrylic esters, methacrylic esters, styrene, acrylonitrile,
Polymers or copolymers of butadiene, vinyl ester, vinyl chloride, vinylidene chloride, acrylamide, methacrylamide, etc. have been used;
A magnetic layer with sufficient surface smoothness, dispersibility, durability, and magnetic properties could not be obtained. In particular, although polyurethane resins have high durability, their interaction with magnetic particles is weak, making it difficult to obtain sufficient dispersibility and surface smoothness. This is because these magnetic particles have a strong cohesive property in the medium, and therefore a stable dispersion cannot be obtained as is. For this purpose, various dispersants have been proposed and used in order to improve the dispersion stability of magnetic particles. (Problem to be solved by the invention) However, conventional dispersants cannot overcome the strong cohesive force of magnetic particles, and once dispersed magnetic particles re-agglomerate within a short period of time, resulting in There is a problem that the magnetic recording medium must be used immediately after preparation, and there are various drawbacks in terms of productivity of the magnetic recording medium. Furthermore, even with this method, the conventional dispersant is an organic compound with a small to medium molecular weight that is essentially different from the binder resin used, so it migrates to the surface of the magnetic layer after it is formed, and can damage the recording head. This caused various problems such as damage. Therefore, there is a strong demand for a binder resin that can overcome the strong cohesive force of magnetic particles and provide a stable dispersion without using a large amount of a dispersant that would cause the problems described above. In order to solve the above-mentioned drawbacks of the prior art and meet the above-mentioned demands, the present inventor has conducted extensive research and found that various problems arise when using a specific binder resin in the manufacture of magnetic recording media. The present invention was completed based on the finding that the above-mentioned drawbacks of the prior art can be solved without substantially using a dispersant. (Means for Solving the Problems) That is, the present invention provides a magnetic recording medium comprising a magnetic layer in which magnetic particles are dispersed in a binder resin on a non-magnetic support. The present invention is a magnetic recording medium characterized by being made of a polyurethane resin having a carboxyl group bonded to the main chain via a bond. To explain the present invention in more detail, the binder resin used in the present invention and which primarily characterizes the present invention is a polyurethane resin having a carboxyl group bonded to the main chain via an ester bond. Such a specific polyurethane resin may be prepared by any method, but a preferred manufacturing method is to prepare it from a polyol and an organic polyisocyanate compound according to a conventional method, using a chain extender as necessary. When manufacturing polyurethane resin,
It can be produced by using a polyol having a carboxyl group in the main chain of the polyol via an ester bond. The above polyol having a carboxyl group is
It is obtained by reacting a polyol having a trifunctional or more functional hydroxyl group with various polycarboxylic acids, preferably a polycarboxylic acid having an acid anhydride group in the molecule, such that at least two hydroxyl groups remain in the polyol. Preferred polyols include trihydric or higher alcohols such as glycerin, diglycerin, polyglycerin, erythritol, pentaerythritol, arabite, sorbitol, sorbitan, mannitrate, mannitan, trimethylolpropane, or ethylene oxide, propylene using these alcohols as initiators. oxide, polyether polyols obtained by polymerizing alkylene oxides such as butylene oxides, polyester polyols containing trivalent or higher hydroxyl groups made of these polyhydric alcohols or polyether polyols and dicarboxylic acids, and the above alkylenes using organic polyamines as initiators. Examples include oxide polymers and polyester polyols having trivalent or higher hydroxyl groups obtained from the polymers and dicarboxylic acids. In the present invention, polyether triols having a molecular weight of about 90 to 4,000 are particularly preferred among these polyols. Further, as the polycarboxylic acid to be reacted with the above polyol, any polycarboxylic acid having two or more carboxyl groups can be used, and preferred examples include oxalic acid,
malonic acid, succinic acid, glutaric acid, adipic acid,
Pimelic acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, methylmaleic acid, methylfumaric acid, itaconic acid, citraconic acid, mesaconic acid, acetylenic acid, malic acid, methylmalic acid, citric acid, isocitric acid, tartaric acid,
Examples include phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, naphthalene dicarboxylic acid, and their alkyl esters, acid halides, acid anhydrides, etc. Among the above polycarboxylic acids, the most preferred in the present invention are It is an acid anhydride of something that can have an acid anhydride group. The reaction between the polyol as described above and the polycarboxylic acid as described above determines the ratio of the obtained carboxylic acid-modified polyol to diol, for example, 1% of the triol.
It is preferable to react at a ratio of 1 mole of dicarboxylic acid anhydride to 1 mole of dicarboxylic acid anhydride. The reaction between a polyol and a polycarboxylic acid, especially an acid anhydride of a polycarboxylic acid, is extremely easy and can be carried out according to a conventional method. It may be carried out during or after manufacture. Most preferably, the polyol is modified with carboxylic acid in advance before producing the polyurethane resin. The polyurethane resin having a carboxyl group used in the present invention can be produced by a conventional method using a polyol having a carboxyl group as described above (however, carboxyl modification may be carried out during or after the production of the polyurethane resin). Therefore, it can be easily obtained by reacting it with an organic polyisocyanate compound and, if necessary, using a chain extender in combination to produce a polyurethane resin.
In addition, the above carboxyl group is an alkali metal salt,
Salts such as ammonium salts and organic amines may also be used. The organic polyisocyanate used in the present invention is a compound having at least two isocyanate groups in an aliphatic or aromatic compound, and has been widely used as a synthetic raw material for polyurethane resins. Any of these known organic polyisocyanates are useful in the present invention. Particularly preferred organic polyisocyanates are as follows. Tolylene diisocyanate, 4-methoxy-1,3-phenylene diisocyanate, 4-isopropyl-1,3-phenylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 4-butoxy-1,3-phenylene Diisocyanate, 2,4-diisocyanate-diphenyl ether, mesitylene diisocyanate, 4,4'-methylenebis(phenyl isocyanate), diylylene diisocyanate, 1,5-naphthalene diisocyanate, benzidine diisocyanate, o-nitrobenzidine diisocyanate, 4, 4-dibenzyl diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-tetramethylene diisocyanate, 1,10-decamethylene diisocyanate, 1,4-cyclohexylene diisocyanate, xylylene diisocyanate, 4,4'-methylenebis(cyclohexyl) isocyanate), 1,5-tetrahydronaphthalene diisocyanate, isophorone diisocyanate, etc. Further, chain extenders that may be used in the present invention include ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol,
1,6-hexanediol, ethylenediamine,
1,2-propylene diamine, trimethylene diamine, tetramethylene diamine, hexamethylene diamine, decamethylene diamine, isophorone diamine, m-xylylene diamine, hydrazine,
There is water etc. The polyurethane resin having a carboxyl group or a salt thereof used in the present invention can be manufactured from the above-mentioned main materials in a solvent or without a solvent, using a catalyst if necessary, and the manufacturing conditions may vary. A conventionally known method may also be used. Furthermore, in the present invention, conventionally known polyols can be used in combination in any proportion during the production of the polyurethane resin as described above. Preferred examples of such conventionally known polyols include polyethylene adipate, polyethylene propylene adipate, polyethylene butylene adipate, polydiethylene adipate, polybutylene adipate, and polyethylene succinate, each having a hydroxyl group as an end group and having a molecular weight of 300 to 4000. , polybutylene succinate, polyethylene sebacate, polybutylene sebacate, polytetramethylene ether glycol, poly-ε-
Examples include caprolactone diol, polyhexamethylene adipate, carbonate polyol, polyethylene glycol, and polypropylene glycol. The magnetic recording medium of the present invention is mainly characterized by using the above-mentioned specific binder resin as the binder resin forming the magnetic layer. At this time, conventionally known binder resins can be used in combination in any proportion. Examples of these binder resins include vinyl chloride resins, vinylidene chloride resins, vinyl chloride/vinyl acetate/vinyl alcohol copolymer resins, alkyd resins, epoxy resins, acrylonitrile-butadiene resins, polyurethane resins, Nitrocellulose resin, polybutyral resin, polyester resin, silicone resin,
Melamine resin, urea resin, acrylic resin,
Examples include polyamide resins, and particularly preferred are polyurethane resins. These resins can be used alone or as a mixture. Examples of magnetic particles used in the present invention include:
Iron, chromium, nickel, cobalt, alloys or oxides thereof, and modified products thereof, specifically, cobalt-doped γ-Fe ₂ O ₃ , ferrite, magnetite, CrO _{2 ,} etc.
Examples include Fe ₂ O ₃ and a cobalt-doped bertholed compound of Fe ₂ O ₃ and Fe ₃ O ₄ . The above magnetic particles are merely examples, and
Of course, various magnetic particles other than those exemplified above can also be used in the present invention, and can be used alone or as a mixture. In the present invention, the organic solvent for dissolving and dispersing the binder resin and magnetic particles as described above includes:
Any conventionally known organic solvent can be used. For example, preferred organic solvents include methyl ethyl ketone, methyl-n-propyl ketone, methyl isobutyl ketone, diethyl ketone, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, and acetic acid. Butyl, acetone, cyclohexane, tetrahydrofuran, dioxane, methanol, ethanol, isopropyl alcohol, butanol, methyl cellosolve, butyl cellosolve, cellosolve acetate, dimethyl formamide, dimethyl sulfoxide, pentane, hexane, cyclohexane, heptane, octane, mineral spirits, petroleum ether, Examples include gasoline, benzene, toluene, xylene, chloroform, carbon tetrachloride, chlorobenzene, perchloroethylene, trichloroethrene, and mixtures thereof. The dispersion used in the present invention has the above-mentioned components as essential components, and their usage ratios are the same as in conventional dispersions of magnetic particles.For example, if the entire dispersion is 100 parts by weight, Generally, the magnetic particles account for about 10-50% by weight, the liquid medium accounts for about 50-90% by weight, and the binder resin accounts for about 5-20% by weight. As long as the dispersion used in the present invention contains these components as essential components, other subcomponents other than those mentioned above, such as dispersants, pigments, extender pigments, plasticizers, antistatic agents, surfactants, lubricants, crosslinking agents, etc. , anti-aging agent,
Optional additives such as stabilizers and antifoaming agents may be included. The method of producing the dispersion liquid used in the present invention, which consists of the above-mentioned essential components and optional components, may be any conventionally known method, and generally, while adding the necessary components simultaneously or sequentially, ball milling, mixer treatment, etc. Mixing and dispersing methods such as processing, roll milling, bead milling, gravel milling, sand milling, and high speed impeller processing are suitable. The conditions for such a dispersion method vary depending on the type and size of the magnetic particles to be dispersed, their intended use, etc., but generally they are carried out at a temperature between room temperature and 100°C.
It is sufficient to process for about 5 minutes to 20 hours. In addition, any conventionally known non-magnetic support can be used, for example, with a thickness of 5 to 50 μm.
Polyester film, polypropylene film, cellulose triacetate film, cellulose diacetate film, polycarbonate film, etc. can be used arbitrarily. The magnetic layer is formed by applying the above-mentioned dispersion onto at least one surface of the above-mentioned non-magnetic support by an arbitrary method so that the dry thickness becomes approximately 0.5 to 20 μm, and then drying. It can be formed by Alternatively, a magnetic layer may be formed by coating and drying the dispersion liquid as described above on a base sheet such as a release paper, and then transferring the magnetic layer onto a support by a transfer method. These coating methods, drying methods, transfer methods, etc. may all be conventionally known methods. (Functions/Effects) The magnetic recording medium of the present invention obtained as described above has excellent surface smoothness, electromagnetic conversion characteristics, and uniform dispersion of the magnetic layer to a degree unseen in the prior art.
Furthermore, it shows excellent durability. Such a remarkable effect can be obtained by using a polyurethane resin having a carboxyl group or a salt thereof in the main chain via an ester bond as described above as a binder resin of a dispersion of magnetic particles for forming the magnetic recording medium of the present invention. Due to use. In other words, even in the conventional technology, hydrophilic groups such as carboxyl groups or sulfonic acid groups are introduced directly into the main chain of polyurethane resin to improve affinity for magnetic particles, thereby achieving high dispersibility of magnetic particles. There have been known attempts to
Such conventional modified polyurethane resins could not achieve satisfactory uniform dispersibility or excellent surface smoothness of the magnetic layer. This is because the hydrophilic groups that are compatible with the magnetic particles are directly connected to the main chain of the polyurethane resin, which diminishes the original excellent performance of the main chain polyurethane resin. On the other hand, the polyurethane resin used in the present invention has carboxyl groups or their salts through ester bonds, that is, apart from the main chain, so even if these carboxyl groups or their salts have an affinity for magnetic particles, However, the adverse effect does not reach the main chain polyurethane resin, and the main chain polyurethane resin can still exhibit the original excellent performance of the polyurethane resin. In addition, in the present invention, as a result of using such a specific polyurethane resin as a binder resin, the magnetic particles can be uniformly and stably dispersed without substantially using a dispersant that causes various problems as in the conventional technology. A dispersion of magnetic particles has been achieved, and when this dispersion is used to form a magnetic layer on a non-magnetic support, a previously unknown level of surface smoothness and uniform dispersion of magnetic particles can be achieved. As a result, various problems caused by the lack of surface smoothness and the presence of dispersants in the prior art have been solved. Next, the present invention will be explained in more detail with reference to Examples. In addition, parts and percentages in the text are based on weight unless otherwise specified. Example 1 In a 2 liter flask equipped with a nitrogen inlet tube, a thermometer, a stirrer and a distillation tube, a propylene oxide adduct of glycerin (molecular weight approximately 1500) 1000
1 part, 66.7 parts of succinic anhydride and 53 parts of toluene were introduced, and the temperature was raised to 150-160°C in 1.5 hours, and further heated to 150-160°C.
The reaction was carried out at a temperature of 160°C for 1.5 hours. Thereafter, the pressure inside the container was reduced to 5 to 10 mmHg to remove the solvent and unreacted substances, thereby obtaining a carboxyl group-modified polypropylene diol. This product had a hydroxyl value of 69 and an acid value of 35. 250 parts of the above diol, 750 parts of polycarbonate polyol, 100 parts of 1,4-ditanediol, 285 parts of tolylene diisocyanate, 1286 parts of dimethylformamide and 1286 parts of tetrahydrofuran were mixed and reacted at about 80 to 120°C for 8 hours, A carboxyl group-modified polyurethane resin () used in the present invention was obtained. This polyurethane resin had a molecular weight of about 70,000. Examples 2 to 5 Carboxyl group-modified polyurethane resins () to () used in the present invention were prepared in the same manner as in Example 1, except that the following reaction materials were used in place of each reaction material in Example 1. . Example 2 Carboxyl group-modified polyol; reaction product of propylene oxide adduct of trimethylolpropane and phthalic anhydride (molecular weight approximately 2000, hydroxyl value 52, acid value 26) Production of polyurethane resin () (solvent is omitted) ; Above polyol 600 parts Polybutylene adipate 400 parts Tolylene diisocyanate 180 parts 1,4-butanediol (molecular weight approximately 70,000) 50 parts Example 3 Carboxyl group-modified polyol; Reaction of propylene oxide adduct of glycerin and trimellitic anhydride Product (molecular weight approximately 700,
Hydroxyl value: 125, acid value: 63) Production of polyurethane resin (solvent omitted): 500 parts of the above polyol Polypropylene glycol 500 parts 4,4'-diphenylmethane diisocyanate
476 parts 1,6-hexanediol (molecular weight approximately 70,000)
100 parts Example 4 Carboxyl base-modified polyol; Reaction product of glycerin propylene oxide adduct and glutaric anhydride (molecular weight approximately 1000, hydroxyl value 101, acid value 50) Production of polyurethane resin () (solvent omitted) ); Above polyol 300 parts Polyethylene adipate 700 parts 4,4'-diphenylmethane diisocyanate
382 parts 1,4-ditanediol (molecular weight approx. 30000) 50 parts Example 5 Carboxyl group-modified polyol; reaction product of propylene oxide adduct of trimethylolpropane and maleic anhydride (molecular weight approx. 1000, hydroxyl value 102, acid 51) Production of polyurethane resin (solvent omitted); 100 parts of the above polyol Poly-ε-caprolactone diol 900 parts 4,4'-diphenylmethane diisocyanate
241 parts 1,6-hexanediol (molecular weight approximately 100,000)
50 parts Examples 6 to 10 The following ingredients were dispersed in a ball mill for 45 hours, and 3.2 parts of Teismodyur OL was further added and dispersed for 3 hours to obtain the dispersion used in the present invention ()
I got (). Cobalt doped γ-Fe ₂ O ₃ 100 parts Polyurethane resin of Examples 1 to 5 (~) 35
% solution 71 parts Methyl ethyl ketone 82 parts Toluene 82 parts Cyclohexanone 82 parts The above dispersions () to () were applied to a 15 μm thick polyester film, and magnetic field orientation was performed at 1800 Gauss to form a magnetic layer about 5 μm thick. Then, magnetic recording media () to () of the present invention were created. Comparative Examples 1 to 3 As the binder resin in Example 6, a 35% solution of polyurethane resin (manufactured by Dainichiseika Chemical Industry Co., Ltd., Daiphelamine MAU-2010) and a vinyl chloride-vinyl acetate copolymer resin (manufactured by Sekisui Chemical Co., Ltd., Eslex A) were used. ) 35% solution () and nitrocellulose resin (Asahi Kasei, Cellnova BTH
Comparative magnetic recording media () to () were prepared in the same manner as in Example 6 except that 1/2) 35% solution () was used.
was prepared. The surface smoothness (gloss of the surface of the magnetic layer) and magnetic properties of each of the magnetic recording media obtained in Examples 6 to 10 and Comparative Examples 1 to 3 were investigated, and the following
It was as shown in the table. 【table】

Claims (1)

[Claims] 1. A magnetic recording medium comprising a magnetic layer in which magnetic particles are dispersed in a binder resin on a non-magnetic support, in which the binder resin is a polyurethane-based material having a carboxyl group bonded to the main chain via an ester bond. A magnetic recording medium characterized by being made of resin.