JPH06101114B2 - Magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic recording medium such as a magnetic tape or a magnetic disk, and more specifically, to a magnetic layer formed on a non-magnetic support. It is related to the improvement of the binder.

[Prior art]

Generally, magnetic recording media used in audio equipment, video equipment, computers, etc. (specifically, audio tapes,
Used for video tapes, floppy disks, computer data tapes, etc.) by coating a non-magnetic support such as polyester film with a magnetic paint containing magnetic powder and a binder, and drying it to form a magnetic layer. can get.

Vinyl chloride resin, polyurethane resin, polyester resin, nitrocellulose resin, epoxy resin and the like are generally used as a binder for forming the magnetic layer of such a magnetic recording medium. Among these resins, polyurethane resin contains urethane bond with large cohesive energy, so it has excellent toughness that cannot be obtained with other resins.
It has characteristics such as flexibility and abrasion resistance, and has recently been used as a binder of a magnetic layer in a magnetic recording medium which is required to have durability.

Polyurethane resins are roughly classified into polyester polyol-based polyurethane resins in which polyester polyol is a long-chain polyol and polyether-based polyurethane resins in which polyether polyol is a long-chain polyol.

Polyether polyurethane resin is excellent in water resistance (hydrolysis resistance), mold resistance and flexibility, but is used as a binder for magnetic recording media in combination with polyurethane resin such as vinyl chloride resin, polyester resin, nitrocellulose. It is rarely used due to its generally low compatibility with resins and the like, poor chemical resistance, and poor dispersibility of magnetic powder and inorganic substances.

On the other hand, the polyester polyol polyurethane resin is inferior in water resistance (hydrolysis resistance) and mold resistance to the polyether polyurethane, but due to the presence of the ester group,
It has excellent adhesiveness to the base film, durability such as heat resistance, solvent resistance, and abrasion resistance, and is suitable as a binder for magnetic recording media and is mainly used.

As the use of magnetic recording media such as various tapes and floppy disks expands, the required performance is also diverse, and the demand for higher reliability is increasing. Specifically, high-density recording for recording and reproducing clear sound, images, and signals, high-speed long-time running or long-time running under high temperature and high humidity conditions, and high durability that can withstand long-term storage, etc. Especially demanded. As a means for increasing the density, the magnetic powder is made finer and the magnetic force is increased, and there is a strong tendency to increase the packing density of the magnetic powder in the magnetic layer. However, it becomes difficult to disperse due to the increase in the specific surface area due to the fine particles of the magnetic powder and the increase in the cohesive force due to the increase in the magnetic force as described above, and it is not possible to obtain satisfactory dispersibility and surface properties with conventional binders. It is also difficult to increase the packing density of powder.

On the other hand, the magnetic recording medium is in heavy contact with the magnetic head, roll, etc. during recording and reproduction, so that wear and loss of the magnetic layer and the back coat layer are caused, which causes decrease in reproduction output, fluctuation, noise generation, and increase in dropout. Increased friction coefficient / running defects due to roll contamination due to falling powder, squeaking of tape, and clogging of magnetic head may occur.

Also, during long-term storage, the magnetic layer and pack coat layer deteriorate (decompose) due to the action of heat, oxidation, moisture, etc., and the magnetic layer falls off,
Due to adhesion of the magnetic layer, reproduction output is reduced, fluctuations, noise is generated, dropout is increased, friction coefficient is increased, runnability due to roll dirt due to falling powder, tape squeal, clogging of magnetic head, etc. It may cause defects. Further, under the condition of high humidity for a long period of time, decomposition (deterioration) of the magnetic layer and the back coat layer by microorganisms such as molds and bacteria occurs during long-term storage, which has become a problem.

The magnetic layer contains magnetic powder, binder, lubricant, abrasive, carbon black, dispersant, etc., and the various characteristics of the magnetic recording medium are due to their complex interaction, so that the above-mentioned various defects are caused in the binder. Although it cannot be said to be the cause, a binder system having high durability with improved durability against microorganisms such as scratches, abrasion, temperature, humidity and mold of the binder can be used for high-speed long-time running of a magnetic recording medium or It has been proposed to improve durability during long-term storage. For example, even if limited to urethane binders, 1,6-
Polyester polyol-based polyurethane binder obtained from hexanediol and adipic acid (JP-A-56-13)
7522), a polycarbonate-based polyurethane binder (JP-A-60-13324, etc.), a polyurethane binder containing a side chain OH group that can easily react with polyisocyanate as a curing agent (JP-A-57-113420), a glass transition temperature Tg and a Young's modulus. Aromatic system that improves durability and durability (Japanese Patent Laid-Open No. 62-1024
20) etc. have been proposed.

However, although the durability of the magnetic recording medium using the above-mentioned binder or the like for the magnetic layer and the back coat layer is improved to some extent, it does not reach the level at which all of them can be satisfied as the binder of the magnetic recording medium. For example, polycarbonate-based polyurethane binders have a satisfactory level of durability under high temperature and high humidity conditions, but have poor abrasion resistance at low temperatures and poor adhesion to the base film. The performance cannot be said to be sufficient due to poor runnability due to stains on the roll and clogging of the magnetic head.

The side chain OH group-containing polyurethane binder easily reacts with polyisocyanate as a curing agent to form a highly durable magnetic layer, but it becomes difficult to disperse it in fine magnetic powder or magnetic powder having a high amount of magnetization, resulting in poor performance. Is not enough.

Aromatic polyurethane binders have a glass transition temperature Tg
It has a high durability and is particularly excellent in running durability at high temperatures, but it also has wear resistance at low temperatures and is used as a solvent for magnetic paints. Toluene, methyl ethyl ketone (hereinafter abbreviated as MEK), methyl isobutyl ketone (hereinafter abbreviated as MIBK), cyclohexanone However, the solubility of the magnetic coating material is difficult and the stability of the magnetic coating material becomes a problem. Also, since the glass transition temperature Tg is high and hard,
Due to the difficulty in calendering, there is a problem in surface properties,
The S / N ratio as a magnetic recording medium does not increase.

Furthermore, all the binders that have excellent durability against scratches, abrasion, temperature, and humidity described above are by no means excellent against the deterioration (mold resistance) of the magnetic layer and back coat layer due to mold, bacteria, and other microorganisms. The current situation is that it cannot be said. Further, since the above-mentioned binders are all inferior in terms of dispersibility, their performance was insufficient as a binder for finely divided magnetic powder or magnetic powder having a high magnetization amount.

As described above, a binder system that fully satisfies various properties such as durability, heat resistance, moisture resistance, mechanical strength, and mold resistance, and that also provides satisfactory dispersibility and surface property, has so far been available. It has not been proposed at all, and therefore, there are drawbacks such as poor durability of the magnetic layer, poor running, and deterioration over time, and improvement thereof has been demanded.

[Problems to be solved by the invention]

The present inventors have conducted extensive studies on various polyurethane resins in order to eliminate the above-mentioned defects, and by using a polyester polyol having a specific structure as a long-chain polyol that is a constituent component of the polyurethane resin, durability, heat resistance,
The present invention has been accomplished by finding a binder that satisfies all the properties such as moisture resistance, mechanical strength, and mold resistance, and that provides excellent dispersibility and surface properties.

[Means for solving problems]

That is, the present invention provides a magnetic recording medium comprising a non-magnetic support and a magnetic layer mainly composed of a ferromagnetic powder and a binder, wherein the polyurethane resin contained as the binder constituting the magnetic layer has a molecular weight of (A). A long-chain polyol of 500 to 5,000, (B) a chain extender having a molecular weight of 50 to less than 500, and (C) diisocyanate.
In its chain A polyester polyol having a molecular weight of 5,000
A magnetic recording medium characterized in that it is a segmented polyurethane resin of up to 100,000.

By using the polyurethane resin of the present invention as a binder of a magnetic layer, it has excellent performances such as durability, heat resistance, moisture resistance, mechanical strength, and mold resistance, and also has good dispersion of magnetic powder and magnetic powder. It is possible to obtain a magnetic recording medium having an increased packing density, excellent reliability in long-term running and storage over time, and good electromagnetic conversion characteristics and surface properties.

The polyurethane resin that can be used in the present invention is a polyester polyol as a polyol, and a long-chain polyol (A) having a specific skeleton in the molecule based on the diol constituting the polyol and having a molecular weight of 500 to 5,000 and a molecular weight of 50 to 50.
It is essential to use both polyols with a chain extender (B) of less than 0. In the case of only long-chain polyol, the structure does not contain the segment in which urethane groups are concentrated, that is, the hard segment, so the coating film has no toughness and is tacky, so when used as a binder for magnetic recording media, running stability It is not preferable because there are defects such as lack of running property and tape squeaking. Chain extender (B) and long chain polyol (A)
The molar ratio of the chain extender (B) / long chain polyol (A) is determined by the molecular weight of the long chain polyol, the solubility of the polyurethane resin obtained depending on the type of the chain extender, and the characteristic value. Is 0.05 to 8.0, preferably 0.1 to 5.0.

The long chain polyol (A) used in the production of the polyurethane resin used in the present invention has a specific skeleton structure in the molecular chain. Is to have. Such a polyester polyol can be produced by a known method, that is, a direct esterification method, a transesterification method, or the like.

This can be achieved by using 3-methyl-1,5-pentanediol (hereinafter abbreviated as 3MPD) as the diol component of the polyester polyol having this specific structure. That is,
It is essential to use 3MPD as the diol component of the polyester polyol. This diol may be replaced by other diols. Substitutable diols include
Ethylene glycol, 1,3-propylene glycol, 1,2
-Propylene glycol, 1,4-butanediol (hereinafter
1,4-BD), 1,5-pentanediol, 1,6-hexanediol (hereinafter 1,6-HD), neopentyl glycol, 1,8-octanediol, 1,9-nonanediol , Diethylene glycol, cyclohexane-1,4-diol, cyclohexane-1,4-dimethanol, or ethylene oxide or propylene oxide adduct of bisphenol A, and the like, but a diol having a large carbon number in view of hydrolysis resistance. Needless to say, is preferable. 3MPD should be used for 50 mol% or more, preferably 70 mol% or more of the diol component, as long as durability, water resistance, mold resistance and the like are not impaired.

Examples of the dicarboxylic acid used as a constituent component of the long-chain polyol (A) that can be used in the present invention include aliphatic or aromatic dicarboxylic acids having 5 to 12 carbon atoms and aromatic oxycarboxylic acids. These dicarboxylic acids may be used alone or in combination of two or more. Examples of the aliphatic dicarboxylic acid include glutaric acid, adipic acid (hereinafter abbreviated as AA), pimelic acid, suberic acid, azelaic acid, sebacic acid, etc., and aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid. acid,
Examples of the aromatic oxycarboxylic acid include p-oxybenzoic acid and p- (hydroxyethoxy) benzoic acid.

Polyester polyols such as polybutylene adipate, polyhexane adipate, and polycaprolactone polyol, which are usually used as a raw material of a polyol for a binder of a magnetic recording medium, have a melting point of room temperature or higher, and polyurethane resins using them have different structures. However, all of them have crystallinity due to the raw material polyester polyol. In particular, a polyurethane resin using a diol having a large number of carbon atoms such as 1,6-HD, 1,9-nonanediol or a dicarboxylic acid having a large number of carbon atoms such as sebacic acid in order to enhance hydrolysis resistance and water resistance is recommended. Although being investigated, these polyurethane resins have a stronger crystallinity. When these polyurethane resins are used as a binder for magnetic recording media, they are excellent in hydrolysis resistance, but they have strong crystallinity and are peeled from the base film due to crystal shrinkage when left in a low temperature environment or when running at high speed. Trouble such as poor running may occur due to a decrease in hardness due to melting of crystals due to frictional heat generation.

On the other hand, the binder of the magnetic recording medium containing the polyurethane resin in which 3MPD is used as the diol component of the polyester polyol in the present invention as a constituent component seems to be due to the structure of 3-methyl introduced in the form of a side chain, but it is almost crystalline. It has been found from the study by the present inventors that it does not show the above-mentioned property, has good hydrolysis resistance and water resistance, and surprisingly has excellent resistance to fungi and bacteria which could not be solved until now. In addition, it exhibits physical properties such as scratches and abrasion at low temperatures, which cannot be realized with conventional polyurethane resin binders, and retains room temperature-like properties.

Furthermore, it has good solubility in solvents such as MEK, toluene, MIBK, and cyclohexanone used as solvents for magnetic paints. In particular, toluene and MIB, which have a weak dissolving power, are among these.
It also dissolves well in K and MEK. Due to this improvement in solubility, it exhibits physical properties characteristic of a binder of a magnetic recording medium. That is, since the amount of the chain extender can be increased from the ratio of the polyester polyol and the chain extender that are usually used (short chain polyol (B) / long chain polyol (A)), a segment in which urethane groups are concentrated is introduced into the molecule. Is possible,
It was possible to introduce a soft segment and a hard segment into the molecule separately to make a polyurethane resin with a low glass transition temperature even if it is hard, and it is possible to improve durability and wear resistance. In addition, the improvement of solubility in solvents such as MEK, toluene, MIBK, and cyclohexanone used as a solvent for magnetic paints, shortens the dispersion time,
Considering rationalization of comprehensive dispersion process such as increase of solid content of magnetic paint because improvement of dispersibility such as improvement of dispersion stability of magnetic paint and low viscosity of magnetic paint from urethane resin of the present invention To be

Amorphous polyurethane resin binders include polyurethane resins such as diethylene adipate type, polypropylene adipate type, polypropylene ether glycol type, etc., all of which have poor water resistance and heat resistance, and are binders for magnetic recording media. Since it has a low compatibility with a vinyl chloride resin used together with a polyurethane resin, it is hardly usable as a binder for a magnetic recording medium.

When the molecular weight of the long-chain polyol (A) used in the present invention is less than 500, the concentration of urethane groups becomes large, and the solubility in a solvent and the dispersibility of magnetic powder, which are one of the features of the present invention, decrease. On the other hand, if the molecular weight exceeds 5,000, the urethane group concentration is decreased, and the toughness and abrasion resistance peculiar to the polyurethane resin are decreased, which is not preferable.

If necessary, other polyester polyols, polyester amides, and polyether polyols may be used in combination, but the amount thereof is the characteristics of the present invention such as durability, heat resistance, moisture resistance, mechanical strength, and dispersibility. It is limited to the range that retains the properties and is not specified in advance depending on the properties of the polyol, but generally it should be 30 mol% or less of the total polyol.

The chain extender that can be used in the present invention includes short chain diols, diamines, alkanolamines, and the like. For example, as the short chain diol, ethylene glycol,
1,3-propylene glycol, 1,2-propylene glycol, 1,4-BD, 1,5-pentanediol, 1,6-HD, neopentyl glycol, 1,8-octanediol, 1,9-nonanediol , Diethylene glycol, cyclohexane-1,4-diol, cyclohexane-1,4-dimethanol or diol such as ethylene oxide or propylene oxide adduct of bisphenol A, hexamethylenediamine, xylenediamine, isophoronediamine (hereinafter abbreviated as IPDA), Monoethanolamine (hereinafter MEA
And a diamine such as N, N′-dimethylethylenediamine or an amino alcohol.
Water and urea, which react with the isocyanate group shown by 61-107531 to form a urea bond, can also be used as a chain extender. These above compounds can be used alone or in the form of a mixture thereof.

Examples of the organic diisocyanate (C) that can be used in the present invention include 2,4-tolylene diisocyanate and 2,6
-Tolylene diisocyanate, xylene-1,4-diisocyanate, xylene-1,3-diisocyanate, 4,4 '
Diphenylmethane diisocyanate (hereinafter abbreviated as MDI), 4,4'-diphenyl ether diisocyanate,
2-nitrodiphenyl-4,4'-diisocyanate, 2,
2'-diphenylpropane-4,4'-diisocyanate,
3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, Aromatic diisocyanates such as 3,3′-dimethoxydiphenyl-4,4′-diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, aliphatic diisocyanates such as lysine diisocyanate, isophorone diisocyanate (hereinafter abbreviated as IPDI), hydrogenated tolylene diene Examples thereof include isocyanates and alicyclic diisocyanates such as hydrogenated diphenylmethane diisocyanate.

The molecular weight of the polyurethane resin used in the magnetic recording medium of the present invention is 5,000 to 100,000. If it is less than 5,000, there is no film forming ability because the molecular weight is too small when the polyisocyanate curing agent is not used together, and when the polyisocyanate curing agent is used together, the number of cross-linking points becomes too large and the flexibility and characteristic of the polyurethane resin Wear resistance and elongation are lost, which is not preferable. Generally, the molecular weight of a binder of a magnetic recording medium is related to dispersibility and durability. The lower the molecular weight, the higher the dispersibility but the lower the durability, and the higher the polymer, the lower the dispersibility, but the more advantageous the durability. Generally, it is thought that the polyurethane resin binder of the magnetic recording medium has poor solubility in the solvent used for the magnetic paint, but when the molecular weight is high, the solution viscosity of the polyurethane resin solution becomes high and it is difficult to handle when making the magnetic paint. Since there is a certain limit to increasing the molecular weight in order to enhance the durability because the dispersibility of the magnetic powder will be drastically reduced, the limit was about 100,000, the polyurethane resin binder of the present invention, as described above. Thus, even if the solvent used in magnetic paint has good solubility and the molecular weight is increased, the solution viscosity of the polyurethane resin solution does not become as high as expected, and it is not as sharp as the polyurethane resin binder of general magnetic recording media. No decrease in dispersibility.

In the production of the polyurethane resin according to the present invention, a known method, for example, a bulk polymerization (solid reaction) method of reacting in a molten state, a ketone solvent such as MEK, MIBK and cyclohexanone, an ester such as ethyl acetate or butyl acetate. Solvents, ether solvents such as dioxane, tetrahydrofuran, glycol ethers known as cellosolve, carbitol, etc., acetic acid glycol ethers such as cellosolve acetate, amide solvents such as dimethylacetamide, dimethylformamide, aromas such as toluene, xylene, etc. It is possible to use a solution polymerization method in which the above-mentioned components are reacted in a state of being dissolved in a single solvent or a mixed solvent of a group hydrocarbon solvent, an alcohol solvent such as methanol, ethanol, and isopropanol. When producing the polyurethane resin according to the present invention, a catalyst and a stabilizer can be used if necessary. Examples of the catalyst include nitrogen-containing compounds such as triethylamine and triethylenediamine, dibutyltin dilaurate (hereinafter abbreviated as DBTDL), organometallic compounds such as tin octylate and zinc stearate. As a stabilizer, for example, an ultraviolet absorber such as a substituted benzotriazole, an antioxidant such as a phenol derivative, and a hydrolysis inhibitor can be added as necessary. 2 to the polyurethane resin
When a polyisocyanate curing agent having a functionality or higher is used in combination, a magnetic recording medium having more excellent heat resistance, durability and abrasion resistance can be obtained.

As the bifunctional or higher functional polyisocyanate used as the curing agent, the organic diisocyanate compounds and polymers thereof and the bifunctional or higher functional polyols mentioned as examples of the essential component (C) organic diisocyanate of the polyurethane resin of the present invention may be used. Suitable polyisocyanates having an isocyanate group obtained by reaction with an organic diisocyanate compound and a polymer thereof, polymeric polyisocyanates, polyol adducts of isocyanates,
Examples thereof include isocyanurate and carbodiimide modified products, and the amount thereof should be in the range of 5% to 30% with respect to the binder.

Other resins used in combination with the polyurethane resin of the present invention as a binder of a magnetic recording medium include various polyurethane resins, vinyl chloride-vinyl acetate polymers, polybutyl butyral resins, fibrin resin, polyester resins, Epoxy resins and phenoxy resins, thermosetting resins such as acrylonitrile-butadiene copolymer or reactive resins and unsaturated prepolymers such as urethane acryl type, polyester acryl type, phosphoric acid ester acryl type, allyl type electron beam or Examples thereof include UV curable resins.

The magnetic powder used in the present invention is, for example, γ-Fe ₂ O ₃ , C
O-containing iron oxide magnetic powder such as γ-Fe ₂ O ₃ , OrO ₂ , barium ferrite, and Fe, Ni, Co, Fe-Ni-Co alloy, Fe-Mn-Zn
Various ferromagnetic powders such as alloys can be used.

The polyurethane resin according to the present invention, in addition to magnetic recording media, paints, adhesives, sealing agents, waterproofing agents, flooring materials, artificial leather, fiber treatment agents, elastic fibers, cushioning materials, sheets,
Belts, films, rolls, gears, solid tires,
It can be used for anti-vibration materials, tubes, packing materials, shoe soles (microcellular), etc.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples. The components, ratios, operation sequences and the like shown below can be changed without departing from the spirit of the present invention. "Parts" and "%" in the examples are "parts by weight" and "% by weight" unless otherwise specified.

Synthesis of long-chain polyol (polyester diol) A 2-liter glass 4-neck reaction vessel equipped with a distillation column equipped with a stainless steel stirring blade, a fractionating head with an inner diameter of 18 mm and a height of 300 mm with a reflux condenser, and a nitrogen inlet pipe. Add the diol and dicarboxylic acid shown in Table.1, then add tetrabutyl titanate as a catalyst. The reaction vessel is stirred and heated while passing nitrogen gas under normal pressure, the internal temperature is kept at 190 to 200 ° C., and the produced water is distilled off. When the acid value of the produced ester becomes 1 or less, the vacuum degree is reduced at a rate of 50 to 100 mmHg / 1 hour and finally 2
The state was set to 0 mmHg and the state was maintained for 2 hours to complete the reaction. The characteristic values of the obtained long-chain polyols A, B, C and D are shown in Table 1. The molecular weight is a value calculated from the hydroxyl value.

Furthermore, by structural analysis by ¹³ C-NMR, IR, elemental analysis, etc., it was confirmed that the long-chain polyols A and B were polyester diols derived from 3MPD and AA having OH groups at both ends.

In addition, in the same structural analysis, long-chain polyol C was
It was confirmed that it was derived from AA with 3MPD / 1,4-BD having OH group = 75/25 (molar ratio).

Similarly, long-chain polyol D is 3MPD having an OH group.
/ 1,6-HD = 80/20 (molar ratio) and AA / isophthalic acid = 50/50
(Mole comparison).

Production of polyurethane resin (pu-1-5) In a reaction vessel equipped with a thermometer, stirrer and condenser,
MEK of long chain polyols, chain extenders and solvents shown in Table 2
(1) and the urethanization catalyst (DBTDL) were added and mixed at 40 ° C., and then diisocyanate was added. The reaction generated heat, the internal temperature reached about 80 ° C, and the viscosity increased with time. MEK and cyclohexanone were appropriately added and diluted, and the mixture was kept at this temperature for reaction for 7 hours. MEK amount (2) and cyclohexanone amount (3) were used to obtain a uniform transparent solution. The characteristic values of these polyurethane resins pu-1 to 5 are shown in Table.2.
The molecular weight was determined by GPC.

Polyurethane resin production (pu-6) In the same reaction vessel used for polyurethane resin production (pu-1-5), long-chain polyol C1020 parts, 3MPD59.0 parts, solvent MEK
After adding 1,500 parts and 0.5 part of DBTDL and mixing at 40 ° C., 500.0 parts of isophorone diisocyanate were added. The reaction caused heat generation, the internal temperature reached about 80 ° C, and the viscosity increased slightly with time. The temperature was maintained and the reaction was carried out for 7 hours to obtain an isocyanate group-terminated prepolymer. Then, 1500 parts of cyclohexanone was added and diluted, 115.0 parts of isophoronediamine and 9.1 parts of monoethanolamine having an amine group concentration corresponding to the equivalent isocyanate group content were mixed and dissolved in 970 parts of MEK, and then added from a charging port. The urea formation reaction between the amine group and the prepolymer caused a rapid increase in viscosity, and after 30 minutes, the isocyanate group disappeared, and a uniform transparent solution was obtained. This polyurethane urea resin (pu-6) solution has a solid content of 30%, a viscosity of 6,000 cps / 25 ° C, and a molecular weight of 24,00.
It was 0.

Production of polyurethane resin (pu-7) Long-chain polyol A990 parts, 1,6 in a stainless steel beaker
-Take 59 parts of HG and mix it slowly with a desktop stirrer.
After the temperature was adjusted to ℃, 371.8 parts of flaky MDI was added, and high speed stirring was performed at 2000 rpm for 1 minute.
The mixture was poured onto a heated vat and then left standing at that temperature for 20 hours to complete the reaction. This resin (pu-7) can be easily pelletized with a pelletizer and easily dissolved in MEK / cyclohexanone = 70/30 solvent, with a solid content of 20% and a viscosity of 1,3
It became 00cst / 25 ℃. The molecular weight was 65,000.

Production of Polyurethane Resin (pu-8,9), Comparative Synthesis Examples 1,2 Solid reaction similar to that of pu-7, long-chain polyol B (hydroxyl value 55.2, molecular weight 2,033) and polybutylene adipate (molecular weight 2000) were used as polyols. , 1,4-B as a chain extender
D, MDI as a diisocyanate, 1.0 mol of polyol to 1.0 mol of polyol, 1.0 mol of MDI fixed to 2,0 mol of MDI resin (PU-8, 9) in which the ratio between the polyols was changed, and Comparative Synthesis Example 1, Got 2 The composition properties are shown in Table 3.

Comparative Synthesis Example 3 A homogeneous transparent solution was obtained by the same procedure except that 1000 parts of polybutylene adipate (hydroxyl value 56.1) was used instead of 990 parts of the long-chain polyol A in PU-1. This polyurethane resin solution has a solid content of 30% and a viscosity of 15,000 cSt / 25 ° C.
And its molecular weight was 32,000.

Durability of clear film PU-1 to 9 and resins of Comparative Synthesis Examples 1 to 3 were tested for durability of clear film.

Preparation of clear film: Polyisocyanate (Coronate L) 10 parts (each solid content conversion) was added to 100 parts of resin, and it was coated on a release paper with a knife coater so that a dry film thickness was 100 μm, and after 15 minutes at 80 ° C., 120 ° C. 30 minutes at 6
The sample was cured and dried at 0 ° C. for 3 days to be a sample for durability evaluation.

Heat-resistant water test: The heat-resistant water properties were measured by cutting the sample with JIS No. 4 dumbbell and leaving it in hot water at 80 ° C for 2 weeks.
Tested according to JIS K6301.

TB: Strength at break (Kg / cm ² ) EB: Elongation at break (%) Mold resistance: 5 as described in JIS Z2911-1960 mold resistance test with a clear film made on glucose agar base attached.
Using a fungus of the species, the state of deterioration of the surface was observed by culturing at 30 ° C × 90% RH. The results are shown in Table 4.

Evaluation of Magnetic Paint and Magnetic Layer Example 1 Polyurethane (PU-1) was used to disperse a composition having the following blending ratio in a tabletop sand grind mill (made by Igarashi Kikai KK) for 3 hours, 5 hours, and 8 hours. The obtained magnetic paint was applied on a polyethylene terephthalate film having a thickness of 12 μm and then dried so as to have a thickness of 5 μm, and dried, and the time dependence of the magnetic powder dispersibility was observed from each glossiness and 50 times microscope observation ( (Table 5). Also, 10 wt% of polyurethane resin (A) in terms of resin was added as a curing agent to Coronate-L (manufactured by Nippon Polyurethane Industry Co., Ltd.) as a polyisocyanate group to the magnetic paint obtained by dispersing for the last 8 hours, and further mixed for 1 hour. Thus, a polyethylene terephthalate film having a thickness of 12 μm was applied while being applied with a magnetic field of 2,000 gauss so as to have a thickness of 5 μm after drying, and then left at 60 ° C. for 1 day to obtain a magnetic tape.

Co-γ-Fe ₂ O ₃ 100 parts Polyurethane resin (PU-1) (resin content) 25 parts Lecithin 2 parts Toluene 110 parts MEK 110 parts Cyclohexanone 70 parts Examples 2-9, Comparative Examples 1-4 In Example 1. Using the resins PU-2 to 9 and the polyurethane resins obtained in Comparative Synthesis Examples 1 to 3 instead of the used polyurethane resin (PU-1), the dispersibility and magnetic tape characteristics were evaluated in the same formulation as in Example 1. did. The results are shown in Table 5.

Time dependence of dispersibility: The reflectance of the coating surface from the paint at each dispersion time was observed with a gloss meter at an incident angle of 60 degrees and a reflection angle of 60 degrees. Glossiness: At a incidence angle of 60 degrees with a reflection angle of 60 degrees Seeing reflectance Change in running dynamic friction: 60 ° C x 95% RH x Change in dynamic friction coefficient during running test within 2 weeks Durability: 60 ° C x 95% RH x Adhesion with base after storage for 2 weeks and extraction The deterioration of the binder was observed by the test.

The symbols in each item are as follows.

◎: Change rate of 5% or less ○: Change rate of 5% to 10% △: Change rate of 10% to 20% ×: Change rate of 20% or more As is clear from Tables 3, 4, and 5, Invention Polyurethane resin containing a polyester polyol containing OH and a magnetic recording medium using the same as the binder of the magnetic layer are excellent in dispersibility, durability, particularly water resistance and mold resistance.

[Advantages of the Invention] By using the polyurethane resin of the present invention as a binder of a magnetic layer, it has excellent performances such as durability, heat resistance, moisture resistance, mechanical strength, and mold resistance, and dispersion of magnetic powder. Is also good, the packing density can be increased, long running,
It is possible to obtain a magnetic recording medium which is excellent in high reliability upon storage with time and has good electromagnetic conversion characteristics and surface properties.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a magnetic layer mainly composed of a ferromagnetic powder and a binder formed on a non-magnetic support, wherein a polyurethane resin contained as a binder constituting the magnetic layer has a molecular weight of (A). A long-chain polyol of 500 to 5,000, (B) a chain extender having a molecular weight of 50 to less than 500, and (C) diisocyanate.
In its chain A polyester polyol having a molecular weight of 5,000
A magnetic recording medium characterized by being up to 100,000 segmented polyurethane resin.