JP2001019738A - Thermoplastic polyurethane resin for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyurethane having stable quality without sublimability by melt blending a polyester diol with a low-molecular diol having <=500 molecular weight, reducing the melt viscosity, enabling the melt polymerization and further using a diol having >=200 molecular weight and/or a diol which is a liquid at 20 deg.C as the low-molecular diol. SOLUTION: This thermoplastic polyurethane resin for a magnetic recording medium is obtained by using a component B which is a diol having >=200 molecular weight or a diol that is a liquid at 20 deg.C in the thermoplastic polyurethane obtained by reacting one or more kinds of polyester diols having <=2,000 molecular weight (component A) with the low-molecular diol having <=500 molecular weight (component B) and an organic diisocyanate compound (component C) in a molten state. The polyurethane resin prepared by the method for production can be used as a binder for a magnetic tape to thereby provide the magnetic recording medium having high magnetic powder stability and high durability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder used for a magnetic recording medium such as a magnetic tape and a magnetic disk.

[0002]

2. Description of the Related Art Magnetic tapes, which are general-purpose magnetic recording media,
A floppy disk is made by dispersing needle-shaped magnetic particles having a major axis of 1 μm or less together with additives such as a dispersant, a lubricant and an antistatic agent in a binder solution to form a magnetic paint, and applying this to a polyethylene terephthalate film. It is made.

[0003] The properties required for the binder of the magnetic layer include the dispersibility of magnetic particles, the filling property, the orientation, the durability of the magnetic layer, the abrasion resistance, the heat resistance, the adhesion to the non-magnetic support and the like. And binders play a very important role.

As binders for the magnetic layer, polyurethane resins, polyester resins, nitrocellulose, vinyl chloride / vinyl acetate copolymers, vinyl chloride / vinyl acetate / vinyl alcohol copolymers, acrylonitrile / butadiene copolymers, epoxy resins , Acrylic resin and the like are mainly used.

Among these resins, polyurethane resins are excellent in toughness and abrasion resistance due to intermolecular hydrogen bonding by urethane bonds. It is known that the introduction of a metal sulfonate group into polyurethane as described in JP-A-54-157603 is extremely effective in improving the dispersibility of magnetic powder.

[0006] Further, the polyurethane resin used was mainly a melt type before, but recently, from the viewpoint of cost reduction of a magnetic tape maker, the mainstream has shifted to a solid type which can keep production costs and transportation costs low. And Japanese Patent Publication No. 58-8053, 6
Japanese Patent Application Laid-Open No. 1-231050 and Japanese Patent Publication No. 3-13648 have been proposed.

[0007]

The thermoplastic polyurethane resin obtained by the reaction in the molten state supplies the polyester diol component to the extruder while maintaining a constant flow rate in the molten state, and the polyester diol component is mixed with the corresponding amount of isocyanate in the molten state. It is obtained by reacting. Therefore, it is desirable that the melt viscosity be low in order to quantitatively feed the polyester diol component. When a polyester diol having a high melt viscosity is used, it is difficult to supply the polyester diol at a constant flow rate.

In order to enhance the dispersibility of the magnetic component, it is preferable to introduce a polar group such as a sulfonate group or a phosphonate group. As a result, it becomes difficult to obtain a stable quality polyurethane resin such as a broad molecular weight distribution. When a single component is a polyester diol component having a low melt viscosity, most of the polyester diol component is a polyester diol mainly composed of an aliphatic dibasic acid.

In recent years, it has become an essential condition to impart durability to a magnetic recording medium, but for that purpose, it is necessary to raise the glass transition temperature. However, when a polyester diol mainly composed of an aliphatic dibasic acid is used, the glass transition temperature has been raised by using an aromatic diisocyanate to increase the urethane group concentration. However, when the urethane group concentration is increased, the solubility in a general-purpose solvent decreases, and there is a problem that the dispersibility of the magnetic particles decreases. In addition, there is also a means of blending a low-molecular diol or the like with a polyester diol having a high melt viscosity using an aromatic dicarboxylic acid to reduce the melt viscosity, but when a low-molecular diol that is solid at room temperature with sublimation is used, Sublimation occurs in the mixing tank before being supplied to the extruder, and as a result, the OH
And the NCO value of the isocyanate fluctuate, making it difficult to obtain a stable polyurethane resin.

[0010]

Means for Solving the Problems As a result of intensive studies on the polyurethane resin, the present inventors have reached the present invention. That is, the present invention relates to a heat obtained by reacting at least one kind of polyester diol (component A) having a molecular weight of 2,000 or less, a low molecular diol (component B) having a molecular weight of 500 or less, and an organic diisocyanate compound (component C) in a molten state. An object of the present invention is to provide a thermoplastic polyurethane resin for a magnetic recording medium, wherein the B component is a diol having a molecular weight of 200 or more and / or a diol liquid at 20 ° C.

That is, by mixing a polyester diol having a molecular weight of 2000 or less and a low molecular weight diol having a molecular weight of 500 or less in a molten state, the melt viscosity can be reduced and the mixture can be supplied into the extruder at a constant flow rate. In addition, the low molecular weight diol used at this time uses a diol that is liquid at a molecular weight of 200 or more and / or 20 ° C., so that sublimation does not occur in a mixing tank before being supplied to an extruder,
A solid polyurethane resin of stable quality can be obtained. The components of the polyester diol (A) used here are dibasic acid components, and aromatic dicarboxylic acids are terephthalic acid, isophthalic acid, orthophthalic acid, 1,5
1,4-naphthalic acid, 2,6-naphthalic acid, 4,4′-diphenyldicarboxylic acid, 2,2′-diphenyldicarboxylic acid, 4,4′-diphenylether dicarboxylic acid, etc. Cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,
2-cyclohexanedicarboxylic acid, 4-methyl-1,2
-Cyclohexanedicarboxylic acid, dimer acid, aliphatic dicarboxylic acid include adipic acid, azelaic acid, sebacic acid, dodecandioic acid, etc. As the dicarboxylic acid, it is desirable to use isophthalic acid, orthophthalic acid, alicyclic dicarboxylic acid, or aliphatic dicarboxylic acid.

As the glycol component, specifically, ethylene glycol, 1,3-propanediol, 1,2-butanediol, 1,4-butanediol, 2-methyl-
1,3-propanediol, neopentyl glycol,
1,5-pentanediole, 1,6-hexanediol-
2-butyl-2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2
4-trimethyl-1,3-pentaneddiol, 2-methyloctanediol, diethylene glycol, dipropylene glycol, cyclohexanedimethanol, 1,9
-Nonanediol, 1,10-dodecanediol, tricyclodecanedimethanol, neopentyl hydroxypivalate, ethylene oxide adduct and propylene oxide adduct of bisphenol A, ethylene oxide adduct of hydrogenated bisphenol A And propylene oxide adducts. Especially, neopentyl glycol, 2-butyl-2-ethyl-
1,3 propanediol and neopentyl hydroxypivalate are preferred.

The polyester diol desirably contains a metal sulfonate group in the molecule for the purpose of the present invention. As a raw material for introducing the metal sulfonate group, 5-sodium sulfoisophthalic acid and 5-potassium sulfo acid are used as raw materials. Isophthalic acid, sodium sulfoterephthalic acid,
2-sodium sulfo-1,4-butanediol, 2,
Examples thereof include dicarboxylic acids such as 5-dimethyl-3-sodium sulfo-2,5-hexanediol and glycols, and 5-sodium sulfoisophthalic acid and 5-potassium sulfoisophthalic acid are preferred. The amount of the sulfonic acid metal base in the polyester diol is 10 to 400 equivalent / 10
It is contained in the range of ⁶ g. If it is less than 10 equivalents / 10 ⁶ g, the dispersibility of the magnetic powder is insufficient, and 400 equivalents / 10 ⁶ g.
When the viscosity exceeds the above range, the viscosity of the polyurethane resin solution or the magnetic paint becomes high, and the obstacles in handling and production of the magnetic recording medium increase. A particularly preferred range is 40 to 200 equivalents / 10 ⁶ g.

The polyester diol (A) used in the polyurethane resin of the present invention has a molecular weight of 2,000 or less, preferably 1,000 or less. When the molecular weight exceeds 2,000, the melt viscosity of the polyester diol increases,
It becomes difficult to control the flow rate to the extruder.

The low molecular weight diol (B) having a molecular weight of 500 or less used here is used in a molten state to reduce the melt viscosity of the polyester diol. Examples of the glycol having a molecular weight of 200 or more include diol compounds such as neopentyl hydroxypivalate, bisphenol A ethylene oxide adducts and propylene oxide adducts, and hydrogenated bisphenol A ethylene oxide adducts and propylene oxide adducts. , Polypropylene glycol and the like at 20 ° C.
And liquid glycols such as ethylene glycol, propylene glycol, 1,3-propanediol,
-Butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,5-pentaneddiol, 3-methyl-1,5-pentaneddiol, diethylene glycol, Dipropylene glycol. Especially neopentyl hydroxypivalate,
1,4-butanediol and 2-methyl-1,3-propanediol are preferred.

The organic diisocyanate component (D) of the polyurethane resin used in the present invention includes 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate.
G, p-phenylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate
, Hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy-4,4'-
Biphenylene diisocyanate, 1,5-naphthalenediisocyanate, 2,6-naphthalenediisocyanate, 3,3'-dimethyl-4,4'-diisocyanate
G, 4,4'-diisocyanate-to-diphenyl ether,
1,5-xylylene diisocyanate, 1,3-diisocyanatomethylcyclohexane, 1,4-diisocyanatomethylcyclohexane, 4,4'-diisocyanatocyclohexane, 4,4'-diisocyanatocyclohexyl Methane, isophorone diisocyanate and the like can be mentioned.

The polyurethane resin of the present invention has a molecular weight of 50.
00 to 40,000, preferably 10,000 to 300
00 is used. If the molecular weight is less than 5000, the mechanical strength is insufficient, and the running durability is poor. 40,000 molecular weight
If the ratio exceeds the above range, gelation is likely to occur, dispersibility of magnetic powder, abrasive, carbon black, etc. is deteriorated, and viscosity of the magnetic paint increases.

Although the polyurethane resin of the present invention can be obtained by various methods such as solution polymerization and solid phase polymerization, a polymerization method based on melt polymerization is desirable because low cost of general-purpose magnetic tape materials is required.

In the present invention, in addition to the polyurethane resin used in the present invention, other resins are added for the purpose of controlling flexibility, improving cold resistance and heat resistance, and / or adding a crosslinking agent. It is desirable to mix. Other resins include vinyl chloride resin, cellulose resin, polyester resin, epoxy resin, phenoxy resin, polyvinyl butyral, acrylonitrile / butadiene copolymer and the like. On the other hand, examples of the crosslinking agent include a polyisocyanate compound, an epoxy resin, a melamine resin, a urea resin, an acid anhydride and the like, and among these, a polyisocyanate compound is particularly preferable.

The ferromagnetic particles used in the magnetic layer of the magnetic recording medium of the present invention include γ-Fe ₂ O ₃ and γ-Fe ₂ O
Mixed crystal of ₃ and Fe ₃ O ₄ , γ-Fe ₂ O ₃ coated with cobalt
Alternatively, ferromagnetic oxides such as Fe ₂ O ₄ and barium ferrite, and ferromagnetic alloy powders such as Fe—Co and Fe—Co—Ni can be given.

In the magnetic recording medium of the present invention, if necessary, a plasticizer such as dibutyl phthalate or triphenyl phosphate, dioctyl sodium sulfosuccinate, t-butylphenol polyethylene ether, sodium ethylnaphthalene sulfonate, dilauryl succinate Lubricants such as zinc stearate, soybean oil lecithin and silicone oil, and various antistatic agents can also be added.

[0022]

A low-molecular-weight diol having a molecular weight of 500 or less is melt-blended with a polyester diol having a high melt viscosity to lower the melt viscosity to obtain a polyurethane resin raw material suitable for a melt reaction. Also, low molecular weight diols have a molecular weight of 200
By using liquid glycol at 20 ° C. or above, sublimation does not occur in the mixing tank before supply to the extruder, and a stable quality polyurethane resin can be obtained. The obtained polyurethane resin of the present invention mainly comprises an aromatic polyester polyol component, and has a high glass transition temperature and good solubility in general-purpose solvents such as MEK, toluene and cyclohexanone. As a result, when used as a magnetic recording binder, it has excellent dispersibility of magnetic particles and durability of a magnetic recording medium.

[0023]

The present invention will be specifically illustrated by the following examples. In the examples, “parts” means “parts by weight”. Synthesis examples of polyurethane resin 1-4 Polyester polyol (A) and low molecular diol (B)
Are mixed in a molten state at a mixing ratio of 100/20 (weight ratio) and charged into an extruder, and the organic diisocyanate and the NCO value /
The reaction was performed at an OH value of 0.98. The reaction was carried out at an extruder internal temperature of 180 ° C. and a screw rotation speed of 200. Table 1 shows the characteristics of the polyurethane resin taken out from the nozzle.

[0024]

[Table 1]

Raw material composition and number average molecular weight of abbreviations in the table
(Mn) is as follows. Polyesterdiol (A) Polyol A-1 OPA / DSN // NPG / CHDM / HD (96/4 // 60/20/20 molar ratio) MN = 500 Polyol A-2 IPA / DSN // HPN / EG / CHDM (96/4 // 75/15/10 molar ratio) MN = 600 Polyol A-3 IPA / 1,4CH / DSN // NPG / CHDM / HD (60/36/4 // 50/30/20 molar ratio ) MN = 600 Poly A-4 OPA / AA / DSN // NPG / HD / CHDM (56/40/4 // 60/15/25 molar ratio) MN = 500 Poly A-5 AA / DSN // NPG / CHDM / HD (96/4 // 65/15/20 molar ratio) MN = 500 OPA: orthophthalic acid IPA: isophthalic acid 1,4CH: 1,4-cyclohexanedicarboxylic acid AA: adipic acid DSN: dimethyl 5-sodium sulfo Isophthalic acid NPG: neopentyl glycol HPN: neopentyl hydroxypivalate EG: ethylene glycol CHDM: cyclohexane dimethanol HD: hexanediol Low molecular diol (B) HPN: neopentyl hydroxypival Acid ester 1,4-BD: 1,4-butanediol 2MG: 2-methyl-1,3-propanediol NPG: neopentyl glycol

Comparative Synthesis Examples 1 and 2 of Polyurethane Resin A polyurethane resin was obtained from the raw materials shown in Table 1 in the same manner as in Synthesis Example 1 of polyurethane resin. Table 1 shows the properties of the obtained polyurethane resin.

The number average molecular weight of the polyurethane resin was indicated by gel permeation chromatography in a tetrahydrofuran solution, and the glass transition temperature was indicated by the temperature at the inflection point of the dynamic viscoelasticity storage elastic modulus (E ') measured at 110 Hz. .

Degree of sublimation of low molecular weight diol After the weight of the polyester diol and low molecular weight diol melt-mixed was measured in advance, the mixture was left standing in an oven at 90 ° C. for 12 hours, and the weight after standing was measured to determine the degree of sublimation. Was. Sublimation degree = (initial weight-weight after standing at 90 ° C) ÷ initial weight

Example 1 A composition having the following composition ratio was dispersed in a ball mill for 24 hours, and then a polyisocyanate compound, Millionate MR (manufactured by Nippon Polyurethane Industry Co., Ltd.) was used as a curing agent.
Parts, 0.2 parts of stearic acid and 0.2 parts of butyl stearate were added as a lubricant, and the mixture was further mixed for 1 hour to obtain a magnetic paint. This magnetic paint was applied on a 15 μm-thick polyethylene terephthalate film so that the thickness after drying was 4 μm, and dried while applying a magnetic field of 2000 Gauss.
It was passed through a calender roll at 80 ° C. and a linear pressure of 200 kg / cm to smooth the surface of the magnetic layer to prepare a magnetic tape. The obtained magnetic tape was left at 60 ° C. for 1 day and slit to イ ン チ inch. 30% solution of polyurethane resin obtained in Synthesis Example 1 10 (30% solution of MEK / toluene = 1/1) Magnetic powder (cobalt-coated ferrite BET 45 m ² / g) 15 Cyclohexanone 8 Toluene 8 MEK 8

Examples 2 to 12 Comparative Examples 1 to 8 In the same manner as in Example 1, magnetic tapes were prepared using the polyurethane resins shown in Table 1. The characteristics are shown in Tables 2 and 3.

[0031]

[Table 2]

[0032]

[Table 3] In the table, MAG527 represents a PVC-based copolymer manufactured by UCC.

The gloss of the magnetic layer of the magnetic tape was measured using a 60-degree gloss meter. The squareness ratio of the magnetic layer was measured by using a vibration sample magnetometer (Model BHV-50 manufactured by Riken Denshi Co., Ltd.) in the direction perpendicular to the coating direction.

The wear resistance of the magnetic layer was 4
The state of wear of the magnetic layer after running 100 times at 0 ° C. was observed.
The results are shown in Tables 2 and 3.

[0035]

By using the polyurethane resin obtained by the production method of the present invention as a binder for a magnetic tape, it becomes possible to obtain a magnetic recording medium having both high magnetic powder stability and durability.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J034 BA08 CA04 CB03 CC02 CC03 CC08 DF01 DF16 DF21 DF22 HA01 HA07 HC03 HC12 HC17 HC22 HC64 HC67 HC71 HC73 JA01 QA05 QA07 RA16 4J038 DG111 DG261 MA14 NA22 5D006 BA15 FA00 FA02

Claims (1)

[Claims] 1. A polymer obtained by reacting at least one kind of polyester diol (component A) having a molecular weight of 2,000 or less, a low molecular diol (component B) having a molecular weight of 500 or less, and an organic diisocyanate compound (component C) in a molten state. The thermoplastic polyurethane resin for a magnetic recording medium, wherein the B component is a diol having a molecular weight of 200 or more and / or a diol liquid at 20 ° C. in the thermoplastic polyurethane.