JPS60242516A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having excellent heat resistance, durability, etc. by using a binder prepd. by bringing org. diisocyanate, long chain diol having the mol.wt. in a specific range and ester group-contg. diol having the mol.wt. below a specific value into reaction on a non-magnetic base. CONSTITUTION:The magnetic layer contg. the thermoplastic polyurethane resin formed by bringing the polyester diol which has <=500mol.wt. and expressed by formulas I, II, III (R1, R2, R5, R6, R7 are bivalent hydrocarbon groups, R1 is a trivalent hydrocarbon group, R4 is a monovalent hydrocarbon group), the long chain polyester diol, polyether diol, polycarbonate diol, etc. having the mol.wt. within a 500-8,000 range and org. diisocyanate into reaction as a binder for ferromagnetic powder is formed on the non-magnetic base. Solubility in a general- purpose org. solvent is improved by using the diol expressed by formulas I - IIIand good coatability and dryability are obtained even if the concn. of the urethane base is increased. The magnetic recording medium having excellent heat resistance, wear resistance, durability, etc. is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks. More specifically, the present invention relates to a magnetic recording medium using a thermoplastic polyurethane resin having excellent properties as a binder component of a magnetic layer provided on a nonmagnetic support.

(Relationship with conventional technology) Magnetic tape, which is a general-purpose magnetic recording medium, consists of acicular magnetic particles with a long axis of 1 μm or less in a binder solution along with appropriate additives (dispersants, lubricants, antistatic agents, etc.). A magnetic paint is created by dispersing it in a polyethylene terephthalate film. Conventionally used binders for magnetic particles include vinyl chloride/vinyl acetate copolymer, vinyl chloride Φ vinyl acetate/vinyl alcohol copolymer, vinyl chloride/vinylidene chloride copolymer, polyurethane resin, polyester resin, Acrylonitrile-butadiene copolymers, nitrocellulose, cellulose acetate-butyrate, epoxy resins, acrylic resins, etc. are used. Among these resins, polyurethane resin has properties such as excellent toughness and abrasion resistance that cannot be obtained with other resins due to intermolecular hydrogen bonding caused by urethane bonds, but it is also used for video tapes, computer tapes, floppy disks, etc. Applications that require high performance
cannot be said to be sufficient.

Thermoplastic polyurethane resins, which have traditionally been used as binders for magnetic recording media such as magnetic tapes, can be used by dissolving them in general-purpose organic solvents such as toluene, methyl ethyl ketone, ethyl acetate, butyl acetate, or mixed solvents thereof. It is being However, this general-purpose solvent-soluble thermoplastic polyurethane resin has insufficient properties such as heat resistance, durability, and abrasion resistance. It is known to increase the urethane group concentration in order to improve these properties, but in this case, it becomes insoluble in the general-purpose organic solvents mentioned above, and is insoluble in high-boiling point solvents such as dimethylformamide, N-methylpyrrolidone, and dimethylsulfoxide. It is soluble only in cyclic ethers such as , tetrahydrophthene, and dioxane. These high boiling point, highly polar solvents cause serious problems such as swelling, φ-curving or dissolution of the non-magnetic support, and poor drying properties resulting in reduced workability. There was a limit to the improvement achieved by increasing the urethane group concentration in this way.

(Purpose of the Invention) In order to eliminate the above-mentioned drawbacks, the present inventors have conducted intensive studies on various thermoplastic polyurethane resins, and found that one of the raw materials is
It has been found that by using an ester group-containing diol with a molecular weight of less than 500 as a component, the urethane group concentration can be increased without reducing the solubility in general-purpose organic solvents. It has been found that a magnetic recording medium using this thermoplastic polyurethane resin as a bander for a magnetic layer has extremely excellent properties such as heat resistance, durability, and abrasion resistance.

(Structure of the Invention) That is, the present invention provides a magnetic recording medium in which a magnetic material in which ferromagnetic powder is dispersed in a binder is coated on a non-magnetic support, in which an organic material is used as at least one component of the binder. Diisocyanate (3), a long-chain diol with a molecular weight of 500 to 8,000 (Bl) and a compound with a molecular weight of less than 500 containing two active hydrogens in the molecule (0), and a thermoplastic polyurethane resin that has two active hydrogen atoms in the molecule. (Q is the following general formula (1) to (2)
) is a magnetic recording medium characterized by using a polyurethane resin containing at least one type of ester group-containing diol.

1 [01'J QCR20H (1) 0 0 jl II HOR5QCR6, COR70H (2) C In the formula, R11
R2, R5, Re, and R'r represent a divalent hydrocarbon group, R8 represents a trivalent hydrocarbon group, and R3 represents a monovalent hydrocarbon group. ] The organic diincyanate used in the present invention includes:
2.4-1 lylene diisocyanate, 2.6-lylene diisocyanate, p-phenylene diisocyanate,
diphenylmethane diisocyanate), m-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diynylene diisocyanate, 2.4-naphthalene diisocyanate), 4.4-diphenylene diisocyanate), 4.4'- Diisocyanate-diphenyl ether, 1,5-naphculene isocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,3-diincyanetomethylcyclohexane, l,4-diisocyanatemethylcyclohexane, 4,4'-diisocyanate diisocyanate Examples include cyclohexane, 4,4'-diisocyanate cyclohexylmethane, and isophorone diisocyanate.

Further, the long-chain diol CB) used in the present invention includes 6D, polyester diol, polyether diol, polycarbonate diol, etc. having a molecular weight in the range of 500 to s, ooo.

The carboxylic components of polyester diol include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and 1,5-naphthalic acid, aromatic dicarboxylic acids such as p-oxybenzoic acid, and p-(-hydroxyethoxybenzoic acid). Examples include aliphatic dicarboxylic acids such as group oxycarboxylic acids, succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid.Terephthalic acid, isophthalic acid, adipic acid, and sebacic acid are particularly preferred.

Glycol components of mata polyester diol include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-bentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, Cyfropylene glycol, 2,2,4-trimethyl-1,3-bentanediol, cyclohexane dimetatool, ethylene oxide and propylene oxide adducts of bisphenol A, ethylene oxide adducts and propylene oxide of hydrogenated bisphenol A Adducts include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc.

Raw materials for polyester diol other than those listed above include:
Civic acid containing a sulfonic acid metal base such as 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, sodium sulfoisophthalic acid, etc., and phosphorus-containing dicarboxylic acid represented by the following general formula (1), CID and aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, and dodecanedioic acid.

In formula C, R1 is a monovalent ester-forming functional group.

R2, R, are the same or different groups selected from the group consisting of a monovalent hydrocarbon group having 1 to 10 carbon atoms, a hydrogen atom, and a monovalent ester-forming functional group.

A indicates divalent or trivalent organic residue. Also, n is l
or 2, n2+ R3 each represents an integer of 0 to 4.

(In the formula, R4 is a hydrogen atom, a hydrocarbon group having 1 to 12 carbon atoms that may contain an ester-forming functional group, or M2゜R5 is a divalent or trivalent hydrocarbon group having 1 to 6 carbon atoms. .R6 has 1 carbon atom, which may contain a hydrogen atom or a hydroxyl group.
~12 hydrocarbon groups or M.

M,, M2. M3 is an alkali metal atom. m represents an integer of 0 or 1, and β represents an integer of 1 or 2. ] Polyester diol containing sulfonic acid metal base,
When a polyester diol obtained by using a phosphorus-containing compound represented by the general formula CI) or CID as at least one component of a raw material is used as a component of a raw material for a thermoplastic polyurethane resin, inorganic pigments found in conventional thermoplastic polyurethane resins, It is effective in greatly improving the drawback of low dispersibility of fillers, and when used as a binder in the magnetic layer of coated magnetic recording media, it improves the dispersibility of magnetic particles and improves the dispersibility of magnetic recording media. Properties such as electromagnetic conversion properties due to the dispersibility of magnetic particles are greatly improved.

Other polyester diols include ε-caprola,
Examples include lactone-based polyester diols obtained by complete ring-opening polymerization of lactones such as lactones.

Examples of the polyester diol include polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

The polycarbonate diol has the general formula H+ 0-
R-QC! The long chain diol (represented by O+nROH) has a molecular weight of 500 to s and is ooo O. If the molecular weight is less than 500, the urethane group concentration will increase, and the flexibility and solvent solubility of the resin will decrease. Moreover, when the molecular weight exceeds &000, the urethane group concentration decreases, and the toughness, abrasion resistance, etc. characteristic of polyurethane resins decrease.

An ester group-containing diol with a molecular weight of less than 500 that characterizes the thermoplastic polyurethane resin used in the present invention (0 is represented by the general formula: These are a one-to-one ester compound of a compound having three hydroxyl groups in the molecule and a monocarboxylic acid, or a two-to-one ester compound of a glycol and a dibasic acid.

Specific examples include esters of ethylene glycol and glycolic acid, esters of ethylene glycol and lactic acid, esters of ethylene glycol and ε-hydroxycaproic acid, esters of neopentyl glycol and hydroxyhybaric acid, and esters of neopentyl glycol and lactic acid. Esters, caproic acid monoglyceride, stearic acid monoglyceride, bis-(β-hydroxyethyl)adipate, bis-(β-hydroxyethyl)adipate, bis-
(β-hydroxyethyl) terephthalate, etc. In particular, an ester compound of neopentyl glycol and hydroxyhybaric acid is desirable.

Ester group-containing diols with a molecular weight of less than 500 (compounds with a molecular weight of less than 500 containing two active hydrogens in one molecule other than Q are ethylenediIJ nia -/l/, 1.
3=propylene glycol, 1,4-tetrame fL/7
Glycol, 1,6-hexanediol, cyclohexane dimetatool, xylylene glycol, diethylene glycol, triethylene glycol, bisphenol A
Linear glycols such as ethylene oxide adducts, propylene glycol, neopentyl glycol, 1.2-
Butanediol, 1,3-butanediol, 2,2.4
-) Branched glycols such as dimethyl-1,3-bentanediol, propylene oxide adduct of bisphenol A, amino alcohols such as monoethanolamine, N-methylethanolamine, ethylenediamine, hexamethylenediamine, inphorondiamine, piperazine, etc. Examples include diamines or water.

Examples of compounds other than those mentioned above that contain two active hydrogen atoms and have a molecular weight of less than 500 include phosphorus-containing compounds represented by the following general formula [■].

In formula C, R1 and R2 are monovalent hydrocarbon groups e6, and may be the same or different. R3 and R4 are divalent alkylene groups, oxyalkylene groups, or polyoxyalkylene groups with or without substituents, and may be the same or different. When R3 and R are alkylene groups, X and Y are hydroxyl groups, and when R3 and R4 are oxyalkylene groups or polyoxyal groups, they are hydrogen ffi, S. ] General formula Cu1 as a raw material for thermoplastic polyurethane resin
When the phosphorus-containing compound shown in l) is used, it is effective in improving the low dispersibility of inorganic pigments and fillers, which is a drawback of conventional polyurethane resins, and it is effective as a binder for the magnetic layer in coated magnetic recording media. When used as a magnetic particle, the dispersibility of the magnetic particles is improved, and the properties caused by the dispersibility of the magnetic particles, such as the electromagnetic conversion properties of the magnetic recording medium, are greatly improved.

If the molecular weight of the ester group-containing diol and the low molecular weight compound containing two active hydrogen atoms exceeds 500, it is not preferable because the excellent mechanical strength characteristic of polyurethane resins decreases.

The ratio of each raw material used to produce the thermoplastic polyurethane resin used in the present invention is as follows: a is the number of moles of organic diisocyanate, b is the number of moles of long-chain diol, and is the number of moles of ester group-containing diol with a molecular weight of less than 500, k+. Molecular weight 5 containing two active hydrogens other than ester group-containing diol
When the number of moles of the compound less than 00 is 02, it is expressed in the following range.

1.1〉H2 and ≧0.9 (b + c, + c2)/a determine the molecular weight of the resulting polyurethane resin. This value varies depending on the required performance of the thermoplastic polyurethane resin, the molecular weight of the long chain diol, etc., but if it is 1.1 or more, the molecular weight of the thermoplastic polyurethane resin is small, so it is not suitable for heat resistance and durability as an inder for magnetic particles. , poor wear resistance, etc.

During production, the amount of organic diisocyanate consumed is large due to moisture in the reaction system, (b + C1 + c4) / a
may be less than 1, but it is desirable for storage stability that no unreacted incyanate groups remain in the thermoplastic polyurethane resin.

If (b+c(+c4)/a) is less than 0.9, a large amount of unreacted incyanate groups will remain, which is undesirable because it will be cured by moisture.

(c1+c2)/b is the largest factor that determines the urethane group concentration.If this value is less than 2, the urethane group concentration is low and the mechanical strength is reduced.On the other hand, if it exceeds 50'lt, the urethane group concentration becomes too high and the This is undesirable because it causes a decrease in the magnetic recording density and the occurrence of curl in the magnetic recording medium.

(+/ (cl +(!2)) refers to the proportion of diol containing an ester group in a compound with a molecular weight of less than 500 that contains two active hydrogen atoms per molecule, and if this value is less than 0.25, it will not dissolve in general-purpose solvents. This results in a decrease in performance and is not suitable for the purpose of the present invention.

The polyaddition reaction of thermoplastic polyurethane resins is carried out by the Funschott method in which all components are reacted simultaneously. First, a long chain diol is reacted under conditions with an excess of incyanate, and the resulting incyanate group-terminated prepolymer is further reacted with a chain extender. There is a prepolymer method that involves polymerization. In the case of the thermoplastic polyurethane resin used in the present invention, the Funshot method,
It can also be produced by any prepolymer method. As for the reaction conditions, there are a method in which the raw materials are molten and a method in which the raw materials are dissolved in a solution.

During the production of thermoplastic polyurethane/urea resin, tin octylate, diptyltin dilaurate,
Triethylamine or the like may also be used.

Further, ultraviolet absorbers, hydrolysis inhibitors, antioxidants, etc. may be added before, during, or after the production of the thermoplastic polyurethane/urea resin.

In the present invention, in addition to the thermoplastic polyurethane resin used in the present invention, other resins may be added for the purpose of adjusting flexibility, improving cold resistance, heat resistance, etc., and/or thermoplastic It is desirable to mix all the compounds that react with and crosslink with the polyurethane resin. Other resins include vinyl chloride resins, polyester resins, cellulose resins, epoxy resins, phenoxy resins, polyvinyl butyral, acrylonitrile-butadiene copolymers, and the like.

On the other hand, examples of the compound that crosslinks with the thermoplastic polyurethane resin include polyincyanate compounds, epoxy resins, melamine resins, urea resins, etc. Among these, polyincyanate compounds are particularly desirable.

The ferromagnetic particles used in the magnetic layer of the magnetic recording medium of the present invention include mixed crystals of γ-Fe 20 s J-Fe 304 and Fe 304, CrO2, and cobalt-doped γ-Fe20. + or Fe304, barium ferrite, and Fe-Co.

Examples include ferromagnetic alloy powder such as Fe Co--Ni.

The magnetic recording medium of the present invention may optionally contain plasticizers such as dibutyl phthalate and triphenyl phosphate, dioctyl sulfonodium succinate, t-butylphenol polyethylene ether, and ethylnaphthalene.
Lubricants and various antistatic agents such as sodium sulfonate, dilauryl succinate, zinc stearate, soybean oil lecithin, and silibone oil can all be added.

(Effect of the invention) In the present invention, by using an ester group-containing diol with a molecular weight of less than 500 as one component of the thermoplastic polyurethane resin raw material, the urethane group concentration can be increased without reducing the solubility in general-purpose organic solvents. By using this thermoplastic polyurethane resin as a binder for the magnetic layer, a magnetic recording medium with extremely excellent heat resistance, durability, abrasion resistance, etc. can be obtained.

(Examples) Hereinafter, the present invention will be specifically explained using all Examples. In the examples, parts simply indicate parts by weight.

Synthesis Example 7 100 parts of polybutylene adipate with a molecular weight of 2,000 was placed in a reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser, and after dehydration at 70 to 80°C under a reduced pressure of s mmHg, the mixture was heated to normal pressure. After reconstitution, 74 parts of 4,4-diphenylmethane diisocyanate (MDI) and 0.1 part of dibutyltin dilaurate as a reaction catalyst were charged and reacted at 80°C for 1 hour, followed by 274 parts of toluene, methyl ethyl ketone (
274 parts of MEK) were added and dissolved, and further 10 parts of neopentyl glycol and 40 parts of neopentyl hydroxypivalate were added, and the mixture was further reacted at 80°C for 15 hours. The obtained polyurethane resin solution was pale yellow and transparent, had a solid content concentration of 30%, and a solution viscosity of 8 voids at 25°C.The number average molecular weight of the polyurethane resin was 25.000 in terms of polystyrene as measured by gel permeation chromatography. there were.

Synthesis Example 2 261 parts of toluene, 261 parts of MEK, and 50 parts of polyester diol neopentyl hydroxy pinocrate listed in Table 1 were charged into a reaction vessel equipped with a thermometer, a stirrer, and a reflux type condenser.
After dissolving at 60°C, 74 parts of MDI and 0.1 part of dibutyltin dilaurate as a reaction catalyst were added, and the mixture was reacted at 80°C for 15 hours. The obtained polyurethane resin solution was pale yellow and transparent, the solid content concentration was 30%, and the solution at 25°C had a molecular weight of 260~ and the number average molecular weight of the polyurethane resin was 30.0.
00.

Synthesis Examples 3 to 9, Comparative Synthesis Examples 1 to 8 Synthesis Examples 3 to 9 and Comparative Synthesis Examples 1 to 8 were prepared using the raw materials listed in Table 1-1 and -2 in the same manner as in Synthesis Example 1 or 2.
Polyurethane resin No. 8 was obtained.

Margin below In the table, the abbreviations indicate the following.

PBA: Polybutylene adipate (adipic acid //1.
4-Butanediol Polyester Diol Container: Terephthalic acid/15-sulfonodium isophthalate Isophthalic acid l Ethylene glycol/Neopentyl f Reel = 50/39/1 N5
0150 (Mole ratio 9 Molecular weight 2000 Polyester diol Q3): Terephthalic acid/15-sulfonodium adipic acid Oethylene glycol inphthalate/Neopentyl glycol = 50/48/25
0150 (Mole ratio) Molecular weight 1500 MDI: 4,4-diphenylmethane diisocyanate T
DI: 2,4-)lylene diisocyanate IPDI: Inphoron diincyanate HDI Hexamethylene diinocyanate HPN: Neopentyl hydroxypivalate HCPN: Neopentyl glycol ester of ε-cafuronic acid BHET: Bis(β-hydroxyethyl) terephthalate NPC: Neopentyl glycol DEC: Diethylene glycol BD: 1,4-butanediol HD: 1,6-hexanediol MEK: Methyl ethyl ketone Example 1 Using the polyurethane resin obtained in Synthesis Example 1, the following
After putting the composition in a ball mill and dispersing it for 48 hours, the incyanate compound, Coronate 203
0 (manufactured by Nippon Polyurethane Industry ■) as a hardening agent was added, and the mixture was further mixed for 1 hour to obtain a magnetic paint.
(z It was coated on a polyethylene terephthalate film with a thickness of 12μ while applying a magnetic field of 2000 Gauss so that the thickness after drying was 5μ.After being left at 50℃ for 2 days, 17
A magnetic tape was obtained by slitting it into a 2-inch width.

Examples 2-9. Comparative Examples 1 to 8 Magnetic tape was produced in the same manner as in Example 1, using the polyurethane resin solutions obtained in Synthesis Examples 2 to 9 and Comparative Synthesis Examples 1 to 8 instead of the polyurethane resin obtained in Synthesis Example 1. Obtained. Synthesis Examples 2 to 9 will be referred to as Examples 2 to 9, and Comparative Synthesis Examples 1 to 8 will be referred to as Comparative Examples 1 to 8.

Table 2 shows the characteristics of the magnetic tapes of the above examples and comparative examples.

From the results shown in Table 2, the products of the present invention have excellent properties such as durability and abrasion resistance.

Margin below

Claims (1)

[Claims] In a magnetic recording medium in which a magnetic material in which ferromagnetic powder is dispersed in a binder is coated on a non-magnetic support, at least one component of the binder is an organic di-incyanate (A).
, a thermoplastic polyurethane resin reacted with a long-chain diol (8) having a molecular weight of 500 to 8,000 and a compound (C) having a molecular weight of less than 500 containing two active hydrogen atoms in the molecule; A magnetic recording medium characterized by using a polyurethane resin containing at least one diol containing a molecular weight of less than 500 (where Q is represented by the following general formulas (1) to (2)). 1 HORlQCR20H , (1) (In the formula, R1, R2, R5, R6, R7 represent a divalent hydrocarbon group, R3 represents a trivalent hydrocarbon group, and R6 represents a monovalent hydrocarbon group.)