JPH06172704A - Binder for use in magnetic coating material - Google Patents

Abstract

PURPOSE:To obtain a binder for use in a magnetic coating material, where the binder is improved in respect of compatibility, low viscosity of the coating material, dispersibility of a magnetic substance and magnetic properties by containing a polyurethane resin derived from a polyol and a specific org. polyisocyanate. CONSTITUTION:A polyol (A) comprising a high-molecular polyol having an OH equivalent of 200 to 2,000 and a low molecular polyol is reacted with an org. polyisocyanate (B) contg. at least 10wt.% 2,4'-diphenyl-methane diisocyanate at an (A) to (B) equivalent ratio of 0.6 to 1.5 in the pressence of a tin or lead catalyst at 30 to 180 deg.C to obtain a polyurethane resin having a number-average mol.wt. of 1,000 to 200,000 and a hydroxyl number of 0.5 to 50 as a binder for use in a magnetic coating material. At least 5wt.% of the binder is blended with other polymer material, a magnetic substance, a crosslinking agent and a solvent, and if necessary a dispersant and a lubricant to obtain a magnetic coating material.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a binder for magnetic paint.

[0002]

2. Description of the Related Art Conventionally, it is a known technique to use a polyurethane resin containing an active hydrogen compound and an organic polyisocyanate as a binder for a magnetic paint. It is also a known technique to use 4,4′-diphenylmethane diisocyanate as the organic polyisocyanate.

[0003]

However, as the organic polyisocyanate in the polyurethane resin, 4,4 '
-When using diphenylmethane diisocyanate,
When this polyurethane resin is mixed with a vinyl chloride resin or the like for use as a binder for magnetic paint, the compatibility is poor and the paint viscosity is high. As a result, there is a drawback that the dispersibility of the magnetic material becomes insufficient and the magnetic properties of the obtained magnetic tape deteriorate.

[0004]

Means for Solving the Problems As a result of intensive investigations by the present inventors, a binder for a magnetic paint having good compatibility with a vinyl chloride resin, a low paint viscosity, and an excellent dispersibility of a magnetic material was obtained. , As an organic polyisocyanate 2,
It has been found that these problems can be solved by using a polyurethane resin in which 4'-diphenylmethane diisocyanate is used in a specific ratio, and the present invention has been accomplished.

That is, in the present invention, the OH equivalent is 200 to
In the component (B), a polyol component (A) composed of 2,000 high molecular weight polyols (A1) and a low molecular weight polyol (A2) and a polyurethane resin (C) derived from an organic polyisocyanate component (B). 2,4'-
It is a binder for magnetic paints, characterized by containing 10% by weight or more of diphenylmethane diisocyanate (B1).

The 2,4'-diphenylmethane diisocyanate (B1) used in the present invention is usually contained in the organic polyisocyanate component in an amount of 10% by weight or more, preferably 2%.
It is 0% by weight or more. If the content of (B1) is less than 10% by weight, the compatibility with vinyl chloride resin, etc. deteriorates,
The viscosity of magnetic paint increases.

As an organic polyisocyanate component (B
Other organic polyisocyanates for use with 1) include aromatic diisocyanates (1,3- and / or 1,4-phenylene diisocyanates, 2,4- and / or 2,6-tolylene diisocyanates, 4,4 ′.
-Diphenylmethane diisocyanate, etc.); aliphatic diisocyanate (hexamethylene diisocyanate, tetramethylxylylene diisocyanate, etc.); alicyclic diisocyanate (isophorone diisocyanate, dicyclohexylmethane diisocyanate, etc.); modified polyisocyanate (water-modified hexamethylene diisocyanate, isophorone diisocyanate) Trimer, 2,4-
And / or a trimethylolpropane modified product of 2,6-tolylene diisocyanate) and an isocyanate-terminated prepolymer can be used in combination. Of these, preferred are aromatic diisocyanates, and particularly preferred is 4,4'-diphenylmethane diisocyanate.

OH equivalent in the present invention 200 to 2,000
Examples of the high molecular weight polyol (A1) of 0 include polyester diol, polyether polyol, and polycarbonate diol.

The polyester diol includes a condensed polyester diol obtained by reacting a low molecular weight diol and a dicarboxylic acid, a polylactone diol obtained by ring-opening polymerization of a lactone, and the like. As the low-molecular diol, alkylene glycols (ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,
3-butanediol, neopentyl glycol, 1,6
-Hexanediol, 1,8-octamethylenediol, 1,10-decanediol, etc.); low molecular weight diols having a cyclic group {cyclohexanediol, glycols such as cyclohexanedimethanol, and JP-B-45-
Those described in No. 1474 [bis (hydroxymethyl) cyclohexane, xylylene glycol, bis (hydroxyethyl) benzene, 1,4-bis (2-hydroxyethoxy) benzene, 4,4'-bis (2-hydroxyethoxy)] -Diphenylpropane (ethylene oxide adduct of bisphenol A) and the like]}; and a mixture of two or more thereof.

Polyester diols can be prepared by a conventional method, for example, by using a low molecular weight diol, dicarboxylic acid or its ester-forming derivative [for example, an anhydride (maleic anhydride, phthalic anhydride, etc.), an ester (dimethyl terephthalate, etc.),
Halide or the like], or an anhydride thereof and an alkylene oxide (for example, ethylene oxide and / or propylene oxide), or (addition polymerization) of a lactone to an initiator (low molecular weight diol). .

Specific examples of these polyester diols include polyethylene phthalate, polybutylene phthalate, polyhexamethylene phthalate, polyneopentyl phthalate, polyethylene adipate, polybutylene adipate, polyhexamethylene adipate, polyneopentyl adipate, polyethylene propylene adipate. , Polyethylene butylene adipate, polybutylene hexamethylene adipate, polydiethylene adipate,
Examples include poly (polytetramethylene ether) adipate, polyethylene azelate, polyethylene sebacate, polybutylene azelate, polybutylene sebacate, polycaprolactone diol, polyvalerolactone diol, and mixtures or copolymers of two or more thereof. . Other than this, the phthalic acid-modified polycaprolactone polyol described in JP-A-62-202324 can also be used.

As the polyether polyol, an alkylene oxide of the above-mentioned low molecular weight diol (C2-C4 alkylene oxide: ethylene oxide, propylene oxide, 1,2-, 2,3-, 1,4-butylene oxide, etc.) Addition product: a product obtained by ring-opening polymerization or ring-opening copolymerization (block and / or random polymerization) of an alkylene oxide having 2 to 4 carbon atoms [eg polyethylene glycol, polypropylene glycol, polyethylene-
Polypropylene (block and / or random) glycol, polytetramethylene glycol, polytetramethylene-ethylene (block and / or random) glycol, polytetramethylene-propylene (block and / or random) glycol, polyhexamethylene ether glycol, etc. ]; An alkylene oxide adduct of a low molecular weight triol (glycerin, trimethylolpropane, hexanetriol, etc.): and a mixture of two or more thereof.

As the polycarbonate diol, a low molecular weight diol; for example, 1,4-butanediol, 1,5-
Pentane diol, 1,6-hexane diol and carbonate; for example, compounds obtained by reacting ethylene carbonate, trimethylene carbonate, tetramethylene carbonate can be mentioned.

Further, high molecular weight polyols other than these (A
Polymer polyols and polybutadiene polyols can also be used as 1).

The OH equivalent of the polymeric polyol (A1) is
It is 200 to 2,000, preferably 400 to 1,500. When the OH equivalent is less than 200, the resulting polyurethane resin becomes brittle and the scratch resistance decreases. Also,
When the OH equivalent exceeds 2,000, the resulting polyurethane resin has insufficient resin strength, and wear resistance, scratch resistance and the like are deteriorated.

Low molecular weight polyol (A2) in the present invention
Examples of the low molecular weight diols (alkylene glycols, low molecular weight diols having a cyclic group, etc.) described in the section of high molecular weight polyol (A1), and glycerin,
Trimethylolpropane, trimethylolethane, hexanetriol, pentaerythritol, diglycerin, α-methylglucoside, sorbitol, xylit, mannitol, glucose, fructose, saccharose, and other trihydric alcohols; and two or more of these alcohols A mixture etc. are mentioned. Among these, preferred are low molecular weight diols, and particularly preferred are alkylene glycols having 2 to 10 carbon atoms.

Further, in the present invention, by introducing a functional group into the polyurethane resin, the dispersibility as a binder for magnetic coating can be further improved. As a method of introducing it into the molecule, there is a method of using a low-molecular polyol having a functional group as the low-molecular polyol (A2) used in the present invention. Examples of this functional group include a carboxyl group, a sulfonic acid group, a phosphoric acid group or a metal salt thereof, an ammonium salt, an amino group and a sulfobetaine group. It is preferably a carboxyl group, and examples thereof include dimethylpropionic acid.

The average OH equivalent of the entire polyol component (A) is usually 100 to 1,600. When the OH equivalent of (A) is less than 100, the resulting polyurethane resin becomes a brittle resin with poor film-forming properties and is not sufficient as a binder for magnetic paints. On the other hand, when the OH equivalent exceeds 1,600, the dispersibility of the magnetic material is deteriorated, the resin strength becomes insufficient, and the abrasion resistance and scratch resistance are deteriorated.

In reacting (A) and (B),
The equivalent ratio of (A) and (B) is usually 0.6 to 1.5, preferably 0.8 to 1.2, and particularly preferably 0.9 to 1.1. When the equivalent ratio is less than 0.6 or exceeds 1.5, the molecular weight of the polyurethane resin obtained by the reaction of (A) and (B) becomes low and the dispersibility decreases, resulting in insufficient resin strength and abrasion resistance. , Scratch resistance and hydrolysis resistance are reduced. The above reaction can be carried out in the presence or absence of a solvent inert to the isocyanate group.
Examples of the solvent include ester solvents (ethyl acetate, butyl acetate, etc.), ether solvents (dioxane, tetrahydrofuran, etc.), ketone solvents (cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, etc.), aromatic hydrocarbon solvents (toluene). , Xylene, etc.) and mixed solvents of two or more thereof.

As a reaction method, a method of charging (A) and (B) into a reaction vessel at a time and reacting them, (A) and (B)
And a method of performing multi-stage reaction, and a method of allowing premixed (A) and (B) to pass through a heated multi-screw extruder to react. The reaction temperature is generally 30 to 180 ° C, preferably 60 to 120 ° C.
In the reaction, a catalyst used in a usual urethane reaction for promoting the reaction, for example, a tin-based catalyst (trimethyltin laurate, trimethyltin hydroxide,
It is also possible to use dimethyltin dilaurate, dibutyltin dilaurate, stannas octoate, etc.), a lead-based catalyst (red oleate, red 2-ethylhexoate, etc.) and the like.

The polyurethane resin (C) obtained by reacting (A) and (B) usually has a number average molecular weight of 1,000.
~ 200,000, preferably 3,000 to 150,0
00. When the number average molecular weight is less than 1,000, the physical properties of the resin are deteriorated and the durability of the magnetic tape is deteriorated. On the other hand, when the number average molecular weight exceeds 200,000, the viscosity of the coating material increases and the dispersibility of the magnetic material deteriorates. The polyurethane resin (C) has a hydroxyl value of usually 0.5 to 50, preferably 1 to 20.

The polyurethane resin (C) obtained by reacting (A) and (B) can be used as it is as a binder for magnetic paints, but if necessary, other polymeric materials usually used as binders for magnetic paints. Can be used together. Examples of the polymer material include polyvinyl chloride-based [vinyl chloride-vinyl acetate copolymer (VYHH; UCC
Co., Ltd., S-REC C; Sekisui Chemical Co., Ltd.), vinyl chloride-vinyl acetate-vinyl alcohol copolymer (VAGH; UC
Company C, S-REC A; Sekisui Chemical Co., Ltd.), vinyl chloride-
Vinylidene chloride-acrylonitrile copolymer (Saran;
Asahi Dow, etc.)], polyurethane-based [polyurethane resin (Esten; manufactured by Goodrich, etc.)], butadiene-based [acrylonitrile-butadiene copolymer (Hiker 1)
482; manufactured by Nippon Zeon Co., Ltd., etc.], acrylics (acrylic ester copolymers, etc.), nitrocellulose, phenoxy resins, epoxy resins and the like.

As the magnetic substance used in the magnetic coating material, iron oxide [eg γ-Fe ₂ O ₃ (γ-hematite)], CrO ₃ (chromium trioxide), alloy type magnetic substance [eg Co -Γ-Fe ₂ O ₃ (cobalt ferrite or cobalt-doped γ-iron oxide), Fe-Co-Cr],
Examples include pure iron Fe (metal powder), iron nitride, iron carbide, and the like.

A cross-linking agent for cross-linking the polyurethane resin is usually used in the magnetic paint. Examples of the cross-linking agent include NCO group-containing compounds and active hydrogen-containing compounds. As the NCO group-containing compound, polyisocyanate [modified MDI (Millionate ME; manufactured by Hodogaya Chemical Co., Ltd.), 3,3′-dimethoxy-4,4′-diisocyanate, etc.] and NCO group-terminated prepolymer [polyisocyanate (TDI, MDI, etc.) And NPO group-terminated prepolymers such as polyols (low molecular weight polyols, polyether polyols, polyester polyols, etc.) such as Desmodur L (manufactured by Bayer) and Coronate L (manufactured by Nippon Polyurethane)]. As the active hydrogen-containing compound, polyamine [tolylenediamine (TDA),
4,4′-diamino-3,3′-dichlorodiphenylmethane and the like] and polyols (low molecular weight polyol, polyether polyol, polyester polyol and the like). The amount of the crosslinking agent added is usually 0 to 25% by weight, preferably 2 to 15% by weight, based on the polyurethane resin. Two
If it exceeds 5% by weight, the flexibility of the resin tends to decrease.

In addition, if necessary, a dispersant (a surfactant such as anion, nonion or cation (eg, sodium dodecylbenzenesulfonate) or lecithin), and a lubricant (higher fatty acid ester such as butyl stearate), etc. may be added. You can also

A solvent is used for the magnetic paint to adjust the viscosity. As this solvent, the same solvents as those described in the section of polyurethane resin formation reaction, that is, ester solvents (ethyl acetate, butyl acetate, etc.), ether solvents (dioxane, tetrahydrofuran, etc.), ketone solvents (cyclohexanone, Methyl ethyl ketone, methyl isobutyl ruketone, etc.), aromatic hydrocarbon solvents (toluene, xylene, etc.), and mixed solvents of two or more thereof can be used. Among these, preferred are mixed solvents of ketone type and aromatic hydrocarbon type.

The proportion of the polyurethane resin (C) in the magnetic coating is usually 5% by weight or more, preferably 5 to 40% by weight, based on the weight of the coating.

As a method for producing a magnetic coating material, a binder for a magnetic coating material, a solvent and a magnetic material are optionally mixed in advance with a premixer or the like, and then magnetically mixed with a mixing / dispersing machine (ball mill, paint conditioner, sand grinder, sand mill, plast mill, etc.). Examples include a method of dispersing the body and filtering. This magnetic paint can be applied to a support film for a magnetic recording medium to prepare a magnetic recording medium (magnetic tape or the like). As this support film,
Paper, cellophane, acetate, polyester (PET),
Examples of the film include reinforced polyester (PEN) and polyimide. Of these films, a polyester film is often used. When the magnetic coating is applied to the support film, the coating thickness is usually several μ to several tens μ. Examples of the coating method include a doctor blade method and a transfer printing method (gravure method, reverse roll method, etc.).
The film coated with the magnetic coating material is then subjected to steps such as orientation, drying, surface processing, cutting and winding to obtain a magnetic recording medium. A magnetic recording medium generally comprises a support film and a magnetic layer (a magnetic material, a binder for a magnetic coating, etc.), but an intermediate layer (undercoat layer) provided between the support film and the magnetic layer. , Those having magnetic layers on both sides of the support film, those having magnetic layers having different magnetic properties stacked, those having a protective layer on the magnetic layer, those having a back coat layer on the support film, etc. is there.

[0029]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited thereto. In the following, "part" means "part by weight". Example 1 OH obtained from adipic acid and 1,4-butanediol
1.02 mol of polyester diol with an equivalent weight of 500 and 1,
3 mol of 4-butanediol and 2,4'-diphenylmethane diisocyanate (hereinafter abbreviated as 2,4'-MDI) 2
2 mol of 4,4'-diphenylmethane diisocyanate (hereinafter abbreviated as 4,4'-MDI) are reacted to react with polyurethane resin (C-1) (hydroxyl value 5.1; number average molecular weight 15,200 by GPC measurement; Weight average molecular weight 4
8,640) was obtained. Using this (C-1) as a binder, a mixture having the following composition was mixed and dispersed with a paint conditioner to prepare a magnetic coating material (D-1). This magnetic paint was applied to a polyester film (dry film thickness: 5 μm), and a magnetic field of 1000 Oe was applied for orientation to obtain a tape. Further, this tape was treated with a calendar roll to obtain a magnetic tape (E-1).

Example 2 OH obtained from adipic acid and 1,4-butanediol
Polyurethane resin (C-2) (hydroxyl group obtained by reacting 1.03 mol of equivalent 500 polyester diol, 3 mol of ethylene glycol, 0.8 mol of 2,4'-MDI and 3.2 mol of 4,4'-MDI A valency of 3.6; a number average molecular weight of 14,240; a weight average molecular weight of 45,600) was used to prepare a magnetic coating material (D-2) in the same manner as in Example 1 to obtain a tape (E-2).

Example 3 Polycaprolactone diol 1.0 having an OH equivalent of 1000
Polyurethane resin obtained by reacting 1 mol, 0.9 mol of ethylene glycol, 0.1 mol of dimethylolpropionic acid, 1.4 mol of 2,4'-MDI and 0.6 mol of 4,4'-MDI (C- 3) (hydroxyl value 3.8; number average molecular weight 25,120; weight average molecular weight 77,810) was used to prepare a magnetic coating material (D-3) in the same manner as in Example 1,
A tape (E-3) was obtained.

Comparative Example 1.02 mol of a polyester diol obtained from adipic acid and 1,4 butanediol and having an OH equivalent of 500, and 1,4
-A urethane resin (C-4) obtained by reacting 3 mol of butanediol with 2,4'-MDI 0.2 and 3.8 mol of 4,4'-MDI (hydroxyl value 5.0; number average molecular weight 1
7,200; weight average molecular weight 53,320) was used to prepare a magnetic coating material (D-4) in the same manner as in Example 1 to obtain a magnetic tape (E-4).

Test Example 1 The magnetic paints obtained in Examples 1 to 3 and Comparative Example (D-1)
-D-4) viscosity was measured. The results are shown in Table 1. BL
A viscometer (manufactured by Tokyo Keiki Co., Ltd.) was used to measure at 25 ° C.

[0034]

[Table 1]

Test Example 2 The surface glossiness of the magnetic tapes (E-1 to E-4) was measured in order to see the dispersibility of the magnetic powder of the magnetic paints obtained in Examples 1 to 3 and Comparative Example. The results are shown in Table 2. As a gloss meter, a digital variable angle gloss meter manufactured by Nippon Denshoku Industries Co., Ltd. was used to measure a specular reflectance of 75 °. The numerical value is shown as a relative value (%) in comparison with the case where the reflectance of the standard plate is 95.

[0036]

[Table 2]

Test Example 3 Magnetic tapes (E-) obtained in Examples 1 to 3 and Comparative Example
Magnetic properties 1 to E-4) were measured. The results are shown in (Table 3). The squareness ratio (Br / Bm) was measured using a vibrating sample magnetometer manufactured by Sakata Seisakusho. The magnetization density Bm in the orientation direction of the magnetic tape and the residual magnetic flux Br were measured to determine the ratio Br / Bm of the two.

[0038]

[Table 3]

[0039]

The binder for magnetic paint of the present invention has the following effects as compared with the conventional ones. (1) Since the viscosity of the magnetic coating material obtained by using the binder for magnetic coating material of the present invention is low, the coating line can be speeded up, and the magnetic substance can be easily moved during orientation, and the magnetic characteristics can be improved. (2) The dispersibility in the magnetic material is excellent, and the magnetic characteristics of the magnetic tape are further improved. (3) It has excellent calendering properties when manufacturing magnetic tapes. (4) Excellent adhesion to the support film. From the above effects, the binder of the present invention is, for example, audio tape, video tape, computer tape, data recorder tape, video sheet,
It is useful as a binder for magnetic paints for metal tapes, metal disks, and magnetic cards.

Claims (3)

[Claims] 1. A polyurethane resin (C) derived from a polyol component (A) consisting of a high molecular weight polyol (A1) and a low molecular weight polyol (A2) having an OH equivalent of 200 to 2,000 and an organic polyisocyanate component (B). ) And containing 2,4'-diphenylmethane diisocyanate (B1) in an amount of 10% by weight or more in the component (B). 2. The polyurethane resin (C) has a hydroxyl value of 0.5 to 50 and a number average molecular weight of 1,000 to 20.
The binder for a magnetic coating composition according to claim 1, which has an amount of 10,000. 3. The binder for a magnetic coating composition according to claim 1, wherein the low molecular weight polyol (A2) is a low molecular weight diol containing a carboxyl group.