JPH0641267A - Binder for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the binder improved in pigment dispersion and wet-heat resistance by mixing a specified thermoplastic polyurethane resin with a specified low-molecular-weight polyisocyanate. CONSTITUTION:An organic diisocyanate is polymerized with a diol containing an -SO3X group (wherein X is an alkali metal) in the molecular chain or a mixture thereof with an at least dihydric polyol containing no -SO3X in the molecular chain and containing a tertiary hydroxyl group in the molecular chain to obtain a thermoplastic polyurethane resin containing -SO3X groups and tertiary hydroxyl groups in the molecular chain. 100 pts.wt. of this resin is mixed with 3-40 pts.wt. low-molecular-weight polyisocyanate containing at least two isocyanate groups in the molecule and having a molecular weight of 150-7000.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder for thermomagnetic recording media, and more specifically to a thermoplastic polyurethane resin having --SO ₃ X groups (where X is an alkali metal atom) and a tertiary hydroxyl group in the molecular chain. And a binder for a magnetic recording medium, which comprises a low molecular weight polyisocyanate having two or more isocyanate groups and imparts improved properties such as pigment dispersibility and resistance to moist heat.

[0002]

2. Description of the Related Art Thermoplastic polyurethane resins are used for synthetic leather, paints, adhesives and magnetic recording media because of their organic solvent solutions by utilizing the properties of high elasticity, flexibility, abrasion resistance, cold resistance and strength. Widely used as a binder. But,
Thermoplastic polyurethane resin has heat resistance, hydrolysis resistance,
It has the disadvantage of poor resistance to moist heat. Further, in recent years, the binder of the thermoplastic polyurethane resin has a poor dispersibility of the magnetic powder when used, and due to this, it is not possible to obtain a satisfactory electromagnetic characteristic.

Conventionally, various methods for solving these drawbacks have been proposed, but the high elasticity, abrasion resistance, flexibility, cold resistance, and inherent properties of thermoplastic polyurethane resins have been proposed.
It was impossible to improve the above-mentioned drawbacks without impairing properties such as strength.

[0004]

DISCLOSURE OF THE INVENTION The inventors of the present invention have earnestly studied on a method of improving the above-mentioned drawbacks without impairing the excellent performances of thermoplastic polyurethane resin as a binder for magnetic recording media. That the pigment dispersibility is improved and that a low molecular weight polyisocyanate is used in combination by using a -SO ₃ X group (where X is an alkali metal atom) and a tertiary hydroxyl group introduced therein As a result, they have found a binder that improves durability such as wet heat resistance and abrasion resistance of the urethane resin after curing, and completed the present invention.

[0005]

That is, the present invention provides a thermoplastic polyurethane resin (A) containing a —SO ₃ X group (X; alkali metal atom) and a tertiary hydroxyl group in the molecular chain.
And a binder for a magnetic recording medium comprising a low molecular weight polyisocyanate (B) having two or more isocyanate groups.

The thermoplastic polyurethane resin (A) used in the present invention has a number average molecular weight of 10,000 to 5 in particular.
10,000, more preferably 15,000 to 45.0
00. The average number of —SO ₃ X groups in one molecule of the thermoplastic polyurethane resin is 0.2 or more, preferably 0.5 to 10, particularly preferably 0.5 to 5, and the number of tertiary hydroxyl groups is 0. It is desirable that it is 2 or more, preferably 0.5 or more, and more preferably about 1 to 20, and X is an alkali metal atom, but preferably Na or K.
That is, if the number average molecular weight is less than 10,000, the polyurethane resin has poor mechanical properties, abrasion resistance, and wet heat resistance,
If it is more than 50,000, the abrasion resistance of the polyurethane resin is improved, but the pigment dispersibility is extremely deteriorated, and it often becomes difficult to form a coating material. In addition, in one molecule −
When the number of SO ₃ X groups is less than 0.2, it is difficult to improve the pigment dispersibility, and when the number of SO ₃ X groups is more than 10, the solubility of the —SO ₃ X group is increased and the water resistance is poor, which is not preferable. . Further, if the number of tertiary hydroxyl groups in one molecule is less than 0.2, it is difficult to improve the wet heat resistance of the urethane resin after curing.

Both ends of the thermoplastic polyurethane resin used in the present invention may have an isocyanate group or a hydroxyl group, one end may be an isocyanate group and the other end may be a hydroxyl group.

In the molecular chain used in the present invention, --SO₃X
Polyurethane Resin Containing Radical Group and Tertiary Hydroxyl Group
Fat (A) is an organic diisocyanate (A₁) And in the molecular chain
To-SO₃A diol containing an X group (A₂) Alone and
-SO in diol and molecular chain ₃Number of hydroxyl groups not including X groups
Having 2 or more tertiary hydroxyl groups
(A ₃) It can be obtained by polymerizing with a mixture of
(A₁) And (A₂) Polymer and (A₁) And (A₃)of
You may make polymers separately and polymerize them.
They may be mixed and used.

As the organic diisocyanate (A ₁ ),
Hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, xylene diisocyanate, cyclohexane diisocyanate, toluidine diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, p-phenylene diisocyanate, m- Phenylene diisocyanate, 1,
Included are 5-naphthalene diisocyanates and mixtures thereof. Of these, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate and mixtures thereof are preferred.

The diol (A ₂ ) containing a —SO ₃ X group in the molecular chain is a dialkylsulfoisoate such as sodium dimethylisophthalate-5-sulfonate or sodium dimethylsuccinatesulfonate in the example of —SO ₃ Na. Dibasic acids such as phthalates and dialkylsulfosuccinates-sodium sulfonates or their esters with succinic acid, maleic acid, adipic acid, glutanoic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid , Terephthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid and other dibasic acids and mixtures of these acid esters with 2 to 1 carbon atoms
Glycols having 0, for example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 2,3-butylene glycol, 1,4-
Butylene glycol, 2,2'-dimethyl 1,3-propanediol, diethylene glycol, 1,5-pentamethylene glycol, 1,6-hexamethylene glycol, cyclohexane 1,4-diol, cyclohexane-1,4-dimethanol, etc. 50 of the molecular weight obtained by polycondensation of the above glycol alone or a mixture thereof.
Mention may be made of polyester diols of 0 to 6,000. In addition, a mixture of dialkanol sulfoisophthalate and dialkanol sulfosuccinate obtained by transesterification of the ester of sodium sulfonate and an excess of glycol having 2 to 10 carbon atoms and unreacted glycol is given. be able to.

As the polyols (A ₃ ) having a tertiary hydroxyl group which does not contain a —SO ₃ X group, a molecular weight of 500 to 500 which does not contain a tertiary hydroxyl group having a linear terminal hydroxyl group is used.
6,000 diols may be mixed, or carbon number 2
A low molecular weight diol having 10 to 10, a triol having 4 to 10 carbon atoms having a tertiary hydroxyl group in the molecular chain, a terminal hydroxyl group obtained by using these triols, and at least one tertiary hydroxyl group in the molecular chain Molecular weight of 50 or more
Polyols such as polyether polyol and polyester polyol of 0 to 6,000 may be used alone.

Molecular weight having linear terminal hydroxyl group 500-
Examples of the 6,000 diol include polyester polyol and polyether polyol. As the polyether polyol, polyethylene glycol,
Examples thereof include polypropylene glycol and polytetramethylene glycol. As the polyester polyol, polycondensation of the above-mentioned glycol having 2 to 10 carbon atoms alone or a mixture with the above-mentioned dibasic acid containing no —SO ₃ X group and these acid esters or acid halides alone or a mixture. And a polycaprolactone diol obtained by ring-opening addition polymerization of a lactone such as ε-caprolactone in the presence of glycol or the like.

As the low molecular weight diol having 2 to 10 carbon atoms, glycols used in the production of the above polyesters may be used alone or in a mixture. Further, diols obtained by adding 2 to 4 mol of ethylene oxide and propylene oxide to bisphenol A, hydroquinone and the like can be mentioned. Of the above, aliphatic diols are suitable for both the diol having a linear terminal hydroxyl group and a molecular weight of 500 to 6,000 and the low molecular weight diol having a carbon number of 2 to 10.

4 carbon atoms having a tertiary hydroxyl group in the molecular chain
Examples of the triol of 10 include 1,2,3-hydroxy-2-methyl-propane, 1,2,3-hydroxy-2-ethylpropane and 1,2,4-hydroxy-2.
Examples include monomers or mixtures of methylbutane, 1,2,5-hydroxy-2-methylpentane, 1,3,5-hydroxy-3-methylpentane, 1,3,6-hydroxy-3-methylhexane and the like. To be

Further, the molecular weight having the above-mentioned tertiary hydroxyl group is 50.
Examples of the polyether polyols include polypropylene ether polyols obtained by adding propylene oxide, ethylene oxide or butylene oxide to a polyol of 0 to 6,000, polyethylene polyols and polybutylene polyols.

Further, polyesters obtained by polycondensation of the dibasic acids and their acid esters and acid halides in a miscible system of a triol having a tertiary hydroxyl group and the low molecular weight glycol are mentioned. -Polycaprolactone polyols obtained by ring-opening addition polymerization of a lactone such as caprolactone in the presence of a mixture with the triol and glycol.

It is essential that the hydroxyl group in the molecular chain of the above polyol is tertiary. Primary and secondary hydroxyl groups have a higher reactivity with isocyanates than tertiary hydroxyl groups, resulting in a high molecular weight or reticulation phenomenon of polyurethane, making it difficult to form thermoplastic polyurethane resin. It is due to. Further, in the production of the thermoplastic polyurethane resin used in the present invention, the OH / NCO molar ratio of the polyol and the organic diisocyanate is set to 0 in consideration of impurities (moisture, acid, hydrolyzed chlorine, etc.) in each raw material. 85-1.15 / 1.00 preferably 0.95-
1.05 / 1.0 is good. If it deviates from these ranges, the various performances required in the present invention cannot be obtained, which is not preferable.

If necessary, a catalyst and various stabilizers can be used in the thermoplastic polyurethane having SO ₃ X groups and tertiary hydroxyl groups thus obtained. Examples of the catalyst include tertiary amines such as triethylamine and triethylenediamine, nitrogen compounds such as morpholine and N-methylmorpholine, metal salts such as potassium acetate and zinc stearate, and organometallic compounds such as dibutyltin dilaurate and dibutyltin oxide. Can be mentioned. The above-mentioned various performances of the thermoplastic polyurethane can be remarkably stabilized by adding a stabilizer for ultraviolet rays such as substituted benzotriazoles and a stabilizer for thermal oxidation such as phenol derivatives as stabilizers.

Further, in producing the thermoplastic polyurethane resin, a conventionally known method can be used. If desired, the reaction mixture is sufficiently mixed in the presence of a catalyst, and then the reaction mixture is flat or flat. Flowing on the surface and heating, then crushing after cooling, pouring the reaction mixture into an extruder and dimethylformamide, toluene,
Xylene, benzene, dioxane, cyclohexanone,
A conventional production method such as a solution reaction method in which a reaction is carried out in a single or mixed solvent type organic solvent such as methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate or butyl acetate can be used.

Of these, when used as a binder for a magnetic recording medium, it dissolves toluene, xylene, benzene, etc., which have low affinity with water and low solubility, including those for dissolving and diluting solid thermoplastic polyurethane resin. Cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate and the like, which have excellent properties, are suitable.

In the present invention, it is necessary to finally use the above thermoplastic polyurethane resin after curing it with an appropriate curing agent, and low molecular weight polyisocyanate is most suitable as the curing agent.

The isocyanate group used in the present invention is 2
The number of low molecular weight polyisocyanates (B) is not less than,
Examples include organic diisocyanates and low molecular weight polyisocyanates having two or more isocyanate groups used in the production of the thermoplastic polyurethane resin (for example, a compound in which a low molecular weight polyol has an isocyanate compound as a terminal isocyanate group) and the like, and a molecular weight of 150 to 7 , 0
It is about 00. Examples of the low molecular weight polyisocyanate having two or more isocyanate groups include the following compounds.

[0023]

[Chemical 1]

A commercially available product of this formula is Barnock D-7.
50, Chris Bonn NX (Product of Dainippon Ink and Chemicals, Inc.), Desmodur L (Product of Sumitomo Bayer Co., Ltd.), Coronate L (Product of Nippon Polyurethane Co., Ltd.), Takenate D
102 (product of Takeda Pharmaceutical Co., Ltd.) and the like.

[0025]

[Chemical 2]

Commercially available product Barnock D-950 (product of Dainippon Ink and Chemicals, Inc.) triphenylmethane 4,
4 ', 4 "-triisocyanate

[0027]

[Chemical 3]

The ratio of the thermoplastic polyurethane resin (A) to the low molecular weight polyisocyanate (B) is not particularly limited, but preferably 3 parts of the low molecular weight polyisocyanate is added to 100 parts of the thermoplastic polyurethane resin. By adding about 40 parts and curing, the mechanical strength, abrasion resistance, heat resistance, moist heat resistance, solvent resistance and adhesion of the binder after curing can be greatly improved.

If necessary for the binder of the present invention, a thermoplastic polyurethane resin usually used, vinyl chloride-
Vinyl acetate-based copolymer, fibrin-based resin, vinyl chloride polymer, polyvinyl butyral-based resin, thermoplastic polyester resin, vinyl chloride-vinyl propionate-based copolymer,
By using commercially available products such as epoxy resin and phenoxy resin as they are, they can be used for improving the dispersibility of the pigment, adjusting the hardness of the resin, and the like.

The magnetic powder of the present invention means, for example, γ-Fe ₂
Conventionally known magnetic powder such as O ₃ powder can be used. This magnetic powder is 100 to 1000 with respect to 100 parts by weight of the binder.
Parts by weight, preferably 100 to 350 parts by weight, are used.

Next, the present invention will be described with reference to examples.
This is merely one aspect, and the present invention is not limited to the embodiments. In addition, all "parts" in the text are based on weight.

[0032]

【Example】

[Examples 1 to 3 and Comparative Examples 1 to 5] 1,4-butanediol, adipic acid, 5-sodium sulfodimethylisophthalate having a molecular weight of 2,000 (adipic acid / 5
The range of the molar ratio of sodium sulfodimethylisophthalate is shown in Table-1. After mixing 1 mol of a polyester diol having a hydroxyl value of 56.1) and 0.1 part of 1,3,5-hydroxy-3-methylpentane (compounding ratio is shown in Table 1) dibutyltin dilaurate, 4,4'- Diphenyl-methane diisocyanate was added with NCO / OH = 1.00 / 1.
The molar ratio of 02 was added. Before mixing these components, add polyol and isocyanate to 80 ° C and 5 respectively.
Heated to 0 ° C.

In adding the isocyanate to the polyol mixture, it is necessary to add about 1 in order to achieve intimate contact of the components.
Mechanical mixing was performed for minutes. The reaction mixture is then added to 120
Pour onto a vat heated to ℃ for 1 hour, then 10
The reaction was completed by leaving still at 0 ° C. for 20 hours to prepare a thermoplastic polyurethane resin binder.

Table 1 shows the measurement results of the number of —SO ₃ Na groups, the number of tertiary hydroxyl groups, the solubility in organic solvents, the number average molecular weight, and the dispersibility of the magnetic powder of the obtained thermoplastic polyurethane resin binder. .

[0035]

[Table 1]

The method for measuring the binder composed of the thermoplastic polyurethane resin shown in Table 1 is described below.

Note 1) Measurement of the number of —SO ₃ groups contained; Elemental analysis method The pretreatment was changed to SO ₄ ⁻ by an oxygen flask combustion method, and this group was measured by an ion chromatography (manufactured by Dionic) and Converted to ₃ Na groups.

Note 2) It was calculated based on the charging ratio and the number average molecular weight of the thermoplastic polyurethane resin, assuming that all the tertiary hydroxyl groups were unreacted.

Note 3) Solubility measurement in organic solvent Evaluation in the state of a cyclohexanone solution having a non-volatile content of 20% ⊚: All were dissolved even at 50 ° C. and room temperature (23 ° C.), and the solution was transparent and had good stability.

◯: A transparent solution completely dissolved at 50 ° C., a transparent jelly state at room temperature. Separated into a solid layer. X: Suspended at 50 ° C, separated into a cloudy opaque solution layer and a solid layer at room temperature.

Note 4) Measurement of number average molecular weight: The molecular weight was measured in terms of polystyrene by gel permeation analysis. Measuring instrument (LC-08 type), detector (RI): Nippon Analytical Industry Co., Ltd. Measuring column: Showa Denko KK Shodex (Sho-)
dex) A-806, A-805, A-804, A-8
03, 5 series of A-802

Note 5) Dispersibility of magnetic powder Thermoplastic polyurethane resin obtained in Examples 1-3 or Comparative Examples 1-5 150 parts Cyclohexanone 600 parts Methyl ethyl ketone 250 parts γ-Fe ₂ O ₃ magnetic powder 300 parts The mixture was kneaded in a ball mill for 20 hours, and the resulting magnetic coating material was applied to a polyethylene terephthalate substrate film having a thickness of 10 μm so that the thickness after drying was 10 μm and dried, and the magnetic layer was formed under a microscope (40 ×). The surface condition of the powder was observed and the dispersibility of the magnetic powder was evaluated. The evaluation criteria are shown below.

⊚: Very good ○: Excellent Δ: Normal ×: Inferior

Example 4 1.0 mol of polytetrahydrofuran having a molecular weight of 1,000 (hydroxyl value 112), DES
(Nippon Hydrazine Co., Ltd., 5-sodium sulfobis β
-Hydroxyethyl isophthalate / ethylene glycol 35/65 weight ratio) 0.5 mol, dibutyltin dilaurate 0.2 part, 2,4-tolylene diisocyanate /
A thermoplastic polyurethane resin binder was prepared in the same manner as in Example 1 with a molar ratio of 2,6-tolylene diisocyanate (80/20 mixture) NCO / OH = 1.00 / 1.02.

[Example 5] 1,3,5-hydroxy-3
-1.0 mol of polycaprolactone having a molecular weight of 3,000 (hydroxyl value of 37.4) using methylpentane as an initiator, D
ES 0.8 mol, dibutyltin dilaurate 0.2 parts,
1,6-hexamethylene diisocyanate NCO / OH
A thermoplastic polyurethane resin binder was prepared in the same manner as in Example 1 with a molar ratio of 1.00 / 1.02.

However, the reaction was carried out at a temperature of isocyanate of 35 ° C. in both Example 4 and Example 5.

The items of —SO ₃ Na group number, solubility in organic solvent, number average molecular weight and dispersibility of magnetic powder of the thermoplastic polyurethane resins obtained in Examples 4 to 5 were measured by the same method as described above. The results are shown in Table-2.

Furthermore, Examples 1 to 5 and Comparative Examples 3 to 5
Table 3 shows the measurement results of the moist heat resistance of the cured film obtained by using the polyisocyanate of the thermoplastic polyurethane resin obtained in 1. as the crosslinking agent.

[0049]

[Table 2]

[0050]

[Table 3]

Note 5) Moisture and heat resistance of cured film A solution consisting of 5 parts of Vernock D-750 (a low molecular weight polyisocyanate manufactured by Dainippon Ink and Chemicals, Inc.) was applied to 100 parts of a cyclohexanone solution having a nonvolatile content of 20% on a release paper. The physical properties of the coatings having a thickness of about 100μ obtained by drying at 80 ° C. for 5 minutes and then at 120 ° C. for 10 minutes, and the coatings after 2 weeks at 70 ° C. and 95% relative humidity. Was measured.

Physical properties of the coating: Autogra IM-100 type According to JIS K-6301 manufactured by Shimadzu Corporation. From the results of Tables 1 and 2, it was confirmed that the binders of the present invention according to Examples 1 to 5 contributed to the improvement of the dispersibility of the magnetic powder without impairing the solubility in the organic solvent.

<Abrasion Resistance Test of Magnetic Tape> 40 parts of thermoplastic polyurethane resin binder obtained in Examples 1 to 5 or Comparative Examples 2 to 4 Vinylite VAGH (manufactured by Union Carbide USA, vinyl chloride-vinyl acetate Polymer) 60 parts Cyclohexanone 300 parts Methyl ethyl ketone 300 parts γ-Fe ₂ O ₃ magnetic powder 350 parts Carbon black 12 parts Moisturizing lubricant 5 parts After kneading the above mixture in a ball mill for 24 hours, burnock D-750 (large) After adding 20 parts of low molecular weight polyisocyanate manufactured by Nippon Ink Chemical Co., Ltd. and kneading for 1 hour, the magnetic paint obtained was dried on a polyethylene terephthalate substrate film having a thickness of 10 microns to have a thickness of 10 microns. Was coated and dried, and cut into a predetermined width to prepare a magnetic recording tape. And abrasion resistance was measured.

The measuring method was to rub the magnetic surface of each tape with a rotating disk and measure the amount of abrasion of the coating film. The results are shown in Fig. 1.

From FIG. 1, it was confirmed that the magnetic tapes using the binders of Examples 1 to 5 exhibited superior durability performance.

[0056]

The binder of the present invention can provide a magnetic recording medium excellent in magnetic powder dispersibility, resistance to moist heat, abrasion resistance, fluidity, permanent elongation, solubility in organic solvents and the like.

[0057]

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between wear amount (mg) and time (minutes) of magnetic tapes using the thermoplastic polyurethane resins obtained in Examples 1 to 5 and Comparative Examples 2 to 4. .

Claims (1)

[Claims] 1. A thermoplastic polyurethane resin (A) having a —SO ₃ X group (where X is an alkali metal atom) and a tertiary hydroxyl group in the molecular chain, and a low molecular weight polyisocyanate having two or more isocyanate groups. A binder for a magnetic recording medium comprising (B).