JPH0581968B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a binder for magnetic recording media, and more particularly to a binder for magnetic recording media characterized by containing a specific polyurethane resin that has excellent dispersibility and adhesion of magnetic powder. In recent years, as the uses of magnetic recording media such as audio tapes and home VTR tapes have expanded, the required performance has also become more diverse, and the demand for high reliability during recording and playback has increased in particular. . Specific examples include high-density recording for reproducing clear images and sounds, high-speed running for long periods of time under harsh conditions such as high temperature and high humidity, and the ability to prevent magnetic powder from falling off from the magnetic layer. Examples include things that do not occur. The important function of the binder is to maintain the characteristics and physical properties of the magnetic layer mentioned above. Therefore, there is a demand for materials with excellent durability such as wear resistance. For this reason, various binders have been researched in order to satisfy these properties.
A polyurethane resin has been proposed as the main binder, which imparts good wear resistance to the magnetic layer and improves the durability of the magnetic recording medium. The polyurethane resin used as this binder is a prepolymer with a relatively low molecular weight (for example, less than 10,000), which is made by modifying a polyol with isocyanate, etc., and has many functional groups, and a prepolymer with a relatively low molecular weight (for example, less than 10,000), which has very few functional groups and has a relatively high molecular weight ( For example, 10,000 or more thermoplastic polyurethane resins. The thermoplastic polyurethane resin used as a binder component has a molecular weight of 10,000 to 50,000, especially 15,000 to 50,000.
35,000 substantially linear polyurethane resin is commonly used, and at present there is still room for improvement in terms of dispersibility of magnetic powder. Polyurethane resins with a molecular weight of 50,000 or more improve the abrasion resistance of the magnetic layer, but they often severely deteriorate the dispersibility of magnetic powder, making it difficult to form them into paints. On the other hand, urethane prepolymer (molecular weight less than 10,000)
Although polyurethane resin is superior to polyurethane resin in terms of dispersibility of magnetic powder, it has disadvantages such as the magnetic powder falling off and becoming sticky due to inferior abrasion resistance of the magnetic layer.Urethane resin, which has better abrasion resistance, It was difficult to obtain the prepolymer. The present inventor has proposed a method for improving the above drawbacks.
As a result of various studies, -SO ₃ X group (however,
Pigment dispersibility and adhesion are improved by using a polyurethane resin into which X is an alkali metal atom), an aromatic ring, and a tertiary hydroxyl group, and by using a low molecular weight polyisocyanate in combination. Moisture and heat resistance of urethane resin after curing,
The present invention was completed by discovering that it also improves durability such as abrasion resistance. That is, the present invention has (A-1) an SO ₃ X group (however, an alkali metal atom) in the molecular chain;
2) The polyurethane resin has 30% or less of aromatic rings derived from those contained in the polyol, and (A-3) has a tertiary hydroxyl group at a position other than both ends of the main chain (A-4) The present invention provides a binder for magnetic recording media comprising a polyurethane resin (A) having a molecular weight of 5,000 to 50,000 and a low molecular weight polyisocyanate (B) having two or more isocyanate groups. The polyurethane resin (A) used in the present invention has a number average molecular weight of 5,000 to 50,000, preferably 3,000 to 50,000.
30,000, more preferably 8,000 to 20,000. The average number of -SO ₃
10 is desirable, and X is an alkali metal atom, preferably Na or K. Some aromatic rings are derived from isocyanates and polyols, but isocyanate-based aromatic rings increase the concentration of urethane groups, resulting in a decrease in adhesion, so we recommend using aromatic rings derived from those contained in polyols. The amount thereof in the polyurethane resin is desirably 30% or less, preferably 3 to 20%. Further, if the number average molecular weight is less than 5,000, it is difficult to obtain a polyurethane resin having -SO ₃ If _the number of -SO ₃
This is not preferred because the increased hydrophilicity of the group leads to poor solubility in organic solvents and poor water resistance. Furthermore, if the number of tertiary hydroxyl groups in one molecule is less than 0.5, it is difficult to improve the heat and humidity resistance of the urethane resin after curing. Moreover, if the aromatic ring content in the polyurethane resin exceeds 30%, the solubility in organic solvents will be significantly reduced, and if it is less than 3%, no improvement in adhesion will be obtained, which is not preferable. The polyurethane resin (A) used in the present invention may have an isocyanate group or a hydroxyl group at both ends, or an isocyanate group at one end and a hydroxyl group at the other end, but preferably a hydroxyl group at both ends. It is. The polyurethane resin used in the present invention includes organic diisocyanate (A ₁ ) and (A ₂ ) containing -SO ₃ X groups in the molecular chain, diol (A ₃ ) containing an aromatic ring, and the diol. and in the molecular chain −
Polyols (A ₄ ) containing SO ₃
It can be obtained by polymerizing a mixture of
Polymer of (A ₁ ) and (A ₂ ), Polymer of (A ₁ ) and (A ₃ ), Polymer of (A ₁ ) and (A ₃ ), (A ₁ ) and (A ₂ ) +
Separately prepare a polymer of (A ₃ ), a polymer of (A ₁ ) and (A ₂ ) + (A ₄ ), and a polymer of (A ₁ ) and (A ₃ ) + (A ₄ ). They may be polymerized or a mixture of these may be used. Examples of the organic diisocyanate (A ₁ ) include 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, 1,5
- naphthylene diisocyanate and mixtures thereof. Preferably, it is a non-aromatic diisocyanate. Diols (A _{2 )} containing -SO ₃ Dibasic acids such as sulfosuccinate - sodium sulfonate or their esters and succinic acid, maleic acid, adipic acid, glutaric acid, pimelic acid,
Dibasic acids such as superric acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, hexahydroterephthalic acid, and hexahydroisophthalic acid, and mixtures of these acid esters and glycols having 2 to 10 carbon atoms. 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,
Examples include polyester diols having a molecular weight of 500 to 6,000 obtained by polycondensation with glycols such as cyclohexane-1,4-diol and cyclohexane-1,4-dimethanol alone or with a mixture thereof. Further, a mixture of dialkanol sulfoisophthalate and dialkanol sulfosuccinate and unreacted glycol obtained by transesterification reaction between the ester of sodium sulfonate and excess glycol having 2 to 10 carbon atoms. can be mentioned. As diols (A ₃ ) having an aromatic ring,
Preferred are polyester diols and polyether diols having a molecular weight of 500 to 3,000, such as aromatic dibasic acids such as terephthalic acid and isophthalic acid, or their esters alone or in combination with the above aliphatic dibasic acids and their acid esters. Examples include polyester diols obtained by polycondensing the above glycols alone or in mixtures. Further examples include polyether diols in which 2 to 4 moles of ethylene oxide, butylene oxide, or propylene oxide are added to bisphenol A, hydroquinone, or the like. -SO ₃ Polyols containing tertiary hydroxyl groups (A ₄ ) that do not contain X groups have a molecular weight of 500
~6000 diols may be mixed, or low molecular weight diols having 2 to 10 carbon atoms, triols having 4 to 10 carbon atoms having a tertiary hydroxyl group in the molecular chain, and these triols can be used. Terminal hydroxyl group and at least one tertiary hydroxyl group in the molecular chain
Polyols such as polyether polyols and polyester polyols having a molecular weight of 500 to 6,000 or more may be used alone. 4 to 10 carbon atoms with tertiary hydroxyl group in the molecular chain
As the triol, for example, 1,2,3-hydroxy-2-methyl-propane, 1,2,3-hydroxy-2-ethylpropane, 1,2,4-hydroxy-2-methylbutane, 1,2,5 Monomers or mixtures such as -hydroxy-2-methylpentane, 1,3,5-hydroxy-3-methylpentane, and 1,3,6-hydroxy-3-methylhexane are mentioned. In addition, the molecular weight having the above-mentioned tertiary hydroxyl group is 500~
Examples of polyether polyols include polypropylene ether polyol, polyethylene polyol, and polybutylene polyol, which are obtained by adding propylene oxide, ethylene oxide, or butylene oxide to polyol 6000. Furthermore, examples include polyesters obtained by polycondensing a triol having a tertiary hydroxyl group and the low molecular weight glycol with the dibasic acid, these acid esters, and acid halides; Examples include polycaprolactone polyols obtained by ring-opening addition polymerization of a lactone such as caprolactone in the presence of a mixture of the triol and glycol. It is essential that the hydroxyl group in the molecular chain of the polyol be tertiary. Primary and secondary hydroxyl groups have faster reactivity with isocyanates than tertiary hydroxyl groups, leading to higher molecular weight or reticulation of polyurethane, making it difficult to produce linear polyurethane resin. This is due to Furthermore, if necessary, an aliphatic diol having a linear terminal hydroxyl group and having a molecular weight of 500 to 6,000 can be used. Examples of diols having a linear terminal hydroxyl group and having a molecular weight of 500 to 6,000 include polyester polyols and polyether polyols. Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like. The polyester polyol has 2 to 10 carbon atoms as described above.
with a glycol alone or in a mixture having -
Examples include polyester polyols obtained by polycondensing the aforementioned dibasic acids that do not contain an SO ₃ Examples include polycaprolactone diols subjected to ring-opening addition polymerization in the presence of. In addition, when producing the polyurethane resin (A) used in the present invention, the OH/NCO molar ratio of polyol and organic diisocyanate is set to 1.00, taking into account impurities (moisture, acid, hydrolyzed chlorine, etc.) in each raw material.
~2.00/1.00, preferably 1.00~1.50/1.0.
If it deviates from these ranges, it is not preferable because the excellent performances required by the present invention cannot be obtained. If necessary, a catalyst and various stabilizers can be used in the thus obtained polyurethane resin having an SO ₃ X group, an aromatic ring, and a tertiary hydroxyl group. Examples of catalysts 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. By incorporating stabilizers against ultraviolet light such as substituted benzotriazoles and stabilizers against thermal oxidation such as phenol derivatives, the above-mentioned properties of polyurethane can be significantly stabilized. Furthermore, in producing the above-mentioned polyurethane resin, conventionally known methods can be used, and if desired, after sufficiently mixing the reactants in the presence of a catalyst, the reaction mixture is placed on a flat plate or flat surface. A method of pouring the reaction mixture into an extruder, heating it, cooling it and then crushing it; a method of injecting the reaction mixture into an extruder; and a method of dimethylformamide, toluene, xylene, benzene, dioxane, cyclohexanone, methyl ethyl ketone,
Conventional production methods such as a solution reaction method in which the reaction is carried out in a single or mixed organic solvent such as methyl isobutyl ketone, ethyl acetate, and butyl acetate can be used. Among these, when used for magnetic paints, including those for dissolving and diluting solid thermoplastic polyurethane resin, toluene, xylene, benzene, etc., which have low affinity and solubility with water, and cyclohexanone, methyl ethyl ketone, which have excellent solubility, , methyl isobutyl ketone, ethyl acetate, butyl acetate and the like are preferred. In the present invention, it is essential to use the polyurethane resin (A) after curing with a suitable curing agent, and low molecular weight polyisocyanate is used as the curing agent.
(B) is used. Examples of the low molecular weight polyisocyanate (B) having two or more isocyanate groups used in the present invention include organic diisocyanates used in the production of the polyurethane resin (A) and low molecular weight polyisocyanates having two or more isocyanate groups (for example, low molecular weight polyisocyanates having two or more isocyanate groups). Examples include compounds in which a molecular weight polyol is terminally sisocyanate grouped with a sisocyanate compound, and have a molecular weight of about 150 to 7,000. Examples of low molecular weight polyisocyanates having two or more isocyanate groups include the following compounds.

[C] Commercially available products of this formula include Burnock D-750,
Crisbon NX (Dainippon Ink & Chemicals Co., Ltd. product),
Desmodeur L (Sumitomo Bayer product), Coronate L (Nippon Polyurethane product), Takenate
Examples include D102 (product of Takeda Pharmaceutical Co., Ltd.).

[Chemical] Commercial product Burnock D-950 (Dainippon Ink & Chemicals Co., Ltd. product) Triphenylmethane 4,4',4''-triisocyanate

[ka]

[Chemical formula] The polyurethane resin (A) of the present invention itself has excellent dispersibility and adhesion to substrates, but it is used in combination with a low molecular weight polyisocyanate (B). Although the ratio of polyurethane resin (A) and low molecular weight polyisocyanate (B) is not particularly limited,
Preferably, by adding 3 to 100 parts of the above-mentioned low molecular weight polyisocyanate to 100 parts of the above-mentioned polyurethane resin and curing the urethane resin, the mechanical strength, abrasion resistance, heat resistance, moist heat resistance, and resistance of the urethane resin after curing are further improved. Solvent properties and adhesion to substrates can be improved. In addition, if necessary for the above thermosetting urethane resin, a commonly used thermoplastic polyurethane resin,
Vinyl chloride-vinyl acetate copolymer, cellulose resin, vinyl chloride polymer, polyvinyl butyral resin, thermoplastic polyester resin, vinyl chloride-
By using commercially available products such as vinyl propionate copolymers, epoxy resins, and phenoxy resins in combination, they can be used to improve the dispersibility of pigments, adjust the hardness of resins, and the like. Next, the present invention will be explained with reference to examples, but these are only one aspect and the present invention is not limited only by the examples. In addition, all "parts" in the text indicate weight standards. Example [1] Range of aromatic rings in polyurethane resin Polyester diol (P-1) with a molecular weight of 1000 (hydroxyl value 112) consisting of ethylene glycol and adipic acid, and ethylene glycol, terephthalic acid, and perisophthalic acid (terephthalic acid/isophthalic acid) acid, 0.4/0.6 molar ratio) with a molecular weight of 1000
(hydroxyl value 112) polyester diol (P-
100 parts of the mixture of 2) (the blending ratio is shown in Table 1),
After mixing 100 ppm of dibutyltin dilaurate, hexamethylene diisocyanate was mixed with NCO/OH
They were added at a molar ratio of =1.00/1.03. Before mixing these components, the polyol and isocyanate were heated to 100°C and 40°C, respectively. The isocyanate was added to the polyol mixture with mechanical mixing for approximately 1 minute to ensure intimate contact of the components. Next, this reaction mixture was poured onto a pot heated to 120°C for 1 hour and then left to stand at 100°C for 20 hours to complete the reaction, thereby preparing a polyurethane resin. Table 1 shows the measurement results of the aromatic ring content of the obtained polyurethane resin, solubility in organic solvents, number average molecular weight, and dispersibility of the magnetic powder adhering to the polyester film.

【table】

[Table] From Table 1, it can be seen that adhesion is improved when the aromatic ring content is 3 to 30%. However, it is clear that it is necessary to improve the dispersibility of magnetic powder. [2] Number of SO ₃ Na groups in polyurethane resin, number of tertiary hydroxyl groups, and molecular weight range of polyurethane resin Molecular weight 2000 (adipic acid/5-sodium Table 2 shows the molar ratio range of sulfodimethyl isophthalate.
is shown. Polyester diol with hydroxyl value 56.1), the aromatic ring-containing polyester diol (P-2), 1,3,5-hydroxy-3-
After mixing methylpentane (see Table 2 for the recipe) and 100 ppm dibutyltin dilaurate (based on polyol), add hexamethylene diisocyanate.
A polyurethane resin was prepared in the same manner as in 1 with NCO/OH ^- 0.80/1.00 to 1.05/1.00. Aromatic ring content of the obtained polyurethane resin,
Number of SO ₃ Na groups (Note 6), Number of tertiary hydroxyl groups (Note 7),
Table 2 shows the measurement results of solubility in organic solvents, number average molecular weight, adhesion to polyester film (Note 8), and dispersibility of the magnetic powder.

【table】

【table】

[Table] [3] Moisture and heat resistance of uncured film and cured film (3-1) Moisture and heat resistance of uncured film A dimethylformacide solution with a non-volatile content of 20% was applied to release paper, heated at 80℃ for 5 minutes, then heated at 120℃ for 5 minutes. ℃
The physical properties of the film with a thickness of approximately 100μ obtained by drying for 10 minutes at 70℃
The physical properties of the film were measured after 3 weeks at a relative humidity of 95%. The results are shown in Table-3. (3-2) Moisture and heat resistance of cured film Cyclohexanone solution with non-volatile content 20% 100
A solution consisting of 15 parts of Burnock D-720 (a low molecular weight isocyanate manufactured by Dainippon Ink and Chemicals Co., Ltd.) (40 parts for Example 2 and 25 parts for Example 2) was applied onto a release paper, and the mixture was heated at 80°C for 5 parts. minute, next
Approximately 100μ film thickness obtained by drying at 120℃ for 10 minutes
The physical properties of the films and the further development of these films.
The physical properties of the film were measured after 3 weeks at 70°C and 95% relative humidity. The results are shown in Table-3. Film physical properties: Autogra IM-100 type, according to JIS K-6301 manufactured by Shimadzu Corporation.

【table】

Claims (1)

[Scope of Claims] 1 (A-1) having an SO ₃ 30% or less in the polyurethane resin, and (A-3) has a tertiary hydroxyl group at a position other than both ends of the main chain (A-3)
-4) Polyurethane resin with a molecular weight of 5000 to 50000
A binder for magnetic recording media comprising (A) and a low molecular weight polyisocyanate (B) having two or more isocyanate groups.