JPH0551008B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to polyurethane resins, and more particularly, to a method for producing polyurethane resins having excellent pigment dispersibility and coating surface smoothness. [Prior Art] Polyurethane resins have excellent abrasion resistance, flexibility, strength, etc., and are therefore widely used in paints, synthetic leathers, and adhesives. Among these, research has been actively conducted recently to improve the use of binders for magnetic recording media. A magnetic recording medium is manufactured by applying a magnetic paint consisting of magnetic powder, a binder, an organic solvent, and other additives as necessary onto a non-magnetic substrate such as a polyester film, and drying the coating. Magnetic recording media are
In order to obtain excellent electrical properties such as high playback output and high signal-to-noise ratio, the binder requires uniform dispersion of magnetic powder and high smoothness of the magnetic coating surface.
Moreover, there is a demand for something with excellent durability. Therefore, in order to satisfy these performances,
Various binders have been studied, and polyurethane resin has been proposed as a resin that improves the durability of magnetic recording media. Conventionally used thermoplastic polyurethane resins are made by reacting a long chain polyol having hydroxyl groups at both ends with an organic diisocyanate and a relatively low molecular weight chain extender such as a diol or diamine having two active hydrogen atoms. Polyester polyols or polyether polyols are mainly used as long chain polyols having hydroxyl groups at both ends. As such polyester polyol,
In general, polyesters synthesized from ethylene glycol, 1,4-butylene glycol or 1,6-hexane glycol, etc. and adipic acid are mentioned, and polyether polyols include polymers or copolymers of ethylene oxide and propylene oxide, Furthermore, polytetramethylene ether glycol, which is a polymer of tetrahydrofuran, is used. However, polyurethane resins using these polyols cannot be said to have sufficient dispersibility of magnetic powder and surface smoothness of the magnetic coating, and polyurethane resins using the above polyester polyols have poor moist heat resistance. On the other hand, polyurethane resins using polyether polyols contain ether bonds and therefore have the drawbacks of being susceptible to oxidative deterioration and having poor heat resistance. Furthermore, Japanese Patent Application No. 138983/1983 describes that the dispersibility of magnetic powder, the surface smoothness and durability of the magnetic layer can be improved by using a polyurethane resin obtained by the reaction of polycaprolactone polyol and an organic diisocyanate compound. However, the dispersibility of magnetic powder,
The surface smoothness of the magnetic layer is insufficient. [Object of the Invention] An object of the present invention is to provide a polyurethane resin that is excellent in pigment dispersibility and smoothness of the surface of a coating film, particularly a polyurethane resin that is excellent as a binder for magnetic recording media. In view of the current situation, the present inventors conducted various studies, and as a result, they polymerized ε-caprolactone using a polyol containing a carboxyl group as an initiator as a polyhydroxy compound having two or more active hydrogen atoms in the molecule. The number average molecular weight obtained by
10,000 carboxyl group-containing polycaprolactone polyol and by reacting this with a polyisocyanate compound to contain a thermoplastic urethane resin in the binder, a conventional thermoplastic urethane resin is used. The object of the present invention has been achieved by discovering that a magnetic recording medium can be obtained which has far superior dispersibility of magnetic powder, surface smoothness of the magnetic layer, and heat and humidity resistance compared to the previous method. [Structure of the present invention] The gist of the present invention is that a polyurethane resin obtained by the reaction of a polyhydroxy compound having two or more active hydrogens in the molecule and a polyisocyanate compound has two or more active hydrogens in the molecule. A polyhydroxy compound having a number average molecular weight of 300 to 10,000 obtained by polymerizing ε-caprolactone using a polyol containing a carboxyl group as an initiator.
The present invention provides a method for producing a polyurethane resin with improved filler dispersibility, characterized by using a compound containing a carboxyl group-containing polycaprolactone polyol. The thermoplastic polyurethane resin has a number average molecular weight of 1000 to 70000, preferably 2000 to 70000.
50000. If the number average molecular weight is less than 1000, the mechanical properties of the polyurethane resin will be poor and the durability of the magnetic recording medium will be poor. If it is more than 70,000, the dispersibility of the magnetic powder will be poor and the surface smoothness of the magnetic recording medium will be poor. The method for producing the polyurethane resin used in the present invention is appropriately selected from known production methods, taking into consideration the degree of polymerization of the desired polyurethane resin, the type of raw materials used, and the like. For example, if necessary,
Usually, an inert solvent is used for the isocyanate group, and if necessary, a regular urethanization catalyst is used.
A carboxyl group-containing polycaprolactone polyol is reacted with a polyisocyanate compound at a temperature range of 10 to 150°C, preferably 20 to 130°C, in an amount such that the hydroxyl groups are stoichiometrically in excess of the isocyanate groups. A method for obtaining a polyurethane resin containing a carboxyl group, or a method for producing a prepolymer having an isocyanate group at the terminal by reacting a polyhydroxy compound that does not contain a carboxyl group with a stoichiometrically excess diisocyanate compound, and then A method for obtaining a polyurethane resin containing a hydroxyl group at the terminal by reacting a carboxyl group-containing polycaprolactone polyol with a chain extender such as a diol, diamine, triol, or a carboxyl group-containing polycaprolactone polyol or a polyhydroxy compound that does not contain a carboxyl group. , a method of simultaneously reacting a chain extender and an organic diisocyanate compound to obtain a polyurethane resin having terminal hydroxyl groups, and the like. The carboxyl group-containing polycaprolactone polyol used in the present invention can be prepared according to a known method.
A compound with an average molecular weight of 300 to 10,000 obtained by ring-opening polymerization of ε-caprolactone in the presence of a catalyst using a polyol containing at least one carboxyl group and at least two hydroxyl groups in the molecule as an initiator. things are used. Examples of polyols containing at least one carboxyl group and at least two hydroxyl groups in the molecule include dimethylolpropionic acid; reaction products of acid anhydrides and polyols, such as trimethylolpropane monosuccinate, trimethylolethane; Compounds such as monosuccinate and glycerin monophthalate can be used. Examples of polyols that do not contain carboxyl groups include known polyhydroxy compounds that are generally used for producing polyurethane resins, such as low molecular weight glycols, polyethers, polyesters, polyacetals, polythioethers, polybutadiene glycols, and silicon-containing polyols. Polyols, phosphorus-containing polyols, etc. can be used. Examples of low molecular weight glycols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, pentaethylene glycol, hexamethylene glycol, neopentyl glycol,
2-ethyl-1,3-hexanediol, N-alkyldiethanolamine, bisphenol A, etc. are used. Furthermore, it is also possible to partially mix and use low molecular weight polyols such as trimethylolpropane. Examples of polyethers include ethylene oxide,
Examples include polymerization products or copolymers of propylene oxide, tetrahydrofuran, and the like. Further, polyethers or mixed ethers obtained by condensation of the above-mentioned low-molecular-weight glycols, and products obtained by addition-polymerizing ethylene oxide or propylene oxide to these polyethers and the above-mentioned low-molecular-weight glycols can also be used. As the polythioether, it is particularly suitable to use thioglycol alone or a condensation product of thioglycol and other glycols. Examples of polyacetals include 1,4-butanediol and formaldehyde or 4,
Examples include water-insoluble polyacetal obtained from 4'-dioxyethoxydiphenyldimethylmethane and formaldehyde. Examples of polyesters include polyesters obtained by dehydration condensation reaction from low-molecular-weight glycols and dibasic acids, and lactone polyols obtained by ring-opening polymerization of lactones such as ε-caprolactone in the presence of the above-mentioned low-molecular glycols. Can be mentioned. In addition, some of the above polyhydroxy compounds include
It is also possible to use a mixture of trifunctional or higher functional polyols. In the present invention, the content of the carboxyl group-containing polycaprolactone polyol is preferably at least 10 wt% based on the total amount of the polyhydroxy compound having two or more active hydrogens in the molecule. If the usage ratio is less than 10 wt%, the dispersibility of the magnetic powder, the surface smoothness of the magnetic coating film, and the heat-and-moisture resistance, which are the characteristics of the present invention, cannot be sufficiently expressed, which is not preferable. The polyisocyanate compounds used in the present invention to react with polyhydroxy compounds to produce polyurethane resins include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenyl Methane diisocyanate, naphthalene-1,5-diisocyanate, toridine diisocyanate, xylylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, lysine ethyl ester diisocyanate, 4,4'-methylene bis( Organic diisocyanate compounds such as cyclohexyl isocyanate), ω,ω'-diisocyanate and dimethylcyclohexane, and adducts of these organic diisocyanate compounds and polyhydric alcohols can be used. Among these organic diisocyanates, good results have been obtained with urethane resins using organic diisocyanates containing diisocyanates having cyclohexyl groups, and in particular, with diisocyanates containing isophorone diisocyanate, good results have been obtained. The urethane resin using NAT is particularly excellent in the dispersibility of magnetic powder and the surface smoothness of the magnetic layer. Chain extenders used in the production of polyurethane resins include glycols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, and pentanediol, bisphenol A, and hydroquinone bis(2). -hydroxyethyl ether), p-xylylene glycol, glycols with aromatic rings such as bis(β-hydroxyethyl) phthalate, ethylenediamine, propylenediamine, hydrazine, piperazine, isophoronediamine, metaphenylenediamine, 4,4 '-Diaminodiphenylmethane, 3,3'-dichloro-
Diamines such as 4,4'-aminodiphenylmethane can be used. It is also possible to use the aforementioned polyhydroxy compounds as chain extenders. In the present invention, the solvent for producing the polyurethane resin is usually methyl ethyl ketone, methyl isobutyl ketone, which is inert to isocyanate groups,
Ketones such as cyclohexanone, esters such as ethyl acetate and butyl acetate, aromatic hydrocarbon solvents such as toluene and benzene, and tetrahydrofuran are used. Catalysts for producing polyurethane resin include tin-based, silver-based, and ordinary urethanization reaction catalysts.
A tertiary amine catalyst is used. Examples of tin-based catalysts include dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin dioctoate, and stannath octoate. Examples of iron-based catalysts include iron acetylacetonate and ferric chloride. Examples of tertiary nitrogen catalysts include triethylamine and triethylenediamine. The magnetic layer of a magnetic recording medium is prepared by kneading a binder, magnetic powder, and, if necessary, each added component with an appropriate organic solvent to prepare a magnetic paint, which is coated on the surface of a nonmagnetic support and then dried. It is formed by As a binder, in addition to the polyurethane resin obtained in the present invention and a low molecular weight polyisocyanate compound as a crosslinking agent, vinyl chloride-vinyl acetate copolymer, nitrocellulose, epoxy resin, and phenoxy resin used as a usual binder component are used. ,
It is also possible to use a mixture of thermoplastic polyurethane resins and the like. Examples of low molecular weight polyisocyanate compounds include adducts of isocyanate compounds having two or more isocyanate groups (adducts with divalent or trivalent polyhydric alcohols, adducts with dimers, trimers, etc.); adduct body etc.) can be used. Examples of such low-molecular weight polyisocyanate compounds include, for example, Deesmodyur L and Deesmodyur N manufactured by Bayer, Coronate L and Coronate HL manufactured by Nippon Polyurethane Industries, Ltd., and Coronate HL manufactured by Mitsubishi Chemical Industries, Ltd. Mitsuku GP105A,
Examples include Mitek NY218A (registered trademark of Mitsubishi Chemical Industries, Ltd.). These low molecular weight polyisocyanate compounds are used in a proportion of 3 to 50% (by weight) of the total amount of binder. The magnetic powder used in the magnetic recording medium of the present invention includes conventionally used and known magnetic powders, such as γ-iron oxide, cobalt-coated γ-iron oxide, cobalt-doped γ-iron oxide, CrO ₂ , alloy magnetic powder, metal magnetic powder, etc. In addition, when forming the magnetic layer of a magnetic recording medium,
Various commonly used additives, as required.
For example, antistatic agents, carbon black, lubricants,
It is also possible to add non-magnetic inorganic pigments and the like. Non-magnetic supports include polyester (e.g. polyethylene terephthalate), polyamide,
Polyolefin, cellulose derivatives, nonmagnetic metals, paper, etc. are used, and the shapes thereof include films, tapes, sheets, cards, disks, etc. The polyurethane resin of the present invention has uses other than binders for magnetic recording media, such as paper coating agents containing fillers such as titanium oxide, water-dispersed type obtained by neutralizing carboxyl groups in the resin with a base, It can also be used as a water-based urethane resin. Furthermore, the polyurethane resin of the present invention can be used as a polyurethane resin that is cured by electron beams or ultraviolet light by introducing an acrylic group or a methacrylic group, and because it has excellent pigment dispersibility, a coating film with excellent surface smoothness can be obtained. It will be done. Any method may be used to introduce the acrylic or methacrylic group that causes a curing reaction with electron beams or ultraviolet rays; for example, a method in which an equimolar reaction product of diisoiricyanate and hydroxyalkyl acrylate is reacted with the polyurethane resin of the present invention. can be mentioned. In addition, although the case where the polyurethane resin of the present invention is used as a magnetic layer of a magnetic recording medium has been described above, the polyurethane resin of the present invention can be used not only for the magnetic layer but also for the so-called top coat layer (of the magnetic layer) of the magnetic recording medium. It can also be applied to the upper surface layer), the back coat layer (the lower layer of the base film), and the undercoat layer (the intermediate layer between the magnetic layer and the base film). Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist of the present invention is exceeded. In the following, the number average molecular weight was measured by gel permeation chromatography.
The columns are 2 G2000 and 1 G3000 manufactured by Toyo Soda.
The experiment was carried out at 40°C using a book and one G4000 using tetrahydrofuran as a solvent. Polystyrene was used as an internal standard. Example 1 (1) Production of polyurethane resin-1 The number average molecular weight was measured in a four-necked flask equipped with a thermometer, a stirrer, a dropping funnel, and a condenser with a drying tube.
1250 bifunctional polycaprolactone polyol (Plaxel 212: manufactured by Daicel Chemical Industries, Ltd., Plaxel is a trademark) 313 g, with a number average molecular weight of 1000 obtained by ring-opening polymerization of ε-caprolactone using dimethylolpropionic acid as an initiator. 250 g of polycaprolactone polyol and 1013 g of methyl isobutyl ketone were charged, the internal temperature was raised to 80° C., and the mixture was stirred. To this was added dropwise 113 g of 4,4'-diphenylmethane diisocyanate from the dropping funnel. After completion of the dropwise addition, a heating reaction was carried out at 80° C. for 9 hours to obtain polyurethane resin-1 having hydroxyl groups and carboxyl groups. (2) Manufacture of magnetic recording media Polyurethane resin-1 300 parts Nitrocellulose (FM manufactured by Daicel Chemical Industries, Ltd.)
-200) 150 parts Vinyl chloride-vinyl acetate copolymer (1000GKT manufactured by Denki Kagaku Kogyo Co., Ltd.) 50 parts Lecithin 10 parts Carbon black 40 parts Co-containing γ-Fe ₂ O ₃ 740 parts Methyl ethyl ketone 920 parts Methyl isobutyl ketone 310 parts Cyclohexanone 310 parts After kneading the mixture with the above composition in a sand grind mill for 6 hours,
50 parts of GP105A (manufactured by Mitsubishi Chemical Industries, Ltd.: TDI and trimethylolpropane reactant) were mixed and filtered to obtain a magnetic paint. This magnetic paint was applied onto a polyethylene terephthalate film so that the film thickness after drying was 5 μm, the solvent was removed using a hot air dryer, and the surface was smoothed by calendering. Thereafter, a magnetic recording medium was obtained by heat treatment at 60°C for 24 hours. Table 1 shows the results of measuring the surface reflectance of the magnetic coating film of the obtained magnetic recording medium. Example 2 (1) Production of polyurethane resin-2 Into the same apparatus as in Example 1, 313 g of bifunctional polycaprolactone polyol (Plaxel 212: manufactured by Daicel Chemical Industries, Ltd.) with a number average molecular weight of 1250 and dimethylolpropionic acid were added. 250 g of polycaprolactone polyol with a number average molecular weight of 1000 obtained by ring-opening polymerization of ε-caprolactone as an agent;
995 g of methyl isobutyl ketone and 0.08 g of dibutyltin dilaurate were charged, the internal temperature was brought to 80° C., and the mixture was stirred. 100 g of isophorone diisocyanate was added dropwise to this. After the dropwise addition was completed, a heating reaction was carried out at 80° C. for 9 hours to obtain polyurethane resin-2 having hydroxyl groups and carboxyl groups. (2) Manufacture of magnetic recording medium A magnetic recording medium was manufactured in the same manner as in Example 1, except that polyurethane resin-2 was used instead of polyurethane resin-1. Table 1 shows the results of measuring the surface reflectance of the magnetic coating film of the obtained magnetic recording medium. Example 3 (1) Production of polyurethane resin-3 100 g of 4,4'-diphenylmethane diisocyanate and 807 g of methyl isobutyl ketone were charged into the same apparatus as in Example 1, and the mixture was stirred at an internal temperature of 80°C. 438 g of bifunctional polycaprolactone polyol having a number average molecular weight of 1250 was added dropwise to this. After the dropwise addition was completed, a heating reaction was carried out at 80°C for 2 hours to produce a prepolymer having isocyanate groups at the terminals. Subsequently, this reaction product was added dropwise to a mixed solution of 75 g of polycaprolactone polyol having a number average molecular weight of 1000 obtained by ring-opening polymerization of ε-caprolactone using dimethylolpropionic acid as an initiator and 113 g of methyl isobutyl ketone.
After the dropwise addition was completed, a heating reaction was carried out at 90°C for 10 hours to obtain polyurethane resin-3 having hydroxyl groups and carboxyl groups. (2) Manufacture of magnetic recording medium A magnetic recording medium was manufactured in the same manner as in Example 1, except that polyurethane resin-3 was used instead of polyurethane resin-1. Table 1 shows the results of measuring the surface reflectance of the magnetic coating film of the obtained magnetic recording medium. Comparative Example 1 (1) Production of Polyurethane Resin-4 625 g of bifunctional caprolactone polyol with a number average molecular weight of 1250, 1088 g of methyl isobutyl ketone, and 0.09 g of dibutyltin dilaurate were charged into the same apparatus as in Example 1, and the internal temperature was raised to 80°C. Stirred. This includes isophorone diisocyanate.
100g was dropped. After the addition was completed, a heating reaction was carried out at 80° C. for 9 hours to obtain polyurethane resin-4. (2) Manufacture of magnetic recording medium A magnetic recording medium was manufactured in the same manner as in Example 1, except that polyurethane resin-4 was used instead of polyurethane resin-1. Table 1 shows the results of measuring the surface reflectance of the magnetic coating film of the obtained magnetic recording medium. Comparative Example 2 (1) Production of Polyurethane Resin-5 100 g of diphenylmethane diisocyanate and 450 g of methyl isobutyl ketone were charged into the same apparatus as in Example 1, and the mixture was stirred at an internal temperature of 80°C. To this was added dropwise 350 g of polyester diol having a number average molecular weight of 1000 consisting of 1,4-butanediol and adipic acid. 2 at 80℃ after completion of dripping
A heating reaction was carried out for a period of time to produce a prepolymer with terminal isocyanate groups. Subsequently, this reaction product was added dropwise to a mixed solution of 5.4 g of 1,4-butanediol and 233 g of methyl isobutyl ketone. After the dropwise addition was completed, a heating reaction was carried out at 80°C for 8 hours to obtain polyurethane resin-5. (2) Manufacture of magnetic recording medium A magnetic recording medium was manufactured in the same manner as in Example 1, except that polyurethane resin-5 was used instead of polyurethane resin-1. Table 1 shows the results of measuring the surface reflectance of the magnetic coating film of the obtained magnetic recording medium. Furthermore, a solution of 11 parts of Mitek GP105A as a crosslinking agent was applied to 100 parts of the polyurethane resin obtained in Examples 1 and 2 and Comparative Examples 1 and 2.
Mechanical properties of a cured film with a thickness of about 100μ obtained by leaving it at room temperature for 30 minutes and then drying it at 80℃ for 4 hours, and the cured film after 2 weeks under moist heat conditions of 70℃ and 95% relative humidity. The mechanical properties of the material were measured. The results are shown in Table 2. Example 4 (1) Production of polyurethane resin-6 750 g of polycaprolactone polyol with a number average molecular weight of 1500 obtained by ring-opening polymerization of ε-caprolactone using dimethylolpropionic acid as an initiator in the same apparatus as in Example 1, 1294 g of methyl isobutyl ketone was charged, the internal temperature was raised to 80°C, and the mixture was stirred. To this was added dropwise 113 g of 4,4'-diphenylmethane diisocyanate. After dripping
A heating reaction was carried out at 80° C. for 9 hours to obtain polyurethane resin-6 having hydroxyl groups and carboxyl groups. Polycaprolactone polyol/polyhydroxy compound (A) of the present invention ×100=100% (2) Manufacture of magnetic recording medium Example 1 except that polyurethane resin-6 was used instead of polyurethane resin-1 of Example 1. A magnetic recording medium was manufactured in the same manner as described above. Table 1 shows the results of measuring the surface reflectance of the magnetic coating film of the obtained magnetic recording medium.

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[Effects of the present invention]

The polyurethane resin of the present invention is a resin obtained by the reaction of a polyisocyanate compound and the above-specified polyhydroxy compound, and has superior effects in dispersibility, surface smoothness, and heat-and-moisture properties compared to conventional products. It is something.

Claims (1)

[Claims] 1 A polyurethane resin obtained by the reaction of a polyhydroxy compound having two or more active hydrogens in the molecule and a polyisocyanate compound, which contains a carboxyl group as a polyhydroxy compound having two or more active hydrogens in the molecule Production of a polyurethane resin with improved filler dispersibility characterized by using a compound containing a carboxyl group-containing polycaprolactone polyol with a number average molecular weight of 300 to 10,000 obtained by polymerizing ε-caprolactone using a polyol as an initiator. Method.