JPH0547891B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording medium with improved wear resistance. Polyester resins with sulfonic acid groups are
Since it has excellent dispersibility in magnetic powder, it has been used as a main binder in magnetic recording media, ie, magnetic tapes such as video tapes and audio tapes. However, in recent years, with the spread of home video and audio equipment in general households, the performance requirements for such magnetic tapes have become increasingly strict. There is a need for products with excellent performance. Such performance is largely due to the physical properties of the magnetic binder, but since there is a limit to its improvement with the binder alone, conventionally a crosslinking agent such as an isocyanate compound is blended in addition to the main component resin. However, there is a limit to the improvement in abrasion resistance even when the compound is blended, and the tape itself tends to become brittle. In other words, the abrasion resistance of magnetic tapes, etc. does not simply mean that they are hard, but that they are good if they can withstand frictional heat from the magnetic head and at the same time have appropriate elongation and flexibility. Therefore, such requirements cannot be met by blending isocyanate compounds. In addition, blending these compounds complicates work and requires extreme care in handling, so in the industry, there is no need to worry about blending such compounds, as the resin itself has wear resistance and is resistant to magnetic particles. There is also a desire to develop a magnetic recording medium with excellent dispersibility. However, as a result of intensive research in order to solve this problem, the inventor of the present invention found that the resin contained a molecular weight of 500 to
3000 polytetramethylene glycol component is bound to 5 to 15% by weight of the entire polyester resin,
Moreover, it was discovered that a magnetic recording medium based on a polyester resin containing 0.2 to 10 mol% of a sulfonic acid base component based on the polyhydric carboxylic acid component has excellent performance, and in order to complete the present invention. It has arrived. The polyester resin used in the present invention is
In particular, by introducing a specific amount of polytetramethylene glycol component with a specific molecular weight (hereinafter abbreviated as PTMG) into the resin, the above-mentioned performance can only be obtained and it can be used as a magnetic recording medium. If a polyglycol other than PTMG, such as polyethylene glycol, is used in place of PTMG, it may cause problems such as insufficient water resistance and deterioration over time. This goal cannot be achieved. The composition of the resin will be explained in detail below. First, the PTMG introduced into the polyester resin needs to have a molecular weight of 500 to 3,000, more preferably 700 to 2,000. If the molecular weight is less than 500, it is difficult to improve the abrasion resistance, and if it is more than 3,000, the compatibility with the solvent decreases and the dispersibility becomes poor, so that it cannot be used practically. PTMG is also incorporated into the polyester resin at 5-15% by weight. If it is less than 5% by weight, the wear resistance that is a feature of the present invention cannot be obtained,
When the amount is more than 15% by weight, the dispersibility of the magnetic particles becomes poor. The sulfonic acid base component introduced into the resin together with PTMG is in the range of 0.2 to 10 mol%, more preferably 0.4 to 5 mol%, based on the polyhydric carboxylic acid component. Below 0.2 mol%, the dispersibility decreases, while 10
When the amount exceeds mol%, the solubility of the resin in the solvent deteriorates, resulting in deterioration of workability during coating. There are no particular restrictions on the method of introducing the group, but specifically the following methods are available. 1) A method in which a polyhydric alcohol containing a sulfonic acid group is used as a component of a polyester resin. 2) A method in which a sulfonic acid group-containing polycarboxylic acid is used as a component of a polyester resin. Among these methods, method 1) is the most advantageous overall in terms of production method and performance of the resin obtained. In method 1), the sulfonic acid group-containing polyhydric alcohol is preferably an unsaturated polyhydric alcohol to which an acidic sulfite is added. The reaction is carried out, for example, by heating an unsaturated polyhydric alcohol and an acidic sulfite to about 70°C in the presence of iron oxide. Such unsaturated polyhydric alcohols include 3-
Butene-1,2-diol, 2-butene-1,4
-diol, 2,5-dimethyl-3-hexene-
Olefinic glycols such as 2,5-diol,
1,5-hexadiene-3,4-diol, 2.
Examples include diolefin glycols such as 6-octadiene-4,5-diol. As the acidic sulfite base, acidic sodium sulfite, acidic potassium sulfite, etc. are practically used. Alternatively, a sulfonic acid group-containing polyhydric alcohol can also be prepared by reacting two or more epoxy group-containing compounds with an acidic sulfite. In the method 2), examples of the sulfonic acid group-containing polycarboxylic acid include 5-sodiosulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 2-sodiosulfoterephthalic acid, and 2-potassium sulfoterephthalic acid. When producing a polyester resin, the above components are condensed with a polyhydric carboxylic acid and a polyhydric alcohol. There is no problem in using commonly used polyhydric carboxylic acids and polyhydric alcohols, but the most preferable composition for magnetic recording media, and in which the characteristics of the present invention are significantly exhibited, is a) 40% of the polyhydric carboxylic acid component. ~100 mol% is terephthalic acid and/or isophthalic acid, b) 40 to 100 mol% of the polyhydric alcohol component is ethylene glycol and/or neopentyl glycol, c) The sulfonic acid group-containing monomer is a polyhydric carboxylic acid component d) 5 to 15% by weight of PTMG having a molecular weight of 500 to 3000 based on the total polyester resin is preferred. In a), terephthalic acid and isophthalic acid are 40
If the amount is less than mol%, the strength of the resin tends to be insufficient. In b), if the ethylene glycol or neopentyl glycol is outside this range, the resin strength may be insufficient as in a), or the solubility in general-purpose solvents may deteriorate, resulting in a decrease in workability. Examples of polyvalent carboxylic acids other than the above include oxalic acid, malonic acid, dimethylmalonic acid, succinic acid,
Glutaric acid, adipic acid, trimethyladipic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaic acid, sebacic acid, 1,3-cyclohexanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexane Dicarboxylic acid, phthalic acid, 2,5-norbornanedicarboxylic acid, 1,4-naphthalic acid, diphenic acid,
4,4'-oxybenzoic acid, diglycolic acid, thiodipropion, 4,4'-sulfonyldibenzoic acid,
Examples include saturated carboxylic acids such as 2,5-naphthalene dicarboxylic acid. Among these, aliphatic dicarboxylic acids are preferably used in an amount of 50 mol % or less based on the acid component. If necessary, unsaturated carboxylic acids such as maleic acid, maleic anhydride, fumaric acid, itaconic acid, and citraconic acid may be used in combination. The above carboxylic acid may be in the form of a lower alkyl ester or an acid chloride. Polyhydric alcohol components other than the above include diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol,
Examples include 1,4-butanediol, 1,6-hexanediol, cyclohexanedimethanol, pentaerythritol, trimethylolpropane, and glycerin. Furthermore, if necessary, 3-butene-1,2 diol,
Olefinic glycols such as 2-butene-1,4 diol, 2,5-dimethyl-3-hexene-2,5 diol, 1,5-hexadiene-3,4 diol, 2,6-octadiene-4,5- It is also possible to use unsaturated polyhydric alcohols such as diols. Any conventionally known method can be used to produce the resin, but usually 1.3 to 3 mol of polyhydric alcohol component and 0.002 to 0.1 mol of sulfonic acid group-containing monomer are used per 1 mol of polyhydric carboxylic acid component. Mol,
PTMG0.009 to 0.04 mol (however, if the molecular weight is 1000
A stirrer with the ester catalyst, polycondensation catalyst, and stabilizer, either all at once or in the appropriate order at a ratio of (converted to PTMG),
The mixture is charged into a reaction vessel equipped with a total condenser, partial condenser, and torque meter, and esterified at a temperature of 150 to 230°C, followed by polycondensation under reduced pressure if necessary to obtain the desired product. As the esterification catalyst, dibutyltin oxide or zinc acetate is used, as the polycondensation catalyst, antimony oxide, etc. are used, and as the stabilizer, phosphoric acid, triethyl phosphoric acid, etc. are used. The polyester resin thus obtained is used as a magnetic recording medium by blending magnetic powder and other substances necessary for magnetic recording tapes, but excellent wear resistance can be obtained even without the addition of isocyanate compounds. It will be done. Of course, this does not in any way hinder the blending of isocyanate compounds, and if necessary, they may be used in an amount of about 0.1 to 10% by weight based on the polyester resin. Conventionally known isocyanate compounds include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,
4 and 2,6-tolylene diisocyanate mixture, 4,4'-diphenylmethane diisocyanate, m-phenylene diisocyanate, xylylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate ester, 1,4-cyclohexylene diisocyanate , 4,4'-dicyclohexylmethane diisocyanate, 3,3'-dimethyl-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 3,3'-dichloro-4,4' -biphenylene diisocyanate, 1,5-naphthalene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, etc. are used. Compositions of tolylene diisocyanate and 4,4'-diphenylmethane diisocyanate, carbodiimide-modified 4,4'-diphenylmethane diisocyanate, and modified products such as adducts of the above isocyanates to trimethylolpropane and the like can also be used. . The above-mentioned isocyanate compounds may be used alone or as a mixture of two or more. Magnetic powders include pure iron, γ-Fe ₂ O ₃ , CrO ₃ ,
Fe ₂ O ₃ (Co), Fe ₃ O ₄ , Fe ₃ O ₄ (Co), Co−Fe, Co
−Ni, Co−Ni−Fe, Fe−Ni−Zn, Fe−Mn−
Zn, Co-Ni-Fe-B, Co-Ni-P, Fe-Co-
Examples include Ni-P. The blending ratio of the polyester resin and magnetic powder is not particularly limited, but is often set to a weight ratio of 1:1 to 1:7. The above components are uniformly mixed with a suitable solvent such as cellosolve acetate, butyl cellosolve acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, benzene, toluene, xylene, etc., and coated onto the substrate. In this case, crosslinking agents such as epoxy resins and melamine resins, known binders other than the polyester resin of the present invention such as polyester, ethyl cellulose, nitrocellulose, vinyl chloride-vinyl acetate copolymers, and plasticizers such as dibutyl phthalate and triphenyl phosphate. In addition, appropriate amounts of lubricants, antistatic agents, wetting agents, anti-grooming agents, etc. may be added. The base material is film, tape, sheet, disk,
It may be a card, a drum, etc., and various materials are selected depending on the form. For example, when the substrate is in the form of a film or tape, films or tapes made of acetyl cellulose, polyester, polycarbonate, polyvinyl chloride, polypropylene, polyimide, etc. are used. As a means for applying the composition onto the substrate, a doctor knife method, a blade coating method, a reverse roll method, a gravure method, a cast coating method, a spray coating method, etc. are all employed. After the composition is applied onto the substrate directly or via an anchor coat layer, the coating film is subjected to a magnetic field orientation treatment using a solenoid coil or the like while it is still undried, and then dried. The magnetic recording medium thus obtained is used for magnetic recording tapes, video recording tapes, tapes for computers and measuring instruments, magnetic cards, magnetic disks, etc., and has excellent wear resistance as well as dispersibility of magnetic powder. It has excellent smoothness and gloss. Next, the magnetic recording medium of the present invention will be further explained by giving an example. Example 1 In a four-necked flask equipped with a thermometer, a stirrer, and a packed column, 0.5 mol of terephthalic acid was added under a nitrogen stream.
0.4 mol of isophthalic acid, 0.1 mol of sebacic acid, 0.75 mol of ethylene glycol, 0.7 mol of neopentyl glycol, 0.005 mol of 2-sodiosulfo-1.4-butanediol and 0.02 mol of PTMG with a molecular weight of 1000 are charged together with 0.1 part of dibutyltin oxide.
Esterification reaction was carried out at 150°C to 230°C with stirring, then 0.1 part of antimony trioxide was added and condensation was carried out at 220°C to 260°C under reduced pressure of 1 torr or less to obtain a polyester resin. When the resin was analyzed, the content of PTMG was 8.5% by weight based on the entire resin, and the content of sulfonic acid groups was 0.5% by mole based on the polyhydric carboxylic acid component. The performance of the polyester resin as a binder for magnetic tape was evaluated in accordance with the following. 130 parts of polyester resin, 190 parts of γ-Fe ₂ O ₃ , 290 parts of toluene, 3 parts of dioctyl sulfonodium succinate, 3 parts of silicone oil, 190 parts of methyl ethyl ketone, 100 parts of methyl isobutyl ketone,
60 parts of n-butavanol was dispersed for 70 hours using a ball mill, and then filtered and defoamed to obtain a magnetic paint. This magnetic coating was applied onto a 25μ thick polyethylene terephthalate film (stretched product) using the doctor knife method, then oriented in a parallel magnetic field of 1000 oersted, and then dried at 80°C to form a 5μ thick magnetic coating. was formed. The following tests were conducted on this magnetic coating film. Abrasion resistance: After curing the obtained magnetic tape at 40° C. for 3 days, it was evaluated using a taper type abrasion tester based on the number of rotations until the magnetic layer fell off. Breaking strength/breaking elongation: Peel off the magnetic layer from the base material,
After curing for 3 days at 40℃, autograph 50mm/
min, measured at 20°C. Gloss (smoothness): Based on 60°-60° reflective gloss rate. Hardness: The coating surface was scratched with a pencil in accordance with JIS K 5401, and the highest hardness value without scratches was shown. The results are shown in Table 1. Comparative Example 1 Instead of the polyester resin used in Example 1
Polyester resin made without PTMG
A magnetic paint was prepared in the same manner except that 130 parts were used.
A similar evaluation was conducted. Comparative Example 2 130 parts of the polyester resin and isocyanate compound used in Comparative Example 1 (Japan Polyurethane Industry)
Example 1 except that 8 parts of Coronate L) was used in combination.
A magnetic paint was prepared in the same manner as above, and the same evaluation was performed. The results of Comparative Examples 1 and 2 are shown in Table 2. Examples 2 to 6, Comparative Examples 3 to 6 Polyester resins having the compositions shown in Table 1 were produced according to Example 1, and their performance was evaluated in the same manner as in the same example. The results of Examples are shown in Table 1, and the results of Comparative Examples are shown in Table 2. Examples 7 and 8 For reference, 8 parts of an isocyanate compound (same as that used in Comparative Example 2) was added to the polyester resin having the composition shown in Table 1, and the evaluation was carried out in the same manner as in Example 1. I went there. As shown in Table 1, the wear resistance data is even better than when no isocyanate compound is used (Examples 1 to 6), but other than that, the data is almost the same. ,PTMG
The difference between Examples 1 to 6 and the example (comparative example) in which the compound was not used is obvious. Comparative Example 7 An experiment was carried out according to Example 1, except that the content of the sulfonic acid group-containing monomer was 0.1 mol% (based on the carboxylic acid component). The results are summarized in Table 3. Comparative Example 8 Content of sulfonic acid group-containing monomer was 15 mol%
An experiment was carried out according to Example 1, except that (for the carboxylic acid component). The results are summarized in Table 3.

[Table] Unit is mole.

[Table] (Note) Abbreviations and units are the same as in Table 1.

【table】

[Table] (Note) Abbreviations and units are the same as in Table 1.

Claims (1)

[Scope of Claims] 1. A polytetramethylene glycol component having a molecular weight of 500 to 3,000 is bound in the resin in an amount of 5 to 15% by weight based on the entire polyester resin, and a sulfonic acid base component is bonded to a polycarboxylic acid component of 0.2% by weight relative to the polycarboxylic acid component. ~10 mol%
A magnetic recording medium whose main ingredient is a polyester resin containing polyester resin. 2. The composition of the polyester resin containing a sulfonic acid base component and a polytetramethylene glycol component is: a) 40 to 100 mol% of the polycarboxylic acid component is terephthalic acid and/or isophthalic acid; b) a polyhydric alcohol component 40 to 100 mol% of ethylene glycol and/or neopentyl glycol, c) sulfonic acid group-containing monomer is 0.2 to 10 mol% of the polyhydric carboxylic acid component d) Polytetramethylene glycol with a molecular weight of 500 to 3000 2. The magnetic recording medium according to claim 1, wherein the component is 5 to 15% by weight based on the entire polyester resin. 3. Claim 2, wherein the sulfonic acid group-containing monomer is a sulfonic acid group-containing polyhydric alcohol.
Magnetic recording medium described in Section 1.