JPH0677304B2 - Binder for magnetic recording medium - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a polyester-based binder for a magnetic recording medium having a sulfonate group introduced therein.

2. Description of the Related Art Conventionally, various kinds of binders for magnetic recording media have been used, but recently, a polyester-based high-performance binder having a sulfonate group introduced therein has been proposed. That is, JP-A-54-28603 discloses a binder for a magnetic recording medium, which is made of polyester using a dicarboxylic acid containing a sulfonic acid metal salt as a part of an acid component, and JP-A-54-151417. The publication discloses a binder for a magnetic recording medium, which is composed of a mixture of the polyester and a thermoplastic resin and / or a thermosetting resin.
Further, JP-A-54-132418 discloses a binder for a magnetic recording medium, which is made of polyester using a sulfonate group-containing glycol as a part of the glycol component.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, a binder made of a polyester containing a sulfonate group as described above is mixed with magnetic particles and a solvent to prepare a magnetic coating material, which is applied to a substrate,
When performing calendering for polishing or surface smoothing after magnetic field orientation treatment and drying, the magnetic coating film tends to stick to the calender roll, so the conditions during calendering are not strictly controlled. There was a risk of defective products.

In the above publications, a magnetic tape is wound by adding a crosslinking agent such as an epoxy resin, an isocyanate compound, and a melamine resin when a magnetic paint is prepared by mixing a polyester binder with magnetic particles and a solvent. There is a description that it prevents the blocking of the coating film and softening of the coating film due to frictional heat with the magnetic head, but the treatment with such a crosslinking agent is performed on the tape after calendering. However, it is different from the technique for preventing the coating film from sticking to the calender call during calendering.

The present invention aims to provide a high-quality binder in which adhesion to a calender roll is effectively prevented without impairing various excellent performances of a polyester having a sulfonate group introduced therein as a binder for a magnetic recording medium. To do.

Means for Solving Problems The magnetic recording medium binder of the present invention has a content of a sulfonate group in a polyester segment of 0.2 to 10 mol% with respect to a total amount of an acid component and a glycol component,
A sulfonate group-containing polyester segment having a hydroxyl value of 3 to 20 KOHmg / g and an acid value of 0 to 2 KOHmg / g is characterized by being composed of a chain-length-extended polyester bonded by 2 to 5 units via a diisocyanate compound. Therefore, by finding out that such a specific chain-length-extended polyester is used as a binder for a magnetic recording medium, the above problems have been solved.

The present invention will be described in detail below.

The polyester constituting the sulfonate group-containing polyester segment in the present invention is obtained by subjecting an acid component and a glycol component to a condensation reaction in an inert atmosphere at a temperature of about 150 to 260 ° C.

Here, as the acid component, terephthalic acid, isophthalic acid,
Phthalic acid, 2,5-norbornanedicarboxylic acid, 1,4-naphthalic acid, 1,5-naphthalic acid, diphenic acid, 4,4′-
Oxybenzoic acid, diglycolic acid, thiodipropionic acid, 4,4'-sulfonyldibenzoic acid, 2,5-naphthalenedicarboxylic acid, oxalic acid, malonic acid, dimethylmalonic acid,
Examples include succinic acid, glutaric acid, adipic acid, dodecanedicarboxylic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaic acid, sebacic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. . An unsaturated carboxylic acid such as maleic acid, maleic anhydride, fumaric acid, itaconic acid or citraconic acid may be used in a small amount.

As the glycol component, ethylene glycol propylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, bisphenol dioxypropyl ether, 1,3-butanediol, 1,4-
Butanediol, 2,3-butanediol, 1,6-hexanediol, 2-ethyl-1,3-hexanediol, 2,2,4
-Trimethyl-1,3-pentanediol, neopentyl glycol, 1,4-cyclohexanedimethanol and the like can be mentioned. A small amount of trihydric or higher alcohol such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol can be used together.

Among the above-mentioned acid components and glycol components, those containing terephthalic acid and / or isophthalic acid and an aliphatic dicarboxylic acid as main acid components and ethylene glycol and neopentyl glycol as main glycol components are particularly preferable. The optimum composition is: acid component terephthalic acid and / or isophthalic acid 40 to 90 mol% aliphatic dicarboxylic acid 10 to 60 mol% glycol component ethylene glycol 30 to 70 mol% neopentyl glycol 30 to 70 mol% other glycols 0 to 30 It is mol%. By using such a specific component in a specific amount, a polyester having a well-balanced solubility, adhesive strength, cohesive strength, non-adhesiveness, hardness and the like can be obtained.

As a method of introducing a sulfonate group into polyester,
(A) A method using a sulfonic acid group-containing polyvalent carboxylic acid such as 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, 2-potassium sulfoterephthalic acid or esters thereof as the acid component (B) a method of reacting a polybasic acid having an unsaturated bond with an acidic sulfite to obtain a sulfonate-containing polybasic acid and using this as an acid component, (c)
A method of reacting a polyhydric alcohol having an unsaturated bond with a production sulfite to obtain a sulfonate-containing polyhydric alcohol and using this as a glycol component, (d) using an unsaturated carboxylic acid as a part of the acid component A method for producing a polyester having an unsaturated bond, a method of adding an acidic sulfite salt to the unsaturated bond, (e) a compound having an epoxy group and an acidic sulfite are reacted to obtain a sulfonate group-containing polyfunctional monomer, A method of reacting this with an acid component or a polyhydric alcohol is adopted.

The introduced amount of the sulfonate group is set to 0.2 to 10 mol% with respect to the total amount of the acid component and the glycol component constituting the polyester. If the amount is too small, the performance as a binder for the magnetic recording medium will be poor, while if the amount is too large, the solvent solubility will be insufficient.

In addition to the above components, ethylenediamine, trimethylenediamine, putrescine, cadapellin, hexamethylenediamine, 2-hydroxyethyl-p-toluidine, 2-carboxyethyl-p-toluidine, β-propiolactam, γ-proline. When a small amount of nitrogen-containing compounds such as piolactam, γ-butyrolactam, γ-valerolactam, ε-caprolactam, and heptolactam (for example, 0.2 to 10 mol% based on the total amount of the acid component and the glycol component constituting the polyester) are condensed. It is preferable because the dispersibility of the magnetic particles is further improved.

Polyester is obtained by the condensation reaction, but in the present invention, the hydroxyl value of the obtained polyester is 3 to 20.
The charged amount of the acid component and the glycol component is selected and the reaction conditions are set so that the KOHmg / g and the acid value are 0 to 2KOHmg / g. A polyester with a hydroxyl value of less than 3 KOHmg / g is not practical because it requires harsh conditions to produce it.On the other hand, when the hydroxyl value exceeds 20 KOHmg / g, the effect of preventing adhesion to calendar rolls is recognized. It will be difficult. On the other hand, when the acid value exceeds 2 KOHmg / g, the reactivity with the diisocyanate compound in the next step becomes poor and it becomes difficult to extend the chain length.

And in the present invention, the polyester thus obtained is extended in chain length with a diisocyanate compound. Examples of the diisocyanate compound include tolylene diisocyanate, diphenylmethane-4,4'-diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, 1,4-
Examples thereof include tetramethylene diisocyanate. The diisocyanate compound has 2 isocyanate groups in the molecule.
Isocyanate-based compound, which must have individual functional groups other than isocyanate groups,
For example, adducts of isocyanate with trimethylolpropane, triethylene glycol, etc. are not suitable.

The chain length extension requires that the polyester segment is bonded to 2 to 5 units through the diisocyanate compound. If it is less than 2 units, the effect of preventing attachment of the calender roll is insufficient, while if it exceeds 5 units, it is called polyester. Instead, it becomes polyurethane, and the excellent performance of the polyester magnetic recording binder is impaired.

The chain extension reaction is carried out at a temperature of 40 to 40 with the above polyester and diisocyanate compound in the presence of no catalyst or a suitable catalyst.
This can be achieved by reacting at about 120 ° C. By this reaction, a target chain-extended polyester, that is, a polyester in which a sulfonate group-containing polyester segment having a hydroxyl value of 3 to 20 KOHmg / g and an acid value of 0 to 2 KOHmg / g is bonded via a diisocyanate compound is obtained.

The magnetic paint may be prepared by adding magnetic particles and a solvent to the chain-extended polyester and mixing them uniformly.

Magnetic particles include pure iron, γ-Fe ₂ O ₃ (Co), CrO ₃ , and Fe ₂
O ₃ (Co), Fe ₃ O ₄ , Fe ₃ O ₄ (Co), Co-Fe, Co-Ni, Co-
Ni-Fe, Co-Ni-Zn, Fe-Mn-Zn, Co-Ni-Fe-B, Co
-Ni-P, Fe-Co-Ni-P, etc. may be mentioned. The blending ratio of the chain-lengthening polyester and the magnetic particles is 1: 1 by weight.
It is often set to 1: 7.

Examples of the solvent include cellosolve acetate, butyl cellosolve acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, benzene, toluene, xylene and the like.

When preparing the magnetic paint, other known binders, plasticizers, wetting agents, antistatic agents, anti-grooming agents, thermoplastic resins, thermosetting resins and the like can be added as necessary.

The base material to which the magnetic paint is applied may be any of film, tape, sheet, disk, card, drum and the like. In the case of the film or tape, examples of the material include acetyl cellulose, polyester, polycarbonate, polypropylene, polyimide, polyvinyl chloride and the like.

The magnetic coating material may be applied onto the substrate by any of the doctor knife method, blade coating method, reverse roll method, gravure method, cast coating method, spray coating method and the like.

After the magnetic coating material is applied to the substrate directly or via the anchor coat layer, a magnetic field orientation treatment is performed by a solenoid coil or the like while the coating film is not dried, and then dried. Then, this is subjected to a glossing or smoothing treatment between calender rolls. When the above chain-extended polyester is used as a binder, no trouble such as adhesion of the coating film to the calender roll occurs during calendering. Further, it is not softened by frictional heat between it and the magnetic head, and blocking does not occur even if it is handled in a state wound on a tape.

The magnetic recording medium thus obtained is an audio tape,
Used for video tape, computer / measuring instrument tape, magnetic card, magnetic disk, etc.

EXAMPLES Next, the present invention will be further described with reference to Examples. Hereinafter, “part” means “part by weight”.

Example 1 A four-necked flask equipped with a thermometer, a stirrer, and a packed column was charged with 0.5 mol of terephthalic acid, 0.35 mol of isophthalic acid, 0.15 mol of adipic acid, 0.6 mol of ethylene glycol, and 0.7 mol of neopentyl glycol in a nitrogen stream. , Diethylene glycol 0.2 mol, 2-sodiosulfo-1,4-butanediol 0.005 mol and dibutyltin oxide 0.1%
(For all systems) is charged and the esterification reaction is performed at 140-240 ° C, then antimony trioxide 0.1% (for all systems)
Was added and condensed at 220 to 260 ° C. under a reduced pressure of 1 Torr to obtain a sulfonate group-containing polyester having a hydroxyl value of 6 KOHmg / g and an acid value of 0.8 KOHmg / g.

Next, add toluene 21 to the reaction product (polyester) in the flask.
0 parts, 1.5 parts of hexamethylene diisocyanate are added,
The reaction was carried out at a temperature of 80 to 100 ° C for 2 hours and then aged at 60 ° C for 24 hours. As a result, the sulfonic acid group-containing polyester segment is transferred through the diisocyanate compound to
A unit-bonded chain-extended polyester was obtained.

This chain-length-extended polyester was applied onto an aluminum sheet by the doctor knife method and dried, and after drying, a coating film having a thickness of 5 μ was formed.

In order to examine the thermal activity of the formed coating film, another aluminum sheet is overlaid on the coating film on the aluminum sheet, heated and pressed by a heat sealer, and the softened coating film adheres to the upper aluminum sheet. When the temperature was examined, it was 110 ° C.

The temperature of the calender roll during calendering is 60-100
Since it is about ℃, the above-mentioned chain length extended polyester,
It shows that the coating film does not adhere to the calender roll even when the magnetic coating is prepared by mixing magnetic particles or a solvent with this, and coating on the substrate, orientation treatment, and calendering after drying. . The case where the thermal activity of the magnetic paint is measured will be described below.

130 parts of the above chain length-extended polyester, 190 parts of γ-FeO, 3 parts of dioctylsulfosodium succinate, 3 parts of silicone oil, 290 parts of methyl ethyl ketone, 190 parts of toluene
Parts, methyl isobutyl ketone 100 parts, n-butanol 60
Parts were dispersed and mixed for 70 hours using a ball mill, and then filtered and defoamed to prepare a magnetic paint.

When the thermal activity of this magnetic paint was examined in the same manner as above, the lowest temperature at which adhesion started was 130 ° C.

Further, the above magnetic coating material was applied onto a polyethylene terephthalate film having a thickness of 25 μm by a doctor knife method, and then subjected to orientation treatment in a parallel magnetic field of 1000 Oersted,
Then, it was dried at 80 ° C. to obtain a magnetic coating film having a thickness of 5 μ, and further polishing was performed by passing it between calender rolls at a temperature of 100 ° C. However, adhesion of the coating film to the calender roll did not occur at all.

The 60 ° -60 ° reflection gloss ratio of this magnetic coating film was 99%, which was excellent in smoothness. Further, the squareness ratio, that is, the ratio Mr / Ms of the saturation magnetization Ms to the residual magnetization Mr of the magnetic hysteresis curve was 0.86, and a favorable result was obtained.

Comparative Example 1 When the thermal activity of the polyester before the above chain length extension was examined in the same manner, the lowest temperature at which adhesion started was as low as 70 ° C.

Comparative Example 2 Desmodur L (manufactured by Bayer, West Germany) which is an isocyanate compound in 100 parts of polyester before the chain length extension
When the thermal activity of the binder prepared by mixing 15 parts by weight and uniformly mixing was examined, the lowest temperature at which adhesion started was 50 ° C. Further, when the thermal activity of the magnetic coating material prepared in the same manner as in Example 1 was examined except that this binder was used,
The lowest temperature at which adhesion started was 80 ° C.

Example 2 Same as Example 1 except that 0.002 mol of 2-sodiosulfo-1,4-butanediol was replaced with 0.02 mol of dimethyl 5-sodium sulfoisophthalate, and the charging ratio of terephthalic acid was 0.48 mol. Esterification was performed to obtain a sulfonate group-containing polyester having a hydroxyl value of 10 KOHmg / g and an acid value of 1.2 KOHmg / g.

Next, 250 parts of toluene and 2.6 parts of toluidine diisocyanate were added to this polyester, and the mixture was reacted at a temperature of 80 to 100 ° C. for 2 hours and then aged at 60 ° C. for 24 hours. As a result, a chain length-extended polyester in which 3 units of the sulfonate group-containing polyester segment were bonded via the diisocyanate compound was obtained.

The thermal activity of this chain-extended polyester was 100 ° C., and the thermal activity of a magnetic coating material prepared using the same in the same manner as in Example 1 was 120 ° C.

EFFECTS OF THE INVENTION The binder of the present invention is mixed with magnetic particles and a solvent to prepare a magnetic coating material, applied to a base material, subjected to magnetic field orientation treatment, and dried, and then for polishing or smoothing the surface. There is no problem that the magnetic coating film sticks to the calender roll during calendering. Therefore,
The production of magnetic recording media is stable because there is no risk of defective products being produced without strict control of calendering conditions.

The various excellent properties of the polyester having the sulfonate group introduced therein as a binder for a magnetic recording medium are not impaired at all, and there is no risk of softening due to frictional heat with the magnetic head.

Claims (2)

[Claims] 1. The content of a sulfonate group in a polyester segment is 0.2 to 10 mol% with respect to the total amount of an acid component and a glycol component, and a hydroxyl value is 3 to 20 KOHmg / g,
The sulfonic acid group-containing polyester segment having an acid value of 0 to 2 KOHmg / g is 2 to 5 through the diisocyanate compound.
A binder for a magnetic recording medium, which comprises a unit-chain-extended polyester. 2. The polyester segment contains terephthalic acid and / or isophthalic acid as a main acid component and an aliphatic dicarboxylic acid, and ethylene glycol and neopentyl glycol as main glycol components. Binder as described.