JPS6093622A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve dispersibility of magnetic powder and to improve the durability and heat resistance of a magnetic layer by incorporating an urethane resin contg. isophorone diisocyanate and diphenylmethane diisocyanate and having a hydroxyl group at the terminal into a binder. CONSTITUTION:The urethane resin used is expressed by the general formula I . The isocyanate component of resin is isophorone diisocyanate (formula II) and diphenylmethane diisocyanate (formula III) which are preferably incorporated at 1-30wt% by the total weight of the urethane resin. This kind of the urethane resin contributes to a decrease in paint viscosity and consequently to an improvement in dispersion of the magnetic powder and an improvement in the fluidity of the paint. Said resin improves further the durability and heat resistance of the magnetic layer owing to the structure having the strong main chain contg. an arom. ring.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the improvement of a binder for a magnetic recording medium, and an object of the present invention is to provide a magnetic recording medium with excellent dispersibility of magnetic powder, durability, and heat resistance. The medium is made by coating and drying a magnetic paint consisting of magnetic powder, a binder, an organic solvent, and other necessary components on a substrate such as a polyester film.The binder used at this time has excellent dispersibility. , high output for magnetic recording media.

It is desirable to have a material that can provide excellent electrical properties such as a high S/N ratio, as well as excellent durability and heat resistance.For this reason, various studies have been conducted on binder resins. However, even in urethane resins to which hydroxyl groups have been added, those using diphenylmethane diisocyanate (hereinafter referred to as MDI) as the diisocyanate still have poor dispersibility, and isophorone diisocyanate ( Products using 0), hereinafter abbreviated as IPDI, have improved dispersibility but have shortcomings in durability and heat resistance @Other tolylene diisocyanates and xylene diisocyanates.

Alternatively, urethane using hexamethylene diisocyanate or the like has not yet achieved the above objective.

Therefore, the magnetic powder has excellent dispersibility and durability.

In order to obtain a nine-binder resin with excellent heat resistance, as a result of various studies, it was found that if (IPDI) and (MDI) were used together as diisocyanates for addition polymerization and a urethane resin having a hydroxyl group at the end was used as a binder, magnetic properties could be obtained. The inventors have discovered that the dispersibility of the powder is improved and the durability and heat resistance of the magnetic layer are also improved, leading to the present invention.

The urethane resin used in this invention is represented by the following general formula: 〇mat~40n; 1~10p, 2~10q+an integer of 2~12. - That is, the incyanate component of the urethane resin used in this invention is isophorone diiso, and both are preferably contained in an amount of 1 to 30% by weight based on the entire urethane resin. If the former is too large, the abrasion resistance of the urethane resin Solvent resistance deteriorates, and if the latter is present too much, the dispersibility of the resin decreases, and conversely, if too much of the latter is present, the effects of the present invention will not be noticeable. This type of urethane resin has good solubility in organic solvents, so the viscosity of the paint can be lowered, resulting in excellent dispersion of magnetic powder.It also has good spinnability, so it improves the fluidity of the paint and creates smooth magnetic particles. Helps form layers. Furthermore, O has a structure with a strong main chain containing an aromatic ring, which improves the durability and heat resistance of the magnetic layer.The urethane resin can be prepared as follows.

That is, first, obtain a polyester polyol by polycondensing diol (n+1) moles and n moles of an organic dibasic acid.In this case, the polyester polyol has a molecular composition of 6
00 to 2500 is preferable and increases the hydroxyl value.
Therefore, it may contain a portion of triol. In this way-C
After dehydrating the nine polyester polyols obtained, an addition reaction is carried out with IPDI in the presence of a catalyst. As a catalyst, for example, dipgurtin dilaurate (■),
Examples include tin octylate (■) and lead nanthenate. The IPDI-added polyester polyol thus obtained is further subjected to an addition reaction with MDI. Suitable diols used here are diols having 2 to 12 carbon atoms, such as ethylene glycol, diethylene glycol, furopylene glycol, diglobylene glycol, futhylene gelicol, triethylene glycol, butanediol, neo Examples include pentyl glycol, bentanediol, hexanediol, octanediol, etc.◇Bisphenol dioxyethyl ether, bisphenol dioxyethyl ether, etc. can also be used. Triols include trimethylolethane, trimethylolpropane, hexa/
Examples include triol, glycerol, etc. Preferred dibasic acids are dicarboxylic acids with the general formula (%), such as conolilic acid, adipic acid, cepatic acid, maleic anhydride, fumaric acid, etc. , itaconic acid, citraconic anhydride, phthalic anhydride, phthalic acid, isophthalic acid.

Terephthalic acid, tetrahydrophthalic anhydride, 3°6-nindomethylenetetrahydrophthalic anhydride.

Tetrochlorophthalic anhydride, het acid, etc. can also be used. Polyester polyols can also be synthesized by anionic polymerization of lactones and diols. For example, polycaprolactone glycol is obtained from ethylene glycol and ε-caprolactone, details ViW-R, 5o
rensen, T., W-Campbell.

”Preparative Methods of P
"Olymer Chemistry".

2nd Ed, P 156. Tohn Wile
y, New York ('68).

This type of urethane resin has a structural feature of IPDI that is not an aromatic ring but an alicyclic one, so it has good solubility and can lower paint viscosity, resulting in excellent dispersion of magnetic powder and stringiness. Because of its good properties, it improves the fluidity of paint and forms a smooth magnetic layer when used as a binder. Furthermore, since the molecule as a whole has a strong main chain structure containing an aromatic ring, the magnetic layer can have sufficient durability and heat resistance.

Examples of organic solvents that can be used in this invention include cyclohexanone, tetrahydrofuran, methyl ethyl ketone, dimethyl formamide, methyl imbutyl ketone, toluene, and xylene, used alone or in combination. Also, examples of magnetic powders include γ-FegOa, etc. powder,
Fbs04 or intermediate oxide of both, Co-containing Fe
5Os, Co-containing Fe5Oa, Cr0w powder as well as Fe powder.

Various conventionally known magnetic powders such as metal powder 2 alloy powder such as Co powder are widely included. In addition, the mixing ratio of the urethane resin and magnetic powder is preferably in the range of 1:9 to 4:6 by weight. If the amount of urethane resin used is too large, the magnetic flux density will decrease and the electrical characteristics will deteriorate. If the amount is too small, voids may be formed in the magnetic layer or powder may fall off frequently.

Incidentally, in order to improve the strength, durability and heat resistance of the magnetic layer, an isocyanate compound having at least a trifunctional or higher functional isocyanate group can be used in combination.

In this invention, the incyanate compound used in combination as necessary has at least two or more incyanate groups,
Those with a molecular weight of 2,000 or less are preferable, and trifunctional isocyanate compounds which are triol adducts of linear trifunctional incyanate and diisocyanate having incyanate groups at both ends are suitable for bamboo. .

Specific examples include COLOOT manufactured by Nippon Polyurethane Industries, Ltd. and DESMODULE L manufactured by Bayer. These incyanate compounds contain trifunctional or trifunctional incyanate groups that react with the terminal hydroxyl groups of the urethane resin and crosslink, thereby increasing the strength and durability of the magnetic layer.

Heat resistance is further improved.The blending ratio of the urethane resin and incyanate compound is preferably in the range of 9:1 to 5:5 by weight; if too much isocyanate compound is used, the magnetic layer may become hard and stiff. There is a risk that the dispersibility will decrease, and if it is too small, the desired effects in terms of durability and heat resistance cannot be obtained.

Examples of the magnetic powder used in this invention include γ-F
elon powders FegOa+ or intermediate oxides of these, Co-containing FeQOs, Co-containing Feg0
In addition to 41Cr0t powder, various conventionally known magnetic powders such as metal powders such as Fe powder, Co powder, etc. are widely included.

In addition, organic solvents include cyclohexanone, tetrahydrofuran, methyl ethyl ketone, dimethyl formamide,
Methyl isobutyl ketone, toluene, etc. are used alone or in combination□. Next, examples of the present invention will be explained◇ First, as shown in Table 1 below, four types of urethane resins AB, C,
A sample D was produced, and this resin was used in the following Examples and Comparative Examples.

Table 1 Example I Co-containing r -Fe*Os 80 parts by weight Urethane resin A 20 #Silaphosphoric acid 5 Cyclohexanone 50 Methyl ethyl ketone 50 A mixture of this composition was prepared by dispersing it in a ball mill for 120 hours. A magnetic paint was applied onto a 12 μm thick polyester film to a dry thickness of about 6 μm, dried, surface treated, and then cut to a width of 10 inches to produce a magnetic tape.

Example 2 A magnetic tape was produced in the same manner as in Example 1 except that urethane resin B was used instead of urethane resin A in Example 1.

Example 3 A magnetic tape was produced in the same manner as Example IK except that 5 parts by weight of Coronet L (trifunctional incyanate manufactured by Nippon Polyurethane Industries, Ltd.) was added.

Comparative Example 1 A magnetic tape was made in the same manner as in Example 1 except that C was used instead of urethane resin A in Example 1.Comparative Example 2 D was used instead of urethane resin A in Example 1. Magnetic tapes were made in the same manner as in Example 1, except for the following: ◎ The magnetic tapes obtained in each Example and Comparative Example were measured for squareness ratio (Br78m), s sensitivity, and tested for heat resistance and durability. 0 heat resistance test is 200 at one end of the tape.
Wrap it around a 36 mm glass tube while applying a load of
The presence or absence of adhesion between the wound layers was observed, and the durability test was conducted after running a predetermined length of magnetic tape 200 times in sliding contact with a magnetic head at a running speed of 4.75 am/sec. Table 2 below shows the results of measuring the level drop and output fluctuation. As is clear from this table, the magnetic tapes obtained by the present invention (Examples 1 to 3) have better dispersibility than conventional magnetic tapes (Comparative Examples 1 to 2), and therefore have a high squareness ratio (Br78m). In particular, the magnetic tape containing trifunctional incyanate (Example 3) has high sensitivity, excellent heat resistance, and durability.
Durability is improved O. Regarding the adhesion between each layer of the tape in terms of heat resistance, ◎ means that no adhesion phenomenon was observed, and ○ means that there was adhesion but there was no problem in unwinding the tape. Cases in which it was impossible to unwind the tape due to adhesion were expressed as X.

Table 2 Applicant: Hitachi Maxell, Ltd. Representative Atsushi Nagai

Claims (2)

[Claims] (1) Contains isophorone diisocyanate and diphenylmethane diisocyanate as incyanate components,
A magnetic recording medium characterized by having a magnetic layer containing a urethane resin having a hydroxyl group at the end in a binder. (2) The magnetic recording medium 0 according to claim 1, characterized in that the binder component contains at least a bifunctional or higher-functional low molecular weight incyanate compound.