JPS6022412B2 - Stabilization method for magnetic coatings - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for stabilizing magnetic coatings, and more specifically to a method for stabilizing magnetic coatings.
The present invention relates to a method for stabilizing a magnetic coating film containing a polymer compound having an H group and a urethane prepolymer having two or more isocyanate groups.

Since magnetic recording media such as magnetic tapes require magnetic coatings with excellent durability, various improvements have been made to the binders that bind magnetic powder onto the substrate. A large amount of urethane prepolymer having groups is used together with a vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and the isocyanate groups in the urethane prepolymer and the OH groups in the vinyl chloride-vinyl acetate-vinyl alcohol copolymer are combined. There are some that improve wear resistance by reacting.

However, this type of urethane prepolymer has a relatively slow reactivity, and therefore has the disadvantage that a large amount of the urethane prepolymer that undergoes the reaction remains, resulting in a decrease in heat resistance and running stability.

As another example, a crosslinking agent having an isocyanate group at the end is used together with a vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and the isocyanate group in the cross-linking agent and the vinyl chloride-vinyl acetate-vinyl alcohol copolymer are combined. OH inside
There are some products that react with groups to crosslink and connect them into a rope-like structure to improve wear resistance, but as with the urethane prepolymer, unreacted crosslinking agent remains, reducing heat resistance and running stability. do.

As a result of various studies from this point of view, the present invention is based on the general formula (RCOO)2Sn (where R is carbon It is a hydrocarbon group of number 8 to 20.

) of the organic acid represented by urethane prepolymer.
Add over 0.1% by weight to 10% by weight as a catalyst, and after dispersing and mixing in a ball mill for at least 1 hour, apply this on a substrate, and then
By leaving the magnetic coating at a temperature of ~60 qo for at least 1 hour, the magnetic coating is stabilized and the above-mentioned drawbacks are eliminated.

A stannous salt of an organic acid is added to a magnetic paint made of a combination of the above-mentioned copolymer, which is a type of polymeric compound having an OH group, and a urethane prepolymer having two or more isocyanate groups, and then the stannous salt of an organic acid is mixed in a Pall mill. After dispersing and mixing for at least one hour, and further applying the thus prepared magnetic coating material onto the substrate, the magnetic paint is mixed for at least one hour at a temperature of 0 to 60 QO.
If left for more than a period of time, the catalytic action of the stannous salt of the organic acid to which the catalyst has been added becomes effective, and the OH groups in the copolymer and the isocyanate groups in the urethane prepolymer react rapidly, and the isocyanate groups remain. Since the urethane prepolymers also react with each other and become polymerized, the amount of urethane prepolymers that remain unreacted becomes extremely small, and the magnetic coating film is stabilized and its heat resistance is improved.

If the amount of the organic acid stannous salt added is less than 0.1% by weight with respect to the urethane prepolymer, it will not exhibit an effective catalytic effect, and if it exceeds 1% by weight, there is a risk that it will leach onto the surface of the magnetic recording medium. Therefore, it is preferably within the range of 0.1 to 10% by weight.

Suitable stannous salts of organic acids used in this invention include tin 2-methyl-hexylate, tin naphthenate, tin octylate, tin laurate, tin stearate, etc., with the general formula (RCOO)2Sn (However, R has 8 to 20 carbon atoms.
of hydrocarbons and may contain branches.

), for example, Toei Kako Co., Ltd.
Tin hexoate and the like can be suitably used.
This type of stannous salt of an organic acid is highly compatible with polymeric compounds having OH groups such as urethane prepolymers and vinyl chloride-vinyl acetate-vinyl alcohol copolymers used as binders, and is used in magnetic paints. Even when added, the stability of the magnetic paint is not affected, and its catalytic effect is exhibited when it is dispersed and combined in a ball mill for more than one hour.
When left at a temperature of 1 hour or more, the catalytic action is fully exerted even in the magnetic coating, promoting the reaction of the urethane prepolymer and stabilizing the magnetic coating. Further, examples of urethane brevolimers having two or more isocyanate groups include Takenate L-1007, L-1128, manufactured by Takeda Pharmaceutical Company, Ltd.
L-1150, L-1151 to L-1153, L-1
155, L-1156, L-2705 L-2710,
L-27601-2790 Coronate L-75 manufactured by Nippon Polyurethane Kogyo Co., Ltd. and the like.

Examples of the polymer compound having an OH group include vinyl chloride-vinyl acetate-vinyl alcohol copolymer. In a magnetic paint containing such a polymer compound having an OH group and a urethane prepolymer, the stannous salt of the organic acid mentioned above is added in an amount of 0.1% by weight based on the urethane prepolymer.
In order to fully exhibit the catalytic action of the organic acid stannous salt, the magnetic paint prepared by adding more than i to a total weight percent of i is mixed and dispersed in a Pall mill for at least 16 hours. After applying on top, 0-60k0
It is preferable to delaminate for at least 1 hour at a temperature of
If the dispersion mixing time in the ball mill is shorter than one round time, the temperature at which the product is left after coating is lower than 000, or the time at which it is left for less than 1 hour, the above-mentioned organic acid stannous salt The catalytic effect of the tape is not sufficiently exhibited, and tape deformation occurs when the temperature at which the tape is left is set higher than 60 oo.

Next, embodiments of the invention will be described.

Example y-Fe203 magnetic powder 16 cloud cover vinyl chloride-vinyl acetate-vinyl alcohol copolymer
, 24 Urethane prepolymer having two or more isocyanate groups
16 Toluene
150 〃Methyl isobutyl ketone
i50〃Hexoate tin
0.4 Prepare a magnetic paint by dispersing and mixing these compositions in a ball mill for one hour, apply this onto a polyester base film, dry it, leave it at 2000 for 2 hours, and then cut it into a specified size. and created magnetic tape.

Comparative Example A magnetic tape was prepared in the same manner as in the example except that tin hexoate was omitted from the coating composition in the example.

The reactivity of the urethane prepolymer having two or more isocyanate groups was tested in order to examine the stability of the magnetic coating film on the magnetic tapes obtained in Examples and Comparative Examples.
The test method involved Soxhlet extraction of the binder in the magnetic coating film of each magnetic tape obtained using tetrahydrofuran containing 0.1% by weight of diethylamine. Company-made H
The relationship between absorbance and elution volume was measured using LC-802UR). The drawings show the above results and the relationship between absorbance and elution volume for unreacted urethane prepolymers; curve 1 is for the example, curve 2 is for the comparative example, and curve 2 is for the comparative example. 3 shows the urethane prepolymer produced by the reaction.

From this curve 3, peaks B and C on the right shoulder of curves 1 and 2 are considered to be unreacted urethane prepolymer, and curve 1
．． Peak A in No. 2 is considered to be the peak of the reacted urethane prepolymer.

Therefore, the baseline b of peak A, peak B, and peak C
The urethane prepolymer reactivity can be expressed numerically by measuring the height from The smaller the value, the better the reaction of the urethane prepolymer. Table 1 shows the measurement results. From Table 1, it can be seen that the magnetic coating film produced by the method of the present invention is stabilized with a small amount of unreacted urethane prepolymer.

The results of heat resistance tests on the magnetic tapes obtained in Examples and Comparative Examples are shown in Table 2.

The test method was as follows. Apply a load of 500 yen weight to 36 pieces of tape cut to 1/4 inch.
It was wound around a glass tube, kept at 4,000°C and a relative humidity of 80% for two hours, left at room temperature for 24 hours, and then rewound without applying any load.

As is clear from the upper table of Table 2, the magnetic tape obtained by applying the magnetic coating film according to the present invention has improved heat resistance compared to the comparative example as a result of the stabilization of the magnetic coating film.

[Brief explanation of drawings]

The drawing is a graph showing the relationship between absorbance and port volume for Examples of the present invention, Comparative Examples, and unreacted urethane prepolymers. 1... Example, 2... Comparative example, 3... Unreacted urethane prepolymer, b... Baseline.

Claims (1)

[Scope of Claims] 1 In a magnetic paint containing a polymer compound having an OH group and a urethane prepolymer having two or more isocyanate groups, A stannous salt of an organic acid represented by (a hydrocarbon group) is added to the urethane prepolymer in an amount of more than 0.1% by weight and less than 10% by weight, and after dispersion and mixing, the magnetic coating is applied to a substrate. 1. A method for stabilizing a magnetic coating film, which comprises coating the film on top of the magnetic coating film and leaving it for at least 1 hour at a temperature of 0 to 60°C.