JPS61134919A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the titled medium having an excellent surface smoothness, good properties of a productivity, an electromagnetic conversion and a durability by uniformly dispersing fine magnetic powders to a specific polyurethane resin to form a dispersion, and by coating the obtd. dispersion on a nonmagnetic substrate to form a layer capable of producing a magnetic property. CONSTITUTION:If a mol. wt. of polyester polyol is >1200, a polyurethane resin becomes soft. While, if a mol. wt. of polyester-polyol is <800, said resin becomes hard. A magnetic property of the titled medium is affected by a kind of a chain extender. A surface smoothess of the titled medium due to a calender roll remarkably increases by incorporating <0.2 mol 3-6 C a branched diol per a mol of a polyester-polyol to said medium. The more the mol. wt. of the polyurethane increases, the more the durability of the magnetic tape improves. Conversely, the dispersibility of the magnetic powders decreases. When the mol. wt. of the polyurethane resin is >50000, the electromagnetic conversion of the magnetic tape affects the most. Conversely, if mol. wt. of the polyurethane resin is <30000, the magnetic powders contd. in the prescribed medium drops, thereby occuring a drop out.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to magnetic recording media such as video tapes and audio tapes.

BACKGROUND OF THE INVENTION Generally, magnetic recording media are obtained by coating a film of polyester or the like with a magnetic paint consisting of magnetic powder, a binder, an organic solvent, and trace amounts of additives such as a dispersant and a lubricant. Among the above components, the binder has the dispersibility of magnetic powder,
It is required to have good adhesion to the base film, simple surface smoothing treatment, electromagnetic conversion characteristics, durability, etc. In the following text, we will discuss magnetic tape, which is a type of magnetic recording medium, as an example.

Problems to be Solved by the Invention However, in the case of such magnetic tapes, the higher the performance of the magnetic tape, the higher the rigidity and the better the electromagnetic conversion characteristics and durability. However, the dispersibility of magnetic powder, etc., and surface smoothing treatment were difficult.

In view of the current situation, it is an object of the present invention to provide a magnetic recording medium with excellent productivity, electromagnetic conversion characteristics, and durability. The recording medium has an average molecular weight of 800~
It is composed of a combination of a 12oO polyester polyol, diphenylmethane diisocyanate, and a branched diol having 3 to 6 carbon atoms, and has a polyol composition in which the molar ratio of the branched diol to 1 of the polyester polyol is less than 0.2, and the molecular weight is 30000~50000
It is composed of polyurethane resin, fine powder magnetic particles, polyinsyanate as a dispersant and curing agent, etc.

Function: With the aim of developing high-performance magnetic tapes, we have studied the structure of binders, especially polyurethane resins, and the properties of magnetic tapes.
Through extensive research, we have arrived at the present invention.

When the molecular weight of the polyester polyol exceeds 1,200, the polyurethane resin becomes soft, resulting in a decrease in the rigidity of the magnetic tape, poor tape runnability, especially at high temperatures and high humidity, and the edges of the magnetic tape may be bent. This can cause magnetic powder to fall off. On the other hand, if the molecular weight is less than 800, the polyurethane resin will be hard and the rigidity of the magnetic tape will be high, but the surface smoothing treatment by calender rolls tends to be poor. It has also been found that the type of chain extender also affects magnetic tape properties. That is, it has been found that by using a branched diol having 3 to 0 carbon atoms in an amount of less than 0.2 mol per 1 mole of polyester polyol, the surface smoothing treatment by a calender roll is significantly improved. Regarding the molecular weight of polyurethane resin, the greater the molecular weight, the better the durability of the magnetic tape, but on the other hand, the dispersibility of magnetic powder etc. tends to deteriorate, and especially when the molecular weight exceeds 50,000, the electromagnetic conversion characteristics of the magnetic tape etc. has a negative impact. On the contrary, the molecular weight is 3000
If it is less than 0, the strength as a binder is weak, and magnetic powder etc. will fall off during running, causing dropouts.

Examples of such polyurethane resin raw materials include diethylene glycol, 1
, 3-propanediol, 1,4-butanediol, 1
．． Products made by dehydration condensation reaction between polyhydric alcohols such as θ-hexanediol and saturated polybasic acids such as adipic acid, phthalic acid, isophthalic acid, and terephthalic acid, branched diols used as chain extenders, Examples include 1,3-butanediol, 1,5-hexanediol, 1,2-propylene glycol, neopentyl glycol, and the like.

If an unbranched diol is used as a chain extender, and the average molecular weight of the polyester polyol exceeds 1,200 and the molecular weight of the polyurethane resin exceeds 50,000, surface smoothing with a calendar roll will be poor, resulting in poor productivity and electromagnetic Conversion characteristics are not good. If the average molecular weight of the polyester polyol is less than 800, the molar ratio of the branched diol to 1 is 0.2 or more, and the molecular weight of the polyurethane resin is less than 30,000, the surface smoothing process using a calender roll is still poor and production is difficult. Its properties and electromagnetic conversion characteristics are also poor. Furthermore, the durability was not good.

On the other hand, when a branched diol is used as a chain extender, the average molecular weight of the polyester polyol is 800 to 12oO.
The molar ratio of branched diol to 1 is less than 0.2, and the molecular weight of the polyurethane resin is 30,000 to 60.
When it is 000, it is easy to perform surface smoothing treatment by calendar cooling, and the productivity and electromagnetic conversion characteristics are good. Moreover, the durability was also good.

Example This will be explained in more detail below based on examples.

(Example 1) ■ Composition of polyurethane resin - Polyester polyol (PBA-1000)...
Polyester polyol with a molecular weight of 10oO obtained by a combined dehydration reaction of adipic acid and 1,4-butanediol °diisocyanate... Diphenylmethane diisocyanate diol... 1.3-butanediol diol/polyester Polyol (molar ratio)...
...0.19 Molecular weight of polyurethane resin (number average molecular weight by GPC) ...... ■Composition of magnetic paint (parts by weight) ...100 Part Cor-r-
Fe203 Polyurethane ・・・・・・・・・・・・・・・
10 parts nitrocellulose (HIG manufactured by M Kasei Kogyo ■) 10 parts stearic acid 1 part methyl ethyl atone
・・・・・・・・・・・・・・・ 110 parts toluene
・・・・・・・・・・・・・・・ 110 parts After dispersing this composition in a ball mill for 24 hours, a polyisocyanate compound (manufactured by Nippon Polyurethane Industry ■,
Collenate-L) was added in an amount of 20 parts, thoroughly stirred and mixed, and filtered through a filter with an opening of 3 μm to obtain a magnetic paint. Then, this magnetic paint was applied onto a 16 μm thick polyethylene terephthalate base film, then dried, and the surface was smoothed using a calendar roll.
The resin was cured by heating at 60° C. for 24 hours.

The sheet thus obtained was cut into H-inch pieces to form a sample tape. Examples 2 and 3 below. Comparative Examples 1 and 2 are also the same, except for the composition of the polyurethane resin, from the magnetic coating composition and dispersion method to the tape cutting.

(Example 2) ■ Composition of polyurethane resin - Polyester polyol (PHA-800...
・Polyester polyol diisocyanate with a molecular weight of 8oO obtained by the dehydration condensation reaction of adipic acid and 1,6-hexanediol・・・・・・Diphenylmethane diisocyanate diol・・・・・・ Neopentyl glycol diol/polyester polyol (mole ratio)···
...0.15 ” -Molecular weight of polyurethane resin (number average molecular weight by GPC)... (Example 3) ■Composition of polyurethane resin -Polyester polyol (PEPh-1200)...
・Polyester polyol/diisocyanate with 200 molecular nodes obtained by dehydration condensation reaction of isophthalic acid and ethylene glycol...Diphenylmethane diisocyanate/diol... 1.6-hexanediol/diol/polyester polyol (mol) ratio)···
...0.10 - Molecular weight of polyurethane resin (number average molecular weight by GPC) - (Comparative example 1) - Composition of polyurethane resin - Polyester polyol (P BA-1csoo) -
...Polyester polyol diisocyanate with a molecular weight of 15oO obtained by dehydration condensation reaction of adipic acid and 1,4-butanediol ...Diphenylmethane diisocyanate diol ...1,4-butanediol Diol/polyester polyol (molar ratio)...
...0.18 - Molecular weight of polyurethane resin (number average molecular weight by GPC) ... (Comparative example 2) ■ Composition of polyurethane resin - Polyester polyol (PPA-600) ...
...Polyester polyol/diisocyanate with a molecular weight of 600 obtained by dehydration condensation reaction of adipic acid and 1,3-propanediol...Diphenylmethane diisocyanate/diol...1,3-butanediol/diol/ Polyester polyol (mole ratio)...
...0.30 - Molecular weight of polyurethane resin (number average molecular weight by GPC) ... The evaluation results of each sample above are shown in Table 11 and Table 2. The filtration rate mentioned here is based on a filter with an opening of 3 μm and an air pressure of 3. OKp/Cd is a ratio indicating how much of the magnetic paint after dispersion can be filtered, and is calculated by dividing the weight of the magnetic paint after filtration by that before filtration and multiplying it by 100. The degree of filtration is used as a measure of dispersibility, and if it is 90 or more, the dispersibility is good. Also,
When judging durability, look at the number of dog outs per minute after running 200 passes (120 minutes of tape) in an environment of 40° C. and 85% RH. In addition, to judge the ease of surface smoothing with a calender roll, increase the calender speed, and if the electromagnetic conversion characteristics (especially color S/N) do not decrease, surface smoothing will be easy and productivity will improve. It is determined that it will lead to.

As can be seen from Examples 1 and 2.3 in Table 1, the molar ratio of branched diol having 3 to 6 carbon atoms to 1 average molecular weight polyester polyol is less than 0.2, and the molecular weight is 30
When a polyurethane resin having a molecular weight of 000 to 5o00 is used, electromagnetic conversion characteristics and durability are improved. Moreover, as shown in the figure, even if the calendering speed was increased, the color S/N did not decrease, and it was found that a tape whose surface could be easily smoothed was produced, contributing to improved productivity.

Table 1 Effects of the Invention As described above, according to the magnetic recording medium according to the present invention, it is possible to obtain the effects that the surface can be easily smoothed and productivity, electromagnetic conversion characteristics, and durability are improved.

[Brief explanation of the drawing]

The figure is a diagram showing the relationship between calender speed and color S/N in Examples and Comparative Examples of the present invention.

Claims (1)

[Claims] Finely powdered magnetic particles are uniformly dispersed in a polyurethane resin made of a combination of a polyester polyol with an average molecular weight of 800 to 1,200, diphenylmethane diisocyanate, and a branched diol with a carbon number of 3 to 6, mixed with a curing agent, and then coated on a nonmagnetic support. The composition of the polyurethane resin is such that the molar ratio of the branched diol to 1 of the polyester polyol is less than 0.2, and the molecular weight of the polyurethane resin is 30,000 to 30,000. 50,000 magnetic recording medium.