JPS6139922A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility of magnetic powder, carbon black, Al2O3, etc. and to improve durability by incorporating a specific polyurethane resin, nitrocellulose and low-molecular isocyanate compd. as a binder component into a magnetic layer. CONSTITUTION:The polyurethane resin which is obtd. from a mixture composed of butyrene adipate and tertiary alcohol and 4,4'-diphenyl methane diisocyanate, has tertiary OH in the position except both terminals of the principal chain and has 20,000-30,000 average mol.wt., nitrocellulose and low mol.wt. isocyanate compd. are used as the binder for the magnetic layer. A magnetic paint is prepd. by dispersing the magnetic powder, carbon black as an antistatic agent and Al2O3 as a polishing agent into an org. solvent soln. of such binder. The paint is coated on a substrate and is dried to form the magnetic layer. The magnetic recording medium which has the excellent durability of the magnetic layer and is suitable particularly for a flexible disk is thus obtd.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a magnetic recording medium having excellent dispersibility of magnetic powder Cargin Black, A4205 (aluminum oxide), etc., and excellent durability of the magnetic layer. It is.

[Prior art]

Generally, magnetic recording media such as audio tapes, video tapes, and flexible disks are made by using magnetic powder on a non-magnetic support such as polyester film.

The magnetic layer is formed by applying a magnetic paint consisting of various additives such as a binder, a solvent, a dispersant, a lubricant, an antistatic agent, and an abrasive. In addition, there is a demand for highly reliable products that can withstand long-term operation under harsh conditions such as high temperature, high humidity, and low temperature and low humidity.

In order to meet this demand, a binder is required that has excellent dispersibility of magnetic powder, excellent electromagnetic conversion characteristics such as reproduction output signal dispersion 1 overwriting characteristics, and excellent durability such as wear resistance. ing.

Various studies have been conducted on such binders, one of which has been proposed to be a combination of 41J urethane resin and vinyl chloride-vinyl acetate-vinyl alcohol copolymerization.

The reason for this is that although polyurethane resin alone has difficulty dispersing with magnetic powder, it has relatively excellent durability, and that vinyl chloride-vinyl acetate-vinyl alcohol copolymer alone does not have magnetic properties. Although the binder has excellent dispersibility with powder, the removability of the magnetic layer is insufficient, so both binders are used in combination.

However, in cases where excellent dispersibility and durability are required, they are still insufficient.

[Purpose of the invention]

The present invention provides a particularly excellent flexible disk among magnetic recording media having excellent dispersibility of magnetic powder carbon black, At203, etc., and excellent durability of the magnetic layer, which eliminates the above-mentioned conventional drawbacks. It is.

[Structure of the invention]

That is, the present invention uses a mixture of butylene anovate and tertiary alcohol as a binder for the magnetic layer. :4,4.
An average molecular weight of 20,000 to 3o, oo, which has a tertiary hydroxyl group at a position other than both ends of the main chain obtained by reacting '-nobuenylmethane diisocyanate.

It is characterized by containing a polyurethane resin, nitrocellulose, and a low molecular weight incyanate compound.

[Effect]

Since the present invention contains a polyurethane resin having tertiary hydroxyl groups at positions other than both ends of the main chain as a binder for magnetic paint, it has increased affinity with magnetic powder and can be used in paints such as carbon black and Al2O2. Monodispersity can be improved without causing color separation phenomenon.

Furthermore, by containing nitrocellulose and low molecular weight incyanate, the magnetic layer can be given appropriate flexibility and can withstand long-term running under harsh conditions such as high temperature and high humidity, low temperature and low humidity. Excellent reliability 1. ．． Emagnetic layer, 1゜Plate thickness: 4゜The polyurethane resin used in the present invention is butylene adipate obtained by polycondensation of dicarboxylic acid of adipic acid and 1,4-butylene glycol. : , 1
', 2,3-hydroxy-2-methyl-zorono and 711
12.3-Hydroxy-ethyl-propane.

Both ends of the main chain obtained by reacting 4,4'-diphenylmethane diisocyanate as an organic diisocyanate with a mixture of tertiary alcohols such as 1.2,5-hydroxy-2-methyl-propane. Average molecular weight 2 with a tertiary hydroxyl group in a position other than Q, OOO
~30,000 polyurethane resin.

The amount X of hydroxyl groups other than both ends of the polyurethane resin used in the present invention is 0 (x (0,025 mmol/L/
gr is preferable, and if it exceeds 0.025 mmVgr, the dispersibility of the magnetic powder will improve, but the modulation will increase, which is not preferable for flexible disks. Furthermore, when crosslinking with a low molecular weight isocyanate compound, the magnetic layer is hardened on the contrary, resulting in a decrease in durability2.Furthermore, carbon black A
In the case of containing an additive with poor dispersibility such as At203, the color separation phenomenon of carbon black At206 etc. in the paint may occur, which is undesirable.

The average molecular weight of the polyurethane resin used in the present invention is
The average molecular weight is preferably 20,000 to 30,000. If the average molecular weight is less than 20,000, the dispersibility of the magnetic powder is excellent, but the magnetic layer has poor abrasion resistance and lacks stability in long-term running. .

The nitrocellulose used in the present invention includes:

The average degree of polymerization and nitrogen content are each 35 to 110. and 10
．． As long as it is in the range of 7 to 12.2 H (average degree of substitution 1.9 to 23), a commercially available product is RIG manufactured by Asahi Kasei Corporation.
1/16, HIG 1/8. HIG 1/4.
HIG 1/2. HIG 1° and LIG 1/B,
LIG 1/4. LIG 1/2 or R81/16, R31/B manufactured by Taisel Chemical Industry Co., Ltd.
R8i74゜R81/2 and SS 1/s, ss
1/4. There are SS 1/2 etc.

The low molecular weight incyanate compound used in the present invention includes: 2.4-) lylene diisocyanate.

2.6-) lylene isocyanate), 4.4'-
Diisocyanates such as diphenylmethane diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, inholodiisocyanate, and quizylene diisocyanate, and trifunctional low molecular weight incyanate compounds obtained by reacting 3 moles of these diisocyanates with 1 mole of triol are commercially available. A large variety of products can be used.

For example, 1 Coronate manufactured by Nippon Polyurethane Co., Ltd.

Coronate HL, Coronate) 2036. Coronate 2014, Coronate 3015. Coronet)
14. Sumino Yule L, Sumino Yule T80
゜Takenate D102, manufactured by Narita Pharmaceutical Industries, Ltd. Takenate D103. Takenate D103H, Takenate) M2
O3゜Takenate M403. Takenate M408.
Rithgon UX and Krisbon CI manufactured by Dainippon Ink Chemical Co., Ltd.
, -2, etc.

A tertiary chain at a position other than both ends of the main chain obtained from the mixture of butylene adipate and tertiary alcohol used in the present invention and 4,4'-nophenylmethane diisocyanate.
Average molecular weight with hydroxyl groups of 20.000 to 30.0
00 (D!!j) It is preferable that the blending ratio of oil and nitrocellulose is in the range of 8A to 4/6 at a weight ratio of 2, and if it deviates from this range, the magnetic layer will not have adequate flexibility as a flexible disk. will not be able to be granted.

In addition, the amount of the low molecular weight incyanate compound used in the present invention is 10% based on the total amount of the binder component.
-30 weight ratio is preferable; if it is too small, the effect of the present invention cannot be obtained, and if it is too large, the dispersibility of the magnetic powder will be impaired.

As the magnetic powder used in the present invention, r-Fe205
The commonly known magnetic powder of Co-coated r7Fe203 powder is used.

Examples of organic solvents include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, esters such as methyl acetate, ethyl acetate, and butyl acetate, aromatic hydrocarbons such as benzene, toluene, and xylene, and methyl chloride.

It is desirable to use at least two or more chlorinated hydrocarbons such as ethylene chloride and carbon tetrachloride.

Further, a dispersant, lubricant, abrasive, antistatic agent, etc. may be added as necessary.

The magnetic recording medium of the present invention is manufactured by a conventional method. The magnetic powder, a binder component, and a solvent are placed on a non-magnetic support such as polyester terephthalate.

Furthermore, a magnetic layer may be formed by applying a magnetic paint containing various additives as required by a known method.

Hereinafter, one aspect of the present invention will be explained in detail.

[Example 1] HC = 3000e Isocyanate (manufactured by Nippon Polyurethane Co., Ltd.) (average particle size 30 mμ) Solvent: MEK/Toluene/Cyclohexanone-6Vt5ψtO part This composition was milled in a sand mill.
After mixing and dispersing for 2 hours, a magnetic paint was prepared, and this magnetic paint was then applied onto a polyester terephthalate support with a thickness of 75 μm and dried to a thickness of 2 μm. ? A magnetic layer of No. 1 was formed. Next, this magnetic layer was applied to a disk having an outer diameter of 130% to prepare a sample.

[Example 2] γ-Fe203 of Example 1 was converted to Cor-Fe20s (
Slanting ratio 10° average grain size o, 35, He = 6
A sample was prepared in the same manner at 50 DEG).

[Comparative Example 1] A sample was prepared in the same manner as in Example 1, except that a polyurethane resin containing no tertiary hydroxyl group was used at positions other than both ends of the main chain in place of the polyurethane eyeliner in Example 1. Created.

[Comparative Example 2] Example 1 except that a polyurethane resin containing 0.04 mil/car of tertiary hydroxyl group at a position other than both ends of the main chain was used in place of the polyurethane resin of Example 1. A sample was prepared in the same manner as in Example 1.

[Comparative Example 3] The average molecular weight of the polyurethane resin of Example 1 was 40.00.
A sample was prepared in the same manner as in Example 1, except that it was set to 0.

The following tests were conducted on the samples prepared in the above Examples and Comparative Examples.

<Color separation phenomenon of paint> Sample the paint mixed with a sand mill in a measuring cylinder, and after leaving it for 5 hours, visually observe the condition and check for carbon black on the upper and lower parts of the paint.

The composition of At203 was analyzed.

<Reproduction output signal dispersion> Insert the prepared sample into the jacket and use a magnetic recording/reproduction tester to select a specific track.

A 125 kHz signal was recorded, and the dispersion of the entire reproduced output signal at that time was measured.

<Modulation> Insert the prepared sample into the jacket and place it on a specific track (O○ track) using a magnetic recording/reproducing tester.

A 125 kHz signal was recorded and measured using a linear equation.

-B -x 1o o (ch) A+B A: Average reproduction output signal of approximately 2,000 magnetic flux reversals including the maximum reproduction output signal within one rotation of the specific track B: Average reproduction output signal of approximately 2,000 magnetic flux reversals including the maximum reproduction output signal within one rotation of the specific track Average playback output signal containing approximately 2,000 magnetic flux reversals (durability test) The prepared sample was inserted into a noyacket, a signal of p 125 kHz was recorded using a magnetic recording and playback tester, and the temperature was 50°C.

80 RH' under test environment conditions of 5°C and 30% RH.

The temporal change in the reproduction output signal was read while it was in contact with a magnetic head, and the time required for the reproduction output signal to reach 80% of the initial reproduction output signal was measured.

The results obtained are shown in Table 1.

The sample prepared according to the present invention can obtain excellent electromagnetic conversion characteristics with small reproduction output signal dispersion and modulation without causing color separation in paints such as carbon black and 'HT2O3. ,
It can be seen that it is an excellent binder that can withstand long-term running under harsh conditions such as high temperature and high humidity, and low temperature and low humidity.

Below blade - day

Claims (1)

[Claims] 1. In a magnetic recording medium formed by coating a magnetic paint on a non-magnetic support, a mixture of butylene adipate and tertiary alcohols and 4,4'-
A magnetic recording medium comprising a polyurethane resin having an average molecular weight of 20,000 to 30,000 and having tertiary hydroxyl groups at positions other than both ends of the main chain obtained from diphenylmethane diisocyanate, nitrocellulose, and a low molecular weight isocyanate compound.