JPH01173431A - Manufacture of coating type magnetic medium - Google Patents

Abstract

PURPOSE:To improve durability by making the glass transition temperature of a first magnetic layer after hardening processing higher than the glass transition temperature of a second magnetic layer before the hardening processing. CONSTITUTION:The glass transition temperature (Tg1) of the first magnetic layer after the hardening processing is made higher than the glass transition temperature (Tg2) of the second magnetic layer before the hardening processing, and calender processing temperature T is made within the range of Tg1>T> Tg2. Further, carbon black whose oil absorption is 30-500ml/100g and whose BET specific surface area is 30-1,500m<2>/g is added to the first magnetic layer by 1-20% to dielectric powder in the magnetic layer. Further, a non-magnetic supporting body is made of a polyethyleneterephthalate film, and saturated polyester resin whose solubility parameter is within the range of 8.5-9.5 is made to be contained as the binder component of the first magnetic layer by more than 40% to the total binder component. Thus, superior electromagnetic transducing characteristic and the superior durability are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a coated magnetic medium having excellent electromagnetic conversion characteristics and excellent durability.

<Conventional technology> In recent years, with the demand for higher density magnetic recording media.

Even in so-called coated magnetic media, which consists of applying a magnetic coating consisting of magnetic powder and a binder onto a non-magnetic support, the magnetic powder is made finer and the magnetic layer is made thinner.

There is a tendency for surface smoothing and increase in magnetic powder volume filling rate to be promoted more and more. In particular, with regard to surface smoothing and increasing the volumetric filling rate of magnetic powder, it is a hot topic to increase the dispersion degree of magnetic powder. Efforts have been made to further increase the number of rolls and improve roll surface precision.

On the other hand, durability becomes extremely difficult because thinning the magnetic layer, smoothing the surface, and increasing the volume filling rate of the magnetic powder result in a decrease in mechanical strength and an increase in the coefficient of friction.

Furthermore, since thinning of the film also causes problems such as deterioration of light-shielding properties and conductivity, it is desired to develop a new medium design technique to solve these problems. In order to meet these demands, conventionally, lubricants such as higher fatty acids or their derivatives, fluorine-based oils, and silicones, and non-magnetic inorganic fine powders with a Mohs hardness of 7 or more have been used alone or in combination in the magnetic layer. Attempts have been made to include

<Problems to be Solved by the Invention> However, the durability required for coated magnetic media, which is achieved by thinning the film, smoothing the surface, and increasing the magnetic powder volume filling rate, cannot be achieved at the expense of electromagnetic conversion characteristics. However, it was not yet possible to secure sufficient capacity.

-For example, if an attempt is made to ensure durability by adding too much lubricant to a coated magnetic medium with a film thickness of 1 μm, it is a matter of heat that this will lead to deterioration of the electromagnetic conversion characteristics.

If a flexible disk is used for a long time under high temperature and high humidity, the lubricant will overbleed, resulting in abnormal rotation of the disk or a decrease in reproduction output due to head dirt, and further damage to the magnetic layer due to the head dirt. Partial peeling occurred, posing a practical problem.

The present invention relates to a method of manufacturing a coated magnetic medium.

The purpose is to eliminate these conventional drawbacks and provide a magnetic recording medium that has excellent electromagnetic conversion characteristics and excellent durability.

Means to solve problems〉 According to the invention.

■ By forming a first magnetic layer on a non-magnetic support and hardening it without calendering, applying a second magnetic layer, calendering it, and then hardening it. A method of manufacturing a coated magnetic medium.

■ Glass transition temperature (T
g1) is higher than the glass transition temperature (Tgz) of the second magnetic layer before curing treatment, and the calendering temperature T is T
Reed in the range of gl > T > Tgz.

■ Furthermore, the oil absorption amount is 30 to 500 in the first magnetic layer.
m/100iP, BET specific surface area is 30-1500m
'/f? 1 to 20% of carbon black is added to the ferromagnetic powder in the magnetic layer.

(2) Furthermore, the nonmagnetic support is a polyethylene terephthalate film, and the binder component of the first magnetic layer is a saturated polyester resin having a solubility noclameter in the range of 8.5 to 9.5. 40% of
A method for manufacturing a coated magnetic medium characterized by containing the above is obtained.

What is the calendaring process performed in the present invention?

This is a process in which a web coated with a magnetic layer is flowed under pressure between a heated mirror-finished metal roll and an elastic roll with a smooth surface that backs it up, but a mirror-finished metal roll may be used in place of the elastic roll. . What is the nip pressure (linear pressure) during the calendering process?

Although it depends on the material of the elastic roll backing up the mirror-finished metal roll, 100 to 350 kQ/cm is appropriate.

The surface temperature of the mirror-finished metal roll, that is, the calendering temperature, needs to be lower than the glass transition temperature of the first magnetic layer after hardening treatment and higher than the glass transition temperature of the second magnetic layer. If this condition is not met, the effects of the present invention cannot be fully exhibited, so care must be taken. The carbon black used in the first magnetic layer in the present invention is as follows.

It is sufficient if the oil absorption is in the range of 30 to 500 m//10 (1) and the BET specific surface area is in the range of 30 to 1500 m/ji'.

Many commercially available products can be used. -For example, $3250 manufactured by Mitsubishi Kasei. 3750°+39
50. Conductex SC, Conductex 975, RAVEN 32 manufactured by Columbian Carbon
00.

RAVEN 1255 etc. The amount of carbon black added is 1 to 20% based on the ferromagnetic powder of the first magnetic layer.
Weight % is appropriate. If the amount is less than this, the light-shielding property, conductivity, and lubricant retention ability will be insufficient, and if it is more than this, the electromagnetic conversion characteristics will deteriorate, which is undesirable. The saturated polyester resin used as the binder may have a solubility parameter in the range of 8.5 to 9.5, and the amount used is 40% by weight of the total binder component in the first magnetic layer. The above is preferable, and examples of the curing method for the first magnetic layer include heat treatment, electron beam irradiation treatment, etc., although it varies depending on the binder system used.
Regarding the degree of curing of the first magnetic layer, it is preferable that the residual concentration of reactive groups contributing to the curing reaction of the system is 50% or less of the initial concentration of reactive groups. In particular, when the binder components of the first magnetic layer and the second magnetic layer are the same, if the first magnetic layer is not sufficiently hardened, the glass transition temperature between the two magnetic layers may decrease. This is not preferable because the difference narrows, and therefore a wide range of calendering temperatures cannot be achieved. In addition,
If the glass transition temperature of the binder component of the first magnetic layer is sufficiently higher than the glass transition temperature of the binder component of the second magnetic layer, it is not necessary to set the degree of curing acceleration to 50% or less. However, in this case, care must be taken to prevent the first magnetic layer from dissolving and mixing with the second magnetic layer when coating the second magnetic layer.

Effect> The two inventors consider the mechanism of action of the present invention as follows. Namely.

(2) A small deviation in solubility parameters between the polyethylene terephthalate film, which is a non-magnetic support, and the first magnetic layer contributes to improved adhesion.

■ Since the first magnetic layer is not calendered, the volume occupancy of pores in the first magnetic layer is relatively high.
Excellent lubricant loading properties.

■ Carbon black in the first magnetic layer is conductive.

Not only light blocking properties but also lubricant loading properties are further improved. These effects provide excellent durability. moreover.

(2) Since the second magnetic layer is selectively calendered (31), the volume occupancy of the ferromagnetic powder in the second magnetic layer is improved, and as a result, the electromagnetic conversion characteristics are improved. That is, the magnetic layer is
By forming the layered structure, durability can be improved without deteriorating the p-electromagnetic conversion characteristics.

<Example> Next, examples of the present invention will be described.

Example 1 Co-γ iron oxide (He=7000e) -100
Parts by weight Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (vinyl chloride component 90%, vinyl acetate component 4-fiber, vinyl alcohol component 6%, Tg 74°C)...20 parts by weight Saturated polyester resin A (tensile strength at break) 500k
VCrn2. Solubility parameters 9.2. Tg67°C1
NV 30%)
...30 parts by weight saturated polyester resin B (tensile υ
Breaking strength 501 (g/cm2. Solubility parameter 8.9
．． Tg6℃, NV30%)...40i parts carbon black (manufactured by Mitsubishi Chemical Corporation +3750) ・
・・155 parts by weight Mia Millstearate
... 3 parts by weight hexadecyl stearate
... 7M parts methyl ethyl ketone
...90 parts by weight Cyclohexanone ...45 Heavy i-3 toluene ...90
Parts by weight After mixing the above composition in a ball mill for 72 hours, an incyanate compound (C-3 manufactured by Nippon Priurethane Co., Ltd.
041) 12 parts by weight was added and kneaded for 2 hours to obtain a magnetic paint for the first magnetic layer. This was placed on a 75 μm thick teriethylene tere 7 tallate film so that the thickness after drying was 0.6 μm.
The magnetic layer was coated so as to have a thickness of .mu.m, and then cured for 72 hours at a constant temperature of 45.degree. Q to obtain a first magnetic layer. A magnetic paint for the second magnetic layer having the following composition was applied onto the obtained first magnetic layer so that the thickness after drying was 0.4 μm, and the nip pressure was 300 kFhrl and the metal roll surface temperature was 50 μm. Calendar treatment was carried out under the conditions of 4°C.
Diameter 3.5 after curing for 72 hours at a constant temperature of 5℃
A sample was punched into an inch disc.

Co-γ iron oxide (Hc=7000e)...
xooit part vinyl chloride vinyl dichloride-vinyl alcohol copolymer (vinyl chloride component 90%, vinyl acetate component 4
H, vinyl alcohol component 6%, Tg 74℃)...
8 parts by weight saturated polyester resin (tensile strength at break 50
19'2m2. Solubility parameter 8.9, 'rg
6℃, NV30%)...56 parts by weight α-ht2 o 5
... 7 parts by weight I-amyl stearate
...1 part by weight hexadecyl stearate ...2 parts by weight methyl ethyl ketone ...90 parts by weight cyclohexanone ...45 parts by weight toluene
... 90M parts Incyanate compound (Nippon Polyurethane Co., Ltd. FFC-3041) ... 8 parts by weight Comparative Example 1 Same as Example 1 except that the calender treatment after coating the second magnetic layer in Example 1 was not performed. Samples were obtained in a similar manner.

Comparative example 2 The thickness of the first magnetic layer in Example 1 was 1 μm.

A sample was obtained in the same manner as in Example 1 except that the second magnetic layer was not provided.

Comparative Example 3 A sample was obtained in the same manner as in Example 1 except that the first magnetic layer in Example 1 was not provided and the thickness of the second magnetic layer was 1 μm.

Comparative Example 4 A sample was obtained in the same manner as in Example 1 except that the carbon black in the first magnetic layer in Example 1 was removed.

Comparative Example 5 Saturated polyester resin A in the first magnetic layer in Example 1 (97 cm2. Solubility in tensile υ breaking strength 500)
” 7 Mefi 9.2 r Tg 67℃, NY30
%) and saturated polyester resin B (tensile strength at break 50 kg7cm, solubility parameter 8.9.
60 parts by weight of a polyurethane resin with a solubility A' rammeter of 10.5 (Tg6℃, NV30%)°40 parts by weight (NV3
A sample was prepared in the same manner as in Example 1, except that 5%) was used.

Comparative Example 6 A sample was obtained in the same manner as in Example 1 except that the calender treatment temperature in Example 1 was changed to 23°C.

Each of these samples was tested for durability and frequency characteristics using the methods described below.

■ Durability test After recording a saturated signal with a frequency of 500 kHz on the sample.

It is assembled into a 3.5-inch flexible disk jacket with a liner pasted on it, and this is used as a 3.5-inch flexible disk drive (135 TPI, 300 TPI).
rpm), and a durability test was conducted under an atmosphere of 60° C. and 80% RH.

■ Frequency characteristic test Commercially available 3.5 inch flexible disk drive (13
5TPI, 300 rpm) and optical gear? length 0.65
A 1rm Mn-Zn ferrite head was installed, various frequency signals were recorded at a write current of 15 mA (1,2 AT), and the recording density (half-value reversal density Dso) at which the reproduced signal amplitude was the sacrifice of the solitary wave output was determined. .

These results are shown in Table 1, and as is clear from this table, according to the above examples, a coated magnetic medium having good electromagnetic conversion characteristics and excellent durability can be obtained.

Below is the gold white table 1 Ha0 1500xlO//s or less... × Half-value inversion density: 30KFRPI or more...030KFR
PI or higher... × 9°C-1; Other days <Effects of the invention> As explained above, according to the present invention, a coated magnetic medium with good electromagnetic conversion characteristics and excellent durability can be obtained. It will be done.

Note that the effects of the present invention are not limited to Co-γ iron oxide, and similar effects can be obtained with magnetic materials such as γ-iron oxide, Ba-ferrite, and metal.2 Regarding the types of ferromagnetic powders, The effects of the present invention are not limited to this embodiment, and are not limited to flexible disks.

Similar effects can be obtained with magnetic recording media such as audio tapes and video tags, and the form of the magnetic recording media is not limited to this embodiment.

Claims (1)

[Claims] (1) After forming a first magnetic layer on a non-magnetic support and performing a hardening process without calendering, a second magnetic layer is applied, a calendaring process is performed, and a further hardening process is performed. A method of manufacturing a coated magnetic medium according to the present invention, the glass transition temperature (Tg_
1) is higher than the glass transition temperature (Tg_2) of the second magnetic layer before the hardening process, and the calendering temperature T is T
g_1>T>Tg_2, and further, the first magnetic layer has an oil absorption of 30 to 500 ml/100 g and a BET specific surface area of 30 to 500 ml/100 g.
1500 m^2/g of carbon black is added in an amount of 1 to 20% based on the ferromagnetic powder in the magnetic layer, the non-magnetic support is a polyethylene terephthalate film, and the binder component of the first magnetic layer is added. A method for producing a coated magnetic medium, characterized in that 40% or more of the total binder component contains a saturated polyester resin having a solubility parameter in the range of 8.5 to 9.5.