JPH01173428A - 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, conductive titanium oxide fine powder whose oil absorption is more than 15ml/100g and whose powder resistance is less than 60OMEGAcm is added in the first magnetic layer by 3-30% to dielectric powder in the magnetic layer. Furthermore, a non-magnetic supporting body is made of polyethyleneterephthalate film, and polyurethane resin whose solubility parameter is within the range of 9.0-9.5 is made to be contained by more than 40% of total binder component as the binder component of the first magnetic layer. Thus, superior electro-magnetic conversion 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 that has submerged electromagnetic conversion characteristics and is excellent in durability.

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

Even in so-called coated magnetic media in which a magnetic coating consisting of magnetic powder and a binder is coated on a non-magnetic support, it is possible to make the magnetic powder particles finer and to make the magnetic layer thinner.1.Smooth the surface and increase the volume filling rate of the magnetic powder. There is a tendency for this trend to be accelerated more and more.

In particular, regarding surface smoothing and increasing the magnetic powder volume filling rate, it goes without saying that the degree of dispersion of the magnetic powder can be increased.

Even in roll polishing, so-called calendering, which has been widely used in the past, efforts have been made to increase the processing pressure and improve the roll surface precision.

On the other hand, regarding durability, the magnetic layer has been made thinner.

Smoothing the surface and increasing the volume filling rate of magnetic powder are extremely difficult because they result in a decrease in mechanical strength and an increase in the coefficient of friction. Furthermore, there are some disadvantages associated with thinning the film, such as light-shielding properties,
Since the problem of deterioration of conductivity also arises, it is desired to develop a new medium design technique to solve these problems.

In order to meet these requirements, higher fatty acids or their derivatives, or fluorine-based oils have conventionally been used in the magnetic layer.

Attempts have been made to include lubricants such as silicone and non-magnetic inorganic fine powders with a Mohs hardness of 7 or higher, either singly or in combination.

<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, the film thickness is 1μ
If an attempt is made to ensure durability by adding too much lubricant to a coated magnetic medium, it is inevitable that the electromagnetic conversion characteristics will deteriorate, and the flexible disk format will continue to be used for long periods of time under high temperature and high humidity conditions. This causes overbleeding of the lubricant, resulting in abnormal rotation of the disk, reduction in reproduction output due to head contamination, and furthermore, partial peeling of the magnetic layer due to the head contamination, which poses practical problems.

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

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

A last resort to solving problems According to the invention.

(2) After forming a first magnetic layer on a non-magnetic support and performing a hardening treatment without calendering.

Apply the second magnetic layer and perform calendering.

A method of manufacturing a coated magnetic medium by further performing a curing treatment.

■Glass transition temperature (Tg) after curing treatment of the first magnetic layer
1) is higher than the glass transition temperature (Tg2) of the second magnetic layer before the hardening process, and the calendering temperature T is higher than Tg2.
,>T>Tg2.

■Furthermore, the first magnetic layer has an oil absorption of 15 mt/10
Powder resistance is 60Ωcm (100KP/cm2
The following conductive titanium oxide fine powder was added in an amount of 3 to 30% based on the ferromagnetic powder in the magnetic layer.

(2) Furthermore, the non-magnetic support is a polyethylene terephthalate film, and a polyurethane resin having a solubility parameter in the range of 9.0 to 9.5 is used as the binder component of the first magnetic layer. A method for manufacturing a coated magnetic medium characterized by containing 40% or more is obtained.

What is the calendaring process performed in the present invention?

It is a process in which a web coated with a magnetic layer is flowed under pressure between a heated mirror-finished metal roll and a smooth-surfaced elastic roll that backs it up.

A mirror-finished metal roll may be used instead of the elastic roll. The nip pressure (linear pressure) during the calendering process is suitably 100 to 350 KP/crn, although it depends on the material of the elastic roll backing up the mirror-finished metal roll.

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.

In the present invention, the conductive titanium oxide fine powder used for the first magnetic layer has an oil absorption of 15 ml/100 g or more and a powder resistance of 60 Ω or less (100 KV/, value based on Lz compact), It is sufficient if the average grain size is equal to or smaller than the thickness of the first magnetic layer.

Examples include white conductive titanium oxide, which has a tin oxide-based conductive layer coated on the surface of titanium oxide fine powder, and black conductive titanium oxide fine powder called titanium black. What is the amount of conductive titanium oxide added?

A suitable amount is 3 to 30% by weight based on the ferromagnetic powder in the first magnetic layer.

If the amount is less than this, the light-shielding property, conductivity, and lubricant retention ability will be insufficient, and if the amount is more than this, the electromagnetic conversion characteristics will deteriorate, which is not preferable.

The polyurethane resin used as a binder for the first magnetic layer may have a solubility parameter in the range of 9.0 to 9.5, and the amount used should be determined based on the total bonding in the first magnetic layer. It is preferably 40% by weight or more of the agent components.

Methods for curing 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 hardening 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 times or less of the initial reactive group concentration.

In particular, when the binder components of the first and second magnetic layers are the same, the glass transition temperature between the two magnetic layers must be sufficiently cured. This is not preferable because the difference narrows, and therefore a wide range of calendering temperatures cannot be achieved.

Note that 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, the degree of curing acceleration does not necessarily need to be 50 degrees or less. However, in this case, care must be taken to prevent the first magnetic layer from melting and mixing with the second magnetic layer when coating the second magnetic layer.

Effect> The nine 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.

The following is gold and white■ Because the first magnetic layer is not calendered, the first
The volume occupancy of pores in the magnetic layer is relatively high, and the lubricant loading property is excellent.

■The conductive titanium oxide in the first magnetic layer is conductive.

In addition to light blocking properties, it further improves lubricant loading properties.

These effects provide excellent durability.

moreover.

(2) Since the second magnetic layer is selectively calendered, 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, by forming the magnetic layer into a two-layer structure, durability can be improved without deteriorating electromagnetic conversion characteristics.

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

Example 1 C・-γ iron oxide (H・=7000e) ・N
Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (vinyl chloride component 90%, vinyl acetate component 4%, vinyl alcohol component 6%, Tg 74°C)...
・・20 parts by weight polyurethane resin (tensile breaking strength 660 K9/c
IrL2 solubility parameters 9.2. Tg17℃, N
V35%) ω Part by weight White conductive titanium oxide (300W manufactured by Bancho Sangyo Co., Ltd.)
・・・・・・15 parts by weight i-amyl stearate ・・・・・・3 parts by weight hexadecyl stearate ・・・・・・・・・
7 parts by weight methyl ethyl ketone...
・90 parts by weight cyclohexanone...
...45 parts by weight toluene...
...90 m t parts The above composition was mixed in a ball mill for 72 hours, and then 12 parts by weight of an incyanate compound (C-3041 manufactured by Nippon Polyurethane Co., Ltd.) was added and kneaded for 2 hours to form the first magnetic layer. A magnetic paint for use was obtained.

This was coated on a polyethylene terecotalate film with a thickness of 75 μm so that the thickness after drying was 0.6 μm, and keying was performed for 72 hours at a constant temperature of 45°C to form the first magnetic layer. Obtained.

On the obtained first magnetic layer, a magnetic paint for a second magnetic layer having the following composition was applied so that the thickness after drying was 0.4 μm, and a nip pressure of 300 KP/, two metal rolls were applied. Calendar treatment was performed at a surface temperature of 50°C, and this was heated to 45°C.
After curing for 72 hours at a constant temperature of .degree. C., a disk-shaped sample having a diameter of 3.5 inches was punched out.

Co-7” iron oxide (He = 7000e)...
-100 parts by weight vinyl chloride-hinyl acetate-vinyl alcohol copolymer (vinyl chloride component 90%, vinyl acetate component 4%, vinyl alcohol component 6%).

7g74°C) 8 parts by weight polyurethane resin (tensile strength at break 470 Ky
/,,2 Solubility parameters 9.9. Tg4℃, NV
35%) 48 parts by weight α-ht2o, 7 parts by weight Meamyl stearate 1 part by weight Hexadecyl stearate 2 parts by weight Methyl ethyl ketone・Track 9o parts by weight Cyclohexanone 45 parts by weight Toluene 9 offii parts Incyanate compound (C-3041 manufactured by Nippon Polyurethane Co., Ltd.)
...Song 8 parts by weight Comparative Example 1 A sample was obtained in the same manner as in Example 1 except that the calender treatment after coating the second magnetic layer in Example 1 was not performed.

Comparative Example 2 A sample was obtained in the same manner as in Example 1 except that the first magnetic layer in Example 1 had a thickness of 1 μm and the second magnetic layer was not provided. - Comparative Example 3 The first magnetic layer in Example 1 was not provided.

A sample was obtained in the same manner as in Example 1 except that 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 white conductive titanium oxide in the first magnetic layer in Example 1 was removed.

Comparative Example 5 Polyurethane resin (
solubility parameter 9.2) to solubility parameter 10.5
A sample was obtained in the same manner as in Example 1 except that the polyurethane resin was used instead.

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.

These samples were tested for durability and frequency characteristics using the methods described below.

■Durability test After recording a signal with a frequency of 500kHz in saturation, it was assembled into a 3.5-inch flexible disk jacket with a liner pasted on it, mounted in a 3.5-inch flexible disk drive (135TPL 300rpm), and heated at 60℃- A durability test was conducted in an 80% RH atmosphere.

0 Frequency characteristics test Commercially available 3.5 inch flexible disk drive (13
5 TPI, 300 rpm) with an optical gap length of 0.65
Incorporates a μm Mn-Zn ferrite head.

Various frequency signals were recorded at a write current of 15 mA (1,2 AT), and the recording density (half-value inversion density D50) at which the reproduced signal amplitude became 1 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.

Table 1 below: Durability: 1500x10 bath or more ・・・・・・○
1,500
RPI or less... .

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.9 Regarding the types of ferromagnetic powder, It is not limited to this embodiment. Further, the effects of the present invention are not limited to flexible disks, and similar effects can be obtained with magnetic recording media such as audio tapes and video tapes, and the form of the magnetic recording medium is not limited to this embodiment.

Claims (1)

[Claims] 1) After forming a first magnetic layer on a non-magnetic support and performing a curing treatment without calendering, a second magnetic layer is applied and calendered, and further A method of manufacturing a coated magnetic medium by performing a hardening treatment, the method comprising: increasing 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 furthermore, the first magnetic layer has an oil absorption of 15 ml/100 g or more and a powder resistance of 60 Ωcm (value based on 100 Kg/cm^2 compacted powder).
The following conductive titanium oxide fine powder is added in an amount of 3 to 30% based on the ferromagnetic powder in the magnetic layer, and further, the non-magnetic support is a polyethylene terephthalate film, and the binder component of the first magnetic layer is A method for producing a coated magnetic medium, characterized in that 40% or more of the total binder component contains a polyurethane resin having a solubility parameter in the range of 9.0 to 9.5.