JPS5810769B2 - magnetic sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic sheet that prevents tracking errors.

It has been known to prevent tracking errors by preventing the temperature of the magnetic sheet recorder from rising or by providing the magnetic sheet recorder with a special track detection circuit.

However, these methods require complicated equipment;
Instead, it is common practice to use a magnetic sheet made of materials with as low a coefficient of thermal expansion as possible for the support film and the magnetic layer to prevent tracking errors.

However, even with such a magnetic sheet, tracking errors occur when used at temperatures of 40 to 60 degrees Celsius, especially at 10 degrees Celsius.
Magnetic sheets recorded at temperatures as low as
) had the disadvantage that tracking errors would occur even when played back.

This tracking error causes a depression in the output envelope and also causes a problem that the SZN ratio deteriorates.

Furthermore, because conventional magnetic sheets have local nonuniform thermal expansion coefficients, local differences in elongation cause deformations such as dents, and this deformation causes partial sagging of the output envelope and deformation of the magnetic layer. It was causing destruction.

As a result of repeated research to eliminate the above-mentioned drawbacks, the inventor of the present invention has found that tracking errors are less likely to occur if the ratio of the thermal expansion coefficients in the longitudinal direction and the width direction of the support film is brought closer to 1. They discovered this and completed the present invention.

The present invention expands the usable temperature range to 40-60℃.
It is an object of the present invention to provide a magnetic sheet that does not cause tracking errors even when used continuously at a temperature of .

Another object of the present invention is to provide a magnetic sheet which is stabilized by eliminating local non-uniformity in coefficient of thermal expansion and by reducing thermal contraction.

The present invention provides a magnetic sheet in which a non-magnetic support film coated with a magnetic layer is subjected to calender roll treatment to smooth the surface, and the ratio of the coefficient of thermal expansion in the longitudinal direction and the width direction of the support film is 0.7. It is characterized in that it is in the range of 1.3 to 1.3.

This magnetic sheet is produced by coating a magnetic layer on a non-magnetic support film, drying it, and then applying a calendar roll treatment to smooth the surface. It is obtained by heat treatment until it reaches a range of 0.7 to 1.3.

The magnetic sheet of the present invention is composed of a magnetic layer and a non-magnetic support film.

The magnetic layer is made of magnetic powder or metal.

The ferromagnetic fine powder used in the present invention is γ-Fe20
3Co-containing γ-Fe203, Fe304, Co
Contains Fe304, CrO2t Co Nt P
Known ferromagnetic fine powders such as alloys, Co-Ni-Fe alloys, etc. can be used, and specifically, Japanese Patent Publications No. 14090/1982, Japanese Patent Publications No. 18372/1972, and Japanese Patent Publications No. 47/220
62 Publication, Special Publication No. 47-22513, Special Publication No. 4
6-28466, Japanese Patent Publication No. 46-38755, Japanese Patent Publication No. 47-4286, Japanese Patent Publication No. 47-1242
Publication No. 2, Special Publication No. 47-17284, Special Publication No. 17284, Special Publication No. 17284
Those described in Japanese Patent Publication No. 18509 and Japanese Patent Publication No. 47-18573 can be used.

As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used.

The thermoplastic resin has a softening temperature of 150°C or less, an average molecular weight of 10,000 to 200,000, and a degree of polymerization of about 20.
0 to 500, such as vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic acid ester acrylonitrile copolymer, acrylic acid ester vinylidene chloride copolymer, acrylic Acid ester styrene copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer Polymers, polyamide resins, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymers, polyester resins, chlorovinyl ether acrylic esters, etc. Polymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof are used.

Methods for coating the magnetic layer on the support film include air doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure cord, kiss coating, cast coating, and spray coating. Coats etc. can be used, and detailed explanations thereof are given in "Coating Engineering" published by Shokusen Shoten, pages 253 to 277 (published March 20, 1970).

In this way, the magnetic layer is applied to a thickness of 0.1 to 20 microns.

Materials for the non-magnetic support film include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polyethylene and polypropylene; cellulose diacetate, cellulose triacetate, cellulose acetate butyrate, and cellulose acetate propionate. cellulose derivatives such as; vinyl resins such as polyvinyl chloride and polyvinylidene chloride; plastics such as polycarbonate, polyimide, and polyamideimide;

These support films may be transparent or opaque depending on the intended use of the magnetic recording medium.

The magnetic sheet of the present invention is obtained by coating a magnetic layer on the above-mentioned support film, drying it, and then subjecting it to calender roll treatment.

The strength of the support film in the longitudinal direction is strengthened in advance in order to prevent cutting or permanent deformation during coating of the magnetic layer.

This causes the support film to have different coefficients of thermal expansion in the longitudinal direction and in the width direction.

For example, a biaxially stretched polyethylene terephthalate support film has a coefficient of thermal expansion of 1.1 x 10"%/°C in the longitudinal direction and 0.15 x 10"%/°C in the width direction.
The ratio is 0.14.

If the ratio of thermal expansion coefficients is small in this way, when the magnetic sheet is reproduced at a temperature different from that at which it was recorded, the extension of the magnetic sheet from the center will differ due to the difference in thermal expansion coefficients, and the magnetic head and recording track will be misaligned. This may cause tracking errors.

This changes the output and degrades the reproduced image,
Dropouts occur.

Temperature changes also cause non-isotropic permanent shrinkage, resulting in partial tracking errors.

Furthermore, local non-uniformity in the coefficient of thermal expansion occurs, causing local output envelope drooping and magnetic layer destruction as described above.

The above-mentioned tracking error or permanent shrinkage can be solved by making the ratio of the coefficient of thermal expansion in the longitudinal direction and the width direction of the magnetic sheet close to 1.

This can be achieved by forming a magnetic layer on a non-magnetic support film, subjecting it to a calendar roll treatment for surface smoothing, and then heat-treating it.

Note that such heat treatment cannot be applied to magnetic tapes rather than porcelain sheets.

This is because heat treatment weakens the longitudinal strength required for the magnetic tape, causing permanent deformation of the magnetic tape.

Magnetic sheets have extremely small forces (
It is thought to be 1/150 to 1/200 of normal tape.

), the heat treatment described above can be carried out without any problem even if the strength is reduced.

The time and temperature for heat treatment vary depending on the nonmagnetic support film and binder used.

Generally, it is desirable that the temperature be lower than the glass transition point of the nonmagnetic support film and at a temperature that does not cause deterioration of the magnetic layer coated on the nonmagnetic support film.

There are no particular restrictions regarding time.

The ratio of the coefficient of thermal expansion in the longitudinal direction and the width direction was measured by the following method.

A magnetic sheet that had been heat-treated in advance under predetermined conditions (for example, 60° C. for 30 minutes) was cut into a size of 1 cfrL×15 crfL, and marks were placed on the sample at two positions 10 crfL apart.

Change the temperature by 20℃ (from 15℃ to 35℃)
The coefficient of thermal expansion was determined by examining the extension between the two marks.

The following method was used for the practical test.

A preheated magnetic sheet was recorded at 15°C,
The maximum output of the magnetic sheet and the envelope of the output of the magnetic sheet at that time were investigated.

Next, the temperature of the sheet coder was maintained so that the atmosphere around the magnetic sheet was always 35° C., and the maximum output and the envelope of the output of the magnetic sheet at that temperature were examined.

The goodness of tracking of the magnetic sheet was determined by comparing the output envelope at 15° C. and the output envelope at 35° C.

The smaller this difference is, the better the tracking characteristics are.

If this difference exceeds 3 dB, tracking is poor.

As shown in the examples below, the magnetic sheet has a ratio of thermal expansion coefficients in the longitudinal direction and the width direction of the support film of 0.7 to 1.
It was found that the tracking of the magnetic sheet is good when the value is 1.3.

A more preferable range is 0.9 to 11.

If it is less than 0.7 or more than 1.3, tracking errors will become large and it cannot be used as a magnetic sheet.

As described above, in the present invention, the magnetic sheet is heat-treated to have a ratio of thermal expansion coefficients of 0.7 to 1.3, thereby significantly reducing tracking errors.

This reduction in tracking errors resulted in fewer dropouts of the magnetic sheet, making it difficult for the S/N ratio to deteriorate.

Furthermore, the operating temperature range of the magnetic sheet has become wider, from 40 to
It is now possible to play back without tracking errors even at 60 degrees Celsius.

In addition, thermal shrinkage of the magnetic sheet was reduced, and dimensional changes over time were reduced, resulting in improved dimensional stability.

Furthermore, local non-uniformity in the coefficient of thermal expansion was corrected, making it possible to prevent disturbance of the output envelope or destruction of the magnetic layer.

Examples are shown below.

Example 1 Bi-terephthalate is obtained by transesterification from terephthalic acid and ethylene glycol.

This bis-terephthalate is polymerized to obtain polyethylene terephthalate having a thickness of 25.4 μm.

A magnetic coating liquid having the following composition was coated onto this polyethylene terephthalate to a thickness of 10 μm.

(Magnetic Coating Liquid) After the above magnetic coating liquid was applied to a non-magnetic support film of polyethylene terephthalate, a calendar roll treatment was performed.

Thereafter, it was cut into magnetic sheets having an outer diameter of 24 cIrL and an inner diameter of 2 CrrL, heat-treated in advance, and placed in a sheet recorder.

The sheet recorder rotated at 3600 rpm, and the magnetic head was positioned at 101 from the center of the sheet.

The track width was 200μ, and the head material was ferrite.

An IMHz signal was recorded on the magnetic sheet at 15°C, and
℃ playback and tracking was examined in the output envelope of the sheet.

Note that this magnetic sheet had an envelope of 0.2 dB or less at 15°C.

The measurement results are shown in Table 1.

As is clear from Table 1 above, the ratio of thermal expansion coefficients is 0.
Sheet No. in the range of 7 to 1.3, 1003 to 100
It was found that the tracking error of Sample No. 5 was significantly improved compared to Sample A1001 which was not subjected to heat treatment.

Note that the reason why the reproduction envelope and the coefficient of thermal expansion do not completely match is considered to be because the magnetic sheet has extremely slight irregular expansion and contraction.

Example 2 A magnetic coating solution having the composition shown in Example 1 was applied to a thickness of 8μ on a non-magnetic support film of cellulose triacetate having a thickness of 22μ.

Thereafter, calender roll treatment was performed.

Thereafter, a test was conducted in the same manner as in Example 1, and the results shown in Table 2 were obtained.

As shown in Table 2, the ratio of thermal expansion coefficients is 0.7~
Sheets A2oo3 to 2005 in the range 1.3 are S
The IN ratio, tracking, dropout, etc. were good.

Claims (1)

[Claims] 1. In a magnetic sheet in which a non-magnetic support film coated with a magnetic layer is subjected to calender roll treatment to smooth the surface, after the calender roll treatment, heat treatment is performed to improve the longitudinal direction and width of the support film. A magnetic sheet characterized in that the ratio of the coefficients of thermal expansion in the directions is in the range of 0.7 to 1.3.