JPS60263318A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having an excellent lubricating effect and an excellent electromagnetic convertion characteristic and running stability by forming a back coat layer contg. >=1 kind among sorbic acid, sorbic acid deriv. and metallic salt of sorbic acid on the rear of a substrate on the front of which a magnetic layer is provided. CONSTITUTION:The back coat layer incorporated therein with the sorbic acid expressed by CH3CH=CHCH=CHCOOH and >=1 kind among the ester, amide and metallic salt thereof together with inorg. powder such as alpha-Fe2O3, CrO3, MgO, SiC or the like and carbon black is formed on the surface of the non- magnetic substrate on the side opposite from the surface on which the magnetic layer is provided. The above-mentioned sorbic acid and the deriv. thereof contribute to an improvement in the dispersibility of the filler and have a lubricating effect. The magnetic recording medium having the low color noise and the excellent running stability and durability is thus obtd. without deteriorating the electromagnetic conversion characteristic.

Description

[Detailed Description of the Invention] [Technical Field and Objective] The present invention relates to a magnetic recording medium such as a magnetic tape in which a bank coat layer is provided on the back side of a substrate having a magnetic layer on the surface, and its purpose is to improve running stability. The object of the present invention is to provide a magnetic recording medium such as a magnetic tape that has good properties and excellent electromagnetic conversion characteristics.

[Background technology]

In recent years, especially in magnetic recording media such as video tapes,
In order to reduce noise and improve output, we use extremely smooth polyester film etc. as the base.
Although the surface smoothness of the magnetic layer is made as smooth as possible by using extremely fine magnetic powder, the smoother the base is used, the more difficult it is to contact guide rolls during running. The coefficient of friction increases, making running unstable. Therefore, in order to reduce the coefficient of friction and improve running stability,
A bank coat layer is provided on the back surface of a substrate having a magnetic layer by applying a filler such as barium sulfate, calcium carbonate, carbon blank, or red iron together with a binder resin.

However, these fillers used in the bank coat layer have poor dispersibility in the binder resin and may aggregate, forming relatively rough irregularities on the surface of the bank coat layer.
When a video tape or the like is stored in a wound state, the unevenness on the surface of the bank coat layer is transferred to the surface of the magnetic layer, resulting in a problem in that the output is lowered, the noise is increased, and the electromagnetic conversion characteristics are deteriorated. .

[Summary of the invention]

In view of the current situation, this invention has conducted various studies in order to improve the dispersion of the filler contained in the back coat layer into the binder resin and improve running stability without causing deterioration of electromagnetic conversion characteristics. As a result, when at least one sorbic acid compound selected from sorbic acid, sorbic acid derivatives, and sorbic acid metal salts is contained in the bank coat layer, the dispersibility of the filler contained in the bank coat layer is sufficiently improved. This improves the surface smoothness of the bank coat layer, and since these sorbic acid compounds have a lubricating effect, the coefficient of friction is reduced, improving running stability without deteriorating electromagnetic conversion characteristics. This has been made clear.

It has not yet been clearly elucidated why such sorbic acid, sorbic acid derivatives, and sorbic acid metal salts have a remarkable ability to disperse the filler in the paint for the back coat layer. Considering its unique chemical structure, ■ By having a conjugated double bond in the molecule, the electron density is localized within the molecule and the polarizability is increased, which increases functionality. Because both bonds have a trans (trans-trans) structure, the functional group is located at the outermost end of the molecule, making it statistically and geometrically likely that the functional group will be unevenly distributed on the surface of the dispersant. (1) Sorbic acid and sorbic acid metal salts have 6 carbon atoms, and sorbic acid derivatives usually have 12 or less carbon atoms, so they have an appropriate melting point and are used as binders to give paints good fluidity. Three points are presumed: that it is easy to mix into the resin.

The sorbic acid used in this invention has the chemical formula CH
A compound represented by 3CH=CHCH=CHCOOH,
It has a conjugated double bond in its molecule, both of which are trans, has a relatively small molecular weight, adheres well to the filler surface, and is compatible with the binder resin. Therefore, when this sorbic acid is contained in the paint for the back coat layer, the dispersibility of the filler in the binder resin is sufficiently improved, no aggregation of the filler occurs, and the surface smoothness of the back coat layer is improved. Become good. Therefore, when winding a video tape or the like, the unevenness of the back coat layer does not transfer to the surface of the magnetic layer, and the electromagnetic conversion characteristics do not deteriorate. In addition, this sorbic acid acts as a dispersant for fillers and has an excellent lubricating effect, so the coefficient of friction on the surface of the back coat layer is sufficiently reduced, resulting in a magnetic recording medium with excellent running stability and electromagnetic conversion characteristics. .

Further, as the sorbic acid derivative used in this invention, for example, methyl ester of sorbic acid C1H
, C00CH3, ethyl ester C5H, COOC2H
5, Propyl ester C51 (, C00C3H a, Butyl ester cs H7C00C4H9, Amide C5H7
CON H2, nitrile C5H aCN, anilide c5H
ACONHC6H2, phenylhydrazide cs H,C
0NHNHCsHs etc. are mentioned as suitable ones, and these sorbic acid derivatives also have a conjugated double bond in the molecule like the above-mentioned sorbic acid, both of these double bonds are trans, and the molecular weight is relatively small. , it adheres well to the surface of the filler and is also compatible with the binder resin. Therefore,
When these sorbic acid derivatives are included in the paint for the back coat layer, the same effect as when using sorbic acid described above can be obtained, and the dispersibility of the filler in the binder resin is sufficiently improved. There is no aggregation of the filler, the surface smoothness of the back coat layer is improved, and the electromagnetic conversion characteristics are not deteriorated. In addition, like the above-mentioned sorbic acid, this sorbic acid derivative also acts as a dispersant for fillers and has a lubricating effect. Therefore, the coefficient of friction on the surface of the back coat layer is reduced, and it has excellent running stability and electromagnetic conversion characteristics. A magnetic recording medium is obtained.

Further, the sorbic acid metal salt used in the present invention is a compound represented by the general formula % (where M is a metal), and has a similar structure in the molecule as the sorbic acid and sorbic acid derivatives described above. It has a military service double bond, both of these double bonds are trans, and the molecular weight is relatively small.
It adheres well to the filler surface and is compatible with the binder resin. Therefore, when these sorbic acid metal salts are included in the bank coat shoe paint, the same effect as when using sorbic acid and sorbic acid derivatives described above can be obtained, and the dispersion of the filler in the binder resin is improved. The properties are sufficiently improved, no aggregation of the filler occurs, the surface smoothness of the back coat layer is improved, and the electromagnetic conversion characteristics do not deteriorate. In addition, like the sorbic acid described above, this sorbic metal salt also acts as a dispersant for fillers and has a lubricating effect. Therefore, the coefficient of friction on the surface of the back coat layer is reduced, and it has excellent running stability and electromagnetic conversion characteristics. A magnetic recording medium is obtained. Specific examples of such metal sorbic acid salts include sodium salt, potassium salt, lithium salt, copper salt, magnesium salt, calcium salt, strontium salt, barium salt, zinc salt, cadmium rum salt, Examples include aluminum salts, tin salts, lead salts, titanium salts, zirconium salts, etc., and any of them are preferably used.

5 Such back coat layers containing sorbic acid, sorbic acid derivatives, and sorbic acid metal salts are usually prepared by mixing and dispersing these sorbic acid compounds together with fillers, binder resins, organic solvents, etc. It is formed by preparing a layered coating material, applying it to the back side of a substrate such as a polyester film on which a magnetic layer has been previously formed, and drying it. The content in the back coat layer formed in this way is 0 to the filler in the bank coat layer.
．． It is preferable to contain it within the range of 1 to 5% by weight; if it is too small, the desired effect may not be obtained, and if it is too large, it may bleed out.1. . In addition, if the thickness of such a back coat layer is thinner than 0.1μ, the desired effect will not be obtained, and if it is thicker than 3μ, curling will occur with the bank coat layer inside. The thickness is preferably within the range of 0.5 to 2 μm, and more preferably within the range of 0.5 to 2 μm. Any one of the sorbic acid, sorbic acid derivative, and sorbic acid metal salt contained in the bank coat layer may be used alone, or two or more types may be used in combination.

Fillers used in such a back coat layer include carbonaceous powders such as graphite and carbon black, as well as α-Fe203 powder, Cr2O3 powder, Al2O3 powder, BaSO4 powder, CaCO3 powder,
MgO powder, BaCO3 powder, ZnO powder, Cu2O powder, CuO powder, Si3N4 powder, SiC powder, TiO
Inorganic powders such as 2 powders are also suitably used;
In this case, in order to form fine irregularities on the surface of the back coat layer and obtain good running stability, particles with an average particle size within the range of 0.05 to 2μ are used throughout the back coat layer. It is preferably used within a range of 20 to 80% by weight based on the total amount with solid components.

In addition, a lubricant may also be used in this bank coat layer, and examples of the lubricant used in combination include aliphatic lubricants, hydrocarbon lubricants, fluorine-based lubricants, and silicone-based lubricants. Preferably used. The amount used is preferably within the range of 5% by weight or less based on the total amount of all filler components in the bank coat layer.

Suitable binder resins include those commonly used in the past, such as vinyl chloride-vinyl acetate copolymers, polyvinyl butyral resins, cellulose resins, polyurethane resins, and isocyanate compounds. As the organic solvent, conventionally used organic solvents such as methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, and dimethyl formamide can be used alone or in combination of two or more.

In addition, the magnetic layer formed on the surface of the substrate is made of γ-Fe20
3 powder, Fe3O4 powder, co-containing-Fe203 powder, Co-containing Fe3O4 powder, Fe powder, Co powder, Fe
- A magnetic paint is prepared by mixing and dispersing magnetic powder such as Ni powder with a conventionally commonly used binder resin, organic solvent, etc., and this magnetic paint is applied to the surface of a substrate and dried. Others, Co, Nis Fe, Co
-A method such as depositing a ferromagnetic material such as Ni alloy, Go-Cr alloy, Co-P, Co-N11 i-P on a substrate by means such as vacuum evaporation, ion blasting, sputtering, plating, etc. It is formed.

As described above, when sorbic acid, sorbic acid derivatives, and sorbic acid metal salts are contained in the puncture coat layer, the dispersibility of the filler is improved and the surface smoothness of the bank coat layer is improved. The lubricating effect of the acidic compound is exerted and the coefficient of friction becomes sufficiently small.
Driving stability is improved without deteriorating electromagnetic conversion characteristics,
A magnetic recording medium with excellent running stability and electromagnetic conversion characteristics can be obtained.

〔Example〕

Next, embodiments of the invention will be described.

Example I CO-containing r-Fe203 powder 100 parts by weight (average particle size 0.4μ) Nitrocellulose (16% solution) 56.3 Carbon black 4 α~Fe203 (granular) 5 Cr2O31tt Zinc stearate 0.5 Cyclohexanone 9011 Toluene 90 This composition was mixed and dispersed using a high speed stirrer for 2 to 5 hours, and then mixed and dispersed using a sand grinder.

Next, 40 parts by weight of a polyurethane resin (20% solution), 40 parts by weight of a trifunctional low molecular weight isocyanate compound (75% solution), 1 -butyl stearate, 2 parts myristic acid, 35 parts cyclohexanone, 35 parts toluene, were added as appropriate. Add in the following order, mix and disperse with a high-speed stirrer, and then
A magnetic paint was prepared by passing it through a 1μ filter. This magnetic paint was applied to the surface of a polyester film with a thickness of 13 μm to a dry thickness of approximately 5 μm, dried, and then calendered.
μ) A composition of 170% nitrocellulose (16% solution), 130% cyclohexanone, and 130% toluene was mixed and dispersed in a ball mill for 10 hours, and then
After mixing and dispersing 2.0 parts by weight of sorbic acid for 50 hours, this was mixed with polyurethane resin (15% solution) 95, trifunctional low molecular weight isocyanate 10, and myristic acid 2 (75% solution). A back coat layer paint was prepared by blending the following compositions in an appropriate order: n-butyl stearate 1 cyclohexanone 40 toluene 40 It was coated on the back side of the polyester film on which the magnetic layer was formed and dried to form a back coat layer. Afterwards, this was cut to a specified width and a videotape was made.

Example 2 In preparing the back coat layer paint in Example 1,
Instead of barium sulfate powder with an average particle size of 0.08μ,
A videotape was produced in the same manner as in Example 1, except that the same amount of calcium carbonate with an average particle size of 0.08 μm was used, and the amount of sorbic acid was changed from 2.0 parts by weight to 0.5 parts by weight. It was.

Example 3 In preparing the back coat layer paint in Example 1,
The amount of barium sulfate used was changed from 100 parts by weight to 80 parts by weight, and 10 parts by weight of granular α-Fe203 powder (average particle size 1.0μ) and 10 parts by weight of carbon black (average particle size 43mμ) were added. In addition, a videotape was made in the same manner as in Example 1 except that the amount of sorbic acid used was changed from 2.0 parts by weight to 3.0 parts by weight.

Example 4 In the preparation of the back coat layer paint in Example 1, the amount of sorbic acid used was varied from 2.0 parts by weight to 0.1 parts by weight.
A videotape was made in the same manner as in Example 1 except that the amount was changed to 2 parts by weight.

Example 5 In the preparation of the back coat layer paint in Example 1,
A videotape was produced in the same manner as in Example 1 except that the amount of sorbic acid used was changed from 2.0 parts by weight to 5.0 parts by weight.

Example 6 In preparing the back coat layer paint in Example 1,
A videotape was made in the same manner as in Example 1, except that the same amount of sorbic M-n-butyl was used in place of sorbic acid.

Example 7 In preparing the back coat layer paint in Example 1,
A videotape was made in the same manner as in Example 1, except that the same amount of potassium sorbate was used in place of sorbic acid.

Example 8 5 In the preparation of the back coat layer paint in Example 1, 50% of vinyl chloride-vinyl acetate-vinyl alcohol copolymer (<20% solution) was added in place of nitrocellulose.
A videotape was produced in the same manner as in Example 1, except that the amount of polyurethane resin used was changed from 40 parts by weight to 35 parts by weight.

Comparative Example 1 In the preparation of the back coat layer paint in Example 1,
A videotape was made in the same manner as in Example 1 except that sorbic acid was omitted.

Comparative Example 2 In preparing the back coat layer paint in Example 2,
A videotape was made in the same manner as in Example 2 except that sorbic acid was omitted.

Comparative Example 3 In the preparation of the back coat layer paint in Example 3,
A videotape was made as in Example 3 except that sorbic acid was omitted.

Comparative Example 4 A videotape was made in the same manner as in Example 8 except that sorbic acid was omitted in the preparation of the backcoat layer paint in Example 8.

For each magnetic tape obtained in each Example and each Comparative Example, the surface roughness, running stability, and friction coefficient of the magnetic layer were measured by the following methods, and a tape storage test was conducted.

<Surface Roughness of Magnetic Layer> The center line average roughness (Ra) of the videotape was calculated using a stylus type surface roughness meter.

<Running Stability> Using a VH3 type VTR, the videotape was run 1000 times, and then tape deformation was observed. No tape deformation was observed (○), tape deformation was slightly observed (△), Those with significant tape deformation were evaluated as (x).

<Friction coefficient> Calculate the friction coefficient of the back coat layer when the back coat layer side of the videotape is placed on a stainless steel pin with a diameter of 20 mm and the tape is run at a winding angle of 90 degrees at a tape feed rate of 3 mm/sec. Ta.

8 <Tape storage test> Using a VH3 system VTR, record and playback a one-color chroma signal on a videotape before and after storage at 60'C for 48 hours, and measure the AM noise of the playback signal using a color video noise measuring device. The amount of decrease in the color S/N ratio after tape storage was determined by measuring the amount of color S/N ratio and calculating the S/N ratio.

The table below shows the results.

19 table! [Effects of the Invention] As is clear from the above table, the magnetic tapes obtained by the present invention (Examples 1 to 8) are superior to the conventional magnetic tapes (Comparative Examples 1 to 8).
4), the surface roughness of the back coat layer is smaller, the friction coefficient is the same, and the color S/N ratio decreases less in the tape storage test. Therefore, the magnetic recording medium obtained by this invention has a lower surface roughness in the back coat layer. It can be seen that the dispersibility of the lubricant is good, the surface condition of the back coat layer is good, the coefficient of friction is small, and the running stability is excellent, as well as the electromagnetic conversion characteristics are excellent.

Patent applicant: Hitachi Maxell, Ltd.

Claims (1)

[Claims] 1. Sorbic acid,
A magnetic recording medium comprising a bank coat layer containing at least one sorbic acid compound selected from sorbic acid derivatives and sorbic acid metal salts.