JPS6161230A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a medium having low light transmittivity and excellent erasing characteristic by using iron oxide magnetic powder for the magnetic powder to be incorporated into a magnetic layer made into double-layered structure, incorporating Fe<2+> at a lower ratio into the magnetic powder to be used on the inside layer adjacent to a substrate and incorporating the Fe<2+> at a higher ratio into the magnetic powder to be used for the surface side. CONSTITUTION:The magnetic powder incorporated into the 1st layer adjacent to the non-magnetic substrate and the 2nd layer adjacent to said layer of a magnetic recording medium provided with the magnetic layer made of the double-layer consisting of said layers on the substrate consists of the iron oxide magnetic powder having >=30m<2>/g specific surface area by a nitrogen adsorption method. The ratio of the Fe<2+> of the magnetic powder to be used for the 1st layer is required to be <3.5wt%. The erasing characteristic in an initial period and upon lapse of time is poor if the ratio exceeds said value. The Fe<2+> content of the magnetic powder to be used for the 2nd layer is 3.5-10wt%, more preferably 3.5-9wt%. More specifically, the light transmittivity increases and the detection of a t ape end by the effect of light is made difficult if the content is <3.5wt%. The erasing characteristic in the initial period and upon lapse of time is poor if the content exceeds 10wt%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to magnetic tapes and other magnetic recording media.

[Conventional technology]

In recent years, high-density recording and high signal-to-noise ratios have been promoted in videotapes, and the magnetic powder used has also become finer, with smaller particle sizes having a specific surface area of 30 resistance/g or more determined by the nitrogen adsorption method. ing.

On the other hand, as a type of magnetic powder, γ-Fe is preferable because it allows recording and reproduction with an appropriate coercive force, convenience of handling, and other reasons. 03
Iron oxide-based magnetic powders such as CO-containing r-r;etas and the like are commonly used.

However, these iron oxide-based magnetic powders have a brown to brown color, and when such magnetic powders are made into fine particles, the light transmittance of the magnetic layer increases, making it difficult to transmit light such as in VH3 video tape recorders. In a method that detects the end of the tape, malfunctions are likely to occur.

In order to solve this drawback, conventional measures have been taken to increase the amount of pigments with high photoresistance such as carbon black, but these pigments have poor dispersibility or occupy a large proportion in the magnetic layer. As a result, the surface smoothness and electromagnetic conversion characteristics of the magnetic layer deteriorate. It is also possible to increase the thickness of the magnetic layer to reduce the light transmittance, but tape thickness standards for magnetic tapes are determined by each application, and the increase in thickness of the magnetic layer increases the thickness of the tape, such as polyester film. The thickness of the support must be increased by X, which reduces the surficial strength of the tape, leading to trouble.

Therefore, this inventor focused on the color of iron oxide magnetic powder,
The lower the content of F 614 contained in this magnetic powder, the brighter brown it appears, and conversely, the higher the content of F e 2', the more brownish to black it tends to be.
For example, if the e2 content is high, the Fe2 content is FeO.
When a magnetic tape was manufactured using iron oxide-based magnetic powder with an equivalent content of 7.0% by weight or more, it was found that the light transmittance of the magnetic layer could be reduced without taking measures such as increasing the amount of pigment as described above. I found it.

However, subsequent studies revealed that the Fe 2
Using magnetic powder with a high content of +1 can reduce the optical transmittance of the magnetic layer (if
It was found that this caused a problem that made it difficult to put it into practical use as a magnetic tape. Therefore, in order to solve this problem, in addition to the above-mentioned magnetic powder with a high Fe2° content (1), magnetic powders with a low Fe2° content such as Fe0IA
An attempt was made to mix magnetic powder with a total content of 2.0% by weight or less, but if a large amount of magnetic powder with a low Fe Z' content was mixed, the light transmittance could not be satisfied, and conversely, Fe! When a large amount of magnetic powder with a high + content is blended, the above-mentioned erasing properties deteriorate, and even when various blending ratios of both of the two properties were investigated, it was not possible to satisfy both properties.

[Problem that the invention seeks to solve]

In view of the above, the present invention solves the problem of deterioration of erasing characteristics both initially and over time when the light transmittance is lowered by increasing the Fe content of fine particulate iron oxide magnetic powder. The object of the present invention is to obtain a magnetic recording medium that satisfies both the light transmittance and the above-mentioned erasing characteristics.

[Failure to solve the problem]

As a result of intensive studies to achieve the above object, the inventor found that in order to achieve both light transmittance and erasing characteristics by setting the Fe2 content, the magnetic layer must be set in the car i configuration as described above. Based on this idea, we created a two-layer structure for the magnetic layer, and used magnetic powder with less Fez° content in the inner layer on the support side, where it is difficult to erase magnetic records. Fe on the surface layer where it is easy to target
When we tried using magnetic powder with a high 2° content, we found that the conventional t
This invention was completed based on the knowledge that a magnetic recording medium with low light transmittance and excellent initial and aging erase characteristics, which was not possible with the 1W configuration, could be obtained.

That is, the present invention provides a magnetic recording medium in which a magnetic layer having a two-layer structure consisting of a first layer adjacent to this support and a second layer adjacent to this layer is provided on a non-ffl support. The magnetic powder contained in both of the above layers is composed of iron oxide magnetic powder with a specific surface area of 30 m/g or more determined by the nitrogen adsorption method, and the proportion of Fe'' in the magnetic powder of the first layer is FeO. The proportion of Fe2 in the magnetic powder of the second layer is 3.5 to 3.5% in terms of FeO.
This relates to a magnetic recording medium characterized in that the amount is 10% by weight.

[Structure and operation of the invention]

In this invention, the magnetic powder used for the first and second magnetic layers has a specific surface area (hereinafter referred to as BE) determined by the nitrogen adsorption method.
(referred to as T-method specific curve) is 30 m/g or more, preferably 3
0 to 60 m/g of iron oxide-based magnetic powder, which includes iron oxide strip powder as well as iron oxide magnetic powder containing other metals such as CO in various ways. Contains powder. By using the above-mentioned fine powder, high-density recording and high S/N ratio can be easily achieved.

The proportion of the above-mentioned magnetic powder pFe'' used in the first layer is 3.5% by weight in terms of FeO (hereinafter referred to as Fe2 content in the car).
If it exceeds the above value, the erasing characteristics both at the initial stage and after aging will deteriorate. Note that if the above ratio becomes too small, the light transmittance tends to increase, so it is usually preferable that the above Fe2 content is 0.1% by weight or more.

Further, the magnetic powder used for the second layer is Fe similar to the above.
”° content is 3.5 to 10%, preferably 3.5 to 10%
It is necessary that the content is less than 3.5% by weight, 1% by weight. In other words, if the above content is less than 3.5fffffi%, the light transmittance becomes high and it becomes difficult to detect the end of the tape by light. Moreover, if the content exceeds 10% by weight, the erasing characteristics both initially and after aging will deteriorate.

In order to set the content of Fe24 in the iron oxide +i type as described above, conventional methods such as reducing FezOxt53 to a desired degree by appropriate means or oxidizing Fe5O-+53 to a desired degree by appropriate means are known methods. It can be carried out in the dark using the method described above, and various Fe
``You can easily obtain the content.

To obtain the magnetic recording medium of the present invention, for example, each required magnetic paint is prepared by mixing 11 parts of the above-mentioned specific magnetic powder used in the first and second layers with an appropriate binder, and then The first required magnetic paint is coated on a non-magnetic support such as a polyester film using any O cloth means and dried to form a first layer.After calendering is carried out by a conventional method,
A second necessary fn-based paint may be applied on the first layer in the same manner as described above, dried, and calendered to form the second layer.

The thickness of the magnetic layer consisting of the first and second layers is preferably about 3 to 8 μm, and the thickness ratio of the first layer/second layer is at most 1/4 to 6/1, preferably 3 /2 to 4/1. In particular, by setting the thickness ratio of the first layer/second layer as described above, good results can be obtained in both the light transmittance and the erasing characteristics at the initial stage and after aging. Obtainable.

The binder used above includes vinyl chloride resin, cellulose resin, polyurethane resin, polyester resin,
Any conventionally known binder such as isocyanate compounds can be used. Each magnetic paint contains carbon black, α-Fe! rs, A1. Various additives such as conventional fillers for reinforcing paint films such as O, CrtO, etc., groove lubricants such as fatty acids, fatty acid esters, silicone lubricants, and fluorine-based lubricants can be optionally added. Further, the magnetic paint may be an organic solvent type or a water dispersion type.

〔Effect of the invention〕

As described above, in this invention, when using fine particulate iron oxide magnetic powder as the magnetic powder, the magnetic layer is composed of two layers + R, and the Fe of the magnetic powder used in the inner layer adjacent to the support is ``Conversely, the magnetic powder used in the surface layer has a high Fe!'' content, so the light transmittance is low, and the erasability is good both at the initial stage and after aging. An excellent magnetic recording medium can be obtained.

〔Example〕

Examples of the present invention will be described below in comparison with comparative examples. In addition, in the following, parts shall mean parts by weight.

Example 1 Particulate α-Fe, O, Soybean (average particle size 1.0 μm) 5.2 parts Zinc stearate O, S part Cyclohexanone -90 parts Toluene 90 parts The following components were added in an appropriate order to the composition which had been premixed for 10 hours and then completely dispersed using a sand mill, and mixed using a high speed stirrer to prepare the first required magnetic paint.

Myristic acid 2 parts Cyclohexanone 40 parts Toluene
40 parts Next, apply the above magnetic paint to the pores l.
After passing the IJm filter through i11, 17 and 13
A first magnetic layer having a thickness of 2.0 μm was formed by coating and drying the film on a polyester film having a good surface smoothness of 2.0 μm.

On the other hand, the following ingredients were premixed using a high-speed stirrer for 5 to 10 hours, and then well dispersed using a sand mill.

Cr, Q, powder (average particle size 1.0um) 0.8 parts Al2
O, powder (average particle size 0.4.crm) 2.0 parts Zinc stearate 0.5 parts Cyclohexanone 90 parts Toluene
To 90 parts of the resulting composition, the following ingredients were added in an appropriate order and mixed using a high-speed stirrer to prepare a magnetic paint for the second calendar month.

Myristic acid 2 parts n-butyl stearate 1 part cyclohexanone
40 parts toluene
40 parts of this magnetic paint was passed through a filter with a pore size of 1 .mu.m, then coated on the first layer and dried, followed by calendering to form a second magnetic layer having a thickness of 3.0 .mu.m. Thereafter, slits were made to a width of 1/2 inch to produce a magnetic tape of the present invention.

Example 2 The thickness of the first layer was changed from 2.0 μm to 3.0 μm,
Except that the FeZ° content of the Co-containing r-vex Off powder used in the second layer was changed from 3.5% by weight to 4.5% by weight, and the thickness was changed from 3.0 μm to 2.0 μm. ,
A magnetic tape was produced in the same manner as in Example 1.

Example 3 2F of CO-containing -Fe2O2 powder used for the first layer
The eZ-content was changed from 3.0% by weight to 2.0% by weight, the thickness was changed from 2.0 μm to 3.0 μm, and the Co-containing r-Fe used in the second layer, O:l The Fe content of the powder was increased from 3.5% to 6.0% by weight, and the thickness was increased to 3.5% by weight.
A magnetic tape was produced in the same manner as in Example 1 except that the thickness was changed from 0 μm to 2.0 μm.

Example 4 CO-containing r-Fe used in the first layer, Fe2° of 03 powder
The content was changed from 3.0% by weight to 0.3% by weight, the thickness was changed from 2.0 μm to 3.0 μm, and the Co content used in the second layer was changed to r-Fe and Fe in the Os powder. "The content is 3.5
A magnetic tape was produced in the same manner as in Example 1, except that the weight was changed from 1% to 9.0% by weight and the thickness was changed from 3.0 μm to 2.0 μm.

Example 5 The BET method surface area deviation of the Co-containing r-FezO3 powder used for the first and second layers also decreased from 40 m/g to 30 m/g.
A magnetic tape was produced in the same manner as in Example 1 except that the magnetic tape was changed to g.

Comparative Example 1 Fe1 of CO-containing r-Fe, O, i9 used for second layer
- A comparative magnetic tape was produced in the same manner as in Example 1, except that the content was changed from 3.5% by weight to 2.5% by weight.

Comparative Example 2 The Fe'' content of the CO-containing r-FezO powder used for the first layer was changed from 3.0% by weight to 0.3% by weight, and the thickness was changed to 2% by weight.
．． The Co-containing layer was changed from 0 μm to 3.0 μm and used in the second layer. Fe2゜ content of powder is 3.5
A magnetic tape for comparison was produced in the same manner as in Example 1, except that the thickness was changed from 12.0% to 12.0% and the thickness from 3.0 μm to 2.0 μm.

Comparative Example 3 CO-containing r-FezO used in the first layer = Fe 1
4 content times was changed from 3.0% by weight to 460% by weight, the thickness was changed from 2.0 μm to 3.0 μm, and the thickness of the second layer was changed from 3.0 μm to 2.0 μm. A magnetic tape for comparison was produced in the same manner as in Example 1.

Comparative Example 4 Fe
2゛Contains fffi 3.0 weight 9A color 12.0 weight 9
Co-containing r-Fe was changed from A and used for the second layer!
0, BET ratio slope surface area of powder Om2/g to 30.
l/g, Fe” content from 3.5% to 0.3
A magnetic tape for comparison was produced in the same manner as in Example 1 except that the weight percentage was changed.

Comparative example 5 Co-containing γ-FezO without providing the first layer.

A magnetic paint having the same composition as the second magnetic Ω material for stones in Example 1 was prepared, except that the Fe content of the powder was changed from 3.5% by weight to 0.3% by weight. Directly onto the same polyester film as in Example 1 with a similar method.
The cloth was dried and calendered to a thickness of 5.0 μm (7
) A magnetic layer was formed and a magnetic tape for comparison was produced.

Comparative example 6 Co-containing -Fe, O without providing the first layer.

A magnetic paint having the same composition as the second Ishikawa magnetic paint in Example 1 was prepared, except that the Fe2° content of the powder was changed from 3.5% by weight to 9.0% by weight. Implementation agent 1
A magnetic tape for comparison was prepared by directly coating the same polyester film as above, drying it, and calendering to form a magnetic layer having a thickness of 5.0 μm.

For each of the magnetic tapes of Examples 1 to 5 and Comparative Examples 1 to 6 described above, the light transmittance and initial and after-time erasing characteristics were measured and evaluated using the following methods. The results were as shown in the table below. The measurement conditions were in accordance with the VH3 video cassette system standard.

Light transmittance> A magnetic tape was placed between a 9.000 angstrom light source and a photosensor, and the light transmitted through the magnetic tape was measured with the photosensor.

Erasing characteristics> Record an IKIIz signal 10 dB higher than the specified level with a specified bias current using a VHS system VTR, then immediately erase a portion of it, and calculate the difference between the output of the erased portion and the reproduced output of the unerased portion. was measured.

Changes in erase characteristics over time> Record an IKHz signal 10 dB higher than the specified level with a specified bias current using a VH3 type VTR, and then calculate the erase rate of the portion erased immediately and the erase rate of the portion erased after 100 hours. The difference was measured.

As is clear from the above results, the BET ratio normal surface area is 30n? / If the Fe'' content of the magnetic powder used for the first layer is 3.
Less than 5% by weight, Fe”° of the above magnetic powder used in the second layer
The magnetic tapes containing 3.5 to 10% by weight (Examples 1 to 5) have low light transmittance and good erasing characteristics both initially and after aging. On the other hand, Fe2 in any layer
゛Magnetic tapes whose content is outside the scope of the present invention (Comparative Examples 1 to 4) and magnetic tapes with a single magnetic layer (Comparative Examples 5,
In case 6), either the light transmittance is high or the erasing characteristics at the initial stage and after aging are poor.

Claims (1)

[Claims] (1) A magnetic recording medium comprising a two-layered magnetic layer comprising a first layer adjacent to this support and a second layer adjacent to this layer on a non-magnetic support, in which both of the above layers are provided. The magnetic powder contained in the powder has a specific surface area of 30% by nitrogen adsorption method.
m^2/g or more of iron oxide magnetic powder, and the proportion of Fe^2^+ in the magnetic powder of the first layer is FeO
A magnetic recording medium characterized in that the proportion of Fe^2^+ in the magnetic powder of the second layer is less than 3.5% by weight in terms of FeO.