JPH09255341A - Powder for base layer of coating type magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a base layer having excellent surface smoothness and enough strength by using an iron oxyhydroxide powder having specified physical properties to form a base layer of a coating type magnetic recording medium. SOLUTION: This powder for the base layer of a coating type magnetic recording medium is an iron oxyhydroxide powder comprising acicular particles having <=0.5μm average major axial length and >=0.40g/cm<3> tapping density. The powder for the base layer can be obtd. by the production method generally used to obtain an iron oxyhydroxide powder. Further, by adding a proper amt. of Al to the iron oxyhydroxide, heat resistance and storage stability can be enhanced. The amt. of Al is specified to about 0.1 to 30wt.%. Al is incorporated by depositing on the surface of iron oxyhydroxide particles or by making a solid soln. in the iron oxyhydroxide particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine particle powder used for an underlayer of a coating type magnetic recording medium.

[0002]

2. Description of the Related Art In a so-called coating type magnetic recording medium in which a magnetic layer is formed on a support by coating a coating with a binder resin (binder) in which magnetic powder is dispersed and contained, a low noise is produced. In order to obtain high output characteristics, it is desired to make the thickness of the magnetic layer thinner. For this reason, a non-magnetic powder containing a non-magnetic powder dispersed in a binder resin is provided between the magnetic layer and the support. A multi-layered coating type magnetic recording medium has been proposed which forms a layer coating (hereinafter referred to as an underlayer).

Conventionally, spherical titanium oxide powder or acicular iron oxide powder has been mainly used as the non-magnetic powder for forming the underlayer. A magnetic recording medium having such an underlayer is disclosed in, for example, JP-A-63-187.
418, JP-A-4-167225, JP-A-6-60362, and JP-A-6-131653.

[0004]

When non-magnetic powder for forming such an underlayer uses spherical titanium oxide, sufficient strength cannot be obtained when formed into a tape, and it is difficult to form fine particles. However, the acicular iron oxide powder used in the manufacturing method cannot avoid inter-particle sintering, resulting in insufficient surface smoothness. Therefore, in the conventional coating type multilayer magnetic recording medium, the surface smoothness and the tape strength were insufficient, and the characteristics of the magnetic layer could not be sufficiently obtained. The present invention aims to solve this problem.

[0005]

According to the present invention, a coating comprising needle-shaped particles having an average major axis length of 0.5 μm or less and iron oxyhydroxide powder having a tap density of 0.40 g / cm ³ or more. For the underlayer of the magnetic recording medium, the powder for the underlayer of the coating type magnetic recording medium comprising iron oxyhydroxide powder containing 0.1 to 30% by weight of Al, and the average major axis length is 0.5 μm or less. Consists of acicular particles and has a BET specific surface area of 40 m ^2.
/ g or more of iron oxyhydroxide powder for the underlayer of the coating type magnetic recording medium, and the average major axis length is 0.01 to 0.5μ
Provided is a powder for an underlayer of a coating type magnetic recording medium, which comprises acicular iron oxyhydroxide particles having an average minor axis length of 0.05 μm or less in m.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The underlayer powder according to the present invention is obtained by a conventional method for producing iron oxyhydroxide powder. For example, a suspension containing a ferrous hydroxide colloid obtained by adding an equivalent amount or more of an alkali hydroxide aqueous solution to a ferrous salt aqueous solution is added.
A method in which an oxygen-containing gas is ventilated at a temperature of 80 ° C. or lower at a temperature of H11 or higher to carry out an oxidation reaction, or an oxygen-containing gas is ventilated in a suspension obtained by reacting an aqueous solution of ferrous salt and an aqueous solution of alkali carbonate. Iron oxyhydroxide can be produced by a method of carrying out an oxidation reaction. The iron oxyhydroxide powder obtained by such a method has no treatment step at a high temperature as compared with the case of producing a needle-shaped iron oxide powder, and therefore does not have interparticle sintering. This iron oxyhydroxide has a major axis of 0.5
It has been found that when the powder is a fine and highly-packed powder having a size of μm or less, when it is dispersed in a resin binder and applied to a support, extremely good surface smoothness is exhibited. Long axis length 0.5
Fine acicular particles of iron oxyhydroxide of less than μm are characterized by having a very short minor axis length and a high acicular ratio compared to those of other lower layer materials. It is well oriented, and the tape strength is improved in addition to the surface smoothness.

Furthermore, a suitable amount of Al is added to the iron oxyhydroxide.
It was found that heat resistance and storage stability were increased by adding the compound. Especially when Al is solid-dissolved in iron oxyhydroxide,
The thermal stability is much higher than when it is simply applied to the surface. When the content of Al is 0.1 to 20% by weight, the iron oxyhydroxide powder does not deteriorate even at a high temperature in the drying step for forming the tape and can exist stably. Al content is 0.
If the amount is less than 1% by weight, the effect of Al content is insufficient. If the Al content is more than 30% by weight, the specific surface area of the powder becomes large and the dispersibility becomes poor. Here, the content of Al means the content of Al element in the compound when Al is contained as a compound.

In order to add Al to iron oxyhydroxide, water-soluble salts such as Al ₂ (SO ₄ ) ₃ , Al (NO ₃ ) ₃ and AlCl ₃ as well as NaAlO ₂ (sodium aluminate) are used. Compounds such as water-soluble aluminic acid can be used.

To deposit Al on the surface of iron oxyhydroxide particles by using these Al compounds, for example, these Al compounds are dissolved in an alkaline aqueous solution and the iron oxyhydroxide is dispersed in this solution. After that, it can be carried out by blowing carbon dioxide gas or adding an acid for neutralization. As crystalline or amorphous Al ₂ O ₃ .nH ₂ O (hydrated aluminum oxide), Al is deposited on the particle surface. Be worn.

On the other hand, in order to form a solid solution of Al in iron oxyhydroxide particles, an aqueous solution of a ferrous salt such as FeSO ₄ or FeCl ₂ is neutralized with a neutralizing agent such as NaOH, Na ₂ CO ₃ or NH ₄ OH. After soaking, it is oxidized by air or the like to obtain α-FeOOH, γ-
The above water-soluble Al salt or aluminate may be added to the reaction system for producing FeOOH or the like. The powder surface according to the present invention may be controlled in particle surface property by using other elements such as Si and Y.

The underlayer using the powder of the present invention has excellent surface smoothness and sufficient strength as will be shown in Examples described later, which is to adjust the size, shape and properties of the powder appropriately. It is achieved by

The powder properties required and preferred for this are as follows: [Particle size] It is needle-like with an average major axis length of 0.01 to 0.5 µm, an average minor axis length of 0.01 to 0.05 µm, and an average axial ratio of 1 to 30. [Specific surface area] 10 to 300 m ² / g as measured by BET method
May be in the range of, preferably 40 m ² / g or more, more preferably from 40 to 150 m ² / g. [Tap density] 0.3 to 0.8 g / cm ³ , preferably 0.4
It is preferably 0 g / cm ³ or more. [Compressed density] 0.5 to 3.0 g / cm ³ , preferably 1.0 to 2.0.
It is 0 g / cm ³ . [True Specific Gravity] It is preferably 3.0 to 6.0 g / cm ³ , and more preferably 3.5 to 4.3 g / cm ³ . [Crystal grain size] 10 to 200 angstroms, preferably 50 to 150 angstroms.

Since the powder of the present invention has a high compression density and a high tap density with respect to the true specific gravity, it tends to be densely packed into the coating film when calendered during the tape forming process, which acts to improve the tape surface smoothness. In particular, the shorter the shortest axis length (shortest axis length), the better the tape surface smoothness. The shortest axis length is reflected in the crystal grain size and the specific surface area.

Further, the surface treatment state and pH of the powder also affect the dispersibility at the time of forming a coating material, and thus affect the surface smoothness. The preferred ranges are as follows, and good surface smoothness can be obtained by adjusting to this range. [Adsorption amount of stearic acid] It is desirable that the amount is 0.1 to 3.0 mg / m ² . [Resin adsorption amount] 0.5 to 4.0 mg / m ² is desirable. [PH] The powder pH is preferably 6 to 11.

[Water content] It is desirable that the content is 3.0% by weight or less. Although the viscosity of the paint and the amount of binder adsorbed will change depending on the water content, the water content should be 3 to obtain the optimum viscosity for multilayer coating.
% Or less is good.

The non-magnetic underlayer using the iron oxyhydroxide powder having the above characteristics has more excellent surface smoothness and strength as shown in the examples. In the coating type multilayer magnetic recording medium to which the underlayer according to the present invention is applied, the magnetic layer and the support are not particularly limited.

For example, as a support for forming the coating film of the non-magnetic underlayer, polyesters such as polyethylene terephthalate, polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone A known film such as aramid or aromatic polyamide can be used.

[0018]

EXAMPLES Examples of the underlayer powder according to the present invention will be shown below, and the characteristic values in each example were measured as follows.

The average major axis length (indicated by I in the table), the average minor axis length (indicated by d in the table) and the axial ratio (indicated by I / d in the table) were all measured from an electron micrograph at 108,000 times.
The average value of 0 particles was used. The crystal grain size (the same Dx) is
From the profile obtained using an X-ray diffractometer (11
The full width at half maximum of the peak corresponding to the (0) plane was obtained, and this was substituted into Scherrer's equation for calculation.

The specific surface area (the same BET) was measured by the BET method. The amount of adsorbed stearic acid (same as STA) was determined by dispersing the sample powder in a 2% MEK solution of stearic acid, sinking the sample powder with a centrifuge, and determining the concentration of the supernatant liquid to determine the amount adsorbed per specific surface area. Was calculated as Resin adsorption amount (same resin) is 2% MIB of polyurethane resin
Using the K solution, the amount of stearic acid adsorbed was calculated by the same method.

The powder pH was measured according to JIS K5101. The true specific gravity was measured by a liquid immersion method using toluene as a solvent. Compressed density (CD) is 80 kgf / cm
^This is the density when compressed by ² . Tap density (TA
P) was measured according to JIS K5101. Water is 10
It is the separated and adsorbed water (% by weight) at 0 ° C.

Surface smoothness is 3 according to Kosaka Laboratory Ltd.
The evaluation was performed by measuring the Ra (roughness) of the surface of the underlayer of the tape using a dimensional fine shape measuring device (ET-30HK). The strength was measured by measuring the strength of the tape on which the underlayer was formed.

Example 1 A coating material having the following composition is prepared. Iron oxyhydroxide 100 parts by weight (long axis length = 0.15 μm in this example) Polyurethane resin 20 parts by weight Methyl ethyl ketone 165 parts by weight Cyclohexanone 65 parts by weight Toluene 165 parts by weight Stearic acid 1 part by weight Acetylacetone 1 part by weight Centrifugal ball mill for 1 hour The coating composition having the above composition obtained by dispersion is applied onto a base film made of polyethylene terephthalate using an applicator to obtain a target thickness of about 3 μm.
To form a non-magnetic underlayer. Various characteristic values of the iron oxyhydroxide powder used and the properties of the obtained underlayer are shown in Table 1 together with the following examples and comparative examples.

[Embodiment 2] Iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of the above-mentioned Example 1, and a major axis length of
The non-magnetic underlayer was the same as in Example 1 except that iron oxyhydroxide having a thickness of 0.15 μm and Al = 0.2 wt% was used.

[Embodiment 3] Iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of the above-mentioned Example 1, and a major axis length of
The non-magnetic underlayer was the same as in Example 1 except that iron oxyhydroxide having a thickness of 0.15 μm and Al = 1.0 wt% was used.

[Embodiment 4] Iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of the above Example 1, and a major axis length of
A non-magnetic underlayer was formed in the same manner as in Example 1 except that iron oxyhydroxide having a thickness of 0.15 μm and Al = 2.5% by weight was used.

[Embodiment 5] Iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of the above-mentioned Example 1, and a major axis length of
A non-magnetic underlayer was formed by changing the same to Example 1 except that iron oxyhydroxide having a thickness of 0.15 μm and Al = 5.0 wt% was used.

[Embodiment 6] Iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of the above-mentioned Example 1, and a major axis length of
The non-magnetic underlayer was made the same as in Example 1 except that iron oxyhydroxide having a thickness of 0.15 μm and Al = 30.0% by weight was used.

[Embodiment 7] Iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of the above Example 1, and a major axis length of
A nonmagnetic underlayer was formed by changing the same to Example 1 except that iron oxyhydroxide having a solid solution of 0.15 μm and Al = 1.0% by weight was used.

[Embodiment 8] Iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of Example 1, is used as the major axis length =
A non-magnetic underlayer was formed by changing the same to Example 1 except that iron oxyhydroxide having a solid solution of 0.15 μm and Al = 2.5% by weight was used.

[Embodiment 9] Iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of the above Example 1, and a major axis length of
A non-magnetic underlayer was formed by changing the same to Example 1 except that iron oxyhydroxide having a solid solution of 0.15 μm and Al = 5.0% by weight was used.

[Embodiment 10] Iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of the first embodiment, is mixed with oxyhydroxide having a major axis length of 0.15 μm and Al of 10.0% by weight. Instead of iron hydroxide, the other conditions were the same as in Example 1 to form a non-magnetic underlayer.

[Embodiment 11] Iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of the first embodiment, is mixed with oxyhydroxide having a major axis length of 0.15 μm and Al = 20.0% by weight. Instead of iron hydroxide, the other conditions were the same as in Example 1 to form a non-magnetic underlayer.

[Embodiment 12] The iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of the first embodiment, is changed to an iron oxyhydroxide having a major axis length of 0.10 μm under other conditions. A nonmagnetic underlayer was formed in the same manner as in Example 1.

[Example 13] The iron oxyhydroxide having a major axis length of 0.15 µm in the coating material of Example 1 was changed to an iron oxyhydroxide having a major axis length of 0.30 µm under other conditions. A nonmagnetic underlayer was formed in the same manner as in Example 1.

[Embodiment 14] Iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of the first embodiment, is coated with oxyhydroxide having a major axis length of 0.05 μm and Al = 5.0% by weight. Instead of iron hydroxide, the other conditions were the same as in Example 1 to form a non-magnetic underlayer.

[Example 15] Iron oxyhydroxide having a major axis length = 0.15 µm, which constitutes the coating material of the above Example 1, was coated with oxyhydroxide having a major axis length = 0.10 µm and Al = 5.0% by weight. Instead of iron hydroxide, the other conditions were the same as in Example 1 to form a non-magnetic underlayer.

[Example 16] Iron oxyhydroxide having a major axis length of 0.15 µm, which constitutes the coating material of the above-mentioned Example 1, was coated with iron oxyhydroxide having a major axis length of 0.30 µm and Al = 5.0% by weight. Instead of iron hydroxide, the other conditions were the same as in Example 1 to form a non-magnetic underlayer.

[Example 17] Iron oxyhydroxide having a major axis length of 0.15 µm, which constitutes the coating material of the above-mentioned Example 1, was mixed with major oxyhydroxide having a major axis length of 0.05 µm and Al = 5.0% by weight. Instead of iron hydroxide, the other conditions were the same as in Example 1 to form a non-magnetic underlayer.

[Embodiment 18] Iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of the above-mentioned Example 1, is mixed with major oxyhydroxide having a major axis length of 0.10 μm and Al = 5.0% by weight. Instead of iron hydroxide, the other conditions were the same as in Example 1 to form a non-magnetic underlayer.

Example 19 Iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of the above Example 1, was mixed with major oxyhydroxide having a major axis length of 0.30 μm and Al = 5.0% by weight. Instead of iron hydroxide, the other conditions were the same as in Example 1 to form a non-magnetic underlayer.

[Embodiment 20] Iron oxyhydroxide having a major axis length of 0.15 μm and a major axis length of 0.50 μm and Al = 5.0% by weight of solid solution oxy, which constitutes the coating material of the above Example 1, is dissolved. Instead of iron hydroxide, the other conditions were the same as in Example 1 to form a non-magnetic underlayer.

Comparative Example 1 Iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of Example 1, is used as the major axis length =
A non-magnetic underlayer was formed under the same conditions as in Example 1 except that α-Fe ₂ O ₃ having a thickness of 0.10 μm was used.

[Comparative Example 2] Iron oxyhydroxide having a major axis length of 0.15 µm, which constitutes the coating material of the above-mentioned Example 1, has an average diameter =
The non-magnetic underlayer was formed by changing the titanium oxide to 0.035 μm and making the other conditions the same as in Example 1.

[Comparative Example 3] Iron oxyhydroxide having a major axis length of 0.15 µm, which constitutes the coating material of Example 1, was used as the major axis length =
The non-magnetic underlayer was the same as in Example 1 except that iron oxyhydroxide having a thickness of 0.15 μm and Al = 35.0 wt% was used.

Comparative Example 4 Iron oxyhydroxide having a major axis length of 0.15 μm, which constitutes the coating material of Example 1, is used as the major axis length =
A nonmagnetic underlayer was formed by changing the same to Example 1 except that iron oxyhydroxide having a solid solution of 0.15 μm and Al = 35.0% by weight was used.

Comparative Example 5 Iron oxyhydroxide having a major axis length of 0.15 μm constituting the coating material of Example 1 was used, and a major axis length =
The non-magnetic underlayer was the same as in Example 1 except that the iron oxyhydroxide was 0.005 μm.

[Comparative Example 6] Iron oxyhydroxide having a major axis length of 0.15 µm and a major axis length of the coating material of Example 1 was
The iron oxyhydroxide having a thickness of 0.60 μm was used, and the other conditions were the same as in Example 1 to obtain a non-magnetic underlayer.

[Comparative Example 7] Iron oxyhydroxide having a major axis length of 0.15 µm, which constitutes the coating material of Example 1, was used.
A non-magnetic underlayer was formed by changing the iron oxyhydroxide of 0.60 μm and Al = 5.0% by weight to the other conditions under the same conditions as in Example 1.

[Comparative Example 8] Iron oxyhydroxide having a major axis length of 0.15 µm, which constitutes the coating material of Example 1, was used as the major axis length =
The nonmagnetic underlayer was the same as in Example 1 except that iron oxyhydroxide having a solid solution of 0.60 μm and Al = 5.0% by weight was used.

[0051]

[Table 1]

As can be seen from the results in Table 1, the underlayer using the iron oxyhydroxide powder according to the present invention has a smaller roughness than the comparative example and has excellent surface smoothness and sufficient strength. I understand.

[0053]

As described above, according to the present invention,
A non-magnetic underlayer having excellent surface smoothness and sufficient strength can be formed. Therefore, the thickness of the magnetic layer can be made thinner, and the characteristics of the magnetic layer can be sufficiently obtained. , It can greatly contribute to obtain a coated multi-layer magnetic recording medium with low noise and high output characteristics.

Continuation of front page (72) Inventor Yoshifumi Horikawa 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd.

Claims (13)

[Claims] 1. A powder for an undercoat layer of a coating type magnetic recording medium, which comprises needle-like particles having an average major axis length of 0.5 μm or less and a tap density of 0.40 g / cm ³ or more. 2. A powder for an underlayer of a coating type magnetic recording medium, which comprises iron oxyhydroxide powder containing 0.1 to 30% by weight of Al. 3. The underlayer powder according to claim 2, wherein Al is contained by being deposited on the surface of the iron oxyhydroxide particles. 4. The underlayer powder according to claim 2, wherein Al is contained as a solid solution in the iron oxyhydroxide particles. 5. An acicular particle having an average major axis length of 0.5 μm or less, a tap density of 0.40 g / cm ³ or more, and 0.1 to
A powder for an underlayer of a coating type magnetic recording medium, which comprises iron oxyhydroxide powder containing 30% by weight of Al. 6. A needle-shaped particle having an average major axis length of 0.5 μm or less and a specific surface area by BET method of 10 to 300 m ^2.
/ g of iron oxyhydroxide powder for the underlayer of the coating type magnetic recording medium. 7. A needle-like particle having an average major axis length of 0.5 μm or less and having a specific surface area by the BET method of 10 to 300 m ² / g.
A powder for an undercoat layer of a coating type magnetic recording medium comprising iron oxyhydroxide powder containing 0.1 to 30% by weight of Al. 8. An acicular particle having an average major axis length of 0.5 μm or less, a tap density of 0.40 g / cm ³ or more and BE.
Specific surface area by T method is 10 ~ 300m ² / g, 0.1 ~ 3
A powder for an underlayer of a coating type magnetic recording medium, which comprises iron oxyhydroxide powder containing 0% by weight of Al. 9. A powder for an undercoat layer of a coating type magnetic recording medium, comprising acicular iron oxyhydroxide particles having an average major axis length of 0.01 to 0.5 μm and an average minor axis length of 0.05 μm or less. 10. A needle-like particle having an average major axis length of 0.01 to 0.5 μm and an average minor axis length of 0.05 μm or less.
Powder for an undercoat layer of a coating type magnetic recording medium, which is composed of iron oxyhydroxide powder containing 30 to 30% by weight of Al. 11. BE composed of needle-like particles having an average major axis length of 0.01 to 0.5 μm and an average minor axis length of 0.05 μm or less,
Powder for an undercoat layer of a coating type magnetic recording medium, which comprises iron oxyhydroxide powder having a specific surface area of 10 to 300 m ² / g by T method. 12. BE composed of needle-like particles having an average major axis length of 0.01 to 0.5 μm and an average minor axis length of 0.05 μm or less.
Specific surface area by T method is 10 ~ 300m ² / g, 0.1 ~ 3
A powder for an underlayer of a coating type magnetic recording medium, which comprises iron oxyhydroxide powder containing 0% by weight of Al. 13. An acicular particle having an average major axis length of 0.01 to 0.5 μm and an average minor axis length of 0.05 μm or less, a tap density of 0.40 g / cm ³ or more, and a specific surface area by BET method. Of 10 to 300 m ² / g and 0.1 to 30% by weight of Al
A powder for an underlayer of a coating type magnetic recording medium, which comprises iron oxyhydroxide powder containing.