JPS63131321A - magnetic recording medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a magnetic recording medium, and more particularly, the present invention relates to a magnetic recording medium that has excellent surface smoothness, running stability, and abrasion resistance, and that exhibits no deterioration of these physical properties even after long-term running. This invention relates to a magnetic recording medium with excellent magnetic properties.

<Prior art> Magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks are widely used in the audio, video, and computer fields, and in recent years, they are becoming more compact and thinner. As the demand for magnetic recording media increases, the surface of the magnetic layer of magnetic recording media is becoming smoother and more 1119.

However, thin film tapes with smooth surfaces have low strength, deformation,
Not only is it easily damaged, but it also has drawbacks such as irregular winding during winding and unwinding, and poor running performance.

As a method to improve this drawback, a binder such as epoxy resin, vinyl oxide resin, polyurethane resin, or urea resin is coated with CaCO3, B on the nonmagnetic support on the side opposite to the magnetic layer.
A method of providing a bank coat layer containing dispersed inorganic powders such as S○a, TiO, etc. is known.

However, in order to obtain running stability effects in this method, it is necessary to use inorganic powder with a relatively large particle size of about 0.5 to 2 μm, but in this case, the surface condition of the back coat layer is If the magnetic media are stored or left in a rolled or stacked state, the adjacent magnetic layer surfaces will be damaged or uneven, resulting in loss of magnetic properties.

Furthermore, in the case of hard inorganic powder, it may cause fatal damage such as damaging the magnetic head.

On the other hand, if the particle size of the inorganic powder used is small (for example, 0.
Although it is known to propose a back coat layer that does not reduce the magnetic properties or damage the magnetic head (1 μm or less), this method does not provide sufficient running stability, which is the original objective.

<Problems to be Solved by the Invention> In view of the above circumstances, the present inventors have developed a product that has excellent surface smoothness, running stability, and abrasion resistance, does not deteriorate in these physical properties even during long-term running, and has excellent magnetic properties. With the aim of obtaining a magnetic recording medium without a decrease in magnetic properties, as a result of intensive studies, we found that all of the above objectives can be met if a specific alumina hydrate is incorporated into the binder that forms the back coat layer. The inventors discovered that a magnetic recording medium could be obtained and completed the present invention.

Means for Solving Problems> That is, the present invention provides a magnetic recording medium having a magnetic layer on one side of a nonmagnetic support and a back coat layer on the other side, in which the back coat layer has the general formula Al2O3'xH
To provide a magnetic recording medium characterized by containing an alumina hydrate represented by the formula .chi.

The present invention will be explained in more detail below.

The alumina hydrate used in the present invention has the -S formula A1. O
, xH2O (in the formula, χ is 2.9 to 0.1, preferably 2.5 to 0.5), and more specifically has a hexagonal plate-like crystal structure. χ−
A 1 to s, -Altol, boehmite, f
) -A 1 zoz, r A j! ! 01, θ
-Aj! , O, etc., are a mixture of these.

Examples of such alumina hydrate include a method of firing alumina (Aj!(OH)z) obtained by the Bayer method;
Alternatively, it can be obtained by known methods such as a method of firing an alumina gel obtained by hydrolysis of an organoaluminum compound, or a method of firing an alumina hydrate obtained by thermal decomposition of ammonium alum or ammonium dawsonite. I can do it.

If the amount of crystallized water in the alumina hydrate is 2.9 or more, it may be because the hardness of the alumina hydrate is low that the abrasion resistance of the back coat layer decreases during repeated use, and This is not preferable because it may cause problems such as deterioration of magnetic properties due to the influence of dust generated by peeling off from the coating layer or the like.

On the other hand, if the crystalline water ratio of the alumina hydrate is less than 0.1, it will not be possible to obtain a back coat layer with a smooth surface, resulting in serious damage such as damage to the adjacent magnetic layer or magnetic head. This is undesirable as it may cause serious problems.

Moreover, general formula A1. The particle size of the alumina represented by O,.χH7o is about 2 .mu.m or less, preferably 1 .mu.m or less, and usually 0.3 .mu.m to 1, Q, c+m is used.

If alumina having a particle size larger than 2 μm is used, the smoothness of the back coat layer will be reduced, which will have an adverse effect on magnetic properties, etc., which is not preferable.

In the present invention, the amount of the alumina hydrate applied to the back coat layer is in the range of about 50 parts by weight to about 400 parts by weight based on 100 parts by weight of the binder.

If the amount of alumina relative to the binder exceeds 400 parts by weight, the alumina will peel off during tape running, which is undesirable. On the other hand, if it is less than 50 parts by weight,
The effect of improving running stability and wear resistance cannot be obtained.

In the present invention, the binder that can be used in the back coat layer may be any binder that is normally applied to known back coats, and is not particularly limited. Examples include resins, polyamide resins, phenol resins, vinyl chloride resins, cellulose derivatives, polyester resins, etc. alone or in mixtures thereof.

The back coat layer is formed on the non-magnetic support by mixing the alumina hydrate powder with a binder and, if necessary, a solvent such as toluene and various additives to form a bank coat paint according to a conventional method. It may be coated and formed on a non-magnetic support by a known method such as a calendar roll or a roll coater.

Non-magnetic supports include polyester, polyethylene terephthalate, polyethylene naphthalate polyamide,
Known non-magnetic supports for magnetic recording media, such as plastic films such as polyamide, are used.

In addition, the back coat layer may contain antistatic agents such as carbon blank, CaC○, .
Ba50m, Tie, s Al.

It is of course possible to add inorganic powder such as O3.

Even though the 6-layer recording medium of the present invention uses alumina hydrate with large particle size and high hardness for the bank coat layer, why is it that the conventional CaCO5, Ba5Oa, TiOz?
Although it is not clear why the alumina hydrate has a plate-like crystal structure and is superior in running stability without damaging the magnetic layer or in-air head, etc., it is possible to use alumina hydrate in roll coaters. It is presumed that this is because a smooth back coat layer is formed because the coating is compatible with the coating method for back coat paints, such as calender rolls, etc., and is coated on a non-magnetic support with good distribution.

<Effects of the Invention> According to the present invention described in detail above, by adding and using a specific alumina hydrate to Bank Coat JW, it has excellent surface smoothness, running stability, and abrasion resistance, and has excellent surface smoothness, running stability, and abrasion resistance. It is also possible to supply a magnetic recording medium with no change in the surface condition of the initial backcoat layer and no deterioration in magnetic properties, etc., and its industrial value is extremely great.

<Examples> The present invention will be explained below based on Examples and Comparative Examples.
The present invention is not limited to these Examples and Comparative Examples.

Examples 1 to 4 and Comparative Examples 1 to 3 A magnetic paint having the following composition was prepared.

CO gold-containing r FetOx 100 parts by weight (average particle size 0.4 μm) Polyurethane resin 40 parts by weight Nitrilocellulose 2 (11 parts Vinyl chloride-vinyl acetate copolymer 10 parts by weight Resilene 2 parts by weight Myristic acid 1 part by weight Lauric acid
1 part by weight methyl ethyl ketone
72 parts by weight Toluene 50 parts by weight Cyclohexanone 80 parts by weight Carbon black 2 parts by weight The above composition was thoroughly mixed in a ball mill, and after adding 10 parts of a polyfunctional isocyanate, it was filtered through a filter with an average pore size of 1 μm.

The obtained magnetic paint was applied to the surface of a film having a polyethylene tereftate base with a thickness of 12 μm to a dry thickness of 5 μm.
It was applied so that

Next, C consisting of each composition shown in Table 1 below.

A back coat coating material was prepared and applied to the surface of the base film opposite to the magnetic layer to a dry thickness of 0.5 μm to form a back coat layer.

Thereafter, the magnetic layer was calendered and the film was cut into 12.7 mm widths to produce magnetic tapes for video, Examples 1 to 4 and Comparative Examples to 3.

For each sample tape obtained by this method, commercially available VH3
The tape characteristics were investigated using a VTR of this type. The results are shown in Table 2.

In addition, the measurement method in Table 2 was carried out by the following method.

(Surface Roughness) The surface of the back coat layer was measured with a surface roughness meter to determine the center line average roughness.

(Tape Damage) Using a VH3 type VTR, each of the above magnetic tapes was passed through 100 times, and the surface of the back coat was observed with the naked eye, and it was judged whether there were many or few scratches.

(Decrease in S/'N ratio) Using a VH3 type VTR, the video S/N ratio of the running surface of each magnetic tape after running 100 times is
The amount of decrease in N ratio was measured.

(Abrasion coefficient) Using a rotating 1' ram type surface property measuring device manufactured by Shinto Kagaku Co., Ltd., a load of 39 g and a rotation speed of 66.
Measured at 9 rpm.

Claims (3)

[Claims] (1) In a magnetic recording medium that has a magnetic layer on one side of a nonmagnetic support and a back coat layer on the other side, the back coat layer has the general formula Al_2O_3 xH_2O (where x is 2.9 to 0.1) A magnetic recording medium comprising an alumina hydrate represented by: (2) The magnetic recording medium according to claim 1, wherein x of the alumina hydrate is 2.5 to 0.5. (3) The magnetic recording medium according to claim 1, wherein the particle size of the alumina hydrate is 2 μm or less.