JPH0845072A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To maintain satisfactory dispersibility of magnetic powder even when the total amt. of a binder (contg. a curing agent) and a lubricant is reduced and to obtain a magnetic recording medium excellent in electromagnetic transducing characteristics and durability by adding a specified dispersant at the time of preparing a magnetic coating material. CONSTITUTION:When the top of a polyethylene terephthalate film is coated with a magnetic coating material contg. a binder and magnetic powder mixed with a solvent, ammonium salt of 12-18C monocarboxylic acid or 12-18C monocarboxylic acid and an aq. ammonia soln. or gaseous ammonia are added as a dispersant. Vinyl chloride resin having sulfonic acid groups or polyurethane having sulfonic acid groups is used as the binder. Iron-based metallic magnetic powder is effective as the magnetic powder. The solvent is, e.g. methyl ethyl ketone or toluene.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a high density coating type magnetic recording medium.

[0002]

2. Description of the Related Art Conventionally, a magnetic recording medium such as a magnetic recording tape is formed by applying a magnetic coating material containing a binder and magnetic powder onto a support. ing. Since the dispersibility of the magnetic paint has a great influence on magnetic recording, it is widely practiced to add a low molecular weight dispersant such as lecithin to the binder and the magnetic powder when the magnetic paint is produced. There is. Further, in recent years, as the above-mentioned magnetic powder, fine magnetic powder mainly composed of metal powder, which is required to have high output and high durability, has been used, but it is more difficult to disperse the fine magnetic powder. Therefore, a self-dispersing polar group-containing binder in which a vinyl chloride resin or a polyurethane resin contains a sulfonic acid group or a salt thereof is being used in place of the above low-molecular-weight dispersant such as lecithin.

However, since the dispersibility of the conventional magnetic paint prepared by using the above-mentioned conventional low-molecular-weight dispersant and polar group-containing binder is not sufficient, the dispersibility can be improved by using many binder components. However, the magnetic coating film of the magnetic recording medium formed by using these magnetic paints does not satisfy the physical properties required in terms of magnetic properties and durability. In addition, there is a demand for a magnetic recording medium having excellent magnetic characteristics and durability.

Therefore, the object of the present invention is to determine the dispersibility of the magnetic powder used in the magnetic coating material in the binder component (hardening agent).
To provide a method for producing a magnetic recording medium capable of obtaining a magnetic recording medium excellent in electromagnetic conversion characteristics and durability, which can be made extremely excellent even if the total amount of organic substances such as oil and lubricant is reduced. It is in.

[0005]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that the above object can be achieved by adding a specific dispersant during the production of a magnetic coating material. did.

The present invention has been made based on the above findings, and in a method for producing a magnetic recording medium, in which a magnetic coating material containing a binder and magnetic powder is applied onto a support,
A method for producing a magnetic recording medium, characterized in that an ammonium salt of a monocarboxylic acid having 12 to 18 carbon atoms (or a monocarboxylic acid having 12 to 18 carbon atoms and aqueous ammonia or ammonia gas) is added when the magnetic coating material is prepared. Is provided.

The method of manufacturing the magnetic recording medium of the present invention will be described in detail below. The magnetic paint used in the present invention contains a binder and magnetic powder.

As the binder, those usually used in magnetic paints can be used without particular limitation, but sulfonic acid group-containing vinyl chloride resin, sulfonic acid group-containing polyurethane and the like are particularly preferably used.

As the above-mentioned magnetic powder, those usually used in magnetic paints can be used without particular limitation, but metallic magnetic powder mainly composed of iron and having a specific surface area of 35 m ² / g or more has a particularly excellent effect. And thus can be preferably used.

The mixing ratio of the binder and the magnetic powder is
The binder 12 to 2 is added to 100 parts by weight of the magnetic powder.
It is preferably 0 part by weight.

The magnetic paint can be obtained by mixing the binder and the magnetic powder with a solvent. Examples of the solvent include methyl ethyl ketone, toluene, cyclohexanone, THF and the like, and when used, they can be used alone or as a mixture. The amount of the above solvent used is usually a solid content (the above binder, the above magnetic powder, etc.).
It is 120 to 180 parts by weight with respect to 100 parts by weight.
In addition to the binder and the magnetic powder, the magnetic coating material is usually carbon black, alumina, α-Fe ₂
Powder components such as O ₃ and chromium oxide; components such as fatty acid and fatty acid ester, which are used in ordinary magnetic paints such as lubricant components are contained.

The ammonium salt of a monocarboxylic acid having 12 to 18 carbon atoms used in the magnetic paint is a component used as a dispersant, and specifically, lauric acid, myristic acid, palmitic acid, stearic acid, Examples thereof include ammonium salts of monocarboxylic acids such as oleic acid, linoleic acid, linoleic acid and isostearic acid.

The amount of the ammonium salt of monocarboxylic acid used is 0.5 to 100 parts by weight of the magnetic powder.
It is preferably 3 parts by weight. The amount of the dispersant used is
If it is less than 0.5 parts by weight, the dispersing effect cannot be obtained, and if it exceeds 3 parts by weight, the dispersibility of the paint is improved, but the surface property of the coating film after calendaring is deteriorated and the output is lowered. It is preferably in the range.

Further, in the present invention, a monocarboxylic acid having 12 to 18 carbon atoms and ammonia water or ammonia gas may be used as a dispersant in place of the above ammonium salt of monocarboxylic acid (hereinafter referred to as dispersion). The term "agent" is a generic term for both). In this case, the amount of the above-mentioned monocarboxylic acid and ammonia water or ammonia gas used is the same as the amount of the above-mentioned ammonium salt of monocarboxylic acid used. As the above-mentioned monocarboxylic acid having 12 to 18 carbon atoms, the above-mentioned monocarboxylic acid is appropriately used,
The ammonia concentration in the above-mentioned ammonia water is 20
It is preferably about 30% by weight. By simultaneously using the monocarboxylic acid and the ammonia water or the ammonia gas, both react with each other during the dispersion of the magnetic coating material to form an ammonium salt of the monocarboxylic acid. The same effect as salt (excellent dispersibility) can be obtained. Further, the monocarboxylic acid and the ammonia water or the ammonia gas are such that the ammonia in the ammonia water or the ammonia gas is 0.
It is preferable to mix the ammonia water or the ammonia gas in a mixing ratio of 5 to 1.5 mol.

Examples of the support used in the present invention include polyethylene terephthalate film, polyethylene naphthalate film and polyamide film, and the thickness of the support is preferably 1 to 300 μm.

To carry out the method for producing a magnetic recording medium of the present invention, the dispersant is added at the time of preparation of the magnetic coating material, and the obtained magnetic coating material is applied onto the support. It can be carried out.

The above magnetic paint can be easily prepared as follows. That is, the magnetic powder,
The binder, the dispersant, and the powder component are charged together with a part of the solvent into a closed Nauta mixer to carry out premixing to obtain a mixture. The obtained mixture is kneaded by a continuous pressure kneader or the like, and then a part of the solvent is added to dilute it, and after dispersion treatment using a sand mill or the like,
The above lubricant component is mixed and filtered, and further, a curing agent such as triisocyanate, an acid anhydride, an amine compound and the remaining solvent are mixed and dispersed to obtain the above magnetic coating material.

Further, in the present invention, the above-mentioned magnetic coating material is applied onto the above-mentioned support, followed by a drying step and the like, and a heat treatment is carried out in the drying step to thermally decompose the ammonium salt of the monocarboxylic acid. Preferably. The above-mentioned drying step is usually 3000 to 10000 by a known method.
After carrying out Gaussian magnetic field orientation, 10 at 80 to 110 ° C.
It is preferable to carry out for more than a second. By performing the above drying step, the ammonium salt of monocarboxylic acid is decomposed into monocarboxylic acid and ammonia, and the produced monocarboxylic acid can be used as a lubricant component in the magnetic coating film. still,
At this time, the by-product ammonia volatilizes and is removed from the coating film.

Further, in the present invention, it is preferable to form a back coat layer on the surface of the support opposite to the surface coated with the magnetic paint. As the material and method for forming the back coat layer, generally known materials and methods can be appropriately selected and applied.

The magnetic recording medium obtained as described above is
A magnetic recording medium such as a magnetic tape in which a magnetic coating film is formed on a support, and since it has excellent dispersibility of the above magnetic paint, it has excellent electromagnetic conversion characteristics and durability.

[0021]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

[Example 1] (Blending of magnetic paint I) (parts by weight) -Acicular metal powder mainly composed of iron 100 (coercive force 1750 Oe, saturation magnetization 130 emu / g, average major axis length 0.13 μm, ratio) Surface area 55 m ² / g) ・ Alumina (average particle size 0.3 μm) 7 ・ Carbon black (average particle size 20 nm) 1 ・ Sulfonic acid group-containing vinyl chloride acrylate copolymer 8 ・ Sulfonic acid group-containing polyurethane resin 6 ・Dispersant shown in [Table 1] Compounding amount shown in [Table 1] 2-Ethylhexyl oleate 2-Polyisocyanate 3 ["Coronate L", trade name, Nippon Polyurethane Industry Co., Ltd.]-Mixed solvent (methyl ethyl ketone / toluene / cyclohexane) , 2: 1: 2, weight ratio) Balance

The magnetic coating material I was premixed by adding the composition having the above composition to a Nauta mixer (solid content 80 wt%).
Then, after pretreatment with a continuous pressure kneader, the mixture was diluted with the above mixed solvent until the solid content became 40 wt%, and further dispersed by a two continuous sand mill. The end point of the dispersion was the point when the increase in the gloss of the coating film formed by the coating material during dispersion disappeared.

Next, the obtained magnetic coating material I was coated on a polyethylene terephthalate film having a thickness of 10 μm as a support so as to have a dry film thickness of 2.5 μm by an extrusion coating device, and undried. In this state, a magnetic field orientation treatment was performed with a solenoid (5000 gauss), and then a drying process was performed in a drying furnace (90 ° C.), and then the film was wound. After the completion of the drying step, the magnetic coating film is subjected to calendar treatment (linear pressure of 300 kg / cm, 90 ° C.), and then the coating material containing carbon black and a binder as main components is coated on the uncoated surface of the support with the above magnetic coating material I. Coating and drying were carried out in the same manner as in the method to form a back coat layer, followed by slitting to obtain a magnetic tape (8 mm width) as a magnetic recording medium. Using the obtained magnetic tape, performance tests such as electromagnetic conversion characteristics and durability test shown below were conducted. The fluidity (dispersibility) of the magnetic coating material was also evaluated as described below, and the amount of ammonia in the magnetic coating film after the drying step was also measured. The results are shown in [Table 1].

[Measurement Method] Output (7 MHz) The obtained 8 mm wide magnetic tape was loaded into an 8 mm VTR cassette to obtain a test 8 mm VTR tape cassette. Obtained test 8mm VTR tape cassette and commercial Hi8V
Using a device modified from TR, 7M was added to the above magnetic tape.
A Hz signal was recorded and the output (reproduction output) when the signal was reproduced was measured. The recording wavelength of 7MHz is 0.54μ
It was m.・ Durability test [Still durability test]: 8 mm VT of the obtained magnetic tape
Attached to R deck, environmental temperature is -5 ° C, initial output is 10
The output after a still test for 2 hours is calculated as 0%,
The output was expressed as% of the initial output. -Fluidity of magnetic paint: The number of seconds was measured visually and under pressure filtration (membrane filter 5 µm, 1 kg / cm ² , paint 200 cc), and evaluated according to the following evaluation criteria. ◯: Good fluidity less than 30 seconds Δ: A little poor fluidity 30 seconds or more and 2 minutes or less X: Liquid separation (agglomeration) 2 minutes or more ・ Ammonia amount in coating film: 0.1 N NaOH EtOH
10 cm in 10 ml of methyl ethyl ethone in which 1 ml of solution was dissolved
After dipping the magnetic coating film of No. ² at room temperature for 24 hours, the supernatant was quantified by liquid chromatography.

Example 2 A magnetic coating material II was prepared in the same manner as in Example 1 except that the dispersant shown in [Table 1] was used as the dispersant in the compounding amount shown in [Table 1]. A magnetic tape as a magnetic recording medium was obtained, and the obtained magnetic tape was subjected to the same performance test as in Example 1. The results are shown in [Table 1].

Example 3 A magnetic coating material III was prepared in the same manner as in Example 1 except that the dispersant shown in [Table 1] was used as the dispersant in the compounding amount shown in [Table 1]. A magnetic tape as a magnetic recording medium was obtained, and the obtained magnetic tape was subjected to the same performance test as in Example 1. The results are shown in [Table 1].

[Example 4] As the dispersant, the dispersant shown in [Table 1] was used in the compounding amount shown in [Table 1]. At the time of dispersion, myristic acid was first premixed with each component (solid content: 80).
wt%) and further ammonia water (ammonia content 3
0 wt%) and dispersed and mixed for 10 minutes. Magnetic paint IV
A magnetic coating material IV was prepared in the same manner as in Example 1 except that the magnetic tape as a magnetic recording medium was obtained, and the obtained magnetic tape was subjected to the same performance test as in Example 1. The results are shown in [Table 1].

Comparative Example 1 A magnetic coating material V was prepared in the same manner as in Example 1 except that the dispersant shown in [Table 1] was used as the dispersant in the compounding amount shown in [Table 1]. A magnetic tape as a magnetic recording medium was obtained, and the obtained magnetic tape was subjected to the same performance test as in Example 1. The results are shown in [Table 1].

[Comparative Example 2] A magnetic coating material VI was prepared in the same manner as in Example 1 except that the dispersant shown in [Table 1] was used as the dispersant in the compounding amount shown in [Table 1]. A magnetic tape as a magnetic recording medium was obtained, and the obtained magnetic tape was subjected to the same performance test as in Example 1. The results are shown in [Table 1].

Comparative Example 3 A magnetic coating material VII was prepared in the same manner as in Example 1 except that the dispersant shown in [Table 1] was used as the dispersant in the compounding amount shown in [Table 1]. A magnetic tape as a magnetic recording medium was obtained, and the obtained magnetic tape was subjected to the same performance test as in Example 1. The results are shown in [Table 1].

Comparative Example 4 A magnetic coating material VIII was prepared in the same manner as in Example 1 except that a dispersant was not used (in this case, 2 parts by weight of myristic acid was added when the solvent was diluted) to prepare a magnetic recording medium. Then, the same performance test as in Example 1 was performed on the obtained magnetic tape. The results are shown in [Table 1].

Comparative Example 5 10 parts by weight of a sulfonic acid group-containing vinyl chloride acrylic copolymer as a binder component, 8 parts by weight of a sulfonic acid group-containing polyurethane resin, and 4 parts of Coronate L were used.
A magnetic paint was prepared in the same manner as in Comparative Example 4 except that the weight part was changed.
IX was prepared to obtain a magnetic tape as a magnetic recording medium, and the obtained magnetic tape was subjected to the same performance test as in Example 1. The results are shown in [Table 1].

[0034]

[Table 1]

[0035]

EFFECTS OF THE INVENTION According to the present invention, the dispersibility of the magnetic powder used in the magnetic coating material is made extremely excellent even if the total amount of organic substances such as the binder component (hardening agent) and the lubricant is reduced. It is possible to obtain a magnetic recording medium excellent in electromagnetic conversion characteristics and durability. Further, when a further drying step is performed, ammonium can be removed by thermal decomposition in the drying step, and the monocarboxylic acid remaining in the magnetic coating film can be reused as a lubricant for the coating film. A magnetic recording medium having excellent electromagnetic conversion characteristics and durability can be obtained.

More specifically, attempts have been made so far to raise or lower the polar group concentration in order to improve the dispersibility of various polar group-containing binders, and various low molecular dispersants alone or the above polar group-containing binders. Although the dispersibility was improved by the combined use with and the like, none of them could satisfy the dispersibility, durability, and electric characteristics at the same time. Also,
In order to achieve high-density recording, it is an essential condition to increase the magnetic powder concentration in the coating film and obtain a magnetic coating film having excellent surface smoothness of the coating film. It was not possible to obtain a magnetic coating material that forms a magnetic coating film that satisfies the above conditions. In the present invention, since the above-mentioned dispersant is used, the above-mentioned dispersant that improves the dispersing effect during coating is decomposed into monocarboxylic acid and ammonia gas in the drying step after coating, and the ammonia gas is evaporated. After that, the above monocarboxylic acid remains as a lubricant component in the coating film.
Therefore, according to the present invention, the magnetic powder concentration in the magnetic paint can be increased, and a magnetic recording medium excellent in coating film surface smoothness can be obtained.

Claims (3)

[Claims] 1. A method for producing a magnetic recording medium, which comprises coating a support with a magnetic coating material containing a binder and magnetic powder, wherein an ammonium salt of a monocarboxylic acid having 12 to 18 carbon atoms is prepared when the magnetic coating material is prepared. (Or a monocarboxylic acid having 12 to 18 carbon atoms and aqueous ammonia or ammonia gas) is added. 2. The method for producing a magnetic recording medium according to claim 1, wherein the ammonium monocarboxylic acid salt is thermally decomposed in a drying step after coating the magnetic coating on the support. 3. The method of manufacturing a magnetic recording medium according to claim 1, wherein the magnetic powder is a metal powder mainly composed of iron.