JPS62223815A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve an electromagnetic conversion characteristic, running durability and adhesiveness by incorporating a binder, specific carbon black and specific fatty acid or the deriv. thereof into a conductive undercoat layer. CONSTITUTION:The conductive undercoat layer contains 100pts.wt. binder, 30-60pts.wt. carbon black having 100-300m<2>/g surface area by a BET method and <=0.1mum average particle size and 1-10pts.wt. fatty acid or the deriv. thereof having >=40 deg.C m.p. Not only the uniform dispersion of a coating material is made difficult by the thickening of said compd. but also the deteriorated surface characteristic of the magnetic surface is resulted from the increased surface roughness of the conductive undercoat layer to adversely affect the electromagnetic conversion characteristic if the surface area of the carbon black is <100m<2>/g. Conversely the dispersion of the carbon black into the binder is made difficult and the adhesiveness of the conductive undercoat layer to a nonmagnetic base is debased if the surface area exceeds 300m<2>/g. The surface roughness of the conductive undercoat layer is increased and the deteriorated surface characteristic of the magnetic surface is resulted to adversely affect the electromagnetic conversion characteristic if the average particle size of the carbon black exceeds 0.1mum.

Description

Detailed Description of the Invention "Object of the Invention" (Industrial Application Field) The present invention relates to a magnetic recording medium that has excellent adhesion to a non-magnetic support, running durability, and electromagnetic conversion characteristics, and particularly relates to a The present invention relates to a magnetic recording medium with excellent surface properties and adhesion to a non-magnetic support during processing.

(Prior Art) In recent years, magnetic recording media have come to be used as recording media for recording large amounts of information in a wide range of fields such as audio, video, and computers. Densification is increasingly required.

One possible method for increasing the density of a magnetic recording medium is to increase the density of ferromagnetic particles.

(Problems to be Solved by the Invention) However, as the density of ferromagnetic particles increases, the adhesion of the magnetic layer to the non-magnetic support decreases, and the chargeability of the magnetic layer increases, causing the running of the magnetic recording medium. A problem arises in that durability decreases. As a countermeasure to this problem, it has been proposed to provide a conductive undercoat film under the magnetic layer, but conventional conductive undercoat layers have poor surface properties during the manufacturing process of magnetic recording media, and have poor adhesion to non-magnetic supports. As a result, the surface properties of the magnetic layer deteriorate, smudges and the like tend to appear in the coating direction, and the electromagnetic conversion characteristics are also poor.

The present invention was made to solve these conventional problems, and an object of the present invention is to provide a magnetic recording medium with excellent running durability, adhesion to a non-magnetic support, and electromagnetic conversion characteristics.

[Structure of the Invention] (Means for Solving the Problems) That is, the magnetic recording medium of the present invention has a magnetic recording medium in which a conductive undercoat layer is provided between a nonmagnetic support and a magnetic layer containing ferromagnetic fine particles. In the recording medium, the conductive undercoat layer is (a) a binder and (b) a binder.
Surface area by BET method is 100-300Tl'12/g
Carbon black with an average particle size of 0.1 μm or less
(iii) 1 to 10 parts by weight of a fatty acid or a derivative thereof having a melting point of 40° C. or higher.

The undercoat layer of the present invention has a surface area of 100 to 100 by the BET method.
300Tl'12/g, preferably 200-3001T
12/g and an average particle size of 0.1 μm or less is used. In the present invention, the surface area of the carbon black used in the undercoat layer is limited as described above for the following reason. In other words, if the surface area of carbon black is less than 100V+2/Q, the paint will not only thicken and become difficult to disperse uniformly, but also increase the surface roughness of the conductive undercoat layer, leading to a decrease in the surface properties of the magnetic surface. This will have a negative effect on electromagnetic conversion characteristics. Conversely, if the surface area exceeds 3007I+2/g, it becomes difficult to disperse into the binder and the adhesion of the conductive undercoat layer to the non-magnetic support decreases. Furthermore, the average particle diameter of the carbon black was limited to 0.1 μm.
This is because, if it exceeds this, the surface roughness of the conductive undercoating film becomes large, leading to a decrease in the surface properties of the magnetic surface and having an adverse effect on the electromagnetic conversion characteristics.

The above carbon black is 3 parts per 100 parts by weight of the binder.
It is blended in a proportion of 0 to 60 parts by weight. If the amount is less than 30 parts by weight, the surface resistivity of the conductive undercoat layer will increase, and if it exceeds 60 parts by weight, the conductive undercoat layer will become brittle and have poor adhesion, causing carbon black, etc. to fall off. It becomes like this.

As the fatty acid used in the present invention, both saturated and unsaturated fatty acids having a melting point of 40° C. or higher can be used. If the melting point is less than 40°C, bleeding from the conductive undercoat layer is likely to occur, causing stickiness on the surface of the magnetic layer, which is undesirable. Fatty acids are binders 10
It is blended in an amount of 1 to 5 parts by weight per 0 parts by weight. The blending amount is 1
If the conductive undercoat layer is applied below the molding area, a blocking phenomenon (peeling of the conductive undercoat layer) will occur when it is cured.On the other hand, if the conductive undercoat layer exceeds 10 layers M, bleeding from the conductive undercoat layer is likely to occur. Neither is preferable. Note that derivatives such as esters of these fatty acids can also be used if necessary. Examples of these fatty acids or their derivatives include fatty acids such as lauric acid, myristic acid, palmitic acid, and stearic acid, and fatty acid esters consisting of saturated fatty acids having 12 to 16 carbon atoms and monohydric alcohols having 4 to 12 carbon atoms. can be mentioned.

Curable resins, particularly polyurethane resins, are suitable as the binder used in the conductive undercoat layer of the present invention. Examples of such polyurethane resins include N-2301, N-2304, B, and F manufactured by Nippon Polyurethane Industries Co., Ltd.
Erasen 5F03 manufactured by Gudrich may be mentioned. It is also preferred to use nitrocellulose together with these polyurethane resins. An example of such nitrocellulose is FM-200 manufactured by Daicel. As the curing agent used for these curable resins, isocyanate-based curing agents are preferred. Examples of such isocyanate-based curing agents include Coronate manufactured by Nippon Polyurethane Industries, Ltd. and Takenate XL-10007 manufactured by Takeda Pharmaceutical Company Limited. Note that the binding material used in the present invention is not limited to such a curable resin, and a non-curable resin may be used as necessary.

The ferromagnetic powder used in the magnetic layer of the present invention includes Co
-7Fe203 and other acicular iron oxides, CrO2, Fe-C0
Examples thereof include metal powders such as, ultrafine particles such as hexagonal plate-shaped particles such as Ba-ferrite, and the like. The magnetic layer is made of these ferromagnetic powders using known materials such as vinyl chloride/vinyl acetate copolymer, binder such as polyurethane resin, carbon black, filler such as aluminum oxide, and stearic acid. It is used as a magnetic paint by mixing with lubricants, solvents, hardeners, etc.

Further, as the non-magnetic support used in the present invention, known ones used as bases for various magnetic tapes, floppy disks, etc. can be used, for example,
A polyester film or the like is used as the tape base, and a polyester sheet or aluminum substrate is used as the floppy disk base.

To manufacture the magnetic recording medium of the present invention, first, the above-mentioned carbon black and fatty acid are uniformly dispersed in a binder,
Further, if necessary, a curing agent is added and applied to a nonmagnetic support to form a conductive undercoat layer.

Next, a magnetic layer containing ferromagnetic powder may be applied on top of these conductive undercoating layers by a conventional method.

(Function) The conductive undercoat layer of the magnetic recording medium of the present invention has good adhesion to the non-magnetic support and acts to improve its surface properties, thereby improving the surface properties and non-magnetic properties of the magnetic layer. The adhesion to the support is improved, and the running durability of the magnetic recording medium is improved.
Adhesion to non-magnetic supports and electromagnetic conversion characteristics are improved.

(Example) The present invention will be explained in more detail with reference to Examples below. Note that "parts" in the following examples indicate parts by weight.

Example 1 (Composition of paint for forming conductive undercoat layer) Carbon black 40 parts (surface area 22
0TI12/g, fine particles 0.02μm) Stearic acid
3 part polyurethane resin
80 parts Nitrocellulose 20 parts Solvent (MEK/Toluene/Cyclohexanone) (1/
1/1) 98 parts Coronate 1 10 parts (composition of paint for forming magnetic layer) Barium ferrite powder (average particle size 0.08 μm, Hc 7000e) 10
0 parts Vinyl chloride/vinyl acetate copolymer 6 parts Polyurethane resin 10 parts Carbon
Bipartite aluminum oxide
2 parts lubricant 1.5 parts solvent (MEK/toluene/cyclohexanone) (1/1/
1) 180 parts curing agent 6 parts Prepare a paint for forming a conductive undercoat layer using the above formulation, and apply this paint to a 10 μm thick polyethylene terephthalate layer with a dry thickness of 0.3 μm.
The conductive undercoat layer was formed by applying the following coating and curing it to form a conductive undercoat layer. Roughly, a magnetic layer prepared according to the above-mentioned composition was coated on the conductive undercoat layer, and calendering and slitting were performed to prepare a magnetic tape having a magnetic layer thickness of 4 μm.

Comparative Example 1 In the composition of the paint for forming a conductive undercoat layer of Example 1, carbon black was added in a surface area of 325 TIlz/! A conductive undercoat layer was formed in the same manner as in Example 1, except that the conductive undercoat layer was replaced with that of Example 1, and a magnetic layer was formed in roughly the same manner as in Example 1 to prepare a magnetic tape.

Comparative Example 2 A conductive undercoat layer was formed in the same manner as in Example 1, except that stearic acid was removed from the composition of the paint for forming a conductive undercoat layer in Example 1, and in the same manner as in Example 1. A magnetic layer was formed to create a magnetic tape.

Comparative Example 3 A magnetic tape was prepared in the same manner by applying the magnetic layer of Example 1 directly onto a 10 μm thick polyethylene terephthalate. These magnetic tapes were tested for electromagnetic characteristics, running properties, and peeling tests. The results are shown in the table below. Note that each characteristic in the table was measured as follows.

Electromagnetic conversion characteristics: Modified a commercially available VH3 type VTR,
Recording and playback are performed at a center frequency of 5MHz, and from 5MHz to 0.
7M)+2 S/N ratio (relative value with Comparative Example 3 as OdB) Running performance test: Measured by running repeatedly using a commercially available VTR and jitter meter Peeling test: Place the magnetic side of the magnetic tape on a cylinder with a load of 50 (lf) at 40°C and 80% RH.
After standing for a day, the state of peeling of the magnetic surface was observed (see the margin below). From the table above, it can be seen that the magnetic tape prepared in Example 1 had excellent running durability and adhesion without deterioration of electromagnetic conversion characteristics.

[Effects of the Invention] As is clear from the above examples, the magnetic recording medium of the present invention has excellent electromagnetic conversion characteristics, running durability, and adhesion, and improves reliability in magnetic tapes, magnetic disks, etc. can be done.

Claims (2)

[Claims] (1) A magnetic recording medium in which a conductive undercoat layer is provided between a nonmagnetic support and a magnetic layer containing ferromagnetic fine particles, wherein the conductive undercoat layer comprises (a) 100 parts by weight of a binder; ) The surface area according to the BET method is 100 to 300 m^2/
g, 30 to 60 parts by weight of carbon black with an average particle diameter of 0.1 μm or less;
10 parts by weight of a magnetic recording medium. (2) The magnetic recording medium according to claim 1, wherein the binder is made of polyurethane or a mixture of polyurethane and nitrocellulose.