JPS59201219A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium having improved running durability and low deterioration in electromagnetic conversion characteristic by providing a back layer of specific average centerline hardness (Ra) contg. carbon black, graphite and talc on the base surface of a magnetic recording medium opposite to the magnetic layer thereof. CONSTITUTION:A back layer is formed on the surface of a magnetic recording medium opposite to the magnetic layer thereof by using a mixture contg. the three components; carbon black having 0.05-0.15mu average primary particle size, graphite having <=10mu average primary particle size and talc having <=10mu average primary particle size at 10:1-1:10 weight ratio between the carbon black and the graphite and contg. the talc powder at 5:95-95:5 by the total weight of the carbon black and the graphite with polyisocyanate, epoxy resin, etc. as a hardener. The magnetic medium of which the back layer has <=0.035mu surface roughness Ra, and which has excellent running durability, obviates generation of stripping powder, etc., prevents the transfer of the ruggedness on the back layer to the magnetic layer and has a particularly excellent video S/N ratio is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium having a back layer, and its main purpose is to improve running durability.

Magnetic recording media are required to have a high degree of durability because they are run and wound at high speed. In order to improve this durability, a method has been proposed in which a magnetic recording medium is provided with a back layer and carbon black and graphite powder are contained in the back layer (Tokuko Sho Geter 102
≠ / issue). However, the running durability of the above technology is still insufficient, and in video tapes, unevenness on the surface of the pack layer is transferred to the surface of the magnetic layer, resulting in changes in electromagnetic conversion characteristics such as color signal-to-noise ratio (
8/N) may deteriorate. For this reason, it is important to control the irregularities on the surface of the backing layer, and improvements have been desired in this regard as well.

An object of the present invention is to provide a magnetic recording medium in which the running durability of the coating film is improved and the deterioration of the electromagnetic conversion characteristics is reduced.

That is, the present invention provides: 1) a magnetic recording medium in which a magnetic layer is provided on a non-magnetic support and a back layer is provided on the other surface, where the back layer is a)
A magnetic recording medium characterized by containing carbon black, a) graphite, and c) talc (talcum) powder, wherein the centerline average roughness Ra of the surface of the nonmagnetic support (cutoff 0.01 mm) is o. , o3zttm or less; 3) the average particle size of carbon black is o, o3zttm or less;
l) and 2 characterized in that r~0.11 μm
), the magnetic recording medium described in .

4) 1) characterized by containing a hardening agent in the back layer
, 2) and 3).

In addition to conventionally used carbon black and graphite, the present invention is characterized by containing soft talcum powder with a Mohs hardness of 7; Mi=4. Talcum powder has the effect of improving the running durability by providing appropriate unevenness on the surface without damaging the running system of the videotape recorder.

Carbon black has an average particle size of o,
or-o, i-μm is preferable, and 0.07 to 01
72 μm is more preferable.

If it is smaller than these ranges, it tends to reduce the running durability improvement effect, and if it is larger, the unevenness on the surface of the back layer tends to be easily transferred to the surface of the magnetic layer.

The shape of graphite is scaly, granular, lumpy,
There are various types such as soil, but scale-like is the most effective for improving running durability.

The content ratio of carbon black and graphite is preferably 102/~/:lO in terms of weight ratio, and more preferably j:/~l:j. Furthermore, 3:/~l:3 is preferable.

If the graphite content is too low, the running durability improvement effect will be reduced, and if it is too high, it will peel off from the backing layer.
The peeling powder contaminates the running system, which is not desirable.

The average particle size of the graphite is less than 10 μm, preferably 0.0/-38 m1, preferably 0.0! ~
It is 3 μm. If it is too large than these ranges, peeling tends to occur, and if it is too small, the effect of improving running durability will be reduced.

The talcum powder used in the present invention has an average particle size of 70 μm or less, preferably 0.5 μm or less. θ/−jμm 1, preferably θ, OS~3 μm. What is the amount of talcum powder added to the total weight of carbon black and graphite? =2! ~Rij:! Ashi, lO: riO~ri0
:10 is more preferable, and 3θ near 0 to 70:30 is even more preferable. If the Merck flour content is too high, the antistatic effect will be reduced, and if it is too low, the running durability improving effect will be reduced.

Examples of the nonmagnetic support used in the present invention include polyethylene terephthalate, polyamide, polyethylene naphthalate, polyimide, triacetyl cellulose, and the like.

The surface property of the pack layer side of the support is determined by the center line average roughness (RaH cutoff o, ormm) of 0°0.3jt μm.
By doing the following, it is possible to reduce the deterioration of electromagnetic conversion characteristics due to the transfer of the unevenness on the surface of the pack layer to the magnetic surface. Also, the Ra on the magnetic layer surface side is also 0.033 μm.
By doing the following, the surface of the magnetic layer becomes smoother,
Electromagnetic conversion characteristics such as video S/N and color S/N can be improved.

The curing agents used in the present invention include polyisocyanates, polyamides, epoxy resins, polyamines, melamine resins, phenolic resins, silicone resins, and other thermosetting resins and moisture-curing resins, which are commonly used in magnetic tapes. is used. The amount of curing agent added is based on the total binder weight io.

% by weight, preferably 10-♂O parts by weight, and 20-♂O parts by weight.
Parts by weight are more preferred.

It is necessary for the curing agent to have a fine three-dimensional network structure in order to obtain the effects of the present invention, and for this purpose, the molecular weight is preferably less than 2,000, more preferably less than /000. Also,
The curing agent is polyfunctional, and the number of functional groups in one molecule is preferably three or more, in which case the effects of the present invention can be effectively obtained.

By combining these individual technologies at the same time,
Unexpected and significant effects can be obtained regarding running durability and electromagnetic conversion characteristics.

Other additives in the back layer include inorganic extender pigments such as magnesium silicate, calcium carbonate, aluminum silicate, barium sulfate, and clay, organic particles such as benzoguanamine resin, abrasives used in the magnetic layer described below, and interfaces. An activator, lubricant, etc. are used as necessary.

Ferromagnetic powder used in the present invention, method for producing magnetic paint, binder used in the magnetic layer and back layer, additives used in the magnetic layer (e.g. dispersant, lubricant, abrasive, antistatic agent, etc.) , the manufacturing method of magnetic recording media, etc. are described in Japanese Patent Publication No. Shoj [-, 2t190.

The present invention will be explained in more detail below with reference to Examples.

In the examples, "parts" indicate parts by weight.

Example 1 Magnetic layer composition Co-added iron oxide (Hc6400e) 300 parts Salt-vinyl acetate copolymer 30 parts (containing 10% vinyl alcohol) Polyurethane resin 20 parts Polyisocyanate 20% Cr203j parts Oleic acid 7 parts Ethyl stearate 7 parts Methyl ethyl ketone too much toluene
300 parts Back layer composition Graphite 30 parts (scaly, average particle size 1 μ) Talc powder (average particle size 3 μ) 300 parts Nitrocellulose
110 parts Curing agent (polyisocyanate) 0 parts Nitrile butadiene rubber ≠ θ parts Methyl ethyl ketone + 2 to 00 parts Prepare the composition of the magnetic layer using a sand mill, prepare the back layer using a ball mill, and prepare polyester with a thickness of ljμ. Each on a support! μ thickness, /,
A magnetic tape (sample plate/) was prepared by coating the sample to a thickness of 2 μm.

However, the polyester support has a diameter of 0°030 on both sides.
μ was used.

Example 2 Samples (A, 2.A3) were prepared in which the support was changed to a support having a temperature a shown in Table A1.

Example 3 Samples (Ahiro) were prepared in Example 3, except that the size of the carbon black in the back layer was changed as shown in Table 1.

Example 4 A sample (A) was prepared in which the curing agent in the back layer was removed in Example 4. However, the weight part of the curing agent was
was divided into nitrocellulose and nitrile butadiene rubber, and the weight of the binder dough was kept constant.

Comparative example l.

In Example 1, the talc powder in the back layer composition was removed,
The weight part was divided into 9 parts between carbon black and graphite to prepare a sample (AJ) with a constant total powder weight.

The test results for samples A/~Al are shown in Table 1.

An outline of the evaluation method is shown below.

The magnetic tape is Vl (incorporated into an 8 format video cassette,
Evaluation was performed using a VH8 video tape recorder.

The running durability was determined by running the magnetic tape repeatedly and measuring the number of times deep scratches were observed on the surface of the pack layer by visual measurement.

Checks were performed every 70 times.

Video S/N is expressed in comparison to standard tape.

Table 1 shows the video S/N when the signal was recorded, stored under ≠r time≠00CtO%RH, and played back.

Sample AI according to the present invention has superior running durability and video S/N compared to comparative sample AI.

When the back layer contains a curing agent, running durability is significantly improved.

If the Ra of the support is 0.03jμn1 or less, video S
/N is improved, but this is due to the smoothing effect on the surface of the magnetic layer and
This is because it has the effect of suppressing the transfer of irregularities on the surface of the back layer to the surface of the magnetic layer by smoothing the surface of the back layer.

Sample flat! When carbon black of 0.03 μm is used, the running durability is slightly inferior to that of 0.02 μm.

Claims (1)

[Scope of Claims] l) A magnetic recording medium in which a magnetic layer is provided on a non-magnetic support and a back layer is provided on the other surface, wherein the back layer is a)
A magnetic recording medium characterized by containing carbon black, a) graphite, and c) Merck powder. 2) The centerline average roughness (Ra) of the surface of the nonmagnetic support is 0.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a diameter of 0.036 μm or less. 3) The average particle size of carbon black is 0.01
~05/! The magnetic recording medium according to claims 1) and 2), characterized in that the magnetic recording medium is μm. 4) A magnetic recording medium according to claims 1), 2) and 3), characterized in that the back layer contains a curing agent.