JPH01134717A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To lower the coefft. of friction to guide parts and to improve traveling stability by compounding a fine particulate carbon black and graphitized carbon black respectively having specific average particle sizes into a back coat layer. CONSTITUTION:The fine particulate carbon black having 0.01-0.035mum average particle size and the graphitized carbon black having 0.1-0.5mum average particle size are incorporated into the back coat layer. The graphitized carbon black has the graphite layer structure in which the particle surfaces resemble concentrically to the crystal structure of the graphite. One particle thereof has lubricative property in all directions and has an extremely large antifriction effect in coefft. of friction and, therefore, said carbon black lowers both the coeffts. of friction of both materials made of plastic such as polyacetal and metal such as stainless steel to guide pins. Low noises and the excellent traveling stability are thereby obtd. even when this medium is used for apparatus using the guide pins consisting of both the materials in combination.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magnetic recording medium such as a magnetic tape, which has a magnetic layer on the front side of a non-magnetic support and a back coat layer on the back side.

[Conventional technology]

In general, magnetic recording media such as magnetic tape have a magnetic layer containing magnetic powder and a binder formed on the surface of a non-magnetic support such as a polyester film, but with the recent increase in the density of magnetic recording, There is a tendency to increase the residual magnetic flux density, improve the output, and reduce noise by reducing the particle size of the magnetic powder used and improving the surface smoothness of the magnetic layer.

However, there is a problem in that the running stability of the magnetic layer deteriorates as the surface smoothness of the magnetic layer increases.
As a means to cope with this problem and to prevent dust from adhering to the non-magnetic support due to charging, it has been common practice to provide a back coat layer on the back side of the non-magnetic support opposite to the magnetic layer.

This backcoat layer is typically A lz O's, C
r z O3, T s Oz, αF e 203,
B a S 04 , Ca CO3, B a CO3-
, M g COz , SIC, etc., and fine particulate carbon black with an average particle size of about 0.01 to 0.03 μm are bound together with a suitable binder, and the above-mentioned inorganic compound While the powder imparts an appropriate surface roughness to the surface of the layer, the conductivity of the carbon black helps prevent static electricity. In addition, stearic acid,
Liquid or semi-solid lubricants such as fatty acids such as myristic acid or esters thereof may also be blended (unspecified literature).

[Problem that the invention seeks to solve]

However, in recent years, in order to prevent the irregularities on the surface of the backcoat layer from being transferred to the magnetic layer during winding and causing noise, the surface of the backcoat layer has also tended to be smoothed. A problem has arisen in that the coefficient of friction of the surface of the back coat layer with respect to the guide portion of the recording/reproducing device increases, and sufficient running stability is not achieved.

Also, when adding a lubricant to the back coat layer, if the amount is too large, the surface of the layer will become sticky and adhere to the guide section of recording/playback equipment, causing stains. There were limitations, and it was not possible to sufficiently reduce the coefficient of friction against the guide portion. Furthermore, the guide pins in the guide section of recording and reproducing equipment that the back coat layer comes into sliding contact with include metal guide pins such as stainless steel and plastic guide pins made of polyacetal. Achieving a low coefficient of friction is extremely difficult and has been a challenge for some time.

This invention has been made in view of the above-mentioned circumstances, and has a back coat layer that has good surface smoothness and is less likely to generate noise due to the transfer of its unevenness, and has a low coefficient of friction with respect to the guide section of recording and reproducing equipment. In particular, it is an object of the present invention to provide a magnetic recording medium that has a low coefficient of friction against guide pins made of art materials such as metal and plastic, and has excellent running stability.

[Means for solving problems]

As a result of intensive studies to achieve the above object, the inventors found that when two specific types of carbon black are combined in the back coat layer, the surface smoothness and surface electrical properties of the back coat layer are improved. Both are good, and the coefficient of friction against guide pins made of art materials such as metal and plastic is low. The present inventors have discovered that a magnetic recording medium that exhibits low noise and excellent running stability even when used, has led to the creation of this invention.

That is, the present invention provides a magnetic recording medium having a magnetic layer on the front side of a nonmagnetic support and a back coat layer on the back side, in which the back coat layer contains particles with an average particle diameter of 0.01 to 0.
．． The present invention relates to a magnetic recording medium characterized in that it contains fine particulate carbon black with a diameter of 0.035 μm and graphitized carbon black with an average particle diameter of 0.1 to 0.5 μm.

[Structure and operation of the invention]

As described above, the magnetic recording medium of the present invention includes two layers of finely divided carbon black and graphitized carbon black, each having a specific average particle size, in the back coat layer.
It is characterized by containing carbon black.

Among these components, fine particulate carbon black has an antistatic effect due to its conductivity, similar to the carbon black conventionally blended into the back coat layer, and the performance test results of Example 1, which will be described later, are As is clear from the relationship between the change in the blending ratio of Ryoryoku-Bon black and the surface roughness and video S/N ratio in Table 1, it shows an effect of appropriately smoothing the surface of the back coat layer.

Therefore, in the magnetic recording medium of the present invention, the above-mentioned antistatic effect prevents recording signal dropouts and noise generation due to dust adhesion, and there is also less noise generation due to transfer of unevenness of the back coat layer to the magnetic layer. Become something.

The average particle diameter of such fine particulate carbon black is 0.01-0.035. crm range, 0.03
If it is larger than 5 μm, the surface of the back coat layer will not be smoothed sufficiently, and if it is smaller than 0.01 μm, it is difficult to obtain.

On the other hand, graphitized carbon black is carbon black that has a graphitized layer along the particle surface, and is generally carbon black made of fine particulate carbon obtained by incomplete combustion or thermal decomposition of natural gas, petroleum, etc. It is manufactured by heat treatment at a high temperature of 2.700 to 3,000°C.

The carbon black particles used as the raw material mentioned above are usually made up of several carbon layer planes in which about 90 carbon atoms are arranged in a hexagonal network, stacked almost parallel to each other with a gap of about 3.5 mm. The fine structure of carbon black particles, which are aggregates of crystallites, is that near the surface of the particle, the crystallites are arranged parallel to or almost parallel to the surface, and inside the particle, the direction of the crystallites is irregular. It is believed that this is the case. The arrangement of carbon atoms between the carbon layer planes within the crystallite is not regular and has a so-called turbostratic structure. When this raw material carbon black is heat-treated at the above temperature, the distance between the planes of each carbon layer decreases and crystallites grow, and the carbon black particle surface becomes a shell-like graphite with parallel carbon layer planes. Changes to a layered structure.

In this way, graphitized carbon black has a concentric graphite layer structure similar to the crystalline structure of graphite on the particle surface, and the particles have lubricating ability in all directions, greatly reducing the coefficient of friction. As shown in Tables 1 to 3 showing the performance test results of Examples 1 to 3, which will be described later, the back coat layer containing this material is made of plastic such as polyacetasel and stainless steel. It shows the effect of significantly reducing the coefficient of friction against guide pins made of metal art materials such as.

The average particle size of the graphitized carbon black used in this invention is 0.1 to 0.5 μm, and when this average particle size is smaller than 0.1 μm, the friction coefficient of the back coat layer against the guide pin of the above-mentioned image material is reduced. If the thickness is larger than 0.5 μm, the surface smoothness of the back coat layer will deteriorate. The graphitized carbon black preferably has a graphite layer structure on the particle surface side with a thickness that accounts for an average of about 5 to 30% of the particle radius.

The blending ratio of fine particulate carbon black and graphitized carbon black is 951 in weight ratio of the former/latter.
The preferred range is 5 to 70/30. If the former ratio is too low, the surface of the back coat layer will be rough and the antistatic effect will be insufficient; on the other hand, if the latter ratio is too low, plastic and The effect of reducing the coefficient of friction on the guide pin made of metal art material is no longer exhibited satisfactorily.

It is preferable that the amount of Ryouryoku-Bon Black added to the back coat layer is about 40 to 200 parts by weight in total based on 100 parts by weight of the binder. If this amount is too small, the above effect will not be fully exhibited, and if it is too large, the binding force of the binder will be insufficient and the backcoat itself will tend to fall off due to a decrease in abrasion resistance.

In addition, as a suitable commercially available product of Ryoriki-Bon Black, fine particulate carbon black is available under the trade name RAVEN3500 manufactured by Colombian. Same RAVEN2000. Same RAV
ENI 250. Same RAVEN1035. Same RAVEN
890. Examples include C0NDUCTEX-3C, MONARCH800, MOGUL-L, VULCAN-XC-72R, and VULCAN-P manufactured by Cabot Corporation, and graphitized carbon black such as #4040 manufactured by Mitsubishi Chemical Corporation. can be mentioned.

In the present invention, a non-magnetic inorganic compound powder for reinforcement or a lubricant may be blended in the back coat layer together with the above two types of carbon black as necessary.

As the above-mentioned inorganic compound powder, any of various non-magnetic powders conventionally blended into the back coat layer of magnetic recording media can be used, and a specific example is AIZ.
O:l, Crz 03, Tilt, (X Fe
z o3, BaSO4, CaC0= , BaCO3, M
Examples include gCO3 and SiC, and two or more of these may be used in combination. Moreover, the average particle diameter of these powders is 0.
The thickness is preferably 0.05 to 0.5 μm. Further, the blending amount of these powders is preferably about 10 to 60% by weight based on the total amount of the two types of carbon black.

As the above-mentioned lubricant, any of the lubricants conventionally used in the back coat layer of magnetic recording media can be used, but monobasic fatty acids having about 12 to 18 carbon atoms, and these fatty acids are particularly preferred. and a monohydric alcohol having about 3 to 12 carbon atoms, dimethylpolysiloxane, methylphenylsiloxane, and the like. Further, the blending amount thereof is preferably about 2 to 10% by weight based on the total amount of the two types of carbon black.

Formation of the back coat layer in the magnetic recording medium of the present invention may be carried out according to a conventional method. A back coat paint consisting of the above-mentioned components, a binder, and an organic solvent is prepared, and this paint is applied to the magnetic layer on the surface side. It may be applied to the back side of the non-magnetic support after or before formation and dried. Note that the thickness of this back coat layer is 0.5 to 2 μm.
It is better to set it as a degree.

The above-mentioned binders include conventional binders such as cellulose resins such as nitrocellulose, vinyl chloride-vinyl acetate copolymers containing or not containing functional groups such as hydroxyl groups and carboxyl groups, polyurethane resins, phenolic resins, and amino resins. Various thermoplastic or thermosetting resins known as binders for back coat layers, as well as radiation-sensitive resins with unsaturated double bonds that are cross-linked and cured by radiation such as electron beams, may be used alone or in combination of two or more. Furthermore, a crosslinking agent component such as an isocyanate compound that reacts with the functional group of the functional group-containing resin to effect crosslinking and curing may be added.

Examples of the organic solvent that can be used include ketone solvents such as methyl ethyl ketone and cyclohexanone, ester solvents such as ethyl acetate, alcohol solvents such as isopropyl alcohol, and aromatic hydrocarbon solvents such as toluene. may be used together.

Furthermore, as the non-magnetic support, in addition to those made of synthetic resin materials such as polyethylene terephthalate and polyamide, those made of non-magnetic metal materials can also be used.

The magnetic layer of the magnetic recording medium of this invention is not particularly limited,
In addition to a coated magnetic layer containing magnetic powder and a binder, it also includes a magnetic layer made of a ferromagnetic metal thin film. The above magnetic powder is T FezO3+ Fe 30s
, CO-containing 7-Fe2O, acicular oxide magnetic powder such as CrO□, Ba, Sr.

Plate-shaped ferrite magnetic powder such as P-b ferrite, Fe,
Examples include magnetic metal powders such as Ni, Co, or alloys thereof. Further, as the binder, the same binder as that for the back coat layer described above can be used. In addition to the magnetic powder and the binder, various additives such as an abrasive, a filler, an antistatic agent, and a lubricant may be added to the above-mentioned coated magnetic layer as necessary.

〔Effect of the invention〕

Since the magnetic recording medium of the present invention contains fine particulate carbon black and graphitized carbon black each having a specific average particle diameter in the back coat layer, the surface smoothness of the back coat layer is good. It is difficult to generate noise due to the transfer of the unevenness to the magnetic layer, and it also prevents dropouts and noise due to dust adhesion due to charging. In particular, it has the excellent feature of having a low coefficient of friction against both metal and plastic guide pins, and exhibiting good running stability regardless of the type of recording and reproducing equipment used.

〔Example〕

Hereinafter, this invention will be specifically explained based on examples.

In addition, in the following, parts mean parts by weight. Further, fine particulate carbon black A and graphitized carbon black B used in the back coat layer in each example are shown below.

Fine particulate carbon black A><Graphitized carbon black B> B4...Average particle diameter 0.075 μm Average thickness of graphite layer structure 0.01 μm Note that A4
．． B3,84 is carbon black outside the average particle size range defined in this invention.

Example I CO-containing T FeZO3 magnetic powder 100 parts myristic acid 3 parts n-butyl stearate 3 parts cyclohexanone
1) 5 parts toluene 1) 5
After thoroughly cross-dispersing the above composition using a sand grinder mill, 5 parts of a polyisocyanate compound (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added to prepare a magnetic paint, and this paint was mixed into a polyethylene film with a thickness of 13 μm. The dry thickness on one side of the terephthalate film is 3.0
A magnetic layer was formed by coating to a thickness of μm, drying, and calendering.

Next, the following composition: Carbon black Al+81 100 parts cyclohexanone 500 parts Toluene
A composition containing 500 parts of carbon black At and B1 in the ratio shown in Table 1 below was thoroughly cross-dispersed using a sand grinder mill, and then 15 parts of a polyisocyanate compound (coronate as described above) was added. A back coat paint was prepared. This paint was applied to the surface of the polyethylene terephthalate film opposite to the magnetic layer to a dry thickness of 1.0 μm.
A back coat layer was formed by coating and drying to give a thickness of m, and each portion was cut into a 2 inch width to prepare a videotape.

Regarding sample tapes 1 to 7 obtained by varying the blending ratio of carbon black AI and Bl in Example 1,
The coefficient of friction of the bank coat layer with respect to metal and plastic guide bottles, the surface roughness of the same layer, and the video S/N ratio were measured. The results are shown in Table 1 below. The measurement method for each item is as follows.

<Friction coefficient> 5US3 with a diameter of 4R and a surface roughness of 0.28.
04 cylinder with a diameter of 4 and a surface roughness of 0.53.
Each fi polyacetal cylinder is supported horizontally,
Hang the videotape at a 90 degree angle with the back coat layer side as the contact surface, and place 30g on one end of the tape.
The stress (T) was determined when the other end was held horizontally and pulled at a speed of 14 fins/sec while applying a load of 1. The friction coefficient (μ) was determined by applying this stress (T) to the following formula.

2 T π 30 The friction coefficient μ [M] for the 5US304 cylinder against the metal guide pin, and the friction coefficient μ (P) for the plastic guide pin for the polyacetal cylinder.

Surface roughness> The average surface roughness (CLA value) was measured using a stylus roughness meter under conditions of a stylus speed of 0.06 m/sec and a cutoff of 0.08 ur.

(Video S/N) The signal-to-noise ratio during playback was measured using a video color noise meter, and the reference tape in Example 1 without the back coat layer (other configurations were the same as the tape in Example 1) was used. ) is expressed as a relative value when the value is OdB.

From the results in Table 1, sample tapes Nos. 2 to 6, especially Nos. 2 to 4, in which fine particulate carbon black and graphitized carbon black were blended in the back coat layer, had good surface smoothness of the back coat layer. It can be seen that the video S/N ratio is high, and the friction coefficient of the back coat layer against the guide pins made of both metal and plastic is small, indicating good running stability. On the other hand, sample tape r+h1, which has a back coat layer that does not contain graphitized carbon black, has an excellent surface smoothness of the back coat layer, but has a high coefficient of friction against both metal and plastic guide pins. It is clear that there is a problem with driving stability. It also has a back coat layer that does not contain fine particulate carbon black.

Sample tape Kan 7 has a low coefficient of friction against the guide pins made of both materials, but the surface smoothness of the back coat layer is poor.
It can be seen that the video S/N ratio is extremely poor. In addition,
From the results in Table 1, it can be seen that the blending ratio of fine particulate carbon black A and graphitized carbon black B is preferably about 9515 to 7O/30 in weight ratio of A/H.

Example 2 Fiber rope resin (same as Example 1) 50 parts Polyurethane resin (same as Example 1) 35 parts cyclohexanone
500 parts toluene
After thoroughly cross-dispersing 500 parts of the above composition in a sand grinder mill, a polyisocyanate compound (
A back coat paint was prepared by adding 15 parts of the same material as in Example 1). This paint was applied to the back side of a polyethylene terephthalate film with a magnetic layer formed on the front side using the same method as in Example 1 to a dry thickness.

A back coat layer was formed by coating and drying to a thickness of 0.8 m, and the film was cut to a width of 172 inches to produce a videotape.

Regarding sample tapes IVkL8 to 14 obtained by changing the types of car pump racks A and B in Example 2,
The friction coefficient μ [M] was measured in the same manner as in Example 1.

μ(P) and surface roughness were measured. The results are shown in Table 2.

Table 2 From the results shown in Table 2, even if the back coat layer contains both fine particulate carbon black and graphitized carbon black, the sample tape N1)lO,1)
If the average particle size of the graphitized carbon black is too small, as in sample tape ff1)4, the coefficient of friction against both metal and plastic guide pins will increase; It is clear that if it is too large, the surface smoothness of the back coat layer will be insufficient, which is not preferable.

Example 3 Particulate carbon black A1 50 parts Graphitized carbon black 10 parts Cellulose resin (Example 1
) 50 parts cyclohexanone
500 parts toluene 500
A back coat paint was prepared in the same manner as in Example 1 using the above composition and 15 parts of a polyisocyanate compound (same as in Example 1), and this paint was used to coat a video in the same manner as in Example 1. A tape was made.

Example 4 13as instead of CaC0z powder in back coat paint
A videotape was produced in the same manner as in Example 3, except that 40 parts of powder (average particle size: 0.1 μm) was used.

Example 5 Particulate carbon black A1 82 parts Cellulose resin (same as Example 1) 50 parts cyclohexanone
500 parts toluene
A back coat paint was prepared in the same manner as in Example 1 using 500 parts of the above composition and 15 parts of the polyisocyanate compound (same as in Example 1), and using this paint in the same manner as in Example 1. A magnetic tape was made.

Example 6 A videotape was prepared in the same manner as in Example 5, except that 5 parts of CrzO powder (average particle size 0.3 crm) was used in place of the α-A lz O3 powder in the back coat paint. Created.

Example 7 The same procedure as in Example 5 was carried out, except that 50 parts of vinyl chloride-vinyl acetate copolymer (trade name Kosuretsu A, manufactured by Block Chemical Co., Ltd.) was used instead of the cellulose resin in the back coat paint. A videotape was made.

Comparative Example: In place of graphitized carbon black B1 in the back coat paint, non-graphitized coarse particle carbon black (trade name Sepacalb M manufactured by Colombian) was used.
TC-1. A videotape was produced in the same manner as Sample Tape No. 3 of Example 1, except that particles with an average particle diameter of 0.35 μm were used.

Regarding each videotape obtained in Examples 3 to 7 and Comparative Example, friction coefficients μ[M], μ[
P) and surface roughness were measured. The results are shown in Table 3.

Table 3 From the results in Table 3, it was found that the videotape of the present invention (Example 3)
-7) Even when various non-magnetic inorganic compound powders are blended in the back coat layer in addition to fine particulate carbon black and graphitized carbon black, the surface smoothness of the core layer is good and the surface smoothness of the core layer is good, and even when the back coat layer is mixed with fine particulate carbon black and graphitized carbon black, the surface smoothness of the core layer is good. It can be seen that the coefficient of friction is low against the guide pin. on the other hand,
In a videotape using non-graphitized coarse-grained carbon black instead of graphitized carbon black (comparative example), the back coat layer had excellent surface smoothness and a small coefficient of friction against the metal guide pin, but It is clear that for plastic guide pins a very high coefficient of friction results.

Claims (4)

[Claims] (1) In a magnetic recording medium comprising a magnetic layer on the front side of a non-magnetic support and a back coat layer on the back side, an average particle diameter of 0.01 to 0.035 μm is contained in the back coat layer.
fine particulate carbon black with an average particle size of 0.1 to 0.
．． A magnetic recording medium comprising graphitized carbon black of 5 μm. (2) The magnetic recording medium according to claim (1), wherein the weight ratio of particulate carbon black/graphitized carbon black is in the range of 95/5 to 70/30. (3) The graphitized carbon black has a graphite layer structure on the particle surface side with a thickness that accounts for an average of 5 to 30% of the particle radius.
The magnetic recording medium according to item 1) or item (2). (4) The total amount of fine particulate carbon black and graphitized carbon black is 40 to 200 parts by weight based on 100 parts by weight of the binder in the back coat layer. 3) The magnetic recording medium according to any one of items 3).