JPH027223A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To lower the coefft. of friction to a guide part and to improve traveling stability by incorporating fine particulate carbon black, coarse particulate carbon black and fine particulate calcium carbonate powder respectively having specific average particle size into a back coating layer. CONSTITUTION:The fine particulate carbon black having 0.01-0.08mum average particle size, the coarse particulate carbon black having 0.2-0.5mum average particle size and the fine particulate calcium carbonate powder having 0.01-0.045mum average particle size are incorporated into the back coating layer. The fine particulate carbon black effectively prevents electrostatic charge by the electrical conductivity thereof and adequately smoothes the surface of the back coating layer. The coarse particulate carbon black lowers the coefft. of friction to guide pins. The fine particulate calcium carbonate powder lowers the coefft. of friction to the guide pins made of plastic. The coeffts. of friction of the two materials made of the metal and plastic to the guide pins are lowered in this way and the good traveling stability is exhibited.

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 back coat layer is usually made of Al2O3, Crl 0
3, TjO2, (X Fez 03, BaSO4
, CaCC)1 , BaC0, , MgCO3, Si
Non-magnetic inorganic compound powder such as C and average particle size 0.0
It is made by binding carbon black in the form of fine particles of about 1 to 0.03 μm with a suitable binder, and while imparting an appropriate surface roughness to the layer surface with the above inorganic compound powder,
The conductivity of carbon black helps prevent static electricity. In addition, a liquid or semi-solid lubricant such as fatty acids such as stearic acid and myristic acid or esters thereof may be blended into the back coat layer in order to reduce the coefficient of friction (documents unknown). .

[Problem to be Solved by the Invention] However, in recent years, the surface of the back coat layer has been smoothed to prevent unevenness on the surface of the back coat layer from being transferred to the magnetic layer during winding and causing noise. This smoothing tends to increase the coefficient of friction of the surface of the backcoat layer with respect to the guide portion of the recording/reproducing device, causing the problem that sufficient running stability cannot be 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. In particular, it is an object of the present invention to provide a magnetic recording medium that has a low coefficient of friction with respect to guide pins made of both metal and plastic materials and has excellent running stability.

[Means to solve the problem]

As a result of extensive studies to achieve the above object, the inventors found that when two specific types of carbon black and a specific non-magnetic inorganic compound powder are combined in the back coat layer, the back coat The surface smoothness and surface electrical properties of the layer are both good, and the coefficient of friction against guide pins made of both metal and plastic materials is low. The present inventors have discovered that a magnetic recording medium that exhibits low noise and excellent running stability can be obtained by using any of the same devices that also include a guide bin, and have thus come up with the present invention.

That is, the present invention provides 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, in which the back coat layer has an average particle diameter of 0.01.
Contains fine particulate carbon black of ~0.08 μm, coarse particulate carbon black of average particle size of 0.2 to 0.5 μm, and fine particulate calcium carbonate powder of average particle size of 0.01 to 0.045 μm. The present invention relates to a magnetic recording medium characterized by:

Further, in the present invention, in the magnetic recording medium, the weight ratio of fine particulate carbon black/coarse particulate carbon black is in the range of 9515 to 70'/30, and the fine particulate carbon black and coarse particulate carbon black is the total amount of both binders in the back coat layer.
A configuration in which the back coat layer contains 50 to 150 parts by weight of calcium carbonate powder based on 100 parts by weight of the binder is preferable. It is a mode.

[Structure and operation of the invention]

The magnetic recording medium of the present invention is characterized in that, as described above, fine particulate carbon black, coarse particulate carbon black, and fine particulate calcium carbonate powder each having a specific average particle diameter are blended in the back coat layer. .

Among these ingredients, fine particulate carbon black has an antistatic effect due to its conductivity, similar to the carbon black conventionally mixed in the back coat layer, and also shows the performance test results of Example 1 described below. As is clear from the relationship between the change in the blending ratio of Ryouryoku-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.

On the other hand, as is clear from the relationship between the change in the blending ratio of carbon black and the coefficient of friction against the guide pin in Table 1, coarse particulate carbon black has a significantly lower coefficient of friction μCM) against the metal guide pin. Shows a reducing effect. In addition, the fine particulate calcium carbonate powder is particularly suitable for plastics, as is clear from the relationship between the blending ratio change of the fine particulate calcium carbonate powder and the coefficient of friction against the guide pin in Table 3 showing the performance test results of Example 3, which will be described later. Coefficient of friction μ(P) for guide pin manufactured by
The reduction effect is remarkable. Therefore, the magnetic recording medium of the present invention has a low coefficient of friction of the back coat layer with respect to the guide portion of the recording/reproducing device, and especially a low coefficient of friction with respect to the guide pin made of art materials such as metal and plastic, and has a low coefficient of friction with respect to the guide portion of the recording/reproducing device used. It shows good running stability regardless of the conditions.

The average particle diameter of the fine particulate carbon black used in this invention is 0. O ranges from 1 to 0.08 μm, and 0.08
If the diameter is larger than .mu.m, the surface of the back coat layer will not be smoothed sufficiently, and those smaller than 0.01 .mu.m are difficult to obtain. In addition, the average particle diameter of coarse carbon black is in the range of 0.2 μm to 0.5 μm, and if it is smaller than 0.2 μm, the effect of reducing the coefficient of friction against metal guide bins will not be sufficiently exhibited; When the thickness is larger than 0.5 μm, the surface of the back coat layer becomes rough, and there is a problem that the unevenness is transferred to the surface of the magnetic layer during winding, making it easy to generate noise. On the other hand, the average particle diameter of the fine particulate calcium carbonate powder is in the range of 0.01 to 0.045 μm,
If it is larger than 0.045 μm, the effect of reducing the coefficient of friction, especially for plastic guide bins, will be insufficient, and if it is smaller than 0.01 μm, it is difficult to obtain.

The blending ratio of fine particulate carbon black and coarse particulate carbon black is the former/latter weight ratio of 9515 to 7.
A range of approximately 0/30 is preferable; 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, friction against the metal guide bin will increase. The effect of reducing the coefficient will no longer be achieved satisfactorily.

The amount of these ingredients for the back coat layer is determined by the amount of both fine particles and coarse particles.
It is preferable that the total amount of both is about 50 to 150 parts by weight per 100 parts by weight of the binder.
It is preferable to use about parts by weight. If the amount of these compounds is too small, the above-mentioned effects will not be fully exhibited, and if the amount is too large, the binding force of the binder will be insufficient, and the back coat itself will be susceptible to powder falling 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 M manufactured by Cabot Corporation.
OGLIL-L, same REC; UL-99R, same 5TER
ING-R, MONARCH800, VULCAN
-XC-72R, VULCAN-P, product name RAVEN3500 manufactured by Colombian. Same RAVEN2000
．． Same RAVEN1250. Same RAVEN 1035. Same RAVEN890. Coarse particle carbon blacks include Sepacarb MTCI and RAVEN manufactured by Colombiya.
-MTP, trade name Thermax MT manufactured by Cancurb
Examples include. On the other hand, suitable commercially available fine particulate calcium carbonate powders include Calflex C2, Calflex D, and Micron 200 manufactured by U.S. Coal Co., Ltd.
, Shiroishi Kogyo Co., Ltd. under the trade name Hakuenka CC1 and Shiroenka O.

In the present invention, in addition to the above two types of carbon black and fine particulate calcium carbonate powder, a non-magnetic inorganic compound powder for reinforcement and a lubricant may be blended into the back coat layer 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.
O2, Crz C3, T10z, ex-Few Ox
, Ba5Oa , CaC0, , BaCow , MgC
Examples include Oa, S i C, etc., and two or more of these may be used in combination. Furthermore, among these, α-Fe20
．． and CaC0z (coarse particles) are particularly effective. In addition, the average particle diameter of these powders is 0.05 to 0.5
It is preferable to set it to μm.

Further, the blending amount of these powders is preferably about 5 to 25% by weight based on the total amount of the two types of carbon black. On the other hand, as the above-mentioned lubricant, any lubricant that has been conventionally used in back coat layers of magnetic recording media can be used.

Formation of the backcoat layer in the magnetic recording medium of the present invention may be carried out according to a conventional method. A backcoating 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 preferably about 0.5 to 2 μm.

The above-mentioned binders include cellulose resins such as nitrocellulose, vinyl chloride-vinyl acetate copolymers containing or not containing functional groups such as hydroxyl groups, carboxyl groups, sulfone groups, and phosphoric acid groups, polyurethane resins, and phenolic resins. Various thermoplastic or thermosetting resins conventionally known as binders for backcoat layers, such as resins and amino resins, as well as radiation-sensitive resins with unsaturated double bonds that are cross-linked and cured by radiation such as electron beams, are used alone. They can be used alone or in combination of two or more, and a crosslinking agent component such as an isocyanate compound that reacts with the functional group of the functional group-containing resin to crosslink and cure the resin 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 powders include γ-FezO2, Fes Oa +
Co-containing -F e 203+ Acicular oxide magnetic powder such as CrO□, Ba, Sr.

Plate-shaped ferrite magnetic powder such as pb ferrite, Fe, N
Examples include metal magnetic powders such as I, 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, coarse particulate carbon black, and fine particulate calcium carbonate powder each having a specific average particle diameter in the back coat layer, the surface of the back coat layer It has good smoothness and is less likely to generate noise due to the transfer of unevenness to the magnetic layer, and also prevents dropouts and noise due to dust adhesion due to charging, and also prevents backing against the guide section of recording and reproducing equipment. The coating layer has a low coefficient of friction, especially against guide bins made of metal and plastic art materials, and has the excellent feature of exhibiting good running stability regardless of the type of recording/playback equipment used. .

In the above magnetic recording medium, the weight ratio of fine particulate carbon black/coarse particulate carbon black was 951.
By setting the ratio to be in the range of 5 to 70/30, both the surface smoothing and antistatic effect of the former and the friction coefficient reduction effect on metal guide pins of the latter can be maximized without sacrificing one or the other. be able to.

In addition, the amount of binder added in the back coat layer was set to 10
By setting the total amount to 50 to 150 parts by weight for Ryoryoku-Bon Black and 20 to 50 parts by weight for fine particulate calcium carbonate powder, the binding strength of the binder will not be reduced. It becomes possible to fully exhibit each effect within the range.

〔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, coarse particulate carbon black B, and calcium carbonate powder C used in the back coat layer in each example are shown below.

Coarse particle carbon black (Coarse particle carbon black B) <Calcium carbonate powder C> C4...Product name Hakuenka CCR (average particle size 0.08 μm) manufactured by Shiroishi Kogyo Co., Ltd. Carbon black A4. B3 and calcium carbonate powder C4 are outside the average particle size range defined in this invention.

Example 1 Co-containing 7FezO: + magnetic powder 100 parts myristic acid 3 parts cyclohexanone
115 parts toluene
115 parts The above composition was mixed sufficiently using a sand grinder mill, and then 5 parts of a polyisocyanate compound (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added to prepare a magnetic paint. A magnetic layer was formed by coating one side of a polyethylene terephthalate film to a dry thickness of 3.0 μm, drying, and calendering.

Next, the following composition; Carbon black A1+81 100 parts Calcium carbonate powder 01 40 parts Carbon black (average particle size 0.024 μm) 6 parts α-AI, O, powder (average particle size 0.25 μm) 8 parts Cyclohexanone toluene 500 After thoroughly cross-dispersing a composition containing 500 parts of carbon black A1 and B1 in the ratio shown in Table 1 below using a sand grinder mill, a polyisocyanate compound (
A back coat paint was prepared by adding 15 parts of Coronate L) mentioned above. Then, this paint was applied to the surface of the polyethylene terephthalate film on which the magnetic layer was formed, on the side opposite to the magnetic layer, to a dry thickness of 1.0 μm.
It was dried to form a back coat layer, and cut into 1/2 inch width to produce a videotape.

Regarding sample tapes 1 to 7 obtained by varying the blending ratio of carbon black A1 and B1 in Example 1,
The friction coefficient of the back coat layer with respect to metal and plastic guide bins, 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> 5US with a diameter of 41 mm and a surface roughness of 0.28.
A cylinder made of 304 and a cylinder made of polyacetal with a diameter of 4 mm and finished with a surface roughness of 0.53 are each 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 pulled at a speed of 141 m/sec without applying a load, and the friction coefficient (μ) was determined by applying this stress (T) to the following formula.

t30 The friction coefficient μ [M] for the cylinder made of 5US304 with respect to the metal guide bottle, and the friction coefficient μCP) for the cylinder made of polyacetal against the plastic guide bottle.

Surface roughness> Using a stylus type roughness meter, the surface average roughness (CLA
value) was measured.

(Video S/N) The signal-to-noise ratio during playback was measured using a video color noise meter. ) is expressed as a relative value when the value is OdB.

From the results in Table 1, sample tapes Arashi 2 to 6, especially Nos. 2 to 4, in which fine particulate carbon black and coarse particulate 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, the sample tape Nchl, which has a back coat layer that does not contain coarse particulate carbon black, has excellent surface smoothness of the back coat layer, but has a high coefficient of friction and poor running stability, especially against metal guide pins. It turns out that there is a problem. Sample tape level 7, which has a back coat layer that does not contain fine particulate carbon black, has a low coefficient of friction against the guide bins made of both materials, but the surface smoothness of the back coat layer is poor, and the video S/N ratio is low. It can be seen that the ratio is extremely poor.

Furthermore, from the results in Table 1, it can be seen that fine particulate carbon black A
It can be seen that the preferred blending ratio of carbon black and coarse particulate carbon black B is about 9515 to 70/30 in terms of A/B weight ratio.

Example 2 Calcium carbonate powder CI 40 parts Cellulose resin (same as Example 1) 50 parts Polyurethane resin (same as Example 1) 35 parts cyclohexanone
500 parts toluene 5
After thoroughly cross-dispersing the above composition using a sand grinder mill, 15 parts of a polyisocyanate compound (same as in Example 1) was added to prepare a bank coat paint. This paint was applied to the back side of a polyethylene terephthalate film with a magnetic layer formed on the front side in the same manner as in Example 1 so that the dry thickness was 1.0 μm, and dried to form a back coat. A videotape was produced by cutting it into 2-inch widths.

The friction coefficient μ [M] was measured in the same manner as in Example 1 for the sample tapes 11h8 to 11h13 obtained by changing the types of carbon blacks A and B in this Example 2.

μ(P), surface roughness and video S/N ratio were measured.

The results are shown in Table 2.

It is clear that the coefficient of friction for Table 2 becomes high, and if the average particle diameter of the fine particulate carbon black is too large as in sample tape tooth 13, the surface smoothness of the back coat layer becomes insufficient, and both are unfavorable. It is.

Example 3 Carbon black A1 90 parts Carbon black B1 10 parts Calcium carbonate powder C
1. 0 to 50 parts cellulose resin (same as Example 1) 50 parts From the results in Table 2, it is clear that fine particulate carbon black and coarse particulate carbon black are combined in the back coat layer. Also, when the average particle size of the coarse carbon black is too small, as in Sample Tape No. 10, it is especially important to use a metal guide pin. Cyclohexanone 500 parts Toluene 500 parts )15
A backcoat paint was prepared in the same manner as in Example 1 using the following parts, and a videotape was produced in the same manner as in Example 1 using this paint.

Regarding sample tapes 14 to 20 obtained by varying the blending amount of calcium carbonate powder CI in this Example 3, the coefficient of friction μCP) with respect to a plastic guide bottle was measured in the same manner as in Example 1. A white signal was recorded using a tape recorder and then played back, and the deviation of the horizontal synchronization signal was measured as jitter using a jitter meter. The results are shown in Table 3.

Table 3 From the results shown in Table 3, it is clear that the fine particulate calcium carbonate powder, when incorporated into the back coat layer, greatly contributes to reducing the coefficient of friction and jitter for plastic guide bottles. However, if this amount exceeds a certain level, the above-mentioned reduction effect approaches its limit, and therefore, it is understood that an amount of about 20 to 50 parts by weight relative to 100 parts by weight of the binder is sufficient.

Example 4 Carbon black AI 90 parts Carbon black Bl 1.0 parts Calcium carbonate powder C 140 parts tx-Fe203 powder 5 parts (average particle size 0.10 μm) Cellulose resin (same as Example 1) 50 parts Polyurethane resin 35 parts (same as Example 1) 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 a polyisocyanate compound (same as in Example 1),
A videotape was produced in the same manner as in Example 1 using this paint.

Example 5 A videotape was produced in the same manner as in Example 4, except that the same amount of calcium carbonate C2 was used in place of calcium carbonate C1 in the back coat paint.

Example 6 A videotape was produced in the same manner as in Example 4, except that calcium carbonate C3 was used instead of calcium carbonate C1 in the back coat paint.

Example 7 A videotape was produced in the same manner as in Example 6, except that carbon black A3 was used instead of carbon black A1 in the back coat paint.

Example 8 A videotape was produced in the same manner as in Example 6, except that calcium carbonate powder C4 was used in place of the α-Fe203 powder in the back coat paint.

Example 9 Vinyl chloride-vinyl acetate copolymer (trade name: VAGA manufactured by UCC Co., Ltd.) was used in place of the cellulose resin in the back coat paint.
) A videotape was produced in the same manner as in Example 6, except that 50 parts of the sample were used.

Comparative Example 1 A videotape was produced in the same manner as in Example 4, except that calcium carbonate powder C4 was used in place of calcium carbonate powder CI in the back coat paint.

Comparative Example 2 A videotape was produced in the same manner as in Example 4, except that the calcium carbonate powder C1 of the back coat paint was not used.

Comparative Example 3 Example 4 except that calcium carbonate powder CI and carbon black B1 of the back coat paint were not used.
A videotape was made in the same manner.

For each videotape obtained in Examples 4 to 9 and Comparative Examples 1 to 3, the friction coefficient μ
], μ[P], surface roughness, and video S/N ratio, and jitter was also measured in the same manner as in Example 3. The results are shown in Table 4.

From the results in Table 4, the videotape of this invention (Example 4)
~9), in addition to two types of carbon black in the form of fine particles and coarse particles, each having a specific average particle size range, and fine particle calcium carbonate powder, various non-magnetic inorganic compound powders were blended into the back coat layer. Even in cases where the surface smoothness of the nuclear layer is good and the surface smoothness is low compared to metal and plastic guide pins! It can be seen that this is the γ friction coefficient.

On the other hand, there is a video tape (Comparative Example 1) in which calcium carbonate powder with a large average particle size is blended in place of the fine-grained calcium carbonate powder specified in the present invention in the back coat layer, and a videotape in which the above-mentioned fine-grained calcium carbonate powder is blended. It can be seen that in the case of the videotape (Comparative Example 2), which was not used, the coefficient of friction and jitter against the plastic guide pin were both high. In addition, the videotape (Comparative Example 3) in which the above-mentioned fine-grained calcium carbonate powder and coarse-grained carbon blank were not blended in the back coat layer had high friction against guide pins made of both metal and plastic materials. It is clear that the coefficient and jitter are also very high.

Patent applicant: Hitachi Maxell, Ltd.

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, fine particulate carbon black with an average particle size of 0.01 to 0.08 μm is contained in the back coat layer. and an average particle diameter of 0.2 to 0.
Coarse particle carbon black of 5 μm and average particle size of 0.
A magnetic recording medium characterized in that it contains fine particulate calcium carbonate powder of 0.01 to 0.045 μm. (2) The magnetic recording medium according to claim 1, wherein the weight ratio of fine particulate carbon black/coarse particulate carbon black is in the range of 95/5 to 70/30. (3) Claim (1) or (2) wherein the total amount of fine particulate carbon black and coarse particulate carbon black is 50 to 150 parts by weight based on 100 parts by weight of the binder in the back coat layer. The magnetic recording medium described in . (4) The magnetic recording medium according to any one of claims (1) to (3), wherein the back coat layer contains 20 to 50 parts by weight of finely divided calcium carbonate powder based on 100 parts by weight of the binder.