JPH02267723A - Magnetic recording medium provided with back coating layer containing nonmagnetic powder - Google Patents

Abstract

PURPOSE:To obtain the recording medium which does not cause scintillation etc., by providing a back coating layer which contains carbon black powder having a prescribed grain size and inorg. powder having prescribed characteristics and has a prescribed value or below in the interlayer coefft. of friction with a magnetic layer. CONSTITUTION:This magnetic recording medium is provided with the back coating layer which contains at least one kind of the carbon black powder having the average grain sizes ranging 20 to 100mmu and the inorg. powder having 3 to 6 Mohs' hardness and has <=0.27 interlayer coefft. of friction with the magnetic layer. The graininess and film reinforcing effect of the particles are effectively utilized by using the carbon black having such average grain size and the inorg. powder having such hardness, by which a strength of the back coating layer is increased to improve a durability, dispersion fillers, binders, etc., are controlled overall and the coefft. of friction and contact area are uniformized to suppress the interlayer coefft. of friction to <=0.27. The scintillation and drop-out of the magnetic tape are thus eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, and particularly to improving the surface properties of a back coat layer.

[Prior art]

Magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks are widely used in the audio, video, and computer fields. Among these, for example, regarding magnetic tape in the video field, when recording and playing back images, the cassette is loaded into the video deck, and the tape is attached to a guide pole or guide roller. While being guided and traveling, the magnetic head rubs and scans the magnetic head. At this time, in order to record and reproduce images, the tape must be running normally and its winding condition must be uniform so that it can be reused over and over again. Since the tape is usually made of a material with high electrical resistance, the surface quality of the tape that comes into contact with the guide pole etc. is required to be suitable for running and to have an antistatic effect.

In order to improve the sensitivity, especially the output in the high frequency range, the surface of the magnetic layer is finished to be smooth so that the sliding condition of the magnetic tape against the magnetic head does not change. However, when the surface of the magnetic layer becomes extremely smooth as described above, dynamic frictional resistance is large, which tends to cause problems in running properties.

Furthermore, when a magnetic tape is run on a video deck, not only the surface of the magnetic tape, but also the back surface of the magnetic tape is exposed to the guide poles mentioned above.
If the running performance and durability of the back side of the magnetic tape are not good because it is rubbed by the guide roll, sudden tension is applied irregularly to the running magnetic tape, which causes the magnetic layer to be excessively applied to the magnetic head. Because it will be rubbed,
Not only will the magnetic layer be damaged and the magnetic powder in the magnetic layer peel off, but the tension at which the magnetic tape is wound will fluctuate, resulting in unwinding, irregular winding, uneven tape edges, and shinching. This causes uneven running of the tape when it is reused. When these things happen, skew
Image or electromagnetic characteristics such as jitter, dropout, and S/N deteriorate.

For these improvements, it has been proposed to provide a bank coat layer on the back side of the magnetic tape.

For example, there are some in which an inorganic powder is contained in a resin layer. This is done by roughening the surface of the back coat layer to reduce the area of contact with guide poles and the like, thereby reducing the coefficient of friction. For example, JP-A-57-130234, JP-A-58-161135, JP-A-57-53825, and JP-A-58-2415 all show examples using inorganic powders, and many of these also include the particle size. Limited ones are shown.

In place of the above-mentioned inorganic powder, it has also been proposed to use saw pump racks, for example,
It is stated in No. 1. This is aimed at antistatic and light shielding effects based on the conductivity of carbon black, as well as surface roughening effects due to its particles. However, since the average particle size of the carbon black used is 10 to 20 mμ, The backcoat layer formed using this dispersion has extremely poor dispersibility, and the aggregated particles give a rough surface to the backcoat layer, and since the aggregated particles do not have a strong binding force with the binder, they not only easily peel off, but also easily peel off the tape. When the particles are wound and come into contact with each other, the large-sized particles of the T-collection cause unevenness in the magnetic layer.

Due to the poor dispersibility of carbon black having such a small particle size, it is difficult to obtain an average roughness that does not cause unevenness in the magnetic layer as described above, and the surface thereof tends to become excessively rough.

Furthermore, an attempt has been made to use carbon black with a relatively small average primary particle size of 10 to 60 mμ and carbon black with an average primary particle size of 100 mμ or more as texture to reduce the frictional resistance of the back coat layer (Unexamined Japanese Patent Publication No. Showa 60-45
No. 938, No. 60-45939, No. 60-25023
No. 60-38725, No. 60-107729,
No. 59-185027, No. 59-223937, No. 57-111828, No. 50-147308, etc.).

However, simply using carbon black based on the particle size of the carbon black does not sufficiently improve running performance and durability.

Also, using inorganic powder and carbon black together (Japanese Patent Application Laid-open No. 1983
-210534, 60-25022, 60-2
No. 5023), there is a method aiming at the synergistic effect, but there is still room for further investigation, and there is a risk that the back coat layer provided to improve the characteristics of the magnetic recording medium will only increase the problems with the medium.

For example, fillers have merits and demerits depending on their hardness, and their selection is important, and it is also necessary to consider the physical properties of the finish, such as the quality of the finish and the quality of counterfeits.

[Purpose of the invention]

In view of the above, an object of the present invention is to provide a magnetic recording medium (magnetic recording medium) which has a back coat with good dispersibility of carbon black contained therein, high film strength, and long durability, and which does not cause cinching or dropout. (hereinafter collectively referred to as magnetic tape).

[Structure of the invention]

The object of the present invention is to contain at least one type of carbon black powder having an average particle size in the range of 20 to 100 mμ, and an inorganic powder having a Mohs hardness of 3 to 6, and having an interlayer friction coefficient of 0.0. This is achieved by a magnetic recording medium provided with a back coat layer having a thickness of 27 or less.

[Function and effect of the invention]

In the present invention, the average particle size of carbon black is selected, and the granularity and film reinforcing effect of inorganic powder particles with a Mohs hardness of 3 to 6 are utilized to improve the strength and durability of the back coat q (hereinafter referred to as BC layer). By comprehensively controlling the dispersed filler, binder, etc., the surface adhesion (friction coefficient) and contact area are adjusted to suppress the interlayer friction coefficient to 0.27 or less. can be eliminated.

Furthermore, by transferring light-shielding carbon black from the magnetic layer to the 80th layer, the electromagnetic properties of the magnetic tape can be improved without reducing the light-shielding properties of the magnetic tape.

To describe the individual configurations of the present invention, first, if the average particle size of carbon black exceeds 100 mμ, the surface roughness becomes large, and the roughness is transferred to the magnetic layer, impairing the electromagnetic properties of the magnetic layer. The dispersibility is poor, and the powder of aggregates falls off, resulting in the occurrence of Dlo.

In the present invention, the particle size of carbon black is 20 to 1
The carbon black may have a single particle size distribution peak between 00 mμ, but it is preferable to use two or more types of carbon black having different distribution peaks.

In addition, when the Mohs hardness of the inorganic powder particles exceeds 6, BC
The transfer of roughness from JI to the magnetic layer becomes severe, and the ball mill used in the production of paint is abraded, and the abraded powder becomes an impurity that causes Dlo, etc., and furthermore, the damage to process members becomes severe.

On the other hand, if the Mohs hardness is 3 or less, the core effect of improving membrane strength is lost, and the membrane strength is reduced by warping.

If the interlayer friction coefficient exceeds 0.27, cinching occurs, resulting in peeling of the 80 layer and abnormal running performance. Furthermore, surface roughness R
a is the center line average roughness of cutoff 0-08mm 0. O1
A range of 0.03 μm is preferred.

Next, the present invention will be explained in detail.

Among the carbon blacks with average particle diameters of 20 to 100 mμ, specific examples of carbon blacks having an average particle size of 20 to 50 mμ include: Manufactured by Columbia Carbon Co., Ltd.; Raven 5250, 1255.1250, 1200, 1
170,1040°1035.1030.1020.8
90.850.825 Manufactured by Capo7; Black Pearls L.

Regal 400, 600.500R, 500, 330,
99 Palcan XC-72, P manufactured by Mitsubishi Chemical Corporation; CF9; # 50, 52.45, 44, 40, 32, 30, 40
00.

M A -100,7,8,11 may be mentioned, the average particle size of which lies between 20 and 50 mμ.

Further, specific examples of coarse particle carbon black having an average primary particle size of 50 to 100 mμ include: Niraben 14,410, 420, 430, and 450 manufactured by Columbia Carbon Co., Ltd.

Inorganic powders having a Mohs hardness of 3 to 6 according to the present invention include silicon oxide, titanium oxide, aluminum oxide, zinc oxide, calcium carbonate, barium carbonate, barium sulfate, calcium sulfate, zinc sulfate, tin oxide, chromium oxide, silicon carbide, Calcium carbide, α-Fe203, kaolin, boron nitride,
Examples include zinc fluoride and molybdenum dioxide.

In the back coat paint formulation according to the present invention, the wt% of the inorganic powder to the carbon black is 2.0 to 2.0.
0.01, more preferably 1.0 to 0.05.

Further, the total weight of the filler including the carbon black and the inorganic powder is 50-500 (Wt), preferably 6O-400v with respect to 1 ooff weight part (wt) of the binder.
It is t.

In the present invention, an organic filler may be used in combination with carbon black and inorganic powder, and benzoguanamine-based and/or melamine-based resin powder is particularly preferred for use in combination with carbon black.

The binder used in the back coat layer is preferably nitrocellulose, and a polyurethane resin may also be used in combination.

By selecting a polyol, the polyurethane resin according to the present invention can contain an ether bond in the polyurethane main chain, a general ester bond in which the adjacent atom is carbon, a carbonate ester bond, or a combination of two or more thereof in addition to the urethane bond. It's okay to stay. Furthermore, for example, fluorine, silicon or sulfone groups may be introduced into the main chain and side chains in order to improve lubricity or dispersibility.

The average molecular weight is preferably 500 to 200,000.

The mixing weight ratio of the polyurethane resin and cellulose resin is 0.
．． 05 to IO30, preferably 0.1 to 5.0.

By using nitrocellulose with a specified molecular weight as described above, it is possible to improve dispersibility, heat resistance, toughness, and block resistance.It also has a small friction coefficient and is extremely effective in preventing interlayer adhesion. It is possible to improve running stability under high temperature and high humidity conditions.

In addition, in terms of productivity, paints containing nitrocellulose disperse filler more quickly than vinyl chloride paints, making the paint itself more stable and less likely to cause filler reagglomeration.

In the present invention, the binder contains polyisocyanate as a curing agent.

Aromatic polyisocyanates that can be used include, for example, tolylene diisocyanate (TDI) and adducts of these polyisocyanates and active hydrogen compounds, and those having an average molecular weight of 100 to 3,000 are preferred.

Examples of aliphatic polyisocyanates include hexamethylene diisocyanate (HMDI) and adducts of these incyanates and active hydrogen compounds. Among these aliphatic polyisocyanates and adducts of these polyisocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3.000 are preferred. Among the aliphatic polyisocyanates, non-alicyclic polyisocyanates and adducts of these compounds and active hydrogen compounds are preferred.

The amount of the polyisocyanate added is 1/20 to 7/10, more preferably 1/10 of the weight of the binder.
-1/2.

Dispersants used in the back coat layer according to the present invention include lecithin, phosphoric esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinic esters, and known surfactants. etc. and these salts, and also,
Salts of polymeric dispersants having negative organic groups (eg -00OH, -PO, H) can also be used. These dispersants may be used alone or in combination of two or more. These dispersants are added in an amount of 1 to 20 wL per 100 wt of binder.

Examples of antistatic agents that may be used include the above-mentioned carbon black, conductive powders such as graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds; natural surfactants such as saponin. ;
Nonionic surfactants such as alkylene oxide, glycerin, and glycidol; higher alkylamines,
Cationic surfactants such as quaternary ammonium salts, pyridine, other heterocycles, phosphoniums or sulfoniums; anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester groups, phosphate ester groups, etc. Examples include amphoteric activators such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like.

In the present invention, it is preferable not to use a commonly used lubricant. The use of conventionally known lubricants increases the coefficient of friction, which may cause abnormal running due to increased torque and reduce running durability.

The back coat paint configured as above has a dry thickness of 0.
．． The coating is applied to a thickness of 1 to 2.0 μm, preferably 0.2 to 1.5 μm.

The magnetic layer according to the present invention may be a coated magnetic layer using magnetic powder, a binder, a dispersant, a lubricant, etc., or a thin film formed by a vapor deposition method, a sputtering method, a vapor deposition method, etc. It may also be a type magnetic layer.

Examples of magnetic materials include γ-Fe203. Co-containing γ-Fe, O, Co coating-Fe, O, Fe, O,
, Goo Fe50. .

Co-coated Feign, oxide magnetic material such as CrO2, e.g. Fe.

Ni, Go, Fe-Ni alloy, Fe-Go gold alloy Fe-AQ gold alloy F-1-Ni alloy, Fe-N1
-P alloy, Fe-N1-Go gold alloy Fe -M
n-Zn alloy, Fe-Ni-Zn alloy, Fe-C
o-Ni-Cr alloy, Fe-C.

N1-P alloy, Go-Ni alloy, Co-P alloy,
Examples include various ferromagnetic materials such as co-Cr alloy and other metal magnetic powders mainly composed of Fe, old metal, Co, and AQ. Additives to these metal magnetic materials include Si, Cu, and Zn.
, Af2. Elements such as P, Mn, and Cr or compounds thereof may be included.

Hexagonal ferrite such as barium ferrite and iron nitride are also used.

Furthermore, conventionally known materials can be used for the binder, curing agent, dispersant, antistatic agent, lubricant, abrasive, and filler used in the magnetic layer.

Solvents to be blended in the back coat and magnetic paint or diluting solvents during application of this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, 70 panol, and butanol; ; Esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol monoacetate; glycol dimethyl ether, glycol monoethyl ether, dioxane,
Ethers such as tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, xylene; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform,
Halogenated hydrocarbons such as dichlorobenzene can be used.

Examples of the support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. Metals such as Cu, A(2, Zn, etc.), glass, boron nitride, silicon carbide, ceramics, etc. can also be used.

The thickness of these supports is approximately 3 to 100 μm, preferably 5 to 50 μm in the case of a film or sheet, approximately 30 μm to 10 mm in the case of a disk or card, and cylindrical in the case of a drum. The type is determined depending on the recorder used.

An intermediate layer for improving adhesion may be provided between the support and the back coat layer or magnetic layer.

The coating method for forming the above layer on the support is as follows:
Air knife coat, blade coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, spray coat 1, etc. can be used, but are not limited to these.

〔Example〕

The present invention will be specifically explained using examples.

Examples 1 and 2 and Comparative Examples (1) to (5) The following formulation I
Thoroughly mix and disperse the magnetic paint using a ball mill, add 6wt of polyfunctional incyanate as a hardening agent, filter through a 1 μm filter, and reverse coat onto a 13 μm thick polyethylene terephthalate base to give a dry film thickness of 4.5 μm. A sample film was obtained by coating with a roll coater. The film was subjected to supercalender treatment.

Next, compositions of different formulations (back coat paints) for each sample shown in Table 1 were dispersed in a ball mill for 24 hours to obtain Barafco-1 paints for each sample. The paint was coated on the back side of the sample film with a dry film thickness of 1.0 using a reverse roll coater.
The tapes were coated to a thickness of .mu.m, dried to form a back coat layer, and slit to a width of 1/2 inch to obtain Example sample tapes 1 and 2 and Comparative Example sample tapes (1) to (5).

Prescription■ (Magnetic paint) (WL)C
O-containing -Feze3100 Polyurethane 8 Vinyl chloride monovinyl acetate copolymer 12 Stearic acid Butyl myristate Stearic acid Alumina Carbon black lecithin Cyclohexanone Methyl ethyl ketone Toluene 0.8 0.5 0.5 0.5 -G Table 1 Prescription n (BC layer paint ) Table 2 (Note) *+ (15mμ), etc. (average particle size) *2
(0.5μm; 4), etc. (average particle size; Mohs hardness) Hon, Seltsuba BTHI/2; Asahi Kasei Ne, N-2304; Nippon Polyurethane Hon, Coronel L; Samples obtained as above Nippon Polyurethane Regarding, its characteristics (note) A
: None, B: Very little, C: Present, D: Somewhat much, E: Much In Examples 1 and 2 containing the carbon black and inorganic powder according to the present invention, the interlayer friction after virgin tape and 200 baths was The coefficient is small, and cinching, bank coat layer scraping, and tape damage are extremely rare. Furthermore, it runs stably. In addition, it has excellent uniform dispersibility, so
The surface roughness can also be made extremely fine, there is no deterioration of Dlo, and the durability is sufficient even in repeated running.

On the other hand, a comparative example (which does not contain the combination of carbon black and inorganic powder according to the present invention and has an interlaminar friction coefficient of 0.27 or more)
1) to (5) lack stable running performance.

Furthermore, it is inferior in terms of chroma S/N and back coat layer abrasion.

Example and Comparative Example Sample measurement method (a) D/O-width 5 psec, depth -1
6dB, and width 15 psec + depth -16d
Number of Dlo occurrences per minute (b) of B Tape damage, shinching, and back coat layer scraping...The tape after running 200 passes was visually evaluated.

(C) Surface roughness: Center line average roughness (d) of cutoff 0-08 mm Coefficient of interlayer friction: Using the same equipment as in (c) at 23°C and 160% RH, 20
g, wrap it around a stainless steel drum with a diameter of [32+ nm] with the magnetic layer facing up, and place one sample tape on top of it.
It was wound at 80° and run on the BC surface at 0.2 cm/sec, and the exit tension after one minute was measured and calculated from equation (1).

(e) Rio? S/H measurement/HR-71,
00 (manufactured by Victor Company of Japan), 4.5 MII z was recorded at the maximum recording current, and the noise voltage during reproduction was measured.

Claims (1)

[Claims] At least one particle having an average particle size in the range of 20 to 100 mμ
Contains seed carbon black powder and inorganic powder with a Mohs hardness of 3 to 6, and has an interlayer friction coefficient of 0 with the magnetic layer.
．． A magnetic recording medium provided with a back coat layer having a thickness of 27 or less.