JPS6314324A - Magnetic recording medium provided with carbon black-containing back coat layer - Google Patents

Abstract

PURPOSE:To prevent the generation of tape damages after repeated travelings by incorporating two kinds of carbon blacks which are specified in specific surface area and oil absorption as nonmagnetic powder into a back coat layer. CONSTITUTION:This magnetic recording medium has a magnetic layer on one face of a substrate and has the back coat layer contg. a binder and nonmagnetic powder on the other face of the substrate. The back coat layer contains the carbon black having 50-900m<2>/g specific surface area and 40-110ml(DBP)/100g oil absorption and the carbon blacks having 15-90m<2>/g specific surface area and 110-500ml(DBP)/100g oil absorption as well as 10-50m<2>/g specific surface area and 20-110ml(DBP)/100g oil absorption. The running property and durability of a magnetic tape are thereby improved.

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. Of 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 placed on the id pole or id 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 constantly running, and its winding must be uniform so that it can be reused repeatedly. Moreover, 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 balls, etc. must be suitable for running, and must also have an e-electrical prevention effect. Ru.

The surface of the magnetic layer is finished to be smooth in order to improve the sensitivity, especially the output in the high frequency range, and to prevent the sliding condition of the magnetic tape against the magnetic head from changing. 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 running a magnetic tape with a video tape, not only the front side of the magnetic tape but also the back side is rubbed by the above-mentioned id poles and id rolls, so if the running performance and durability of the back side of the magnetic tape are not good, Excessive tension is applied to the running magnetic tape, which causes the magnetic layer to rub excessively against the magnetic head, which not only causes damage to the magnetic layer and flaking of magnetic powder in the magnetic layer, but also
The strength of the winding tension of the magnetic tape fluctuates, the winding pressure fluctuates, the winding shape becomes disordered, the edges of the tape become uneven, and when the tape is reused, the running of the tape becomes uneven. When these things happen, skew, jitter, S/
Images such as N or electromagnetic characteristics deteriorate.

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

For example, there is one in which the tatmt layer contains S rocky powder. This is done by roughening the surface of the backfoot layer to reduce the area of contact with the idle ball and the like, thereby reducing the coefficient of friction. For example, JP-A-57-1302
No. 34, JP-A-58-161135, JP-A-57-53,825, and JP-A-58-2415 all show examples using 811-free powder; Many of these have limited particle sizes.

Products using carbon black instead of the above-mentioned inorganic powder have also been proposed; 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, but since the average particle size of the carbon black used is 10 to 20 zμ, The dispersibility of the tape is extremely poor, and the aggregated particles give the backcoat layer formed using this dispersion a rough surface, and the aggregated particles do not have a strong binding force with the paint, so 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 aggregated particles may cause unevenness in the magnetic layer, and even if carbon bras with such small particle diameters are used, the above magnetic properties cannot be achieved. It is difficult to achieve an average roughness that does not cause unevenness in the layer, and the surface tends to become excessively rough.

Furthermore, as a means to reduce the frictional resistance of the backcoat layer, attempts have been made to use a combination of carbon black with a relatively small average-order particle size of 10 to 60μ and carbon black with an average-order particle size of 100μ1 or more. Kaisho 60-459
No. 38, No. 60-45939, No. 60-25023, No. 60-38725, No. 60-107729, No. 59-185027, No. 59-223937, No. 5
7-ml No. 828, No. 50-147308, etc.). However, a combination of particles that focuses solely on particle size is not sufficient to improve runnability and durability.

[Purpose of the invention]

In light of the above circumstances, the objects of the present invention are to: 1) obtain a bank coat layer that has a small coefficient of dynamic friction, low tape density, and does not cause damage to the tape after repeated running, 2) has excellent uniform dispersibility, and To obtain a video tape which can make the roughness of the coat surface fine and has good chroma S/N characteristics without transferring the roughness of the puncture coat layer to the magnetic layer.

[Structure of the invention]

The object of the present invention is to provide a magnetic recording medium having a magnetic layer on one side of a support and a back coat layer containing a binder and a non-magnetic powder on the other side of the support. Carbon black (A>) with a specific surface area of 50 to 900z2/y and oil absorption of 40 to 110z4 (DBP)/100g and a carbon black with a specific surface area of 15 to 90z2/l? and an oil absorption of 110 to 500 mouths (DBP) /100. and specific surface area force 0-50z2/l?t' oil absorption amount 20-11
0zf(DBP)/100yT carbon black (
This is achieved by a magnetic recording medium characterized by containing B).

Next, the present invention will be explained in detail.

In accordance with the purpose of the present invention, the study focused on the combination of various characteristics of the carbon blank, and the oil absorption amount indicated using the specific surface area (BET value) and dibutyl 7 talley (DBP) rather than the average particle size. I learned that this is mainly related to objective characteristics.

In other words, to improve durability, specific surface area (s) with excellent uniform dispersibility is required.
is 50-900+'/y and oil absorption 1(a) is 40-110
Carbon blacks in the range x1/1009 (range A in Figure 1) are preferred.

On the other hand, in order to reduce the dynamic frictional resistance, the specific surface area (s) that makes it easy to create so-called stractures should be 15 to 90w2/
g and the oil absorption amount (a) is in the range of 110-500f/100y, and 3 is in the range of 10-50w2/g and a is 20-11 (hj'
It has been found that carbon blacks in the range consisting of /100y (range B in Figure 1) are preferred.

However, it has been found that when carbon blacks in both ranges are used together, the effects of each are not canceled out and exhibit their effects as additives.

Specific examples of carbon black in the range A are: manufactured by Columbia Carbon Company; Raven 1035.1255.1000.200014
00, and 66D1 manufactured by Kyabot; Black Pearls 1000.900, 880.130
Examples include: 0 and L1 Palcan 9, Monarch 8001 manufactured by Mitsubishi Chemical Corporation; CF-9, #90, I4000, etc.

Further, specific examples of carbon blacks falling within the above range B include: manufactured by Columbia Carbon Company; Raven 410.420.450.99 and 14; manufactured by Cabot; Schooling\11 NS;

Denki Kagaku Co., Ltd. HS-100, Mitsubishi Kasei Co., Ltd.
#208. #22B%$3500, #5
5, #35, #56, Asahi Carbon Co., Ltd.; HS-500, and the like.

In the back coat paint formulation according to the present invention, the weight to total solid weight ratio of all fillers including those other than carbon black is 0.10 to 0.80, preferably 0.20 to 0.70.

Moreover, organic or inorganic fillers may be used in combination with fillers other than carbon black.

All of the various resins conventionally used for magnetic tapes can be used as the binder, but polyurethane resins and fiber i'X resins to which polyincyanate is added are particularly preferred.

Furthermore, improving physical properties, electromagnetic conversion characteristics, and productivity,
Various conventionally used additives may be added to improve the performance.

As the organic filler used in combination with the carbon black, acrylic styrene resin, benzoguanamine resin powder, melamine resin powder, and 7-talocyanine pigment are preferable, but polyolefin Ml (fat powder, polyester resin powder, polyamide resin Examples include powder, polyimide resin powder, boria) ethylene 84 fat powder, and the like.

In particular, benzoguanamine-based and/or melamine-based A1 fat powders are preferred for use in combination with carbon black.

In addition, inorganic powders include silicon oxide, titanium oxide, aluminum oxide, calcium carbonate, barium carbonate, barium sulfate, calcium sulfate, zinc sulfate, zinc oxide, tin oxide, chromium oxide, silicon carbide, calcium carbide, CrF.
Examples include ezO1, talc, kaolin, boron nitride, zinc fluoride, and molybdenum dioxide.

Polyurethane flfJ used in the back coat layer
]W is synthesized by the reaction of a polyol and a polyisocyanate, but the polyurethane resin according to the present invention can be synthesized by selecting a polyol to form a general polyurethane resin in which the polyurethane main chain has an ether bond and the adjacent atom is carbon. ester bond, carbonate ester bond, or two of them
A combination of two or more may be included in the urethane bond.

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.

As the miscellaneous resin according to the present invention, cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester, etc. can be used. Cellulose ethers include methylcellulose, ethylcellulose, propylcellulose, isopropylcellulose, butylcellulose, methylethylcellulose, methylhydroquine ethylcellulose, ethylhydroxyethylcellulose, carboxymethylcellulose, carboxymethylcellulose sodium [, lnitroxyethylcellulose, benolcellulose, cyano] ethyl cellulose, vinyl cellulose,
Nitrocarboxine methylcellulose, aminoethylcellulose, aminoalcoholulose, etc. can be used. No cellulose (as the Taibo ester, nitrocellulose, cellulose sulfate, cellulose y4 acid, etc. can be used. Also,
Examples of cellulose organic acid esters include acetyl cellulose, propionyl cellulose, butyryl cellulose, methacryloyl cellulose, talol acercetylulose,
β-oxyprobionyl cellulose, benzoyl cellulose, p-toluenesulfonate cellulose, acetylpropionyl cellulose, acetyl butyryl cellulose, etc. can be used. Among these cellulose resins, nitrocellulose is preferred.

The mixing weight ratio of the polyurethane resin and cellulose resin is 0.
．． 05 to 10.0, preferably 0.1 to 5.0.

By using cellulose (fat, especially nitrocellulose) as in the present invention, it is possible to improve heat resistance, toughness, and stiffness blocking properties, and the coefficient of friction is small, preventing interlayer adhesion.
This has a remarkable effect and can improve running stability, especially in high temperature and high humidity conditions.

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

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

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

Examples of aliphatic polyisocyanates include hexamethylene diisocyanate (HMDI) and adducts of these isocyanates 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 to the binder is particularly preferably 0.05 to 0.7 of the sum of their weights.
It is 10-0.5.

Further, the surface roughness of the backfoot layer according to the present invention is preferably 0.05 μm or less in terms of center line average roughness (Ra) of cut off O, 08zz in terms of running properties and electromagnetic conversion characteristics. .

Dispersants used in the back coat layer according to the present invention include lecithin, phosphate esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinates, known surfactants, etc. and salts thereof, and negative aged groups (e.g. -COOH, -PO.11
) can also be used.

These dispersants may be used alone or in combination of two or more.

These dispersants are used in an amount of 1 to 2 parts by weight per 100 parts by weight of the binder.
It is added in an amount of 0 parts by weight.

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. ; 7-ion surfactants such as alkylene oxide, glycerin, and glycidol; higher alkyl amines,! Cationic surfactants such as quaternary ammonium salts, birinone, other heterocycles, phosphoniums or sulfoniums; carboxylic acids, sulfonic acids, phosphoric acids,
Examples include 7-ion surfactants containing acidic groups such as sulfate ester groups and phosphate ester groups; amphoteric surfactants such as amino acids, amine/sulfonic acids, and sulfuric or phosphoric esters of amino alcohols.

The uniqueness of the present invention is that by using a lubricant that is different from the conventional lubricant instead of a commonly used lubricant, the coefficient of friction increases, and the increase in torque causes abnormality in running and reduces running durability. .

The back coat paint planted as described above has a dry thickness of 0.
．． It is coated in an amount of 1 to 2.0 μl, preferably 0.2 to 1.5 μl.

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-Fe2O3, Co-containing-Fe20=, Co-coated-Fe, 0. , Fe, 0. ,
Co-containing Fe50<, Co-coated oxide magnetic materials such as FezO4, Cr0z, etc., such as Fe, Ni, Co, Fe-old alloy, Fe-Co alloy, Fe-^! alloy, F- to l-old alloy, Fe-old-P alloy, Fe-Ni-Co alloy, Fe-
Mn-Zn alloy, Fe-Ni-Zn alloy, Fe-Co
-N 1-Cr alloy, Fe -Co -N i-P alloy, Co-Ni alloy, Co-P alloy, Co-Cr alloy, etc. Various metal magnetic powders mainly composed of Fe, old, co, ^l, etc. Examples include ferromagnetic materials.

Additives to these metal magnetic materials include Si, Cu,
Zn, ^1. 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, and the binder, hardening agent, dispersant, antistatic agent, and filler used in the magnetic layer are those explained for the back coat layer above. can.

Also, conventionally used lubricants can be used.

Furthermore, an abrasive can be added if necessary.

Abrasives that may be used include commonly used materials such as fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial diamond,
Garnet, emery (main components: frundum and magnetite), etc. are used. These abrasives have an average particle size of 0.05μI
A particle size of II to 5 μl is used, particularly preferably 0.1 to 2 μl. These abrasives are magnetic powder 100%
It is added in an amount of 1 to 20 parts by weight.

The solvents to be added to the back coat and magnetic paint, or the diluting solvents used when applying this paint, include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propatool, and phthanol. ; Esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol monoacetate; glycol dimethyl ether, glycol monoethyl ether, nooxane,
Ethers such as tetrahydro-7rane; aromatic hydrocarbons such as benzene, toluene, xylene; methylene chloride, ethylene chloride, tetrachloride U! , chloroform, halogenated hydrocarbons such as sochlorobenzene, etc. can be used.

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-7-talate, polyolefins such as polypropylene, cellulose derivatives such as cellulose 177 acetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. Metals such as Zn, glass, BN, Si carbide, ceramics such as porcelain, ceramics, etc. can also be used.

The thickness of these supports is approximately 3 to 100 μl in the case of a film or sheet, preferably 5 to 50 μl, approximately 30 μl to 10 μl in the case of a disk or card, and approximately 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 doctor foot, blade coat, air knife foot, squeeze coat, impregnated foot, reverse roll coat, trans7 roll coat, gravure foot, kiss coat, cast coat, spray coat, etc. can be used, but are not limited to these.

(Example) The present invention will be specifically explained using examples.

Examples 1 to 11 and Comparative Examples (1) to (4) Magnetic paints of the following formulation I were sufficiently mixed and dispersed in a ball mill, 5 parts of polyfunctional incyanate was added as a hardening agent, and 1 μl filtered! The mixture was applied to a polyethylene terephthalate base having a thickness of 13 μl using a reverse roll coater to give a dry film thickness of 4.5 μl to obtain a sample film.

The film was subjected to supercalender treatment.

Next, a composition of formula (1) (back coat paint), which was different for each sample shown in Table 1, was dispersed in a ball mill for 5 hours to obtain a back coat paint for each sample. The paint was applied to the back side of the sample IT1 film using a reverse roll coater to a dry film thickness of 0.8μ, dried to form a packfoot layer on each film, and slit into a 172 inch width to form Example Sample Tape 1.
-11 and comparative example sample tapes (1) to (4) were obtained.

Prescription ■ (Magnetic paint) (Parts by weight) Co
Contains - Fe203 100 Polyurethane 12 PVC-vinyl acetate copolymer 8 Butyl stearate 0.8 Myristic acid 0.8 Alumina
5 Carbon black 5 Lecithin 4 Ncrohexane 100 / Thylethyl ketone 50 Toluene 10 (16゛Cuゝ゛, 7;)' The properties of the Vernon sample and 200 Bath sample obtained as described above were checked, and the results were as follows. are shown in Table-3.

Example 1 containing carbon black according to the present invention
Samples No. 1 to 11 have a small coefficient of friction on the virgin tape and after 200 passes, and there is very little abrasion of the back coat layer and very little damage to the tape. Furthermore, since the running is stable, the skew and jitter characteristics are also excellent.

In addition, because it has excellent uniform dispersibility, it is possible to make the surface roughness extremely fine, and there is no deterioration of chroma S/H.
It also has sufficient durability in repeated running.

On the other hand, Comparative Examples (1) to (4) that do not contain the combination of carbon blacks according to the present invention have extremely high coefficients of friction;
It lacks stable running performance and has poor skew and chroma characteristics. Further, (2) to (4) have poor uniform dispersibility and are very poor in terms of chroma S/N and back coat layer abrasion.

[Brief explanation of the drawing]

The fpJ1 diagram shows the relationship between the specific surface area and oil absorption amount of carbon black according to the present invention. Applicant Konishiroku Photo Industry Co., Ltd. Figure 1

Claims (1)

[Claims] In a magnetic recording medium having a magnetic layer on one side of a support and a back coat layer containing a binder and non-magnetic powder on the other side of the support, the non-magnetic powder has a specific surface area of 50 ~900m^2/g, oil absorption 40~110
ml(DBP)/100g of carbon black (A), specific surface area is 15-90m^2/g, oil absorption is 110-
500ml (DBP)/100g and specific surface area 10~
Oil absorption amount is 20-110ml at 50m^2/g (DBP)
/100g of carbon black (B).