JPS62162227A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the titled medium having a high light shielding property, small surface roughness, reduced interlayer friction with a magnetic layer, and excellent traveling durability by incorporating carbon black having 100-300m<2>/g specific surface (BET value) and <=4pH into the backcoat layer. CONSTITUTION:Carbon black having 100-300m<2>/g BET value and <=4pH and, as required, a mixture with org. or inorg. power as a filler are dispersed and suspended to obtain a paint which is coated on a carrier. The resistance to the edge damage and traveling stability are affected by the distribution of the filler and the distribution in the coated film resulting from the difference in sp.gr. with the mixed filler. Accordingly, the surface resistivity of the magnetic layer is preferably adjusted to 10<7>-10<14>OMEGA.cm, and the surface resistivity of the back layer is controlled to 10<8>-10<15>OMEGA.cm. Polyurethane having wear resistance is preferably used as the binder. The recording medium having high adhesive force to other substances, which resists repeated stress and is mechanically tough, and having excellent wear resistance and weatherability can be obtained.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to magnetic recording media, particularly magnetic tape.

(Background of the Invention) As magnetic recording becomes more dense, noiseless, and lasts longer, and magnetic recording equipment becomes more sophisticated, smaller, and thinner, magnetic recording media (hereinafter referred to as magnetic tape) are required to meet the following requirements. Performance is also becoming wider and higher.

Particularly in video tapes, as noise-free technology (higher S/N) progresses, the surfaces of the support and magnetic layer need to be smoother. In addition, as video tapes become narrower and longer, the tape becomes thinner, resulting in a loss of tape toughness.
Edge damage is likely to occur during high-speed feeding, high-speed winding or loading, and 7-inch roll length in a video recorder.

Furthermore, due to the electrification on the back side of the tape, clumps, fallen magnetic powder, and fillers adhere to the tape and are transferred to the magnetic layer during the tape winding operation or other occasions, resulting in noise and dropouts.

In order to eliminate such poor performance of the magnetic tape, a back coat layer using a suitable filler and binder is provided.

Non-magnetic inorganic powder is used as the filler in Japanese Patent Application Laid-open No. 57-1.
No. 30234, No. 58-161135, No. 57-53
No. 825, No. 58-2415, Special Publication No. 50-3927
The surface smoothness is improved by roughening the surface.

On the other hand, in the Vl (S type video deck), the end is detected based on the degree of light transmission of the videotape, so it is necessary to give the tape a light transmittance below a predetermined value (light shielding property above a predetermined value). In the case of an 8 ml videotape, it is necessary to compensate for the lack of light-shielding property provided by the magnetic layer alone by incorporating carbon black dispersed in the back coat layer.

Filling the back coat layer with the filler described above increases the surface smoothness and toughness of the tape, improves runnability, edge folding, etc. Fillers with particularly high Mohs hardness improve running durability, and the bank coat layer itself improves. On the other hand, there is less wear and tear on the parts arranged in the video deck's tape circuit ((wear and tear).

cause damage. Furthermore, if an inorganic compound filler with a high Mohs' hardness is used and the surface is rough to a large extent, the roughness of the surface will be imprinted on the magnetic layer as a replica, causing unevenness on the surface and deteriorating the electromagnetic conversion characteristics.

Furthermore, in the case of commonly used inorganic compound fillers, K can hardly contribute to increasing the light-shielding properties of the back coat layer. On the other hand, if carbon black, which is highly effective in increasing the light-shielding property, is used as a filler, the back coat layer, which generally has a thickness of 0.3 to 2 μm, can greatly contribute to the light-shielding property of the magnetic tape. Moreover, carbon black can be significantly reduced from the magnetic layer by that much, and the filling rate of magnetic powder can therefore be increased, contributing to improved electromagnetic conversion characteristics. Furthermore, if the conductivity is increased, the adhesion of electrostatic dust and debris can be suppressed better than with K, and dropout can be prevented.

However, when carbon black is used as a filler, running durability decreases, problems such as wear and tear of the back coat layer and edge breakage worsen, and the productivity of bank coat paints greatly deteriorates due to poor dispersibility of carbon black. do.

The technical contradictions mentioned above have not yet been satisfactorily resolved.

(Objective of the Invention) The object of the present invention is to solve the above-mentioned technical contradictions related to the back coat layer. ,+31
To provide a back coat formulation that has low friction with the magnetic layer and does not cause loosening of the winding (so-called cinching phenomenon); and (4) no scuffing of the back coat and excellent running durability.

Another object of the present invention is to provide a high quality magnetic tape having a back coat layer formed of a coating material based on the back coat formulation.

(Structure of the Invention) As a result of earnestly attempting to eliminate the above-mentioned technical compatibility in violation of the purpose of the present invention, it has become clear that the target performance can be changed by using carbon black that has a specific characteristic range. Became.

That is, in a magnetic recording medium having a magnetic layer on one side of a nonmagnetic support and a back coat layer on the other side, the back coat layer has a specific surface area (BET value) of 100 to 300 r.
The object of the present invention can be achieved by a magnetic recording medium characterized in that it contains carbon grains having a rl/l and a pH of 4 or less.

In addition, as an aspect of the present invention, the carbon blank has a T value of 100 to 300 i/! 1, preferably 100-200
m/g.

In addition, the surface electrical resistivity of the back coat layer side is 107 to 10
14Ω·m1 is preferably to8 to 1014Ω·m, more preferably 1011 to 10I4Ω·m. In addition, on the magnetic layer side, it is 108 to 1015Ω・2, preferably 10
9 to I QIS Ω·cm.

When the surface resistivity is below the lower limit, edge damage is likely to occur, and when it is above the upper limit, the charging property becomes thick (dropout may easily occur, etc.), and other problems may occur.

Furthermore, it is preferable that the binder of back coat N contains a P tn thread resin and a polyurethane resin, and that polyinsyanate is added in a weight ratio of 0.45 or more based on the amount of polyurethane resin.

Generally, acidic carbon black is said to have excellent dispersibility. In particular, when the BET value is 100 m1/g or less, carbon black with a large specific axial particle size is dispersed on the coating film, which allows high-speed winding and
Although winding loosening during fast forwarding is improved, the surface roughness of the back layer is large, and as a back layer for magnetic media that requires shorter wavelength recording, roughness is likely to be transferred to the magnetic layer (this is a drawback). It started to become.

On the other hand, if the BET value is 300 m'/9 or more,
Although dispersion becomes somewhat difficult, a back layer containing carbon black within the above range as a filler has the advantage of being uniquely resistant to edge damage during loading and 77 q-denging. However, when focusing on overall driving performance, the coating film has a surprisingly rough surface.
Living room friction increases and tends to induce loosening of the winding.

Carbon black with pH≦4 and BET value of 100 to 300 m'/g is not as strong against edge damage as carbon blank with BET value of ≧300 m'/, 9, but it has excellent dispersibility and is effective in forming coatings. It has been found that the surface roughness can be adjusted to a very small level, and interlayer friction with the magnetic layer can be appropriately reduced.

By using this carbon black in combination with other fillers in an appropriate ratio and adding a certain amount of polyisocyanate or more, a back coat layer with excellent running durability and less edge damage during loading and loading is created. The fact that it is possible to obtain a magnetic medium also
As a result of the research, we were able to add new knowledge.

Strength against edge damage, other running stability,
It does not depend on the simple quantitative ratio of carbon black and mixed filler, but depends on the dispersion state of the filler and the distribution state in the coating film due to the difference in specific gravity between the filler and the mixed filler. From this point of view, in the present invention, the surface resistance 107 to 1014 of the magnetic layer is
Ω・(7), surface resistance of back layer 108~1015Ω・
Preferably it is α.

Next, the present invention will be explained in more detail.

The back coat layer according to the present invention is formed by coating a support with a back coat paint in which carbon black is dispersed and suspended in a binder, and the back coat paint contains organic and inorganic fillers in addition to carbon blank. You may.

Furthermore, conventionally used techniques and additives may be used to adjust electromagnetic characteristics, physical properties, or productivity.

Further, the dispersibility of carbon black is good and stable when the pH measured in a slurry with water is 4 or less, and there is little re-agglomeration and good stagnation and dispersion.

If the dispersibility in the paint is good, the light shielding efficiency is high, the conductivity and toughness are improved, and problems such as edge bending are reduced.

In the present invention, as the filler used in combination with carbon black, organic powder or inorganic powder is used or mixed.

The organic powder used in the present invention is preferably acrylic styrene resin, benzoguanamine resin powder, melamine resin powder, or phthalocyanine pigment, but includes polyolefin resin powder, polyester resin powder, polyamide resin powder, or polyimide resin. Powder, polyfluoroethylene resin powder, etc. can also be used, and inorganic powders include silicon oxide, techno oxide, aluminum oxide, calcylanocarbonate, barium sulfate, zinc oxide, tin oxide, aluminum oxide, pm oxide, silicon carbide, and carbide. Calcium, α-Fe
203, talc, kaolin, aluminum sulfate, boron nitride, zinc fluoride, and molybdenum dioxide.

7 for the total solid content of the filler in the back coat layer! The I:1tlt: ratio is preferably from 0.2 to 09, more preferably from 03 to 0.7.

As the binder used in the back coat layer according to the present invention, abrasion-resistant polyurethane can be mentioned. It has strong adhesion to other substances, is mechanically strong to withstand repeated stress or bending, and has good abrasion and scratch resistance.

Furthermore, if a cellulose resin and a vinyl chloride copolymer are also contained in addition to polyurethane, the dispersibility of the magnetic powder in the magnetic layer will be improved and its mechanical strength will be increased. However, if the cellulose resin and vinyl chloride copolymer are used alone, the layer will become too hard, but this can be prevented by containing the above-mentioned polyurethane.

Usable cellulose resins include cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester, and the like. The vinyl chloride copolymer described above may be partially hydrolyzed. Preferable examples of the vinyl chloride copolymer include copolymers containing vinyl chloride and vinyl acetate.

Phenoxy resins can also be used.

Phenoxy resin has advantages such as high mechanical strength, excellent dimensional stability, good heat resistance, water resistance, chemical resistance, and good adhesiveness.

These advantages are complementary to the above-mentioned polyurethane, and the tape's physical properties can be significantly improved in stability over time.

Furthermore, in addition to the binders described above, mixtures of thermoplastic resins, thermosetting resins, reactive resins, and electron beam curable resins may be used.

Among the binders, a combination of polyurethane resin and cellulose resin, particularly dinitrocellulose, is preferred as the resin used for the back coat layer. The mixing weight ratio of both is 9/r to 2/8, preferably 8/2 to 3/7, with polyurethane as the molecule.

In the present invention, polyisocyanate can be included as a curing agent in the binder.

Aromatic polyisocyanates that can be used include, for example, tolylene diincyanate (TDI) and adducts of these polyincyanates and active hydrogen compounds, and those with 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 incyanates and active hydrogen compounds.

Among these aliphatic polyincyanates and adducts of these polyincyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Among the aliphatic polyinsyanates, non-alicyclic polyinsyanates and adducts of these compounds and active hydrogen compounds are preferred.

The amount of the polyinsyanate added to the binder is 0.1-0.7 of the sum of both weights, particularly preferably 0.
．． It is 15-0.5.

The paint used to form the back coat layer may contain additives such as a dispersant, a lubricant, an organic matting agent, an antistatic agent, and the like, if necessary.

Dispersants used in the back coat layer according to the present invention include lecithin, phosphoric acid ester, 7ξmino compound, furkyl sulfate, fatty acid amide, higher alcohol, polyethylene oxide, sulfosuccinic acid, sulfosuccinic acid ester, and known surfactants, etc. and their salts,
Also, negative organic groups (e.g. -COOTI, -Po311
) can also be used. These dispersants may be used alone or in combination of two or more. These dispersants are binders to
It is added in an amount of 1 to 20 parts by weight per oz.

In addition, as lubricants, fatty acids such as silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, palmitic acid, oleic acid, stearic acid, behenic acid, and miljstic acid, and butyl stearic acid are used. Fatty acid esters such as ester, octyl palmitate, and octyl myritate can also be used.

These lubricants contain 100 parts by weight of binder;
．． It is added in an amount of 0.02 to 20 parts by weight.

Antistatic agents that may be used include carbon black, conductive powders such as graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-stinmon oxide compounds, and natural surfactants such as saponin. ;
7-ion surfactants such as fullkylene oxide, glycerin, and glycidol: higher alkyl 7-mines,
Cationic surfactants such as quaternary ammonium salts, pyridine, other heterocycles, phosphoniums or sulfoniums: 7-ion surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester groups, phosphate ester groups, etc. Agents: Examples include amphoteric activators such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of 7-mino alcohols, and the like.

The back coat paint configured as above has a dry thickness of 0.
．． The coating is applied to a thickness of 3 to 2.0 μm, preferably 0.5 to 1.5 μm.

The magnetic layer according to the present invention may be a dispersed magnetic layer in which magnetic powder or the like is dispersed or suspended in a binder, further dispersed, or using a lubricant, etc., or may be formed by a vapor deposition method, a Suhanotar method, or a paper deposition method. The magnetic layer may be a thin film type magnetic layer formed by a method or the like.

Examples of magnetic materials include r -Fe2O3, Co-containing r -Fe2O3, Co-coated 1-Fe2O3, Fe3
O4, CO-containing Fe3O4, Co-coated Fe5r4, Cr
Oxide magnetic substances such as O2, e.g. Fe, Ni, Co, F
e-Ni alloy, Fe-Co alloy, Fe-N1-P alloy,
Fe-Ni-Co alloy, Fe-Mn-Zn alloy,
Fe-Ni-Zn alloy, FeCo-Ni-Cr
alloy, F'e -Co -Ni-P alloy, Co-Ni alloy, Co-P alloy, Co-Cr alloy etc. Fe, Ni,
Examples include various ferromagnetic materials such as metal magnetic powder containing Co as a main component. Additives to these metal magnetic materials include Si, Cu, Zn, A/, P, Mn, Cr.
It may contain elements such as or compounds thereof.

Also used are 60,000-grade ferrites such as barium ferrite, and iron nitride.

In addition, binders, curing agents, dispersants, and
As for the lubricant, antistatic agent, and filler, those explained for the bank coat layer 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, flundum, artificial flundum, diamond, artificial diamond,
Garnet, emery (main ingredients: corundum and magnetite), etc. are used. These abrasives have an average particle size of 0.05~
A size of 5 μm is used, particularly preferably a size of 0.5 μm.
It is 1 to 2 μm.

These abrasives are used in an amount of 1 to 20 parts by weight per 100 parts by weight of the binder.
It is added in a range of parts by weight.

Solvents blended in the above bank coat and magnetic paint or diluting solvents during application of this paint include chthons such as acetone, methyl ethyl ketone, methyl imbutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propatool, butanol, etc. Esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol senoacetate, etc.: glyfur dimethyl ether, glycol monoethyl ether, dioxane,
Ethers such as tetrahydrofuran: aromatic hydrocarbons such as benzene, toluene, xylene; halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, RI:Ip form, dichlorobenzene, etc. can be used. .

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate, but metals such as Cu1Al and Zn,
Glass, BN.

Ceramics such as Si carbide, porcelain, and earthenware can also be used.

The thickness of these supports is about 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm,
In the case of a disk or card shape, it is about 30 μm to 10J11, and in the case of a drum shape, it is used in a cylindrical shape, and the shape 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 coat, grade coat, air knife coat, squeeze coat, impregnated foot, reverse roll foot, transfer roll coat, gravure coat, kiss foot, cast coat, spray foot, etc. can be used, but are not limited to these.

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

Example 1 A magnetic paint having the following formulation was thoroughly mixed and dispersed using a ball mill, 5 parts of polyfunctional incyanate was added as a hardening agent, and 1
The mixture was filtered through a 13 μm thick polyethylene terephthanate base and coated with a reverse rule coater to a dry film thickness of 5 μm to obtain a sample film. The film was subjected to supercalender treatment.

Next, the composition of backcoat paint formulation (2), which was different for each sample shown in Table 1, was dispersed in a ball mill for 5 hours to obtain a backcoat paint for each sample. The paint was applied to the back side of the sample film using a reverse rule coater to a dry film thickness of 1.0 μm, and dried to form a bank coat layer on each.
Example sample tapes 1 to IO were slit to a width of 2 inches.
1 and Comparative Example Sample Tapes (1) to ■) were obtained.

Formulator (magnetic paint) (parts by weight) Co containing r
-Fe203100 Polyurethane 12 Vinyl chloride monovinyl acetate copolymer 8 Dutyl stearate 08 Myristic acid 0.8 Alumina 5 Carbon black 5 Lecithin 4 Cyclohexanone 100 Methyl ethyl ketone 50 Toluene 10 Prescription ■ (Back coat paint) Carbon black A6 used for back coat paint ■ ~■
In addition to the composition shown in Table 1, the same amounts of 200 parts by weight of methyl ethyl ketone and 200 parts by weight of toluene were used in the back coat paint formulation.

The condition of the tape was checked after 400 repeated running tests on the above sample, and the results are shown in Table 2. observation.

(Good) ◎○Δ× (Poor) Winding appearance: (Scinching occurs) (No occurrence) ◎○Δ× (Occurred) From the above results, there is no transfer of roughness to the magnetic layer and continuous running is repeated. Examples show that the back surface is not scraped, the winding does not loosen, and the light transmittance is low.
．． It is 6. Other than that, f7) Those using C0B (carbon black) have problems with back surface scraping or winding appearance, and those that do not use C1B are undesirable due to high light transmittance.

Furthermore, in combinations of C, B and other inorganic fillers other than those in the examples, the difference from the examples is particularly significant in terms of light transmittance. This is considered to be because the dispersion state of C0B is inferior to that of the example.

Claims (3)

[Claims] (1) In a magnetic recording medium having a magnetic layer on one side of a nonmagnetic support and a back coat layer on the other side, the back coat layer has a specific surface area (BET value) of 100 to 300 m.
A magnetic recording medium characterized by containing carbon black having a pH of 4 or less. (2) The surface electrical resistivity of the back coat layer side and the magnetic layer side of the magnetic recording medium is 10^7 to 10^1^4, respectively.
The magnetic recording medium according to claim 1, which has a resistance of Ω·cm and 10^8 to 10^1^5 Ω·cm. (3) The binder of the back coat layer contains a cellulose resin and a polyurethane resin, and a polyisocyanate is added at a weight ratio of 0.45 or more to the polyurethane resin. Second
Magnetic recording medium described in Section 1.