JPS6273421A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To eliminate the troubles in the physical property of a film and the unstable traveling at high temp. and humidity by composing the nonmagnetic powder of at least one kind among magnesium carbonate, barium carbonate, calcium sulfate and zinc sulfate each having specified mean particle diameter and specifying the thickness and surface roughness of the backcoat layer. CONSTITUTION:The magnetic powder is composed of at least one kind among magnesium carbonate, barium carbonate, calcium sulfate and zinc sulfate each having 0.01-0.8mum mean particle diameter, the thickness of the backcoat layer is preferably regulated to 0.5-1.2mum and the average surface roughness Ra on the center line is preferably controlled to 0.025-0.035mum. When the mean particle diameter of the magnesium carbonate, etc., is at >0.8mum, powder is excessively released and cinching is caused by a sudden start and a sudden stop at <0.01mum. Meanwhile, when the thickness of the backcoat layer is at >1.5mum, a cupping phenomenon wherein the medium is spirally curled in the lengthwise direction is caused, hence the contact with a head is disturbed and the electromagnetic transducing characteristic is deteriorated.

Description

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

BACKGROUND OF THE INVENTION Magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks are widely used in the audio, video, and combiator fields. Among these, for example, regarding magnetic tape in the video field, magnetic tape stored in a cassette is used to record and play back images.
This cassette is mounted on a video deck, and the tape runs along a route while its front and back sides are rubbed by guide balls and guide rollers, and is rubbed and scanned by a magnetic head.

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 when the magnetic tape runs on a circuit.

However, the other side of the magnetic layer of the magnetic tape has a similar effect on the above fluctuations, and when the running performance and durability of the other side are poor, excessive tension is applied to the running magnetic tape, causing damage to the magnetic layer. Not only does powder drop occur, but the winding shape is disturbed, the edges of the tape become uneven, and the image or electromagnetic conversion characteristics such as skew, jitter, and RPM S/N deteriorate.

Therefore, a back coat layer is provided on the back side of the magnetic tape support to improve running properties and durability against guide balls, guide rolls, guide rollers, etc. In this back coat layer, K is non-magnetic. There is one in which the layer contains inorganic powder as a filler. This is a method in which the surface of the back coat layer is roughened to reduce the contact area with guide balls, etc., and to reduce the frictional resistance.
No. 1135, No. 57-53825, No. 58-2415
Examples using inorganic powders are shown in both Japanese Patent Publication No. 50-3927, and many of these also show those with a limited particle size of 70. However, even with these inorganic powders, sufficient lubricity cannot be obtained (for example, as with the alumina particles described in Japanese Patent Publication No. 50-3927, the back coat layer may come into contact with guide pins, etc.). When doing so, especially when the guide pin etc. is an organic resin member, K scrapes the bottle etc. and impairs the function of the guide pin to smoothly guide and run the magnetic tape.

One of these causes is that inorganic powders generally have a wide variety of particle shapes and are not constant, and also have a wide particle size distribution, which causes the surface of the bank coat layer to become rougher than necessary.

From this, for example, measures can be taken such as setting the center line average roughness Ra of the surface roughness of the back coat layer to 0.010 to 0.050 μm and the dynamic friction coefficient μ from 0.10 to 0.36. It is necessary to improve the runnability and durability of the back coat layer without imprinting irregularities on the magnetic layer.

In addition, since inorganic powder has a relatively strong affinity for water, it absorbs moisture in the air during use, and the surface of the bank coat layer tends to stick to guide balls, etc., and the adhesion causes the running magnetic tape to suddenly It is easy to cause so-called stick-slip, where the vehicle repeatedly stops and starts suddenly. Further, the moisture may change the quality of the magnetic powder, resulting in deterioration of performance.

Further, the solid powder filler such as the above-mentioned inorganic powder must be contained in the back coat layer etc. in a sufficiently well dispersed state. Therefore, the fillers used are required to have good dispersibility.

In particular, the recent miniaturization and high density of video equipment has made the path of the magnetic tape more complex, and the tape has more opportunities to come into contact with guide balls, guide rules, and even magnetic heads, resulting in more frequent scratches and even more friction. There is a need for improved wear resistance and durability to prevent dust from falling off.

(Objectives of the Invention) The objects of the present invention are (11) having good film physical properties, (2) not causing interlayer adhesion, (3) having good filler uniform dispersibility, and (4)
) has high durability for repeated running, and (4) has a back coat layer with good paint stability, preventing problems with film properties, unstable running at high temperatures and high humidity, damage to tape or video deck guides, and electromagnetic conversion failures. The object of the present invention is to provide a magnetic recording medium (hereinafter referred to as a magnetic tape) that does not require a magnetic tape.

(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 non-magnetic powder on the other side, in which the non-magnetic powder has an average At least one of magnesium carbonate, barium carbonate, calcium sulfate, and zinc sulfate with particles @ 0.01 to 0.8 μm, and the thickness of the layered coating layer is 1.5 μm.
In the following, this is achieved by a magnetic recording medium characterized in that its surface roughness is 0.05 μm or less in center line average roughness (Ra).

Next, the present invention will be specifically explained.

For the non-magnetic powder according to the present invention, at least one of magnesium carbonate, barium carbonate, calcium sulfate, and zinc sulfate is selected in consideration of its solubility, chemical stability, hardness, or cost.

The average particle size of the magnesium carbonate etc. is 0.01-08μ
m, if it is larger than 0.8 μm, powder fall will be severe, and if it is smaller than 0.01 μm, the degree of roughening will be too small, and cinching (local loosening of the winding) may occur when suddenly starting or stopping. many.

In addition, when the thickness of the back coat layer is 1.5 μm or more,
A cupping phenomenon occurs in which the head curls in a spiral shape in the longitudinal direction, causing trouble in head contact and deteriorating electromagnetic conversion characteristics.

In the present invention, the film thickness is set to 1.5 to suppress the cupping phenomenon.
The thickness should be kept below μm, preferably 0.5 to 1.2 μm.

Furthermore, the center line average roughness ILa) of the back coat layer is 0.
．． 0.05 μm or less to improve surface properties, preferably (Ra) is 0.02 to 0.05 μm, particularly preferably 0.025. ~0.035 ttm.

In the present invention, an organic powder can be used in combination with the carbonate and sulfate powder according to the present invention as the non-magnetic powder.

The organic powder is preferably acrylic styrene resin, benzoguanamine resin powder, melamine resin powder, or phthalocyanine pigment, but polyolefin resin powder, polyester resin powder, polyamide resin powder,
Polyimide resin powder, poly7onated ethylene resin powder, etc. can also be used.

Furthermore, inorganic powders used in combination with the carbonate and sulfate powders according to the present invention include silicon oxide, titanium oxide, aluminum oxide, calcium carbonate, barium sulfate, zinc oxide,
Examples include tin oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, α-Fe2e3, talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, and molybdenum dioxide.

The weight of the filler contained in the back coat layer is 0.2 to 0.9, preferably 0.3 to 0.7 of the total solid weight.

In the present invention, conventional techniques can be used to create the magnetic tape of the present invention.

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 materials, is mechanically strong to withstand repeated stress or bending, and has good abrasion resistance and weather resistance.

Furthermore, if a cellulose resin and a vinyl chloride copolymer are also contained in addition to boron 1/tan, the dispersibility of the filler in the back coat layer will be improved and its mechanical strength will be increased.

However, if only the cellulose resin and the vinyl chloride copolymer are used, the layer becomes 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 binders complement each other in length and width, and when they harmonize with each other, the stability of the tape's physical properties over time can be significantly improved.

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, polycrethane resins and cellulose resins, especially 2) p cell 2, are used as resins for the back coat layer.
A combination with - is preferred. The mixing weight ratio of both is 9/1 to 2/8, preferably 8/2 to 3/7, based on polyurethane as a molecule.

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

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

Examples of the aliphatic polyisocyanate include hexamethylene diynecyanate (HMDI) and adducts of these incyanates and active hydrogen compounds.

Among these aliphatic polyisocyanates 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 polyisocyanates, 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 to 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, and an antistatic agent, if necessary.

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, sulfoconophosphates, and known surfactants. and their salts, as well as negative organic groups (e.g. -COOHl-PO3H)
It is also possible to use salts of polymeric dispersants having . These dispersants may be used alone; or two or more types may be used in combination. These dispersants are
It is added in an amount of 1 to 20 parts by weight per 00 parts by weight.

In addition, lubricants include silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, fatty acids such as lauric acid, palmitic acid, oleic acid, stearic acid, behenic acid, myristic acid, and butyl stearate. Fatty acid esters such as octyl palmitate and octyl myritate can also be used. These lubricants are added in an amount of 0.02 to 20 parts by weight based on 100 parts by weight of the binder.

Antistatic agents that may be used include 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 fullkylene oxide type, glycerin type, and glycidol type; higher fulkyl heptamines,
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 active agents such as sulfuric acid or phosphoric acid esters of amino acids, 7-minosulfonic acids, and 7-minoalcohols.

Furthermore, by adding carbon black as a light shielding agent to the back coat layer and the magnetic layer according to the present invention, the dispersibility of carbon black in both layers can be improved without impairing light shielding and conductivity.

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

Examples of magnetic materials include γ-Feze3, Co-containing 1
- Fe2O3, Co adhesion 1 - Fe2e3, Fe3O
4. Co-containing Fe3O4, Co-coated Pe304, C
Oxide magnetic materials such as rO2, e.g. Fe, Ni, Co
, Fe-Ni alloy, Fe-Co alloy, Fe-N1-P
alloy, re -Ni-Co alloy, Fe -Mn -Zn
alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-
Cr alloy, Fe-Co-Ni-P alloy, Co-Ni
Alloys, Co-P alloys, Co-Cr alloys, 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 8i, Cu%Zn, Al, P, and Mn.

It may contain elements such as C or compounds thereof. Also, hexagonal ferrite such as Hariwamu ferrite,
Iron nitride is also used.

In addition, binders, curing agents, dispersants, and
As for the lubricant, antistatic agent, and matting agent, those explained for the back 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, corundum, artificial frundum, diamond, artificial diamond,
Zaku 1 stone, 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 to be blended in the above back coat and magnetic paint or diluting solvents during application of this paint include ketones such as 7setone, methyl ethyl ketone, methyl imbutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, gropanol, butanol, etc. ; Methyl acetate,
Esters such as ethyl acetate, butyl acetate, ethyl lactate, and ethylene glycol monoacetate; Ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, and tetrahydrofuran; Aromatic hydrocarbons such as benzene, toluene, and xylene; Methylene chloride, Hydrocarbons such as ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene can be used.

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polybutene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. ,l,Zn
metal, glass, BN etc.

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, the diameter is about 30 μm to 10 μm, and in the case of a drum shape, a cylindrical shape is used, 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, impregnation coat, reverse roll foot, transfer rule coat, gravure coat,
Kiss coat, cast coat, tinkle coat, etc. can be used, but are not limited to these.

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

Examples 1 to 4 The composition of the following magnetic coating formulation I was thoroughly mixed and dispersed in a ball mill, 5 parts of polyfunctional incyanate was added as a hardening agent, and passed through a 1 μm filter to form a polyethylene terephthalate base having a thickness of 13 μm. A sample film was obtained by coating with a reverse rule coater so that the dry film thickness was 5 μm. 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 surface of the sample film using a reverse roll coater to a dry film thickness of 1.0 μm, dried to form a back coat layer, and each portion was slit into a 2-inch width to form Example Sample Tape 1. -4, and Comparative Example Sample Tapes (1) and (21) were obtained.

Magnetic paint formulation T (parts by weight) Co containing r
-Fe203Zo.

Polyurethane 12 PVC-vinyl acetate copolymer 8 Butyl stearate 0.8 Myristic acid 0.8 Alumina 5 Carbon black 5 Lecithin 4 Cyclohexanone Zo.

Methyl ethyl ketone 50 Toluene 10 Back coat paint prescription■ Table-1 (Note) The numbers in parentheses indicate the average particle size.

The sample obtained after 5K as described above was tested for the first time (0-bath, virgin tape) and after 200 repeated runs (200
We checked the tape condition, physical properties, and electromagnetic conversion characteristics of the tape (pass), and the results are listed in Table 2.
-,,, From the above-mentioned coating-2 - By using MgCO3 filler, it is possible to obtain a back coat with excellent durability that does not cause BC scraping. Furthermore, the increase in the coefficient of friction after repeated running is also small.

・MgC0a has excellent uniform dispersion and can have fine surface roughness, so the deterioration of chroma S/N is small.

・Carbon black takes time to disperse, and it is difficult to make the surface roughness fine, so the strength of the coating film is low. In addition, some glabellar adhesion may occur.

・Titanium oxide is superior to carbon black, but it lacks durability compared to MgCO3.

Examples 5 to 8 Example samples 5 to 8 of magnetic tapes having magnetic layers based on magnetic paint formulation I as in the previous examples, and different back coat layers based on back coat paint formulations shown in Table 3 below. Comparative samples (3) and (4) were prepared, and the characteristics were measured in the same manner as above, and the results are listed in Table 4.

Back coat paint prescription■ Table-3 (Note) The number in parentheses is the average particle diameter.

From Clothing-4: Using barium carbonate filler makes it possible to obtain a highly durable back coat that does not suffer from BC scraping.

Furthermore, the increase in the coefficient of friction after repeated running is also small.

・Barium carbonate has excellent uniform dispersion and can have a fine surface roughness, so the deterioration of chroma S/N is small.

- Carbon black takes time to disperse and is difficult to finely roughen, resulting in poor coating film strength.

In addition, some glabellar adhesion may occur.

・Titanium oxide is better than carbon black, but it lacks durability compared to barium carbonate.

Examples 9 to 11 Example samples 9 to 11 and comparative example samples (5) and (6) were prepared in the same manner as in the above examples by combining the magnetic paint formulation I and the back coat paint formulation II shown in Table 5 below. The characteristics were measured in the same manner as shown in Table 6.

Back coat paint prescription■ Table-5 (Note) The number in parentheses is the average particle diameter.

The backcoat layer that uses calcium sulfate as a filler has excellent durability and has a small increase in coefficient of slippage during repeated running. Glabella adhesion is also good.

Further, due to uniform dispersion, there is no deterioration of G=78/N.

Examples 12 to 14 Example samples 12 to 14 and comparative samples (7) to (8) were prepared in the same manner as in the above examples by combining the magnetic paint formulation I and the back coat paint formulation V shown in Table 7 below. create and
Characteristics were similarly measured and the results are shown in Table 8. Back coat paint formulation V Table 7 (Note) The numbers in parentheses are the average particle diameters.

Zinc sulfate or BC used in the C filler exhibits little performance deterioration during repeated running and has excellent durability.

In addition, there is no glabellar stickiness like carbon BC, and the running properties are good.

Since uniform dispersion can be performed, there is little deterioration in chroma S/N.

Measurement method for Examples and Comparative Examples (Al tape was packed in a VHS cassette, heated at 20°C for 6
The bus was run 200 times using an NV-6200 (Matsushita Electric Co., Ltd.) deck in a 0% group. At the same time, the RF output drop was also measured.

lb) Tape damage was visually evaluated after running 200 passes.

(cl BC dynamic friction coefficient...23℃, 60%■
(In particular, the running performance tester manufactured by Yokohama System Co., Ltd. (TBT-30)
0D), set the input rotor to 20.9) 1m, and place one sample tape in a stainless steel bottle with a diameter of 3.8J1m.
It was run at 800 curls and 3.3 CIrL/1 MIC, and the outlet tensilon was measured and calculated from the following formula.

m-, hereafter the margin exit tension μm-1! n(-) π BC surface roughness Ra (μm) Cutoff 0 with three-dimensional roughness measuring instrument 5E-3FK (Koita Institute)
．． 25. It was determined by measuring 2.5 dragon lengths on the sample surface with a stylus pressure of 30 cm.

(el chroma S/N measurement... H-7100 (
Maximum recording current is 4.5MH using
It was determined by recording z and measuring the noise voltage during playback.

if) Adhesion test: Wrap a 1/2 inch wide tape with a pressure of 1i+, leave it at 60°C, 180% temperature for 24 hours, leave it at room temperature for another 24 hours, unwind it, and check the resistance when pulling it apart. Items that were present were evaluated as present, and items that were absent were evaluated as absent.

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 nonmagnetic powder on the other side, the nonmagnetic powder has an average particle size of 0.01 to 0.8μ.
m, at least one of magnesium carbonate, barium carbonate, calcium sulfate, and zinc sulfate, and the back coat layer has a thickness of 1.5 μm or less and a surface roughness of 0.05 μm in center line average roughness (Ra). A magnetic recording medium characterized by the following: