JPH0770043B2 - Magnetic recording medium - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to magnetic recording media having an improved back layer. More specifically, the present invention relates to a magnetic recording medium that has improved wear resistance without deteriorating electromagnetic conversion characteristics, has a back layer that is less likely to be scraped by running friction, and has excellent dropout characteristics.

BACKGROUND OF THE INVENTION Magnetic recording media are widely used for recording electromagnetic signals, and are tape-shaped, disk-shaped, or
Alternatively, various forms such as a card are used. Of these magnetic recording media, tape-shaped ones are used as magnetic recording media for audio, video, computers, etc. (hereinafter, in the present invention, such tape-shaped (long-shaped) media are used. The magnetic recording medium may be simply referred to as "magnetic tape").

In recent years, as the demand for high density recording has increased, a metal thin film magnetic recording layer formed by a vapor deposition method such as vacuum deposition, sputtering, ion plating, or a plating method such as electroplating or electroless plating. A magnetic recording medium having a (magnetic layer) has attracted attention and has been put to practical use.

In such a magnetic recording medium, the surface of the magnetic layer is finished to be smooth in order to improve the output particularly in the short wavelength region. Further, recently, in order to obtain a magnetic tape having good running performance and durability, a magnetic tape having a back layer (back coat layer) on the surface of the non-magnetic support having no magnetic layer has been developed and used. Has been done.

However, the above-mentioned back layer provided by the conventional technique increases the dropout (DO) of magnetic recording due to "scraping" due to contact with the magnetic head or the like when the magnetic tape is running, and the friction coefficient increases, Further, the edge of the magnetic tape is easily broken, and the performance of the back layer is required to be further improved.

Further, in the magnetic tape provided with the back layer, when the magnetic tape is wound in a roll shape and stacked, the unevenness of the back layer surface is transferred to the magnetic layer, and the electromagnetic conversion characteristics of the magnetic layer, especially the C / N characteristics are improved. There is a problem of damage, and further improvement of the surface of the back layer is required.

[Object of the Invention] An object of the present invention is to provide a back layer that improves wear resistance without deteriorating electromagnetic conversion characteristics, has excellent running durability without increasing a friction coefficient, and has little abrasion due to running friction. And to provide a magnetic recording medium having excellent dropout characteristics.

SUMMARY OF THE INVENTION The present invention provides a magnetic layer comprising a magnetic layer on the surface of one side of a non-magnetic support and a back layer on the surface of the other side of which a inorganic powder is dispersed in a binder. In the recording medium, the inorganic powder of the back layer is a plate-like inorganic powder having a particle size of 0.01 to 1.0 μm and a plate ratio of 10 to 50, and 50 to 300 parts by weight of carbon black with respect to 100 parts by weight of the plate inorganic powder. And a back layer having a thickness of 0.01 to 1.5 μm.

Detailed Description of the Invention A magnetic recording medium having a magnetic layer on the surface of one side of a non-magnetic support and a back layer on the surface of the other side is already known. The present invention has a novel and improved characteristic structure in the back layer, and for the portions other than the back layer of the magnetic recording medium, the prior art relating to respective materials, shapes, etc. is used in the present invention. can do.

For example, as the non-magnetic support, a plastic such as polyethylene terephthalate, a metal, a ceramics, or the like in the shape of a tape, a disk, a drum, or the like is used after pretreatment such as corona discharge treatment or plasma treatment, if necessary. it can.

Further, as the magnetic layer, for example, on a non-magnetic support,
Ferromagnetic materials such as iron, cobalt, nickel or alloys containing them as a main component or their oxides are vacuum-deposited,
Examples thereof include a metal thin film type magnetic layer formed by a vapor deposition method such as sputtering or ion plating, or a plating method such as an electroplating method and an electroless plating method. Further, it may be a magnetic layer formed by coating a composition in which ferromagnetic fine powder is dispersed in a binder. As the ferromagnetic fine powder, γ-iron oxide-based ferromagnetic powder, cobalt-containing γ-iron oxide-based ferromagnetic powder, ferromagnetic metal fine powder, barium ferrite, strontium ferrite and the like are used. Further, the magnetic layer may optionally contain various additives and additives known per se.

Since the characteristic structure of the magnetic recording medium of the present invention is the structure of the back layer, the structure of the back layer will be mainly described below.

In the back layer of the magnetic recording medium of the present invention, a binder is dispersed with an inorganic powder containing a plate-like inorganic powder having a plate-like ratio of 10 to 50 and carbon black, and is 1.5 μm or less and 0.01 μm or less.
It has a thickness of m or more.

The "particle diameter" and "plate ratio" of the plate-like inorganic powder are
It is defined as follows.

"Particle Diameter" The powder is flat, and its planar shape is not particularly limited, and may be any shape such as a circle, an ellipse, a triangle, a quadrangle, or another polygon. "Particle size" is the average value of the maximum differential length and the minimum differential length in such a shape. The ratio of the maximum transfer length to the minimum transfer length is preferably 10 to 1, and particularly 5 to 1.

"Plate ratio""Plateratio" is the ratio of the particle size to the thickness of the powder (particle size / thickness).

As the plate-like inorganic powder, the particle size is 0.01 ~ 1.0μ
m, especially 0.2 to 0.8 μm, and a plate ratio of 10 to 50, especially 10
Inorganic powders of ~ 30 are preferred. If the particle diameter of the plate-like inorganic powder is larger than the above range, the dispersibility of the inorganic powder and the strength of the back layer tend to be lowered. Further, even if the plate-like ratio is smaller than the above range and approaches a needle-like shape or a lump-like shape, or conversely, if it is larger than the above-mentioned range, abrasion of the back layer due to running friction increases, and the electromagnetic conversion characteristics of the magnetic recording medium are increased. Dropout increases with decreasing.

The type of the plate-like inorganic powder in the present invention is not particularly limited, and those naturally produced or synthesized can be used. Examples of naturally-occurring plate-like inorganic powders include powders of kaolinite, illite, sericite, vermiculite, montmorillonite, etc., which are tabular, and examples of synthesized plate-like inorganic powders. As Al ₂ O ₃ , Fe ₂ O ₃ , Cr ₂ O ₃ , ZnO, MgCO ₃ , BaS
Examples thereof include powders such as O ₄ and Al (OH) ₃ which are tabular. Particularly preferred plate-like inorganic powder is a plate-like iron oxide-based non-magnetic powder, for example, a plate-like powder of α-Fe ₂ O ₃ .

The plate-like inorganic powder having the above particle size and plate-like ratio can be easily produced by a method known per se. For example, a tabular powder of α-Fe ₂ O ₃ can be obtained by gradually dividing a triethanolamine iron (III) complex by a hydrothermal reaction. The shape of α-Fe ₂ O ₃ produced depending on the type of anion coexisting at that time changes, for example, particles on a disk are obtained from a perchlorate solution, and a hexagonal plate is obtained from a solution containing sodium acetate. -Like particles are obtained.

Furnace black, thermal black, color black, acetylene black and the like can be used as the carbon black. As the properties of carbon black, the average particle size is 5 to 1000 mμ (electron microscope), the nitrogen adsorption method specific surface area is 1 to 800 m ² / g, the pH is 4 to 11 (JIS K6221), and the dibutyl phthalate oil absorption is 10
It is preferably 800 ml / 100 g (JIS K6221). Regarding the size of carbon black, 5 to 100 mμ of carbon black is used to reduce the surface electric resistance of the coating film.
50 to 1000 mμ of carbon black is used to control the strength of the coating film, and finer carbon black (100 mμ is used to smooth the surface of the coating film to reduce spacing loss). For the purpose of roughening and reducing the coefficient of friction of
mμ or more) is used. Fine particle carbon black and coarse particle carbon black may be used in combination. Further, carbon black in which a part of the surface of carbon black is guarified or grafted can also be used.

The mixing ratio of the plate-like inorganic powder and the carbon black is preferably 50 to 300 parts by weight, and particularly preferably 50 to 200 parts by weight, with respect to 100 parts by weight of the plate-like inorganic powder. If the blending ratio of carbon black is less than the above range, the chargeability of the magnetic recording medium is increased, so that dust is likely to adhere and dropout increases. On the other hand, when the amount is more than the above range, the durability is lowered, the back layer is scraped, and the dropout is increased.

The binder used for forming the back layer of the present invention is not particularly limited, and known thermoplastic resins, thermosetting resins, reactive resins, and these which have been conventionally used as binders for magnetic recording media. Mixtures of can be used.

The thermoplastic resin has a softening temperature of 150 ° C. or lower and an average molecular weight of 10,000 to 300,000, and examples thereof include vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer and vinyl acrylonitrile chloride. Polymer, acrylic acid ester acrylonitrile copolymer, acrylic acid ester vinylidene chloride copolymer, acrylic acid ester styrene copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid Ester styrene copolymer,
Urethane elastomer, nylon-silicone resin, nitrocellulose-polyamide resin, polyvinyl fluoride,
Vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene butadiene copolymer, Examples thereof include polyester resins, chlorovinyl ether acrylate copolymers, amino resins, various synthetic rubber thermoplastic resins, and the like.

Further, the thermosetting resin or the reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and by heating after coating and drying, the molecular weight becomes extremely large, for example, phenol resin , Phenoxy resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicon resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin, high molecular weight polyester resin and isocyanate prepolymer mixture , Mixture of methacrylate copolymer and diisocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, mixture of low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate, polyamine Butter and mixtures thereof.

Further, these binders may have other functional groups known per se, and among these functional groups,
_{SO 3 M, -SO 2 M,} -COOM, -NH 2, -N + R 4, -OH, a phosphate group, at least one functional group selected from the group consisting of phosphoric acid ester group (wherein, M is A hydrogen atom or an alkali metal atom is shown, and R is a lower alkyl group having 10 or less carbon atoms. These functional groups are preferably contained in an amount of 1 × 10 ⁻⁶ to 1 × 10 ⁻² equivalents per 1 g of the resin. The binder has a glass transition temperature Tg of 40
It is preferably at least ℃, especially at 60 ℃.

The binder may further contain a compound having two or more isocyanate groups (polyisocyanate). As such a polyisocyanate, for example,
Tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate,
Isocyanates such as oxyrylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, reaction products of these isocyanates and polyalcohols, and condensation of these isocyanates The polyisocyanate etc. which were produced can be mentioned. Examples of the above polyisocyanates include Coronate L, Coronate HL, Coronate 2030, Coronate 20 from Nippon Polyurethane Co., Ltd.
31, Millionate MR, Millionate MLT, Takeda Pharmaceutical Co., Ltd., Takenate D-102, Takenate D-110
N, Takenate D-200, Takenate D-202, and Sumitomo Bayer Co., Ltd. sell product names such as Death Module L, Death Module L, Death Module IL, Death Module N, and Death Module HL.

The mixing ratio of the binder and the inorganic powder in the back layer of the magnetic recording medium of the present invention is preferably 40 to 200 parts by weight, and particularly 50 to 130 parts by weight, per 100 parts by weight of the inorganic powder. When the compounding ratio of the binder is less than the above range, the running durability of the magnetic recording medium is deteriorated, and when it is more than the above range, the packing density of the inorganic powder becomes low, so that in the back layer of the magnetic recording medium. The desired surface electric resistance cannot be obtained, or the coefficient of friction tends to increase.

The thickness of the back layer of the magnetic recording medium of the present invention is 1.5 μm or less, preferably 0.5 to 1.0 μm. When the thickness of the back layer is larger than the above range, the running property of the tape becomes unstable.

A method of forming a back layer on the surface of the non-magnetic support opposite to the surface on which the magnetic layer is formed is already known, and the back layer of the magnetic magnetic recording medium of the present invention is basically the same as the back surface of the support by the same scanning. Can be formed. That is, for example, a coating solution in which the inorganic powder, the binder component, and optionally other additives are dispersed or dissolved in an organic solvent is prepared, and the coating solution is applied to the surface of the support and then dried. Then, the solvent is evaporated and the binder component is further cured to form the back layer.

Regarding the organic solvent, the method and apparatus for dispersion and kneading, the method and apparatus for applying the coating solution to the support, and the like when preparing the above-mentioned coating solution, conventional techniques known per se can be used.

The magnetic layer and the back layer may be attached to the support either first or at the same time. Further, after coating either one of the magnetic layer and the back layer (preferably the magnetic layer), the coating layer (preferably the magnetic layer) is cured through a drying step and, if desired, a heating and curing step, and the other layer. It is also possible to apply a layer (preferably a back layer), and similarly perform a drying step and a heat curing treatment step to obtain a magnetic tape raw fabric.

A lubricant may be present on the surface of the back layer of the magnetic recording medium of the present invention. As a method of allowing the lubricant to be present on the surface of the back layer, a method of dissolving or dispersing the lubricant in the coating liquid of the back layer, a method of applying a thin film of an organic solvent solution of the lubricant and drying, and an organic solvent of the lubricant Examples include a method of applying the solution to the surface of the magnetic layer and then stacking the magnetic layer and the back layer.

Examples of lubricants include higher fatty acids, metal soaps, higher fatty acid amides, higher fatty acid esters, mineral oils, oil-based organic compounds, silicon oil, inorganic fine powder, plastic fine powder, α-olefin polymer, and liquid at room temperature. Unsaturated hydrocarbons, fluorocarbons and mixtures thereof.

Next, examples and comparative examples of the present invention will be shown.

In each example, "part" means "part by weight".

[Examples 1 to 3] The surface of a polyethylene terephthalate base (non-magnetic support) having a thickness of 14 µm was coated with a magnetic coating material prepared by the following composition and method so that the thickness after drying was 6.0 µm. Oriented, dried, calendered.

Then, a back layer coating liquid prepared by the composition and method described below was applied to the polyethylene terephthalate surface not coated with the magnetic paint so that the thickness after drying was 1.0 μm.

After coating, drying and surface smoothing treatments were performed, and immediately wound.

The wound original fabric was heat-cured at 40 ° C. for 48 hours in that state, and then the original fabric was slit into a width of 1 inch to prepare a sample tape.

This sample tape was evaluated by the following methods, and the results are shown in Table 1.

Magnetic coating composition Co-containing γ-Fe ₂ O ₃ powder (Nitrogen adsorption specific surface area: 40 m ² / g powder
Hc: 850Oe) 300 parts Vinyl chloride-vinyl acetate copolymer (VMCH, Union Carbide) 40 parts Polyurethane resin (UR8300, Toyobo Co., Ltd.) 17
Parts carbon black (average particle size: 20 mμ) 15 parts lecithin 1.5 parts oleic acid 3 parts octyl laurate 4 parts lauric acid 3 parts butyl acetate 700 parts methyl ethyl ketone 300 parts Part of the above composition was put in a ball mill and thoroughly kneaded The rest is placed in a ball mill and kneaded thoroughly to obtain a polyisocyanate compound (Coronate 3040, Nippon Polyurethane Co., Ltd.)
(Manufactured by Mfg. Co., Ltd.) and further kneaded and dispersed to prepare a magnetic paint.

Back layer coating liquid composition Nitrocellulose 25 parts Urethane resin (Nippon Polyurethane Co., Ltd .: N-2301) 1
5 parts Polyisocyanate (Nippon Polyurethane Co., Ltd .: Coronate L) 40 parts Carbon black (Contex, SC average particle size: 3
0 mμ) 10 parts Plate-like α-Fe ₂ O ₃ powder (particle size and plate ratio of each example are as shown in Table 1) 10 parts Methyl ethyl ketone 480 parts After the above composition was put into a ball mill and kneaded and prepared After adding 25 parts of a polyisocyanate compound (Coronate 2030, manufactured by Nippon Polyurethane Co., Ltd.) and uniformly kneading and dispersing, the viscosity was adjusted to obtain a back layer coating liquid.

[Evaluation of sample tape] Electromagnetic conversion characteristics (C / N) Each sample was applied to a VHS type VTR and the ratio of noise to reproduced RF output was measured. The C / N value was shown as a relative value when the C / N value of the VHS type video tape "Super XG-T-120" (manufactured by Fuji Photo Film Co., Ltd.) was 0 dB.

Amount of back layer scraping The scratched state of the back layer surface when each unused sample was run 200 times on a VHS type VTR, the number of scratches was counted with a microscope with a magnification of 50, and 0 scratches were marked with 1 or 1. △ for 3
4-9 were evaluated as x and 10 or more were evaluated as xx.

Number of dropouts The number of dropouts after repeated running of 250 passes is shown. Dropout is 15 at the dropout counter
The number of times the playback output level dropped by 16 dB or more for 5 x 10 ^-6 sec or more / 5 minutes was displayed.

[Comparative Examples 1 and 2] As the plate-like inorganic powder, plate-like α-Fe ₂ O ₃ having a plate-like ratio outside the scope of the present invention (particle size and plate-like ratio are as shown in Table 1) was used. Otherwise the same as in Example 1,
A sample tape was made.

The evaluation results of this sample tape are shown in Table 1.

[Comparative Examples 3 and 4] In Example 1, except that granular (Comparative Example 3) or acicular (Comparative Example 4) α-Fe ₂ O ₃ was used instead of the plate-shaped α-Fe ₂ O ₃ . Similarly, a sample tape was prepared.

The evaluation results of this sample tape are shown in Table 1.

Comparative Examples 5 and 6 In place of the plate-like α-Fe ₂ O ₃ , bulk CaCO ₃ (Comparative Example 5) or bulk α-Al ₂ O ₃ (Comparative Example 6) was used, but Example 1 was used. A sample tape was prepared in the same manner as in.

The evaluation results of this sample tape are shown in Table 1.

[Comparative Example 7] A sample tape was prepared in the same manner as in Example 1 except that the plate-like α-Fe ₂ O ₃ was not used and the amount of carbon black used was changed to 20 parts by weight.

The evaluation results of this sample tape are shown in Table 1.

As is clear from the results shown in Table 1, the sample tapes obtained in the respective examples have a very small back layer scraping and a very small number of dropouts without deterioration of electromagnetic conversion characteristics. On the other hand, in the sample tapes obtained in Comparative Examples 1 and 2, the electromagnetic conversion characteristics were deteriorated, the back layer was scraped and the number of dropouts was increased, and the sample tapes obtained in Comparative Examples 4 and 5 were The electromagnetic conversion characteristics are deteriorated, the back layer is scraped and the number of dropouts is extremely increased, and the sample tapes obtained in Comparative Examples 3 and 6 have deteriorated electromagnetic conversion characteristics and an increased number of dropouts. In the sample tape obtained in Comparative Example 7, the abrasion of the back layer was extremely increased.

[Advantages of the Invention] The magnetic recording medium of the present invention has improved electromagnetic resistance without deterioration of electromagnetic conversion characteristics, and has excellent running durability without increasing the coefficient of friction and abrasion of the back layer due to running friction. It is a magnetic recording medium which has less dropout characteristics and excellent dropout characteristics.

Claims (4)

[Claims] 1. A magnetic recording medium comprising a magnetic layer on the surface of one side of a non-magnetic support, and a back layer comprising inorganic powder dispersed in a binder on the surface of the other side. The inorganic powder of the back layer has a particle size of 0.01 to 1.0 μm, a plate-like inorganic powder having a plate ratio of 10 to 50, and 50 to 300 parts by weight of carbon black with respect to 100 parts by weight of the plate-like inorganic powder, A magnetic recording medium characterized in that the thickness of the back layer is in the range of 0.01 to 1.5 μm. 2. The magnetic recording medium according to claim 1, wherein the plate-shaped inorganic powder is a plate-shaped iron oxide powder. 3. The magnetic recording medium according to claim 1, wherein the plate-shaped inorganic powder is a plate-shaped powder of α-Fe ₂ O ₃ . 4. The magnetic recording according to claim 1, wherein the compounding ratio of the binder and the inorganic powder in the back layer is 40 to 200 parts by weight of the binder per 100 parts by weight of the inorganic powder. Medium.