JPS60111328A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium such as a magnetic tape or the like which has a back coat layer having good mechanical strength and has excellent running stability by providing the back coat layer contg. a resin curable by radiations and carbon black. CONSTITUTION:A back layer contains a resin curable by radiations and the carbon black subjected to a surface treatment by a radical forming compd. Formation of such back coat layer is accomplished by dissolving and dispersing the carbon black subjected to the surface treatment by the radical forming compd., the resin curable by radiations and, if necessary, a thermoplastic resin, etc. in an org. solvent and preparing the paint for the back coat layer. Such paint is coated on the rear of a base body such as a polyester film on the surface of which a magnetic layer is preliminarily formed and thereafter radiations are irradiated to the coating to polymerized and cure the coated layer or the paint for the back coat layer is coated on one surface of a base body such as a polyester film prior to formation of the magnetic layer and thereafter radiations are irradiated to polymerize and cure the paint, by which said layer is formed. The process for coating the paint for the back coat layer on the base body after formation of the magnetic layer thereon and irradiating radiations to the coated layer to polymerize and cure the same is more preferable to reduce substantially noise.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium such as a magnetic tape having a bank coat layer having good mechanical strength and excellent running stability.

In recent years, in magnetic recording media such as magnetic tape, recording,
In order to make the playback time as long as possible, tapes are being made thinner, and magnetic tapes that tend to be thinner are required to have high elastic modulus, good mechanical strength, and excellent running stability. be done.

For this reason, in magnetic tapes, etc., a back coat layer is provided on the back side of the base material with a magnetic layer in order to prevent winding irregularities and scratching of the base film during high-speed winding, and to improve running stability and durability. In recent years, attempts have been made to provide a back coat layer using a radiation-curable resin.
7) After coating the Ft paint on the substrate, it is irradiated with radiation to radiation-polymerize the radiation-curable resin to make it as thin as possible (,
Moreover, a method of forming a Basokuko-1 layer with excellent mechanical strength has been proposed.

However, in this method, when carbon black, which has been commonly used in the past, is used in combination, this type of carbon blank has radical reaction inhibiting sites on its particle surface, and these radical reaction inhibiting sites 1- are damaged by radiation irradiation. It preferentially reacts with the radicals generated in the binder resin, and the irradiated radiation does not effectively contribute to curing the resin, resulting in insufficient curing of the radiation-curable resin and damage to the back coat layer. The problem is that the elastic modulus and mechanical strength of the rubber are not sufficiently improved, and the running stability cannot be sufficiently improved.

As a result of various studies in view of the current situation, the inventors of the present invention used a carbon blank surface-treated with a radical-generating compound together with a radiation-curable resin in place of the conventionally commonly used carbon blank. When a coating layer paint is prepared and applied to the back side of the substrate having a magnetic layer on the surface, and then irradiated with radiation, the radical reaction inhibition sites on the surface of the carbon blank particles and the radicals generated in the binder resin are combined. The reaction is well suppressed, and the radiation-curable resin is polymerized and cured by radiation without impairing the conductivity of carbon black, increasing the modulus of elasticity of the hack coat layer, increasing mechanical strength, and improving running stability. The inventors have discovered that a magnetic recording medium with excellent properties can be obtained, and have come up with the present invention.

The carbon black used in this invention is preferably obtained by surface-treating a carbon blank generally used for magnetic recording media with a radical-generating compound capable of generating radicals, and the radical-generating compound includes: General formula % Formula % It is also an alkyl group having 1 to 5 carbon atoms. ), such as acrylic acid, methyl acrylate, ethyl acrylate, methacrylic acid, methyl methacrylate, compounds represented by the general formula %, such as hydrogen peroxide, dimethyl peroxide, diethyl peroxide , general formula % formula % , hendiyl peroxide, naphthoyl peroxide, lauroyl peroxide, general formula % formula % compounds, for example, henzene diazothiophenyl ether, 4-chlorobenzenediazothiophenyl ether,
4-Bromhenzendiazothiophenyl ether, 4-
Nitrobenzene diazothiophenyl ether, 2-(phenyldiazomercapto)naphthalene, 2-(4-methoxyphenyldiazomercapto)naphthalene, 2-(4
- Nitrogenyl diazomercapto) naphthalene, benzenediazothioglycolic acid, 4-brobenzenediazothioglycolic acid, 4-nitrohenzenediazothioglycolic acid, general formula % formula %. ), such as 2,2'-azobisisobutyronitrile, 1,1'-azobis-1-cyclohexanenitrile, α,α'-azobisopene]nitrile, α,α'-azobis Isohexonitrile, α,
α′-azobisisoheptonitrile, etc. are preferably used. Carbon blanks surface-treated with these radical-generating compounds reduce the number of radical reaction inhibition sites on the carbon black particle surface. Therefore, this type of carbon blank can be used in combination with radiation-curable resins to prevent radiation. When irradiated, the radical reaction inhibition sites on the particle surface do not preferentially react with the radicals generated in the binder resin, unlike in conventional carbon plastics, and the radiation-curable resin can be cured well. As a result, the elastic modulus of the back coat layer is increased, mechanical strength is strengthened, and running stability is improved. The amount of radical-generating compounds used for surface treatment of such carbon blanks is
If it is less than 0.01 mol per mol of carbon black, 1. The radical reaction inhibition sites on the surface of the carbon blank particles cannot be sufficiently reduced, and if the amount exceeds 10 moles, the radical-generating compound will react with the radicals generated in the binder resin. If the amount is too large, the binder resin will not harden sufficiently, so the amount of radical-generating compound 0.01 to 1 mole of carbon blank
It is preferable to use within the range of 10 mol, and 0.1 to 5 mol.
More preferably, it is used in a molar range. In addition, if the amount of carbon blank surface-treated with a radical-generating compound used is less than 25% by weight based on the total amount of binder resin contained in the back coat layer, a good antistatic effect cannot be obtained; If the amount is more than 20% by weight, the durability of the bank coat layer will deteriorate, so it is preferably used within the range of 25-400% by weight, and more preferably within the range of 70-230% by weight.

Further, the radiation-curable resin used in this invention is not particularly limited, but has a molecular weight of 20 (10
Those having a functional group number of 1 to 20 and less than 0 are preferably used. This type of radiation-curable resin is in a liquid state, and when it is applied to a substrate together with a carbon blank and then irradiated with radiation, it crosslinks to form a moderately polymerized and hardened back coat layer, and the back coat layer has a high modulus of elasticity. This increases mechanical strength and improves running stability. Specific examples of such radiation-curable resins include dipentaerythritol hekiza acrylate, dipentaerythritol pentaacrylate, urethane acrylic oligomer, epoxy acrylic oligomer, oligoester acrylic oligomer, spiroacecool acrylic oligomer, and the like. , Specific examples of commercially available products include Nippon Kayaku Co., Ltd.'s DPHA, DPPA, Toagosei Co., Ltd.'s M
-6250, M-7100, M-8130, M-110
0, M-1200, Thiokol U-782, U-7
83, U-788, U-893, SP4 manufactured by Showa Kobunshi Co., Ltd.
Examples include 010, U-3000, E-4000, and 3200.3500.3600.3700 manufactured by Celanese.

Such radiation-curable resins may be used alone or in combination of two or more as a binder resin and cured by radiation irradiation, but they may also be used in combination with commonly used thermoplastic resins. Thermoplastic resins used in combination include vinyl chloride-vinyl acetate copolymers, polyvinyl butyral resins, cellulose resins, polyurethane resins,
Any conventionally commonly used compounds such as isocyanate compounds are preferably used in combination. As described above, the amount of radiation curable resin used in combination with thermoplastic resin is preferably within the range of 1 to 70% by weight based on the total amount of binder resin. It is not possible to sufficiently improve the running stability and durability by increasing the elastic modulus and strengthening the mechanical strength, and if it is too large, the Barafco-1 layer becomes too hard and brittle.

The radiation used to polymerize and cure the radiation-curable resin mentioned above includes β-rays such as electron beams, ultraviolet rays, and X-rays.
T-rays such as UV rays are preferably used, and when ultraviolet rays are used, a sensitizer is used at the same time to make the effect of irradiation more efficient. It is preferable for such radiation irradiation to use radiation with an acceleration voltage of 150 to 750 KV so that the absorbed dose is 3 to 1.5 Mrad. If the absorbed dose is too small, the radiation curable resin may be crosslinked. The desired effect cannot be obtained due to insufficient binding.

To form the back coat layer of the present invention, a carbon blank surface-treated with the above-mentioned radical-generating compound,
Radiation-curable resin and, if necessary, a commonly used thermoplastic resin, etc. are dissolved in an organic solvent and dispersed to prepare a bank coat layer paint, which is then used to form a polyester film on which a magnetic layer is previously formed on the surface. After coating on the back side of the substrate, the coating is polymerized and cured by irradiation with radiation, or by coating the above-mentioned hack coat layer paint on one side of the substrate such as a polyester film before forming the magnetic layer, and then irradiation with radiation. This is done by polymerization and curing. In order to sufficiently reduce noise, it is more preferable that after forming the magnetic layer, a back coat layer paint is applied and polymerized and cured by irradiation with radiation.

As the organic solvent used here, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dimethylformamide, etc. are used alone or in combination of two or more.

Note that various commonly used additives, such as dispersants, lubricants, abrasives, etc., may be optionally added to the back coat layer paint.

Next, embodiments of the invention will be described.

Example 1 α-Fe magnetic powder 800 parts by weight (particle size 0.3μ, axial ratio 8) Eslesoku A (manufactured by Tanezu Kagaku Kogyo Co., Ltd. 100, vinyl chloride-vinyl acetate-vinyl alcohol copolymer) Adeka New Ace YT -4,0040 (polyester polyol manufactured by Asahi Denka) Carbon blank 32 Hengara 40 Myristic acid 7 N-butyl stearate 8 Toluene 815 Cyclohexanone 815 These mixtures were placed in a ball mill and mixed and dispersed for 48 hours. After that, 40 parts by weight of Coronate L (manufactured by Nippon Polyurethane Kogyo Co., Ltd., a trifunctional low molecular weight isocyanate compound) was added and dispersed under high speed shear for 1 hour to prepare a magnetic paint. This magnetic coating material was applied onto a polyester film having a thickness of 10 .mu.m to a dry thickness of 3.17 mm, subjected to magnetic field orientation treatment, dried, and surface treated.

Next, 150 parts by weight of carbon blank MOC; UL-L (carbon blank manufactured by Cabosoto) was mixed with 3000 parts by weight of a 5% aqueous solution of hydrogen peroxide, and after being left at 40°C for 24 hours, it was filtered and dried. Using the carbon blank obtained by the above treatment, a back coat layer paint consisting of the following composition was prepared by mixing and dispersing in a ball mill for 50 hours.

This hack coat layer paint was applied to the opposite side of the polyester film on which the magnetic layer was formed on one side to a dry thickness of 1 μm, dried, and then applied to an accelerating voltage using an electrocurtain type radiation accelerator manufactured by ES1. 165KV,
It was cured by irradiating radiation in a nitrogen atmosphere with a total irradiation dose of 10 Mrad.

After that, it was cut to a specified width to make magnetic tape.

Back coat layer paint Esresoku A (Tanezu Chemical Industry Co., Ltd., 135 parts by weight of vinyl chloride-vinyl acetate-vinyl alcohol) DPHA (Nippon Kayaku Co., Ltd., Dipe 165 inter-erythritol hexaacrylate) Carbon black lO5 Barium sulfate 595 Myristic acid 7 Cyclohexanone 1665 l.Luene 1665 Example 2 150 parts by weight of the same untreated carbon black MOGUL-L used in Example 1 was added to 10% by weight of acrylic acid. Mixed with 3000 parts by weight of toluene solution, then placed in a 1 cm thick Pareso I, using an electron beam accelerator EPS-750 manufactured by Nissin High Voltage Co., Ltd.
Radiation was applied at an accelerating voltage of 750 KV and a total irradiation dose of 0.5 Mrad. Then after filtering and washing with ether,
Example 1 except that the carbon blank obtained by vacuum drying and thus treated was used in the same amount in place of the carbon blank treated with hydrogen peroxide in the composition of the back coat layer paint in Example 1. A magnetic tape was made in the same manner as in 1.

Example 3 In the composition of the back coat layer paint in Example 1,
A magnetic tape was produced in the same manner as in Example 1, except that the same amount of Eslesoc BLS (polyvinyl butyral resin manufactured by Block Chemical Industry Co., Ltd.) was used in place of Eslesoc A.

Example 4 In the composition of the back coat layer paint in Example 1,
A magnetic tape was prepared in the same manner as in Example 1, except that the same amount of nitrocellulose H1 (Nitrocellulose, published by Asahi Kasei Kogyo Co., Ltd.) was used in place of Esuresoku A.

Example 5 In the composition of the back coat layer paint in Example 1,
A magnetic tape was produced in the same manner as in Example 1, except that the same amount of MHLOI (polyurethane resin manufactured by Honey Kasei Co., Ltd.) was used in place of Esuresoku A.

Example 6 In the composition of the back coat layer paint in Example 1,
A magnetic tape was produced in the same manner as in Example 1, except that the same amount of M-1100 (urethane acrylate manufactured by Toagosei Co., Ltd.) was used in place of DPHA.

Example 7 In the composition of the back coat layer paint in Example 1,
A magnetic tape was prepared in the same manner as in Example 1, except that the same amount of 3200 (epoxy acrylate 1- manufactured by Celanese Co., Ltd.) was used in place of D P HA.

Example 8 In the treatment of carbon black in Example 1, the same amount of a 25% by weight ether solution of 2゜2'-azobisisobutyronitrile was used in place of the 5% by weight water/8 solution of hydrogen peroxide. Carbon black was treated in the same manner as in Example 1, except that this carbon blank was used in the same amount in place of the carbon blank treated with hydrogen peroxide in the composition of the back coat layer paint of Example 1. A magnetic tape was made in the same manner as in Example 1.

Example 9 In the composition of the back coat layer paint in Example 1,
A magnetic tape was produced in the same manner as in Example 1, except that the same amount of M-1100 (urethane acrylate manufactured by Toagosei Co., Ltd.) was used in place of Eslenok A.

Comparative Example 1 In the composition of the back coat layer paint in Example 1,
A magnetic tape was prepared in the same manner as in Example 1, except that the same amount of untreated carbon blank MOGUL-■ was used in place of the carbon blank treated with hydrogen peroxide.

Regarding the magnetic tapes obtained in each example and comparative example,
Wow and flutter and video SN to check running stability
The ratio was measured. Wow and flutter was measured by recording and reproducing a 3RHz signal and performing auditory correction, and the video S/N ratio was measured by loading the obtained magnetic tape into a video deck at 40℃ and 80%.
Recording and playback were repeated 100 times under RH conditions, and changes in video S/N ratio between the first and 100th times were measured.

The table below shows the results.

As is clear from the table above, the magnetic tapes obtained in Examples 1 to 9 all showed less change in video S/N ratio and less wow and flutter than the magnetic tape obtained in Comparative Example 1. It can be seen from the above that the magnetic recording medium obtained by the present invention has good mechanical strength and excellent running stability.

Patent applicant: Hitachi Maxell, Ltd.

Claims (1)

[Claims] 1. A magnetic recording medium characterized in that a back coat layer containing a radiation-curable resin and carbon black surface-treated with a radical-generating compound is provided on the opposite side of a substrate having a magnetic layer on one side.