JPS63138524A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To prevent adhesion of substrates to each other via an under coating layer and swelling of the under coating layer by a solvent in a magnetic coating compd. by providing the under coating layer consisting of a specific radiation curing resin to the titled medium. CONSTITUTION:The under coating layer consisting of the structural units expressed by formulas I and II is formed on the substrate and a magnetic layer is provided thereon. The under coating layer is obtd. by coating the coating compd. contg. nitrocellulose (A) contg. (meth)acrylate double bonds and polyurethane and (meth)acrylate (B) on the substrate and projecting radiations to the coating to cure the same. The component A is obtd. by introducing the (meth) acrylate via, for example, a diisocyanate compd. into the nitrocellulose. The component B is preferably multifunctional acrylate having <5,000mol.wt. In formulas, R1 denotes H, CnH2n+1; n denotes 1-8; R2 denotes the polyurethane.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium and a method of manufacturing the same, and more particularly to a magnetic recording medium with excellent durability and electromagnetic conversion characteristics and a method of manufacturing the same.

[Conventional technology]

In general, in magnetic recording media made by coating and drying a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components on a substrate such as a polyester film, the adhesion of the magnetic layer to the substrate is In order to improve this, it is possible to provide an undercoat layer between the magnetic layer and the substrate, which is mainly made of polyester resin, vinyl chloride-vinyl acetate copolymer, or a mixture of nitrocellulose and polyisocyanate. It is being said. (Unexamined Japanese Patent Publication No. 57-1
(No. 98536) [Problems to be Solved by the Invention] However, such conventional undercoat layers are hardened by heat treatment to harden the undercoat layer coated on the substrate. The adhesive between the two may prevent the base from coming apart, and when applying magnetic paint on the undercoat, the undercoat may swell due to the solvent in the magnetic paint.
After drying, there is a problem that the interface between the undercoat layer and the magnetic layer is disturbed, resulting in uneven coating and a decrease in electromagnetic conversion characteristics. Furthermore, in the conventional undercoat layer, the adhesion between the magnetic layer and the substrate is still insufficient, and as a result, the durability of the magnetic layer cannot be sufficiently improved.

[Means for solving problems]

This invention was made as a result of various studies in view of the current situation, and includes an acrylate or methacrylate double bond between a base and a magnetic layer formed on the base and a molecular weight of 300 or more. An undercoat paint containing nitrocellulose containing polyurethane and acrylate or methacrylate with a molecular weight of less than 5000 is applied, and this is irradiated with radiation to cure it to form the structural unit -CH2-CR, -COO- CH2-CRI -COO. - (However, R1 is H or CnH2fl+1, and . is 1 to
It is an integer of 8. ) and CH20NO2 (where R2 is polyurethane), the substrates can be bonded to each other via the undercoat layer or a magnetic layer can be formed on the undercoat layer. In order to prevent the undercoat layer from swelling due to the solvent in the magnetic paint during the process, and to sufficiently improve the adhesion between the substrate and the magnetic layer, the electromagnetic conversion characteristics and durability of the resulting magnetic recording medium can be sufficiently improved. It has been improved.

In this invention, the undercoat layer provided between the substrate and the magnetic layer is made of a combination of nitrocellulose containing acrylate or methacrylate double bonds and polyurethane with a molecular weight of 300 or more, and acrylate or methacrylate with a molecular weight of less than 5000. After mixing and dispersing these radiation-curable resins with an organic solvent, non-magnetic powder, and other necessary ingredients to prepare an undercoat layer paint, this is applied onto a substrate such as a polyester film and irradiated with radiation. It is formed.

In this way, the undercoat layer formed by using a radiation-curable resin and curing the radiation-curable resin by irradiation with radiation is
Since there is no need to perform heat treatment for curing, the substrates are not bonded together by this undercoat layer and cannot be unrolled, and since the undercoat layer is sufficiently hardened when the magnetic layer is applied, the undercoat layer is The layer does not swell, and the electromagnetic conversion characteristics do not deteriorate due to uneven coating on the surface of the magnetic layer. In particular, when the above-mentioned radiation-curable nitrocellulose and acrylate or methacrylate are used in combination, curing by radiation irradiation takes place quickly and sufficiently, so adhesion between substrates and uneven coating on the surface of the magnetic layer can be effectively prevented. I can do it. Furthermore, when the radiation-curable nitrocellulose is cured by irradiation with radiation, the nitrocellulose is internally plasticized by the polyurethane contained in the nitrocellulose, so its adhesion to the substrate is improved.
Adhesion between the substrate and the magnetic layer is also improved. Furthermore, since this radiation-curable nitrocellulose has excellent dispersibility of non-magnetic powder, it is possible to disperse the non-magnetic powder contained in the undercoat layer well and improve the surface smoothness of the undercoat layer. I can do it,
By improving the surface smoothness of the magnetic layer formed on this,
Electromagnetic conversion characteristics can be sufficiently improved.

In this way, when the radiation-curable nitrocellulose and acrylate or methacrylate are used in combination and irradiated with radiation, three-dimensional crosslinking of these radiation-curable resins occurs, resulting in structural units -CH2-CR, -COO. - CH2-CR, -COO- (However, R1 is H or Cn H2n+1, and is 1 to
It is an integer of 8. ) and CH20NO2 (where R2 is polyurethane) is formed, and the electromagnetic conversion characteristics and durability are sufficiently improved.

The radiation-curable nitrocellulose used in such an undercoat layer is polyurethane containing acrylate or methacrylate double bonds and having a molecular weight of 300 or more, in order to improve adhesion to the substrate after radiation irradiation. Such radiation-curable nitrocellulose is preferably used to cure 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, etc. through diisocyanate compounds such as hexamethylene diisocyanate, tolylene diisocyanate, and isophorone diisocyanate. , 2-hydroxypropyl acrylate or methacrylate into nitrocellulose. The amount of acrylate or methacrylate introduced into the nitrocellulose is preferably within the range of 0.005 to 1.0 mol per kg of nitrocellulose.

In addition, the acrylate or methacrylate used in combination is preferably a polyfunctional acrylate or methacrylate with a molecular weight of less than 15,000, in order to improve the curing properties of the coating film after radiation irradiation. For example, dipentaerythritol, hexaacrylate, trimethylol Propane triacrylate, trimethylolpropane trimethacrylate, neopentyl glycol diacrylate and the like are preferably used. Specific examples of commercially available products include, for example, DPHASDPCA-60 manufactured by Nippon Kayaku Co., Ltd.
, DPCA-120, A-TMPT, PEG-400D
A,,HDDA,D-310゜D-320,D-330
Examples include. In addition, 2-hydroxyethyl acrylate, etc. and Coronate L manufactured by Bhon Polyurethane Kogyo Co., Ltd.
A reaction product of 2-hydroxyethyl acrylate or the like and Coronate HL manufactured by Nippon Polyurethane Industries, Ltd. may also be used.

When such radiation-curable nitrocellulose and polyfunctional acrylate are used together, the mixing ratio is preferably within the range of 9:1 to 1:9 (weight ratio of trocellulose to acrylate), If the amount of radiation-curable nitrocellulose is too small, the shrinkage of the coating film becomes large, and the substrate after the undercoat layer is formed curls with the coating film inside, which impairs the suitability for applying the magnetic paint. On the other hand, if the amount is too large, the curing properties of the coating film will be poor and uneven coating will occur when the magnetic layer is applied.

The radiation used to polymerize and cure these radiation-curable resins is preferably beta rays such as electron beams, and gamma rays such as ultraviolet rays or X-rays. Sometimes a sensitizer is used at the same time to make the effect of irradiation more efficient. It is preferable to irradiate such radiation using radiation with an accelerating voltage of 150 to 750 KV so that the absorbed dose is 3 to 15 Mrad. If the absorbed dose is too small, the crosslinking of the radiation-curable resin may be insufficient. The desired effect cannot be obtained.

The undercoat layer formed in this way usually contains non-magnetic powder for reinforcement, and has an average particle size of 0.1 to 3 μm.
Non-magnetic powders such as carbon black and oxide powders are preferably used. Specific examples include, in addition to carbon black, A1□03 powder, (X-Fe2Q3 powder, CaCO3 powder, MgO powder, Cr2O3 powder, Ba
SO4 powder, B a CO3 powder, ZnO powder, Cu2
Suitable examples include O powder, CuO powder, and T i O2 powder. The amount used is preferably within the range of 20 to 80 M% based on the total solid components of the undercoat layer, and if it is too small, the undercoat layer will not be sufficiently reinforced.
If the amount is too large, the surface roughness of the undercoat layer will increase, causing an increase in noise in the magnetic layer.

The thickness of the undercoat layer formed in this way is within the range of 0.1 to 5 μm so that it can sufficiently contain the above-mentioned non-magnetic powder and ensure good adhesion between the substrate and the magnetic layer. It is preferable to

The magnetic layer on the undercoat layer is formed using γ-Fe203 powder, Fe
3O4 powder, Co-containing r-Fe203 powder, CO-containing F
Various conventionally known magnetic powders such as e3O4 powder, Fe powder, Co powder, Fe-Ni powder, barium ferrite, and strontium ferrite are mixed and dispersed together with a binder resin and an organic solvent to prepare a magnetic paint. It is formed by applying a paint onto an undercoat layer formed on a substrate and drying it.

In addition, various commonly used additives such as lubricants, dispersants, abrasives, antistatic agents, etc. may be appropriately added to the magnetic paint.

〔Example〕

Next, embodiments of the invention will be described.

Example 1 174 parts by weight of tolylene diisocyanate was placed in a 4-bottle flask of No. 111, heated to 80°C in a N2 stream, and then 116 parts by weight of 2-hydroxyethyl acrylate and 0.05 parts by weight of tin octylate were added. and 0.05 parts by weight of hydroquinone at a temperature of 80°C in a four-way flask.
Control the temperature to ~85℃.

The mixture was added dropwise under controlled conditions, and after the addition was completed, the mixture was stirred at 80° C. for 3 hours. Next, 90 parts by weight of 1,4-butanediol was added dropwise thereto, and after the addition was completed, the mixture was stirred at 80° C. for an additional 3 hours, and then cooled. Thereafter, this was dissolved in methyl ethyl ketone to obtain a 25% by weight solution of urethane acrylate.

On the other hand, nitrocellulose (manufactured by Daicel Chemical Industries, Ltd., R3
After drying I/2), it was dissolved in methyl ethyl ketone to obtain a 30% by weight solution of nitrocellulose.

25 of the urethane acrylate obtained as above
5.2 parts by weight of the molten solution by weight, 1.6 parts by weight of 1.6-hexamethylene diisocyanate, and 333.3 parts by weight of the nitrocellulose solution were mixed and melted, and the mixture was heated at 30°C in a N2 stream for 48 hours. By stirring, radiation-curable nitrocellulose was synthesized. Using the radiation-curable nitrocellulose thus obtained, radiation-curable nitrocellulose 240 parts by weight polyfunctional acrylate (Japan 160 manufactured by Kayaku Co., Ltd., DPCA-
120) Carbon black (manufactured by Cabosoto 450, Palkan XC-72) Red iron 150 Cyclohexanone 1000 Toluene
The composition of 1,000 mm was mixed and dispersed in a ball mill for 24 hours to prepare the undercoat layer paint. This undercoat layer paint was applied onto a polyester film with a thickness of 10 Ijm to a dry thickness of 1.0 μm, dried, and subjected to surface smoothing treatment, and then subjected to an electron beam accelerator manufactured by ESi. An undercoat layer was formed by irradiating an electron beam at 3 Mrad in an atmosphere with an oxygen concentration of 300 ppm at an accelerating voltage of 165 KV.

Next, on the undercoat layer on this polyester film, a magnetic paint having the following composition was applied so that the dry thickness was 2.5 μm.
After coating, drying, and surface smoothing, it was cut into 8 mm widths to make video tapes.

Magnetic paint α-Fe magnetic powder (long axis 0.1 μm, 800 parts by weight m, axial ratio 10) Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (manufactured by Block Chemical Industry Co., Ltd., S-LEC A) Polyurethane resin (large Nippon In 60〃Ki Kagaku Kogyo Co., Ltd., T-5250) Polyisocyanate (Nippon Poly 40〃Urethane Kogyo Co., Ltd., Coronate L) Alumina (Jinju Kagaku Kogyo Co., Ltd., 48〃A OS -
48) Carbon black (Cabot 50, Mogul L) myristic acid 40 n-butyl stearate 16 cyclohexanone
1000 Toluene
1000 Example 2 Using the radiation-curable nitrocellulose obtained in Example 1, 60 parts by weight of radiation-curable nitrocellulose polyfunctional acrylate (manufactured by Nippon Kayaku 40, DPCA-60)
) Cyclohexanone 450 Toluene
The composition of No. 450 was thoroughly mixed and dissolved, and this was applied onto a polyester film having a thickness of 10 μm to a dry thickness of 0.2 μm and dried. After that, using an electron beam accelerator manufactured by ESi, the acceleration voltage was set to 1.
65, an undercoat layer was formed by irradiating 5 Mrad of electron beam in an atmosphere with an oxygen concentration of 300 ppm.

Next, on the undercoat layer on this polyester film, the same magnetic paint used in Example 1 was applied to a dry thickness of 3.5 μm.
After coating, drying, and surface smoothing, the film was cut to a width of 8 mm to make a videotape.

Comparative Example 1 Vinyl chloride-vinyl acetate-vinyl 80 parts by weight Alcohol copolymer (manufactured by U, C, C, VAGH) Polyisocyanate (Nippon Poly 20, manufactured by Urethane Kogyo Co., Ltd., coronated) Cyclohexanone 450 Toluene
450 After thoroughly mixing and melting this composition, coating it on a 108 m thick polyester film to a dry thickness of 0.2 μm and drying it,
Heat treatment was performed in an atmosphere at 60° C. for 24 hours to form an undercoat layer.

Next, on the undercoat layer on this polyester film, the same magnetic paint used in Example 1 was applied to a dry thickness of 3.5 μm.
After coating, drying, and surface smoothing, the film was cut to a width of 8 mm to make a videotape.

The video S/N and C/N of the video tapes obtained in each example and comparative example were measured using an 8 mm C0D-V8 manufactured by Sony Corporation with adjusted recording current. Also 4
When performing still playback at ℃, the carrier output was 6 (fB
Durability was investigated by measuring the time it took for the film to deteriorate.

Table 1 below shows the results.

Table 1 [Effects of the Invention] As is clear from the above table, the video tapes obtained in Examples 1 and 2 had lower video S/N and C/N than the video tape obtained in Comparative Example 1. It can be seen that the magnetic recording medium obtained by the present invention has sufficiently improved electromagnetic conversion characteristics and durability.

Claims (1)

[Claims] 1. On the substrate, there is a structural unit ▲a mathematical formula, a chemical formula, a table, etc.▼ (However, R_1 is H or C_nH_2_n_+_1, and n is an integer from 1 to 8.) and ▲A mathematical formula, There are chemical formulas, tables, etc. ▼ (However, R_2 is polyurethane.) A magnetic recording medium characterized by providing an undercoat layer containing a resin having the following and providing a magnetic layer on this undercoat layer. 2. On the substrate, apply an undercoat paint containing nitrocellulose containing polyurethane with an acrylate or methacrylate double bond and a molecular weight of 300 or more, and an acrylate or methacrylate with a molecular weight of less than 5,000, and apply radiation to this. A method for manufacturing a magnetic recording medium, which comprises forming an undercoat layer by irradiation and then providing a magnetic layer on the undercoat layer.