JPH04214217A - Magnetic recording medium with its transparency improved - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium substantially transparent to visible light. CONSTITUTION:This magnetic recording medium has a magnetic recording layer in which magnetic fine particles are dispersed in a binder. The superfine particles of SiO2, Al2O3, etc., having a higher refractive index than the binder are dispersed in the binder, and the obtained dispersion is applied on a transparent support to obtain the magnetic recording medium.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to magnetic recording materials and, more particularly, to providing a magnetic recording medium that is substantially transparent to visible light.

0002

2. Description of the Related Art Magnetic recording is widely used in video tapes, audio cassettes, proppy disks, magnetic cards, and the like. Among these applications, there was no particular need to increase the light transmittance any further than the requirement that the light transmittance be not too high for videotape reader detection. However, considering the use of magnetically overlapping the image area of a photographic light-sensitive material to record photographing conditions and other information, it is important that the photographic light-sensitive material has as little coloration as possible and high transmittance to light. is needed. If magnetic recording is performed digitally, the required S/N ratio is small, so the amount of magnetic material applied can be reduced to 1/1 of that of video tapes and audio cassettes.
The light transmittance can be increased by setting it to 1/10 to 1/100. Such a concept is disclosed in Japanese Patent Publication No. 42-4539, Japanese Patent Publication No. 57-6576, etc. However, even in these cases, the problem was that the visible light transmittance of the magnetic layer was low. Although it is possible to increase the light transmittance by lowering the magnetic material density in the magnetic recording layer, it is difficult to extract sufficient magnetic output. Furthermore, in order to increase the magnetic output, it is necessary to increase the density of the magnetic material in the magnetic recording layer. In this case, a disadvantage arises in that the light transmittance becomes low. Therefore, it has been extremely difficult to achieve both optical transmittance and magnetic properties such as magnetic output. It has been desired to develop a magnetic recording medium having a magnetic recording layer that has a high transmittance to visible light and a large magnetic output.

0003

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium that is substantially transparent to visible light.

0004

[Means for Solving the Problems] The above object is to provide a magnetic recording medium having a magnetic recording layer in which fine magnetic particles are dispersed in a non-magnetic binder, in which the non-magnetic binder contains ultra-fine particles whose refractive index is larger than that of the non-magnetic binder. This problem was solved by a magnetic recording medium characterized by dispersed particles.

The present invention will be explained in detail below. The ferromagnetic powder used as magnetic fine particles in the present invention includes ferromagnetic iron oxide fine powder, Co-containing ferromagnetic iron oxide fine powder, ferromagnetic chromium dioxide fine powder, ferromagnetic alloy powder,
Examples include barium ferrite powder. It is effective that the acicular ratio of ferromagnetic iron oxide and chromium dioxide is about 2/1 to 20/1, preferably 5/1 or more, and the average length is about 0.2 to 2.0 μm. Ferromagnetic alloy powder has a metal content of 75wt%
80 wt% or more of the metal content is ferromagnetic metal (i.e., Fe, Co, Ni, Fe-Ni, Co-Ni, Fe
-Co-Ni) with a major axis of about 1.0 μm or less. Any magnetic material may be used as the magnetic material used in the present invention. The content of magnetic fine particles in the magnetic recording layer in the present invention is 3 g or less per m2, preferably 0.
．． It is desirable that the amount is 0.01 g to 1 g.

The binder for the magnetic recording layer used in the present invention may be a thermoplastic resin, a thermosetting resin, a radiation curable resin, a reactive resin, or any of the known thermoplastic resins, thermosetting resins, radiation curable resins, and reactive resins that have been conventionally used as binders for magnetic recording media. Mixtures, hydrophilic binders such as gelatin can be used. The Tg of the above resin is -40°C to 150°C, and the weight average molecular weight is 1
It is from 10,000 to 300,000, preferably from 10,000 to 100,000.

[0007] As the above-mentioned thermoplastic resin, vinyl chloride
Vinyl acetate copolymer, vinyl chloride, copolymer of vinyl acetate and vinyl alcohol, maleic acid and/or acrylic acid, vinyl chloride/vinylidene acetate copolymer, vinyl chloride/acrylonitrile copolymer, ethylene/vinyl acetate copolymer Vinyl copolymers such as polymers, cellulose derivatives such as nitrocellulose, cellulose acetate propionate, cellulose acetate butyrate resin, acrylic resin, polyvinyl acetal resin, polyvinyl butyral resin, polyester polyurethane resin, polyether polyurethane, polycarbonate polyurethane Rubber resins such as resins, polyester resins, polyether resins, polyamide resins, amino resins, styrene butadiene resins, butadiene acrylonitrile resins, silicone resins, and fluorine resins can be mentioned. Among these, vinyl chloride resin is preferred because it has high dispersibility of ferromagnetic fine powder.

[0008] The above-mentioned thermosetting resin or reactive resin has a molecular weight that becomes extremely large when heated.
For example, phenolic resin, phenoxy resin, epoxy resin, curable polyurethane resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose-smelamine resin, high molecular weight polyester resin and isocyanate. Mixture of prepolymers, urea formaldehyde resin,
Included are mixtures of low molecular weight glycols/high molecular weight diols/polyisocyanates, polyamine resins, and mixtures thereof.

[0009] As the radiation-curable resin, a thermoplastic resin having a carbon-carbon unsaturated bond bonded thereto as a radiation-curable functional group is used. Preferred functional groups include acryloyl and methacryloyl groups. In the bond molecules listed above, polar groups (epoxy group, CO2 M, OH, NR2, NR3 M, SO3 M
, OSO3 M, PO3 M2 , OPO3 M2 ,
However, M is hydrogen, an alkali metal, or ammonium, and when a plurality of M's are present in one group, they may be different from each other. R is hydrogen or an alkyl group. ) may be introduced. The binders listed above may be used alone or in combination, and can be cured by adding a known isocyanate-based crosslinking agent and/or a radiation-curable vinyl monomer.

The isocyanate crosslinking agent is a polyisocyanate compound having two or more isocyanate groups, such as tolylene diisocyanate, 4,4'-magnephenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5 - Isocyanates such as diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane diisocyanate, reaction products of these isocyanates and polyalcohols,
and polyisocyanates produced by condensation of these isocyanates. These polyisocyanates are available from Nippon Polyureta Kogyo Co., Ltd. as Coronate L, Coronate HL, Coronate H, Coronate EH,
Coronate 2014, Coronate 2030, Coronate 2031, Coronate 2036, Coronate 3015,
Coronate 3040, Coronate 3041, Millionate MR, Millionate MTL, Daltosec 1350,
Daltosec 2170, Daltosec 2280, Takenate D102, Takenate D1 from Takeda Pharmaceutical Co., Ltd.
10N, Takenate D200, Takenate D202, Sumidur N75 from Sumitomo Bayer, Desmodur L, Desmodur 1L, Desmodur N, Desmodur HL from West German Bayer, Burnock D850 from Dainippon Ink & Chemicals Co., Ltd. , Burnock D8
It is commercially available under trade names such as 02.

The radiation-curable vinyl monomer is a compound that can be polymerized by radiation and has one or more carbon-carbon unsaturated bonds in its molecule, such as (meth)allylic acid esters, (meth)allylic acid esters, Examples include acrylamides, allyl compounds, vinyl esters, vinyl heterocyclic compounds, N-vinyl compounds, styrene, (meth)acrylic acid, crotonic acid, itaconic acid, and olefinic acid. Among these, diethylene glycol di(
Polyethylene glycol (meth)acrylates such as meth)acrylate, triethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate
Acrylate, dipentaerythritol penta(meth)
Acrylate, dipentaerythritol hexa(meth)
Examples include acrylates and reaction products of polyisocyanates and hydroxy (meth)acrylate compounds.

[0012] These crosslinking agents preferably account for 5 to 45 wt% of the total binder containing crosslinking agents.

[0013] Also, as a hydrophilic binder, Research Disclosure No. 17643, 26 pages,
and same no. 18716, page 651, and exemplifies water-soluble polymers, cellulose esters, latex polymers, water-soluble polyesters, and the like. Examples of water-soluble polymers include gelatin, gelatin derivatives,
Casein, agar, sodium alginate, starch, polyvinyl alcohol, polyacrylic acid copolymer, maleic anhydride copolymer, etc., and cellulose esters include carboxymethyl cellulose, hydroxyethyl cellulose, etc. Latex polymers include vinyl chloride-containing copolymers, vinylidene anhydride-containing copolymers, acrylic acid ester-containing copolymers, vinyl acetate-containing copolymers,
butadiene-containing copolymers, etc. Among these, gelatin is most preferred. Further, gelatin derivatives and the like may be used in combination with gelatin.

As the gelatin, any of so-called lime-treated gelatin, acid-treated gelatin, enzyme-treated gelatin, gelatin derivatives, modified gelatin, etc. can be used, and among them, lime-treated gelatin and acid-treated gelatin are preferably used.

The magnetic recording layer containing gelatin is preferably hardened. Hardeners that can be used in the magnetic recording layer include:
For example, aldehyde compounds such as formaldehyde and glutaraldehyde, ketone compounds such as diacetyl and cyclopentanedione, bis(2-chloroethylurea), 2-hydroxy-4,6-dichloro-1,3,
5-triazine, etc. U.S. Pat. No. 3,288,77
No. 5, No. 2,732,303, British Patent No. 974,7
Compounds containing reactive halogens, divinyl sulfone, 5-acetyl-1,3-diacryloylhexahydro-1,3,5-triazine, etc., described in No. 23 and No. 1,167,207, etc. U.S. Patent Nos. 3 and 6
No. 35,718, No. 3,232,763, compounds with reactive olefins described in British Patent No. 994,869, N-hydroxymethylphthalimide, and others, U.S. Patent No. 2,732,316 No. 2,
N-methylol compounds described in US Pat. No. 586,168 etc., isocyanates described in US Pat. No. 3,103,437 etc., US Pat. No. 3,017,28
0, aziridine compounds described in U.S. Patent No. 2,983,611, etc., acid derivatives described in U.S. Pat.
Examples include epoxy compounds described in US Pat. No. 3,091,537 and the like, and halogencarboxaldehydes such as mucochloric acid. Alternatively, as a hardening agent for inorganic compounds, chromium alum, zirconium sulfate, Japanese Patent Publications No. 56-12853, No. 58-32699,
Belgian Patent No. 825,726, JP-A-60-2251
No. 48, No. 51-126125, Special Publication No. 58-506
No. 99, JP-A No. 52-54427, U.S. Patent No. 3,32
1,313 etc. Examples include carboxyl group-activated hardeners. The amount of hardener used is usually 0.01 to 30% by weight, preferably 0.05 to 20% by weight, based on dry gelatin.

[0016] The thickness of the transparent magnetic recording layer is 0.1 to 10μ.
m, preferably 0.2 to 5 μm.

[0017] As the film support in the present invention,
Although not particularly limited, various plastic films can be used, and preferred ones include cellulose derivatives (e.g., diacetyl-, triacetyl-, propionyl-,
butanoyl, acetylpropionyl acetate, etc.), polyamides, polycarbonates described in U.S. Pat. Terephthalate, polyethylene-1,2-diphenoxyethane-4
, 4'-dicarboxylate, polybutylene terephthalate, polyethylene naphthalate), polystyrene, polypropylene, polyethylene, polymethylbentene, polysulfone, polyethersulfone, polyarylate, polyetherimide, etc., and particularly preferred is triacetyl cellulose. , polyethylene terephthalate. A plasticizer may be added to these supports for the purpose of imparting flexibility. Particularly for cellulose esters, plasticizer-containing materials such as triphenyl phosphate, biphenyl diphenyl phosphate, and dimethyl ethyl phosphate are commonly used. Although these supports vary depending on the type of polymer, the thickness ranges from a sheet of about 1 mm to a thin film of about 20 μm depending on the purpose, but the thickness range of 50 μm to 300 μm is commonly used. The molecular weight of these support polymers is preferably 10,000 or more, more preferably 20,000 to 80,000.

The term "substantially transparent to visible light" as used in the present invention varies depending on the usage. For example, when a magnetic recording layer is provided on the entire surface of a photographic light-sensitive material, it is preferable that the maximum value of the spectral density of the magnetic recording layer in the visible range is 0.2 or less. This corresponds to a light transmittance of 63% or more.

It is preferable that the magnetic output has a C/N ratio of 25 dB or more.

The refractive index (wavelength in nm) of a magnetic material is 2.42 (589 nm) for magnetite, and is considered to be around this level for γ-hematite, barium ferrite, and the like. Further, the refractive index of the main binder materials is as shown in Table 1, and is usually about 1.1 to 1.5. Generally, the refractive index of the magnetic material is greater than the refractive index of the binder. Therefore, in the case of a magnetic recording layer in which magnetic fine particles are simply dispersed in a binder, a portion of the incident light is scattered, resulting in a decrease in light transmittance. In order to reduce light scattering, the difference between the refractive index of the magnetic material and the refractive index of the binder should be small. Since it is very difficult to lower the refractive index of magnetic materials,
It is better to increase the refractive index of the binder. By dispersing ultrafine particles having a larger refractive index than the binder in the binder, it is possible to increase the overall refractive index of the binder. More preferably, in order to bring the refractive index of the binder closer to that of the magnetic material, ultrafine particles having a higher refractive index than the magnetic fine particles are dispersed in the binder. In this way, light scattering due to the magnetic fine particles in the magnetic recording layer can be reduced and light transmittance can be significantly improved.

[0021] Therefore, as an example of ultrafine particles having a large refractive index used in the present invention, TiO2 (refractive index 2.
61 (wavelength 589 nm), Al2 O3 (wavelength 589 nm)
(546 nm)), SiO2 (1.54 (58 nm)
9nm)), CaCO3 (1.658 (589n)
m), cadmium sulfide (2.57 (550 nm))
, cadmium iodide (2.7 (600 nm)), thallium bromide-cadmium iodide (2.65 (560 nm)
)), etc. In addition, any ultrafine particles having a higher refractive index than the binder may be used. When these ultrafine particles are dispersed in a binder, it cannot be expected to increase the light transmittance if the ultrafine particles themselves scatter a lot of light. Therefore, the particle size of the ultrafine particles is preferably 0.1 μm or less so that light scattering of visible light does not become a problem. More preferably, it is 0.05 μm or less. The content of ultrafine particles in the magnetic recording layer in the present invention is 1 m2
It is desirable that the amount is 25 g or less, preferably 0.01 g to 5 g.

The transparent magnetic recording layer can be provided by coating or printing. As the application method, various methods such as doctor coating, extrusion coating, slide cord, roller coating, and gravure coating can be considered. Alternatively, a support having a magnetic recording layer may be created by co-casting a polymer solution in which magnetic particles and ultrafine particles having a high refractive index are dispersed and a polymer solution for forming the support. In this case, it is preferable that the polymer in which the magnetic particles and ultrafine particles are dispersed is substantially the same as the polymer for preparing the support. Improved lubricity and antistatic properties for the magnetic recording layer.
It may also have functions such as preventing adhesion and improving friction and wear characteristics, or it may provide these functions by providing another functional layer. Specifically, antistatic agents, lubricants, abrasives, matting agents, surfactants, and the like can be contained. If necessary, a protective layer may be provided adjacent to the magnetic recording layer to improve scratch resistance. Furthermore, an intermediate layer may be provided between the support and the magnetic recording layer. The refractive index of the intermediate layer is preferably between the refractive index of the support and the magnetic recording layer. After providing the magnetic recording layer, it is also possible to perform a calendering process on this layer to improve smoothness and improve the S/N ratio of the magnetic output.

[0023]

[Examples] The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the Examples unless it goes beyond the gist of the present invention. Example 1. A magnetic coating liquid having the following composition was kneaded in a ball mill for 50 hours. (Magnetic coating liquid 1) Magnetic fine particles (diameter 0.1 μm, thickness 0.03 μm,
Coercive force 900Oe, magnetization 62emu
/g of barium ferrite)
2g TiO2 (
particle size 0.02μm)
150g Vinyl chloride-vinyl acetate copolymer
50g butyl acetate

400g (comparative magnetic coating liquid 2) Magnetic fine particles (diameter 0.1 μm, thickness 0.03 μm,
Coercive force 900Oe, magnetization 62emu
/g of barium ferrite)
2g vinyl chloride
vinyl acetate copolymer
50g butyl acetate

After dispersing 400 g, magnetic coating liquid 1 is applied onto the entire surface of the support on a cellulose triacetate film having a thickness of 122 μm using an extrusion coating method. Before the coating solution dried, a treatment was performed using a cobalt magnet so that the magnetic material was sufficiently oriented. After drying the solvent, calendering was performed and the film was wound. The dry thickness of the magnetic layer was 3 μm. The residual magnetic flux density was 14.5G. A comparative magnetic coating liquid was also applied to the same thickness in the same manner. This also had a residual magnetic flux density of 14.5G.

A signal of 200 tpi was recorded on the film thus obtained using a magnetic head with a track width of 1.5 mm. This signal was reproduced using the same magnetic head. Since the playback signal level was low, a preamplifier was added during playback to amplify the signal by 90dB. As a playback signal,
A signal with a C/N ratio of 29.3 dB was obtained for each sample.

The light transmittance of this film was 56% at a wavelength of 545 nm for the comparative film, whereas it was 70% for the film coated with the magnetic coating liquid 1 of the present invention.
Met. In the comparative film, the transmittance is lower than 63%, which corresponds to an optical density of 0.2, but in the film of the present invention, it is 63% or more, indicating that the light transmittance is significantly improved.

Example 2. A magnetic coating liquid having the following composition was kneaded in a ball mill for 50 hours. (Magnetic coating liquid 3) Magnetic fine particles (diameter 0.03 μm, thickness 0.3 μm,
Co-modified iron oxide particles with coercive force of 850 Oe and magnetization of 80 emu/g)
2g TiO2 (particle size 0.
02μm)
60g vinyl chloride
vinyl acetate copolymer
50g butyl acetate

400g (comparative magnetic coating liquid 4) Magnetic fine particles (diameter 0.03 μm, thickness 0.3 μm,
Co-modified iron oxide particles with coercive force of 850 Oe and magnetization of 80 emu/g)
2g Vinyl chloride-vinyl acetate copolymer
50g butyl acetate

400
After g dispersion, magnetic coating liquid 3 is applied on a cellulose triacetate film having a thickness of 122 μm in exactly the same manner as in Example 1. Before the coating solution dried, a treatment was performed using a cobalt magnet so that the magnetic material was sufficiently oriented. After drying the solvent, calendering was performed and the film was wound up. The dry thickness of the magnetic layer was 1.5 μm. The residual magnetic flux density was 19G. A comparative magnetic coating liquid was also applied to the same thickness in the same manner. This also had a residual magnetic flux density of 19G.

A 200 tpi signal was recorded on the film thus obtained in the same manner as in Example 1, and the reproduced signal was measured. As a playback signal, each sample has 29
．． A signal with a C/N ratio of 6 dB was obtained.

The light transmittance of this film was 55% at a wavelength of 545 nm for the film coated with comparative magnetic coating liquid 4, while it was 63% for the film coated with magnetic coating liquid 3 of the present invention. there were. The comparative film has a transmittance of 63% or less, while the film of the present invention has a transmittance of 63% or less.
3% or more, and it can be seen that the light transmittance is not significantly improved even in the magnetic recording layer using Co-modified iron oxide as the magnetic fine particles.

In the above embodiments, plate-shaped barium ferrite and needle-shaped Co-modified iron oxide were used. Various materials used as magnetic recording materials can be used, such as granular magnetite and CrO2.

[0030]

[Effects of the Invention] As shown in Examples 1 and 2, according to the present invention, it is possible to perform recording with a sufficient C/N ratio for recording and reproducing information, and the magnetic material is highly transparent to visible light. It becomes possible to have a recording layer.

Claims (3)

[Claims] 1. A magnetic recording medium having a magnetic recording layer in which fine magnetic particles are dispersed in a non-magnetic binder, characterized in that ultra-fine particles having a refractive index larger than that of the non-magnetic binder are dispersed in the non-magnetic binder. Medium. 2. A magnetic recording medium having a magnetic recording layer in which fine magnetic particles are dispersed in a non-magnetic binder, characterized in that ultra-fine particles having a refractive index larger than that of the magnetic fine particles are dispersed in the non-magnetic binder. Medium. 3. The magnetic recording medium according to claim 1, wherein the ultrafine particles have a size of 0.1 μm or less.