JPH04195726A - Magnetic material having improved transparency - Google Patents

Abstract

PURPOSE:To obtain a magnetic material having a higher transparency by covering the surface of magnetic particles with a material having the refractive index n3 and selecting a value of n3 not existing between n1 and n2 in a magnetic recording layer consisting of a magnetic material having the refractive index n2 dispersed into a binder having the refractive index n1. CONSTITUTION:The surface of magnetic particles are covered with a material having the refractive index n3 and a value of n3 is selected to the value not existing between n1 and n2 in a magnetic recording layer consisting of a magnetic material having the refractive index n2 dispersed into a binder having the refractive index n1. Namely, the light is reflected at the surface of particle and absorption by internal magnetic particles is reduced by covering a magnetic material having a large absorption coefficient in the visible light region with a material having a different refractive index and a small absorption coefficient in the visible light region. Thereby, a magnetic recording layer having a high transparency can be obtained while executing the recording ensuring the CN ratio sufficient for recording and playback of information.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to magnetic recording materials, and in particular to providing a magnetic recording layer that is substantially transparent to visible light.

[Conventional technology]

Magnetic recording is widely used in video tapes, audio cassettes, floppy disk magnetic cards, etc.

In these applications, there was no particular need to increase the light transmittance, as the light transmittance was required not to be too large for detection by a videotape reader.

However, considering the use of magnetic recording over the image area of photographic film to record photographing conditions and other information, it is necessary for photographic film to have as little coloration and high transmittance as possible against light. It's coming. [If recording is performed digitally, the required signal-to-noise ratio is small, so the amount of magnetic material applied is 1/10 to 1/100 of that of video tape, audio cassette, etc., and the light transmittance is 1. I can do something.

This idea was developed by Fuji Film (Special Publication No. 42-4539
), EK (Japanese Patent Publication No. 57-6576), etc.

However, in this case as well, the problem was that the magnetic material had absorption in the visible region and was colored red or black, so the absorption in these wavelength regions was not reduced.

In addition to applications that inherently require high transparency, there are also many applications where pale or near-white colors are preferred for aesthetic reasons, such as magnetic stripes for magnetic cards and cash cards. There is also a need to provide a magnetic recording layer on the back side of a photographic print to record information related to the front photograph, but if it is darkly colored black or brown, its commercial value is low. It would be of great industrial value if a white or highly brightly colored, lightly colored magnetic material could be produced for such uses.

(Problem to be solved by the invention) For such uses, it is sufficient to have a playback signal output of 1/10 to 1/100 compared to audio tapes and video tapes that are intended to record information digitally. and non-magnetic around the magnetic particles and claimed in claim 1.''
The aim of the present invention is to provide a layer having a refractive index such that the magnetization per particle can be increased by F.

In order to solve the above problem, by coating a magnetic material with a high absorption rate in the visible light range with a material with a different refractive index and a low absorption coefficient in the visible light range, light is reflected on the surface of the particle and the internal magnetism is generated. This is intended to reduce absorption due to grain Tc.

(Means for Solving the Problems) The present invention provides the following features: (1) In a magnetic recording layer made of a magnetic material having a refractive index n2 dispersed in an inder having a refractive index n+, the surface of the magnetic particles has a refractive index A magnetic material t4゜ is coated with a material of n, and nff is selected so that it is not between n+ and nz. (2) A material having a higher refractive index than the magnetic particle on the surface of the magnetic particle. 2. The magnetic material according to claim 1, characterized in that the magnetic material has a low light absorption rate.

(3) Claim 1 is a magnetic recording material characterized by using a coating cavity in which the magnetic material of Claim 2 is dispersed in a binder.

(4) The magnetic recording material according to claim 3, having a light transmittance of 63% or more.

(5) The magnetic recording material according to claim 3, characterized in that the light absorption is 50% or less compared to a case where the magnetic body is not coated with a material having a refractive index of n.

(6) The magnetic material according to Claims 1 and 2, wherein the coating material of the magnetic body is titanium dioxide.

(7) The magnetic recording material according to claims 3.4 and 5, wherein the magnetic coating material is titanium dioxide.

achieved by.

To explain the present invention in more detail, in a magnetic recording layer made of a magnetic material having a refractive index n1 dispersed in a binder having a refractive index n, the surface of the magnetic particles has a refractive index n
A magnetic material characterized by being coated with a material selected so that 3 does not fall between n, , and n is an optical condition for obtaining maximum reflectance due to a thin film on the surface, and as in the present application, In a system where fine particles are dispersed, the incident direction of light is also distributed.
The physical properties of the thin film on the surface of the IG particles change depending on the production conditions, and the wavelength of the IG particles also covers the visible light range. This is something that can be done.

In addition, considering that the refractive index of the I)19 material on the surface is that the refractive index of the binder material used for -C is about 14 to 1.5, and there are few materials with a smaller refractive index, the second claim It is best to choose something with a large refractive index, such as a term.

In order to increase the transmittance, it is necessary to avoid the particles of the same composition, which is the largest in the case of pigments, and to allow for fine powderization, coating film thickness, noise level of the magnetic reproduction signal, etc. By making the particles coarser in the range, scattering of light on the particle surface is taken into consideration, so the particle size after coating can be determined so as to obtain increased transmittance within the required range.Conversely, the coloring when viewed by reflection can be determined. In order to reduce this, choose the size that maximizes the concealment power. Those skilled in the art can easily determine the conditions according to each application, but they can generally be selected depending on the wavelength of visible light in the binder.

The refractive index (wavelength in nm) of the magnetic material is magnetite 2°42 (589), and r-hematite and barium ferrite are also considered to be around this level.

On the other hand, TiO□rutile 2. is a white material with significant refraction.
61 (589), cadmium sulfide 2.57 (550
), cadmium iodide 2.7 (600), thallium bromide-thallium iodide 2.65 (560), etc., and the material to be coated can be selected with reference to these values.

As the binder used in the present invention, known thermoplastic resins, thermosetting resins, radiation curable resins, reactive resins, and mixtures thereof, which are conventionally used as binders for magnetic recording media, can be used. .

The above fat has a Tg of -40'C to 150'C and a weight average molecular weight of 10,000 to 300,000, preferably 10,000 to 10,000.

Examples of the thermoplastic resin include vinyl chloride/vinegar 6-vinyl copolymer, vinyl chloride, vinyl acetate and vinyl alcohol,
Copolymers with maleic acid and/or acrylic acid, vinyl copolymers such as vinyl chloride/vinylidene chloride copolymers, vinyl chloride/acrylonitrile copolymers, ethylene/vinyl acetate copolymers, nitrocellulose, cellulose acetate Propionate, cellulose derivatives such as cellulose acetate butyrate resin, acrylic resin,
Rubber resins such as polyvinyl acetal resin, polyvinyl butyral resin, polyester polyurethane resin, polyether polyurethane, polycarbonate polyurethane resin, polyester resin, polyether resin, polyamide resin, amino resin, styrene butadiene resin, butadiene acrylonitrile resin, silicone resin Examples include resins and fluororesins.

Among these, vinyl chloride resin is preferred because it has high dispersibility of ferromagnetic fine powder.

The above-mentioned thermosetting resins or reactive resins are those whose molecular weight becomes extremely large when heated, such as phenol resins, phenoxy resins, epoxy resins, curable polyurethane resins, urea resins, melamine resins, acrylic resins,
silicone resins, acrylic reactive resins, epoxy-polyamide resins, nitrocellulose melamine resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/polyisocyanates, polyamine resins, and Mixtures of these may be mentioned.

The radiation-curable resin used is one in which a group having a carbon-carbon unsaturated bond is bonded to the thermoplastic resin as a radiation-curable functional group. Preferred functional groups include acryloyl and methacryloyl groups.

In the binder molecules listed above, polar groups (epoxy groups, CO
,M,Of(,NRZ, NR3X,5off11,O
Introducing 3OffM, poffM, 0POJz, where M is hydrogen, alkali metal or ammonium, and when there are multiple M's in one group, they may be different from each other, R is hydrogen or an alkyl group) This is preferable in terms of the dispersibility and durability of the magnetic material, and the effect of adding the fluorine-containing oligomer surfactant of the present invention is noticeable.

The content of polar groups is 10-7 per gram of polymer.
~10-3 equivalents, preferably even 10-'~10
-"equivalent is the preferred range.

The polymeric 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 thread binder.

As an isocyanate-based crosslinking agent, two isocyanate groups are used.
Polyisocyanate compounds having at least 100% polyisocyanate, such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate,
xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-F luidine diisocyanate,
Examples include isocyanates such as isophorone diisocyanate and triphenylmethane diisocyanate 7-ate, reaction products of these isocyanates and polyalcohols, and polyisocyanates produced by condensation of these isocyanates 1. These polyisocyan 7-
1. is Nippon Polyurethane Industry Co., Ltd. Karakoro Daiichi L,
Coronate HL, Coronate H, Coronate EH, Coronate 2014, Coronate 2030, Coronate 203
1, Coronate 2036, Coronate 3015, Coronate 3040, Coronate 3041, Millionate MR
3 Millionate MTL, Daltomonoku 1350, Daltosenku 2170, Daltomonoku 2280, Takenate D102, Takenate DIION from Sokoen Yakuhin Kogyo Co., Ltd.
, Takenate D200, Takenate D202, from Sumitomo Bayer Co., Ltd., Sumidur N75, Desmodule from West German Bayer, Desmodule IL, Desmodule N, Desmodule HL, parts from Dainippon Ink & Chemicals Co., Ltd. It is commercially available under trade names such as D850 and Hanononoku D802.

Radiation-cured vinyl thread yarns are compounds that can be polymerized by radiation irradiation and have one or more carbon-carbon unsaturated bonds in their molecules, such as (meth)acrylic esters, (meth) ) Acrylamides, allyl compounds, vinyl esters, vinyl esters, vinyl heterocyclic rings (71, N-vinyl compounds, styrene, (meth)
Examples include acrylic acid, crotonic acid, itaconic acid, and olefinic acid. Among these, (meth)acrylates of polyethylene glycol, such as diethylene glycol di(meth)acrylate and triethylene glycol di(meth)acrylate, which have two or more (meth)acryloyl groups, are preferred! , trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol penta(meth)acrylate, reaction of polyisocyanate with hydroxy(meth)acrylate compound There are things, etc.

These crosslinking sides account for 5 to 45% of the total binder including the crosslinking side.
-t% is preferred.

Additionally, hydrophilic binders can be used in the magnetic recording materials of the present invention.

The hydrophilic binder used is Research Disclosure Nα17643.26 page and IF;1
Nct18716, page 651, water-soluble polymers, cellulose esters, latex polymers,
Examples include water-soluble polyester. Water-soluble polymers include gelatin, gelatin derivatives, casein,
These include agar, sodium alginate, starch, polyvinyl alcohol, polyacrylic acid copolymer, maleic anhydride copolymer, etc., and cellulose esters include carboxymethyl cellulose, hydroxyethyl cellulose, etc. Examples of the latex polymer include vinyl chloride-containing copolymers, vinylidene chloride-containing copolymers, acrylic acid ester-containing copolymers, vinyl acetate-containing copolymers, and butanoene-containing copolymers.

Among these, gelatin is most preferred.

During the manufacturing process, gelatin is produced by
For an alkaline bath? ! ? So-called alkali-treated (lime-treated) gelatin that is subjected to M, acid-treated gelatin that is immersed in an acid bath, and double immersion that has undergone both treatments? Either No. 11 gelatin or enzyme-treated gelatin may be used.

If necessary, a portion may be added to colloidal albumin, casein, cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, agar, sodium alginate, starch derivatives, sugar derivatives such as dextran, synthetic hydrophilic colloids such as polyvinyl alcohol, poly-N- Vinylpyrrolidone, polyacrylic acid copolymer,
Polyacrylamide or derivatives thereof, partial hydrolysates, gelatin derivatives, etc. may be used in combination with gelatin.

It is preferred to harden the magnetic recording material containing gelatin.

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-chloroethyl urea), and 2-
Hydroxy-4゜6-dichloro-1,3,5-1-riazine, and others U.S. Pat. No. 3,288,775, No. 2
．． 732.303, British Patent No. 974.723, British Patent No. 1.167.207, etc., compounds containing reactive halogens, divinyl sulfone, 5-acetyl-1,3-diacryloyl hexahydro -1,3,
5-Triazine, etc. U.S. Patent No. 3.635.71
No. 8, No. 3,232°763, British Patent No. 994,8
Compounds with reactive olefins, N-hydroxymethylphthalimide, etc., as described in U.S. Pat.
N-methylol compounds described in US Pat. No. 3,103,437, etc., isocyanates described in US Pat. No. 3,103,437, etc.; Ol7.280, same 2.
Aziridine compounds described in U.S. Patent Nos. 2725.294 and 2,725.
Acid derivatives described in US Pat. No. 295, etc., U.S. Pat.
．． Examples include epoxy compounds described in No. 091.537, etc., and halogen carboxaldehydes such as mucochloric acid. Or, as a hardening agent for inorganic compounds, use chromium light pan, zirconium sulfate,
-12853, Belgian Patent No. 58-32699, Belgian Patent No. 825.726, Japanese Patent Application Laid-open No. 60"225148, Japanese Patent Application Publication No. 126125-1987, Japanese Patent Publication No. 58-50699,
JP 52-54427, U.S. Patent No. 3,321,31
Examples include carboxyl group-activated hardeners described in No. 3 and the like.

The amount of hardener used is usually 0.01 to dry gelatin.
-30% by weight, preferably 0.05-20% by weight.

The thickness of the magnetic recording layer is 0.1μ to 10μ, preferably 0.1μ to 10μ.
It is 5μ to 5μ, more preferably 1μ to 3μ.

The magnetic recording material of the present invention can contain an antistatic agent, a lubricant, a matting agent, a surfactant, and the like.

(Example) The present invention will be explained in more detail by giving specific examples below.
The invention is not limited to the examples unless it goes beyond the gist of the invention.

Example 1 Magnetic material Particle diameter: 0.1μ, thickness: 0.03μ, coercive force: 9
000e, barium ferrite with magnetization of 62 emu/g is dispersed in water, and Tie is placed on top of it, 0 (type), average 0
．． 01.0.02.0,03.0°04μ, by the hydrolysis method of acidic titanium sulfate. Using salt vinyl acetate with a refractive index of 1.54 as a binder, 25 g of binder per 1 g of effective magnetic material in the particles, 50 g of butyl acetate as a solvent, and sufficiently dispersed in a ball mill to prepare a uniform coating solution. It was applied so that the thickness was 2μ.

The residual magnetic flux density was 14-15G. A magnetic head with a track width of 1.5 mm was used to record and reproduce 200 tpi signals. Since the signal level was low in the measurement, one stage of preamplifier was added and the gain was increased so that the noise of the medium became the noise of the reproduced output, and a signal with a CN ratio of 29 to 30 dB was obtained.

At this time, the transmittance at a wavelength of 545 nm is 5.
6%, respectively, were 60.66, 72.80%. The limit of light transmittance varies depending on the method of use, but when using it as a support film for photographic negative film, there is a strong demand to keep the coloration to the current level due to the exposure conditions in the photo processing laboratory, and taking this into consideration, optical density is 0. A transmittance of 63% or more corresponding to .2 is desirable.
Those coated with 0°02μ or more fall within this range.

Example 2 Magnetic material Particle diameter 0.03μ, length 0.3μ, coercive force 8
CO-modified iron oxide particles with 500 eS magnetization of 80 emu/g were dispersed in water, and TiO
．． It was formed by the hydrolysis method of acidic titanium sulfate so that it was 0.02.0.05μ. Using salt-vinyl acetate with a refractive index of 1.54 as a binder, 25 g of binder was removed per 1 g of effective magnetic material in the particles, 50 g of butyl acetate was added, and the mixture was sufficiently dispersed in a ball mill to prepare a uniform coating solution, which was then dried. It was coated to a thickness of 1.5 μm. The residual magnetic flux density was 18-20G. This is track width 1゜5
A signal of 200 tpi was recorded and reproduced using a magnetic head of 1.0 m to obtain a signal with a CN ratio of 28 to 30 dB. The measurements were carried out in the same manner as in Example 1.

At this time, the transmittance at a wavelength of 545 nm is 5.
2%, respectively, were 68.71.75%.

Example 3 Magnetic material Barium ferrite with a particle diameter of 0.25μ, a thickness of 0.04μ, a coercive force of 9550e, and a magnetization of 5Qemu/g is dispersed in water, gelatin is added to a concentration of 1%, and then acidic T i O by the hydrolysis method of titanium sulfate
T was formed to have an average thickness of 0.12 μm. A type without T i Oz coating was also prepared. After washing this with water using the inclined water washing method, the refractive index was 1.5.
42 gelatin was added as a binder. In this example, the ratio was set to 25 g of binder and 75 g of water per 50 g of powder. This was dispersed using a Desba type disperser to prepare a uniform coating solution, which was coated in a magnetic field to a dry thickness of 8 μm and dried. The residual magnetic flux density is type 5.
00, and the product of this example was 80G.

This is 500tpi with a magnetic head of trunk width 3.5-
A signal with a CN ratio of 60 dB was obtained using the recording/reproducing ε type, and a signal with a CN ratio of 45 dB was obtained using the product of this example. In this example, a commercially available magnetic card league was used for measurement because it had a sufficiently large output. Comparing the appearance of this product, the type has a dark w color, but the product in this example is white, so this -1- is really true.

Letters written with pens or colored pencils were clear, and letters and figures could be printed with a beautiful finish.

Although several embodiments have been given above, it goes without saying that the present invention is not limited to these embodiments.
In addition to modified iron oxide, there are also various types of magnetic recording materials used as magnetic recording materials, such as metal magnetic materials whose main component is metallic iron with an oxidation stabilizing film on the surface, acicular and granular magnetite, Cry, etc. materials are available.

(Effects of the Invention) As shown in Example 1.2, according to the present invention, a highly transparent magnetic recording layer can be obtained while recording with a sufficient CN ratio for recording and reproducing information. This coloration due to spectral absorption inherent to the 11μ substance can be reduced by using the material of the present invention, and the coloration can be reduced.

As is clear from a comparison of Examples 1 and 2, when the particle size is sufficiently small compared to the wavelength of light, the effect of light scattering by the particles is small, so the amount of transmitted light increases and transparency is improved. Ru. Furthermore, the grain transmittance may become small if the particle size is around the wavelength of light in the vicinity of the maximum hiding power, so the size in this area can also be considered. This relationship cannot be determined by simple numbers because the optical constants (refractive index, absorption coefficient) of the particles and binder, the size and shape of the particles, their distribution, and the wavelength and direction of incidence of light are intricately related. Given these conditions, those skilled in the art can easily find the optimal conditions among them. The effect of reducing the transparency as a result of such condition setting 7 should be selected to be 65% or more, preferably 70% or more in applications such as photographic slides where observation is made through this layer.

As shown in Example 3, in applications where the magnetic recording layer is viewed with reflected light, it is sufficient to reduce the degree of coloration, and it is preferable to use the particle film S1, which is slightly different from that described in F, that is, the scattering of light on the particle surface. It is desirable to increase the reflectance and reduce the inherent coloring of the magnetic material. In this case, a particle size L7 that maximizes the so-called hiding power (nearly half the wavelength of light) is preferable. For applications such as magnetic cards, cash cards, and photo prints, the magnetic recording layer should not be red or black, but should preferably be white, or if not, lightly colored.The extent of this depends on the spectral absorption inherent to the magnetic material. The peak wavelength of at least 50% for those not treated according to the present invention.
%, preferably 20% or less, from the perspective of the practical test.

Claims (7)

[Claims] (1) In a magnetic recording layer made of a magnetic material having a refractive index n_2 dispersed in a binder having a refractive index n_1, the surface of the magnetic particles is coated with a material having a refractive index n_3, and n_3 is the same as n_1 and n_2. A magnetic material characterized by being selected so that there is no difference between the two. (2) The magnetic material according to claim 1, characterized in that the surface of the magnetic particles is coated with a material having a higher refractive index than the magnetic particles. (3) A magnetic recording material characterized by using a coating film in which the magnetic material according to claim 1 or 2 is dispersed in a binder. (4) The magnetic recording material according to claim 3, having a light transmittance of 63% or more. (5) The magnetic recording material according to claim 3, characterized in that the light absorption is 50% or less compared to a case where the magnetic body is not coated with a material having a refractive index of n_3. (6) The magnetic material according to Claims 1 and 2, wherein the coating material of the magnetic body is titanium dioxide. (7) The magnetic recording material according to any one of claims 3, 4 and 5, wherein the magnetic coating material is titanium dioxide.