JP2020107374A - Optical recording medium - Google Patents

Abstract

To provide a highly wear- and sweat-resistant magnetic recording medium.SOLUTION: A magnetic recording medium 10 provided herein comprises a magnetic recording layer 2, a shield layer 3, and a printed layer 5 laminated in the described order. The shield layer 3 contains an aluminum powder and shield layer binder resin containing a polyurethane and nitrocellulose, where nitrocellulose content in the shield layer binder resin is 10-40 mass%, inclusive, with respect to a total mass of the shield layer binder resin.SELECTED DRAWING: Figure 1

Description

The present invention relates to a magnetic recording medium.

For example, as prepaid cards such as a book card (registered trademark), a QUO card (registered trademark), and a telephone card, a magnetic recording medium that uses magnetic recording is used for managing the type of card, the balance, and the like. The magnetic recording medium has, for example, a magnetic recording layer, a hiding layer, and a printing layer in this order on a base material, and further has a protective layer (overprint layer) formed on the printing layer and serving as the outermost layer. May be.

The magnetic recording layer in the magnetic recording medium contains a dark magnetic material such as ferrite and exhibits, for example, a dark brown color. Therefore, in order to make the printed layer provided thereon visible, the dark color of the magnetic recording layer is hidden. There is a need to.

The hiding layer in the magnetic recording medium has a function of hiding the dark color of the magnetic recording layer and making the printed layer provided on the hiding layer visible. As the hiding layer, for example, silver ink containing aluminum powder is widely used.

Patent Document 1 discloses a magnetic recording that includes a silver ink for concealing a magnetic layer and a magnetic barcode in a magnetic recording medium, including aluminum powder surface-treated with a coupling agent, and a mixture of a polyurethane resin and a phenoxy resin. Silver ink for media is described.

Patent Document 2 discloses that in a heat-sensitive magnetic recording medium having a magnetic recording layer, a hiding layer, and a heat-sensitive recording layer, the hiding layer should include an aluminum paste and a binder in which nitrocellulose and an acrylic resin are mixed. Have been described.

Patent Document 3 describes an overprint card in which a concealing layer, a white layer, and a surface protective layer are laminated in this order on a card substrate. Further, in Patent Document 3, a masking ink formed by kneading a resin-coated aluminum powder in a binder is used for forming the masking layer, and vinyl chloride-vinyl acetate is used as a resin binder of the masking ink. It is described that one kind or two or more kinds of thermoplastic resins such as a copolymer resin, a urethane resin, a polyester resin and a cellulose resin can be appropriately used in combination.

JP, 6-212109, A JP-A-8-183279 JP, 2011-25444, A

The magnetic recording medium in the related art lacks abrasion resistance when it is inserted into a magnetic card reader/writer to perform reading and/or writing processing, and when the reading and writing are repeated, the surface printing layer and the concealing layer are worn out. Then, the magnetic recording layer may be exposed. Further, when the magnetic recording medium comes into contact with human sweat, there is a problem that the adhesion between the magnetic recording layer and the concealing layer is impaired and peeling occurs.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium having excellent wear resistance and sweat resistance in order to solve the above problems in the prior art.

The present invention that achieves the above object is as follows.
<<Mode 1>>
A magnetic recording medium having a magnetic recording layer, a hiding layer, and a printing layer in this order,
The hiding layer contains aluminum powder and a hiding layer binder resin,
The hiding layer binder resin contains polyurethane and nitrocellulose,
The content ratio of nitrocellulose in the hiding layer binder resin is 10% by mass or more and 40% by mass or less based on the whole hiding layer binder resin,
Magnetic recording medium.
<<Mode 2>>
2. The magnetic recording medium according to aspect 1, wherein the content ratio of nitrocellulose in the hiding layer binder resin is 20% by mass or more and 35% by mass or less based on the whole hiding layer binder resin.
<<Mode 3>>
Aspect 1 or 2 in which the viscosity symbol for nitrocellulose defined by solution viscosity measurement according to JIS-K-6703 is H1/16, H1/8, H1/4, H1/2, H1, or H2. The magnetic recording medium according to.
<<Mode 4>>
4. The magnetic recording medium according to any one of aspects 1 to 3, wherein the magnetic recording layer is a layer containing a magnetic material, carbon, and a binder resin for the magnetic recording layer.
<<Mode 5>>
The magnetic recording medium according to aspect 4, wherein the binder resin for the magnetic recording layer contains polyester urethane.
<<Mode 6>>
The magnetic recording medium according to any one of aspects 1 to 5, further comprising a protective layer on a surface of the print layer opposite to the concealment layer.
<<Mode 7>>
7. The magnetic recording medium according to any one of aspects 1 to 6, which has a heat-sensitive recording layer between the hiding layer and the printing layer.
<<Mode 8>>
8. The magnetic recording medium according to any one of aspects 1 to 7, which has a base material layer on the surface of the magnetic recording layer opposite to the concealing layer.

According to the present invention, a magnetic recording medium having excellent wear resistance and sweat resistance is provided.

FIG. 1 is a schematic sectional view showing an example of the magnetic recording medium of the present invention. FIG. 2 is a schematic cross-sectional view showing another example of the magnetic recording medium of the present invention.

<Magnetic recording medium>
The magnetic recording medium of the present invention is
A magnetic recording medium having a magnetic recording layer, a hiding layer, and a printing layer in this order,
The hiding layer contains aluminum powder and a hiding layer binder resin,
The hiding layer binder resin contains polyurethane and nitrocellulose,
The content ratio of nitrocellulose in the hiding layer binder resin is 10% by mass or more and 40% by mass or less based on the whole hiding layer binder resin.

The magnetic recording medium of the present invention is
The printing layer, on the surface opposite to the hiding layer, may further have a protective layer,
On the surface of the magnetic recording layer opposite to the concealing layer, a base material layer may be further provided,
A heat-sensitive recording layer may be further provided between the hiding layer and the printing layer.

FIG. 1 shows a schematic sectional view showing an example of the magnetic recording medium of the present invention. The magnetic recording medium (10) of FIG. 1 has a magnetic recording layer (2), a hiding layer (3), and a printing layer (5) in this order. The magnetic recording medium (10) further has a protective layer (6) on the surface of the printing layer (5) opposite to the hiding layer (3), and the hiding layer (3) of the magnetic recording layer (2). The base material layer (1) is provided on the surface opposite to the surface. The printed layer (5) exists only in the regions that form characters, patterns, designs, etc., and in the other regions, the hiding layer (3) and the protective layer (6) are in direct contact with each other.

FIG. 2 shows a schematic sectional view showing another example of the magnetic recording medium of the present invention. The magnetic recording medium (20) of FIG. 2 has a magnetic recording layer (2), a hiding layer (3), and a printing layer (5) in this order. The magnetic recording medium (20) further has a protective layer (6) on the surface of the printing layer (5) opposite to the concealing layer (3), and the concealing layer (3) of the magnetic recording layer (2). It has a base material layer (1) on the surface opposite to and has a heat sensitive recording layer (4) between the hiding layer (3) and the printing layer (5). In the magnetic recording medium (20) of FIG. 2, the printing layer (5) exists only in the regions that form characters, patterns, designs, etc., and in the other regions, the thermosensitive recording layer (4) and the protective layer ( 6) is in direct contact with.

In the magnetic recording medium of the present invention, the hiding layer binder resin contained in the hiding layer contains polyurethane and nitrocellulose, and the content ratio of the nitrocellulose in the hiding layer binder resin is 10 with respect to the entire binder resin. It is from 40% by mass to 40% by mass. As a result, the wear resistance and sweat resistance of the magnetic recording medium of the present invention are remarkably improved.

In a conventional magnetic recording medium, a mixture of polyurethane and a phenoxy resin has been frequently used as a binder resin for a hiding layer, as described in Patent Document 1, for example. It is considered that this is because the concealing layer has the advantages of both the polyurethane and the phenoxy resin. That is, it is considered that polyurethane has high toughness, and the hiding layer containing polyurethane is excellent in abrasion resistance and plasticizer resistance, and has high surface strength. Further, since phenoxy resin has high heat resistance, light resistance, plasticizer resistance, and excellent adhesiveness, it is considered that these properties are exhibited in the hiding layer containing the phenoxy resin. Further, the phenoxy resin has a high "colorability", and there is an advantage that the concealing layer containing the phenoxy resin has a bright color tone.

However, the phenoxy resin is expensive and has problems such as odor. Therefore, a hiding layer material that does not use the phenoxy resin has been desired.

In the present invention, a specific amount of nitrocellulose is used instead of the phenoxy resin in the prior art. Nitrocellulose is excellent in compatibility with polyurethane, but is inferior in colorability, is excessively hard and brittle, and is easily combustible. Therefore, it has not been conventionally used as a hiding layer material for magnetic recording media. However, the present inventors have found that by using polyurethane in combination with a specific amount of nitrocellulose, a hiding layer material superior to conventional materials can be obtained, and completed the present invention.

Hereinafter, each layer of the magnetic recording medium of the present invention will be described in order.

<Hiding layer>
The hiding layer in the magnetic recording medium of the present invention contains aluminum powder and a hiding layer binder resin,
The hiding layer binder resin contains polyurethane and nitrocellulose,
The content ratio of nitrocellulose in the hiding layer binder resin is 10% by mass or more and 40% by mass or less based on the whole hiding layer binder resin.

(Aluminum powder)
The aluminum powder may be a non-leafing type aluminum powder having a small particle size (4 μm to 5 μm) or a scaly leafing type aluminum powder having a large particle size (10 μm to 15 μm), or a mixture thereof. May be The aluminum powder may have its surface modified with a suitable coupling agent. This coupling agent may be, for example, a silane coupling agent, a titanium coupling agent, or the like.

The aluminum powder may be supplied, for example, as contained in the aluminum paste, and may be provided for forming the hiding layer as a mixture of the aluminum paste and a hiding layer binder resin described later. Here, the aluminum paste is a mixture of aluminum powder, a paste binder, and a suitable solvent in a paste form.

The paste binder may be, for example, nitrocellulose or acrylic resin, or a mixture thereof.

The content ratio of aluminum powder in the aluminum paste may be, for example, about 50% by mass or more and 90% by mass or less.

As the solvent of the aluminum paste, for example, mineral spirits may be used.

(Binder resin for hiding layer)
The binder resin for the hiding layer contains polyurethane and nitrocellulose.

-Polyurethane-
The polyurethane in the binder resin for the hiding layer is a polymer having a urethane bond (-NH-C(=O)-), and may be, for example, one produced by a polyaddition reaction between a diisocyanate compound and a diol compound. .. As the polyurethane in the present invention, for example, a urethane-modified copolymerized polyester having an aromatic polyester as a basic skeleton and a urethane component bonded to a side chain; a repeating unit of ester and a repeating unit of urethane in a skeleton Urethane-modified copolyester; and the like may be used.

As the polyurethane in the hiding layer binder resin, a commercially available product may be used, and for example, “Vylon UR” series manufactured by Toyobo Co., Ltd. may be used.

-Nitrocellulose-
The nitrocellulose in the hiding layer binder resin is not particularly limited and may be appropriately selected and used from, for example, those commercially available under the name of “industrial nitrification cotton” and the like. As the nitrocellulose, in particular, in accordance with JIS-K-6703, viscosity symbols defined by solution viscosity measurement of a nitrocellulose solution using a mixed solvent of ethanol, toluene, and ethyl acetate are H1/16 and H1/. Those having 8 or H1/4, or H1/2, H1, or H2 can be preferably used. Nitrocellulose having a viscosity code of H1/16 to H1/4 is a solution in which a predetermined steel ball falls between the marked lines in a solution having a solid content of 25% by mass for 1.0 second or more and 8.9 seconds or less. Is. Nitrocellulose having a viscosity code of H1/2 to H2 has a time in which a predetermined steel ball falls between marked lines in a solution having a solid content of 20 mass% is 3.0 seconds or more and 2.5 seconds or less. ..

Examples of commercial products that can be suitably used as nitrocellulose in the binder resin for the concealing layer can include, but are not limited to, the following.
Asahi Kasei's BTH-2, BTH-1, BTH-1/2, BTH-1/4, BTH-1/8, BT-SL, etc.;
HIG2, HIG1, HIG1/2, HIG1/4, HIG1/8, HIG1/16 etc. made by SNPE of France;
RS2, RS1, RS1/2, RS1/4, RS1/8, RS1/16 and the like manufactured by Daicel Corporation.

The content ratio of nitrocellulose in the hiding layer binder resin is 10% by mass or more and 40% by mass or less based on the whole hiding layer binder resin. From the viewpoint of improving sweat resistance, the content ratio of nitrocellulose is 15% by mass or more, 20% by mass or more, 25% by mass or more, or 30% by mass or more based on the whole binder resin for the hiding layer. Well, from the viewpoint of maintaining high wear resistance and balancing sweat resistance and wear resistance, it may be 35 mass% or less, 30 mass% or less, or 25 mass% or less. The content ratio of nitrocellulose may be typically 15% by mass or more and 35% by mass or less based on the whole binder resin for the hiding layer.

(Percentage of binder resin used for the hiding layer)
The ratio of the binder resin for the hiding layer in the hiding layer is 50 parts by mass or more, 75 parts by mass or more, 100 parts by mass with respect to 100 parts by mass of the aluminum paste in order to secure the adhesiveness and the mechanical strength of the hiding layer. The amount may be 125 parts by mass or more, 150 parts by mass or more, or 175 parts by mass or more, and 500 parts by mass or less and 400 parts by mass or less with respect to 100 parts by mass of the aluminum paste in order to secure sufficient hiding property. , 350 parts by mass or less, 300 parts by mass or less, 250 parts by mass or less, or 200 parts by mass or less.

The proportion of the hiding layer binder resin used in the hiding layer is shown below in terms of a value based on 100 parts by mass of the aluminum powder. The use ratio of the hiding layer binder resin in the hiding layer is 55 parts by mass or more, 85 parts by mass or more, 110 parts by mass or more, 140 parts by mass or more, 165 parts by mass or more, or 195 parts by mass with respect to 100 parts by mass of the aluminum powder. The amount may be not less than 1,000 parts by mass, not more than 1,000 parts by mass, not more than 800 parts by mass, not more than 700 parts by mass, not more than 600 parts by mass, not more than 500 parts by mass, or not more than 400 parts by mass.

(Other ingredients)
The hiding layer contains aluminum powder and a binder resin for the hiding layer, but may contain other components. Examples of other components in the concealing layer include titanium oxide and the like.

(Thickness of the hiding layer)
The thickness of the hiding layer in the magnetic recording medium of the present invention is typically 0.5 μm or more and 4 μm or less, preferably 1 μm or more and 2 μm or less.

<Magnetic recording layer>
The magnetic recording layer in the magnetic recording medium of the present invention may be a layer containing a magnetic material, carbon, and a binder resin for the magnetic recording layer.

(Magnetic material)
The magnetic material in the magnetic recording layer may be, for example, barium ferrite, strontium ferrite, γ-Fe ₂ O ₃ , Co-deposited γ-Fe ₂ O ₃ , acicular iron powder, CrO ₂ or the like. The magnetic material may have an appropriate shape, for example, in the case of particles, the particle size may be 10 μm or less, and may be 0.10 μm or more and 5 μm or less.

(carbon)
The carbon in the magnetic recording layer may be carbon black. The carbon black may be furnace black, channel black, acetylene black, thermal black or the like, and one or more selected from these may be used.

(Binder resin for magnetic recording layer)
The binder resin for the magnetic recording layer in the magnetic recording layer may be, for example, polyester, polyester urethane, polyurethane, alkyd resin, vinyl resin or the like, and one or more selected from these may be used. It is preferable that the binder resin for the magnetic recording layer contains polyester urethane from the viewpoint of enhancing the adhesiveness to the hiding layer.

(Other ingredients)
The magnetic recording layer contains a magnetic material, carbon, and a binder resin for the magnetic recording layer, but may contain other components. Examples of other components in the concealing layer include a dispersant, a defoaming agent, methyl ethyl ketone, and cyclohexanone.

(Thickness of magnetic recording layer)
The thickness of the magnetic recording layer in the magnetic recording medium of the present invention is typically 5 μm or more and 15 μm or less, preferably 10 μm or more and 12 μm or less.

<Print layer>
The printing layer is composed of ink that forms desired characters, patterns, designs, etc., and is visually recognized due to the difference in color tone from the underlying concealing layer or, if present, the heat-sensitive recording layer. Therefore, the printing layer may have a color distinguishable from the hiding layer or the heat-sensitive recording layer. Since the hiding layer typically takes on a silver or gray color, the printing layer when the lower layer is the hiding layer may be a dark color such as black, red, blue, green, violet or brown.

The print layer may be present only in the area forming the character, pattern, design, etc., and the print layer may not be present in the other areas (for example, the blank part of the triangle of the character “A”).

The printing layer may be formed by a known printing ink, and may or may not have a substantial thickness as the printing layer.

<Protective layer>
The magnetic recording medium of the present invention may further have a protective layer on the surface of the printing layer opposite to the hiding layer. The protective layer has a function of coating and protecting the printing layer, and a function of imparting mechanical strength to the magnetic recording medium of the present invention together with a base material layer described later to improve handleability of the magnetic recording medium.

The protective layer may be made of, for example, a material selected from polyester, (meth)acrylic resin, urethane resin, urethane acrylate, polyester acrylate, cellulose, styrene resin, silica and the like.

As described above, it is assumed that the print layer exists only in the areas that form characters, patterns, designs, etc. and that the print layer does not exist. The protective layer in such an area may be in direct contact with the concealing layer or the heat-sensitive recording layer further below the printing layer.

The thickness of the protective layer is typically 0.5 μm or more and 3 μm or less, preferably 1 μm or more and 2 μm or less, as the thickness in the region where the printing layer does not exist.

<Thermal recording layer>
The magnetic recording medium of the present invention may further have a heat sensitive recording layer between the hiding layer and the printing layer. The heat-sensitive recording layer is a layer capable of presenting visible characters, patterns, designs, etc. when the heat-sensitive recording with a thermal head or the like causes only the heated portion to change color.

The thermosensitive recording layer may contain a thermosensitive coloring material and a binder resin.

(Thermal coloring material)
The thermosensitive coloring material may be composed of, for example, a combination of a color developer and a leuco dye.

-Developer-
As the developer, a compound having a phenolic hydroxyl group that functions as a proton source during the color development reaction of the leuco dye can be preferably used. Examples of the color developer preferably used in the present invention include 4,4′-isopropylidenephenol, benzyl-p-hydroxybenzoate, 4,4′-dihydroxy-3,5′-diallyldiphenylsulfone, and methyl-bis(hydroxyphenyl). ) Acetate, gallic acid ester, p-phenylphenol and the like can be mentioned, and one or more selected from these may be used.

-Leuco dye-
The leuco dye is colorless before the reaction, but when it is heated, it reacts with the protons generated from the color developer to change into a colored chemical species. As a result, only the heated portion is discolored, and visible characters, patterns, designs, etc. are presented. The color change of the leuco dye may be reversible or irreversible.

Examples of leuco dyes include crystal violet lactone, 3-indolino-3-p-dimethylaminophenyl-6-dimethylaminophthalide, 3-diethylamino-7-chlorofluorane, and 2-(2-chlorophenylamine)-. Diethylaminofluorane, 2-(2-fluorophenylamino)-6-diethylaminofluorane, 2-(2-fluorophenylamino)-6-di-n-butylaminofluorane, 3-diethylamino-7-cyclohexylaminofluor Olane, 3-diethylamino-5-methyl-7-t-butylfluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-p-butylanilinofluorane , 3-cyclohexylamino-6-chlorofluorane, 2-anilino-3-methyl-6-(N-ethyl-p-toluidino)-fluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3, -Pyrrolidino-7-cyclohexylaminofluorane, 3-N-methylcyclohexylamino-6-methyl-7-anilinofluorane, 3-N-ethylpentylamino-6-methyl-7-anilinofluorane and the like. And one or more selected from these may be used.

(Binder resin)
Examples of the binder resin in the heat-sensitive recording layer include hydroxyethyl cellulose, carboxymethyl cellulose, nitrocellulose, polyvinyl alcohol, starch, styrene-maleic acid copolymer, poly(meth)acrylate alkyl, polystyrene, (meth)acrylic acid- Examples thereof include styrene copolymer, polyester, acrylonitrile-butadiene-styrene copolymer (ABS), polyurethane, and polyester urethane, and one or more selected from these may be used.

(Thickness of thermal recording layer)
The thickness of the thermosensitive recording layer may be 1 μm or more, 2 μm or more, or 3 μm or more, and may be 10 μm or less, 8 μm or less, or 6 μm or less.

<Base material layer>
The magnetic recording medium of the present invention may have a base material layer on the surface of the magnetic recording layer opposite to the concealing layer. The base material layer has a function of imparting mechanical strength to the magnetic recording medium of the present invention and improving handleability of the magnetic recording medium.

As the base material layer, for example, a sheet made of synthetic resin such as polyethylene terephthalate (PET), polyacetate, polystyrene, epoxy resin, polyvinyl chloride (PVC), polycarbonate (PC), or synthetic paper is used. Good.

The thickness of the base material layer may be 50 μm or more, 60 μm or more, 70 μm or more, 80 μm or more, 90 μm or more, or 100 μm or more, and may be 500 μm or less, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, or 100 μm or less. You can

<<Method of manufacturing magnetic recording medium>>
A method of manufacturing the magnetic recording medium of the present invention will be described by taking the magnetic recording medium (10) shown in FIG. 1 as an example.

The magnetic recording medium (10) shown in FIG. 1 has, for example, a magnetic recording layer (2), a hiding layer (3), a printing layer (5), and a protective layer (6) on a base material layer (1). It may be manufactured by forming sequentially.

The formation of each layer may be performed by applying a coating liquid in which the constituent components of each layer are dissolved or dispersed in an appropriate solvent to form a coating film, and curing the obtained coating film.

The solvent of the coating liquid, solubility or dispersibility of components contained in the coating liquid, may be appropriately selected from the viewpoint of volatility, stability, safety, etc., for example, pentane, hexane, heptane, benzene, It may be one or more selected from toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, butyl acetate, tetrahydrofuran, dioxane, dimethylformamide, dimethyl sulfoxide, chloroform, propanol, butanol, water and the like.

The application of the coating liquid was appropriately selected from known printing methods or coating methods such as offset printing, screen printing, gravure coating, bar coating, knife coating, etc. according to the characteristics of each coating liquid. May be done by a method.

The coating film may be cured by one or more treatments selected from heating, light irradiation, evacuation, air drying, etc., depending on the characteristics of the coating liquid.

1. Preparation of Hiding Layer-Forming Coating Composition A hiding layer-forming coating material having the following composition was prepared. Details of the hiding layer binder resin in the hiding layer forming coating material will be described in each example.

(Composition of coating for forming the hiding layer)
Aluminum paste: 5.89 parts by mass (aluminum powder: 2.95 parts by mass)
Binder resin for hiding layer: 11.75 parts by mass (total amount)
Solvent: Mixed solvent composed of 46.18 parts by mass of methyl ethyl ketone and 46.18 parts by mass of toluene

2. Preparation of magnetic recording layer-forming coating material A magnetic recording layer-forming coating material was prepared by mixing 100 parts by mass of the main component and 4.5 parts by mass of an isocyanate curing agent as a curing agent. The main component is a composition containing barium ferrite as a magnetic material, carbon black as carbon, and polyester urethane resin as a binder resin for the magnetic recording layer.

3. Production of Magnetic Recording Medium A PET film (film thickness 188 μm) was used as a substrate.

The magnetic recording layer-forming coating material was applied onto the base material using a bar coater and heat-dried at 120° C. for 1 minute to form a magnetic recording layer having a thickness of 10 μm. On the obtained magnetic recording layer, a coating material for forming a masking layer was applied using a bar coater and heat-dried at 120° C. for 1 minute to form a masking layer having a thickness of 1 μm. UV ink was applied on the obtained hiding layer by offset printing, and UV of 160 W was irradiated to perform curing and drying treatment to form a printing layer. Further, a protective layer ink for offset printing is applied thereon, UV of 160 W is irradiated for curing and drying treatment to form a protective layer having a film thickness of 1 μm, thereby forming a base material, a magnetic recording layer, and concealment. A magnetic recording medium having a layer, a printed layer, and a protective layer in this order was produced. The thickness of the protective layer is the thickness of the printing layer in the area where ink does not exist.

4. Evaluation (1) Adhesion After forming the magnetic recording layer and the concealing layer on the substrate, forming the printing layer, and forming the protective layer, a cellotape (registered trademark) peeling test was performed. For the Cellotape (registered trademark) peeling test, the product name "Cellotape CT-18" manufactured by Nichiban Co., Ltd. was used, and when the tape was attached and peeled on the formed layer, the coating film was continuously peeled off. The length was examined, and when the coating film did not peel continuously for 5 mm or more, the adhesion was evaluated as "A (good)", and when the coating film peeled continuously for 5 mm or more, as the adhesion "C (poor)". ..

(2) Abrasion resistance The abrasion resistance was evaluated according to the method described in "5.4 Abrasion resistance of magnetic stripe" of JIS X 6302-2 "Test method for identification card". However, friction with the dummy head was applied to the protective layer of the magnetic recording medium, and the dummy head was reciprocated 2,000 times at a moving speed of 500 mm/s. When the magnetic recording medium after the test is observed from the protective layer side, the abrasion resistance is “A (good)” when the magnetic recording layer is not visible, and the abrasion resistance is “C (defective” when the magnetic recording layer is visible. )”.

(3) Surface Strength The surface hardness of the magnetic recording medium on the protective layer side was examined in accordance with JIS K 5600 "General Test Method for Paints", Part 5, Section 4, "Scratch Hardness (Pencil Method)". When the surface hardness was "H" or more, the surface strength was "A (good)", and when it was "F" or less, the surface strength was "C (bad)".

(4) Plasticizer resistance Under a condition of an environmental temperature of 20° C., a plastic eraser (manufactured by Tombow Pencil Co., Ltd., product name “MONO eraser”) was placed on the surface of the magnetic recording medium on the side of the protective layer. It was pressure bonded for 48 hours at a pressure of 0.6 kPa. After that, the eraser was removed, the plasticizer resistance was "A (good)" when the coating film did not peel off when the eraser mounting position was scratched with a nail, and the plasticizer resistance "C" when the coating film peeled off. (Poor)" was evaluated.

(5) Ethanol resistance The magnetic recording medium was immersed in an aqueous ethanol solution having a concentration of 70% by mass for 2 minutes, and dried by air drying. Then, the product name “Cellotape CT-18” manufactured by Nichiban Co., Ltd. was attached on the surface of the protective layer side, and then peeled off. At this time, ethanol resistance "A (good)" when the coating film did not peel off, ethanol resistance "B (possible)" when the coating film peeled off only slightly, and where the coating film peeled off was clear When confirmed, it was evaluated as ethanol resistance “C (poor)”.

(6) Sweat resistance test was carried out using acidic and alkaline artificial sweat fluids. The magnetic recording medium was immersed in each artificial sweat solution for 100 hours, air-dried, and then subjected to a cellotape (registered trademark) peel test and an abrasion resistance test.

Cellotape (registered trademark) peeling test was performed by applying a product name "Cellotape CT-18" manufactured by Nichiban Co., Ltd. on the surface of the protective layer side of the magnetic recording medium after immersion in the artificial sweat solution, and then peeling the coated film. When it did not come off, it was designated as "A (good)", when the paint film peeled off only slightly, it was designated as "B (good)", and when the peeled part of the paint film could be clearly confirmed, it was designated as "C (bad)". evaluated.

The abrasion resistance test was performed by reciprocating the dummy head 500 times in the same manner as in “(2) Abrasion resistance” on the surface of the magnetic recording medium on the protective layer side after immersion in the artificial sweat solution. When the magnetic recording medium after the abrasion test is observed from the side of the protective layer, "A (good)" means that the magnetic recording layer is not visible, and "B (possible)" means that the magnetic recording layer is slightly visible. When the magnetic recording layer was clearly confirmed, it was evaluated as "C (defective)".

(7) Colorability When the obtained magnetic recording medium was observed from the protective layer side, it was visually inspected whether or not it appeared colored yellow, and when no yellow coloration was observed, "A (good) )”, and when yellow coloring was observed, it was evaluated as “C (defective)”.

(8) Temperature and humidity resistance The magnetic recording medium was allowed to stand in a thermo-hygrostat at a temperature of 55° C. and a relative humidity of 90% RH for 24 hours, and then the product name “Cellotape” manufactured by Nichiban Co., Ltd. on the surface of the protective layer side. "CT-18" was attached and peeled, and when the coating film was not peeled off, the temperature and humidity resistance was evaluated as "A (good)", and when the coating film was peeled off, the temperature and humidity resistance was evaluated as "C (poor)".

<<Examples 1-3 and Comparative Examples 1-3>>
In "2. Preparation of hiding layer-forming coating material", as the hiding layer binder resin in the main agent, those listed in Table 1 are used alone or as a mixture, and a magnetic recording medium is prepared by the above method. It was produced and evaluated. The evaluation results are shown in Table 1.

In Table 1, the content ratio of nitrocellulose shows the mass ratio (mass %) of nitrocellulose to the total mass of the hiding layer binder resin.

Comparative Examples 1 to 3 and Example 1 are compared.

The binder resin for the hiding layer of Comparative Example 1 was composed only of a polyurethane resin and did not contain nitrocellulose. The magnetic recording medium of Comparative Example 1 was excellent in the adhesion and wear resistance of each layer, but was significantly inferior in sweat resistance. The binder resin for the hiding layer in Comparative Example 2 was composed of a polyurethane resin and 23% by mass of a phenoxy resin. The hiding layer binder resin in Comparative Example 3 is composed of a polyester resin and 23% by mass of nitrocellulose. The magnetic recording media of Comparative Examples 2 and 3 were not improved in sweat resistance as compared with the magnetic recording media of Comparative Example 1.

On the other hand, the binder resin for the hiding layer of Example 1 is composed of polyurethane resin and nitrocellulose. The magnetic recording medium of Example 1 has improved sweat resistance as compared with the magnetic recording mediums of Comparative Examples 1 to 3. In addition, the use of nitrocellulose did not impair physical properties other than sweat resistance.

From the above, when the polyurethane resin and nitrocellulose are used as the binder resin for the hiding layer in the magnetic recording medium, the sweat resistance of the magnetic recording medium is improved as compared with the case where the polyurethane resin is used alone. Was verified. When the polyester resin or the phenoxy resin was used as in the magnetic recording media of Comparative Examples 2 and 3, the effect of improving sweat resistance was not obtained.

Next, Examples 1 to 3 and Comparative Examples 1 and 4 will be compared.

As described above, the magnetic recording medium of Comparative Example 1 in which the binder resin for the concealing layer was composed of only the polyurethane resin was extremely inferior in sweat resistance. In Examples 1 to 3, the hiding layer binder resin contains a polyurethane resin and nitrocellulose. The magnetic recording medium of Example 1, in which the content ratio of nitrocellulose in the binder resin was 15% by mass, was improved in sweat resistance as compared with the magnetic recording medium of Comparative Example 1, and other physical properties were not impaired. It was Furthermore, in Examples 2 and 3, the content ratios of nitrocellulose in the binder resin were 23% by mass and 35% by mass, respectively. In the magnetic recording media of Examples 2 and 3, sweat resistance was further improved and other physical properties were not impaired.

However, as in the magnetic recording medium of Comparative Example 4, when the content ratio of nitrocellulose in the hiding layer binder resin exceeds 40% by mass, the resistance of the magnetic recording medium to the perspiration is irrelevant regardless of whether or not the magnetic recording medium comes into contact with sweat. Abrasion was impaired.

From the above, in the hiding layer of the magnetic recording medium, the hiding layer binder resin contains polyurethane and nitrocellulose, and the content ratio of nitrocellulose in the hiding layer binder resin is 10% by mass with respect to the entire binder resin. It was verified that when the content of the magnetic recording medium is 40% by mass or more and 40% by mass or less, the sweat resistance of the magnetic recording medium is improved without impairing various physical properties such as adhesion and abrasion resistance of each layer.

DESCRIPTION OF SYMBOLS 1 Base material layer 2 Magnetic recording layer 3 Concealment layer 4 Thermal recording layer 5 Printing layer 6 Protective layer 10, 20 Magnetic recording medium

Claims (8)

A magnetic recording medium having a magnetic recording layer, a hiding layer, and a printing layer in this order,
The hiding layer contains aluminum powder and a hiding layer binder resin,
The hiding layer binder resin contains polyurethane and nitrocellulose,
The content ratio of the nitrocellulose in the hiding layer binder resin is 10% by mass or more and 40% by mass or less based on the whole hiding layer binder resin,
Magnetic recording medium. The magnetic recording medium according to claim 1, wherein the content ratio of the nitrocellulose in the hiding layer binder resin is 15% by mass or more and 35% by mass or less with respect to the entire hiding layer binder resin. The viscosity symbol of the nitrocellulose defined by solution viscosity measurement according to JIS-K-6703 is H1/16, H1/8, H1/4, H1/2, H1, or H2. Or the magnetic recording medium according to 2. The magnetic recording medium according to claim 1, wherein the magnetic recording layer is a layer containing a magnetic material, carbon, and a binder resin for the magnetic recording layer. The magnetic recording medium according to claim 4, wherein the binder resin for the magnetic recording layer contains polyester urethane. The magnetic recording medium according to claim 1, further comprising a protective layer on a surface of the print layer opposite to the concealment layer. The magnetic recording medium according to claim 1, further comprising a thermal recording layer between the hiding layer and the printing layer. The magnetic recording medium according to claim 1, further comprising a base material layer on a surface of the magnetic recording layer opposite to the concealing layer.

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