Composition for concealment layer, and magnetic recording medium having concealment layer

Abstract

To provide a composition for concealment which prevents blocking even if a concealment layer is formed using a non-leafing type aluminum pigment, on the other hand, can obtain brightness and concealment property equivalent to the case using a leafing type aluminum pigment, and a magnetic recording medium having a concealment layer formed using the same.SOLUTION: A composition for a concealment layer contains an aluminum pigment, resin beads, and a binder resin, wherein a ratio (P / R) of a solid content weight (P) of the aluminum pigment to a solid content weight (R) of the binder resin is within a range of 0.5-1, and 3-7 pts.wt. of the resin beads are contained with respect to 100 pts.wt. of the aluminum pigment.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a composition for a concealing layer. In particular, the present invention relates to a composition used for a concealing layer that conceals a colored magnetic recording layer or a magnetic bar code, and to a magnetic recording medium provided with such a concealing layer. [Background technology]

[0002] Conventionally, magnetic recording media having a magnetic recording layer and a thermosensitive recording layer on one side of a substrate have been known. In such magnetic recording media, a masking layer is formed between the magnetic recording layer and the thermosensitive recording layer to mask the black color of the magnetic recording layer so that characters and the like formed on the thermosensitive recording layer can be seen. As the masking layer, a masking layer mainly composed of an aluminum pigment is used because it is desirable to have a thin film thickness and high masking ability.

[0003] Patent Document 1 discloses a magnetic thermosensitive recording medium in which a magnetic recording layer, a concealing layer, and a thermosensitive recording layer are at least laminated in sequence on one side of a substrate, the concealing layer being formed from a mixed ink of leafing-type aluminum paste and titanium dioxide.

[0004] Furthermore, Patent Document 2 discloses a thermosensitive magnetic recording medium having a magnetic recording layer, a concealing layer provided on the magnetic recording layer, and a thermosensitive recording layer provided on the concealing layer, characterized in that the concealing layer contains an aluminum paste that is a mixture of non-leafing type aluminum powder and leafing type aluminum powder. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-262886 [Patent Document 2] Japanese Patent Application Publication No. 8-183279 Summary of the Invention [Problem to be solved by the invention]

[0006] The aluminum pigments contained in the aluminum paste used to form the concealing layer include leafing type aluminum pigments, which are often scaly, and non-leafing type aluminum pigments, which are often particulate, and these differ in properties such as surface tension. Leafing-type aluminum pigments are often used for the concealing layer because a thin film thickness and high concealing properties are desirable. However, in the case of leafing-type aluminum pigments, the relatively large scale-like particles may float to the surface of the coating film when the concealing layer is formed, which may result in poor adhesion of the concealing layer.Furthermore, the scale-like particles tend to aggregate, which may cause problems when forming the concealing layer and in the performance of the concealing layer formed. This issue is explained in more detail below with reference to the figures.

[0007] FIG. 2 shows a schematic diagram of an opening in a screen printing plate that is typically used when forming a concealing layer. Furthermore, FIG. 3 shows a schematic diagram of a problem that occurs when a concealing layer is formed by printing using a screen printing plate having such openings and a conventional composition for a concealing layer. When the concealing layer is formed on the magnetic recording layer by screen printing, if a high mesh plate (approximately 460 lines / inch) is used to form the concealing layer as a thin film, coarse particles or aggregated particles may clog the openings of the screen printing plate, as shown in Figure 3(a). In addition, the screen printing plate has intersections where vertical and horizontal lines are interwoven, and if the aluminum pigment enters these intersections, as shown in Figure 3(b), the aluminum pigment may block the openings. In such a state, the ink will not be discharged from the openings of the screen printing plate, and pinholes will occur in the coating film formed by printing. Similarly, when the concealing layer is formed by coating, if the particles of the aluminum pigment are too large, the aluminum pigment will easily get caught by the coating head, which may cause problems such as coating streaks.

[0008] To solve the problems that can occur when using these leafing-type aluminum pigments, non-leafing-type aluminum pigments, which have a relatively small particle size, are sometimes used. Non-leafing-type aluminum pigments can be uniformly dispersed in the coating film, resulting in good coating adhesion. However, when a concealing layer is formed by a coating film using a non-leafing type aluminum pigment, the coating film thickness must be thick in order to obtain the same brightness and concealing properties as when a leafing type aluminum pigment is used. On the other hand, when the coating film thickness is thick, there is a problem that a phenomenon (blocking) occurs in which a part of the concealing layer peels off between sheets when the sheets on which the concealing layer is formed are stacked.

[0009] The present invention provides a concealing composition that does not cause blocking even when a concealing layer is formed using a non-leafing type aluminum pigment, while at the same time providing brightness and concealing properties similar to those obtained when a leafing type aluminum pigment is used, and a magnetic recording medium having a concealing layer formed using the same. [Means for solving the problem]

[0010] In other words, the present invention is a composition for a concealing layer comprising an aluminum pigment, resin beads, and a binder resin, wherein the ratio (P / R) of the solid content weight (P) of the aluminum pigment to the solid content weight (R) of the binder resin is in the range of 0.5 to 1, and the resin beads are contained in a ratio of 3 to 7 parts by weight per 100 parts by weight of the aluminum pigment.

[0011] In the composition for a concealing layer of the present invention, urethane beads having an average particle size D50 of 0.5 μm to 10 μm can be suitably used as the resin beads.

[0012] In the composition for a concealing layer of the present invention, an aluminum pigment having an average particle size of 5 μm to 20 μm and an average thickness of 0.01 μm to 0.1 μm can be suitably used.

[0013] In the composition for a concealing layer of the present invention, a thermoplastic resin having a weight average molecular weight of 1,000 to 50,000 and a glass transition temperature of 0° C. to 15° C. can be suitably used as the binder resin.

[0014] The composition for a concealing layer of the present invention may further contain, as the binder resin, a thermoplastic resin other than the thermoplastic resin, which has a weight average molecular weight of 1,000 to 50,000 and a glass transition temperature of -20°C to 40°C.

[0015] The present invention also relates to a magnetic recording medium having a concealing layer containing these compositions for a concealing layer, the magnetic recording medium having at least one of a magnetic recording layer and a magnetic barcode on a substrate, and having the concealing layer having the above-mentioned thickness of 0.2 μm to 10 μm on the magnetic recording layer or on the magnetic barcode.

[0016] The present invention also relates to a magnetic recording medium further comprising a heat-sensitive recording layer on the concealing layer. Effect of the Invention

[0017] According to the present invention, even when a concealing layer is formed using a non-leafing type aluminum pigment, blocking does not occur, while at the same time, brightness and concealing properties can be obtained similar to those obtained when a leafing type aluminum pigment is used, and it is also possible to prevent blocking from occurring between sheets when sheets having a concealing layer formed thereon are stacked. [Brief description of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view that illustrates a schematic diagram of an example of a magnetic recording medium having a concealing layer using the concealing layer composition of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing an example of an opening of a screen printing plate, where (a) is a plan view and (b) is a cross-sectional view. [Diagram 3] FIG. 1 is a schematic diagram showing clogging of an opening of a screen printing plate, where (a) is a plan view and (b) is a cross-sectional view. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present invention is a composition for a concealing layer, which contains an aluminum pigment, resin beads, and a binder resin.

[0020] Aluminum pigments are generally flake-shaped aluminum pigments formed by thinly spreading aluminum powder, and are preferably used to conceal colored magnetic recording layers and magnetic barcodes by taking advantage of their thin flake shape and metallic luster. Aluminum pigments are sometimes classified into two types, leafing type and non-leafing type, depending on the difference in the surface tension of the particles. Either type of aluminum pigment may be used in the present invention, but non-leafing type aluminum pigments are preferably used in the present invention because they can be treated on the surface with a coupling agent or the like, and therefore can be more easily dispersed in binder resins.

[0021] The average particle size of the aluminum pigment used in the present invention is preferably 5 μm to 20 μm, more preferably 8 μm to 12 μm. The average thickness of the aluminum pigment is preferably 0.01 μm to 0.1 μm, more preferably 0.025 μm to 0.08 μm.

[0022] Resin beads are generally spherical with a uniform particle size and excellent heat and chemical resistance, making them ideal for use in inks and cosmetic pigments. The resin type of the resin beads used in the present invention can be one or more types selected from polyethylene, polystyrene, polymethyl methacrylate, acrylic urethane, polybutyl methacrylate, polymethacrylic acid ester, polymethyl methacrylate-styrene copolymer, polyethylene naphthalate, etc. In particular, in the composition for a concealing layer of the present invention, urethane beads having chemical resistance and appropriate hardness are preferably used, and the preferred average particle size D50 of the urethane beads is 0.5 μm to 10 μm, more preferably 1 μm to 5 μm. Since the urethane beads are insoluble in the organic solvent contained in the paint or ink, they can maintain their original bead shape in the ink and even after the coating film is formed.

[0023] The binder resin used in the present invention is preferably a thermoplastic resin having a weight average molecular weight of 1,000 to 50,000 and a glass transition temperature of 0° C. to 15° C. As the thermoplastic resin, one or more types may be arbitrarily selected from polyester resin, urethane resin, nitrocellulose resin, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, acrylic resin, polyester urethane resin, etc.

[0024] The composition for the concealing layer of the present invention may further contain, as a binder resin, a thermoplastic resin other than the above thermoplastic resin, which has a weight average molecular weight of 1000 to 50000 and a glass transition temperature of -20°C to 40°C. As the thermoplastic resin, one or more types may be arbitrarily selected and used from polyester resin, urethane resin, nitrocellulose resin, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, acrylic resin, polyester urethane resin, etc. By further containing another thermoplastic resin, it becomes possible to adjust the solubility and flowability of the resin during the production of the paint or ink.

[0025] It is preferable to select a binder resin having a glass transition temperature lower than that of the substrate of the object to be concealed to which the concealing layer using the concealing layer composition of the present invention is applied. For example, if the substrate of the object to be concealed is PET, it is preferable to select a binder resin having a glass transition temperature in the range of -20°C to 50°C. By selecting such a binder resin, it is possible to ensure the fluidity of the ink when forming a coating film in the screen printing or coating process, and to dry the coating film at a temperature that does not cause thermal deformation of the PET substrate in the drying process after the coating film is formed.

[0026] The composition for a concealing layer of the present invention contains aluminum pigment, resin beads, and a binder resin, and can be mixed with a solvent to form a paste-like ink or paint, which can be used to form a concealing layer by screen printing or coating on an object to be concealed having a magnetic recording layer, a magnetic barcode, or the like. In the composition for a concealing layer of the present invention, the ratio (P / R) of the solid content weight (P) of the aluminum pigment to the solid content weight (R) of the binder resin is in the range of 0.5 to 1. Preferably, P / R is in the range of 0.75 to 0.85. If P / R is less than 0.5, the content of the aluminum pigment is reduced, making it difficult to obtain suitable metallic color brightness and concealing properties. On the other hand, if P / R is greater than 1.0, adhesion to the object to be concealed, such as a magnetic recording layer, becomes poor, and blocking is likely to occur. The composition for the concealing layer of the present invention contains 3 to 7 parts by weight of resin beads per 100 parts by weight of aluminum pigment. By adding the resin beads in this ratio, the occurrence of blocking can be effectively suppressed.

[0027] In the concealing layer composition of the present invention, a solvent for ink can be used to make the aluminum pigment into a paste-like ink or paint. As the solvent, an organic solvent is preferable, and there is no particular limitation as long as it dissolves the binder resin contained in the concealing layer composition of the present invention. For example, ketone-based solvents include acetone, MEK, MIBK, DIBK, MIPK, cyclohexanone, diacetone alcohol, and isophorone; aromatic hydrocarbon-based solvents include toluene, xylene, solvent naphtha, normal hexane, isohexane, cyclohexane, ethylcyclohexane, methylcyclohexane, normal heptane, isooctane, normal decane, normal pentane, isopentane, benzene, and cyclobenzene; ester-based solvents include ethyl acetate, butyl acetate, methoxybutyl acetate, amyl acetate, normal propyl acetate, isopropyl acetate, methyl lactate, ethyl lactate, and butyl lactate; glycol-based solvents include ethylene glycol, diethylene glycol, triethylene glycol, and propylene glycol; and petroleum-based solvents include mineral spirits and various solvents. The amount of solvent used should be an amount that allows the ink viscosity to be adjusted to tens to tens of thousands of mPa·s in accordance with the manufacturing conditions. In general, it is preferable to use a solvent in an amount that results in a paint viscosity of 10 to 100 mPa·s for coating, a viscosity of 50 to 1,000 mPa·s for gravure printing ink, and a viscosity of 1,000 mPa·s to 10,000 mPa·s for screen printing ink.

[0028] The composition for a concealing layer of the present invention can be used as a concealing layer of a magnetic recording medium having at least one of a magnetic recording layer and a magnetic barcode provided on a substrate, and is particularly suitable for use in a magnetic recording medium having a heat-sensitive recording layer provided on the concealing layer. Fig. 1 is a cross-sectional view showing a typical example of a magnetic recording medium using the composition for a concealing layer of the present invention. Fig. 1 shows a thermal recording type magnetic recording medium 1 having a magnetic recording layer 3, a magnetic barcode 4, a concealing layer 5, a thermal recording layer 6, and a protective layer 7 provided on one side of a substrate 2.

[0029] The substrate of the magnetic recording medium of the present invention may be made of polyethylene terephthalate, polypropylene, polycarbonate, vinyl chloride, paper, or a composite material such as YUPO, but is not particularly limited to these. The substrate is usually preferably 50 μm to 500 μm thick, more preferably 100 μm to 300 μm thick.

[0030] The magnetic recording layer of the magnetic recording medium of the present invention (if present) can be formed by dispersing a magnetic material such as barium ferrite, γ-iron oxide, ε-iron oxide, carbonyl iron powder, etc., in one or more binder resins selected from polyurethane, vinyl chloride, vinyl alcohol-vinyl acetate copolymer, acrylic resin, nitrocellulose resin, polyester resin, etc., and optionally containing a dispersant and / or a hardener such as an isocyanate. The thickness of the magnetic recording layer is preferably 5 μm to 30 μm, more preferably 10 μm to 20 μm.

[0031] The magnetic barcode of the magnetic recording medium of the present invention (if present) can be formed by dispersing a magnetic material such as γ-iron oxide, ε-iron oxide, carbonyl iron powder, etc., in one or more binder resins selected from polyurethane, vinyl chloride, vinyl alcohol-vinyl acetate copolymer, acrylic resin, nitrocellulose resin, polyester resin, etc., and optionally containing a dispersant and / or a hardener such as an isocyanate. The thickness of the magnetic barcode is preferably 2 μm to 20 μm, more preferably 5 μm to 10 μm.

[0032] The concealing layer of the magnetic recording medium of the present invention contains the above-mentioned concealing composition of the present invention and is provided on the magnetic recording layer or the magnetic barcode with a thickness of 0.2 μm to 10 μm. The thickness of the concealing layer is preferably 0.5 μm to 5 μm.

[0033] In the magnetic recording medium of the present invention, the heat-sensitive recording layer is not particularly limited as long as it can form characters or patterns by applying heat, but typically, a leuco-based heat-sensitive recording layer containing a dye precursor and a color developer is preferably used. The thickness of the heat-sensitive recording layer is 1 μm to 10 μm, preferably 2.5 μm to 6 μm.

[0034] As described above, the magnetic recording medium of the present invention may have a protective layer. The protective layer may be formed using a material containing an ultraviolet-curable resin, an electron-beam-curable resin, a polyester resin, a urethane resin, a nitrocellulose resin, a vinyl chloride resin, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinyl acetate-vinyl alcohol copolymer, an acrylic resin, a polyester urethane resin, or the like, and may contain a lubricant or a filler as necessary. The thickness of the protective layer is preferably 1 μm to 5 μm, more preferably 1.5 μm to 3 μm.

[0035] The magnetic recording layer, magnetic barcode, concealing layer, thermal recording layer, and protective layer can be formed by coating methods such as gravure coating, knife coating, bar coating, roll coating, and comma coating, or printing methods such as screen printing and offset printing. In this case, IR drying and hot air drying can be used in combination as necessary. EXAMPLES

[0036] The following examples are provided to better understand the present invention and its advantages, but the present invention is not limited to these examples. In the examples and comparative examples, the thicknesses of the layers are as follows, and no magnetic barcode layer was formed.

[0037] Base material: 188 μm polyethylene terephthalate (Toray Industries, Inc. E20) Magnetic recording layer 15μm Concealing layer 2μm Thermal recording layer 4μm Protective layer 2μm

[0038] Example 1 The magnetic recording layer was formed by thoroughly kneading and dispersing the following composition and applying it onto the substrate. Magnetic powder: Barium ferrite (Toda Kogyo Co., Ltd. MC127) 100 parts by weight Binder resin: Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 30 parts by weight (Nissin Chemical Industry Co., Ltd.) Hardener: Coronate L (Nippon Polyurethane Industry Co., Ltd.) 3 parts by weight Solvent: Methyl ethyl ketone / toluene (7 / 3) appropriate amount

[0039] The concealing layer was prepared by the following method. First, 30 parts by weight of vinyl chloride-vinyl acetate-vinyl alcohol copolymer (Nissin Chemical Industry Co., Ltd.) was mixed with 70 parts by weight of methyl ethyl ketone / toluene (7 / 3), stirred and dissolved to prepare a screen printing binder with a solid content (R) of 30%. Next, the following composition, in which the ratio (P / R) of the solid content weight of the aluminum pigment (P) to the solid content weight of the binder resin (R) was 1.0, was thoroughly kneaded and dispersed, and a concealing layer was formed on the magnetic recording layer by screen printing. Non-leafing type aluminum paste (Toyo Aluminum Co., Ltd., Model No. 2172, solid content (P) 68.25%) 100 parts by weight 30% Screen Printing Binder 227.5 parts by weight Urethane resin beads (Seiko Advance Co., Ltd., 3 μm) 5 parts by weight Solvent: Methyl ethyl ketone / toluene (7 / 3) appropriate amount

[0040] The heat-sensitive recording layer was formed on the concealing layer by thoroughly kneading and dispersing the following composition. Solution A: Fluoran leuco dye (TG-31 manufactured by Nippon Kayaku Co., Ltd.) 10 parts by weight Acrylic emulsion (Movinyl 730 manufactured by Hoechst Chemical Co., Ltd.) 20 parts by weight 5 parts by weight of water Solution B: 4-hydroxy-4'-isopropyloxydiphenylsulfone 10 parts by weight Acrylic emulsion (Movinyl 730 manufactured by Hoechst Chemical Co., Ltd.) 20 parts by weight 5 parts by weight of water Liquid A and liquid B were mixed in a 1:1 ratio, stirred with a high-speed impeller, and formed on the concealing layer using screen printing.

[0041] The protective layer was formed by offset printing using offset ink UV161 medium UV curing ink manufactured by T&K TOKA Corporation.

[0042] Example 2 In Example 1, the amount of urethane beads added was 3 parts by weight, and the concealing layer was formed on the magnetic recording layer.

[0043] Example 3 In Example 1, the amount of urethane beads added was changed to 7 parts by weight, and the concealing layer was formed on the magnetic recording layer.

[0044] Comparative Example 1 In Example 1, the hiding layer was formed on the magnetic recording layer without adding urethane beads.

[0045] Comparative Example 2 In Example 1, the amount of urethane beads added was changed to 2 parts by weight, and the concealing layer was formed on the magnetic recording layer.

[0046] Comparative Example 3 In Example 1, the amount of urethane beads added was changed to 10 parts by weight, and the concealing layer was formed on the magnetic recording layer.

[0047] Example 4 In Example 1, a leafing type aluminum pigment (manufactured by Toyo Aluminum KK, model number 0100M) was used instead, and a masking layer was formed on the magnetic recording layer.

[0048] The following evaluations were carried out for the Examples and Comparative Examples. The evaluation results are shown in Table 1.

[0049] Concealment: Since the magnetic recording layer is black and the concealing layer is silver metallic, the luminance L* value was used for evaluation. The measuring device and measuring conditions are as follows: Measuring instrument X-Rite eXact Measurement conditions: Illuminant / observer field of view: D50 / 2 degrees Density status ISO status E Density White Standard Absolute Evaluation criteria: 〇: L* value: less than 75±5, ×: 755 or more

[0050] Blocking: After forming the substrate / magnetic recording layer / hiding layer configuration, five sheets were stacked so that the hiding layer and substrate were in contact with each other, and a 1g / mm 2 After storing the sheet for 48 hours in an environment of 40°C and 90% humidity, the sheet was peeled off and visually confirmed whether the concealing layer had been transferred to the substrate. Evaluation criteria: ◯: no transfer of the concealing layer; ×: peeling or transfer of the concealing layer

[0051] Productivity: When the concealing layer was continuously printed by screen printing, the screen was visually inspected for tears. Evaluation criteria: No problem, ×: Plate breakage during continuous production

[0052] [Table 1]

[0053] Examples 1 to 3 showed good results without any particular problems. On the other hand, blocking occurred between the sheets in Comparative Examples 1 and 2. In Comparative Example 3, the silver luster of the aluminum was lost due to the addition of too many urethane beads. In Example 4, there were no particular problems with surface concealment and blocking, but the ink was prone to getting caught in the mesh of the screen. No plate breakage occurred, but traces of the aluminum pigment were observed. Therefore, the evaluation was △, and the overall evaluation was △. [Explanation of symbols]

[0054] 1 Magnetic recording media 2 Base material 3. Magnetic recording layer 4. Magnetic barcode 5 Hidden Layer 6. Thermal recording layer 7 Protective layer 8 Screen mesh 9. Aluminum Pigments

Claims

1. A composition for a hiding layer comprising an aluminum pigment, resin beads, and a binder resin, wherein the ratio (P / R) of the solid content weight (P) of the aluminum pigment to the solid content weight (R) of the binder resin is in the range of 0.5 to 1, and the resin beads are included in a proportion of 3 to 7 parts by weight with respect to 100 parts by weight of the aluminum pigment. A composition for a hiding layer.

2. The composition for a hiding layer according to claim 1, wherein the resin beads are urethane beads having an average particle diameter D50 of 0.5 μm to 10 μm.

3. The composition for a hiding layer according to claim 1, wherein the aluminum pigment has an average particle diameter of 5 μm to 20 μm and an average thickness of 0.01 μm to 0.1 μm.

4. The composition for a laminated hiding layer according to claim 1, wherein the binder resin includes a thermoplastic resin having a weight average molecular weight of 1,000 to 50,000 and a glass transition temperature of 0°C to 15°C.

5. The composition for a laminated hiding layer according to claim 4, wherein the binder resin further includes a thermoplastic resin different from the thermoplastic resin, having a weight average molecular weight of 1,000 to 50,000 and a glass transition temperature of -20°C to 40°C.

6. A magnetic recording medium having a hiding layer containing the composition for a hiding layer according to claim 1, having at least one of a magnetic recording layer and a magnetic bar code on a substrate, and having the hiding layer with a thickness of 0.2 μm to 10 μm on the magnetic recording layer or the magnetic bar code. A magnetic recording medium.

7. The magnetic recording medium according to claim 6, further having a thermal recording layer on the hiding layer.

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