Composition for concealing layer and magnetic recording medium having a concealing 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 hiding layer. In particular, the present invention relates to a composition used for a hiding layer that hides a colored magnetic recording layer or a magnetic barcode, and a magnetic recording medium provided with such a hiding layer.

Background Art

[0002] Conventionally, a magnetic recording medium having a magnetic recording layer and a thermosensitive recording layer on one side of a substrate has been known. In such a magnetic recording medium, a hiding layer for hiding the black-based color of the magnetic recording layer is formed between the magnetic recording layer and the thermosensitive recording layer in order to visually recognize characters or the like formed on the thermosensitive recording layer. As the hiding layer, a hiding layer mainly composed of an aluminum pigment has been used because it is desirable to have a thin film thickness and high hiding properties.

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

[0004] Further, Patent Document 2 discloses a thermosensitive magnetic recording medium having a magnetic recording layer, a hiding layer provided on the magnetic recording layer, and a thermosensitive recording layer provided on the hiding layer, wherein the hiding layer contains an aluminum paste in which a non-leafing type aluminum powder and a leafing type aluminum powder are mixed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] The aluminum pigments contained in aluminum paste used to form the opacity layer include leafing-type aluminum pigments, which are often in the form of flakes, and non-leafing-type aluminum pigments, which are often in the form of parts. These differ in properties such as surface tension. For the opacity layer, leafing-type aluminum pigments are often used because a thin film thickness and high opacity are desirable. However, with leafing-type aluminum pigments, relatively large flake-like particles can rise to the surface of the coating when forming the opacity layer, resulting in poor adhesion of the opacity layer. In addition, flake-like particles tend to aggregate, causing problems during the formation of the opacity layer and affecting the performance of the formed opacity layer. The following diagram will provide a more detailed explanation of this problem.

[0007] Figure 2 schematically shows the opening of a screen printing plate typically used when forming a concealing layer. Furthermore, Figure 3 schematically illustrates the problems that arise when forming an opacity layer by printing using a conventional opacity layer composition with a screen printing plate having such an opening. When forming an opacity layer on a magnetic recording layer by screen printing, if a high-mesh screen (approximately 460 lines / inch) is used with the aim of forming the opacity layer as a thin film, coarse or aggregated particles may clog the openings of the screen printing screen, as shown in Figure 3(a). In addition, there are intersections where vertical and horizontal lines are interwoven on the screen printing screen, and if aluminum pigment gets into these intersections, as shown in Figure 3(b), the aluminum pigment can clog the openings. In such a state, ink cannot be ejected from the openings of the screen printing screen, and pinholes will occur in the coating film formed by printing. Similarly, when forming an opacity layer by coating, if the aluminum pigment particles are too large, the aluminum pigment is more likely to get caught in the coating head, which can cause coating streaks.

[0008] To address potential problems that may arise when using these leafing-type aluminum pigments, non-leafing-type aluminum pigments with relatively small particle sizes are sometimes used. Since non-leafing-type aluminum pigments can be uniformly dispersed in the coating film, the adhesion of the coating film is good. However, when forming an opacity layer using a coating film with non-leafing aluminum pigments, the same brightness and opacity as when using leafing aluminum pigments tend not to be obtained unless the coating film thickness is increased. On the other hand, when the film thickness is increased, a problem occurs in which a portion of the opacity layer peels off between sheets (blocking) when the sheets with the opacity layer are stacked.

[0009] The present invention provides an opacity composition that does not cause blocking even when forming an opacity layer using a non-leafing type aluminum pigment, while at the same time being able to obtain the same brightness and opacity as when using a leafing type aluminum pigment, and a magnetic recording medium having an opacity layer formed using the same. [Means for solving the problem]

[0010] In other words, the present invention relates to an opacity layer composition 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 composition contains 3 to 7 parts by weight of the resin beads per 100 parts by weight of the aluminum pigment.

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

[0012] The present invention's opacity layer composition can suitably use 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.

[0013] In the opacity layer composition 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 opacity layer composition of the present invention may further include, as the binder resin, a thermoplastic resin other than 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.

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

[0016] The present invention also relates to a magnetic recording medium having a thermal recording layer further on the concealing layer. [Effects of the Invention]

[0017] According to the present invention, even when a blocking layer is formed using a non-leafing type aluminum pigment, blocking does not occur, and on the other hand, the same brightness and hiding power as those obtained when using a leafing type aluminum pigment can be obtained, and when sheets having a blocking layer formed thereon are stacked, it is possible to prevent blocking from occurring between the sheets.

Brief Description of the Drawings

[0018] [Figure 1] It is a cross-sectional view schematically showing an example of a magnetic recording medium having a blocking layer using the blocking layer composition of the present invention. [Figure 2] It is a schematic view showing an example of an opening of a screen printing plate, where (a) is a plan view and (b) is a cross-sectional view. [Figure 3] It is a schematic view showing the state of clogging of an opening of a screen printing plate, where (a) is a plan view and (b) is a cross-sectional view.

Embodiments for Carrying Out the Invention

[0019] The present invention is a blocking layer composition containing an aluminum pigment, resin beads, and a binder resin.

[0020] Aluminum pigments are generally flaky aluminum pigments obtained by thinly extending aluminum powder, and are preferably used to hide colored magnetic recording layers and magnetic barcodes by taking advantage of their thin flake shape and metallic luster. Aluminum pigments may be classified into two types, a leafing type and a non-leafing type, due to differences in the surface tension of the particles, etc. In the present invention, either type of aluminum pigment may be used, but non-leafing type aluminum pigments are preferably used in the present invention because they can be treated with a coupling agent or the like on the surface, so that the dispersibility in the binder resin can be improved.

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

[0022] Resin beads are generally spherical, have a uniform particle size, and possess excellent heat and chemical resistance, making them suitable for use in inks and cosmetic pigments. As for the resin beads used in the present invention, one or more resins can be arbitrarily selected from polyethylene, polystyrene, polymethyl methacrylate, acrylic urethane, polybutyl methacrylate, polymethacrylate ester, polymethyl methacrylate-styrene copolymer, polyethylene naphthalate, etc. In particular, the concealing layer composition of the present invention preferably uses urethane beads having chemical resistance and appropriate hardness, 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 urethane beads are insoluble in organic solvents contained in paints and inks, they can maintain their original bead shape in the ink and even after the coating film is formed.

[0023] The binder resin used in this 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. The thermoplastic resin can be arbitrarily selected from one or more types, such as polyester resin, urethane resin, nitrocellulose resin, vinyl chloride resin, vinyl chloride / vinyl acetate copolymer, vinyl chloride / vinyl acetate / vinyl alcohol copolymer, acrylic resin, and polyester urethane resin.

[0024] The opacity layer composition of the present invention may further include, as a binder resin, a thermoplastic resin other than the above-mentioned 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. As the thermoplastic resin, one or more can be arbitrarily selected from polyester resins, urethane resins, nitrocellulose resins, vinyl chloride resins, vinyl chloride / vinyl acetate copolymers, vinyl chloride / vinyl acetate / vinyl alcohol copolymers, acrylic resins, polyester urethane resins, etc. By further including another thermoplastic resin, it becomes possible to adjust the resin solubility and fluidity during the manufacture of paints and inks.

[0025] As the binder resin, it is preferable to select one that has a glass transition temperature lower than the glass transition temperature 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 during film formation in screen printing and coating processes, and to dry the film at a temperature that does not cause thermal deformation of the PET substrate during the drying process after film formation.

[0026] The present invention provides an opacity layer composition comprising an aluminum pigment, resin beads, and a binder resin, which can be mixed with a solvent to form a paste-like ink or paint that can be used to form an opacity layer on an object to be concealed, such as a magnetic recording layer or a magnetic barcode, by screen printing or coating. In the opacity layer composition of the present invention, the ratio (P / R) of the solid content weight of the aluminum pigment (P) to the solid content weight of the binder resin (R) 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 amount of aluminum pigment decreases, making it difficult to obtain suitable metallic color brightness and opacity. 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, deteriorates, and blocking is more likely to occur. The present invention provides an opacity layer composition containing 3 to 7 parts by weight of resin beads per 100 parts by weight of aluminum pigment. By adding resin beads in this proportion, the occurrence of blocking can be effectively suppressed.

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

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

[0029] The substrate for the magnetic recording medium of the present invention can 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 made of a material with a thickness of preferably 50 μm to 500 μm, and more preferably 100 μm to 300 μm.

[0030] The magnetic recording layer of the magnetic recording medium of the present invention (if present) is formed by dispersing a magnetic material such as barium ferrite, γ-iron oxide, ε-iron oxide, or carbonyl iron powder 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 using a dispersant or a curing agent such as an isocyanate. The thickness of the magnetic recording layer is preferably 5 μm to 30 μm, and more preferably 10 μm to 20 μm.

[0031] The magnetic barcode of the magnetic recording medium of the present invention (if present) is formed by dispersing a magnetic material such as γ-iron oxide, ε-iron oxide, or carbonyl iron powder 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 using a dispersant or a curing agent such as an isocyanate. The thickness of the magnetic barcode is preferably 2 μm to 20 μm, and more preferably 5 μm to 10 μm.

[0032] The concealing layer of the magnetic recording medium of the present invention contains the concealing composition of the present invention described above, and is provided on the magnetic recording layer or 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 thermal recording layer is not particularly limited as long as it can form characters or patterns by applying heat, but typically a leuco-based thermal recording layer containing a dye precursor and a color developer is preferably used. The thickness of the thermal 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 materials such as ultraviolet-curable resin, electron beam-curable resin, 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., and may contain lubricants or fillers as needed. The thickness of the protective layer is preferably 1 μm to 5 μm, and more preferably 1.5 μm to 3 μm.

[0035] The magnetic recording layer, magnetic barcode, concealment 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 by printing methods such as screen printing and offset printing. In such cases, IR drying and hot air drying can be used in combination as needed. [Examples]

[0036] The following examples illustrate the present invention and its advantages, but the present invention is not limited to these examples. In the examples and comparative examples, the thickness of each layer was as follows, and no magnetic barcode layer was formed.

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

[0038] (Example 1) The magnetic recording layer was formed by thoroughly mixing and dispersing the following compositions and applying them to a substrate. Magnetic powder: Barium ferrite (MC127, manufactured by Toda Kogyo Co., Ltd.) 100 parts by weight Binder resin: 30 parts by weight of a copolymer of vinyl chloride, vinyl acetate, and vinyl alcohol. (Nisshin 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 using the following method. First, 30 parts by weight of vinyl chloride / vinyl acetate / vinyl alcohol copolymer (Nisshin 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 solids content (R) of 30%. Next, the following composition, in which the ratio (P / R) of the solid content weight of aluminum pigment (P) to the solid content weight of binder resin (R) is 1.0, was thoroughly kneaded and dispersed, and an opacity layer was formed on the magnetic recording layer by screen printing. Non-leafing type aluminum paste (Manufactured by Toyo Aluminum Co., Ltd., Model No. 2172, Solid content weight (P) 68.25%) 100 parts by weight 30% screen printing binder, 227.5 parts by weight Urethane resin beads (Seiko Advance Co., Ltd., 3μm) 5 parts by weight Solvent: Methyl ethyl ketone / toluene (7 / 3) appropriate amount

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

[0041] The protective layer was formed by offset printing using T&K TOKA's UV161 medium UV-curing offset ink.

[0042] (Example 2) In Example 1, the amount of urethane beads added was 3 parts by weight to form an opacity layer on the magnetic recording layer.

[0043] (Example 3) In Example 1, the amount of urethane beads added was 7 parts by weight to form an opacity layer on the magnetic recording layer.

[0044] (Comparative Example 1) In Example 1, an opacity 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 2 parts by weight to form an opacity layer on the magnetic recording layer.

[0046] (Comparative Example 3) In Example 1, 10 parts by weight of urethane beads were added to form an opacity layer on the magnetic recording layer.

[0047] (Example 4) In Example 1, a leafing-type aluminum pigment (Toyo Aluminum Co., Ltd., model number 0100M) was used to form the opacity layer on the magnetic recording layer.

[0048] The following evaluations were performed on the examples and comparative examples. The evaluation results are shown in Table 1.

[0049] Opacity: Since the magnetic recording layer is black and the opacity layer is silver metallic, the luminance L* value was used for evaluation. The measuring instrument and measurement conditions were as follows: Measuring instrument X-Rite eXact Measurement conditions: Illuminant / Observer field of view D50 / 2 degrees Concentration Status ISO Status E White color standard (absolute) Evaluation Criteria: ○: L* value less than 75±5, ×: 755 or higher

[0050] Blocking: After forming with a substrate / magnetic recording layer / concealing layer, five sheets are stacked so that the concealing layer and substrate are in contact, 1g / mm² 2 After applying the load and storing the sheet in a 40°C, 90% humidity environment for 48 hours, the sheet was peeled off and visually inspected to confirm whether the concealing layer had transferred to the substrate. Evaluation Criteria ○: No disintegration of the concealing layer, ×: Peeling or disintegration of the concealing layer present.

[0051] Productivity: When the opacity layer was continuously printed using screen printing, the screen plate was visually inspected for any tears. Evaluation Criteria: No problems, ×: Printouts due to continuous production

[0052] [Table 1]

[0053] Examples 1 to 3 showed good results without any particular problems. On the other hand, Comparative Examples 1 and 2 showed blocking between the sheets. 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 opacity or blocking, but there was a tendency for the material to get caught in the mesh of the screen. Although no screen breakage occurred, traces of dragged aluminum pigment were observed. Therefore, the evaluation was △, and the overall evaluation was also △. [Explanation of Symbols]

[0054] 1 Magnetic recording medium 2 Base material 3. Magnetic recording layer 4. Magnetic barcode 5. Concealment layer 6. Thermal recording layer 7 Protective layer 8-screen mesh version 9. Aluminum pigment

Claims

1. A composition for an opacity layer comprising an aluminum pigment, resin beads, and a binder resin, wherein the ratio (P / R) of the solid content weight of the aluminum pigment (P) to the solid content weight of the binder resin (R) is in the range of 0.5 to 1, and the composition contains 3 to 7 parts by weight of the resin beads per 100 parts by weight of the aluminum pigment. The aforementioned resin beads are urethane beads with an average particle size D50 of 0.5 μm to 10 μm. A composition for concealing layers.

2. The aluminum pigment has an average particle size of 5 μm to 20 μm and an average thickness of 0.01 μm to 0.1 μm, as described in claim 1, for the opacity layer composition.

3. The concealing lamination composition according to claim 1, wherein the binder resin comprises 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.

4. The concealing lamination composition according to claim 3, wherein the binder resin further comprises a thermoplastic resin other than 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.

5. A magnetic recording medium having a concealing layer comprising the concealing layer composition described in claim 1, wherein the substrate has at least one of a magnetic recording layer and a magnetic barcode, and the concealing layer having a thickness of 0.2 μm to 10 μm is located on the magnetic recording layer or the magnetic barcode.

6. The magnetic recording medium according to claim 5, further comprising a thermal recording layer on the concealed layer.

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