JP2008276006A - Magnetic display sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic display sheet having stable dispersibility of reddish brown γ iron oxide, having clear contrast and capable of displaying clear and reddish brown characters, images, or the like. <P>SOLUTION: The magnetic display sheet is characterized by comprising a writing transparent sheet, a solid dispersion layer having microcapsules in which a dispersion solution including a white pigment and reddish brown γ iron oxide is included and a support, which are laminated in this order, and including the γ iron oxide and the dispersion solution, wherein a product of the specific surface area of the reddish brown γ iron oxide and the viscosity (25°C) of the dispersion solution is in a range of 240 to 680. Individually, a combination of the specific surface area of the γ iron oxide and the viscosity (25°C) of the dispersion solution is any one selected from combinations that when the specific surface area is 14 m<SP>2</SP>/g, the viscosity (25°C) is ≤44 mPa s, when the specific surface area is ≤20 m<SP>2</SP>/g, the viscosity (25°C) is ≤33 mPa s, and when the specific surface area is ≤24 m<SP>2</SP>/g, the viscosity (25°C) is ≤28 mPa s. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnetic display sheet, and more particularly to a magnetic display sheet capable of drawing characters / images in reddish-brown colors other than black and capable of displaying clear red-brown characters and images with high contrast.

Conventionally, as a magnetic display sheet, a microcapsule magnetic display plate having a microcapsule solid dispersion layer on a support and further having a transparent sheet for writing as an uppermost layer is known. Contains liquid, white pigment and magnetic particles. Such a magnetic display plate can be used without any problem for writing such as writing characters with good contrast because the magnetic particles are generally black iron oxide (see, for example, Patent Document 1). In addition, with the expansion of the use of microcapsule magnetic display boards, the use of interference colors such as pearl pigments in magnetic display boards is proposed to color writing lines and characters (to make colors other than black). Attempts have been made to color characters other than black, for example, black characters using interference colors (see, for example, Patent Document 2).
Patent No. 2841291 (Claims) Japanese Patent No. 3572045

However, the magnetic display sheet described in Patent Document 1 as described above can write clear characters, but the color of the characters is limited to black, and colorization is not proposed. Further, in the magnetic display sheet described in Patent Document 2, even if an attempt is made to color the black color of the character in the interference color, it is difficult to realize it because the black color is superior to the interference color.
Therefore, the present inventors have selected and investigated a color other than black from among magnetic materials, and surprisingly, reddish brown γ-iron oxide in iron oxide has a surface area and a microcapsule inclusion liquid, It has been found that by defining the so-called viscosity of the dispersion liquid, it is possible to display clear reddish brown characters / images with good contrast, and the present invention has been made here.

  Therefore, the problem to be solved by the present invention is to provide a magnetic display sheet having stable dispersibility of reddish brown γ-iron oxide and capable of displaying clear reddish brown characters / images with good contrast. is there.

The above-mentioned problems of the present invention include a transparent sheet for writing, a solid dispersion layer having a microcapsule containing a dispersion containing white pigment and reddish brown γ-iron oxide, a support in this order, and the reddish brown γ− This is achieved by a magnetic recording sheet comprising γ-iron oxide having a product of the specific surface area of iron oxide and the viscosity (25 ° C.) of the dispersion in the range of 240 to 680 and the dispersion.

  In the magnetic display sheet of the present invention, the product of the specific surface area of the reddish brown γ-iron oxide and the viscosity of the dispersion (25 ° C.) is in the range of 240 to 680 and the dispersion. In addition, a stable dispersibility of reddish brown γ-iron oxide can be obtained, and the obtained display can display excellent reddish brown characters / images with good contrast.

  The best embodiment of the present invention will be described below, but this is an example and the present invention is not limited to this.

  The magnetic display sheet of the present invention comprises a transparent sheet for writing, a solid dispersion layer having a microcapsule containing a dispersion containing white pigment and reddish brown γ-iron oxide, and a support in this order, and the reddish brown γ -The product of the specific surface area of an iron oxide and the viscosity (25 degreeC) of the said dispersion liquid has (gamma) -iron oxide and a dispersion liquid in the range of 240-680.

In the magnetic display sheet of the present invention, the microcapsule is, for example, a gelatin-coated microcapsule. In the step of forming the gelatin-coated microcapsule, the microcapsule includes reddish brown γ-iron oxide, a white pigment, It contains a solvent and contains additives such as suspending agents and dispersing agents. In the present invention, the product of the specific surface area of the reddish brown γ-iron oxide and the viscosity (25 ° C.) of the dispersion has γ-iron oxide and the dispersion in the range of 240 to 680, so that the contrast is good. An excellent effect that a clear reddish brown character / image can be drawn is obtained. The specific surface area (m ² / g) of reddish brown γ-iron oxide used in the present invention is preferably in the range of 14-24. Further, the viscosity of the dispersion (25 ° C.) has a good contrast over a wide range from a low viscosity to a high viscosity, and the excellent effect of the present invention that a clear reddish brown character / image can be drawn is obtained. However, although excellent effects of the present invention high viscosity in the case of using a low dispersion numerically specific surface area of γ- iron oxide red-brown (m 2 ^{/ g)} obtained, the specific surface area (m ² / When a reddish brown γ-iron oxide having a high g) is used, it is necessary to make the viscosity of the dispersion relatively low.

In the present invention, the product of the specific surface area of the reddish brown γ-iron oxide and the viscosity (25 ° C.) of the dispersion has γ-iron oxide and the dispersion in the range of 240 to 680, so that the contrast is good. Vivid reddish brown characters / images can be drawn, but preferably the product of the specific surface area of γ-iron oxide and the viscosity (25 ° C.) of the dispersion is in the range of 330 to 675, more preferably 336. In the range of ˜672, and more preferably in the range of 616 to 672, the contrast is good and a clear reddish brown character / image can be drawn. Further, if the specific surface area (m ² / g) of γ-iron oxide and the viscosity (25 ° C.) of the dispersion are individually expressed, the specific surface area (m ² / g) of γ-iron oxide used in the present invention. When the specific surface area (m ² / g) is 14 to 24, the viscosity of the dispersion (25 ° C.) is 44 to 14 mPa · s. When the surface area (m ² / g) is 14, the viscosity (25 ° C.) of the dispersion is 31 to 44 mPa · s, and when the specific surface area (m ² / g) is 20, the viscosity of the dispersion (25 ° C.). Is 23 to 33 mPa · s, and when the specific surface area (m ² / g) is 24, the viscosity (25 ° C.) of the dispersion is 14 to 28 mPa · s. Thus, in the present invention, the specific surface area (m ² / g) is a continuous range of 14 to 24, and the viscosity (25 ° C.) of the dispersion is also a preferable range of 31 to 44 mPa · s. can get.
Incidentally, the tendency of the combination of the specific surface area (m ² / g) of reddish brown γ-iron oxide and the viscosity of the dispersion (25 ° C.) is that the viscosity of the dispersion (25 ° C.) is high from a low viscosity as described above. Since contrast is good over a wide range up to the viscosity and clear reddish brown characters / images can be drawn, it is considered that good results can be obtained even when the specific surface area (m ² / g) is smaller than 14.

Solvents that satisfy the conditions of the dispersion used in the present invention include water such as octane, nonane, decane, dodecane, toluene, benzene, xylene, ethylbenzene, mesitylene, tetralin, dodecylbenzene, cyclohexane, cyclopentane, and phenylxylylethane. A hydrocarbon solvent having a solubility in water of 1% or less; an alcohol solvent having a solubility in water of 1% or less, such as 2-peptanol, 3-peptanol, octanol, 2-ethyl-1-hexanol, and the like, isobutyl acetate, Water such as pentyl acetate, benzyl acetate, 2-ethylhexyl acetal, ethyl butyrate, butyl butyrate, isopentyl butyrate, ethyl benzoate, propyl benzoate, butyl benzoate, dibutyl maleate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate Solubility in water is 1 The following ester solvents, and the like. These solvents may be used alone or in combination of two or more. Preferred solvents are toluene, xylene, ethylbenzene, dodecylbenzene, cyclohexane, phenylxylylethane, octanol, dibutyl phthalate, dioctyl phthalate, and preferred combinations are phenylxylylethane and ethylbenzene, toluene and dodecylbenzene, Cyclohexane and dibutyl phthalate.

The reason why the solubility of the solvent in water is limited to 1% or less is that during the capsule manufacturing process, oil enemies are dispersed in water for encapsulation. In addition, in the present invention, white pigments, anti-settling agents, dispersants, capsule particle diameters, binders, display plate materials, microcapsule manufacturing methods, and the like are well-known techniques related to microcapsule magnetic display plates in this technical field. It is preferable to use the same as described in Japanese Patent No. 2841291 or a similar method. The matters described in the patent publication can be used in the present invention. Of these, examples of particularly preferable items include titanium dioxide, lithopone, zinc white, Examples include lead white and zinc sulfide. Anti-precipitation agents include anhydrous silicic acid, hydrous silicic acid, silicates (sodium silicate, potassium silicate, aluminum silicate, calcium silicate, etc.), finely divided alumina, silica powder, diatomaceous earth, carion, hard clay, soft clay, bentonite, pole Examples thereof include fine calcium carbonate, ultrafine activated calcium carbonate, calcium bicarbonate, hydrated basic magnesium carbonate, barium sulfate, and benzidine yellow. These may be used alone or in combination of two or more. Examples of the dispersant include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, anionic aliphatic ester mixture, and polycarboxylic acid amine salt. The average particle size of the microcapsules used in the present invention is 80 μm to 600 μm, preferably 100 μm to 400 μm. The transparent sheet for writing is preferably a transparent film such as polyester or polyethylene, but is not limited thereto. Moreover, the thickness of this film is 50 micrometers-250 micrometers, Preferably it is 75 micrometers-150 micrometers. As the support, paper, fibrous material, plywood, metal, transparent or opaque synthetic resin is used.

The magnetic display sheet of the present invention can be used for various applications. For example, it can be used for cards such as a cash card, a cashless card, a credit card, and a prepaid card. Children's toys such as picture books, children's drawing boards, character practice devices, various game boards, character practice boards, calligraphy practice boards, memo boards for mobile memos, writing memo boards, conference blackboards, clean rooms And various information boards, electronic bulletin boards, personal computer display panels, and the like.

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this example is for demonstrating this invention, and this invention is not limited to this.
[Production Example] The microcapsules used in the present invention were produced as follows.
(1) Preparation of gelatin aqueous solution Gelatin was added to water, stirred and dissolved at 50 ° C. to prepare a 5% by weight gelatin aqueous solution.
(2) Preparation of gum arabic aqueous solution Gum arabic was added to water and stirred and dissolved at 50 ° C. to prepare a 5% by weight gum arabic aqueous solution.
(3) Gelatin shell formation step 100 g of 5% by weight aqueous gelatin solution and 100 g of 5% by weight aqueous gum arabic solution are mixed, heated to about 50 ° C., and slowly added with the following inclusion liquid 100 g while stirring, with an average particle size of 300 μm. Stir until. Thereafter, 200 g of water at 50 ° C. was added, and the pH was adjusted to 4.7 with 15% by mass acetic acid, and the resulting solution was cooled to 25 ° C. Then, after rapidly cooling to 10 ° C., a 25% glutaraldehyde aqueous solution was added to obtain a microcapsule used for a magnetic display sheet comprising a gelatin shell.

(4) Preparation of dispersion liquid to be contained in microcapsule [Dispersion liquid 1]
γ-iron oxide (specific surface area: 14)
[Product name: γ-MRD (Titanium Industry Co., Ltd.), reddish brown] 3g
White pigment [TIPAQUE R-820 (trade name); manufactured by Ishihara Sangyo Co., Ltd.] 20 g
Phenylxylylethane 60.5g
Ethylbenzene 15g
Anti-settling agent [Aerosil (trade name): Nippon Aerosil Co., Ltd.] 1g
Dispersant [Nopco Santo K963 (trade name): manufactured by San Nopco] 0.5g
The total amount of all the components of Dispersion 1 is 100 g. When this Dispersion 1 is sufficiently stirred with a homomixer, the viscosity (25 ° C.) is measured with a BL-type rotational viscometer (manufactured by Tokyo Keiki Co., Ltd.), and 31 mPa · s. Met.

[Dispersion 2]
γ-iron oxide (specific surface area: 14)
[Product name: γ-MRD (Titanium Industry Co., Ltd.), reddish brown] 3g
White pigment [TIPAQUE R-820 (trade name); manufactured by Ishihara Sangyo Co., Ltd.] 20 g
Phenylxylylethane 70.5g
Ethylbenzene 5g
Anti-settling agent [Aerosil (trade name): Nippon Aerosil Co., Ltd.] 1g
Dispersant [Nopco Santo K963 (trade name): manufactured by San Nopco] 0.5g
The total amount of all the components of Dispersion 2 was 100 g, and the viscosity (25 ° C.) measured under the same conditions as Dispersion 1 was 44 mPa · s.

[Dispersion 3]
γ-iron oxide (specific surface area: 20)
[Product name: MX-450 (manufactured by Toda Kogyo, reddish brown)] 3 g
White pigment [TIPAQUE R-820 (trade name); manufactured by Ishihara Sangyo Co., Ltd.] 20 g
Phenylxylylethane 45.5g
30g ethylbenzene
Anti-settling agent [Aerosil (trade name): Nippon Aerosil Co., Ltd.] 1g
Dispersant [Nopco Santo K963 (trade name): manufactured by San Nopco] 0.5g
The total amount of all the components of Dispersion 3 was 100 g, and the viscosity (25 ° C.) measured under the same conditions as Dispersion 1 was 23 mPa · s.

[Dispersion 4]
γ-iron oxide (specific surface area: 20)
[Product name: MX-450 (manufactured by Toda Kogyo, reddish brown)] 3 g
White pigment [TIPAQUE R-820 (trade name); manufactured by Ishihara Sangyo Co., Ltd.] 20 g
Phenylxylylethane 60.5g
Ethylbenzene 15g
Anti-settling agent [Aerosil (trade name): Nippon Aerosil Co., Ltd.] 1g
Dispersant [Nopco Santo K963 (trade name): manufactured by San Nopco] 0.5g
The total amount of all the components of Dispersion 4 was 100 g, and the viscosity (25 ° C.) measured under the same conditions as Dispersion 1 was 33 mPa · s.

[Dispersion 5]
γ-iron oxide (specific surface area: 24)
[Product name: γ-THD (manufactured by Toda Kogyo, reddish brown)] 3 g
White pigment [TIPAQUE R-820 (trade name); manufactured by Ishihara Sangyo Co., Ltd.] 20 g
Phenylxylylethane 35.5g
40g ethylbenzene
Anti-settling agent [Aerosil (trade name): Nippon Aerosil Co., Ltd.] 1g
Dispersant [Nopco Santo K963 (trade name): manufactured by San Nopco] 0.5g
The total amount of all the components of Dispersion 5 was 100 g, and the viscosity (25 ° C.) measured under the same conditions as Dispersion 1 was 14 mPa · s.

[Dispersion 6]
γ-iron oxide (specific surface area: 24)
[Product name: γ-THD (manufactured by Toda Kogyo, reddish brown)] 3 g
White pigment [TIPAQUE R-820 (trade name); manufactured by Ishihara Sangyo Co., Ltd.] 20 g
Phenylxylylethane 50.5g
Ethylbenzene 25g
Anti-settling agent [Aerosil (trade name): Nippon Aerosil Co., Ltd.] 1g
Dispersant [Nopco Santo K963 (trade name): manufactured by San Nopco] 0.5g
The total amount of all the components of Dispersion 6 was 100 g, and the viscosity (25 ° C.) measured under the same conditions as Dispersion 1 was 28 mPa · s.

[Dispersion 7]
γ-iron oxide (specific surface area: 14)
[Product name: γ-MRD (Titanium Industry Co., Ltd.), reddish brown] 3g
White pigment [TIPAQUE R-820 (trade name); manufactured by Ishihara Sangyo Co., Ltd.] 20 g
75.5 g of phenylxylylethane
Anti-settling agent [Aerosil (trade name): Nippon Aerosil Co., Ltd.] 1g
Dispersant [Nopco Santo K963 (trade name): manufactured by San Nopco] 0.5g
The total amount of all the components of Dispersion 7 was 100 g, and its viscosity (25 ° C.) was measured under the same conditions as Dispersion 1. As a result, it was 53 mPa · s.

[Dispersion 8]
γ-iron oxide (specific surface area: 20)
[Product name: MX-450 (manufactured by Toda Kogyo, reddish brown)] 3 g
White pigment [TIPAQUE R-820 (trade name); manufactured by Ishihara Sangyo Co., Ltd.] 20 g
Phenylxylylethane 55.5g
Ethylbenzene 20g
Anti-settling agent [Aerosil (trade name): Nippon Aerosil Co., Ltd.] 1g
Dispersant [Nopco Santo K963 (trade name): manufactured by San Nopco] 0.5g
The total amount of all the components of Dispersion 8 was 100 g, and the viscosity (25 ° C.) measured under the same conditions as Dispersion 1 was 38 mPa · s.

[Dispersion 9]
γ-iron oxide (specific surface area: 24)
[Product name: γ-THD (manufactured by Toda Kogyo, reddish brown)] 3 g
White pigment [TIPAQUE R-820 (trade name); manufactured by Ishihara Sangyo Co., Ltd.] 20 g
Phenylxylylethane 60.5g
Ethylbenzene 15g
Anti-settling agent [Aerosil (trade name): Nippon Aerosil Co., Ltd.] 1g
Dispersant [Nopco Santo K963 (trade name): manufactured by San Nopco] 0.5g
The total amount of all components of dispersion 9 was 100 g, and the viscosity (25 ° C.) measured under the same conditions as dispersion 1 was 34 mPa · s.

[Examples 1-6, Comparative Examples 1-3]
(1) Microcapsule magnetic display sheet After separating the microcapsule slurry containing γ-iron oxide obtained by using dispersions 1 to 9 with a sieve of 600 μm mesh, the microcapsules of 600 μm or less were subjected to vacuum filtration and dehydrated, A microcapsule cake partially containing water was obtained. 20 g of the cake is mixed with 10 g of an aqueous urethane resin [Hydran HW-301 (trade name): manufactured by Dainippon Ink & Chemicals, Inc.], and a coating liquid having a viscosity (25 ° C.) of 3,500 mPa · s (BL type rotational viscometer). Got. The obtained coating solution was applied to a 100 μm polyethylene terephthalate (PET) film to a thickness of 1 mm by a bar coater method, dried with warm air at 60 ° C., and adhered to the PET film. A capsule layer was obtained. Next, a photocurable resin adhesive (made by Chemtech) is applied to the microcapsule layer with a thickness of 200 μm by a bar coater method, and a 50 μm PET film is superimposed on the microcapsule layer to irradiate with ultraviolet rays to form a microcapsule magnetic display sheet. Got.

(2) Evaluation and evaluation method of microcapsule magnetic display sheet: Using the produced microcapsule magnetic display sheet, for writing, a writing magnetic pen having a diameter of 1 mm and 1,000 gauss was applied to the surface of the display sheet, and a speed of 200 mm / The quality was evaluated by moving in seconds. For erasing lines written on the surface of the display sheet, an erase rubber magnet of 100 × 30 mm, thickness of 2 mm, and 300 gauss was applied to the back surface of the display sheet and moved at a speed of 100 mm / second to evaluate the erased state. In the evaluations in the table, ◯ was able to write a clear line on the writing surface. On the erasing surface, it could be completely erased by one round trip. Δ indicates that some of the line quality is faint on the writing surface. On the erasing surface, it could be completely erased by two reciprocations. X: The writing quality was very faint or the line could not be written. On the erasing surface, erasing could not be performed even after two reciprocations. The obtained results are shown in Table 1. When the numerical values in Table 1 are further plotted, the graph shown in FIG. 1 is obtained, and the range that can be used in the present invention becomes clear.

As is clear from Table 1, the relationship between the specific surface area of the dispersion and the viscosity of the dispersion is inversely proportional. When the specific surface area is 14, the viscosity of the dispersion can be used even at a high viscosity of 31 to 44, When the specific surface area is 20, the viscosity of the dispersion is 23 to 33, and the usable viscosity is low. Further, when the specific surface area is 24, the viscosity of the dispersion becomes 14 to 28, which is even higher. Therefore, in a preferable example of the present invention, when the specific surface area is 14 to 24 and the viscosity of the dispersion is used in the range of 31 to 44 to 14 to 28, the stable dispersibility of reddish brown γ-iron oxide is obtained. It can be said that the obtained microcapsule magnetic display sheet capable of displaying clear reddish brown characters / images with good contrast is obtained.

The magnetic display sheet of the present invention can be used in any field such as business use, business use, and home use. Specifically, it can be used for cards such as cash cards, cashless cards, credit cards, prepaid cards, etc., and as a general purpose, for example, toys for infants such as picture books for infants, drawing boards for infants, characters Practice equipment, various game boards, letter practice boards, calligraphy practice boards, memo boards for mobile memos, writing memo boards, conference blackboards, various information boards in clean rooms, electronic bulletin boards, PC display panels It can be used easily and easily, and has extremely useful industrial properties.

It is the graph showing the relationship between the specific surface area of (gamma) -iron oxide which concerns on this invention, and the viscosity (25 degreeC) of a dispersion liquid.

Explanation of symbols

○ You can write clear lines on the writing surface.
△ Some of the line quality is faint on the writing surface.
× The line quality is poor on the writing surface.

Claims (1)

A transparent sheet for writing, a solid dispersion layer having a microcapsule containing a dispersion containing white pigment and reddish brown γ-iron oxide, a support, in this order,
A magnetic recording sheet comprising γ-iron oxide and a dispersion in which the product of the specific surface area of the reddish brown γ-iron oxide and the viscosity (25 ° C.) of the dispersion is in the range of 240 to 680.