JPH03211081A - Duplication-proof sheet - Google Patents

Abstract

PURPOSE:To ensure that a latent image appears as a warning when an image is dupli cated and interpretating an image is made impossible by printing a latent image using an ink containing a reversible, thermally discoloring material which thermally colors, on the surface of a base. CONSTITUTION:A sheet consists of an electron-donative coloring organic compound, an electron-receptive compound, a discoloration temperature adjusting agent and a low voltatility solvent as essential elements. If the sheet is set on a contact glass of a copy mounting table and then is exposed to light for duplication, the electron- donative coloring organic compound and the electron-receptive compound become colored and a latent image is visualized as a visual image and duplicated. Then a copy is taken out of the glass and cooled. Consequently, the latent image pattern is discharged again and becomes invisible. The required reversible, thermally discoloring material is the one which is colorless as long as it is exposed to a normal temperature, and is so highly responsive that a color of high density is thermally developed and has a high coloring density. The preferable electron-donative coloring organic com pound is a material which absorbs a large amount of light, especially in the photosensi tive wavelength zone during color development among other indolenophthalide compounds.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to paper that can prevent copying and forgery by electrophotographic copying machines, and is useful for maintaining the confidentiality of documents that are confidential to third parties, such as in confidential facsimiles. and other new fields.

[Prior Art] In order to prevent document forgery, hidden printing is performed so that warning characters appear when copies are made. For example, a latent image such as a character, symbol, or pattern made of fine halftone dots is printed on the surface of the paper in advance, and a different printing pattern such as a background pattern is applied on the latent image (Special Publication No. 55-45400.58-4).
7708, Utility Model Publication No. 81-122889, Japanese Patent Application Publication No. 1999-1-1
87870), a combination of multiple line groups at a specific angle (Japanese Patent Publication No. 59-23023), a latent image printed using silver ink and concealed with a colored pattern or background pattern (JP-A-5L-20395) ), and one in which a metal-colored photovolatile film is formed by vapor deposition (Utility Model Application Publication No. 58-198172).

With these methods, when printing only a latent image pattern, the pattern is clearly visible from the beginning, so in order to hide it, the background area other than the latent image is camouflaged with a ground pattern, etc. There is a drawback that it is difficult to see the original because of the way it looks.

Furthermore, the manufacturing process is complicated, and as a method for manufacturing the original plate, for example, Japanese Patent Application Laid-Open No. 60-119560.60-230657.8
2-170984, etc., but it is disadvantageous that the process is long and requires advanced technology, resulting in high cost.

With the improvement in the performance of copying machines and their widespread use in the market, it is now possible for anyone to easily obtain a large number of sophisticated copies, which has led to the risk of leakage of confidential information due to unauthorized copying of confidential documents and literature. This has been attracting attention as a social problem, such as copyright infringement due to unauthorized copying of original materials.

Under these circumstances, many copy prevention and counterfeit prevention methods have been proposed, but no product has yet been developed that meets the needs of users. Therefore, in order to prevent document forgery using a copying machine, when copying documents, characters, symbols, patterns, etc. such as ``invalid'', ``copy'', ``copy not allowed'', etc. are placed so that it can be recognized that the paper is not genuine. One way to prevent this is to use hidden printing to make it appear.

[Problems to be Solved by the Invention] The present invention is normally colorless and completely invisible, but when copied using an electrophotographic copying machine, for example, characters such as "copy", "copy not allowed", [invalid J rVo I DJ], etc. The purpose of the present invention is to provide a sheet of paper on which latent images for warning such as symbols and marks appear, making the intended copy image illegible.

[Means for Solving the Problems] The structure of the present invention for solving the above problems is to print a latent image on the surface of a substrate using an ink containing a reversible thermochromic material that is colorless at room temperature but develops color when heated. This is copy-protected paper.

The paper of the present invention is different from conventional hidden printing in which a latent image pattern is camouflaged with halftone dots, etc., and is characterized by forming a latent image on a substrate using ink containing a reversible thermochromic material that develops color with heat. Although electrophotographic copying machines differ depending on the model and operating conditions, the temperature of the contact glass surface of the original platen during normal use can reach around 40°C due to the heat dispersed during exposure and the heat generated from the heat fixing unit. ing. The paper of the present invention contains an electron-donating color-forming organic compound, an electron-accepting compound, a discoloration temperature regulator, and a low-volatility solvent as essential components. This method takes advantage of the property that these components undergo reversible thermal discoloration when heated.When copying is performed by placing paper on the contact glass of the document table and exposing it to light, a latent image is formed by the contact glass and the heat generated during exposure. The electron-donating color-forming organic compound and electron-accepting compound contained in the ink develop color, and the completely invisible latent image is clearly visualized as a visible image and copied. .

If the document is removed from the contact glass and allowed to cool, the developed latent image pattern will be discolored again and will no longer be visible.

This function is reversible, so repeated runs will give the same result.

The substrate used in the present invention is not particularly limited, and may be paper, plastic sheet, or a composite thereof, which has been conventionally used for various recording and printing purposes. These substrates are preferably white for ease of reading, but they can also be colored to the extent that readability is not impaired. Next, the reversible thermochromic material used in the ink that forms the latent image on the substrate is as colorless as possible at room temperature, and is a thermoresponsive material with a high color density that is sensitive to heat during copying. Needed.

The electron-donating color-forming organic compound, which is the coloring agent used in the present invention, may be used alone or in a mixture of two or more, and is itself a colorless or light-colored dye precursor. For example, triphenylmethane phthalide compounds, fluoran compounds, phenothiazine compounds, leucoolamine compounds, rhodamine lactam compounds, spiropyran compounds,
It is preferable to select a material from among indolinophthalide compounds and the like that absorbs a large amount of light having the spectral wavelength characteristics of the light source of a copying machine, particularly in the wavelength range sensitive to the photoreceptor, when colored.

As specific examples, the following can be used alone or in combination of two or more.

3.3-bis(p-dimethylaminophenyl) phthalide, 3.3-bis(p-dimethylaminophenyl) 6-dimethylaminophthalide (also known as crystal violet lactone), 3.3-bis(p-dimethylamino phenyl) 6-diethylaminophenyl, 3.3-bis(p-dimethylaminophenyl) 6-chlorophthalide, 8.3-bis(p-dibutylaminophenyl) phthalide, 3-(2°-hydroxy-4′-dimethylamino phenyl) -3-(2°-methoxy-5'-chlorophenyl) phthalide, 3-(2°-hydroxy-4'-dimethylaminophenyl) -3-(2°-methoxy-5'-nitrophenyl) Phthalide, 3-(2°-hydroxy-4′-diethylaminophenyl)-3-(2′-methoxy-5°-methylphenyl)phthalide, 3-(2°-methoxy-4′-dimethylaminophenyl)-3 -(2°-hydroxy-4′-chloro5°-methylphenyl)phthalide, 3-cyclohexylamino-6-chlorofluoran, 3-dimethylamino-5,7-dimethylfluoran, 3-diethylamino-7 -chlorofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 9-(N-p-)dyl-N-ethylamino)6-methyl-7-ani Linofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-diethylamino-7,8-benzfluorane, 2-(N-(3°-trifluoromethylphenyl)amino)-6- Dinitylaminofluoran, 3-diethylamino-7-(0-chloroanilino)fluoran, 3-dibutylamino-7-(0-chloroanilino)fluoran, 3-N-methyl-N-amylamino-6-methyl-7-
Anilinofluorane, 3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6
-Methyl-7-anilinofluorane, 3-(N,N-diethylamino)-5-methyl 7-(N
, N-dibenzylamino)fluoran, 3-diethylamino-5-chloro-7-(N-benzyl-trifluoromethylanilino)fluoran, 3-diethylamino-5-chloro-7-(α-phenylethylamino)fluoran , 3-(N-ethyl-p-toluidino)-7-(α-phenylethylamino)fluoran, 3-diethylamino-7-(0-methoxycarbonylphenylamino)fluoran, 3-diethylamino-5-methyl-7- (α-phenylethylamino)fluorane, 3-diethylamino-7-piperidinofluorane, 2-chloro-3-(N-methyltoluidino)7-(p-
n-butylanilino)fluoran, 3-(N-methyl-
N-isopropylamino)-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 8-N-ethyl-N-(2-ethoxypropyl)amino-6 -Methyl-7-anilinofluorane, 3-(N-benzyl-N-cyclohexylamino)-5,8-benzo-7-α-naphthylamino-4'-bromofluorane, 3-diethylamino-6 -chloro-7-anilinofluorane, 3-diethylamino-6-methyl-7-mesitidino 4
', 5''-benzofluorane, 3-N-methyl-N-isobutyl-6-methyl-7-anirite fluorane, 3-N-ethyl-N-isoamyl-6-methyl-7-anirite fluorane, 3-diethylamino-6-methyl-7-(2°.

4°-dimethylanilino)fluoran, 2-18.6-
Bis(diethylamino)-9-(.

chloranilino)xanthylbenzoic acid lactam) benzoylleucomethylene blue 6°-chloro-8°-methoxy-benzoindolino-spirobilane, 6°-bromo-3°-methoxy-benzoindolino-spirobilane, etc.

Next, the electron-accepting compound that causes the electron-donating color-forming organic compound to develop color when heated can be selected from color developers commonly used in thermal paper, but compared to systems that reversibly erase the color when heated, Therefore, the selection range is narrow, and particularly preferable electron-accepting compounds include gallic acid esters 1 such as dodecyl gallate, cetyl gallate, and stearyl gallate, dodecyl protocatechuate, cetyl protocatechuate, stearyl protocatechuate, benzyl protocatechuate, etc. These include protocatechuic acid esters, esters of parahydroxybenzoic acid such as methyl parahydroxybenzoate, propyl parahydroxybenzoate, and urea.

Examples of the discoloration temperature regulator include higher alcohols, esters, acid amides, carboxylic acids, etc., such as lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, methyl margarate, ethyl palmitate, and methyl stearate. ester, stearic acid ethyl ester, stearic acid propyl ester, behenic acid ethyl ester, palmitic acid decyl ester laurylamine, cetylamine,
palmitic acid ethylamide, capric acid, lauric acid,
Myristic acid, etc.

The low volatility solvent can be selected from those commonly used as vacuum oils. Examples include a2 alkylnaphthalene compounds, diarylalkane compounds, alkyl biphenyl compounds, terphenyl compounds, and triallylmethane compounds. For example, dimethylnaphthalene, diethylnaphthalene, diisopropylnaphthalene, 1-methyl-1-dimethylphenyl-
1 phenylmethane, 1-methyl-1-ethylphenyl-
Examples include 1-phenylmethane, dimethylbiphenyl, diethylbiphenyl, diisopropylbiphenyl, hydrogenated terphenyl, and tritolylmethane.

It is necessary to select an appropriate mixing ratio of each component depending on the physical properties of the material used, but in reality it can be selected from a fairly wide range. Electron-donating color-forming organic compound: Electron-accepting compound: Color change temperature The mixing ratio (weight) of the regulator is 1:1
-10: A range of 5-50 is suitable.

The mixing ratio of the low-volatile solvent is in the range of 80 to 80% by weight, and if it is too low, the thermal response speed and color density will not improve. If the amount of 3 is too large, the reversibility of color development and decolorization will be poor, and in particular, the color will not return to light sufficiently during decolorization. The mechanism by which low-volatile solvents affect color development and decolorization is not fully understood, but it is related to the solubility of the three components to be mixed, especially the solubility of electron-accepting compounds, and they have the ability to dissolve when heated. During cooling, it is necessary not to inhibit the crystallization of the three components. In other words, the effects of the electron-donating color-forming organic compound, the electron-accepting compound, and the discoloration temperature regulator are temperature-dependent, and in the presence of a low-volatile solvent, the discoloration temperature regulator and the electron-accepting compound become less volatile when heated. The electron-donating color-forming organic compound and the electron-accepting compound interact to produce color. Next, it is thought that upon cooling, the dissolved discoloration temperature adjusting agent and electron-accepting compound crystallize, and the electron-accepting compound separates from the electron-donating color-forming organic compound and discolors.

The paper of the present invention can be produced by dispersing the reversible thermochromic material having the above-mentioned composition in a vehicle, or by forming it into microcapsules by a known encapsulation method such as coacervation, interfacial polymerization, in-5-itu polymerization, etc. It is produced by preparing an ink that is encapsulated and dispersed in a vehicle, and printing a latent image by gravure printing, offset printing, flexographic printing, screen printing, or the like.

[Example] Hereinafter, the present invention will be specifically explained with reference to Examples.

Note that parts in the examples represent parts by weight.

Example 1 3-N-Methyl-N-cyclohexylamino-〇-methyl-7-anilite fluorane 1 part cetyl gallate 5 parts n-cetyl alcohol
20 parts diisopropylnaphthalene 1
Two parts were uniformly melted at 80°C, mixed with 100 parts of 3% polyvinyl alcohol (PVA 217E manufactured by Kuraray), and dispersed in a ball mill to form an ink. The resulting ink No. 5 was applied to high-quality paper, air-dried, and then its reversible color change properties were examined. The color rapidly changed from colorless to black at 43°C. Upon cooling, the color disappeared and became colorless, and this phenomenon repeatedly showed the same behavior.

Example 2 3-dibutylamino-〇-methyl 7-anilitous fluorane 1 part dodecyl gallate 4 parts n-myristyl alcohol 10 parts diisopropylnaphthalene 30
Part 1: Melt the above four components uniformly at about 100°C.

100 parts of a 5% aqueous gelatin solution adjusted to pH 7.0 was heated to 80°C, and 30 parts of the melt was added dropwise while also heated to 80°C, using a mixer to form microdroplets of 2 to 10 μm. Emulsify and disperse so that

Next, 120 parts of a 5% gum arabic aqueous solution heated to 80°C was added, diluted with 70°C warm water at 220°C, and heated to 120 parts with stirring.
0% acetic acid was gradually added to adjust the pH to 4.3 to cause coacervation, and then the mixture was cooled to 10°C for gelation, followed by the addition of 2 parts of 25% glutaraldehyde. Then, the pH was adjusted to 9 and stirring was continued for 12 hours to obtain a gelatin-walled microcapsule slurry.

Ten parts of the centrifuged microcapsule particles were dispersed in 15 parts of an acrylic ester emulsion (solid content 30%), and isolated character patterns were gravure printed on high-quality paper. When information was recorded on this paper using a printer, it was printed as clearly as when printed on ordinary white paper, and no hidden character patterns were observed.

This document can be used as a manuscript using an electrophotographic copying machine (Recopy PT).
5510), the hidden character pattern was clearly copied in black.

When the original was taken out of the copying machine, it returned to its original state at room temperature, the hidden character pattern disappeared, and the recorded information was easily readable. This test was repeated 10 times, but no decline in function was observed.

Example 3 7 3-diethylamino-6-methyl 7-dibenzylaminofluorane 1 part Benzyl protocatechuate 5 parts n-butyl stearate 10 parts Diethylnaphthalene 1
6 parts The above four ingredients are uniformly melted at about 100°C.

100 parts of an 8% aqueous gelatin solution was heated to 80°C, and 30 parts of the melt and 8.5 parts of an epoxy resin (Epicoat 828 manufactured by Yuka Shell Epoxy) were added dropwise while heated to 80°C, using a mixer. emulsify and disperse to form fine droplets of 2 to 10 μm.

Add epoxy resin curing agent aliphatic polyamine (Epicure U manufactured by Yuka Shell Epoxy) to the obtained emulsion under constant stirring.
Dissolve 3.5 parts in 7 parts of water and gradually add it, and bring the temperature of the solution to 8.
The mixture was kept at 0° C. and stirred for 4 hours to obtain a microcapsule slurry with an epoxy resin wall.

One part of the centrifuged microcapsule particles was dispersed in 30 parts of 5% ethyl cellulose and 5 parts of vinyl acetate emulsion, and 8 hidden character patterns were screen printed on high-quality paper. Information was recorded using this paper using an electrophotographic copying machine. A hidden character pattern appeared immediately after copying, but it disappeared after a few minutes and returned to the same state as a normal copy. When the same test as in Example 2 was conducted, the hidden characters appeared clearly and showed the same behavior.

Example 4 3-diethylamino-7-dibenzylaminofluorane 0.5 parts 3-diethylamino-6-methyl 7-anilite fluorane 0.5 parts Dodecyl gallate 4 parts n-myristyl alcohol 10 parts Dimethylnaphthalene 2
0 part is uniformly melted at about 100°C.

100 parts of a 4% aqueous solution of ethylene-maleic anhydride copolymer whose pH was adjusted to 5.0 was heated to 80°C, the melt was added thereto, and the mixture was emulsified into microdroplets of 2 to 10 μm using a homomixer. Dispersed.

The obtained emulsion was maintained at 75°C and a prepolymer of melamine-pho9 lumalin (three-phase chemical conicalc M
10 parts of X-031) were added dropwise, the pH was adjusted to 4.5 with acetic acid, and the reaction was carried out with stirring for 4 hours to obtain a microcapsule slurry with a melamine-formaldehyde resin wall.

A manuscript was prepared in the same manner as in Example 2 using centrifuged microcapsule particles, and an electrophotographic copying machine (Recopy FT40) was prepared.
60, 55, 10, and 6080), all of them produced copies with hidden characters clearly visible. The hidden text on the manuscript disappeared at room temperature and returned to its original state.

[Effects of the Invention] As described above, the paper of the present invention allows the creation of uncolored, easy-to-read manuscripts that are similar to ordinary printed matter by printing hidden character patterns using a heat-colorable reversible thermochromic material. When this document is used as a manuscript and copied using an electrophotographic copying machine, the hidden character pattern clearly appears in the copy, which is effective in preventing copying and counterfeiting.

0

Claims (3)

[Claims] (1) Anti-copying paper on which a latent image is printed on the surface of the base material using ink containing a reversible thermochromic material that is colorless at room temperature but develops color when heated. (2) A claim in which the reversible thermochromic material that develops color upon heating contains an electron-donating color-forming organic compound, an electron-accepting compound, a color-change-accepting compound, a color-change temperature regulator, and a low-volatility solvent as essential components ( 1) Copy prevention paper as described. (3) The anti-copying paper according to claim (2), wherein the content of the low-volatile solvent is in the range of 30 to 80% by weight of the essential components.