JPH0156918B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a transfer sheet for producing confidential documents that can obtain a latent image made of a fluorescent whitening agent that can be identified under a fluorescent inspection light in a dark room on a plain paper surface, and a transfer sheet thereof. It is about the method.

Traditionally, creating secret documents involved exposing them. This is when you write pictures or letters on plain paper with a specific solution and let it dry. After the writing, it becomes difficult to see, but when you burn the plain paper with fire, the pictures and letters will reappear. For example, it is caused by the blue color caused by cobalt chloride. Color development, blackening due to carbonization of cellulose with dilute sulfuric acid, and blackish brown due to squeezed orange juice.

However, this roasted product shows discoloration even before it is roasted, and does not meet the intended requirements.

On the other hand, JP-A-56-75659 discloses a recording medium for producing secret documents that obtains a magnetic latent image on a magnetic recording sheet. In this method, pressure-sensitive paper, a magnetic recording sheet, and a high magnetic permeability material are sequentially laminated, and a magnetic latent image is obtained by pressing the pressure-sensitive paper with a magnetic pen. This method has the advantage that magnetic recording can be performed while viewing a visible image using pressure-sensitive paper during recording, but it has the disadvantage of using a magnetic pen and magnetic powder.

As a result of research to solve the above-mentioned drawbacks, the present inventor has discovered that microcapsules containing a solution of a fluorescent brightener dissolved in water or an oily vehicle and waxes are formed on a support. To provide a transfer sheet for creating secret documents, which is coated with a paper transfer type recording layer.

Furthermore, a transfer sheet for producing confidential documents, which is formed by coating a plain paper transfer type recording layer containing waxes and microcapsules containing a fluorescent brightener solution dissolved in water or an oil-based vehicle on a support. In the recording method, a latent image of a fluorescent whitening agent is formed on the surface of the plain paper by overlapping the plain paper transfer type recording layer side and plain paper and printing under pressure from the non-plain paper transfer type recording layer. The present invention provides a recording method for a transfer sheet for creating secret documents, in which the latent image is identified under a fluorescent inspection light in a dark room.

It is an object of the present invention to provide a method for printing on the non-coated surface of the transfer sheet when the above-mentioned transfer sheet for creating secret documents and plain paper are overlapped and pressure printing is performed on the non-coated surface of the transfer sheet using pen pressure from a ballpoint pen or the like. At the same time, the microcapsules (hereinafter abbreviated as fluorescent brightener-containing capsules) containing a fluorescent brightener solution dissolved in water or an oily vehicle on the coated surface are destroyed, resulting in fluorescent whitening on the plain paper surface. The agent is transferred to obtain a latent image.
The obtained latent image is indistinguishable in a visible state, can only be confirmed by using a fluorescent inspection light, and cannot be identified by normal handling.

That is, a transfer sheet for creating a secret document is required by the provider of the sheet, and when used by a user without any prior knowledge, the user will not notice the latent image printed under pressure on the plain paper surface. This is because the latent image cannot be visually identified. on the other hand,
The donor can read the latent image in a dark room using a fluorescent inspection light. As a result, confidential documents can be protected from being known to others.

By the way, for capsules containing fluorescent brighteners, various microencapsulation methods, such as complex coacervation method, interfacial polymerization method, in
Depending on the properties of the fluorescent brightener itself, it can be used in situ, spray drying, in-liquid curing, etc. without any difficulty.

When using a fluorescent brightener capsule, which is a component of the plain paper transfer type recording layer of the present invention, in combination with waxes, the use of waxes has the advantage that the fluorescent brightener can be transferred to the plain paper surface extremely efficiently. There is. For efficient transfer, the amount of wax used is preferably 5 to 100 percent by weight based on the solid content of the capsule.

The fluorescent brighteners of the present invention are water-soluble and oil-soluble, and are exemplified below. Water-soluble derivatives of 4,4'-diaminostilbendisulfonic acid (e.g. Color Index Name 24,
84, 85, 86, 87, 90, 104, 134, 166, 167, 168,
169), stilbenes [triazinyl derivatives] (e.g., 14, 22, 32, 37, 153, 173), stilbenes (e.g., 174, 175, 176, 177), coumarin derivatives (e.g., 52), bisoxazole (e.g., 91, 172), 4,4'-bistriazinylaminostilbene-2,2'-disulfonic acid derivatives, benzoxazole derivatives, and pyrazoline derivatives. In addition, oil-soluble ones include metal complex type systems (for example, color index name).
Yellow61, 80, Orange37, 40, 44, Red8, 83,
84, 121) Monoazo type (e.g. Orange6 as above), triarylmethane type (e.g. Violet8 as above,
Blue2), anthraquinones (e.g. same as above)
Blue36), phthalocyanine type (e.g. same as above)
Blue55), naphthalimide derivatives, bisbenzoxazolyl derivatives, etc. Among these exemplified fluorescent brighteners, those in a colored and visible state can be used by making the background of plain paper the same color. When the fluorescent brightener is water-soluble, water can be used, and when it is oil-soluble, a nonvolatile vehicle such as vegetable oil, animal oil, mineral oil, or synthetic oil can be used as the vehicle.

The amount of fluorescent brightener is 0.2 to 3 weight percent dissolved in the water or oil vehicle. Preferably it is 0.5 to 2 weight percent.

Waxes used in combination with fluorescent whitening agents include animal-based waxes such as beeswax, spermaceti wax, Chinese wax, and lanolin; plant-based waxes such as candelilla wax, carnauba wax, wood wax, rice wax, and sugarcane wax; Montan wax,
Mineral waxes such as ozokerite, ceresin, and lignite waxes; petroleum waxes such as paraffin waxes and microcrystalline waxes;
modified waxes such as montan wax derivatives, paraffin wax derivatives, and microcrystalline wax derivatives; hydrogenated waxes such as castor wax and opal wax; synthetic waxes such as low molecular weight polyethylene and its derivatives; acra wax and distearyl ketone; caproic acid amide, caprylic acid amide, pelargonic acid amide, capric acid amide, lauric acid amide,
Tridecylic acid amide, myristic acid amide,
Fatty acid amide waxes such as ethylene bisstearamide, caproleic acid amide, myristoleic acid amide, oleic acid amide, elaidic acid amide, linoleic acid amide, erucic acid amide, ricinoleic acid amide,
Mention may be made of those selected from unsaturated fatty acid amides such as linolenic acid amide. And these can be used alone or in combination.

The transfer sheet for creating secret documents according to the present invention can be produced by coating the entire surface of the support with a general coater such as an air knife coater as an aqueous dispersion coating solution, or by spray-drying microcapsules, etc. After drying, if necessary, mix uniformly with powdered microcapsules at the melting temperature of wax to form a coating solution, and print on a part of the support using an ordinary carbon printing machine. You can choose to.

When preparing the coating liquid according to the present invention, a liquid property improver can be added depending on various coaters and printing machines. Examples include thickeners that keep the viscosity constant and surfactants that improve dispersibility, but it is clear that they are not limited to these.

Paper is mainly used as the support for forming the coating layer according to the present invention, but various nonwoven plastic films, synthetic papers, metal foils, composite sheets of combinations of these, and sheets embossed with each of these may also be used.

Hereinafter, the present invention will be specifically explained with reference to Examples. Note that "parts" indicate parts by weight.

Example 1 Microcapsules containing a fluorescent brightener were prepared as follows.

100 parts of a 10% aqueous solution of ethylene-maleic anhydride copolymer, 10 parts of urea, 1 part of resorcinol, and 200 parts of water
A mixed solution was prepared, and the pH was adjusted to 3.5 using a 20% aqueous sodium hydroxide solution. Fluorescent brightener 2.5bis(5′tertiarybutylbenzoxazolyl(2))thiophene [Product name Uvitex OB, CIBA-GEIGY
Co., Ltd.] 1.4 parts Hysol SASN-296 [Giali-
The solution was dissolved in 140 parts of ethane-based solvent (manufactured by Nippon Petrochemical Co., Ltd.) to obtain a fluorescent brightener solution. This fluorescent brightener solution was emulsified and dispersed in the above mixed aqueous solution to form 5 oil droplets.
After bringing the temperature to ~6μ, 25 parts of a 37% formalin aqueous solution was added and the temperature of the system was maintained at 55°C while stirring.

After reacting for 2 hours, it was cooled and the pH of the system was adjusted to 9.5.
and finished encapsulation.

50 parts of fluorescent brightener-containing capsules prepared as described above (as solid content), 45 parts of 45% paraffin wax emulsion, 25 parts of wheat starch, 48
Mix and stir 50 parts of %SBR latex and add water.
A water dispersion coating solution with a solid content of 20% was prepared. This coating solution was applied onto a base paper having a basis weight of 48 g/m ² using a Mayer bar at a weight of 6 g/m ² .

The coated side of the obtained transfer sheet for creating secret documents was placed opposite to plain paper, and pressure printing was performed using a ballpoint pen from the non-coated side. When the printed portion of the plain paper was visually observed, it was not possible to identify the printed portion at all in a visible state. Subsequently, when the printed area was irradiated with a fluorescent inspection light (manufactured by Tokyo Kogaku Kikai Co., Ltd., model Fl-3L) in a dark room, a printed image showing clear fluorescent light could be confirmed.

Example 2 Triarylmethane was used in place of the fluorescent brightener 2,5-bis(5'tert-butylbenzooxazolyl(2))thiophene in the fluorescent brightener-containing capsule prepared in Example 1. Fluorescent brightener Victoria Blue-F4R
(manufactured by BASF) was used for encapsulation and coating.

The coated surface of the obtained transfer sheet for creating secret documents became bluish. On the other hand, the plain paper had a similar bluish background. When pressure printing was performed in the same manner as in Example 1, it was impossible to visually identify the image, but the identification of the printed image on blue plain paper could be clearly confirmed using a fluorescent inspection lamp in a dark room.

Claims (1)

[Scope of Claims] 1. A secret in which a plain paper transfer type recording layer comprising waxes and microcapsules containing a fluorescent brightener solution dissolved in water or an oily vehicle is coated on a support. Transfer sheet for document creation. 2. A transfer sheet for producing secret documents, which is made by coating a support with a plain paper transfer type recording layer consisting of microcapsules containing a fluorescent brightener solution dissolved in water or an oily vehicle and waxes. In the recording method, a latent image of a fluorescent whitening agent is formed on the surface of the plain paper by overlapping the plain paper transfer type recording layer side and plain paper and printing under pressure from the non-plain paper transfer type recording layer, A recording method for a transfer sheet for creating secret documents, in which the latent image is identified under a fluorescent inspection light in a dark room.