JP2006255925A - Method for preparing hidden picture and printed matter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preparing a hidden picture by which a first image can be formed by a high image quality like a photograph, and a second image can be formed so that it is hardly visually recognized by viewing in an ordinary visible light region, and these can be performed easily and at a low cost. <P>SOLUTION: Ink A for an inkjet printer comprising a pigment and a dispersing medium for dispersing this, and ink B for the inkjet printer comprising a pigment with the same color as that for the pigment of the ink A, a dispersing medium and a sensible functional material, and in which the solid body is formed into the same color so that discrimination of the color by viewing is impossible in at least a visible light region to the solid body of the ink A, are prepared. A first image 1 is formed on the substrate by using the ink A by the inkjet method, and a second image 2, which can be discriminated from the first image by sensing the functional material, is formed on the substrate by using the ink B by the inkjet method. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for creating a hidden picture using an inkjet method, and a printed material on which a hidden picture is formed by this method.

For valuable printed matter such as tickets, certificates, certificates, securities, and cash vouchers, in order to prevent counterfeiting and ensure its security, a hidden picture is partly formed.
Hidden pictures cannot be visually recognized under visible light, and the first image that can be visually confirmed under normal visible light is not visible, not to mention its design. The second image is formed by being present in the same area as the first image. In other words, since the hidden picture made up of the second image is intended to ensure security as described above, it is extremely important that it cannot be seen at all by normal visual observation.

For creating such a hidden picture, for example, a fluorescent material that emits light by receiving ultraviolet light such as a backlight is used (see, for example, Patent Document 1). As this fluorescent substance, there are dye-based and pigment-based materials, but dye-based materials generally have low weather resistance. Therefore, when used outdoors or when long-term reliability is required, pigment-based materials are used. Many things are used.
In addition, a method has been proposed in which a second image that cannot be visually recognized under visible light is formed under a fluorescent material (see, for example, Patent Document 2).
JP 2000-256591 A JP 2001-96889 A

  However, when the second image is formed under the fluorescent material as in Patent Document 2, it is not possible to form the first image that can be visually recognized in a normal state, and is therefore sufficient as a hidden picture. There is a problem of not functioning. In the first place, in order to conceal, it is necessary to apply the pigment layer flatly, and an uncommon large-scale apparatus is required.

  In addition, when a pigment-based fluorescent material is used as in Patent Document 1, since the pigment is solid, when the second image is formed over the first image, it is colorless. However, depending on how light is applied, the presence of the second image in the visible light region may become apparent due to refraction or the like.

  The present invention has been made in view of the above circumstances. The object of the present invention is to form a first image with a high image quality such as a photograph and to form a second image in a normal visible light range. Hidden picture creation method that can be formed so that visual recognition is difficult, and that can be done easily and at low cost, and security function and display function obtained by using this creation method It is to provide a printed matter provided with.

The method for creating a hidden picture according to the present invention includes an ink A for an ink jet printer comprising a pigment and a dispersion medium for dispersing the pigment,
The solid body after containing the pigment of the same color as the pigment of the ink A, a dispersion medium, and a functional material that can be sensed and discharged and dried by an ink jet printer is a solid after the ink A is discharged and dried. Prepare an ink B for an inkjet printer formed in the same color that makes it impossible to discriminate the color visually at least in the visible light range with respect to the body,
On the base material, at least using the ink A, the first image is formed by an inkjet method,
A second image that can be distinguished from the first image by sensing the functional material using the ink B is formed on the base material by an inkjet method.

  According to this method for creating a hidden picture, the first image and the second image are formed by the ink jet method using the ink A and the ink B. Therefore, the first image for visual recognition particularly in the visible light range. This image can be formed with high image quality such as a photograph. Further, since the ink B is formed so that the solid body of the ink B becomes the same color as that of the solid body of the ink A at least in the visible light range, the color cannot be visually determined. Therefore, it is difficult to distinguish between the ink A and the ink B, and it is difficult to visually recognize the second image formed by the ink B in a normal visible light range. Therefore, the second image functions well as a hidden picture. Furthermore, by only preparing ink A and ink B, a hidden picture can be easily and inexpensively formed by an existing inkjet printer.

In the method for creating a hidden picture, when the first image and the second image partially overlap each other, the overlapping part is formed using only the ink B, and the first part other than the overlapping part is formed. It is preferable that the image area is formed only with the ink A.
In this way, the second image in the overlapping portion has higher image quality, and as a result, the entire second image has higher image quality.

In the method for creating a hidden picture, the functional material is at least one of a fluorescent light emitting material, an infrared light reflecting material, an infrared light absorbing material, an ultraviolet light reflecting material, an ultraviolet light absorbing material, and a magnetic material. Preferably it consists of.
By using such a material as the functional material, for example, the second image is recognized or observed by applying ultraviolet light or near ultraviolet light with a black light, or sensing with an infrared camera or a magnetic sensor. It becomes possible.

In the method for creating a hidden picture, the average radius and average thickness of the solid body of 1 dot after being discharged and dried by an ink jet printer as the ink B are discharged and dried by the ink jet printer of the ink A. It is preferable to use one that has been adjusted to have a difference of 10% or less with respect to the average radius and average thickness of the solid body of 1 dot.
In this manner, the solid body of ink B has almost the same texture as the gloss as well as the color of the solid body of ink A. Therefore, the ink A and the ink visually observed in the normal visible light range. Since discrimination from B becomes more difficult, the function of the second image as a hidden picture is further enhanced.

In this method for creating a hidden picture, the ink A has the same optical characteristics in the visible light region as the functional material of the ink B, and the functional material has substantially the same functionality. It is preferable to contain a dummy material that does not exist.
By including the dummy material in this way, the texture of the solid body of ink A and the texture of the solid body of ink B are almost the same, and therefore, it is difficult to discriminate even when touched or not visually. The function as a hidden picture of the second image is further enhanced.

Further, in the method for creating a hidden picture, a plurality of types having different pigments are prepared as the ink A, and a plurality of types corresponding to the ink A are prepared as the ink B. It is preferable to form a first color image using the ink A and a plurality of types of inks B.
In this way, it is possible to form the first image with higher quality and higher quality.

In this method for creating a hidden picture, the first image is a color image, the second image is partially overlapped with the first image, and the overlapping portion is also a color image. In addition, the first image is color-divided into a plurality of color-divided images, and the overlapping portion in each color-divided image is formed using only the ink B of the corresponding color, and the overlapping portion in each color-divided image It is preferable that the first image regions other than the above are formed only with the ink A of the corresponding color.
In this way, the second image in the overlapping portion has higher image quality, and as a result, the entire second image has higher image quality.

In the method for creating a hidden picture, it is preferable to use a plurality of types of the ink B having different functional materials.
In this way, the second image can be recognized or observed by a plurality of different sensing methods. Therefore, for example, when the second image has a security function, the function is further enhanced. Is possible.

The printed matter of the present invention is characterized by having a first image and a second image formed by the previous creation method.
According to this printed matter, the first image formed with a high image quality such as a photograph and the second image that is difficult to visually recognize in the normal visible light range are formed. The function of a general printed matter is sufficiently exhibited by one image, and the second image functions well as a hidden picture.

In this printed matter, the second image is preferably provided as a security function.
If the printed matter of the present invention is applied to valuable printed matter such as tickets, certificates, certificates, securities, and vouchers, it becomes possible to confirm the authenticity by the second image. Can be secured.

In the printed matter, it is preferable that the second image is provided as a display function.
By using the second image in a design, a commercial display, or the like, for example, using black light or the like, it is possible to exhibit a good display function.

The present invention will be described in detail below.
The method for creating a hidden picture of the present invention prepares ink A and ink B for an ink jet printer, and uses these ink A and ink B to form a first image and a second image on a substrate by an ink jet method. This is a method of forming an image.

Ink A contains a pigment and a dispersion medium for dispersing the pigment.
As the pigment of the ink A, the same pigment as that of the ink B described later is basically used.
As a black pigment when ink A (or ink B) is black ink. Carbon blacks (CI pigment black 7) such as furnace black, lamp black, acetylene black, channel black, or metals such as copper oxide, iron oxide (CI pigment black 11), titanium oxide Organic pigments such as aniline black (CI Pigment Black 1) can be used.

When the ink A (or ink B) is a color ink, examples of the color pigment include C.I. I. Pigment Yellow 1 (Fast Yellow G), 3, 12 (Disazo Yellow AAA), 13, 14, 17, 24, 34, 35, 37, 42 (Yellow Iron Oxide), 53, 55, 74, 81, 83 (Disazo Yellow HR), 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 138, 153, 180, C.I. I. Pigment Red 1, 2, 3, 5, 17, 22 (Brilliant First Scarlet), 23, 31, 38, 48: 2 (Permanent Red 2B (Ba)), 48: 2 (Permanent Red 2B (Ca)), 48 : 3 (Permanent Red 2B (Sr)), 48: 4 (Permanent Red 2B (Mn)), 49: 1, 52: 2, 53: 1, 57: 1 (Brilliant Carmine 6B), 60; 1, 63: 1, 63: 2, 64: 1, 81 (Rhodamine 6G rake), 83, 88, 101 (Bengara), 104, 105, 106, 108 (Cadmium red), 112, 114, 122 (Quinacridone magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 185, 190, 193, 209, 219, . I. Pigment violet 19, 23, C.I. I. Pigment Blue 1, 2, 15 (phthalocyanine blue R), 15: 1, 15: 2, 15: 3 (phthalocyanine blue G), 15: 4, 15: 6 (phthalocyanine blue E), 16, 17: 1, 56 , 60, 63, C.I. I. Pigment Green 1, 4, 7, 8, 10, 17, 18, 36, etc. can be used.
In addition, when the ink A (or ink B) is a white ink, titanium oxide, zinc oxide, zinc sulfide, or the like can be used as a white pigment.

  As such a pigment, a pigment produced by a pulverization method, a synthesis method, or a precipitation method and prepared into a powder having a particle size of 25 μm or less is used. In particular, in the present invention, an ink for an inkjet printer is used. It is desirable to use one having a diameter adjusted to 1 μm or less. If the particle diameter is adjusted to 1 μm or less in this way, it is possible to reliably prevent clogging from occurring in the ejection head of an ink jet printer. However, depending on the ejection driving method and type of the ejection head, there are those that can be used without clogging even if the particle size is about 25 μm as described above. Can also be used in the present invention.

  The amount of the pigment added is preferably in the range of 0.5 to 30% by weight of the entire ink A, although it varies depending on the type. By setting it as such a range, after the ink A is discharged on a base material and dried, the color peculiar to a pigment will be exhibited favorably.

As a dispersion medium for dispersing such a pigment, a solution containing water as a main component is particularly preferably used. In addition, as a method of dispersing the pigment in such a solution (dispersion medium), it can be appropriately selected from the following dispersion methods according to the type of the pigment and the like.
A method in which the pigment surface is hydrophilized in advance and self-dispersed in the above solution (dispersion medium).
A method in which a low molecular weight surfactant is added to the above solution (dispersion medium) and dispersed in this solution.
A method in which a polymer dispersant is added to the above solution (dispersion medium) and dispersed in this solution.
A method in which a polymerizable surfactant is added to the above solution (dispersion medium) and a polymerized film is formed on the pigment to be dispersed in the solution.

In addition to the above-described dispersion methods, any conventionally known dispersion method can be adopted as long as dispersion stability that enables ejection by an inkjet method is obtained as ink for an ink jet printer.
Here, in order to obtain dispersion stability that enables ejection by the ink jet method, for example, it is preferable to cover most of the pigment with a polymer material. In this case, in particular, the polymer dispersion in the solution (dispersion medium) A method of adding and dispersing the agent is preferable.

Examples of the polymer dispersant used in such a method include non-hydrophilic groups such as aromatic rings, alkyl groups and halogenated hydrocarbons, carboxylic acid groups, sulfate groups, sulfite groups, nitrate groups, nitrite groups, 1 ~ Acrylic and methacrylic radical polymerization with hydrophilic group such as quaternary amine group, amide group, amino group, hydroxyl group and neutral group such as ester group, carbonate group, ether group, cyano group, Examples of the polymer include those having the above-described group in the main chain or side chain by a bond such as an ester bond, an amide bond or a urethane bond.
In order to provide ink characteristics, several types of hydrophilic solvents and a surfactant may be added to the above solution (dispersion) to form ink A for an ink jet printer.

In contrast to such ink A, ink B basically differs in that it contains a functional material that can be sensed. That is, the ink B contains a pigment having the same color as the pigment of the ink A, a dispersion medium, and a functional material that can be sensed. The solid material after the ink A is discharged and dried is formed in the same color that makes it impossible to distinguish the color visually at least in the visible light range.
As the pigment, the same pigment as that used in the ink A as described above is preferably used. However, different materials can be used as long as they have the same color as the pigment used in ink A, and after being discharged and dried as ink B, the ink A exhibits a color that is hardly discernable by visual inspection. It is.

Examples of the functional material that can be sensed include a fluorescent light emitting material, an infrared light reflecting material, an infrared light absorbing material, an ultraviolet light reflecting material, an ultraviolet light absorbing material, and a magnetic material. It contains at least one of these.
Such a functional material is one whose position is recognized and observed by a special sensing method according to the material. As will be described later, a second image formed using this is used as an image. It can be recognized and observed. For such a functional material, a plurality of different types of materials may be included in the ink B. In that case, the second image is recognized and observed by a plurality of different sensing methods. become.

  Fluorescent materials do not emit light even when exposed to light in the visible light range, but emit light when exposed to ultraviolet light or near-ultraviolet light using a black light or the like, or irradiated with infrared light. . Therefore, by applying ultraviolet light, near-ultraviolet light, or infrared light, visual recognition becomes possible for the first time, and observation becomes possible, or recognition becomes possible by using a dedicated special device. In addition, regarding this fluorescent light-emitting material, sensing in the present invention includes emitting light by applying ultraviolet light, near-ultraviolet light, or infrared light, and recognizing the light visually or by a special device.

  Infrared light reflecting materials and infrared light absorbing materials can be recognized and observed with an infrared camera, etc., by reflecting or absorbing the infrared light when irradiated with infrared light. It is what I did. Similarly, an ultraviolet light reflecting material or an ultraviolet light absorbing material is one that can be recognized and observed by a sensor, etc., by reflecting or absorbing the ultraviolet light when irradiated with ultraviolet light. is there. Further, the magnetic material can be recognized and observed by a magnetic sensor or the like. Note that the above infrared light reflecting material, infrared light absorbing material, ultraviolet light reflecting material, and ultraviolet light absorbing material are recognized by the camera or sensor corresponding to the application of infrared light or ultraviolet light. It is sensing in the invention. In addition, regarding the magnetic material, the recognition in the present invention is to recognize this by a magnetic sensor or the like.

  In such a functional material, as a fluorescent light emitting material, an organic fluorescent substance or an inorganic fluorescent substance can be used regardless of the composition as long as it is solid. The excitation wavelength for fluorescence emission may be any wavelength such as infrared light as long as it is in the wavelength range other than the visible light range in addition to the black light of 254 nm and 365 nm. In addition, regarding the emission wavelength, when the image using this fluorescent light-emitting material is intended for the display function as described later, it is desirable to be in the visible light range, but for the purpose of the security function. In the case of a thing, in addition to the visible light region, an ultraviolet light region or an infrared light region may be used as long as it can be recognized and observed using a special device.

As the fluorescent light-emitting material, inorganic phosphors include, for example, JP-A-50-6410, JP-A-61-65226, JP-A-64-22987, JP-A-64-60671, Inorganic phosphors described in JP-A-1168911, JP-A-2003-87761, and the like can be appropriately selected and used.
The inorganic phosphor ^{_{compounds, Sr 2 P 2 O 7:}} Sn 4+, Sr 4 Al 14 O 25: Eu 2+, BaMgAl 10 O 17: Eu 2+, SrGa 2 S 4: Ce 3+, CaGa 2 S 4: _{^{ce 3+, (Ba, Sr)}} (Mg, Mn) Al 10 O 17: Eu 2+, (Sr, Ca, Ba, Mg) 10 (PO 4) 6 C l2: Eu 2+, BaAl 2 Si 2 O 8: Eu ²⁺ , Sr ₅ (PO ₄ ) ₃ Cl: Eu ²⁺ , Sr ₂ P ₂ O ₇ : Eu ²⁺ , Sr (H ₂ PO ₄ ) ₂ : Eu ²⁺ , (BaMg) Al ₁₆ O ₂₇ : Eu ²⁺ , Mn ²⁺ , ^{_{Sr 4 Al 14 O 25: Eu}} 2+, (Sr, Ba) Al 2 Si 2 O 8: Eu 2+, (Ba, Mg) 2 SiO 4: Eu 2+, Y 2 SiO 5: C _{^{3+, Tb 3+, Sr 2 P}} 2 O 7 -Sr 2 B 2 O 5: Eu 2+, (Ba, Ca, Mg) 5 (PO 4) 3 Cl: Eu 2+, Sr 2 Si 3 O 8 -2SrCl 2: _{^{eu 2+, Zr 2 SiO 4,}} MgAl 11 O 19: Ce 3+, Tb 3+, Ca 2 Y 8 (SiO 4) 6 O 2: Tb 3+, (GF-12) Y 3 Al 5 O 12: Tb 3+, La ^{_{3 Ga 5 SiO 14: Tb 3+}} , Y 2 O 2 S: Eu 3+, (Ba, Mg) 2 SiO 4: Eu 3+, (Ba, Mg) Al 16 O 27: Eu 3+, (Ba, Ca, Mg) ₅ (PO ₄ ) ₃ Cl: Eu ³⁺ , YVO ₄ : Eu ³⁺ , CaS: Eu ³⁺ , YAlO ₃ : Eu ³⁺ , Ca ₂ Y ₈ (SiO ₄ ) ₆ O ₂ : Eu ³⁺ , LiY ₉ (S iO ₄ ) ₆ O ₂ : Eu ³⁺ , YVO ₄ : Eu ³⁺ Bi ²⁺ , Gd ₂ O ₂ S: Eu ³⁺ , CaS: Eu ³⁺ Cl ⁻ , (CaMg) ₃ (PO ₄ ) ₂ : Sn ²⁺ These can be used in combination with the crystal matrix as an activator or coactivator.

Examples of the crystal matrix include ZnS, SrS, GaS, (Zn, Cd) S, SrGa ₂ S ₄ , YO ₃ , Y ₂ O ₂ S, Y ₂ O ₃ , Y ₂ SiO ₃ , SnO ₂ , and Y ₃ Al _5. O ₁₂ , Zn ₂ SiO ₄ , Sr ₄ Al ₁₄ O ₂₅ , CeMgAl ₁₀ O ₁₉ , BaAl ₁₂ O ₁₉ , BaMgAl ₁₀ O ₁₇ , BaMgAl ₁₄ O ₂₃ , Ba ₂ Mg ₂ Al ₁₂ O ₂₂ , Ba ₂ Mg ₄ Al _{8 O 18, Ba 3 Mg 5 Al} 18 O 35, (Ba, Sr, Mg) O · aAl 2 O 3, (Ba, Sr) (Mg, Mn) AlO, (Ba, Sr, Ca) (Mg, Zn, _{Mn) Al 10 O 17, Sr} 2 P 2 O 7, (La, Ce) PO 4, Ca 10 (PO 4) 6 (F, Cl) 2, (Sr, Ca, Ba, Mg) 10 _{PO 4) 6 C 12, GdMgB} 5 O 10, may be mentioned (Y, Gd) BO ₃ and the like.

Also, for infrared light reflecting materials, infrared light absorbing materials, ultraviolet light reflecting materials, and ultraviolet light absorbing materials, if the absorption in the visible light region does not significantly change the absorption spectrum of the pigment used Any conventionally known one can be used.
Magnetic materials include single metals mainly composed of iron, cobalt, nickel, etc., alloys, other metals, various iron oxides containing oxides such as cobalt, rare earths containing Sm, Nd, Pr, etc. Any one such as a magnet can be used.

  About such a functional material, it is necessary to disperse | distribute with respect to said dispersion medium (solution) with the same dispersion method using the same surfactant or polymer dispersing agent etc. as the pigment to be used. This is because, when particles having different dispersion states are mixed, dispersion stability is often significantly impaired. The additives such as pigments and functional materials in the ink B may be dispersed by the same dispersion method using the same surfactant or polymer dispersant as the additives such as the pigment in the ink A. desirable. By doing so, it is possible to make the properties of the ink A and the properties of the ink B substantially the same, so that there is no difference in ejection in the ink jet method described later.

  Although the amount of the functional material added varies depending on the type of material, the weight ratio with respect to the pigment blended in the ink B is 0.5 or less, for example, 0.01 to 0.5. In this way, by setting the amount to less than half of the blending amount of the pigment, it is possible to secure the target color by the pigment and avoid the uncomfortable appearance. In addition, also in this ink B, it is preferable that the addition amount of the pigment is 0.5 to 30% by weight of the entire ink B as in the case of the ink A. By setting it as such a range, after the ink B is discharged on a base material and dried, the color peculiar to a pigment is satisfactorily exhibited. In addition, in ink B, the amount of the dispersion medium is reduced by adding the functional material compared to ink A, so that the weight ratio of the pigment to the total weight of ink is the same as that of ink A.

  However, if a functional material is added only to the ink B as described above, and the corresponding amount of the ink A is a dispersion medium, the concentration of the solid content is naturally different between the ink A and the ink B. . Therefore, a dummy material may be added to the ink A so that the solid content concentration is the same as that of the ink B. As the dummy material, a material having optical properties in the visible light region that are substantially the same as the functional material of the ink B and substantially not having the functionality of the functional material is used.

  Here, the functional material has substantially no functionality means that when the functional material added to the ink A is a fluorescent light emitting material, it does not have a fluorescent light emitting ability, or A functional material and a material having a significantly different fluorescence emission ability. Further, when the functional material added to the ink A is an infrared light reflecting material or an infrared light absorbing material, it does not have infrared light reflecting ability or absorbing ability, or This means that the reflectivity or absorption ability of infrared light is significantly different. When the functional material added to the ink A is an ultraviolet light reflecting material or an ultraviolet light absorbing material, it does not have an ultraviolet light reflecting ability or an absorbing ability, or the functional material and the ultraviolet light reflecting ability. Or the thing whose absorption ability differs remarkably. Furthermore, when the functional material added to the ink A is a magnetic material, it means that the functional material does not have magnetism or has a magnetic property significantly different from that of the functional material.

In addition, the optical property in the visible light region is equivalent to the functional material of the ink B means that the dummy material has light absorption property, light reflectivity, refractive index, etc. in the visible light region. This means that it is the same level as the above functional material.
As such a dummy material, specifically, when the functional material has almost no color in the visible light range, so-called extender pigments such as silica, alumina, talc, kaolin, mica, calcium carbonate, It is appropriately selected and used according to the refractive index. Further, among the functional materials described above, a functional material having a different sensing type from the functional material added to the ink B may be used as the dummy material.

  Such a dummy material is adjusted to have the same particle size as that of the functional material, and is added to the ink A in the same amount (or the same amount) as the functional material as described above. It is preferable to do this. By doing so, the ink A has the same solid content concentration as that of the ink B, and therefore the physical properties such as the viscosity are almost the same, so that the ejection property by the ink jet method is also substantially the same. In addition, in the ink B, when the amount of the functional material added is sufficiently small relative to the pigment, and therefore the solid content concentration is hardly affected, the addition of the dummy material is omitted in the ink A. May be.

  By adding a dummy material to ink A and making the solid content concentration of ink A and the solid content concentration of ink B substantially the same, these inks A and B were discharged onto a substrate and dried as described later. Later, the size of the solid body of one dot can be made substantially the same. That is, as the ink B, the average radius and the average thickness of the one-dot solid body after being ejected and dried by the ink-jet printer are defined as the average radius of the one-dot solid body after being ejected and dried by the ink-jet printer. And it becomes easy to adjust so that it may become a difference within 10% with respect to average thickness.

  Thus, if the difference between the average radius and the average thickness of the solid body is set to, for example, 10% or less between the ink A and the ink B, the solid body of the ink B is compared with the solid body of the ink A. Not only the color but also the texture such as gloss is almost the same, so it becomes more difficult to distinguish between the ink A and the ink B by visual observation in a normal visible light range. In particular, by adding a dummy material to the ink A to adjust the difference between the solid bodies, it is possible to make it difficult to discriminate not only the visual texture but also the touch feeling.

  Depending on the type of pigment or functional material used, even if the difference in average radius or average thickness of the solid body exceeds 10%, there is almost no visual discrimination between ink A and ink B. In such a case, it is not necessary to adjust the solid content concentration using the dummy material. Further, even when the difference in average radius or average thickness of the solid body is within 10% without adding the dummy material, it is not necessary to add the dummy material and adjust the solid content concentration. In this case, however, the solid content concentration may be adjusted by adding a dummy material.

  In addition, the ink A may be only one type exhibiting one color, but a plurality of types having different pigments and thus exhibiting different colors may be prepared. In this case, it is preferable for printing with a plurality of colors, particularly color printing, instead of printing with a single color. In this case, only one type of ink B that exhibits one color may be prepared, or multiple types of colors corresponding to the ink A may be prepared. And these 1 type or multiple types of ink A and 1 type or multiple types of ink B can be used for the printing by the inkjet printer mentioned later as an ink set.

  As such an ink set, black and white, black and other color colors, white and other color colors, two types of ink A and ink B, that is, two colors × 2 = four types of ink Ink set, magenta, cyan, yellow, black, white, and other colors 3 colors x 2 = 6 types of ink set, magenta, cyan, yellow, black 4 colors x 2 = 8 types of ink Ink set consisting of magenta, cyan, yellow, black and white, 5 colors x 2 = 10 types of ink set, magenta, cyan, yellow, light magenta, light cyan, black and 6 colors x 2 = 12 types of ink Ink set, magenta, cyan, yellow, red, green, and black 6 colors x 2 = 12 types of ink set Etc., color combinations are considered are various kinds, it is possible to more ink colors often obtain a high-definition image.

  When an ink set comprising such ink A and ink B is prepared, a first image is formed on the base material by an inkjet method using at least the ink A, and the ink B is formed on the base material. Is used to form a second image by an inkjet method. Here, the first image is a normal image that can be visually recognized in the visible light range, and the second image can be distinguished from the first image by sensing the functional material. It is an image that becomes.

  As an ink jet printer for ejecting such ink A and ink B onto a substrate, for example, an ink jet printer having an ejection head (ink jet head) shown in FIGS. 1A and 1B is preferably used. As shown in FIG. 1A, the ejection head 34 includes, for example, a stainless steel nozzle plate 12 and a diaphragm 13, and both are joined via a partition member (reservoir plate) 14. A plurality of cavities 15 and reservoirs 16 are formed between the nozzle plate 12 and the diaphragm 13 by the partition member 14, and the cavities 15 and the reservoirs 16 communicate with each other via a flow path 17. Yes.

  Each cavity 15 and the inside of the reservoir 16 are filled with ink, and the flow path 17 between them functions as a supply port for supplying ink from the reservoir 16 to the cavity 15. In addition, a plurality of hole-shaped nozzles 18 for ejecting ink from the cavity 15 are formed in the nozzle plate 12 in a state of being aligned vertically and horizontally. On the other hand, a hole 19 that opens into the reservoir 16 is formed in the diaphragm 13, and an ink tank (not shown) is connected to the hole 19 via a tube (not shown).

  Also, a piezoelectric element (piezo element) 20 is joined to the surface of the diaphragm 13 opposite to the surface facing the cavity 15 as shown in FIG. The piezoelectric element 20 is sandwiched between a pair of electrodes 21 and 21 and is configured to bend so as to protrude outward when energized.

The diaphragm 13 to which the piezoelectric element 20 is bonded in such a configuration is bent together with the piezoelectric element 20 at the same time, thereby increasing the volume of the cavity 15. Then, the cavity 15 and the reservoir 16 are in communication with each other, and when the reservoir 16 is filled with ink, the ink corresponding to the increased volume in the cavity 15 is transferred from the reservoir 16 to the flow path 17. Flows in through.
When the energization to the piezoelectric element 20 is released from such a state, both the piezoelectric element 20 and the diaphragm 13 return to their original shapes. Accordingly, since the cavity 15 also returns to its original volume, the pressure of the ink inside the cavity 15 rises, and the ink droplet 22 is ejected from the nozzle 18.

  The ejection method of the ejection head may be other than the electromechanical transducer using the piezoelectric element (piezo element) 20 described above. For example, a scheme using an electrothermal transducer as an energy generating element, a charge control type, It is also possible to employ a continuous method such as a pressure vibration type, an electrostatic suction method, or a method in which an electromagnetic wave such as a laser is irradiated to generate heat and ink is ejected by the action of this heat generation.

An example in which the first image and the second image are formed on the substrate by using the ink set composed of the ink A and the ink B by the discharge head 34 is described with reference to FIGS. To explain. Note that ordinary printing paper is used as the base material in this example.
FIG. 2A shows a first image 1 that is a normal image that can be visually recognized in the visible light region. In this example, the first image 1 is formed by three color inks A composed of magenta, yellow, and cyan and three inks B composed of magenta, yellow, and cyan. Here, for the three colors of ink A and ink B, the same pigment is used for the same color, and a dummy material is added to ink A. As a result, in the ink A and the ink B, the solid bodies after being discharged and dried by the discharge head 34 are not different in texture such as color and gloss at least in the visible light range. ing.

  FIG. 2B shows an annular second image 2 that can be discriminated from the first image 1 by sensing the functional material, and includes magenta, yellow, It is formed by three colors of ink B made of cyan. Note that FIG. 2B is an image that is recognized and observed depending on the type of the functional material added to the ink B, and does not necessarily exhibit a color. FIG. 2B shows the image shown in FIG. The second image 2 is shown by a method (horizontal line) different from the above notation. In addition, any kind of functional material added to the ink B can be used in this example, and is not particularly defined.

  In the first image 1 and the second image 2 as described above, a part thereof, in this example, the entire region of the second image 2 is indicated by a two-dot chain line in FIG. The first image 1 and the second image 2 are overlapped portions 3. In this example, the overlapping portion 3 is formed using only the ink B, and the region of the first image 1 other than the overlapping portion 3 is formed using only the ink A.

  In general, an inkjet printer driver performs color separation for each ink color that uses an image to be printed, ejects ink of each color according to each color image, and prints a color-separated image. I try to get an image. Therefore, in this example as well, the first image 1, which is a normal image, is divided into three colors, magenta, yellow, and cyan, to be used, and M (magenta) and Y ( Color-separated images for each color of yellow and C (cyan) are formed as data in an ink jet printer or by an external device.

  In each of the color-divided images of M, Y, and C in FIG. 3A, the diagonal line that rises to the right represents the color of magenta (M), the dot represents the color of yellow (Y), and the diagonal line that descends to the right represents Represents the color of cyan (C). In addition, for each oblique line representing magenta and cyan, a thick line represents that the color is dark, and a thin line represents that the color is light. For dots representing yellow, the larger each point, the darker the color, and the smaller the dot, the lighter the color. These notations are the same in FIG. 2A, and in FIG. 2A, colors such as light blue, green, and pink are expressed by mixing M, Y, and C colors. ing.

Then, the first image 1 shown in FIG. 2A is obtained by driving the driver and ejecting ink A and ink B from the ejection head 34 based on the data thus formed.
However, a second image 2 that is a hidden picture is also formed in the first image 1. At this time, as described above, the overlapping portion 3 is formed using only the ink B, and the region of the first image 1 other than the overlapping portion 3 is formed using only the ink A.

  That is, for the overlapping portion 3 shown in FIG. 2A, M, Y, and C color-separated images are formed using only the three colors of ink B as shown in FIG. 3B. In addition, for each region of the first image 1 other than the overlapping portion 3, each color-divided image is formed using only the ink A of the corresponding color. By forming the first image 1 and the second image 2 in this way, the first image 1 cannot be discriminated from the first image 1 by visual observation in the visible light region. A second image 2 that can be distinguished from the first image 1 can be formed only by sensing the functional material. Therefore, the second image 2 can function as a hidden picture.

  In actual ejection by the ejection head 34, the M, Y, and C color division images in FIG. 3B and the M, Y, and C color division images in FIG. Six types of ink are ejected from different nozzles 18 of the ejection head 34, respectively. Alternatively, a plurality of ejection heads 34 may be prepared, and different inks may be ejected from the nozzles 18 of these ejection heads 34.

  According to such a method for creating a hidden picture, the first image 1 and the second image 2 are formed by the ink jet method using the ink A and the ink B, so that the first image 1 and the second image 2 are visually recognized particularly in the visible light range. Therefore, the first image 1 can be formed with high image quality such as a photograph. That is, since there is no design restriction for either the first image 1 or the second image 2, a high-definition image can be formed. In particular, for the second image 2 which is a hidden picture, it is possible to express lightness and fineness equivalent to those of the first image 1.

  Further, since the ink B is formed so that the solid body of the ink B becomes the same color as that of the solid body of the ink A at least in the visible light range, the color cannot be visually determined. Therefore, it is difficult to discriminate between the ink A and the ink B, and it is difficult to visually recognize the second image 2 formed by the ink B in a normal visible light range. Therefore, the second image 2 functions well as a hidden picture. Furthermore, by only preparing ink A and ink B, a hidden picture can be easily and inexpensively formed by an existing inkjet printer.

In addition, since the overlapping portion 3 is formed using only the ink B, the second image 2 is formed only from the ink B. For example, the ink B is not covered by the ink A. Degradation of the image quality of the second image can be prevented.
In addition, the hidden picture composed of the first image 1 and the second image 2 can be created as an infinite pattern by combining different images, and there are no restrictions on the types of functional materials. This type of ink can also be created. Therefore, since a high degree of freedom can be obtained, it is extremely excellent from the viewpoint of design and security.

That is, according to the method for creating a hidden picture of the present invention, by creating a hidden picture consisting of the first image and the second image on the base material, a printed matter having a security function and a display function in particular is created. can do.
For example, a printing paper for forming valuable printed matter such as tickets, certificates, certificates, securities, and vouchers is used as a base material, and letters, numbers, designs, etc. necessary for valuable printing are formed as the first image. By forming a company name, various logos, or the like as the second image, it is possible to confirm the authenticity by the second image. Therefore, forgery and the like can be prevented and the security can be ensured satisfactorily.
In particular, for the second image, the design and description can be easily changed, and the type of functional material can be easily changed. For example, by changing these periodically, etc. , Security can be further enhanced.

  In addition, by applying the printed matter to various designs, commercial displays, and the like, for example, the second image can be lifted up with black light or the like, so that a good display function can be exhibited.

(A), (b) is a schematic block diagram of an ejection head. (A) is a figure which shows a 1st image, (b) is a figure which shows a 2nd image. (A)-(c) is a figure which shows a color division image.

Explanation of symbols

1 ... 1st image, 2 ... 2nd image, 3 ... Overlapping part,
34 ... Discharge head (inkjet head)

Claims (11)

Ink A for an inkjet printer comprising a pigment and a dispersion medium for dispersing the pigment,
The solid body after containing the pigment of the same color as the pigment of the ink A, a dispersion medium, and a functional material that can be sensed and discharged and dried by an ink jet printer is a solid after the ink A is discharged and dried. Prepare an ink B for an inkjet printer formed in the same color that makes it impossible to discriminate the color visually at least in the visible light range with respect to the body,
On the base material, at least using the ink A, the first image is formed by an inkjet method,
A hidden picture, wherein the ink B is used to form a second image that can be distinguished from the first image by sensing the functional material using the ink B. How to create   When the first image and the second image partially overlap, the overlapping portion is formed using only the ink B, and the first image region other than the overlapping portion is formed using only the ink A. The method for creating a hidden picture according to claim 1.   The said functional material consists of at least 1 sort (s) of a fluorescent light-emitting material, an infrared light reflection material, an infrared light absorption material, an ultraviolet light reflection material, an ultraviolet light absorption material, and a magnetic material, 2. A method for creating a hidden picture according to 2.   As the ink B, the average radius and average thickness of a one-dot solid body after being discharged and dried by an ink-jet printer are the average radius of the one-dot solid body after being discharged and dried by the ink-jet printer. The method for creating a hidden picture according to any one of claims 1 to 3, wherein the average thickness is adjusted so as to be within 10%.   The ink A contains a dummy material that has optical properties in the visible light region that are equivalent to those of the functional material of the ink B and that does not substantially have the functionality of the functional material. The method for creating a hidden picture according to claim 4, wherein:   A plurality of types having different pigments are prepared as the ink A, and a plurality of types corresponding to the ink A are prepared as the ink B, and the plurality of types of ink A and the plurality of types of ink B are used. The method according to claim 1, wherein a first color image is formed.   When the first image is a color image and the second image is partially overlapped with the first image and the overlapping portion is also a color image, the first image is color-divided. A plurality of color-divided images, the overlapping portions in each color-divided image are formed using only the ink B of the corresponding color, and the first image areas other than the overlapping portions in the respective color-divided images are respectively corresponding The method for creating a hidden picture according to claim 6, wherein the ink A is formed only with the color A.   The method for creating a hidden picture according to any one of claims 1 to 7, wherein a plurality of types of different functional materials are used as the ink B.   A printed matter comprising a first image and a second image formed by the method for creating a hidden picture according to claim 1.   The printed matter according to claim 9, wherein the second image is provided as a security function.   The printed matter according to claim 9, wherein the second image is provided as a display function.

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