A pressure-display paper and its application in inkless printing

Abstract

The present invention relates to the field of inkless printing technology, and particularly to a pressure-sensitive display paper and its application in inkless printing. This pressure-sensitive display paper sequentially includes a bottom-color base paper, an absorption layer, and a top-color pressure paper; the top-color pressure paper includes color-developing microcapsules with a transparent material as the wall material and a first pigment as the core material; the absorption layer includes a material that can react with the first pigment to change the first pigment from a colored state to a colorless state; the bottom-color base paper includes a second pigment. In this application, the color-developing microcapsules in the pressed part of the top-color pressure paper are ruptured to release the first pigment to react with the material of the absorption layer, so that the color of the pressed part irreversibly becomes transparent and colorless, thereby revealing the color of the second pigment of the bottom-color base paper below it. The bottom-color base paper can be prepared in various colors through the prior art. Therefore, inkless printing of any color is achieved, and the long-term preservation of the printed pattern is ensured based on the irreversible color change.

Description

Technical Field

[0001] The present invention relates to the technical field of inkless printing, and in particular, to a pressure-display paper and its application in inkless printing. Background Art

[0002] Generally speaking, ink is a necessary raw material for printing. However, in the context of the increasing popularity and strictness of environmental protection requirements, environmentally friendly inks and even inkless printing have become new technological directions for research and development nowadays. Most of the existing inkless printing technologies are realized through thermosensitive materials or photosensitive materials.

[0003] The principle of photosensitive materials in inkless printing is as follows: a photosensitive color-forming material such as diacetylene is pre-coated on a substrate. When these photosensitive color-forming materials are exposed to a suitable energy source (such as a laser), the substrate will change color, thus achieving the purpose of inkless printing. However, it has the following problems: First, the printed content on this paper will disappear over time, making it only suitable for temporary printed materials such as newspapers. For products that need to be permanently preserved, this technology is useless. Second, the photosensitive materials can only change between specific colors, resulting in limited color options for printed products and making them unsuitable for use as the iconic packaging of commodities.

[0004] The principle of thermosensitive materials in inkless printing is similar to that of photosensitive materials: a thermochromic material is coated on the printing substrate. Currently, a variety of thermochromic materials have been developed on the market. Such thermochromic materials can change from colorless to magenta, cyan, yellow, and black at different temperatures. These materials all contain thermochromic organic compounds such as triarylmethane, fluorane, spiropyran, etc. When heated, a carbon atom in the compound system changes from sp 3 hybrid state to sp 2 hybrid titanium, and the originally separated π system changes into a complete π system, absorbing the corresponding spectral energy, thereby causing the thermochromic material to change from colorless to colored. The problems it has are as follows: First, when providing heat to the part to be printed on the printing substrate to make it change color, due to the conduction of heat, the parts that do not need to be printed will also heat up and change color, resulting in the problem of unclear printing edges. Second, due to its characteristic that the color is easily affected by temperature, there are relatively high requirements for the storage and transportation environment of printed products, which is not conducive to long-term preservation and is not suitable for use as the packaging of commodities. Third, it can also only change between specific colors, resulting in limited color options for printed products.

[0005] Based on this, there is an urgent need to develop an inkless printing technology that can achieve printing in any color and is not easily faded. Summary of the Invention

[0006] The present invention aims to solve the above problems and provides a pressure-display paper and its application in inkless printing.

[0007] The technical solution for the present invention to solve the problem is to first provide a pressure-display paper, which sequentially includes a background base paper, an absorption layer, and a top-color pressing paper;

[0008] The top-color pressing paper includes color-developing microcapsules with a transparent material as the wall material and a first pigment as the core material;

[0009] The absorption layer includes a material that can react with the first pigment to change the first pigment from a colored state to a colorless state;

[0010] The background base paper includes a second pigment with a color different from that of the first pigment.

[0011] The basic concept of this application is that by causing the color-developing microcapsules in the pressed part of the top-color pressing paper to rupture and release the first pigment to react with the absorption layer material, the color of the pressed part irreversibly becomes transparent and colorless, thereby revealing the color of the second pigment of the background base paper below. The background base paper can be prepared in various colors through the prior art. Therefore, inkless printing of any color is achieved, and the long-term preservation of the printed pattern is ensured based on irreversible color change.

[0012] There are various specific implementation manners, which are different based on the selection of the first pigment, the material of the absorption layer, and the color change principle.

[0013] In one embodiment, the first pigment is nano-zinc oxide; the absorption layer includes polyvinyl acetate, first microcapsules with a first solvent as the core material, and second microcapsules with a second solvent as the core material. The first solvent is a solvent that can dissolve the nano-zinc oxide, and the second solvent is a solvent that can dissolve the polyvinyl acetate.

[0014] The specific principle is as follows: The top-color pressing paper appears nearly white through nano-zinc oxide. When under pressure, the color-developing microcapsules in the pressed part rupture, release nano-zinc oxide, and are driven close to the absorption layer under the action of pressure. At the same time, the first microcapsules and second microcapsules in the pressed part of the absorption layer rupture respectively to release the first solvent and the second solvent. The nano-zinc oxide and the first solvent together form a nano-zinc oxide sol system, and the polyvinyl acetate and the second solvent together form a dispersion system. The nano-zinc oxide sol system and the dispersion system together form a colorless and transparent nano-ZnO / PVAc composite sol system, and finally a colorless and transparent ZnO / PVAc composite film can be obtained by drying, making the pressed part appear colorless and transparent, revealing the background base paper below.

[0015] The source of the nano-zinc oxide is not restricted. Suitable preparation methods include: Hydrothermal method: This is a method for preparing nano-zinc oxide through chemical reactions in a high-temperature and high-pressure aqueous solution. Usually, at appropriate temperature, pressure, and reaction time, an appropriate amount of zinc salt and alkali solution are reacted to generate nano-zinc oxide. Sol-gel method: This is a method of gradually converting a solution into a gel or solid. When preparing nano-zinc oxide, usually a suitable zinc salt and a sol agent are mixed to form a sol, and then through heat treatment or drying, the sol is transformed into a gel, and finally nano-zinc oxide is obtained.

[0016] The source of polyvinyl acetate is not restricted. It can be prepared by using commercially available analytical pure materials or by common methods in the prior art. Suitable preparation methods for polyvinyl acetate include: Emulsion polymerization method: Vinyl acetate, a surfactant, and an emulsifier are added to water to form an emulsion system. Through heating and stirring, the emulsion is polymerized into polyvinyl acetate. An initiator or starter may be added during the polymerization process to initiate the polymerization reaction. Solution polymerization method: Vinyl acetate is dissolved in a suitable solvent to form a polymer solution. An initiator or starter is added, and through the action of heating or ultraviolet light, the polymerization reaction is initiated. After the polymerization reaction is completed, the solvent is removed by distillation or other methods to obtain polyvinyl acetate.

[0017] The first solvent capable of dissolving nano-zinc oxide is preferably one or both of ethanol and isopropanol.

[0018] The second solvent capable of dissolving polyvinyl acetate is preferably one or several of benzene, acetone, and chloroform.

[0019] The selection of the wall material in the first microcapsule and the second microcapsule is not restricted. It is preferably a brittle material that is easily broken under pressure, and optionally one or several of polyethylene, polypropylene, polymethyl methacrylate, and polyvinyl alcohol.

[0020] The preparation methods of the color-developing microcapsule, the first microcapsule, and the second microcapsule are not restricted. Suitable preparation methods include known chemical and physical methods for forming polymer capsules. Representative examples of chemical methods include complex coacervation method, interfacial polymerization method, polymer-polymer incompatibility method, in-situ polymerization method, centrifugal force process, and immersion nozzle process. Representative implementations of physical methods include spray drying, fluid bed coating, centrifugal extrusion, and rotary suspension centrifugation.

[0021] In the above embodiments, since the discoloration principle theoretically involves three-step combination processes, to ensure that the combination of nano-zinc oxide and the first solvent is not interfered by the second solvent and polyvinyl acetate, as a preference of the present invention, the absorbent layer includes a first layer and a second layer along the direction from the top-color pressing paper to the bottom-color base paper. The first microcapsules are disposed in the first layer, and the polyvinyl acetate and the second microcapsules are disposed in the second layer. Through the layer design, when the paper is pressed, the nano-zinc oxide combines with the first solvent to form a nano-zinc oxide sol system and then contacts the second solvent and polyvinyl acetate.

[0022] In the above embodiments, the discoloration of the pressed part can be achieved only by applying pressure. To avoid accidental discoloration of the paper due to pressure, as a preference of the present invention, the wall material of the first microcapsules includes a pressure-breaking material and a thermal-breaking material. The thermal-breaking material includes a phase-change material, and the pressure-breaking material includes a brittle material. By adding the thermal-breaking material, the first microcapsules can be completely broken to release the first solvent to disperse the nano-zinc oxide to make it colorless only under the dual action of pressure and temperature. In specific use, it is preferred to embed the thermal-breaking material with the pressure-breaking material and then embed the first solvent in sequence. The phase-change material can optionally be paraffin, and the brittle material can be selected from the brittle materials listed above that are easy to break after being pressed.

[0023] In another embodiment, the first pigment is a ternary complex composed of a color former, a developer, and a temperature-control solvent; the absorbent layer includes a photocatalyst that catalyzes the decomposition of the developer.

[0024] The specific principle is as follows: The first pigment belongs to a ternary component thermochromic system. The color former is an electron donor compound that can provide a discoloration structure, the developer is an electron acceptor compound, and the melting point of the temperature-control solvent determines the discoloration temperature of the system. In the low-temperature solid state, the color former with electron-donating properties can interact with the electron acceptor developer to form a complex, triggering a change in the molecular structure of the color former, and the system presents a colored state; as the temperature rises, the complex redissolves in the temperature-control solvent, and the interaction between the color former and the developer is destroyed by the solvent, and the system presents a colorless state. Therefore, by making the color-developing microcapsules in the pressed part of the top-color pressing paper break and release the first pigment, and at the same time assisted by heating, the color former and the developer of the first pigment can be separated and become colorless, revealing the underlying bottom-color base paper; then, the photocatalyst in the absorbent layer catalyzes the decomposition of the developer, so that the color former can no longer be affected by the developer to change color, realizing irreversible discoloration.

[0025] Among them, the color former includes fluoran and triarylmethane phthalide, preferably one or two of thermosensitive red and thermosensitive green.

[0026] The color developers are mostly weakly acidic substances, such as phenolic hydroxyl compounds (bisphenol A, bisphenol AF, gallate esters, etc.), hydroxyl compounds (alkyl acids such as hexanoic acid, stearic acid), and preferably one or two of bisphenol A, ethyl gallate, and TGSH. The color developer can also be a material with a low steam enthalpy value and easy volatility to accelerate the removal of the color developer after the color-developing microcapsules rupture, and preferably one or several of methylphenol and nonylphenol.

[0027] The temperature-controlled solvent can be selected from fatty alcohols, thiols, ethers, ketones, phosphatidic acids, carboxylic acid esters, and amides, preferably materials with a phase change temperature between 40°C and 60°C, and preferably one or several of dodecanol, tetradecanol, and hexadecanol.

[0028] The photocatalyst can be selected as titanium dioxide.

[0029] In any embodiment, the transparent material is used to isolate the first pigment and the papermaking adhesive substance, and at the same time does not affect the color of the first pigment; the transparent material is preferably a brittle material that is easily broken under pressure, and one or several of polyethylene, polymethyl methacrylate, polyvinyl alcohol, polyethylene wax, and melamine resin can be selected.

[0030] In any embodiment, as a preference of the present invention, the absorption layer has through holes to accelerate absorption. Suitable preparation methods for the absorption layer with through holes include adding volatile solvents, carbonate fillers, or introducing gases during the dispersion process of the absorption layer material.

[0031] In any embodiment, as a preference of the present invention, the top-color pressing paper includes a transparent fiber mesh and a slurry filled in the fiber mesh, and the color-developing microcapsules are dispersed in the slurry. The strength of the top-color pressing paper is ensured by the fiber mesh to avoid the problem of overall cracking of the top-color pressing paper caused by the rupture of the color-developing microcapsules.

[0032] The preparation principle of the transparent fiber mesh is as follows: as much lignin as possible is removed from the plant fibers. Lignin contains a large number of unsaturated groups that will produce absorption peaks for visible light, affecting transparency. Suitable preparation methods are: mechanical treatment: the cell walls of plant fibers are broken through refining or beating to obtain a cellulose fiber solution for preparing paper; chemical treatment: lignin is removed by chemical reagents to extract nanofibrillated cellulose fibers, and paper is prepared from the nanofibrillated cellulose fibers.

[0033] To help the color-developing microcapsules adhere to the fiber mesh, as a preference of the present invention, the slurry further includes an adhesive. The adhesive is used to disperse and adhere the color-developing microcapsules evenly together, and preferably can disperse and adhere to the wall material of the color-developing microcapsules and cannot adhere to the first pigment after curing to allow the microscopic movement of the first pigment. Suitable adhesives include one or several of polyvinyl alcohol, polyurethane, polyimide, chitosan, and gelatin.

[0034] The embossed paper of the present application is mainly used in inkless printing technology, so another object of the present invention is to provide an embossed paper for use in inkless printing.

[0035] As the preferred embodiment of the present invention, the application method comprises the following steps:

[0036] S1. Pressing the printing mold onto the top color pressing paper of the pressed paper, pressurizing the color microcapsules to rupture;

[0037] S2. Continue to apply pressure, and if necessary, heat and light, until the pressurized area becomes colorless;

[0038] S3. Remove the printing mold and complete the printing.

[0039] As a preferred embodiment of the present invention, the printing mold includes an upper pressing mold and a lower receiving mold, and the embossed paper is clamped between the upper pressing mold and the lower receiving mold.

[0040] Further preferably, the lower receiving mold is provided with a negative pressure hole, and while pressurizing, negative pressure adsorption is performed on the part of the embossing paper to be printed to avoid lateral diffusion of the core material after the microcapsules are ruptured.

[0041] Beneficial effects of the present invention:

[0042] The present application causes the color-developing microcapsules of the pressed part of the top color pressing paper to rupture and release the first pigment to react with the absorbing layer material, so that the color of the pressed part irreversibly changes to transparent and colorless, thereby revealing the color of the second pigment of the bottom color base paper underneath. The bottom color base paper can be prepared in various colors using existing technology, thereby achieving inkless printing of any color and ensuring the long-term preservation of the printed pattern based on the irreversible color change. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a printed product effect diagram obtained in Example 1. DETAILED DESCRIPTION

[0044] The following are specific embodiments of the present invention, and further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0045] Example 1

[0046] A embossed paper is prepared by the following steps:

[0047] (1) Preparation of base paper: 92 parts by weight of bleached kraft chemical pulp of softwood and 8 parts by weight of ultramarine blue pigment were mixed and stirred evenly, and then paper-made to obtain a light blue base paper.

[0048] (2) Preparation of top color press paper:

[0049] Preparation of polymethyl methacrylate-coated nano-zinc oxide color-developing microcapsules: By mass, 1 part of stearic acid, 15 parts of zinc chloride, and 100 parts of ethanol were mixed and stirred at 70 °C for 2 h. During this process, 2 drops of distilled water were added every 30 min. After the reaction, a ZnO nano-suspension was obtained for standby. 14 parts of methyl methacrylate, 1 part of propyl methacrylate, and 0.3 part of azobisisobutyronitrile were mixed and then mixed with 0.1 part of the above ZnO nano-suspension as the oil phase; 12 parts of styrene-maleic anhydride copolymer was dissolved in 200 parts of distilled water as the water phase; the oil phase was added to the water phase under stirring and sheared at a speed of 6000 r / min for 10 min to obtain an emulsion; the emulsion was reacted at 70 °C for 6 h to obtain a microcapsule suspension; and the microcapsules were obtained by filtration and drying.

[0050] Papermaking: By mass, 92 parts of softwood bleached kraft chemical pulp and 8 parts of color-developing microcapsules were mixed and stirred evenly, and then sheeted to obtain a slightly white top-colored press paper.

[0051] (3)Preparation of the absorption layer

[0052] Preparation of the first microcapsules of polyvinyl alcohol-coated ethanol: By mass, 1 part of ethanol and 0.3 part of glycerol monolaurate were added to 10 parts of vegetable oil and dispersed evenly to obtain a mixture; 1 part of the mixture and 0.3 part of sodium dodecylbenzenesulfonate were added to 10 parts of polyvinyl alcohol solution, dispersed evenly, and then filtered and dried to obtain the first microcapsules.

[0053] Preparation of the second microcapsules of polyvinyl alcohol-coated acetone: By mass, 1 part of acetone and 0.3 part of glycerol monolaurate were added to 10 parts of palm oil and dispersed evenly to obtain a mixture; 1 part of the mixture and 0.3 part of sodium dodecylbenzenesulfonate were added to 10 parts of polyvinyl alcohol solution, dispersed evenly, and then filtered and dried to obtain the second microcapsules.

[0054] Mixing: By mass, 15 parts of polyvinyl acetate was dissolved in 100 parts of acetone, and then 8 parts of the first microcapsules and 20 parts of the second microcapsules were added and dispersed evenly for standby.

[0055] (4)Preparation of the pressure-developing paper:

[0056] The base color paper was placed on a negative pressure adsorption device, then a layer of absorption layer was coated, and after standing for 10 min, the top-colored press paper was laminated and pressed at a pressure of 20 Kpa, and then dried at room temperature to obtain the pressure-developing paper.

[0057] (5)An application method of the pressure-developing paper, comprising the following steps:

[0058] S1. Press the printing mold onto the top color pressing paper of the prepared embossed paper, and apply pressure to 80Kpa to rupture the color-developing microcapsules.

[0059] S2. Continue to apply pressure until the pressurized area becomes colorless.

[0060] S3. Remove the printing mold and dry at room temperature to complete the printing.

[0061] like Figure 1 As shown, the resulting print exhibits a light blue pattern on the top color pressed paper.

[0062] Example 2

[0063] This embodiment is basically the same as Embodiment 1, and the only difference is that:

[0064] (3) During the preparation of the absorption layer, when mixing:

[0065] Mixing: According to the mass ratio, 7 parts of polyvinyl acetate are added to 50 parts of acetone to dissolve, and then 8 parts of the first microcapsules are added and dispersed evenly to obtain a first coating; 8 parts of polyvinyl acetate are added to 50 parts of acetone to dissolve, and then 20 parts of the second microcapsules are added and dispersed evenly to obtain a second coating.

[0066] (4) During the preparation of embossed paper:

[0067] Place the base paper with the bottom color on the negative pressure adsorption device, apply a layer of the second coating, and let it stand for 5 minutes; then apply a layer of the first coating, and let it stand for 5 minutes; then overlap the top color pressing paper and press it at a pressure of 20Kpa, and then dry it at room temperature to obtain the pressed paper.

[0068] Example 3

[0069] This embodiment is basically the same as Embodiment 1, and the only difference is that:

[0070] (3) During the preparation of the absorption layer, when preparing the first microcapsule:

[0071] Preparation of first microcapsules of ethanol coated with polyvinyl alcohol: According to parts by mass, 1 part of ethanol and 0.3 parts of glycerol monolaurate are added to 10 parts of paraffin wax, and dispersed evenly to obtain a mixture; 1 part of the mixture and 0.3 parts of sodium dodecylbenzene sulfonate are added to 10 parts of polyvinyl alcohol solution, dispersed evenly, filtered and dried to obtain the first microcapsules.

[0072] Example 4

[0073] This embodiment is basically the same as Embodiment 1, and the only difference is that:

[0074] (3) During the preparation of the absorption layer, when mixing:

[0075] Mixing: By mass, 15 parts of polyvinyl acetate are added to 100 parts of acetone and dissolved. Then, 8 parts of the first microcapsules, 20 parts of the second microcapsules, and 5 parts of sodium bicarbonate are added and dispersed evenly for standby.

[0076] (4)Preparing the pressure-sensitive display paper:

[0077] Place the base color paper on the negative pressure adsorption device, then coat a layer of the absorption layer. After standing for 10 min in an environment of 50 °C, stack the top color pressure paper on it and press it with a pressure of 20 Kpa, and then dry it at room temperature to obtain the pressure-sensitive display paper.

[0078] Example 5

[0079] This example is basically the same as Example 1, and the only difference is that:

[0080] (2)During the preparation of the top color pressure paper:

[0081] Preparing the transparent fiber mesh: By mass, 2.5 parts of sodium hydroxide, 0.4 part of sodium sulfite, and 50 parts of water are mixed to obtain a solution; after crushing the plant raw materials into debris, 5 parts of the plant debris are placed in 50 parts of the solution, cooked at 80 °C for 5 h, and then transferred to distilled water for cleaning; then the product is further treated in a water bath with hydrogen peroxide, and taken out after the product turns white; cleaned and dispersed with distilled water to obtain a solution with a cellulose solid content of 50%; then the cellulose solution is dried by vacuum filtration to obtain the fiber mesh.

[0082] Papermaking: By mass, 20 parts of polyvinyl alcohol and 8 parts of color-developing microcapsules are mixed and stirred evenly, coated on the fiber mesh, and dried to obtain the top color pressure paper.

[0083] Example 6

[0084] This example is basically the same as Example 1, and the only difference is that:

[0085] (5)A method for applying the pressure-sensitive display paper includes the following steps:

[0086] S1. The printing mold includes an upper pressing mold and a lower receiving mold, and the lower receiving mold is provided with negative pressure holes; the pressure-sensitive display paper is clamped between the upper pressing mold and the lower receiving mold, the upper pressing mold is pressurized to 80 Kpa, and at the same time the lower receiving mold provides a negative pressure adsorption of 10 Kpa.

[0087] S2. Continuously apply pressure and negative pressure adsorption until the pressed area becomes colorless.

[0088] S3. Remove the printing mold and dry it at room temperature to complete the printing.

[0089] Example 7

[0090] A pressure-display paper is prepared through the following steps:

[0091] (1) Prepare the base-color base paper: According to mass parts, mix 92 parts of softwood bleached sulfate chemical pulp and 8 parts of ultramarine blue pigment evenly, then carry out papermaking to obtain a light blue base-color base paper.

[0092] (2) Prepare the top-color pressure paper:

[0093] Prepare polymethyl methacrylate-coated nano-zinc oxide color-developing microcapsules: According to mass parts, mix 1 part of stearic acid, 15 parts of zinc chloride and 100 parts of ethanol, and stir and react at 70 °C for 2 h. During this process, add 2 drops of distilled water every 30 min. After the reaction, obtain a ZnO nano-suspension for standby. Mix 14 parts of methyl methacrylate, 1 part of propyl methacrylate and 0.3 part of azobisisobutyronitrile, and mix with 0.1 part of the above ZnO nano-suspension as the oil phase; dissolve 12 parts of styrene-maleic anhydride copolymer in 200 parts of distilled water as the water phase; add the oil phase to the water phase under stirring and shear at a speed of 6000 r / min for 10 min to obtain an emulsion; react the emulsion at 70 °C for 6 h to obtain a microcapsule suspension, filter and dry to obtain color-developing microcapsules.

[0094] Prepare a transparent fiber web: According to mass parts, mix 2.5 parts of sodium hydroxide, 0.4 part of sodium sulfite and 50 parts of water to obtain a solution; crush the plant raw materials into debris, then put 5 parts of plant debris into 50 parts of the solution, cook at 80 °C for 5 h and then transfer to distilled water for cleaning; then continue to carry out water bath treatment on the product with hydrogen peroxide, and take out the product after it turns white; wash and disperse with distilled water to obtain a solution with a cellulose solid content of 50%; then dry the cellulose solution by vacuum filtration to obtain a fiber web.

[0095] Papermaking: According to mass parts, mix 20 parts of polyvinyl alcohol and 8 parts of color-developing microcapsules evenly, coat them on the fiber web, and dry to obtain the top-color pressure paper.

[0096] (3) Prepare the absorption layer

[0097] Prepare the first microcapsules of polyvinyl alcohol-coated ethanol: According to mass parts, add 1 part of ethanol and 0.3 part of glycerol monolaurate to 10 parts of paraffin wax and disperse evenly to obtain a mixture; add 1 part of the mixture and 0.3 part of sodium dodecylbenzenesulfonate to 10 parts of polyvinyl alcohol solution, disperse evenly, then filter and dry to obtain the first microcapsules.

[0098] Preparation of second microcapsules of acetone coated with polyvinyl alcohol: According to parts by mass, 1 part of acetone and 0.3 parts of glycerol monolaurate are added to 10 parts of palm oil, and dispersed evenly to obtain a mixture; 1 part of the mixture and 0.3 parts of sodium dodecylbenzene sulfonate are added to 10 parts of polyvinyl alcohol solution, and after uniform dispersion, the mixture is filtered and dried to obtain second microcapsules.

[0099] Mixing: After adding 7 parts of polyvinyl acetate to 50 parts of acetone and dissolving them, add 8 parts of the first microcapsules and 3 parts of sodium bicarbonate and disperse them evenly to obtain a first coating; after adding 8 parts of polyvinyl acetate to 50 parts of acetone and dissolving them, add 20 parts of the second microcapsules and 2 parts of sodium bicarbonate and disperse them evenly to obtain a second coating.

[0100] (4) Preparation of embossed paper:

[0101] Place the base paper with the bottom color on the negative pressure adsorption device, apply a layer of the second coating, and let it stand for 5 minutes; then apply a layer of the first coating, and let it stand for 5 minutes; after standing for 10 minutes in a 50℃ environment, overlap the top color pressing paper, press it at a pressure of 20Kpa, and then dry it at room temperature to obtain the pressed paper.

[0102] (5) A method for applying a embossed paper, comprising the following steps:

[0103] S1. The printing mold includes an upper pressing mold and a lower receiving mold, and the lower receiving mold is provided with a negative pressure hole; the embossing paper is clamped between the upper pressing mold and the lower receiving mold, the upper pressing mold is pressurized to 80Kpa, and the lower receiving mold provides 10Kpa of negative pressure adsorption.

[0104] S2. Continue to apply pressure and negative pressure until the pressurized area becomes colorless.

[0105] S3. Remove the printing mold and dry at room temperature to complete the printing.

[0106] Example 8

[0107] This embodiment is basically the same as Embodiment 1, and the only difference is that:

[0108] (1) In the process of preparing the base paper, 92 parts by weight of bleached softwood kraft chemical pulp and 8 parts by weight of carbon black pigment are mixed and stirred evenly, and then papermaking is performed to obtain a black base paper.

[0109] Example 9

[0110] A embossed paper is prepared by the following steps:

[0111] (1)Preparation of the base color paper: According to parts by mass, 92 parts of bleached softwood kraft chemical pulp and 8 parts of ultramarine blue pigment are mixed and stirred evenly, and then sheeted to obtain a light blue base color paper.

[0112] (2)Preparation of the top color pressing paper:

[0113] Preparation of the color-developing microcapsules: According to the molar ratio, 1 part of thermosensitive red, 3 parts of bisphenol A, and 80 parts of myristyl alcohol are mixed and evenly mixed in a water bath at 50 °C, and then cooled to room temperature to obtain a ternary complex. The ternary complex, Tween 20, and deionized water are mixed and heated in a water bath at 50 °C, and emulsified at a speed of 8000 rpm for 1 h to obtain an emulsion. Formaldehyde, melamine, and deionized water are mixed and the pH is adjusted to 8.5, and then stirred and reacted at a speed of 600 rpm in a water bath at 70 °C for 1 h to obtain a prepolymer. 1 part of the emulsion is placed in a water bath at 70 °C, and 4 parts of the prepolymer are added while stirring. After adding, the pH of the mixed solution is adjusted to 6.5, and then stirred at 70 °C and 600 rpm, and the pH is adjusted downward in the order of 6.5, 5.5, 4.5, and 3.5 every 1 h. After adjusting to 3.5, continue to stir for 1 h. After the reaction is completed, filter and wash with absolute ethanol to obtain the color-developing microcapsules.

[0114] Papermaking: According to parts by mass, 92 parts of bleached softwood kraft chemical pulp and 8 parts of color-developing microcapsules are mixed and stirred evenly, and then sheeted to obtain a red top color pressing paper.

[0115] (3)Preparation of the absorption layer:

[0116] Tetrabutyl titanate is added dropwise to deionized water at room temperature, and a white precipitate is obtained after magnetic stirring; after the white precipitate is filtered and washed, it is mixed with 30% hydrogen peroxide and stirred magnetically, and the precipitate dissolves to obtain a sol. After cooling to room temperature, the sol is diluted with polyvinyl alcohol and reserved.

[0117] (4)Preparation of the pressure-developing paper:

[0118] The base color paper is placed on a negative pressure adsorption device, and then a layer of absorption layer is coated. After standing for 10 min, the top color pressing paper is laminated, and pressed at a pressure of 20 Kpa, and then dried at room temperature to obtain the pressure-developing paper.

[0119] (5)An application method of the pressure-developing paper, including the following steps:

[0120] S1. Press the printing mold onto the top color pressing paper of the obtained pressure-developing paper, and apply pressure up to 80 Kpa to break the color-developing microcapsules;

[0121] S2. Continuously apply pressure and heat to 50 °C at the same time until the pressed area becomes colorless; then perform ultraviolet light irradiation treatment on the pressed area at 50 °C for 10 min.

[0122] S3. Remove the printing mold, then dry at room temperature to complete the printing.

[0123] Comparative Example 1

[0124] This comparative example is basically the same as Example 1, except that: the first pigment is not microencapsulated.

[0125] During the process of preparing the top-color pressure paper:

[0126] Papermaking: Mix 92 parts of softwood bleached kraft chemical pulp and 8 parts of nano-zinc oxide by mass, stir evenly, and then carry out papermaking to obtain off-white top-color pressure paper.

[0127] Printed Matter Detection

[0128] Use a color difference detector to detect the printed products obtained in the examples and comparative examples, and detect the color of the background base paper and the color difference with the color of the printed pattern. The detection results are shown in Table 1 below.

[0129] Tensile Strength Detection of Pressure-Exposed Paper

[0130] According to the detection method in "GB-T 12914-2008 Paper and Board - Determination of Tensile Strength", detect the tensile strength of the pressure-display paper and the printed paper after printing obtained in the examples and comparative examples. The detection results are shown in Table 1 below.

[0131] Table 1.

[0132]

[0133] As shown in Table 1, it can be seen that the pressure-display paper prepared in this application has good tensile strength before and after printing, and the pressure-display reaction process has little influence on the tensile strength of the paper; at the same time, the color of the printed pattern is not much different from the color of the background base paper, indicating that the color of the top-color pressure paper can be better converted into transparent and colorless, ensuring the clarity of the pressure-display printed pattern.

[0134] Further, it can be seen from the comparison between Example 1 and Comparative Example 1 that coating the first pigment can effectively ensure the conversion of the color state of the first pigment, and avoid excessive reduction of the tensile strength after printing by the adhesion of the wall material in the top-color pressure paper all the time. It can be seen from the comparison between Example 1 and Examples 2 and 4 that by setting two absorption layers and providing through holes in the absorption layer, the conversion effect of the color state can be further improved. It can be seen from the comparison between Example 1 and Example 5 that by adding a fiber mesh, the tensile strength of the paper before and after printing can be effectively improved. It can be seen from the comparison between Example 1 and Example 6 that by adding a negative pressure adsorption step during the printing pressurization process, the conversion effect of the pressure display color state can be further improved.

[0135] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar methods for substitution, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A pressure-display paper, characterized in that: It successively includes a background base paper, an absorption layer, and a top-color pressing paper; The top-color pressing paper includes color-developing microcapsules with a transparent material as the wall material and a first pigment as the core material; The absorption layer includes a material that can react with the first pigment to change the first pigment from a colored state to a colorless state; The background base paper includes a second pigment with a color different from that of the first pigment.

2. The pressure-display paper according to claim 1, wherein: The first pigment is nano-zinc oxide; The absorption layer includes polyvinyl acetate, first microcapsules with a first solvent as the core material, and second microcapsules with a second solvent as the core material. The first solvent is a solvent that can dissolve the nano-zinc oxide, and the second solvent is a solvent that can dissolve the polyvinyl acetate.

3. The pressure-display paper according to claim 2, wherein: The absorption layer includes a first layer and a second layer in the direction from the top-color pressing paper to the background base paper. The first microcapsules are disposed in the first layer, and the polyvinyl acetate and the second microcapsules are disposed in the second layer.

4. A pressure-display paper according to claim 2, characterized in that: The wall material of the first microcapsules includes a brittle material and a phase-change material; the brittle material is selected from one or more of polyethylene, polypropylene, polymethyl methacrylate, and polyvinyl alcohol.

5. The pressure-display paper according to claim 1, wherein: The first pigment is a ternary compound composed of a color former, a developer, and a temperature-control solvent; The absorption layer includes a photocatalyst for catalyzing the decomposition of the developer.

6. A pressure-display paper according to claim 1, characterized in that: The top-color pressing paper includes a transparent fiber mesh and a slurry filled in the fiber mesh, and the color-developing microcapsules are dispersed in the slurry.

7. A pressure-display paper according to claim 1, characterized in that: The absorption layer has through holes.

8. Application of the pressure-display paper according to any one of claims 1-7 in inkless printing.

9. The application of the pressure-display paper according to claim 8 in inkless printing, characterized in that: It includes the following steps: S1. Press a printing mold onto the top-color pressing paper of the pressure-display paper, and apply pressure to break the color-developing microcapsules; S2. When the first pigment is nano-zinc oxide, continuously apply pressure until the pressed area becomes colorless; When the first pigment is a ternary compound composed of a color former, a developer, and a temperature-control solvent, continuously apply pressure and assist with heating and illumination until the pressed area becomes colorless; S3. Remove the printing mold to complete the printing.

10. The application of the pressure-display paper in inkless printing according to claim 9, wherein: In steps S1 and S2, while applying pressure with the printing mold, negative pressure adsorption is performed on the part of the pressure-display paper to be printed.

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