Corrugated carton with variable color indicia and process for making same

Abstract

This invention relates to a corrugated cardboard box with color-changing markings and its manufacturing process, belonging to the field of cardboard box manufacturing. The surface of the corrugated cardboard box has a color-changing marking area, which, from bottom to top, includes: a pre-coating layer containing a color developer, and a layer of functionalized porous polymer particles loaded with a leuco dye and a phase-change organic medium. The key feature is that when the ambient temperature exceeds the phase-change temperature of the organic medium, the medium melts into a liquid state and carries the dye to the pre-coating layer, where it comes into contact with the color developer and undergoes an irreversible color-changing reaction, forming a bright blue-purple warning marking.

Description

Technical Field

[0001] This invention belongs to the field of cardboard box manufacturing and relates to a corrugated cardboard box with color-changing markings and its manufacturing process. Background Technology

[0002] Corrugated cardboard boxes, as lightweight, low-cost, and recyclable packaging containers, are widely used in many fields such as food, pharmaceuticals, electronic components, and fresh food cold chain, undertaking the core functions of product protection, warehousing and turnover, and logistics transportation. In actual circulation, some commodities (such as fresh products, thermally sensitive electronic components, and biological agents) have strict requirements for storage and transportation temperatures. Exceeding the temperature limit can lead to a decline in product quality, performance failure, or even scrapping, causing economic losses to businesses and consumers.

[0003] Existing corrugated cardboard boxes typically only offer basic load-bearing and protective functions, lacking the ability to provide intuitive warnings about changes in ambient temperature. While some high-value goods are equipped with independent temperature recorders, such devices are costly, complex to operate, and cannot provide "visual warnings." Professional personnel are required to interpret the data to determine if the goods have been exposed to excessive temperatures, making it difficult to meet the efficient and convenient quality control needs of large-scale logistics scenarios. Therefore, developing a corrugated cardboard box with temperature-responsive color-changing markings, capable of automatically displaying color warnings when temperatures exceed limits, is of significant practical importance for improving the level of safety management in product storage and logistics. Summary of the Invention

[0004] The purpose of this invention is to provide a corrugated cardboard box with color-changing markings and its manufacturing process, wherein the markings on the corrugated cardboard box can undergo irreversible color changes when the temperature exceeds a preset value.

[0005] The objective of this invention can be achieved through the following technical solutions: In a first aspect, the present invention provides a corrugated cardboard box with color-changing markings, comprising a box body, wherein the surface of the box body is provided with a color-changing marking area, the color-changing marking area comprising: A. A dye layer comprising porous polymer particles, wherein the pores of the porous polymer particles are loaded with leuco dye and organic medium. B. Pre-coating, which is fixed to the surface of the corrugated paper substrate by a thermoplastic polymer carrier and contains a color developer; When the temperature exceeds the phase transition temperature of the organic medium, it melts into a liquid state and carries the leuco dye to the pre-coating layer, causing the leuco dye to come into contact with the color developer and undergo a color development reaction.

[0006] The dye layer refers to a continuous or discontinuous film layer printed or coated on the pre-coating layer, using a polymer binder as a carrier and containing the functionalized porous polymer particles. Its main function is to support the thermal triggering unit and provide a pathway for dye migration. Its core function is to contain and protect the porous polymer particles loaded with leuco dye and organic media. When not triggered, it physically isolates the reactants (leuco dye) from the pre-coating layer; when triggered, it provides a channel for dye migration.

[0007] A pre-coating is a coating applied directly to the surface of a corrugated paper substrate, using a thermoplastic polymer as a binder and containing the color developer. Its primary function is to provide and fix the color developer, forming a stable reaction interface; secondly, it achieves a strong bond with the surface of the corrugated paper substrate through the thermoplastic polymer carrier.

[0008] The term "porous polymer particles" as used herein refers to hydrophobic polymer microspheres with an open, interconnected pore structure. Polyethylene (PE) or polypropylene (PP) is preferred because it has good compatibility with organic media, stable chemical properties, and is easy to process into particles with the desired pore size and porosity.

[0009] Preferably, the thermoplastic polymer carrier is an ethylene-vinyl acetate copolymer. Ethylene-vinyl acetate copolymer (EVA) is a common thermoplastic polymer. In the pre-coating of this invention, it serves as a film-forming adhesive carrier. During the hot pressing or drying process after coating, EVA encapsulates and bonds the solid color developer particles together, while simultaneously melting and adhering itself to the surface of the corrugated cardboard, forming a strong and flexible color-developing functional layer that provides a stable reaction substrate for the upper dye layer.

[0010] Preferably, the leuco dye is crystal violet lactone. Crystal violet lactone (CVL) is a typical leuco dye, which is colorless or light-colored in itself. Under acidic conditions, its lactone ring structure opens, forming a quinone dye molecule with a conjugated structure, thus exhibiting a blue-violet color. This reaction is sensitive and has high color contrast.

[0011] Preferably, the organic medium is at least one of tetradecyl alcohol, hexadecyl alcohol, and octadecyl alcohol. These long-chain fatty alcohols have well-defined melting phase transition temperatures. For example, hexadecyl alcohol has a melting point of approximately 49-52°C. As phase change functional materials, their melting points determine the trigger temperature threshold of this designation. Simultaneously, they are excellent solvents for leuco dyes (such as CVL) in the molten state, ensuring effective dye carrying and migration.

[0012] Preferably, the color developer comprises an alkyl gallate and a solid organic sulfonic acid.

[0013] Preferably, the alkyl gallate is lauryl gallate.

[0014] Preferably, the solid organic sulfonic acid is dinonylnaphthalenesulfonic acid or dodecylbenzenesulfonic acid. Solid organic sulfonic acids (such as dinonylnaphthalenesulfonic acid, DNNDSA) are proton donors (H... + The acidic color developer, with its solid-state properties, ensures stable presence in the pre-coating. Alkyl gallate esters (such as lauryl gallate, GL) play multiple roles in this system: their phenolic hydroxyl structure acts as an auxiliary color developer, enhancing the color development effect; their long alkyl chains (such as lauryl C12) strongly interact with paper fibers and polymer carriers, acting as molecular anchors to firmly fix the entire color development system onto the paper substrate, greatly improving the abrasion resistance of the color pattern. The combination of these two components harmonizes color development reactivity and coating adhesion.

[0015] Preferably, the color-changing marking area further includes a transparent protective layer covering the dye layer. The transparent protective layer can be a water-based abrasion-resistant varnish or a UV-cured varnish. Its main function is to physically protect the underlying dye layer, preventing it from being damaged during circulation due to friction, scratches, or contamination, ensuring the integrity and readability of the marking, while not affecting heat transfer.

[0016] The core of the solution lies in constructing a "temperature switch" based on physical phase transitions. Porous polymer particles act as both "micro-storage tanks" and "controllable channels." At room temperature (below a predetermined temperature), the organic medium, serving as the "core material," is in a solid state, acting like a "plug" to block the micropores of the particles, firmly locking the leuco dye inside and ensuring the stability of the label during storage and normal transportation. When the ambient temperature reaches or exceeds the preset trigger temperature (i.e., the phase transition point of the organic medium), the organic medium undergoes a solid-liquid phase transition, transforming into a liquid state. The liquid organic medium not only unblocks the pores but also acts as a solvent and carrier, actively migrating the dissolved leuco dye through the pores. In the pre-coating layer, the leuco dye encounters the pre-fixed color developer and undergoes a rapid acid-induced color-developing chemical reaction (such as crystal violet lactone opening its ring and turning blue-violet under acidic conditions), producing a vivid and irreversible color change.

[0017] Secondly, the present invention provides a manufacturing process for corrugated cardboard boxes with color-changing markings, comprising the following steps: (1) Provide porous polymer particles, and load a molten mixture containing leuco dye and organic medium into its pores through an impregnation process, and then cool and solidify to obtain functionalized particles; (2) The pre-coating is formed in a predetermined area on the surface of the corrugated cardboard; (3) Disperse the functionalized particles obtained in step (1) in the binder and print them on the pre-coating layer described in step (2) to form a dye layer; (4) The processed corrugated cardboard is then formed into cartons.

[0018] First, a base pre-coating layer (B layer) containing a color developer is prepared on the cardboard. Then, a functional dye layer (A layer) containing a heat-triggered unit is prepared on it. Finally, the carton is formed.

[0019] Preferably, in step (2), a pre-coating layer is formed by hot pressing or coating. The "hot pressing" method refers to bonding a pre-made functional film containing a color developer and an EVA carrier to a designated area of ​​the cardboard using equipment with heating and pressure devices (such as a flatbed hot press). This method results in a uniform film formation and strong adhesion. The "coating" method refers to applying a slurry containing a color developer, polymer binder, and solvent to the surface of the cardboard by methods such as scraping, roller coating, or printing, followed by drying to remove the solvent and form a fixed layer. This method offers high flexibility and facilitates pattern variations.

[0020] Preferably, step (3) also includes a drying step, with the temperature not exceeding 30°C. After the dye layer is formed by printing, it is cured into a film by low-temperature drying (such as airflow or dehumidification drying at ≤30°C). To ensure that the heat during the drying process will never reach or exceed the phase transition temperature of the organic medium, thereby completely avoiding accidental and uncontrollable premature color development on the production line and ensuring the functional integrity of the finished product.

[0021] The beneficial effects of this invention are: This invention is based on the physical triggering mechanism of "solid blockage-liquid migration" of porous particles, which realizes an irreversible color reaction after exceeding the temperature. The color-changing mark is firmly bonded to the carton body through the coating, making it wear-resistant and tamper-proof. The triggering temperature can be flexibly set by adjusting or replacing the organic medium to meet the monitoring needs of multiple temperatures and multiple scenarios. Detailed Implementation

[0022] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0023] Example 1 A manufacturing process for a corrugated cardboard box with color-changing markings includes the following steps: Raw material ratio: Porous polyethylene granules: 100g Crystal violet lactone (CVL): 10g Tetradecyl alcohol (purity 99%, melting point 38-40℃): 90g Ethylene-vinyl acetate copolymer (EVA, VA content 26%): 70g Lauryl gallate (GL): 15g Dinonylnaphthalenesulfonic acid (DNNDSA): 15g Water-based acrylic pressure-sensitive adhesive latex (50% solids content): 40g Preparation process: (1) CVL and tetradecyl alcohol were heated and melted in a constant temperature water bath at 55°C. Under nitrogen protection, the mixture was stirred until completely dissolved to form a homogeneous and transparent solution. Porous polyethylene particles were loaded into a vacuum impregnation tank, and a vacuum of -0.095 MPa was applied for 15 minutes. While maintaining the vacuum, the molten mixture was slowly injected into the impregnation tank to immerse the particles. After the vacuum was released, a pressure of 0.3 MPa was applied and maintained for 30 minutes. After impregnation, the pressure was released, and the excess core material mixture that was not adsorbed was filtered out. The loaded wet particles were spread out under ventilation and cooled to solidify, resulting in off-white to light yellow functionalized particles.

[0024] (2) Add EVA to 200g of ethyl acetate solvent and stir at 50°C until dissolved. Add GL and DNNDSA and continue stirring at 40°C for 2 hours to obtain a uniform slurry. Apply the slurry to the predetermined marking area of ​​the corrugated cardboard. Then transfer the cardboard to a 50°C oven to dry. After the solvent evaporates, a pre-coating is formed.

[0025] (3) Place 100g of functionalized granules and 40g of water-based acrylic pressure-sensitive adhesive latex in a low-speed mixing tank and mix at 30rpm for 30 seconds to obtain a uniform suspension slurry. Apply the slurry to the pre-coated area. Then place the cardboard in a constant temperature and ventilation environment at (25±2)℃ and let it dry horizontally for 30 minutes to form a dye layer.

[0026] (4) The processed cardboard is die-cut (crimping lines avoid the marking area), creasing, and automatically glued to the box to make finished corrugated boxes.

[0027] Example 2 A manufacturing process for a corrugated cardboard box with color-changing markings includes the following steps: Raw material ratio: Porous polyethylene granules: 100g Crystal violet lactone (CVL): 10g Cetyl alcohol (purity 98%, melting point 52-54℃): 90g EVA (VA content 28%): 75g GL: 12.5g DNNDSA: 12.5g Water-based acrylic pressure-sensitive adhesive latex (50% solids content): 40g Preparation process: (1) CVL and cetyl alcohol were heated and melted in a constant temperature water bath at 60°C, and stirred under nitrogen protection until completely dissolved to form a homogeneous and transparent solution. Porous polyethylene particles were loaded into a vacuum impregnation tank, and a vacuum was drawn to -0.095 MPa and maintained for 15 minutes. While maintaining the vacuum, the molten mixture was slowly injected into the impregnation tank to immerse the particles. After the vacuum was released, a pressure of 0.3 MPa was applied and maintained for 30 minutes. After impregnation, the pressure was released, and the excess core material mixture that was not adsorbed was filtered out. The loaded wet particles were spread out under ventilation conditions and cooled and solidified to obtain off-white functionalized particles.

[0028] (2) EVA, GL and DNNDSA are premixed and melt-blended and granulated at 115°C using a twin-screw extruder. The masterbatch is made into a film using a casting machine. The film is cut and placed in the cardboard marking area. It is then hot-pressed for 10 seconds at 90°C and 0.5MPa using a flatbed hot press to form a pre-coating.

[0029] (3) Place 100g of functionalized granules and 40g of water-based acrylic pressure-sensitive adhesive latex in a low-speed mixing tank and mix at 30rpm for 30 seconds to obtain a uniform suspension slurry. Apply the slurry to the pre-coated area. Then place the cardboard in a constant temperature and ventilation environment at (25±2)℃ and allow it to dry horizontally for 30 minutes to form a dye layer. After the dye layer is completely dry, print a layer of water-based abrasion-resistant varnish on its surface, and then dry it to form a transparent protective layer.

[0030] (4) The processed cardboard is die-cut (crimping lines avoid the marking area), creasing, and automatically glued to the box to make finished corrugated boxes.

[0031] Example 3 A manufacturing process for a corrugated cardboard box with color-changing markings includes the following steps: Raw material ratio: Porous polypropylene granules: 100g CVL: 10g Octadecyl alcohol (purity 97%, melting point 58-60℃): 90g EVA (VA content 28%): 75g GL: 12.5g DNNDSA: 12.5g Water-based acrylic pressure-sensitive adhesive latex (50% solids content): 40g Preparation process: (1) CVL and octadecyl alcohol were heated and melted in a constant temperature water bath at 60°C, and stirred under nitrogen protection until completely dissolved to form a homogeneous and transparent solution. Porous polypropylene particles were loaded into a vacuum impregnation tank, and a vacuum was drawn to -0.095 MPa and maintained for 15 minutes. While maintaining the vacuum, the molten mixture was slowly injected into the impregnation tank to immerse the particles. After the vacuum was released, a pressure of 0.4 MPa was applied and maintained for 40 minutes. After impregnation, the pressure was released, and the excess core material mixture that was not adsorbed was filtered out. The loaded wet particles were spread out under ventilation conditions and cooled and solidified to obtain off-white functionalized particles.

[0032] (2) Add EVA to 200g of ethyl acetate solvent and stir at 50°C until dissolved. Add GL and DNNDSA and continue stirring at 40°C for 2 hours to obtain a uniform slurry. Apply the slurry to the predetermined marking area of ​​the corrugated cardboard. Then transfer the cardboard to a 50°C oven to dry. After the solvent evaporates, a pre-coating is formed.

[0033] (3) Place 100g of functionalized granules and 40g of water-based acrylic pressure-sensitive adhesive latex in a low-speed mixing tank and mix at 30rpm for 30 seconds to obtain a uniform suspension slurry. Apply the slurry to the pre-coated area. Then place the cardboard in a constant temperature and ventilation environment at (25±2)℃ and let it dry horizontally for 30 minutes to form a dye layer.

[0034] (4) The processed cardboard is die-cut (crimping lines avoid the marking area), creasing, and automatically glued to the box to make finished corrugated boxes.

[0035] Comparative Example 1 Compared with Example 2, the difference is that the water-based acrylic pressure-sensitive adhesive latex is replaced with an equal amount of conventional water-based acrylic binder (50% solid content), while other conditions remain unchanged.

[0036] The preparation process is the same as in Example 2.

[0037] Results: After being kept in a constant temperature environment of 46℃ for 60 minutes, only a few light purple spots appeared, and it was impossible to form a complete and uniform blue-purple mark.

[0038] Comparative Example 2 Compared with Example 2, the difference is that in step (3), the drying temperature is increased to 50°C, and the other preparation processes are the same as in Example 2.

[0039] Result: The dried marking area showed a distinct blue-purple background and completely lost its temperature monitoring function.

[0040] Comparative Example 3 Compared with Example 2, the difference is that in the preparation of the pre-coating in step (2), no EVA is added at all, and only GL and DNNDSA powders are wetted with ethanol and then coated.

[0041] Result: The resulting pre-coating was a loose powder layer with poor adhesion. It was severely damaged during printing, making it impossible to conduct effective testing on the final product.

[0042] Performance testing: Trigger temperature measurement: Place the sample on a programmable constant temperature hot plate, and maintain the temperature for 30 minutes at each 0.5℃ increase, observing the color change of the marked area. Trigger temperature: The temperature at which the marked area begins to show a stable and visible blue-purple color (forming a clear contrast with the background).

[0043] Anti-false triggering test (storage stability): Place the untriggered sample in a constant temperature environment 5°C below its nominal triggering temperature and store for 10 days. Check whether any color development appears in the marking area.

[0044] The results above show that all three embodiments exhibit significant and irreversible color changes at the set temperature points.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A corrugated cardboard box with color-changing markings, comprising a box body, characterized in that, The surface of the enclosure is provided with a color-changing marking area, which includes: A. A dye layer comprising porous polymer particles, wherein the pores of the porous polymer particles are loaded with leuco dye and organic medium. B. Pre-coating, which is fixed to the surface of the corrugated paper substrate by a thermoplastic polymer carrier and contains a color developer; When the temperature exceeds the phase transition temperature of the organic medium, it melts into a liquid state and carries the leuco dye to the pre-coating layer, causing the leuco dye to come into contact with the color developer and undergo a color development reaction.

2. A corrugated cardboard box with color-changing markings according to claim 1, characterized in that, The porous polymer particles are porous polyethylene or polypropylene particles.

3. A corrugated cardboard box with color-changing markings according to claim 1, characterized in that, The leuco dye is crystal violet lactone.

4. A corrugated cardboard box with color-changing markings according to claim 1, characterized in that, The organic medium is at least one of tetradecanol, hexadecyl alcohol, and octadecyl alcohol.

5. A corrugated cardboard box with color-changing markings according to claim 1, characterized in that, The colorimetric agent comprises alkyl gallic acid ester and solid organic sulfonic acid.

6. A corrugated cardboard box with color-changing markings according to claim 5, characterized in that, The alkyl gallate is lauryl gallate.

7. A corrugated cardboard box with color-changing markings according to claim 5, characterized in that, The solid organic sulfonic acid is dinonylnaphthalene sulfonic acid or dodecylbenzene sulfonic acid.

8. A process for preparing a corrugated cardboard box with color-changing markings as described in any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Provide porous polymer particles, and load a molten mixture containing leuco dye and organic medium into its pores through an impregnation process, and then cool and solidify to obtain functionalized particles; (2) The pre-coating is formed in a predetermined area on the surface of the corrugated cardboard; (3) Disperse the functionalized particles obtained in step (1) in the binder and print them on the pre-coating layer described in step (2) to form a dye layer; (4) The processed corrugated cardboard is then formed into cartons.

9. The preparation process according to claim 8, characterized in that, In step (2), a pre-coating layer is formed by hot pressing or coating.

10. The preparation process according to claim 8, characterized in that, Step (3) also includes a drying step, with the temperature not exceeding 30°C.

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