Waterborne coatings and their applications

Abstract

This invention discloses a water-based coating and its application. The water-based coating comprises 70 to 99 parts of an aqueous film-forming substance and 1 to 30 parts of a foaming material. After the water-based coating dries to form a movable layer, the foaming material can foam under specific conditions, and the aqueous film-forming substance can undergo thermally induced dissociation. After the water-based coating is applied to a substrate and dried to form a movable layer, the aqueous film-forming substance undergoes physical fusion or chemical cross-linking to form a three-dimensional network structure. Under specific conditions, the foaming material can foam, and the internal stress generated during the foaming process can cause the aqueous film-forming substance with the three-dimensional network structure to undergo thermally induced rupture and dissociation, resulting in a significant reduction in the molecular weight of the aqueous film-forming substance, and consequently a significant reduction in the adhesion of the movable layer, thus allowing it to be removed. Therefore, the above-mentioned water-based coating can be used to prepare reusable substrates.

Description

Technical Field

[0001] This invention relates to the field of coating technology, and more particularly to a water-based coating and its application. Background Technology

[0002] In existing technologies, water-based coatings are widely used for surface treatment of printed materials, forming a coating on the surface of the printed image to protect the printed image layer. Since printed materials may experience high temperature and humidity environments in summer warehouses or shipping containers, the coating needs to possess high stability, including excellent resistance to high-temperature dissociation and moisture resistance. Failure to meet these performance standards can lead to serious quality issues. To verify its stability, anti-tack tests are typically conducted at 70°C and 90% humidity. Therefore, preventing thermal dissociation of water-based film-forming substances in the coating at high temperatures is a technical problem that those skilled in the art must overcome.

[0003] In the printing industry, the image layer formed by ink is in direct contact with the substrate layer. Ink has the characteristics of permeability, thin ink layer and high adhesion. Therefore, the image layer on the substrate layer cannot be removed. This means that a large amount of proofing material used in the printing process cannot be reused, which increases the cost pressure on printing companies.

[0004] Therefore, it is necessary to provide a water-based coating and its application to solve the above problems. Summary of the Invention

[0005] A water-based coating, by weight, comprises the following components:

[0006] 70 to 99 parts of aqueous film-forming substance; and

[0007] 1 to 30 parts of foaming material;

[0008] After the water-based coating dries to form a movable layer, the foaming material can foam under specific conditions, and the water-based film-forming substance can undergo thermal dissociation. After the water-based film-forming substance undergoes thermal dissociation, the adhesion of the movable layer decreases and it can be removed.

[0009] In one embodiment, the aqueous film-forming substance is selected from at least one of polyurethane resin, acrylic resin, polyvinyl alcohol and its modified resins, polyethylene oxide resin, starch and its derivatives, polyvinylpyrrolidone, and environmentally responsive block copolymers.

[0010] In one embodiment, the specific environment is a dry heating environment, and the thermally induced dissociation is thermally induced fracture dissociation.

[0011] In one embodiment, the material further includes 3 to 15 parts of an aqueous material, the specific environment being a dry heating environment, and the thermally induced dissociation being thermally induced cracking dissociation and thermally induced swelling dissociation.

[0012] In one embodiment, the aqueous material is selected from at least one of sulfate hydrates, carbonate hydrates, aqueous chlorides, aqueous silicates, aqueous organic acid salts, and aqueous phosphates.

[0013] In one embodiment, the specific environment is a wet heating environment, and the thermally induced dissociation is thermally induced cracking dissociation and thermally induced swelling dissociation.

[0014] In one embodiment, the specific environment is a steam-heated environment, and the thermal dissociation is fully thermally induced cracking dissociation and moderately thermally induced swelling dissociation.

[0015] In one embodiment, the specific environment successively includes a dry heating environment and a wet heating environment, and the thermally induced dissociation successively includes thermally induced cracking dissociation and moderately limited thermally induced swelling dissociation.

[0016] In one embodiment, the dry heating temperature is 70°C-130°C.

[0017] In one embodiment, the foaming material is a mixed foaming material.

[0018] In one embodiment, the foaming material is selected from at least one of physical foaming materials, chemical foaming materials, inorganic foaming materials, environmentally friendly foaming materials, and composite foaming materials.

[0019] In one embodiment, the physical foaming material is selected from any one of volatile liquids, compressed gases, supercritical fluids, foamed microspheres, expanded graphite, vermiculite powder, and expanded hexagonal boron nitride; the chemical foaming material is selected from any one of azo foaming materials, sulfonyl hydrazine foaming materials, carbonate foaming materials, hydrazine / acyl hydrazine foaming materials, hydrazine / acyl hydrazine foaming materials, and reactive foaming materials; the inorganic foaming material is selected from any one of carbonate foaming materials, metal hydride foaming materials, and silicate foaming materials; the environmentally friendly foaming material is selected from any one of bio-based foaming materials, HFOs foaming materials, and natural product foaming materials; and the composite foaming material is selected from any one of endothermic-exothermic composite foaming materials, acid-base reactive foaming materials, and metal-organic composite foaming materials.

[0020] In one embodiment, the foaming material has a specific induction temperature, which is 60°C-200°C.

[0021] In one embodiment, the particle size of the foamed material is 1 micrometer to 50 micrometers.

[0022] The aforementioned water-based coating, after being applied to a substrate and dried to form a movable layer, allows the water-based film-forming substances to undergo physical fusion or chemical cross-linking to form a three-dimensional network structure. Under specific conditions, the foaming material can foam, and the internal stress generated during the foaming process can cause the water-based film-forming substances with the three-dimensional network structure to undergo thermally induced rupture and dissociation, resulting in a significant reduction in the molecular weight of the water-based film-forming substances. Consequently, the adhesion of the movable layer is significantly reduced, allowing it to be removed. Therefore, the aforementioned water-based coating can be used to prepare reusable substrates.

[0023] The application of any of the above-mentioned water-based coatings on a substrate. Detailed Implementation

[0024] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0025] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is considered to be "connected" or "connected" to another element, it can be directly connected to the other element or there may be an intervening element. The terms "upper," "lower," "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0026] The following detailed explanation of water-based coatings will be provided in conjunction with specific embodiments.

[0027] One embodiment of the water-based coating includes 70 to 99 parts of a water-based film-forming substance and 1 to 30 parts of a foaming material.

[0028] The water-based film-forming substance has a mass fraction of 70 to 99 parts. The water-based film-forming substance plays two roles in water-based coatings: on the one hand, it enables the water-based coating to dry and form a film, forming a mobile layer, which can be firmly attached to the substrate layer; on the other hand, after the mobile layer is formed, the water-based film-forming substance can undergo thermal dissociation under specific conditions.

[0029] Specifically, during the drying process of waterborne coatings, the waterborne film-forming substances undergo physical fusion and chemical cross-linking to form a movable layer with a three-dimensional network structure. This three-dimensional network structure ensures strong adhesion of the movable layer. The movable layer exhibits strong stability and water resistance in medium and low temperature environments, thus meeting practical application requirements. Its strong water resistance is due to two main reasons: First, the hydrophobic groups (such as long-chain alkyl groups and fluorine / silicon modified groups) in the waterborne film-forming substances are tightly arranged after water evaporation, forming a dense cross-linked network structure that effectively blocks water penetration. Second, while the waterborne film-forming substances contain a small number of hydrophilic groups (such as carboxylic acid groups and hydroxyl groups), these hydrophilic groups are either encapsulated by hydrophobic segments or fixed through cross-linking reactions during film formation, preventing them from fully contacting water molecules.

[0030] Optionally, the aqueous film-forming substances that can be used to prepare waterborne coatings include, but are not limited to: polyurethane resins, acrylic resins, polyvinyl alcohol and its modified resins, polyethylene oxide resins, starch and its derivatives, polyvinylpyrrolidone, and environmentally responsive block copolymers.

[0031] Furthermore, aqueous film-forming substances containing ester groups include, but are not limited to: polyurethane resins, acrylic resins, polyvinyl alcohol and its modified resins, starch and its derivatives. Aqueous film-forming substances containing ether bonds include, but are not limited to: polyurethane resins, polyvinyl alcohol and its modified resins, polyethylene oxide resins, starch and its derivatives.

[0032] In some embodiments, the aqueous film-forming substance is a commercially available aqueous varnish, aqueous primer, aqueous clear varnish, aqueous matte varnish, or aqueous ink. The mass percentage of the aqueous film-forming substance in the commercially available aqueous varnish, aqueous primer, aqueous clear varnish, aqueous matte varnish, or aqueous ink is usually within the component range defined in this invention. Therefore, it can be directly used as the aqueous film-forming substance of this invention.

[0033] The foaming material has a mass fraction of 1 to 30 parts. The foaming material can foam under specific temperature conditions. The foaming process can generate internal stress in the movable layer. The internal stress can cause the water-based film-forming substance to undergo thermal rupture and dissociation.

[0034] Optionally, foamed materials can be classified as: physical foamed materials, chemical foamed materials, inorganic foamed materials, environmentally friendly foamed materials, and composite foamed materials.

[0035] Specifically, physically foamed materials include, but are not limited to: volatile liquids, compressed gases, supercritical fluids, foamed microspheres, expanded graphite, vermiculite powder, and expanded hexagonal boron nitride.

[0036] Optionally, the volatile liquid foaming material includes, but is not limited to: pentane (C5H 12 ), butane (C4H) 10), dichloromethane (CH2Cl2), HFC-134a. Compressed gas foaming materials include, but are not limited to: nitrogen (N2), carbon dioxide (CO2), and air. Supercritical fluid foaming materials include, but are not limited to: supercritical carbon dioxide (scCO2), supercritical nitrogen (scN2), and supercritical argon (scAr).

[0037] Chemical foaming materials include, but are not limited to: azo foaming materials, sulfonyl hydrazine foaming materials, carbonate foaming materials, hydrazine / acyl hydrazine foaming materials, hydrazine / acyl hydrazine foaming materials, and reactive foaming materials.

[0038] Specifically, azo-based foaming materials include, but are not limited to: azodicarbonamide (AC), azobisisobutyronitrile (AIBN), barium azodicarboxylate (BAB), and azodicarbonate (ADC). Sulfonyl hydrazine-based foaming materials include, but are not limited to: p-toluenesulfonyl hydrazine (TSH), benzenesulfonyl hydrazine (BSH), and diphenyl sulfone-3,3'-disulfonyl hydrazine (DPSH). Carbonate-based foaming materials include, but are not limited to: sodium bicarbonate (NaHCO3), ammonium bicarbonate (NH4HCO3), and ammonium carbonate ((NH4)2CO3). Nitro / nitroso-based foaming materials include, but are not limited to: nitrosopentamethylenetetramine (foaming material H), nitroguanidine (NG), and 2,2'-dinitrobenzene (DNB). Hydrazine / acyl hydrazine-based foaming materials include, but are not limited to: 4,4'-oxobisbenzenesulfonyl hydrazine (OBSH), trihydrazine triazine (THT), and 5-phenyltetrazole (5-PT). Reactive foaming materials include, but are not limited to: water (H2O, polyurethane), hydrogen peroxide (H2O2, rubber foam), and isocyanate self-reactive systems.

[0039] Inorganic foaming materials include, but are not limited to: carbonate foaming materials, metal hydride foaming materials, and silicate foaming materials.

[0040] Specifically, carbonate foaming materials include, but are not limited to: magnesium carbonate (MgCO3), calcium carbonate (CaCO3, endothermic), and zinc carbonate (ZnCO3). Metal hydride foaming materials include, but are not limited to: aluminum hydride (AlH3), magnesium hydride (MgH2), and sodium borohydride (NaBH4). Silicate foaming materials include, but are not limited to: water glass (Na2SiO3) and bentonite.

[0041] Environmentally friendly foaming materials include, but are not limited to: bio-based foaming materials, HFOs foaming materials, and natural product foaming materials.

[0042] Specifically, bio-based foaming materials include, but are not limited to: polylactic acid (PLA) microspheres, starch-based granules, and cellulose foaming materials. HFOs foaming materials include, but are not limited to: HFO-1234ze, HFO-1336mzz, and HFO-1233zd. Natural product foaming materials include, but are not limited to: coconut oil derivatives and soybean oil-based polyols.

[0043] Composite foaming materials include, but are not limited to: endothermic-exothermic composite foaming materials, acid-base reactive foaming materials, and metal-organic composite foaming materials.

[0044] Specifically, endothermic-exothermic composite foaming materials include, but are not limited to: sodium bicarbonate and azodicarbonamide, citric acid and sodium bicarbonate. Acid-base reactive foaming materials include, but are not limited to: calcium carbonate and stearic acid, zinc oxide and stearic acid. Metal-organic composite foaming materials include, but are not limited to: aluminum hydride and polysiloxane, magnesium carbonate and azo compounds.

[0045] In one embodiment, the foaming material is foamed microspheres, which have a core-shell structure consisting of a polymer shell and a foaming agent core. When the temperature exceeds the induction temperature of the foaming agent core, the polymer shell softens, and the foaming agent core releases a large amount of gas. Under the pressure of the core, the volume of the foamed microspheres expands rapidly, thereby generating indirect internal stress within the movable layer through the shell, causing thermally induced rupture and disintegration of the movable layer. The foamed microspheres are hollow spheres after foaming.

[0046] In another embodiment, the foaming material is expanded graphite. Graphite molecules have a parallel hierarchical structure, and the molecules between the layers are bound together by van der Waals forces. Expanded graphite is expanded by inserting an expanding agent between the layer molecules. When the ambient temperature is higher than the induction temperature of the expanding agent, the expanding agent decomposes and releases a large amount of gas. The pressure generated by the gas pushes the graphite molecules between the layers to expand violently along the axial direction, thereby generating internal stress within the movable layer and causing thermally induced fracture and dissociation of the movable layer. The expanded graphite after expansion has a popcorn-like appearance.

[0047] In another embodiment, the foaming material is modified sodium bicarbonate. The modified sodium bicarbonate particles are coated with a hydrophobic layer. When the ambient temperature is higher than the induction temperature of 60°C, the modified sodium bicarbonate particles can decompose to generate a large amount of carbon dioxide gas, thereby generating internal stress in the movable layer and causing thermally induced cracking and disintegration of the movable layer.

[0048] In another embodiment, the foaming material is azobisisobutyronitrile (AIBN). Azobisisobutyronitrile particles are insoluble in water and have an induction temperature of 90-115°C. When the ambient temperature is higher than the induction temperature, the AIBN particles can decompose to generate a large amount of nitrogen gas, which can generate a large amount of gas in the movable layer, thereby generating internal stress in the movable layer and causing thermally induced cracking and disintegration of the movable layer.

[0049] In another embodiment, the foaming material is p-toluenesulfonyl hydrazine, which is insoluble in water. Its initiation temperature is 110-130°C. When the ambient temperature is higher than the initiation temperature, the p-toluenesulfonyl hydrazine particles can decompose to generate a large amount of nitrogen gas, and can generate a large amount of gas in the movable layer, thereby generating internal stress in the movable layer and causing thermal cracking and disintegration of the movable layer.

[0050] In another embodiment, the foaming material is 4,4'-oxobis(benzenesulfonyl)hydrazine (OBSH). OBSH particles are insoluble in water, and their initiation temperature is 150-160°C. When the ambient temperature is higher than the initiation temperature, the OBSH particles decompose to generate a large amount of nitrogen and water vapor, which can produce a large amount of gas within the movable layer. This generates internal stress within the movable layer and causes thermally induced cracking and dissociation. OBSH particles are widely used in TPU and shoe material foaming processes. Notably, the water vapor generated during OBSH foaming can induce thermal swelling and dissociation of the aqueous film-forming material; this dual dissociation helps to promote the removal of the movable layer.

[0051] In another embodiment, the foaming material is azodicarbonamide, which is insoluble in water and has an induction temperature of 195-210°C. When the ambient temperature is higher than the induction temperature, the azodicarbonamide particles can decompose to generate a large amount of nitrogen and carbon monoxide, and can generate a large amount of gas in the movable layer, thereby generating internal stress in the movable layer and causing thermally induced cracking and disintegration of the movable layer.

[0052] In another embodiment, the foaming material is a mixed foaming material, comprising a first foaming material and a second foaming material. The first foaming material has a first induction temperature, and the second foaming material has a second induction temperature, which is higher than the first induction temperature. When the ambient temperature is higher than the first induction temperature, the first foaming material foams, creating pores in the removable layer while maintaining high adhesion, allowing ordinary offset printing inks to penetrate and dry within the removable layer without causing it to peel off during printing. When the ambient temperature is higher than the second induction temperature, the second foaming material foams, significantly reducing the adhesion of the removable layer, thus allowing it to be removed.

[0053] Optionally, the mass ratio of the first foaming material to the second foaming material is 10% to 30%.

[0054] In some embodiments, the foamed material is in granular form. During the release of gas by the heat-sensitive component, the generated gas causes the volume of the foamed material particles to expand, and the internal stress is indirectly provided by the outer surface of the foamed material particles. In other embodiments, the foamed material is dissolved and dispersed in a substrate layer, and the internal stress is directly provided by the released gas molecules.

[0055] Optionally, the particle size of the foaming material is 1 micrometer to 50 micrometers. Water-based coatings can be prepared using foaming materials with particle sizes within this range, and can be applied by offset printing, gravure printing, screen printing, or coating methods.

[0056] Preferably, the mass fraction of the foaming material is 5 to 15 parts. After foaming, the removable layer of the foaming material in this range can achieve a good removal effect.

[0057] Optionally, the initiation temperature of the foaming material is 60℃-200℃. This range of initiation temperatures is relatively low, and the substrate layer is not easily deformed during initiation.

[0058] Preferably, the initiation temperature of the foaming material is 60℃-130℃. When the base layer material is paper, this temperature can control the degree of deformation of the base layer within a low range.

[0059] In this invention, the specific environment includes a dry heating environment and a wet heating environment, and thermal dissociation includes thermally induced cracking dissociation and thermally induced swelling dissociation.

[0060] In this embodiment, the specific environment is a dry heating environment, and the thermally induced dissociation is thermally induced fracture dissociation.

[0061] Specifically, after the water-based coating dries to form a movable layer, when the ambient temperature of the dry heating environment is higher than the initiation temperature of the foaming material, the heat-sensitive components can release a large amount of gas through decomposition, evaporation, or sublimation. The gas directly or indirectly generates internal stress in the movable layer. The internal stress can cause the molecular chains of the water-based film-forming material with a three-dimensional network structure to break, the molecular weight to decrease significantly, and a large number of pores to be generated in the movable layer, resulting in volume expansion. This significantly reduces the adhesion, rigidity, and strength between the movable layer and the substrate layer, thereby allowing the movable layer to be removed from the substrate layer.

[0062] It should be noted that thermally induced decomposition causes the chemical bonds in the molecules of aqueous film-forming substances to break, therefore, thermally induced decomposition is irreversible.

[0063] Optionally, dry heating can be selected from any one of infrared heating, heat pressing, ultrasonic heating, and plasma heating.

[0064] However, it should be noted that under dry heating conditions, temperature has two effects on the adhesion of the movable layer: Firstly, high temperature promotes the full cross-linking and curing of the aqueous film-forming material in the movable layer, forming a dense three-dimensional network structure, thereby enhancing the adhesion of the movable layer to a certain extent; secondly, the foaming of the foaming material will generate internal stress within the movable layer, which will lead to two possible results:

[0065] (1) When the internal stress generated by the foaming material is less than the chemical bond energy of the three-dimensional network structure, some of the gas generated by the foaming material will leak outward through the microscopic pores between molecules, thus partially releasing the internal stress. The internal stress has limited impact on the hierarchical structure of the movable layer, therefore, the movable layer will still maintain a high adhesive force. Experiments have shown that under dry heating conditions, when the ambient temperature is higher than 130℃, the temperature has a high crosslinking promoting effect on the aqueous film-forming material. The internal stress generated by the foaming material is usually less than the chemical bond energy of the three-dimensional network structure, and the movable layer still maintains a high adhesive force. Although the movable layer 20 can be removed, the removal is difficult.

[0066] (2) When the internal stress generated by the foaming material exceeds the chemical bond energy of the three-dimensional network structure, the internal stress will directly destroy the hierarchical structure of the movable layer, causing the molecular chains of the aqueous film-forming material in the movable layer to break, the molecular weight to decrease significantly, and a large number of pores to be generated in the movable layer. This significantly reduces the adhesion between the movable layer and the substrate layer, but the movable layer still maintains the integrity of the hierarchical structure. At this time, although the movable layer can be removed, the removal efficiency is relatively low. Experiments have shown that under dry heating conditions, when the ambient temperature is below 130℃, the temperature has a low effect on promoting the crosslinking of aqueous film-forming materials. The internal stress generated by the foaming material is usually greater than the chemical bond energy of the three-dimensional network structure. The internal stress can destroy the adhesion of the movable layer, but too low a temperature will affect the foaming effect of the foaming material. Therefore, it is necessary to grasp the temperature balance point of dry heating.

[0067] In another embodiment, the specific environment is a wet heating environment, and thermal dissociation includes both thermal cracking dissociation and thermal swelling dissociation. Dual thermal dissociation is beneficial to significantly improve the removal efficiency of the movable layer.

[0068] Specifically, during the wet heating process, when the ambient temperature is higher than the induction temperature of the heat-sensitive component, the foaming of the foaming material can cause the movable layer to undergo thermally induced rupture and dissociation. Specifically, the heat-sensitive component can release a large amount of gas through decomposition, evaporation, or sublimation. The gas directly or indirectly generates internal stress in the movable layer. The internal stress can cause the molecular chains of the aqueous film-forming substances in the movable layer to break, the molecular weight to decrease significantly, and a large number of pores to be generated in the movable layer, resulting in volume expansion. This significantly reduces the adhesion, rigidity, and strength between the movable layer and the substrate layer, thereby allowing the movable layer to be removed from the substrate layer.

[0069] Meanwhile, aqueous film-forming substances with a three-dimensional network structure can undergo thermal swelling and dissociation under wet heating conditions because: (1) High temperature will activate and destroy the cross-linked structure of aqueous film-forming substances. Specifically, the energy provided by the wet heating environment can destroy secondary forces such as hydrogen bonds and van der Waals forces between molecules of aqueous film-forming substances, leading to the loosening of the cross-linked network. Furthermore, if the aqueous film-forming substance contains heat-sensitive groups, such as ester groups and ether bonds, the wet heating environment may also cause the chemical bonds of the heat-sensitive groups to break. (2) Exposure and swelling of hydrophilic groups. Specifically, under wet heating conditions, the movement of resin chain segments intensifies, and the originally encapsulated hydrophilic groups are re-exposed, combining with water molecules to form hydrogen bonds, triggering thermal swelling and dissociation of the mobile layer. When the thermal swelling and dissociation is at a moderate limit, the mobile layer softens and the adhesion is greatly reduced. When the thermal swelling and dissociation is at a full limit, the mobile layer is in a colloidal state. When the degree of swelling exceeds the tolerance limit of the cross-linked network, the mobile layer may even gradually dissolve in hot water. Therefore, the mobile layer that has undergone thermal swelling and dissociation can be removed by scraping or by dissolving it directly.

[0070] It should be noted that thermo-induced swelling dissociation only causes the hydrogen bonds of the molecules of the aqueous film-forming substance to break, and thermo-induced swelling dissociation is partially reversible. When the water dries, although the mobile layer still has a complete film structure, the adhesion will be greatly reduced.

[0071] Optionally, wet heating can be water bath heating or steam heating.

[0072] Preferably, the wet heating method is steam heating, which can produce the following beneficial effects:

[0073] (1) When high-temperature steam acts on the movable layer, it condenses to form water droplets and releases a large amount of heat, causing the temperature of the movable layer to reach 120℃-150℃ in a very short time. This temperature is exactly within the optimal foaming temperature range of most foamed materials. This temperature can cause the foamed material to generate ultimate internal stress and cause the movable layer to undergo sufficient thermally induced rupture and disintegration. In addition, when the foamed material is foamed microspheres, the condensed water droplets can also protect the foamed microspheres and prevent the shell material of the microspheres from melting due to excessive temperature.

[0074] (2) The high-temperature steam provided by the steam heating environment can enter the interior of the movable layer through the pores. The high-temperature steam can simultaneously cause thermal swelling and dissociation of the aqueous film-forming material on the surface and inside the movable layer. Thermal swelling and dissociation can destroy the original hydrogen bonds between the molecules of the aqueous film-forming material and combine with water molecules to generate new hydrogen bonds, thereby causing the molecular chains of the aqueous film-forming material with a three-dimensional network structure to break and the molecular weight to decrease significantly. Externally, this manifests as a significant decrease in the adhesion, rigidity and strength of the movable layer while maintaining its hierarchical structure. The significant decrease in the adhesion, rigidity and strength of the movable layer helps to further enhance the effect of thermal cracking and dissociation. By controlling the heating time, the degree of thermal dissociation can be controlled. When the thermal swelling and dissociation is at a moderate limit and the thermal cracking and dissociation is at a fully developed level, the dual dissociation synergistic effect ultimately causes the movable layer to disintegrate into powder polymerized by low adhesion. The powder polymerized by low adhesion can be easily removed by scraping or adsorption, thereby greatly enhancing the removal efficiency of the movable layer.

[0075] It should be understood that when steam heating time is excessive, the liquid water produced by steam condensation continues to increase, thus allowing the movable layer to undergo sufficient thermal swelling and dissociation. Therefore, the ideal steam heating time is 2-4 seconds.

[0076] It should be noted that the disintegration phenomenon generated by moderate thermal swelling and disintegration and full thermal rupture is something that cannot be achieved by dry heating, nor by other wet heating methods, and is something that existing foaming processes need to avoid as much as possible.

[0077] (3) Steam heating has fast heat conduction and short time consumption, and can significantly reduce the deformation of the substrate. Comparative experiments show that in order to cause moderate thermal dissociation of the movable layer, steam heating takes 2-4 seconds, water bath heating takes 3-5 seconds, hot pressing takes 6-8 seconds, and infrared heating takes 30-120 seconds.

[0078] (4) The movable layer obtained by steam heating has a high moisture content and is polymerized together with low binding force. Therefore, dust pollution will not be generated during the cleaning operation.

[0079] (5) Steam heating does not produce wastewater and is environmentally friendly.

[0080] In another embodiment, the water-based coating also includes 3 to 15 parts of water-containing material, the specific environment being a dry heating environment, and the thermal dissociation including thermally induced cracking dissociation and dethermally induced swelling dissociation.

[0081] Specifically, the removable layer contains both foaming material and aqueous material. When the ambient temperature is higher than the induction temperature, the foaming material causes thermally induced cracking and dissociation of the removable layer. The aqueous material contains free water or water of crystallization, which releases water molecules at high temperatures. These water molecules can undergo limited thermal swelling and dissociation with the aqueous film-forming substance. The synergistic effect of both thermally induced cracking and limited thermal swelling significantly reduces the adhesion of the removable layer, allowing it to be removed.

[0082] The application scenario of this implementation is as follows: In the traditional tinplate printing field, the ink is thermosetting ink, which needs to be baked at 130℃-170℃ for 10-15 minutes after printing. When the water-based coating only contains foaming material, after forming a removable layer, because the heating time required for the foaming material to foam is much shorter than the drying time of the thermosetting ink, the thermosetting ink is not dry while the foaming material is foaming, and it still has good flexibility. The layered ink layer can maintain an intact hierarchical structure through stretching deformation. External water vapor cannot penetrate the ink layer to the removable layer. Therefore, the removable layer only undergoes thermal cracking and dissociation. At the same time, because the heating temperature is higher than 130℃, the high temperature will promote the crosslinking of the water-based film-forming substance. Overall, the internal stress generated by the foaming material will be less than the chemical bond energy of the three-dimensional network structure. Therefore, the removable layer still maintains high adhesion and is difficult to remove. However, when water-based coatings contain both foaming materials and water-containing materials, after the movable layer is prepared, it is in a sealed state due to the barrier effect of the base layer and ink. In the sealed environment, the high temperature causes a large number of water molecules released by the water-containing materials, which can transform the external dry heating environment into the internal wet heating environment. This causes the movable layer to undergo both thermally induced cracking and dissociation and minimally thermally induced swelling and dissociation, ultimately resulting in a significant reduction in the adhesion of the movable layer.

[0083] Optionally, the aqueous materials include, but are not limited to: sulfate hydrates, carbonate hydrates, aqueous chlorides, aqueous silicates, aqueous organic acid salts, and aqueous phosphates.

[0084] Optionally, the sulfate salts include, but are not limited to: copper sulfate pentahydrate, ferrous sulfate heptahydrate, sodium sulfate decahydrate, zinc sulfate heptahydrate, magnesium sulfate heptahydrate, nickel sulfate hexahydrate, potassium aluminum sulfate dodecahydrate, cobalt sulfate heptahydrate, magnesium sulfate hexahydrate, chromium sulfate nonahydrate, calcium sulfate dihydrate, and manganese sulfate pentahydrate.

[0085] Optionally, carbonate hydrates include, but are not limited to: magnesium carbonate pentahydrate, magnesium carbonate trihydrate, sodium carbonate decahydrate, basic copper carbonate, calcium carbonate dihydrate, cobalt carbonate hydrate, nickel carbonate hydrate, zinc carbonate hydrate, barium carbonate hydrate, strontium carbonate hydrate, lithium carbonate monohydrate, and potassium carbonate monohydrate.

[0086] Optionally, the hydrous chlorides include, but are not limited to: magnesium chloride hexahydrate, calcium chloride dihydrate, cobalt chloride hexahydrate, manganese chloride tetrahydrate, nickel chloride hexahydrate, copper chloride dihydrate, ferric chloride hexahydrate, aluminum chloride hexahydrate, stannous chloride tetrahydrate, and strontium chloride hexahydrate.

[0087] Optionally, hydrated silicates include, but are not limited to: hydrated silica gel, hydrated sodium silicate, hydrated zeolite, hydrated bentonite, and hydrated sepiolite.

[0088] Optionally, the hydrous organic acid salts include, but are not limited to: sodium acetate trihydrate, sodium citrate dihydrate, ferrous ammonium sulfate heptahydrate, potassium antimony tartrate tetrahydrate, and sodium tartrate dihydrate.

[0089] Optionally, the hydrous phosphates include, but are not limited to: sodium dihydrogen phosphate dihydrate, potassium dihydrogen phosphate monohydrate, ammonium dihydrogen phosphate hydrate, disodium hydrogen phosphate dodecahydrate, dipotassium hydrogen phosphate trihydrate, trisodium phosphate dodecahydrate, sodium pyrophosphate decahydrate, copper pyrophosphate dihydrate, sodium hexametaphosphate hydrate, calcium hydrogen phosphate dihydrate, and sodium tripolyphosphate hexahydrate.

[0090] In another embodiment, the specific environment includes a dry heating environment and a wet heating environment sequentially, and the thermally induced dissociation includes thermally induced cracking dissociation and thermally induced swelling dissociation sequentially.

[0091] Specifically, dry heating is first used to foam the foaming material in the removable layer. The internal stress generated by the foaming material causes thermal rupture and dissociation of the removable layer. This thermal rupture and dissociation reduces the molecular weight of the aqueous film-forming substance, decreases the adhesion, and creates numerous pores in the removable layer, while maintaining the integrity of the layer's hierarchical structure. After proofing and printing, wet heating is used to cause thermal swelling and dissociation of the aqueous film-forming substance in the removable layer, thereby significantly reducing the adhesion of the removable layer.

[0092] Preferably, the thermally induced cracking dissociation is a minimal thermally induced cracking dissociation. Minimal thermally induced cracking dissociation allows the movable layer to maintain strong adhesion while generating a large number of pores, thereby preventing powder shedding from the movable layer during the printing process due to low adhesion, which would affect the printing quality.

[0093] Specifically, the degree of thermally induced decomposition can be controlled by adjusting the temperature and time of dry heating, thereby controlling the size and number of pores.

[0094] It should be noted that during the dry heating process, the upper limit of the temperature needs to be controlled to prevent the aqueous film-forming substances in the movable layer from fully cross-linking and solidifying due to high temperature.

[0095] Preferably, the dry heating method is infrared or hot air heating, and the heating temperature is 70℃-130℃.

[0096] Furthermore, the dry heating method is infrared heating, with a heating temperature of 70℃-100℃.

[0097] Preferably, the wet heating method is steam heating.

[0098] One possible application scenario for this implementation is as follows: In the field of conventional offset printing, the drying methods for conventional offset printing inks are penetration drying and oxidative film-forming drying. After the removable layer undergoes minimal thermal rupture and dissociation through dry heating, a large number of micropores will be generated in the removable layer. These micropores can create conditions for the penetration drying of conventional offset printing inks. After the printing process is completed, the removable layer can be easily removed by simply applying wet heating to the printed sheet to cause moderate thermal swelling and dissociation of the removable layer.

[0099] In another embodiment, the water-based coating also includes 1 to 10 parts of adsorbent material. By adding adsorbent material, the adsorption of the movable layer can be increased, thereby improving the adsorption and drying effect of the movable layer on ink during proofing and printing.

[0100] Optionally, the adsorbent material includes, but is not limited to, zeolite powder, titanium dioxide, and silica powder.

[0101] The aforementioned water-based coating, after being applied to a substrate and dried to form a movable layer, allows the water-based film-forming substances to undergo physical fusion or chemical cross-linking to form a three-dimensional network structure. Under specific conditions, the foaming material can foam, and the internal stress generated during the foaming process can cause the water-based film-forming substances with the three-dimensional network structure to undergo thermally induced rupture and dissociation, resulting in a significant reduction in the molecular weight of the water-based film-forming substances. Consequently, the adhesion of the movable layer is significantly reduced, allowing it to be removed. Therefore, the aforementioned water-based coating can be used to prepare reusable substrates.

[0102] The application of any of the above-mentioned water-based coatings in a substrate. A reusable substrate can be prepared, and by removing the removable layer, the base layer can be reused, thereby significantly reducing material costs.

[0103] It should be noted that the descriptive terms such as "minimum," "moderate," and "sufficient" used in this specification are relative classifications based on the implementation gradient of the technical solution and do not constitute absolute quantitative standards. These classifications can be made using the following technical indicators:

[0104] (1) "Minimum" refers to the minimum necessary degree of implementation to achieve the basic function of the technical solution. For example, when the aqueous film-forming substance undergoes minimum thermal swelling and dissociation, the water content of the movable layer is 5% to 40% (excluding); when the aqueous film-forming substance undergoes minimum thermal cracking and dissociation, the volume of the foaming material in the movable layer increases by 5% to 40% (excluding).

[0105] (2) "Moderate limit" refers to the typical degree in the conventional implementation conditions in this field, such as when the aqueous film-forming material undergoes moderate thermal swelling and dissociation, the water content of the movable layer is 40% to 80% (excluding); when the aqueous film-forming material undergoes moderate thermal cracking and dissociation, the volume of the foaming material in the movable layer increases by 40% to 80% (excluding).

[0106] (3) “Sufficient” refers to the degree to which the optimal implementation effect is achieved or exceeded. For example, when the aqueous film-forming substance undergoes sufficient thermal swelling and dissociation, the water content of the movable layer reaches more than 80%; when the aqueous film-forming substance undergoes sufficient thermal rupture and dissociation, the volume of the foaming material in the movable layer increases by more than 80%.

[0107] The following are specific examples.

[0108] Example 1

[0109] This embodiment provides a water-based coating comprising 70 parts of a water-based film-forming substance and 1 part of a foaming material. In this embodiment, the water-based film-forming substance is a water-based acrylic copolymer resin emulsion, provided by Guangdong Bohai Chemical Technology Co., Ltd., with product number WE1225B. The foaming material is expanded graphite, provided by Shanghai Youmo Composite Materials Co., Ltd., with product number PX and a particle size of 1000 mesh.

[0110] The aforementioned water-based coating, after being applied to a substrate and dried to form a movable layer, allows the water-based film-forming substances to undergo physical fusion or chemical cross-linking to form a three-dimensional network structure. Under dry heating conditions, the foaming material can foam, and the internal stress generated during the foaming process can cause the water-based film-forming substances with the three-dimensional network structure to undergo thermally induced rupture and dissociation, resulting in a significant reduction in the molecular weight of the water-based film-forming substances. Consequently, the adhesion of the movable layer is significantly reduced, allowing it to be removed. Therefore, the aforementioned water-based coating can be used to prepare reusable substrates.

[0111] Example 2

[0112] This embodiment provides a water-based coating comprising 80 parts of water-based film-forming substance and 5 parts of foaming material.

[0113] In this embodiment, the aqueous film-forming substance is an aqueous polyurethane resin emulsion, provided by Guangzhou Ruilin New Materials Co., Ltd., model number RL-8302. The foaming material is foamed microspheres, provided by Shanghai Xuyun New Materials Technology Co., Ltd., model number XL714H.

[0114] After the above-mentioned water-based coating is applied to the substrate and dried to form a movable layer, the water-based film-forming substance can undergo both thermally induced cracking dissociation and moderately thermally induced swelling dissociation in a steam heating environment. This dual dissociation helps to significantly improve the removal efficiency of the movable layer.

[0115] Example 3

[0116] This embodiment provides a water-based coating comprising 90 parts of water-based film-forming substance, 10 parts of foaming material and 3 parts of water-containing material.

[0117] In this embodiment, the aqueous film-forming substance is an aqueous polyurethane resin emulsion, provided by Guangzhou Ruilin New Materials Co., Ltd., model number RL-8302. The foaming material is foamed microspheres, provided by Shanghai Xuyun New Materials Technology Co., Ltd., model number XL714H. The aqueous material is magnesium carbonate pentahydrate.

[0118] The aforementioned water-based coating, after being applied to a substrate and dried to form a removable layer, allows the foaming material to cause thermally induced particle size reduction in the water-based film-forming substance under dry heating conditions. The water molecules released by the water-containing material cause minimal thermal swelling and dissociation of the water-based film-forming substance. Under the synergistic effect of both thermally induced particle size reduction and minimal thermal swelling, the adhesion of the removable layer is significantly reduced, allowing it to be removed. This water-based coating can be used for traditional tinplate printing.

[0119] Example 4

[0120] This embodiment provides a water-based coating comprising 99 parts of a water-based film-forming substance, 15 parts of a foaming material, and 15 parts of a water-containing material.

[0121] In this embodiment, the aqueous film-forming substance is a commercially available aqueous varnish, model TLAV701, provided by Guangdong Tianlong Ink Group Co., Ltd. The foaming material is 4,4'-oxobis(benzenesulfonyl)hydrazine (OBSH), provided by Shanghai Longdi Chemical Co., Ltd., model LANXESS OBSH-75. The aqueous material is sodium acetate trihydrate.

[0122] The aforementioned water-based coatings use commercially available water-based varnishes as water-based film-forming substances. The additives in the water-based varnishes help improve the printability or coating suitability of the water-based coatings.

[0123] Example 5

[0124] This embodiment provides a water-based coating, which is similar to the water-based coating provided in Example 5, except that the foaming material is azobisisobutyronitrile, provided by Shandong Yousheng Chemical Co., Ltd., with item number 1888 and a mass fraction of 20 parts.

[0125] The aforementioned water-based coating first employs dry heating to cause minimal thermal cracking and separation of the removable layer. After printing and proofreading, wet heating is then used to cause moderate thermal swelling and dissociation of the water-based film-forming substances in the removable layer, thereby significantly reducing the adhesion of the removable layer.

[0126] Example 6

[0127] This embodiment provides a water-based coating, which is similar to the water-based coating provided in Example 6, except that the foaming material is sodium bicarbonate, provided by Guangzhou Lailedi New Materials Co., Ltd., model number 365, in parts by weight of 30.

[0128] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method of removing a removable layer, characterized by, The removable layer is formed by coating and drying the water-based paint on the base layer; The water-based paint includes the following components in mass parts: Water-based film-forming substance 70-99 parts; and Foaming material 1-30 parts; After the water-based paint is dried to form the removable layer, the foaming material is foamed and the water-based film-forming substance is fully thermally broken and moderately thermally swelled and dissolved under the heating for 2-4 seconds in a steam environment, and the removable layer is broken into powder by low bonding force and removed from the base layer under the synergistic effect of the double dissolution; When the water-based film-forming substance is moderately thermally swelled and dissolved, the water content of the removable layer is greater than or equal to 40% and less than 80%; when the water-based film-forming substance is fully thermally broken, the volume of the foaming material in the removable layer is increased by more than 80%; the water-based film-forming substance is selected from at least one of polyurethane resin, acrylic resin, polyvinyl alcohol and modified resin thereof, polyethylene oxide-based resin, starch and derivatives thereof, and polyvinylpyrrolidone; the foaming material is selected from at least one of physical foaming material, chemical foaming material, and inorganic foaming material; the physical foaming material is selected from any one of foaming microspheres, expanded graphite, vermiculite powder, and expanded hexagonal boron nitride; the chemical foaming material is selected from any one of azo-based foaming material, carbonate-based foaming material, and hydrazine-based foaming material; the inorganic foaming material is selected from any one of metal hydride foaming material and silicate-based foaming material.

2. The method of claim 1, wherein, The foaming material has an initiation temperature of 60-200℃.

3. The method of claim 1, wherein the removable layer is removed by a method selected from the group consisting of: The foaming material has a particle size of 1-50 microns. ​