An easy-to-tear cover aluminum foil and a method for manufacturing the same

Abstract

The application discloses an easy-to-tear cover aluminum foil and a preparation method thereof. The preparation method comprises the following steps: unwinding the aluminum foil; coating a protective agent on one side of the aluminum foil to form a protective agent coating; performing flash drying on the protective agent coating, wherein the flash drying is performed by using infrared radiation heating, the radiation wavelength is 2-4 micrometers, the radiation intensity is 50-80 kW / m2, the flash drying time is 1-3 seconds, and the surface temperature of the protective agent coating after the flash drying is 80-100 DEG C and the surface is in a semi-dry film state; coating heat-sealing glue on the other side of the aluminum foil, so that the heat-sealing glue is in contact with and penetrates into the semi-dry protective agent coating to form an interpenetrating transition layer; performing one-time heating and drying on the aluminum foil, so that the protective agent coating and the heat-sealing glue are simultaneously solidified, and the one-time heating and drying temperature is not higher than 180 DEG C; and cooling and winding the dried aluminum foil. According to the technical scheme, the aluminum foil grain growth is inhibited, the tensile strength and the elongation rate are kept excellent. Meanwhile, a one-time cooling step is omitted, the production line length is shortened, and the equipment investment and energy consumption are reduced.

Description

Technical Field

[0001] This invention relates to the field of easy-tear aluminum foil technology, specifically to an easy-tear aluminum foil and its preparation method. Background Technology

[0002] Currently, the easy-tear cap solution used for sealing food cans such as milk powder cans and coffee cans consists of tinplate, plain iron, coated iron cap ring, and aluminum foil film. The aluminum foil film refers to a sealing film made by coating aluminum foil with a coating material.

[0003] A prior Chinese patent discloses a method for preparing an easy-tear aluminum foil, comprising the following steps: (1) unwinding the aluminum foil; (2) applying a protective agent with a coating amount of 1.0-1.2 g / m²; (3) heating and drying in a drying chamber at a temperature of 190-210℃; (4) cooling the protective layer; (5) applying a heat-sealing adhesive with a coating amount of 9.5-11.0 g / m²; (6) heating and drying in a drying chamber at a temperature of 160-200℃; (7) cooling the heat-sealing layer; and (8) winding the aluminum foil.

[0004] However, the aluminum foil preparation process in this invention has the following problems: after the protective agent is applied, it needs to be completely dried in a drying chamber at a temperature of 190 to 210 degrees Celsius, then cooled to 40 to 45 degrees Celsius. A heat-sealing adhesive is then applied to the other side of the aluminum foil, followed by heating and drying again to 160 to 200 degrees Celsius, and then cooling again. In this process, the aluminum foil undergoes two cycles of high-temperature drying and cooling. During the first drying, the aluminum foil temperature approaches 200 degrees Celsius, then drops sharply to 40 degrees Celsius during cooling. During the second drying, the temperature rises again to over 160 degrees Celsius, and then drops sharply again during cooling. Aluminum foil is a thin metal material, typically 0.02 to 0.05 millimeters thick. Repeated thermal cycling causes the internal grains of the aluminum foil to recover and recrystallize, resulting in grain size growth and a decrease in dislocation density. Macroscopically, this manifests as a decrease in tensile strength and elongation. Furthermore, the two drying cycles require two sets of heating and cooling equipment, leading to high energy consumption. The intermediate cooling step also occupies production line space, limiting production efficiency. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, the present invention provides a method for preparing an easy-tear aluminum foil cover to solve at least some of the technical problems mentioned in the background art.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing an easy-tear aluminum foil cover, comprising the following steps: Aluminum foil unwinding; A protective agent is applied to one side of the aluminum foil to form a protective agent coating. The protective agent coating is flash-baked using infrared radiation heating with a radiation wavelength of 2-4 μm, a radiation intensity of 50-80 kW / m², and a flash-baking time of 1-3 seconds. After flash-baking, the surface temperature of the protective agent coating is 80-100℃ and the surface is in a semi-dry film state. Heat-sealing adhesive is applied to the other side of the aluminum foil, allowing the heat-sealing adhesive to come into contact with and penetrate the semi-dry protective coating, forming an interpenetrating transition layer. The aluminum foil is subjected to a single heating and drying process to simultaneously cure the protective coating and the heat sealant. The temperature of the single heating and drying process does not exceed 180°C. The dried aluminum foil is cooled and then wound up.

[0007] The specific effects of this invention are as follows: First, this invention combines two drying processes into a single drying process, the core of which lies in the design of the flash drying step. Specifically, after the protective agent is applied, it is not subjected to complete drying and cooling, but instead undergoes flash drying. Flash drying uses infrared radiation heating with a wavelength of two to four micrometers. This wavelength range falls within the characteristic absorption peaks of carbonyl and hydroxyl groups in acrylic resin. The energy is preferentially absorbed by the protective agent coating rather than penetrating to the aluminum foil itself, thus limiting the temperature rise of the aluminum foil. The radiation intensity is fifty to eighty kilowatts per square meter, and the flash drying time is one to three seconds. Under this high-intensity, short-duration energy input, the solvent on the surface of the protective agent coating evaporates rapidly, forming a semi-dry film. The surface resin undergoes initial cross-linking and shaping, but 40% to 50% of the solvent remains internally. After flash drying, the surface temperature of the protective agent coating is eighty to one hundred degrees Celsius. This temperature is higher than the boiling point of ethyl acetate, ensuring sufficient removal of the surface solvent, but it is lower than the glass transition temperature of acrylic resin. The resin is not completely cured, and the coating still retains flexibility.

[0008] Secondly, since the protective coating is in a semi-dry film state after flash drying, the heat-sealing adhesive is directly applied to the other side of the aluminum foil without a cooling step. At this time, the overall temperature of the aluminum foil is still close to 80 to 100 degrees Celsius. When the heat-sealing adhesive is applied to the aluminum foil surface, the solvent in the heat-sealing adhesive is preheated upon contact with the high-temperature aluminum foil, reducing its viscosity and facilitating leveling and wetting of the aluminum foil surface. Subsequently, the aluminum foil directly enters a primary heating and drying process, with the temperature not exceeding 180 degrees Celsius. During the primary heating and drying process, the coatings on both sides of the aluminum foil are heated simultaneously. The residual solvent in the protective coating evaporates from the surface to the gas phase and migrates from the interior to the surface; the solvent in the heat-sealing adhesive coating also migrates from the interior to the surface and evaporates. The coatings on both sides cure simultaneously, resulting in symmetrical thermal stress on both sides of the aluminum foil. This avoids the asymmetrical thermal stress caused by drying one side first and then the other side in existing technologies, thereby reducing aluminum foil warping.

[0009] Finally, the aluminum foil undergoes only one process of heating from room temperature to below 180 degrees Celsius and then cooling, instead of the two heating to around 200 degrees Celsius as in existing technologies. According to the principles of heat treatment of metallic materials, the recrystallization temperature of aluminum foil is approximately 150 degrees Celsius. Existing technologies involve two exposures to high temperatures approaching or exceeding 200 degrees Celsius, resulting in a long cumulative heat treatment time and significant grain growth. In this embodiment, the highest drying temperature does not exceed 180 degrees Celsius, and the cumulative heat treatment time is shortened by approximately 40%, thus suppressing grain growth and maintaining excellent tensile strength and elongation. Simultaneously, the elimination of a cooling step shortens the production line length and reduces equipment investment and energy consumption.

[0010] Optionally, the primary heating and drying adopts a gradient temperature increase method, which includes a low-temperature volatilization zone, a medium-temperature curing zone, and a high-temperature setting zone in sequence. The temperature of the low-temperature volatilization zone is 60-80℃, the temperature of the medium-temperature curing zone is 100-130℃, and the temperature of the high-temperature setting zone is 150-180℃.

[0011] The specific effects of this invention are as follows: This invention divides the single-stage heating and drying process into three temperature zones: a low-temperature evaporation zone, a medium-temperature curing zone, and a high-temperature setting zone. In the low-temperature evaporation zone, the temperature is 60-80 degrees Celsius. This temperature is below the solvent's boiling point but sufficient to provide the driving force for evaporation. The solvent on the surface of the heat-sealing adhesive slowly migrates to the surface, preventing the formation of a hard shell, and keeping the internal solvent channels unobstructed. Residual solvent inside the protective agent also migrates to the surface simultaneously, escaping from the micropores of the film formed during flash drying. In the medium-temperature curing zone, the temperature is 100-130 degrees Celsius. The resin molecular chains begin to crosslink, but the crosslinking density is controlled. The coating maintains its microporous structure, allowing the solvent to continue escaping. Simultaneously, the resin viscosity increases, and the coating sets. In the high-temperature setting zone, the temperature is 150-180 degrees Celsius. The resin is completely crosslinked, and the coating becomes dense. The three temperature zones are sequentially connected, allowing the solvent to migrate gradually from the inside of the coating to the outside. The evaporation rate matches the crosslinking rate, resulting in uniform, bubble-free curing of the coating and a smooth, pinhole-free surface.

[0012] Optionally, the duration of the low-temperature evaporation zone is 40%-50% of the total duration of the single heating and drying, the duration of the medium-temperature curing zone is 30%-40% of the total duration of the single heating and drying, and the duration of the high-temperature setting zone is 10%-20% of the total duration of the single heating and drying.

[0013] The specific effects of this invention are as follows: In this invention, the low-temperature evaporation zone accounts for 40% to 50% of the total heating and drying time. At this ratio, the solvent has sufficient time to migrate to the coating surface and evaporate, while the resin undergoes only slight pre-crosslinking, which does not affect subsequent setting. The medium-temperature curing zone accounts for 30% to 40%, during which the resin gradually crosslinks while maintaining its microporous structure, and the coating gradually hardens from the inside out. The high-temperature setting zone accounts for 10% to 20%, sufficient to complete the final crosslinking without excessive baking, avoiding resin thermal degradation and yellowing. With this time allocation, the solvent evaporation rate matches the resin crosslinking rate, the coating gradually hardens from the surface to the inside, and the internal and external stresses are uniform, avoiding curling and deformation caused by a hardened surface and a soft inner layer. The final coating exhibits excellent smoothness and gloss.

[0014] Optionally, during the primary heating and drying process, a suction device is provided on the side of the aluminum foil coated with heat-sealing adhesive, and the air velocity of the suction device is 3-5 m / s; a blowing device is provided on the side of the aluminum foil coated with protective agent, and the blowing device blows an airflow with a temperature of 40-60℃ and an air velocity of 5-8 m / s.

[0015] The specific effects of this invention are as follows: An air suction device with a wind speed of three to five meters per second is installed on the heat-sealing adhesive side to promptly remove solvent vapor from the heat-sealing adhesive surface, maintaining the concentration gradient between the coating surface and the gas phase and promoting continuous solvent evaporation. A blowing device is installed on the protective agent side, blowing an airflow at a temperature of forty to sixty degrees Celsius with a wind speed of five to eight meters per second. This temperature is lower than the drying zone temperature but higher than room temperature, cooling the aluminum foil to prevent thermal annealing and dispersing the solvent vapor trapped in the gaps on the back of the aluminum foil. This reduces the partial pressure of the solvent in the gas phase on the protective agent side, forming a concentration gradient from the protective agent coating to the gas phase, causing residual solvent in the protective agent to migrate to the surface and be discharged. The differentiated ventilation design on both sides ensures that the heat-sealing adhesive solvent is drawn upwards and the protective agent solvent is blown downwards, with no interference between the solvent discharge paths on both sides. This allows both coating layers to dry simultaneously and thoroughly, further shortening the drying time.

[0016] Optionally, the protective agent includes acrylic resin and solvent, and the heat sealant includes acrylic resin, olefin resin and solvent. The acrylic resin in the protective agent has a molecular weight of 5,000-15,000, and the acrylic resin in the heat sealant has a molecular weight of 20,000-50,000.

[0017] The specific effects of this invention are as follows: This invention limits the molecular weight of the acrylic resin in the protective agent to 5,000 to 15,000. This molecular weight range ensures moderate viscosity of the protective agent solution, good leveling properties during coating, a dense and continuous coating after drying, and a certain degree of flexibility to adapt to aluminum foil stamping deformation. The function of the heat-sealing adhesive is to heat-seal and bond with the tinplate cap ring, requiring high cohesive strength and heat-sealing strength. If the resin molecular weight is too low, the cohesive strength of the heat-sealing adhesive is insufficient, making it prone to stringing or peeling during heat sealing; if the molecular weight is too high, the solution viscosity is high, making it difficult to accurately control the coating amount, and narrowing the heat-sealing temperature window with the tinplate. This invention limits the molecular weight of the acrylic resin in the heat-sealing adhesive to 20,000 to 50,000. This molecular weight range ensures sufficient cohesive strength and heat-sealing strength in the heat-sealing adhesive, while allowing for controllable solution viscosity and precise coating amount. The difference in molecular weight between the two resins optimizes the functions of both the protective agent and the heat-sealing adhesive. The thin layer of the protective agent is flexible and dense, while the thick layer of the heat-sealing adhesive is strong and adhesive. During the first drying process, the two resins cure simultaneously within their respective temperature windows without interfering with each other.

[0018] Optionally, the acrylic resin in the protective agent has hydroxyl and carboxyl functional groups, and the acrylic resin in the heat sealant has epoxy and amino functional groups. When the semi-dry film-state protective agent coating comes into contact with the heat sealant, the hydroxyl and carboxyl groups in the protective agent undergo a condensation reaction with the epoxy and amino groups in the heat sealant in the high-temperature setting zone to form chemical bonds.

[0019] The specific effects of this invention are as follows: the hydroxyl and carboxyl groups in the protective agent are polar functional groups, giving the protective agent an affinity for the aluminum foil surface; the epoxy and amino groups in the heat sealant are reactive functional groups, giving the heat sealant adhesion to tinplate and its own cross-linking ability. In the high-temperature setting zone during the single-stage heating and drying process, at a temperature of 150 to 180 degrees Celsius, the hydroxyl and carboxyl groups in the protective agent can form hydrogen bonds or coordination bonds with the alumina layer on the aluminum foil surface, enhancing the adhesion between the protective agent and the aluminum foil; simultaneously, the epoxy groups in the heat sealant, after ring opening, react with the amino groups to form a three-dimensional cross-linked network, improving the strength and heat resistance of the heat sealant. More importantly, in the high-temperature setting zone, the hydroxyl and carboxyl groups remaining on the surface of the protective agent may undergo a trace condensation reaction with the epoxy and amino groups that have penetrated from the heat sealant, forming a chemical bridge in the aluminum foil interface area, indirectly connecting the coatings on both sides through chemical bonding on the aluminum foil surface, resulting in a more robust overall structure. The bond energy of this chemical bond is much higher than that of the intermolecular forces, which ensures that the coating and aluminum foil will not separate during subsequent high-temperature sterilization at 121 degrees Celsius or stamping processes, and the heat-sealing adhesive layer remains intact and does not degrade.

[0020] Optionally, the flash drying is performed using far-infrared radiation heating, wherein the wavelength of the far-infrared radiation is 3-4μm, the radiation intensity is 60-70kW / m², the flash drying time is 1.5-2.5 seconds, and the surface temperature of the protective agent coating after flash drying is 85-95℃.

[0021] The specific effects of this invention are as follows: the flash drying parameters are further limited to a far-infrared radiation wavelength of 3 to 4 micrometers, a radiation intensity of 60 to 70 kilowatts per square meter, a time of 1.5 to 2.5 seconds, and a surface temperature of 85 to 95 degrees Celsius. The wavelength of 3 to 4 micrometers is at the strong absorption peak of the carbonyl group in the acrylic resin. The energy is absorbed by the coating surface, resulting in shallow penetration. The aluminum foil itself absorbs little energy, and the temperature rise is controlled within 10 degrees Celsius, preventing thermal softening of the aluminum foil during the flash drying stage. The product of the radiation intensity of 60 to 70 kilowatts per square meter and the time of 1.5 to 2.5 seconds results in an energy input of 90 to 175 kilojoules per square meter. This energy is sufficient to evaporate the surface solvent and form a film, but insufficient to completely remove the internal solvent. The surface temperature is 85 to 95 degrees Celsius, which is about 8 to 18 degrees Celsius higher than the boiling point of ethyl acetate (77 degrees Celsius). This provides sufficient kinetic energy for solvent removal from the surface layer, but is below the boiling point of water. If the protective agent contains trace amounts of moisture, the moisture will not be removed and will remain inside the coating, preventing embrittlement caused by excessive drying. Within this parameter window, the stability of the semi-dry film is optimal, and the curing behavior of the coating during subsequent drying is controllable.

[0022] Optionally, the surface viscosity of the protective coating after flash baking is 500-2000 mPa·s, and the surface viscosity is detected by an online rotational viscometer.

[0023] The specific effects of this invention are as follows: a surface viscosity of 500 to 2000 mPa·s is a quantifiable characterization of the semi-dry film state, forming a dual control guarantee with flash drying parameters. When the viscosity is below 500 mPa·s, the coating is close to a fluid state, easily causing sagging due to gravity or tension during aluminum foil travel, resulting in uneven coating thickness and edge accumulation. When the viscosity is above 2000 mPa·s, the coating is too hard, leading to poor resin chain mobility during subsequent drying, reduced wetting and anchoring effects on the aluminum foil surface, and decreased adhesion. Through real-time detection using an online rotary viscometer, the operator can directly adjust the flash drying radiation intensity or time based on the viscosity reading, eliminating the need for offline sampling and weighing, thus achieving closed-loop control of the production process. When the viscosity deviates from the target range, the system automatically adjusts the radiation intensity or travel speed to ensure the consistency of the semi-dry state of each roll of aluminum foil, thereby guaranteeing uniform and stable coating thickness and performance of the final product.

[0024] Optionally, the thickness of the aluminum foil is 0.02-0.05 mm, the coating amount of the protective agent is 1.0-1.2 g / m², and the coating amount of the heat sealant is 9.5-11.0 g / m².

[0025] The specific effects of this invention are as follows: The aluminum foil thickness is 0.02 to 0.05 mm, which balances the formability and barrier properties of the easy-tear cap. A thickness below 0.02 mm results in a high pinhole rate, increased oxygen permeability, insufficient barrier properties, and easy breakage during stamping; a thickness above 0.05 mm results in a high tearing force, making it difficult for the elderly or children to open, and increasing material costs. The protective agent coating amount is 1.0 to 1.2 grams per square meter, corresponding to a dry film thickness of 2 to 3 micrometers. This thickness is sufficient to form a continuous protective layer covering pinholes and defects on the aluminum foil surface, but excessive thickness increases costs and reduces the flexibility of the aluminum foil, making the protective agent layer prone to cracking during stamping. The heat-sealing adhesive coating amount is 9.5 to 11.0 grams per square meter, corresponding to a dry film thickness of 8 to 10 micrometers. This thickness ensures a heat-sealing strength of at least 15 Newtons per 15 millimeters with the tinplate cap ring, but excessive thickness prolongs drying time and increases the internal stress of the heat-sealing adhesive, making it prone to delamination after long-term storage. The above parameters are matched with the flash drying and single-stage drying processes. The thin layer of protective agent quickly reaches a semi-dry state after flash drying, and the thick layer of heat sealant has sufficient time to remove solvent in the low-temperature evaporation zone of the single-stage drying. The difference in thickness between the two layers is compensated by the distribution of gradient heating time, and finally the coatings on both sides are cured evenly, and the overall performance of the aluminum foil is balanced.

[0026] A second aspect of the present invention provides an easy-tear aluminum foil, which is prepared by the above-described method for preparing easy-tear aluminum foil.

[0027] The specific effects of this invention are as follows: the aluminum foil undergoes only one high-temperature drying process, resulting in fine grains and excellent mechanical properties; the interface between the coatings on both sides and the aluminum foil is firmly bonded, the protective agent layer is dense and glossy, and the heat-sealing adhesive layer is strong, tough, and heat-resistant. In terms of performance, the aluminum foil exhibits improved tensile strength and elongation, making it less prone to breakage during stamping; the interlayer peel strength is also improved, preventing coating separation during high-temperature sterilization and long-term storage. When this easy-tear lid aluminum foil is used in food packaging such as milk powder cans and coffee cans, the aluminum foil can be completely torn off along the edge of the can upon opening, leaving no residual fragments, ensuring high safety. Furthermore, the bright and attractive appearance of the aluminum foil enhances the product's perceived quality. Attached Figure Description

[0028] Figure 1 This is a schematic flowchart of a method for preparing an easy-tear aluminum foil cover according to the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] like Figure 1As shown, the first aspect of the present invention provides a method for preparing an easy-tear aluminum foil cover, comprising the following steps: Aluminum foil unwinding; A protective agent is applied to one side of the aluminum foil to form a protective coating. The protective coating is flash-baked using infrared radiation heating with a wavelength of 2-4μm, a radiation intensity of 50-80kW / m², and a flash-baking time of 1-3 seconds. After flash-baking, the surface temperature of the protective coating is 80-100℃ and the surface is in a semi-dry film state. Apply heat-sealing adhesive to the other side of the aluminum foil, allowing the heat-sealing adhesive to come into contact with and penetrate the semi-dry protective coating, forming an interpenetrating transition layer; The aluminum foil is heated and dried once to cure the protective coating and heat sealant at the same time. The temperature of the first heating and drying should not exceed 180℃. The dried aluminum foil is cooled and then wound up.

[0031] First, this invention combines two drying processes into a single drying process, the core of which lies in the design of the flash drying step. Specifically, after the protective agent is applied, it is not subjected to complete drying and cooling, but instead undergoes flash drying. Flash drying uses infrared radiation heating with a wavelength of two to four micrometers. This wavelength range falls within the characteristic absorption peaks of the carbonyl and hydroxyl groups in acrylic resin. The energy is preferentially absorbed by the protective agent coating rather than penetrating to the aluminum foil itself, thus limiting the temperature rise of the aluminum foil. The radiation intensity is fifty to eighty kilowatts per square meter, and the flash drying time is one to three seconds. Under this high-intensity, short-duration energy input, the solvent on the surface of the protective agent coating evaporates rapidly, forming a semi-dry film. The surface resin undergoes initial cross-linking and shaping, but 40% to 50% of the solvent remains internally. After flash drying, the surface temperature of the protective agent coating is eighty to one hundred degrees Celsius. This temperature is higher than the boiling point of ethyl acetate, ensuring sufficient removal of the surface solvent, but it is lower than the glass transition temperature of the acrylic resin. The resin is not completely cured, and the coating still retains flexibility.

[0032] Secondly, since the protective coating is in a semi-dry film state after flash drying, the heat-sealing adhesive is directly applied to the other side of the aluminum foil without a cooling step. At this time, the overall temperature of the aluminum foil is still close to 80 to 100 degrees Celsius. When the heat-sealing adhesive is applied to the aluminum foil surface, the solvent in the heat-sealing adhesive is preheated upon contact with the high-temperature aluminum foil, reducing its viscosity and facilitating leveling and wetting of the aluminum foil surface. Subsequently, the aluminum foil directly enters a primary heating and drying process, with the temperature not exceeding 180 degrees Celsius. During the primary heating and drying process, the coatings on both sides of the aluminum foil are heated simultaneously. The residual solvent in the protective coating evaporates from the surface to the gas phase and migrates from the interior to the surface; the solvent in the heat-sealing adhesive coating also migrates from the interior to the surface and evaporates. The coatings on both sides cure simultaneously, resulting in symmetrical thermal stress on both sides of the aluminum foil. This avoids the asymmetrical thermal stress caused by drying one side first and then the other side in existing technologies, thereby reducing aluminum foil warping.

[0033] Finally, the aluminum foil undergoes only one process of heating from room temperature to below 180 degrees Celsius and then cooling, instead of the two heating to around 200 degrees Celsius as in existing technologies. According to the principles of heat treatment of metallic materials, the recrystallization temperature of aluminum foil is approximately 150 degrees Celsius. Existing technologies involve two exposures to high temperatures approaching or exceeding 200 degrees Celsius, resulting in a long cumulative heat treatment time and significant grain growth. In this embodiment, the highest drying temperature does not exceed 180 degrees Celsius, and the cumulative heat treatment time is shortened by approximately 40%, thus suppressing grain growth and maintaining excellent tensile strength and elongation. Simultaneously, the elimination of a cooling step shortens the production line length and reduces equipment investment and energy consumption.

[0034] Considering that if a single high temperature is used for heat drying, the heat-sealing adhesive coating will be quite thick, with a coating amount of 9.5 to 11.0 grams per square meter. The surface solvent will evaporate rapidly, forming a hard shell, while the internal solvent will be sealed in. Vapor pressure buildup will cause the coating to blister. Although the protective coating has undergone flash drying, it still contains solvent. At high temperatures, the solvent expands violently, breaking through the surface film and creating pinholes. As an alternative implementation, the single heat drying process uses a gradient temperature increase, successively including a low-temperature evaporation zone (60-80℃), a medium-temperature curing zone (100-130℃), and a high-temperature setting zone (150-180℃).

[0035] This invention divides the single-stage heating and drying process into three temperature zones: a low-temperature evaporation zone, a medium-temperature curing zone, and a high-temperature setting zone. In the low-temperature evaporation zone, the temperature is 60-80 degrees Celsius. This temperature is below the solvent's boiling point but sufficient to provide the driving force for evaporation. The solvent on the surface of the heat-sealing adhesive slowly migrates to the surface, preventing the formation of a hard shell, and keeping the internal solvent channels unobstructed. Residual solvent inside the protective agent also migrates to the surface simultaneously, escaping from the micropores of the film formed during flash drying. In the medium-temperature curing zone, the temperature is 100-130 degrees Celsius. The resin molecular chains begin to crosslink, but the crosslinking density is controlled. The coating maintains its microporous structure, allowing the solvent to continue escaping. Simultaneously, the resin viscosity increases, and the coating sets. In the high-temperature setting zone, the temperature is 150-180 degrees Celsius. The resin is fully crosslinked, and the coating becomes dense. The three temperature zones are sequentially connected, allowing the solvent to migrate gradually from the inside of the coating to the outside. The evaporation rate matches the crosslinking rate, resulting in a uniform, bubble-free, and smooth surface without pinholes.

[0036] Considering that the duration allocation of the three temperature zones directly affects the balance between solvent evaporation and resin curing, if the low-temperature evaporation zone is too short, the solvent will not migrate sufficiently before entering the medium-temperature curing zone. This causes the resin to prematurely cross-link and seal the solvent channels, leading to solvent vapor accumulation inside the coating and eventually breaking through the surface to form bubbles. Conversely, if the low-temperature evaporation zone is too long, production efficiency will decrease, and excessive pre-crosslinking of the resin will result in insufficient fluidity during subsequent high-temperature setting, leading to poor surface gloss. As an optional implementation, the duration of the low-temperature evaporation zone is 40%-50% of the total drying time for one heating cycle, the medium-temperature curing zone is 30%-40% of the total drying time for one heating cycle, and the high-temperature setting zone is 10%-20% of the total drying time for one heating cycle.

[0037] In this embodiment of the invention, the low-temperature evaporation zone accounts for 40% to 50% of the total heating and drying time. At this ratio, the solvent has sufficient time to migrate to the coating surface and evaporate, while the resin undergoes only slight pre-crosslinking, which does not affect subsequent setting. The medium-temperature curing zone accounts for 30% to 40%, during which the resin gradually crosslinks while maintaining its microporous structure, and the coating gradually hardens from the inside out. The high-temperature setting zone accounts for 10% to 20%, sufficient to complete the final crosslinking without excessive baking, avoiding resin thermal degradation and yellowing. With this time allocation, the solvent evaporation rate matches the resin crosslinking rate, the coating gradually hardens from the surface inwards, and the internal and external stresses are uniform, avoiding curling and deformation caused by a hardened surface and a soft inner layer. The final coating exhibits excellent smoothness and gloss.

[0038] Considering that during the single-stage heating and drying process, the solvent in the heat-sealing coating evaporates upwards, if there is no airflow to guide it, the solvent vapor will form a saturated layer on the surface of the heat-sealing adhesive. The partial pressure of the solvent in the gas phase will be close to the partial pressure of the solvent on the coating surface, the concentration gradient will decrease, the driving force for evaporation will decrease, and the drying rate will decrease. Although the protective agent coating is located on the other side of the aluminum foil, its residual solvent will also migrate to the coating surface after heating. If there is no airflow on the back of the aluminum foil, the solvent vapor will remain in the gap between the back of the aluminum foil and the equipment, increasing the resistance to the diffusion of the protective agent solvent into the gas phase and decreasing the curing rate. As an optional implementation, during the single-stage heating and drying process, a suction device is provided on the side of the aluminum foil coated with heat-sealing adhesive, with a wind speed of 3-5 m / s; a blowing device is provided on the side of the aluminum foil coated with protective agent, blowing an airflow at a temperature of 40-60°C at a wind speed of 5-8 m / s.

[0039] In this embodiment of the invention, a suction device is installed on the heat-sealing adhesive side, with a wind speed of three to five meters per second, to promptly remove solvent vapor from the surface of the heat-sealing adhesive, maintain the concentration gradient between the coating surface and the gas phase, and promote continuous solvent evaporation. A blowing device is installed on the protective agent side, blowing an airflow at a temperature of forty to sixty degrees Celsius with a wind speed of five to eight meters per second. This temperature is lower than the drying zone temperature but higher than room temperature, both cooling the aluminum foil to prevent thermal annealing and dispersing solvent vapor trapped in the gaps on the back of the aluminum foil, reducing the partial pressure of the solvent in the gas phase on the protective agent side, forming a concentration gradient from the protective agent coating to the gas phase, and promoting the migration and discharge of residual solvent from the protective agent to the surface. This differentiated ventilation design on both sides ensures that the heat-sealing adhesive solvent is drawn upwards and the protective agent solvent is blown downwards, with the solvent discharge paths on both sides not interfering with each other. This allows both coatings to dry simultaneously and thoroughly, further shortening the drying time.

[0040] Considering that the difference in resin molecular weight between the protective agent and the heat sealant directly affects the interfacial bonding between each coating and the aluminum foil, as well as the mechanical properties of the coating itself, the protective agent functions as anti-oxidation, gloss, and barrier properties. It needs to form a dense, thin layer. If the resin molecular weight is too high, the solution viscosity is high, resulting in poor leveling during coating, uneven coating thickness, and a brittle, hard coating after drying, making it prone to cracking during stamping. If the molecular weight is too low, the coating strength is insufficient, and the wear resistance is poor. As an optional implementation, the protective agent includes acrylic resin and a solvent, and the heat sealant includes acrylic resin, olefin resin, and a solvent. The acrylic resin in the protective agent has a molecular weight of 5000-15000, and the acrylic resin in the heat sealant has a molecular weight of 20000-50000.

[0041] This invention specifies that the molecular weight of the acrylic resin in the protective agent is between 5,000 and 15,000. This molecular weight range ensures that the protective agent solution has moderate viscosity, good leveling properties, and a dense, continuous coating after drying, while also possessing a certain degree of flexibility to adapt to aluminum foil stamping deformation. The function of the heat-sealing adhesive is to heat-seal and bond with the tinplate cap ring, requiring high cohesive strength and heat-sealing strength. If the resin molecular weight is too low, the heat-sealing adhesive lacks cohesive strength, making it prone to stringing or peeling during heat sealing; if the molecular weight is too high, the solution viscosity is high, making precise control of the coating amount difficult, and narrowing the heat-sealing temperature window with the tinplate. This invention specifies that the molecular weight of the acrylic resin in the heat-sealing adhesive is between 20,000 and 50,000. This molecular weight range ensures that the heat-sealing adhesive has sufficient cohesive strength and heat-sealing strength, while the solution viscosity is controllable, allowing for precise coating amount. The difference in molecular weight between the two resins optimizes the functions of both the protective agent and the heat-sealing adhesive. The protective agent layer is flexible and dense in thin layers, while the heat-sealing adhesive layer is strong and tough in thick layers. During a single drying process, the two resins cure simultaneously within their respective temperature windows without interfering with each other.

[0042] As an optional implementation, the acrylic resin in the protective agent has hydroxyl and carboxyl functional groups, and the acrylic resin in the heat sealant has epoxy and amino functional groups. When the protective agent coating in a semi-dry film state comes into contact with the heat sealant, the hydroxyl and carboxyl groups in the protective agent and the epoxy and amino groups in the heat sealant undergo a condensation reaction in the high-temperature setting zone to form chemical bonds.

[0043] The hydroxyl and carboxyl groups in the protective agent are polar functional groups, giving it an affinity for the aluminum foil surface. The epoxy and amino groups in the heat sealant are reactive functional groups, giving the heat sealant adhesion to tinplate and its own cross-linking ability. In the high-temperature setting zone during the single-stage heating and drying process, at temperatures of 150 to 180 degrees Celsius, the hydroxyl and carboxyl groups in the protective agent can form hydrogen bonds or coordination bonds with the alumina layer on the aluminum foil surface, enhancing the adhesion between the protective agent and the aluminum foil. Simultaneously, the epoxy groups in the heat sealant undergo ring-opening and react with the amino groups to form a three-dimensional cross-linked network, improving the strength and heat resistance of the heat sealant. More importantly, in the high-temperature setting zone, the hydroxyl and carboxyl groups remaining on the protective agent surface may undergo a trace condensation reaction with the epoxy and amino groups that have penetrated from the heat sealant, forming a chemical bridge in the aluminum foil interface area. This indirectly connects the coatings on both sides through chemical bonding on the aluminum foil surface, resulting in a more robust overall structure. The bond energy of this chemical bond is much higher than that of the intermolecular forces, which ensures that the coating and aluminum foil will not separate during subsequent high-temperature sterilization at 121 degrees Celsius or stamping processes, and the heat-sealing adhesive layer remains intact and does not degrade.

[0044] As an optional implementation method, flash drying uses far-infrared radiation heating. The wavelength of the far-infrared radiation is 3-4 μm, the radiation intensity is 60-70 kW / m², the flash drying time is 1.5-2.5 seconds, and the surface temperature of the protective coating after flash drying is 85-95°C. The flash drying parameters are further limited to a far-infrared radiation wavelength of 3-4 μm, a radiation intensity of 60-70 kW / m², a time of 1.5-2.5 seconds, and a surface temperature of 85-95°C. The wavelength of 3-4 μm is at the strong absorption peak of the carbonyl group in the acrylic resin. The energy is absorbed by the coating surface, the penetration depth is shallow, and the aluminum foil itself absorbs little, controlling the temperature rise to within 10°C, thus preventing the aluminum foil from softening during the flash drying stage. The product of the radiation intensity of 60-70 kW / m² and the time of 1.5-2.5 seconds results in an energy input of 90-175 kilojoules / m², which is sufficient to evaporate the surface solvent and form a film, but not enough to completely remove the internal solvent. The surface temperature is 85 to 95 degrees Celsius, which is about 8 to 18 degrees Celsius higher than the boiling point of ethyl acetate (77 degrees Celsius). This provides sufficient kinetic energy for solvent removal from the surface layer, but is below the boiling point of water. If the protective agent contains trace amounts of moisture, the moisture will not be removed and will remain inside the coating, preventing embrittlement caused by excessive drying. Within this parameter window, the stability of the semi-dry film is optimal, and the curing behavior of the coating during subsequent drying is controllable.

[0045] As an optional implementation, the surface viscosity of the protective coating after flash drying is 500-2000 mPa·s, which is detected by an online rotational viscometer. A surface viscosity of 500-2000 mPa·s provides a quantifiable characterization of the semi-dry film state, forming a dual control guarantee with the flash drying parameters. If the viscosity is below 500 mPa·s, the coating is close to a fluid state, easily causing sagging due to gravity or tension during aluminum foil travel, resulting in uneven coating thickness and edge accumulation. If the viscosity is above 2000 mPa·s, the coating is too hard, leading to poor resin chain mobility during subsequent drying, reduced wetting and anchoring effects on the aluminum foil surface, and decreased adhesion. Real-time detection with an online rotational viscometer allows operators to directly adjust the flash drying radiation intensity or time based on the viscosity reading, eliminating the need for offline sampling and weighing, thus achieving closed-loop control of the production process. When the viscosity deviates from the target range, the system automatically adjusts the radiation intensity or travel speed to ensure the consistency of the semi-dry state of each roll of aluminum foil, thereby guaranteeing uniform and stable coating thickness and performance of the final product.

[0046] As an optional implementation, the aluminum foil thickness is 0.02-0.05 mm, the protective agent coating amount is 1.0-1.2 g / m², and the heat-sealing adhesive coating amount is 9.5-11.0 g / m². The aluminum foil thickness is 0.02 to 0.05 mm, a range that balances the formability and barrier properties of the easy-tear cap. A thickness below 0.02 mm results in high pinhole rate, increased oxygen permeability, insufficient barrier properties, and a tendency to break during stamping; a thickness above 0.05 mm results in high tearing force, making it difficult for the elderly or children to open, and also increases material costs. The protective agent coating amount is 1.0 to 1.2 grams per square meter, corresponding to a dry film thickness of 2 to 3 micrometers. This thickness is sufficient to form a continuous protective layer covering pinholes and defects on the aluminum foil surface, but excessive thickness increases costs and reduces the flexibility of the aluminum foil, making the protective agent layer prone to cracking during stamping. The heat-sealing adhesive coating amount is 9.5 to 11.0 grams per square meter, corresponding to a dry film thickness of 8 to 10 micrometers. This thickness ensures a heat-sealing strength of at least 15 Newtons per 15 millimeters with the tinplate cap ring. However, excessive thickness prolongs the drying time and increases the internal stress of the heat-sealing adhesive, making it prone to delamination after long-term storage. The above parameters are matched with the flash drying and single-stage drying processes. The thin layer of protective agent quickly reaches a semi-dry state after flash drying, while the thick layer of heat-sealing adhesive has sufficient time to remove solvents in the low-temperature evaporation zone of the single-stage drying process. The difference in thickness between the two layers is compensated by the gradient heating time distribution, resulting in uniform curing of the coatings on both sides and balanced overall performance of the aluminum foil.

[0047] The second aspect of this invention provides an easy-tear aluminum foil, which is prepared by the aforementioned method. The aluminum foil undergoes only one high-temperature drying process, resulting in fine grains and excellent mechanical properties. The coatings on both sides are firmly bonded to the aluminum foil interface, the protective agent layer is dense and glossy, and the heat-sealing adhesive layer is strong and heat-resistant. In terms of performance, the aluminum foil exhibits improved tensile strength and elongation, making it less prone to breakage during stamping; the interlayer peel strength is also improved, preventing coating separation during high-temperature sterilization and long-term storage. When used in food packaging such as milk powder cans and coffee cans, this easy-tear aluminum foil can be completely torn off along the edge of the can upon opening, leaving no residual fragments, ensuring high safety. Furthermore, the bright and attractive appearance of the aluminum foil enhances the product's perceived quality.

[0048] The following description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the present invention.

[0049] Example 1

[0050] A method for preparing an easy-tear aluminum foil cover includes the following steps: (1) Unwinding aluminum foil: Unwind aluminum foil with a thickness of 0.03mm onto the machine at a speed of 55m / min and a tension of 9kg.

[0051] (2) Protective agent coating: A protective agent is coated on one side of the aluminum foil by an anilox roller coating method. The protective agent includes acrylic resin and ethyl acetate solvent, wherein the molecular weight of the acrylic resin is 10,000 and it has hydroxyl and carboxyl functional groups. The coating amount is 1.1 g / m², forming a protective agent coating.

[0052] (3) Flash baking: The protective agent coating is flash baked using far-infrared radiation heating with a wavelength of 3.5 μm and a radiation intensity of 65 kW / m². The flash baking time is 2 seconds. After flash baking, the surface temperature of the protective agent coating is 90°C and the surface is in a semi-dry film state. The semi-dry film is judged by the criterion that it is not sticky to the touch and can be scratched with a fingernail. There is no cooling step between the flash baking and the subsequent heat-sealing adhesive coating.

[0053] (4) Heat-sealing adhesive coating: Heat-sealing adhesive is applied to the other side of the aluminum foil using a direct coating method. The heat-sealing adhesive includes acrylic resin, polyolefin resin, and ethyl acetate solvent, wherein the acrylic resin has a molecular weight of 35,000 and contains epoxy and amino functional groups, and the coating amount is 10.0 g / m². The heat-sealing adhesive is applied to the protective agent coating in a semi-dry film state. The solvent in the heat-sealing adhesive is miscible with the residual solvent on the surface of the protective agent. The high molecular weight acrylic resin in the heat-sealing adhesive penetrates into the surface of the protective agent, while the low molecular weight acrylic resin in the protective agent diffuses into the bottom layer of the heat-sealing adhesive, forming an interpenetrating transition layer with a thickness of about 1.2 μm.

[0054] (5) Primary heating and drying: The aluminum foil is subjected to primary heating and drying using a gradient heating method, which includes a low-temperature volatilization zone, a medium-temperature curing zone, and a high-temperature setting zone in sequence. The low-temperature volatilization zone has a temperature of 70°C, a length of 45% of the total length of the primary heating and drying, and a dwell time of 6 seconds; the medium-temperature curing zone has a temperature of 115°C, a length of 35% of the total length of the primary heating and drying, and a dwell time of 5 seconds; the high-temperature setting zone has a temperature of 165°C, a length of 20% of the total length of the primary heating and drying, and a dwell time of 3 seconds. During the primary heating and drying process, the side of the aluminum foil coated with heat-sealing adhesive is the heat-sealing adhesive side, and the side of the aluminum foil coated with protective agent is the protective layer side; the heat-sealing adhesive side is equipped with an upper suction device with a wind speed of 4 m / s; the protective layer side is equipped with a lower blowing device that blows air at a temperature of 50°C with a wind speed of 6.5 m / s. There is no pre-drying step before the primary heating and drying.

[0055] In the high-temperature setting zone, the hydroxyl and carboxyl groups in the protective agent undergo a condensation reaction with the epoxy and amino groups in the heat sealant to form chemical bonds, and the interpenetrating transition layer is transformed into a covalent bonded interface.

[0056] (6) Cooling: The dried aluminum foil is cooled by cold air and cooling rollers. The temperature of the aluminum foil after cooling is 40°C. The pressure of the cooling roller is 5.5 kg and the temperature of the cooling roller is 22°C.

[0057] (7) Aluminum foil winding: The winding tension is 11 kg.

[0058] After preparation, the easy-tear aluminum foil was examined by scanning electron microscopy. The thickness of the interpenetrating transition layer between the protective layer and the heat-sealing layer was 1.2 μm. In a 180° peel strength test, the peel strength between the protective layer and the aluminum foil layer was 28 N / 15 mm, and the peel strength between the aluminum foil layer and the heat-sealing layer was 22 N / 15 mm. The aluminum foil underwent a tensile test, showing a tensile strength of 190 MPa and an elongation after fracture of 3.5%.

[0059] Example 2

[0060] A method for preparing an easy-tear aluminum foil cover includes the following steps: (1) Unwinding aluminum foil: Unwind aluminum foil with a thickness of 0.02mm onto the machine at a speed of 50m / min and a tension of 8kg.

[0061] (2) Protective agent coating: A protective agent is applied to one side of the aluminum foil by a direct scraping coating method. The protective agent includes acrylic resin and ethyl acetate solvent, wherein the molecular weight of the acrylic resin is 5000 and it has hydroxyl and carboxyl functional groups. The coating amount is 1.0 g / m², forming a protective agent coating.

[0062] (3) Flash baking: The protective agent coating is flash baked using far-infrared radiation heating with a wavelength of 3 μm and a radiation intensity of 50 kW / m². The flash baking time is 3 seconds. After flash baking, the surface temperature of the protective agent coating is 80°C and the surface is in a semi-dry film state. There is no cooling step between the flash baking and the subsequent heat-sealing adhesive coating.

[0063] (4) Heat-sealing adhesive coating: Heat-sealing adhesive is applied to the other side of the aluminum foil using a textured roller coating method. The heat-sealing adhesive includes acrylic resin, polyolefin resin, and ethyl acetate solvent, wherein the acrylic resin has a molecular weight of 20,000 and contains epoxy and amino functional groups, and the coating amount is 9.5 g / m². The heat-sealing adhesive is applied to the protective coating in a semi-dry film state to form an interpenetrating transition layer with a thickness of approximately 0.8 μm.

[0064] (5) Primary heating and drying: The aluminum foil is subjected to primary heating and drying using a gradient heating method. The low-temperature volatile zone has a temperature of 60°C, a length of 50% of the total length of the primary heating and drying, and a dwell time of 8 seconds; the medium-temperature curing zone has a temperature of 100°C, a length of 30% of the total length of the primary heating and drying, and a dwell time of 5 seconds; the high-temperature setting zone has a temperature of 150°C, a length of 20% of the total length of the primary heating and drying, and a dwell time of 3 seconds. During the primary heating and drying process, an upper suction device with a wind speed of 3 m / s is provided on the heat-sealing adhesive side; a lower blowing device is provided on the protective layer side, blowing an airflow at a temperature of 40°C with a wind speed of 5 m / s. No pre-drying step is performed before the primary heating and drying.

[0065] In the high-temperature setting zone, the hydroxyl and carboxyl groups in the protective agent undergo a condensation reaction with the epoxy and amino groups in the heat sealant to form chemical bonds.

[0066] (6) Cooling: The dried aluminum foil is cooled by cold air and cooling rollers. The temperature of the aluminum foil after cooling is 35°C. The pressure of the cooling roller is 5kg and the temperature of the cooling roller is 20°C.

[0067] (7) Aluminum foil winding: The winding tension is 10 kg.

[0068] After preparation, the easy-tear aluminum foil was examined by scanning electron microscopy. The thickness of the interpenetrating transition layer between the protective layer and the heat-sealing layer was 0.8 μm. In a 180° peel strength test, the peel strength between the protective layer and the aluminum foil layer was 25 N / 15 mm, and the peel strength between the aluminum foil layer and the heat-sealing layer was 20 N / 15 mm. The aluminum foil underwent a tensile test, showing a tensile strength of 195 MPa and an elongation after fracture of 3.8%.

[0069] Example 3

[0070] A method for preparing an easy-tear aluminum foil cover includes the following steps: (1) Unwinding aluminum foil: Unwind aluminum foil with a thickness of 0.05mm onto the machine at a speed of 60m / min and a tension of 10kg.

[0071] (2) Protective agent coating: A protective agent is coated on one side of the aluminum foil by an anilox roller coating method. The protective agent includes acrylic resin and ethyl acetate solvent, wherein the molecular weight of the acrylic resin is 15,000 and it has hydroxyl and carboxyl functional groups. The coating amount is 1.2 g / m², forming a protective agent coating.

[0072] (3) Flash baking: The protective agent coating is flash baked using far-infrared radiation heating with a wavelength of 4μm and a radiation intensity of 80kW / m². The flash baking time is 1 second. After flash baking, the surface temperature of the protective agent coating is 100℃ and the surface is in a semi-dry film state. There is no cooling step between the flash baking and the subsequent heat-sealing adhesive coating.

[0073] (4) Heat-sealing adhesive coating: Heat-sealing adhesive is applied to the other side of the aluminum foil using a direct coating method. The heat-sealing adhesive includes acrylic resin, polyolefin resin, and ethyl acetate solvent, wherein the acrylic resin has a molecular weight of 50,000 and contains epoxy and amino functional groups, and the coating amount is 11.0 g / m². The heat-sealing adhesive is applied to the protective coating in a semi-dry film state to form an interpenetrating transition layer with a thickness of approximately 2.0 μm.

[0074] (5) Primary heating and drying: The aluminum foil is subjected to primary heating and drying using a gradient heating method. The temperature of the low-temperature volatile zone is 80℃, the length is 40% of the total length of the primary heating and drying, and the residence time is 5 seconds; the temperature of the medium-temperature curing zone is 130℃, the length is 40% of the total length of the primary heating and drying, and the residence time is 5 seconds; the temperature of the high-temperature setting zone is 180℃, the length is 20% of the total length of the primary heating and drying, and the residence time is 3 seconds. During the primary heating and drying process, an upper suction device is provided on the heat-sealing adhesive side with a wind speed of 5 m / s; a lower blowing device is provided on the protective layer side, blowing air at a temperature of 60℃ with a wind speed of 8 m / s. There is no pre-drying step before the primary heating and drying.

[0075] In the high-temperature setting zone, the hydroxyl and carboxyl groups in the protective agent undergo a condensation reaction with the epoxy and amino groups in the heat sealant to form chemical bonds.

[0076] (6) Cooling: The dried aluminum foil is cooled by cold air and cooling rollers. The temperature of the aluminum foil after cooling is 45°C. The pressure of the cooling roller is 6kg and the temperature of the cooling roller is 25°C.

[0077] (7) Aluminum foil winding: The winding tension is 12kg.

[0078] The prepared easy-tear aluminum foil was examined by scanning electron microscopy, and the thickness of the interpenetrating transition layer between the protective layer and the heat-sealing layer was 2.0 μm. In a 180° peel strength test, the peel strength between the protective layer and the aluminum foil layer was 26 N / 15 mm, and the peel strength between the aluminum foil layer and the heat-sealing layer was 21 N / 15 mm. The aluminum foil underwent a tensile test, and the tensile strength was 188 MPa, with an elongation at break of 3.2%.

[0079] It should be noted that the test samples for the peel strength were all 15 mm wide as the test reference.

[0080] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an easy-tear aluminum foil cover, characterized in that, Includes the following steps: Aluminum foil unwinding; A protective agent is applied to one side of the aluminum foil to form a protective agent coating. The protective agent coating is flash-baked using infrared radiation heating with a radiation wavelength of 2-4 μm, a radiation intensity of 50-80 kW / m², and a flash-baking time of 1-3 seconds. After flash-baking, the surface temperature of the protective agent coating is 80-100℃ and the surface is in a semi-dry film state. Heat-sealing adhesive is applied to the other side of the aluminum foil, allowing the heat-sealing adhesive to come into contact with and penetrate the semi-dry protective coating, forming an interpenetrating transition layer. The aluminum foil is subjected to a single heating and drying process to simultaneously cure the protective coating and the heat sealant. The temperature of the single heating and drying process does not exceed 180°C. The dried aluminum foil is cooled and then wound up.

2. The method for preparing the easy-tear aluminum foil according to claim 1, characterized in that, The primary heating and drying process employs a gradient temperature increase method, which sequentially includes a low-temperature volatilization zone, a medium-temperature curing zone, and a high-temperature setting zone. The temperature of the low-temperature volatilization zone is 60-80℃, the temperature of the medium-temperature curing zone is 100-130℃, and the temperature of the high-temperature setting zone is 150-180℃.

3. The method for preparing the easy-tear aluminum foil according to claim 2, characterized in that, The duration of the low-temperature volatilization zone is 40%-50% of the total duration of the single heating and drying, the duration of the medium-temperature curing zone is 30%-40% of the total duration of the single heating and drying, and the duration of the high-temperature setting zone is 10%-20% of the total duration of the single heating and drying.

4. The method for preparing the easy-tear aluminum foil according to claim 1, characterized in that, During the initial heating and drying process, a suction device is provided on the side of the aluminum foil coated with heat-sealing adhesive, and the air velocity of the suction device is 3-5 m / s; a blowing device is provided on the side of the aluminum foil coated with protective agent, and the blowing device blows air at a temperature of 40-60℃ with a wind velocity of 5-8 m / s.

5. The method for preparing the easy-tear aluminum foil according to claim 2, characterized in that, The protective agent includes acrylic resin and solvent, and the heat sealant includes acrylic resin, olefin resin and solvent. The acrylic resin in the protective agent has a molecular weight of 5,000-15,000, and the acrylic resin in the heat sealant has a molecular weight of 20,000-50,000.

6. The method for preparing the easy-tear aluminum foil according to claim 5, characterized in that, The acrylic resin in the protective agent has hydroxyl and carboxyl functional groups, and the acrylic resin in the heat sealant has epoxy and amino functional groups. When the semi-dry film-state protective agent coating comes into contact with the heat sealant, the hydroxyl and carboxyl groups in the protective agent and the epoxy and amino groups in the heat sealant undergo a condensation reaction in the high-temperature setting zone to form chemical bonds.

7. The method for preparing the easy-tear aluminum foil according to claim 1, characterized in that, The flash drying process uses far-infrared radiation heating, with a wavelength of 3-4 μm, a radiation intensity of 60-70 kW / m², a flash drying time of 1.5-2.5 seconds, and a surface temperature of 85-95℃ after flash drying.

8. The method for preparing the easy-tear aluminum foil according to claim 1, characterized in that, The surface viscosity of the protective coating after flash baking is 500-2000 mPa·s, and the surface viscosity is detected by an online rotational viscometer.

9. The method for preparing the easy-tear aluminum foil according to claim 1, characterized in that, The aluminum foil has a thickness of 0.02-0.05 mm, the protective agent has a coating amount of 1.0-1.2 g / m², and the heat sealant has a coating amount of 9.5-11.0 g / m².

10. An easy-tear aluminum foil cover, characterized in that, The easy-tear aluminum foil is prepared by the method for preparing easy-tear aluminum foil according to any one of claims 1-9.

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