Intelligent adhesive tape glue capable of automatically adjusting viscosity at different temperatures and application thereof

Abstract

The invention discloses glue for an intelligent adhesive tape capable of automatically adjusting viscosity at different temperatures and application of the glue. The glue comprises the following components in percentage by weight: 5-15% of modified polyvinyl alcohol; 10%-30% of a temperature-sensitive modifier, which is poly (N-isopropylacrylamide) or a derivative thereof; 1.0%-2.0% of a cross-linking agent, which is glutaraldehyde or boric acid ester; 3%-5% of a thickening agent which is carboxymethyl cellulose or xanthan gum; 5%-10% of an antifreeze agent which is glycerol or ethylene glycol; 0.1%-0.3% of a stabilizer which is an antioxidant; 60%-70% of a solvent which is a mixed solvent of water and ethanol; according to the invention, through innovative formula and process optimization, excellent performance of the glue in cold-chain food packaging is realized. The sealing agent has the advantages of intelligent viscosity adjustment, excellent sealing strength, easy stripping and good storage stability, provides a safer, more reliable and more environment-friendly solution for the food packaging industry, and has remarkable market competitiveness and application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of adhesive tape glue, and specifically relates to intelligent adhesive tape glue capable of automatically adjusting viscosity at different temperatures and application thereof. Background Art

[0002] In the field of frozen and refrigerated food packaging, heat and pressure sealing is the most common sealing method. Although heat and pressure sealing can provide a strong sealing effect, it has the following significant shortcomings in actual use:

[0003] 1. Difficult to open the heat-pressed seal

[0004] Limitations of cutting the seal: The material of the heat-pressed seal is permanently fused after being heated at high temperatures. The seal is strong and difficult to tear open manually. Users usually need to use tools such as scissors to cut the seal when taking food, which is inconvenient.

[0005] Poor user experience: For frozen and refrigerated foods, especially liquid or powdered foods, the sealing materials are often irregular after being cut, which can easily cause food leakage or loss.

[0006] 2. Repeated sealing is not possible

[0007] Unable to restore the seal: The heat-sealed material cannot be restored to its original state after opening, and the user needs to use additional clips or zipper bags to reseal it; this is particularly inconvenient for foods that need to be taken out multiple times (such as frozen meat, fruits and vegetables, seasonings, etc.).

[0008] Food safety hazards: Temporary sealing methods (such as clips) may reduce the sealing of packaging bags, making food prone to moisture absorption, oxidation or deterioration after contact with air; during the transportation or storage of cold chain food, poor sealing will directly affect the preservation effect.

[0009] 3. Existing heat-pressing seals are not suitable for frequent use

[0010] For small packaged foods that need to be taken repeatedly (such as sauces, frozen fruits, etc.), existing packaging cannot meet the needs of users to open and seal repeatedly. The need to reseal food after thawing (such as frozen semi-finished products and fresh food used in batches) cannot be achieved through hot press sealing.

[0011] Although glue can be used as a sealing method to replace heat and pressure sealing, it has certain advantages in flexible operation and repeatability, but the existing glue technology still has the following significant disadvantages in the application of frozen and refrigerated food packaging:

[0012] 1. Unstable performance in low temperature environment

[0013] Low temperature hardening: Existing glue is easy to harden at freezing to refrigeration temperature (-18℃ to 10℃), losing elasticity and flexibility, resulting in a decrease in sealing strength.

[0014] Stratification and sedimentation: The thickener or particle components in the glue are prone to stratification and sedimentation under low temperature conditions, resulting in uneven viscosity and unstable sealing effect.

[0015] Ice crystal influence: Ice crystals formed in a freezing environment will destroy the network structure of the glue, affecting the sealing of the seal.

[0016] 2. Difficult to achieve intelligent viscosity adjustment

[0017] The viscosity of existing glue is usually fixed, which makes it difficult to adapt to the dual needs of refrigeration and room temperature environments: Insufficient viscosity at low temperatures: The adhesion and strength of glue in low temperature environments are weak and cannot provide sufficient sealing performance;

[0018] Difficult to peel at high temperature: At room temperature or high temperature, the viscosity of the glue is difficult to reduce, resulting in users having to use too much force to open the seal, which may even damage the packaging bag.

[0019] 3. Sagging problem under high temperature conditions

[0020] Existing glue is prone to sagging in high temperature environments: when the viscosity of the glue decreases, the fluidity increases, causing the glue to flow out of the seal, destroying the appearance of the package; the sagging phenomenon may also cause the sealing effect of the seal to decrease.

[0021] 4. Insufficient hydrophobicity

[0022] Existing glues exhibit poor hydrophobicity in high humidity or frozen environments: after the glue absorbs moisture, the seal adhesion may decrease, reducing the sealing performance of the packaging; glue that lacks hydrophobic properties may cause glue to adhere when food is accidentally touched during removal, affecting food safety. Summary of the invention

[0023] The purpose of the present invention is to provide glue for smart tape that automatically adjusts viscosity at different temperatures and its application. The present invention achieves excellent performance of glue in cold chain food packaging through innovative formula and process optimization. Its intelligent viscosity adjustment, excellent sealing strength, easy peeling and good storage stability provide a safer, more reliable and environmentally friendly solution for the food packaging industry, with significant market competitiveness and application value.

[0024] The technical solution adopted by the present invention is as follows:

[0025] A smart adhesive tape glue that automatically adjusts viscosity at different temperatures, the glue comprising the following components calculated by weight percentage:

[0026] Modified polyvinyl alcohol: 5% to 15%;

[0027] Thermosensitive modifier: 10% to 30%, which is poly(N-isopropylacrylamide) or its derivatives;

[0028] Cross-linking agent: 1.0% to 2.0%, glutaraldehyde or borate;

[0029] Thickener: 3% to 5%, which is carboxymethyl cellulose or xanthan gum;

[0030] Antifreeze: 5% to 10%, glycerol or ethylene glycol;

[0031] Stabilizer: 0.1% to 0.3%, antioxidant;

[0032] Solvent: 60% to 70%, a mixed solvent of water and ethanol.

[0033] The glue is in a high viscosity state at a freezing to refrigeration temperature range of -18°C to 10°C, with a viscosity of 4000 to 9000 mPa·s; and is in a low viscosity state at a temperature above 30°C, with a viscosity of 500 to 2000 mPa·s.

[0034] The molecular weight of the modified polyvinyl alcohol is 80,000-120,000 g / mol, and the degree of hydroxyl substitution is 80%-90%. The critical phase transition temperature of the temperature-sensitive modifier is 30° C.-35° C., and is adjusted by copolymerization by introducing acrylic acid, methacrylic acid or octyl acrylate.

[0035] Wherein, the antifreeze agent is glycerol or ethylene glycol, which is used to reduce the freezing point of the glue and enhance the flexibility and stability in a low temperature environment;

[0036] The thickener is used in an amount of 4% to improve the viscosity stability of the glue in a frozen to refrigerated environment.

[0037] A smart adhesive tape uses the smart adhesive tape glue and is suitable for bag sealing of food that needs to be frozen, cooled or refrigerated.

[0038] The tape provides high-strength sealing performance in a freezing, cooling or refrigerating environment, and the bag opening peel strength is above 2N / cm; after being removed from the freezing or refrigerating environment and heated to above 30°C, a critical phase transition is achieved, making the bag opening easy to peel off or reseal.

[0039] A method for preparing the glue for the smart tape comprises the following steps:

[0040] (1) adding modified polyvinyl alcohol to a mixed solvent, heating it to 80° C. to 90° C., and stirring to dissolve it to form a uniform solution;

[0041] (2) gradually adding the temperature-sensitive modifier to the cooled polyvinyl alcohol solution and stirring evenly;

[0042] (3) adding a cross-linking agent and adjusting the pH value to 6-7 to promote the cross-linking reaction;

[0043] (4) Add antifreeze agent and thickener and continue stirring until completely dissolved;

[0044] (5) using a high shear homogenizer to homogenize and disperse the mixture;

[0045] (6) Degassing under vacuum conditions to obtain the glue.

[0046] Before adding the temperature-sensitive modifier in step (2), the temperature-sensitive modifier is subjected to ultrasonic treatment at 20 to 40 kHz for 10 to 15 minutes to improve the dispersibility and uniformity of the temperature-sensitive modifier.

[0047] The method further comprises step (7): after the degassing in step (6) is completed, the glue is subjected to secondary cross-linking treatment of the polymer network, specifically comprising: selectively activating the methacrylate photoresponsive group in the thermosensitive modifier by ultraviolet light irradiation with a wavelength of 365 nm for 10 to 20 minutes to enhance the stability of the polymer network, thereby improving the anti-sagging performance of the glue in a high temperature environment and the selective residual performance after peeling.

[0048] The method further comprises step (8): after the preparation is completed, the glue is subjected to a freezing cycle treatment, the glue is frozen at -18°C for 6 hours, then thawed for 6 hours, and repeated 2 to 3 times to enhance the stability of the glue within the freezing to refrigeration temperature range.

[0049] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0050] 1. Significant temperature responsiveness, adaptable to different application scenarios

[0051] Within the freezing to refrigeration temperature range (-18°C to 10°C), the glue exhibits high viscosity, ensuring the sealing strength and sealing effect, and is particularly suitable for cold chain food packaging; in a high temperature environment (above 30°C), the viscosity decreases rapidly, making it easy to open the seal and reuse, meeting the convenient needs of thawing food.

[0052] 2. Excellent sealing performance to meet cold chain requirements

[0053] The glue seal strength in the freezing to refrigeration environment reaches 2.3-2.6N / cm, ensuring the integrity of the packaging during cold chain transportation. The synergistic effect of thickeners (such as carboxymethyl cellulose) and antifreeze agents (such as glycerol) enhances the flexibility and network stability of the glue under low temperature conditions; the freezing cycle treatment further improves the performance consistency and storage stability of the glue in the freezing to refrigeration temperature range.

[0054] 3. Excellent peeling performance, reducing food contamination

[0055] Under high temperature conditions, the collapse of the glue molecular chains and the dispersion of the hydrophobic particles significantly reduce the difficulty of packaging peeling; and even when it accidentally comes into contact with food, it can effectively avoid food surface contamination and meet food safety requirements.

[0056] 4. Anti-sagging performance under high temperature environment

[0057] During the preparation process, the photoresponsive groups (such as methacrylate) of the thermosensitive modifier are activated by ultraviolet light (365nm) to form a dense polymer network, which improves the anti-sagging performance under high temperature environment and ensures that the glue can still maintain a stable physical form under high temperature conditions. It avoids the phenomenon of glue flowing or dripping under high temperature, which is suitable for packaging scenarios with high environmental requirements.

[0058] 5. Storage stability is significantly improved

[0059] Through freeze-thaw cycles, the dispersion stability and performance consistency of the glue in low-temperature storage are significantly improved; the treated glue is less likely to delaminate or degrade in performance during long-term cold chain transportation. Untreated glue may cause particle sedimentation or performance degradation due to low temperature environment. After treatment, the performance of the glue is stable and the adaptability is significantly enhanced.

[0060] 6. Low cost and environmentally friendly

[0061] The glue mainly uses modified polyvinyl alcohol (PVA), temperature-sensitive modifier (PNIPAM copolymer) and water-based solvent, which is low-cost and has a wide range of material sources; the solvent uses a mixed system of water and ethanol, which is environmentally friendly and safe and meets the requirements of green packaging. The glue preparation process does not require complex equipment and can be completed using conventional stirring, homogenization and light treatment, making industrial production extremely convenient.

[0062] The present invention achieves excellent performance of glue in cold chain food packaging through innovative formula and process optimization. Its intelligent viscosity adjustment, excellent sealing strength, easy peeling and good storage stability provide a safer, more reliable and environmentally friendly solution for the food packaging industry, with significant market competitiveness and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0064] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0065] See also Figure 1 The present invention relates to a smart adhesive tape adhesive that automatically adjusts viscosity at different temperatures. The adhesive comprises the following components calculated by weight percentage:

[0066] Modified polyvinyl alcohol: 5% to 15%; the molecular weight of the modified polyvinyl alcohol is 80,000 to 120,000 g / mol, and the degree of hydroxyl substitution is 80% to 90%;

[0067] Thermosensitive modifier: 10% to 30%, which is poly(N-isopropylacrylamide) or its derivatives; the critical phase transition temperature of the thermosensitive modifier is 30° C. to 35° C., and is adjusted by copolymerization by introducing acrylic acid, methacrylic acid or octyl acrylate;

[0068] Cross-linking agent: 1.0% to 2.0%, glutaraldehyde or borate;

[0069] Thickener: 3% to 5%, which is carboxymethyl cellulose or xanthan gum; the thickener dosage is 4%, which is used to improve the viscosity stability of the glue in a frozen to refrigerated environment;

[0070] Antifreeze agent: 5% to 10%, which is glycerol or ethylene glycol; the antifreeze agent is glycerol or ethylene glycol, which is used to lower the freezing point of the glue and enhance the flexibility and stability in low temperature environments;

[0071] Stabilizer: 0.1% to 0.3%, antioxidant;

[0072] Solvent: 60% to 70%, a mixed solvent of water and ethanol.

[0073] The glue is in a high viscosity state with a viscosity of 4000 to 9000 mPa·s in the freezing to refrigeration temperature range of -18°C to 10°C; it is in a low viscosity state with a viscosity of 500 to 2000 mPa·s at a temperature above 30°C.

[0074] Among them, the synergistic effect of thickener and antifreeze

[0075] Thickener (carboxymethyl cellulose or xanthan gum): The thickener combines with the solvent molecules through its hydrophilic molecular chain, significantly improving the viscosity stability of the glue in a low temperature environment. The amount of thickener is controlled at 4%, which not only ensures low temperature performance, but also avoids the problem of residue in a high temperature environment.

[0076] Antifreeze (glycerol or ethylene glycol): Antifreeze lowers the freezing point of the solution, preventing the glue from crystallizing or hardening under freezing conditions. At the same time, antifreeze improves the adaptability of the glue in freezing environments by enhancing the flexibility of the solution.

[0077] Synergistic effect: thickeners provide structural stability, antifreeze agents enhance flexibility, and together they ensure the performance consistency of the glue at -18°C to 10°C.

[0078] Among them, the viscosity adjustment mechanism of the temperature-sensitive modifier is:

[0079] The main chain of poly(N-isopropylacrylamide) (PNIPAM) is composed of acrylamide repeating units, and the side chains have isopropyl and amide groups. The amide group (-CONH2) is highly hydrophilic and can bind to water molecules through hydrogen bonds; the isopropyl side chain is a hydrophobic group, and its hydrophobicity increases significantly when the temperature rises. Acrylic acid, methacrylic acid or octyl acrylate monomers are introduced to form modified PNIPAM through copolymerization.

[0080] Thermosensitive phase transition mechanism

[0081] (1) Low temperature (-18°C to 10°C): High viscosity state

[0082] Molecular chain swelling mechanism: At low temperatures, the amide groups of PNIPAM bind to water molecules through hydrogen bonds, and the molecular chains are in a swollen state. In the swollen state, water molecules penetrate between polymer chains, forming a gel-like network structure. The hydrogen bonds between polymer chains and the structural water formed by water molecules work together to significantly increase the viscosity of the solution; the swollen molecular chains improve the adhesion and mechanical strength of the glue through physical entanglement and intermolecular forces.

[0083] Network structure stability: Under low temperature conditions, the swollen network structure has a high elastic modulus and can resist external mechanical stress under freezing conditions; the matrix network composed of modified polyvinyl alcohol and cross-linking agent exhibits high viscosity (4000-9000 mPa·s) as a whole.

[0084] (2) High temperature (above 30°C): low viscosity state

[0085] Molecular chain collapse mechanism: When the temperature exceeds the phase transition temperature (30℃~35℃), the hydrogen bonds between the amide group of the PNIPAM molecular chain and the water molecules break; the hydrophobic effect of the isopropyl side chain dominates, and the molecular chain gradually collapses from the swollen state into a tight spherical structure.

[0086] Formation of hydrophobic micro-regions: The aggregated molecular chains form micro-regions through hydrophobic interaction, and the solution changes from a homogeneous system to a system with microphase separation characteristics; the flow resistance between molecular chains is significantly reduced, resulting in a rapid decrease in solution viscosity (500-2000mPa·s). At high temperatures, the glue becomes more fluid, facilitating the peeling operation, while reducing the adhesion between the packaging material and the food surface.

[0087] (3) Precise control of phase transition temperature

[0088] The role of introducing comonomers: Acrylic acid (AA): enhances the hydrophilicity of the molecular chain and increases the phase transition temperature; methacrylic acid (MAA): moderately balances hydrophilicity and hydrophobicity, and adjusts the phase transition temperature to 30°C ~ 35°C; octyl acrylate (OAA): increases the hydrophobicity of the molecular chain and reduces the phase transition temperature.

[0089] Advantages of copolymerization modification: By adjusting the type and proportion of copolymer monomers, the temperature range of viscosity change of the glue can be accurately controlled; the copolymer structure enhances the mechanical strength of the molecular chain and the stability after phase transition.

[0090] (4) Network synergy of thermosensitive modifiers in glue

[0091] Synergistic effect with thickeners: Thickeners (such as carboxymethyl cellulose) further enhance viscosity through intermolecular entanglement in low-temperature environments; in high-temperature environments, the molecular chains of the thickener limit the aggregation speed of the molecular chains of PNIPAM through physical effects, making its viscosity change smoother.

[0092] Synergistic effect with cross-linking agent: The cross-linking agent (such as glutaraldehyde or borate) fixes part of the chain segments of the temperature-sensitive modifier through chemical cross-linking; it improves the swelling capacity of the molecular chain and the morphological stability after collapse.

[0093] Furthermore, the glue contains modified hydrophobic nanoparticles, which are modified silica with hydrophilic groups grafted on the surface, and the added amount is 1% to 2%, which is used to enhance the hydrophobicity of the glue.

[0094] Specific:

[0095] 1. Surface modification mechanism

[0096] The structure of hydrophobic particles: The hydrophobic nanoparticle substrate is silicon dioxide (SiO 2 ), which usually has a large number of silanol groups (-Si-OH) on its surface, making it hydrophilic. In order to exert the hydrophobic properties in water-based glue, it is necessary to chemically modify its surface and introduce hydrophobic groups (such as organosilane, long-chain alkyl, fluorinated groups, etc.).

[0097] The role of surface grafted hydrophilic groups: The modification process grafts hydrophilic groups (such as carboxyl, amine or alcohol) onto the particle surface through chemical reactions: The function of the hydrophilic groups is to form a stable dispersion state in the water-based system; reduce the tendency of particles to agglomerate and improve compatibility with water-based solvents.

[0098] Exposure of the hydrophobic core: During use or drying, the hydrophilic groups are gradually destroyed or covered up by the external environment, and the hydrophobic core is exposed on the surface: The composition of the hydrophobic core, the hydrophobic modification groups (such as alkyl silane, fluorinated silane) are exposed; the high surface energy characteristics of the inner core of the silica particles promote water repellency.

[0099] 2. Dispersion and function in water-based glue

[0100] Dynamic dispersion mechanism: In order to avoid agglomeration of particles in a water-based system, a dynamic dispersion process (low-speed stirring at 200-300 rpm) is adopted: during the stirring process, the hydrophilic groups grafted on the surface form hydrogen bonds with water molecules to ensure uniform distribution of particles; the particle size after dispersion is usually in the range of 50-200 nm, with good stability.

[0101] Stable intermolecular interactions: When the glue is used in a frozen to refrigerated environment, the hydrophobic nanoparticles maintain a uniform distribution and form a network with the thickener and thermosensitive modifier through intermolecular interactions: the high surface energy of the silica particles enhances the stability of the network; the hydrophilic groups ensure the controllable dispersibility of the particles in a low-temperature environment.

[0102] 3. Hydrophobicity enhancement process

[0103] Changes in glue when it is peeled off or dried: After the glue is used, the interaction between the hydrophilic group and the solvent molecules is weakened:

[0104] As the solvent evaporates, the hydrophobic modification groups are gradually exposed; the hydrophobic groups (such as long-chain alkyl groups or fluorides) are arranged on the surface of the particles to form a dense hydrophobic layer.

[0105] Specific performance of the hydrophobic layer: the surface water contact angle increases to >90°, showing good hydrophobic properties; the glue forms an interfacial water repellent layer on the food surface, reducing adhesion and contamination.

[0106] 4. Overall effect of improving hydrophobicity

[0107] If the glue accidentally touches the food, the hydrophobic particles can reduce the chemical and physical adhesion between the glue and the food surface to ensure the hygiene of the food and the reusability of the packaging.

[0108] Effect in frozen to refrigerated environments: Hydrophobic particles improve the sealing stability in low temperature environments by synergizing with the network of thickeners and cross-linkers: The performance of the glue remains consistent during cold chain transportation; Avoiding the loss of sealing strength due to particle agglomeration.

[0109] A smart tape uses smart tape glue and is suitable for bag sealing of foods that need to be frozen, cooled or refrigerated. The tape provides high-strength sealing performance in a freezing, cooling or refrigerated environment, and the bag opening peel strength is above 2N / cm; after being removed from the freezing or refrigerated environment and heated to above 30°C, it reaches a critical phase transition, making the bag opening easy to peel off or re-seal.

[0110] A method for preparing glue for smart tape comprises the following steps:

[0111] (1) adding modified polyvinyl alcohol to a mixed solvent, heating it to 80° C. to 90° C., and stirring to dissolve it to form a uniform solution;

[0112] (2) gradually adding the temperature-sensitive modifier to the cooled polyvinyl alcohol solution and stirring evenly;

[0113] (3) adding a cross-linking agent and adjusting the pH value to 6-7 to promote the cross-linking reaction;

[0114] (4) Add antifreeze agent and thickener and continue stirring until completely dissolved;

[0115] (5) using a high shear homogenizer to homogenize and disperse the mixture;

[0116] (6) The glue is obtained after degassing under vacuum conditions.

[0117] Furthermore, after the degassing in step (6) is completed, hydrophobic nanoparticles are added and stirred at a low speed of 200 to 300 rpm for 30 minutes to enhance the hydrophobic properties and storage stability of the glue; before the thermosensitive modifier is added in step (2), it is subjected to an ultrasonic treatment at 20 to 40 kHz for 10 to 15 minutes to improve the dispersibility and uniformity of the thermosensitive modifier.

[0118] Furthermore, the method also includes step (7): after the degassing in step (6) is completed, the glue is subjected to secondary cross-linking treatment of the polymer network, specifically including: selectively activating the methacrylate photoresponsive group in the thermosensitive modifier by ultraviolet light irradiation with a wavelength of 365nm and a time of 10 to 20 minutes to enhance the stability of the polymer network, thereby improving the anti-sagging performance of the glue in a high temperature environment and the selective residual performance after peeling.

[0119] Specific:

[0120] 1. Basic structure of polymer network

[0121] (1) Primary cross-linked basic network

[0122] The basic network of the glue is formed by modified polyvinyl alcohol and a crosslinking agent (such as glutaraldehyde or boric acid ester). The chemical crosslinking reaction is achieved in a water-based environment through the following process: glutaraldehyde reacts with the hydroxyl groups of polyvinyl alcohol to form ether bonds; boric acid ester forms a stable three-dimensional network through multi-point coordination with the hydroxyl groups. The primary crosslinking provides a basic polymer network structure to ensure high viscosity in low temperature environments; it also provides reaction sites for secondary crosslinking by ultraviolet light.

[0123] (2) Introduction of photoresponsive groups

[0124] The introduction of photoresponsive groups (such as methacrylate and styrene groups) into the thermosensitive modifier (poly(N-isopropylacrylamide)) is achieved through copolymerization modification. The photoresponsive groups have an absorption peak in a specific wavelength range (such as 365 nm) and are excited to generate free radicals under ultraviolet light.

[0125] 2. Chemical reaction mechanism of UV secondary cross-linking

[0126] (1) Excitation of photoresponsive groups

[0127] When ultraviolet light (wavelength 365nm) acts on the photoresponsive group (such as methacrylate), the light energy is absorbed to excite the chemical bonds of the group: the C=C double bond in the photoresponsive group is broken to form highly active free radicals; the free radicals have high reactivity and can form new chemical bonds with the reaction sites (such as C=C or hydroxyl) in adjacent molecules.

[0128] (2) Free radical cross-linking reaction

[0129] The free radicals generated by the excitation react with double bonds in other molecules (such as styrene or methacrylate units); the free radicals can also react with the hydroxyl groups of polyvinyl alcohol through chain transfer to further crosslink. The main chemical bonds formed include CC bonds, COC bonds, and covalent crosslinks between styrene groups.

[0130] 3. Strengthening effect of secondary cross-linking on polymer network

[0131] (1) Enhance network density

[0132] The network structure formed by the primary cross-linking is relatively loose, and the interaction between the chain segments is weak; the secondary cross-linking builds more cross-linking points between the polymer chains, making the network structure denser and more stable. The glue is not easy to sag under high temperature conditions (above 30°C); the elastic modulus of the network is increased, and the selective residual performance after peeling is enhanced.

[0133] (2) Improve anti-sagging performance

[0134] The dense network formed by secondary cross-linking can better lock the molecular chain segments: under high temperature conditions, the cross-linking points limit the free movement of the molecular chain segments; preventing the glue from sagging or dripping under the action of gravity.

[0135] 4. Effect of UV secondary crosslinking on performance at different temperatures

[0136] (1) Low temperature performance

[0137] The secondary cross-linking process has little effect on low-temperature performance: in the range of -18°C to 10°C, the chemical bonds in the polymer network are highly stable; the high viscosity state of the glue is mainly provided by the primary cross-linking.

[0138] (2) High temperature performance

[0139] The contribution of secondary cross-linking is particularly significant under high temperature conditions: the anti-sagging performance of the polymer network is significantly improved above 30°C; and the glue distribution after peeling is more controllable.

[0140] 5. Process optimization of UV secondary cross-linking

[0141] 365nm is the main absorption peak of methacrylate and styrene groups; other wavelengths (such as 254nm) may introduce non-selective reactions and affect the cross-linking efficiency.

[0142] The illumination time is controlled within 10 to 20 minutes to ensure sufficient cross-linking and avoid over-reaction; too long illumination may lead to excessive cross-linking and affect the flexibility of the glue.

[0143] LED or mercury lamp is used as the light source to ensure that the sample surface is evenly illuminated.

[0144] Furthermore, the method also includes step (8): after the preparation is completed, the glue is subjected to a freezing cycle treatment, the glue is frozen at -18°C for 6 hours, and then thawed for 6 hours, and repeated 2 to 3 times to enhance the stability of the glue in the freezing to refrigeration temperature range.

[0145] 1. Optimization of molecular chains by freeze-thaw cycles

[0146] (1) Molecular chain behavior under low temperature environment

[0147] Frozen state (-18℃): The mobility of solvent molecules (such as water and ethanol) decreases or even freezes in a low-temperature environment; the molecular chains of the thermosensitive modifier become more stretched due to the low-temperature swelling effect, forming close contact with other components (such as thickeners and cross-linking agents); the physical entanglement and hydrogen bonding between the swollen molecular chains are further enhanced. During the low-temperature freezing process, the position of the molecular chains tends to be stable, and the arrangement of the molecular chains becomes more regular; the porosity in the polymer network decreases, forming a denser structure.

[0148] (2) Thawed state (room temperature)

[0149] Molecular chain behavior after thawing: The solvent thaws, and the molecular chains regain some mobility; the thermosensitive modifier may partially collapse due to the temperature rise effect, making the entanglement structure between the molecular chains tend to be optimized; the hydrophobic particles are redispersed during the thawing process, further improving the uniformity of the system. The micro defects (such as micropores or microcracks) generated during the freezing process are self-healed during the thawing stage; the forces between the molecular chains are more uniform, enhancing the stability of the network.

[0150] 2. Strengthening effect of freezing cycle on polymer network

[0151] (1) Network Reconstruction

[0152] The freeze-thaw cycle promotes the dynamic reconstruction of the polymer network: during the freezing stage, cross-linking agents (such as glutaraldehyde or borate) form more chemical cross-linking points at specific positions of the molecular chain; during the thawing stage, physical entanglement and non-covalent forces between molecules are further adjusted to enhance the density of the overall network structure. The polymer network becomes more stable and can resist temperature fluctuations in cold chain transportation.

[0153] (2) Dispersion stability of hydrophobic particles

[0154] Hydrophobic nanoparticles may aggregate during the freezing process and redisperse during the thawing stage: the hydrophilic groups grafted on the surface prevent the particles from irreversibly agglomerating by interacting with solvent molecules (such as water and ethanol); after the freezing cycle, the hydrophobic particles are more evenly distributed in the glue, enhancing the storage stability and performance of the glue.

[0155] 3. Optimization of thickener and antifreeze performance

[0156] (1) Molecular chain reorganization of thickener

[0157] Thickeners (such as carboxymethyl cellulose or xanthan gum) form temporary molecular chain aggregates during the freezing stage; after thawing, these aggregates are redispersed, making the thickener molecular chains more uniform. The freeze-thaw cycle avoids the problem of molecular chain stratification caused by long-term storage and enhances the viscosity stability of the glue in low-temperature environments.

[0158] (2) Enhanced effect of antifreeze

[0159] Antifreeze agents (such as glycerol or ethylene glycol) reduce the formation of ice crystals by interacting with water molecules during the freezing process: during the freezing stage, antifreeze agents form local high concentration areas in the water phase, destroying the lattice structure of water; after thawing, the antifreeze agents are evenly distributed, further improving the flexibility of the system. After freezing cycle treatment, the flexibility of the glue and its ability to adapt to low temperature environments are significantly enhanced.

[0160] 4. Comprehensive effects of microstructural changes

[0161] (1) Optimization of polymer networks

[0162] After the freezing cycle, the chemical cross-linking points and physical entanglement points in the network increase; the arrangement of the molecular chains becomes more regular, forming a highly elastic and high-strength network structure.

[0163] (2) Coordinated distribution of hydrophobic particles and thickeners

[0164] The uniform distribution of hydrophobic particles and thickeners results in more consistent glue properties: the freezing phase promotes particle aggregation; the thawing phase optimizes particle distribution through dynamic dispersion.

[0165] in conclusion

[0166] The freezing cycle treatment significantly improves the stability of the glue in the freezing to refrigeration temperature range through mechanisms such as molecular chain reorganization, cross-linking point strengthening, and hydrophobic particle dispersion optimization caused by temperature changes. This process effectively solves the problem of performance fluctuations in cold chain transportation and extends the storage life and application performance of the product.

[0167] Within the formulation range, glues were prepared and tested according to different components. The results are summarized as follows:

[0168]

[0169] Viscosity change over temperature range

[0170] Data features:

[0171] The viscosity of tests 1 to 6 was maintained at 8000 to 8800 mPa·s in the range of freezing to refrigeration temperature (-18°C to 10°C), showing excellent high viscosity characteristics.

[0172] As the temperature rises to above 20°C, the viscosity of the test sample decreases rapidly, and at 30°C and above, it exhibits a low viscosity of 690-760 mPa·s, reflecting the temperature-sensitive regulation performance.

[0173] Significant differences:

[0174] Low temperature (-18℃ to 10℃): The test samples all maintain high viscosity to ensure sealing strength.

[0175] High temperature (30℃ and above): The low viscosity of the test sample is reduced to 500~760mPa·s, which is easy to peel.

[0176] Test Parameters

[0177] High viscosity test: The viscosity test was carried out at -18℃, -10℃, 0℃ and 10℃, using a viscometer.

[0178] Low viscosity test: The viscosity test was carried out at 20℃, 30℃ and 40℃ and measured using a viscometer.

[0179] Consistency verification: Repeat the test on 3 groups of samples and take the average value.

[0180] The high viscosity range (8000-8800 mPa·s) of the glue of the present invention ensures the sealing strength of cold chain food packaging. The temperature-sensitive property enables the glue to quickly reduce its viscosity (690-760 mPa·s) under high temperature conditions, making it easy to peel without affecting the surface of food.

[0181] The present invention exhibits obvious advantages in cold chain food packaging scenarios, especially in terms of sealing firmness and peeling convenience.

[0182] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A smart adhesive tape glue that automatically adjusts viscosity at different temperatures, characterized by: The glue comprises the following components calculated by weight percentage: Modified polyvinyl alcohol: 5% to 15%; Thermosensitive modifier: 10% to 30%, which is poly(N-isopropylacrylamide) or its derivatives; Cross-linking agent: 1.0% to 2.0%, glutaraldehyde or borate; Thickener: 3% to 5%, which is carboxymethyl cellulose or xanthan gum; Antifreeze: 5% to 10%, glycerol or ethylene glycol; Stabilizer: 0.1% to 0.3%, antioxidant; Solvent: 60% to 70%, a mixed solvent of water and ethanol. The glue is in a high viscosity state at a freezing to refrigeration temperature range of -18°C to 10°C, with a viscosity of 4000 to 9000 mPa·s; and is in a low viscosity state at a temperature above 30°C, with a viscosity of 500 to 2000 mPa·s.

2. The smart adhesive tape glue capable of automatically adjusting viscosity at different temperatures according to claim 1, characterized in that: The molecular weight of the modified polyvinyl alcohol is 80,000-120,000 g / mol, and the degree of hydroxyl substitution is 80%-90%. The critical phase transition temperature of the temperature-sensitive modifier is 30° C.-35° C., and is adjusted by copolymerization by introducing acrylic acid, methacrylic acid or octyl acrylate.

3. The smart adhesive tape glue capable of automatically adjusting viscosity at different temperatures according to claim 1, characterized in that: The antifreeze agent is glycerol or ethylene glycol, which is used to lower the freezing point of the glue and enhance the flexibility and stability in a low temperature environment.

4. The smart adhesive tape glue capable of automatically adjusting viscosity at different temperatures according to claim 1, characterized in that: The thickener is used in an amount of 4% to improve the viscosity stability of the glue in a frozen to refrigerated environment.

5. A smart tape, characterized in that: The adhesive tape uses the glue for the smart adhesive tape and is suitable for bag sealing of food that needs to be frozen, cooled or refrigerated.

6. The smart tape according to claim 5, characterized in that: The adhesive tape provides high-strength sealing performance in a freezing, cooling or refrigerating environment, and the bag opening peel strength is above 2N / cm; after being removed from the freezing or refrigerating environment and heated to above 30°C, a critical phase transition is achieved, so that the bag opening can be easily peeled off or re-sealed.

7. A method for preparing the glue for the smart tape, characterized in that: The following steps are involved: (1) adding modified polyvinyl alcohol to a mixed solvent, heating it to 80° C. to 90° C., and stirring to dissolve it to form a uniform solution; (2) gradually adding the temperature-sensitive modifier to the cooled polyvinyl alcohol solution and stirring evenly; (3) adding a cross-linking agent and adjusting the pH value to 6-7 to promote the cross-linking reaction; (4) Add antifreeze agent and thickener and continue stirring until completely dissolved; (5) using a high shear homogenizer to homogenize and disperse the mixture; (6) Degassing under vacuum conditions to obtain the glue.

8. A method for preparing the glue for the smart tape according to claim 7, characterized in that: Before adding the temperature-sensitive modifier in step (2), the temperature-sensitive modifier is subjected to ultrasonic treatment at 20 to 40 kHz for 10 to 15 minutes to improve the dispersibility and uniformity of the temperature-sensitive modifier.

9. The method for preparing the glue for the smart tape according to claim 7, characterized in that: The method further comprises a step (7): after the degassing in step (6) is completed, the glue is subjected to a secondary cross-linking treatment of the polymer network, specifically comprising: selectively activating the methacrylate photoresponsive group in the thermosensitive modifier by ultraviolet light irradiation with a wavelength of 365 nm for 10 to 20 minutes to enhance the stability of the polymer network, thereby improving the anti-sagging performance of the glue in a high temperature environment and the selective residual performance after peeling.

10. A method for preparing the glue for the smart tape according to claim 9, characterized in that: The method further comprises step (8): after the preparation is completed, subjecting the glue to a freezing cycle treatment, freezing the glue at -18°C for 6 hours, then thawing it for 6 hours, and repeating this process 2 to 3 times to enhance the stability of the glue within the range of freezing to refrigeration temperature.

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