A low temperature resistant water soluble cold chain label material and a preparation method thereof

Abstract

The application relates to the technical field of label materials, and specifically discloses a low-temperature-resistant water-soluble cold-chain label material and a preparation method thereof. The preparation method comprises the following steps: S1, uniformly mixing an ethanol aqueous solution, an acrylate soft monomer and part of an initiator to obtain a premix; S2, uniformly mixing the ethanol aqueous solution, an amphoteric acrylate monomer and a functional monomer under an inert atmosphere, heating, adding the remaining initiator, carrying out heat preservation reaction, adding the premix, continuing heat preservation reaction, cooling, uniformly mixing a water-soluble polyester resin, triglycerol and a block polyether, and obtaining a mixed glue solution; S3, uniformly mixing the mixed glue solution and a crosslinking agent, defoaming, coating the mixed glue solution on the lower surface of a substrate, solidifying, attaching a release film, die cutting, and obtaining the low-temperature-resistant water-soluble cold-chain label material. The label material prepared by the application is stable in adhesion under low-temperature, high-humidity and wide-temperature fluctuation environments, can be quickly degummed by flowing clean water at room temperature, and has no residual gum.

Description

Technical Field

[0001] This application relates to the technical field of label materials, and more specifically, it relates to a low-temperature resistant, water-soluble cold chain label material and its preparation method. Background Technology

[0002] The thawing and marinating of fresh ingredients in the kitchens and central kitchens of chain restaurants is a core process for food safety control. This process is based on a closed-loop control of time and temperature, and there are mandatory standardized requirements for the thawing, marinating, storage and disposal of ingredients. Labels, as the only visual carrier of control information, must be affixed to low surface energy substrates such as PP turnover boxes. After the store closes every day, the turnover boxes must be rinsed with clean water to ensure that the labels can be quickly removed without any residue. Labels are the core basic material to ensure compliance of the process and avoid food safety risks.

[0003] Existing conventional water-soluble labels mostly use acrylic pressure-sensitive adhesive systems, relying on monomers such as acrylic acid and hydroxyethyl acrylate to introduce a large number of strongly polar groups such as carboxyl and hydroxyl groups to achieve core performance: on the one hand, the interaction between polar groups provides basic cohesion for the adhesive layer; on the other hand, the formation of hydrogen bonds between polar groups and water molecules endows the adhesive layer with water solubility, achieving the effect of "quick degumming with water, no residue, and biodegradability," possessing natural advantages of being environmentally friendly, low-toxicity, and easy to clean. However, such labels have obvious limitations in scene adaptability: in a -15℃ frozen storage environment, the intermolecular forces of acrylic pressure-sensitive adhesive increase sharply, the space for molecular chain movement is greatly restricted, and the toughness of the adhesive layer decreases significantly. Under the conditions of low-temperature bonding, wide temperature fluctuations, and continuous high humidity during thawing / marinating, cracking, curling, and detachment are very likely to occur.

[0004] Patent application CN108659752A discloses a water-soluble polyacrylate pressure-sensitive adhesive for labels, prepared from the following raw materials in parts by weight: 60-80 parts of soft acrylate monomer, 0-5 parts of hard acrylate monomer, 15-30 parts of functional monomer, 5-10 parts of reactive anionic emulsifier, 0.3-0.5 parts of initiator, 100-150 parts of organic solvent, 5-10 parts of plasticizer, and 10-16 parts of pH adjuster; wherein the soft acrylate monomer is one or more of butyl acrylate and isooctyl acrylate; the hard acrylate monomer is one or two of methyl acrylate and methyl methacrylate; the functional monomer is one or more of acrylic acid and hydroxyethyl acrylate; and the reactive anionic emulsifier is ammonium methacryloyloxy polyoxypropylene sulfate.

[0005] In this technical solution, the functional monomers introduced contain a large number of carboxyl and hydroxyl polar groups. Although the bonding strength is high and it can be removed by rinsing with water, its core performance still relies on the intermolecular forces formed by the carboxyl and hydroxyl polar groups to provide cohesion and adhesion. Under freezing conditions (-15℃), the intermolecular forces between polar groups are significantly enhanced, and the mobility of molecular chain segments decreases, resulting in increased brittleness and loss of flexibility. It is prone to cracking and detachment during low-temperature bonding or temperature changes. Summary of the Invention

[0006] In order to improve the low-temperature adhesion stability and high humidity resistance and swelling resistance of label materials, while retaining the core advantages of rapid degumming with water and no residue, this application provides a low-temperature resistant water-soluble cold chain label material and its preparation method.

[0007] In a first aspect, this application provides a method for preparing a low-temperature resistant, water-soluble cold chain label material, employing the following technical solution: A method for preparing a low-temperature resistant, water-soluble cold chain label material, comprising the following steps by weight: S1: Mix 60-90 parts of ethanol aqueous solution, 60-80 parts of acrylate soft monomer, and part of initiator to obtain a premix; S2: Under an inert atmosphere, mix 20-40 parts of an aqueous ethanol solution, 15-25 parts of amphoteric acrylate monomer and 3-8 parts of functional monomer, heat to 55-65°C, add the remaining initiator, keep the reaction at this temperature for 15-25 min, add the premix, continue the reaction at this temperature for 150-210 min, cool to 40-50°C, add 40-45 parts of water-soluble polyester resin (based on solid content), 3-8 parts of triglycerides and 2-5 parts of block polyether, mix well to obtain a mixed adhesive solution; S3: Mix the mixed adhesive and crosslinking agent (0.5-1.5 parts), degas, apply to the lower surface of the substrate, cure, attach the release film, and die-cut to obtain a low-temperature resistant water-soluble cold chain label material.

[0008] In this technical solution, amphoteric acrylate monomers and functional monomers are copolymerized under the action of an initiator to form hydrophilic prepolymer segments with zwitterionic structures as the core and rich in strongly polar groups. Due to the electrostatic self-assembly effect of strong positive and negative charges within the molecules, these prepolymer segments spontaneously form nanoscale hydrophilic microdomains in the system. These microdomains construct a stable non-freezing hydration layer through strong ionic hydration, exhibiting excellent antifreeze ability and hydrophilic properties. Subsequently, a hydrophobic acrylate soft monomer premix is ​​added, forcing it to extend to the periphery of the hydrophilic microdomains and copolymerize into a continuous phase. This polymerization sequence forms a microscopic phase separation structure within the adhesive layer, with ionic microdomains as the core and hydrophobic soft chains as the shell. In this structure, the continuous phase formed by the hydrophobic soft chains provides the adhesive layer with excellent interfacial wettability and initial tack, while the hydrophilic ionic microdomains encapsulate and anchor functional components such as water-soluble polyester resin, triglycerides, and block polyethers around them, preventing migration and loss during subsequent use and ensuring the long-term stability of label performance.

[0009] Further, the curing process specifically involves: first holding at 55~65℃ for 3~4 minutes, then raising the temperature to 85~95℃ and holding for 3~5 minutes, then raising the temperature to 105~110℃ and holding for 2~3 minutes.

[0010] In this technical solution, low-temperature insulation is used to remove low-boiling-point solvents from the adhesive layer; medium-temperature insulation provides a suitable temperature for the coordination crosslinking reaction between zirconium acetylacetonate and carboxyl groups, promoting the full and uniform formation of dynamic crosslinking bonds and enhancing the cohesive force of the adhesive layer; high-temperature insulation is used for the shaping and curing of the adhesive layer, further strengthening the structural stability of the adhesive layer and its adhesion to the substrate.

[0011] Furthermore, the amphoteric acrylate monomers include sulfobetaine methacrylate and carboxybetaine methacrylate.

[0012] In this technical solution, the positive and negative charge spacing of carboxybetaine and sulfobetaine is complementary, which can greatly enhance the electrostatic self-assembly effect of hydrophilic segments, making the formed hydrophilic microregions more uniform in size and more stable in structure. At the same time, the non-icing hydration layer of the hydrophilic microregions is doubly strengthened, further improving the system's cryogenic resistance.

[0013] Furthermore, the acrylate soft monomer is at least one of butyl acrylate and isooctyl acrylate.

[0014] Furthermore, the functional monomer is at least one of acrylic acid and hydroxypropyl acrylate.

[0015] Furthermore, the crosslinking agent is zirconium acetylacetonate.

[0016] In this technical solution, zirconium acetylacetonate is used as a dynamic coordination crosslinking agent. Its tetravalent zirconium ions can form metal coordination dynamic crosslinking bonds with the carboxyl groups of functional monomers. At room temperature, the crosslinking bonds stably associate, providing sufficient cohesive force for the adhesive layer and avoiding problems such as glue overflow and slippage during room temperature storage and use. At low temperature, the crosslinking bonds can dissipate impact and thermal stress through reversible fracture-reorganization, without forming rigid crosslinking points, effectively balancing the room temperature cohesive force and low temperature flexibility of the adhesive layer. Under the condition of rinsing with running water at room temperature, water molecules quickly penetrate into the adhesive layer and compete with the carboxyl groups for coordination sites. The dynamic crosslinking network rapidly and reversibly dissociates as the adhesive layer swells, and the adhesive layer instantly loses its adhesive force to the substrate, achieving rapid overall de-adhesion of the label and leaving no glue residue on the substrate surface.

[0017] Furthermore, the initiator is azobisisobutylamidine hydrochloride.

[0018] Furthermore, the amount of azobisisobutylamidine hydrochloride used is 0.6% to 1.0% of the total mass of the acrylate soft monomer, the amphoteric acrylate monomer, and the functional monomer.

[0019] Furthermore, the water-soluble polyester resin is polyester resin AQ-55S.

[0020] In this technical solution, the water-soluble polyester resin AQ-55S contains a large number of polar groups, which on the one hand provide the basic film-forming properties and cohesive force for the adhesive layer, and on the other hand, its macromolecular chain segments undergo deep physical entanglement under the strong electrostatic field of zwitterionic monomers, which can work synergistically with the antifreeze components in the system to inhibit the crystallization of free water molecules and enhance the viscoelasticity of the system in a cryogenic environment.

[0021] Furthermore, the block polyether is poloxamer 188.

[0022] In this technical solution, the block polyether poloxamer 188 has a unique triblock structure of hydrophilic-oleophilic-hydrophilic. Under extremely cold conditions, its flexible polyether segments can effectively increase the free volume between polymer chains, playing an excellent role in internal plasticization and antifreeze. When rinsed with water, its extremely high surface activity can rapidly reduce interfacial tension, accelerate the penetration of water molecules into the interior of the adhesive layer, and synergistically promote the dissociation and degumming of the adhesive layer.

[0023] Furthermore, in step S2, after adding the water-soluble polyester resin, the steps also include adding 1 to 3 parts by weight of trehalose and 0.5 to 2 parts by weight of sodium hyaluronate.

[0024] In this technical solution, trehalose can inhibit the formation of ice crystals at low temperatures, prevent the adhesive layer from becoming brittle, and improve freeze-thaw stability; sodium hyaluronate can dissipate temperature stress and prevent the adhesive layer from cracking. The two work together to enhance the low-temperature weather resistance of the adhesive layer.

[0025] Furthermore, in step S2, after adding the water-soluble polyester resin, the step of adding 1 to 3 parts by mass of an organic amine neutralizer is also included.

[0026] Furthermore, the organic amine neutralizer is 2-amino-2-methyl-1-propanol.

[0027] In this technical solution, the organic amine neutralizer neutralizes some of the carboxylic acid groups into polymer salts, which rapidly absorb water and swell during the cleaning process. Combined with the reversible dissociation of the dynamic cross-linked network upon contact with water, the label can be peeled off as a complete film without any residue.

[0028] Furthermore, in step S2, after adding the water-soluble polyester resin, the step also includes adding 1.5 to 2.5 parts by mass of free betaine.

[0029] In this technical solution, free betaine is a small-molecule zwitterionic compound that can synergistically work with the ionic micro-regions of the polymer backbone to uniformly fill the free volume between molecular chains, optimizing the uniformity of hydrophilic and hydrophobic distribution of the adhesive layer. On the one hand, it improves the interfacial wettability and adhesion stability of the adhesive layer to the low-surface-energy PP substrate, enhances the anti-swelling ability in high-humidity environments, and maintains the low-temperature flexibility of the adhesive layer. On the other hand, it can quickly dissolve in water and form nano-water channels in the adhesive layer, guiding water to quickly penetrate to the bonding interface, further shortening the label delamination time.

[0030] Secondly, this application provides a low-temperature resistant, water-soluble cold chain label material prepared using the above-described preparation method.

[0031] In this technical solution, amphoteric acrylate monomers undergo copolymerization with soft acrylate monomers and functional monomers to construct a polymer backbone containing an internal salt-type zwitterionic structure. The amphoteric monomers carry strong positive and negative charges within the same molecule, forming dense ionic microregions that firmly adsorb and lock triglycerides, block polyethers, and water-soluble polyester resins around these microregions. This electrostatic coupling and steric hindrance effect not only prevents the migration and loss of components such as triglycerides under thawing and high-humidity conditions but also constructs a non-icing hydration layer between polymer chains, allowing the pressure-sensitive adhesive layer to maintain a wide free volume and excellent flexibility even at low temperatures.

[0032] In summary, this application has the following beneficial effects: This application successfully constructed a phase-separated structure at the microscopic level of the adhesive layer, with zirconium acetylacetonate as the core and hydrophobic soft chains as the shell. Combined with a zirconium acetylacetonate dynamic crosslinking system and multiple functional additives, it achieved a performance balance between stable adhesion over a wide temperature range and rapid, residue-free debonding with water. All raw materials used in this application meet food contact safety standards, making it perfectly suited for the entire process of thawing and marinating in the catering cold chain. It can meet the core requirements of long-term low-temperature bonding and daily high-frequency rinsing and reuse of PP turnover boxes. Attached Figure Description

[0033] Figure 1 The Fourier transform infrared spectra of the mixed adhesive and the cured finished adhesive layer in Example 1 are shown. Figure 2 Fourier transform infrared spectra of the cured adhesive layers in Examples 1, 3, 5 and 7; Figure 3 The images show the Fourier transform infrared spectra of the cured adhesive layers of Example 1 and Comparative Example 2. Detailed Implementation

[0034] The present application will be further described in detail below with reference to the embodiments.

[0035] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0036] Sulfonated betaine methacrylate is the inner salt of 2-(methacryloyloxy)ethyl-N,N-dimethyl-N-(3-sulfopropyl)ammonium hydroxide, food grade, with a purity of ≥99%. Carboxybetaine methacrylate is 2-(methacryloyloxy)ethyl-N,N-dimethyl-N-carboxymethylammonium hydroxide inner salt, food grade, purity ≥99%; Butyl acrylate, isooctyl acrylate, acrylic acid, hydroxypropyl acrylate, food grade, purity ≥99.5%; Azobisisobutylamidine hydrochloride, food grade, purity ≥98%; AQ-55S polyester resin, food-grade water-based sulfonated polyester, with a solid content of 30%; Zirconium acetylacetonate, food grade, purity ≥99%; Triglycerides, food grade, purity ≥95%; Poloxamer 188, food grade; 2-Amino-2-methyl-1-propanol, food grade, purity ≥99%; Trehalose, food grade, purity ≥99%; Sodium hyaluronate: food grade, number average molecular weight 20,000 Da; The chemical name of free betaine is trimethylglycine, food grade, with a purity of ≥99%.

[0037] Example 1 The preparation method of the low-temperature resistant water-soluble cold chain label material in this embodiment includes the following steps: S1: Mix 80g of ethanol aqueous solution (volume ratio of ethanol to deionized water is 3.5:1), 70g of butyl acrylate, and 0.60g of azobisisobutylamidine hydrochloride to obtain a premix. S2: Under a nitrogen atmosphere, 30g of ethanol aqueous solution, 10g of sulfobetaine methacrylate, 10g of carboxybetaine methacrylate and 5g of acrylic acid were mixed and heated to 56℃. 0.35g of azobisisobutylamidine hydrochloride was added and the reaction was kept at this temperature for 20min. The premix prepared in S1 was then added dropwise to the reaction system at a constant pressure dropping funnel at a constant rate, with the dropping time controlled at 100min. After the dropping was completed, the reaction was kept at this temperature for another 210min. After the reaction was completed, the mixture was cooled to 45℃ and 40g of polyester resin AQ-55S1, 5g of triglycerides and 4g of poloxamer 188 were added. The stirring speed was controlled at 400rpm and the mixture was stirred continuously for 60min. The solid content was adjusted to 45% to obtain a mixed adhesive solution. S3: Mix the adhesive solution and 1g of zirconium acetylacetonate, stirring at 300rpm for 10 minutes until uniformly dispersed. Transfer to a vacuum degassing machine and degas for 15 minutes under a vacuum of 400Pa. After degassing, coat the lower surface of a 75μm thick thermal synthetic paper substrate, controlling the wet coating thickness to 45μm. After coating, place in a three-stage gradient oven for curing. The curing process is as follows: first, hold at 55℃ for 4 minutes, then raise the temperature to 85℃ and hold for 5 minutes, then raise the temperature to 105℃ and hold for 3 minutes. After curing, cool to room temperature of 25℃ and mix with 58g / m 2 White glassine release paper is rolled and laminated, then die-cut and wound up. It is then cured for 36 hours in a clean environment at 25°C and 50% relative humidity to obtain a finished low-temperature resistant water-soluble cold chain label material.

[0038] Example 2 The preparation method of the low-temperature resistant water-soluble cold chain label material in this embodiment includes the following steps: S1: Mix 60g of ethanol aqueous solution (volume ratio of ethanol to deionized water is 3.5:1), 60g of butyl acrylate, and 0.35g of azobisisobutylamidine hydrochloride to obtain a premix. S2: Under a nitrogen atmosphere, 20g of ethanol aqueous solution, 10g of sulfobetaine methacrylate, 5g of carboxybetaine methacrylate and 3g of acrylic acid were mixed and heated to 65℃. 0.15g of azobisisobutylamidine hydrochloride was added and the reaction was maintained at this temperature for 15min. The premix prepared in S1 was then added dropwise to the reaction system at a constant pressure dropping funnel at a constant rate, with the dropping time controlled at 90min. After the dropping was completed, the reaction was maintained at this temperature for another 150min. After the reaction was completed, the mixture was cooled to 40℃ and 30g of polyester resin AQ-55S1, 3g of triglycerides and 2g of poloxamer 188 were added. The stirring speed was controlled at 400rpm and the mixture was stirred continuously for 60min. The solid content was adjusted to 45% to obtain a mixed adhesive solution. S3: Mix the adhesive solution and 0.5g of zirconium acetylacetonate, stirring at 300rpm for 10 minutes until uniformly dispersed. Transfer to a vacuum degassing machine and degas for 15 minutes under a vacuum of 400Pa. After degassing, coat the lower surface of a 75μm thick thermally sensitive synthetic paper substrate, controlling the wet coating thickness to 45μm. After coating, place in a three-stage gradient oven for curing. The curing process is as follows: first, heat to 55℃ for 4 minutes, then heat to 85℃ for 5 minutes, and then heat to 105℃ for 3 minutes. After curing, cool to room temperature of 25℃ and mix with 58g / m 2 White glassine release paper is rolled and laminated, then die-cut and wound up. It is then cured for 36 hours in a clean environment at 25°C and 50% relative humidity to obtain a finished low-temperature resistant water-soluble cold chain label material.

[0039] Example 3 The preparation method of the low-temperature resistant water-soluble cold chain label material in this embodiment includes the following steps: S1: Mix 90g of ethanol aqueous solution (volume ratio of ethanol to deionized water is 3.5:1), 60g of butyl acrylate, 20g of isooctyl acrylate, and 0.75g of azobisisobutylamidine hydrochloride to obtain a premix. S2: Under a nitrogen atmosphere, 40g of ethanol aqueous solution, 15g of sulfobetaine methacrylate, 10g of carboxybetaine methacrylate, 5g of acrylic acid and 3g of hydroxypropyl acrylate were mixed and heated to 60℃. 0.35g of azobisisobutylamidine hydrochloride was added and the reaction was maintained at this temperature for 25min. The premix prepared in S1 was added dropwise to the reaction system at a constant pressure dropping funnel at a constant rate, with the dropping time controlled at 120min. After the dropping was completed, the reaction was maintained at this temperature for another 190min. After the reaction was completed, the mixture was cooled to 50℃ and 150g of polyester resin AQ-55S, 1g of 2-amino-2-methyl-1-propanol, 8g of triglycerides and 5g of poloxamer 188 were added. The stirring speed was controlled at 400rpm and the mixture was stirred continuously for 60min. The solid content was adjusted to 45% to obtain a mixed adhesive solution. S3: Mix the adhesive solution and 1.5g of zirconium acetylacetonate, stirring at 300rpm for 10 minutes until uniformly dispersed. Transfer to a vacuum degassing machine and degas for 15 minutes under a vacuum of 400Pa. After degassing, coat the lower surface of a 75μm thick thermally sensitive synthetic paper substrate, controlling the wet coating thickness to 45μm. After coating, place in a three-stage gradient oven for curing. The curing process is as follows: first, heat to 65℃ for 3 minutes, then heat to 95℃ for 3 minutes, and then heat to 110℃ for 2 minutes. After curing, cool to room temperature of 25℃ and mix with 58g / m 2 White glassine release paper is rolled and laminated, then die-cut and wound up. It is then cured for 36 hours in a clean environment at 25°C and 50% relative humidity to obtain a finished low-temperature resistant water-soluble cold chain label material.

[0040] Example 4 The difference between this embodiment and embodiment 3 is as follows: S2: Under a nitrogen atmosphere, 40g of ethanol aqueous solution, 15g of sulfobetaine methacrylate, 10g of carboxybetaine methacrylate, 5g of acrylic acid and 3g of hydroxypropyl acrylate were mixed and heated to 60℃. 0.35g of azobisisobutylamidine hydrochloride was added and the reaction was maintained at this temperature for 25min. The premix prepared in S1 was added dropwise to the reaction system at a constant pressure dropping funnel at a constant rate, with the dropping time controlled at 120min. After the dropping was completed, the reaction was maintained at this temperature for another 190min. After the reaction was completed, the mixture was cooled to 50℃ and 150g of polyester resin AQ-55S, 1g of trehalose, 0.5g of sodium hyaluronate, 1g of 2-amino-2-methyl-1-propanol, 8g of triglycerides and 5g of poloxamer 188 were added. The stirring speed was controlled at 400rpm and the mixture was stirred continuously for 60min. The solid content was adjusted to 45% to obtain a mixed adhesive solution. Everything else is the same as in Example 3.

[0041] Example 5 The difference between this embodiment and embodiment 4 is that: S2: Under a nitrogen atmosphere, 40g of ethanol aqueous solution, 15g of sulfobetaine methacrylate, 10g of carboxybetaine methacrylate, 5g of acrylic acid and 3g of hydroxypropyl acrylate were mixed and heated to 60℃. 0.35g of azobisisobutylamidine hydrochloride was added and the reaction was maintained at this temperature for 25min. The premix prepared in S1 was added dropwise to the reaction system at a constant pressure dropping funnel at a constant rate, with the dropping time controlled at 120min. After the dropping was completed, the reaction was maintained at this temperature for another 190min. After the reaction was completed, the mixture was cooled to 50℃ and 150g of polyester resin AQ-55S, 3g of trehalose, 2g of sodium hyaluronate, 3g of 2-amino-2-methyl-1-propanol, 8g of triglycerides and 5g of poloxamer 188 were added. The stirring speed was controlled at 400rpm and the mixture was stirred continuously for 60min. The solid content was adjusted to 45% to obtain a mixed adhesive solution. The rest is the same as in Example 4.

[0042] Example 6 The difference between this embodiment and embodiment 3 is as follows: S2: Under a nitrogen atmosphere, 40g of ethanol aqueous solution, 15g of sulfobetaine methacrylate, 10g of carboxybetaine methacrylate, 5g of acrylic acid and 3g of hydroxypropyl acrylate were mixed and heated to 60℃. 0.35g of azobisisobutylamidine hydrochloride was added and the reaction was maintained at this temperature for 25min. The premix prepared in S1 was added dropwise to the reaction system at a constant pressure dropping funnel at a constant rate, with the dropping time controlled at 120min. After the dropping was completed, the reaction was maintained at this temperature for another 190min. After the reaction was completed, the mixture was cooled to 50℃ and 150g of polyester resin AQ-55S, 1.5g of trimethylglycine, 1g of 2-amino-2-methyl-1-propanol, 8g of triglycerides and 5g of poloxamer 188 were added. The stirring speed was controlled at 400rpm and the mixture was stirred continuously for 60min. The solid content was adjusted to 45% to obtain a mixed adhesive solution. Everything else is the same as in Example 3.

[0043] Example 7 The difference between this embodiment and embodiment 3 is as follows: S2: Under a nitrogen atmosphere, 40g of ethanol aqueous solution, 15g of sulfobetaine methacrylate, 10g of carboxybetaine methacrylate, 5g of acrylic acid and 3g of hydroxypropyl acrylate were mixed and heated to 60℃. 0.35g of azobisisobutylamidine hydrochloride was added and the reaction was maintained at this temperature for 25min. The premix prepared in S1 was added dropwise to the reaction system at a constant pressure dropping funnel at a constant rate, with the dropping time controlled at 120min. After the dropping was completed, the reaction was maintained at this temperature for another 190min. After the reaction was completed, the mixture was cooled to 50℃ and 150g of polyester resin AQ-55S, 2.5g of trimethylglycine, 1g of 2-amino-2-methyl-1-propanol, 8g of triglycerides and 5g of poloxamer 188 were added. The stirring speed was controlled at 400rpm and the mixture was stirred continuously for 60min. The solid content was adjusted to 45% to obtain a mixed adhesive solution. Everything else is the same as in Example 3.

[0044] Comparative Example 1 The preparation method of the low-temperature resistant water-soluble cold chain label material in this comparative example includes the following steps: S1: Under a nitrogen atmosphere, 120g of ethanol aqueous solution, 20g of sulfobetaine methacrylate, 5g of acrylic acid, 70g of butyl acrylate and 0.95g of azobisisobutylamidine hydrochloride were mixed and heated to 56℃ and reacted for 330min. After the reaction was completed, the mixture was cooled to 45℃, and 140g of polyester resin AQ-55S, 5g of triglycerides and 4g of poloxamer 188 were added. The stirring speed was controlled at 400rpm and the mixture was stirred continuously for 60min. The solid content was adjusted to 45% to obtain a mixed adhesive solution. S2: Mix the adhesive solution and 1g of zirconium acetylacetonate, stirring at 300rpm for 10 minutes until uniformly dispersed. Transfer to a vacuum degassing machine and degas for 15 minutes under a vacuum of 400Pa. After degassing, coat the lower surface of a 75μm thick thermally sensitive synthetic paper substrate, controlling the wet coating thickness to 45μm. After coating, place in a three-stage gradient oven for curing. The curing process is as follows: first, heat to 55℃ for 4 minutes, then heat to 85℃ for 5 minutes, and then heat to 105℃ for 3 minutes. After curing, cool to room temperature of 25℃ and mix with 58g / m 2 White glassine release paper is rolled and laminated, then die-cut and wound up. It is then cured for 36 hours in a clean environment at 25°C and 50% relative humidity to obtain a finished low-temperature resistant water-soluble cold chain label material.

[0045] Comparative Example 2 The difference between this comparative example and Example 1 is as follows: Sulfobetaine methacrylate was replaced by an equal amount of dimethylaminoethyl methacrylate. Everything else is the same as in Example 1.

[0046] Performance testing The finished low-temperature resistant water-soluble cold chain label materials prepared in Examples 1-7 and Comparative Examples 1-2 were subjected to the following performance tests. The specific results are shown in Tables 1 and 2.

[0047] The performance testing content is as follows: (1) Water absorption rate test: The sample was placed for 7 days at 23±2℃ and 80% relative humidity, and the water absorption rate of the sample was calculated by weighing. (2) Low temperature peel strength: According to GB / T 2792-2014 standard, the test sample was frozen at -15℃ for 72h and the 180° peel strength was tested (the test substrate was PP sheet). (3) Simulated freeze-thaw test: After attaching the label to the PP board, freeze at -15℃ for 12 hours, and quickly switch between -15℃ and 25℃ 10 times, with each switch lasting about 2 minutes. Observe whether the label edges show any peeling, bubbles, or cracking. (4) Adhesion at room temperature: According to GB / T 4851-2014 standard, under the standard environment of 23±2℃ and relative humidity of 50%±10%, after the label is attached to the PP board, a 1kg standard weight is suspended, and the adhesion time of the label without slippage or falling off is tested. (5) Water degumming performance test: In flowing water at 23±2℃, record the time it takes for the label to completely detach from the PP substrate surface without any adhesive residue remaining on the substrate.

[0048] Table 1. Performance test data of the label materials prepared in Examples 1-7 and Comparative Examples 1-2

[0049] Table 2. Test data on temperature resistance and delamination properties of the label materials prepared in Examples 1-7 and Comparative Examples 1-2.

[0050] In Examples 1-3, an ordered hydrophilic-hydrophobic phase separation structure was constructed through stepwise polymerization and synergistic interaction with zwitterionic monomers. This achieved a balance between low water absorption, high and low temperature bonding strength, excellent temperature change resistance, and rapid degumming with water. The basic performance fully meets the core usage requirements of cold chain thawing and pickling scenarios.

[0051] In Examples 4 and 5, the introduction of trehalose and sodium hyaluronate further reduced the water absorption rate of the adhesive layer, significantly improved the low-temperature peel strength and holding time, and enhanced the long-term low-temperature storage stability of the label, making it suitable for longer-term cold chain storage and transportation conditions.

[0052] In Examples 6 and 7, the introduction of trimethylglycine significantly shortens the degumming time with water while maintaining the low water absorption rate, high and low temperature bonding performance, and temperature change resistance of the adhesive layer. This significantly improves the cleaning and reuse efficiency of the turnover box and precisely matches the daily high-frequency turnover needs of catering stores.

[0053] In Comparative Example 1, the one-step mixing and polymerization method could not form the ordered phase separation structure of this application. The water absorption rate of the adhesive layer increased significantly, the low-temperature bonding strength decreased significantly, and the edges curled and cracked after freeze-thaw cycles.

[0054] In Comparative Example 2, replacing the core zwitterionic monomer with a single cationic monomer failed to construct an internal salt-type antifreeze ionic microdomain, resulting in a significant decrease in the low-temperature antifreeze properties and interfacial bonding of the adhesive layer, and edge curling after freeze-thaw cycles.

[0055] from Figures 1-3 The Fourier transform infrared spectrum shows that: Figure 1 In the middle, 1710 cm of the mixed adhesive before curing -1 There is a distinct absorption valley of free -COOH at this point, corresponding to the C=O stretching vibration; this peak weakens after curing; simultaneously, after curing, the peak at 1560 cm⁻¹... -1 New COO - The absorption valley of the antisymmetric stretching vibration is attributed to the carboxyl group and Zr. 4+ Post-coordination COO - The antisymmetric stretching vibration, with displacement relative to the free carboxylate, indicates that the carboxylate ion has coordinated with the zirconium ion; 960 cm⁻¹ -1 The newly added absorption valleys are attributed to the vibrational modes of the Zr-OC framework formed after coordination. These changes indicate that zirconium acetylacetonate underwent a coordination crosslinking reaction with the carboxyl groups of acrylic acid, and a dynamic crosslinking network was formed during the curing process.

[0056] Figure 2 In the four sets of embodiments, the overall spectral morphology is basically the same, all containing 1730 cm⁻¹. -1 Ester group C=O, 1560cm -1 COO - Antisymmetric stretching vibration, 1040 cm -1 S=O sulfonic acid group, 960cm -1 The presence of common characteristic peaks, such as those related to Zr-OC framework vibration, confirms that copolymers containing zirconium acetylacetonate structures and zirconium acetylacetonate crosslinking networks were synthesized in all examples. The main differences between the examples are: due to a slightly higher amount of sulfobetaine methacrylate, the S=O peak in Example 3 is slightly deeper than that in Example 1; due to the effects of trehalose and sodium hyaluronate, the OH peak in Example 5 is significantly broadened and deepened, reaching 1075 cm⁻¹. -1 The COC peak is wider in the vicinity; due to the effect of trimethylglycine, the CN peak in Example 7 is deeper than that in Example 1.

[0057] Figure 3 In Comparative Example 2, sulfobetaine methacrylate was replaced by dimethylaminoethyl methacrylate in equal mass. The S=O characteristic peak disappeared, and the CN peak of the tertiary amine appeared. The spectral difference precisely corresponded to the formulation difference, indicating that sulfobetaine methacrylate in Example 1 did indeed participate in the copolymerization reaction. The C=C double bond peaks of both groups of samples disappeared, indicating that the polymerization reaction could proceed normally under both formulations. In addition, both groups of samples formed Zr crosslinking networks, but Comparative Example 2, due to the lack of zwitterionic internal salt structure, showed a decrease in low-temperature peel strength and edge curling after freeze-thaw.

[0058] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a low-temperature resistant, water-soluble cold chain label material, characterized in that, By weight, the steps include: S1: Mix 60-90 parts of ethanol aqueous solution, 60-80 parts of acrylate soft monomer, and part of initiator to obtain a premix; S2: Under an inert atmosphere, mix 20-40 parts of an aqueous ethanol solution, 15-25 parts of amphoteric acrylate monomer and 3-8 parts of functional monomer, heat to 55-65°C, add the remaining initiator, keep the reaction at this temperature for 15-25 min, add the premix, continue the reaction at this temperature for 150-210 min, cool to 40-50°C, add 40-45 parts of water-soluble polyester resin (based on solid content), 3-8 parts of triglycerides and 2-5 parts of block polyether, mix well to obtain a mixed adhesive solution; S3: Mix the mixed adhesive and crosslinking agent (0.5-1.5 parts), degas, apply to the lower surface of the substrate, cure, attach the release film, and die-cut to obtain a low-temperature resistant water-soluble cold chain label material.

2. The method for preparing the low-temperature resistant water-soluble cold chain label material according to claim 1, characterized in that, The amphoteric acrylate monomers include sulfobetaine methacrylate and carboxybetaine methacrylate.

3. The method for preparing the low-temperature resistant water-soluble cold chain label material according to claim 2, characterized in that, The acrylate soft monomer is at least one of butyl acrylate and isooctyl acrylate.

4. The method for preparing the low-temperature resistant water-soluble cold chain label material according to claim 2, characterized in that, The functional monomer is at least one of acrylic acid and hydroxypropyl acrylate.

5. The method for preparing the low-temperature resistant water-soluble cold chain label material according to claim 1, characterized in that, The water-soluble polyester resin is polyester resin AQ-55S.

6. The method for preparing the low-temperature resistant water-soluble cold chain label material according to claim 1, characterized in that, The crosslinking agent is zirconium acetylacetonate.

7. The method for preparing the low-temperature resistant water-soluble cold chain label material according to claim 1, characterized in that, In step S2, after adding the water-soluble polyester resin, the steps also include adding 1-3 parts by weight of trehalose and 0.5-2 parts by weight of sodium hyaluronate.

8. The method for preparing the low-temperature resistant water-soluble cold chain label material according to claim 1, characterized in that, In step S2, after adding the water-soluble polyester resin, the step of adding 1.5 to 2.5 parts by mass of free betaine is also included.

9. A low-temperature resistant, water-soluble cold chain label material prepared by the preparation method according to any one of claims 1 to 8.

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