Preparation method of water-washing removable PETG label adhesive and application of product of water-washing removable PETG label adhesive

Abstract

The invention belongs to the technical field of thermal shrinkage label films, and particularly relates to a preparation method of a water-washing removable PETG label adhesive and application of a product of the water-washing removable PETG label adhesive, the water-washing removable PETG label adhesive is formed by adopting an emulsion polymerization method on the basis of PSt / P (BA-MMA) core-shell structure emulsion, and the application of the adhesive in PETG labels is provided. The problems that an existing adhesive is high in adhesive capacity and serious in residue are solved, the balance of adhesive force and cohesive force is achieved through the core-shell microsphere structure, the wetting power with a base material is reduced, the compatibility with the base material is reduced, and the performance that the adhesive is removed by washing is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of heat shrinkable label films, and particularly relates to a preparation method of a water-washable and removable PETG label adhesive and application of the product. Background Art

[0002] Removable labels are functional labels that, due to their removable, residue-free nature, eliminate adhesive contamination during bottle post-processing, significantly improving the efficiency and value of bottle recycling and reuse. Currently, removable pressure-sensitive adhesives are mostly made with a cross-linked, low-viscosity formula. However, after prolonged use, especially in high-temperature and high-humidity environments, the adhesive exhibits permanent adhesive properties, making it difficult to completely remove from the bottle, often leaving some adhesive residue. Summary of the Invention

[0003] In response to the problems in the prior art, the present invention provides a water-washable and removable PETG label adhesive, which solves the problem that the existing adhesives have strong adhesive ability but serious residue. The core-shell microsphere structure is used to achieve a balance between adhesive force and cohesive force, reduce the wetting force with the substrate, reduce the compatibility with the substrate, and improve the performance of the adhesive in being removed by water.

[0004] In order to achieve the above technical objectives, the technical solution of the present invention is: A method for preparing a water-washable and removable PETG label adhesive comprises the following steps: Step 1: alkali washing, water washing, and reduced pressure distillation of 2-ethylhexyl acrylate to remove the polymerization inhibitor, wherein the alkali washing adopts a sodium hydroxide solution with a mass fraction of 5%; Step 2: Mix methacrylic acid, N-hydroxymethyl acrylamide, 1,4-butanediol diacrylate, sodium laurylaminopropionate, 25% by mass ammonia water, and deionized water to form a pre-emulsion; Step 3: Place the PSt / P(BA-MMA) core-shell structure emulsion into a reactor, introduce nitrogen into the reactor to form a nitrogen atmosphere, and then heat the reactor to 80° C. with stirring; add 50% potassium persulfate solution and stir evenly to obtain a premixed emulsion; Step 4: adding the polyvinyl alcohol solution and prelactic acid dropwise to the premixed emulsion, respectively; adding the remaining 50% of the potassium persulfate solution after the addition is completed; and keeping the temperature to react for 3 hours to obtain an emulsion with a solid content of 50%; the polyvinyl alcohol solution and prelactic acid are added at the same rate of 45-50 drops / min; Step 5: Add 10% ammonia water to 100 parts of the above emulsion to adjust the pH to 6.5, add 3 parts of silicone defoamer and 8 parts of tackifier to obtain a water-washable and removable PETG label adhesive.

[0005] The mass ratio of the emulsion with a solid content of 50% is: 80-90 parts of PSt / P (BA-MMA) core-shell structure emulsion, 40-50 parts of 2-ethylhexyl acrylate, 7-9 parts of polyvinyl alcohol solution, 3 parts of methacrylic acid, 2 parts of N-hydroxymethyl acrylamide, 2 parts of 1,4-butanediol diacrylate, 3 parts of sodium dodecylaminopropionate, 0.02 parts of potassium persulfate solution, 0.85 parts of 25% ammonia water by mass, and 20 parts of deionized water.

[0006] The polyvinyl alcohol solution is a polyvinyl alcohol aqueous solution with a mass concentration of 12.5%.

[0007] The potassium persulfate solution is an aqueous solution with a mass concentration of 0.2%.

[0008] The organosilicon defoamer is Dow Corning DOW SIL62.

[0009] The thickener is a sodium polyacrylate thickener, specifically 5% ammonium salt of Premier ADE-60, with a viscosity of 3700 cp.

[0010] The PSt / P (BA-MMA) core-shell structure emulsion adopts a seed semi-continuous dropwise emulsion polymerization method to synthesize a polystyrene / polybutyl acrylate and methyl methacrylate copolymer [PSt / P (BA-MMA)] core-shell structure emulsion of the inner layer of the adhesive particles; the emulsion is composed of two parts: the synthesis of the seed emulsion and the synthesis of the P (BA-MMA) shell outside the core.

[0011] The synthesis of the seed emulsion is the synthesis of a polystyrene core, and the mass ratio of the seed emulsion is 60 parts of polystyrene, 40 parts of deionized water, 2.4 parts of sodium lauryl sulfate, 1.3 parts of nonylphenol polyvinyl ether, 0.018 parts of potassium persulfate solution, and 0.3 parts of a pH buffer, wherein the potassium persulfate solution is a potassium persulfate solution with a mass fraction of 0.18%, and the pH buffer is sodium bicarbonate; the synthesis of the seed emulsion comprises the following steps: a1, alkali washing, water washing, and reduced pressure distillation of styrene to remove the polymerization inhibitor; the alkali washing is carried out by a2, adding styrene, deionized water, sodium lauryl sulfate, nonylphenol polyvinyl ether, and sodium bicarbonate into a reactor, and removing oxygen with nitrogen. After vigorously stirring for 30 minutes under nitrogen, pre-emulsification is obtained. a2, heating the pre-emulsion to 70°C, adding 60% potassium persulfate solution, and keeping the temperature at 45°C with a stirring speed of 200-230 rpm; a3, adding the remaining 40% potassium persulfate solution into the reactor to fully react the monomers. Keep the temperature at 70°C for 2.5 hours to obtain a polystyrene core.

[0012] The mass ratio of the core-outer P (BA-MMA) shell is: 40 parts of butyl acrylate, 20 parts of methyl methacrylate, 0.018 parts of initiator, and 3.7 parts of emulsifier solution; wherein the initiator is a potassium persulfate solution with a mass fraction of 0.18%, the emulsifier in the emulsifier solution is composed of 2.4 parts of sodium lauryl sulfate and 1.3 parts of nonylphenol polyvinyl ether, and the mass concentration of the emulsifier solution is 6%. The synthesis of the outer core P (BA-MMA) shell includes the following steps: b1, alkali washing, water washing and reduced pressure distillation of butyl acrylate and methyl methacrylate respectively to remove the polymerization inhibitor; b2, butyl acrylate, methyl methacrylate, emulsifier solution and initiator solution are mixed and stirred to form a pre-emulsion; b3, the pre-emulsion is slowly added dropwise to the seed emulsion, and the mixture is kept at 70°C for reaction for 3 hours; the dropping speed is 20-25 drops / min; b4, the solution after the reaction is completed is cooled to room temperature, and filtered through gauze to obtain a PSt / P (BA-MMA) core-shell structure emulsion with a core-shell ratio of 1:1 and a solid content of 50%.

[0013] The water-washable and removable PETG label adhesive is applied to a PETG label film to prepare the water-washable and removable PETG label film.

[0014] The PETG label film has an ABA three-layer structure, formed through a three-layer co-extrusion, cast film, and stretching process. The thickness of the PETG label film is 38-45μm, with a shrinkage rate of 60-65% in TD and 15-20% in MD. It also has a light transmittance of ≥87%, demonstrating excellent printing performance.

[0015] The label film is mainly printed in gravure printing mode, with the designed pattern and text printed on one side to form a label film roll.

[0016] The washable and removable PETG label is prepared by evenly applying the washable and removable PETG label adhesive to a release paper using a coating process on a coating machine, with a release force of ≤20g / 25mm. The adhesive is then dried and cured at 90-150°C, followed by online cooling to form an adhesive layer on the release paper surface. The unprinted surface of the PETG label film is laminated with the adhesive-coated surface of the release paper using a laminating device on the coating machine. The laminating process is followed by winding and cutting to obtain the washable and removable PETG label.

[0017] The PETG label is removed from the release paper of the washable and removable PETG label by a labeling machine or manual operation, and then pasted on the packaging container (bottle) to become a product label.

[0018] During the recycling process, the PETG label attached to the container surface is treated with 80°C hot water or steam for 20-90 seconds. The label film automatically detaches from the container, leaving no adhesive residue on the container. At this time, the PETG label film, due to its elastic properties, shrinks and curls in the hot water, sinking to the bottom of the water.

[0019] This washable, removable PETG label adhesive is formed through emulsion polymerization of a Pst / P(BA-MMA) core-shell emulsion. This core-shell emulsion-based polymeric adhesive increases the adhesive's Tg and maintains good adhesion over a wider temperature range, particularly at low temperatures. During use, the adhesive contains a large number of ester groups, which are present in the polyacrylate polymer. The PETG label material also contains a large number of ester groups. The two have similar polarity, resulting in excellent compatibility and strong adhesion. However, glass, used as a container, is a non-polar material, differing from the polarity of the acrylic polymer, resulting in poor adhesion. Therefore, to ensure strong adhesion between the label and non-polar materials such as glass, a certain amount of polyvinyl alcohol is added to the adhesive. Polyvinyl alcohol reduces the interfacial tension between the non-polar material and the adhesive, increasing the adhesive's glass strength and initial tack. At the same time, polyvinyl alcohol is a hot water-soluble material with good solubility in 80°C hot water. During the immersion process in 80°C hot water, the grafted polyvinyl alcohol molecular chains will partially break and dissolve, which will reduce the adhesion of the adhesive and improve the hot water removal performance of the label.

[0020] In the PSt / P(BA-MMA) core-shell structure, styrene is a very weakly polar monomer, while PSt is a non-polar substance. Within the adhesive structure layer composed of the polar acrylate polymer shell, these non-polar styrene polymer cores form interstitial breakpoints, reducing the adhesive's cohesion. Furthermore, the styrene core structure reduces the effective content of the acrylate polymer, which plays a bonding role in adhesives of the same thickness, resulting in a relative decrease in adhesion. Secondly, because the PSt / P(BA-MMA) core-shell structure is formed by a polymerization reaction, there is strong chemical bonding and physical entanglement of the polymer chains between the core and shell. During use, the two behave as a single material, thus achieving a controlled reduction in cohesion.

[0021] Adding N-hydroxymethyl acrylamide as a cross-linking agent to the adhesive can provide a self-cross-linking system containing hydroxymethyl groups, increase the molecular weight and Tg of the adhesive, and help to improve the cohesion of acrylic adhesives. At the same time, it expands the temperature range of adhesive bonding, but has little effect on the total peel strength and shear adhesion failure temperature.

[0022] During use, PETG heat-shrinkable label film has a high shrinkage rate. The immersion temperature is 80°C, which is higher than the Tg of the PETG material. Under the action of this heat, it can break the constraints of the shrink film's shaping process on the molecular segments and achieve the purpose of self-shrinkage. Although the shrinkage force generated during the shrinkage process does not act directly on the adhesive layer like the peeling force, it can also eliminate some of the adhesive force, reducing the adhesion between the label and the bottle body, making it easier for the label to fall off the container.

[0023] It can be seen from the above description that the present invention has the following advantages: 1. The present invention solves the problem of strong adhesive ability and serious residue of existing adhesives. It uses the core-shell microsphere structure to ensure the bonding effect while reducing the wetting force with the substrate, reducing the compatibility with the substrate, and improving the performance of the adhesive being removed by water washing.

[0024] 2. The present invention utilizes the copolymerization of polyvinyl alcohol on the surface of core-shell microspheres to improve the adhesion between the label and the adhesive, and adds a bifunctional acrylic monomer into the shell layer to form intra-particle crosslinking, thereby increasing the cohesive force of the adhesive and reducing the peeling force. DETAILED DESCRIPTION

[0025] The present invention is described in detail with reference to the embodiments, but no limitation is imposed on the claims of the present invention.

[0026] The synthesis method of the PSt / P (BA-MMA) core-shell structure emulsion comprises: synthesis of a seed emulsion and synthesis of a P (BA-MMA) shell outside the core; The mass ratio of the seed emulsion is 60 parts of polystyrene, 40 parts of deionized water, 2.4 parts of sodium lauryl sulfate, 1.3 parts of nonylphenol polyvinyl ether, 0.018 parts of potassium persulfate solution, and 0.3 parts of pH buffer, wherein the potassium persulfate solution is a potassium persulfate solution with a mass fraction of 0.18%, and the pH buffer is sodium bicarbonate. The synthesis of the seed emulsion comprises the following steps: a1, alkali washing, water washing, and reduced pressure distillation of styrene to remove the polymerization inhibitor; the alkali washing uses 5% sodium hydroxide; a2, Styrene, deionized water, sodium lauryl sulfate, nonylphenol polyvinyl ether, and sodium bicarbonate were added to a reactor, and oxygen was removed with nitrogen. The mixture was vigorously stirred under nitrogen for 30 minutes to obtain a pre-emulsion. In step a2, the pre-emulsion was heated to 70°C, 60% potassium persulfate solution was added, and the mixture was stirred at 200-230 rpm and kept at 45°C for reaction. In step a3, the remaining 40% potassium persulfate solution was added to the reactor to fully react the monomers. The mixture was kept at 70°C for 2.5 hours to obtain a polystyrene core.

[0027] The mass ratio of the core P (BA-MMA) shell is: 40 parts of butyl acrylate, 20 parts of methyl methacrylate, 0.018 parts of initiator, and 3.7 parts of emulsifier solution; wherein the initiator is a potassium persulfate solution with a mass fraction of 0.18%, the emulsifier in the emulsifier solution is composed of 2.4 parts of sodium lauryl sulfate and 1.3 parts of nonylphenol polyvinyl ether, and the mass concentration of the emulsifier solution is 6%. The synthesis of the outer core P (BA-MMA) shell includes the following steps: b1, alkali washing, water washing and reduced pressure distillation of butyl acrylate and methyl methacrylate respectively to remove the polymerization inhibitor; b2, butyl acrylate, methyl methacrylate, emulsifier solution and initiator solution are mixed and stirred to form a pre-emulsion; b3, the pre-emulsion is slowly added dropwise to the seed emulsion, and the mixture is kept at 70°C for reaction for 3 hours; the dropping speed is 20-25 drops / min; b4, the solution after the reaction is completed is cooled to room temperature, and filtered through gauze to obtain a PSt / P (BA-MMA) core-shell structure emulsion with a core-shell ratio of 1:1 and a solid content of 50%.

[0028] Example 1 A method for preparing a water-washable and removable PETG label adhesive comprises the following steps: Step 1, weighing the raw materials according to the ratio: 80 parts of PSt / P (BA-MMA) core-shell structure emulsion, 50 parts of 2-ethylhexyl acrylate, 7 parts of polyvinyl alcohol solution, 3 parts of methacrylic acid, 2 parts of N-hydroxymethyl acrylamide, 2 parts of 1,4-butanediol diacrylate, 3 parts of sodium dodecylaminopropionate, 0.02 parts of potassium persulfate solution, 0.85 parts of 25% ammonia water, and 20 parts of deionized water; the polyvinyl alcohol solution uses a polyvinyl alcohol aqueous solution with a mass concentration of 12.5%; the potassium persulfate solution uses an aqueous solution with a mass concentration of 0.2%; Step 2, alkali washing, water washing, and reduced pressure distillation of 2-ethylhexyl acrylate to remove the polymerization inhibitor; Step 3, methacrylic acid, N-hydroxymethyl acrylamide, 1,4-butanediol diacrylate, sodium laurylaminopropionate, 25% by mass ammonia water and deionized water are stirred uniformly to prepare a pre-emulsion; Step 4: Place the PSt / P(BA-MMA) core-shell structure emulsion into a reactor, introduce nitrogen into the reactor to form a nitrogen atmosphere, and then heat the reactor to 80° C. with stirring; add 50% potassium persulfate solution and stir evenly to obtain a premixed emulsion; Step 5: Add the polyvinyl alcohol solution and pre-lactic acid dropwise to the premixed emulsion, respectively. After the addition is completed, add the remaining 50% of the potassium persulfate solution, and keep the temperature to react for 3 hours to obtain an emulsion with a solid content of 50%. The polyvinyl alcohol solution and pre-lactic acid are added at the same rate of 45-50 drops / min. In step 6, 10% ammonia water was added to 100 parts of the above emulsion to adjust the pH to 6.5, and 3 parts of an organosilicon defoamer and 8 parts of a tackifier were added to obtain a water-washable and removable PETG label adhesive. The organosilicon defoamer was Dow Corning DOW SIL62, and the tackifier was 5% of the ammonium salt of Premilast ADE-60 with a viscosity of 3700 cp.

[0029] The washable and removable PETG label adhesive is applied to a PETG label film to produce a washable and removable PETG label. The PETG label film has an ABA three-layer structure, formed through a three-layer co-extrusion, cast film, and stretching process. The PETG label film has a thickness of 38-45 μm, a shrinkage (TD) of 60-65%, a shrinkage (MD) of 15-20%, and a light transmittance of ≥87%, demonstrating excellent printing properties. The label film is gravure-printed, with the designed pattern and text printed on one side, resulting in a label film roll.

[0030] The washable and removable PETG label adhesive is evenly distributed on the release paper through a coating process on a coating machine, with a release force of ≤20g / 25mm. It is then dried and solidified at 90-150℃ and cooled online to form an adhesive layer on the surface of the release paper. The unprinted surface of the PETG label film and the surface of the release paper coated with the adhesive layer are then laminated through the laminating device of the coating machine. After winding and cutting, the washable and removable PETG label is obtained.

[0031] The PETG label is removed from the release paper of the water-washable and removable PETG label by a labeling machine or manual operation, and then pasted on the packaging container (bottle) to become a product label.

[0032] After testing, the adhesive strength and adhesion of the water-washable removable PETG label adhesive are: Adhesion strength (PETG film) 9.2N / 25mm. Adhesion strength (glass bottle) 2.5N / 25mm; Adhesion strength (PET bottle) 7.3N / 25mm.

[0033] Simulate the process of soaking and removing labels from packaging (bottles) to test whether PETG labels can be removed by washing.

[0034] Sample: Washable removable PETG label attached to glass bottle.

[0035] Place the glass bottle with the water-removable PETG label in a constant temperature cleaning tank, use 80℃ hot water as the cleaning medium, and soak for ≤90s.

[0036] Observe the changes in the water-removable PETG label during the immersion process.

[0037] A comparative test was conducted using traditional self-adhesive plastic labels and commercially available washable removable PETG labels.

[0038] The case is shown as follows by comparing the example 1 with the conventional adhesive plastic label and the commercialized water-washable removable PETG label (comparative example 1):

[0039] Example 2 A preparation method of a water-washable removable PETG label adhesive comprises the following steps: Step 1, according to the proportion, the raw materials are weighed: 85 parts of PSt / P(BA-MMA) core-shell structure emulsion, 45 parts of acrylic acid-2-ethylhexyl ester, 8 parts of polyvinyl alcohol solution, 3 parts of methacrylic acid, 2 parts of N-hydroxymethyl acrylamide, 2 parts of 1,4-butanediol diacrylate, 3 parts of sodium dodecyl amino propionate, 0.02 parts of potassium persulfate solution, 0.85 parts of 25% ammonia water, and 20 parts of deionized water; the polyvinyl alcohol solution is a polyvinyl alcohol aqueous solution with a mass concentration of 12.5%; the potassium persulfate solution is an aqueous solution with a mass concentration of 0.2%; Step 2, the acrylic acid-2-ethylhexyl ester is subjected to alkali washing, water washing, and reduced pressure distillation to remove the polymerization inhibitor; Step 3, the methacrylic acid, N-hydroxymethyl acrylamide, 1,4-butanediol diacrylate, sodium dodecyl amine propionate, 25% ammonia water, and deionized water are stirred uniformly to prepare a pre-emulsion; Step 4, the PSt / P(BA-MMA) core-shell structure emulsion is put into a reactor, nitrogen is introduced to form a nitrogen atmosphere, and then the stirring is heated to 80℃; 50% potassium persulfate solution is added and stirred uniformly to obtain a premixed emulsion; Step 5, the polyvinyl alcohol solution and the pre-acid are added dropwise into the above premixed emulsion, and then the remaining 50% potassium persulfate solution is added after the dropwise addition is completed, and the reaction is kept for 3h to obtain an emulsion with a solid content of 50%; the dropwise addition rates of the polyvinyl alcohol solution and the pre-acid are the same, both being 45-50 drops / min; Step 6, based on 100 parts of the above emulsion, 10% ammonia water is added, adjusted to pH 6.5, 3 parts of silicone defoaming agent and 8 parts of tackifier are added to obtain a water-washable removable PETG label adhesive, wherein the silicone defoaming agent is Dow Corning DOW SIL62; the tackifier is 5% ammonium salt of Pluriol ADE-60 with a viscosity of 3700cp.

[0040] The washable and removable PETG label adhesive is applied to a PETG label film to produce a washable and removable PETG label. The PETG label film has an ABA three-layer structure, formed through a three-layer co-extrusion, cast film, and stretching process. The PETG label film has a thickness of 38-45 μm, a shrinkage (TD) of 60-65%, a shrinkage (MD) of 15-20%, and a light transmittance of ≥87%, demonstrating excellent printing properties. The label film is gravure-printed, with the designed pattern and text printed on one side, resulting in a label film roll.

[0041] The washable and removable PETG label adhesive is evenly distributed on the release paper through a coating process on a coating machine, with a release force of ≤20g / 25mm. It is then dried and solidified at 90-150℃ and cooled online to form an adhesive layer on the surface of the release paper. The unprinted surface of the PETG label film and the surface of the release paper coated with the adhesive layer are then laminated through the laminating device of the coating machine. After winding and cutting, the washable and removable PETG label is obtained.

[0042] The PETG label is removed from the release paper of the water-washable and removable PETG label by a labeling machine or manual operation, and then pasted on the packaging container (bottle) to become a product label.

[0043] After testing, the adhesive strength and adhesion of the water-washable removable PETG label adhesive are: Adhesion strength (PETG film) 11.1N / 25mm. Adhesion strength (glass bottle) 3.1N / 25mm; Adhesion strength (PET bottle) 8.2N / 25mm.

[0044] Simulate the process of soaking and removing labels from packaging (bottles) to test whether PETG labels can be removed by washing.

[0045] Sample: Washable removable PETG label attached to glass bottle.

[0046] Place the glass bottle with the water-removable PETG label in a constant temperature cleaning tank, use 80℃ hot water as the cleaning medium, and soak for ≤90s.

[0047] Observe the changes in the water-removable PETG label during the immersion process.

[0048] A comparative test was conducted using traditional self-adhesive plastic labels and commercially available washable removable PETG labels.

[0049] Comparison of Example 2 with a traditional self-adhesive plastic label and a commercially available water-removable PETG label (Comparative Example 2) shows the following:

[0050] Example 3 A method for preparing a water-washable and removable PETG label adhesive comprises the following steps: Step 1, weighing the raw materials according to the ratio: 90 parts of PSt / P (BA-MMA) core-shell structure emulsion, 40 parts of 2-ethylhexyl acrylate, 9 parts of polyvinyl alcohol solution, 3 parts of methacrylic acid, 2 parts of N-hydroxymethyl acrylamide, 2 parts of 1,4-butanediol diacrylate, 3 parts of sodium dodecylaminopropionate, 0.02 parts of potassium persulfate solution, 0.85 parts of 25% ammonia water, and 20 parts of deionized water; the polyvinyl alcohol solution uses a polyvinyl alcohol aqueous solution with a mass concentration of 12.5%; the potassium persulfate solution uses an aqueous solution with a mass concentration of 0.2%; Step 2, alkali washing, water washing, and reduced pressure distillation of 2-ethylhexyl acrylate to remove the polymerization inhibitor; Step 3, methacrylic acid, N-hydroxymethyl acrylamide, 1,4-butanediol diacrylate, sodium laurylaminopropionate, 25% by mass ammonia water and deionized water are stirred uniformly to prepare a pre-emulsion; Step 4: Place the PSt / P(BA-MMA) core-shell structure emulsion into a reactor, introduce nitrogen into the reactor to form a nitrogen atmosphere, and then heat the reactor to 80° C. with stirring; add 50% potassium persulfate solution and stir evenly to obtain a premixed emulsion; Step 5: Add the polyvinyl alcohol solution and pre-lactic acid dropwise to the premixed emulsion, respectively. After the addition is completed, add the remaining 50% of the potassium persulfate solution, and keep the temperature to react for 3 hours to obtain an emulsion with a solid content of 50%. The polyvinyl alcohol solution and pre-lactic acid are added at the same rate of 45-50 drops / min. In step 6, 10% ammonia water was added to 100 parts of the above emulsion to adjust the pH to 6.5, and 3 parts of an organosilicon defoamer and 8 parts of a tackifier were added to obtain a water-washable and removable PETG label adhesive. The organosilicon defoamer was Dow Corning DOW SIL62, and the tackifier was 5% of the ammonium salt of Premilast ADE-60 with a viscosity of 3700 cp.

[0051] The washable and removable PETG label adhesive is applied to a PETG label film to produce a washable and removable PETG label. The PETG label film has an ABA three-layer structure, formed through a three-layer co-extrusion, cast film, and stretching process. The PETG label film has a thickness of 38-45 μm, a shrinkage (TD) of 60-65%, a shrinkage (MD) of 15-20%, and a light transmittance of ≥87%, demonstrating excellent printing properties. The label film is gravure-printed, with the designed pattern and text printed on one side, resulting in a label film roll.

[0052] The washable and removable PETG label adhesive is evenly distributed on the release paper through a coating process on a coating machine, with a release force of ≤20g / 25mm. It is then dried and solidified at 90-150℃ and cooled online to form an adhesive layer on the surface of the release paper. The unprinted surface of the PETG label film and the surface of the release paper coated with the adhesive layer are then laminated through the laminating device of the coating machine. After winding and cutting, the washable and removable PETG label is obtained.

[0053] The PETG label is removed from the release paper of the water-washable and removable PETG label by a labeling machine or manual operation, and then pasted on the packaging container (bottle) to become a product label.

[0054] After testing, the adhesive strength and adhesion of the water-washable removable PETG label adhesive are: Adhesion strength (PETG film) 11.7N / 25mm. Adhesion strength (glass bottle) 4.0N / 25mm; Adhesion strength (PET bottle) 8.7N / 25mm.

[0055] Simulate the process of soaking and removing labels from packaging (bottles) to test whether PETG labels can be removed by washing.

[0056] Sample: Washable removable PETG label attached to glass bottle.

[0057] Place the glass bottle with the water-removable PETG label in a constant temperature cleaning tank, use 80℃ hot water as the cleaning medium, and soak for ≤90s.

[0058] Observe the changes in the water-removable PETG label during the immersion process.

[0059] A comparative test was conducted using traditional self-adhesive plastic labels and commercially available washable removable PETG labels.

[0060] Comparison of Example 3 with a traditional self-adhesive plastic label and a commercially available water-removable PETG label (Comparative Example 3) shows the following:

[0061] It is understood that the above specific description of the present invention is only used to illustrate the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that the present invention can still be modified or replaced with equivalents to achieve the same technical effects; as long as the use requirements are met, they are all within the scope of protection of the present invention.

Claims

1. A method for preparing a water-washable removable PETG label adhesive, characterized in that: The steps include: Step 1, alkali washing, water washing, and reduced pressure distillation of 2-ethylhexyl acrylate to remove the polymerization inhibitor; Step 2: Mix methacrylic acid, N-hydroxymethyl acrylamide, 1,4-butanediol diacrylate, sodium laurylaminopropionate, 25% by mass ammonia water, and deionized water to form a pre-emulsion; Step 3: Place the PSt / P(BA-MMA) core-shell structure emulsion into a reactor, introduce nitrogen into the reactor to form a nitrogen atmosphere, and then heat the reactor to 80° C. with stirring; add 50% potassium persulfate solution and stir evenly to obtain a premixed emulsion; Step 4: adding the polyvinyl alcohol solution and prelactic acid dropwise to the premixed emulsion, respectively; adding the remaining 50% of the potassium persulfate solution after the addition is completed; and keeping the temperature to react for 3 hours to obtain an emulsion with a solid content of 50%; the polyvinyl alcohol solution and prelactic acid are added at the same rate of 45-50 drops / min; Step 5: Add 10% ammonia water to 100 parts of the above emulsion to adjust the pH to 6.5, add 3 parts of silicone defoamer and 8 parts of tackifier to obtain a water-washable and removable PETG label adhesive.

2. The method for preparing the water-washable and removable PETG label adhesive according to claim 1, wherein: The mass ratio of the emulsion with a solid content of 50% in the step 4 is: 80-90 parts of PSt / P (BA-MMA) core-shell structure emulsion, 40-50 parts of 2-ethylhexyl acrylate, 7-9 parts of polyvinyl alcohol solution, 3 parts of methacrylic acid, 2 parts of N-hydroxymethyl acrylamide, 2 parts of 1,4-butanediol diacrylate, 3 parts of sodium dodecylaminopropionate, 0.02 parts of potassium persulfate solution, 0.85 parts of 25% ammonia water by mass, and 20 parts of deionized water.

3. The method for preparing the water-washable and removable PETG label adhesive according to claim 2, wherein: The polyvinyl alcohol solution is a polyvinyl alcohol aqueous solution with a mass concentration of 12.5%.

4. The method for preparing the water-washable and removable PETG label adhesive according to claim 2, wherein: The potassium persulfate solution is an aqueous solution with a mass concentration of 0.2%.

5. The method for preparing the water-washable and removable PETG label adhesive according to claim 2, wherein: The organosilicon defoamer is Dow Corning DOW SIL62.

6. The method for preparing the water-washable and removable PETG label adhesive according to claim 1, wherein: The thickener is a sodium polyacrylate thickener, specifically 5% ammonium salt of Premier ADE-60, with a viscosity of 3700 cp.

7. The method for preparing the water-washable and removable PETG label adhesive according to claim 1, wherein: The PSt / P (BA-MMA) core-shell structure emulsion adopts a seed semi-continuous dropwise emulsion polymerization method to synthesize a polystyrene / polybutyl acrylate and methyl methacrylate copolymer [PSt / P (BA-MMA)] core-shell structure emulsion of the inner layer of the adhesive particles; the emulsion is composed of two parts: the synthesis of the seed emulsion and the synthesis of the P (BA-MMA) shell outside the core.

8. The method for preparing the water-washable and removable PETG label adhesive according to claim 7, wherein: The synthesis of the seed emulsion is the synthesis of a polystyrene core, and the mass ratio of the seed emulsion is 60 parts of polystyrene, 40 parts of deionized water, 2.4 parts of sodium lauryl sulfate, 1.3 parts of nonylphenol polyvinyl ether, 0.018 parts of potassium persulfate solution, and 0.3 parts of a pH buffer, wherein the potassium persulfate solution is a potassium persulfate solution with a mass fraction of 0.18%, and the pH buffer is sodium bicarbonate.

9. The method for preparing the water-washable and removable PETG label adhesive according to claim 7, wherein: The mass ratio of the core-outer P (BA-MMA) shell is: 40 parts of butyl acrylate, 20 parts of methyl methacrylate, 0.018 parts of initiator, and 3.7 parts of emulsifier solution; wherein the initiator is a potassium persulfate solution with a mass fraction of 0.18%, the emulsifier in the emulsifier solution is composed of 2.4 parts of sodium lauryl sulfate and 1.3 parts of nonylphenol polyvinyl ether, and the mass concentration of the emulsifier solution is 6%.

10. The method for preparing the water-washable and removable PETG label adhesive according to claim 1, wherein: The water-washable and removable PETG label adhesive is applied to a PETG label film to prepare a water-washable and removable PETG label.

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