A modified waterborne polyurethane primer for multilayer petg heat shrinkable sleeve label paper

Abstract

The present application relates to the technical field of PETG heat shrinkable film, in particular to a modified water-based polyurethane primer for multilayer PETG heat shrinkable film sleeve label paper. The lap joint of conventional multilayer PETG heat shrinkable film sleeve label paper is poor after hygrothermal aging, and edge lifting failure easily occurs. To solve the above problems, the present application provides a modified water-based polyurethane primer for multilayer PETG heat shrinkable film sleeve label paper. Through the modified water-based polyurethane primer designed by a specific formula, the synergistic bonding reinforcement among the PETG heat shrinkable film, the UV printing layer and the acrylate pressure-sensitive adhesive layer at the final lap joint interface is creatively realized. The primer effectively bridges the difference in thermal expansion coefficient between itself and the acrylate pressure-sensitive adhesive, greatly reduces the internal stress caused by the asynchronous expansion and contraction in a humid and hot environment, and significantly improves the interface hydrolysis resistance, thereby ensuring the bonding durability of the lap joint interface in a long-term harsh environment and completely eliminating the edge lifting and interlayer peeling phenomena.

Description

Technical Field

[0001] This invention relates to the field of PETG heat shrink film technology, and specifically to a modified waterborne polyurethane primer for multilayer PETG heat shrink film labeling paper. Background Technology

[0002] PETG heat shrink film is widely used for labeling various commodities, especially cylindrical containers (such as beverage bottles and cosmetic bottles), due to its excellent transparency, high shrinkage rate, and environmentally friendly recyclability. To meet decorative and information display needs, UV inks are often used to print patterns on PETG film. However, PETG film has low surface polarity and high inertness, resulting in poor direct adhesion to UV inks. During subsequent storage, transportation, or use, the printed patterns are prone to peeling off, a phenomenon known as "ink detachment," which severely affects the product's appearance and brand image.

[0003] To address the issue of ink detachment, the industry typically introduces a water-based polyurethane primer layer between the PETG film and the UV printing layer. Water-based polyurethane possesses excellent adhesion, flexibility, and environmental friendliness, effectively bridging the PETG film and UV inks, significantly improving interlayer adhesion, and thus essentially solving the ink detachment problem for flat or full-coverage printed labels.

[0004] However, with the diversification of label designs and the increasing complexity of application scenarios, new technical challenges have emerged. Many label designs are not full-coverage printing, meaning that unprinted transparent blank areas are left around the UV-printed pattern. When such multi-layer PETG heat-shrinkable film sleeve labels are applied to cylindrical products, the labels need to be wrapped around the circumference of the container and secured with overlapping ends. In the overlapping area, the bottom acrylic pressure-sensitive adhesive layer of the label comes into direct contact with and bonds to the exposed waterborne polyurethane undercoat layer on top of the PETG film. In practical applications, especially in harsh environments with high temperature and humidity, this overlapping structure has inherent defects: on the one hand, the coefficients of thermal expansion of the acrylic pressure-sensitive adhesive and the conventional waterborne polyurethane coating are significantly different, and under ambient temperature fluctuations, their expansion and contraction are asynchronous, generating internal stress; on the other hand, the hydrolytic resistance of conventional waterborne polyurethane resin is relatively insufficient, and its physical properties are prone to degradation in high humidity environments. These two factors combined cause the bonding interface at the overlap to weaken after long-term humid and hot aging, making it prone to failure problems such as interlayer peeling and edge lifting (curling), which damages the integrity and aesthetics of the label, and may even cause the label to fall off the container in parts.

[0005] Therefore, developing a novel modified waterborne polyurethane primer that, while ensuring excellent initial adhesion to PETG substrates and UV inks, significantly improves its interfacial adhesion durability with acrylic pressure-sensitive adhesives under humid and hot environments, and enhances its hydrolytic resistance and dimensional stability, to completely solve the problem of edge curling at the overlap of non-full-coverage printed labels, has become an urgent technical problem to be solved in this field. This invention addresses this problem. Summary of the Invention

[0006] The existing technology has the problem that the overlap of conventional multi-layer PETG heat shrink film labeling paper is poor after humid heat aging, and is prone to edge curling failure. To address the above problems, this invention provides a modified waterborne polyurethane primer for multi-layer PETG heat shrink film labeling paper, which comprises the following components by weight:

[0007] Anionic waterborne polyurethane dispersion: 60-85 parts;

[0008] Waterborne epoxy acrylate emulsion: 15-40 parts;

[0009] Wetting and leveling agent: 0.1-1.5 parts;

[0010] Defoamer: 0.05-0.8 parts;

[0011] Crosslinking agent: 0.5-3.0 parts;

[0012] Deionized water: 5-15 parts.

[0013] Preferably, the anionic aqueous polyurethane dispersion is first produced by a condensation reaction between a diol and a diacid to generate an aromatic polyester diol with a number-average molecular weight of 1000-2000. Then, the aromatic polyester diol undergoes an addition reaction with a diisocyanate, a polytetramethylene ether diol with a number-average molecular weight of 500-2000, and / or a bisphenol A type polyether diol with a number-average molecular weight of 500-1500 to generate an isocyanate-terminated prepolymer. The prepolymer then undergoes a chain extension reaction with a hydrophilic chain extender in the presence of a cosolvent to introduce carboxyl groups into the molecular structure of the prepolymer, resulting in a hydrophilic polyurethane (the amount of hydrophilic chain extender added does not exceed 8.5% of the weight of the prepolymer). Finally, the hydrophilic polyurethane is sequentially terminated with a monohydric alcohol (the hydroxyl groups in the monohydric alcohol react with the residual NCO- in the hydrophilic polyurethane), neutralized with alkali (the amount of alkali added is equivalent to the amount of hydrophilic chain extender), deionized, dispersed, stirred, and emulsified, the cosolvent is removed, and the mixture is sieved to obtain the anionic aqueous polyurethane dispersion. Bisphenol A type polyether diol is polymerized from bisphenol A and ethylene oxide.

[0014] Preferably, the diol is composed of a primary hydroxyl diol and a secondary hydroxyl diol, with a molar ratio of secondary hydroxyl diol to primary hydroxyl diol of (3-3.5):1. The mechanism of action of the secondary hydroxyl diol in the synthesis of anionic aqueous polyurethane dispersions is as follows:

[0015] (1) Primary hydroxyl groups have high reactivity, high crosslinking density, high molecular chain rigidity, and poor film flexibility; while secondary hydroxyl groups have moderate reactivity with NCO groups, which can form a more uniform and elastic network structure, giving the coating better toughness and elasticity. However, secondary hydroxyl groups have lower reactivity. Therefore, mixing primary and secondary hydroxyl groups is not only beneficial for controlling reactivity, but also can make the coating have good toughness and elasticity;

[0016] (2) The adhesive strength of acrylic pressure-sensitive adhesives mainly relies on physical wetting and intermolecular forces such as van der Waals forces and hydrogen bonds. Polyurethane containing secondary hydroxyl groups has moderate flexibility, which enables it to form a closer contact with acrylic pressure-sensitive adhesives and form stronger hydrogen bond forces.

[0017] Preferably, the primary hydroxy diol includes one or more of 1,6-hexanediol, 1,4-cyclohexanediol, ethylene glycol, and diethylene glycol.

[0018] Preferably, the secondary hydroxyl diol includes one or two of 2-methyl-1,3-pentanediol, 1,2-propanediol, and 2,2,4-trimethyl-1,3-pentanediol.

[0019] Preferably, the dicarboxylic acid includes at least one aromatic dicarboxylic acid and at least one aliphatic dicarboxylic acid with a carbon chain length of 9 to 10 carbon atoms, and the molar ratio of the aromatic dicarboxylic acid to the aliphatic dicarboxylic acid is (1-1.05):1.

[0020] Preferably, the dicarboxylic acid further includes at least one aliphatic dicarboxylic acid with a carbon chain length of 8 or less.

[0021] Preferably, the diisocyanate includes one or both of IPDI and HDI.

[0022] Preferably, the hydrophilic chain extender includes one or both of dimethylolpropionic acid (DMPA) and 2,2-dimethylolbutyric acid (DMBA).

[0023] Preferably, the co-solvent is N-methylpyrrolidone (NMP).

[0024] Preferably, the crosslinking agent includes one or more of aziridine crosslinking agents (such as BASF XL-50 and BASF XL-100) or carbodiimide crosslinking agents (such as Nisshinbo CARBODILITE SV-02 and SV-06).

[0025] The mechanism of action of the crosslinking agent in the modified waterborne polyurethane primer in this invention is as follows:

[0026] In carbodiimide, the -N=C=N- group combines with the carboxyl group, converting the -OH group in the carboxyl group into an ionic group (by forming an O-acylisourea intermediate). This allows a weaker nucleophile (such as an amine) to successfully attack the carbonyl carbon, ultimately forming a stable amide bond.

[0027] The simplified chemical reaction formula is as follows:

[0028] .

[0029] Preferably, the waterborne epoxy acrylate emulsion includes one or more of the following: Cytec CYCLOMER P(ACA)Z200, Cytec CYCLOMER P(ACA)Z250, Changxing Chemical 6312-100, Changxing Chemical 6315-100, DSM NeoCryl XK-62, Zhanxin DRYCRYL7631, Tongde Chemical TD-2021, and BASF Joncryl 537.

[0030] The mechanism of action of waterborne epoxy acrylate in modified waterborne polyurethane primer in this invention is as follows:

[0031] Epoxy acrylate resin imparts excellent hardness and scratch resistance to the coating film; simultaneously, its outstanding acid and alkali resistance allows it to withstand humid and hot environments across a wide pH range. Thanks to its moderate molecular weight, epoxy acrylate resin exhibits good compatibility with polyurethane. After film formation, the resin can form stronger hydrogen bonds with the acrylate pressure-sensitive adhesive layer, thereby significantly improving interlayer adhesion. Under UV radiation, the unsaturated carbon-carbon double bonds on the epoxy acrylate molecular chain undergo free radical polymerization or photocrosslinking reactions with the unsaturated double bonds on the reactive diluents (monomers) or other prepolymers in UV-cured inks to form covalent bonds, significantly enhancing the interfacial bonding force between the coating and the ink, thus improving interlayer adhesion.

[0032] Preferably, the wetting and leveling agent includes one or more of TEGO Wet 270, TEGO Glide 410, BASF Hydropalat 436, Air Chemical Surfynol 104E, BYK-346, Nopco SN-1540, and Efka EFKA-3033.

[0033] Preferably, the defoamer includes one or more of TEGO Foamex 810, TEGO Airex 902W, BYK-024, BYK-028, Nopco SN-154, Air Chemical Surfynol DF-210, and Efka EFKA-2526.

[0034] A multi-layer PETG heat-shrinkable film label is composed of, from bottom to top, a release paper, an acrylic pressure-sensitive adhesive layer, a vacuum-metallized layer, a PETG layer, a modified waterborne polyurethane primer layer, and a UV printing layer. The modified waterborne polyurethane primer layer is exposed in the blank areas around the edges of the UV printing layer. In use, after removing the release paper, the acrylic pressure-sensitive adhesive layer is applied circumferentially to a cylindrical product (such as an alkaline dry cell battery). The label wraps around the cylindrical product, and the two ends of the label overlap in the blank areas at the edges of the UV printing layer. At the overlap, the acrylic pressure-sensitive adhesive layer and the blank areas at the edges of the UV printing layer are bonded together vertically.

[0035] Beneficial effects:

[0036] (1) This invention fundamentally solves the problem of edge curling due to damp heat aging at the overlap of non-full-coverage printed labels. Through a modified waterborne polyurethane primer with a specific formulation design, this invention creatively achieves synergistic bonding and strengthening among the PETG substrate, UV ink, and the final overlap interface of the acrylate pressure-sensitive adhesive. The key lies in the fact that the anionic waterborne polyurethane dispersion, through the use of a specific ratio of primary / secondary hydroxyl diols, a dicarboxylic acid system with both aromatic and long-chain aliphatic structures, and preferably alicyclic or aliphatic diisocyanates such as IPDI / HDI, and with strict control over the amount of hydrophilic chain extender, ultimately forms a polyurethane network with excellent hydrolysis resistance, high cohesive strength, and excellent dimensional stability. Simultaneously, the introduced waterborne epoxy acrylate not only further enhances the chemical bonding and physical anchoring effect with the UV ink, but also interacts with the polyurethane resin to form a denser and more stable coating. This modified waterborne polyurethane primer effectively reduces the difference in thermal expansion coefficient between itself and the acrylic pressure-sensitive adhesive, significantly reduces the internal stress caused by asynchronous expansion and contraction in humid and hot environments, and significantly improves the hydrolysis resistance of the interface, thereby ensuring the bonding durability of the overlapping interface under long-term harsh environments and completely eliminating edge lifting and interlayer peeling.

[0037] (2) The modified waterborne polyurethane primer provided by this invention exhibits excellent initial adhesion to PETG substrates, providing a solid foundation for subsequent printing. Secondly, it has extremely strong interlayer bonding with UV inks, fundamentally solving the risk of "ink stripping". Furthermore, the coating itself possesses excellent flexibility and compatibility with heat-shrinkable films, preventing cracking or affecting the overall appearance during label shrinkage. Finally, the addition of a crosslinking agent further enhances the crosslinking density and durability of the coating, improving the overall reliability of its performance.

[0038] (3) The multilayer PETG heat shrink film label prepared using the primer of this invention is not only suitable for conventional environments, but can also be stably applied to harsh conditions such as high temperature and high humidity, which greatly expands the application range and market competitiveness of the product. The label is firmly attached to the cylindrical container with smooth edges, and can maintain its complete and beautiful appearance even after long-term use, effectively maintaining the brand image.

[0039] (4) The primer of this invention is based on a water-based system, which is in line with the development trend of green and environmental protection. Its components are reasonably matched, the preparation process is mature, it is compatible with existing coating and printing production processes, and it is easy to realize industrialization and promotion, with significant economic and social benefits. Attached Figure Description

[0040] Figure 1 This invention provides a schematic diagram of the structure of a multilayer PETG heat shrink film label.

[0041] Figure 2 The results of the thermal aging and warping tests for Example 1 and Comparative Example 1 are shown in the attached instruction manual. Figure 2 As shown, the label paper obtained in Example 1 did not exhibit any curling after being pasted onto the surface of the glass rod and subjected to a heat aging test, while the label paper obtained in Comparative Example 1 exhibited curling after being pasted onto the surface of the glass rod and subjected to a heat aging test.

[0042] Figure 3 Example 1: A diagram showing the usage state of the label affixed to the surface of a dry cell battery. Detailed Implementation

[0043] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the present invention.

[0044] The acrylic pressure-sensitive adhesive used in the following embodiments of the present invention was purchased from Zongyan Chemical, and the model can be GPA-900 or SK-Dyne™ 2090.

[0045] The UV inks used for UV printing in the following embodiments of the present invention were purchased from Hangzhou Hua Ink Co., Ltd., and the model can be UV FLEXO EX / EX-HA or UV FLEXO 600-LO.

[0046] Example 1

[0047] A multilayer PETG heat shrink film label is composed of, from bottom to top, release paper, acrylic pressure-sensitive adhesive layer, vacuum metallized layer, PETG layer, modified waterborne polyurethane primer layer and UV printing layer. The white areas around the edges of the UV printing layer expose the modified waterborne polyurethane primer layer underneath.

[0048] The acrylic pressure-sensitive adhesive used in the acrylic pressure-sensitive adhesive layer was purchased from Zongyan Chemical, and the model is GPA-900.

[0049] The UV ink used in the UV printing layer was purchased from Hangzhou Hua Ink Co., Ltd., and its model is UV FLEXO EX.

[0050] The modified waterborne polyurethane primer used in the modified waterborne polyurethane primer layer consists of the following components by weight:

[0051] Anionic waterborne polyurethane dispersion: 70 parts

[0052] Waterborne epoxy acrylate emulsion (Cyclomer P(ACA)Z250, solid content 80%): 30 parts

[0053] Wetting and leveling agent (TEGO Wet 270): 0.5 parts

[0054] Defoamer (BYK-028): 0.2 parts

[0055] Crosslinking agent (carbodiimide, Nisshinbo CARBODILITE SV-02): 1.5 parts

[0056] Deionized water: 10 parts.

[0057] The preparation method of the modified waterborne polyurethane primer is as follows:

[0058] Mix all components according to the formula and stir evenly at 500 rpm.

[0059] The preparation method of anionic aqueous polyurethane dispersion is as follows:

[0060] (1) Preparation of aromatic polyester diols

[0061] Under nitrogen protection, 279.1 g of 1,6-hexanediol (HDO), 82.0 g of 2-methyl-1,3-pentanediol (MPD), 318.5 g of sebacic acid (SA), 261.7 g of isophthalic acid (IPA), and 0.75 g of tetrabutyl titanate catalyst were added to a reactor and subjected to an esterification reaction at atmospheric pressure at 180°C for 4 hours. Subsequently, the vacuum was controlled below -0.09 MPa, and the temperature was gradually increased to 180°C to continue the polycondensation reaction for 2 hours, reducing the acid value to below 3 mg KOH / g. Finally, the reaction was carried out at 230°C under high vacuum (-0.095 MPa) for 2 hours, and the endpoint was controlled by monitoring the acid value and hydroxyl value until a light yellow, transparent, viscous polyester diol product with a hydroxyl value of 112 ± 2 mg KOH / g and an acid value below 0.2 mg KOH / g was obtained, which is the target product, an aromatic polyester diol (number average molecular weight of approximately 1000).

[0062] (2) The aromatic polyester diol obtained in step (1) is mixed with polytetramethylene ether diol (PTMG, BASF, Poly THF® 1000) with a number average molecular weight of 1000, isophorone diisocyanate (IPDI) and dibutyltin dilaurate in a weight ratio of 80:20:45:0.03. Then the temperature of the reaction system is raised to 85℃ and reacted for 2 hours. The NCO radical in the reaction system is monitored by di-n-butylamine titration to reach the theoretical value (the theoretical value of NCO radical is 5.85%, the theoretical value of NCO radical = [molar amount of NCO radical in the reaction system - molar amount of hydroxyl radical in the reaction system] × 42 / total mass of all raw materials in step (2) × 100%), and the prepolymer is obtained. The temperature of the reaction system was then lowered to 70°C. Then, hydrophilic chain extender dimethylolpropionic acid (DMPA) (7.9% of the total mass of the prepolymer) and N-methylpyrrolidone (NMP) were added to the reaction system as solvents. The weight ratio of NMP to aromatic polyester diol was 5:80. The reaction was continued to be stirred for 1 hour. Then, n-butanol, the end-capping agent, was added to the reaction system (the amount of n-butanol was 1.05 equivalents of the residual NCO molar amount; the formula for calculating the residual NCO molar amount is [(total NCO molar amount - hydroxyl molar amount of aromatic polyester diol - hydroxyl molar amount of polytetramethylene ether diol - hydroxyl molar amount of DMPA) × 42] / total mass of all raw materials in step (2)). The end-capping reaction was carried out at 65°C until the NCO content in the reaction system was 0. After the reaction was completed, the reaction system was cooled to 40°C, and then triethylamine (equimolar equivalent to the carboxyl group of DMPA) was added to the reaction system and stirred and neutralized for 10 minutes. Then, under high-speed stirring (1200 rpm), the reaction product was slowly dispersed in 200 parts of deionized water and stirred and emulsified for 30 minutes. After emulsification, the product was heated at 50°C and the emulsification process was carried out at -0.095 rpm. Reduced pressure distillation for 2 hours at MPa was used to remove residual solvent NMP. Finally, the mixture was filtered through a 100-mesh filter to obtain an anionic aqueous polyurethane dispersion with a solid content of 40.2%. Testing showed that the hard segment content of the anionic aqueous polyurethane dispersion was 37%, the Tg was 36℃, and the MFFT was 4℃.

[0063] The specific preparation method of multi-layer PETG heat shrink film label paper is as follows:

[0064] (1) Vacuum metallization was performed on one side of a 20μm thick PETG heat shrink film (as the PETG layer, purchased from SK Chemicals in South Korea) to form a uniform vacuum-deposited aluminum layer (40nm thick), and then rolled up for later use.

[0065] (2) The modified waterborne polyurethane primer is uniformly coated on the other side of the PETG heat shrink film to form a modified waterborne polyurethane primer layer. A 250-mesh anilox roller is used, and the temperatures of the three-section oven of the coating machine are set to 60℃, 80℃, and 65℃ respectively, with a machine speed of 120 m / min. The dry adhesive weight is controlled at 1.0±0.1 g / m by adjusting the doctor blade pressure. 2 ;

[0066] (3) Apply acrylic pressure-sensitive adhesive evenly to PET release paper and dry to obtain acrylic pressure-sensitive adhesive layer (20μm thick).

[0067] (4) On the laminating machine, the acrylic pressure-sensitive adhesive layer of the PET release paper is rolled and bonded to the vacuum-deposited aluminum layer on the surface of the PETG heat shrink film, and then wound up for later use;

[0068] (5) Perform non-full-page UV printing on the surface of the modified waterborne polyurethane primer layer on the PETG heat shrink film to obtain a UV printing layer (18μm thick), and then die-cut it into a multi-layer PETG heat shrink film label paper with a size of 60mm×200mm (denoted as PETG label-1).

[0069] Specific applications of multi-layer PETG heat shrink film for labeling:

[0070] When using the multi-layer PETG heat shrink film label paper obtained above, after removing the release paper, the acrylic pressure-sensitive adhesive layer is circumferentially adhered to the outer wall of the alkaline dry cell. After the label paper wraps around the outer wall of the alkaline dry cell, the two ends of the label paper overlap in the blank area at the edge of the UV printing layer (where the modified water-based polyurethane primer layer is fully exposed). The overlap width is 10mm. At the overlap, the acrylic pressure-sensitive adhesive layer and the blank area at the edge of the UV printing layer are bonded together vertically.

[0071] Example 2 is the same as Example 1, except that in Example 2, the same weight proportions of bisphenol A type polyether diol (BPE-10) with a number average molecular weight of 660 were used instead of the polytetramethylene ether diol (PTMG) with a number average molecular weight of 1000 in Example 1. The solid content of the anionic aqueous polyurethane dispersion obtained in Example 2 was 39.7%. Testing showed that the hard segment content of the anionic aqueous polyurethane dispersion was 36.5%, the Tg was 38°C, and the MFFT was 6°C. The multilayer PETG heat-shrinkable film label obtained in Example 2 is designated as PETG Label-2.

[0072] Example 3 is the same as Example 1, except that the waterborne epoxy acrylate emulsion used in Example 3 is DSM NeoCryl XK-62 with a solid content of 42%. The wetting and leveling agent used is Air Chemical Surfynol 104E. The defoamer used is Nopco SN-154. The crosslinking agent is an aziridine-based crosslinking agent, specifically BASF XL-10. The solid content of the anionic waterborne polyurethane dispersion obtained in Example 3 is 38.4%. Testing showed that the hard segment content of the anionic waterborne polyurethane dispersion was 41.6%, the Tg was 38°C, and the MFFT was 5°C. The multilayer PETG heat-shrinkable film label obtained in Example 3 is designated PETG Label-3.

[0073] Example 4 is the same as Example 1, except that the waterborne epoxy acrylate emulsion used in Example 4 is Changxing Chemical 6312-100, with a solid content of 38%. The wetting and leveling agent used is Efka EFKA-3033. The defoamer used is TEGO Foamex 810. The crosslinking agent is carbodiimide, and the crosslinking agent used is Nisshinbo CARBODILITE SV-06. The solid content of the anionic waterborne polyurethane dispersion obtained in Example 4 is 40%. Testing showed that the hard segment content of the anionic waterborne polyurethane dispersion was 42%, the Tg was 36℃, and the MFFT was 5.4℃. The multilayer PETG heat-shrinkable film label obtained in Example 4 is designated PETG Label-4.

[0074] Example 5 is the same as Example 1, except that the waterborne epoxy acrylate emulsion used in Example 5 is ZINX DRYCRYL 7631 with a solid content of 39%. The wetting and leveling agent used is BASF Hydropalat 436. The defoamer used is BYK-024. The crosslinking agent is an aziridine crosslinking agent, specifically BASF XL-50. The solid content of the anionic waterborne polyurethane dispersion obtained in Example 5 is 41%. Testing showed that the hard segment content of the anionic waterborne polyurethane dispersion was 43%, the Tg was 35°C, and the MFFT was 6.7°C. The multilayer PETG heat-shrinkable film label obtained in Example 5 is designated PETG Label-5.

[0075] Example 6 is the same as Example 1, except that the number average molecular weight of polytetramethylene ether glycol (model Poly THF® 2000) in Example 6 is 2000. The solid content of the anionic aqueous polyurethane dispersion obtained in this example is 40.3%. Testing showed that the hard segment content of the anionic aqueous polyurethane dispersion was 37.69%, the Tg was 33.8℃, and the MFFT was 3.6℃. The multilayer PETG heat-shrinkable film label obtained in Example 6 is designated PETG Label-6.

[0076] Example 7 is the same as Example 1, except that the number average molecular weight of polytetramethylene ether glycol (model Poly THF® 650) in Example 7 is 650. The solid content of the anionic aqueous polyurethane dispersion obtained in Example 7 is 39%. Testing showed that the hard segment content of the anionic aqueous polyurethane dispersion was 36.1%, the Tg was 34.4℃, and the MFFT was 4.6℃. The multilayer PETG heat-shrinkable film label obtained in Example 7 is designated PETG Label-7.

[0077] Example 8 is the same as Example 2, except that the number-average molecular weight of the bisphenol A type polyether diol in Example 8 is 1500. The solid content of the anionic aqueous polyurethane dispersion obtained in Example 8 is 38.9%. Testing showed that the hard segment content of the anionic aqueous polyurethane dispersion was 37.5%, the Tg was 39°C, and the MFFT was 6.9°C. The multilayer PETG heat-shrinkable film label obtained in Example 8 is designated PETG Label-8.

[0078] Example 9 is the same as Example 2, except that the number average molecular weight of the bisphenol A type polyether diol in Example 9 is 500. The solid content of the anionic aqueous polyurethane dispersion obtained in Example 9 is 40%. Testing showed that the hard segment content of the anionic aqueous polyurethane dispersion was 36.1%, the Tg was 38.3℃, and the MFFT was 13.5℃. The multilayer PETG heat-shrinkable film label obtained in Example 9 is designated as PETG Label-9.

[0079] Example 10 is the same as Example 1, except that the modified waterborne polyurethane primer used in Example 10 is composed of the following components by weight:

[0080] Anionic waterborne polyurethane dispersion: 60 parts

[0081] Waterborne epoxy acrylate emulsion: 15 parts

[0082] Wetting and leveling agent: 0.1 parts

[0083] Defoamer: 0.05 parts

[0084] Crosslinking agent: 0.5 parts

[0085] Deionized water: 5 parts.

[0086] The solid content of the anionic aqueous polyurethane dispersion obtained in Example 10 was 39.6%. Testing showed that the hard segment content of the anionic aqueous polyurethane dispersion was 40.1%, the Tg was 39.7℃, and the MFFT was 14.1℃. The multilayer PETG heat-shrinkable film label obtained in Example 10 is designated PETG Label-10.

[0087] Example 11 is the same as Example 1, except that the modified waterborne polyurethane primer used in Example 11 is composed of the following components by weight:

[0088] Anionic waterborne polyurethane dispersion: 85 parts

[0089] Waterborne epoxy acrylate emulsion: 40 parts

[0090] Wetting and leveling agent: 1.5 parts

[0091] Defoamer: 0.8 parts

[0092] Crosslinking agent: 3 parts

[0093] Deionized water: 15 parts.

[0094] The solid content of the anionic aqueous polyurethane dispersion obtained in Example 11 was 39.5%. Testing showed that the hard segment content of the anionic aqueous polyurethane dispersion was 44%, the Tg was 40.4℃, and the MFFT was 16.8℃. The multilayer PETG heat-shrinkable film label obtained in Example 11 is designated PETG Label-11.

[0095] Comparative Example 1 is the same as Example 1, except that Comparative Example 1 uses the same amount of commercially available waterborne polyurethane primer (Zibo Baowei New Material Technology Co., Ltd., waterborne polyurethane 008B for PET film) instead of the modified waterborne polyurethane primer in Example 1. The multilayer PETG heat shrink film sleeve label obtained in Comparative Example 1 is designated as PETG Label-12.

[0096] Comparative Example 2 is the same as Example 1, except that in the synthesis of aromatic polyester diol, 361.1 g of 1,6-hexanediol (HDO) and 0 g of 2-methyl-1,3-pentanediol (MPD) were used. The multilayer PETG heat-shrinkable film label obtained in Comparative Example 2 is designated as PETG Label-13.

[0097] Comparative Example 3 is the same as Example 1, except that in the synthesis of the aromatic polyester diol, 0 g of 1,6-hexanediol (HDO) and 361.1 g of 2-methyl-1,3-pentanediol (MPD) were used. The multilayer PETG heat-shrinkable film label obtained in Comparative Example 3 is designated as PETG Label-14.

[0098] Comparative Example 4 is the same as Example 1, except that in the synthesis of aromatic polyester diol in Comparative Example 4, 580.2 g of sebacic acid (SA) and 0 g of isophthalic acid (IPA) were used. The multilayer PETG heat-shrinkable film label obtained in Comparative Example 4 is designated as PETG Label-15.

[0099] Comparative Example 5 is the same as Example 1, except that in the synthesis of aromatic polyester diol, Comparative Example 5 used 0g of sebacic acid (SA) and 580.2g of isophthalic acid (IPA). The multilayer PETG heat-shrinkable film label obtained in Comparative Example 5 is designated as PETG Label-16.

[0100] Comparative Example 6 is the same as Example 1, except that 580.2 g of 1,9-azelaic acid was used in Comparative Example 6 to replace sebacic acid (SA) and isophthalic acid (IPA) in Example 1 during the synthesis of aromatic polyester diol. The multilayer PETG heat shrink film sleeve label obtained in Comparative Example 6 is designated as PETG Label-16.

[0101] Comparative Example 7 is the same as Example 1, except that in the synthesis of the aromatic polyester diol, 180.55 g of 1,6-hexanediol (HDO) and 180.55 g of 2-methyl-1,3-pentanediol (MPD) were used. The molar ratio of 1,6-hexanediol (HDO) to 2-methyl-1,3-pentanediol (MPD) was 1:1. The multilayer PETG heat-shrinkable film label obtained in Comparative Example 7 is designated as PETG Label-17.

[0102] Comparative Example 8 is the same as Example 1, except that in the synthesis of the aromatic polyester diol, Comparative Example 8 used 219.8 g of sebacic acid (SA) and 360.4 g of isophthalic acid (IPA). The molar ratio of sebacic acid (SA) to isophthalic acid (IPA) was approximately 1:2. The multilayer PETG heat-shrinkable film label obtained in Comparative Example 8 is designated as PETG Label-18.

[0103] Comparative Example 9 is the same as Example 1, except that the modified waterborne polyurethane primer in Comparative Example 9 did not contain waterborne epoxy acrylate emulsion, and the weight of the anionic waterborne polyurethane dispersion added was 100 parts. The multilayer PETG heat-shrinkable film label obtained in Comparative Example 9 is designated as PETG Label-19.

[0104] Comparative Example 10 is the same as Example 1, except that the modified waterborne polyurethane primer in Comparative Example 10 contains 70 parts by weight of waterborne epoxy acrylate emulsion and 30 parts by weight of anionic waterborne polyurethane dispersion. The multilayer PETG heat-shrinkable film label obtained in Comparative Example 10 is designated as PETG Label-20.

[0105] Comparative Example 11 is the same as Example 1, except that no crosslinking agent was added to the modified waterborne polyurethane primer of Comparative Example 11. The multilayer PETG heat shrink film sleeve label obtained in Comparative Example 11 is designated as PETG Label-21.

[0106] Performance testing

[0107] Initial adhesion: According to GB / T 9286-1998 standard, the "PETG layer-modified primer layer-UV printing layer" was tested by cross-cut adhesion test (cross-cut spacing 1mm, cut through to the PETG substrate), and 3M 610 tape was used for peeling, and each layer was rated. Grade 5B (the edges are completely smooth, and no cross-cuts are peeled off).

[0108] Adhesion after damp heat aging: The labels obtained in the examples and comparative examples were affixed to glass rods and then placed in a constant temperature and humidity chamber (conditions: 60±2℃, 90±5%RH) for 15 days. After removal, they were allowed to recover for 24 hours under standard conditions (23±2℃, 50±5%RH), and the adhesion at the same location was tested and rated. The rating remained 5B (completely smooth edges, no peeling).

[0109] Heat aging and warping test: Labels obtained from the examples and comparative examples were affixed to glass rods and then placed in a forced-air drying oven at 45±2℃ for 30 days. After cooling to room temperature (23℃), the edges of the overlap between the pressure-sensitive adhesive and the base coating were visually inspected using a 10x magnifying glass to observe for any warping or bubbling. The test results for Example 1 (no warping) and Comparative Example 1 (warping) are shown in Table 1 and the instructions attached. Figure 2 As shown in the attached instruction manual. A diagram illustrating the usage state of the label obtained in Example 1 affixed to the surface of a dry cell battery is also included. Figure 3 As shown.

[0110] Water resistance test: The multilayer PETG heat shrink film labels obtained in the examples and comparative examples were completely immersed in deionized water at 40°C for 72 hours. After being removed and dried, the adhesion was immediately tested and rated.

[0111] Rating method: Refer to GB / T 9286-2021, use a cross-cut tester to cut a 1mm / 2mm / 3mm grid (penetrating to the substrate), clean it, peel it off with 3M Scotch tape, and then rate it.

[0112] Grade 0: Smooth cut, no detachment.

[0113] Level 1: Minor shedding at the intersection (≤5%).

[0114] Grade 2: Shedding at edges / intersections (5%–15%).

[0115] Level 3: Partial whole-piece detachment (15%–35%).

[0116] Level 4: Large areas of peeling (35%–65%).

[0117] Level 5: Severe shedding (>65%).

[0118] The test results are shown in Table 1.

[0119] Table 1 Test Items Initial adhesion (grade) Adhesion after damp heat aging (grade) Heat aging causes warping (yes or no) Water resistance (grade) Example 1 0 1 no 0 Example 2 0 0 no 1 Example 3 0 1 no 0 Example 4 0 0 no 0 Example 5 0 1 no 1 Example 6 0 1 no 0 Example 7 0 1 no 1 Example 8 0 0 no 0 Example 9 0 1 no 0 Example 10 0 0 no 0 Example 11 0 1 no 1 Comparative Example 1 0 2 yes 3 Comparative Example 2 0 1 yes 1 Comparative Example 3 1 2 yes 1 Comparative Example 4 2 4 yes 3 Comparative Example 5 1 3 yes 2 Comparative Example 6 1 2 yes 2 Comparative Example 7 1 2 yes 2 Comparative Example 8 1 3 yes 3 Comparative Example 9 2 4 yes 4 Comparative Example 10 2 3 yes 3 Comparative Example 11 0 2 yes 3 .

[0120] Based on the test results in Table 1, the following conclusions can be drawn:

[0121] In this invention, the aromatic polyester diol has both primary and secondary hydroxyl groups, and the film combines hardness, toughness and elasticity, so that the primer and PETG substrate can still maintain their adhesion after thermal aging and damp heat aging.

[0122] Furthermore, the primer formed by water-based epoxy emulsion and polyurethane resin in this invention has a higher adhesion to UV ink than the primer formed by using water-based polyurethane dispersion alone, and its adhesion and water resistance do not decrease after damp heat testing.

[0123] On the other hand, Comparative Example 11 shows that the coating of the composition without carbodiimide crosslinking has significantly reduced adhesion after water resistance testing.

[0124] In summary, the moderate flexibility of polyurethane containing secondary hydroxyl groups allows it to form a closer contact and stronger hydrogen bond with acrylic pressure-sensitive adhesives. This effectively bridges the difference in thermal expansion coefficients between the two materials, significantly reduces internal stress caused by asynchronous expansion and contraction in humid and hot environments, and significantly improves the interface's hydrolysis resistance. This ensures the bonding durability of the overlap interface under long-term harsh environments and completely eliminates edge lifting and interlayer delamination.

[0125] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A modified waterborne polyurethane primer for multilayer PETG heat-shrink film labeling paper, characterized in that, By weight, it includes the following ingredients: Anionic waterborne polyurethane dispersion: 60-85 parts; Waterborne epoxy acrylate emulsion: 15-40 parts; Wetting and leveling agent: 0.1-1.5 parts; Defoamer: 0.05-0.8 parts; Crosslinking agent: 0.5-3.0 parts; Deionized water: 5-15 parts.

2. The modified waterborne polyurethane primer for multilayer PETG heat-shrinkable film labeling paper according to claim 1, characterized in that, The anionic waterborne polyurethane dispersion is first produced by the condensation reaction of a diol and a diacid to generate an aromatic polyester diol with a number average molecular weight of 1000-2000. Then, the aromatic polyester diol undergoes an addition reaction with a diisocyanate, a polytetramethylene ether diol with a number average molecular weight of 500-2000, and / or a bisphenol A type polyether diol with a number average molecular weight of 500-1500 to generate an isocyanate-terminated prepolymer. The prepolymer then undergoes a chain extension reaction with a hydrophilic chain extender in the presence of a cosolvent to introduce carboxyl groups into the molecular structure of the prepolymer, resulting in a hydrophilic polyurethane. Finally, the hydrophilic polyurethane is sequentially subjected to monohydric alcohol termination, alkali neutralization, deionization dispersion, stirring and emulsification, removal of the cosolvent, and sieving to obtain the anionic waterborne polyurethane dispersion.

3. The modified waterborne polyurethane primer for multilayer PETG heat-shrinkable film labeling paper according to claim 2, characterized in that, Diols are composed of primary hydroxy diols and secondary hydroxy diols, with a molar ratio of (3-3.5):1 between the secondary and primary hydroxy diols.

4. The modified waterborne polyurethane primer for multilayer PETG heat-shrinkable film labeling paper according to claim 3, characterized in that, Primary hydroxy diols include one or more of 1,6-hexanediol, 1,4-cyclohexanediol, ethylene glycol, and diethylene glycol.

5. A modified waterborne polyurethane primer for multilayer PETG heat-shrinkable film labeling paper according to claim 3, characterized in that, Secondary hydroxy diols include one or both of 2-methyl-1,3-pentanediol and 1,2-propanediol.

6. A modified waterborne polyurethane primer for multilayer PETG heat-shrinkable film labeling paper according to claim 2, characterized in that, Dicarboxylic acids include at least one aromatic dicarboxylic acid and at least one aliphatic dicarboxylic acid with a carbon chain length of 9 to 10 carbon atoms, wherein the molar ratio of aromatic dicarboxylic acid to aliphatic dicarboxylic acid is (1-1.05):

1.

7. A modified waterborne polyurethane primer for multilayer PETG heat-shrinkable film labeling paper according to claim 2, characterized in that, Hydrophilic chain extenders include one or both of DMPA and DMBA.

8. The modified waterborne polyurethane primer for multilayer PETG heat-shrinkable film labeling paper according to claim 1, characterized in that, Crosslinking agents include one or both of carbodiimide crosslinking agents and aziridine crosslinking agents.

9. A multi-layer PETG heat-shrinkable film label, characterized in that, From bottom to top, it is composed of release paper, an acrylic pressure-sensitive adhesive layer, a vacuum metallized layer, a PETG layer, a modified waterborne polyurethane primer layer as described in any one of claims 1-8, and a UV printing layer. The white areas around the edges of the UV printing layer expose the modified waterborne polyurethane primer layer underneath.

10. A multilayer PETG heat-shrinkable film label according to claim 9, characterized in that, When using, after removing the release paper, the acrylic pressure-sensitive adhesive layer is applied circumferentially to the cylindrical product. After the label wraps around the cylindrical product, the two ends of the label overlap in the blank area at the edge of the UV printing layer. At the overlap, the acrylic pressure-sensitive adhesive layer and the blank area at the edge of the UV printing layer are bonded together vertically.

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