Preparation method of PETG halogen-free label film

Abstract

This invention provides a method for preparing a halogen-free PETG label film, belonging to the field of label film preparation technology. The method includes: corona treatment of a PETG substrate layer; coating the substrate surface with a halogen-free functional coating liquid containing waterborne polyurethane acrylic composite resin, nano-inorganic modifier, and crosslinking agent; bonding the coated substrate layer and the halogen-free adhesive layer together and then sending them into a curing oven, where the functional coating and the interlayer bonding with the adhesive layer are simultaneously completed under segmented programmed temperature rise conditions, resulting in physical entanglement and chemical crosslinking at the interface; and finally, cooling and shaping to obtain the label film. This invention significantly enhances the interlayer bonding strength through a simultaneous curing and composite process. The resulting product has a light transmittance ≥91%, haze ≤2.5%, peel strength ≥8N / 25mm, and performance retention ≥90% after damp heat aging. Furthermore, the chlorine and bromine content are both ≤900ppm, meeting the halogen-free standard.

Description

Technical Field

[0001] This invention relates to the field of label film preparation technology, and in particular to a method for preparing a halogen-free PETG label film. Background Technology

[0002] In the packaging of electronic appliances and daily chemical products, PETG label film is widely used due to its excellent transparency and processing performance. With increasingly stringent international environmental regulations restricting halogenated substances, the development of halogen-free label film has become an industry trend. In existing technologies, PETG label film is typically produced by melt extrusion and biaxial stretching to form a substrate layer, and then coated with a functional layer and a pressure-sensitive adhesive layer to meet printing and labeling requirements.

[0003] However, current preparation methods still face several technical bottlenecks. Firstly, traditional processes often employ a step-by-step curing method, where the functional coating is fully cured before being laminated with the adhesive layer. This results in only physical adsorption at the coating-adhesive interface, leading to insufficient interlayer bonding and making the coating prone to edge lifting or label detachment under high temperature and humidity conditions. Secondly, to balance transparency and adhesion, existing halogen-free formulations often require the introduction of multiple additives. However, the poor compatibility of these components can easily cause increased coating haze or surface precipitation, affecting optical quality and printability. Thirdly, the separate processing of functional curing and adhesive lamination in the preparation process is lengthy, energy-intensive, and difficult to meet the requirements of efficient continuous production.

[0004] Furthermore, existing halogen-free label films exhibit poor long-term weather resistance, with peel strength significantly decreasing after damp heat aging, failing to meet the long-lifecycle traceability requirements of electronic devices. Meanwhile, regarding environmental compliance, while some products claim to be halogen-free, their chlorine and bromine content remains close to the standard limits due to limitations in raw material purity or process contamination, posing compliance risks. Summary of the Invention

[0005] In view of this, the present invention aims to provide a method for preparing halogen-free PETG label film to solve or alleviate the technical problems existing in the prior art.

[0006] The technical solution of this invention is implemented as follows: a method for preparing a halogen-free PETG label film, comprising the following steps: S1. Substrate pretreatment: Provide PETG resin raw materials, form a PETG substrate layer through melt extrusion, biaxial stretching and heat setting processes, and perform corona treatment on at least one side; S2. Preparation and application of functional coating: A halogen-free functional coating liquid is applied to the surface of the PETG substrate layer after corona treatment; the halogen-free functional coating liquid contains waterborne polyurethane acrylic composite resin, nano-inorganic modifier and crosslinking agent. S3. Coating synchronous curing and lamination: The coated PETG substrate layer and a halogen-free adhesive layer are bonded together using a lamination device, and then sent into a curing oven for synchronous curing and interlayer bonding under a specific temperature program; the specific temperature program causes the functional coating and adhesive layer to form physical entanglement and chemical cross-linking in the interface area. S4. Cooling and post-processing: The product obtained in step S3 is cooled and shaped to obtain the PETG halogen-free label film.

[0007] As an improvement, the specific temperature program in step S3 specifically includes: First stage: Treat at 70-85℃ for 1-3 minutes to allow the functional coating to initially form a film and retain its reactive activity, while the adhesive layer begins to soften. Second stage: Treat at 110-125℃ for 2-4 minutes to accelerate the cross-linking reaction of the functional coating and allow the adhesive layer to fully melt and flow, and interpenetrate with the interface of the functional coating. The third stage: process at 130-145℃ for 1-2 minutes to complete the final curing of the functional coating and the interlayer shaping with the adhesive layer.

[0008] As an improvement, the waterborne polyurethane acrylic composite resin in step S2 has a core-shell structure and a glass transition temperature of -10°C to 10°C; the halogen-free adhesive layer is a hot melt pressure-sensitive adhesive based on styrene-isoprene-styrene block copolymer, and its melt viscosity at the first stage processing temperature is 5000-15000 cP.

[0009] As an improvement, the parameters of the biaxial stretching process in step S1 are: longitudinal stretching temperature 85-90℃, stretching ratio 3.2-3.4; transverse stretching temperature 88-93℃, stretching ratio 3.4-3.6; and the surface tension after corona treatment is not less than 50mN / m.

[0010] As an improvement, the halogen-free functional coating liquid in step S2 comprises, by mass parts: 80-100 parts of waterborne polyurethane acrylic composite resin, 5-10 parts of nano-silica and / or nano-titanium dioxide, and 3-5 parts of aziridine or carbodiimide crosslinking agent; the average particle size of the nano-inorganic modifier is 15-40 nm, and it has undergone surface organic modification.

[0011] As an improvement, the raw materials of the halogen-free adhesive layer in step S3 include, by mass parts: 30-50 parts of styrene-isoprene-styrene block copolymer, 20-40 parts of hydrogenated terpene resin, 10-20 parts of softener, and 0.5-1.0 parts of antioxidant; the adhesive layer is pre-coated on the release film and separated from the release film before bonding.

[0012] As an improvement, the pressure of the bonding process in step S3 is 0.3-0.6 MPa; during the simultaneous curing and interlayer bonding process, the bonded film is subjected to online ultraviolet irradiation with an irradiation dose of 20-100 mJ / cm². 2 .

[0013] As an improvement, the cooling and shaping in step S4 is carried out by rapid cooling, so that the film temperature drops from the curing temperature to below 50°C within 10 seconds; after cooling, the non-functional coating surface of the label film is subjected to online corona treatment or coated with an antistatic layer.

[0014] As an improvement, the final PETG halogen-free label film has a light transmittance of ≥91%, a haze of ≤2.5%, and a 180° peel strength to stainless steel plates of ≥8N / 25mm; after aging in an environment of 85℃ and 85%RH for 500 hours, the 180° peel strength retention rate is ≥90%.

[0015] As an improvement, the functional coating surface of the label film can be printed with halogen-free UV-cured ink, and the label film as a whole meets the halogen-free requirements of IEC61249-2-21 standard, with chlorine and bromine content ≤900ppm.

[0016] The embodiments of this invention, employing the above technical solutions, offer the following advantages: By immediately bonding the functional coating to the adhesive layer and performing a three-stage programmed temperature-controlled synchronous curing process, the coating, while retaining its reactive state, undergoes interfacial interpenetration and chemical cross-linking with the molten adhesive layer, significantly enhancing interlayer bonding strength. This solves the problem of traditional step-by-step curing, where interface delamination is easily caused by physical adsorption. Simultaneously, the use of a core-shell structured waterborne polyurethane acrylic composite resin combined with surface-modified organic nano-inorganic particles achieves high uniform dispersion of each component in a halogen-free system, effectively preventing increased coating haze or surface precipitation, thus balancing high transparency and excellent printability. Furthermore, this process integrates curing and lamination into a continuous flow, significantly shortening the production cycle and reducing energy consumption. The all-component design eliminates halogen introduction from the source, ensuring that the chlorobromine content of the product is far below international standard limits, and maintaining excellent peel strength retention even after damp heat aging. This solves the problem of balancing interlayer reliability, optical quality, environmental compliance, and weather resistance in existing methods.

[0017] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of the invention will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a graph showing the trend of peel strength retention rate in Experimental Example 3 of the present invention. Detailed Implementation

[0020] The invention will be more readily understood by referring to the following detailed description of preferred embodiments and included examples. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of conflict, the definitions in this specification shall prevail.

[0021] As used herein, the terms “prepared from” and “comprising” are synonymous. The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0022] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for conventional impurities associated with them. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0023] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including the ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0024] The singular form includes the plural objects of discussion unless the context clearly indicates otherwise. "Optional" or "any one" means that the matter or event described thereafter may or may not occur, and the description includes both the possibility that the event occurs and the possibility that the event does not occur.

[0025] Approximate terms used in the specification and claims to modify quantities indicate that the invention is not limited to that specific quantity, but also includes acceptable modifications close to that quantity that do not alter the relevant essential function. Correspondingly, the use of "about," "approximately," etc., to modify a numerical value means that the invention is not limited to that precise value. In some instances, approximate terms may correspond to the precision of the instrument used to measure the value. In this application's specification and claims, scope definitions can be combined and / or interchanged, unless otherwise stated, these scopes include all subscopes contained therein.

[0026] Furthermore, the indefinite articles “a” and “an” preceding the elements or components of this invention do not impose any limitation on the quantity (i.e., number of times) of the elements or components. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers to the singular form.

[0027] Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0028] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the experimental materials and test strains used in the following examples were purchased from commercial channels. Example 1

[0029] A method for preparing a halogen-free PETG label film includes the following steps: S1. Substrate pretreatment: Provide PETG resin raw materials, form a PETG substrate layer through melt extrusion, biaxial stretching and heat setting processes, and perform corona treatment on at least one side; The parameters of the biaxial stretching process are as follows: longitudinal stretching temperature 85℃, stretching ratio 3.2; transverse stretching temperature 88℃, stretching ratio 3.4; and the surface tension after corona treatment is not less than 50mN / m.

[0030] S2. Preparation and application of functional coating: A halogen-free functional coating liquid is applied to the surface of the PETG substrate layer after corona treatment; the halogen-free functional coating liquid contains waterborne polyurethane acrylic composite resin, nano-inorganic modifier and crosslinking agent. The waterborne polyurethane acrylic composite resin has a core-shell structure and a glass transition temperature of -10℃; the halogen-free adhesive layer is a hot melt pressure-sensitive adhesive based on styrene-isoprene-styrene block copolymer, and its melt viscosity at the first stage processing temperature is 5000 cP.

[0031] The halogen-free functional coating liquid comprises, by mass, 80 parts of waterborne polyurethane acrylic composite resin, 5 parts of nano-silica and / or nano-titanium dioxide, and 3 parts of aziridine or carbodiimide crosslinking agent; the average particle size of the nano-inorganic modifier is 15 nm, and it has undergone surface organic modification.

[0032] S3. Coating synchronous curing and lamination: The coated PETG substrate layer and a halogen-free adhesive layer are bonded together using a lamination device, and then sent into a curing oven for synchronous curing and interlayer bonding under a specific temperature program; the specific temperature program causes the functional coating and adhesive layer to form physical entanglement and chemical cross-linking in the interface area. The raw materials of the halogen-free adhesive layer include, by mass parts: 30 parts of styrene-isoprene-styrene block copolymer, 20 parts of hydrogenated terpene resin, 10 parts of softener, and 0.5 parts of antioxidant; the adhesive layer is pre-coated on the release film and separated from the release film before bonding.

[0033] The specific temperature program includes: First stage: Treat at 70℃ for 1 minute to allow the functional coating to initially form a film and retain its reactive activity, while the adhesive layer begins to soften. Second stage: Treat at 110℃ for 2 minutes to accelerate the cross-linking reaction of the functional coating and allow the adhesive layer to fully melt and flow, interpenetrating with the functional coating interface; The third stage: process at 130℃ for 1 minute to complete the final curing of the functional coating and the interlayer shaping with the adhesive layer.

[0034] The pressure during the lamination process is 0.3 MPa; during the simultaneous curing and interlayer bonding process, the laminated film is subjected to online ultraviolet irradiation at a dose of 20 mJ / cm². 2 .

[0035] S4. Cooling and post-processing: The product obtained in step S3 is cooled and shaped to obtain the PETG halogen-free label film.

[0036] The cooling and shaping process employs rapid cooling, causing the film temperature to drop from the curing temperature to below 50°C within 10 seconds. After cooling, the non-functional coating surface of the label film is subjected to online corona treatment or coated with an antistatic layer.

[0037] During implementation, the final PETG halogen-free label film has a light transmittance of ≥91%, a haze of ≤2.5%, and a 180° peel strength to stainless steel plate of ≥8N / 25mm; after aging in an environment of 85℃ and 85%RH for 500 hours, the 180° peel strength retention rate is ≥90%.

[0038] The functional coating surface of the label film can be printed with halogen-free UV-cured ink, and the label film as a whole meets the halogen-free requirements of IEC61249-2-21 standard, with chlorine and bromine content ≤900ppm. Example 2

[0039] A method for preparing a halogen-free PETG label film includes the following steps: S1. Substrate pretreatment: Provide PETG resin raw materials, form a PETG substrate layer through melt extrusion, biaxial stretching and heat setting processes, and perform corona treatment on at least one side; The parameters of the biaxial stretching process are as follows: longitudinal stretching temperature 88℃, stretching ratio 3.3; transverse stretching temperature 90℃, stretching ratio 3.5; and the surface tension after corona treatment is not less than 50mN / m.

[0040] S2. Preparation and application of functional coating: A halogen-free functional coating liquid is applied to the surface of the PETG substrate layer after corona treatment; the halogen-free functional coating liquid contains waterborne polyurethane acrylic composite resin, nano-inorganic modifier and crosslinking agent. The waterborne polyurethane acrylic composite resin has a core-shell structure and a glass transition temperature of 0°C; the halogen-free adhesive layer is a hot-melt pressure-sensitive adhesive based on styrene-isoprene-styrene block copolymer, and its melt viscosity at the first stage processing temperature is 10000 cP.

[0041] The halogen-free functional coating liquid comprises, by mass, 90 parts of waterborne polyurethane acrylic composite resin, 8 parts of nano-silica and / or nano-titanium dioxide, and 4 parts of aziridine or carbodiimide crosslinking agent; the average particle size of the nano-inorganic modifier is 27 nm, and it has undergone surface organic modification.

[0042] S3. Coating synchronous curing and lamination: The coated PETG substrate layer and a halogen-free adhesive layer are bonded together using a lamination device, and then sent into a curing oven for synchronous curing and interlayer bonding under a specific temperature program; the specific temperature program causes the functional coating and adhesive layer to form physical entanglement and chemical cross-linking in the interface area. The raw materials of the halogen-free adhesive layer include, by mass parts: 40 parts of styrene-isoprene-styrene block copolymer, 30 parts of hydrogenated terpene resin, 15 parts of softener, and 0.8 parts of antioxidant; the adhesive layer is pre-coated on the release film and separated from the release film before bonding.

[0043] The specific temperature program includes: First stage: Treat at 78℃ for 2 minutes to allow the functional coating to initially form a film and retain its reactive activity, while the adhesive layer begins to soften. Second stage: Treat at 118℃ for 3 minutes to accelerate the cross-linking reaction of the functional coating and allow the adhesive layer to fully melt and flow, interpenetrating with the interface of the functional coating; The third stage: process at 138℃ for 1.5 minutes to complete the final curing of the functional coating and the interlayer shaping with the adhesive layer.

[0044] The pressure during the lamination process is 0.45 MPa; during the simultaneous curing and interlayer bonding process, the laminated film is subjected to online ultraviolet irradiation at a dose of 60 mJ / cm². 2 .

[0045] S4. Cooling and post-processing: The product obtained in step S3 is cooled and shaped to obtain the PETG halogen-free label film.

[0046] The cooling and shaping process employs rapid cooling, causing the film temperature to drop from the curing temperature to below 50°C within 10 seconds. After cooling, the non-functional coating surface of the label film is subjected to online corona treatment or coated with an antistatic layer.

[0047] During implementation, the final PETG halogen-free label film has a light transmittance of ≥91%, a haze of ≤2.5%, and a 180° peel strength to stainless steel plate of ≥8N / 25mm; after aging in an environment of 85℃ and 85%RH for 500 hours, the 180° peel strength retention rate is ≥90%.

[0048] The functional coating surface of the label film can be printed with halogen-free UV-cured ink, and the label film as a whole meets the halogen-free requirements of IEC61249-2-21 standard, with chlorine and bromine content ≤900ppm. Example 3

[0049] A method for preparing a halogen-free PETG label film includes the following steps: S1. Substrate pretreatment: Provide PETG resin raw materials, form a PETG substrate layer through melt extrusion, biaxial stretching and heat setting processes, and perform corona treatment on at least one side; The parameters of the biaxial stretching process are as follows: longitudinal stretching temperature 90℃, stretching ratio 3.4; transverse stretching temperature 93℃, stretching ratio 3.6; and the surface tension after corona treatment is not less than 50mN / m.

[0050] S2. Preparation and application of functional coating: A halogen-free functional coating liquid is applied to the surface of the PETG substrate layer after corona treatment; the halogen-free functional coating liquid contains waterborne polyurethane acrylic composite resin, nano-inorganic modifier and crosslinking agent. The waterborne polyurethane acrylic composite resin has a core-shell structure and a glass transition temperature of 10°C; the halogen-free adhesive layer is a hot-melt pressure-sensitive adhesive based on styrene-isoprene-styrene block copolymer, and its melt viscosity at the first stage processing temperature is 15000 cP.

[0051] The halogen-free functional coating liquid comprises, by mass parts: 80-100 parts of waterborne polyurethane acrylic composite resin, 10 parts of nano-silica and / or nano-titanium dioxide, and 3-5 parts of aziridine or carbodiimide crosslinking agent; the average particle size of the nano-inorganic modifier is 40 nm, and it has undergone surface organic modification.

[0052] S3. Coating synchronous curing and lamination: The coated PETG substrate layer and a halogen-free adhesive layer are bonded together using a lamination device, and then sent into a curing oven for synchronous curing and interlayer bonding under a specific temperature program; the specific temperature program causes the functional coating and adhesive layer to form physical entanglement and chemical cross-linking in the interface area. The raw materials of the halogen-free adhesive layer include, by mass parts: 50 parts of styrene-isoprene-styrene block copolymer, 40 parts of hydrogenated terpene resin, 20 parts of softener, and 1.0 part of antioxidant; the adhesive layer is pre-coated on the release film and separated from the release film before bonding.

[0053] The specific temperature program includes: First stage: Treat at 85℃ for 3 minutes to allow the functional coating to initially form a film and retain its reactive activity, while the adhesive layer begins to soften. Second stage: Treat at 125℃ for 4 minutes to accelerate the cross-linking reaction of the functional coating and allow the adhesive layer to fully melt and flow, interpenetrating with the functional coating interface; The third stage: process at 145℃ for 2 minutes to complete the final curing of the functional coating and the interlayer shaping with the adhesive layer.

[0054] The pressure during the lamination process is 0.6 MPa; during the simultaneous curing and interlayer bonding process, the laminated film is subjected to online ultraviolet irradiation at a dose of 100 mJ / cm². 2 .

[0055] S4. Cooling and post-processing: The product obtained in step S3 is cooled and shaped to obtain the PETG halogen-free label film.

[0056] The cooling and shaping process employs rapid cooling, causing the film temperature to drop from the curing temperature to below 50°C within 10 seconds. After cooling, the non-functional coating surface of the label film is subjected to online corona treatment or coated with an antistatic layer.

[0057] During implementation, the final PETG halogen-free label film has a light transmittance of ≥91%, a haze of ≤2.5%, and a 180° peel strength to stainless steel plate of ≥8N / 25mm; after aging in an environment of 85℃ and 85%RH for 500 hours, the 180° peel strength retention rate is ≥90%.

[0058] The functional coating surface of the label film can be printed with halogen-free UV-cured ink, and the label film as a whole meets the halogen-free requirements of IEC61249-2-21 standard, with chlorine and bromine content ≤900ppm.

[0059] Experimental Example 1: Comparison of Simultaneous Curing Process vs. Traditional Step-by-Step Curing Process 1. Experimental objective: This experiment aims to quantitatively compare the key performance differences between the core process of this invention (simultaneous curing and lamination) and the traditional process (curing first and then laminating) in the preparation of PETG halogen-free label film. The advanced nature of the process of this invention is verified from three core dimensions: interlayer bonding strength, production efficiency, and product appearance.

[0060] 2. Experimental materials and equipment: Substrate: Corona-treated PETG substrate (surface tension 52mN / m) produced in the same batch.

[0061] Functional coating liquid: prepared according to the formulation of Example 2 (90 parts of waterborne polyurethane acrylic composite resin, 8 parts of nano silica, and 4 parts of carbodiimide crosslinking agent).

[0062] Adhesive: SIS-based hot melt pressure-sensitive adhesive formulated according to the formulation in Example 2.

[0063] Main equipment: precision coating machine, double roller thermal lamination device, multi-segment programmable temperature-controlled curing oven (including UV irradiation unit), material tensile testing machine, optical microscope, timer.

[0064] 3. Detailed experimental procedures: Step 1: Sample Preparation 1. Substrate preparation: Cut the same roll of PETG substrate into two rolls of the same width, and label them as roll A (for the experimental group) and roll B (for the control group).

[0065] 2. Functional coating application: Using the same coating machine, with the same wet film thickness (50 μm) and coating speed (10 m / min), the prepared functional coating liquid was applied to the same corona-treated surface of rolls A and B, respectively. This operation ensured that the initial state of the coating surface of the two sets of samples was consistent.

[0066] Step Two: Implementation of Key Processes (Differentiated Steps) Experimental group (synchronous curing process of this invention): 1. Lamination: Immediately after coating, the A roll substrate is laminated with the adhesive layer (adhesive layer thickness 25μm) pre-coated on the release film in the lamination device, and the lamination pressure is set to 0.45MPa.

[0067] 2. Simultaneous Curing: The bonded three-layer composite structure (PETG substrate / uncured functional coating / adhesive layer / release film) is immediately fed into a programmable temperature-controlled curing oven. The oven temperature program is set according to this invention: First stage: 80℃, for 2 minutes.

[0068] Second stage: 118℃, treatment for 3 minutes. Midway through this stage, apply 60 mJ / cm². 2 Dosage of online ultraviolet irradiation.

[0069] Third stage: 138℃, for 1.5 min.

[0070] 3. After curing, peel off the release film to obtain the finished label film sample A1.

[0071] Control group (traditional step-by-step curing process): 1. Pre-curing: The coated B-roll substrate is separately placed into the curing oven and cured at 130℃ for 3 minutes to ensure complete cross-linking and curing of the functional coating. After removal, it is cooled to room temperature.

[0072] 2. Lamination: On the surface of the cured functional coating after cooling, the same adhesive layer (with release film) is hot-pressed together under the same pressure of 0.45MPa.

[0073] 3. Curing: Cur the composite structure in an oven at 100℃ for 2 minutes to set the adhesive layer.

[0074] 4. After curing, peel off the release film to obtain the finished label film sample B1.

[0075] Step 3: Performance Testing and Characterization 1.180° Peel Strength Test: According to GB / T2792 standard, the adhesive surfaces of samples A1 and B1 are bonded to a standard stainless steel plate, and rolled back and forth three times with a 2kg standard pressure roller. After standing for 20 minutes, a 180° peel test is performed on a material tensile testing machine at a speed of 300mm / min. At least 5 valid data points are required for each sample group, and the average value and standard deviation are taken.

[0076] 2. Visual inspection: Under standard light source, visually inspect samples A1 and B1 for bubbles and wrinkles between layers. Also, take samples and observe the cross-section and surface morphology under a 100x optical microscope.

[0077] 3. Failure Mode Analysis: Observe the residue on the back of the stainless steel plate and label film after the peel test to determine whether the failure occurred at the interface or inside the material.

[0078] 4. Process time record: Accurately record the continuous production time of the experimental group and the control group in the key processes (curing, lamination, and ripening) from coating to the production of the finished film, excluding the shared time for cooling and winding.

[0079] 4. Specific experimental data and results: Table 1: Comparison of performance data between simultaneous curing and traditional step-by-step curing processes 5. Experimental Conclusion: Conclusion 1: The synchronous curing process has achieved a fundamental improvement in the interlayer bonding strength.

[0080] Data support: The peel strength jumped from 5.2 N / 25 mm in the control group to 9.8 N / 25 mm in the experimental group, an increase of 89%.

[0081] Mechanism analysis: The 5.2 N / 25 mm of the control group represents the limit achievable through physical adsorption and mechanical bonding between the adhesive and the cured coating surface. The 9.8 N / 25 mm of the experimental group demonstrates that, under the temperature program of this invention, the melt flow of the adhesive layer and the initial film formation of the functional coating while retaining its activity occur simultaneously. Deep physical entanglement of molecular chains occurs at the interface, and under UV irradiation and heat, the active groups of the functional coating and the adhesive may undergo partial chemical cross-linking, thus forming a high-strength interpenetrating network (IPN) transition layer.

[0082] 2. Conclusion 2: The synchronous curing process effectively eliminates interface defects and improves the consistency and reliability of product appearance.

[0083] Data support: Visual observation and microscopic inspection results showed that the control group product had "orange peel" and potential microbubbles due to poor interface wetting, while the experimental group product had a perfectly fused interface.

[0084] Mechanism Analysis: In traditional stepwise processes, the surface energy of the cured functional coating decreases and it loses its fluidity. The high-viscosity molten adhesive cannot completely wet its surface, resulting in microscopic voids (stress concentration points) at the interface. This is not only an appearance defect but also a potential cause of delamination failure during long-term use. The simultaneous process, which performs lamination while the functional coating still has good fluidity, achieves liquid-liquid or semi-liquid-liquid contact, thereby obtaining a defect-free ideal interface.

[0085] 3. Conclusion 3: The synchronous curing process significantly improves production efficiency through process integration.

[0086] Data support: Key process time was reduced by 19%, and the process was changed from multi-step discrete to one-step continuous.

[0087] Mechanism analysis: This efficiency improvement not only saves time, but also means reduced energy consumption, faster production pace, and improved product consistency (reducing fluctuations in intermediate links). It reflects the systemic advantages brought about by this invention's upgrade of "composite" from simple "physical bonding" to "reactive bonding" deeply integrated with the curing process.

[0088] Test Example 2: Testing of Key Physical and Optical Properties of the Product 1. Experimental objective: This experiment aims to conduct systematic and quantitative key performance tests on PETG halogen-free label films prepared using different process parameters (Examples 1, 2, and 3) according to the technical indicators described in claim 9 and the specification of this invention. The focus is on verifying whether their optical properties (transmittance, haze) and basic mechanical properties (peel strength) meet the standards, and evaluating the stability and consistency of product performance under different process parameters.

[0089] 2. Sample preparation: Sample source: Finished PETG halogen-free label films prepared in different batches on the same production line according to the methods and parameters described in Examples 1, 2, and 3 of this invention. For each example, at least 10 meters of continuously produced film rolls with no appearance defects were taken.

[0090] Sample pretreatment: Place all samples in a standard testing environment (temperature: 23±2°C, relative humidity: 50±5%) for no less than 24 hours to achieve temperature and humidity equilibrium. 3. Detailed experimental procedures and test methods: 3.1 Transmittance and Haze Tests: Test standard: GB / T2410-2008 "Determination of light transmittance and haze of transparent plastics" Test equipment: Integrating sphere haze meter (e.g., Murakami Color Technology Research Institute NDH-7000 model).

[0091] Test steps: 1. Start the equipment and preheat it, and perform zero-point and standard plate calibration.

[0092] 2. From the sample film of each embodiment, cut at least 5 specimens with a size of not less than 50mm × 50mm evenly in the transverse direction. Ensure that the surface of the specimens is clean and free of scratches, dust and fingerprints.

[0093] 3. Place the sample into the sample holder, ensuring it is flat and wrinkle-free.

[0094] 4. Measure the transmittance (Tt) and haze (H) of each sample.

[0095] 5. For each of the five test data points in each embodiment, calculate the mean and standard deviation.

[0096] 3.2180° peel strength test: Test standard: GB / T2792-2014 "Test method for peel strength of adhesive tapes" Testing equipment: Electronic universal testing machine (e.g., Instron 3365 series), equipped with a 2kg standard pressure roller.

[0097] Test substrate: Standard 302 stainless steel plate (surface roughness Ra 0.4μm ± 0.1μm), cleaned with acetone and dried before testing.

[0098] Test steps: 1. Cut at least 5 sample strips, each 25 mm ± 0.5 mm wide and at least 300 mm long, longitudinally from the sample film of each embodiment.

[0099] 2. Attach the adhesive side of the sample strip to one end of a clean stainless steel plate, ensuring there are no air bubbles. Use a 2kg standard pressure roller to roll back and forth three times along the length at a speed of approximately 10mm / s.

[0100] 3. After bonding, let stand for 20 minutes under standard testing conditions.

[0101] 4. Clamp the sample plate in the lower fixture of the testing machine, fold the free end of the sample back 180°, and clamp it in the upper fixture, ensuring that the peeling angle is 180°.

[0102] 5. Set the tensile speed to 300 mm / min, start the testing machine, and record the force curve over a length of at least 100 mm during the peeling process.

[0103] 6. Discard the data from the initial 25mm and the last 25mm from the curve, and take the average force value of the middle stable part as the peel strength of the sample (unit: N / 25mm).

[0104] 7. For the five test data points of each embodiment, calculate their mean and standard deviation.

[0105] 3.3 Thickness uniformity test: Test standard: GB / T6672-2001 "Mechanical Measurement Method for Determination of Thickness of Plastic Films and Sheets" Test equipment: Contact digital micrometer (resolution 0.001mm).

[0106] Test steps: 1. Samples were taken from the head, middle and tail portions of the sample film roll for each embodiment.

[0107] 2. On each sample, select at least 9 measurement points at equal intervals along the transverse (width direction) (e.g., 10mm from the edge, 1 / 4 width, 1 / 2 width, 3 / 4 width, 10mm from the edge on the other side, and then take the midpoint, etc.).

[0108] 3. Gently measure the total thickness at each point using a micrometer and record the data.

[0109] 4. Calculate the average thickness at all measurement points for each embodiment ( ), and find the maximum value ( ) and minimum value ( ).

[0110] 5. Calculate the thickness deviation: .

[0111] 4. Specific experimental data and results: Table 2: Key Physical and Optical Performance Test Data of PETG Halogen-Free Label Film 5. Experimental Conclusion: 1. Conclusion 1: All products in the embodiments meet and exceed the preset optical and adhesive performance indicators, proving that the present invention has a wide process window and good stability.

[0112] Data support: The transmittance (91.5%-92.1%) and haze (2.0%-2.3%) data of the three examples are all clearly higher than the thresholds of "≥91%" and "≤2.5%", and the data fluctuation range is small (low standard deviation).

[0113] Mechanism analysis: This is due to the excellent transparency of the water-based halogen-free functional coating itself, and the fact that the particle size (15-40nm) of the nano-inorganic modifiers (silica / titanium) is much smaller than the wavelength of visible light. After surface organic modification, they are highly uniformly dispersed in the resin matrix, minimizing light scattering. The high transparency of the PETG substrate itself is also fundamental.

[0114] 2. Conclusion 2: The peel strength data verified the universality advantage of the simultaneous curing process, and Example 2 (intermediate parameters) showed the best overall performance.

[0115] Data support: The peel strength of all three examples (8.5, 9.8, 9.2 N / 25 mm) far exceeds the minimum requirement of 8 N / 25 mm. Notably, Example 2 (9.8 N / 25 mm) exhibits the highest strength and a relatively smaller standard deviation (±0.5).

[0116] Mechanism Analysis: All embodiments employed a "simultaneous curing" core process, thus achieving high interfacial adhesion. The parameters in Embodiment 1 were relatively conservative (temperature and time were taken at their lower limits), potentially leading to insufficient interpenetrating crosslinking between the functional coating and the adhesive layer. The parameters in Embodiment 3 were more aggressive, potentially causing premature gelation of the functional coating and affecting the melt wetting of the adhesive. The parameters in Embodiment 2 (intermediate values) achieved the optimal balance between promoting interfacial reaction and ensuring sufficient material flow and wetting, thus obtaining the highest peel strength and best process stability (low standard deviation).

[0117] 3. Conclusion 3: Excellent thickness uniformity is an important guarantee for achieving high performance consistency.

[0118] Data support: The thickness deviation of the three embodiments was controlled within ±3%, indicating that the production process (biaxial stretching, coating, and lamination) was precisely controlled.

[0119] Mechanism analysis: Uniform thickness directly affects the uniformity of optical performance (haze) and adhesive performance (adhesive content per unit area). Precise temperature control and stretch ratio in the biaxial stretching process, as well as stable control of the composite pressure, are key to obtaining products with high uniformity.

[0120] Test Example 3: Environmental Durability and Aging Performance Testing 1. Experimental objective: This experiment aims to simulate a harsh, long-term humid and hot environment to evaluate the changes in the key performance (peel strength) of the PETG halogen-free label film prepared according to this invention over time. By quantitatively analyzing its performance retention rate after aging at 85°C and 85% relative humidity (RH) for different times, it verifies whether it meets and exceeds the indicator of peel strength retention rate ≥90% after 500 hours of aging, and evaluates its long-term reliability.

[0121] 2. Test sample: Sample: A halogen-free PETG label film prepared using the process parameters of Example 2. This example was selected because it performed best in the comprehensive performance test and is representative.

[0122] Specifications: The initial 180° peel strength of the sample has been tested and used as a baseline (0-hour data).

[0123] 3. Test equipment and materials: Constant temperature and humidity test chamber: Temperature and humidity control accuracy: Temperature ±0.5°C, Humidity ±2%RH.

[0124] Electronic universal testing machine: Same as test example 2.

[0125] Standard stainless steel plate, 2kg pressure roller, acetone, etc.: Same as in test example 2.

[0126] Standard environmental conditioning chamber: used for conditioning samples before testing (23±2°C, 50±5%RH).

[0127] 4. Detailed experimental procedures: Step 1: Sample Preparation and Pretreatment 1. Cut several sample strips, each 25 mm wide and approximately 400 mm long, longitudinally from the same batch of film rolls. Ensure the cut edges are neat and free of burrs.

[0128] 2. Place all test strips and standard stainless steel plates together in a standard testing environment (23±2°C, 50±5%RH) for at least 24 hours to acclimatize.

[0129] 3. Randomly select one set (at least 5 strips) from all the test strips and immediately test their initial peel strength as in step two, using it as the "0-hour" baseline value.

[0130] Step 2: Accelerated aging treatment and sampling 1. Lay the remaining test strips flat on the special sample rack of the test chamber, ensuring sufficient gaps between the test strips and between the test strips and the chamber walls to ensure uniform airflow.

[0131] 2. Set the parameters of the constant temperature and humidity test chamber to: temperature 85°C, relative humidity 85%RH. After the temperature and humidity inside the chamber reach the set values ​​and stabilize, place the sample rack containing the sample inside and start timing.

[0132] 3. At 168 hours (1 week), 500 hours (approximately 21 days), and 1000 hours (approximately 42 days) of aging, remove a set of samples (at least 5 samples) from the test chamber.

[0133] 4. Immediately place the removed sample into a standard environmental conditioning chamber and condition it at 23±2°C and 50±5%RH for 24 hours to eliminate the influence of the temporary heat and humidity state of the sample before testing on the bonding performance.

[0134] Step 3: Post-aging performance testing and characterization 1. Peel strength test: For each aging time point, the conditioned samples were taken out and subjected to a 180° peel strength test according to the same test standard (GB / T2792-2014) and parameters (roller pressing 3 times, resting for 20 min, tensile speed 300 mm / min) as the "0 hour" sample. The peel force curve and average peel strength of each sample were recorded.

[0135] 2. Visual observation: Visually observe and record changes in the appearance of the sample at each sampling time, such as whether it turns yellow, becomes sticky, wrinkles, warps, or has precipitates.

[0136] 3. Data Calculation: Calculate the average of at least 5 valid test data points at each aging time point. ) and standard deviation.

[0137] Calculate the peel strength retention rate at each time point: in, This represents the average value of the initial peel strength at "0 hours".

[0138] 5. Specific experimental data and results: Table 3: Aging performance data of PETG halogen-free label film at 85°C / 85%RH 6. Experimental Conclusion: 1. Conclusion 1: The label film prepared by this invention fully meets and exceeds the key technical indicator of peel strength retention rate ≥90% after 500 hours of aging.

[0139] Supporting data: After 500 hours of rigorous aging, the sample's peel strength was 9.0 N / 25 mm, with a retention rate of 91.8%, clearly exceeding the 90% requirement. This demonstrates the product's superior reliability under simulated long-term humid and hot conditions.

[0140] Mechanism analysis: This excellent performance is attributed to: (1) Halogen-free and hydrogenated modification of the adhesive system: Hydrogenated terpene resin has higher thermal oxidation stability and UV aging resistance than ordinary terpenes or petroleum resins, and is less likely to produce small molecule acidic substances; the SIS base polymer itself has good water resistance. (2) Strong interpenetrating network (IPN) structure: As demonstrated in Experiment 1, the interface layer formed by simultaneous curing can effectively resist stress relaxation and interfacial desorption caused by humid heat. (3) Barrier effect of functional coating: The cross-linked and dense functional coating can partially block water vapor and heat from directly and quickly attacking the weak links between the adhesive layer and the interface.

[0141] 2. Conclusion 2: The product exhibits a gradual and predictable performance degradation trend during long-term aging, which verifies its stable material system.

[0142] Data support: From 0 to 1000 hours, the peel strength showed a monotonous and gradual downward trend, without a precipitous drop. The retention rates at 168 hours, 500 hours, and 1000 hours were 96.9%, 91.8%, and 83.7%, respectively, and the degradation curves conformed to the typical performance degradation law of polymer materials under humid and hot environments.

[0143] Mechanism analysis: The slow decline in performance mainly stems from two aspects: first, the slow thermo-oxidative aging of the polymer molecular chains and tackifying resins in the adhesive leads to a decrease in molecular weight or slight cross-linking, macroscopically manifested as a slight decrease in cohesive strength and yellowing; second, a humid and hot environment may cause a small amount of hydrolysis reaction at the interface. However, the overall smooth degradation curve indicates that the material formulation and process design effectively slow down these aging processes.

[0144] 3. Conclusion 3: The appearance changes are consistent with the performance data. Yellowing is the main appearance aging phenomenon, but it does not lead to functional failure.

[0145] Data support: As the aging time increased, the yellowing of the samples gradually intensified, which was synchronized with the slow decline in peel strength. However, even after 1000 hours, the samples remained flat, without serious defects such as delamination, stickiness, or adhesive migration.

[0146] Mechanism analysis: Yellowing mainly originates from the oxidation of resin components in the adhesive, producing chromophores, a common phenomenon in hot-melt pressure-sensitive adhesives at high temperatures. Importantly, this appearance change was not accompanied by severe softening of the adhesive layer (maintaining the cohesive failure mode in the peel test) or delamination from the substrate, indicating that the function was not lost due to the appearance change, and the overall integrity of the material system remained good.

[0147] Experiment Example 4: Verification of Halogen-Free Environmental Characteristics 1. Experimental objective: This experiment aims to quantitatively test the halogen content of the PETG halogen-free label film prepared by this invention in accordance with internationally recognized standards, so as to objectively verify whether it meets the requirements of the IEC61249-2-21 standard (chlorine and bromine content ≤900ppm, total ≤1500ppm), thereby confirming the "halogen-free" characteristic of this invention from the perspective of environmental regulatory compliance.

[0148] 2. Selection of test standards and methods: Testing standard: IEC61249-2-21:2003 Materials for printed circuit boards and other interconnect structures - Part 2-21: Reinforced substrates / cladding foils / flame retardants (vertical burning test) - Copper-clad modified epoxy woven E-glass fiber laminates (halogen-free)

[0149] Detection method: Combustion-Ion Chromatography (CICh) is employed. This method is the authoritative method recommended by the International Electrotechnical Commission (IEC) for detecting halogen content in electronic and electrical products, and it has the advantages of high sensitivity, good accuracy, and the ability to simultaneously detect multiple halogen ions.

[0150] Alternative validation method: Use X-ray fluorescence spectroscopy (XRF) for rapid screening and result comparison to increase the reliability of the results.

[0151] 3. Sample preparation: Sample source: Approximately 10 grams of the finished PETG halogen-free label film prepared in Example 2 were taken. To ensure that the sample is representative of the entire product structure, the sample included the substrate layer, functional coating layer, and adhesive layer.

[0152] Preprocessing: 1. Cleaning: Wipe the sample surface with a halogen-free reagent (such as isopropanol) to remove any possible contaminants.

[0153] 2. Grinding and Homogenization: The sample was ground into a uniform powder with a particle size of less than 1 mm using halogen-free ceramic shears and a ball mill under liquid nitrogen cooling. This step is crucial to ensure that the test sample represents the average composition of the overall material.

[0154] 3. Mixing and Reduction: After the powder is thoroughly mixed, the test sample of about 1.0g is reduced by the "quartering method" and placed in a desiccator for later use.

[0155] 4. Detailed experimental procedures: Step 1: Decomposition of oxygen bomb combustion samples 1. Accurately weigh 0.05 g (accurate to 0.0001 g) of homogenized sample powder and place it in a halogen-free quartz sample cup.

[0156] 2. Place the sample cup into the oxygen bomb (oxygen pressure approximately 2.5 MPa) and add an appropriate amount of absorption solution (usually an alkaline hydrogen peroxide solution).

[0157] 3. Introduce high-purity oxygen, ignite the sample with electricity, and allow it to burn completely under high pressure and oxygen-rich conditions. During this process, organic halogens in the sample are converted into hydrogen halides (HCl, HBr, etc.) and absorbed by the absorbent.

[0158] Step 2: Ion Chromatography Analysis 1. Transfer the absorbent from the oxygen bomb to a volumetric flask, dilute to volume with deionized water, and filter if necessary to obtain the solution to be tested.

[0159] 2. Use an ion chromatograph equipped with an anion separation column and a conductivity detector.

[0160] 3. Inject chloride ions (Cl) separately - ) standard solution and bromide ion (Br - Use standard solutions to plot a standard curve.

[0161] 4. Inject the test solution, perform qualitative analysis based on retention time, and quantitatively calculate the Cl content in the solution using a standard curve based on peak area. - and Br - The concentration.

[0162] Step 3: Result Calculation 1. Calculate the content of chlorine (Cl) and bromine (Br) in the sample based on the measured ion concentration, sample weight, and final volume.

[0163] 2. Calculation formula: C: Ion concentration (mg / L) measured by chromatography; V: Sample volume at constant volume (L); D: Dilution factor; W: Sample weight (g); 3. Each sample should be tested in at least three parallel tests, and the arithmetic mean should be used as the final reported value.

[0164] Step 4: Rapid XRF Screening (Verification) 1. Press another portion of the homogenized powder into flat sheets.

[0165] 2. The sample was scanned using an energy-dispersive X-ray fluorescence spectrometer (ED-XRF).

[0166] 3. Using the instrument's built-in halogen-free material analysis program or standard sample calibration curve, perform semi-quantitative analysis of the intensity signals of chlorine (Cl) and bromine (Br), and compare the results with those of ion chromatography.

[0167] 5. Specific experimental data and results: Table 4: Halogen content detection data of PETG halogen-free label film (oxygen bomb combustion-ion chromatography) Note: The XRF rapid screening results showed a consistent trend with the ion chromatography results, with Cl and Br signal intensities being extremely low, both indicating "not detected" or "far below the limit," thus verifying the reliability of the main data.

[0168] 6. Experimental Conclusion: 1. Conclusion 1: The product fully meets and significantly exceeds international halogen-free standards, demonstrating excellent environmental protection characteristics.

[0169] Data support: The measured chlorine content was 420 ppm and the bromine content was 150 ppm, both far below the standard limit of 900 ppm for each individual item; the total of 570 ppm was also far below the limit of 1500 ppm. All data showed a margin of safety exceeding 50%, which is not a "borderline" compliance, but rather a sufficient design safety margin.

[0170] Mechanism analysis: This result is directly attributed to the halogen-free design concept of the entire component of this invention: Substrate: PETG resin itself does not contain halogens.

[0171] Functional coating: The core resin is waterborne polyurethane acrylic, the crosslinking agent is aziridine or carbodiimide, and the nanomaterial is silicon dioxide / titanium, all of which are free of chlorine and bromine.

[0172] Adhesives: Based on SIS and hydrogenated terpene resins, these adhesives replace traditional flame-retardant adhesives that may contain bromine or systems that use chlorinated solvents and tackifying resins.

[0173] The introduction of halogens was eliminated at the source.

[0174] 2. Conclusion 2: The good repeatability of the test data indicates that the composition of the product is stable between batches and the production process is controllable.

[0175] Data support: The data fluctuations in the three parallel tests were very small (standard deviation of 4-10 ppm), indicating that the sampling was uniform, the testing method was accurate, and it also reflects that the product formula was uniformly mixed and the production was highly consistent.

[0176] Logical relevance: The low standard deviation data enhances the credibility of the conclusion that "the product consistently meets halogen-free requirements," which is crucial for industrial products that require bulk supply and must pass customer inspection upon arrival.

[0177] 3. Conclusion 3: The detection values ​​of trace amounts are consistent with objective laws, and the results are true and reliable.

[0178] Data Explanation: The chlorine and bromine detected at the ppm level (parts per million) were not intentionally added in this invention, but originated from: (1) trace amounts of halogens present as impurities in the raw materials; and (2) background pollution in the production environment, utensils, or water. This extremely low level of "background value" is far below the standard limit and is completely reasonable and acceptable. This, on the contrary, proves the authenticity and sensitivity of the test.

[0179] Test Example 5: Surface Properties and Printability Test of Functional Coatings 1. Experimental objective: This experiment aims to systematically evaluate the physical properties (surface energy) of the functional coating surface of the PETG halogen-free label film of the present invention and its actual performance as a printing substrate. The focus is on verifying its compatibility with halogen-free UV-curable inks, print quality, and final ink adhesion, thereby demonstrating that this functional coating not only achieves strong bonding with the adhesive layer but also integrates excellent printability.

[0180] 2. Test sample: Sample: Finished PETG halogen-free label film prepared in Example 2 (functional coating side facing out).

[0181] Comparative sample (optional): PETG substrate film that has not undergone functional coating treatment and has only been corona treated.

[0182] Test ink: Commercially available high-performance halogen-free UV-LED curable screen printing ink (compliant with IEC61249-2-21 standard).

[0183] 3. Detailed experimental procedures: Step 1: Surface Energy Measurement (Dyne Pen Method) 1. Principle: Use a dyne pen (test liquid) with known surface tension to write on the coating surface. If the liquid film continuously shrinks into a bead shape within 2 seconds, it indicates that the surface tension of the coating is lower than the value of the test liquid; if a continuous and uniform liquid film can be maintained for at least 2 seconds, it indicates that the surface tension is equal to or higher than the value.

[0184] 2. Operation: Start testing from a low value reaching the pen (e.g., 38 mN / m).

[0185] On a clean, flat sample surface, draw a liquid line about 3 cm long using a dyne pen.

[0186] Start timing immediately and observe the changes in the liquid level over 2 seconds.

[0187] Gradually use higher dyne values ​​(e.g., 40, 42, 44, ... up to 58 mN / m) and repeat the test until you find the highest dyne value that can keep the liquid film continuously and uniformly maintained for ≥2 seconds.

[0188] This value is the dyne value (approximate surface tension) of the sample surface. Each sample is tested at least 3 different locations.

[0189] Step Two: Screen Printing Test 1. Screen making: Use 100T (approximately 155 mesh) polyester screen to make a test screen. The pattern includes: solid color blocks, fine lines (0.2mm wide), and small text (size 4).

[0190] 2. Printing: The sample is flattened and fixed on the screen printing machine's worktable.

[0191] Use a hard polyurethane squeegee (hardness approximately 70 Shore A) to squeegee at a fixed angle and speed.

[0192] After printing, the sample is immediately passed through a UV-LED curing tunnel (dominant wavelength 395nm, light intensity: 80mW / cm²). 2 To ensure an irradiation dose of 300 mJ / cm at the conveyor belt speed. 2 .

[0193] 3. Print quality assessment: Under standard light (D65), visually assess the following items and with the aid of a 10x magnifying glass: Leveling property: Whether the ink automatically levels into a smooth surface, and whether there are pinholes or fisheyes.

[0194] Sharpness: Whether the edges of the lines are clear, and whether there are jagged edges or ink bleeding.

[0195] Opacity: Whether the solid color blocks are even and without any transparent background.

[0196] Step 3: Ink adhesion test (100-cross test) 1. Grid Cutting: In the printed and fully cured solid color area, use a multi-blade cutter (1mm blade spacing) to cut a grid. The blades must cut through the ink layer to the functional coating substrate, forming a 10×10 square grid with a side length of 1mm.

[0197] 2. Cleaning: Use a soft-bristled brush to gently brush along the diagonal of the grid 5 times to remove loose debris.

[0198] 3. Tape application and removal: Apply 3M 610 (or equivalent adhesive) tape firmly to the grid area, ensuring there are no air bubbles.

[0199] Rub the back of the tape vigorously with your finger or an eraser to ensure it makes full contact with the test surface.

[0200] Within 60±30 seconds, hold one end of the tape and quickly (not slowly) tear the tape off the surface at an angle as close to 180° as possible.

[0201] 4. Result Evaluation: Under illumination, examine the ink peeling in the grid area using a magnifying glass, and classify it according to GB / T9286-2021 standard: Level 0: The cut edges are completely smooth, and there is no detachment within the mesh.

[0202] Level 1: A small amount of coating has peeled off at the intersection of the cuts, but the affected cross-cut area is no more than 5%.

[0203] Level 2: Coating peeling occurs at the intersection of cuts and / or along the edges of cuts, with the affected cross-cut area exceeding 5% but not exceeding 15%.

[0204] Level 3: The coating is partially or completely detached in large fragments along the cut edge, and / or partially or completely detached at different locations on the grid, with the affected cross-cut area being greater than 15% but not more than 35%.

[0205] Level 4: Large fragments of coating peel off along the cut edge, and / or some squares partially or completely peel off, with the affected cross-cut area greater than 35% but not greater than 65%.

[0206] Level 5: The degree of detachment exceeds that of Level 4.

[0207] 5. Test at least 3 different printing areas for each sample.

[0208] 4. Specific experimental data and results Table 5: Test data on surface properties and printability of functional coatings 5. Experimental Conclusion: 1. Conclusion 1: The functional coating has high surface energy, providing an ideal basis for wetting and spreading of inks.

[0209] Data support: A dyne value of ≥54mN / m is a very high value, significantly exceeding the minimum standard required for conventional plastic printing (38mN / m).

[0210] Mechanism analysis: High surface energy mainly comes from two aspects: (1) Introduction of nano-inorganic particles (SiO2 / TiO2): Nanoparticles modified with organic matter form a micro-rough structure and abundant polar sites on the coating surface. (2) Polar groups (such as carboxyl and hydroxyl groups) of the waterborne polyurethane acrylic resin itself. High surface energy effectively reduces the contact angle of the ink, enabling it to spread quickly and evenly, which is the fundamental reason for obtaining excellent leveling and high printing sharpness.

[0211] 2. Conclusion 2: Functional coatings and halogen-free UV inks exhibit excellent compatibility and adhesion.

[0212] Data support: The cross-cut test results reached the highest level "0", and only minimal ink cohesion damage occurred after rigorous testing.

[0213] Mechanism analysis: Strong adhesion stems from the dual effects of chemical and physical processes: (1) Chemical bonding: Residual active groups in the functional coating (such as acrylate double bonds and crosslinking active groups) may undergo copolymerization with the UV ink during the curing process to form chemical bonds. (2) Physical anchoring and interpenetration: The micro-rough structure of the coating provides mechanical anchoring points for the ink; at the same time, in the liquid stage after ink coating and before UV curing, the monomers / oligomers in the ink can slightly swell and penetrate into the polymer network on the coating surface, forming physical interpenetration after curing, thereby generating extremely strong mechanical locking force.

[0214] 3. Conclusion 3: This functional coating successfully integrates the functions of a "strong interface layer" and a "high-quality printing surface".

[0215] Logical connection: Test data shows that the same functional coating surface can form a strong bond with the back adhesive layer with a peel strength of 9.8N / 25mm through a synchronous curing process (see Test Example 2), and also provide strong adhesion for the front ink with a cross-cut adhesion test grade of 0. This breaks the traditional design of label films, which often require an additional special printing primer coating on the substrate.

[0216] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in the present invention, and these should all be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a halogen-free PETG label film, characterized in that, Includes the following steps: S1. Substrate pretreatment: Provide PETG resin raw materials, form a PETG substrate layer through melt extrusion, biaxial stretching and heat setting processes, and perform corona treatment on at least one side; S2. Preparation and application of functional coating: A halogen-free functional coating liquid is applied to the surface of the PETG substrate layer after corona treatment; the halogen-free functional coating liquid contains waterborne polyurethane acrylic composite resin, nano-inorganic modifier and crosslinking agent. S3. Coating synchronous curing and lamination: The coated PETG substrate layer and a halogen-free adhesive layer are bonded together using a lamination device, and then sent into a curing oven for synchronous curing and interlayer bonding under a specific temperature program; the specific temperature program causes the functional coating and adhesive layer to form physical entanglement and chemical cross-linking in the interface area. S4. Cooling and post-processing: The product obtained in step S3 is cooled and shaped to obtain the PETG halogen-free label film.

2. The method for preparing a halogen-free PETG label film according to claim 1, characterized in that, The specific temperature program mentioned in step S3 specifically includes: First stage: Treat at 70-85℃ for 1-3 minutes to allow the functional coating to initially form a film and retain its reactive activity, while the adhesive layer begins to soften. Second stage: Treat at 110-125℃ for 2-4 minutes to accelerate the cross-linking reaction of the functional coating and allow the adhesive layer to fully melt and flow, interpenetrating with the interface of the functional coating. The third stage: process at 130-145℃ for 1-2 minutes to complete the final curing of the functional coating and the interlayer shaping with the adhesive layer.

3. The method for preparing a halogen-free PETG label film according to claim 2, characterized in that, The waterborne polyurethane acrylic composite resin in step S2 has a core-shell structure and a glass transition temperature of -10°C to 10°C; the halogen-free adhesive layer is a hot melt pressure-sensitive adhesive based on styrene-isoprene-styrene block copolymer, and its melt viscosity at the first stage processing temperature is 5000-15000 cP.

4. The method for preparing a halogen-free PETG label film according to claim 1, characterized in that, The parameters of the biaxial stretching process in step S1 are: longitudinal stretching temperature 85-90℃, stretching ratio 3.2-3.4; transverse stretching temperature 88-93℃, stretching ratio 3.4-3.6; and the surface tension after corona treatment is not less than 50mN / m.

5. The method for preparing a halogen-free PETG label film according to claim 1, characterized in that, The halogen-free functional coating liquid in step S2 comprises, by mass parts: 80-100 parts of waterborne polyurethane acrylic composite resin, 5-10 parts of nano silica and / or nano titanium dioxide, and 3-5 parts of aziridine or carbodiimide crosslinking agent; the average particle size of the nano inorganic modifier is 15-40 nm, and it has undergone surface organic modification.

6. The method for preparing a halogen-free PETG label film according to claim 1, characterized in that, The raw materials of the halogen-free adhesive layer in step S3 include, by mass parts: 30-50 parts of styrene-isoprene-styrene block copolymer, 20-40 parts of hydrogenated terpene resin, 10-20 parts of softener, and 0.5-1.0 parts of antioxidant; the adhesive layer is pre-coated on the release film and separated from the release film before bonding.

7. The method for preparing a halogen-free PETG label film according to claim 6, characterized in that, The pressure of the bonding process in step S3 is 0.3-0.6 MPa; during the simultaneous curing and interlayer bonding process, the bonded film is subjected to online ultraviolet irradiation with an irradiation dose of 20-100 mJ / cm². 2 .

8. The method for preparing a halogen-free PETG label film according to claim 1, characterized in that, The cooling and shaping process in step S4 involves rapid cooling, which reduces the film temperature from the curing temperature to below 50°C within 10 seconds. After cooling, the non-functional coating surface of the label film is subjected to online corona treatment or coated with an antistatic layer.

9. A method for preparing a PETG halogen-free label film according to any one of claims 1-8, characterized in that, The final PETG halogen-free label film has a light transmittance of ≥91%, a haze of ≤2.5%, and a 180° peel strength to stainless steel plate of ≥8N / 25mm. After aging in an environment of 85℃ and 85%RH for 500 hours, the 180° peel strength retention rate is ≥90%.

10. The method for preparing a halogen-free PETG label film according to claim 9, characterized in that, The functional coating surface of the label film can be printed with halogen-free UV-cured ink, and the label film as a whole meets the halogen-free requirements of IEC61249-2-21 standard, with chlorine and bromine content ≤900ppm.

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