A multilayer composite polyester film and a method for producing the same

Abstract

The application provides a multilayer composite structure polyester film, characterized in that the polyester film is sequentially stacked with a heat sealing layer, a core layer and a corona layer; the heat sealing layer is made of a novel metallocene polyethylene, the core layer is made of a blending material of syndiotactic copolymerized polypropylene and polybutylene terephthalate, and the corona layer is made of a composite system of ethylene-butyl acrylate copolymer, linear low-density polyethylene and nano silicon dioxide; and the application also provides a preparation method of the multilayer composite structure polyester film, and the heat sealing performance is greatly improved in the application. Low-energy-consumption high-speed heat sealing: the heat sealing layer is made of a novel metallocene polyethylene (mPE), and the melting point (about 120 DEG C) of the novel metallocene polyethylene is significantly lower than that (125-130 DEG C) of traditional LDPE, the heat sealing temperature is reduced by 10-20 DEG C, the novel metallocene polyethylene is suitable for high-speed packaging production lines (>= 300 times / min), and the energy consumption is reduced by 15-20%.

Description

Technical Field

[0001] This invention relates to the field of polyester film manufacturing technology, specifically to a polyester film with a multilayer composite structure and its preparation method, which is suitable for the demand for high-performance films in packaging, electronics, optics and other fields. Background Technology

[0002] Traditional polyester films (such as BOPET) have limitations in heat-sealing properties, mechanical strength, and surface activity: Insufficient heat-sealing: Polyester materials have high melting points, requiring high-temperature heat sealing, which can easily lead to packaging deformation or increased energy consumption. Limited mechanical properties: Single-layer structures struggle to balance high modulus, flexibility, and impact resistance. Poor surface activity: Insufficient adhesion for printing or coatings, requiring additional treatment. Existing multilayer composite films improve performance through complementary interlayer functions, but still suffer from weak interlayer bonding, complex processing, and high costs. For example, traditional heat-sealing layer materials (such as LDPE) have insufficient heat-sealing strength, core layer materials (such as homopolymer PP) struggle to balance rigidity and toughness, and corona treatment layer surface treatment effects are unstable. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a multilayer composite polyester film, characterized in that the polyester film is sequentially stacked with a heat-sealing layer, a core layer, and a corona layer; the heat-sealing layer is made of a novel metallocene polyethylene, the core layer is made of a blend of syndiotactic copolymer polypropylene and polybutylene terephthalate, and the corona layer is made of a composite system of ethylene-butyl acrylate copolymer, linear low-density polyethylene, and nano-silica.

[0004] The present invention further provides that the thickness ratio of the heat-sealing layer, the core layer and the corona layer is (0.5-0.7):(3-5):1.

[0005] The present invention further specifies that the mass ratio of ethylene-butyl acrylate copolymer, linear low-density polyethylene and nano silica in the corona layer is (50-70):(25-40):(1-5).

[0006] The present invention further specifies that the mass ratio of ethylene-butyl acrylate copolymer, linear low-density polyethylene and nano-silica in the corona layer is 60:30:2.

[0007] The present invention further specifies that the core layer is made of syndiotactic copolymer polypropylene and polybutylene terephthalate in a mass ratio of (4-8):1.

[0008] The present invention further provides that the intrinsic viscosity of the polybutylene terephthalate at 25 degrees Celsius is between 1.2 and 1.5 dL / g.

[0009] A method for preparing a multilayer composite polyester film, the method comprising the following steps:

[0010] A novel metallocene polyethylene was fed into extruder I, while syndiotactic copolymer polypropylene and polybutylene terephthalate were fed into extruder II. Ethylene-butyl acrylate copolymer, linear low-density polyethylene, and nano-silica were mixed uniformly in a specific ratio and then fed into extruder III, where they were heated and melted separately. In extruder II, a twin-screw extruder was used to ensure thorough mixing of SPP and PBT, utilizing the shearing and mixing action of the screws to achieve uniform dispersion. In extruder III, a high-speed mixer was used for pre-mixing, followed by further homogenization by the extruder screws.

[0011] Extruders I, II, and III simultaneously extrude thin films through a T-die, which are then cooled and solidified to form the final film. A low-temperature circulating water cooling system is used to control the cooling water temperature between 15 and 20°C, ensuring rapid and uniform cooling of the film and preventing uneven internal stress and crystallization defects caused by uneven cooling.

[0012] The film was subjected to corona treatment to obtain the thin film with good surface activity. The corona treatment parameters were: voltage 8–10 kV, frequency 20–30 kHz, and treatment time 0.5–1.0 s. Suitable corona parameters can ensure that the surface of the corona layer obtains sufficient roughness and chemical activity without causing excessive damage to the film.

[0013] Compared with existing technologies, the advantages and beneficial effects of this invention are as follows: Breakthrough improvement in heat-sealing performance. Low-energy, high-speed heat sealing: The heat-sealing layer uses a novel metallocene polyethylene (mPE), whose melting point (approximately 120℃) is significantly lower than that of traditional LDPE (125-130℃), reducing the heat-sealing temperature by 10-20℃. This makes it suitable for high-speed packaging production lines (≥300 times / minute), reducing energy consumption by 15-20%. High-strength heat-sealing interface: The narrow molecular weight distribution and high crystallinity of mPE endow the film with excellent heat-sealing strength (≥8N / 15mm), which is more than 30% higher than that of traditional LDPE heat-sealing layers (5-6N / 15mm). Furthermore, there is no crystal point or embrittlement phenomenon after heat sealing, making it suitable for high-temperature retorting or frozen packaging. Synergistic optimization of core layer mechanical properties and a balanced stiffness-toughness design: The high modulus (≥1200MPa) of syndiotactic copolymer polypropylene (sPP) and the toughness (cantilever beam notched impact strength ≥30kJ / m) of polybutylene terephthalate (PBT) 2The island structure is formed through dynamic mixing using a twin-screw extruder, giving the film both rigidity and wrinkle resistance as well as puncture resistance. Temperature adaptability is expanded: the introduction of PBT broadens the core layer's operating temperature range to -40℃ to 150℃, making it suitable for cold chain transportation and high-temperature sterilization packaging. Precise regulation of corona layer surface activity and nano-enhanced surface modification: nano-silica (1-5wt%) in the corona layer is pre-dispersed in a high-speed mixer and mixed using a screw extruder to form a uniform distribution. During corona treatment, it generates micro-nano roughness (Ra 0.2-0.5μm), which, combined with the polar groups (-COOH) of EBA, stabilizes the surface tension at 42-45mN / m, resulting in printing adhesion ≥3.5N / 15mm without the need for primer treatment. Long-term stability: the addition of nano-SiO2 inhibits the decay of surface activity after corona treatment (surface tension remains ≥40mN / m after 30 days of storage), an improvement of more than 50% compared to traditional corona layers (which decay to below 35mN / m). The enhanced interlayer bonding mechanism and compatible interface design: The core layer SPP and the heat-sealing layer mPE form a transition layer (100-200nm thick) through molecular chain diffusion, with a peel strength ≥5N / 15mm; the corona layer EBA and the core layer SPP enhance interfacial adhesion through polar interaction, avoiding delamination defects. Low-temperature circulating water cooling (15-20℃) ensures matching crystallization rates of each layer, reduces internal stress by more than 60%, and achieves a film curl ≤2mm / m, making it suitable for high-speed printing and lamination processing. Detailed Implementation

[0014] The invention can be further understood by referring to the following detailed description of preferred embodiments and included examples. Unless otherwise stated, 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 application pertains. If the definitions of specific terms disclosed in the prior art are inconsistent with any definitions provided in this application, the definitions provided in this application shall prevail.

[0015] A multilayer composite polyester film, characterized in that the polyester film is provided with a heat-sealing layer, a core layer and a corona layer stacked sequentially; the heat-sealing layer is made of a novel metallocene polyethylene, the core layer is made of a blend of syndiotactic copolymer polypropylene and polybutylene terephthalate, and the corona layer is made of a composite system of ethylene-butyl acrylate copolymer, linear low-density polyethylene and nano-silica.

[0016] The present invention further provides that the thickness ratio of the heat-sealing layer, the core layer and the corona layer is (0.5-0.7):(3-5):1.

[0017] The present invention further specifies that the mass ratio of ethylene-butyl acrylate copolymer, linear low-density polyethylene and nano silica in the corona layer is (50-70):(25-40):(1-5).

[0018] The present invention further specifies that the mass ratio of ethylene-butyl acrylate copolymer, linear low-density polyethylene and nano-silica in the corona layer is 60:30:2.

[0019] The present invention further specifies that the core layer is made of syndiotactic copolymer polypropylene and polybutylene terephthalate in a mass ratio of (4-8):1.

[0020] The present invention further provides that the intrinsic viscosity of the polybutylene terephthalate at 25 degrees Celsius is between 1.2 and 1.5 dL / g.

[0021] A method for preparing a multilayer composite polyester film, the method comprising the following steps:

[0022] A novel metallocene polyethylene was fed into extruder I, while syndiotactic copolymer polypropylene and polybutylene terephthalate were fed into extruder II. Ethylene-butyl acrylate copolymer, linear low-density polyethylene, and nano-silica were mixed uniformly in a specific ratio and then fed into extruder III, where they were heated and melted separately. In extruder II, a twin-screw extruder was used to ensure thorough mixing of SPP and PBT, utilizing the shearing and mixing action of the screws to achieve uniform dispersion. In extruder III, a high-speed mixer was used for pre-mixing, followed by further homogenization by the extruder screws.

[0023] Extruders I, II, and III simultaneously extrude thin films through a T-die, which are then cooled and solidified to form the final film. A low-temperature circulating water cooling system is used to control the cooling water temperature between 15 and 20°C, ensuring rapid and uniform cooling of the film and preventing uneven internal stress and crystallization defects caused by uneven cooling.

[0024] The film was subjected to corona treatment to obtain the thin film with good surface activity. The corona treatment parameters were: voltage 8–10 kV, frequency 20–30 kHz, and treatment time 0.5–1.0 s. Suitable corona parameters can ensure that the surface of the corona layer obtains sufficient roughness and chemical activity without causing excessive damage to the film.

[0025] Compared with existing technologies, the advantages and beneficial effects of this invention are as follows: Breakthrough improvement in heat-sealing performance. Low-energy, high-speed heat sealing: The heat-sealing layer uses a novel metallocene polyethylene (mPE), whose melting point (approximately 120℃) is significantly lower than that of traditional LDPE (125-130℃), reducing the heat-sealing temperature by 10-20℃. This makes it suitable for high-speed packaging production lines (≥300 times / minute), reducing energy consumption by 15-20%. High-strength heat-sealing interface: The narrow molecular weight distribution and high crystallinity of mPE endow the film with excellent heat-sealing strength (≥8N / 15mm), which is more than 30% higher than that of traditional LDPE heat-sealing layers (5-6N / 15mm). Furthermore, there is no crystal point or embrittlement phenomenon after heat sealing, making it suitable for high-temperature retorting or frozen packaging. Synergistic optimization of core layer mechanical properties and a balanced stiffness-toughness design: The high modulus (≥1200MPa) of syndiotactic copolymer polypropylene (sPP) and the toughness (cantilever beam notched impact strength ≥30kJ / m) of polybutylene terephthalate (PBT) 2 The island structure is formed through dynamic mixing using a twin-screw extruder, giving the film both rigidity and wrinkle resistance as well as puncture resistance. Temperature adaptability is expanded: the introduction of PBT broadens the core layer's operating temperature range to -40℃ to 150℃, making it suitable for cold chain transportation and high-temperature sterilization packaging. Precise regulation of corona layer surface activity and nano-enhanced surface modification: nano-silica (1-5wt%) in the corona layer is pre-dispersed in a high-speed mixer and mixed using a screw extruder to form a uniform distribution. During corona treatment, it generates micro-nano roughness (Ra 0.2-0.5μm), which, combined with the polar groups (-COOH) of EBA, stabilizes the surface tension at 42-45mN / m, resulting in printing adhesion ≥3.5N / 15mm without the need for primer treatment. Long-term stability: the addition of nano-SiO2 inhibits the decay of surface activity after corona treatment (surface tension remains ≥40mN / m after 30 days of storage), an improvement of more than 50% compared to traditional corona layers (which decay to below 35mN / m). The enhanced interlayer bonding mechanism and compatible interface design: The core layer SPP and the heat-sealing layer mPE form a transition layer (100-200nm thick) through molecular chain diffusion, with a peel strength ≥5N / 15mm; the corona layer EBA and the core layer SPP enhance interfacial adhesion through polar interaction, avoiding delamination defects. Low-temperature circulating water cooling (15-20℃) ensures matching crystallization rates of each layer, reduces internal stress by more than 60%, and achieves a film curl ≤2mm / m, making it suitable for high-speed printing and lamination processing.

[0026] Example 1

[0027] Material proportions:

[0028] Heat-sealing layer: Novel metallocene polyethylene (mPE), 100%;

[0029] Core layer: Syndiotactic copolymer polypropylene (sPP) to polybutylene terephthalate (PBT) in a mass ratio of 6:1 (PBT intrinsic viscosity 1.3 dL / g, 25℃);

[0030] Corona layer: Ethylene-butyl acrylate copolymer (EBA): Linear low-density polyethylene (LLDPE): Nano silica (SiO2) = 60:30:2;

[0031] Layer thickness ratio: heat seal layer: core layer: corona layer = 0.6:4:1 (total thickness 50μm).

[0032] Preparation process:

[0033] Extrusion parameters:

[0034] Extruder I (heat seal layer): temperature 180℃, screw speed 150rpm;

[0035] Extruder II (core layer): Twin-screw extruder, temperature 220℃, speed 200rpm;

[0036] Extruder III (corona layer): Temperature 190℃, speed 180rpm;

[0037] T-die head temperature: 200℃, die lip gap: 0.2mm.

[0038] Cooling and molding:

[0039] Low-temperature circulating water cooling system, water temperature 18℃, traction speed 120m / min.

[0040] Corona treatment:

[0041] Voltage 9kV, frequency 25kHz, processing time 0.8s.

[0042] Performance testing:

[0043] Heat sealing performance: heat sealing temperature 130℃, heat sealing strength 8.5N / 15mm;

[0044] Mechanical properties:

[0045] Tensile strength (longitudinal / transverse): 85MPa / 80MPa;

[0046] Tensile modulus: 1250 MPa;

[0047] Notched impact strength of cantilever beam: 30kJ / m 2 ;

[0048] Surface properties:

[0049] Surface tension: 43 mN / m;

[0050] Printing adhesion: 3.8N / 15mm;

[0051] Interlayer bonding: peel strength 5.1 N / 15 mm;

[0052] Thermal stability: DSC test shows that the core layer has a melting point of 165℃ and a thermal decomposition temperature of 320℃.

[0053] Example 2

[0054] Heat-sealing layer: Novel metallocene polyethylene (mPE), 100%;

[0055] Material proportions:

[0056] Core layer: sPP:PBT = 8:1 (PBT intrinsic viscosity 1.5 dL / g);

[0057] Corona layer: EBA:LLDPE:Nano SiO2 = 70:25:5;

[0058] Layer thickness ratio: 0.7:5:1 (total thickness 60μm).

[0059] Preparation process:

[0060] Extrusion parameters:

[0061] Extruder II temperature 230℃, speed 220rpm;

[0062] Extruder III: Temperature 200℃, Rotation speed 200rpm;

[0063] The temperature of the T-shaped die head is 210℃.

[0064] Cooling and molding:

[0065] Water temperature 15℃, traction speed 100m / min.

[0066] Corona treatment:

[0067] Voltage 10kV, frequency 30kHz, processing time 1.0s.

[0068] Performance testing:

[0069] Heat seal strength: 9.0 N / 15 mm (135℃);

[0070] Mechanical properties:

[0071] Tensile strength: 90 MPa (longitudinal);

[0072] Notched impact strength of cantilever beam: 32kJ / m 2 ;

[0073] Surface properties:

[0074] Surface tension: 45 mN / m;

[0075] Printing adhesion: 4.0N / 15mm;

[0076] Interlayer bonding: peel strength 5.5 N / 15 mm;

[0077] Low temperature resistance: Impact strength retention rate ≥90% at -40℃.

[0078] Example 3

[0079] Material proportions:

[0080] Heat-sealing layer: Novel metallocene polyethylene (mPE), 100%;

[0081] Core layer: sPP:PBT = 4:1 (PBT intrinsic viscosity 1.2 dL / g);

[0082] Corona layer: EBA:LLDPE:Nano SiO2 = 50:40:1;

[0083] Layer thickness ratio: 0.5:3:1 (total thickness 40μm).

[0084] Preparation process:

[0085] Extrusion parameters:

[0086] Extruder II temperature 210℃, speed 180rpm;

[0087] Extruder III: Temperature 180℃, Rotation speed 160rpm;

[0088] The temperature of the T-shaped die head is 190℃.

[0089] Cooling and molding:

[0090] Water temperature 20℃, traction speed 150m / min.

[0091] Corona treatment:

[0092] Voltage 8kV, frequency 20kHz, processing time 0.5s.

[0093] Performance testing:

[0094] Heat seal strength: 8.0 N / 15 mm (125℃);

[0095] Mechanical properties:

[0096] Tensile strength: 80 MPa (transverse);

[0097] Elongation at break: 350% (longitudinal);

[0098] Surface properties:

[0099] Surface tension: 42 mN / m;

[0100] Interlayer peel strength: 4.8 N / 15 mm;

[0101] Processing efficiency: Production speed 150m / min, no crystal points or fisheye defects.

[0102] Comparative Example 1 (Traditional Three-Layer Composite Membrane)

[0103] Material proportions:

[0104] Heat-sealing layer: Low-density polyethylene (LDPE, melting point 125-130℃), 100%;

[0105] Core layer: Homopolymer polypropylene (hPP), 100%;

[0106] Corona layer: linear low-density polyethylene (LLDPE) + 3wt% antistatic agent (such as ethoxylated amines);

[0107] Layer thickness ratio: heat seal layer: core layer: corona layer = 1:2:0.5 (total thickness 50μm).

[0108] Performance testing:

[0109] Heat seal strength: 5.5 N / 15 mm (140℃);

[0110] Surface tension: 38 mN / m (after corona treatment);

[0111] Interlayer peel strength: 3.2 N / 15 mm;

[0112] Preparation process:

[0113] Extrusion parameters:

[0114] Heat seal layer: Single screw extruder, temperature 180℃;

[0115] Core layer: Single screw extruder, temperature 200℃;

[0116] Corona layer: Single screw extruder, temperature 170℃;

[0117] T-die temperature: 190℃.

[0118] Cooling and molding:

[0119] Cooling water temperature 25℃, traction speed 80m / min.

[0120] Corona treatment:

[0121] Voltage 6kV, frequency 15kHz, processing time 0.3s.

[0122]

[0123] Comparative Analysis of Examples

[0124] Example Description

[0125] Core layer ratio optimization:

[0126] Example 1 (sPP:PBT = 6:1) exhibits the best overall mechanical properties, balancing rigidity and toughness;

[0127] Example 2 (8:1) improves rigidity, but slightly reduces impact strength;

[0128] Example 3 (4:1) has enhanced flexibility and is suitable for bending scenarios.

[0129] Influence of nano-SiO2 content in the corona layer:

[0130] Example 1 (2%) showed the best surface tension and adhesion;

[0131] Example 2 (5%) showed increased roughness but decreased material flowability;

[0132] Example 3 (1%) showed insufficient surface activity and required higher corona voltage compensation.

[0133] Layer thickness ratio and process compatibility:

[0134] Example 3 (layer thickness ratio 0.5:3:1) has the fastest production speed and is suitable for low-cost, high-speed packaging;

[0135] Example 2 (0.7:5:1) has the highest interlayer bonding strength, making it suitable for high barrier requirements.

[0136] Conclusion: This invention achieves a comprehensive improvement in heat sealability, mechanical properties, surface activity, and processing efficiency through synergistic optimization of material ratio, process parameters, and layer structure, which is significantly superior to traditional composite films.

[0137] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A multilayer composite polyester film, characterized in that, The polyester film is sequentially stacked with a heat-sealing layer, a core layer, and a corona layer. The heat-sealing layer is made of metallocene polyethylene, the core layer is made of a blend of syndiotactic copolymer polypropylene and polybutylene terephthalate, and the corona layer is made of a composite system of ethylene-butyl acrylate copolymer, linear low-density polyethylene, and nano-silica. The layer thickness ratio of the heat-sealing layer, core layer, and corona layer is (0.5-0.7):(3-5):

1. The mass ratio of ethylene-butyl acrylate copolymer, linear low-density polyethylene, and nano-silica in the corona layer is (50-70):(25-40):(1-5). The mass ratio of syndiotactic copolymer polypropylene and polybutylene terephthalate in the core layer is (4-8):

1. The intrinsic viscosity of polybutylene terephthalate at 25 degrees Celsius is between 1.2 and 1.5 dL / g.

2. The polyester film with a multilayer composite structure according to claim 1, characterized in that, The mass ratio of ethylene-butyl acrylate copolymer, linear low-density polyethylene and nano-silica in the corona layer is 60:30:

2.

3. A method for preparing a multilayer composite polyester film, used to prepare the multilayer composite polyester film of any one of claims 1-2, characterized in that, The preparation method includes the following steps: (1) Metallocene polyethylene is fed into extruder I, syndiotactic copolymer polypropylene and polybutylene terephthalate are fed into extruder II, and ethylene-butyl acrylate copolymer, linear low-density polyethylene and nano silica are mixed evenly in proportion and then fed into extruder III, and heated and melted separately; wherein, in extruder II, in order to ensure that syndiotactic copolymer polypropylene and polybutylene terephthalate are fully mixed, a twin-screw extruder is used to achieve uniform dispersion by utilizing the shearing and mixing action of the screw; in extruder III, a high-speed mixer is used for premixing, and then the screw of the extruder is used for further uniform mixing; (2) Extruder I, Extruder II, and Extruder III are simultaneously extruded in thin film form through T-die, and cooled to form a film; the cooling process adopts a low-temperature circulating water cooling system to control the cooling water temperature at 15-20℃, ensuring rapid and uniform cooling of the film and avoiding uneven internal stress and crystallization defects caused by uneven cooling. (3) The membrane is subjected to corona treatment to obtain a thin film with good surface activity. The corona treatment parameters are: voltage 8-10kV, frequency 20-30kHz, and treatment time 0.5-1.0s. The appropriate corona parameters can ensure that the surface of the corona layer has sufficient roughness and chemical activity, without causing excessive damage to the thin film.

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