High-stiffness PET (Polyethylene Terephthalate) film and preparation process thereof

Abstract

The invention relates to a high-stiffness PET (polyethylene terephthalate) film and a preparation process thereof. The process comprises the following steps: (a) premixing PET resin and functional master batch according to a mass ratio of 95: 5-98: 2, and drying until the water content is less than or equal to 50ppm; (b) carrying out melt extrusion at 270-290 DEG C through a double-screw extruder to form a cast sheet with the thickness of 1.0-1.5 mm; (c) longitudinally stretching the cast sheet at the preheating temperature of 85-95 DEG C, the stretching ratio of 3.0-4.0, the stretching temperature of 100-110 DEG C and the stretching rate of 10-15 m / min; (d) transversely stretching the longitudinally stretched membrane at the preheating temperature of 100-110 DEG C, the stretching ratio of 3.5-4.5 and the stretching temperature of 115-125 DEG C, and carrying out heat setting at the temperature of 200-220 DEG C for 5-8 seconds; (e) cooling and winding, wherein the winding tension is controlled to be 50-80 N / m; the functional master batch is prepared from 0.5 to 1.5 percent of nano titanium dioxide, 2 to 3 percent of polyester type anti-shrinking agent and the balance of PET (Polyethylene Terephthalate) carrier resin. Through the synergistic effect of fine crystallization induced by the nucleating agent and biaxial stretching, the elastic modulus of the film is increased to 4.5-5.0 GPa, and is increased by 20%-30% compared with that of a traditional process (3.8-4.2 GPa). The tensile strength is larger than or equal to 180 MPa, the elongation at break is larger than or equal to 100%, and high-end application requirements are met.

Description

Technical Field

[0001] The invention belongs to the field of polymer material processing and modification, and in particular relates to a high-stiffness PET film and a preparation process thereof. Background Art

[0002] PET (polyethylene terephthalate) film has become the preferred material for packaging, electronics, printing and other industries due to its excellent mechanical strength, transparency and chemical corrosion resistance. However, in high-end application scenarios (such as lithium battery separator coating and high-temperature label printing), traditional PET film faces the following problems:

[0003] Insufficient stiffness: The elastic modulus is usually 3.0-4.0GPa (ASTM D882). During high-temperature post-processing (such as oven heating, hot pressing and lamination), the film will deform and bulge due to the relaxation of molecular chains.

[0004] The heat shrinkage rate is too high: the longitudinal heat shrinkage rate at 180°C is ≥1.5%, and the transverse heat shrinkage rate is ≥2.0% (ASTM D1204), which affects the dimensional accuracy;

[0005] Poor crystallization uniformity: In the traditional stretching process, the crystalline and amorphous regions are unevenly distributed, resulting in anisotropy of mechanical properties.

[0006] In order to improve the stiffness of PET film, the existing technology mainly adopts the following methods:

[0007] Increasing the film thickness: for example, from 12μm to 25μm, although it can improve stiffness, it will cause the material cost to increase by 30%-50%, and the flexibility will decrease (bending radius ≥5mm, which cannot meet the needs of flexible electronics);

[0008] Add inorganic fillers: such as calcium carbonate (CaCO 3 ), talcum powder, etc., with an addition amount of 5%-10%), but it will significantly reduce the transmittance (haze increases from 1.0% to more than 5.0%), and the interface between the filler and the matrix is ​​prone to stress concentration, resulting in a 10%-20% decrease in tensile strength;

[0009] Chemical modification: such as copolymerization modification to introduce rigid segments (such as naphthalene dicarboxylate), but the process is complicated and the resin intrinsic viscosity (IV value) decreases by 0.1-0.2dL / g, affecting processability. Summary of the invention

[0010] The present invention aims to provide an industrial preparation process for high-stiffness PET film, and achieves the following objectives through the synergistic effect of material modification, process regulation and structural design:

[0011] To achieve the above object, the present invention provides the following technical solutions:

[0012] A preparation process of a high-stiffness PET film, characterized in that it comprises the following steps:

[0013] (a) premixing PET resin and functional masterbatch in a mass ratio of 95:5-98:2 and drying to a moisture content of ≤50ppm;

[0014] (b) melt extruding at 270-290° C. through a twin-screw extruder to form a cast sheet having a thickness of 1.0-1.5 mm;

[0015] (c) longitudinally stretching the cast sheet: preheating temperature 85-95° C., stretching ratio 3.0-4.0, stretching temperature 100-110° C., stretching rate 10-15 m / min;

[0016] (d) stretching the longitudinally stretched film transversely: preheating temperature 100-110° C., stretching ratio 3.5-4.5, stretching temperature 115-125° C., and heat setting at 200-220° C. for 5-8 seconds;

[0017] (e) Cooling and winding, controlling the winding tension to 50-80N / m;

[0018] The functional masterbatch contains 0.5-1.5% of nano titanium dioxide, 2-3% of polyester anti-shrinkage agent, and the balance is PET carrier resin.

[0019] The present invention further arranges the polyester anti-shrinkage agent to be polybutylene terephthalate (PBT), and the glass transition temperature thereof is 40-50°C.

[0020] The present invention further sets the stretching ratio of the longitudinal stretching to the transverse stretching to be 1:1.1-1.2.

[0021] The present invention further arranges the heat setting process to adopt segmented temperature reduction control, specifically including:

[0022] a) The first stage: 200-220℃, stay for 3-5s;

[0023] b) The second stage: 180-190℃, stay for 2-3s;

[0024] c) The third stage: 150-160°C, stay for 1-2 seconds.

[0025] The present invention further provides that the particle size of the nano titanium dioxide is 20-50 nm, and the BET specific surface area is ≥50 m 2 / g.

[0026] The present invention further provides that during the longitudinal stretching process, the temperature difference between the preheating zone and the stretching zone is ≤15°C, and the transverse temperature deviation of the membrane is ≤2°C.

[0027] The present invention further sets the temperature of the melt extrusion die head to 280-285°C and the temperature of the cooling roller to 20-25°C.

[0028] The present invention further sets the addition amount of nano titanium dioxide in the functional masterbatch to be 1.0-1.5%, and the addition amount of the polyester anti-shrinkage agent to be 2.5-3.0%.

[0029] The present invention further sets the total energy input of the transversely stretched film in the heat setting stage to be 120-150 kJ / m 2 , calculated by the formula E=∑(Ti·ti·0.15)E=∑(Ti·ti·0.15), where Ti is the temperature (°C) and ti is the residence time (s).

[0030] The present invention also provides a high-stiffness PET film preparation process. The high-stiffness PET film prepared by the process is characterized in that its elastic modulus is ≥4.5 GPa, the longitudinal heat shrinkage is ≤1.0% and the transverse heat shrinkage is ≤1.2% after baking at 180°C for 3 minutes, the light transmittance is ≥88%, and the haze is ≤1.5%.

[0031] Beneficial effects of the present invention:

[0032] Improved mechanical properties: Through the synergistic effect of fine crystallization induced by nucleating agents and biaxial stretching, the elastic modulus of the film is increased to 4.5-5.0GPa, which is 20%-30% higher than the traditional process (3.8-4.2GPa). The tensile strength is ≥180MPa and the elongation at break is ≥100%, meeting the needs of high-end applications.

[0033] High temperature deformation resistance:

[0034] After the film is baked at 180℃ for 3 minutes, the surface flatness (Ra) is ≤0.1μm (laser confocal microscope test), without bulging or warping. The thermal shrinkage is ≤1.0% in the longitudinal direction and ≤1.2% in the transverse direction, which is more than 50% lower than the traditional process.

[0035] Optical performance retention:

[0036] The transmittance is ≥88%, and the haze is ≤1.5%, which is equivalent to the unmodified film (transmittance 90%, haze 0.9%), and significantly better than the solution with the addition of inorganic fillers (transmittance ≤85%, haze ≥3.0%).

[0037] Process economy:

[0038] The amount of functional masterbatch added is only 2%-5%, the increase in raw material cost is ≤3%, and there is no need to modify the existing production line, which is suitable for large-scale production. DETAILED DESCRIPTION

[0039] The following is a detailed description of the implementation methods of the present application, so that the implementation process of how the present application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0040] Embodiment 1:

[0041] This embodiment provides a preparation process of a high-stiffness PET film, characterized in that it includes the following steps:

[0042] (a) premixing PET resin and functional masterbatch in a mass ratio of 95:5-98:2 and drying to a moisture content of ≤50ppm;

[0043] (b) melt extruding at 270-290° C. through a twin-screw extruder to form a cast sheet having a thickness of 1.0-1.5 mm;

[0044] (c) longitudinally stretching the cast sheet: preheating temperature 85-95° C., stretching ratio 3.0-4.0, stretching temperature 100-110° C., stretching rate 10-15 m / min;

[0045] (d) stretching the longitudinally stretched film transversely: preheating temperature 100-110° C., stretching ratio 3.5-4.5, stretching temperature 115-125° C., and heat setting at 200-220° C. for 5-8 seconds;

[0046] (e) Cooling and winding, controlling the winding tension to 50-80N / m;

[0047] The functional masterbatch contains 0.5-1.5% of nano titanium dioxide, 2-3% of polyester anti-shrinkage agent, and the balance is PET carrier resin.

[0048] The present invention further arranges the polyester anti-shrinkage agent to be polybutylene terephthalate (PBT), and the glass transition temperature thereof is 40-50°C.

[0049] The present invention further sets the stretching ratio of the longitudinal stretching to the transverse stretching to be 1:1.1-1.2.

[0050] The present invention further arranges the heat setting process to adopt segmented temperature reduction control, specifically including:

[0051] a) The first stage: 200-220℃, stay for 3-5s;

[0052] b) The second stage: 180-190℃, stay for 2-3s;

[0053] c) The third stage: 150-160°C, stay for 1-2 seconds.

[0054] The present invention further provides that the particle size of the nano titanium dioxide is 20-50 nm, and the BET specific surface area is ≥50 m 2 / g.

[0055] The present invention further provides that during the longitudinal stretching process, the temperature difference between the preheating zone and the stretching zone is ≤15°C, and the transverse temperature deviation of the membrane is ≤2°C.

[0056] The present invention further sets the temperature of the melt extrusion die head to 280-285°C and the temperature of the cooling roller to 20-25°C.

[0057] The present invention further sets the addition amount of nano titanium dioxide in the functional masterbatch to be 1.0-1.5%, and the addition amount of the polyester anti-shrinkage agent to be 2.5-3.0%.

[0058] The present invention further sets the total energy input of the transversely stretched film in the heat setting stage to be 120-150 kJ / m 2 , calculated by the formula E=∑(Ti·ti·0.15)E=∑(Ti·ti·0.15), where Ti is the temperature (°C) and ti is the residence time (s).

[0059] Example 2: This example provides a high-stiffness PET film preparation process. The prepared high-stiffness PET film has an elastic modulus ≥4.5 GPa, a longitudinal heat shrinkage ≤1.0%, a transverse heat shrinkage ≤1.2% after baking at 180°C for 3 minutes, a light transmittance ≥88%, and a haze ≤1.5%.

[0060] The present invention has the following advantages:

[0061] Improved mechanical properties: Through the synergistic effect of fine crystallization induced by nucleating agents and biaxial stretching, the elastic modulus of the film is increased to 4.5-5.0GPa, which is 20%-30% higher than the traditional process (3.8-4.2GPa). The tensile strength is ≥180MPa and the elongation at break is ≥100%, meeting the needs of high-end applications.

[0062] High temperature deformation resistance:

[0063] After the film is baked at 180℃ for 3 minutes, the surface flatness (Ra) is ≤0.1μm (laser confocal microscope test), without bulging or warping. The thermal shrinkage is ≤1.0% in the longitudinal direction and ≤1.2% in the transverse direction, which is more than 50% lower than the traditional process.

[0064] Optical performance retention:

[0065] The transmittance is ≥88%, and the haze is ≤1.5%, which is equivalent to the unmodified film (transmittance 90%, haze 0.9%), and significantly better than the solution with the addition of inorganic fillers (transmittance ≤85%, haze ≥3.0%).

[0066] Process economy:

[0067] The amount of functional masterbatch added is only 2%-5%, the increase in raw material cost is ≤3%, and there is no need to modify the existing production line, which is suitable for large-scale production.

[0068] The product of Example 2 was tested to obtain the following data:

[0069] Table 1: Performance comparison between examples and comparative examples

[0070] sample Elastic modulus(GPa) 180℃ heat shrinkage (%) Light transmittance (%) Haze(%) Example 1 4.8 0.8(MD),1.0(TD) 89 1.3 Comparative Example (without masterbatch) 3.9 1.8(MD),2.5(TD) 90 0.9 <![CDATA[Comparative Example (only TiO 2 )]]> 4.2 1.5(MD),2.0(TD) 86 2.1

[0071] For example, certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different terms to refer to the same component. This specification and claims do not use differences in names as a way to distinguish components, but use differences in the functions of components as the criteria for distinction. For example, "including" mentioned throughout the specification and claims is an open term, so it should be interpreted as "including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve technical problems within a certain error range and basically achieve technical effects.

[0072] It should be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a product or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such product or system. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the product or system including the elements.

[0073] The above description shows and describes several preferred embodiments of the present invention, but as before, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the invention concept of this article through the above teachings or the technology or knowledge of the relevant field. And the changes and modifications made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A process for preparing a high-stiffness PET film, characterized in that: The following steps are involved: (a) premixing PET resin and functional masterbatch in a mass ratio of 95:5-98:2 and drying to a moisture content of ≤50ppm; (b) melt extruding at 270-290° C. through a twin-screw extruder to form a cast sheet having a thickness of 1.0-1.5 mm; (c) longitudinally stretching the cast sheet: preheating temperature 85-95° C., stretching ratio 3.0-4.0, stretching temperature 100-110° C., stretching rate 10-15 m / min; (d) stretching the longitudinally stretched film transversely: preheating temperature 100-110° C., stretching ratio 3.5-4.5, stretching temperature 115-125° C., and heat setting at 200-220° C. for 5-8 seconds; (e) Cooling and winding, controlling the winding tension to 50-80N / m; The functional masterbatch contains 0.5-1.5% of nano titanium dioxide, 2-3% of polyester anti-shrinkage agent, and the balance is PET carrier resin.

2. The process for preparing a high stiffness PET film according to claim 1, characterized in that: The polyester anti-shrinkage agent is polybutylene terephthalate (PBT), and its glass transition temperature is 40-50°C.

3. The process for preparing a high stiffness PET film according to claim 1, characterized in that: The stretching ratio of the longitudinal stretching to the transverse stretching is 1:1.1-1.

2.

4. The process for preparing a high stiffness PET film according to claim 1, characterized in that: The heat setting process adopts segmented temperature reduction control, which specifically includes: a) The first stage: 200-220℃, stay for 3-5s; b) The second stage: 180-190℃, stay for 2-3s; c) The third stage: 150-160°C, stay for 1-2 seconds.

5. The process for preparing a high stiffness PET film according to claim 1, characterized in that: The particle size of the nano titanium dioxide is 20-50nm, and the BET specific surface area is ≥50m 2 / g.

6. The process for preparing a high stiffness PET film according to claim 1, characterized in that: During the longitudinal stretching process, the temperature difference between the preheating zone and the stretching zone is ≤15°C, and the transverse temperature deviation of the film is ≤2°C.

7. The process for preparing a high stiffness PET film according to claim 1, characterized in that: The temperature of the melt extrusion die is 280-285°C, and the temperature of the cooling roller is 20-25°C.

8. The process for preparing a high stiffness PET film according to claim 1, characterized in that: The added amount of nano titanium dioxide in the functional masterbatch is 1.0-1.5%, and the added amount of the polyester anti-shrinkage agent is 2.5-3.0%.

9. The process for preparing a high stiffness PET film according to claim 1, characterized in that: The total energy input of the transversely stretched film during the heat setting stage is 120-150 kJ / m 2 , calculated by the formula E=∑(Ti·ti·0.15)E=∑(Ti·ti·0.15), where Ti is the temperature (°C) and ti is the residence time (s).

10. A high-stiffness PET film prepared by the process for preparing a high-stiffness PET film according to any one of claims 1 to 9, characterized in that: Its elastic modulus is ≥4.5GPa, after baking at 180°C for 3 minutes, its longitudinal heat shrinkage is ≤1.0%, its transverse heat shrinkage is ≤1.2%, its light transmittance is ≥88%, and its haze is ≤1.5%.