Preparation method of polyester base film for small and medium-sized electronic product carriers

Abstract

The invention relates to a preparation method of a polyester base film for a medium and small-sized electronic product carrier, which comprises the following steps: carrying out esterification and polycondensation reaction on terephthalic acid, ethylene glycol and 0.5-2mol% of comonomer under the action of a catalyst to prepare a modified polyester chip with intrinsic viscosity of 0.65-0.75 dL / g; drying the modified polyester chips and the nano CaCO3 master batch, mixing, melting at the temperature of 275-285 DEG C through a single-screw extruder and a double-screw extruder, and extruding to a cooling roller casting sheet through a distribution block-die head; performing longitudinal stretching, on-line coating and transverse stretching on the casting piece to form a stretching film; and carrying out heat setting on the stretched film, cooling and rolling to complete the preparation of the polyester base film. According to the preparation method disclosed by the invention, the modified polyester chips and the small-particle-size master batch are introduced, and a two-way stretching process and an online coating technology are optimized, so that the preparation of the high-performance polyester base film of which the haze is less than or equal to 1.0%, the hot shrinkage rate is less than or equal to 0.2% at 85 DEG C for 48 hours and the coating thickness is 30-50nm is realized.

Description

Technical Field

[0001] This invention relates to the field of polyester-based film preparation, and in particular to a method for preparing a polyester-based film for carriers of small and medium-sized electronic products. Background Technology

[0002] Polyester-based films are widely used as carrier materials for display devices due to their excellent optical properties and mechanical strength. However, existing polyester-based films have the following shortcomings: (1) High haze: The haze of traditional PET film is usually >1.5%, which affects the clarity of the display; (2) High heat shrinkage rate: The heat shrinkage rate at 85℃ for 48 hours is >0.5%, which leads to unstable dimensions after module assembly; (3) Poor coating uniformity: Offline coating is prone to coating defects (such as pinholes and streaks), and online coating is difficult to control the thickness accuracy of ultra-thin coatings (<50nm).

[0003] Patent CN113635643A discloses a polyester film and its preparation method. The haze of the polyester film prepared by this patent method can be reduced to 1.2%, but the heat shrinkage rate of the polyester film is not specified. In addition, patent CN119610587A proposes a high-gloss polyester base film and its preparation process. The preparation process in this patent improves the gloss of the polyester film by online coating, but it also does not address the issue of controlling the low heat shrinkage rate of the polyester film.

[0004] Therefore, developing polyester-based films that combine low haze, low heat shrinkage, and ultra-thin coatings has become an urgent technical problem to be solved. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a polyester-based film for carriers of small and medium-sized electronic products that has the characteristics of low haze, low thermal shrinkage and ultra-thin coating.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is: a method for preparing a polyester-based film for carriers of small and medium-sized electronic products, the innovation of which is: including the following steps: S1: Preparation of modified polyester chips: Terephthalic acid, ethylene glycol and 0.5-2 mol% of comonomers are esterified and polycondensed under the action of a catalyst to obtain modified polyester chips with an intrinsic viscosity of 0.65-0.75 dL / g. The esterification reaction temperature is 230-250℃ and the pressure is 0.2-0.3 MPa. The polycondensation reaction temperature is 270-285℃ and the pressure is ≤100 Pa. S2: Melt extrusion and casting. Modified polyester chips are mixed with dried nano-CaCO3 masterbatch with a particle size of less than 1μm. The mixture is melted at a temperature of 275-285℃ using a single-screw and twin-screw extruders and then extruded through a distribution block-die to a cooling roller for casting. The temperature of the cooling roller is 25-30℃. S3: Biaxial stretching. After longitudinal stretching, online coating and transverse stretching, a stretched film is formed. The thickness of the stretched film is 38-75μm with a tolerance of ±1%. The preheating temperature for longitudinal stretching is 70-80℃, the stretching temperature is 80-90℃, and the stretching ratio is 3.0-4.0 times. The preheating temperature for transverse stretching is 110-130℃, the stretching temperature is 160-180℃, and the stretching ratio is 3.5-4.0 times. S4: Heat setting and cooling. The stretch film is fully heat-set at 220-250℃ using a gradient heating method. After setting, it is cooled to below 50℃ using a gradient cooling method and then wound up using a winding roller to complete the preparation of the polyester base film. The prepared polyester base film has a light transmittance >92%, haze ≤1%, and clarity of over 99.5%.

[0007] Furthermore, in step S2, the main extrusion uses a single-screw extruder, and the auxiliary extrusion uses a twin-screw extruder.

[0008] Furthermore, in step S3, far-infrared heating is used during longitudinal stretching, and low shrinkage of the stretching film is achieved by adjusting the spacing of the chain clamp tracks during transverse stretching.

[0009] Furthermore, in step S3, during online coating, a micro-gravure coating head is used to apply an aqueous coating liquid to the surface of the stretch film. The film is then dried during transverse stretching, resulting in a double-sided coating with a thickness of 30-50 nm formed by the aqueous coating liquid on the surface of the stretch film, and the uniformity of the coating is within ±3 nm.

[0010] Furthermore, the aqueous coating liquid is composed of a coating raw material and a solvent. The coating raw material is a UV-curable waterborne polyurethane resin, a melamine-based crosslinking agent, and an ionic leveling agent, and the solvent is a water / alcohol mixture.

[0011] Furthermore, in step S4, an antistatic component is also provided on the front side of the take-up roller.

[0012] Furthermore, in step S4, during the gradient heating to achieve heat setting, there are four setting sections, each 3-6m long, with temperatures of 180℃, 220℃, 240℃, and 240℃ respectively; during the gradient cooling to achieve cooling, there are four cooling sections, each 3-6m long, with temperatures of 220℃, 180℃, 150℃, and 120℃ respectively; the conveying speed of the stretch film is 140-160m / min.

[0013] Furthermore, under conditions of 85℃ and 48h, the transverse and longitudinal bidirectional thermal shrinkage rate of the polyester-based film is <0.2%.

[0014] The advantages of this invention are as follows: The preparation method of this invention, by introducing modified polyester chips and small particle size masterbatch, and optimizing the biaxial stretching process and online coating technology, achieves the preparation of high-performance polyester base film with haze ≤1.0%, heat shrinkage rate ≤0.2% at 85℃×48h, and coating thickness of 30-50nm.

[0015] This invention reduces crystallinity by copolymerizing modified polyester chips, controls heat shrinkage by combining precise stretching and heat setting processes, and achieves uniform coverage of ultra-thin coatings using microgravure coating, making it suitable for high-end display fields such as smartphones and wearable devices.

[0016] During stretching, for longitudinal stretching, low-temperature heating using far-infrared technology effectively improves the adhesion between the film and the roller, preventing the film from wrapping around the roller; while for transverse stretching, low shrinkage of the stretched film can be achieved by adjusting the spacing between the chain clamp tracks.

[0017] By adding an antistatic component to the front side of the take-up roller, the polyester base film is destaticated before being wound up, which improves the flatness of the master roll. Detailed Implementation

[0018] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0019] The method for preparing the polyester-based film for carriers of small and medium-sized electronic products according to the present invention is achieved through the following steps: S1: Preparation of modified polyester chips: Terephthalic acid, ethylene glycol and 0.5-2 mol% of comonomers are esterified and polycondensed under the action of a catalyst to obtain modified polyester chips with an intrinsic viscosity of 0.65-0.75 dL / g. The esterification reaction temperature is 230-250℃ and the pressure is 0.2-0.3 MPa. The polycondensation reaction temperature is 270-285℃ and the pressure is ≤100 Pa.

[0020] S2: Melt extrusion and casting. Modified polyester chips are mixed with dried nano-CaCO3 masterbatch. The particle size of the nano-CaCO3 masterbatch is less than 1μm. Using this small-particle-size nano-CaCO3 masterbatch is beneficial for uniform dispersion after melting. The mixture is melted at a temperature of 275-285℃ using a single-screw or twin-screw extruder, and then extruded through a distribution block-die to a cooling roller for casting. The temperature of the cooling roller is 25-30℃.

[0021] In the above steps, a single-screw extruder is used for the main extrusion and a twin-screw extruder is used for the auxiliary extrusion.

[0022] S3: Biaxial stretching. After longitudinal stretching, online coating, and transverse stretching, a stretched film is formed. The thickness of the stretched film is 38-75μm with a tolerance of ±1%. The preheating temperature for longitudinal stretching is 70-80℃, and low temperature is used to predict and promote molecular chain orientation. The stretching temperature is 80-90℃, and the stretching ratio is 3.0-4.0 times. The preheating temperature for transverse stretching is 110-130℃, and the stretching temperature is 160-180℃. This gradual heating method avoids stress concentration, and the stretching ratio is 3.5-4.0 times.

[0023] In the above steps, far-infrared heating is used during longitudinal stretching, and low shrinkage of the stretch film is achieved by adjusting the spacing between the chain clamp tracks of the transverse stretching device during transverse stretching.

[0024] During online coating, a micro-gravure coating head with a line count of 220-250 is used to coat the surface of the stretch film. The water-based coating liquid is applied to the surface of the stretch film at a ratio of 1.1-1.2 to the speed of the stretch film. The film is dried during transverse stretching to prevent cracking. This results in a double-sided coating with a thickness of 30-50 nm formed on the surface of the stretch film, with a uniformity of ±3 nm. The uniformity of the coating is tested using F20 and the cross-cut test. Adhesion is tested using ASTM D3359, and the adhesion is ≥4B.

[0025] The water-based coating liquid is made by mixing coating raw materials and solvents. The coating raw materials are UV-curable water-based polyurethane resin, melamine-based crosslinking agent and ionic leveling agent, and the solvent is a water / alcohol mixture. The combination of UV-curable water-based polyurethane resin, melamine-based crosslinking agent and ionic leveling agent in the coating raw materials improves the adhesion of the coating.

[0026] S4: Heat setting and cooling. A gradient heating method is used to fully heat set the stretch film at 220-250℃. During this gradient heating process, there are four setting sections, each 3-6m long, with temperatures of 180℃, 220℃, 240℃, and 240℃ respectively. This temperature-controlled heat setting relaxes the orientation molecular chains, reducing internal stress. After setting, the film is gradient cooled to below 50℃ and then wound up using take-up rollers. During the gradient cooling process, there are four cooling sections, each 3-6m long. The temperatures of each cooling section are 220℃, 180℃, 150℃, and 120℃, respectively. The conveying speed of the stretched film is 140-160m / min. This completes the preparation of the polyester base film. The prepared polyester base film is tested with UV-Vis and shows a light transmittance >92%, haze ≤1%, and clarity above 99.5%. In terms of appearance, the polyester base film is free of track marks, crystal points, burrs, scratches, and dark lines in the coating.

[0027] In the above steps, an antistatic component is also provided on the front side of the take-up roller. In this embodiment, the antistatic component uses an ion bar for antistatic removal. By adding an antistatic component on the front side of the take-up roller, the polyester base film is destaticated before winding, which improves the flatness of the master roll winding.

[0028] Under conditions of 85℃ and 48h, the transverse and longitudinal bidirectional heat shrinkage rate of the polyester film is <0.2%. The heat shrinkage rate is tested according to GB / T 13541-2017.

[0029] Examples 1-4 illustrate the preparation of polyester-based films using the methods described above: In Example 1, in step S2, 1μm small-particle-size nano-CaCO3 masterbatch was selected; in step S3, the longitudinal stretching ratio was 3.3 times, the longitudinal stretching temperature was 83℃, the transverse stretching ratio was 3.8 times, and the transverse stretching temperature was 150℃. During transverse stretching, the spacing between the chain clamp tracks of the transverse stretching equipment was adjusted. The UV-curable waterborne polyurethane resin was a mixture of two polyurethane resins, Resin A: Resin B = 2:5. Resin A was a polyurethane resin with unsaturated double bonds, and Resin B was a polyurethane resin with good extensibility. The coating amount was 4g / m². 2 The solid content is 4%; in step S4, the heat setting temperature is 240℃.

[0030] The performance of the polyester-based film was tested. The haze of the polyester-based film was 0.9%, the light transmittance was 92.5%, the heat shrinkage rate (MD) was 0.18%, the heat shrinkage rate (TD) was 0.13%, the coating thickness was 42nm, and the uniformity was ±3nm.

[0031] In Example 2, compared with Example 1, step S2 was replaced with large-particle-size CaCO3 masterbatch with a particle size of 3 μm, and the other conditions were the same as in Example 1.

[0032] Performance tests were conducted on the polyester-based film. The haze of the polyester-based film was 1.6%, and a large number of microscopic agglomeration points were found, which did not meet the requirements.

[0033] In Example 3, compared with Example 1, in step S3, the spacing between the chain clamp tracks of the lateral pulling device is not adjusted, and the other conditions are the same as in Example 1.

[0034] The performance of the polyester-based film was tested, and the bidirectional heat shrinkage rate was 0.3%, which does not meet the requirements.

[0035] In Example 4, compared with Example 1, in step S3, a common waterborne polyurethane coating is used as the water coating liquid, and the other conditions are the same as in Example 1.

[0036] The performance of the polyester-based film was tested. After UV curing of the adhesive coating, the cross-cut adhesion test was performed. The film showed obvious peeling and an adhesion of 1-2B, which did not meet the requirements.

[0037] The preparation method of this invention, through copolymerization modification, precise stretching, and ultrathin coating technology, produces polyester-based films that meet the stringent requirements of small and medium-sized electronic products for optical, thermal stability, and coating quality, and has significant industrial application value.

[0038] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a polyester-based film for use as a carrier in small and medium-sized electronic products, characterized in that: Includes the following steps: S1: Preparation of modified polyester chips: Terephthalic acid, ethylene glycol and 0.5-2 mol% of comonomers are esterified and polycondensed under the action of a catalyst to obtain modified polyester chips with an intrinsic viscosity of 0.65-0.75 dL / g. The esterification reaction temperature is 230-250℃ and the pressure is 0.2-0.3 MPa. The polycondensation reaction temperature is 270-285℃ and the pressure is ≤100 Pa. S2: Melt extrusion and casting. Modified polyester chips are mixed with dried nano-CaCO3 masterbatch with a particle size of less than 1μm. The mixture is melted at a temperature of 275-285℃ using a single-screw and twin-screw extruders and then extruded through a distribution block-die to a cooling roller for casting. The temperature of the cooling roller is 25-30℃. S3: Biaxial stretching. After longitudinal stretching, online coating and transverse stretching, a stretched film is formed. The thickness of the stretched film is 38-75μm with a tolerance of ±1%. The preheating temperature for longitudinal stretching is 70-80℃, the stretching temperature is 80-90℃, and the stretching ratio is 3.0-4.0 times. The preheating temperature for transverse stretching is 110-130℃, the stretching temperature is 160-180℃, and the stretching ratio is 3.5-4.0 times. S4: Heat setting and cooling. The stretch film is fully heat-set at 220-250℃ using a gradient heating method. After setting, it is cooled to below 50℃ using a gradient cooling method and then wound up using a winding roller to complete the preparation of the polyester base film. The prepared polyester base film has a light transmittance >92%, haze ≤1%, and clarity of over 99.5%.

2. The method for preparing a polyester-based film for a carrier of small and medium-sized electronic products according to claim 1, characterized in that: In step S2, the main extrusion uses a single-screw extruder, and the auxiliary extrusion uses a twin-screw extruder.

3. The method for preparing a polyester-based film for carriers of small and medium-sized electronic products according to claim 1, characterized in that: In step S3, far-infrared heating is used during longitudinal stretching, and low shrinkage of the stretching film is achieved by adjusting the spacing of the chain clamp tracks during transverse stretching.

4. The method for preparing a polyester-based film for a carrier of small and medium-sized electronic products according to claim 1, characterized in that: In step S3, during online coating, a micro-gravure coating head is used to apply an aqueous coating liquid to the surface of the stretch film. The film is then dried during transverse stretching, resulting in a double-sided coating with a thickness of 30-50 nm formed by the aqueous coating liquid on the surface of the stretch film, and the uniformity of the coating is within ±3 nm.

5. The method for preparing a polyester-based film for a carrier of small and medium-sized electronic products according to claim 4, characterized in that: The aqueous coating liquid is composed of a coating raw material and a solvent. The coating raw material is a UV-curable waterborne polyurethane resin, a melamine-based crosslinking agent and an ionic leveling agent, and the solvent is a water / alcohol mixture.

6. The method for preparing a polyester-based film for a carrier of small and medium-sized electronic products according to claim 1, characterized in that: In step S4, an antistatic component is also provided on the front side of the take-up roller.

7. The method for preparing a polyester-based film for a carrier of small and medium-sized electronic products according to claim 1, characterized in that: In step S4, during the gradient heating for heat setting, there are four setting sections, each 3-6m long, with temperatures of 180℃, 220℃, 240℃, and 240℃ respectively; during the gradient cooling for cooling, there are four cooling sections, each 3-6m long, with temperatures of 220℃, 180℃, 150℃, and 120℃ respectively; the stretch film is conveyed at a speed of 140-160m / min.

8. The method for preparing a polyester-based film for a carrier of small and medium-sized electronic products according to claim 1, characterized in that: Under conditions of 85℃ and 48h, the transverse and longitudinal bidirectional thermal shrinkage rate of the polyester film is <0.2%.