Optical film with low elastic modulus and high stability and preparation method thereof

Abstract

The application discloses an optical film with high stability and low elastic modulus and a preparation method thereof, and relates to the technical field of optical films and preparation. The optical film is an ABA type three-layer co-extrusion polyester film, and the A layer is a surface layer and the B layer is a core layer. The A layer is a low-melting-point polyester blend A, which is composed of high-viscosity polyester PET and low-melting-point polyester PETG in a percentage by weight. The B layer is a low-melting-point polyester blend B, which is composed of low-melting-point polyester PETG, high-viscosity polyester PET and polyester PET in a percentage by weight. The optical film is prepared through the steps of pre-blending, drying and crystallizing, extruding after melt mixing, longitudinal and transverse stretching, and heat setting. The application has the advantages that PETG and PET can be blended to crystallize and reduce the melting point, so that the melting point of the blended system is reduced; the toughness of the optical polyester film is improved, and the optical polyester film has high mechanical properties and good optical properties.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical film and preparation technology, and particularly relates to an optical film with low elastic modulus and high stability and a preparation method. BACKGROUND

[0002] In recent years, with the full popularization of display, in order to further improve the service life of the display screen, the polyester film with low elastic modulus has a place to use. The elastic modulus can represent the ability of the polyester film to resist deformation of external factors. In the TFT-LCD display field, when used as the base material of the flexible screen, the optical film needs to have a low elastic modulus. The flexible screen has the characteristics of being bendable and flexible, and its durability is higher than that of the traditional screen.

[0003] At present, it is difficult to control the low elastic modulus in the production of optical polyester film. The core technical problem is the lack of raw materials that can well meet the requirement of low elastic modulus. In order to meet the requirement of low elastic modulus, the existing technology usually adopts flexible resin and PET blending, but this method has poor low elastic modulus stability, the quality is greatly affected, the production process is complex, and the cost is increased. Therefore, it is necessary to provide an optical film with high low elastic modulus stability and a preparation method. SUMMARY

[0004] The technical problem to be solved by the present application is to provide an optical film with high low elastic modulus stability and a preparation method, which can solve the problems of poor low elastic modulus stability, great quality influence, complex production process and cost increase of the optical film obtained by blending flexible resin and PET in the prior art.

[0005] To solve the above technical problems, the technical scheme of the present application is as follows: the optical film is an ABA type three-layer co-extrusion polyester film, wherein the A layer is a surface layer, and the B layer is a core layer.

[0006] The A layer is a low-melting-point polyester blend A, which is composed of the following substances in percentage by weight: high-viscosity polyester PET 80-90%, and high-viscosity low-melting-point polyester PETG 10-20%.

[0007] The B layer is a low-melting-point polyester blend B, which is composed of the following substances in percentage by weight: high-viscosity low-melting-point polyester PETG 10-25%, high-viscosity polyester PET 15-30%, and polyester PET 55-80%.

[0008] The high-viscosity polyester PET has an intrinsic viscosity of 0.70-0.82 dL / g and a melting point of 245-260 DEG C; the high-viscosity low-melting-point polyester PETG has an intrinsic viscosity of 0.70-0.82 dL / g and a melting point of 225-240 DEG C; and the polyester PET has an intrinsic viscosity of 0.62-0.68 dL / g and a melting point of 245-265 DEG C.

[0009] The optical film is prepared by pre-blending, drying crystallization, extrusion after melt mixing, casting and then longitudinal and transverse stretching, and heat setting.

[0010] Further, the high-viscosity polyester PET is BG801 bottle-grade polyester chip, the high-viscosity low-melting-point polyester PETG is BG804 bottle-grade polyester chip, and the polyester PET is one of FG600 base material type film-grade polyester chip and FG610 master batch type film-grade polyester chip.

[0011] Further, the optical film has a thickness of 36-125 μm.

[0012] Further, the optical film has an elastic modulus less than 1800 MPa.

[0013] An optical film with high stability and low elastic modulus is prepared by the following steps.

[0014] S1: high-viscosity low-melting-point polyester PETG, high-viscosity polyester PET and polyester PET are sent into corresponding hoppers of a main extruder through a suction system, and a loss balance is used to control the ratio of the materials, to obtain low-melting-point polyester blend B of core layer raw materials, which is fully mixed, dried, vacuumized and dehumidified, to remove water, powder, impurities and oligomers in the melt of the B layer raw materials, and the dried low-melting-point polyester blend B is sent into an extruder I, melted at a temperature of 220-290 DEG C, accurately measured by a metering pump according to the set thickness, and then extruded from a lip die, to obtain a main extrusion B layer melt;

[0015] S2: high-viscosity low-melting-point polyester PETG and high-viscosity polyester PET are sent into corresponding hoppers of an auxiliary extruder through a suction system, and a loss balance is used to control the ratio of the materials, to obtain low-melting-point polyester blend A of surface layer raw materials, which is fully mixed, dried, vacuumized and dehumidified, to remove water, powder, impurities and oligomers in the melt of the A layer raw materials, and the auxiliary extrusion A layer melt is obtained by extruding the melt after melt mixing;

[0016] S3: the single-layer main extrusion B layer melt and the two-layer auxiliary extrusion A layer melt are converged and extruded in a three-layer die at a temperature of 220-290 DEG C, to obtain a melt with a three-layer co-extrusion structure of ABA type;

[0017] S4: the melt of the ABA type three-layer co-extrusion structure is attached to the surface of a large cooling drum at 14-40℃ by electrostatic force to obtain a cast sheet of the ABA type three-layer co-extrusion structure;

[0018] S5: the cast sheet of the ABA type three-layer co-extrusion structure is fed into a longitudinal stretching section at a speed of 7-80 m / min, the length of which is 2-6 m and the temperature of which is 64-90℃, and after being stretched by 2.8-3.5 times under the heating of infrared heating lamps, the stretched sheet is cooled to 22-45℃ in a cooling section, at this time, the stretched sheet is fed into a transverse stretching box at a speed of 20-280 m / min, and then is fed into a preheating section with a length of 4.5-9 m and a temperature of 85-135℃, and then is stretched by 2.8-4.4 times in a transverse stretching section with a length of 9-18 m and a temperature of 100-160℃, and then is shaped in a heat setting section with a length of 15-21 m and a temperature of 180-245℃, and then is cooled in a cooling section with a length of 9-18 m and a temperature of 20-35℃ and at room temperature in two stages, and then is flattened, de-electrified and wound after thickness measurement and feedback to obtain an optical film product with low elastic modulus and high stability.

[0019] The present application has the following advantages:

[0020] (1) The low elastic modulus optical film is prepared by using a low melting point polyester prepared by blending high viscosity and low melting point polyester PETG and polyester PET, and the PETG and PET both belong to polyester, and the polyester has similar chemical structures, and the similar compatibility in the mixing process, and the blending can crystallize and reduce the melting point, so that the melting point of the blending system is reduced, which lays a technical and material foundation for preparing the low elastic modulus polyester film.

[0021] (2) Under a certain amount of EG and CHDM, the introduction of cyclohexane units in the molecular chain reduces the regularity of the entire molecular chain, and makes the crystallization of PETG difficult, and the main chain of PETG has a cyclohexyl group more than PET, the volume of the cyclohexyl group is large, the number of single bonds that can rotate internally on the chain is relatively reduced, the rigidity of the molecular chain is increased, the gap between the molecular chains is increased, the toughness of the optical polyester film is improved, and the special process of longitudinal and transverse stretching and low ratio stretching is adopted to reduce the crystallinity of the polyester film, so that the film becomes softer and tougher.

[0022] (3) The preparation process of the low elastic modulus optical polyester film product is simple, easy to operate, and has strong practicability, and the low elastic modulus polyester film prepared by the low melting point polyester blend has high mechanical properties and good optical properties. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with specific embodiments. The following embodiments can make the skilled in the art more fully understand the present application, but the present application is not limited in the scope of the described embodiments.

[0024] The specific embodiment adopts the following technical scheme: the optical film is an ABA type three-layer co-extrusion polyester film, wherein the A layer is a surface layer, and the B layer is a core layer;

[0025] The A layer is a low-melting-point polyester blend A, which is composed of the following substances in percentage by weight: high-viscosity polyester PET 80-90%, high-viscosity low-melting-point polyester PETG 10-20%; the B layer is a low-melting-point polyester blend B, which is composed of the following substances in percentage by weight: high-viscosity low-melting-point polyester PETG 10-25%, high-viscosity polyester PET 15-30% and polyester PET 55-80%.

[0026] The high-viscosity polyester PET has an intrinsic viscosity of 0.70-0.82 dL / g and a melting point of 245-260℃; the high-viscosity low-melting-point polyester PETG has an intrinsic viscosity of 0.70-0.82 dL / g and a melting point of 225-240℃; the polyester PET has an intrinsic viscosity of 0.62-0.68 dL / g and a melting point of 245-265℃; the high-viscosity polyester PET is BG801 bottle-grade polyester chip, the high-viscosity low-melting-point polyester PETG is BG804 bottle-grade polyester chip, and the polyester PET is one of FG600 base material type film-grade polyester chip and FG610 master batch type film-grade polyester chip.

[0027] The optical film is prepared by the steps of pre-blending, drying and crystallizing, extruding after melting and mixing, casting and then stretching in vertical and horizontal directions, and heat setting, and has a thickness of 36-125 μm and an elastic modulus of less than 1800 MPa.

[0028] A method for preparing an optical film with high stability and low elastic modulus, comprising the following steps:

[0029] S1: at room temperature, high-viscosity low-melting-point polyester PETG, high-viscosity polyester PET and polyester PET are sent to the corresponding hoppers of the main extruder through a material suction system, and are discharged by weight percentage control using a loss-on-ignition balance, to obtain core layer raw material low-melting-point polyester blend B, which is fully mixed, dried, vacuumized and dehumidified, to remove water, powder, impurities and oligomers in the B layer raw material melt, and the dried low-melting-point polyester blend B is sent to the extruder I, melted at a temperature of 220-290℃, accurately metered by a metering pump according to the set thickness, and then extruded from a lip die, to obtain the main extrusion B layer melt;

[0030] S2: The high-viscosity low-melting polyester PETG and the high-viscosity polyester PET are sent into the corresponding hoppers of the auxiliary extruder through the suction system, and the proportioning and discharging are controlled by using the loss weight scale according to the above weight percentage to obtain the low-melting polyester blend A of the surface layer raw material, which is fully mixed, dried, vacuumized and dehumidified to remove the water, powder, impurities and oligomers in the A layer raw material melt, and then the auxiliary extrusion A layer melt is obtained after the melt kneading and extrusion of the auxiliary extruder;

[0031] S3: The single-layer main extrusion B layer melt and the two-layer auxiliary extrusion A layer melt are converged and extruded in the three-layer die at a temperature of 220-290°C to obtain the melt of the ABA type three-layer co-extrusion structure;

[0032] S4: The melt of the ABA type three-layer co-extrusion structure is electrostatically attached to the surface of a large cooling drum at a temperature of 14-40°C to obtain the ABA type three-layer co-extrusion structure cast sheet;

[0033] S5: The ABA type three-layer co-extrusion structure cast sheet is longitudinally stretched at a speed of 7-80 m / min into a longitudinal stretching section with a length of 2-6 m and a temperature of 64-90°C, and after being stretched by 2.8-3.5 times under the heating of an infrared heating lamp, the stretched sheet is cooled to 22-45°C in a cooling section, at this time, the longitudinally stretched sheet is fed into a transverse stretching box at a speed of 20-280 m / min, enters a preheating section with a length of 4.5-9 m and a temperature of 85-135°C, and then is stretched by 2.8-4.4 times in a transverse stretching section with a length of 9-18 m and a temperature of 100-160°C, and is then shaped in a heat setting section with a length of 15-21 m and a temperature of 180-245°C, and then is cooled in a cooling section with a length of 9-18 m and a temperature of 20-35°C and at room temperature in two stages, and then is obtained after the thickness measurement feedback, flattening, electrostatic removal and winding, and the optical film product with high stability and low elastic modulus is obtained.

[0034] In a certain amount of EG and CHDM, due to the introduction of cyclohexane units in the molecular chain, the regularity of the entire molecular chain is reduced, making it difficult for PETG to crystallize, the PETG main chain has a cyclohexyl group more than PET, the volume of the cyclohexyl group is large, the number of single bonds that can rotate internally on the chain is relatively reduced, the rigidity of the molecular chain is increased, the gap between the molecular chains is increased, the toughness of the optical polyester film is improved, and the special process of longitudinal and transverse stretching and low-stretching low-temperature stretching is adopted to reduce the crystallinity of the polyester film, so that the film becomes softer and tougher.

[0035] The raw materials and amounts of the A layer and the B layer of the optical film in Examples 1-7 are shown in Table 1 below.

[0036] Table 1: Raw materials and amounts of the A layer and the B layer of the optical film in Examples 1-7 (unit: %)

[0037]

[0038] The preparation process conditions of the optical film in Examples 1-7 are shown in Table 2 below.

[0039] Table 2: Preparation process conditions of the optical film in Examples 1-7

[0040]

[0041] The optical films with high stability of low elastic modulus prepared in Examples 1-7 above were subjected to performance tests, and the test data comparison is shown in Table 3.

[0042] Table 3: Performance test data comparison of the optical films prepared in Examples 1-7

[0043]

[0044]

[0045] Note: T / % is the light transmittance, which is the percentage of the light flux that passes through the transparent or translucent body to the incident light flux; H / % is the haze, which is the percentage of the light intensity that deviates from the incident light by more than 2.5° to the total transmitted light intensity; C / % is the clarity, which is the degree of hindrance of the light transmission by the particles in the transparent or translucent body; TD direction is the width direction of the film, and MD direction is the length direction of the film.

[0046] Market products refer to multi-layer co-extrusion PET films with the same purpose existing in the market, market product D is treated by coating, and market product E is an optical grade polyester-based film.

[0047] From the above data, it can be seen that the optical films prepared in Examples 4-7 have higher mechanical properties, good optical properties, and lower elastic modulus with high stability, compared with Examples 1-3 and market products D and E, the product preparation process is simple and easy to operate, has strong practicality, and is especially suitable for flexible screen release films and protective films of display screens.

[0048] The above shows and describes the basic principles and main features of the present application, as well as the advantages of the present application. It should be understood by those skilled in the art that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. An optical thin film with low elastic modulus and high stability, characterized in that: The optical film is an ABA-type three-layer co-extruded polyester film, wherein layer A is the surface layer and layer B is the core layer; The A layer is a low-melting-point polyester blend A, which is composed of the following substances by weight percentage: 80% to 90% high-viscosity polyester PET and 10% to 20% high-viscosity low-melting-point polyester PETG. The B layer is a low-melting-point polyester blend B, which is composed of the following substances by weight percentage: 10% to 25% high-viscosity low-melting-point polyester PETG, 15% to 30% high-viscosity polyester PET, and 55% to 80% polyester PET. The high-viscosity polyester PET has an intrinsic viscosity of 0.70–0.82 dL / g and a melting point of 245–260°C; the high-viscosity, low-melting-point polyester PETG has an intrinsic viscosity of 0.70–0.82 dL / g and a melting point of 225–240°C; the polyester PET has an intrinsic viscosity of 0.62–0.68 dL / g and a melting point of 245–265°C. The high-viscosity polyester PET is BG801 bottle-grade polyester chips, the high-viscosity low-melting-point polyester PETG is BG804 bottle-grade polyester chips, and the polyester PET is one of FG600 base material type film-grade polyester chips and FG610 masterbatch type film-grade polyester chips. The elastic modulus of the optical thin film is less than 1800 MPa; The optical film is made by pre-blending, drying and crystallizing, extruding after melt mixing, casting and then biaxially stretching and heat setting. The specific steps are as follows: S1: High viscosity low melting point polyester PETG, high viscosity polyester PET and polyester PET are fed into the corresponding bins of the main extruder through the feeding system. The proportion of feeding is controlled by the loss-in-weight scale to obtain the core layer raw material low melting point polyester blend B. It is fully mixed, dried, vacuumed and dehumidified to remove the moisture, powder, impurities and oligomers in the B layer raw material melt. The dried low melting point polyester blend B is sent to extruder I and melted at a temperature of 220-290°C. After being accurately measured by the metering pump according to the set thickness, it is extruded from the lip die to obtain the main extruded B layer melt. S2: High-viscosity low-melting-point polyester PETG and high-viscosity polyester PET are fed into the corresponding hopper of the auxiliary extruder through the feeding system. The proportion of feeding is controlled by the loss-in-weight scale to obtain the surface raw material low-melting-point polyester blend A. It is thoroughly mixed, dried, vacuumed and dehumidified to remove moisture, powder, impurities and oligomers from the A layer raw material melt. After melt mixing by the auxiliary extruder, it is extruded to obtain the auxiliary extruded A layer melt. S3: The single-layer main extrusion B-layer melt and the two-layer auxiliary extrusion A-layer melt are combined and extruded in a three-layer die at a temperature of 220-290℃ to obtain an ABA-type three-layer co-extrusion melt. S4: The melt of the ABA-type three-layer co-extrusion structure is electrostatically attached to the surface of a large cooling drum at 14-40℃ for cooling to obtain a casting of the ABA-type three-layer co-extrusion structure. S5: The ABA-type three-layer co-extruded sheet is fed into a longitudinal stretching section 2–6 m long and 64–90°C at a speed of 7–80 m / min. Under infrared heating, it is stretched 2.8–3.5 times its original length and then cooled to 22–45°C in a cooling section. The longitudinally stretched sheet is then fed into a transverse stretching box at a speed of 20–280 m / min and enters a preheating section 4.5–9 m long and 85–135°C. It is then stretched 2.8–4.4 times its original length in a transverse stretching section 9–18 m long and 100–160°C. After that, it is heat-set in a heat-setting section 15–21 m long and 180–245°C. Then, it is cooled in two stages: a cooling section 9–18 m long and 20–35°C, and at room temperature. Finally, after thickness measurement feedback, flattening, static electricity removal, and winding, a finished optical thin film with low elastic modulus and high stability is obtained.

2. The optical thin film with high stability and low elastic modulus according to claim 1, characterized in that: The thickness of the optical thin film is 36–125 μm.

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