Polyethylene naphthalate film and preparation method thereof

Abstract

The invention provides a polyethylene naphthalate film and a preparation method thereof.The preparation method includes the three steps of pre-crystallization treatment, rapid hot stretching and annealing treatment.The preparation method includes the steps that a PEN casting piece is heated to the temperature range higher than the glass-transition temperature and kept for 15-60 minutes, small-size microcrystals are formed in the PEN casting piece, and the PEN casting piece is formed; the microcrystals can be used as nucleation points for stretching induced crystallization, so that the crystallization rate and uniformity in the subsequent stretching process are improved; then, the crystallized PEN casting piece is rapidly stretched at the temperature of 140-170 DEG C, and the deformation rate is 0.1-1 s <-1 >; the PEN molecular chain is highly oriented along the stretching direction, and meanwhile, the formation of oriented crystals is promoted, so that the modulus and the strength of the film are improved; and finally, carrying out annealing treatment on the PEN film obtained after rapid hot stretching in a range of 150-180 DEG C. The steps are favorable for further perfecting an oriented crystal structure, improving the crystallinity and effectively releasing internal stress, so that the dimensional stability and the heat resistance of the film are improved.

Description

Technical Field

[0001] The invention relates to the technical field of membrane materials and preparation thereof, in particular to a polyethylene naphthalate film and a preparation method thereof. Background Art

[0002] Polyethylene naphthalate (PEN) is a high-performance polyester material. Due to its excellent mechanical strength, heat resistance, gas barrier and electrical insulation properties, it has wide application potential in flexible electronics, photovoltaic packaging, display substrates, high-end packaging and other fields. Compared with traditional polyethylene terephthalate (PET), PEN has a higher glass transition temperature (T g ), better heat resistance and lower water vapor permeability, making it more advantageous in the high-end functional film market. However, the performance of PEN film is highly dependent on the preparation process, especially the control of crystallinity, orientation and residual internal stress, which has a significant impact on its final mechanical and thermal properties.

[0003] The existing PEN film preparation method usually adopts the process of melt extrusion-casting-hot stretching, in which hot stretching-induced crystallization is a key step to improve the strength and modulus of the film. The traditional method mainly uses uniaxial or biaxial stretching to orient and crystallize the molecular chains in a specific direction under the action of a thermal field. However, due to the high glass transition temperature (about 120°C) and slow crystallization rate of PEN, it is often difficult to achieve uniform and sufficient crystallization in a short time without optimizing the stretching process, resulting in limited mechanical properties of the film. In addition, in the traditional stretching process, if the crystal nucleus is insufficient, the molecular chain may be difficult to crystallize quickly, forming an amorphous region, thereby affecting the dimensional stability and heat resistance of the film.

[0004] Therefore, how to prepare high modulus and high strength PEN film to meet the application requirements of high-end functional materials has become an urgent problem to be solved in the current technical field. Summary of the invention

[0005] In view of the above problems existing in the prior art, the present invention provides a polyethylene naphthalate film and a preparation method thereof, so as to prepare a PEN film with high crystallinity and high orientation, thereby significantly improving the mechanical properties and crystallinity of the PEN film, making it suitable for flexible electronics, photovoltaic packaging, high-end electrical insulation and other fields.

[0006] The specific content of the invention is as follows: In a first aspect, the present invention provides a method for preparing a polyethylene naphthalate film. The preparation method comprises: Pre-crystallization treatment: The PEN casting sheet is heated to a temperature higher than the glass transition temperature and kept warm for 15-60 minutes to allow pre-crystallization to occur inside the PEN casting sheet, forming a preheated PEN film with small-sized crystallites; Rapid thermal stretching: 0.1-1s -1 The preheated PEN film is rapidly stretched at a deformation rate to form a stretched PEN film; Annealing treatment: the stretched PEN film is subjected to annealing treatment to obtain the polyethylene naphthalate film.

[0007] The heating temperature of the pre-crystallization treatment is 145-210° C., and the holding time is 30-60 minutes.

[0008] Optionally, the rapid stretching is performed at 140-170°C.

[0009] Optionally, the stretching multiple of the rapid stretching is 2-6 times.

[0010] Optionally, the annealing treatment is performed at a temperature of 150-180° C. and for a time of 10-30 min.

[0011] Optionally, the PEN casting sheet has a thickness of 80-300 microns.

[0012] Optionally, the intrinsic viscosity of the PEN masterbatch used to prepare the PEN flakes is 0.60-0.80 dL / g.

[0013] In a second aspect, the present invention provides a polyethylene naphthalate film, wherein the polyethylene naphthalate film is obtained by the preparation method described in the first aspect.

[0014] Optionally, the polyethylene naphthalate film has a modulus of 9.1-12.0 GPa and a film strength of 315-452 MPa.

[0015] Optionally, the polyethylene naphthalate film has a crystallinity of 32-42% and a grain orientation factor of 0.65-0.86.

[0016] The present invention provides a polyethylene naphthalate film, wherein the preparation method comprises a three-step process of "pre-crystallization treatment-rapid thermal stretching-annealing treatment". The present invention heats the PEN cast sheet to a temperature higher than the glass transition temperature (T g ) and keep it for 15-60 minutes. During this process, small-sized microcrystals are formed inside the PEN casting, which can serve as nucleation points for stretch-induced crystallization, improving the crystallization rate and uniformity in the subsequent stretching process; then the crystallized PEN casting is rapidly stretched in the range of 140-170℃, and the deformation rate is controlled at 0.1-1s -1, the stretching ratio is 2-6 times. This step makes the PEN molecular chain highly oriented along the stretching direction, and promotes the formation of oriented crystallization, thereby improving the modulus and strength of the film; finally, the present invention anneals the PEN film obtained after rapid hot stretching in the range of 150-180°C for 10-30 minutes. This step helps to further improve the oriented crystal structure, improve the crystallinity, and effectively release the internal stress, thereby improving the dimensional stability and heat resistance of the film.

[0017] Compared with the conventional stretch-induced crystallization method, the above-mentioned preparation method provided by the present invention has the following beneficial effects: (1) Improve the modulus and strength of the film: Microcrystals are formed during the preheating stage, which serve as nucleation points during the stretching process, promoting the uniform growth of oriented crystals, making the molecular chains highly oriented, and significantly improving the tensile modulus and fracture strength of the PEN film. Compared with traditional methods, the resulting PEN film exhibits higher rigidity and tensile strength, and is suitable for high-end flexible electronics and photovoltaic packaging.

[0018] (2) Optimizing crystallization behavior and improving crystallinity: In the process of stretching traditional PEN films, insufficient crystallization may lead to a decrease in the mechanical properties of the film. However, the present invention induces the formation of small-sized crystallites during the preheating stage, combines rapid stretching to promote oriented crystallization, and further improves the crystal structure during the annealing process, thereby significantly improving the crystallinity of the PEN film and enhancing its dimensional stability, heat resistance and mechanical strength.

[0019] (3) Reduce residual stress and improve dimensional stability: The optimized annealing process (temperature 150-180°C, time 10-30 minutes) can effectively release the residual internal stress during the stretching process, avoid film warping, shrinkage or cracking, and improve the stability of the film during subsequent processing and use, making it more adaptable in applications such as high-precision electronic devices and optical films.

[0020] (4) Wide range of applications and strong market competitiveness: Since the PEN film of the present invention has high modulus, high strength, high crystallinity, low residual stress and excellent heat resistance, it can be widely used in flexible circuit substrates, photovoltaic packaging films, high-end electrical insulation materials, display substrates and other fields, providing a more excellent material choice for the high-end functional film market. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 A flow chart of a polyethylene naphthalate film and a preparation method thereof provided in an embodiment of the present invention is shown; Figure 2 The XRD curve diagram of the polyethylene naphthalate film provided by the embodiment of the present invention is shown; Figure 3 The DSC curve of the polyethylene naphthalate film provided by the embodiment of the present invention is shown. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means a limitation on the present invention and its application or use. Based on the embodiments of the present invention, any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts falls within the scope of protection of the present invention. In addition, all other embodiments obtained by ordinary technicians in this field without carrying out creative work belong to the scope of protection of the present invention.

[0024] In the embodiment, no specific experimental steps or conditions are indicated, and the operation or conditions of the conventional experimental steps described in the prior art in this field can be carried out. The reagents used and other instruments that do not indicate the manufacturer are conventional reagent products that can be obtained commercially. In addition, the accompanying drawings are only schematic diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the figures represent the same or similar parts, and thus their repeated description will be omitted. Some block diagrams shown in the accompanying drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0025] Technologies, methods, and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the description of the present invention.

[0026] In the description of the present invention, it should be understood that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0027] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] Since PEN has a high glass transition temperature (about 120 ° C) and a slow crystallization rate, it is often difficult to achieve uniform and sufficient crystallization in a short time without optimizing the stretching process, resulting in limited mechanical properties of the film. In addition, in the traditional stretching process, if the crystal nucleus is insufficient, the molecular chain may be difficult to crystallize quickly, forming an amorphous region, thereby affecting the dimensional stability and heat resistance of the film. The traditional method is usually accompanied by high residual internal stress after stretching, which easily causes the film to warp, crack or shrink in size in subsequent applications, limiting its application in high-end flexible electronics, optical devices and photovoltaic packaging. Therefore, in the preparation process of the PEN film, the present invention optimizes the crystallization behavior, improves the crystallinity and reduces the internal stress, so as to prepare a high modulus and high strength PEN film to meet the application requirements of high-end functional materials; the specific implementation content is as follows: In a first aspect, the present invention provides a method for preparing a polyethylene naphthalate film. Figure 1 The flowchart of the method for preparing the polyethylene naphthalate film provided in the embodiment of the present invention is shown as follows: Figure 1 As shown, the preparation method includes a three-step process of pre-crystallization treatment-rapid thermal stretching-annealing treatment, specifically including: S1. The PEN casting sheet is heated to a temperature higher than the glass transition temperature and kept at this temperature for 15-60 minutes to allow pre-crystallization to occur inside the PEN casting sheet, thereby forming a preheated PEN film sheet having small-sized crystallites.

[0029] In the specific implementation, this embodiment uses a PEN cast sheet with a thickness of 80-300 microns to prepare the polyethylene naphthalate film, and the intrinsic viscosity of the PEN masterbatch used to prepare the PEN cast sheet is 0.60-0.80 dL / g to ensure the processability of the material and the stability of the final product; In specific implementation, this embodiment heats the PEN cast sheet to a temperature higher than the glass transition temperature and keeps it at this temperature for 15-60 minutes. The high temperature promotes the formation of small-sized crystallites inside the PEN cast sheet. The formed small-sized crystallites serve as nucleation points during the stretching process, promote the uniform growth of oriented crystals, make the molecular chains highly oriented, and significantly improve the tensile modulus and fracture strength of the PEN film.

[0030] In some embodiments, the heating temperature of the pre-crystallization treatment is 145-210° C. and the holding time is 30-60 min to ensure that a sufficient number of small-sized crystallites are formed inside the PEN casting sheet.

[0031] S2, 0.1-1s -1 The preheated PEN film is quickly stretched at a deformation rate to form a stretched PEN film.

[0032] In the specific implementation, the PEN casting sheet is pre-crystallized in step S1, and small-sized microcrystals are induced inside the PEN casting sheet, which is further rapidly stretched to promote oriented crystallization. In this embodiment, the pre-crystallized PEN casting sheet is rapidly stretched at 140-170°C, the stretching multiple is 2-6 times, and the deformation rate during stretching is 0.1-1 s -1 , making the PEN molecular chains highly oriented along the stretching direction and promoting the formation of oriented crystals, thereby improving the modulus and strength of the film.

[0033] S3, annealing the stretched PEN film to obtain the polyethylene naphthalate film.

[0034] In the specific implementation, the PEN casting sheet is subjected to the pre-crystallization treatment in step S1, and small-sized microcrystals are induced inside the PEN casting sheet, which is further subjected to rapid stretching to promote oriented crystallization. In this embodiment, the PEN casting sheet after the pre-crystallization treatment is rapidly stretched at 140-170°C, the stretching multiple is 2-6 times, and the deformation rate during stretching is 0.1-1s -1 , making the PEN molecular chains highly oriented along the stretching direction and promoting the formation of oriented crystals, thereby improving the modulus and strength of the film.

[0035] In the second aspect, the present invention provides a polyethylene naphthalate film, which is obtained by the preparation method described in the first aspect; the obtained polyethylene naphthalate film has a modulus of 9.1-12.0 GPa, a film strength of 315-452 MPa, a crystallinity of 32-42%, and a grain orientation factor of 0.65-0.86. It has high application value in the fields of flexible electronics, photovoltaic packaging, display substrates, high-end packaging, etc.

[0036] In order to enable those skilled in the art to more clearly understand the present invention, a polyethylene naphthalate film and a preparation method thereof according to the present invention are now described in detail through the following examples.

[0037] Example 1 A PEN sheet with a thickness of 100 μm was prepared with a masterbatch having an intrinsic viscosity of 0.7 dL / g. The PEN sheet was placed in a film stretching machine and preheated at 150°C for 30 minutes to obtain a preheated PEN film with small-sized microcrystals inside. The film was then heat-stretched at 145°C to obtain a stretched PEN film. During the stretching process, the film deformation rate was maintained at 1 s -1 , the stretching ratio is 5 times; finally, the stretched PEN film is annealed at 160°C for 20 minutes to obtain a PEN film.

[0038] Example 2 A PEN film with a thickness of 200 μm prepared from a masterbatch with an intrinsic viscosity of 0.65 dL / g was placed in a film stretching machine and preheated at 150°C for 30 minutes to obtain a preheated PEN film with small-sized microcrystals inside. The film was then heat-stretched at 145°C to obtain a stretched PEN film. During the stretching process, the film deformation rate was maintained at 1 s -1 , the stretching ratio is 5 times; finally, the stretched PEN film is annealed at 160°C for 20 minutes to obtain a PEN film.

[0039] Example 3 A PEN film with a thickness of 100 μm prepared from a masterbatch with an intrinsic viscosity of 0.7 dL / g was placed in a film stretching machine and preheated at 180°C for 30 minutes to obtain a preheated PEN film with small-sized microcrystals inside. The film was then heat-stretched at 145°C to obtain a stretched PEN film. During the stretching process, the film deformation rate was maintained at 1 s -1 , the stretching ratio is 5 times; finally, the stretched PEN film is annealed at 160°C for 20 minutes to obtain a PEN film.

[0040] Example 4 A PEN film with a thickness of 100 μm prepared from a masterbatch with an intrinsic viscosity of 0.7 dL / g was placed in a film stretching machine and preheated at 150°C for 15 minutes to obtain a preheated PEN film with small-sized microcrystals inside. The film was then heat-stretched at 145°C to obtain a stretched PEN film. During the stretching process, the film deformation rate was maintained at 1 s -1 , the stretching ratio is 5 times; finally, the stretched PEN film is annealed at 160°C for 20 minutes to obtain a PEN film.

[0041] Example 5 A PEN film with a thickness of 100 μm prepared from a masterbatch with an intrinsic viscosity of 0.7 dL / g was placed in a film stretching machine and preheated at 150°C for 30 minutes to obtain a preheated PEN film with small-sized microcrystals inside. The film was then hot stretched at 160°C to obtain a stretched PEN film. During the stretching process, the film deformation rate was maintained at 1 s -1 , the stretching ratio is 5 times; finally, the stretched PEN film is annealed at 160°C for 20 minutes to obtain a PEN film.

[0042] Example 6 A PEN film with a thickness of 100 μm prepared from a masterbatch with an intrinsic viscosity of 0.7 dL / g was placed in a film stretching machine and preheated at 150°C for 30 minutes to obtain a preheated PEN film with small-sized microcrystals inside. The film was then hot stretched at 145°C to obtain a stretched PEN film. During the stretching process, the film deformation rate was maintained at 0.1 s -1 , the stretching ratio is 5 times; finally, the stretched PEN film is annealed at 160°C for 20 minutes to obtain a PEN film.

[0043] Example 7 A PEN film with a thickness of 100 μm prepared from a masterbatch with an intrinsic viscosity of 0.7 dL / g was placed in a film stretching machine and preheated at 150°C for 30 minutes to obtain a preheated PEN film with small-sized microcrystals inside. The film was then heat-stretched at 145°C to obtain a stretched PEN film. During the stretching process, the film deformation rate was maintained at 1 s -1 , the stretching ratio is 4 times; finally, the stretched PEN film is annealed at 160°C for 20 minutes to obtain a PEN film.

[0044] Example 8 A PEN film with a thickness of 100 μm prepared from a masterbatch with an intrinsic viscosity of 0.7 dL / g was placed in a film stretching machine and preheated at 150°C for 30 minutes to obtain a preheated PEN film with small-sized microcrystals inside. The film was then heat-stretched at 145°C to obtain a stretched PEN film. During the stretching process, the film deformation rate was maintained at 1 s -1 , the stretching ratio is 5 times; finally, the stretched PEN film is annealed at 170°C for 20 minutes to obtain a PEN film.

[0045] Example 9 A PEN film with a thickness of 100 μm prepared from a masterbatch with an intrinsic viscosity of 0.7 dL / g was placed in a film stretching machine and preheated at 150°C for 30 minutes to obtain a preheated PEN film with small-sized microcrystals inside. The film was then heat-stretched at 145°C to obtain a stretched PEN film. During the stretching process, the film deformation rate was maintained at 1 s -1 , the stretching ratio is 5 times; finally, the stretched PEN film is annealed at 160°C for 25 minutes to obtain a PEN film.

[0046] Example 10 A PEN film with a thickness of 100 μm prepared from a masterbatch with an intrinsic viscosity of 0.7 dL / g was placed in a film stretching machine and preheated at 210 °C for 30 minutes to obtain a preheated PEN film with small-sized microcrystals inside. It was then heat-stretched at 170 °C to obtain a stretched PEN film. During the stretching process, the film deformation rate was maintained at 1 s -1 , the stretching ratio is 5 times; finally, the stretched PEN film is annealed at 160°C for 25 minutes to obtain a PEN film.

[0047] Performance Testing: The following performance tests were performed on the PEN films obtained in Examples 1-10 above: (1) After the PEN film is cut into dumbbell-shaped specimens, its mechanical properties are tested on a tensile testing machine (GB / T1040.1-2018).

[0048] (2) Perform synchrotron radiation X-ray diffraction (WAXD) tests on the preheated PEN film and PEN cast sheet to obtain the crystal structure of the preheated PEN film, such as crystal type, grain orientation factor, etc. The obtained one-dimensional XRD curve is shown in Figure 2 .like Figure 2 As shown in the figure, only one amorphous peak appears in the XRD curve of the PEN cast sheet, proving that no crystals are formed. However, three obvious diffraction peaks appear in the curve of the preheated PEN film, corresponding to the (010), (100) and (110) crystal planes of the α triclinic form, confirming the formation of crystals.

[0049] (3) Weigh 5 mg of PEN film and PEN sheet respectively, and test the crystallinity using differential scanning calorimetry (DSC). The obtained DSC curve is shown in Figure 3 .like Figure 3 As shown in the figure, the PEN casting sheet has obvious cold crystallization peaks and melting peaks, which indicates that its crystallinity is relatively low. However, the PEN film has no cold crystallization peaks, only melting peaks, which indicates that the crystallinity of the sample is relatively high.

[0050] The test results are shown in Table 1: Table 1 Synthesis process and properties of stretched PEN films of Examples 1-10

[0051] From the PEN film performance data obtained in comparative examples 1-10, it can be seen that the embodiments of the present invention control (optimize) the heating temperature and holding time of the pre-crystallization treatment, the temperature of rapid stretching, the stretching deformation rate and stretching ratio, the annealing temperature and annealing time to obtain a high-performance PEN film with a modulus of 9.1-12.0 GPa, a strength of 315-452 MPa, a crystallinity of 32-42%, and a grain orientation factor of 0.65-0.86. This ensures that the PEN film provided by the present invention has high application value in the fields of flexible electronics, photovoltaic packaging, display substrates, high-end packaging, etc.

[0052] Comparative Example 1 A 50 μm thick PEN sheet prepared from a masterbatch with an intrinsic viscosity of 0.5 dL / g was placed in a film stretching machine and preheated at 150°C for 30 min. It was then hot stretched at 145°C with a film deformation rate of 1 s -1 , the stretching ratio is 5 times; then it is annealed at 160°C for 20 minutes to obtain a PEN film.

[0053] Comparative Example 2 A PEN cast sheet with a thickness of 100 μm prepared from a masterbatch with an intrinsic viscosity of 0.7 dL / g was placed in a film stretching machine and preheated at 100°C for 120 min; it was then hot stretched at 145°C with a film deformation rate of 1 s -1 , the stretching ratio is 5 times; then it is annealed at 160°C for 20 minutes to obtain a PEN film.

[0054] Comparative Example 3 A PEN cast sheet with a thickness of 100 μm prepared from a masterbatch with an intrinsic viscosity of 0.7 dL / g was placed in a film stretching machine and preheated at 150°C for 30 min; then it was hot stretched at 100°C with a film deformation rate of 1 s -1 , the stretching ratio is 5. Under this condition, the PEN film is easy to break and cannot be formed into a film.

[0055] Comparative Example 4 A PEN cast sheet with a thickness of 100 μm prepared from a masterbatch with an intrinsic viscosity of 0.7 dL / g was placed in a film stretching machine and preheated at 150°C for 30 minutes; then it was hot stretched at 145°C with a film deformation rate of 1 s -1 , the stretching ratio is 7 times. Under this condition, PEN becomes fibrous and cannot form a film.

[0056] Comparative Example 5 A PEN cast sheet with a thickness of 100 μm prepared from a masterbatch with an intrinsic viscosity of 0.7 dL / g was placed in a film stretching machine and preheated at 150°C for 30 minutes; then it was hot stretched at 145°C with a film deformation rate of 1 s -1 , the stretching ratio is 5 times; then it is annealed at 110°C for 40 minutes to obtain a stretched PEN film.

[0057] Comparative Example 6 A PEN cast sheet with a thickness of 100 μm prepared from a masterbatch with an intrinsic viscosity of 0.7 dL / g was placed in a film stretching machine and preheated at 150°C for 30 minutes; then it was hot stretched at 145°C with a film deformation rate of 1 s -1 , the stretching ratio is 5 times; then it is annealed at 240°C for 40 minutes to obtain a stretched PEN film.

[0058] Performance Test: The following performance tests were performed on the PEN films obtained in the above comparative examples 1-6: (1) After the PEN film is cut into dumbbell-shaped specimens, its mechanical properties are tested on a tensile testing machine (GB / T1040.1-2018).

[0059] (2) Perform X-ray diffraction (XRD) test on the PEN film to obtain the crystal structure of the PEN film, such as crystal type, grain orientation factor, etc.

[0060] (3) Weigh 5 mg of PEN film and test the crystallinity of the film using differential scanning calorimetry (DSC).

[0061] The test results are shown in Table 2: Table 2 Comparative Examples 1-6 Synthesis process and PEN film properties

[0062] In Comparative Example 1, the intrinsic viscosity of the masterbatch and the thickness of the PEN cast film are not within the range provided in the embodiments of the present invention (the thickness of the PEN cast film is 80-300 microns, and the intrinsic viscosity of the PEN masterbatch is 0.60-0.80 dL / g). This results in the PEN film obtained in the comparative example having good fluidity but poor tensile properties, and being unable to form highly oriented crystals, and ultimately obtaining a PEN film with low modulus and poor strength.

[0063] In Comparative Example 2, the preheating temperature is 100 degrees Celsius, which is lower than the glass transition temperature, and an effective crystal nucleus cannot be formed, resulting in low crystallinity during the subsequent thermal stretching process. Therefore, the PEN film product has a low modulus and poor performance.

[0064] In Comparative Example 3, the stretching temperature of the preheated PEN film is 100 degrees Celsius, which is lower than the glass transition temperature. This causes the PEN cast sheet to be unable to deform and break at this strain rate, and thus cannot form a film.

[0065] In Comparative Example 4, the stretching ratio was too high, resulting in film breakage.

[0066] In Comparative Example 5, the annealing temperature is too low, the crystal nucleus cannot be perfected, and the lattice defects lead to poor mechanical properties.

[0067] In Comparative Example 6, the annealing temperature is too high, resulting in the melting and destruction of the formed crystalline structure, resulting in low modulus and poor strength of the obtained PEN film.

[0068] According to Examples 1-10 and Comparative Examples 1-6, the method for preparing polyethylene naphthalate film disclosed in the present invention can prepare a PEN film having a modulus of 9.1-12.0 GPa, a strength of 315-452 MPa, a crystallinity of 32-42%, and a grain orientation factor of 0.65-0.86. The obtained PEN film has high modulus, high strength, high crystallinity, low residual stress and excellent heat resistance, and can be widely used in flexible circuit substrates, photovoltaic encapsulation films, high-end electrical insulation materials, display substrates and other fields, providing a more excellent material choice for the high-end functional film market.

[0069] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0070] For the method embodiments, for the sake of simplicity, they are all described as a series of action combinations, but those skilled in the art should know that the present invention is not limited by the order of the actions described, because according to the present invention, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and components involved are not necessarily required by the present invention.

[0071] The above is a detailed introduction to a polyethylene naphthalate film and a preparation method thereof provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for a person skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A method for preparing a polyethylene naphthalate film, characterized in that: The preparation method comprises: Pre-crystallization treatment: The PEN casting sheet is heated to a temperature higher than the glass transition temperature and kept warm for 15-60 minutes to allow pre-crystallization to occur inside the PEN casting sheet, forming a preheated PEN film with small-sized crystallites; Rapid thermal stretching: 0.1-1s -1 The preheated PEN film is rapidly stretched at a deformation rate to form a stretched PEN film; Annealing treatment: the stretched PEN film is subjected to annealing treatment to obtain the polyethylene naphthalate film.

2. The method for preparing the polyethylene naphthalate film according to claim 1, characterized in that: The heating temperature of the pre-crystallization treatment is 145-210° C., and the holding time is 30-60 minutes.

3. The method for preparing the polyethylene naphthalate film according to claim 1, characterized in that: The rapid stretching is performed at 140-170°C.

4. The method for preparing the polyethylene naphthalate film according to claim 1, characterized in that: The rapid stretching has a stretching multiple of 2-6 times.

5. The method for preparing the polyethylene naphthalate film according to claim 1, characterized in that: The annealing treatment is carried out at a temperature of 150-180°C and for a time of 10-30 min.

6. The method for preparing the polyethylene naphthalate film according to claim 1, characterized in that: The PEN casting sheet has a thickness of 80-300 microns.

7. The method for preparing the polyethylene naphthalate film according to claim 1, characterized in that: The intrinsic viscosity of the PEN masterbatch used to prepare the PEN flakes is 0.60-0.80 dL / g.

8. A method for preparing a polyethylene naphthalate film, characterized in that: The polyethylene naphthalate film is obtained by the preparation method described in any one of claims 1 to 7.

9. The polyethylene naphthalate film according to claim 8, characterized in that: The modulus of the polyethylene naphthalate film is 9.1-12.0 GPa, and the film strength is 315-452 MPa.

10. The polyethylene naphthalate film according to claim 8, characterized in that: The polyethylene naphthalate film has a crystallinity of 32-42% and a grain orientation factor of 0.65-0.86.

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