Highly transparent photochromic polyester film and method for making same
By introducing surface-modified inorganic photochromic nanoparticles in situ during the polyester synthesis stage, the problems of shedding and transparency of photochromic polyester films were solved, achieving high transparency, rapid color change and stability, simplifying the preparation process and improving the overall performance of the film.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIANGSU SHUANGXING COLOR PLASTIC NEW MATERIALS
- Filing Date
- 2026-04-27
- Publication Date
- 2026-08-04
AI Technical Summary
Existing photochromic polyester films are prone to peeling and color-changing function decay during long-term use or in harsh environments, and have poor transparency and mechanical properties. Moreover, the preparation process is complex and inefficient.
By introducing surface-modified inorganic photochromic nanoparticles in situ during the polyester synthesis stage, nanoscale dispersion and chemical anchoring of these nanoparticles in the polyester molecular chain are achieved, thus preparing a photochromic polyester film with high transparency, rapid color change, and stability.
It achieves high transparency, rapid color-changing response and excellent stability, extends service life, simplifies the preparation process and reduces environmental burden.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of polymer materials technology, specifically relating to a highly transparent photochromic polyester film and its preparation method. Existing technology
[0002] Photochromic materials are functional materials whose molecular structure or state changes under irradiation with specific wavelengths (such as ultraviolet light), resulting in a color change, and which can reversibly return to their original state after the light exposure stops. Polyethylene terephthalate (PET) film is widely used in packaging, electronics, construction, and automotive industries due to its excellent mechanical, optical, thermal stability, and processing properties. Combining photochromic functionality with PET film has led to the development of photochromic polyester film, which can be applied to high-end fields such as smart window films, anti-counterfeiting labels, optical storage, and sensors, and has broad market prospects.
[0003] Currently, the preparation of photochromic polyester films mainly employs a coating method, which involves coating a layer containing a photochromic compound onto the surface of a pre-formed PET base film. For example, Chinese patent CN102785441B discloses a method for preparing a photochromic composite film, which involves spraying a solution containing photochromic microcapsules onto the surface of a polyvinyl alcohol film. However, the coating method has several inherent drawbacks: First, the photochromic layer and the base film are physically bonded, resulting in weak interfacial adhesion. Under long-term use or harsh environments (such as friction, bending, and humid heat), problems such as coating peeling and precipitation of color-changing substances can easily occur, leading to a decline or even failure of the color-changing function and a short service life. Second, the surface coating affects the original gloss and transparency of the film, increasing haze and making it difficult to meet the requirements of applications with high optical quality. Furthermore, the coating process involves the use of organic solvents, increasing process complexity and environmental burden, and resulting in relatively low production efficiency.
[0004] To overcome the shortcomings of coating methods, some researchers have attempted to directly add photochromic agents to polyester resins and prepare photochromic films through melt blending. For example, Chinese patent application CN103804873A discloses a photochromic polyester film, which is prepared by melt extrusion after blending photochromic masterbatch with polyester chips. However, simple melt blending has the following problems: photochromic agents (especially inorganic photochromic agents) have poor compatibility with the polyester matrix and are prone to agglomeration in the matrix, forming large-sized particles. This not only significantly reduces the transparency and mechanical properties of the film but also leads to uneven color change response and a slower rate. At the same time, the high shear force of inorganic particles during melt processing may damage their structure or surface state, affecting the color change performance. In addition, photochromic agents may undergo thermal degradation or side reactions with polyester in high-temperature melts, resulting in a decrease in color change performance.
[0005] Therefore, developing a photochromic polyester film that combines high transparency, rapid color-changing response, excellent color-changing stability, and long service life, and exploring its green and efficient preparation method, remains a technical challenge that needs to be solved by those skilled in the art. Summary of the Invention
[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a highly transparent, rapidly color-changing, and stable photochromic polyester film and its preparation method. This invention introduces surface-modified inorganic photochromic nanoparticles in situ into the polyester molecular chain during the polymerization stage, achieving nanoscale dispersion and firm anchoring of the photochromic agent in the polyester matrix, thereby significantly improving the film's optical transparency, color-changing rate, and durability.
[0007] The objective of this invention is achieved through the following technical solution: a highly transparent photochromic polyester film, wherein the film is composed of a photochromic polyester layer, the photochromic polyester layer contains in-situ polymerized, surface-modified inorganic photochromic nanoparticles, the haze of the film is ≤3%, and the color changes within 5 seconds under sunlight.
[0008] In this invention, "in-situ polymerization" refers to introducing specially surface-modified inorganic photochromic nanoparticles into the reaction system during the polyester synthesis (esterification or polycondensation) stage, allowing them to participate in the polymerization process as a reactive component. This results in the uniform and stable dispersion and bonding of the nanoparticles within the polyester matrix while the polyester molecular chains grow. This differs from the traditional melt blending method.
[0009] In this invention, "surface modification" refers to chemically treating the surface of inorganic photochromic nanoparticles to graft organic functional groups (such as hydroxyl, carboxyl, ester groups, etc.) that can react with polyester monomers or molecular chains onto their surface, thereby improving their compatibility with the polyester matrix and establishing chemical bonds.
[0010] Preferably, the inorganic photochromic nanoparticles are rare-earth phosphate nanoparticles coated with amorphous TiO2, such as LaPO4:Ce,Tb or similar materials, with an average particle size of 50-200 nm. The amorphous TiO2 coating not only protects the internal rare-earth phosphates but also provides abundant surface hydroxyl groups, facilitating subsequent coupling agent modification. Controlling the particle size at the nanoscale is crucial to ensuring the high transparency of the final film.
[0011] Preferably, the surface modification involves treating the inorganic photochromic nanoparticles with a silane coupling agent or a titanate coupling agent to graft active functional groups onto their surface that can react with the polyester matrix. For example, an amino-containing silane coupling agent (such as KH550) can be used, whose amino groups can react with the terminal carboxyl groups of the polyester; or an epoxy-containing silane coupling agent (such as KH560) can be used, whose epoxy groups can react with the terminal carboxyl or hydroxyl groups of the polyester. Through this chemical bonding, the nanoparticles are firmly "anchored" in the polyester matrix, completely solving the problems of detachment and migration.
[0012] Preferably, the inorganic photochromic nanoparticles in the photochromic polyester layer comprise 0.5-5% by mass. Within this range, the film achieves satisfactory color-changing depth while maintaining extremely high transparency and excellent mechanical properties.
[0013] Preferably, the intrinsic viscosity [η] of the photochromic polyester layer is 0.65-0.85 dL / g, which ensures that the film has good processing performance and mechanical strength.
[0014] The present invention also provides a method for preparing the above-mentioned highly transparent photochromic polyester film, comprising the following steps:
[0015] (1) Preparation of surface-modified inorganic photochromic nanoparticle suspension: Inorganic photochromic nanoparticles, coupling agent and ethylene glycol are mixed and ultrasonically dispersed and mechanically stirred under inert gas protection to obtain a uniform and stable suspension.
[0016] (2) In-situ polymerization to prepare photochromic polyester chips: Purified terephthalic acid, ethylene glycol and the suspension prepared in step (1) are added to the reactor and esterification and polycondensation reactions are carried out under the action of a catalyst to obtain photochromic polyester melt. After extrusion, pelletizing and drying, photochromic polyester chips are obtained.
[0017] (3) Preparation of photochromic polyester film: After drying the photochromic polyester slices obtained in step (2), the film is melt-extruded, cast, biaxially stretched and heat-set to obtain a highly transparent photochromic polyester film.
[0018] In the preparation method of this invention, step (1) is crucial. By carrying out the coupling reaction in the polymerizable monomer ethylene glycol, effective surface modification and pre-dispersion of the nanoparticles are achieved. Furthermore, the resulting suspension can be directly used in the polymerization reaction, avoiding intermediate separation steps and simplifying the process. Ultrasonic dispersion helps to break up the soft agglomerates of nanoparticles, allowing them to be initially dispersed in ethylene glycol.
[0019] Preferably, in step (1), the inorganic photochromic nanoparticles have a mass fraction of 5-15% in the suspension, the coupling agent has a mass fraction of 1-5% of the inorganic photochromic nanoparticles, the ultrasonic dispersion time is 30-90 minutes, and the stirring temperature is 20-60℃.
[0020] Preferably, in step (2), the esterification reaction is carried out at a temperature of 220-260℃ and a pressure of 0.2-0.4 MPa; the polycondensation reaction is carried out at a temperature of 275-285℃ and an absolute pressure of 50-200 Pa, and the reaction time is 60-120 minutes.
[0021] Preferably, in step (3), the longitudinal stretching ratio of the biaxial stretching is 3.0-4.0 times, the transverse stretching ratio is 3.0-4.0 times, the heat setting temperature is 210-230℃, and the time is 5-30 seconds.
[0022] Preferably, in step (3), the thickness of the resulting film is 20-100 μm, which can be adjusted according to different application requirements.
[0023] Compared with the prior art, the present invention has the following beneficial effects:
[0024] Extremely high transparency: By introducing nanoscale, surface-modified photochromic particles in situ during the polymerization stage, their uniform dispersion at the nanoscale in the polyester matrix is achieved without macroscopic agglomerates. Therefore, the film has extremely low haze (≤3%), high light transmittance, and clear vision.
[0025] Ultra-fast color-changing response: The nanoscale color-changing particles have a large specific surface area and high efficiency in interacting with light. At the same time, they are uniformly dispersed in the matrix, which allows the color-changing reaction to proceed synchronously and rapidly throughout the entire film volume, achieving rapid color change within 5 seconds.
[0026] Excellent color stability and durability: The surface-modified nanoparticles are linked to the polyester molecular chain by chemical bonds and are firmly anchored in the matrix. They will not migrate, agglomerate or fall off, which fundamentally solves the failure problem of coating or blending products and greatly extends the service life.
[0027] Excellent bulk properties: The reinforcing and toughening effect of nanoparticles, coupled with the fact that the polyester main chain structure is not damaged, allows the film to maintain the original high tensile strength, high elongation at break and good thermal stability of the polyester material.
[0028] The green and environmentally friendly preparation process adopts in-situ polymerization, which avoids the use of a large amount of organic solvents in the coating method. The process is short, environmentally friendly, and easy to achieve industrial continuous production.
[0029] In summary, the high-transparency photochromic polyester film provided by this invention combines the advantages of high transparency, rapid color change, excellent stability, and environmental friendliness, and can meet the stringent requirements of fields such as smart window film, high-end anti-counterfeiting, and optical devices, and has extremely high application value and market prospects. Detailed Implementation
[0030] The present invention will be further described below with reference to the embodiments. Example 1
[0031] (1) Preparation of surface-modified inorganic photochromic nanoparticle suspension: 100 g of rare earth phosphate photochromic nanoparticles (e.g., self-made or custom-made) with an average particle size of approximately 80 nm and coated with amorphous TiO2 were weighed and added to a 2 L beaker containing 900 g of ethylene glycol. Then, 3 g of titanate coupling agent (e.g., isopropyltris(dioctylpyrophosphate)titanate) was added. The beaker was placed in an ultrasonic cleaner and ultrasonically dispersed at 40 kHz frequency and 200 W power for 60 minutes, while mechanical stirring was performed at 300 rpm. After dispersion, a uniform and stable suspension was obtained, with no visible precipitate.
[0032] (2) In-situ polymerization preparation of photochromic polyester chips: In a 20L stainless steel polymerization reactor, 6000g purified terephthalic acid (PTA), 2400g ethylene glycol (EG), 200g of the suspension prepared in step (1), and 2.0g antimony trioxide catalyst were added sequentially. The reactor was sealed, and the air inside was replaced three times with high-purity nitrogen. Stirring was started, and the temperature was increased. Esterification reaction was carried out at a pressure of 0.25-0.35 MPa, and the temperature inside the reactor was gradually increased from 220℃ to 250℃. When the water output reached 95% of the theoretical value, the esterification reaction ended, and the pressure was released to atmospheric pressure. Then, the temperature was slowly increased and a vacuum was drawn to enter the polycondensation stage. The temperature was raised to 275℃ within 30 minutes, while the absolute pressure of the system was reduced to below 100 Pa. Polycondensation reaction was carried out under these conditions for 90 minutes, and the stirring power was gradually increased during the reaction. When the stirring power reached the set value, the reaction ended, and the vacuum was broken with nitrogen. The melt was extruded through a die, water-cooled, and pelletized to obtain photochromic polyester chips. The intrinsic viscosity [η] of the chips was measured to be 0.78 dL / g, in which the mass fraction of inorganic photochromic nanoparticles was approximately 1.2% (estimated from the feed rate).
[0033] (3) Preparation of a highly transparent photochromic polyester film: The photochromic polyester chips obtained in step (2) were dried in a vacuum drum dryer at 150°C for 6 hours to reduce their moisture content to below 50 ppm. The dried chips were then fed into a single-screw extruder and melt-extruded at 280°C, casting the film through a T-die onto a cooling drum to form a cast sheet. The cast sheet was then biaxially stretched: first longitudinally at 85°C by 3.5 times, and then transversely at 110°C by 3.5 times. The stretched film was heat-set at 220°C for 20 seconds, and then drawn, trimmed, and wound to obtain a highly transparent photochromic polyester film with a thickness of approximately 50 μm. Example 2
[0034] This embodiment is basically the same as Example 1, except that the coupling agent used in step (1) is silane coupling agent KH550 (γ-aminopropyltriethoxysilane), and its dosage is 2 g. In step (2), the polycondensation reaction time is 100 minutes, and the final intrinsic viscosity [η] of the slice is 0.81 dL / g. In step (3), the longitudinal stretching ratio is 4.0 times, the transverse stretching ratio is 4.0 times, the heat setting temperature is 230℃, and the final film thickness is approximately 30 μm. Example 3
[0035] This embodiment is basically the same as Embodiment 1, except that in step (1), the amount of inorganic photochromic nanoparticles used is 200 g, the amount of ethylene glycol is 800 g, and the amount of titanate coupling agent is 6 g, resulting in a particle mass fraction of 20% in the suspension. In step (2), the amount of suspension added is 400 g. In the obtained slices, the mass fraction of inorganic photochromic nanoparticles is approximately 2.4%, and the intrinsic viscosity [η] is 0.75 dL / g. In step (3), the final film thickness is approximately 80 μm.
[0036] Comparative Example 1
[0037] Photochromic polyester films were prepared using a melt blending method. Commercially available glossy polyester chips (intrinsic viscosity 0.80 dL / g) were blended with pure polyester chips (blank chips) prepared in Example 1 without added photochromic agent. Simultaneously, unmodified rare-earth phosphate photochromic nanoparticles (average particle size 80 nm) used in Example 1 were mixed with the above-mentioned blended chips at a mass fraction of 1.2% in a high-speed mixer. The mixture was then added to a twin-screw extruder for melt blending and granulation to obtain a photochromic masterbatch. This masterbatch was then mixed with glossy polyester chips in a specific ratio to achieve a final film with a photochromic particle content of approximately 1.2%. Subsequent extrusion, stretching, and shaping steps were the same as in Example 1 to obtain a comparative film.
[0038] Comparative Example 2
[0039] Photochromic polyester films were prepared using a coating method. A commercially available 50 μm optical-grade transparent PET film was used as the substrate. The coating solution was prepared by dispersing the unmodified rare-earth phosphate photochromic nanoparticles (average particle size 80 nm) used in Example 1 in an ethyl acetate solution containing acrylate resin. The solid content was approximately 10%, with the photochromic particles accounting for approximately 5% of the solid content. The coating solution was uniformly coated onto the surface of the PET film using a wire-bar coating method, resulting in a wet film thickness of approximately 10 μm. The film was then dried at 100°C for 5 minutes to remove the solvent and cure the coating, thus obtaining the photochromic composite film.
[0040] Performance Testing and Evaluation
[0041] The photochromic polyester films prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to the following performance tests:
[0042] Haze: Tested using a haze meter in accordance with GB / T 2410-2008 standard.
[0043] Color change response time: Illuminate the thin film sample with a simulated sunlight source (xenon lamp, light intensity 100,000 lux) and record the time required for the sample to change from white (or colorless) to a color change that is clearly visible to the human eye (e.g., turning pale yellow).
[0044] Color change reversibility and stability test: The sample was exposed to simulated sunlight for 5 minutes to allow it to fully develop color, and then moved to a dark room to allow it to fade. This constitutes one cycle. After repeating this cycle 100 times, the color change response time was tested again, and any decay in color change performance was observed.
[0045] Migration resistance test: The film sample is tightly bonded to white filter paper and placed in an oven at 80°C for 72 hours. After removal, observe whether there is any color substance migrating or precipitating on the filter paper.
[0046] Tensile strength: Tested in accordance with GB / T 1040.3-2006 standard.
[0047] The test results are summarized in Table 1.
[0048]
[0049] The results in Table 1 show that:
[0050] Regarding haze: The haze of Examples 1-3 of this invention is ≤3%, which is much lower than 8.5% of Comparative Example 1 and 4.2% of Comparative Example 2, indicating that in-situ polymerization and nanoscale dispersion significantly improve the optical transparency of the film.
[0051] Color change response speed: The initial color change response time of this embodiment is only 2-3 seconds, which is much faster than the 10-15 seconds of the comparative example, proving the rapid response advantage brought by the uniform dispersion of nanoparticles.
[0052] Color change stability: After 100 color change cycles, the response time of the embodiment of the present invention remained almost unchanged, while the response time of Comparative Example 1 slowed down significantly (from 15 seconds to 45 seconds), and Comparative Example 2 also showed a significant decrease. This indicates that the chemical bonding effect of in-situ polymerization greatly improves the color change stability.
[0053] Migration resistance: In the embodiments of the present invention, no substance migrated at high temperature, while Comparative Example 1 showed slight yellowing, and Comparative Example 2 showed obvious color substance migration, proving that the coating of the coating method is unstable.
[0054] Mechanical properties: The tensile strength of the embodiments of the present invention is higher than 200 MPa, which is better than that of the comparative example, indicating that the uniform dispersion of nanoparticles plays a reinforcing role without damaging the matrix.
[0055] In summary, the high-transparency photochromic polyester film and its preparation method provided by this invention successfully overcome many defects of the prior art, and have achieved significant technical progress in terms of transparency, color-changing rate, color-changing stability and overall performance, and have extremely high industrial application value.
[0056] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make changes to some of the technical features without creative effort, and all such changes should be included within the scope of patent protection of this invention.
Claims
1. A highly transparent photochromic polyester film, characterized in that, The film is composed of a photochromic polyester layer containing in-situ polymerized, surface-modified inorganic photochromic nanoparticles. The haze of the film is ≤3%, and it changes color within 5 seconds under sunlight.
2. The high-transparency photochromic polyester film according to claim 1, characterized in that, The inorganic photochromic nanoparticles are rare earth phosphate nanoparticles with amorphous TiO2 coated on their surface, and their average particle size is 50-200 nm.
3. The high-transparency photochromic polyester film according to claim 1, characterized in that, The surface modification involves treating the inorganic photochromic nanoparticles with a silane coupling agent or a titanate coupling agent to graft active functional groups onto their surface that can react with the polyester matrix.
4. The high-transparency photochromic polyester film according to claim 1, characterized in that, In the photochromic polyester layer, the mass fraction of inorganic photochromic nanoparticles is 0.5-5%.
5. The high-transparency photochromic polyester film according to claim 1, characterized in that, The intrinsic viscosity [η] of the photochromic polyester layer is 0.65-0.85 dL / g.
6. A method for preparing a highly transparent photochromic polyester film as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Preparation of surface-modified inorganic photochromic nanoparticle suspension: Inorganic photochromic nanoparticles, coupling agent and ethylene glycol are mixed, and ultrasonically dispersed and stirred to obtain a uniform and stable suspension; (2) In-situ polymerization to prepare photochromic polyester chips: Purified terephthalic acid, ethylene glycol and the suspension prepared in step (1) are added to the reactor and esterification and polycondensation reactions are carried out under the action of a catalyst to obtain photochromic polyester melt. After extrusion, pelletizing and drying, photochromic polyester chips are obtained. (3) Preparation of photochromic polyester film: After drying the photochromic polyester slices obtained in step (2), the film is melt-extruded, cast, biaxially stretched and heat-set to obtain a highly transparent photochromic polyester film.
7. The preparation method according to claim 6, characterized in that, In step (1), the inorganic photochromic nanoparticles have a mass fraction of 5-15% in the suspension, the coupling agent has a mass fraction of 1-5% of the inorganic photochromic nanoparticles, and the ultrasonic dispersion time is 30-90 minutes.
8. The preparation method according to claim 6, characterized in that, In step (2), the polycondensation reaction is carried out at a temperature of 275-285℃ and an absolute pressure of 50-200 Pa for a reaction time of 60-120 minutes.
9. The preparation method according to claim 6, characterized in that, In step (3), the longitudinal stretching ratio of the biaxial stretching is 3.0-4.0 times, the transverse stretching ratio is 3.0-4.0 times, and the heat setting temperature is 210-230℃.
10. The preparation method according to claim 6, characterized in that, In step (3), the thickness of the resulting film is 20-100 μm.