Anti-yellowing low-moisture-absorption high-dimensional-stability BOPA (Biaxially Oriented Polyamide) film and preparation method thereof

Abstract

The invention relates to the technical field of film packaging, in particular to an anti-yellowing low-moisture-absorption high-dimensional-stability BOPA film and a preparation method thereof. The film is composed of a first surface layer, a core layer and a second surface layer, the surface layers contain anti-yellowing PA particles, anti-sticking master batches and other auxiliaries, and the core layer contains anti-yellowing PA particles and other auxiliaries; wherein the anti-yellowing PA particles are prepared by melt extrusion of low-moisture-absorption PA particles, a compound stabilizer and an end-capping reagent, and the low-moisture-absorption PA particles are prepared by intercalation solid-phase polymerization of PA6, special nylon and flaky nanoparticles; the compound stabilizer is compounded by a heat stabilizer and a light stabilizer; and the end-capping reagent can seal polyamide active groups. The film is prepared through raw material drying, melt extrusion, synchronous two-way stretching, heat setting and corona treatment, keeps excellent mechanical strength and optical transparency, also has low moisture absorption, high dimensional stability and yellowing resistance, and can be widely applied to the field of flexible packaging of food, daily necessities, electronic appliances and the like.

Description

Technical Field

[0001] This invention relates to the field of film packaging technology, and in particular to a BOPA film with anti-yellowing, low moisture absorption, and high dimensional stability, and its preparation method. Background Technology

[0002] Biaxially oriented nylon film (BOPA), as one of the three core films widely used in flexible packaging, has been extensively applied in food packaging, pharmaceutical packaging, cosmetic packaging, and mechanical and electronic product packaging due to its excellent tensile strength, puncture resistance, gas barrier properties, transparency, and printability. However, with the continuous upgrading of packaging technology and increasingly fierce market competition, consumers and downstream application industries are placing higher demands on the comprehensive performance of packaging materials. The inherent defects of existing BOPA films are gradually becoming apparent, making it difficult to meet the needs of high-end applications.

[0003] Existing BOPA films generally suffer from high moisture absorption, resulting in poor dimensional and thermal stability. Especially in high humidity environments, the film's barrier properties rapidly decline, and it is prone to dimensional shrinkage, failing to meet the stringent packaging requirements for high-temperature cooking of food. Furthermore, during film processing, dimensional fluctuations caused by high moisture absorption can lead to wrinkling, misregistration, and corner warping, severely impacting the consistency of the final product's quality. In addition, during processing and subsequent use, BOPA films are susceptible to thermal, photo-, and oxidative degradation of the amide groups in the polyamide molecular backbone due to environmental factors such as high temperature, high humidity, and light exposure. This alters the molecular structure and causes yellowing, which not only damages the aesthetic appearance of the packaged product but also degrades key indicators such as the film's mechanical and barrier properties, severely affecting the practicality and safety of the packaging.

[0004] Given the aforementioned shortcomings of existing technologies, the industry urgently needs to develop a BOPA film that combines low moisture absorption and anti-yellowing properties without sacrificing the film's original physical and mechanical properties, optical appearance quality, and processing stability. This would effectively improve the limitations of existing products and further expand their application scenarios in the high-end flexible packaging field. Summary of the Invention

[0005] To address the technical challenge of developing a BOPA film with low moisture absorption and anti-yellowing properties without sacrificing the film's original physical and mechanical properties, appearance quality, and processing stability, this invention provides an anti-yellowing, low moisture absorption, and high dimensional stability BOPA film. The film structure includes a first surface layer, a core layer, and a second surface layer arranged sequentially from bottom to top. By mass fraction, the first and second surface layers comprise 90% to 97.5% anti-yellowing PA particles, 2% to 7% anti-sticking masterbatch, and 0.5% to 3% other additives; the core layer comprises 97% to 99.5% anti-yellowing PA particles and 0.5% to 3% other additives. The anti-yellowing PA particles consist of 95.4% to 99.9% low-hygroscopic PA particles, 0.05% to 3.4% composite stabilizer, and 0.05% to 1.2% end-capping agent.

[0006] In some embodiments, the low-hygroscopic PA particles are PA6-co-specialty nylon / sheet nanoparticles prepared by intercalation solid-state polymerization of PA6, special nylon, and sheet nanoparticles, comprising the following steps: S101. Add deionized water to the reactor, and add the diacid and diamine corresponding to the special nylon at a molar ratio of 1:1 at 50℃~70℃ while stirring. Stir and react for 1 hour, adjust the pH value to 7.0~7.6, and continue to react for 1 hour~3 hours to obtain a clear and transparent special nylon salt solution. Then, cool, filter and dry to obtain white special nylon salt powder. S102. Caprolactam and sheet nanoparticles are dispersed in deionized water and stirred and sonicated at 80℃~90℃ for 8h~12h to obtain caprolactam / sheet nanoparticle suspension. S103. The special nylon salt obtained in step S101, the caprolactam / sheet nanoparticle suspension obtained in step S102, and 0.01%~0.2% by mass of catalyst are added to the reaction vessel and mixed. The reaction vessel is evacuated, and stirring and heating are started under a high-purity nitrogen atmosphere of 0.1MPa. After the temperature is raised to 210℃~260℃, the reaction is maintained at 2.2MPa~2.4MPa for 3h~5h. S104. After the reaction is complete, the gas is uniformly released to normal pressure, and then the temperature is raised to 260℃~350℃. After polycondensation for 3h~13h, nitrogen gas is introduced to purge back pressure, and the material is cooled and discharged to obtain PA6-co-special nylon / sheet nanoparticle polymer. S105. Extract the PA6-co-special nylon / sheet nanoparticle polymer obtained in step S104 with pure water, then granulate and dry to obtain the low moisture absorption PA particles.

[0007] Furthermore, the special nylon content accounts for 5% to 15% of the mass of the low-hygroscopic PA particles; the sheet-like nanoparticle content accounts for 0.5% to 1% of the mass of the low-hygroscopic PA particles.

[0008] Furthermore, the special nylon is any one or more of PA5652, MXD6, PA6T, and PA9T; the sheet-like nanoparticles are any one or more of montmorillonite, graphene, and alumina; and the catalyst is any one or more of sodium hypophosphite, sodium triphosphate, and sodium polyphosphate.

[0009] In some embodiments, the composite stabilizer is a heat stabilizer and a light stabilizer compounded in a mass fraction ratio of 1:(1~3); the heat stabilizer is a synergistic antioxidant, compounded from a phenolic antioxidant and a phosphite antioxidant in a mass fraction ratio of 1:(0.5~1); the phenolic antioxidant is any one or more of hydroquinone, MIANOX BHT(264), AO-7, and AO-25; the phosphite antioxidant is any one or more of YIPHOS 3010, ZG103, and antioxidant 168; the light stabilizer is a hindered amine light stabilizer; the hindered amine light stabilizer is any one or more of HALS-1, HALS-2, HALS-3, and HALS-4.

[0010] In some embodiments, the capping agent is any one or more of citric acid, ethylene oxide, propylene oxide, propylene isocyanate, p-toluene isocyanate, and o-toluene isocyanate.

[0011] In some embodiments, the anti-yellowing PA particles are obtained by melt extruding the low moisture-absorbing PA particles, composite stabilizer and end-capping agent through a twin-screw extruder at 220°C~265°C, followed by water cooling, pelletizing and drying.

[0012] In some embodiments, the anti-sticking masterbatch comprises, by mass fraction, 3% to 10% of an opening agent, 0.5% to 5% of a slip agent, and 85% to 96.5% of PA6, obtained by melt extrusion at 225°C to 270°C using a twin-screw extruder, followed by water cooling, pelletizing, and drying; the opening agent is any one or more of silica, talc, organosilicon, calcium carbonate, and diatomaceous earth; the slip agent is any one or more of erucamide, oleamide, ethylene bis-stearamide, and PE wax.

[0013] In some embodiments, the other additives are any one or more of the following: catalyst, crosslinking agent, compatibilizer, toughening agent, flame retardant, and antistatic agent.

[0014] This invention also provides a method for preparing the BOPA film with anti-yellowing, low moisture absorption, and high dimensional stability as described above, comprising the following steps: S201. Weigh the raw materials for the first surface layer, core layer and second surface layer according to the mass fraction, and dry them until the moisture content of the raw materials is ≤600ppm. S202. The raw materials of the first surface layer, the core layer and the second surface layer are respectively fed into extruder 1, extruder 2 and extruder 3, and melted and plasticized at 230℃~280℃ to obtain cast sheets. S203. The cast sheet is subjected to hot water treatment and synchronous bidirectional stretching is performed using a magnetic levitation linear motor. The stretching temperature is 130℃~200℃ and the stretching ratio is 2.8×2.8~3.4×3.4. S204. The stretched film is subjected to heat setting treatment at a temperature of 160℃~210℃ for a time of 5s~30s. S205. At least one side of the shaped film is subjected to corona treatment, with a corona treatment power of 5 W / min / m. 2 ~18Wmin / m 2 The film is then wound up and slit to obtain the anti-yellowing, low moisture absorption, and high dimensional stability BOPA film.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention relates to a BOPA film with anti-yellowing properties, low moisture absorption, and high dimensional stability. Without sacrificing the original core performance of BOPA films, it achieves a comprehensive improvement in low moisture absorption, anti-yellowing properties, and high dimensional stability. The film employs a three-layer structure design, using anti-yellowing PA particles as the core raw material. It is composed of low-moisture-absorbing PA particles, a composite stabilizer, and a capping agent, formed through pre-extrusion granulation. This ensures uniform dispersion of the additives, avoids interference from powdered additives in processing, and constructs a highly efficient functional protective system. The low-moisture-absorbing PA particles are prepared through intercalation solid-phase polymerization of PA6 with special nylon and sheet-like nanoparticles. The introduction of special nylon improves the polymer's density and thermal stability, while the sheet-like nanoparticles further optimize barrier properties. The synergistic effect of these two components significantly reduces the film's moisture absorption rate, effectively improving dimensional fluctuations in high-humidity environments and avoiding defects such as wrinkling and misregistration during processing.

[0016] In terms of anti-yellowing performance, the composite stabilizer uses a precise combination of heat stabilizer and light stabilizer. The heat stabilizer is a synergistic combination of phenolic antioxidant and phosphite antioxidant, which can effectively inhibit thermal oxidative degradation. The light stabilizer slows down photo-induced degradation. Together with the end-capping agent, it blocks the active groups of the polyamide molecular chain, forming all-round protection, which greatly improves the film's resistance to yellowing and avoids the deterioration of appearance and performance caused by environmental factors during use.

[0017] Furthermore, the anti-sticking masterbatch added to the surface optimizes the film's processing adaptability and ease of use. Combined with processes such as synchronous bidirectional stretching using a magnetic levitation linear motor, precise heat setting, and corona treatment, the film maintains excellent mechanical strength and optical transparency while improving its low moisture absorption and anti-yellowing properties. Overall process parameters are controllable, product quality is stable, and no additional complex equipment is required. It can be widely used in flexible packaging for food, daily necessities, and electronics, and is particularly suitable for harsh environments such as high-temperature retorting and high-humidity storage, effectively expanding the application range of BOPA film. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the anti-yellowing, low moisture absorption, and high dimensional stability BOPA film structure provided in Embodiment 1 of the present invention.

[0020] Figure label: 10 - First surface layer; 20 - Core layer; 30 - Second surface layer. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] In the description of this invention, it should be noted that the terms "upper", "lower", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0023] The method for preparing the anti-yellowing, low moisture absorption, and high dimensional stability BOPA film provided by this invention is as follows: (1) Preparation of low hygroscopic PA particles S101. Add deionized water to the reactor, and add the corresponding diacid and diamine of special nylon at a molar ratio of 1:1 while stirring at 50℃~70℃. Stir and react for 1 hour, adjust the pH value to 7.0~7.6, and continue to react for 1 hour~3 hours to obtain a clear and transparent special nylon salt solution. After cooling, filtration and drying, obtain white special nylon salt powder. The amount of deionized water added is 30%~40% of the system mass. S102. Disperse caprolactam and 0.5%~1% of low hygroscopic PA particles in deionized water, and stir and sonicate at 80℃~90℃ for 8h~12h to obtain caprolactam / sheet nanoparticle suspension. S103. The special nylon salt obtained in step S101, the caprolactam / sheet nanoparticle suspension obtained in step S102, and 0.01%~0.2% by mass of catalyst are added to the reaction vessel and mixed. The reaction vessel is evacuated, and stirring and heating are started under a high-purity nitrogen atmosphere of 0.1MPa. After the temperature is raised to 210℃~260℃, the reaction is maintained at 2.2MPa~2.4MPa for 3h~5h. S104. After the reaction is complete, the gas is uniformly released to normal pressure, and then the temperature is raised to 260℃~350℃. After polycondensation for 3h~13h, nitrogen gas is introduced to purge back pressure, and the material is cooled and discharged to obtain PA6-co-special nylon / sheet nanoparticle polymer. S105. Extract the PA6-co-special nylon / sheet nanoparticle polymer obtained in step S104 with pure water, then granulate and dry to obtain the low moisture absorption PA particles.

[0024] (2) Preparation of anti-yellowing PA particles By mass fraction, 95.4%~99.9% of low moisture-absorbing PA particles, 0.05%~3.4% of composite stabilizer and 0.05%~1.2% of end-capping agent are added to a twin-screw extruder, melt-extruded into strands at 220℃~265℃, cooled with water, pelletized and dried to obtain the anti-yellowing PA particles.

[0025] (3) Preparation of BOPA film with anti-yellowing, low moisture absorption and high dimensional stability S201. Weigh the raw materials for the first surface layer, core layer, and second surface layer according to their mass fractions, and dry them until the moisture content of the raw materials is ≤600ppm; wherein, the raw materials for the first surface layer and the second surface layer include 90%~97.5% anti-yellowing PA particles, 2%~7% anti-sticking masterbatch, and 0.5%~3% other additives, and the raw materials for the core layer include 97%~99.5% anti-yellowing PA particles and 0.5%~3% other additives; S202. The raw materials of the first surface layer, the core layer and the second surface layer are respectively fed into extruder 1, extruder 2 and extruder 3, and melted and plasticized at 230℃~280℃ to obtain cast sheets. S203. The cast sheet is subjected to hot water treatment and synchronous bidirectional stretching is performed using a magnetic levitation linear motor. The stretching temperature is 130℃~200℃ and the stretching ratio is 2.8×2.8~3.4×3.4. S204. The stretched film is subjected to heat setting treatment at a temperature of 160℃~210℃ for a time of 5s~30s. S205. At least one side of the shaped film is subjected to corona treatment, with a corona treatment power of 5 W / min / m. 2 ~18Wmin / m 2 The film is then wound up and slit to obtain the anti-yellowing, low moisture absorption, and high dimensional stability BOPA film.

[0026] Example 1 This embodiment provides a BOPA film with anti-yellowing properties, low moisture absorption, and high dimensional stability. (See attached document.) Figure 1 As shown, its film structure includes a first surface layer 10, a core layer 20, and a second surface layer 30 arranged sequentially from bottom to top, and is prepared by the following steps: (1) Preparation of low hygroscopic PA particles S101. Add 40% of the system mass of deionized water to the reactor. Add terephthalic acid and hexamethylenediamine at a molar ratio of 1:1 at 70°C while stirring. Stir and react for 1 hour. Adjust the pH value to about 7.2 and continue to react for 3 hours to obtain a clear and transparent PA6T salt solution. After cooling, filtration and drying, obtain white PA6T salt powder. S102. Caprolactam and 0.5% of low-hygroscopic PA particles were dispersed in deionized water and stirred and sonicated at 90°C for 10 hours to obtain a caprolactam / montmorillonite suspension. S103. Add the PA6T salt obtained in step S101, the caprolactam / montmorillonite suspension obtained in step S102, and 0.05% sodium hypophosphite by mass into the reactor and mix. Vacuum the reactor and start stirring and heating under a high-purity nitrogen atmosphere of 0.1 MPa. After the temperature is raised to 250°C, keep the temperature and pressure at 2.3 MPa for 3 hours. S104. After the reaction is complete, the gas is uniformly released to normal pressure, then the temperature is raised to 350℃, and after condensation for 10 hours, nitrogen gas is introduced to purge back the pressure, and the material is cooled and discharged to obtain PA6-co-PA6T / montmorillonite polymer. S105. Extract the PA6-co-PA6T / montmorillonite polymer obtained in step S104 with pure water, then granulate and dry to obtain low hygroscopic PA particles with a PA6T content of 10% and a montmorillonite content of 0.5%.

[0027] (2) Preparation of anti-yellowing PA particles By mass fraction, 98.90% of low moisture-absorbing PA particles, 1.05% of composite stabilizer and 0.05% of end-capping agent are added to a twin-screw extruder, melt-extruded into strands at 220℃~265℃, cooled with water, pelletized and dried to obtain the anti-yellowing PA particles.

[0028] (3) Preparation of BOPA film with anti-yellowing, low moisture absorption and high dimensional stability S201. Weigh the raw materials for the first surface layer, core layer, and second surface layer according to their mass fractions, and dry them until the moisture content of the raw materials is ≤600ppm; wherein, the raw materials for the first surface layer and the second surface layer include 94.5% anti-yellowing PA particles, 5% anti-sticking masterbatch, and 0.5% other additives, and the raw materials for the core layer include 99.5% anti-yellowing PA particles and 0.5% other additives; S202. The raw materials of the first surface layer, the core layer and the second surface layer are respectively fed into extruder 1, extruder 2 and extruder 3, and melted and plasticized at 230℃~280℃ to obtain cast sheets. S203. The cast sheet is treated with hot water and then synchronously stretched in both directions using a magnetic levitation linear motor. The stretching temperature is 140℃ and the stretching ratio is 3.3×3.3. S204. The stretched film is subjected to heat setting treatment at a temperature of 180℃ for 5 seconds. S205. At least one side of the shaped film is subjected to corona treatment, with a corona treatment power of 8 W / min / m. 2 The film is then wound up and slit to obtain the anti-yellowing, low moisture absorption, and high dimensional stability BOPA film.

[0029] In this embodiment, preferably, the composite stabilizer is a heat stabilizer and a light stabilizer compounded in a mass fraction ratio of 1:1; more preferably, the heat stabilizer is AO-7 compounded with antioxidant 168 in a mass fraction ratio of 1:0.5, and the light stabilizer is HALS-1.

[0030] In this embodiment, preferably, the capping agent is citric acid.

[0031] In this embodiment, preferably, the anti-sticking masterbatch is prepared by melt extrusion of 6.5% opening agent, 1% slip agent and 92.5% PA6 in a twin-screw extruder at 225°C to 270°C, followed by water cooling, pelletizing and drying; more preferably, the opening agent is silica and the slip agent is a combination of erucamide and ethylene bis-stearamide.

[0032] In this embodiment, preferably, the other additives include compatibilizers and antistatic agents.

[0033] Example 2 This embodiment provides a BOPA film with anti-yellowing properties, low moisture absorption, and high dimensional stability. The difference from Embodiment 1 of this invention is that the anti-yellowing PA particles are obtained by melt extrusion of 98.33% low moisture absorption PA particles, 1.59% composite stabilizer, and 0.08% end-capping agent using a twin-screw extruder at 220℃~265℃, followed by water cooling, pelletizing, and drying. The selection of other raw materials, component ratios, preparation steps, process parameters, and film thickness are the same as in Embodiment 1 of this invention.

[0034] Example 3 This embodiment provides a BOPA film with anti-yellowing properties, low moisture absorption, and high dimensional stability. The difference from Embodiment 1 of this invention is that the anti-yellowing PA particles are obtained by melt extrusion of 95.77% low moisture absorption PA particles, 3.17% composite stabilizer, and 1.06% end-capping agent using a twin-screw extruder at 220℃~265℃, followed by water cooling, pelletizing, and drying. The selection of other raw materials, component ratios, preparation steps, process parameters, and film thickness are the same as in Embodiment 1 of this invention.

[0035] The present invention also provides the following comparative examples: Comparative Example 1 This comparative example provides a BOPA film, which differs from Example 1 of the present invention in that the anti-yellowing PA particles are replaced with an equal amount of PA6. That is, the first and second surface layers consist of 94.5% PA6, 5% anti-sticking masterbatch, and 0.5% other additives, while the core layer consists of 99.5% PA6 and 0.5% other additives. The selection of other raw materials, component ratios, preparation steps, process parameters, and film thickness are the same as in Example 1 of the present invention.

[0036] Comparative Example 2 This comparative example provides a BOPA film, which differs from Example 1 of the present invention in that the anti-yellowing PA particles are replaced with an equal amount of low-moisture-absorbing PA particles. Specifically, the first and second surface layers consist of 94.5% low-moisture-absorbing PA particles, 5% anti-sticking masterbatch, and 0.5% other additives, while the core layer consists of 99.5% low-moisture-absorbing PA particles and 0.5% other additives. The selection of other raw materials, component ratios, preparation steps, process parameters, and film thickness are the same as in Example 1 of the present invention.

[0037] Comparative Example 3 This comparative example provides a BOPA film, which differs from Example 1 of the present invention in that: in preparing the anti-yellowing PA particles, 0.05% of the capping agent is replaced with an equal amount of low-moisture-absorbing PA particles, that is, the anti-yellowing PA particles are composed of 98.95% low-moisture-absorbing PA particles and 1.05% composite stabilizer. The selection of other raw materials, component ratios, preparation steps, process parameters, and film thickness are the same as in Example 1 of the present invention.

[0038] Comparative Example 4 This comparative example provides a BOPA film, which differs from Example 1 of the present invention in that: in preparing the anti-yellowing PA particles, 1.05% of the composite stabilizer is replaced with an equal amount of low-moisture-absorbing PA particles, that is, the anti-yellowing PA particles are composed of 99.95% low-moisture-absorbing PA particles and 0.05% composite stabilizer. The selection of other raw materials, component ratios, preparation steps, process parameters, and film thickness are the same as in Example 1 of the present invention.

[0039] Comparative Example 5 This comparative example provides a BOPA film, which differs from Example 1 of the present invention in that: when preparing the anti-yellowing PA particles, the amount of low-hygroscopic PA particles added is 91.79%, the amount of composite stabilizer added is 5.13%, and the amount of capping agent added is 3.08%. The selection of other raw materials, component ratios, preparation steps, process parameters, and film thickness are the same as in Example 1 of the present invention.

[0040] The BOPA films prepared in the examples and comparative examples were subjected to the following performance tests, and the results are summarized in Table 1: (1) Tensile strength and elongation at break test: The test shall be conducted in accordance with GB / T 1040-3 Determination of tensile properties of plastics Part 3: Test conditions for thin plastics and sheets; (2) Film haze test: The test shall be conducted in accordance with ASTM D1003 Test method for haze and transmittance of transparent plastics; (3) Water absorption rate test: After conditioning in air at 25℃ and 55% humidity for 48h, the saturated water absorption size change rate and water absorption size change rate of the sample with the same size (length × width × thickness: 5cm × 5cm × 15μm) were tested. (4) Anti-yellowing test: The color difference value after thermal accelerated aging is evaluated, wherein the thermal accelerated aging conditions are 180℃ oven for 2 hours.

[0041] Table 1. Performance test results of BOPA films prepared in the embodiments and comparative examples of the present invention.

[0042] As can be clearly seen from the data in Table 1, the BOPA films prepared in Examples 1-3 possess the advantages of low moisture absorption, anti-yellowing, and high dimensional stability, while also maintaining excellent overall performance, with a saturated water absorption dimensional change rate of only 0.12%~0.17% and a water absorption rate of 0.0051%·min. -1 ~0.0052%·min -1 The anti-yellowing color difference is 2.8~3.9, the tensile strength MD is 229MPa~235MPa and TD is 251MPa~255MPa, the elongation at break MD is 109%~112% and TD is 104%~106%, and the haze is 2.9%~3.0%, achieving a synergistic balance between low moisture absorption, anti-yellowing and mechanical and optical properties.

[0043] Comparative Example 1 uses ordinary PA6 instead of anti-yellowing PA particles, without low hygroscopic modification and anti-yellowing components, and has a saturated water absorption size change rate as high as 2.6% and a water absorption rate of 0.0583%·min. -1 The color difference in anti-yellowing was 20.1, indicating that the moisture absorption and anti-yellowing properties were completely lost, confirming that the anti-yellowing PA particles are the key carriers of the core function of the film.

[0044] Comparative Example 2 replaced the anti-yellowing PA particles with low-hygroscopic PA particles, which only solved the moisture absorption problem of the film. However, due to the lack of composite stabilizer and end-capping agent, the anti-yellowing color difference value reached 11.8, which was much worse than the example. This shows that composite stabilizer and end-capping agent are the core guarantee of anti-yellowing performance, and low-hygroscopic modification alone cannot meet the anti-yellowing requirements.

[0045] In Comparative Example 3, no end-capping agent was added when preparing anti-yellowing PA particles. The anti-yellowing color difference value was 4.5, which was slightly higher than 3.9 in Example 1. The moisture absorption performance did not fluctuate significantly, indicating that although the end-capping agent is not the dominant factor in moisture absorption performance, it can help improve the anti-yellowing effect. The anti-yellowing ability decreased slightly after its absence.

[0046] In Comparative Example 4, no composite stabilizer was added when preparing anti-yellowing PA particles. The anti-yellowing color difference value was 4.8, and the anti-yellowing effect was significantly weaker than that of the example. This verifies that the composite stabilizer is the core component for inhibiting film yellowing, and without it, the efficient anti-yellowing function cannot be achieved.

[0047] In Comparative Example 5, the proportion of low-hygroscopic PA particles in the anti-yellowing PA particles was lower than the specified range, and the composite stabilizer and end-capping agent were excessive, resulting in a significant decrease in tensile strength and elongation at break, an increase in haze to 4.5%, and a saturated water absorption size change rate and rate that were inferior to those of the Example, leading to an imbalance in overall performance.

[0048] Although this article uses a lot of terms such as first surface layer, core layer, second surface layer, PA6, special nylon, PA5652, MXD6, PA6T, PA9T, sheet nanoparticles, montmorillonite, graphene, alumina, sodium hypophosphite, sodium triphosphate, sodium polyphosphate, phenolic antioxidants, phosphite antioxidants, hydroquinone, MIANOX BHT(264), AO-7, AO-25, YIPHOS 3010, ZG103, Antioxidant 168, Hindered Amine Light Stabilizer, HALS-1, HALS-2, HALS-3, HALS-4, Composite Stabilizer, Heat Stabilizer, Light Stabilizer, Synergistic Antioxidant, End-capping Agent, Citric Acid, Ethylene Oxide, Propylene Oxide, Propylene Isocyanate, p-Toluene Isocyanate, o-Toluene Isocyanate, Anti-sticking Masterbatch, Opening Agent, Silica, Talc, Organosilicon, Calcium Carbonate, Diatomaceous Earth, Slip Agent, Erucamide, Oleamide, Ethylene Bis-Stearamide, PE Wax, Other Additives, Catalyst, Crosslinking Agent, Compatibilizer, Toughening Agent, Flame Retardant, Antistatic Agent, Low Moisture Absorption PA Particles, Anti-Yellowing PA Particles, PA6-co-Special Nylon / Sheet Nanoparticle Polymer, BOPA Film, Biaxially Stretched Nylon Film, Deionized Water, Caprolactam, Diacid, Diamine, Special Nylon Salt Solution, Special Nylon The terms used include salt powder, caprolactam / flaky nanoparticle suspension, twin-screw extruder, reactor, magnetic levitation linear motor, mass fraction, water content, stretching temperature, stretching ratio, setting temperature, setting time, corona treatment power, holding pressure, polycondensation time, pH value, moisture absorption, dimensional stability, yellowing degree, haze, tensile strength, elongation at break, saturated water absorption dimensional change rate, water absorption dimensional change rate, color difference value, intercalation solid-phase polymerization, melt extrusion, strand drawing, water cooling, pelletizing, drying, melt plasticizing extrusion, casting, hot water treatment, simultaneous biaxial stretching, heat setting treatment, corona treatment, winding, slitting, vacuuming, heating, heat holding and pressure holding reaction, venting, polycondensation, nitrogen purging back pressure, cooling and discharging, pure water extraction, stirring, ultrasonication, pH adjustment, filtration, drying, weighing, etc., but the possibility of using other terms is not excluded. The use of these terms is merely for the convenience of describing and explaining the nature of the invention; interpreting them as any additional limitation would be contrary to the spirit of the invention.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A BOPA film with anti-yellowing, low moisture absorption, and high dimensional stability, characterized in that: The membrane structure includes a first surface layer (10), a core layer (20), and a second surface layer (30) arranged sequentially from bottom to top. By mass fraction, the first surface layer (10) and the second surface layer (30) comprise 90% to 97.5% anti-yellowing PA particles, 2% to 7% anti-sticking masterbatch, and 0.5% to 3% other additives; the core layer (20) comprises 97% to 99.5% anti-yellowing PA particles and 0.5% to 3% other additives. The anti-yellowing PA particles consist of 95.4% to 99.9% low-hygroscopic PA particles, 0.05% to 3.4% composite stabilizer, and 0.05% to 1.2% end-capping agent.

2. The BOPA film with anti-yellowing, low moisture absorption, and high dimensional stability according to claim 1, characterized in that: The low-hygroscopic PA particles are PA6-co-specialty nylon / sheet nanoparticles prepared by intercalation solid-state polymerization of PA6, special nylon, and sheet nanoparticles, including the following steps: S101. Add deionized water to the reactor, and add the diacid and diamine corresponding to the special nylon at a molar ratio of 1:1 at 50℃~70℃ while stirring. Stir and react for 1 hour, adjust the pH value to 7.0~7.6, and continue to react for 1 hour~3 hours to obtain a clear and transparent special nylon salt solution. Then, cool, filter and dry to obtain white special nylon salt powder. S102. Caprolactam and sheet nanoparticles are dispersed in deionized water and stirred and sonicated at 80℃~90℃ for 8h~12h to obtain caprolactam / sheet nanoparticle suspension. S103. The special nylon salt obtained in step S101, the caprolactam / sheet nanoparticle suspension obtained in step S102, and 0.01%~0.2% by mass of catalyst are added to the reaction vessel and mixed. The reaction vessel is evacuated, and stirring and heating are started under a high-purity nitrogen atmosphere of 0.1MPa. After the temperature is raised to 210℃~260℃, the reaction is maintained at 2.2MPa~2.4MPa for 3h~5h. S104. After the reaction is complete, the gas is uniformly released to normal pressure, and then the temperature is raised to 260℃~350℃. After polycondensation for 3h~13h, nitrogen gas is introduced to purge back pressure, and the material is cooled and discharged to obtain PA6-co-special nylon / sheet nanoparticle polymer. S105. Extract the PA6-co-special nylon / sheet nanoparticle polymer obtained in step S104 with pure water, then granulate and dry to obtain the low moisture absorption PA particles.

3. The BOPA film with anti-yellowing, low moisture absorption, and high dimensional stability according to claim 2, characterized in that: The special nylon content accounts for 5% to 15% of the mass of the low-hygroscopic PA particles; the sheet-like nanoparticle content accounts for 0.5% to 1% of the mass of the low-hygroscopic PA particles.

4. The BOPA film with anti-yellowing, low moisture absorption, and high dimensional stability according to claim 2, characterized in that: The special nylon is any one or more of PA5652, MXD6, PA6T, and PA9T; the sheet-like nanoparticles are any one or more of montmorillonite, graphene, and alumina; and the catalyst is any one or more of sodium hypophosphite, sodium triphosphate, and sodium polyphosphate.

5. The BOPA film with anti-yellowing, low moisture absorption, and high dimensional stability according to claim 1, characterized in that: The composite stabilizer is a mixture of a heat stabilizer and a light stabilizer in a mass fraction ratio of 1:(1~3); The heat stabilizer is a synergistic antioxidant, which is a compound of phenolic antioxidant and phosphite antioxidant in a ratio of 1:(0.5~1); the phenolic antioxidant is any one or more of hydroquinone, MIANOX BHT(264), AO-7, and AO-25; the phosphite antioxidant is any one or more of YIPHOS 3010, ZG103, and antioxidant 168. The light stabilizer is a hindered amine light stabilizer; the hindered amine light stabilizer is any one or more of HALS-1, HALS-2, HALS-3, and HALS-4.

6. The BOPA film with anti-yellowing, low moisture absorption, and high dimensional stability according to claim 1, characterized in that: The capping agent is any one or more of citric acid, ethylene oxide, propylene oxide, propylene isocyanate, p-toluene isocyanate, and o-toluene isocyanate.

7. The BOPA film with anti-yellowing, low moisture absorption, and high dimensional stability according to claim 1, characterized in that: The anti-yellowing PA particles are obtained by melt extruding the low moisture-absorbing PA particles, composite stabilizer and end-capping agent through a twin-screw extruder at 220℃~265℃, followed by water cooling, pelletizing and drying.

8. The BOPA film with anti-yellowing, low moisture absorption, and high dimensional stability according to claim 1, characterized in that: The anti-sticking masterbatch comprises, by mass fraction, 3% to 10% of an opening agent, 0.5% to 5% of a slip agent and 85% to 96.5% of PA6. It is obtained by melt extrusion of the masterbatch into strands at 225°C to 270°C using a twin-screw extruder, followed by water cooling, pelletizing, and drying. The opening agent is any one or more of silica, talc, organosilicon, calcium carbonate, and diatomaceous earth. The slip agent is any one or more of erucamide, oleamide, ethylene bis-stearamide, and PE wax.

9. The BOPA film with anti-yellowing, low moisture absorption, and high dimensional stability according to claim 1, characterized in that: The other additives are any one or more of the following: catalysts, crosslinking agents, compatibilizers, toughening agents, flame retardants, and antistatic agents.

10. A method for preparing a BOPA film with anti-yellowing, low moisture absorption, and high dimensional stability as described in any one of claims 1 to 9, characterized in that, Includes the following steps: S201. Weigh the raw materials for the first surface layer, core layer and second surface layer according to the mass fraction, and dry them until the moisture content of the raw materials is ≤600ppm. S202. The raw materials of the first surface layer, the core layer and the second surface layer are respectively fed into extruder 1, extruder 2 and extruder 3, and melted and plasticized at 230℃~280℃ to obtain cast sheets. S203. The cast sheet is subjected to hot water treatment and synchronous bidirectional stretching is performed using a magnetic levitation linear motor. The stretching temperature is 130℃~200℃ and the stretching ratio is 2.8×2.8~3.4×3.

4. S204. The stretched film is subjected to heat setting treatment at a temperature of 160℃~210℃ for a time of 5s~30s. S205. At least one side of the shaped film is subjected to corona treatment, with a corona treatment power of 5 W / min / m. 2 ~18Wmin / m 2 The film is then wound up and slit to obtain the anti-yellowing, low moisture absorption, and high dimensional stability BOPA film.

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