Heat-resistant blister packaging box and preparation method thereof

Abstract

The application belongs to the technical field of high polymer materials, and particularly relates to a heat-resistant blister packaging box and a preparation method thereof. According to weight parts, the heat-resistant blister packaging box comprises the following raw materials: 100 parts of polylactic acid, 4-8 parts of heat-resistant stabilizer, 1-3 parts of nucleating agent, 0.5-1 parts of chain-extending compatibilizer, 0.1-0.5 parts of antioxidant, and 0.1-0.3 parts of release agent. The application designs a multifunctional heat-resistant stabilizer with an aromatic imide-sulfone-siloxane structure, and constructs a synergistic crystallization system with a phenyl zinc phosphonate nucleating agent, and cooperates with a segmented temperature control rapid heat setting process. The heat distortion temperature of the obtained blister packaging box can reach 93.1 DEG C, the light transmittance is kept above 89.5%, the haze is below 3.5%, the forming cycle is shortened to 6-10 seconds, and there is no small molecule migration risk, so that the industrial production needs of the heat-resistant transparent packaging for food contact are met.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a heat-resistant blister packaging box and its preparation method. Background Technology

[0002] Polylactic acid (PLA) is a bio-based, biodegradable aliphatic polyester made from renewable plant resources (such as corn and cassava starch). Due to its excellent biocompatibility, good mechanical properties, and processing performance, it is considered an ideal material to replace traditional petroleum-based plastics and is widely used in disposable blister packaging boxes, tableware, and food packaging. However, PLA crystallizes extremely slowly under conventional molding processes, with a semi-crystallization time often lasting several minutes to tens of minutes. This results in almost no effective crystallization during rapid cooling processes such as injection molding, casting, and blister molding, leading to products that are typically amorphous with a crystallinity of only 5-10%. This low crystallinity directly causes the heat distortion temperature (HDT) of PLA to generally be below 60°C. When containing hot drinks or soups exceeding 60°C, the packaging easily softens and deforms, severely limiting its application in hot-fill food packaging. At the same time, polylactic acid itself has acceptable light transmittance, but once traditional nucleating agents (such as inorganic particles like talc and zinc phenylphosphonate) are added to increase crystallinity, the product haze increases sharply and becomes opaque or semi-transparent because the crystal size is often larger than the wavelength of visible light (400-700 nm), making it difficult to meet consumers' visual demand for highly transparent packaging.

[0003] To address the aforementioned contradictions, researchers have attempted to promote polylactic acid (PLA) crystallization by adding small organic molecule nucleating agents or crystallization regulators. For example, CN112920574A discloses a highly transparent and heat-resistant PLA material that uses amide compounds (such as ethylene bis-12-hydroxystearamide) as crystallization regulators. Under conditions of compression molding and isothermal crystallization at 90°C for 30-90 seconds, the PLA achieves a crystallinity of 48.6%, a heat distortion temperature (HDT) of 106°C, and a light transmittance of 95%. However, this technology has significant shortcomings: First, to achieve high heat resistance, a relatively long isothermal crystallization time (30-90 s) is required, which severely reduces the efficiency of continuous production processes such as thermoforming and makes it difficult to meet the needs of large-scale industrial production; second, the amide nucleating agent and the polylactic acid matrix are only physically mixed without chemical bonding, and are prone to migrate to the surface of the product under long-term use or high-temperature conditions, which not only affects the appearance and food safety but also leads to a decrease in heat resistance; finally, this technology does not involve the overall structural strength of the finished thermoformed packaging box and cannot be directly applied to the performance evaluation of actual packaging products.

[0004] Furthermore, existing technologies include methods to improve the heat resistance of polylactic acid (PLA) by adding plasticizers, rigid fillers (such as glass fiber and talc), or blending it with other biodegradable materials. However, these methods often come at the cost of transparency or introduce a large number of non-degradable components, thus compromising the material's fully biodegradable properties. Therefore, developing a PLA packaging material that can simultaneously achieve high heat resistance, high transparency, high production efficiency, and good strength under rapid thermoforming conditions (heat setting time <10 s) remains a pressing technical challenge in this field. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a heat-resistant blister packaging box and its preparation method.

[0006] The objective of this invention is achieved through the following technical solution: The first aspect of this invention provides a heat-resistant blister packaging box, comprising the following raw materials in parts by weight: 100 parts polylactic acid, 4-8 parts heat-resistant stabilizer, 1-3 parts nucleating agent, 0.5-1 part chain extender compatibilizer, 0.1-0.5 parts antioxidant, and 0.1-0.3 parts mold release agent; The structural formula of the heat stabilizer is as follows: .

[0007] Furthermore, the preparation process of the heat stabilizer is as follows: (1) Under an inert gas atmosphere, itaconic anhydride and m-phenylenediamine were reacted in acetic acid to obtain intermediate 1; the structural formula of intermediate 1 is as follows: (2) Under an inert gas atmosphere, intermediate 1 and mercaptoacetic acid were reacted in ethanol under the catalysis of triethylamine to obtain intermediate 2; the structural formula of intermediate 2 is as follows: (3) Add intermediate 2 to acetic acid, then add hydrogen peroxide solution to react and obtain intermediate 3; the structural formula of intermediate 3 is as follows: (4) Under the action of a catalyst and a dehydrating agent, intermediate 3 and γ-aminopropyltriethoxysilane are reacted in N,N-dimethylformamide to obtain the heat-resistant stabilizer.

[0008] Further, the molar ratio of m-phenylenediamine and itaconic anhydride in step (1) is 1:(2.1-2.2); the reaction process is as follows: first react at 30-40℃ for 1-1.5 h, then heat to reflux for 5-6 h.

[0009] Further, in step (2), the molar ratio of intermediate 1, triethylamine, and mercaptoacetic acid is 1:(0.1-0.2):(2.1-2.3); the reaction temperature is 45-55 degrees Celsius, and the reaction time is 4-5 h.

[0010] Further, in step (3), the molar ratio of intermediate 2 and hydrogen peroxide is 1:(4.5-5); the reaction temperature is 75-85℃ and the time is 4-6 h.

[0011] Further, the catalyst in step (4) is 4-dimethylaminopyridine; the dehydrating agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride; and the molar ratio of intermediate 3, catalyst, dehydrating agent and γ-aminopropyltriethoxysilane is 1:(0.05-0.1):(2.2-2.4):(2.1-2.2).

[0012] Furthermore, the reaction in step (4) is carried out at a temperature of 25-35°C for 12-16 h.

[0013] Further, the nucleating agent is zinc phenylphosphonate; the chain extender compatibilizer is epoxidized soybean oil or styrene-glycidyl acrylate copolymer ADR; the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a 1:1 mass ratio; and the release agent is stearamide.

[0014] The second aspect of the present invention provides a method for preparing the above-mentioned heat-resistant blister packaging box, wherein the raw materials are mixed and granulated to form a sheet, and the sheet is obtained by blister forming and cutting.

[0015] The present invention has the following advantages over the prior art: 1. This invention designs a multifunctional heat-resistant stabilizer with an aromatic imide-sulfonyl-siloxane structure by using itaconic anhydride as the starting material and modifying it through dehydration, ring closure, mercapto addition, oxidation, and silanization. It is combined with a highly efficient nucleating agent to construct a synergistic crystallization system and combined with segmented temperature-controlled casting and vacuum forming processes, so that polylactic acid materials can achieve high heat resistance, high rigidity, and dimensional stability while maintaining high transparency. This invention systematically solves the defects of conventional polylactic acid vacuum forming products from three levels: molecular structure, crystallization behavior, and processing technology.

[0016] 2. The heat stabilizer molecule of this invention integrates three functional units simultaneously: the aromatic imide rigid core can form a composite nucleation center with zinc phenylphosphonate through hydrogen bonding and π-π stacking, which can induce polylactic acid to form uniform microcrystals with a size much smaller than the wavelength of visible light during the extremely short (6-10 s) rapid heat setting process, thus ensuring high crystallinity and avoiding light scattering; the sulfone polar heat stabilizing center can effectively restrict the thermal motion of polylactic acid molecular chains, further increasing the heat distortion temperature; and the organosilicon side chain chemically bonds with the polylactic acid matrix through the mediation of chain extender compatibilizer, constructing a stable local cross-linked network, which not only enhances the creep resistance of the material and the overall compressive strength of the finished product, but also fundamentally solves the problem of easy migration and precipitation of small molecule additives during long-term use.

[0017] 3. Experimental data show that, with only a small amount of heat-resistant stabilizer and nucleating agent added, the heat distortion temperature (0.45 MPa) of the resulting blister packaging box can reach 93.1℃, the light transmittance remains above 89.5%, and the haze is below 3.5%, which is far superior to the formulation without heat-resistant stabilizer and also significantly superior to the comparative formulation using existing amide nucleating agents. Furthermore, while maintaining high light transmittance and lower haze, this invention also shortens the blister forming cycle to the level of several seconds (6-10 s), and the overall compressive strength of the finished product is significantly improved compared to the formulation without stabilizer, meeting the comprehensive needs of the food packaging industry for heat resistance, transparency, and efficient production. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the synthesis process of the heat-resistant stabilizer of the present invention. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to specific embodiments. However, those skilled in the art should understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the reagents or instruments used are all conventional products obtained through commercial channels.

[0020] In the following examples and comparative examples, the number average molecular weight of polylactic acid is 80,000-100,000; the nucleating agent is zinc phenylphosphonate; the chain extender compatibilizer is epoxidized soybean oil with an epoxy value of 6.0-6.5%; the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a 1:1 mass ratio; and the release agent is stearamide.

[0021] Example 1 A heat stabilizer, the preparation process of which is as follows: Figure 1 As shown, the specific steps are as follows: (1) Itaconic anhydride (21 mmol) was added to glacial acetic acid (65 mL), cooled to 12 °C under nitrogen protection, and m-phenylenediamine (10 mmol) was added in portions. After the addition was complete, the temperature was raised to 35 °C and stirred for 1.2 h. Then the mixture was heated to reflux and reacted for 5.5 h to dehydrate and close the ring. After the reaction solution was cooled to room temperature, it was poured into ice water to precipitate the solid. The solid was filtered, washed three times with water, dried, and recrystallized with anhydrous ethanol to obtain intermediate 1 with a yield of about 92.3%. 1 H NMR (C 16 H 12 N2O4, 400 MHz, DMSO): δ7.57 (s, 1H), 7.45 (t, 1H), 7.30 (d, 2H), 6.40 (s, 2H), 6.06 (s, 2H), 3.21(s, 4H); HRMS(ESI + [M] Calculation yields 296.08, and the value is found to be 296.07.

[0022] (2) Intermediate 1 (10 mmol) and triethylamine (1.5 mmol) were added to anhydrous ethanol (100 mL) and stirred until homogeneous. Under a nitrogen atmosphere and at 25 °C, 22 mmol of mercaptoacetic acid was added dropwise. After the addition was complete, the mixture was heated to 50 °C and stirred continuously for 4.5 h. After the reaction was completed, some of the solvent was removed under reduced pressure, deionized water was added, and the pH was adjusted to 3.5 with 5 wt% dilute hydrochloric acid. The solid precipitated, filtered, washed and dried, and recrystallized with a methanol / water mixed solvent (volume ratio 3:1) to obtain intermediate 2 with a yield of approximately 89.4%. 1 H NMR (C 20 H 20 N2O8S2, 400 MHz, DMSO): δ 12.30 (s, 2H), 7.53 (s, 1H), 7.41 (t,1H), 7.26 (d, 2H), 3.27 (s, 4H), 3.09-3.04 (m, 2H), 2.92-2.87 (m, 4H), 2.58-2.53 (m, 4H); HRMS(ESI + ): [M] Calculation yields 480.07, and the value found is 480.08.

[0023] (3) Add intermediate 2 (10 mmol) to glacial acetic acid (80 mL), heat to 55 °C, and slowly add 30% hydrogen peroxide (47 mmol) solution. After the addition is complete, heat to 80 °C and stir for 5 h. After the reaction is complete, slowly pour the solution into ice water, and a large amount of white solid precipitates. Filter, wash with deionized water until the filtrate is neutral, dry, and recrystallize with methanol / water mixed solvent (volume ratio 4:1) to obtain intermediate 3 with a yield of about 86.2%. 1 H NMR (C 20 H 20 N2O 12 S2, 400 MHz, DMSO): δ 12.37 (s, 2H), 7.60 (s, 1H), 7.49 (t, 1H), 7.34 (d, 2H), 3.92 (s, 4H), 3.55-3.50(m, 2H), 3.32-3.27(m, 2H), 2.98-2.94 (m,2H), 2.74-2.70 (m, 2H), 2.66-2.62 (m, 2H); HRMS(ESI + [M] Calculation yields 544.05, and the value found is 544.06.

[0024] (4) Intermediate 3 (10 mmol) was added to anhydrous N,N-dimethylformamide (DMF, 100 mL), and catalyst 4-dimethylaminopyridine (DMAP, 0.8 mmol) and dehydrating agent 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC•HCl, 23 mmol) were added. The mixture was cooled to 2 °C, and γ-aminopropyltriethoxysilane (KH-550, 21.5 mmol) was added dropwise. After the addition was complete, the mixture was stirred at 30 °C for 14 h. After the reaction was completed, the reaction solution was poured into a large amount of ethyl acetate to precipitate the product. The product was filtered, washed twice with anhydrous ethanol, and dried to obtain the crude product. The crude product was dissolved in a small amount of tetrahydrofuran and slowly added dropwise to n-hexane for precipitation. The product was filtered and dried under reduced pressure at 45 °C to obtain the final heat-resistant stabilizer with a yield of approximately 82.7%. 1 H NMR (C 38 H 62 N4O 16S2Si2, 400 MHz, DMSO): δ 7.98 (s, 2H), 7.57 (s, 1H), 7.45 (t,1H), 7.30 (d, 2H), 4.05 (s, 4H), 3.86-3.82(m, 14H), 3.62-3.58(m, 2H), 3.45-3.41 (t, 4H), 2.88-2.87 (m, 2H), 2.74-2.70 (m, 2H), 2.63-2.62 (m, 2H), 1.62-1.57 (m, 4H), 1.21 (t, 18H), 0.62 (t, 4H) ; HRMS(ESI + ): [M+H] + The calculation yields 951.31, and the result is 951.32.

[0025] Example 2 A heat stabilizer, the preparation process of which is as follows: Figure 1 As shown, the specific steps are as follows: (1) Add itaconic anhydride (22 mmol) to glacial acetic acid (70 mL), cool to 15 °C under nitrogen protection, add m-phenylenediamine (10 mmol) in portions, and after the addition is complete, heat to 40 °C and stir for 1 h; then heat to 120 °C and reflux for 5 h to carry out dehydration and ring closure; after the reaction solution is cooled to room temperature, pour it into ice water to precipitate solid, filter, wash three times with water, dry and recrystallize with anhydrous ethanol to obtain intermediate 1, with a yield of about 91.5%.

[0026] (2) Intermediate 1 (10 mmol) and triethylamine (2 mmol) were added to anhydrous ethanol (110 mL) and stirred until homogeneous. Under a nitrogen atmosphere and at 30 °C, 23 mmol of mercaptoacetic acid was added dropwise. After the addition was complete, the mixture was heated to 55 °C and stirred continuously for 4 h. After the reaction was completed, some of the solvent was removed under reduced pressure, deionized water was added, and the pH was adjusted to 4 with 5 wt% dilute hydrochloric acid. The solid precipitated, filtered, washed and dried, and recrystallized with a methanol / water mixed solvent (volume ratio 3:1) to obtain intermediate 2 with a yield of approximately 88.0%.

[0027] (3) Add intermediate 2 (10 mmol) to glacial acetic acid (90 mL), heat to 60 °C, and slowly add 30% hydrogen peroxide (50 mmol) solution. After the addition is complete, heat to 85 °C and stir for 4 h. After the reaction is complete, slowly pour the solution into ice water, and a large amount of white solid precipitates. Filter, wash with deionized water until the filtrate is neutral, dry, and recrystallize with methanol / water mixed solvent (volume ratio 4:1) to obtain intermediate 3 with a yield of about 85.5%.

[0028] (4) Add intermediate 3 (10 mmol) to DMF (110 mL), add catalyst DMAP (1.0 mmol) and dehydrating agent EDC•HCl (24 mmol), cool to 5 °C, and add KH-550 (22 mmol) dropwise. After the addition is complete, stir the reaction at 35 °C for 12 h. After the reaction is complete, pour the reaction solution into a large amount of ethyl acetate to precipitate, filter, wash twice with anhydrous ethanol, and dry to obtain crude product. Dissolve the above crude product in a small amount of tetrahydrofuran, slowly add it to n-hexane to precipitate, filter, and dry under reduced pressure at 50 °C to obtain the final heat-resistant stabilizer with a yield of about 82.0%.

[0029] Example 3 A heat stabilizer, the preparation process of which is as follows: Figure 1 As shown, the specific steps are as follows: (1) Add itaconic anhydride (21 mmol) to glacial acetic acid (60 mL), cool to 10 °C under nitrogen protection, add m-phenylenediamine (10 mmol) in portions, and after the addition is complete, heat to 30 °C and stir for 1.5 h; then heat to 110 °C and reflux for 6 h to carry out dehydration and ring closure; after the reaction solution is cooled to room temperature, pour it into ice water to precipitate solid, filter, wash three times with water, dry and recrystallize with anhydrous ethanol to obtain intermediate 1, with a yield of about 91.0%.

[0030] (2) Intermediate 1 (10 mmol) and triethylamine (1 mmol) were added to anhydrous ethanol (90 mL) and stirred until homogeneous. Under a nitrogen atmosphere and at 25 °C, 21 mmol of mercaptoacetic acid was added dropwise. After the addition was complete, the mixture was heated to 45 °C and stirred continuously for 5 h. After the reaction was completed, some of the solvent was removed under reduced pressure, deionized water was added, and the pH was adjusted to 3 with 5 wt% dilute hydrochloric acid. The solid precipitated, filtered, washed and dried, and recrystallized with a methanol / water mixed solvent (volume ratio 3:1) to obtain intermediate 2 with a yield of approximately 87.6%.

[0031] (3) Add intermediate 2 (10 mmol) to glacial acetic acid (70 mL), heat to 50 °C, and slowly add 30% hydrogen peroxide (45 mmol) solution. After the addition is complete, heat to 75 °C and stir for 6 h. After the reaction is complete, slowly pour the solution into ice water, and a large amount of white solid precipitates. Filter, wash with deionized water until the filtrate is neutral, dry, and recrystallize with methanol / water mixed solvent (volume ratio 4:1) to obtain intermediate 3 with a yield of about 85.1%.

[0032] (4) Add intermediate 3 (10 mmol) to anhydrous dimethylformamide (DMF, 90 mL), add catalyst DMAP (0.5 mmol) and dehydrating agent EDC•HCl (22 mmol), cool to 0 °C, and add KH-550 (21 mmol) dropwise. After the addition is complete, stir the reaction at 25 °C for 16 h. After the reaction is complete, pour the reaction solution into a large amount of ethyl acetate to precipitate, filter, wash twice with anhydrous ethanol, and dry to obtain crude product. Dissolve the above crude product in a small amount of tetrahydrofuran, slowly add it to n-hexane to precipitate, filter, and dry under vacuum at 40 °C to obtain the final heat-resistant stabilizer with a yield of about 81.4%.

[0033] Example 4 A heat-resistant blister packaging box comprises the following raw materials in parts by weight: 100 parts polylactic acid, 6 parts heat-resistant stabilizer of Example 1, 2 parts nucleating agent, 0.7 parts chain extender compatibilizer, 0.3 parts antioxidant, and 0.2 parts release agent.

[0034] This embodiment also provides a method for preparing the above-mentioned heat-resistant blister packaging box, including the following steps: (a) Polylactic acid, heat stabilizer, nucleating agent, chain extender compatibilizer and antioxidant are added to a high-speed mixer and mixed at 700 rpm for 6 min to obtain a mixture; (b) The mixture is added to a twin-screw extruder and extruded to granulate, thereby obtaining modified granules; the temperature of each section of the extruder is set as follows: feeding section 160°C, melting section 180°C, reaction section 200°C, venting section 190°C, and die head 185°C; the screw speed is 250 rpm and the vacuum degree is -0.07 MPa. (c) The modified granules are cast into sheets using a single-screw extruder. The three-roll calendering temperatures are: 75°C for the first roll, 80°C for the second roll, and 60°C for the third roll. The sheets are then heated to 130°C and transferred to a mold at 100°C for positive and negative pressure thermoforming. After heat setting for 8 seconds, the sheets are cooled to below 40°C for demolding and cut to obtain the heat-resistant thermoformed packaging box.

[0035] Example 5 A heat-resistant blister packaging box comprises the following raw materials in parts by weight: 100 parts polylactic acid, 4 parts heat-resistant stabilizer of Example 1, 1 part nucleating agent, 0.5 parts chain extender compatibilizer, 0.1 parts antioxidant, and 0.1 parts release agent.

[0036] This embodiment also provides a method for preparing the above-mentioned heat-resistant blister packaging box, including the following steps: (a) Polylactic acid, heat stabilizer, nucleating agent, chain extender compatibilizer and antioxidant are added to a high-speed mixer and mixed at 600 rpm for 8 min to obtain a mixture; (b) The mixture is added to a twin-screw extruder and extruded to granulate, thereby obtaining modified granules; the temperature of each section of the extruder is set as follows: feeding section 160℃, melting section 180℃, reaction section 195℃, venting section 190℃, and die head 185℃; the screw speed is 200 rpm and the vacuum degree is -0.06 MPa. (c) The modified granules are cast into sheets using a single-screw extruder. The three-roll calendering temperatures are: 75°C for the first roll, 80°C for the second roll, and 60°C for the third roll. The sheets are then heated to 120°C and transferred to a mold at 95°C for positive and negative pressure thermoforming. After heat setting for 10 seconds, the sheets are cooled to below 40°C for demolding and cut to obtain the heat-resistant thermoformed packaging box.

[0037] Example 6 A heat-resistant blister packaging box comprises the following raw materials in parts by weight: 100 parts polylactic acid, 8 parts heat-resistant stabilizer of Example 1, 3 parts nucleating agent, 1 part chain extender compatibilizer, 0.5 parts antioxidant, and 0.3 parts release agent.

[0038] This embodiment also provides a method for preparing the above-mentioned heat-resistant blister packaging box, including the following steps: (a) Polylactic acid, heat stabilizer, nucleating agent, chain extender compatibilizer and antioxidant are added to a high-speed mixer and mixed at 900 rpm for 5 min to obtain a mixture; (b) The mixture is added to a twin-screw extruder and extruded to granulate, thereby obtaining modified granules; the temperature of each section of the extruder is set as follows: feeding section 160℃, melting section 180℃, reaction section 205℃, venting section 190℃, and die head 185℃; the screw speed is 300 rpm and the vacuum degree is -0.08 MPa. (c) The modified granules are cast into sheets using a single-screw extruder. The three-roll calendering temperatures are: 75°C for the first roll, 80°C for the second roll, and 60°C for the third roll. The sheets are then heated to 140°C and transferred to a mold at 105°C for positive and negative pressure thermoforming. After heat setting for 6 seconds, the sheets are cooled to below 40°C for demolding and cut to obtain the heat-resistant thermoformed packaging box.

[0039] Comparative Example 1 Comparative Example 1 is basically the same as Example 4, except that the heat stabilizer is omitted.

[0040] Comparative Example 2 Comparative Example 2 is basically the same as Example 4, except that the heat stabilizer is replaced with N-(2-hydroxyethyl)stearamide.

[0041] Comparative Example 3 Comparative Example 3 is basically the same as Example 4, except that the amount of heat stabilizer added is increased to 10 parts, while the proportions of other raw materials remain unchanged.

[0042] Comparative Example 4 Comparative Example 4 is basically the same as Example 4, except that the nucleating agent is omitted.

[0043] Test case The modified granules obtained in the examples and comparative examples were cast into sheets with a thickness of 0.4 mm for testing crystallinity, light transmittance, haze, and tensile strength. In addition, the modified granules were hot-pressed to prepare standard specimens with a thickness of 4 mm for testing heat distortion temperature and compressive strength.

[0044] Transmittance and haze testing: Refer to GB / T 2410-2008 "Determination of transmittance and haze of transparent plastics" and use a transmittance and haze tester for testing; Tensile strength test: Refer to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", use a universal electronic testing machine, the tensile speed is 50 mm / min, and the specimen is a type I dumbbell strip cut along the casting direction; Heat distortion temperature test: Refer to GB / T 1634.2-2019 "Determination of load distortion temperature of plastics - Part 2: Plastics and hard rubber", use a heat distortion temperature tester, load is 0.45MPa, heating rate is 120℃ / h, sample size is 80mm×10mm×4mm; Crystallinity test: Differential scanning calorimetry (DSC) was used for testing under nitrogen atmosphere, with a heating rate of 10℃ / min and a temperature range of 30~200℃. Compression strength test: Refer to GB / T 1041-2008 "Determination of compressibility of plastics" and use a universal electronic testing machine. The sample is a standard cubic strip of 10mm×10mm×4mm and the compression speed is 2mm / min. The test results are shown in Table 1.

[0045] Table 1 As can be seen from Table 1, the heat distortion temperature of the packaging boxes obtained in the embodiments of the present invention all reach above 88°C, while maintaining a high transparency with a light transmittance of above 89.5% and a haze of below 3.5%, and a compressive strength of above 25.4 MPa, which meets the requirements for use of heat-resistant blister packaging boxes.

[0046] Compared to Example 4, Comparative Example 1, which omitted the heat stabilizer, had a crystallinity of only 23.5% and a heat distortion temperature of 76.4°C. In contrast, Example 4, which added both the heat stabilizer and zinc phenylphosphonate, showed improved crystallinity and heat distortion temperature. In Comparative Example 4, which omitted zinc phenylphosphonate, the crystallinity was only 17.9% and the heat distortion temperature was 68.3°C, which was insufficient to meet the requirements for heat resistance. This indicates that the synergistic effect of the two can significantly improve the crystallization rate and crystallization perfection of polylactic acid.

[0047] Comparative Example 2 uses amide compounds commonly used in existing technologies. Under the same process conditions, the crystallinity is only 30.7%, the heat distortion temperature is 83.1℃, and the haze is as high as 7.8%, which is significantly lower than the comprehensive performance of Example 4 of the present invention. In Comparative Example 3, after increasing the amount of heat stabilizer to 10 parts, the light transmittance decreased to 85.3%, the haze increased to 6.5%, and the mechanical properties and heat distortion temperature decreased. This indicates that excessive addition will lead to agglomeration and phase separation of the additive. Therefore, the addition range of 4-8 parts in the present invention is more reasonable.

[0048] 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. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A heat-resistant blister packaging box, characterized in that, The raw materials include the following parts by weight: 100 parts polylactic acid, 4-8 parts heat stabilizer, 1-3 parts nucleating agent, 0.5-1 part chain extender compatibilizer, 0.1-0.5 parts antioxidant, and 0.1-0.3 parts mold release agent; The structural formula of the heat stabilizer is as follows: 。 2. The heat-resistant blister packaging box according to claim 1, characterized in that, The preparation process of the heat stabilizer is as follows: (1) Under an inert gas atmosphere, itaconic anhydride and m-phenylenediamine were reacted in acetic acid to obtain intermediate 1; the structural formula of intermediate 1 is as follows: (2) Under an inert gas atmosphere, intermediate 1 and mercaptoacetic acid were reacted in ethanol under the catalysis of triethylamine to obtain intermediate 2; the structural formula of intermediate 2 is as follows: (3) Add intermediate 2 to acetic acid, then add hydrogen peroxide solution to react and obtain intermediate 3; the structural formula of intermediate 3 is as follows: (4) Under the action of a catalyst and a dehydrating agent, intermediate 3 and γ-aminopropyltriethoxysilane are reacted in N,N-dimethylformamide to obtain the heat-resistant stabilizer.

3. The heat-resistant blister packaging box according to claim 2, characterized in that, The molar ratio of m-phenylenediamine and itaconic anhydride in step (1) is 1:(2.1-2.2); the reaction process is as follows: first react at 30-40℃ for 1-1.5 h, then heat to reflux for 5-6 h.

4. The heat-resistant blister packaging box according to claim 2, characterized in that, In step (2), the molar ratio of intermediate 1, triethylamine, and mercaptoacetic acid is 1:(0.1-0.2):(2.1-2.3); the reaction temperature is 45-55℃ and the reaction time is 4-5h.

5. The heat-resistant blister packaging box according to claim 2, characterized in that, In step (3), the molar ratio of intermediate 2 and hydrogen peroxide is 1:(4.5-5); the reaction temperature is 75-85℃ and the time is 4-6 h.

6. The heat-resistant blister packaging box according to claim 2, characterized in that, The catalyst in step (4) is 4-dimethylaminopyridine; the dehydrating agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride; the molar ratio of intermediate 3, catalyst, dehydrating agent and γ-aminopropyltriethoxysilane is 1:(0.05-0.1):(2.2-2.4):(2.1-2.2).

7. The heat-resistant blister packaging box according to claim 6, characterized in that, The reaction in step (4) is carried out at a temperature of 25-35℃ for 12-16 h.

8. The heat-resistant blister packaging box according to claim 1, characterized in that, The nucleating agent is zinc phenylphosphonate; the chain extender compatibilizer is epoxidized soybean oil or styrene-glycidyl acrylate copolymer ADR; the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a 1:1 mass ratio; and the release agent is stearamide.

9. A method for preparing a heat-resistant blister packaging box according to any one of claims 1-8, characterized in that, The raw materials are mixed and granulated to form sheets, which are then vacuum-formed and cut to obtain the final product.

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