A composite packaging material for pearl film bubble bags and a method for preparing the same

Abstract

The application discloses a kind of pearlescent film bubble bag polypropylene composite packaging material and preparation method thereof.The material includes modified polypropylene, calcium carbonate, antioxidant and polypropylene wax;Modified polypropylene is obtained by grafting polypropylene with glycidyl methacrylate and 2-(dodecylamino)ethanol melt ring opening.The material can improve the dispersion of calcium carbonate, reduce interface defects and stress concentration, so that the pearlescent film has light-shielding property, toughness, tear resistance and impact resistance.

Description

Technical Field

[0001] This invention relates to the field of pearlescent bubble wrap technology, and in particular to a composite packaging material for pearlescent bubble wrap and its preparation method. Background Technology

[0002] Pearlescent bubble bags are typically composed of a pearlescent film and a bubble film. The pearlescent film generally uses polypropylene as a matrix with added inorganic particles such as calcium carbonate, produced through melt extrusion and biaxial stretching. During biaxial stretching, interfacial debonding occurs between the polypropylene matrix and the calcium carbonate particles, forming micropores around the calcium carbonate particles. The refractive index difference between the micropores and the polypropylene matrix generates light scattering, giving the film a pearlescent effect, high whiteness, and good opacity. Therefore, appropriately increasing the calcium carbonate content can increase the number of micropores formed during stretching, enhancing the optical effect of the pearlescent film and reducing its apparent density.

[0003] However, calcium carbonate is a polar inorganic material, while polypropylene is a non-polar polymer, resulting in poor interfacial compatibility between the two. As the calcium carbonate content increases, calcium carbonate particles tend to agglomerate within the polypropylene matrix, leading to variations in the number and degree of agglomeration in different regions. During subsequent biaxial stretching, calcium carbonate particles in different dispersion states experience varying degrees of interfacial debonding, resulting in uneven micropore size and distribution. Large agglomerates and the resulting excessively large micropores can also become stress concentration points, making the film prone to cracking and damage during stretching or use. Therefore, improving the dispersion of calcium carbonate in the polypropylene matrix to ensure uniform and controllable micropore formation during stretching, thereby maintaining the pearlescent effect while enhancing the mechanical stability of the pearlescent film, is a pressing technical problem that needs to be solved in the current technology. Summary of the Invention

[0004] This invention provides a polypropylene composite packaging material for pearlescent bubble bags, comprising, by weight, 100 parts modified polypropylene, 18-32 parts calcium carbonate, 0.1-0.5 parts antioxidant, and 0.2-1.0 parts polypropylene wax.

[0005] It should be noted that this application uses 100 parts by weight of modified polypropylene as the continuous resin phase. The modified polypropylene not only improves the interfacial compatibility between polypropylene and calcium carbonate and the dispersion uniformity of calcium carbonate, but also helps to improve the material's own stress transmission and energy dissipation capabilities, and improves its toughness, tear resistance and impact resistance. Adding 18 to 32 parts by weight of calcium carbonate can cause moderate interfacial debonding with the polypropylene matrix during biaxial stretching and form uniform micropores, thereby giving the film a pearlescent appearance, light-blocking properties and lower density. If the amount of calcium carbonate is too low, the number of pores will be insufficient, and the pearlescent and light-blocking effects will not be obvious. If the amount is too high, agglomeration, stress concentration and film breakage are likely to occur. Antioxidants are used to inhibit the thermo-oxidative degradation of modified polypropylene during mixing, extrusion and stretching, and maintain melt stability and mechanical properties. Polypropylene wax is used to improve the wetting, pre-dispersion and melt flowability of calcium carbonate mixtures. 0.2 to 1.0 parts by weight can take into account both dispersion and processing performance. If the amount added is too high, it may cause excessive lubrication, weakened interfacial bonding and decreased mechanical properties of the material.

[0006] As a preferred technical solution for polypropylene composite packaging material for pearlescent bubble bags, the modified polypropylene is prepared by a method comprising the following steps: mixing glycidyl methacrylate-grafted polypropylene with 2-(dodecylamino)ethanol and then performing melt blending, so that the secondary amino group in the 2-(dodecylamino)ethanol undergoes a ring-opening addition reaction with a portion of the epoxy groups in the glycidyl methacrylate-grafted polypropylene, followed by vacuum devolatilization, extrusion, cooling and pelletizing to obtain the modified polypropylene.

[0007] It should be noted that during the melt blending process, the secondary amino group in 2-(dodecylamino)ethanol nucleophilically attacks the epoxy group on the side chain of polypropylene grafted with glycidyl methacrylate, causing the epoxy ring to undergo ring-opening addition and introducing 2-(dodecylamino)ethanol into the polypropylene molecular chain in the form of covalent bonds. At the same time, tertiary amine groups and new β-hydroxy groups are formed, while the original hydroxyethyl and dodecyl segments are retained. Among them, the flexible dodecyl segments have good structural compatibility with the polypropylene matrix, which can improve the entanglement and deformation coordination of molecular chains, allowing external loads to be transferred and dispersed over a larger range, reducing local stress concentration, delaying the generation and propagation of microcracks, thereby improving the toughness, tear resistance and impact resistance of the modified polypropylene itself. The tertiary amine group, hydroxyethyl group and β-hydroxy group can form hydrogen bonds, dipoles and acid-base interactions with the polar sites on the surface of calcium carbonate, improving the wetting and coating of polypropylene on calcium carbonate, reducing the agglomeration of calcium carbonate particles and the interfacial defects formed, thereby reducing the filtration pressure and membrane breakage risk during the extrusion process, and improving the mechanical properties and processing stability of the composite material. By allowing only a portion of the epoxy groups to undergo ring-opening while retaining an appropriate amount of epoxy groups, the interfacial interaction between polypropylene and calcium carbonate can be controlled within a suitable range. This avoids both excessively weak interfacial bonding leading to particle detachment and stress concentration, and excessively strong interfacial bonding hindering proper interfacial debonding during biaxial stretching. This results in the formation of small and uniformly distributed micropores in the pearlescent core layer, thus balancing the low density, light-blocking properties, pearlescent luster, and mechanical strength of the pearlescent film. Vacuum devolatilization after the reaction also removes unreacted 2-(dodecylamino)ethanol and other volatile small molecules, reducing migration, odor, bubble defects, and adverse effects on subsequent stretching and heat-sealing performance.

[0008] As a preferred technical solution for a polypropylene composite packaging material for pearlescent bubble bags, the epoxy content of the glycidyl methacrylate-grafted polypropylene is 0.10-0.15 mmol / g; based on the amount of epoxy in the glycidyl methacrylate-grafted polypropylene being 1 mol, the amount of 2-(dodecylamino)ethanol used is 0.60-0.80 mol.

[0009] It should be noted that controlling the epoxy content of glycidyl methacrylate-grafted polypropylene to 0.10–0.15 mmol / g provides sufficient reaction sites for the ring-opening grafting of 2-(dodecylamino)ethanol, while avoiding excessive polypropylene polarity, abnormal melt viscosity, or decreased processing stability due to excessive grafting amount. Controlling the amount of 2-(dodecylamino)ethanol to 0.60–0.80 mol per mol of epoxy group allows most epoxy groups to undergo ring-opening, introducing flexible dodecyl segments with toughening effects, as well as tertiary amine groups, hydroxyethyl groups, and β-hydroxy groups with interfacial interactions, while retaining a certain amount of unreacted epoxy groups. This allows the modified polypropylene to possess both molecular chain stress buffering capacity and calcium carbonate interfacial regulation capacity. When the amount of 2-(dodecylamino)ethanol is below the above range, the introduced flexible segments and polar groups are insufficient, and the toughening effect of the material itself and the improvement of calcium carbonate dispersion are limited; when the amount is above the above range, the remaining epoxy groups are too few and the polarity of the material may be too strong, which can easily make the interfacial bonding between polypropylene and calcium carbonate too strong, which is not conducive to proper interfacial debonding and micropore formation during biaxial stretching.

[0010] As a preferred technical solution for polypropylene composite packaging material for pearlescent bubble bags, the melt mixing is carried out in a twin-screw extruder, with a melt mixing temperature of 165-180℃, a screw speed of 180-300 r / min, and a material residence time of 90-180 s; the vacuum devolatilization is carried out after melt mixing, with an absolute pressure of 10-30 kPa in the vacuum devolatilization section.

[0011] It should be noted that when the melt mixing temperature is 165–180℃, glycidyl methacrylate-grafted polypropylene can be fully melted, and 2-(dodecylamino)ethanol can be uniformly dispersed in the melt and undergo ring-opening addition with the epoxy groups. This also reduces the possibility of thermo-oxidative degradation of polypropylene and side reactions between hydroxyl groups and residual epoxy groups. A screw speed of 180–300 r / min and a material residence time of 90–180 s provide suitable shear dispersion and reaction time, resulting in a more uniform ring-opening reaction. Insufficient temperature, speed, or residence time can easily lead to incomplete reaction and uneven modification; excessively high or long temperatures may cause polypropylene molecular chain breakage, increased melt flow rate, and decreased material mechanical properties. Controlling the absolute pressure of the vacuum devolatilization section to 10–30 kPa can effectively remove unreacted 2-(dodecylamino)ethanol, moisture, and other volatile small molecules, reducing bubbles, odors, and migration in the granules and films, and improving the stability of subsequent extrusion, stretching, and heat-sealing processes.

[0012] As a preferred technical solution for polypropylene composite packaging material for pearlescent bubble bags, the calcium carbonate is not surface-treated with silane coupling agent, titanate coupling agent or aluminate coupling agent.

[0013] It should be noted that this application does not use silane coupling agents, titanate coupling agents, or aluminate coupling agents to surface treat calcium carbonate. This allows the polar sites on the calcium carbonate surface to directly form hydrogen bonds, dipoles, or acid-base interactions with the tertiary amine groups, hydroxyethyl groups, β-hydroxy groups, and residual epoxy groups in the modified polypropylene. This enables the modified polypropylene itself to wet, coat, and disperse the calcium carbonate, reducing particle agglomeration and interface defects. At the same time, it avoids the coupling agent forming an excessively strong interfacial bond, which would hinder the appropriate interfacial debonding between the polypropylene matrix and calcium carbonate during biaxial stretching. This allows the pearlescent core layer to form a large number of micropores with uniform size, balancing the mechanical properties of the composite material with the low density, light-blocking properties, and pearlescent luster of the pearlescent film. It also reduces the adverse effects of coupling agent decomposition or migration on the film's odor and heat-sealing performance.

[0014] As a preferred technical solution for a polypropylene composite packaging material for pearlescent bubble wrap, the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1 to 1:3; the polypropylene wax has a number average molecular weight of 3000 to 10000 and a dropping melting point of 140 to 160°C; the polypropylene composite packaging material has a melt flow rate of 2 to 8 g / 10 min at 230°C and a load of 2.16 kg.

[0015] It should be noted that antioxidant 1010 is a hindered phenolic primary antioxidant, capable of capturing free radicals generated during the thermo-oxidative degradation of polypropylene, while antioxidant 168 is a phosphite secondary antioxidant, capable of decomposing hydroperoxides. Combining the two in a mass ratio of 1:1 to 1:3 can exert a synergistic antioxidant effect during modification reactions, melt mixing, and film stretching, reducing polypropylene molecular chain breakage, yellowing, and degradation of mechanical properties. Polypropylene waxes with a number-average molecular weight of 3000–10000 and a dropping melting point of 140–160℃ exhibit good compatibility with the polypropylene matrix and can wet calcium carbonate particles during melt mixing, reducing inter-particle friction and melt flow resistance, thereby improving calcium carbonate dispersion and extrusion stability, while also reducing the risk of low-molecular-weight wax migration and precipitation. Controlling the melt flow rate of composite packaging materials to 2–8 g / 10 min can balance the flow and dispersion ability during melt mixing and the melt strength during co-extrusion film formation. When the melt flow rate is too low, it is difficult to plasticize the material and disperse the filler. When it is too high, it is easy to cause film thickness fluctuations, stretching and breaking of the film or a decrease in processing stability due to insufficient melt strength.

[0016] In addition, this application also provides a method for preparing a polypropylene composite packaging material for pearlescent bubble bags, characterized by comprising the following steps: S1. The calcium carbonate is dried to a moisture content of no more than 0.2 wt%. S2. The calcium carbonate, 20-40 wt% of the modified polypropylene, and polypropylene wax are mixed for the first time to obtain a calcium carbonate premix; then the remaining modified polypropylene and antioxidant are added to the calcium carbonate premix for the second mixing to obtain a mixture. S3. The mixture is fed into a twin-screw extruder and subjected to melt mixing, vacuum devouring, extrusion, cooling and pelletizing in sequence to obtain the polypropylene composite packaging material.

[0017] It should be noted that in step S1, the calcium carbonate is first dried to a moisture content of no more than 0.2 wt%, which can reduce the reaction between moisture and the remaining epoxy groups and prevent the generation of bubbles, silver streaks and pores during melt extrusion. In step S2, the calcium carbonate, 20-40 wt% of the total amount of modified polypropylene, and polypropylene wax are first mixed to form a premix with a high calcium carbonate content. This allows the polypropylene wax and modified polypropylene with polar side groups to be preferentially distributed around the calcium carbonate particles, creating conditions for subsequent melt wetting and interfacial coating. Then, the remaining 60-80 wt% of modified polypropylene and antioxidant are added for a second mixing. This can complete the dilution and homogenization of the system while maintaining the pre-dispersion state of calcium carbonate, and reduce the adsorption or premature consumption of antioxidants by calcium carbonate during the first high-temperature and high-speed mixing process. Step S3 uses a twin-screw extruder for melt mixing, which breaks down the soft calcium carbonate agglomerates through distribution mixing and dispersion mixing, so that the components are evenly distributed. Then, vacuum devolatilization is carried out to further remove moisture and volatile small molecules. Finally, after extrusion, cooling and pelletizing, a polypropylene composite packaging material with uniform composition, stable processing and suitable for three-layer co-extrusion biaxial stretching is obtained.

[0018] In a preferred embodiment of a method for preparing a polypropylene composite packaging material for pearlescent bubble wrap, in step S1, the calcium carbonate is dried at 100–120°C for 2–4 h; in step S2, the temperature of the first mixing is 90–110°C, the rotation speed is 800–1500 r / min, and the time is 5–15 min; the temperature of the second mixing is 60–90°C, and the time is 3–10 min; in step S3, the temperature of each zone of the twin-screw extruder is 175–200°C, the screw rotation speed is 200–350 r / min, and the absolute pressure of the vacuum devolatilization section is 10–40 kPa.

[0019] It should be noted that drying calcium carbonate at 100–120℃ for 2–4 hours can fully remove adsorbed water from the particle surface, avoiding the consumption of residual epoxy groups and extrusion bubble defects caused by moisture. The first mixing is carried out at 90–110℃ and 800–1500 r / min for 5–15 minutes, which can use high-speed shearing to break up the soft agglomerates of calcium carbonate, so that the polypropylene wax and some modified polypropylene can fully contact and be evenly distributed with calcium carbonate. The second mixing is carried out at 60–90℃ for 3–10 minutes, which can complete the material homogenization after adding the remaining modified polypropylene and antioxidant, while reducing the heat loss of antioxidant. The temperature control in each zone of the twin-screw extruder is maintained at 175–200℃ to ensure full melting of modified polypropylene and polypropylene wax, and to promote the wetting and coating of calcium carbonate by the melt. The screw speed is controlled at 200–350 r / min to provide the shear force required to break up agglomerates while avoiding excessive shearing that could lead to polypropylene degradation. The absolute pressure control in the vacuum devolatilization section is maintained at 10–40 kPa to effectively remove moisture and volatile small molecules, reducing internal porosity in the granules and subsequent film-forming defects. The combination of these parameters improves the uniformity of calcium carbonate dispersion, melt stability, and continuous film-forming performance, while reducing the risks of increased filtration pressure, die accumulation, and tensile film breakage.

[0020] This application introduces flexible dodecyl segments, tertiary amine groups, and hydroxyl groups into the polypropylene molecular chain via a ring-opening addition reaction between the secondary amino group of 2-(dodecylamino)ethanol and a portion of the epoxy groups in glycidyl methacrylate-grafted polypropylene. The dodecyl segments enhance the entanglement and deformation coordination of the molecular chain, improving the toughness and stress buffering capacity of the modified polypropylene. The tertiary amine groups and hydroxyl groups enhance the interfacial interaction between the polypropylene matrix and calcium carbonate, improving the wetting, coating, and dispersion of calcium carbonate, and reducing particle agglomeration, interfacial defects, and localized stress concentration. By premixing a portion of the modified polypropylene with calcium carbonate and polypropylene wax before adding the remaining modified polypropylene and antioxidant, the dispersion uniformity of calcium carbonate can be further improved. This results in suitable and uniformly distributed micropore sizes formed during biaxial stretching, thereby improving the tensile strength, toughness, tear resistance, impact resistance, and puncture resistance of the pearlescent bubble bag while maintaining high opacity and pearlescent effect, and reducing extrusion pressure fluctuations and the risk of tensile film breakage. Attached Figure Description

[0021] Figure 1 The Fourier transform infrared spectra of polypropylene and the modified polypropylene prepared in Example 1 are shown, where the black curve represents polypropylene and the red curve represents modified polypropylene. Detailed Implementation

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0023] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0024] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0025] Example 1

[0026] This embodiment provides a method for preparing a composite packaging material for pearlescent film bubble bags, including the following steps: S1. Weigh 100 kg of glycidyl methacrylate-grafted polypropylene with an epoxy group content of 0.10 mmol / g and vacuum dry it at 80℃ for 3 h; the amount of epoxy group is 10 mol. According to the molar ratio of epoxy group to 2-(dodecylamino)ethanol of 1:0.60, weigh 6.0 mol of 2-(dodecylamino)ethanol, which is 1.376 kg; after premixing the two raw materials for 5 min, feed them into a co-rotating twin-screw extruder with a length-to-diameter ratio of 40:1. Melt-mix under nitrogen protection at 165℃ and 180 r / min. By adjusting the feeding speed, the material residence time is made to 90 s, so that the secondary amine and some epoxy groups can undergo a ring-opening addition reaction; then the melt is put into a vacuum devolatilization section with an absolute pressure of 30 kPa to remove unreacted small molecules. After extrusion, 25℃ circulating water cooling, air knife dehydration and pelleting, it is dried at 80℃ for 2 h to obtain modified polypropylene.

[0027] S2. Weigh 18 kg of calcium carbonate that has not been surface-treated with silane coupling agent, titanate coupling agent or aluminate coupling agent, on a dry basis, and dry the calcium carbonate in a hot air circulating drying oven at 100℃ for 2 h to make its moisture content not greater than 0.2 wt%; separately weigh 100 kg of modified polypropylene obtained in step S1, 0.05 kg of antioxidant 1010, 0.05 kg of antioxidant 168 and 0.20 kg of polypropylene wax, wherein the mass ratio of antioxidant 1010 to antioxidant 168 is 1:1, and the number average molecular weight of polypropylene wax is 3000 and the dropping melting point is 140℃.

[0028] S3. Add 18 kg of dried calcium carbonate, 20 kg of modified polypropylene, and 0.20 kg of polypropylene wax to a high-speed mixer. The modified polypropylene added for the first time accounts for 20 wt% of the total modified polypropylene. Mix at 90°C and 800 r / min for 5 min to obtain a calcium carbonate premix. Cool the calcium carbonate premix to 60°C, then add the remaining 80 kg of modified polypropylene, 0.05 kg of antioxidant 1010, and 0.05 kg of antioxidant 168. Continue mixing at 500 r / min for 3 min to obtain a mixture.

[0029] S4. The mixture obtained in step S3 is fed into a co-rotating twin-screw extruder. Except for the water-cooled feed inlet, the temperature of each melt mixing zone is set to 175℃, the screw speed is 200 r / min, and the absolute pressure of the vacuum devouring section is 40 kPa. After the material is successively melt-plasticized, dispersed and mixed and vacuum devoured, it is extruded into strips, cooled by circulating water at 25℃, dehydrated by air knife and pelletized to obtain polypropylene composite packaging material. The melt flow rate of the obtained material at 230℃ and 2.16 kg load is controlled to be 2.0 g / 10 min.

[0030] S5. Using homopolymer polypropylene without inorganic fillers, the polypropylene composite packaging material obtained in step S4, and propylene-ethylene random copolymer as raw materials for the outer layer, pearlescent core layer, and heat-sealing layer, respectively, three extruders are used to melt and plasticize the materials and then extrude them through a three-layer co-extrusion die to form a three-layer cast sheet on a cooling roller at 30°C. The resulting sheet is then subjected to a 4-fold longitudinal stretch at 125°C and a 7-fold transverse stretch at 155°C, followed by heat setting and cooling to obtain a three-layer polypropylene pearlescent film with a total thickness of 50 μm, wherein the outer layer thickness is 7.5 μm, the pearlescent core layer thickness is 35 μm, and the heat-sealing layer thickness is 7.5 μm, with the pearlescent core layer accounting for 70% of the total thickness.

[0031] S6. Take a polypropylene bubble film with a propylene-ethylene random copolymer contact surface, and place the heat-sealing layer of the polypropylene pearlescent film obtained in step S5 opposite to the flat contact surface of the polypropylene bubble film. Without setting an adhesive layer, hot press at 115°C and 0.25 MPa for 1.0 s to obtain a pearlescent film and bubble film composite sheet. Cut the two composite sheets into 300 mm × 400 mm pieces, place the bubble films on one side opposite each other, flatten and heat seal the 10 mm wide areas on both sides and the bottom edge, leaving the top opening, to obtain a pearlescent film bubble bag.

[0032] Example 2

[0033] This embodiment provides a method for preparing a composite packaging material for pearlescent film bubble bags, including the following steps: S1. Weigh 100 kg of glycidyl methacrylate-grafted polypropylene with an epoxy group content of 0.12 mmol / g and vacuum dry it at 80℃ for 3 h; the amount of epoxy group is 12 mol. According to the molar ratio of epoxy group to 2-(dodecylamino)ethanol of 1:0.65, weigh 7.8 mol of 2-(dodecylamino)ethanol, which is 1.789 kg; after premixing the two raw materials for 5 min, feed them into a co-rotating twin-screw extruder and melt-mix them at 170℃ and 220 r / min for 120 s under nitrogen protection. Then, let the melt enter the vacuum devolatilization section with an absolute pressure of 25 kPa, and then extrude, cool with circulating water, air dry and pelletize. Dry it at 80℃ for 2 h to obtain modified polypropylene.

[0034] S2. Weigh 22 kg of calcium carbonate that has not been surface-treated with silane coupling agent, titanate coupling agent or aluminate coupling agent, on a dry basis, and dry it at 105℃ for 2.5 h to make the moisture content not greater than 0.2 wt%; separately weigh 100 kg of modified polypropylene, 0.067 kg of antioxidant 1010, 0.133 kg of antioxidant 168 and 0.40 kg of polypropylene wax, wherein the mass ratio of the two antioxidants is 1:2, and the polypropylene wax has a number average molecular weight of 5000 and a dropping melting point of 148℃.

[0035] S3. Add 22 kg of dry calcium carbonate, 25 kg of modified polypropylene and 0.40 kg of polypropylene wax to a high-speed mixer, wherein the modified polypropylene added for the first time accounts for 25 wt% of the total amount. Mix at 95°C and 1000 r / min for 8 min to obtain calcium carbonate premix. Cool the premix to 70°C, add the remaining 75 kg of modified polypropylene, 0.067 kg of antioxidant 1010 and 0.133 kg of antioxidant 168, and continue mixing at 600 r / min for 5 min to obtain a mixture.

[0036] S4. The mixture is fed into a co-rotating twin-screw extruder. The temperatures of each melt mixing zone are set sequentially to 175℃, 180℃, 180℃, 185℃, 185℃, 185℃, 180℃, and 180℃. The screw speed is 250 r / min, and the absolute pressure of the vacuum devouring section is 30 kPa. After melt mixing, vacuum devouring, extrusion, cooling, and pelletizing, polypropylene composite packaging material is obtained. Its melt flow rate at 230℃ and 2.16 kg load is controlled to be 4.0 g / 10 min.

[0037] S5. Homopolymer polypropylene, the polypropylene composite packaging material obtained in step S4, and propylene-ethylene random copolymer are used to form an outer layer, a pearlescent core layer, and a heat-sealing layer, respectively. The three layers are co-extruded to form a cast sheet. The cast sheet is stretched longitudinally by 4.5 times at 130°C and then stretched transversely by 8 times at 158°C. After heat setting and cooling, a polypropylene pearlescent film with a total thickness of 50 μm is obtained, wherein the outer layer thickness is 6 μm, the pearlescent core layer thickness is 38 μm, and the heat-sealing layer thickness is 6 μm. The pearlescent core layer thickness accounts for 76% of the total thickness.

[0038] S6. Place the heat-sealing layer of the polypropylene pearlescent film obtained in step S5 against the flat contact surface of the polypropylene bubble film, and heat-press it at 123°C and 0.25 MPa for 1.0 s without setting an adhesive layer to obtain a composite sheet of pearlescent film and bubble film; place the bubble film of the two composite sheets with one side facing each other, flatten and heat-seal the two sides and the bottom edge, leaving the top opening, to obtain a pearlescent film bubble bag.

[0039] Example 3

[0040] This embodiment provides a method for preparing a composite packaging material for pearlescent film bubble bags, including the following steps: S1. Weigh 100 kg of glycidyl methacrylate-grafted polypropylene with an epoxy group content of 0.13 mmol / g and vacuum dry it at 80℃ for 3 h; the amount of epoxy group is 13 mol. According to the molar ratio of epoxy group to 2-(dodecylamino)ethanol of 1:0.75, weigh 9.75 mol of 2-(dodecylamino)ethanol, which is 2.237 kg. After premixing the two raw materials, feed them into a co-rotating twin-screw extruder and melt-mix them at 175℃ and 260 r / min for 150 s under nitrogen protection. Then, vacuum devolatilize them under an absolute pressure of 20 kPa. After extrusion, cooling with circulating water, air drying and pelletizing, dry at 80℃ for 2 h to obtain modified polypropylene.

[0041] S2. On a dry basis, weigh 27 kg of calcium carbonate that has not been surface-treated with silane coupling agent, titanate coupling agent or aluminate coupling agent, and dry it at 110℃ for 3 h to make the moisture content not greater than 0.2 wt%; separately weigh 100 kg of modified polypropylene, 0.10 kg of antioxidant 1010, 0.25 kg of antioxidant 168 and 0.70 kg of polypropylene wax, wherein the mass ratio of the two antioxidants is 1:2.5, and the polypropylene wax has a number average molecular weight of 8000 and a dropping melting point of 155℃.

[0042] S3. Add 27 kg of dry calcium carbonate, 30 kg of modified polypropylene and 0.70 kg of polypropylene wax to a high-speed mixer, wherein the modified polypropylene added for the first time accounts for 30 wt% of the total amount. Mix at 105℃ and 1250 r / min for 12 min to obtain calcium carbonate premix. Cool the premix to 80℃, add the remaining 70 kg of modified polypropylene, 0.10 kg of antioxidant 1010 and 0.25 kg of antioxidant 168, and continue mixing at 700 r / min for 8 min to obtain a mixture.

[0043] S4. The mixture is fed into a co-rotating twin-screw extruder. The temperatures of each melt mixing zone are set sequentially to 180℃, 185℃, 190℃, 195℃, 195℃, 190℃, 185℃ and 185℃. The screw speed is 300 r / min and the absolute pressure of the vacuum devouring section is 20 kPa. After melt mixing, vacuum devouring, extrusion, cooling and pelletizing, the material is used to obtain polypropylene composite packaging material. Its melt flow rate at 230℃ and 2.16 kg load is controlled to be 6.0 g / 10 min.

[0044] S5. Using homopolymer polypropylene, the polypropylene composite packaging material obtained in step S4, and propylene-ethylene random copolymer as raw materials for the outer layer, pearlescent core layer, and heat-sealing layer, respectively, a three-layer co-extrusion is performed to form a cast thick sheet; the cast thick sheet is stretched longitudinally by 5 times at 135°C and then transversely stretched by 9 times at 160°C. After heat setting and cooling, a polypropylene pearlescent film with a total thickness of 50 μm is obtained, wherein the outer layer thickness is 4 μm, the pearlescent core layer thickness is 42 μm, the heat-sealing layer thickness is 4 μm, and the pearlescent core layer thickness accounts for 84% of the total thickness.

[0045] S6. Place the heat-sealing layer of the polypropylene pearlescent film obtained in step S5 against the flat contact surface of the polypropylene bubble film, and heat-press it at 132°C and 0.25 MPa for 1.0 s without setting an adhesive layer to obtain a composite sheet of pearlescent film and bubble film; cut the obtained composite sheet into bag size, place the bubble film of the two composite sheets with one side facing each other, flatten and heat-seal the two sides and bottom edge, leaving the top opening, to obtain a pearlescent film bubble bag.

[0046] Example 4

[0047] This embodiment provides a method for preparing a composite packaging material for pearlescent film bubble bags, including the following steps: S1. Weigh 100 kg of glycidyl methacrylate-grafted polypropylene with an epoxy group content of 0.15 mmol / g and vacuum dry it at 80℃ for 3 h; the amount of epoxy group is 15 mol. According to the molar ratio of epoxy group to 2-(dodecylamino)ethanol of 1:0.80, weigh 12 mol of 2-(dodecylamino)ethanol, which is 2.753 kg; after premixing the two raw materials for 5 min, feed them into a co-rotating twin-screw extruder and melt-mix them at 180℃ and 300 r / min for 180 s under nitrogen protection. Then, vacuum devolatilize them under an absolute pressure of 10 kPa. After extrusion, cooling with circulating water, air drying and pelletizing, dry at 80℃ for 2 h to obtain modified polypropylene.

[0048] S2. On a dry basis, weigh 32 kg of calcium carbonate that has not been surface-treated with silane coupling agent, titanate coupling agent or aluminate coupling agent, and dry it at 120℃ for 4 h to make the moisture content not greater than 0.2 wt%; separately weigh 100 kg of modified polypropylene, 0.125 kg of antioxidant 1010, 0.375 kg of antioxidant 168 and 1.00 kg of polypropylene wax, wherein the mass ratio of the two antioxidants is 1:3, and the polypropylene wax has a number average molecular weight of 10000 and a dropping melting point of 160℃.

[0049] S3. Add 32 kg of dry calcium carbonate, 40 kg of modified polypropylene and 1.00 kg of polypropylene wax to a high-speed mixer, wherein the modified polypropylene added for the first time accounts for 40 wt% of the total amount. Mix at 110°C and 1500 r / min for 15 min to obtain calcium carbonate premix. Cool the premix to 90°C, add the remaining 60 kg of modified polypropylene, 0.125 kg of antioxidant 1010 and 0.375 kg of antioxidant 168, and continue mixing at 800 r / min for 10 min to obtain a mixture.

[0050] S4. The mixture is fed into a co-rotating twin-screw extruder. The temperatures of each melt mixing zone are set sequentially to 190℃, 195℃, 200℃, 200℃, 200℃, 195℃, 195℃ and 190℃. The screw speed is 350 r / min and the absolute pressure of the vacuum devouring section is 10 kPa. After melt mixing, vacuum devouring, extrusion, cooling and pelletizing, the material is used to obtain polypropylene composite packaging material. The melt flow rate at 230℃ and 2.16 kg load is controlled to be 8.0 g / 10 min.

[0051] S5. Using homopolymer polypropylene, the polypropylene composite packaging material obtained in step S4, and propylene-ethylene random copolymer as raw materials for the outer layer, pearlescent core layer, and heat-sealing layer, respectively, a three-layer co-extrusion is performed to form a cast sheet; the cast sheet is stretched longitudinally by 6 times at 140°C, and then stretched transversely by 10 times at 165°C. After heat setting and cooling, a polypropylene pearlescent film with a total thickness of 50 μm is obtained, wherein the outer layer thickness is 2.5 μm, the pearlescent core layer thickness is 45 μm, and the heat-sealing layer thickness is 2.5 μm, with the pearlescent core layer accounting for 90% of the total thickness.

[0052] S6. Place the heat-sealing layer of the polypropylene pearlescent film obtained in step S5 against the flat contact surface of the polypropylene bubble film, and heat-press it at 140°C and 0.25 MPa for 1.0 s without setting an adhesive layer to obtain a composite sheet of pearlescent film and bubble film; cut the two composite sheets into 300 mm × 400 mm pieces and place the bubble film on one side opposite each other, flatten the 10 mm wide areas on both sides and the bottom edge and heat-seal them, leaving the top opening open to obtain a pearlescent film bubble bag.

[0053] Compare with Example 1 Compared with Example 1, the difference is that step S1 is omitted, and modified polypropylene is not prepared. Instead, 100 parts by weight of unmodified polypropylene is used to replace 100 parts by weight of modified polypropylene. The remaining raw materials, amounts and preparation steps are the same as in Example 1.

[0054] Compare with Example 2 Compared with Example 1, the difference is that in the first mixing process, calcium carbonate, 100 parts by weight of modified polypropylene and polypropylene wax are added to the mixing equipment at one time and mixed, instead of adding the modified polypropylene in two separate times; after the first mixing is completed, an antioxidant is added for the second mixing, and the remaining raw materials, dosages and preparation steps are the same as in Example 1.

[0055] Performance testing methods 1. Opacity: A sample was cut from the pearlescent film area of ​​the bag and measured using an integrating sphere spectrophotometer at D... 65 The Y-value was measured using a standard white board and a black board as backing under light source and 10° observation conditions, respectively, according to the formula "Opacity = Y". 黑背衬 / Y 白背衬 Calculate using "×100%", with no fewer than 10 measurement points per group.

[0056] 2. Tensile properties of the bag body: Strip samples were cut from the flat area of ​​the bag body along the longitudinal and transverse directions of the film forming process, avoiding air bubbles and heat-sealed edges. The tensile strength and elongation at break were determined according to the current GB / T 1040.3—2006. At the same time, the complete stress-strain curve was integrated to obtain the energy absorbed at break.

[0057] 3. Tear resistance: Samples were cut from the pearlescent film area of ​​the bag along the longitudinal and transverse directions, and the tear strength was determined by the Elmendorf method according to GB / T 16578.2—2009. At least 10 samples were taken in each direction, and the results were expressed as mN or N.

[0058] 4. Impact resistance: Samples of uniform size were cut from the flat composite area of ​​the bag body. The mass F of the falling dart that caused 50% of the samples to break was determined using the free-falling dart ladder method according to GB / T 9639.1—2008. 50 Each group should maintain a consistent total thickness of the bag material and observe whether the pearlescent film ruptures through, separates from the bubble wrap, or bursts after impact.

[0059] 5. Puncture Resistance: Cut the bag into specimens no smaller than 100 mm × 100 mm and clamp them on a circular fixture. Using a puncture probe with a hemispherical end, press vertically into the specimen at a speed of 100 mm / min until the bag is completely punctured. Record the maximum puncture force and puncture absorbed energy. Each group should contain no fewer than 5 specimens, and the probe diameter, fixture aperture, and specimen thickness must be consistent.

[0060] Table 1 Performance test results of pearlescent film bubble bags

[0061] As can be seen from Examples 1-4 and Table 1, the pearlescent bubble bags prepared in Examples 1-4 have an opacity of 92.4%-96.1%, longitudinal and transverse tensile strengths of 93.8-111.6 MPa and 169.7-196.2 MPa, respectively, longitudinal and transverse elongation at break of 131.5%-152.7% and 48.2%-59.1%, respectively, and longitudinal and transverse energy absorption at break of 31.2-40.7 MJ / m², respectively. 3 and 24.9~31.8 MJ / m 3 The longitudinal and transverse tearing forces are 574–705 mN and 693–846 mN, respectively, and the impact mass of the dart is F. 50The weight is 462–568 g, the maximum puncture force is 55.1–67.5 N, and the puncture absorption energy is 0.78–1.02 J, indicating that this application can obtain pearlescent bubble bags with high light-shielding properties, tensile strength, toughness, tear resistance, impact resistance, and puncture resistance within the specified component dosage and preparation process range. This is mainly because the modified polypropylene improves the wetting and dispersion uniformity of calcium carbonate in the polypropylene matrix, reduces calcium carbonate agglomeration and the resulting interface defects and local stress concentration, and at the same time makes the micropore size formed during biaxial stretching appropriate and uniformly distributed. Thus, while producing good light scattering and shielding effects, it reduces the risk of microcrack initiation and propagation, and improves the energy absorption and stress buffering capacity of the bag when subjected to tensile, tearing, impact, and puncture loads.

[0062] Combining Example 1, Comparative Example 1, and Table 1, it can be seen that the opacity of Example 1 is 94.7%, which is higher than that of Comparative Example 1 (88.9%); the longitudinal and transverse tensile strengths are 105.8 MPa and 188.6 MPa, respectively, which are higher than those of Comparative Example 1 (76.4 MPa and 137.5 MPa); the longitudinal and transverse tear forces are 682 mN and 814 mN, respectively, which are higher than those of Comparative Example 1 (352 mN and 438 mN); and the dart impact mass F... 50 The g content was increased from 305 g to 545 g, the maximum puncture force increased from 38.7 N to 64.8 N, and the puncture absorption energy increased from 0.43 J to 0.96 J. These results indicate that, compared to unmodified polypropylene, the modified polypropylene of this application can utilize tertiary amine groups, hydroxyethyl groups, and β-hydroxy groups to enhance the interfacial interaction between the polypropylene matrix and calcium carbonate, improving the wetting, coating, and dispersion of calcium carbonate, reducing particle agglomeration and the resulting interfacial defects. Simultaneously, the introduced flexible dodecyl segments can improve the deformation coordination and stress transfer capacity of the polypropylene molecular chains, alleviate local stress concentration, and delay microcrack propagation. Therefore, while improving the uniformity of micropore distribution and opacity, it significantly improves the tensile, tearing, impact, and puncture properties of the bag.

[0063] Combining Example 1, Comparative Example 2, and Table 1, it can be seen that the opacity of Example 1 is 94.7%, which is higher than that of Comparative Example 2 (91.6%); the longitudinal and transverse tensile strengths increased from 87.9 MPa and 157.8 MPa to 105.8 MPa and 188.6 MPa, respectively; the longitudinal and transverse tear forces increased from 476 mN and 582 mN to 682 mN and 814 mN, respectively; and the dart impact mass F... 50The g content was increased from 391 g to 545 g, the maximum puncture force increased from 48.5 N to 64.8 N, and the puncture absorption energy increased from 0.62 J to 0.96 J. These results indicate that first mixing a portion of the modified polypropylene with calcium carbonate and polypropylene wax allows the modified polypropylene to preferentially wet and coat the calcium carbonate particles, forming a uniformly dispersed premix. Adding the remaining modified polypropylene and antioxidant for a second mixing reduces the possibility of secondary agglomeration of calcium carbonate particles under high-filling conditions. Compared to adding all the modified polypropylene at once, this two-stage addition process achieves a more uniform particle distribution and microporous structure, reducing stress concentration points caused by large agglomerates, excessively large micropores, and interface defects, thereby further improving the opacity and overall mechanical properties of the pearlescent bubble bag.

[0064] Combined with Example 1 and Figure 1 It can be seen that unmodified polypropylene at 2950 and 2918 Nearby, asymmetric stretching vibration peaks of -CH3 and -CH2- appear, at 1456. and 1377 Nearby, peaks of methylene scissor vibration and methyl bending vibration appeared, and at 1167... 973 and 841 The surrounding area exhibits characteristic absorptions of the polypropylene carbon chain backbone and isotactic phase; modified polypropylene retains the aforementioned alkyl and polypropylene backbone-related absorptions, indicating that melt mixing and ring-opening addition did not significantly damage the polypropylene backbone. Compared to unmodified polypropylene, modified polypropylene at 3410 A distinct broad absorption band appears nearby, which can be attributed to the O-H stretching vibration of the original hydroxyethyl group of 2-(dodecylamino)ethanol and the β-hydroxy group formed by ring opening of the epoxy group; 1732 The strong absorption peaks nearby correspond to the C=O stretching vibration of the ester carbonyl group in the glycidyl methacrylate grafted side chain, indicating that the GMA graft structure is retained in subsequent reactions; 1260 and 1105 The enhanced absorption in the vicinity is mainly related to the overlapping of C-O-C of the ester or ether bond, the adjacent C-O of the hydroxyl group, and the C-N stretching vibration of the tertiary amine structure, which is consistent with the expected reaction structure of the secondary amine attacking the epoxy group and converting it into a tertiary amine group; 910 The presence of weak epoxy group characteristic absorption in the vicinity, combined with the fact that 2-(dodecylamino)ethanol was used in a molar ratio of less than 1:1 to epoxy groups in Example 1, indicates that some unopened epoxy groups are still retained in the modified polypropylene; 720 The newly added long-chain methylene rocking vibration peaks and the 2920–2850 range are also present. The enhanced absorption of methylene groups in the region supports the introduction of dodecyl segments into modified polypropylene. Therefore, Figure 1 The peak position changes shown are generally consistent with the target structure of the partial epoxy ring-opening addition of 2-(dodecylamino)ethanol to GMA-grafted polypropylene, indicating that the modified polypropylene introduced flexible dodecyl segments, hydroxyl groups and tertiary amine groups while retaining the non-polar polypropylene skeleton, and retained an appropriate amount of epoxy groups. Structurally, this provides a basis for improving the material's deformation coordination ability and its wetting, coating and interfacial compatibility with calcium carbonate.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A polypropylene composite packaging material for pearlescent bubble wrap, characterized in that, By weight, it comprises 100 parts modified polypropylene, 18 to 32 parts calcium carbonate, 0.1 to 0.5 parts antioxidant, and 0.2 to 1.0 parts polypropylene wax.

2. The polypropylene composite packaging material for pearlescent bubble bags according to claim 1, characterized in that, The modified polypropylene is prepared by a method comprising the following steps: mixing glycidyl methacrylate-grafted polypropylene with 2-(dodecylamino)ethanol and then performing melt blending, so that the secondary amino group in the 2-(dodecylamino)ethanol undergoes a ring-opening addition reaction with a portion of the epoxy group in the glycidyl methacrylate-grafted polypropylene, followed by vacuum devolatilization, extrusion, cooling and pelletizing to obtain the modified polypropylene.

3. The polypropylene composite packaging material for pearlescent bubble bags according to claim 2, characterized in that, The epoxy content of the glycidyl methacrylate-grafted polypropylene is 0.10–0.15 mmol / g; based on the amount of epoxy in the glycidyl methacrylate-grafted polypropylene being 1 mol, the amount of 2-(dodecylamino)ethanol used is 0.60–0.80 mol.

4. The polypropylene composite packaging material for pearlescent bubble bags according to claim 2 or 3, characterized in that, The melt mixing is carried out in a twin-screw extruder, with a melt mixing temperature of 165–180°C, a screw speed of 180–300 r / min, and a material residence time of 90–180 s; the vacuum devolatilization is carried out after the melt mixing, with an absolute pressure of 10–30 kPa in the vacuum devolatilization section.

5. The polypropylene composite packaging material for pearlescent bubble bags according to claim 4, characterized in that, The calcium carbonate was not surface treated with silane coupling agent, titanate coupling agent or aluminate coupling agent.

6. The polypropylene composite packaging material for pearlescent bubble bags according to claim 5, characterized in that, The antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1 to 1:3; the polypropylene wax has a number average molecular weight of 3000 to 10000 and a dropping melting point of 140 to 160°C; the polypropylene composite packaging material has a melt flow rate of 2 to 8 g / 10 min at 230°C and a load of 2.16 kg.

7. A method for preparing a polypropylene composite packaging material for pearlescent bubble bags according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. The calcium carbonate is dried to a moisture content of no more than 0.2 wt%. S2. The calcium carbonate, 20-40 wt% of the modified polypropylene, and polypropylene wax are mixed for the first time to obtain a calcium carbonate premix; then the remaining modified polypropylene and antioxidant are added to the calcium carbonate premix for the second mixing to obtain a mixture. S3. The mixture is fed into a twin-screw extruder and subjected to melt mixing, vacuum devouring, extrusion, cooling and pelletizing in sequence to obtain the polypropylene composite packaging material.

8. The preparation method according to claim 7, characterized in that, In step S1, the calcium carbonate is dried at 100–120°C for 2–4 h; in step S2, the temperature of the first mixing is 90–110°C, the rotation speed is 800–1500 r / min, and the time is 5–15 min; the temperature of the second mixing is 60–90°C, and the time is 3–10 min; in step S3, the temperature of each zone of the twin-screw extruder is 175–200°C, the screw rotation speed is 200–350 r / min, and the absolute pressure of the vacuum devolatilization section is 10–40 kPa.

9. A pearlescent film bubble bag, characterized in that, The pearlescent bubble bag comprises a composite of polypropylene pearlescent film and polypropylene bubble film. The polypropylene pearlescent film is a three-layer co-extruded biaxially oriented film, comprising, in sequence, a polypropylene outer layer without inorganic fillers, a pearlescent core layer, and a propylene-ethylene random copolymer heat-sealing layer; the pearlescent core layer is formed from the polypropylene composite packaging material according to any one of claims 1 to 6, and the thickness of the pearlescent core layer accounts for 70 to 90% of the total thickness of the polypropylene pearlescent film.

Images