A composite polypropylene film packaging material and its preparation method

Abstract

The present invention provides a composite polypropylene film packaging material and a preparation method thereof. The packaging material comprises a tough outer layer, a flexible intermediate layer and a rigid inner layer. The tough outer layer comprises the following components: block copolymerized polypropylene, homopolypropylene, POE elastomer, talcum powder; the flexible intermediate layer comprises the following components: random copolymerized polypropylene, homopolypropylene, polyethylene; the rigid inner layer comprises the following components: random copolymerized polypropylene, block copolymerized polypropylene, nano-rigid particles, barium sulfate; the thickness ratio of the tough outer layer, the flexible intermediate layer and the rigid inner layer is 1:(0.8 - 0.9):(1.1 - 1.15). By adding POE elastomer, polyethylene and nano-rigid particles to the outer layer, the intermediate layer and the inner layer respectively, the toughness of the outer layer, the flexibility of the intermediate layer and the hardness of the inner layer are improved, the problem that the existing polypropylene film is easily punctured when packaging frozen meat and raw fish is solved, and thus the breakage rate of the packaging of frozen meat and raw fish products is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of packaging materials, and in particular, to a composite polypropylene film packaging material and a preparation method thereof. Background Art

[0002] Polypropylene is a non-toxic, odorless, tasteless, milky white, highly crystalline polymer and is one of the lightest varieties among all plastics currently. It is particularly stable in water, and its water absorption rate in water is only 0.01%. Polypropylene film is a thermoplastic resin prepared by polymerizing propylene. It is usually thicker, tougher, and has a higher tensile strength, and can be used for greenhouse films, load-bearing packaging bags, etc. According to different processing technologies, polypropylene films can be divided into CPP films, BOPP films, and IPP films. CPP film is a non-stretched, non-oriented flat extrusion film, which has the characteristics of light weight, high transparency, good flatness, good rigidity, strong mechanical adaptability, good slipperiness, high film-making speed, uniform thickness, moisture-proof, oil-resistant, etc. After being made into bags, CPP film can be used for the packaging of food, drugs, stationery, cosmetics, textiles, etc., and has the largest consumption in food packaging. BOPP film is a packaging material with excellent performance. Due to the orientation of molecular chain segments and the increase in crystallinity, the tensile strength, tensile elastic modulus, impact strength, tear strength, flexing life, etc. can be significantly improved, and a strong and tough film with high stiffness can be obtained. In addition, BOPP film has good moisture barrier properties, high gloss, good transparency, good gas barrier properties, moisture-proof, light weight, non-toxic, odorless, good dimensional stability, wide range of use, good printability, and good electrical insulation, and has excellent quality stability and processability. Its comprehensive performance is superior to transparent films such as moisture-proof glass paper and polyethylene film, and is hailed as the "queen of packaging" by the packaging industry. IPP film is a polypropylene film produced by the down-blow water-cooled film-making technology. The optical properties and film thickness deviation of IPP film are slightly lower than those of CPP film and BOPP film, but the preparation process of IPP film is simple and the cost is low. It can be packaged by simply sealing the upper and lower ends. IPP film is mainly used for the packaging of deep-fried snacks, bread, textiles, file folders, record sleeves, seaweed, sports shoes, etc.

[0003] Among them, BOPP film is generally a multi-layer co-extruded film, which is made by co-extruding polypropylene to form a sheet and then stretching it in both the longitudinal and transverse directions. Although BOPP film has excellent strength and toughness compared with other types of polypropylene films, when packaging frozen meat and raw fish stored at low temperature, due to the reduction of the mechanical properties of BOPP film at low temperature, BOPP film is often punctured by broken bones, fish bones, etc., resulting in packaging damage of products. Summary of the Invention

[0004] The present invention provides a composite polypropylene film packaging material. By adding POE elastomer, polyethylene, and nano-rigid particles to the outer surface layer, the middle layer, and the inner surface layer respectively, the toughness of the outer surface layer, the flexibility of the middle layer, and the hardness of the inner surface layer are improved. When the sharp part abuts against the inner surface layer, the opening can be avoided. At the same time, the flexible middle layer gives the inner surface layer room for extension, which can better abut against the sharp part. Improving the toughness of the outer surface layer can prevent the outer surface layer from being torn when the inner surface layer extends outwards, solving the problem that the existing polypropylene film is easily punctured when packaging frozen meat and raw fish, thereby reducing the breakage rate of the packaging of frozen meat and raw fish products.

[0005] To solve the above technical problems, the present invention provides a composite polypropylene film packaging material, including a tough outer surface layer, a flexible middle layer, and a hard inner surface layer. The tough outer surface layer includes the following components: block copolymerized polypropylene, homopolypropylene, POE elastomer, and talcum powder; the flexible middle layer includes the following components: random copolymerized polypropylene, homopolypropylene, and polyethylene; the hard inner surface layer includes the following components: random copolymerized polypropylene, block copolymerized polypropylene, nano-rigid particles, and barium sulfate; the thickness ratio of the tough outer surface layer, the flexible middle layer, and the hard inner surface layer is 1:(0.8 - 0.9):(1.1 - 1.15).

[0006] In a preferred or alternative embodiment, the tough outer surface layer includes block copolymerized polypropylene, homopolypropylene, POE elastomer, and talcum powder in a mass ratio of (20 - 25):(10 - 15):(1 - 3):(0.8 - 1.2). The POE elastomer includes a random copolymer of ethylene and 1-octene, and the content of 1-octene in the POE elastomer is 20% - 25%.

[0007] In a preferred or alternative embodiment, the flexible middle layer includes random copolymerized polypropylene, homopolypropylene, and linear low-density polyethylene in a mass ratio of (15 - 20):(3 - 7):(13 - 18).

[0008] In a preferred or alternative embodiment, the hard inner surface layer includes random copolymerized polypropylene, block copolymerized polypropylene, nano-rigid particles, and barium sulfate in a mass ratio of (15 - 20):(12 - 15):(4 - 6):(1 - 1.5). The nano-rigid particles include modified nano-silica particles and modified nano-silver particles in a mass ratio of (20 - 25):(3 - 5).

[0009] The present invention also provides a preparation method of the composite polypropylene film packaging material for preparing the above packaging material, including:

[0010] S110: Prepare the outer surface mixture, the middle layer mixture, and the inner surface mixture, and separately put them into the outer feeding port, the middle layer feeding port, and the inner layer feeding port of the casting film machine. Control the melting temperature of the casting film machine at 240°C - 250°C, and then extrude and form to obtain a three-layer composite film material;

[0011] S120: Heat the three-layer composite film material to 100°C - 110°C, and then perform longitudinal stretching, controlling the stretching ratio at 5 - 5.5 times. Then heat the longitudinally stretched three-layer composite film material to 170°C - 175°C, and then perform transverse stretching, controlling the stretching ratio at 7 - 7.5 times to obtain a composite polypropylene film packaging material.

[0012] In a preferred or alternative embodiment, the specific preparation steps of the outer surface mixture are as follows:

[0013] S210: Mix homopolypropylene and maleic anhydride grafted polypropylene with a mass ratio of (10 - 15):(1 - 1.5), then add POE elastomer thereto, and perform ultrasonic vibration at a temperature of 80°C - 90°C for 40 min - 50 min to obtain a premix;

[0014] S220: Add block copolymer polypropylene and talcum powder to the premix, stir for 3 min - 5 min, and then perform ultrasonic vibration for 50 min - 60 min to obtain the outer surface mixture.

[0015] In a preferred or alternative embodiment, the specific preparation steps of the middle layer mixture are as follows:

[0016] S310: Add chitosan to pure water, then dropwise add potassium hydroxide and continuously stir at a temperature of 70°C - 75°C for 40 min - 50 min, then add acetic acid to adjust the pH to 4.5 - 5, and then perform vacuum drying at a temperature of 50°C - 55°C to obtain chitosan powder. Uniformly mix linear low density polyethylene, polyurethane acrylate, and chitosan powder with a mass ratio of (13 - 18):(2 - 3):(0.5 - 1.2) to obtain an intermediate mixture;

[0017] S320: Add random copolymer polypropylene and homopolypropylene to the intermediate mixture, and stir at a temperature of 50°C - 60°C for 10 min - 15 min to obtain the middle layer mixture.

[0018] In a preferred or alternative embodiment, the specific preparation steps of the inner surface mixture are as follows:

[0019] S410: Add nano-rigid particles to N,N-dimethylformamide, perform ultrasonic dispersion to obtain dispersed nano-particles, and then load the dispersed nano-particles into a syringe;

[0020] S420: Stir the random copolymer polypropylene and block copolymer polypropylene at a temperature of 35°C - 40°C for 10 min - 15 min to obtain a polypropylene mixture. Then, apply a voltage of 13 kV - 15 kV between the polypropylene mixture and a syringe to allow the dispersed nanoparticles to enter the polypropylene mixture at a rate of 5 ml / min - 8 ml / min, and stir the polypropylene mixture at a rate of 700 r / min - 750 r / min to obtain a particle-modified polypropylene mixture;

[0021] S430: Place the particle-modified polypropylene mixture in an environment of 0°C - 5°C, then add barium sulfate, and quickly stir at a rate of 1200 r / min - 1300 r / min for 5 min - 8 min to obtain an inner surface layer mixture.

[0022] In a preferred or alternative embodiment, the nano-rigid particles are prepared through the following steps:

[0023] S510: Uniformly disperse nano-silica into xylene, then add 3-glycidoxypropyltrimethoxysilane, and stir at a rate of 600 r / min - 750 r / min at a temperature of 40°C - 50°C for 5 h - 6 h. Cool and filter to obtain primary-modified nano-silica particles;

[0024] S520: Uniformly disperse nano-silver into tetrahydrofuran, then add 2-epoxypropyl dodecyl dimethyl quaternary ammonium salt, and stir at a rate of 500 r / min - 560 r / min at a temperature of 60°C - 70°C for 10 h - 12 h. Cool and filter to obtain primary-modified nano-silver particles;

[0025] S530: Add the primary-modified nano-silica particles and primary-modified nano-silver particles to ethyl acetate and mix evenly. Then add 4-methoxy-3-hydroxybenzaldehyde, diethanolamine, and 1-hydroxybenzotriazole, and stir at a rate of 800 r / min - 850 r / min at a temperature of 45°C - 55°C for 7 h - 9 h. Cool and filter to obtain nano-rigid particles.

[0026] In a preferred or alternative embodiment, in S410, the mass ratio of the nano-rigid particles to N,N-dimethylformamide is (6 - 8):(90 - 100), and the ultrasonic dispersion controls the ultrasonic frequency at 40 KHz - 45 KHz and the ultrasonic time at 30 min - 35 min.

[0027] In summary, the present invention has the following beneficial effects:

[0028] (1) The packaging material of the present invention adds nano-rigid particles to the inner surface layer, and at the same time cooperates with a proper proportion of random copolymer polypropylene and block copolymer polypropylene, effectively improving the hardness of the inner surface layer, enabling the inner surface layer to resist the extrusion of sharp parts such as broken bones and fish bones. At the same time, barium sulfate is also added to the inner surface layer of the present invention, which can ensure that the inner surface layer has a certain transparency;

[0029] (2) The packaging material of the present invention adds polyethylene to the middle layer, which can improve the flexibility of the middle layer, so that when the inner surface layer is extruded, it can extend into the middle layer, further resisting the sharp part and ensuring that the outer packaging is not damaged;

[0030] (3) The packaging material of the present invention adds POE elastomer to the outer surface layer, and at the same time cooperates with a proper proportion of block copolymer polypropylene and homopolypropylene, which can effectively improve the toughness of the outer surface layer and prevent the outer surface layer from being broken when the inner surface layer extends outwards;

[0031] (4) The nano-rigid particles in the present invention include modified nano-silica particles and modified nano-silver particles. By modifying the nano-silica and nano-silver particles, the connection between the nano-silica and nano-silver particles and polypropylene can be increased, thus playing a role in further strengthening the hardness. On the other hand, the addition of nano-silver can also improve the antibacterial performance of the polypropylene film;

[0032] (5) In the present invention, in order to make the nano-rigid particles evenly dispersed in the polypropylene mixture, the dispersed nano-particles are added to the stirred polypropylene mixture by means of electrostatic injection. By reducing the contact area between the nano-dispersed particles and the polypropylene mixture during addition, the nano-rigid particles can be more evenly dispersed in the polypropylene mixture. Specific embodiments

[0033] In order to make the above objects, features and advantages of the present invention more obvious and understandable, the following detailed description is made on the specific embodiments of the present invention.

[0034] The specific implementation manner of the present invention provides a composite polypropylene film packaging material, which includes a tough outer layer, a flexible intermediate layer, and a rigid inner layer; the tough outer layer includes block copolymer polypropylene, homopolypropylene, POE elastomer, and talcum powder with a mass ratio of (20 - 25):(10 - 15):(1 - 3):(0.8 - 1.2). The POE elastomer includes a random copolymer of ethylene and 1-octene, and the content of 1-octene in the POE elastomer is 20% - 25%; the flexible intermediate layer includes random copolymer polypropylene, homopolypropylene, and linear low-density polyethylene with a mass ratio of (15 - 20):(3 - 7):(13 - 18); the rigid inner layer includes random copolymer polypropylene, block copolymer polypropylene, nano-rigid particles, and barium sulfate with a mass ratio of (15 - 20):(12 - 15):(4 - 6):(1 - 1.5). The nano-rigid particles include modified nano-silica particles and modified nano-silver particles with a mass ratio of (20 - 25):(3 - 5). The thickness ratio of the tough outer layer, the flexible intermediate layer, and the rigid inner layer is 1:(0.8 - 0.9):(1.1 - 1.15).

[0035] Preferably, the thickness ratio of the tough outer layer, the flexible intermediate layer, and the rigid inner layer is 1:0.87:1.12.

[0036] Preferably, the thickness of the tough outer layer is 2.5 μm.

[0037] Preferably, the tough outer layer includes block copolymer polypropylene, homopolypropylene, POE elastomer, and talcum powder with a mass ratio of 24:11:1.8:0.15.

[0038] Preferably, the flexible intermediate layer includes random copolymer polypropylene, homopolypropylene, and linear low-density polyethylene with a mass ratio of 16:5:14.

[0039] Preferably, the rigid inner layer includes random copolymer polypropylene, block copolymer polypropylene, nano-rigid particles, and barium sulfate with a mass ratio of 18:14:5:1.34.

[0040] Preferably, the nano-rigid particles include modified nano-silica particles and modified nano-silver particles with a mass ratio of 23:4.

[0041] For the convenience of understanding and preparation, a preparation method of the above composite polypropylene film packaging material is provided in this embodiment. The specific preparation steps are as follows:

[0042] S110: Prepare the outer layer mixture, the intermediate layer mixture, and the inner layer mixture, and respectively put them into the outer layer feeding port, the intermediate layer feeding port, and the inner layer feeding port of the casting film machine. Control the melting temperature of the casting film machine at 240°C - 250°C, and then extrude and form to obtain a three-layer composite film material;

[0043] S120: Heat the three - layer composite film material to 100°C - 110°C, then conduct longitudinal stretching, control the stretching ratio at 5 - fold to 5.5 - fold. Then heat the longitudinally stretched three - layer composite film material to 170°C - 175°C, and then conduct transverse stretching, control the stretching ratio at 7 - fold to 7.5 - fold to obtain the composite polypropylene film packaging material.

[0044] Preferably, control the melting temperature of the casting film machine at 246°C.

[0045] Preferably, heat the three - layer composite film material to 105°C, then conduct longitudinal stretching, control the stretching ratio at 5.2 - fold.

[0046] Preferably, heat the longitudinally stretched three - layer composite film material to 172°C, then conduct transverse stretching, control the stretching ratio at 7.4 - fold.

[0047] Among them, the above - mentioned outer - layer mixture is prepared through the following steps:

[0048] S210: Mix homopolypropylene and maleic anhydride - grafted polypropylene with a mass ratio of (10 - 15):(1 - 1.5), then add POE elastomer to it, and conduct ultrasonic vibration for 40 min - 50 min under the temperature condition of 80°C - 90°C to obtain a pre - mixture;

[0049] S220: Add block copolymer polypropylene and talcum powder to the pre - mixture, stir for 3 min - 5 min, and then conduct ultrasonic vibration for 50 min - 60 min to obtain the outer - layer mixture.

[0050] By pre - mixing the POE elastomer in the homopolypropylene, the POE elastomer can be more evenly mixed in the polypropylene material, avoiding the situation of POE elastomer agglomeration or accumulation at the bottom.

[0051] Preferably, the mass ratio of homopolypropylene to maleic anhydride - grafted polypropylene is 11:1.5.

[0052] The above - mentioned middle - layer mixture is prepared through the following steps:

[0053] S310: Add chitosan to pure water, then dropwise add potassium hydroxide and continuously stir for 40 min - 50 min under the temperature condition of 70°C - 75°C. Then add acetic acid to adjust the pH to 4.5 - 5, and then conduct vacuum drying under the temperature condition of 50°C - 55°C to obtain chitosan powder. Mix linear low - density polyethylene, polyurethane acrylate and chitosan powder with a mass ratio of (13 - 18):(2 - 3):(0.5 - 1.2) evenly to obtain the middle - layer mixture;

[0054] S320: Add random copolymer polypropylene and homopolypropylene to the intermediate mixture and stir for 10 min - 15 min at a temperature of 50°C - 60°C to obtain the intermediate layer mixture.

[0055] By adding polyurethane acrylate and chitosan powder, the polypropylene film can be further softened. At the same time, the connection between the outer surface layer, the inner surface layer and the intermediate layer can be increased, and the breakage of the polypropylene film caused by uneven stress between layers can be reduced.

[0056] Preferably, the mass ratio of linear low density polyethylene, polyurethane acrylate and chitosan powder is 17:2.4:0.82.

[0057] The specific preparation steps of the above inner surface layer mixture are as follows:

[0058] S410: Mix nano-rigid particles and N,N-dimethylformamide with a mass ratio of (6 - 8):(90 - 100), disperse them by ultrasonic wave, and control the ultrasonic frequency at 40 KHz - 45 KHz and the ultrasonic time at 30 min - 35 min to obtain dispersed nano-particles, and then load the dispersed nano-particles into a syringe;

[0059] S420: Stir random copolymer polypropylene and block copolymer polypropylene for 10 min - 15 min at a temperature of 35°C - 40°C to obtain a polypropylene mixture, and then apply a voltage of 13 kV - 15 kV between the polypropylene mixture and the syringe to make the dispersed nano-particles enter the polypropylene mixture at a speed of 5 ml / min - 8 ml / min, and stir the polypropylene mixture at a speed of 700 r / min - 750 r / min to obtain a particle-modified polypropylene mixture;

[0060] S430: Place the particle-modified polypropylene mixture in an environment of 0°C - 5°C, then add barium sulfate, and quickly stir at a speed of 1200 r / min - 1300 r / min for 5 min - 8 min to obtain the inner surface layer mixture.

[0061] Through the method of electrostatic injection, the nano-rigid particles can be added to the polypropylene mixture in the form of filaments, reducing the contact area between the nano-rigid particles and the polypropylene mixture during addition, and making the nano-rigid particles more evenly dispersed in the polypropylene mixture. In S530, quickly stirring and adding barium sulfate in the given temperature environment can avoid the flow and aggregation of nano-rigid particles at high temperature.

[0062] Preferably, the mass ratio of nano-rigid particles to N,N-dimethylformamide is 7:95.

[0063] Preferably, control the ultrasonic frequency at 45 KHz and the ultrasonic time at 30 min.

[0064] Preferably, a voltage of 14 kV is applied between the polypropylene mixture and the syringe, so that the dispersed nanoparticles enter the polypropylene mixture at a speed of 6 ml / min, and the polypropylene mixture is stirred at a speed of 720 r / min.

[0065] For the convenience of understanding and production, a preparation method of nano-rigid particles is provided in this embodiment. The specific preparation steps are as follows:

[0066] S510: Uniformly disperse nano-silica into xylene, then add 3-glycidoxypropyltrimethoxysilane, and stir at a speed of 600 r / min - 750 r / min for 5 h - 6 h under the temperature condition of 40°C - 50°C, cool and filter to obtain primary modified nano-silica particles;

[0067] S520: Uniformly disperse nano-silver into tetrahydrofuran, then add 2-epoxypropyl dodecyl dimethyl quaternary ammonium salt, and stir at a speed of 500 r / min - 560 r / min for 10 h - 12 h under the temperature condition of 60°C - 70°C, cool and filter to obtain primary modified nano-silver particles;

[0068] S530: Add the primary modified nano-silica particles and the primary modified nano-silver particles into ethyl acetate and mix evenly, then add 4-methoxy-3-hydroxybenzaldehyde, diethanolamine and 1-hydroxybenzotriazole, and stir at a speed of 800 r / min - 850 r / min for 7 h - 9 h under the temperature condition of 45°C - 55°C, cool and filter to obtain nano-rigid particles.

[0069] In S510, the mass ratio of nano-silica, xylene, and 3-glycidoxypropyltrimethoxysilane is (15 - 22):(120 - 150):(7 - 13).

[0070] In S520, the mass ratio of nano-silver, tetrahydrofuran, and 2-epoxypropyl dodecyl dimethyl quaternary ammonium salt is (7 - 10):(25 - 50):(4 - 8).

[0071] In S530, the mass ratio of the primary modified nano-silica particles, ethyl acetate, 4-methoxy-3-hydroxybenzaldehyde, diethanolamine, and 1-hydroxybenzotriazole is (5 - 12):(40 - 80):(4 - 6):(2 - 3):(1 - 2).

[0072] The technical solutions and effects of the present invention will be illustrated below with specific embodiments.

[0073] Example 1

[0074] This embodiment provides a composite polypropylene film packaging material, which includes a tough outer layer, a flexible intermediate layer, and a rigid inner layer. The rigid inner layer includes random copolymer polypropylene, block copolymer polypropylene, nano-rigid particles, and barium sulfate with a mass ratio of 18:14:5:1.34. The nano-rigid particles include modified nano-silica particles and modified nano-silver particles with a mass ratio of 23:4. The flexible intermediate layer includes random copolymer polypropylene, homopolypropylene, and linear low-density polyethylene with a mass ratio of 16:5:14. The tough outer layer includes block copolymer polypropylene, homopolypropylene, POE elastomer, and talcum powder with a mass ratio of 24:11:1.8:0.15. The thickness ratio of the tough outer layer, the flexible intermediate layer, and the rigid inner layer is 1:0.87:1.12, and the thickness of the tough outer layer is 2.5um.

[0075] The above composite polypropylene film packaging material is prepared through the following steps:

[0076] S1: Mix homopolypropylene and maleic anhydride grafted polypropylene with a mass ratio of 11:1.5, then add POE elastomer to it, and perform ultrasonic vibration for 45 minutes at a temperature of 85°C to obtain a pre-mixed material; add block copolymer polypropylene and talcum powder to the pre-mixed material, stir for 4 minutes, and then perform ultrasonic vibration for 55 minutes to obtain an outer layer mixed material;

[0077] S2: Add chitosan to pure water, then dropwise add potassium hydroxide and continuously stir for 45 minutes at a temperature of 75°C, then add acetic acid to adjust the PH to 4.8, and then perform vacuum drying at a temperature of 52°C to obtain chitosan powder. Uniformly mix linear low-density polyethylene, polyurethane acrylate, and chitosan powder with a mass ratio of 17:2.4:0.82 to obtain an intermediate mixed material; add random copolymer polypropylene and homopolypropylene to the intermediate mixed material, and stir for 15 minutes at a temperature of 55°C to obtain an intermediate layer mixed material;

[0078] S3: Mix nano-rigid particles and N,N-dimethylformamide with a mass ratio of 7:95, perform ultrasonic dispersion, and control the ultrasonic frequency at 45KHz and the ultrasonic time at 30 minutes to obtain dispersed nano-particles, and then load the dispersed nano-particles into a syringe; stir random copolymer polypropylene and block copolymer polypropylene for 15 minutes at a temperature of 40°C to obtain a polypropylene mixed material, and then apply a voltage of 14kV between the polypropylene mixed material and the syringe to make the dispersed nano-particles enter the polypropylene mixed material at a speed of 6ml / min, and stir the polypropylene mixed material at a speed of 720r / min to obtain a particle-modified polypropylene mixed material; place the particle-modified polypropylene mixed material in an environment of 4°C, then add barium sulfate, and quickly stir at a speed of 1200r / min for 7 minutes to obtain an inner layer mixed material;

[0079] S4: Feed the outer layer mixture, the middle layer mixture, and the inner surface layer mixture into the outer layer feeding port, the middle layer feeding port, and the inner layer feeding port of the casting film machine respectively. Control the melting temperature of the casting film machine at 246 °C, and then extrude and form to obtain a three-layer composite film material. Heat the three-layer composite film material to 105 °C, then conduct longitudinal stretching, control the stretching ratio at 5.2 times, and then heat the longitudinally stretched three-layer composite film material to 172 °C, and then conduct transverse stretching, control the stretching ratio at 7.4 times to obtain a composite polypropylene film packaging material.

[0080] Example 2

[0081] This embodiment provides a composite polypropylene film packaging material, which includes a tough outer layer, a flexible middle layer, and a hard inner surface layer. The hard inner surface layer includes random copolymer polypropylene, block copolymer polypropylene, and barium sulfate with a mass ratio of 18:14:1.34. The flexible middle layer includes random copolymer polypropylene, homopolypropylene, and linear low-density polyethylene with a mass ratio of 16:5:14. The tough outer layer includes block copolymer polypropylene, homopolypropylene, POE elastomer, and talc powder with a mass ratio of 24:11:1.8:0.15. The thickness ratio of the tough outer layer, the flexible middle layer, and the hard inner surface layer is 1:0.87:1.12, and the thickness of the tough outer layer is 2.5 um.

[0082] The above composite polypropylene film packaging material is prepared through the following steps:

[0083] S1: Mix homopolypropylene and maleic anhydride grafted polypropylene with a mass ratio of 11:1.5, then add POE elastomer thereto, and perform ultrasonic vibration for 45 min under the temperature condition of 85 °C to obtain a pre-mixture. Add block copolymer polypropylene and talc powder to the pre-mixture, stir for 4 min, and then perform ultrasonic vibration for 55 min to obtain an outer layer mixture.

[0084] S2: Add chitosan to pure water, then dropwise add potassium hydroxide and continuously stir for 45 min under the temperature condition of 75 °C, then add acetic acid to adjust the pH to 4.8, and then perform vacuum drying under the temperature condition of 52 °C to obtain chitosan powder. Uniformly mix linear low-density polyethylene, polyurethane acrylate, and chitosan powder with a mass ratio of 17:2.4:0.82 to obtain an intermediate mixture. Add random copolymer polypropylene and homopolypropylene to the intermediate mixture and stir for 15 min under the temperature condition of 55 °C to obtain a middle layer mixture.

[0085] S3: Stir random copolymer polypropylene and block copolymer polypropylene for 15 min under the temperature condition of 40 °C to obtain a polypropylene mixture. Place the polypropylene mixture in an environment of 4 °C, then add barium sulfate, and quickly stir at a speed of 1200 r / min for 7 min to obtain an inner surface layer mixture.

[0086] S4: Feed the outer surface mixture, the middle layer mixture, and the inner surface mixture into the outer feed port, the middle layer feed port, and the inner layer feed port of the casting film machine respectively. Control the melting temperature of the casting film machine at 246 °C, and then extrude and form to obtain a three-layer composite film material. Heat the three-layer composite film material to 105 °C, and then perform longitudinal stretching, controlling the stretching ratio at 5.2 times. Then heat the longitudinally stretched three-layer composite film material to 172 °C, and then perform transverse stretching, controlling the stretching ratio at 7.4 times to obtain a composite polypropylene film packaging material.

[0087] Example 3

[0088] This example provides a composite polypropylene film packaging material, including a tough outer layer, a flexible middle layer, and a hard inner layer. The hard inner layer includes random copolymer polypropylene, block copolymer polypropylene, nano-rigid particles, and barium sulfate with a mass ratio of 18:14:5:1.34. The nano-rigid particles include modified nano-silica particles and modified nano-silver particles with a mass ratio of 23:4. The flexible middle layer includes random copolymer polypropylene and homopolypropylene with a mass ratio of 16:5. The tough outer layer includes block copolymer polypropylene, homopolypropylene, POE elastomer, and talcum powder with a mass ratio of 24:11:1.8:0.15. The thickness ratio of the tough outer layer, the flexible middle layer, and the hard inner layer is 1:0.87:1.12, and the thickness of the tough outer layer is 2.5 μm.

[0089] The above composite polypropylene film packaging material is prepared through the following steps:

[0090] S1: Mix homopolypropylene and maleic anhydride grafted polypropylene with a mass ratio of 11:1.5, then add POE elastomer thereto, and perform ultrasonic vibration at a temperature of 85 °C for 45 min to obtain a premixed material. Add block copolymer polypropylene and talcum powder to the premixed material, stir for 4 min, and then perform ultrasonic vibration for 55 min to obtain an outer surface mixture.

[0091] S2: Add chitosan to pure water, then dropwise add potassium hydroxide and continuously stir at a temperature of 75 °C for 45 min, then add acetic acid to adjust the pH to 4.8, and then perform vacuum drying at a temperature of 52 °C to obtain chitosan powder. Uniformly mix polyurethane acrylate and chitosan powder with a mass ratio of 2.4:0.82 to obtain an intermediate mixture. Add random copolymer polypropylene and homopolypropylene to the intermediate mixture, and stir at a temperature of 55 °C for 15 min to obtain a middle layer mixture.

[0092] S3: Mix nano-rigid particles and N,N-dimethylformamide with a mass ratio of 7:95, disperse them by ultrasonic wave, control the ultrasonic frequency at 45 KHz and the ultrasonic time at 30 min to obtain dispersed nano-particles, and then load the dispersed nano-particles into a syringe; Stir random copolymer polypropylene and block copolymer polypropylene at 40 °C for 15 min to obtain a polypropylene mixture, then apply a voltage of 14 kV between the polypropylene mixture and the syringe to make the dispersed nano-particles enter the polypropylene mixture at a speed of 6 ml / min, and stir the polypropylene mixture at a speed of 720 r / min to obtain a particle-modified polypropylene mixture; Place the particle-modified polypropylene mixture in an environment of 4 °C, then add barium sulfate, and quickly stir at a speed of 1200 r / min for 7 min to obtain an inner surface layer mixture;

[0093] S4: Feed the outer surface layer mixture, the intermediate layer mixture, and the inner surface layer mixture into the outer feed port, the intermediate feed port, and the inner feed port of a casting film machine respectively, control the melting temperature of the casting film machine at 246 °C, and then extrude and form to obtain a three-layer composite film material; Heat the three-layer composite film material to 105 °C, then conduct longitudinal stretching, control the stretching ratio at 5.2 times, and then heat the longitudinally stretched three-layer composite film material to 172 °C, and then conduct transverse stretching, control the stretching ratio at 7.4 times to obtain a composite polypropylene film packaging material.

[0094] Performance Test

[0095] Conduct tensile strength, elongation at break, and puncture tests on the composite polypropylene film packaging materials prepared in Examples 1-3. The test results are shown in Table 1. The test steps for the puncture test are as follows: Cut a 20 cm × 20 cm sample material, and then use a 0.1 cm2 stylet to conduct puncture, and test the force value of the stylet when the sample is pierced.

[0096] Table 1

[0097]

[0098] It can be found from the data in Table 1 that the addition of nano-rigid particles and linear low-density polyethylene has little effect on the tensile strength and elongation at break of the material, but the composite polypropylene film packaging material added with nano-rigid particles and linear low-density polyethylene can have better puncture resistance.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements 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 composite polypropylene film packaging material, characterized in that, It includes a tough outer layer, a flexible intermediate layer, and a rigid inner layer. The tough outer layer includes the following components: block copolymerized polypropylene, homopolymerized polypropylene, POE elastomer, and talcum powder. The flexible intermediate layer includes the following components: random copolymerized polypropylene, homopolymerized polypropylene, and polyethylene. The rigid inner layer includes the following components: random copolymerized polypropylene, block copolymerized polypropylene, nano-rigid particles, and barium sulfate. The thickness ratio of the tough outer layer, the flexible intermediate layer, and the rigid inner layer is 1:(0.8 - 0.9):(1.1 - 1.15). The raw materials of the rigid inner layer are prepared by the following method: Uniformly disperse nano-silica into xylene, then add 3-glycidoxypropyltrimethoxysilane, and stir at a speed of 600 r / min - 750 r / min for 5 h - 6 h under the temperature condition of 40°C - 50°C, cool and filter to obtain primary modified nano-silica particles; Uniformly disperse nano-silver into tetrahydrofuran, then add 2-epoxypropyl dodecyl dimethyl quaternary ammonium salt, and stir at a speed of 500 r / min - 560 r / min for 10 h - 12 h under the temperature condition of 60°C - 70°C, cool and filter to obtain primary modified nano-silver particles; Add the primary modified nano-silica particles and the primary modified nano-silver particles into ethyl acetate and mix evenly, then add 4-methoxy-3-hydroxybenzaldehyde, diethanolamine, and 1-hydroxybenzotriazole, and stir at a speed of 800 r / min - 850 r / min for 7 h - 9 h under the temperature condition of 45°C - 55°C, cool and filter to obtain the nano-rigid particles; Add the nano-rigid particles into N,N-dimethylformamide, ultrasonically disperse to obtain dispersed nano-particles, then load the dispersed nano-particles into a syringe; Stir random copolymerized polypropylene and block copolymerized polypropylene for 10 min - 15 min under the temperature condition of 35°C - 40°C to obtain a polypropylene mixture, then apply a voltage of 13 kV - 15 kV between the polypropylene mixture and the syringe to make the dispersed nano-particles enter the polypropylene mixture at a speed of 5 ml / min - 8 ml / min, and stir the polypropylene mixture at a speed of 700 r / min - 750 r / min to obtain a particle-modified polypropylene mixture; Place the particle-modified polypropylene mixture in an environment of 0°C - 5°C, then add barium sulfate, and quickly stir at a speed of 1200 r / min - 1300 r / min for 5 min - 8 min to obtain an inner layer mixture.

2. The packaging material according to claim 1, characterized in that, The tough outer layer includes block copolymerized polypropylene, homopolymerized polypropylene, POE elastomer, and talcum powder with a mass ratio of (20 - 25):(10 - 15):(1 - 3):(0.8 - 1.2). The POE elastomer includes a random copolymer of ethylene and 1-octene, and the content of 1-octene in the POE elastomer is 20% - 25%.

3. The packaging material according to claim 1, characterized in that, The flexible intermediate layer comprises random copolymer polypropylene, homopolypropylene, and linear low density polyethylene with a mass ratio of (15-20):(3-7):(13-18).

4. The packaging material according to claim 1, characterized in that, The rigid inner surface layer comprises random copolymer polypropylene, block copolymer polypropylene, nano rigid particles, and barium sulfate with a mass ratio of (15-20):(12-15):(4-6):(1-1.5). The nano rigid particles comprise modified nano silica particles and modified nano silver particles with a mass ratio of (20-25):(3-5).

5. A preparation method of a composite polypropylene film packaging material, characterized in that, The method for preparing the packaging material according to any one of claims 1-4, comprising: S110: Prepare the outer surface layer mixture, intermediate layer mixture, and inner surface layer mixture, and respectively input them into the outer layer feeding port, intermediate layer feeding port, and inner layer feeding port of a casting film machine. Control the melting temperature of the casting film machine at 240°C - 250°C, and then extrude and form to obtain a three-layer composite film material; S120: Heat the three-layer composite film material to 100°C - 110°C, then conduct longitudinal stretching, control the stretching ratio at 5 - 5.5 times, and then heat the longitudinally stretched three-layer composite film material to 170°C - 175°C, and then conduct transverse stretching, control the stretching ratio at 7 - 7.5 times, to obtain the composite polypropylene film packaging material.

6. The preparation method of the packaging material according to claim 5, characterized in that, The specific preparation steps of the outer surface layer mixture are as follows: S210: Mix homopolypropylene and maleic anhydride grafted polypropylene with a mass ratio of (10-15):(1-1.5), then add POE elastomer thereto, and conduct ultrasonic vibration for 40 - 50 minutes under the temperature condition of 80°C - 90°C to obtain a pre-mixture; S220: Add block copolymer polypropylene and talcum powder to the pre-mixture, stir for 3 - 5 minutes, and then conduct ultrasonic vibration for 50 - 60 minutes to obtain the outer surface layer mixture.

7. The preparation method of the packaging material according to claim 5, wherein, The specific preparation steps of the intermediate layer mixture are as follows: S310: Add chitosan to pure water, then dropwise add potassium hydroxide and continuously stir for 40 - 50 minutes under the temperature condition of 70°C - 75°C, then add acetic acid to adjust the pH to 4.5 - 5, and then conduct vacuum drying under the temperature condition of 50°C - 55°C to obtain chitosan powder. Uniformly mix linear low density polyethylene, polyurethane acrylate, and the chitosan powder with a mass ratio of (13-18):(2-3):(0.5-1.2) to obtain an intermediate mixture; S320: Add random copolymer polypropylene and homopolypropylene to the intermediate mixture, and stir for 10 - 15 minutes under the temperature condition of 50°C - 60°C to obtain the intermediate layer mixture.

8. The preparation method of the packaging material according to claim 5, characterized in that, The specific preparation steps of the inner surface layer mixture are as follows: S410: Add the nano rigid particles to N,N-dimethylformamide, conduct ultrasonic dispersion to obtain dispersed nano particles, and then load the dispersed nano particles into a syringe; S420: Stir the random copolymer polypropylene and block copolymer polypropylene at a temperature of 35°C - 40°C for 10 min - 15 min to obtain a polypropylene mixture. Then, apply a voltage of 13 kV - 15 kV between the polypropylene mixture and the syringe to allow the dispersed nanoparticles to enter the polypropylene mixture at a rate of 5 ml / min - 8 ml / min, and stir the polypropylene mixture at a rate of 700 r / min - 750 r / min to obtain a particle-modified polypropylene mixture; S430: Place the particle-modified polypropylene mixture in an environment of 0°C - 5°C, then add barium sulfate, and quickly stir at a rate of 1200 r / min - 1300 r / min for 5 min - 8 min to obtain the inner surface layer mixture.

9. The preparation method of the packaging material according to claim 8, characterized in that, The nano-rigid particles are prepared through the following steps: S510: Uniformly disperse nano-silica in xylene, then add 3-glycidoxypropyltrimethoxysilane, and stir at a rate of 600 r / min - 750 r / min at a temperature of 40°C - 50°C for 5 h - 6 h, cool and filter to obtain primary-modified nano-silica particles; S520: Uniformly disperse nano-silver in tetrahydrofuran, then add 2-epoxypropyl dodecyl dimethyl quaternary ammonium salt, and stir at a rate of 500 r / min - 560 r / min at a temperature of 60°C - 70°C for 10 h - 12 h, cool and filter to obtain primary-modified nano-silver particles; S530: Add the primary-modified nano-silica particles and the primary-modified nano-silver particles to ethyl acetate and mix evenly, then add 4-methoxy-3-hydroxybenzaldehyde, diethanolamine and 1-hydroxybenzotriazole, and stir at a rate of 800 r / min - 850 r / min at a temperature of 45°C - 55°C for 7 h - 9 h, cool and filter to obtain the nano-rigid particles.

10. The method for preparing the packaging material according to claim 8, characterized in that, In the S410, the mass ratio of the nano-rigid particles to the N,N-dimethylformamide is (6 - 8):(90 - 100), and the ultrasonic dispersion controls the ultrasonic frequency at 40 KHz - 45 KHz and the ultrasonic time at 30 min - 35 min.

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