Multilayer coextruded cpp packaging film and process for its production

Abstract

This invention proposes a multilayer co-extruded CPP packaging film and its production process, specifically relating to the field of polymer packaging materials technology. The film comprises a heat-sealing layer, an intermediate layer, and a corona layer connected sequentially. By weight percentage, the heat-sealing layer includes 85-95% base resin, 1-3% slip agent, and 2-4% antistatic agent. The slip agent migrates to the surface to form a lubricating layer, and the antistatic agent forms a conductive network. Both work synergistically to reduce powder adsorption. The base resin is random copolymer PP. The intermediate layer includes 80-90% homopolymer PP and 10-20% high-crystallinity PP. The corona layer is polypropylene resin. This invention provides a multilayer co-extruded CPP packaging film and its production process, which can modify CPP film to possess multifunctional technical characteristics. It simultaneously meets the comprehensive requirements of powder packaging for antistatic properties, moisture barrier properties, transparency, and strong mechanical properties, achieving a self-cleaning effect.

Description

Technical Field

[0001] This invention belongs to the field of polymer packaging materials technology, specifically relating to a multilayer co-extruded cast polypropylene (CPP) packaging film for powder packaging, and the production process of the packaging film. Background Technology

[0002] Cast polypropylene (CPP) film is an unstretched polypropylene film produced through a melt casting and quenching process. It features uniform thickness, high transparency, and good heat-sealing properties, and is widely used in packaging materials for food, pharmaceuticals, and daily chemicals. In the packaging of powdered products (such as milk powder, nutritional supplements, coffee powder, and seasonings), CPP film is often used as the inner heat-sealing material of a composite film. However, existing CPP films face the following technical challenges in powder packaging applications:

[0003] During high-speed packaging, powdered products are easily dispersed and adhered to the sealing area of ​​the packaging bag due to electrostatic adsorption, leading to problems such as inadequate heat sealing, leakage, and package breakage. Specifically, ordinary CPP film is prone to static electricity accumulation during bag making and packaging, which not only attracts dust affecting the packaging appearance and sealing quality but may also limit packaging speed. In addition, high-end powder packaging requires high moisture barrier properties to prevent powder from absorbing moisture and clumping, while also requiring the film to have sufficient rigidity and toughness to adapt to the operation of high-speed automatic packaging machines. Summary of the Invention

[0004] The purpose of this invention is to provide a multilayer co-extruded CPP packaging film and its production process, which solves the technical problem of how to modify CPP film to give it multifunctional characteristics, so that it can simultaneously meet the comprehensive requirements of antistatic properties, moisture barrier, transparency and strong mechanical properties of powder packaging, and achieve the technical effect of self-cleaning.

[0005] A multilayer co-extruded CPP packaging film includes a heat-sealing layer, an intermediate layer, and a corona layer connected sequentially in top and bottom;

[0006] By mass percentage, the heat-sealing layer comprises 85-95% base resin, 1-3% slip agent (organic modified masterbatch with silica core) and 2-4% antistatic agent (nonionic polymer). The slip agent migrates to the surface to form a lubricating layer, and the antistatic agent forms a conductive network. The two work together to reduce powder adsorption. The base resin is random copolymer PP.

[0007] The intermediate layer comprises 80-90% homopolymer PP and 10-20% highly crystalline PP;

[0008] The corona layer is made of polypropylene resin.

[0009] The intermediate layer provides mechanical and barrier functions, using homopolymer PP (HCPP) to ensure rigidity, and incorporating a certain proportion of highly crystalline PP to enhance moisture resistance. The corona layer uses a special polypropylene resin and undergoes a special process to facilitate lamination with other packaging films.

[0010] The antistatic agent is any one of nano-ATO, nano-ITO, nano-AZO, and silver nanowires by mass percentage, and the antistatic agent also contains 0.1-0.3% multi-walled carbon nanotubes.

[0011] The intermediate layer also contains 1-3% nano-additives and 1-3% polyvinyl alcohol by mass percentage. The nano-additives are any one of nano-clay, mica, and montmorillonite. The ratio of nano-additives to polyvinyl alcohol by mass percentage is 1-2.

[0012] The outer side of the heat-sealing layer is provided with a coating, the coating composition of which includes polyvinylidene chloride, polypropylene or polyethylene, and the coating thickness is 0.1-0.5μm; by mass percentage, polyvinylidene chloride / (polypropylene + polyethylene) = 2-5.

[0013] The outer side of the corona layer is provided with a coating, the coating composition of which includes nano-silicon oxide and nano-alumina, and the coating thickness is 0.1-0.5μm; by mass percentage, nano-silicon oxide / nano-alumina = 5-10.

[0014] A manufacturing process for a multilayer co-extruded CPP packaging film specifically includes the following steps:

[0015] Step S1: Add the heat-sealing layer material components into the hopper of screw extruder one, and set the temperature of each zone, screen changing temperature, die head temperature and screw speed;

[0016] Step S2: Add the intermediate layer material components into the hopper of the screw extruder II, and set the temperature of each zone, screen changing temperature, die head temperature and screw speed;

[0017] Step S3: Add the corona layer material components into the hopper of screw extruder three, and set the temperature of each zone, screen changing temperature, die head temperature and screw speed of screw extruder three;

[0018] Step S4: When the temperature reaches the set temperature, all the screw extruders mentioned above are turned on at the same time for melting and extrusion. After melting and extrusion, the extruded material enters the multi-layer co-extrusion blown film machine. The film is blown through the die head to form a three-layer co-extrusion structure. The film is cooled and shaped by the cooling roller (cooling roller temperature 10-25℃). The surface of the corona layer is corona treated.

[0019] Step S5: In a vacuum environment, the heat-sealing layer and the corona layer are vapor-deposited separately to obtain the corresponding coatings, which enhance the adhesion between the coating and the plastic substrate and prevent the brittle ceramic layer from cracking when bent.

[0020] Step S6: After film drawing, blowing, stretching, traction, edge trimming and winding, a multi-layer co-extruded composite packaging film is prepared;

[0021] Step S7: Perform time-sensing processing on the reeled master roll, with a time limit of 24-72 hours.

[0022] The thickness of the multilayer co-extruded film is 20-26 μm, wherein the thickness of the heat-sealing layer is 5-7 μm, the thickness of the intermediate layer is 5-7 μm, and the thickness of the corona layer is 10-12 μm.

[0023] The screw extruder containing the raw materials that make up the heat-sealing layer has the following temperatures from the feed end to the discharge end: Zone 1 155℃, Zone 2 170℃, Zone 3 160℃, runner 165℃, and die 175℃. The adjustable range of these temperatures is ±2℃, and the screw speed is 35±2 rpm.

[0024] The screw extruder 2, which holds the raw materials that make up the intermediate layer, has the following temperature and screw speed in each zone from the feed end to the discharge end: Zone 1 185℃, Zone 2 210℃, Zone 3 205℃, runner 200℃, die head 210℃. The adjustable range of the above temperatures is ±2℃, and the screw speed is 30±2 rpm.

[0025] The screw extruder containing raw materials with corona layers has the following temperature and screw speed in each zone from the feed end to the discharge end: Zone 1 145℃, Zone 2 160℃, Zone 3 175℃, runner 175℃, and die 180℃. The adjustable range of the above temperatures is ±2℃, and the screw speed is 25±2 rpm.

[0026] It should be noted that when implementing this solution, precise control of the melt temperature of each layer is required to ensure full plasticization without affecting the performance of additives; optimization of the cooling roller temperature is necessary to obtain a product with high transparency and stable crystallization, which is beneficial for heat sealing; and control of the film roll tightness and thorough aging treatment are required to promote uniform precipitation of the slip agent. This CPP packaging film for powder packaging is applied in the demanding high-end powder packaging market for milk powder, nutritional supplements, coffee, and condiments, creating greater value for customers.

[0027] The technical details not described in this solution are based on the conventional understanding and operation of those skilled in the art, and can be implemented in conjunction with existing technology, and will not be elaborated here.

[0028] The beneficial effects of this invention are as follows:

[0029] (1) This solution successfully developed a high-performance CPP film for powder packaging. Its innovative three-layer co-extrusion structure and functional formula effectively solved the problem of powder contamination sealing. At the same time, it provides excellent moisture resistance, transparency and mechanical properties. All indicators have reached the predetermined target, and the comprehensive performance is at the leading level in the industry.

[0030] (2) The heat-sealing layer is the inner layer that comes into direct contact with the powder product. By adding a slip agent and a permanent antistatic agent to the heat-sealing layer at the same time, a dual action mechanism is formed. The slip agent migrates to the surface to form a lubricating layer and reduces the coefficient of friction. The antistatic agent forms a conductive network and conducts away static charge in time. The two work together to significantly reduce the adsorption of powder in the sealing area, ensure stable and reliable heat-sealing strength, and effectively solve the problem of powder contamination sealing.

[0031] The intermediate layer provides mechanical support and barrier function, and uses homopolymer polypropylene (HCPP) as the base resin to ensure the rigidity and moisture barrier properties of the film. The corona layer, as a composite functional layer, uses polypropylene resin that has been specially processed. Through corona treatment, its surface has a suitable surface tension, which facilitates its lamination with other packaging film materials.

[0032] This solution employs a three-layer functional structure design, where each layer performs its specific function. The heat-sealing layer is responsible for heat sealing and preventing powder adsorption. The middle layer uses homopolymer PP to ensure rigidity and moisture barrier properties. The corona layer facilitates composite with other materials, achieving an optimized balance of slip properties, antistatic properties, moisture barrier properties, transparency, and mechanical properties.

[0033] (3) To improve antistatic properties and slip properties, functional additives are added to the heat-sealing layer in the film. However, the migration and precipitation of the additives may affect the transparency, heat-sealing strength and composite strength with other layer materials of the film. At this time, multi-walled carbon nanotubes are added to the antistatic agent. This has little effect on the transparency, but improves the heat-sealing strength.

[0034] (4) By precisely controlling the temperature of the cooling roller (10-25℃), the melt film is cooled rapidly, increasing the amorphous area in the polymer and reducing the formation of crystalline phase, which helps to obtain a high-transparency film;

[0035] After special processing, the corona layer has moderate surface tension and excellent bonding strength with outer materials such as PET and BOPP. Through sufficient aging treatment (24-72 hours), the slip agent is promoted to migrate evenly to the surface, avoiding problems such as uneven precipitation of additives or later migration affecting the composite strength during use.

[0036] The CPP packaging film of this invention is particularly suitable for the market of powder products with extremely high packaging requirements, such as high-end milk powder, nutritional supplements, coffee and condiments, and has significant economic value and social benefits.

[0037] (5) In this scheme, a polyvinylidene chloride coating is set on the outside of the heat-sealing layer, which, together with polypropylene and polyethylene, not only has good transparency, but also blocks water vapor, oxygen and grease, greatly improving the moisture barrier performance. The nano-ATO, nano-ITO, nano-AZO or silver nanowires in the heat-sealing layer have good lattice matching with the nano-additives in the intermediate layer, which greatly increases the connection strength between the two.

[0038] To overcome the problem that a single material cannot simultaneously satisfy both "transparency" and "high barrier properties", this solution adds nano-additives and polyvinyl alcohol to the intermediate layer, and uses transparent nano-alumina or nano-silica to maintain both transparency and good moisture resistance.

[0039] (6) Adding nano-silica and nano-alumina coatings to the corona layer helps to form a "maze effect". When water vapor molecules pass through the film, they need to bypass these layers, and the path is greatly extended, thereby reducing the transmittance and increasing the moisture barrier performance.

[0040] In addition, the nano-silicon oxide and nano-alumina coatings in the corona layer and the nano-additives in the intermediate layer have good lattice matching, which greatly improves the bonding strength between the intermediate layer and the corona layer. Detailed Implementation

[0041] To more clearly illustrate the technical features of this solution, the following detailed implementation method will be used to explain the solution.

[0042] Example 1

[0043] A multilayer co-extruded CPP packaging film includes a heat-sealing layer, an intermediate layer, and a corona layer connected sequentially in top and bottom;

[0044] By mass percentage, the heat-sealing layer comprises 85-95% base resin, 1-3% slip agent (organic modified masterbatch with silica core) and 2-4% antistatic agent (nonionic polymer). The slip agent migrates to the surface to form a lubricating layer, and the antistatic agent forms a conductive network. The two work together to reduce powder adsorption. The base resin is random copolymer PP.

[0045] The intermediate layer comprises 80-90% homopolymer PP and 10-20% highly crystalline PP;

[0046] The corona layer is made of polypropylene resin.

[0047] The intermediate layer provides mechanical and barrier functions, using homopolymer PP (HCPP) to ensure rigidity, and incorporating a certain proportion of highly crystalline PP to enhance moisture resistance. The corona layer uses a special polypropylene resin and undergoes a special process to facilitate lamination with other packaging films.

[0048] The antistatic agent is any one of nano-ATO, nano-ITO, nano-AZO, and silver nanowires. In this Example 1, the antistatic agent is nano-ATO.

[0049] In this embodiment 1, the following three experimental groups and control groups are set up to verify the experimental effect:

[0050] Experimental Group 1: 1% slip agent, 4% antistatic agent, the remainder being the base resin; 80% homopolymer PP, 20% high-crystallinity PP; polypropylene resin;

[0051] Experimental Group 2: 2% slip agent, 3% antistatic agent, the remainder being the base resin; 85% homopolymer PP, 15% high-crystallinity PP; polypropylene resin;

[0052] Experimental Group 3: 3% slip agent, 2% antistatic agent, the remainder being the base resin; 90% homopolymer PP, 10% high-crystallinity PP; polypropylene resin;

[0053] Comparative Example 1: Only 2% slip agent was added, no antistatic agent was added, the rest was the base resin; homopolymer PP 85%, high crystallinity PP 15%; polypropylene resin;

[0054] Comparative Example 2: Only 2% antistatic agent was added, no slip agent was added, and the rest was the base resin; homopolymer PP 90%, high crystallinity PP 10%; polypropylene resin; Table 1 shows the performance test table of CPP packaging film under the above test groups and control groups, and the cooling roller temperature was controlled at 15℃.

[0055] Table 1 shows the performance test results of CPP packaging film for each of the above experimental and control groups.

[0056] Group Haze / % Gloss (45°) Coefficient of friction (heat seal layer / iron) Heat seal strength / N / 15mm Water vapor transmission rate / g / m²·24h <![CDATA[Surface resistance / ×10 11 Ω]]> electrostatic half-life Experimental group 1 3.2 92% 0.18 28 4.5 3.2 <2 seconds Experimental group 2 3.0 93% 0.16 30 4.1 3.6 <3 seconds Experimental group 3 3.0 94% 0.15 31 3.7 3.9 <4 seconds Comparison Group 1 3.1 93% 0.19 27 4.1 <![CDATA[>10 13 Oh]]> >23 seconds Comparison Group 2 4.3 86% 0.38 29 4.1 3.5 <5 seconds

[0057] As can be seen from Table 1, according to test groups 1-3, with the increase of slip agent and the decrease of antistatic agent, the haze gradually decreases and tends to stabilize, the gloss gradually increases, the coefficient of friction decreases, the heat seal strength increases, and the surface resistance and electrostatic half-life both increase. With the increase of homopolymer PP content, the water vapor transmission rate decreases. In summary, the principle is that the slip agent migrates to the surface to form a lubricating layer, reducing the coefficient of friction; the antistatic agent forms a conductive network, which promptly conducts away static charge, ensuring stable and reliable heat seal strength; and the use of homopolymer PP in the intermediate layer ensures rigidity and moisture barrier properties.

[0058] Combining control groups 1 and 2, without the addition of an antistatic agent, the resulting film has a coefficient of friction of 0.19, but a surface resistance >10 Ω·cm. 13Ω, electrostatic half-life > 23 seconds, powder adsorption phenomenon is obvious; when no slip agent is added, the surface resistivity of the obtained film is 3.5 × 10 11 It has an Ω value, but the coefficient of friction is 0.43, resulting in poor slipperiness and affecting the operating speed of the packaging machine.

[0059] The specific mechanisms of action of each component in this scheme are analyzed as follows:

[0060] The mechanism of action of the slip agent: In the organic modified masterbatch with silica as the core, silica particles form micro-protrusions on the film surface, which reduces the contact area between the film and the equipment and between the film and the film, and reduces the coefficient of friction; at the same time, the organic modified components give it good compatibility with the polypropylene matrix, avoiding the impact on transparency due to excessive precipitation.

[0061] Mechanism of action of antistatic agents: Non-ionic polymer antistatic agents have migration characteristics and can form a conductive molecular layer on the surface of a film. They react with moisture in the air to conduct away static charge in a timely manner. When used in conjunction with slip agents, the two can migrate to the surface together without interfering with each other, achieving the dual effects of slip and antistatic properties.

[0062] When the cooling roller temperature was controlled at 10℃, the haze of the film obtained in test group 2 was further reduced to 2.8%, and the transparency was higher. This shows that the lower temperature of the cooling roller helps to reduce the haze of the film. For crystalline polymer polypropylene, the cooling rate directly affects its crystallization behavior and final transparency. Using rapid cooling (cooling roller temperature 10-25℃) can "freeze" the polymer molecular chain segments before they have time to arrange themselves in a regular manner, forming more amorphous regions, thereby improving transparency.

[0063] Example 2

[0064] Based on Example 1, Example 2 is presented here.

[0065] The antistatic agent also contains 0.1-0.3% multi-walled carbon nanotubes by weight percentage.

[0066] The intermediate layer also contains 1-3% nano-additives and 1-3% polyvinyl alcohol by weight percentage. The nano-additives are any one of nano-clay, mica, and montmorillonite; the ratio of nano-additives to polyvinyl alcohol by weight percentage is 1-2. In this Example 2, nano-clay is used as the nano-additive.

[0067] In this embodiment 2, based on test group 1 in embodiment 1 above, the following three sets of experiments are designed:

[0068] Experimental group 1A: 0.1% multi-walled carbon nanotubes, 1% nano-additives, and 1% polyvinyl alcohol;

[0069] Experimental group 1B: 0.2% multi-walled carbon nanotubes, 2% nano-additives, and 2% polyvinyl alcohol;

[0070] Experimental group 1C: 0.3% multi-walled carbon nanotubes, 2% nano-additives, and 1% polyvinyl alcohol;

[0071] Table 2 shows the performance test results of CPP packaging film for each of the above test groups. The temperature of the cooling roller was controlled at 15℃.

[0072] Table 2 shows the performance test results of CPP packaging film for each of the above test groups.

[0073] Group Haze% Gloss (45°) Coefficient of friction (heat seal layer / iron) Heat seal strength / N / 15mm Water vapor transmission rate / g / m²·24h <![CDATA[Surface resistance / ×10 11 Ω]]> electrostatic half-life Experimental group 1 3.2 92% 0.18 28 4.5 3.2 <2 seconds Experimental group 1A 3.1 93% 0.18 29 4.1 3.1 <3 seconds Experimental group 1B 3.1 94% 0.17 31 3.9 2.9 <3 seconds Experimental group 1C 3.0 94% 0.17 31 3.8 2.8 <3 seconds

[0074] As can be seen from Table 2, when multi-walled carbon nanotubes were added to the antistatic agent in experimental groups 1A-1C, the effect on transparency was not significant, but the gloss and heat-sealing strength were improved. The addition of nano-alumina or nano-silica slightly reduced the haze to a certain extent. Due to the low resistivity of multi-walled carbon nanotubes, the surface resistance was also reduced, indirectly playing the role of an antistatic agent. Generally speaking, materials with low surface resistance have better antistatic properties because charges flow easily on the material surface and do not easily accumulate to form static electricity; the effect on the static half-life is also not significant.

[0075] The nano-ATO, nano-ITO, nano-AZO, or silver nanowires in the heat-sealing layer have good lattice matching with the nano-additives in the intermediate layer, which greatly increases the bonding strength between the two. This is also an important reason for the improved heat-sealing strength.

[0076] Finally, this solution adds nano-additives and polyvinyl alcohol to the intermediate layer and uses transparent nano-alumina or nano-silica to maintain both transparency and good moisture barrier properties, thereby reducing haze to a certain extent, ensuring gloss, and continuously reducing water vapor transmittance. This overcomes the problem that a single material cannot simultaneously satisfy both "transparency" and "high barrier properties".

[0077] Example 3

[0078] Based on Examples 1 and 2, this Example 3 is presented.

[0079] The outer side of the heat-sealing layer is coated with a coating consisting of polyvinylidene chloride, polypropylene, or polyethylene, with a coating thickness of 0.1-0.5 μm; by mass percentage, polyvinylidene chloride / (polypropylene + polyethylene) = 2-5.

[0080] A coating is provided on the outer side of the corona layer. The coating composition includes nano-silicon oxide and nano-alumina, and the coating thickness is 0.1-0.5μm. The ratio of nano-silicon oxide to nano-alumina is 5-10 by mass percentage.

[0081] In this embodiment 3, based on test group 1A in embodiment 2 above, the following three sets of experiments are designed:

[0082] Experimental group 1A1: polyvinylidene chloride / (polypropylene + polyethylene) = 2, nano-silica / nano-alumina = 5;

[0083] Experimental group 1A2: polyvinylidene chloride / (polypropylene + polyethylene) = 3, nano-silica / nano-alumina = 7;

[0084] Test group 1A3: polyvinylidene chloride / (polypropylene + polyethylene) = 5, nano-silica / nano-alumina = 10; Table 3 shows the performance test table of CPP packaging film for each of the above test groups, and the cooling roller temperature is controlled at 15℃.

[0085] Table 3 shows the performance test results of CPP packaging film for each of the above test groups.

[0086] Group Haze% Gloss (45°) Coefficient of friction (heat seal layer / iron) Heat seal strength / N / 15mm Water vapor transmission rate / g / m²·24h <![CDATA[Surface resistance / ×10 11 Ω]]> electrostatic half-life Experimental group 1A1 3.1 93% 0.18 29 3.7 / / Experimental group 1A2 3.2 93% 0.19 32 3.5 / / Experimental group 1A3 3.2 94% 0.18 33 3.5 / /

[0087] As can be seen from Table 3, setting a polyvinylidene chloride coating on the outside of the heat-sealing layer, combined with polypropylene and polyethylene, not only has good transparency, but also blocks water vapor, greatly improving the moisture barrier performance. This can be clearly seen from the increasing haze and decreasing water vapor transmission rate.

[0088] The nano-ATO in the heat-sealing layer and the nano-additives in the intermediate layer have good lattice matching, which greatly increases the bonding strength between the two. In addition, the nano-silicon oxide and nano-alumina coatings in the corona layer and the nano-additives in the intermediate layer also have good lattice matching, which greatly improves the bonding strength between the intermediate layer and the corona layer, as can be seen from the increasing trend of heat-sealing strength.

[0089] Adding nano-silica and nano-alumina coatings to the corona layer helps to form a "maze effect." When water vapor molecules pass through the film, they need to bypass these layers, and the path is greatly extended, thereby reducing the transmittance and increasing the moisture barrier performance. It can be seen that the water vapor transmittance is continuously decreasing.

[0090] Example 4

[0091] A manufacturing process for a multilayer co-extruded CPP packaging film specifically includes the following steps:

[0092] Step S1: Add the heat-sealing layer material components into the hopper of screw extruder one, and set the temperature of each zone, screen changing temperature, die head temperature and screw speed;

[0093] Step S2: Add the intermediate layer material components into the hopper of the screw extruder II, and set the temperature of each zone, screen changing temperature, die head temperature and screw speed;

[0094] Step S3: Add the corona layer material components into the hopper of screw extruder three, and set the temperature of each zone, screen changing temperature, die head temperature and screw speed of screw extruder three;

[0095] Step S4: When the temperature reaches the set temperature, all the screw extruders mentioned above are turned on at the same time for melting and extrusion. After melting and extrusion, the extruded material enters the multi-layer co-extrusion blown film machine. The film is blown through the die head to form a three-layer co-extrusion structure. After cooling and molding, the surface of the corona layer is corona treated.

[0096] Step S5: In a vacuum environment, the heat-sealing layer and the corona layer are vapor-deposited separately to obtain the corresponding coatings, which enhance the adhesion between the coating and the plastic substrate and prevent the brittle ceramic layer from cracking when bent.

[0097] Step S6: After film drawing, blowing, stretching, traction, edge trimming and winding, a multi-layer co-extruded composite packaging film is prepared;

[0098] Step S7: Perform time-sensing processing on the reeled master roll, with a time limit of 24-72 hours.

[0099] Slip agents need time to migrate to the film surface to function. Sufficient aging treatment (24-72 hours) ensures uniform and stable migration of the slip agent, avoiding changes in the coefficient of friction caused by late migration of the additive during use.

[0100] The thickness of the multilayer co-extruded film is 20-25 μm, wherein the thickness of the heat-sealing layer is 5-7 μm, the thickness of the intermediate layer is 5-7 μm, and the thickness of the corona layer is 10-12 μm.

[0101] The screw extruder containing the raw materials that make up the heat-sealing layer has the following temperatures from the feed end to the discharge end: Zone 1 155℃, Zone 2 170℃, Zone 3 160℃, runner 165℃, and die 175℃. The adjustable range of these temperatures is ±2℃, and the screw speed is 35±2 rpm.

[0102] The screw extruder 2, which holds the raw materials that make up the intermediate layer, has the following temperature and screw speed in each zone from the feed end to the discharge end: Zone 1 185℃, Zone 2 210℃, Zone 3 205℃, runner 200℃, die head 210℃. The adjustable range of the above temperatures is ±2℃, and the screw speed is 30±2 rpm.

[0103] The screw extruder containing raw materials with corona layers has the following temperature and screw speed in each zone from the feed end to the discharge end: Zone 1 145℃, Zone 2 160℃, Zone 3 175℃, runner 175℃, and die 180℃. The adjustable range of the above temperatures is ±2℃, and the screw speed is 25±2 rpm.

[0104] The experimental procedures in Examples 1-3 all use the parameters in Example 4. In order to reduce the experimental cost, the corresponding parameters in Example 4 are all taken as minimum values, which will not be described in detail here.

[0105] Example 5

[0106] Application example: Powder packaging testing

[0107] The CPP film obtained in Example 1 was then used to make packaging bags for milk powder packaging testing. Running on an automatic packaging machine at a speed of 60 bags / minute for 8 consecutive hours, no heat-sealing defects caused by powder adsorption occurred, and the packaging bag sealing strength test pass rate was 99.5%. In contrast, the film obtained in Comparative Example 1, under the same conditions, began to show powder adsorption after 2 hours of operation, resulting in decreased sealing strength and a pass rate of 85%.

[0108] The multi-layer co-extruded CPP packaging film developed in this invention effectively solves the industry problem of powder contamination sealing in powder packaging through an innovative three-layer co-extrusion structure and functional formulation design. At the same time, it provides excellent moisture resistance, transparency and mechanical properties, and its comprehensive performance reaches the leading level in the industry.

[0109] This product can be widely used in the market for powdered products with extremely high packaging requirements, such as high-end milk powder, nutritional supplements, coffee, and condiments, offering significant economic and social benefits. The production process of this invention is mature and feasible, and can be directly implemented on existing three-layer co-extrusion CPP production lines without additional equipment investment, making it easy to promote and apply.

[0110] The technical features of this invention not described can be implemented by or using existing technology, and will not be repeated here. Of course, the above description is not a limitation of this invention, and this invention is not limited to the examples above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of this invention should also be within the protection scope of this invention.

Claims

1. A multilayer co-extruded CPP packaging film, characterized in that, It includes a heat-sealing layer, an intermediate layer, and a corona layer connected sequentially from top to bottom; By weight percentage, the heat-sealing layer comprises 85-95% base resin, 1-3% slip agent and 2-4% antistatic agent. The slip agent migrates to the surface to form a lubricating layer, and the antistatic agent forms a conductive network. The two work together to reduce powder adsorption. The base resin is random copolymer PP. The intermediate layer comprises 80-90% homopolymer PP and 10-20% highly crystalline PP; The corona layer is made of polypropylene resin.

2. The multilayer co-extruded CPP packaging film according to claim 1, characterized in that, The antistatic agent is any one of nano-ATO, nano-ITO, nano-AZO, and silver nanowires by mass percentage, and the antistatic agent also contains 0.1-0.3% multi-walled carbon nanotubes.

3. The multilayer co-extruded CPP packaging film according to claim 1, characterized in that, The intermediate layer also contains 1-3% nano-additives and 1-3% polyvinyl alcohol by weight percentage, wherein the nano-additives are any one of nano clay, mica, and montmorillonite. By mass percentage, the ratio of nano-additives to polyvinyl alcohol is 1-2.

4. The multilayer co-extruded CPP packaging film according to claim 1, characterized in that, The outer side of the heat-sealing layer is provided with a coating, the coating composition of which includes polyvinylidene chloride, polypropylene or polyethylene, and the coating thickness is 0.1-0.5μm; by mass percentage, polyvinylidene chloride / (polypropylene + polyethylene) = 2-5.

5. The multilayer co-extruded CPP packaging film according to claim 1, characterized in that, The outer side of the corona layer is provided with a coating, the coating composition of which includes nano-silicon oxide and nano-alumina, and the coating thickness is 0.1-0.5μm; By mass percentage, nano-silica / nano-alumina = 5-10.

6. A manufacturing process for a multilayer co-extruded CPP packaging film, used to produce the multilayer co-extruded CPP packaging film as described in any one of claims 1-8, characterized in that, Specifically, the steps include the following: Step S1: Add the heat-sealing layer material components into the hopper of screw extruder one, and set the temperature of each zone, screen changing temperature, die head temperature and screw speed; Step S2: Add the intermediate layer material components into the hopper of the screw extruder II, and set the temperature of each zone, screen changing temperature, die head temperature and screw speed; Step S3: Add the corona layer material components into the hopper of screw extruder three, and set the temperature of each zone, screen changing temperature, die head temperature and screw speed of screw extruder three; Step S4: When the temperature reaches the set temperature, all the screw extruders mentioned above are turned on at the same time for melting and extrusion. After melting and extrusion, the extruded material enters the multi-layer co-extrusion blown film machine. The film is blown through the die head to form a three-layer co-extrusion structure. The film is cooled and shaped by the cooling roller, and the surface of the corona layer is corona treated. Step S5: In a vacuum environment, the heat-sealing layer and the corona layer are vapor-deposited separately to obtain the corresponding coatings, which enhance the adhesion between the coating and the plastic substrate and prevent the brittle ceramic layer from cracking when bent. Step S6: After film drawing, blowing, stretching, traction, edge trimming and winding, a multi-layer co-extruded composite packaging film is prepared; Step S7: Perform time-sensing processing on the reeled master roll, with a time limit of 24-72 hours.

7. The production process of a multilayer co-extruded CPP packaging film according to claim 6, characterized in that, The thickness of the multilayer co-extruded film is 20-25 μm, wherein the thickness of the heat-sealing layer is 5-7 μm, the thickness of the intermediate layer is 5-7 μm, and the thickness of the corona layer is 10-12 μm.

8. The production process of a multilayer co-extruded CPP packaging film according to claim 6, characterized in that, The screw extruder containing the raw materials that make up the heat-sealing layer has the following temperatures from the feed end to the discharge end: Zone 1 155℃, Zone 2 170℃, Zone 3 160℃, runner 165℃, and die 175℃. The adjustable range of these temperatures is ±2℃, and the screw speed is 35±2 rpm.

9. The production process of a multilayer co-extruded CPP packaging film according to claim 6, characterized in that, The screw extruder 2, which holds the raw materials that make up the intermediate layer, has the following temperature and screw speed in each zone from the feed end to the discharge end: Zone 1 185℃, Zone 2 210℃, Zone 3 205℃, runner 200℃, die head 210℃. The adjustable range of the above temperatures is ±2℃, and the screw speed is 30±2 rpm.

10. The production process of a multilayer co-extruded CPP packaging film according to claim 6, characterized in that, The screw extruder containing raw materials with corona layers has the following temperature and screw speed in each zone from the feed end to the discharge end: Zone 1 145℃, Zone 2 160℃, Zone 3 175℃, runner 175℃, and die 180℃. The adjustable range of the above temperatures is ±2℃, and the screw speed is 25±2 rpm.