A lightweight microfoamed packaging material

Abstract

The application discloses a kind of light microfoamed packing materials, the light microfoamed packing material is the sandwich microfoamed material of A-B-A structure;Wherein A is the polyvinyl chloride film layer of thickness 0.02-0.2mm;B is the microfoamed layer of thickness 1-10mm;The light microfoamed packing material is obtained by three-layer co-extrusion foaming, by adding the composite foaming agent prepared by SBS glue powder, low alcoholysis degree thermoplastic polyvinyl alcohol powder, foaming agent, inorganic nucleating agent in foaming layer, complete bubble is wrapped, prevent bubble collapse, avoid gas escape under the existence of fiber filler;Foaming agent of different foaming temperature is used when foaming, the gas generation amount of low-temperature foaming agent is small, and it is easy to form many and delicate microbubbles, as initial foaming, construct uniform microbubble;The gas generation amount of high-temperature foaming agent is large, and the foaming temperature is high, further refoaming is carried out on the microbubble constructed at high temperature;By designing foaming agent composition, step foaming is carried out, the bubble wall is avoided to be broken and collapsed due to large gas generation amount foaming once, and stable high-quality microfoamed packing material is obtained.

Description

Technical Field

[0001] This invention belongs to the field of special foaming materials technology, specifically relating to a lightweight micro-foamed packaging material. Background Technology

[0002] With the rapid development of logistics and e-commerce, the requirements for packaging materials are becoming increasingly stringent. On the one hand, packaging materials are required to have good cushioning and protective functions, and to be lightweight, environmentally friendly, and low-cost; on the other hand, packaging materials must meet the requirements for good strength support.

[0003] Polyvinyl chloride (PVC) is abundant, inexpensive, and widely used, possessing enormous development potential in the building materials and packaging materials sectors. For example, PVC foam boards, with their moisture-proof and easy-to-cut characteristics, are widely used in construction, furniture, decorative materials, and advertising displays. In the packaging field, PVC is replacing higher-cost polyethylene and polyurethane, offering a more environmentally friendly and low-carbon alternative.

[0004] Packaging materials made from expanded polyvinyl chloride (PVC) foam have extremely wide applications. They can be used not only as cushioning pads for various types of packaging but also as boxes and pallets for insulated takeout containers, and packaging boxes for precision components such as LCD screens, offering advantages such as lightweight, durability, and shock resistance. However, controlling the foaming process of PVC foam is challenging. Due to PVC's poor plasticity and low melt strength, the use of excessive plasticizers in thermoplastic processing makes it difficult to form stable closed cells. Typical foams exhibit a fine, uneven, and textured surface, leading to reduced support strength and brittleness upon impact. Especially when adding excessive fillers to the foaming system to reduce costs, high filler content can cause gas leakage, resulting in uneven cell structures and rough surfaces, thus affecting the quality of the foam material and causing problems such as easy breakage, reduced support strength, and susceptibility to cracking upon impact. Against this backdrop, the purpose of this invention is to promote the formation of uniform closed-cell microbubbles through the introduction of functional raw materials and process control, thereby endowing packaging materials with excellent cushioning and support properties through microfoaming. Summary of the Invention

[0005] Currently, polyvinyl chloride (PVC) high-filler foam materials have drawbacks as packaging materials, such as low closed-cell density and low support strength. The purpose of this invention is to solve these problems by providing a lightweight micro-foamed packaging material. This material is made by adding a composite foaming agent, which is formulated with SBS powder, low-hydrolysis thermoplastic polyvinyl alcohol powder, foaming agent, and inorganic nucleating agent, to the foaming layer. The SBS powder is easy to form a film, which completely encapsulates the air bubbles, prevents cell collapse, and avoids gas escape in the presence of fiber fillers, thereby achieving the purpose of micro-foaming. At the same time, a thin film layer is designed on the surface of the foam material to further improve the quality of the foam material.

[0006] To achieve the above objectives, the specific technical solution adopted is as follows:

[0007] A lightweight microfoamed packaging material, characterized in that: the lightweight microfoamed packaging material is an ABA-structured sandwich microfoamed material; wherein A is a polyvinyl chloride film layer with a thickness of 0.02-0.2 mm; B is a microfoamed layer with a thickness of 1-10 mm; the lightweight microfoamed packaging material is prepared by the following method:

[0008] (1) Premixing of A layer material: According to the formula design of parts by weight, add 100 parts of polyvinyl chloride, 3-5 parts of MBS resin, 30-40 parts by weight of plasticizer, 1-3 parts of heat stabilizer and 0.2-0.5 parts of lubricant to a high-speed mixer and mix evenly so that the plasticizer can fully penetrate the polyvinyl chloride, and use it as A layer material for later use.

[0009] (2) Premixing of B layer base material: According to the formula design by weight, 100 parts of polyvinyl chloride, 15-20 parts of plasticizer, 35-45 parts of fibrous filler, 1-3 parts of foaming regulator, 1-3 parts of heat stabilizer, and 0.5-1 parts of lubricant are mixed in a high-speed mixer and used as B layer base material for later use.

[0010] (3) Pre-preparation of composite micro-foaming agent: According to the formula design by weight, add 60-70 parts of SBS adhesive powder, 20-30 parts of inorganic nucleating agent, 5-10 parts of low alcoholysis degree thermoplastic polyvinyl alcohol powder, 2 parts of low temperature foaming agent and 3-5 parts of high temperature foaming agent to a high-speed mixer and mix them evenly to prepare the composite micro-foaming agent for later use.

[0011] (4) Using a three-layer co-extrusion twin-screw extruder as the extrusion foaming equipment, A layer material is added to the upper and lower extruders for extrusion; B layer base material is added to the middle extruder for extrusion, and a composite micro-foaming agent is added in the sixth section of the middle extruder by loss-in-weight weighing. The amount of composite micro-foaming agent added is 20% of the weight of B layer base material. Through hot melt extrusion of the three-layer co-extrusion twin-screw extruder, a three-layer composite layer is formed at the T-die. The material is then extruded and foamed through the die, stretched, and shaped by rollers to form a lightweight micro-foamed packaging material with an ABA structure.

[0012] Preferably, the polyvinyl chloride mentioned in step (1) is selected from at least one of SG2, SG3, and SG4; it has good flexibility and film-forming properties, and is distributed on the outer layer of the foamed material. On the one hand, it prevents the gas in the inner foamed layer from escaping and forming unstable cells during foaming; on the other hand, the inner foamed layer uses more fibrous inorganic powder, and the good film-forming layer on the outer layer ensures that the appearance of the foamed material is flat and without bumps.

[0013] Preferably, the MBS resin in step (1) is a methyl methacrylate-butadiene-styrene terpolymer with a methyl methacrylate content of 60-70%. This ensures good compatibility and dispersion of MBS with polyvinyl chloride (PVC) to form a homogeneous phase. MBS not only improves the flow and film-forming properties of PVC, but also, when used as the outer layer of foamed materials, enhances the impact resistance of the foamed materials, giving them good impact resistance when used in packaging materials.

[0014] Preferably, in steps (1) and (2), the plasticizer is selected from at least one of dioctyl phthalate (DOP), diisooctyl phthalate (DIOP), and dibutyl phthalate (DBP) as the main plasticizer, and at least one of dioctyl sebacate (DOS) and epoxidized soybean oil as the secondary plasticizer. The main plasticizer and the secondary plasticizer are used in combination at a mass ratio of 100:5-10.

[0015] Preferably, the heat stabilizer mentioned in steps (1) and (2) is at least one of zinc stearate, calcium stearate, and barium stearate.

[0016] Preferably, the lubricant in step (1) is at least one of silicone powder and polyethylene wax as an external lubricant; using an external lubricant on the outer layer of the foamed material makes it easy to obtain a smooth surface foamed material, and at the same time can improve the water repellency of the foamed material.

[0017] Preferably, the polyvinyl chloride in step (2) is selected from at least one of SG5, SG6, and SG7 as needed.

[0018] Preferably, the lubricant in step (2) is at least one of stearamide, N,N-ethylene bis-stearamide, oleamide, and tristearate as an internal lubricant; using an internal lubricant in the inner layer of the foamed material makes it easier to improve the extrusion processing fluidity of the material.

[0019] Preferably, the foaming regulator in step (2) is a commercially available acrylate foaming regulator; the foaming regulator is used to improve the processing fluidity and melt strength of polyvinyl chloride, and promote uniform and delicate foaming.

[0020] Preferably, the fibrous filler in step (2) is selected from at least one of fibrous wollastonite, calcium sulfate whiskers, and sepiolite fibers. The fibrous filler serves to reduce costs and provides good cushioning, flexibility, and support in the foamed material. In the foamed material, the fibrous fillers are intertwined and interwoven, making them less prone to breakage under impact, effectively increasing the packaging support strength of the foamed packaging material.

[0021] Preferably, the SBS powder in step (3) has a particle size ≤20μm; the low-hydrolysis thermoplastic polyvinyl alcohol powder is obtained by plasticizing polyvinyl alcohol with a degree of hydrolysis of 80-85% with a plasticizer; the SBS powder is a block copolymer of styrene and butadiene, which, when combined with the low-hydrolysis thermoplastic polyvinyl alcohol powder, exhibits good compatibility, adhesion, elasticity, and hot-melt film-forming properties in the polyvinyl chloride system. By preparing a composite foaming agent with a foaming agent and an inorganic nucleating agent, and adding it at the rear end of the extruder after the polyvinyl chloride and fiber filler are completely dispersed, the SBS powder easily forms a film, completely encapsulating the bubbles, preventing cell collapse, and avoiding gas escape in the presence of fiber filler, thereby achieving the purpose of micro-foaming.

[0022] Preferably, the inorganic nucleating agent in step (3) is selected as light calcium carbonate with a particle size range of 3-5 μm.

[0023] Preferably, the low-temperature foaming agent in step (3) is selected from at least one of 4,4-oxobisbenzenesulfonyl hydrazine (OBSH) and sodium bicarbonate; the high-temperature foaming agent is selected from azodicarbonamide (AC). 4,4-oxobisbenzenesulfonyl hydrazine (OBSH) and sodium bicarbonate have low gas evolution, which makes it easy to form many fine microbubbles, and the foaming temperature is low. As the initial foaming agent, they can be used to construct uniform microbubbles. Azodicarbonamide has a large gas evolution and a high foaming temperature, which can further foam the constructed microbubbles at high temperature. By designing the foaming agent composition to carry out step foaming, the rupture and collapse of the bubble wall caused by large-volume foaming in one go is avoided.

[0024] In step (4), the three-layer co-extrusion twin-screw extruder automatically controls the extrusion temperature using a temperature controller and an internal circulation system via a solenoid water valve. The temperature error range is controlled within ±5℃. The temperature control standards are: Section 1: 90℃; Section 2: 100℃; Section 3: 130℃; Section 4: 130℃; Section 5: 120℃; Section 6: 110℃; Section 7: 120℃; Section 8: 140℃; Section 9: 160℃; Section 10: 180℃; Die: 200℃. After the composite micro-foaming agent is added to the sixth section by weighing with a loss-in-weight scale, the foaming agent gradually foams as the temperature rises, thus forming stable, uniform, and fine microbubbles.

[0025] Three-layer co-extrusion can be performed through melt extrusion in independent extrusion units, and then compounded at the die head using a T-shaped die design. This design ensures that different materials are present at different layers of the foam. Furthermore, by adjusting the speed and temperature of each extrusion unit, the thickness and flow rate of each plastic layer can be precisely controlled, thereby guaranteeing the quality and performance of the film.

[0026] In step (4), the foam is extruded through the die. The thickness of layers A and B is controlled by a PLC as needed. The PLC precisely controls the feeding amount and stretching speed to control the thickness of each extruded foam layer. The gap of the shaping rollers is adjusted to accurately determine the thickness of the final product. The photoelectric automatic correction device is used for correction and edge trimming.

[0027] With a wider range of applications, the lightweight micro-foamed packaging material of the present invention has a wide range of thicknesses. When the thickness is less than 2.5 mm, it can be collected by rolling; when the thickness is greater than 2.5 mm, it can be collected by cutting and stacking.

[0028] This invention discloses a lightweight microfoamed packaging material. Through the selection and compounding of raw materials and process control, it can still form fine, uniform, and delicate micro-closed cells even at high filling levels. While achieving lightweight cushioning, the material has good support, anti-warping deformation, and dimensional shrinkage, which greatly improves the quality of microfoamed packaging materials.

[0029] The outstanding features of this invention compared to existing technologies are as follows:

[0030] (1) Polyvinyl chloride has a short molecular chain and low melt strength. During foaming, the melt is insufficient to encapsulate the bubbles. Especially when the filling is high, the foaming gas is very easy to escape and form large bubbles or collapse. The present invention adds a composite foaming agent made of SBS adhesive powder, low degree of alcoholysis thermoplastic polyvinyl alcohol powder, foaming agent and inorganic nucleating agent to the foaming layer. This agent can completely encapsulate the bubbles, prevent the bubbles from collapsing, and avoid gas escape in the presence of high fiber filler, so as to obtain a stable and high-quality micro-foamed packaging material.

[0031] (2) The present invention forms a thin film layer on the surface of the foamed material through three-layer co-extrusion foaming to prevent gas from escaping from the inner foaming layer during foaming and forming unstable cells; the inner foaming layer uses more fibrous inorganic powder, and the outer good film-forming layer ensures that the foamed material has a smooth appearance without bumps.

[0032] (3) In this invention, foaming agents with different gas emission temperatures are used during foaming. Sodium bicarbonate has a small gas emission, which makes it easy to form many fine microbubbles. It also has a low foaming temperature and is used as the initial foaming agent to build uniform microbubbles. Azodicarbonamide has a large gas emission and a high foaming temperature, which further foams the microbubbles that have been built at high temperature. By designing the foaming agent composition to carry out step foaming, the foaming of large volume at one time is avoided from causing the bubble wall to break and collapse.

[0033] (4) The lightweight micro-foamed packaging material of the present invention is easy to prepare, the material thickness is adjustable, and it has good support, impact resistance and cushioning properties; it has a wide range of applications and can be used as a liner, support plate, box plate and other packaging materials. Attached Figure Description

[0034] To further clarify the technical implementation scheme of the present invention, the present invention will be further described below with reference to the accompanying drawings:

[0035] Figure 1 This is a structural schematic diagram of a lightweight micro-foamed packaging material according to the present invention. Detailed Implementation

[0036] The following examples are intended to further describe the implementation process of the technical content of the present invention, and are not intended to limit the scope of protection of the claims of the present invention. Unless otherwise specified in the examples, all tests were conducted under conventional conditions or with conventional materials.

[0037] Raw material preparation:

[0038] Low degree of hydrolysis thermoplastic polyvinyl alcohol powder: obtained by using polyvinyl alcohol with a degree of hydrolysis of 80-85% as a glycerol plasticizer.

[0039] The foaming regulator QL-903 was provided by Linqi Qili Catalyst Co., Ltd.

[0040] Foaming agent regulators HL-100 and HL-200 were provided by Shandong Rike Chemical Co., Ltd.

[0041] Example 1

[0042] A lightweight microfoamed packaging material is an ABA-structured sandwich microfoamed material; wherein A is a 0.05 mm thick polyvinyl chloride film layer; B is a 2 mm thick microfoamed layer; the lightweight microfoamed packaging material is prepared by the following method:

[0043] (1) Premixing of Layer A: According to the formula design by weight, 100 parts of SG4 polyvinyl chloride, 5 parts of MBS resin with 60% methyl methacrylate content, 30 parts of plasticizer dioctyl phthalate, 2 parts of plasticizer epoxidized soybean oil, 1 part of heat stabilizer zinc stearate, 1 part of barium stearate, and 0.3 parts of lubricant polyethylene wax are added to a high-speed mixer and mixed evenly to allow the plasticizer to fully penetrate the polyvinyl chloride, which is then used as Layer A for later use.

[0044] (2) Premixing of B layer base material: According to the formula design by weight, 100 parts of SG7 polyvinyl chloride, 14 parts of plasticizer dioctyl phthalate, 1 part of plasticizer epoxidized soybean oil, 35 parts of fibrous filler calcium sulfate whiskers, 2 parts of HL-100 foaming regulator, 1 part of heat-resistant stabilizer calcium stearate, 1 part of barium stearate, and 1 part of lubricant N,N-ethylene bis-stearamide are mixed evenly in a high-speed mixer and used as B layer base material for later use;

[0045] (3) Pre-preparation of composite micro-foaming agent: According to the formula design by weight, 65 parts of SBS rubber powder with a particle size ≤20μm, 30 parts of light calcium carbonate with a particle size range of 3-5μm, 10 parts of low alcoholysis degree thermoplastic polyvinyl alcohol powder, 2 parts of 4,4-oxobisbenzenesulfonyl hydrazine (OBSH), and 4 parts of azodicarbonamide (AC) are added to a high-speed mixer and mixed evenly to prepare as composite micro-foaming agent for later use.

[0046] (4) A three-layer co-extrusion twin-screw extruder is used as the extrusion foaming equipment. A layer material is added to the upper and lower extruders for extrusion; B layer base material is added to the middle extruder for extrusion, and a composite micro-foaming agent is added in the sixth section of the middle extruder by loss-in-weight weighing. The amount of composite micro-foaming agent added is 20% of the weight of B layer base material. The extrusion temperature of the three-layer co-extrusion twin-screw extruder is automatically controlled by a temperature controller and an electromagnetic water valve for internal circulation. The temperature error range is controlled within ±5℃. The temperature control standards are: Section 1: 90℃; Section 2: 100℃; Section 3: 130℃; Section 4: 130℃; Section 5: 120℃; Section 6: 110℃; Section 7: 120℃; Section 8: 140℃; Section 9: 160℃; Section 10: 180℃; Die: 200℃. Three-layer co-extrusion can be performed through melt extrusion in independent extrusion units, with a T-shaped die designed at the die head for compounding. This design ensures that different materials are present at different layers of the foamed material. As the temperature rises, the foaming agent gradually foams, forming stable, uniform, and fine microbubbles. PLC-controlled linkage is used to precisely control the feed rate and stretching speed to control the thickness of each extruded foam layer; adjusting the gap of the shaping rollers accurately determines the thickness of the final product. A photoelectric automatic correction device is used for correction, edge trimming, and winding to obtain lightweight microfoamed packaging material.

[0047] Example 2

[0048] A lightweight microfoamed packaging material is an ABA-structured sandwich microfoamed material; wherein A is a 0.1 mm thick polyvinyl chloride film layer; B is an 8 mm thick microfoamed layer; the lightweight microfoamed packaging material is prepared by the following method:

[0049] (1) Premixing of Layer A: According to the formula design by weight, 100 parts of SG4 polyvinyl chloride, 5 parts of MBS resin with 60% methyl methacrylate content, 30 parts of plasticizer dioctyl phthalate, 2 parts of plasticizer epoxidized soybean oil, 1 part of heat-resistant stabilizer calcium stearate, 1 part of barium stearate, and 0.3 parts of lubricant polyethylene wax are added to a high-speed mixer and mixed evenly to allow the plasticizer to fully penetrate the polyvinyl chloride, which is then used as Layer A for later use.

[0050] (2) Premixing of B layer base material: According to the formula design by weight, 100 parts of SG5 polyvinyl chloride, 16 parts of plasticizer diisooctyl phthalate, 1 part of plasticizer epoxidized soybean oil, 45 parts of fibrous filler calcium sulfate whiskers, 3 parts of QL-903 foaming regulator, 1 part of heat-resistant stabilizer calcium stearate, 1 part of barium stearate, and 1 part of lubricant oleamide are mixed evenly in a high-speed mixer and used as B layer base material for later use;

[0051] (3) Pre-preparation of composite micro-foaming agent: According to the formula design by weight, 65 parts of SBS rubber powder with a particle size ≤20μm, 30 parts of light calcium carbonate with a particle size range of 3-5μm, 10 parts of low alcoholysis thermoplastic polyvinyl alcohol powder, 2 parts of 4,4-oxobisbenzenesulfonyl hydrazine (OBSH), and 5 parts of azodicarbonamide (AC) are added to a high-speed mixer and mixed evenly to prepare as composite micro-foaming agent for later use.

[0052] (4) A three-layer co-extrusion twin-screw extruder is used as the extrusion foaming equipment. A layer material is added to the upper and lower extruders for extrusion; B layer base material is added to the middle extruder for extrusion, and a composite micro-foaming agent is added in the sixth section of the middle extruder by loss-in-weight weighing. The amount of composite micro-foaming agent added is 20% of the weight of B layer base material. The extrusion temperature of the three-layer co-extrusion twin-screw extruder is automatically controlled by a temperature controller and an electromagnetic water valve for internal circulation. The temperature error range is controlled within ±5℃. The temperature control standards are: Section 1: 90℃; Section 2: 100℃; Section 3: 130℃; Section 4: 130℃; Section 5: 120℃; Section 6: 110℃; Section 7: 120℃; Section 8: 140℃; Section 9: 160℃; Section 10: 180℃; Die: 200℃. Three-layer co-extrusion can be performed through melt extrusion in independent extrusion units, with a T-shaped die designed at the die head for compounding. This design ensures that different materials are present at different layers of the foamed material. As the temperature rises, the foaming agent gradually foams, forming stable, uniform, and fine microbubbles. PLC-controlled linkage is used to precisely control the feed rate and stretching speed to control the thickness of each extruded foam layer; adjusting the gap of the shaping rollers accurately determines the thickness of the final product. A photoelectric automatic correction device is used for correction, edge trimming, on-demand cutting, and stacking to obtain lightweight microfoamed packaging material.

[0053] Example 3

[0054] A lightweight microfoamed packaging material is an ABA-structured sandwich microfoamed material; wherein A is a 0.1 mm thick polyvinyl chloride film layer; B is a 6 mm thick microfoamed layer; the lightweight microfoamed packaging material is prepared by the following method:

[0055] (1) Premixing of Layer A: According to the formula design by weight, 100 parts of SG4 polyvinyl chloride, 5 parts of MBS resin with 60% methyl methacrylate content, 30 parts of plasticizer dioctyl phthalate, 2 parts of plasticizer epoxidized soybean oil, 1 part of heat-resistant stabilizer calcium stearate, 1 part of barium stearate, and 0.3 parts of lubricant polyethylene wax are added to a high-speed mixer and mixed evenly to allow the plasticizer to fully penetrate the polyvinyl chloride, which is then used as Layer A for later use.

[0056] (2) Premixing of B layer base material: According to the formula design by weight, 100 parts of SG6 polyvinyl chloride, 15 parts of plasticizer dibutyl phthalate, 1 part of plasticizer dioctyl sebacate, 40 parts of fibrous filler sepiolite fiber, 2 parts of HL-200 foaming regulator, 1 part of heat-resistant stabilizer calcium stearate, 1 part of barium stearate, and 1 part of lubricant oleamide are mixed evenly in a high-speed mixer and used as B layer base material for later use.

[0057] (3) Pre-preparation of composite micro-foaming agent: According to the formula design by weight, 65 parts of SBS rubber powder with a particle size ≤20μm, 25 parts of light calcium carbonate with a particle size range of 3-5μm, 10 parts of low alcoholysis degree thermoplastic polyvinyl alcohol powder, 2 parts of sodium bicarbonate, and 4 parts of azodicarbonamide (AC) are added to a high-speed mixer and mixed evenly to prepare as composite micro-foaming agent for later use.

[0058] (4) A three-layer co-extrusion twin-screw extruder is used as the extrusion foaming equipment. A layer material is added to the upper and lower extruders for extrusion; B layer base material is added to the middle extruder for extrusion, and a composite micro-foaming agent is added in the sixth section of the middle extruder by loss-in-weight weighing. The amount of composite micro-foaming agent added is 20% of the weight of B layer base material. The extrusion temperature of the three-layer co-extrusion twin-screw extruder is automatically controlled by a temperature controller and an electromagnetic water valve for internal circulation. The temperature error range is controlled within ±5℃. The temperature control standards are: Section 1: 90℃; Section 2: 100℃; Section 3: 130℃; Section 4: 130℃; Section 5: 120℃; Section 6: 110℃; Section 7: 120℃; Section 8: 140℃; Section 9: 160℃; Section 10: 180℃; Die: 200℃. Three-layer co-extrusion can be performed through melt extrusion in independent extrusion units, with a T-shaped die designed at the die head for compounding. This design ensures that different materials are present at different layers of the foamed material. As the temperature rises, the foaming agent gradually foams, forming stable, uniform, and fine microbubbles. PLC-controlled linkage is used to precisely control the feed rate and stretching speed to control the thickness of each extruded foam layer; adjusting the gap of the shaping rollers accurately determines the thickness of the final product. A photoelectric automatic correction device is used for correction, edge trimming, on-demand cutting, and stacking to obtain lightweight microfoamed packaging material.

[0059] Comparative Example 1

[0060] According to the scheme of Example 2, the extrusion of the upper and lower A materials is directly stopped during the process, and the A layer film is not attached to the upper and lower foam layers. During foaming, there is a certain amount of gas leakage from the foam layer, which forms an uneven surface or openings, affecting the appearance quality and impact resistance of the foam material.

[0061] Comparative Example 2

[0062] A lightweight microfoamed packaging material is an ABA-structured sandwich microfoamed material; wherein A is a 0.1 mm thick polyvinyl chloride film layer; B is an 8 mm thick microfoamed layer; the lightweight microfoamed packaging material is prepared by the following method:

[0063] (1) Premixing of Layer A: According to the formula design by weight, 100 parts of SG4 polyvinyl chloride, 5 parts of MBS resin with 60% methyl methacrylate content, 30 parts of plasticizer dioctyl phthalate, 2 parts of plasticizer epoxidized soybean oil, 1 part of heat-resistant stabilizer calcium stearate, 1 part of barium stearate, and 0.3 parts of lubricant polyethylene wax are added to a high-speed mixer and mixed evenly to allow the plasticizer to fully penetrate the polyvinyl chloride, which is then used as Layer A for later use.

[0064] (2) Premixing of B layer base material: According to the formula design by weight, 100 parts of SG5 polyvinyl chloride, 16 parts of plasticizer diisooctyl phthalate, 1 part of plasticizer epoxidized soybean oil, 45 parts of fibrous filler calcium sulfate whiskers, 3 parts of QL-903 foaming regulator, 1 part of heat-resistant stabilizer calcium stearate, 1 part of barium stearate, and 1 part of lubricant oleamide are mixed evenly in a high-speed mixer and used as B layer base material for later use;

[0065] (3) Pre-preparation of composite micro-foaming agent: According to the formula design by weight, 65 parts of SBS rubber powder with a particle size ≤20μm, 30 parts of light calcium carbonate with a particle size range of 3-5μm, 10 parts of low alcoholysis degree thermoplastic polyvinyl alcohol powder, and 7 parts of azodicarbonamide are added to a high-speed mixer and mixed evenly to prepare as composite micro-foaming agent for later use.

[0066] (4) A three-layer co-extrusion twin-screw extruder is used as the extrusion foaming equipment. A layer material is added to the upper and lower extruders for extrusion; B layer base material is added to the middle extruder for extrusion, and a composite micro-foaming agent is added in the sixth section of the middle extruder by loss-in-weight weighing. The amount of composite micro-foaming agent added is 20% of the weight of B layer base material. The extrusion temperature of the three-layer co-extrusion twin-screw extruder is automatically controlled by a temperature controller and an electromagnetic water valve for internal circulation. The temperature error range is controlled within ±5℃. The temperature control standards are: Section 1: 90℃; Section 2: 100℃; Section 3: 130℃; Section 4: 130℃; Section 5: 120℃; Section 6: 110℃; Section 7: 120℃; Section 8: 140℃; Section 9: 160℃; Section 10: 180℃; Die: 200℃. Three-layer co-extrusion can be performed through melt extrusion in independent extrusion units, with a T-shaped die head designed for compounding at the die head. PLC-controlled linkage allows for precise control of the feed rate and stretching speed, controlling the thickness of each extruded foam layer. Adjusting the gap between the shaping rollers ensures accurate determination of the final product thickness. A photoelectric automatic correction device is used for alignment, edge trimming, on-demand cutting, and stacking to obtain lightweight micro-foamed packaging material.

[0067] Compared to Example 2, this experimental scheme used foaming agent AC with high gas emission and high foaming temperature. Due to rapid foaming, the foam wall is prone to rupture, forming open cells, making it difficult to achieve a micro-foaming effect, which manifests as low impact strength in the final material. This defect is more pronounced at high filler levels. For example, in Comparative Example 3, reducing the amount of calcium sulfate whiskers added to 20 parts resulted in reduced gas escape and a decrease in the number of open cells.

[0068] Comparative Example 3

[0069] Following the scheme of Comparative Example 2, the amount of calcium sulfate whiskers added was reduced from 45 parts to 20 parts.

[0070] Comparative Example 4

[0071] A lightweight microfoamed packaging material is an ABA-structured sandwich microfoamed material; wherein A is a 0.1 mm thick polyvinyl chloride film layer; B is an 8 mm thick microfoamed layer; the lightweight microfoamed packaging material is prepared by the following method:

[0072] (1) Premixing of Layer A: According to the formula design by weight, 100 parts of SG4 polyvinyl chloride, 5 parts of MBS resin with 60% methyl methacrylate content, 30 parts of plasticizer dioctyl phthalate, 2 parts of plasticizer epoxidized soybean oil, 1 part of heat-resistant stabilizer calcium stearate, 1 part of barium stearate, and 0.3 parts of lubricant polyethylene wax are added to a high-speed mixer and mixed evenly to allow the plasticizer to fully penetrate the polyvinyl chloride, which is then used as Layer A for later use.

[0073] (2) Premixing of B layer base material: According to the formula design by weight, 100 parts of SG5 polyvinyl chloride, 16 parts of plasticizer diisooctyl phthalate, 1 part of plasticizer epoxidized soybean oil, 45 parts of fibrous filler calcium sulfate whiskers, 3 parts of QL-903 foaming regulator, 1 part of heat-resistant stabilizer calcium stearate, 1 part of barium stearate, and 1 part of lubricant oleamide are mixed evenly in a high-speed mixer and used as B layer base material for later use;

[0074] (3) Pre-preparation of composite micro-foaming agent: According to the formula design by weight, 30 parts of light calcium carbonate with a particle size range of 3-5μm, 2 parts of 4,4-oxobisbenzenesulfonyl hydrazine (OBSH) and 5 parts of azodicarbonamide (AC) are added to a high-speed mixer and mixed evenly to prepare as composite micro-foaming agent for later use.

[0075] (4) A three-layer co-extrusion twin-screw extruder is used as the extrusion foaming equipment. A layer material is added to the upper and lower extruders for extrusion; B layer base material is added to the middle extruder for extrusion, and a composite micro-foaming agent is added in the sixth section of the middle extruder by loss-in-weight weighing. The amount of composite micro-foaming agent added is 6.6% of the weight of B layer base material. The extrusion temperature of the three-layer co-extrusion twin-screw extruder is automatically controlled by a temperature controller and an electromagnetic water valve for internal circulation. The temperature error range is controlled within ±5℃. The temperature control standards are: Section 1: 90℃; Section 2: 100℃; Section 3: 130℃; Section 4: 130℃; Section 5: 120℃; Section 6: 110℃; Section 7: 120℃; Section 8: 140℃; Section 9: 160℃; Section 10: 180℃; Die: 200℃. Three-layer co-extrusion can be performed through melt extrusion in independent extrusion units, with a T-shaped die designed at the die head for compounding. This design ensures that different materials are present at different layers of the foamed material. As the temperature rises, the foaming agent gradually foams, forming stable, uniform, and fine microbubbles. PLC-controlled linkage is used to precisely control the feed rate and stretching speed to control the thickness of each extruded foam layer; adjusting the gap of the shaping rollers accurately determines the thickness of the final product. A photoelectric automatic correction device is used for correction, edge trimming, on-demand cutting, and stacking to obtain lightweight microfoamed packaging material.

[0076] This solution does not use SBS adhesive powder or low-hydrolysis thermoplastic polyvinyl alcohol powder, which results in poor gas encapsulation during foaming, easy cell collapse, and significant gas escape in the presence of fiber fillers, making it difficult to obtain stable and high-quality micro-foamed packaging materials.

[0077] Performance evaluation:

[0078] The density, impact strength, and compressive strength of samples from Examples 1-3 and Comparative Examples 1-4 were tested. The compressive properties of each sample were tested according to GB / T8813-2020 "Determination of Compressive Properties of Rigid Foamed Plastics". The results are shown in Table 1. The impact strength, compressive strength, and density of the simply supported beam were comprehensively compared for evaluation.

[0079] Table 1:

[0080]

[0081] Through comprehensive comparative analysis of test data and performance, the technical solution of this invention incorporates a composite foaming agent formulated with SBS adhesive powder, low-hydrolysis thermoplastic polyvinyl alcohol powder, foaming agent, and inorganic nucleating agent into the foaming layer. This agent completely encapsulates the air bubbles, preventing cell collapse and gas escape in the presence of fibrous fillers, thus achieving the goal of obtaining stable, high-quality micro-foamed packaging materials. It simultaneously achieves good impact and compressive strength at a relatively low foaming density. A thin film layer is formed on the surface of the foamed material to prevent gas escape from the inner foaming layer during foaming, thus preventing the formation of unstable cells. The inner foaming layer uses a large amount of fibrous inorganic powder, and the excellent film-forming outer layer ensures a smooth, even appearance of the foamed material. The foamed material is suitable for various padding and box constructions.

[0082] It should be understood that although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention. Moreover, the descriptions of features or aspects in each embodiment should be applicable to other similar features or aspects in other embodiments. Those skilled in the art should understand that the packaging materials involved in the technical concept of the present invention are not limited to use as packaging materials in the narrow sense, and are all within the protection scope of the present invention without departing from the technical concept of the present invention.

Claims

1. A lightweight micro-foamed packaging material, characterized in that: The lightweight microfoamed packaging material is an ABA-structured sandwich microfoamed material; wherein A is a 0.02-0.2 mm thick polyvinyl chloride film layer; B is a 1-10 mm thick microfoamed layer; the lightweight microfoamed packaging material is prepared by the following method: (1) Premixing of A layer material: According to the formula design of parts by weight, add 100 parts of polyvinyl chloride, 3-5 parts of MBS resin, 30-40 parts by weight of plasticizer, 1-3 parts of heat stabilizer and 0.2-0.5 parts of lubricant to a high-speed mixer and mix evenly so that the plasticizer can fully penetrate the polyvinyl chloride and be used as A layer material for later use. (2) Premixing of B layer base material: According to the formula design of weight parts, 100 parts of polyvinyl chloride, 15-20 parts of plasticizer, 35-45 parts of fibrous filler, 1-3 parts of foaming regulator, 1-3 parts of heat stabilizer and 0.5-1 parts of lubricant are put into a high-speed mixer and mixed evenly to be used as B layer base material. (3) Pre-preparation of composite micro-foaming agent: According to the formula design by weight, 60-70 parts of SBS adhesive powder, 20-30 parts of inorganic nucleating agent, 5-10 parts of low-hydrolysis thermoplastic polyvinyl alcohol powder, 2 parts of low-temperature foaming agent, and 3-5 parts of high-temperature foaming agent are added to a high-speed mixer and mixed evenly to prepare the composite micro-foaming agent for later use; the low-hydrolysis thermoplastic polyvinyl alcohol powder is obtained by plasticizing polyvinyl alcohol with a degree of hydrolysis of 80-85% with glycerol; (4) Using a three-layer co-extrusion twin-screw extruder as the extrusion foaming equipment, A layer material is added to the upper extruder and the lower extruder for extrusion; B layer base material is added to the middle extruder for extrusion, and a composite micro-foaming agent is added in the sixth section of the middle extruder by loss-in-weight weighing. The amount of composite micro-foaming agent added is 20% of the weight of B layer base material. Through hot melt extrusion of the three-layer co-extrusion twin-screw extruder, a three-layer composite layer is formed at the T-die. The material is then extruded and foamed through the die, stretched, and shaped by rollers to form a lightweight micro-foamed packaging material with an ABA structure.

2. The lightweight microfoamed packaging material as described in claim 1, characterized in that: The polyvinyl chloride in step (1) is selected from at least one of SG2, SG3, and SG4; the polyvinyl chloride in step (2) is selected from at least one of SG5, SG6, and SG7.

3. The lightweight microfoamed packaging material as described in claim 1, characterized in that: The MBS resin mentioned in step (1) is a methyl methacrylate-butadiene-styrene terpolymer with a methyl methacrylate content of 60-70%.

4. The lightweight microfoamed packaging material as described in claim 1, characterized in that: In steps (1) and (2), the plasticizer selected is at least one of dioctyl phthalate, diisooctyl phthalate, and dibutyl phthalate as the main plasticizer, and at least one of dioctyl sebacate and epoxidized soybean oil as the secondary plasticizer. The main plasticizer and the secondary plasticizer are used in combination at a mass ratio of 100:5-10.

5. The lightweight microfoamed packaging material as described in claim 1, characterized in that: The heat stabilizer mentioned in steps (1) and (2) is at least one of zinc stearate, calcium stearate, and barium stearate.

6. The lightweight microfoamed packaging material as described in claim 1, characterized in that: The lubricating agent in step (1) is at least one of silicone powder and polyethylene wax as an external lubricant; the lubricating agent in step (2) is at least one of stearamide, N,N-ethylene bis-stearamide, oleamide and tristearate as an internal lubricant.

7. The lightweight microfoamed packaging material as described in claim 1, characterized in that: The foaming regulator mentioned in step (2) is an acrylate foaming regulator.

8. The lightweight microfoamed packaging material as described in claim 1, characterized in that: The particle size of the SBS adhesive powder mentioned in step (3) is ≤20μm.

9. The lightweight microfoamed packaging material as described in claim 1, characterized in that: The inorganic nucleating agent in step (3) is selected from light calcium carbonate with a particle size range of 3-5 μm.

10. The lightweight microfoamed packaging material as described in claim 1, characterized in that: In step (3), the low-temperature foaming agent is selected from at least one of 4,4-oxobisbenzenesulfonyl hydrazine and sodium bicarbonate; the high-temperature foaming agent is selected from azodicarbonamide.

Images