Environment-friendly large-gram-weight packaging composite sheet and solvent-free compounding process thereof

Abstract

The invention discloses an environment-friendly large-gram-weight packaging composite sheet which is formed by compounding three layers of materials including an outer-layer composite film, an aluminum foil layer and an inner-layer composite film, and the outer-layer composite film, the aluminum foil layer and the inner-layer composite film are compounded through bonding layers; and the outer-layer composite film and the inner-layer composite film are prepared by a film blowing process and an improved film formula. The invention further provides a solvent-free compounding process of the environment-friendly large-gram-weight packaging composite sheet. The composite sheet provided by the invention is high in peel strength, good in barrier property, excellent in medium resistance, excellent in comprehensive performance, low in cost, environment-friendly and safe. The solvent-free composite process provided by the invention solves the problems of white points and bubbles on the composite film, insufficient composite peel strength, increased friction coefficient of the composite film, irregular rolling, tunnel phenomenon and the like in the conventional solvent-free composite process, and successfully applies the solvent-free composite process to the preparation of the large-gram-weight packaging composite sheet.

Description

Technical Field

[0001] The invention relates to the technical field of packaging materials, and in particular to an environmentally friendly large-weight packaging composite sheet and a solvent-free composite process thereof. Background Art

[0002] Flexible packaging has the advantages of good barrier properties, light weight, impact resistance, low cost, and convenient use. It greatly extends the shelf life of goods, facilitates circulation, promotes sales, and increases the added value of goods. It has strongly promoted the progress of industries such as food, daily chemicals, and medicine. It is an indispensable part of the development of the world economy. Flexible packaging composite materials are layered structures formed by composite processes and technologies such as lamination, extrusion, and coating to combine substrate layers and adhesive layers with different functions. The current plastic flexible packaging production processes are all aimed at certain products and certain performances, and have their own limitations. At the same time, there are also common problems such as complex production processes, large amounts of raw materials, long production cycles, and organic solvent pollution. There is still a need to develop manufacturing technologies that meet green, safe, and environmentally friendly requirements to meet the market demand for low-cost, green and environmentally friendly flexible packaging materials.

[0003] At present, the commonly used method for preparing flexible packaging composite sheets is the extrusion composite process, which relies on an extruder and a die head. The plastic particles are melted and plasticized in the extruder, and then cast onto the surface of another sheet substrate through the die head, and then cooled to form a composite film. This composite method has the advantages of fast production speed, adjustable thickness of the extruded composite film layer, and low price, but the production control and quality control of this process are difficult, the raw material loss is large, and there are great limitations.

[0004] The solvent-free composite process is a composite method that uses a solvent-free adhesive to coat the substrate and directly bond it to the second substrate. Solvent-free adhesives rarely produce three wastes during the production process, and the composite process does not require drying. Therefore, the solvent-free composite process is a safe, environmentally friendly, economical and efficient composite technology that can meet the needs of green manufacturing of flexible packaging and is widely used in the manufacture of flexible packaging in the fields of food, medicine, electronic products, detergents, cosmetics, etc. However, the solvent-free composite process is generally used in small-weight packaging (used to carry light-weight goods, such as puffed food packaging, etc.), and it is easy to produce small bubbles during the composite process, the interlayer peeling strength is not high, and the medium resistance is general. In addition, since the coating amount of this process is usually low, it is difficult to meet the coating amount requirements of large-weight packaging (used to carry heavy-weight goods, such as toothpaste hoses, cosmetic hoses, etc.), which restricts the application of solvent-free composite technology in the field of large-weight sheets.

[0005] Therefore, it is urgent to develop an environmentally friendly composite sheet with good barrier properties, excellent medium resistance, high interlayer peeling strength and excellent comprehensive performance to produce large-weight packaging, and to improve the solvent-free composite process to solve the above problems in order to cope with the increasingly fierce competition in the field of flexible packaging composite sheets and meet the needs of low-cost, green and environmentally friendly packaging. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an environmentally friendly large-weight packaging composite sheet. The composite material has high peel strength, good barrier properties, excellent medium resistance, excellent comprehensive performance, low cost, and environmental safety. In addition, a composite process for environmentally friendly large-weight packaging composite sheets is provided. The process solves the problems of white spots and bubbles on the composite film, insufficient composite peel strength, increased friction coefficient of the composite film, uneven winding and tunnel phenomenon that exist in conventional solvent-free composite processes, and successfully applies the solvent-free composite process to the preparation of large-weight packaging composite sheets.

[0007] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is to provide an environmentally friendly large-weight packaging composite sheet, wherein the composite sheet is composed of three layers of materials: an outer composite film, an aluminum foil layer, and an inner composite film. The outer composite film, the aluminum foil layer, and the inner composite film are composited by an adhesive layer, and the adhesive layer adopts solvent-free glue; the outer composite film includes a three-layer structure, which includes a printing layer, a filling layer, and a composite layer from the outside to the inside; the inner composite film includes a three-layer structure, which includes a composite layer, a filling layer, and a heat-sealing layer from the outside to the inside; the outer composite film and the inner composite film are made by a film blowing process.

[0008] The composite sheet provided by the present invention is prepared by using an adjusted film formula, and the adjusted film formula is as follows, by mass percentage: the printing layer of the outer composite film comprises 20-40% of low-density polyethylene LDPE and 60-80% of medium-density polyethylene MDPE, the filling layer comprises 20-40% of medium-density polyethylene MDPE and 60-80% of high-density polyethylene HDPE, and the composite layer comprises 40-60% of low-density polyethylene LDPE and 40-60% of linear low-density polyethylene LLDPE; the composite layer of the inner composite film comprises 40-60% of low-density polyethylene LDPE and 40-60% of linear low-density polyethylene LLDPE, the filling layer comprises 20-40% of medium-density polyethylene MDPE and 60-80% of high-density polyethylene HDPE, and the heat-sealing layer comprises 15-35% of low-density polyethylene LDPE, 60-80% of medium-density polyethylene MDPE and 1-5% of a lubricant.

[0009] The present invention adopts three layers of polyethylene to make the outer and inner composite films, wherein the printing layer and the heat sealing layer are made of medium-density polyethylene MDPE, the filling layer is made of high-density polyethylene HDPE, and the composite layer is made of low-density polyethylene LDPE. Although high-density polyethylene HDPE has good chemical resistance, high hardness and mechanical strength, it has a high softening point and a high operating temperature, which is not conducive to processing.

[0010] In order to lower the softening point of the film material and improve the processability of the film material, the technical solution adopted by the present invention is to add low-density polyethylene LDPE with a lower softening point to the printing layer and the heat-sealing layer material, increase a certain proportion of medium-density polyethylene MDPE in the filling layer, and increase a certain proportion of linear low-density polyethylene LLDPE in the composite layer material. The linear low-density polyethylene LLDPE can also enhance the mechanical properties of the material such as tensile strength and impact resistance, while the low-density polyethylene LDPE can increase heat sealing and processability. The printing layer, the filling layer, the composite layer and the heat-sealing layer adopt the above-mentioned film formula, which can not only reduce the melting point of the sheet material and make the polyethylene film easy to process, but also ensure that the composite layer and the aluminum foil layer have a higher bonding strength when compounded by solvent-free glue, so that the product can meet the requirements of performance, processing performance and low cost.

[0011] Furthermore, the thickness of the outer composite film is 135-145 μm, and the thickness of the inner composite film is 95-100 μm.

[0012] Furthermore, the thickness of the aluminum foil layer is 10-15 μm, and the aluminum foil layer has excellent barrier properties and can effectively isolate oxygen, water vapor, odor, etc. in the packaging material.

[0013] Further, the solvent-free glue is Bostik LF686 & H186. In order to screen out solvent-free glue with excellent media resistance, the inventors of the present invention conducted a survey on the mainstream solvent-free glue suppliers on the market, and preliminarily screened Henkel glue 7795 & 6204, Bostik LF686 & H186 and Dow 1209A & B. Since sheet packaging is used for large-gram packaging, such as toothpaste hoses, medicine hoses, sauce hoses, cosmetic hoses, etc., the content activity is relatively high, and the barrier performance requirements of the packaging are relatively high, so the supplier samples of these three glues were immersed in tests to effectively test the media resistance of the materials. The results of the immersion test showed that Henkel glue 7795 & 6204 and Bostik LF686 & H186 did not show stratification and passed the immersion test, while Dow 1209A & B showed stratification and failed the immersion test. In addition, considering the mainstream aluminum-plastic (AL / PE) structure and plastic-plastic (PE / PE) structure of the sheet, the preferred solvent-free glue is Bostik LF686&H186, which meets the sheet's requirements for chemical medium resistance and interlayer peeling performance. The appearance after compounding meets the requirements, without defects such as bubbles and glue spots.

[0014] In the present invention, the working principle of the solvent-free glue is mainly to form adhesion through polymerization reaction. The polymer in the glue, which is usually a long-chain molecule, can firmly adhere two surfaces together by forming covalent bonds. This polymerization reaction enables the solvent-free glue to achieve efficient bonding without using any solvent. It is worth noting that the solvent-free glue has significant advantages over the traditional solvent-based glue. It does not volatilize VOCs (volatile organic compounds) and does not produce irritating odors, so it is more environmentally friendly. At the same time, the production process of solvent-free glue is also more energy-saving and safe, and there is no hidden danger of fire or explosion. In addition, due to the fast curing speed of solvent-free glue, the production efficiency is also higher.

[0015] Another object of the present invention is to provide a solvent-free composite process for an environmentally friendly large-weight packaging composite sheet, wherein the structure of the composite sheet prepared is an outer composite film, an adhesive layer, an aluminum foil layer, an adhesive layer, and an inner composite film from the outside to the inside, and the process comprises the following steps: (1) placing the inner layer composite film on the first unwinding unit of the solvent-free composite machine, placing the aluminum foil layer on the second unwinding unit, coating the heated solvent-free glue on the composite layer surface of the inner layer composite film through the coating unit, and then performing a composite once through the composite unit; (2) winding the composite semi-finished product through a winding unit, and then placing the rolled composite semi-finished product into a curing chamber for curing; (3) placing the semi-finished composite product after aging on the second unwinding unit, placing the outer composite film on the first unwinding unit, coating the heated solvent-free glue on the composite layer surface of the outer composite film through the coating unit, and then performing secondary composite through the composite unit; (4) The composite secondary finished product is rolled up by a rolling unit, and then the rolled secondary composite product is placed in a curing chamber for curing to obtain an environmentally friendly large-weight packaging composite sheet.

[0016] In the further step (1), the first unwinding tension of the composite is 9-11 kg, the second unwinding tension is 7-9 kg, and the glue amount is 1.5-2.5 gsm (gsm means grams per square meter, i.e. g / m 2 ), the batching temperature is 55~65℃, the compounding pressure is 0.33~0.37 MPa, the coating temperature is 55~65℃, and the compounding temperature is 35~45℃.

[0017] In the further step (2), the winding tension of the winding unit is 14-16 kg, the aging temperature of the composite semi-finished product is 38-42° C., and the aging time is 2-4 h.

[0018] Further, in the step (3), the first unwinding tension of the secondary composite is 13-15 kg, the second unwinding tension is 14-16 kg, the glue amount is 1.5-2.5 gsm, the batching temperature is 55-65°C, the coating temperature is 55-65°C, the composite pressure is 0.33-0.37 MPa, and the composite temperature is 35-45°C; In the further step (4), the winding tension of the winding unit is 19-21 kg, the aging temperature of the composite semi-finished product is 43-47° C., and the aging time is 156-180 h.

[0019] In order to solve the problem of white spots and bubbles appearing on the composite film in the solvent-free composite process, the present invention considers that it is caused by insufficient glue applied or foreign matter sticking to the roller. The measures taken by the present invention are to appropriately increase the glue amount (the conventional glue amount of the solvent-free composite process for small-weight packaging is 0.8-2.0 gsm), and regularly check the roller and do a good job of cleaning. In addition, since the isocyanate component in the solvent-free glue will react with water in the air to produce carbon dioxide gas, thereby causing white spots and bubbles to appear on the composite film, the measures taken by the present invention are to increase the composite pressure (the conventional composite pressure of the solvent-free composite process for small-weight packaging is 0.30 MPa) and reduce the relative humidity of the environment.

[0020] In order to solve the problem of insufficient composite peeling strength in the solvent-free composite process, the measures taken by the present invention are to select materials with qualified surface tension and use online corona equipment to perform vacuum degassing treatment before mixing the glue, which can not only eliminate the bubbles contained in the mixed glue, but also improve the peeling performance of the mixed glue.

[0021] In order to solve the problem of increased friction coefficient of the composite film in the solvent-free composite process, the present invention adopts the measure of adding a certain proportion of lubricant to the heat-sealing layer of the inner composite film and controlling the aging temperature within the range of 40-45°C. Since the lubricant will migrate inward at a higher temperature and react with the polyether component in the solvent-free glue of the bonding layer, the consumption of the lubricant will increase and the friction coefficient will increase. Therefore, in addition to adding an appropriate amount of lubricant, the friction coefficient can also be reduced by controlling the aging temperature.

[0022] In order to solve the problems of uneven winding and tunneling in the solvent-free composite process, the present invention adopts the measure of adjusting the winding tension and pressure. Because the winding tension and pressure are abnormal, the film flatness is poor. By adjusting the winding tension and pressure (the conventional winding tension of the solvent-free composite process for small-weight packaging is 8-10 kg) and controlling the adhesive to "constant viscosity transfer" as much as possible, the production quality and stability of the composite film can be effectively improved.

[0023] The advantages and beneficial effects of the present invention are: 1. The composite sheet prepared by the present invention has high peeling strength, good barrier performance, excellent medium resistance and excellent comprehensive performance. The present invention adopts three layers of polyethylene to make the outer and inner composite films, and adopts a low softening point film formula, which not only reduces the softening point of the film material, but also improves the processability of the film material. The tensile strength and stiffness of the final product meet the use requirements, and the interlayer peeling strength after compounding is 6.1N / 15mm; an aluminum foil layer is added between the outer film and the inner film of the composite sheet as a barrier layer, so that it has excellent barrier properties; through immersion testing, solvent-free glue with excellent medium resistance is screened out to meet the requirements of the sheet for chemical medium resistance and interlayer peeling performance. The appearance meets the requirements after compounding, and there are no defects such as bubbles and glue spots.

[0024] 2. The plastic film of the composite sheet provided by the present invention is made of polyethylene material, which is compounded by solvent-free glue. When recycled, it is easy to separate the layers, ensuring that the polyethylene film of the composite sheet can be recycled after separation, which meets the requirements of sustainable development.

[0025] 3. The present invention uses solvent-free glue as a binder, which has the advantages of environmental protection, safety, and energy saving. Solvent-free glue does not volatilize VOCs and does not produce irritating odors, so it is more environmentally friendly. At the same time, the production process of solvent-free glue is also more energy-saving and safe, and there is no hidden danger of fire or explosion. In addition, since the solvent-free glue has a fast curing speed, the production efficiency is also higher.

[0026] 4. The composite process of the solvent-free environmentally friendly composite sheet of the present invention solves the problems of white spots and bubbles on the composite film, insufficient composite peeling strength, increased composite film friction coefficient, uneven winding and tunneling in the conventional solvent-free composite process. By appropriately increasing the amount of glue (the conventional amount of glue is 0.8~2.0 gsm), regularly checking and cleaning the rollers, increasing the composite pressure (the conventional composite pressure is 0.30 MPa), and reducing the relative humidity of the environment, the composite film prepared has no bubbles and glue spots in appearance; by selecting materials with qualified surface tension and using online corona equipment, vacuum degassing treatment is performed before mixing, so as to improve the composite peeling strength; because the lubricant in the composite layer reacts with the polyether component in the solvent-free glue, in addition to adding an appropriate amount of lubricant, the aging temperature can also be controlled within the range of 40~45℃, thereby reducing the friction coefficient of the composite film; by adjusting the winding tension and pressure (the conventional winding tension is 8~10 kg), and controlling the adhesive to "transfer constant viscosity" as much as possible, the uneven winding and tunneling phenomena are solved, the product appearance is smooth, and the production quality and stability of the composite film are effectively improved.

[0027] 5. The present invention successfully applies the solvent-free composite process to the preparation of heavy-weight packaging composite sheets. The prepared composite film has higher strength and durability, and can better protect the packaging contents when it needs to withstand heavy pressure or frequent handling. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the cross-sectional structure of an environmentally friendly large-weight packaging composite sheet in the present invention; In the figure: 1. Outer composite film; 2. Adhesive layer; 3. Aluminum foil layer; 4. Adhesive layer; 5. Inner composite film. DETAILED DESCRIPTION

[0029] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0030] Example 1 In this embodiment, an environmentally friendly large-weight packaging composite sheet material is provided, and the sheet material structure is as shown in FIG. Figure 1, an outer composite film, an adhesive layer, an aluminum foil layer, an adhesive layer, and an inner composite film are arranged in sequence from the outside to the inside. The outer composite film includes a three-layer structure, which includes a printing layer, a filling layer, and a composite layer in sequence from the outside to the inside; the inner composite film includes a three-layer structure, which includes a composite layer, a filling layer, and a heat-sealing layer in sequence from the outside to the inside; the solvent-free glue used in the adhesive layer is Bostik LF686&H186; the outer composite film and the inner composite film are made by a film blowing process.

[0031] Using the adjusted film formula, by weight percentage, the printing layer of the outer composite film includes 30% low-density polyethylene LDPE and 70% medium-density polyethylene MDPE, the filling layer includes 30% medium-density polyethylene MDPE and 70% high-density polyethylene HDPE, and the composite layer includes 50% linear low-density polyethylene LLDPE and 50% low-density polyethylene LDPE; the composite layer of the inner composite film includes 50% linear low-density polyethylene LLDPE and 50% low-density polyethylene LDPE, the filling layer includes 30% medium-density polyethylene MDPE and 70% high-density polyethylene HDPE, and the heat-sealing layer includes 27% low-density polyethylene LDPE, 70% medium-density polyethylene MDPE and 3% lubricant.

[0032] The thickness of the outer composite film is 140 μm, the thickness of the inner composite film is 98 μm, and the thickness of the aluminum foil layer is 12 μm.

[0033] The solvent-free composite process of the environmentally friendly large-weight packaging composite sheet comprises the following steps: (1) The inner layer composite film is placed on the first unwinding unit of the solvent-free laminating machine, and the aluminum foil layer is placed on the second unwinding unit. The heated solvent-free glue is coated on the composite layer surface of the inner layer composite film through the coating unit. The first unwinding tension is 10 kg, the second unwinding tension is 8 kg, the glue amount is 2.0 gsm, the batching temperature is 60°C, and the coating temperature is 60°C. Then, the composite unit is used for one lamination, and the lamination pressure is 0.35 MPa and the lamination temperature is 40°C. (2) The composite semi-finished product is rolled up by a rolling unit with a rolling tension of 15 kg, and then the rolled semi-finished product is placed in a curing room for curing at a curing temperature of 40° C. for 3 h; (3) Place the semi-finished composite product after quick-cooking on the second unwinding unit, and place the outer composite film on the first unwinding unit. Apply the heated solvent-free glue on the composite surface of the outer composite film through the coating unit. The first unwinding tension is 14 kg, the second unwinding tension is 15 kg, the glue amount is 2.0 gsm, the batching temperature is 60°C, and the coating temperature is 60°C. Then, perform secondary composite through the composite unit. The composite pressure is 0.35 MPa and the composite temperature is 40°C. (4) The secondary composite product after the composite is rolled up by a winding unit with a winding tension of 20 kg. The rolled secondary composite product is then placed in a curing chamber for curing at a curing temperature of 45° C. for 168 h.

[0034] Example 2 The difference between the process parameters of Example 2 and Example 1 is: Using the adjusted film formula, by weight percentage, the printing layer of the outer composite film includes 20% low-density polyethylene LDPE and 80% medium-density polyethylene MDPE, the filling layer includes 20% medium-density polyethylene MDPE and 80% high-density polyethylene HDPE, and the composite layer includes 40% linear low-density polyethylene LLDPE and 60% low-density polyethylene LDPE; the composite layer of the inner composite film includes 40% linear low-density polyethylene LLDPE and 60% low-density polyethylene LDPE, the filling layer includes 20% medium-density polyethylene MDPE and 80% high-density polyethylene HDPE, and the heat-sealing layer includes 19% low-density polyethylene LDPE, 80% medium-density polyethylene MDPE and 1% lubricant.

[0035] The thickness of the outer composite film is 135 μm, the thickness of the inner composite film is 95 μm, and the thickness of the aluminum foil layer is 10 μm.

[0036] The solvent-free composite process of an environmentally friendly large-gram-weight packaging composite sheet comprises the following steps: in step (1), the first unwinding tension of the primary composite is 9 kg, the second unwinding tension is 7 kg, the amount of glue applied is 1.5 gsm, the batching temperature is 55°C, the coating temperature is 55°C, the composite pressure is 0.33 MPa, and the composite temperature is 35°C; in step (2), the winding tension of the winding unit is 14 kg, the aging temperature of the primary composite semi-finished product is 38°C, and the aging time is 2 h; in step (3), the first unwinding tension of the secondary composite is 13 kg, the second unwinding tension is 14 kg, the amount of glue applied is 1.5 gsm, the batching temperature is 55°C, the coating temperature is 55°C, the composite pressure is 0.33 MPa, and the composite temperature is 35°C; in step (4), the winding tension of the winding unit is 19 kg, the aging temperature of the secondary composite finished product is 43°C, and the aging time is 156 h.

[0037] Example 3 The difference between the process parameters of Example 3 and Example 1 is: Using the adjusted film formula, by weight percentage, the printing layer of the outer composite film includes 40% low-density polyethylene LDPE and 60% medium-density polyethylene MDPE, the filling layer includes 40% medium-density polyethylene MDPE and 60% high-density polyethylene HDPE, and the composite layer includes 60% linear low-density polyethylene LLDPE and 40% low-density polyethylene LDPE; the composite layer of the inner composite film includes 60% linear low-density polyethylene LLDPE and 40% low-density polyethylene LDPE, the filling layer includes 40% medium-density polyethylene MDPE and 60% high-density polyethylene HDPE, and the heat-sealing layer includes 35% low-density polyethylene LDPE, 60% medium-density polyethylene MDPE and 5% lubricant.

[0038] The thickness of the outer composite film is 145 μm, the thickness of the inner composite film is 100 μm, and the thickness of the aluminum foil layer is 15 μm.

[0039] The solvent-free composite process of an environmentally friendly large-gram-weight packaging composite sheet comprises the following steps: in step (1), the first unwinding tension of the primary composite is 11 kg, the second unwinding tension is 9 kg, the amount of glue applied is 2.5 gsm, the batching temperature is 65°C, the coating temperature is 65°C, the composite pressure is 0.37 MPa, and the composite temperature is 45°C; in step (2), the winding tension of the winding unit is 16 kg, the aging temperature of the primary composite semi-finished product is 42°C, and the aging time is 4 h; in step (3), the first unwinding tension of the secondary composite is 15 kg, the second unwinding tension is 16 kg, the amount of glue applied is 2.5 gsm, the batching temperature is 65°C, the coating temperature is 65°C, the composite pressure is 0.37 MPa, and the composite temperature is 45°C; in step (4), the winding tension of the winding unit is 21 kg, the aging temperature of the secondary composite finished product is 47°C, and the aging time is 180 h.

[0040] The composite sheets prepared according to Examples 1-3 were cut and the performance of the composite sheets prepared in Examples 1-3 of the present invention was tested: Table 1 Main technical requirements of Examples 1-3

[0041] Table 2 Performance test results of the composite sheets obtained in Examples 1-3

[0042] Comparing the performance test results of the composite sheets prepared in Examples 1-3 in Table 2 with the main technical requirements in Table 1, it can be seen that the composite sheets prepared using the film formulation and solvent-free composite process of the present invention not only have improved peel strength, reduced friction coefficient, greatly improved tensile strength, effectively controlled longitudinal and transverse stiffness, and smooth appearance, effectively eliminated white spots and bubbles, and no obvious defects at arm's length. In summary, the composite sheets prepared by the present invention have higher strength and durability, and can meet the use requirements of large-weight packaging.

[0043] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An environmentally friendly large-weight packaging composite sheet, characterized in that: The composite sheet is composed of three layers of materials: an outer composite film, an aluminum foil layer, and an inner composite film. The outer composite film, the aluminum foil layer, and the inner composite film are composited by an adhesive layer, and the adhesive layer uses solvent-free glue; the outer composite film includes a three-layer structure, which includes a printing layer, a filling layer, and a composite layer from the outside to the inside; the inner composite film includes a three-layer structure, which includes a composite layer, a filling layer, and a heat-sealing layer from the outside to the inside; the outer composite film and the inner composite film are made by a blown film process; The composite sheet is prepared by using an improved film formula, and the film formula is as follows, by mass percentage: the printing layer of the outer composite film comprises 20-40% of low-density polyethylene LDPE and 60-80% of medium-density polyethylene MDPE, the filling layer comprises 20-40% of medium-density polyethylene MDPE and 60-80% of high-density polyethylene HDPE, and the composite layer comprises 40-60% of low-density polyethylene LDPE and 40-60% of linear low-density polyethylene LLDPE; the composite layer of the inner composite film comprises 40-60% of low-density polyethylene LDPE and 40-60% of linear low-density polyethylene LLDPE, the filling layer comprises 20-40% of medium-density polyethylene MDPE and 60-80% of high-density polyethylene HDPE, and the heat-sealing layer comprises 15-35% of low-density polyethylene LDPE, 60-80% of medium-density polyethylene MDPE and 1-5% of a lubricant.

2. The environmentally friendly large-weight packaging composite sheet according to claim 1, characterized in that: The thickness of the outer composite film is 135-145 μm, and the thickness of the inner composite film is 95-100 μm.

3. The environmentally friendly large-weight packaging composite sheet according to claim 1, characterized in that: The thickness of the aluminum foil layer is 10-15 μm.

4. The environmentally friendly large-weight packaging composite sheet according to claim 1, characterized in that: The solvent-free glue is Bostik LF686&H186.

5. A solvent-free composite process for environmentally friendly large-weight packaging composite sheets, characterized in that: The structure of the prepared composite sheet from outside to inside is an outer composite film, an adhesive layer, an aluminum foil layer, an adhesive layer, and an inner composite film, and includes the following steps: (1) placing the inner layer composite film on the first unwinding unit of the solvent-free composite machine, placing the aluminum foil layer on the second unwinding unit, coating the heated solvent-free glue on the composite layer surface of the inner layer composite film through the coating unit, and then performing a composite once through the composite unit; (2) winding the composite semi-finished product through a winding unit, and then placing the rolled composite semi-finished product into a curing chamber for curing; (3) placing the semi-finished composite product after aging on the second unwinding unit, placing the outer composite film on the first unwinding unit, coating the heated solvent-free glue on the composite layer surface of the outer composite film through the coating unit, and then performing secondary composite through the composite unit; (4) The composite secondary finished product is rolled up by a rolling unit, and then the rolled secondary composite product is placed in a curing chamber for curing to obtain an environmentally friendly large-weight packaging composite sheet.

6. The solvent-free composite process for environmentally friendly large-weight packaging composite sheets according to claim 5, characterized in that: In the step (1), the first unwinding tension of the composite is 9-11 kg, the second unwinding tension is 7-9 kg, the glue amount is 1.5-2.5 gsm, the batching temperature is 55-65°C, the coating temperature is 55-65°C, the composite pressure is 0.33-0.37 MPa, and the composite temperature is 35-45°C.

7. The solvent-free composite process for environmentally friendly large-weight packaging composite sheets according to claim 5, characterized in that: In the step (2), the winding tension of the winding unit is 14-16 kg, the aging temperature of the composite semi-finished product is 38-42° C., and the aging time is 2-4 h.

8. The solvent-free composite process for environmentally friendly large-weight packaging composite sheets according to claim 5, characterized in that: In the step (3), the first unwinding tension of the secondary composite is 13-15 kg, the second unwinding tension is 14-16 kg, the glue amount is 1.5-2.5 gsm, the batching temperature is 55-65°C, the coating temperature is 55-65°C, the composite pressure is 0.33-0.37 MPa, and the composite temperature is 35-45°C.

9. The solvent-free composite process for environmentally friendly large-weight packaging composite sheets according to claim 5, characterized in that: In the step (4), the winding tension of the winding unit is 19-21 kg, the aging temperature of the composite semi-finished product is 43-47° C., and the aging time is 156-180 h.

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