Plastic extrusion process and extrusion system

Abstract

The invention relates to an extrusion process and an extrusion system of plastic, the plastic is subjected to reaction molding in a screw extrusion device, the plastic passes through a feeding section, a feeding melting section, a reaction section, a molding section and a product extrusion section of the screw extrusion device in sequence, and the extrusion process comprises the following steps: starting the screw extrusion device, plastic is added to a feeding port of the screw extrusion device and enters the feeding section; and nitrogen charging operation is carried out at the position corresponding to the feeding melting section, and meanwhile vacuumizing operation is carried out at the position corresponding to the forming section. According to the invention, the material can be ensured to be in an oxygen-free environment within an effective processing range, side effects of oxygen on the plastic in a heating reaction process are effectively avoided, the conditions of moisture absorption, oxidation and solidification of the material in the processing process are reduced, and the product has no defective pixel or yellow spot phenomenon.

Description

Technical Field

[0001] The invention relates to the technical field of plastic extrusion molding, and in particular to a plastic extrusion process and an extrusion system. Background Art

[0002] With the rapid development of the petroleum industry, the application scope of plastic products is becoming increasingly wide. In some occasions, they can even replace metal, wood, paper, etc., which brings great convenience to people's lives. Therefore, the production process of plastic products is also constantly updated and explored to seek more plastic products with better performance.

[0003] With the rapid development of the plastics industry and the widespread use of plastic products, plastic waste is also increasing, and the "white pollution" problem has had a serious impact on the ecological environment. Because plastic products are difficult to degrade, they have caused serious pollution to the natural environment, soil, oceans, etc. during long-term use, and even threaten human health. In the past decade or so, humans have gradually realized the harm of plastic pollution and have continuously increased the efforts to recycle plastics to cope with the pollution threat caused by waste plastics.

[0004] The recycling of plastics can reduce environmental pollution, increase the circular economy value of plastics, and promote energy conservation and environmental protection. At present, my country often uses the processing technology of extruding recycled plastics to increase the reuse rate of recycled plastics.

[0005] Extrusion molding mainly refers to a method of using the extrusion effect of a screw or a plunger to force the heated and molten polymer material through the die head under pressure to form a shape. The plastic extrusion process can be divided into two stages: the first stage is to plasticize the resin (i.e., high-temperature melting becomes a viscous fluid) and pass it through a specially shaped die under pressure to become a continuum with a cross-section similar to the die shape; the second stage is to use appropriate methods to make the extruded continuum lose its plastic state and become a solid to obtain the desired product. The first stage of the resin plasticization process is mainly completed in the core part of the screw extruder - the extrusion system, which consists of a screw and a barrel.

[0006] Common extrusion molding and granulation processes are not fully deoxidized. The air in the gaps between raw material particles and the venting agent in the barrel provide the possibility for the resin to come into contact with oxygen. The resin needs to undergo a high-temperature plasticization process during the extrusion molding process, and many thermoplastic resins can undergo thermal oxygen aging reactions when in contact with oxygen at high temperatures, resulting in performance degradation.

[0007] For example, Chinese patent application No. 201010555432.0 discloses an extrusion device and an extrusion processing method of a thermoplastic polyester elastomer. The extrusion device provided by the invention adopts an extruder. The extrusion system of the extruder includes a screw, a barrel, a feed port, a die head, and a nitrogen storage device. The nitrogen storage device is connected to the feed port of the extruder by a hose, and a partial pressure regulating valve is installed on the hose. However, the extrusion device and the extrusion processing method of the thermoplastic polyester elastomer still have the following disadvantages or shortcomings: (1) the applicable plastics are limited to thermoplastic polyester elastomers, and the applicable scope is small; (2) it is difficult to ensure that the extrusion process is in an oxygen-free state by only introducing nitrogen at the feed port, and thus it is difficult to ensure the quality of the extruded product.

[0008] For another example, Chinese patent application 202121683798.6 discloses a nitrogen anti-oxidation degradation extrusion pipeline, the utility model includes an extrusion tube fixing seat, the extrusion tube fixing seat is provided with a feed fixing platform, the extrusion tube fixing seat is provided with an extrusion tube cavity extending into the feed fixing platform, the extrusion tube cavity is provided with a rotatable spiral extrusion part, and the feed fixing platform is provided with a masterbatch feed part and a nitrogen filling anti-oxidation component. However, the nitrogen anti-oxidation degradation extrusion pipeline still has the following shortcomings or deficiencies: (1) before extrusion, the air in the extrusion tube cavity is first extracted by the exhaust part, and then the raw material is extruded through the spiral extrusion part after nitrogen is introduced. Since the material will release oxygen-containing gas in the subsequent heating process, it is impossible to ensure that the entire extrusion process is in an oxygen-free nitrogen environment; (2) vacuuming is performed first and then nitrogen is passed, which increases the difficulty of the entire operation.

[0009] Therefore, providing a plastic extrusion process that is simple to operate, has a wide range of applications, and can effectively ensure that various plastics are in a stable oxygen-free environment in the effective processing and molding area has become an issue that the industry urgently needs to solve. Summary of the invention

[0010] In view of the above problems, one of the objects of the present invention is to provide a plastic extrusion process, which can ensure that the material is in an oxygen-free environment within the effective processing range, effectively avoid the side effects of oxygen on the plastic during the heating reaction process, reduce the moisture absorption, oxidation and solidification of the material during the processing, make the product free of bad spots or yellow spots, and at the same time can also improve the density and mechanical properties of the plastic.

[0011] To achieve the above-mentioned purpose, the present invention provides the following technical solutions on one hand: The present invention provides an extrusion process of plastic, wherein the plastic is reaction-molded in a screw extruder, and the plastic passes through the feed section, feed melting section, reaction section, molding section and product extrusion section of the screw extruder in sequence. The extrusion process comprises the following steps: (1) starting the screw extruder, adding the plastic to the feed port of the screw extruder and allowing it to enter the feed section; and (2) performing a nitrogen filling operation at a position corresponding to the feed melting section, and simultaneously performing a vacuum operation at a position corresponding to the molding section.

[0012] Among them, in the extrusion process of plastic, since the feed section is connected to the feed port, it is a normal pressure, non-enclosed environment. If the nitrogen filling operation is performed at the feed section, it is easy to blow away the material, causing feeding difficulties. The applicant found through research that after the material enters the feed melting section, since the plastic is already in a molten state, there is adhesion between the plastic molecules, so the spacing between the molecules is reduced, so the present application fills nitrogen into the feed melting section. In this case, since there will be very little nitrogen remaining between the molecules, the amount of nitrogen used can be effectively reduced, so that under the condition of processing the same amount of the same type of plastic products, the amount of nitrogen used can be reduced by one quarter to one third (relative to the nitrogen introduced at the feed section), reducing costs; in addition, in the present application, not only nitrogen is introduced into the feed melting section, but also vacuum operation is performed at the molding section at the same time, which can also effectively reduce the tendency of air entering the rear end reaction, so that no oxygen molecules enter the plastic products.

[0013] In some embodiments, in step (2), the nitrogen filling pressure is set to 0.1 MPa to 0.4 MPa, which can be 0.11 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa, 0.15 MPa, 0.16 MPa, 0.17 MPa, 0.18 MPa, 0.19 MPa, 0.2 MPa, 0.21 MPa, 0.22 MPa, 0.23 MPa, 0.24 MPa, 0.25 MPa, 0.26 MPa, 0.27 MPa, 0.28 MPa, 0.29 MPa, 0.30 MPa, 0.31 MPa, 0.32 MPa, 0.33 MPa, 0.34 MPa, 0.35 MPa, 0.36 MPa, 0.37 MPa, 0.38 MPa, 0.39 MPa, 0.40 MPa, 0.41 MPa, 0.42 MPa, 0.43 MPa, 0.44 MPa, 0.45 MPa, 0.46 MPa, 0.47 MPa, 0.48 MPa, 0.49 MPa, 0.50 MPa, 0.51 MPa, 0.52 MPa, 0.53 MPa, 0.54 MPa, 0.55 MPa, 0.56 MPa, 0.57 MPa, 0.58 MPa, 0.59 MPa, 6MPa, 0.27MPa, 0.28MPa, 0.29MPa, 0.3MPa, 0.31MPa, 0.32MPa, 0.33MPa, 0.34MPa, 0.35MPa, 0.36MPa, 0.37MPa, 0.38MPa, 0.39MPa or 0.4MPa, so that the air in the gap of the screw extruder can be quickly squeezed out through the feed port by using nitrogen under a certain pressure, so as to realize the oxidation-free working environment of the plastic.

[0014] During the nitrogen filling process, if the nitrogen filling pressure is too low, the normal pressure in the screw extruder will squeeze the nitrogen out of the device, making it difficult for nitrogen to enter and unable to form an oxygen-free environment; if the nitrogen filling pressure is too high, the material will be squeezed out or blown away from the feed port.

[0015] In some embodiments, in step (3), the negative pressure is set to -0.06 MPa to -0.14 MPa, which can be -0.06 MPa, -0.07 MPa, -0.08 MPa, -0.09 MPa, -0.1 MPa, -0.11 MPa, -0.12 MPa, -0.13 MPa or -0.14 MPa, specifically -0.1 MPa.

[0016] During the vacuuming process, if the negative pressure is set too high, the material will be sucked out from the vacuum port; if the negative pressure is set too low, the nitrogen will not be completely sucked out, which will cause pores in the final product.

[0017] In the present application, the applicant discovered through research and a large number of experiments that by filling nitrogen at a specific position of the screw extruder, namely, in the feed melting section, and by properly coordinating and coordinating the nitrogen filling pressure of the feed melting section and the negative pressure of the vacuum operation, it is possible to achieve oxidation-free operation of the entire extrusion system, while avoiding the formation of pores in the final product caused by nitrogen in the system, thereby achieving high-quality products.

[0018] In some embodiments, the plastic includes physically recycled plastic, chemically recycled plastic, and new plastic.

[0019] In some embodiments, the screw extrusion device includes a single screw extruder, a twin screw extruder, a three screw extruder, and a multi-stage screw extruder.

[0020] Among them, single-screw extruder, twin-screw extruder and three-screw extruder all refer to the number of screws, while multi-stage screw extruder refers to two single screws combined together as a first-stage screw extruder or two twin screws combined together as a second-stage screw extruder.

[0021] In some embodiments, the aspect ratio of the screw extruder is 1:28 to 1:72.

[0022] The second aspect of the present invention provides the following technical solution: The present invention provides a plastic extrusion system, including a screw extrusion device, a nitrogen generating device and a vacuum device, the screw extrusion device includes a feeding section, a feeding melting section, a reaction section, a molding section and a product extrusion section, an air inlet is provided at the feeding melting section, an exhaust port is provided at the molding section, the air outlet of the nitrogen generating device is connected to the air inlet at the feeding melting section, and the air exhaust port of the vacuum device is connected to the exhaust port at the molding section.

[0023] By adopting the above technical scheme, the present invention has at least achieved the following technical effects: (1) nitrogen is introduced into the material while it is in a molten state and vacuum treatment is performed in the molding section, so that the material is in a completely oxygen-free environment within the effective processing range, avoiding contact between the material and the air, effectively avoiding the side effects of oxygen on the plastic during the heating reaction process, reducing the moisture absorption, oxidation and solidification of the material during the processing, further ensuring the quality of the molded product, and ensuring that the product has no bad spots or yellow spots; (2) the obtained plastic product has a high density and no bubbles appear when observed with the naked eye; (3) The mechanical properties of plastic products are improved, and the impact strength can be increased by more than 3 times, or even more than 5 times, making it possible for low-energy plastics to replace high-energy plastics; (4) It has a wide range of applicability and use. The process provided by the present invention is applicable to various forms of screw extruders, and to plastics of various properties, such as recycled plastics from physical or chemical recycling. The extrusion process provided by the present invention is applicable. The process of the present invention can not only be used for the processing of recycled plastics, but also for granulation and / or modification of new plastics; (5) It has a high degree of automation and production efficiency, low nitrogen usage, and low production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the process flow of the plastic extrusion process provided by the present invention is shown;

[0025] Figure 2 The schematic diagram of the structure of the plastic extrusion system provided by the present invention is shown;

[0026] Description of reference numerals:

[0027] 1-screw extruder, 11-feeding section, 12-feeding melting section, 120-air inlet, 13-reaction section, 14-forming section, 140-exhaust port, 15-product extrusion section, 2-nitrogen generator, 3-vacuum extraction device. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0029] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "positive", "negative", "front", "back", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the system or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc., are used to define components, only for the convenience of distinguishing the above components, and unless otherwise stated, the above terms have no special meanings and cannot be understood as indicating or implying relative importance.

[0030] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0031] As a non-limiting embodiment, the plastic extrusion process provided by the present invention is that the plastic is reaction-molded in a screw extruder, and the plastic sequentially passes through a feed section, a feed melting section, a reaction section, a molding section, and a product extrusion section of the screw extruder. Figure 1 As shown, the process includes the following steps: first, in step S1, the screw extruder is started, and the plastic is added to the feed port of the screw extruder and enters the feed section. Then, in step S2, a nitrogen filling operation is performed at a location corresponding to the feed melting section, and at the same time, a vacuuming operation is performed at a location corresponding to the molding section.

[0032] The nitrogen filling operation is performed at the feed melting section and the vacuuming operation is performed at the molding section at the same time, so that the air in the gap of the screw extruder can be quickly squeezed out through the feed port by using nitrogen of a certain pressure. At the same time, the vacuuming operation further confirms that the air in the extruder is extracted to achieve a non-oxidizing working environment for the plastic. Moreover, the nitrogen filled can be extracted by performing the vacuuming operation corresponding to the molding section to avoid the formation of pores in the product.

[0033] In this non-limiting embodiment, in step (2), the nitrogen filling pressure is set to 0.1 MPa to 0.4 MPa, and the negative pressure for the vacuum operation is set to -0.06 to -0.14 MPa.

[0034] The plastics applicable to the present invention include new plastics and recycled plastics, wherein processing new plastics includes granulating new plastics and modifying new plastics, recycled plastics include physically recycled plastics and chemically recycled plastics, and the screw extrusion device includes a single-screw extruder, a twin-screw extruder, a three-screw extruder and a multi-stage screw extruder, which has a wide range of applicability and use and great economic benefits.

[0035] In some embodiments, the aspect ratio of the screw extruder is 1:28 to 1:72, and the processing temperature varies according to the specific plastic being processed.

[0036] like Figure 2 As shown, the plastic extrusion system provided by the present invention includes a screw extrusion device 1, a nitrogen generating device 2 and a vacuum device 3. The screw extrusion device 1 includes a feed section 11, a feed melting section 12, a reaction section 13, a molding section 14 and a product extrusion section 15. An air inlet 120 is provided at the feed melting section 12, an exhaust port 140 is provided at the molding section 14, an air outlet (not shown in the figure) of the nitrogen generating device 2 is connected to the air inlet 120, and an exhaust port of the vacuum device 3 is connected to the exhaust port 140.

[0037] Next, the extrusion process of the present invention is specifically described by the following examples.

[0038] Example 1

[0039] The plastic extrusion system provided by the present invention is used to extrude white PP plastic, wherein the nitrogen filling pressure at the feed melting section is set to 0.3 MPa, and the vacuum negative pressure at the molding section is set to -0.1 MPa, to obtain a plastic product (referred to as Example 1 in Table 1).

[0040] Comparative Example 1

[0041] The plastic product was obtained under the same extrusion equipment and the same plastic raw material conditions as in Example 1, without introducing nitrogen or performing vacuum operation.

[0042] Comparative Example 2

[0043] A plastic product is obtained under the same extrusion equipment and the same plastic raw material conditions as in Example 1, with nitrogen introduced into the feeding section but without vacuuming the molding section.

[0044] Comparative Example 3

[0045] A plastic product is obtained under the same extrusion equipment and same plastic raw material conditions as in Example 1, with nitrogen introduced into the feed melting section but without vacuuming in and out of the molding section.

[0046] Comparative Example 4

[0047] The plastic product was obtained under the same process as in Example 1 except that nitrogen charging was performed at the feed melting section and the nitrogen charging pressure was set to 0.05 MPa.

[0048] Comparative Example 5

[0049] The plastic product was obtained under the same process as in Example 1 except that the molding section was vacuumed and the negative pressure was set to -0.02 MPa.

[0050] The performance of the plastic products obtained in Example 1 and Comparative Examples 1 to 5 was tested and recorded in Table 1, wherein the instrument used for testing the impact strength was a pendulum impact tester HIT25P.

[0051] Table 1 Plastic product performance comparison table

[0052]

[0053] It can be seen that the plastic product obtained by the extrusion process of the present invention has a very low probability of producing bad spots, yellow spots and pores, which can greatly ensure the appearance quality of the extruded plastic product, and the nitrogen usage is also significantly reduced, which greatly reduces the production cost. Most importantly, the impact strength of the obtained plastic product has been greatly improved, which can be increased from 3MPa / cm 2 (The original impact strength of PP plastic) is increased to 16MPa / cm 2 The improvement range is up to 5 times or more, and can even be comparable to the impact strength of ABS plastic products (the impact strength of ABS plastic is 15M Pa / cm 2 ), while the price of PP plastic is about 10,000 yuan / ton, and the price of ABS plastic is as high as 150,000 yuan / ton. Therefore, by utilizing the extrusion process of the present invention, cheap raw materials can achieve the performance of high-end materials after processing, making material substitution possible.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A plastic extrusion process, characterized in that: The plastic is reaction-formed in a screw extruder, and the plastic sequentially passes through a feed section, a feed melting section, a reaction section, a forming section, and a product extrusion section of the screw extruder. The extrusion process includes the following steps: (1) starting the screw extruder, adding plastic to the feed port of the screw extruder and allowing the plastic to enter the feed section; and (2) A nitrogen filling operation is performed at a position corresponding to the feed melting section, and a vacuuming operation is performed at a position corresponding to the molding section.

2. The plastic extrusion process according to claim 1, characterized in that: In step (1), the nitrogen filling pressure is set to 0.1 MPa to 0.4 MPa.

3. The plastic extrusion process according to claim 1, characterized in that: In step (3), the negative pressure for the vacuum operation is set to -0.06 MPa to -0.14 MPa.

4. The plastic extrusion process according to any one of claims 1 to 3, characterized in that The plastics include physically recycled plastics, chemically recycled plastics, and new plastics.

5. The plastic extrusion process according to claim 1, characterized in that: The screw extruder includes a single screw extruder, a twin screw extruder, a triple screw extruder and a multi-stage screw extruder.

6. The plastic extrusion process according to claim 5, characterized in that: The aspect ratio of the screw extruder is 1:28 to 1:

72.

7. An extrusion system using the plastic extrusion process according to any one of claims 1 to 6, characterized in that: The extrusion system includes a screw extrusion device, which includes a feed section, a feed melting section, a reaction section, a molding section and a product extrusion section. The extrusion system also includes a nitrogen generator and a vacuum pumping device. An air inlet is provided at the feed melting section, an exhaust port is provided at the molding section, the air outlet of the nitrogen generator is connected to the air inlet provided at the feed melting section, and the air exhaust port of the vacuum pumping device is connected to the exhaust port provided at the molding section.

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