Waste plastic purification and regeneration process

Abstract

The invention discloses a waste plastic purification and regeneration process which comprises the following steps: crushing waste plastic with a coating to obtain crushed plastic; mixing the crushed plastic with an alkaline substance, a polishing aid and a solvent, and then polishing and screening to obtain depainted plastic; sequentially carrying out primary specific gravity separation, secondary specific gravity separation, color separation and electrostatic separation on the depainted plastic to obtain high-purity same-color plastic; and carrying out modification treatment on the high-purity same-color plastic to obtain the high-quality regenerated plastic. According to the method, the coating in the waste plastic is efficiently removed by polishing and depainting in an alkali heat environment, meanwhile, the performance of the plastic material after depainting is not affected, and later modification processing is facilitated; two-stage specific gravity separation is combined with color separation and electrostatic separation, and efficient purification of different types of plastics is achieved, so that high-purity regenerated plastics are obtained.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection and resource recovery, and in particular to a waste plastic purification and regeneration process. Background Art

[0002] Plastics with coatings such as paint can be seen everywhere in our daily lives. In particular, most of the plastic parts used in various products such as automobiles, motorcycles, electric vehicles, and electronic appliances are sprayed with paints or coatings of different colors and types to increase the color, appearance design, attractiveness, and differentiation of the products.

[0003] However, the recycling of plastics with paint coatings is still an industry and social problem. For the paint stripping of waste plastics, the waste plastics are generally soaked in organic solvents for a period of time to make the paint and plastic fall off. This method has a good paint stripping effect, but the cost of organic solvents is high, and a large amount of wastewater is generated after paint stripping and is difficult to handle. In addition, organic solvents generally have a pungent odor, and some are also toxic, which is extremely detrimental to the production and processing and the health of operators. In addition, the color of the plastic soaked in organic solvents is prone to change during the back-end processing, and the performance will also be significantly reduced. In industry practice, there is also a process of sandblasting and polishing to strip paint, but the process is complicated to operate, has high requirements for the operating environment, technology and equipment, and is difficult to apply on a large scale in industry, and the use scenarios are limited.

[0004] In addition, the existing technology is widely used in the cleaning and sorting of waste plastics, but there are certain limitations in the sorting of waste plastics after paint stripping. Due to the different effects of front-end paint stripping, the process requirements for back-end cleaning and sorting are also different. The conventional sorting and purification process is to directly rinse after paint stripping or directly regenerate and granulate after simple color sorting to produce recycled plastic particles, and then modify them to produce high-quality recycled plastic particles. However, due to the different characteristics of painted plastics, plastic products after paint stripping generally contain mixed rubber, plastic substrates of different colors, plastics of different materials, etc., and further sorting is required to obtain high-purity recycled plastics. Summary of the invention

[0005] In order to overcome the above-mentioned defects of the prior art, the purpose of the present invention is to provide a waste plastic purification and regeneration process to solve the technical problems of the traditional process such as easy damage to the performance of plastic materials, serious environmental pollution and high cost.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions: The present invention provides a waste plastic purification and regeneration process, comprising the following steps: S1: crushing the waste plastic with coating to obtain crushed plastic; S2: mixing the crushed plastic with an alkaline substance, a grinding aid and a solvent to obtain a mixed material, and grinding and sieving the mixed material to obtain a paint-stripped plastic; S3: performing primary gravity sorting on the paint-removed plastic to obtain primary sorted plastic; S4: performing secondary gravity sorting on the primary sorted plastic to obtain secondary sorted plastic; S5: After dehydration, the secondary sorted plastics are subjected to color sorting to obtain plastics of the same color; S6: electrostatically sorting plastics of the same color to obtain high-purity plastics of the same color; S7: Modify high-purity plastics of the same color to obtain high-quality recycled plastics.

[0007] Preferably, in step S1, the plastic is crushed into pieces of 2-4 cm.

[0008] Preferably, in step S2, the mixed material includes, by weight, 100 parts of crushed plastic, 1-5 parts of alkaline substance, 2-10 parts of polishing aid, and 0.5-5 parts of solvent.

[0009] Preferably, in step S2, the alkaline substance is one or more of sodium hydroxide and potassium hydroxide; and the polishing aid is sand.

[0010] Preferably, in step S2, the grinding process includes: putting the mixed material into a horizontal grinding tank, and controlling the rotation speed of the horizontal grinding tank to 100-1000 r / min.

[0011] Preferably, a plurality of blades alternately distributed are provided in the horizontal grinding tank.

[0012] Preferably, in step S2, the sieve mesh used in the screening process has an aperture of 1-5 mm.

[0013] Preferably, in step S3, the density of the brine used for primary gravity separation is 1.2-1.5 g / cm 3 .

[0014] Preferably, in step S4, the density of the brine used for the secondary gravity separation is 1.0-1.05 g / cm 3 .

[0015] Preferably, the brine used in the gravity separation in step S3 or step S4 is at least one of a sodium chloride solution and a calcium chloride solution, and more preferably industrial-grade sodium chloride, which has the advantage of low cost.

[0016] Preferably, in step S7, the modification treatment includes melt granulating high-purity plastics of the same color to obtain high-quality recycled plastic particles.

[0017] The beneficial effects of the present invention are: 1. The present invention mixes broken plastic with alkaline substances, grinding aids and solvents, and removes the paint from the waste plastic with coating by physical grinding. The alkaline substances will continuously release a large amount of heat during the dissolution process, which can continuously soften the plastic and the coating, making it easier for the paint coating to separate from the plastic during the grinding process. In addition, the paint is more easily dissolved and separated in a strong alkaline environment, thus avoiding the problems of high cost, poor working environment, and serious pollution of production waste liquid caused by traditional organic solvent immersion. At the same time, the performance of the plastic material after paint removal is not affected, which is convenient for later modification and processing.

[0018] 2. The present invention firstly performs primary gravity sorting to sink polishing aids, metals and other foreign matters on the plastic surface, and then performs secondary gravity sorting on the plastic floating on the water surface, thereby separating plastics of different densities.

[0019] 3. The waste plastics after purification and separation in the present invention can be directly physically or chemically modified to obtain high-quality recycled plastic particles, which reduces processing links and reduces processing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solution of the embodiment of the present invention, the drawings of the embodiment are briefly introduced below.

[0021] Figure 1 The present invention is a schematic diagram of a waste plastic purification and regeneration process flow. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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 creative work are within the scope of protection of the present invention.

[0023] The existing technology generally uses organic solvents or concentrated sulfuric acid soaking, sandblasting and other processes to strip the paint from waste plastics with coatings. However, organic solvents are used in large quantities, are costly, have a pungent odor, are somewhat toxic, require long soaking times, and have high waste liquid treatment costs and a harsh working environment, which have a negative impact on the appearance and performance of the plastic after stripping. Concentrated sulfuric acid is a controlled hazardous chemical with high cost of use, a high risk processing environment, and difficulty in waste liquid treatment. The sandblasting process uses a huge amount of sandblasting and is costly. The sandblasting after stripping needs to be treated as hazardous waste. It is mainly applicable to the stripping of a single plastic part, and cannot achieve industrial large-scale stripping. In view of this, please refer to Figure 1 The embodiment of the present invention provides a waste plastic purification and regeneration process, comprising the following steps: S1: Crushing the coated waste plastics to obtain 2-4 cm broken plastic flakes for subsequent screening and sorting. Coated waste plastics include but are not limited to waste plastic parts with paint coatings such as automobiles, motorcycles, electric vehicles, toys, and electronic and electrical products.

[0024] S2: In parts by mass, 100 parts of crushed plastic, 1-5 parts of alkaline substances, 2-10 parts of grinding aids and 0.5-5 parts of solvents are mixed to obtain a mixed material. The alkaline substance is a strong base, including but not limited to one or more of sodium hydroxide and potassium hydroxide; the grinding aid is sand, and the solvent is preferably water. Then the mixed material is put into a horizontal grinding tank, and the mixed material is ground at a speed of 100-1000r / min. During this process, the strong base releases heat when it meets water, heats the grinding environment, weakens the adhesion between the coating and the plastic, and grinds off the coating under the action of high-speed collision and friction of the grinding aid. Finally, the ground mixture is passed through a sieve with an aperture of 1-5 mm to separate the sand, the polished paint, the coating, the plastic powder and the broken plastic pieces after paint removal to obtain paint-stripped plastic.

[0025] S3: Density 1.2-1.5g / cm 3 The paint-removed plastic is subjected to primary gravity sorting in salt water. Through the primary gravity sorting, sand, metal and other foreign matter on the surface of the plastic sinks, while the plastic floats on the water surface, thereby separating the plastic from impurities and obtaining a primary sorted plastic containing only plastic.

[0026] S4: Density 1.0-1.05g / cm 3 The primary sorted plastic is subjected to secondary specific gravity sorting in salt water to separate plastics of different densities, such as separating ABS / PS and PP to obtain secondary sorted plastics.

[0027] S5: After dehydration, the secondary sorted plastics are color sorted to separate black plastics, multicolored plastics, and plastics with a small amount of coating remaining to obtain plastics of the same color.

[0028] S6: Electrostatically sort the plastics of the same color, separate and remove the plastics of similar density that may be mixed in them, and obtain high-purity plastics of the same color.

[0029] S7: Modify high-purity plastics of the same color to obtain high-quality recycled plastics.

[0030] In the present invention, the modification treatment is a conventional physical or chemical modification process in the art, for example, high-purity plastics of the same color are melt-granulated to obtain high-quality recycled plastic particles.

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below.

[0032] Example 1 A waste plastic purification and regeneration process comprises the following steps: S1: Crushing: Use a crusher to crush the automobile waste plastics, and the output is 2-4 cm broken plastic pieces.

[0033] S2: Paint stripping: By mass, 100 parts of broken plastic pieces, 5 parts of solid sodium hydroxide, 10 parts of sand and 5 parts of water are put into a horizontal grinding tank, wherein 20 grinding blades are alternately distributed on the inner wall of the horizontal grinding tank, and the distance between the top of the blade and the inner surface of the grinding tank is 5 cm. The mixed material is ground at a speed of 500 r / min. Finally, the ground mixture is passed through a 5 mm sieve to separate the sand, the polished paint, the coating, and the plastic powder from the broken plastic pieces after paint stripping to obtain paint stripping plastic.

[0034] S3: First-level gravity sorting: Add the paint-stripped plastic obtained in step S2 into a solution with a density of 1.5 g / cm 3 The paint-removed plastic is subjected to primary gravity sorting in salt water (sodium chloride solution), so that foreign matter such as sand and metal on the surface of the plastic sinks, while the plastic floats on the water surface, thus separating the plastic from impurities and obtaining primary sorted plastic containing only plastic.

[0035] S4: Secondary gravity separation: Add the first-stage separated plastic obtained in step S3 into a mixture with a density of 1.0 g / cm 3 The first-level sorted plastics are subjected to secondary specific gravity sorting in saline (sodium chloride solution) to separate ABS / PS plastics and PP plastics to obtain PP plastics and ABS, PS plastics.

[0036] S5: Color sorting: Use a vertical spin dryer to spin and dehydrate the secondary sorted plastics, and then send them to a color sorter for color sorting. Black plastics, multicolored plastics, plastics with a small amount of coating remaining, and other non-natural color plastics are sorted out to obtain high-purity PP plastics and high-purity ABS, PS mixed plastics.

[0037] S6: Electrostatic separation: The ABS and PS mixed plastics obtained in step S5 are sent to a high-voltage electrostatic bin for electrostatic separation, so that the PS plastics are separated to obtain high-purity ABS plastics.

[0038] S7: Modification treatment: melt-granulate high-purity PP plastic and high-purity ABS plastic separately to obtain high-quality recycled plastic particles.

[0039] Example 2 A waste plastic purification and regeneration process comprises the following steps: S1: Crushing: Use a crusher to crush the automobile waste plastics, and the output is 2-4 cm broken plastic pieces.

[0040] S2: Paint stripping: By mass, 100 parts of broken plastic pieces, 1 part of solid sodium hydroxide, 5 parts of sand and 5 parts of water are put into a horizontal grinding tank, wherein 20 grinding blades are alternately distributed on the inner wall of the horizontal grinding tank, and the distance between the top of the blade and the inner surface of the grinding tank is 5 cm. The mixed material is ground at a speed of 500 r / min. Finally, the ground mixture is passed through a 5mm sieve to separate the sand, the polished paint, the coating, and the plastic powder from the broken plastic pieces after paint stripping to obtain paint stripping plastic.

[0041] S3: First-level gravity separation: Add the paint-stripped plastic obtained in step S2 to a solution having a density of 1.3 g / cm 3 The paint-stripped plastic is subjected to primary gravity sorting in salt water (sodium chloride solution), so that the sand, metal and other foreign matter on the surface of the plastic sinks, while the plastic floats on the water surface, thus separating the plastic from the impurities and obtaining a primary sorted material containing only plastic.

[0042] S4: Secondary gravity separation: The primary separation material obtained in step S3 is added with a density of 1.05 g / cm 3 The first-level sorted plastics are subjected to secondary specific gravity sorting in saline (sodium chloride solution) to separate ABS / PS plastics and PP plastics to obtain PP plastics and ABS, PS plastics.

[0043] S5: Color sorting: Use a vertical spin dryer to spin and dehydrate the secondary sorted plastics, and then send them to a color sorter for color sorting. Black plastics, mixed-color plastics, plastics with a small amount of coating remaining, and other non-natural color plastics are sorted out to obtain high-purity PP plastics and ABS, PS mixed plastics.

[0044] S6: Electrostatic sorting: The ABS and PS plastics obtained in step S5 are sent to a high-voltage electrostatic bin for electrostatic sorting, and the PS plastic is sorted out to obtain high-purity ABS plastic.

[0045] S7: Modification treatment: melt-granulate high-purity PP plastic and high-purity ABS plastic separately to obtain high-quality recycled plastic particles.

[0046] Example 3 A waste plastic purification and regeneration process comprises the following steps: S1: Crushing: Use a crusher to crush the automobile waste plastics, and the output is 2-4 cm broken plastic pieces.

[0047] S2: Paint stripping: By mass, 100 parts of broken plastic pieces, 3 parts of solid sodium hydroxide, 5 parts of sand and 5 parts of water are put into a horizontal grinding tank, wherein 20 grinding blades are alternately distributed on the inner wall of the horizontal grinding tank, and the distance between the top of the blade and the inner surface of the grinding tank is 5 cm. The mixed material is ground at a speed of 500 r / min. Finally, the ground mixture is passed through a 5mm sieve to separate the sand, the polished paint, the coating, and the plastic powder from the broken plastic pieces after paint stripping to obtain paint stripping plastic.

[0048] S3: First-level gravity separation: Add the paint-stripped plastic obtained in step S2 to a solution having a density of 1.2 g / cm 3 The paint-stripped plastic is subjected to primary gravity sorting in salt water (sodium chloride solution), so that the sand, metal and other foreign matter on the surface of the plastic sinks, while the plastic floats on the water surface, thus separating the plastic from the impurities and obtaining a primary sorted material containing only plastic.

[0049] S4: Secondary gravity separation: Add the primary separation material obtained in step S3 to a mixture with a density of 1.02 g / cm 3 The first-level sorted plastics are subjected to secondary specific gravity sorting in saline (sodium chloride solution) to separate ABS / PS plastics and PP plastics to obtain PP plastics and ABS, PS plastics.

[0050] S5: Color sorting: Use a vertical spin dryer to spin and dehydrate the secondary sorted plastics, and then send them to a color sorter for color sorting. Black plastics, mixed-color plastics, plastics with a small amount of coating remaining, and other non-natural color plastics are sorted out to obtain high-purity PP plastics, ABS, and PS plastics.

[0051] S6: Electrostatic sorting: The ABS and PS plastics obtained in step S5 are sent to a high-voltage electrostatic bin for electrostatic sorting, and the PS plastic is sorted out to obtain high-purity ABS plastic.

[0052] S7: Modification treatment: melt-granulate high-purity PP plastic and high-purity ABS plastic separately to obtain high-quality recycled plastic particles.

[0053] Comparative Example 1 This comparative example is substantially the same as Example 1, except that no sodium hydroxide solid is added in the paint stripping process of step S2 in this comparative example.

[0054] The paint stripping efficiency and the purity of the obtained plastics in Examples 1 to 3 and Comparative Example 1 are shown in Table 1.

[0055] Table 1

[0056] In summary, the present invention realizes efficient removal of paint and other coatings on the surface of waste plastics by heat treatment, polishing and paint stripping in an alkaline environment. Compared with organic solvent paint stripping or sandblasting paint stripping processes, the cost is lower and has significant economic advantages. At the same time, it avoids the damage of plastic material performance by traditional paint stripping methods, so that waste plastics still maintain the original physical properties of the material, which is convenient for later modification and processing. Through the first and second level specific gravity sorting, the purity of the material obtained after color sorting and electrostatic sorting is more than 98%, realizing efficient purification and recovery of coated waste plastics.

[0057] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For matters that are not described in detail in some embodiments, reference may be made to the description in other embodiments.

[0058] The above-mentioned embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A waste plastic purification and regeneration process, characterized in that: The following steps are involved: S1: crushing the waste plastic with coating to obtain crushed plastic; S2: mixing the crushed plastic with an alkaline substance, a grinding aid and a solvent to obtain a mixed material, and grinding and screening the mixed material to obtain a paint-stripped plastic; S3: performing primary gravity sorting on the paint-stripped plastic to obtain primary sorted plastic; S4: performing secondary specific gravity sorting on the primary sorted plastic to obtain secondary sorted plastic; S5: dehydrating the secondary sorted plastics and then sorting them by color to obtain plastics of the same color; S6: electrostatically separating the plastics of the same color to obtain high-purity plastics of the same color; S7: modifying the high-purity plastic of the same color to obtain high-quality recycled plastic.

2. The waste plastic purification and regeneration process according to claim 1, characterized in that: In step S1, the broken plastic is fragmented into pieces of 2-4 cm.

3. The waste plastic purification and regeneration process according to claim 1, characterized in that: In step S2, the mixed material includes, by weight, 100 parts of crushed plastic, 1-5 parts of alkaline substance, 2-10 parts of polishing aid, and 0.5-5 parts of solvent.

4. The waste plastic purification and regeneration process according to claim 1, characterized in that: In step S2, the alkaline substance is one or more of sodium hydroxide and potassium hydroxide; and the polishing aid is sand.

5. The waste plastic purification and regeneration process according to claim 1, characterized in that: In step S2, the grinding process includes: putting the mixed material into a horizontal grinding tank, and controlling the rotation speed of the horizontal grinding tank to be 100-1000 r / min.

6. The waste plastic purification and regeneration process according to claim 1, characterized in that: In step S2, the sieve used in the screening process has an aperture of 1-5 mm.

7. The waste plastic purification and regeneration process according to claim 1, characterized in that: In step S3, the density of the brine used for the first-level specific gravity separation is 1.2-1.5 g / cm 3 .

8. The waste plastic purification and regeneration process according to claim 1, characterized in that: In step S4, the density of the brine used for the secondary gravity separation is 1.0-1.05 g / cm 3 .

9. The waste plastic purification and regeneration process according to claim 7 or 8, characterized in that: The salt water is at least one of a sodium chloride solution and a calcium chloride solution.

10. The waste plastic purification and regeneration process according to claim 1, characterized in that: In step S7, the modification treatment includes melt granulating the high-purity same-color plastic to obtain high-quality recycled plastic particles.

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