Mute floor foaming layer and preparation method thereof

Abstract

The invention relates to the technical field of PVC floors, and particularly discloses a mute floor foaming layer and a preparation method thereof. The invention relates to a mute floor foaming layer, which comprises the following materials by weight: 19-20 parts of PVC; 0.15 to 0.25 part of toner; 0.05 to 0.20 part of PE (Poly Ethylene) wax; 57.5 to 60.5 parts of a filling material; 0.15 to 0.25 part of a lubricant; 0.42 to 0.52 part of a foaming agent; 19.1 to 20.2 parts of a recycled material; the filler comprises calcium carbonate and nano montmorillonite. The preparation method comprises the following steps: S1, preparing raw materials; and S2, preparing a foaming layer. The foaming layer can be used in the multi-layer composite floor, and has the advantages of high sound insulation, high strength, long service life and the like.

Description

Technical Field

[0001] The present application relates to the technical field of PVC flooring, and more specifically, to a soundproof flooring foaming layer and a preparation method thereof. Background Art

[0002] As people's living standards improve, the requirements for interior decoration also increase. Both beauty and practicality are indispensable. Traditional hard floors (such as solid wood, composite wood, ceramic tiles, etc.) and stone plastic floors have better decoration effects, but they are more likely to generate noise during use. This noise mainly comes from daily activities such as footsteps, furniture movement, and falling objects. Especially in high-rise buildings or multi-story residential buildings, noise can easily spread through the floor slabs and affect residents on the upper and lower floors.

[0003] In order to improve the sound insulation effect of floor materials, a sound insulation layer is usually added to the floor to block the propagation of sound waves. However, the sound insulation layer usually uses foaming materials, which often have poor foaming uniformity and unreasonable selection of auxiliary materials, resulting in poor strength of the foaming layer, which in turn leads to the defect of a short service life of the foaming layer. Therefore, it is necessary to develop a foaming layer with uniform foaming and long-term sound insulation. Summary of the invention

[0004] In order to improve the defect of poor sound insulation effect of existing floors, the present application provides a soundproof floor foam layer and a preparation method thereof.

[0005] The present application provides a soundproof floor foam layer, which adopts the following technical solution:

[0006] In a first aspect, the present application provides a soundproof floor foam layer, comprising the following materials in parts by weight:

[0007] PVC 19-20 parts;

[0008] Color powder 0.15-0.25 parts;

[0009] PE wax 0.05-0.20 parts;

[0010] Filler 57.5-60.5 parts;

[0011] Lubricant 0.15-0.25 parts;

[0012] Foaming agent 0.42-0.52 parts;

[0013] Calcium zinc stabilizer 0.74-0.83 parts;

[0014] 19.1-20.2 parts of recycled material;

[0015] The filler includes calcium carbonate and nano-montmorillonite.

[0016] By adopting the above technical solution, it is preferred to add a calcium zinc stabilizer to the foaming material. The calcium zinc stabilizer can serve as a foaming aid to improve the foaming effect of the foaming material, so that the foaming material obtains a uniform pore structure and has good internal and external lubrication, thereby improving the dispersion effect of the foaming agent.

[0017] Calcium carbonate and nano-montmorillonite are preferably used as fillers. Both calcium carbonate and nano-montmorillonite can serve as nucleation sites to obtain a dense and uniform cell structure in the foaming layer, and the formed micropores can passivate internal defects, and the microcracks on the filler can absorb more energy, organize and passivate cracks, and effectively improve the mechanical strength of the foaming layer. Calcium carbonate can also be dispersed in the melt to form hot spots, reduce the viscosity and surface tension of the local area, and easily absorb gas to form bubble nuclei when the foaming agent decomposes, thereby enhancing the foaming effect and cell quality of the foaming material and improving the strength of the foaming layer.

[0018] Optionally, the foaming agent includes azodicarbonamide, and the azodicarbonamide is azodicarbonamide modified with zinc stearate.

[0019] By adopting the above technical scheme, azodicarbonamide can be used as a foaming agent, which can be decomposed by heat to release gases such as ammonia, carbon dioxide, and nitrogen, and the gas emission can reach 250-300mL / g, and foaming can be uniformly performed in the foaming layer, and azodicarbonamide can also be used as a nucleating agent to form a cellular structure with a smaller diameter in the foaming material, which can form a gradation effect with the remaining cellular structures in the foaming material, which is beneficial to improving the mechanical strength of the foaming material. Preferably, zinc stearate is used to modify azodicarbonamide, which can promote the decomposition of azodicarbonamide, improve the dispersibility of azodicarbonamide, appropriately reduce the cellular structure, improve the compactness of the foaming material, reduce the possibility of collapse of the cellular structure, and further improve the mechanical strength of the foaming material.

[0020] Optionally, the foaming agent also includes a microsphere foaming agent.

[0021] By adopting the above technical solution, the introduction of the microsphere foaming agent, under heat treatment, the low boiling point material in the microsphere can decompose and produce gas, and the microsphere shell expands to form a hollow spherical body, that is, a regularly shaped pore structure is introduced into the foaming material, the microsphere shell material can be used as an excellent supporting material, and a regularly shaped and non-collapsed pore structure is introduced into the foaming layer. Multiple hollow microspheres can form supporting sites in the foaming material, and multiple supporting sites can support the surrounding pore structure, which is beneficial to improve the mechanical strength of the foaming material and reduce the possibility of collapse of the pore structure. Due to the regular shape of the hollow microspheres, it is beneficial to form a uniformly distributed grading effect in the foaming material, improve the density and uniformity of the pore structure distribution in the foaming material, and further improve the mechanical strength of the foaming material.

[0022] Optionally, the microsphere foaming agent includes the following preparation method: MMA, St, initiator AIBN, foaming agent AC and crosslinking agent are placed in a beaker in an ice water bath to mix into an oil phase; deionized water and PVA aqueous solution are mixed into an aqueous phase. The oil phase and the aqueous phase are poured into a reaction container, stirred and dispersed, heated to react, cooled, discharged, precipitated, filtered, and dried to obtain the microsphere foaming agent.

[0023] By adopting the above technical solution, preferably wrapping the MMA-St shell outside the AC, a regularly shaped hollow sphere can be formed to form a stable support point. Even if the MMA-St shell is broken during the reaction, the broken MMA-St shell can be cross-linked with PVC and loaded on the inner wall of the pore structure, thereby enhancing the inner wall strength of the pores and reducing the possibility of pore collapse. The internal AC can also serve as a nucleation site to form tiny pores, thereby improving the density of the pore structure in the foaming material.

[0024] Optionally, the calcium carbonate is calcium carbonate modified with chlorogenic acid or catechin.

[0025] By adopting the above technical scheme, chlorogenic acid or catechin is preferably used to modify calcium carbonate. Chlorogenic acid and catechin both have a large number of -OH groups and can be grafted on the surface of calcium carbonate, so that calcium carbonate can form hydrogen bonds with the -OH groups on PVC, thereby enabling calcium carbonate to be firmly fixed on the pore wall through hydrogen bonds, reducing the possibility of pore rupture caused by weak bonding sites, stably filling the foaming material, and enabling the foaming material to obtain excellent mechanical strength.

[0026] Optionally, the calcium carbonate is prepared as follows: chlorogenic acid or catechin is mixed with water to obtain a modified liquid with a mass fraction of 3-5%, and the modified liquid is evenly sprayed on the surface of the calcium carbonate, heated and stirred, and dried to obtain modified calcium carbonate.

[0027] Optionally, the filler further includes hemp wool and PAN fiber, and the PAN fiber has a hollow porous structure.

[0028] By adopting the above technical solution, it is preferred to use hemp wool and PAN fiber as fillers, and the hemp wool also forms a fibrous structure. The hemp wool and PAN fibers can be entangled with each other in the foaming layer to form a supporting skeleton structure, which can effectively improve the mechanical strength of the foaming layer and reduce the possibility of collapse of the foaming material during long-term use. Since PAN fiber is a hollow porous structure, the combination with hemp wool fiber can effectively improve the strength of the supporting skeleton in the foaming layer, so that the fiber skeleton stably supports the foaming layer. The hollow porous structure can cooperate with the pore structure in the foaming layer to form a complex pore structure, and the propagation path of sound in the foaming layer is greatly extended, further improving the sound insulation effect of the foaming layer.

[0029] Optionally, the hemp wool is hemp wool modified with a silane coupling agent.

[0030] By adopting the above technical solution, preferably using silane coupling agent to treat the hemp wool, the polarity of the hemp wool is changed, and the possibility of hemp wool agglomeration is reduced. In addition, part of the microsphere foaming material can be loaded, and then a skeleton + microsphere structure can be formed in the foaming layer, which can stably form a supporting structure in the foaming layer, thereby improving the mechanical strength and sound insulation effect of the foaming material.

[0031] Optionally, the PVC includes a suspension resin.

[0032] By adopting the above technical solution and using part of the suspended resin as the main material of the foaming layer, a good closed-cell structure and foam body shape can be obtained in the foaming material.

[0033] In a second aspect, the present application provides a method for preparing a foam layer of a soundproof floor, using the following technical solution:

[0034] A method for preparing a soundproof floor foam layer comprises the following steps:

[0035] S1. Raw material preparation: weigh PVC, color powder, PE wax, filler, lubricant, calcium zinc stabilizer, foaming agent and recycled material respectively by weight and set aside;

[0036] S2. Preparation of foaming layer: PVC, color powder, PE wax, filler, lubricant, calcium zinc stabilizer, foaming agent and recycled material are mixed and conveyed to a twin-screw extruder for extrusion, foaming and molding to obtain a foaming layer.

[0037] In summary, this application has the following beneficial effects:

[0038] 1. Since the present application preferably uses calcium carbonate and nano-montmorillonite as fillers, both calcium carbonate and nano-montmorillonite can serve as nucleation sites, so that a dense and uniform cell structure is obtained in the foaming layer, and the formed micropores can passivate internal defects, and the microcracks on the filler can absorb more energy, organize and passivate cracks, and effectively improve the mechanical strength of the foaming layer. Calcium carbonate can also be dispersed in the melt to form hot spots, reduce the viscosity and surface tension of the local area, and easily absorb gas to form bubble nuclei when the foaming agent decomposes, thereby enhancing the foaming effect and cell quality of the foaming material and improving the strength of the foaming layer.

[0039] 2. In the present application, azodicarbonamide is uniformly foamed in the foaming layer, and azodicarbonamide can also serve as a nucleating agent to form a cellular structure with a smaller diameter in the foaming material, which can form a grading effect with the remaining cellular structures in the foaming material, and is beneficial to improving the mechanical strength of the foaming material. Preferably, zinc stearate is used to modify azodicarbonamide, which can promote the decomposition of azodicarbonamide, improve the dispersibility of azodicarbonamide, appropriately reduce the cellular structure, improve the compactness of the foaming material, reduce the possibility of collapse of the cellular structure, and further improve the mechanical strength of the foaming material.

[0040] 3. The microsphere foaming agent is introduced in the present application. Under heat treatment, the low-boiling point material in the microsphere can decompose and produce gas, and the shell of the microsphere expands to form a hollow spherical body, that is, a regularly shaped pore structure is introduced into the foaming material. The microsphere shell material can serve as an excellent supporting material, and a regularly shaped and non-collapsed pore structure is introduced into the foaming layer. Multiple hollow microspheres can form supporting sites in the foaming material, and multiple supporting sites can support the surrounding pore structure, which is beneficial to improve the mechanical strength of the foaming material and reduce the possibility of collapse of the pore structure. Due to the regular shape of the hollow microspheres, it is beneficial to form a uniformly distributed grading effect in the foaming material, improve the density and uniformity of the pore structure distribution in the foaming material, and further improve the mechanical strength of the foaming material. DETAILED DESCRIPTION

[0041] The present application is further described in detail below with reference to the embodiments.

[0042] Preparation Example

[0043] Preparation example of modified azodicarbonamide

[0044] Preparation Example 1

[0045] Zinc stearate and AC were mixed in a mass ratio of 1:5 and pulverized at high speed to prepare modified azodicarbonamide.

[0046] Preparation Example of Microsphere Foaming Agent

[0047] Preparation Example 2

[0048] MMA (methyl methacrylate; analytically pure), St (styrene; analytically pure), initiator AIBN, foaming agent AC and crosslinking agent (NaNO2) were mixed in a beaker in an ice-water bath according to a mass ratio of 70:10:2:24:0.4 to form an oil phase; 400 mL of deionized water and 80 mL of a 2% PVA aqueous solution were mixed to form a water phase. The oil phase and the water phase were poured into a reaction container, oxygen was removed, stirred and dispersed for 30 minutes, the temperature was raised for reaction, cooled, discharged, precipitated, filtered, and dried to obtain a microsphere foaming agent.

[0049] Modified calcium carbonate preparation example

[0050] Preparation Example 3

[0051] Chlorogenic acid and water are prepared to obtain a modified liquid with a mass fraction of 5%, and the modified liquid is evenly sprayed on the surface of calcium carbonate, heated and stirred, and dried to obtain modified calcium carbonate.

[0052] Preparation Example 4

[0053] The modified solution with a mass fraction of 5% is prepared by mixing catechins with water, and the modified solution is evenly sprayed on the surface of calcium carbonate, stirred with heat, and dried to obtain modified calcium carbonate.

[0054] PAN fiber preparation example

[0055] Preparation Example 5

[0056] 50g PAN powder was dissolved in 200mL DMF (N,N-dimethylformamide) and stirred at constant temperature for 2 hours using a constant temperature heating magnetic stirrer at a temperature of 60°C. After the PAN solution was clear and transparent, 10% PAN mass of MDI (diphenylmethane diisocyanate) was dripped in, and constant temperature stirring was continued until MDI was evenly dispersed. The obtained PAN / MDI / DMF polymer solution was ultrasonicated for 10 minutes for degassing. The prepared solution was transferred to a 10mL sterile plastic syringe, the needle was connected to a PTFE tube, the spinning speed was 19.64mm / min, distilled water was used as a coagulant, the distance from the PTFE tube to the roller was 80cm, and the obtained PAN fiber was collected on a roller with a rotation speed of 20r / min and a surface covered with glossy paper. After ultrasonication for 20 minutes, the obtained PAN fiber was allowed to stand in distilled water, and after no bubbles were produced, it was placed in a 60°C oven to dry to remove moisture.

[0057] Example of hemp wool preparation

[0058] Preparation Example 6

[0059] The hemp wool is immersed in a silane coupling agent KH550 solution (10% by mass), stirred and dispersed, filtered, dried, and crushed to obtain modified hemp wool.

[0060] Example

[0061] Examples 1-3

[0062] On the one hand, the present application provides a soundproof floor foam layer, comprising the following materials: PVC, color powder, PE wax, filler, lubricant, foaming agent, calcium zinc stabilizer and recycled material. The specific quality is shown in the table below.

[0063] Among them, the PVC resin is Yinglite P450PVC resin, the filler includes calcium carbonate and nano-montmorillonite with a mass ratio of 5:1, the foaming agent is AC, the lubricant is an internal lubricant, and the internal lubricant is stearic acid.

[0064] On the other hand, the present application provides a method for preparing a foamed layer of a soundproof floor, comprising the following steps:

[0065] S1. Raw material preparation: weigh PVC, color powder, PE wax, filler, lubricant, calcium zinc stabilizer, foaming agent and recycled material respectively by weight and set aside;

[0066] S2. Preparation of foaming layer: PVC, color powder, PE wax, filler, lubricant, calcium zinc stabilizer, foaming agent and recycled material are mixed and conveyed to a twin-screw extruder for extrusion, foaming and molding to obtain a foaming layer.

[0067] Table 1 Composition of Examples 1-3

[0068]

[0069]

[0070] Example 4

[0071] The difference from Example 2 is that the foaming agent is the modified azodicarbonamide prepared in Preparation Example 1 with the same mass as the foaming agent, which replaces the foaming agent AC in Example 2 to prepare the foaming layer.

[0072] Example 5

[0073] The difference from Example 2 is that the foaming agent is the modified azodicarbonamide prepared in Preparation Example 1 and the microsphere foaming agent prepared in Preparation Example 2 in a mass ratio of 2:1, instead of the foaming agent AC in Example 2, to prepare the foaming layer.

[0074] Example 6

[0075] The difference from Example 2 is that the foaming agent used is the modified azodicarbonamide prepared in Preparation Example 1 and the 180DU45 microsphere foaming agent of Boliken in a mass ratio of 2:1, instead of the foaming agent AC in Example 2, to prepare the foaming layer.

[0076] Example 7

[0077] The difference from Example 2 is that an equal mass of the modified calcium carbonate prepared in Preparation Example 3 is used to replace the calcium carbonate in the filler in Example 2 to prepare the foaming layer.

[0078] Example 8

[0079] The difference from Example 2 is that an equal mass of the modified calcium carbonate prepared in Preparation Example 4 is used to replace the calcium carbonate in the filler in Example 2 to prepare the foaming layer.

[0080] Example 9

[0081] The difference from Example 5 is that the filler includes calcium carbonate, nano-montmorillonite, hemp wool and PAN fiber prepared in Preparation Example 5 in a mass ratio of 5:1:0.5:0.5.

[0082] Example 10

[0083] The difference from Example 5 is that the filler includes calcium carbonate, nano-montmorillonite, the hemp wool prepared in Preparation Example 6 and the PAN fiber prepared in Preparation Example 5 in a mass ratio of 5:1:0.5:0.5.

[0084] Embodiment 11

[0085] The difference from Example 2 is that the PVC includes the Yinglite P450 PVC resin and the Tianjin Botianhua TL-1000 PVC suspension resin in a mass ratio of 5:1.

[0086] Comparative Example

[0087] Comparative Example 1

[0088] The difference between this comparative example and Example 2 is that the filler in this comparative example only includes calcium carbonate.

[0089] Performance testing

[0090] (1) Tensile properties test: The test was conducted in accordance with GB / T1040.1-2018, with a specimen size of 150 mm × 10 mm × 4 mm.

[0091] (2) Impact strength test: The test was conducted in accordance with GB / T 1843-1996 “Plastic cantilever beam impact test method”, with the specimen size of 80 mm × 10 mm × 4 mm.

[0092] (3) Sound insulation performance test: The sound insulation performance of the material is tested in the range of 40-4000Hz at room temperature according to GB / Z 27764-2011.

[0093] Table 2 Performance test

[0094]

[0095] Combining the performance test comparison in Table 2, we can find that:

[0096] 1. By comparing Examples 1-3 with Comparative Example 1, it can be found that the mechanical strength and sound insulation effect of the foamed layer prepared in Examples 1-3 are improved, which shows that calcium carbonate and nano-montmorillonite can be used as nucleation sites in the present application to obtain a dense and uniform pore structure in the foamed layer, and the formed micropores can passivate internal defects, and the microcracks on the filler can absorb more energy, organize and passivate cracks, and effectively improve the mechanical strength of the foamed layer. The calcium zinc stabilizer can be used as a foaming aid to improve the foaming effect of the foaming material, so that the foaming material obtains a uniform pore structure, and has a good internal and external lubrication effect, and improves the dispersion effect of the foaming agent.

[0097] 2. By comparing Example 4 with Example 2, it can be found that the mechanical strength and sound insulation effect of the foamed layer prepared in Example 4 are improved, which indicates that zinc stearate is used to modify azodicarbonamide in the present application. Zinc stearate can promote the decomposition of azodicarbonamide, improve the dispersibility of azodicarbonamide, appropriately reduce the pore structure, improve the density of the foamed material, reduce the possibility of collapse of the pore structure, and further improve the mechanical strength of the foamed material.

[0098] 3. By comparing Examples 5-6 with Example 2, it can be found that the mechanical strength and sound insulation effect of the foamed layer prepared in Examples 5-6 are improved. This shows that the microsphere foaming agent is used in this application. Under heat treatment, the outer shell of the microsphere expands to form a hollow spherical body, and a regularly shaped pore structure is introduced into the foaming material. As an excellent supporting material, a regularly shaped and non-collapsed pore structure is introduced into the foaming layer. Multiple hollow microspheres can form supporting sites in the foaming material, and multiple supporting sites can support the surrounding pore structure, which is beneficial to improve the mechanical strength of the foaming material and reduce the possibility of collapse of the pore structure. Due to the regular shape of the hollow microspheres, it is beneficial to form a uniformly distributed grading effect in the foaming material, improve the density and uniformity of the pore structure distribution in the foaming material, and further improve the mechanical strength of the foaming material.

[0099] 4. By comparing Examples 7-8 with Example 2, it can be found that the mechanical strength and sound insulation effect of the foamed layer prepared in Examples 7-8 are improved, which indicates that chlorogenic acid or catechins are used to modify calcium carbonate in the present application. Chlorogenic acid and catechins both have more -OH groups, which can be grafted on the surface of calcium carbonate, so that calcium carbonate can form hydrogen bonds with the -OH groups on PVC, thereby enabling calcium carbonate to be firmly fixed on the pore wall through hydrogen bonds, reducing the possibility of pore rupture due to weak bonding sites, and stably filling the foaming material.

[0100] 5. By comparing Examples 9-10 with Example 6, it can be found that the mechanical strength and sound insulation effect of the foamed layer prepared in Examples 9-10 are improved, which means that the hemp wool and PAN fiber are used as fillers in this application, and the hemp wool and PAN fiber can be entangled with each other in the foamed layer to form a supporting skeleton structure. Since PAN fiber is a hollow porous structure, the combination with the hemp wool fiber can effectively improve the strength of the supporting skeleton in the foamed layer. The hollow porous structure can cooperate with the pore structure in the foamed layer to form a complex pore structure, and the propagation path of sound in the foamed layer is greatly improved, further improving the sound insulation effect of the foamed layer. The use of silane coupling agent to modify the hemp wool reduces the possibility of hemp wool agglomeration, can load part of the microsphere foaming material, and form a skeleton + microsphere structure in the foaming layer, which can stably form a supporting structure in the foaming layer and improve the mechanical strength and sound insulation effect of the foaming material.

[0101] 6. By comparing Example 11 with Example 2, it can be found that the mechanical strength and sound insulation effect of the foaming layer prepared in Example 11 are improved, which means that the use of part of the suspended resin as the main material of the foaming layer in the present application can achieve a good closed-cell structure and foam shape in the foaming material.

[0102] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A soundproof floor foam layer, characterized in that: The following materials are included by weight: PVC 19-20 parts; Color powder 0.15-0.25 parts; PE wax 0.05-0.20 parts; Filler 57.5-60.5 parts; Lubricant 0.15-0.25 parts; Foaming agent 0.42-0.52 parts; Calcium zinc stabilizer 0.74-0.83 parts; 19.1-20.2 parts of recycled material; The filler includes calcium carbonate and nano-montmorillonite.

2. The soundproof floor foam layer according to claim 1, characterized in that: The foaming agent includes azodicarbonamide, and the azodicarbonamide is azodicarbonamide modified by zinc stearate.

3. The soundproof floor foam layer according to claim 2, characterized in that: The foaming agent also includes a microsphere foaming agent.

4. The soundproof floor foam layer according to claim 3, characterized in that: The microsphere foaming agent comprises the following preparation method: MMA, St, initiator AIBN, foaming agent AC and crosslinking agent are placed in a beaker in an ice water bath and mixed into an oil phase; deionized water and PVA aqueous solution are mixed into a water phase. The oil phase and the water phase are poured into a reaction container, stirred and dispersed, heated to react, cooled, discharged, precipitated, filtered, and dried to obtain the microsphere foaming agent.

5. The soundproof floor foam layer according to claim 1, characterized in that: The calcium carbonate is calcium carbonate modified by chlorogenic acid or catechin.

6. The soundproof floor foam layer according to claim 5, characterized in that: The calcium carbonate is prepared as follows: chlorogenic acid or catechin is mixed with water to obtain a modified liquid with a mass fraction of 3-5%, and the modified liquid is evenly sprayed on the surface of the calcium carbonate, heated and stirred, and dried to obtain modified calcium carbonate.

7. The soundproof floor foam layer according to claim 1, characterized in that: The filler also includes hemp wool and PAN fiber, and the PAN fiber is a hollow porous structure.

8. The soundproof floor foam layer according to claim 7, characterized in that: The hemp wool is hemp wool modified by a silane coupling agent.

9. The soundproof floor foam layer according to claim 7, characterized in that: The PVC includes a suspension resin.

10. The method for preparing a soundproof floor foam layer according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1. Raw material preparation: weigh PVC, color powder, PE wax, filler, lubricant, calcium zinc stabilizer, foaming agent and recycled material respectively by weight and set aside; S2. Preparation of foaming layer: PVC, color powder, PE wax, filler, lubricant, calcium zinc stabilizer, foaming agent and recycled material are mixed and conveyed to a twin-screw extruder for extrusion, foaming and molding to obtain a foaming layer.

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