Environment-friendly low-smoke flame-retardant PVC foamed sheet and preparation method thereof

Abstract

The invention belongs to the technical field of polymer foam materials, and particularly relates to an environment-friendly low-smoke flame-retardant PVC (polyvinyl chloride) foam board and a preparation method thereof. The foamed sheet is prepared from the following raw materials: PVC resin powder, a special modified synergistic flame retardant for PVC, a filler, a foaming regulator, a calcium-zinc stabilizer, polyethylene wax, oxidized polyethylene wax and epoxidized soybean oil, wherein the special modified synergistic flame retardant for PVC is a synergistic flame retardant prepared from DPO modified magnesium-aluminum hydrotalcite. A supercritical carbon dioxide twin-screw extrusion foaming device is adopted for preparation, a PVC special modified synergistic flame retardant is added into the raw materials, the hydrotalcite surface contains a long alkane chain, the interaction among the fillers is weakened, good dispersion in PVC can be realized, free radicals generated during combustion can be quenched, a combustion chain reaction can be terminated, and the flame retardant has a good flame retardant effect. Phosphoric acid substances decomposed by heating can promote the polymer base material to be dehydrated into carbon and insulate heat and oxygen. The prepared board can promote flame-retardant and smoke-suppression effects and is excellent in mechanical property.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer foaming materials, and in particular relates to an environmentally friendly, low-smoke, flame-retardant PVC foaming plate and a preparation method thereof. Background Art

[0002] Although rigid PVC foam boards have certain flame retardancy due to the halogens contained in the PVC matrix itself, they produce high smoke density when burned, which makes them difficult to meet the needs of indoor applications. In addition, high-end PVC foam boards for interior decoration need to have micropores and low density in addition to certain mechanical strength to meet the needs of heat preservation and noise reduction.

[0003] The traditional PVC smoke suppression method is to add a large amount of aluminum hydroxide or magnesium hydroxide to the formula, although this method can improve the flame retardancy of PVC products and reduce the generation of harmful gases and smoke. However, the addition of a large amount of inorganic fillers has the problems of poor dispersibility and excessive use, resulting in a significant decrease in the mechanical properties of PVC products, making it difficult to apply to the preparation of high-performance foamed boards. Patent CN202110115710 also discloses a method for preparing a flame-retardant and smoke-suppressing PVC board containing a copper ion and molybdate ion complex. The method utilizes the synergistic effect of copper ions and molybdate ions with nitrogen elements to have a certain smoke suppression effect, but the method has the following two problems in the production of interior decorative boards: (1) The heavy metal ions introduced in the formula affect the thermal stability of PVC, and the molybdenum compound is expensive, resulting in a significant increase in the formula cost. (2) Although nitrogen is added as a source of intumescent flame retardant, the PVC pyrolysis process is mainly a dechlorination free radical reaction process, so it is difficult to meet the requirements of higher smoke suppression performance. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an environmentally friendly low-smoke flame-retardant PVC foam board and a preparation method thereof, by providing a diphenylphosphine oxide (DPO) modified magnesium aluminum hydrotalcite (Mg6Al2(OH) 16 CO3·4H2O) synergistic flame retardant (abbreviated as: PVC special modified synergistic flame retardant) is added to the rigid PVC foam board and prepared by supercritical carbon dioxide foaming process to obtain microporous low-density environmentally friendly PVC foam board for interior decoration, achieving low smoke flame retardant performance.

[0005] The technical solutions adopted are:

[0006] An environmentally friendly, low-smoke, flame-retardant PVC foam board, the raw materials of which include PVC resin powder, and the raw materials also include, by weight:

[0007] PVC special modified synergistic flame retardant, 5-20 parts;

[0008] 10-100 parts of a filler, wherein the filler is calcium carbonate;

[0009] 2-10 parts of foaming regulator;

[0010] Calcium zinc stabilizer 2-8 parts;

[0011] Polyethylene wax 0.1-0.8 parts;

[0012] Oxidized polyethylene wax 0.1-1.0 part;

[0013] Epoxidized soybean oil 0.2-3.5 parts;

[0014] PVC resin powder, 100 parts.

[0015] Preferably, the modified synergistic flame retardant for PVC is a magnesium aluminum hydrotalcite (Mg6Al2(OH) 16 Synergistic flame retardant prepared by CO3·4H2O)).

[0016] A method for preparing an environmentally friendly, low-smoke, flame-retardant PVC foam sheet comprises the following steps:

[0017] (1) Synthesis of modified synergistic flame retardant for PVC:

[0018] Itaconic anhydride is placed in a four-necked flask equipped with a condenser, a thermometer, a heating device, and a stirring device, heated and stirred, and then DPO is added and stirred evenly, and then heated to 150-160° C. for reaction to obtain compound A;

[0019] Then cool to 60-80°C and add water to continue the reaction;

[0020] Subsequently, stearic acid and a catalyst are added and stirred evenly, and then the temperature is raised to 110-120° C. for negative pressure reaction to obtain compound B; the obtained compound B and hydrotalcite are placed in a high-speed mixer to obtain a modified synergistic flame retardant for PVC;

[0021] (2) PVC resin powder, PVC special modified synergistic flame retardant, filler, environmentally friendly calcium zinc stabilizer, polyethylene wax, oxidized polyethylene wax, and epoxy soybean oil are mixed in a high-speed hot mixing device according to corresponding formula proportions; then, the mixed material is placed in a high-speed cold mixer for cold mixing, and finally the obtained mixed material is placed in a storage tank for use within 24 hours;

[0022] (3) adding the mixed material into a supercritical carbon dioxide twin-screw extruder foaming device, injecting a foaming regulator, performing continuous foaming, adjusting the twin-screw and die heating temperature, adjusting the melt pressure, and extruding;

[0023] (4) After traction and water cooling, environmentally friendly, low-smoke, flame-retardant PVC foam sheets can be obtained.

[0024] Preferably, in step (1), the amount of DPO added is 45-100% of itaconic anhydride, the reaction time after heating to 150-160° C. is 10-12 hours, and the time of adding water to continue the reaction is 5-6 hours; compound A is diphenylphosphine oxide itaconic anhydride (DPO-ITA).

[0025] Preferably, in the step (1), during the negative pressure reaction, the vacuum pressure is expressed to -0.05 MPa, and the reaction time is 2 to 3 hours; the compound B is diphenylphosphine oxide distearate itaconate (DPO-ITA-SA), and the catalyst is anhydrous phosphoric acid.

[0026] Preferably, in step (1), the mass ratio of compound B to hydrotalcite is 1:5-20, the temperature in the high-speed mixer is 100-120° C., and the mixing time is 15-20 min.

[0027] Preferably, in step (2), the mixing time in the high-speed hot mixing device is 15-30, and the cold mixing time is 30-45.

[0028] Preferably, in step (3), the twin-screw heating temperature is set to 150-190°C, and the die temperature is set to 140-170°C.

[0029] Preferably, in step (3), the melt outlet pressure is adjusted to 7.5-20 MPa.

[0030] Preferably, in step (3), the foaming regulator comprises a main foaming agent and an auxiliary foaming agent, the main foaming agent is carbon dioxide, and the auxiliary foaming agent is one or two of ethanol, butane, isobutane, pentane, isopentane, and methyl formate.

[0031] The supercritical carbon dioxide twin-screw extrusion foaming device includes a quantitative feeding system, a twin-screw extruder main unit, a supercritical gas injection system, and a supercritical foaming die. The twin screw ends of the twin-screw extruder main unit are directly connected to the supercritical foaming die. The height of the flow channel inside the supercritical foaming die gradually decreases, the width in the horizontal direction gradually increases, and the position of the extrusion port tends to be stable. Therefore, the height value of the extrusion port position is the smallest and the horizontal width value is the largest. A flow blocking column is set on the inner wall of the flow channel. The height of the flow blocking column is 1 / 8 to 7 / 8 of the flow channel height and can be set as needed. Its function is to increase pressure and achieve stirring. Pressure sensors and temperature sensors can be installed at appropriate positions inside the twin-screw and supercritical foaming die as needed.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention adopts a diphenyl phosphine oxide (DPO) modified magnesium aluminum hydrotalcite (Mg6Al2(OH) 16 CO3·4H2O) synergistic flame retardant (abbreviated as: PVC special modified synergistic flame retardant) is added to the formula of rigid PVC foam board, which can produce the following effects: (1) The phosphorus free radicals generated at high temperature can quench the H·, O· and HO· free radicals generated during combustion, terminating the combustion chain reaction. (2) The phosphoric acid substances decomposed by heat can promote the dehydration of the polymer substrate into carbon. (3) The hydrotalcite rich in aluminum and magnesium hydroxide can not only release crystal water and adsorb solid particles, but also synergistically form an insulation layer with DPO to insulate heat and oxygen. (4) The surface of the hydrotalcite in the prepared PVC special modified synergistic flame retardant contains long alkane chains, and the mutual assistance between fillers is weakened, which can achieve good dispersion in PVC, not only further promoting the flame retardant and smoke suppression effect, but also excellent mechanical properties. (5) The uniformly dispersed PVC special modified synergistic flame retardant has the function of a foaming nucleating agent, which can reduce the pore size of the foam board and is beneficial to the improvement of the mechanical properties of the foam board.

[0034] The present invention adopts a supercritical carbon dioxide twin-screw extrusion foaming device. The twin screws and the improved die head shorten the excessive pressure caused by the long single screw and shorten the high temperature time of the material in the machine, thereby improving the safety of PVC extrusion, reducing the degradation of PVC, and simplifying the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The synthetic route of the modified synergistic flame retardant for PVC in the present invention is shown in FIG.

[0036] Figure 2 This is a smoke density-time diagram of a combustion test of an environmentally friendly, low-smoke, flame-retardant PVC foam board prepared in Example 1 of the present invention.

[0037] Figure 3 This is a smoke density-time diagram of a combustion test of an environmentally friendly, low-smoke, flame-retardant PVC foam board prepared in Example 2 of the present invention.

[0038] Figure 4 This is a smoke density-time diagram of a combustion test of an environmentally friendly, low-smoke, flame-retardant PVC foam board prepared in Example 3 of the present invention.

[0039] Figure 5 This is a smoke density-time diagram of a combustion test of an environmentally friendly, low-smoke, flame-retardant PVC foam board prepared in Comparative Example 1 of the present invention.

[0040] Figure 6 This is a smoke density-time diagram of a combustion test of an environmentally friendly, low-smoke, flame-retardant PVC foam board prepared in Comparative Example 2 of the present invention.

[0041] Figure 7 This is a smoke density-time diagram of a combustion test of an environmentally friendly, low-smoke, flame-retardant PVC foam board prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0042] In order to enable those skilled in the art to better understand the technical solution of the present invention, the preferred implementation scheme of the present invention is described below in conjunction with specific examples, but it should not be understood as a limitation of this patent.

[0043] The experimental methods or test methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are obtained from conventional commercial channels or prepared by conventional methods unless otherwise specified.

[0044] Example 1

[0045] A method for preparing an environmentally friendly, low-smoke, flame-retardant PVC foam sheet comprises the following steps:

[0046] Synthesis of modified synergistic flame retardant for PVC:

[0047] like Figure 1 As shown, itaconic anhydride (ITA) was placed in a four-necked flask equipped with a condenser, a thermometer, and a stirring device, heated and stirred to 110°C, DPO with an itaconic anhydride content of 50% was added and stirred evenly, and then heated to 160°C and reacted for 12 hours to obtain compound A. After cooling to 80°C, an appropriate amount of water was added and the reaction was continued for 6 hours.

[0048] Then, sufficient amount of stearic acid and catalyst were added and stirred evenly, and the temperature was raised to 120°C for negative pressure reaction for 3 hours to obtain compound B. Compound B was obtained and 5-20 times dried magnesium aluminum hydrotalcite (1000-5000 mesh) were placed in a high-speed mixer and mixed for 15 minutes at 115°C to obtain a modified synergistic flame retardant for PVC.

[0049] PVC resin powder, 100 parts; PVC special modified synergistic flame retardant, 5 parts; calcium carbonate 50 parts; foaming regulator 7.5 parts; calcium zinc stabilizer 3.5 parts; polyethylene wax 0.5 parts; oxidized polyethylene 1 part; epoxidized soybean oil 1.8 parts;

[0050] Process parameters: In the twin-screw stage, the twin-screw temperature is set to 185°C, the foaming agent (carbon dioxide) accounts for 3.0% of the PVC weight, the die temperature is 160°C, and the outlet pressure is 9.0-11.0Mpa. After the material is extruded, it is cooled and shaped to form an environmentally friendly flame-retardant PVC foam sheet.

[0051] PVC resin powder, PVC special modified synergistic flame retardant, filler, environmentally friendly calcium zinc stabilizer, polyethylene wax, oxidized polyethylene wax, and epoxy soybean oil are mixed in a high-speed hot mixing device according to corresponding formula proportions; then, the mixed material is placed in a high-speed cold mixer for cold mixing, and finally the obtained mixed material is placed in a storage tank for use within 24 hours;

[0052] Add the mixed material into a supercritical carbon dioxide twin-screw extruder foaming device, inject a foaming regulator, perform continuous foaming, adjust the twin-screw and die head heating temperature, adjust the melt pressure, and extrude;

[0053] Finally, after pulling and water cooling, the environmentally friendly, low-smoke and flame-retardant PVC foam sheet can be obtained.

[0054] like Figure 2 As shown, the prepared environmentally friendly low-smoke flame-retardant PVC foam board was subjected to a combustion test to obtain a curve of smoke density and time. It can be seen from the figure that the maximum smoke density value of the foam board to which 5 parts of PVC special modified synergistic flame retardant were added was 88.4%, and the smoke density level was 68. Compared with Example 1, both the maximum smoke density value and the smoke density level decreased slightly, and the flame retardant effect was slightly improved.

[0055] Example 2

[0056] A method for preparing an environmentally friendly, low-smoke, flame-retardant PVC foam sheet:

[0057] Formula: PVC resin powder, 100 parts; PVC special modified synergistic flame retardant, 10 parts; calcium carbonate 50 parts; foaming regulator 7.5 parts; calcium zinc stabilizer 3.5 parts; polyethylene wax 0.5 parts; oxidized polyethylene 1 part; epoxidized soybean oil 1.8 parts;

[0058] Process parameters: In the twin-screw stage, the twin-screw temperature is set to 185°C, the foaming agent (carbon dioxide) accounts for 3.0% of the PVC weight, the die temperature is 170°C, and the outlet pressure is 12.0-15.0Mpa. After the material is extruded, it is cooled and shaped to form an environmentally friendly flame-retardant PVC foam sheet.

[0059] Other unmentioned contents are the same as those in Example 1.

[0060] like Figure 3 As shown, the prepared environmentally friendly low-smoke flame-retardant PVC foam board was subjected to a combustion test to obtain a curve of smoke density and time. It can be seen from the figure that the maximum smoke density value of the foam board to which 10 parts of PVC special modified synergistic flame retardant was added was 67.9%, and the smoke density level was 47. Compared with Example 1, both the maximum smoke density value and the smoke density level were greatly reduced, and the flame retardant effect was further improved.

[0061] Example 3

[0062] A method for preparing an environmentally friendly, low-smoke, flame-retardant PVC foam sheet:

[0063] Formula: PVC resin powder, 100 parts; PVC special modified synergistic flame retardant, 15 parts; calcium carbonate 50 parts; foaming regulator 7.5 parts; calcium zinc stabilizer 3.5 parts; polyethylene wax 0.5 parts; oxidized polyethylene 1 part; epoxidized soybean oil 1.8 parts;

[0064] Process parameters: In the twin-screw stage, the twin-screw temperature is set to 185°C, the foaming agent (carbon dioxide) accounts for 3.0% of the PVC weight, the die temperature is 170°C, and the outlet pressure is 12.0-15.0Mpa. After the material is extruded, it is cooled and shaped to form an environmentally friendly flame-retardant PVC foam sheet.

[0065] Other unmentioned contents are the same as those in Example 1.

[0066] like Figure 4 As shown, the prepared environmentally friendly low-smoke flame-retardant PVC foam board was subjected to a combustion test to obtain a curve of smoke density and time. It can be seen from the figure that the maximum smoke density value of the foam board to which 15 parts of PVC special modified synergistic flame retardant was added was 48.4%, and the smoke density level was 36. Compared with Example 1, both the maximum smoke density value and the smoke density level were significantly reduced, and the flame retardant effect was greatly improved.

[0067] Comparative Example 1

[0068] A method for preparing an environmentally friendly, low-smoke, flame-retardant PVC foam sheet:

[0069] Formula: PVC resin powder, 100 parts; PVC special modified synergistic flame retardant, 0 parts; calcium carbonate 50 parts; foaming regulator 7.5 parts; calcium zinc stabilizer 3.5 parts; polyethylene wax 0.5 parts; oxidized polyethylene 1 part; epoxidized soybean oil 1.8 parts;

[0070] Process parameters: In the twin-screw stage, the twin-screw temperature is set to 185°C, the foaming agent (carbon dioxide) accounts for 3.0% of the PVC weight, the die temperature is 170°C, and the outlet pressure is 12.0-15.0Mpa. After the material is extruded, it is cooled and shaped to form an environmentally friendly flame-retardant PVC foam sheet.

[0071] Other unmentioned contents are the same as those in Example 1.

[0072] like Figure 5 As shown, the prepared environmentally friendly low-smoke flame-retardant PVC foam board was subjected to a combustion test to obtain a curve of smoke density and time. It can be seen from the figure that the maximum smoke density value of the foam board without the addition of PVC special modified synergistic flame retardant is 90.6%, and the smoke density grade is 77.

[0073] Comparative Example 2

[0074] A method for preparing an environmentally friendly, low-smoke, flame-retardant PVC foam sheet:

[0075] Formula: PVC resin powder, 100 parts; unmodified magnesium aluminum hydrotalcite, 10 parts; calcium carbonate 50 parts; foaming regulator 7.5 parts; calcium zinc stabilizer 3.5 parts; polyethylene wax 0.5 parts; oxidized polyethylene 1 part; epoxidized soybean oil 1.8 parts;

[0076] Process parameters: In the twin-screw stage, the twin-screw temperature is set to 185°C, the foaming agent (carbon dioxide) accounts for 3.0% of the PVC weight, the die temperature is 170°C, and the outlet pressure is 12.0-15.0Mpa. After the material is extruded, it is cooled and shaped to form an environmentally friendly flame-retardant PVC foam sheet.

[0077] Other unmentioned contents are the same as those in Example 1.

[0078] like Figure 6 As shown, the prepared environmentally friendly low-smoke flame-retardant PVC foam board was subjected to a combustion test to obtain a curve of smoke density and time. It can be seen from the figure that the maximum smoke density value of the foam board prepared by adding unmodified magnesium-aluminum hydrotalcite is 84.6%, and the smoke density grade is 68.

[0079] Example 4

[0080] A method for preparing an environmentally friendly, low-smoke, flame-retardant PVC foam sheet:

[0081] Formula: PVC resin powder, 100 parts; PVC special modified synergistic flame retardant, 20 parts; calcium carbonate 50 parts; foaming regulator 7.5 parts; calcium zinc stabilizer 3.5 parts; polyethylene wax 0.5 parts; oxidized polyethylene 1 part; epoxidized soybean oil 1.8 parts;

[0082] Process parameters: In the twin-screw stage, the twin-screw temperature is set to 185°C, the foaming agent (carbon dioxide) accounts for 3.0% of the PVC weight, the die temperature is 170°C, and the outlet pressure is 12.0-15.0Mpa. After the material is extruded, it is cooled and shaped to form an environmentally friendly flame-retardant PVC foam sheet.

[0083] Other unmentioned contents are the same as those in Example 1.

[0084] like Figure 7 As shown in the figure, the prepared environmentally friendly low-smoke flame-retardant PVC foam board was subjected to a combustion test to obtain a curve of smoke density and time. Figure 7It can be seen that the maximum smoke density of the foamed board prepared by adding 20 parts of PVC special modified synergistic flame retardant is 46%, the smoke density level is 36, and the tensile strength is 9.4Mpa. Compared with Example 3, the flame retardant performance is not significantly improved, indicating that the flame retardant effect of adding 20 parts of PVC special modified synergistic flame retardant has reached the limit, and further increasing the amount of PVC special modified synergistic flame retardant will no longer improve the flame retardant effect. Compared with Example 3, the mechanical properties are significantly reduced, indicating that the PVC special modified synergistic flame retardant is used in excess.

[0085] The environmentally friendly, low-smoke, flame-retardant PVC foamed boards prepared in Examples 1-4 and Comparative Examples 1-2 of the present invention were tested, and the data are shown in Table 1.

[0086]

[0087] It can be seen from Table 1 that the environmentally friendly low-smoke flame-retardant PVC foam board prepared in the embodiment of the present invention has an apparent density of 0.32-0.34 g / cm 3 , the highest tensile strength is 11.8Mpa. The foamed boards prepared in Examples 2 and 3 have better tensile strength, and the smoke density level and oxygen index are significantly improved compared with the foamed boards prepared in Comparative Example 2 (adding unmodified magnesium aluminum hydrotalcite). Therefore, the foamed boards prepared by adding the modified synergistic flame retardant for PVC prepared by the present invention have better flame retardant effect, are environmentally friendly and have low smoke.

[0088] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. An environmentally friendly, low-smoke, flame-retardant PVC foam board, whose raw materials include PVC resin powder, characterized in that: The raw materials also include by weight: PVC special modified synergistic flame retardant, 5-20 parts; 10-100 parts of a filler, wherein the filler is calcium carbonate; 2-10 parts of foaming regulator; Calcium zinc stabilizer 2-8 parts; Polyethylene wax 0.1-0.8 parts; Oxidized polyethylene wax 0.1-1.0 part; Epoxidized soybean oil 0.2-3.5 parts; PVC resin powder, 100 parts.

2. The environmentally friendly, low-smoke, flame-retardant PVC foam sheet according to claim 1, characterized in that: The modified synergistic flame retardant specifically for PVC is a synergistic flame retardant prepared by modifying magnesium aluminum hydrotalcite with DPO.

3. The method for preparing an environmentally friendly, low-smoke, flame-retardant PVC foam sheet according to claim 1 or 2, characterized in that: The steps include: (1) Synthesis of modified synergistic flame retardant for PVC: Itaconic anhydride is placed in a four-necked flask equipped with a condenser, a thermometer, a heating device, and a stirring device, heated and stirred, and then DPO is added and stirred evenly, and then heated to 150-160° C. for reaction to obtain compound A; Then cool to 60-80°C and add water to continue the reaction; Subsequently, stearic acid and a catalyst are added and stirred evenly, and then the temperature is raised to 110-120° C. for negative pressure reaction to obtain compound B; the obtained compound B and hydrotalcite are placed in a high-speed mixer to obtain a modified synergistic flame retardant for PVC; (2) PVC resin powder, PVC special modified synergistic flame retardant, filler, calcium zinc stabilizer, polyethylene wax, oxidized polyethylene wax, and epoxy soybean oil are mixed in a high-speed hot mixing device according to corresponding formula proportions; then, the mixed material is placed in a high-speed cold mixer for cold mixing, and finally the obtained mixed material is placed in a storage tank for use within 24 hours; (3) adding the mixed material into a supercritical carbon dioxide twin-screw extruder foaming device, injecting a foaming regulator, performing continuous foaming, adjusting the twin-screw and die heating temperature, adjusting the melt pressure, and extruding; (4) After traction and water cooling, environmentally friendly, low-smoke, flame-retardant PVC foam sheets can be obtained.

4. The method for preparing an environmentally friendly, low-smoke, flame-retardant PVC foam sheet according to claim 3, characterized in that: In the step (1), the amount of DPO added is 45-100% of itaconic anhydride, the reaction time after heating to 150-160° C. is 10-12 hours, and the time of adding water to continue the reaction is 5-6 hours. Compound A is diphenylphosphine oxide itaconic anhydride.

5. The method for preparing an environmentally friendly, low-smoke, flame-retardant PVC foam sheet according to claim 3, characterized in that: In the step (1), during the negative pressure reaction, the vacuum pressure reaches -0.05 MPa, and the reaction time is 2 to 3 hours; the compound B is diphenylphosphine oxide distearate itaconate, and the catalyst is anhydrous phosphoric acid.

6. The method for preparing an environmentally friendly, low-smoke, flame-retardant PVC foam board according to claim 3, characterized in that: In the step (1), the mass ratio of compound B to hydrotalcite is 1:5-20, the temperature in the high-speed mixer is 100-120° C., and the mixing time is 15-20 min.

7. The method for preparing an environmentally friendly, low-smoke, flame-retardant PVC foam board according to claim 3, characterized in that: In the step (2), the mixing time in the high-speed hot mixing device is 15-30 seconds, and the cold mixing time is 30-45 seconds.

8. The method for preparing an environmentally friendly, low-smoke, flame-retardant PVC foam board according to claim 3, characterized in that: In the step (3), the twin-screw heating temperature is set to 150-190°C, and the die temperature is set to 140-170°C.

9. The method for preparing an environmentally friendly, low-smoke, flame-retardant PVC foam board according to claim 3, characterized in that: In the step (3), the melt outlet pressure is adjusted to 7.5-20 MPa.

10. The method for preparing an environmentally friendly, low-smoke, flame-retardant PVC foam board according to claim 3, characterized in that: In the step (3), the foaming regulator includes a main foaming agent and an auxiliary foaming agent, the main foaming agent is carbon dioxide, and the auxiliary foaming agent is one or two of ethanol, butane, isobutane, pentane, isopentane, and methyl formate.

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