WO2016095305A1 - Method for producing uniform thick polypropylene foaming plate - Google Patents

Abstract

Disclosed is a method for producing a uniform thick plate of a polypropylene microcellular foaming structure. The method is mainly characterized in that the foaming pressure, temperature and time need to satisfy the formula t=0.227*(T-150)²+0.004083*(P-17.5)⁴+40, wherein t is the foaming time/min; T is the foaming temperature/°C; P is the foaming pressure/MPa, namely the pressure of high-temperature and high-pressure gas; and the value of t is within 30 to 250 min and preferably, t is within 40 to 230 min. Under the condition of the foaming time, temperature and pressure of the present invention and by means of fixed coordinating relationships, carbon dioxide can be easily diffused, the damage of carbon dioxide gas flow on polypropylene is avoided, the technical defect that the direct foaming of a thick plate cannot be achieved sofar in the prior art is eliminated, a polypropylene microcellular foaming material with a high foaming ratio, a small aperture size, high cell density, high thickness and uniformity in structure is obtained, and a foaming material with foaming thickness being larger than 10 mm is obtained.

Description

Method for producing uniform polypropylene foam thick plate Technical field

The invention relates to the technical field of preparation of polymer foam materials, and specifically designs a production method of uniform polypropylene microporous foam structure thick plates.

Background technique

The polymer microcellular foamed material is specifically a polymer porous foamed material having a cell size smaller than a size of 100 μm and a pore density of more than 1.0 × 10 ⁶ /cm ³ . Due to its light weight, high strength and material saving, microcellular foamed materials have broad application prospects. Among many polymer microcellular foam materials, polypropylene (PP) microcellular foamed materials have good mechanical properties, high heat distortion temperature, chemical resistance, surface protection properties, and are easy to recycle and recycle. The polypropylene microcellular foaming material obtained by foaming with supercritical carbon dioxide or supercritical nitrogen gas is clean and free from contamination. In particular, a polypropylene microporous foamed sheet having a large thickness of a product, such as a thickness of more than 10 mm, is an ideal core material for a sandwich core composite material, and can be applied to a heat insulating board of a heat preservation car, a refrigerated car, a car, a bus, and rail transit. The roof, floor, etc. of the vehicle are used for heat insulation of ships, buildings, and the like.

It is difficult to produce polypropylene foamed slabs by the common continuous extrusion foaming method. Constrained by raw resin, gas dispersion level in the melt, pressure drop rate of the die, heat removal of the foam core, etc., continuous extrusion foaming is only suitable for production thickness is relatively small, generally A microcellular foamed sheet having a thickness of less than 5 mm.

Solid foaming is a common method for preparing polymeric microcellular foamed materials. The solid foaming process means that the foaming temperature is lower than the flow temperature of the polymer, and the polymer is still in a solid state, and the high pressure gas is dissolved and diffused into the polymer matrix, and then the bubble is induced by rapid pressure relief. Hole nucleation and growth foaming process. In the solid state foaming process, the high pressure gas permeates into the polymer matrix by molecular diffusion, and the saturation time to reach the diffusion equilibrium depends on the foaming temperature, the gas pressure, the type of the polymer resin, and the thickness thereof. For the usual solid state foaming process, the gas diffuses more slowly in most polymers, and the saturation time required to reach the equilibrium of dissolution is longer. Especially as the thickness of the product increases, the saturation time will be greatly extended. Therefore, the current solid foaming method is often applied to the preparation of sheets having a small thickness, and when the microporous foamed sheets having a large thickness are prepared, the cells are not uniform, the foaming takes a long time, and the efficiency is low.

Chinese Patent PCT/CN2012/084503 discloses a method for producing a polypropylene microporous foamed slab which uses a polypropylene sheet with a core as a mother board and a flat foaming apparatus for foaming. Due to the core structure of the mother board, the foamed sheet produced by the method has voids left in the core, and the overall structure is not uniform. The void structure of the core structure becomes larger after foaming, and the structure is different, which affects the overall mechanical properties of the sheet. Insulation performance. At the same time, in the subsequent processing of the sheet, the void left by the core cannot be used as a sheet, and a large amount of waste is generated.

Summary of the invention

In view of the deficiencies of the above prior art, the present invention provides a method for producing a uniform polypropylene microcellular foamed structural thick plate, and the specific process includes the following steps:

(1) a temperature control system for providing heat to raise the flat foaming mold to a foaming temperature;

(2) Put the polypropylene mother board with uniform structure into the flat foaming mold, the hydraulic system drives the flat foaming mold to clamp, the hydraulic system is pressurized to 10-35MPa, and the high pressure gas conveying system introduces high temperature into the flat foaming mold. The pressure of high pressure gas, high temperature and high pressure gas is 5-30 MPa, preferably 5-25 MPa, and the foaming temperature and time should be satisfied: t=0.227*(T-150) ² +0.004083*(P-17.5) ⁴ +40, where t For foaming time / min; T is foaming temperature / ° C; P is foaming pressure / MPa, that is, the pressure of high temperature and high pressure gas, wherein t is 30-250min, preferably 40-230min; high temperature and high pressure gas from The surface of the polypropylene mother board diffuses into the polymer matrix;

(3) After reaching the dissolution equilibrium, the rapid pressure relief system quickly releases the gas in the flat foaming mold and recovers it through the gas recovery system. The mold is opened, and the polypropylene mother board is ejected from the mold and foamed to obtain polypropylene micropores. foaming material.

The polypropylene master has a thickness of 2 to 30 mm.

The foaming temperature is lower than the melting point of the polypropylene, preferably, the foaming temperature is 130-160 ° C;

The high temperature and high pressure gas is carbon dioxide or nitrogen or a mixture of the two in any ratio;

The flat foaming mold has a sealing material which is a composite of any one or more of beryllium copper, aluminum, graphite or polytetrafluoroethylene.

The polypropylene mother board is prepared by an extrusion molding line, and the complete extrusion production line includes a mixer, a screw extruder, a special flat extrusion die, a cooling setting table, a spray water tank, a tractor and a cutting machine; The specific preparation process is:

(1) sucking the polypropylene raw material into the hopper of the screw extruder and drying at 70-80 ° C;

(2) The dried raw materials are plasticized and mixed by the screw extruder. The parameters of the screw extruder are set as follows: screw temperature 160-250 ° C, die temperature 160-180 ° C, melt pressure 5-15 MPa, The host speed is 10-50 rpm;

(3) The plasticized polypropylene melt is formed by a special flat extrusion die;

(4) The molten polypropylene extrusion plate is cooled and shaped under the tension of the tractor to obtain preliminary cooling and setting. The traction rate of the tractor is 10-50cm/min, and the temperature of the cooling setting table is 5-20. °C;

(5) The preliminary shaped polypropylene extrusion plate exits the cooling setting table and enters the spray water tank for further cooling, and the spray water temperature is 10-30 ° C;

(6) The sprayed polypropylene extrusion plate is cut by a cutting machine to a certain length to obtain a polypropylene mother board.

The polypropylene raw material is a general-purpose polypropylene, specifically a homopolypropylene or a random copolymer polypropylene. The melt index is from 0.1 to 5.0 g/10 min, preferably from 1.0 to 3.0 g/10 min.

The polypropylene raw material described in the step (1) is added with an auxiliary agent, premixed by a mixer, and then sucked into a screw extruder hopper and dried at 70-80 ° C; the auxiliary agent includes a color master batch and an inorganic material. Filler, flame retardant, antistatic agent, based on 100 parts by weight of polypropylene, 0-2 parts by weight of color masterbatch, 0-10 parts by weight of inorganic filler, 0-30 parts by weight of flame retardant, antistatic agent 0- 15 parts by weight; whether the additive is added and the type is determined according to specific product requirements, wherein the flame retardant and the antistatic agent respectively achieve flame retardant performance and antistatic property, and the application field with high fireproof requirement generally requires polypropylene The foam material has flame retardant properties, and a flame retardant is added at this time; in the field of electronic product packaging application, the polypropylene foam material generally requires antistatic property, and an antistatic agent is added at this time.

Compared with the prior art, the invention has the advantages that the temperature and pressure conditions of the foaming according to the invention are used, and the diffusion of carbon dioxide is facilitated by a fixed synergistic relationship, and the destruction of the polypropylene by the carbon dioxide gas stream is also avoided. Overcoming the technical obstacles that the prior art has been unable to achieve direct foaming of thick plates, and achieving the purpose of obtaining a polypropylene microcellular foaming material with large expansion ratio, small pore size, high cell density, large thickness and uniform structure A foaming material having a foaming thickness of more than 10 mm can be realized. The foamed sheet has good overall mechanical properties and superior heat preservation performance; at the same time, one foaming machine can be assembled with a multi-layer flat mold, and the production efficiency is high.

DRAWINGS

1 is a schematic structural view of a coreless foamed thick plate prepared by the present invention;

Fig. 2 is a schematic view showing the structure of a foamed thick plate having a core hole in a comparative example.

detailed description

The characterization method is as follows:

The apparent density of the microcellular foamed material was measured according to the ISO 845 standard, and the expansion ratio of the final microcellular foamed material was calculated. The expansion ratio R _ex = ρ _polymer /ρ _foam , where ρ _polymer is the density of the unfoamed polymer, and ρ _foam is the apparent density of the microcellular foamed material.

The tensile strength and compressive strength of the microcellular foamed material were measured in accordance with ISO1798, ISO844 and ISO8067, respectively.

Example 1

The invention discloses a method for producing a uniform thick plate of polypropylene microporous foaming structure, which uses a flat foaming device to foam a polypropylene mother board, and the mother board is a uniform structure sheet, and the specific foaming process comprises the following steps:

(1) raising the temperature of the flat foaming mold to a foaming temperature, a foaming temperature of 148 ° C;

(2) Put the polypropylene mother board (11mm) with uniform structure into the flat foaming mold, the hydraulic system drives the flat foaming mold to mold, the hydraulic system is pressurized to 30MPa, and the high pressure gas conveying system is introduced into the flat foaming mold. 18MPa carbon dioxide gas, foaming temperature T is 148 ° C, foaming time t (minutes) meet the following formula:

t=0.227*(T-150) ² +0.004083*(P-17.5) ⁴ +40, (where t is 41 min; T is 148 ° C, P is 18 MPa);

(3) After reaching the diffusion and dissolution equilibrium, the rapid pressure relief system quickly vents the gas in the flat foaming mold and recovers it through the gas recovery system. The mold is opened, and the polypropylene mother board is ejected from the mold and foamed to obtain polypropylene micropores. The foaming material is 25.2 mm.

Example 2

The invention discloses a method for producing a uniform thick plate of polypropylene microporous foaming structure, which uses a flat foaming device to foam a polypropylene mother board, and the mother board is a uniform structural sheet, and the specific foaming process comprises the following steps;

(1) raising the temperature of the flat foaming mold to a foaming temperature, a foaming temperature of 160 ° C;

(2) Put the polypropylene mother board (17mm) with uniform structure into the flat foaming mold, the hydraulic system drives the flat foaming mold to clamp, the hydraulic system is pressurized to 30MPa, and the high pressure gas conveying system is introduced into the flat foaming mold. 25MPa high temperature carbon dioxide gas, foaming temperature T is 160 ° C, foaming time t (minutes) meet the following formula:

t=0.227*(T-150) ² +0.004083*(P-17.5) ⁴ +40, (where t is 76 min; T is 160 ° C, P is 25 MPa);

(3) After reaching the diffusion and dissolution equilibrium, the rapid pressure relief system quickly vents the gas in the flat foaming mold and recovers it through the gas recovery system. The mold is opened, and the polypropylene mother board is ejected from the mold and foamed to obtain polypropylene micropores. The foamed material is 49.7 mm.

Example 3

The invention discloses a method for producing a uniform thick plate of polypropylene microporous foaming structure, which uses a flat foaming device to foam a polypropylene mother board, and the mother board is a uniform structural sheet, and the specific foaming process comprises the following steps:

(1) raising the temperature of the flat foaming mold to a foaming temperature, a foaming temperature of 130 ° C;

(2) Put a polypropylene mother board (3m m) with uniform structure into the flat foaming mold, the hydraulic system drives the flat foaming mold to mold, the hydraulic system is pressurized to 10MPa, and the high pressure gas conveying system is directed into the flat foaming mold. Introducing a high-temperature carbon dioxide gas of 5 MPa, the foaming temperature T is 130 ° C, and the foaming time t (minutes) satisfies the following formula:

t=0.227*(T-150) ² +0.004083*(P-17.5) ⁴ +40, (where t is 231 min; T is 130 ° C, P is 5 MPa);

(3) After reaching the diffusion and dissolution equilibrium, the rapid pressure relief system quickly vents the gas in the flat foaming mold and recovers it through the gas recovery system. The mold is opened, and the polypropylene mother board is ejected from the mold and foamed to obtain polypropylene micropores. The foaming material is 7.7 mm.

Example 4

The invention discloses a method for producing a uniform thick plate of polypropylene microporous foaming structure, which uses a flat foaming device to foam a polypropylene mother board, and the mother board is a uniform structure sheet, and the specific foaming process comprises the following steps:

(1) raising the temperature of the flat foaming mold to a foaming temperature, a foaming temperature of 130 ° C;

(2) Put the polypropylene mother board (18mm) with uniform structure into the flat foaming mold, the hydraulic system drives the flat foaming mold to mold, the hydraulic system is pressurized to 30MPa, and the high pressure gas conveying system is introduced into the flat foaming mold. 25MPa high temperature carbon dioxide gas, foaming temperature T is 130 ° C, foaming time t (minutes) meet the following formula:

t=0.227*(T-150) ² +0.004083*(P-17.5) ⁴ +40, (where t is 144 min; T is 130 ° C, P is 25 MPa);

(3) After reaching the diffusion and dissolution equilibrium, the rapid pressure relief system quickly vents the gas in the flat foaming mold and recovers it through the gas recovery system. The mold is opened, and the polypropylene mother board is ejected from the mold and foamed to obtain polypropylene micropores. The foamed material is 30.8 mm.

Example 5

The invention discloses a method for producing a uniform thick plate of polypropylene microporous foaming structure, which uses a flat foaming device to foam a polypropylene mother board, and the mother board is a uniform structure sheet, and the specific foaming process Including the following steps:

(1) raising the temperature of the flat foaming mold to a foaming temperature, a foaming temperature of 130 ° C;

(2) Put a polypropylene mother board (9m m) with uniform structure into the flat foaming mold, the hydraulic system drives the flat foaming mold to clamp, the hydraulic system is pressurized to 30MPa, and the high-pressure gas conveying system is into the flat foaming mold. Introducing a high-temperature carbon dioxide gas of 18 MPa, the foaming temperature T is 130 ° C, and the foaming time t (minutes) satisfies the following formula:

t=0.227*(T-150) ² +0.004083*(P-17.5) ⁴ +40, (where t is 131 min; T is 130 ° C, P is 18 MPa);

(3) After reaching the diffusion and dissolution equilibrium, the rapid pressure relief system quickly vents the gas in the flat foaming mold and recovers it through the gas recovery system. The mold is opened, and the polypropylene mother board is ejected from the mold and foamed to obtain polypropylene micropores. The foaming material is 18mm.

Example 6

The invention discloses a method for producing a uniform thick plate of polypropylene microporous foaming structure, which uses a flat foaming device to foam a polypropylene mother board, and the mother board is a uniform structural sheet, and the specific foaming process comprises the following steps:

(1) raising the temperature of the flat foaming mold to a foaming temperature, a foaming temperature of 160 ° C;

(2) Put the polypropylene mother board (5mm) with uniform structure into the flat foaming mold, the hydraulic system drives the flat foaming mold to clamp, the hydraulic system is pressurized to 35MPa, and the high pressure gas conveying system is introduced into the flat foaming mold. 30MPa high temperature carbon dioxide gas, foaming temperature T is 160 ° C, foaming time t (minutes) meet the following formula:

t=0.227*(T-150) ² +0.004083*(P-17.5) ⁴ +40, (where t is 163min; T is 160°C, P is 30MPa);

(3) After reaching the diffusion and dissolution equilibrium, the rapid pressure relief system quickly vents the gas in the flat foaming mold and recovers it through the gas recovery system. The mold is opened, and the polypropylene mother board is ejected from the mold and foamed to obtain polypropylene micropores. The foaming material is 15.5 mm.

Example 7

The invention discloses a method for producing a uniform thick plate of polypropylene microporous foaming structure, which uses a flat foaming device to foam a polypropylene mother board, and the mother board is a uniform structural sheet, and the specific foaming process comprises the following steps:

(1) raising the temperature of the flat foaming mold to a foaming temperature, a foaming temperature of 160 ° C;

(2) Put the polypropylene mother board (10mm) with uniform structure into the flat foaming mold, the hydraulic system drives the flat foaming mold to mold, the hydraulic system is pressurized to 30MPa, and the high pressure gas conveying system is introduced into the flat foaming mold. 18MPa high temperature carbon dioxide gas, foaming temperature T is 160 ° C, foaming time t (minutes) meet the following formula:

t=0.227*(T-150) ² +0.004083*(P-17.5) ⁴ +40, (where t is 63 min; T is 160 ° C, P is 18 MPa);

(3) After reaching the diffusion and dissolution equilibrium, the rapid pressure relief system quickly vents the gas in the flat foaming mold and recovers it through the gas recovery system. The mold is opened, and the polypropylene mother board is ejected from the mold and foamed to obtain polypropylene micropores. The foamed material is 20.9 mm.

Example 8

The invention discloses a method for producing a uniform thick plate of polypropylene microporous foaming structure, which uses a flat foaming device to foam a polypropylene mother board, and the mother board is a uniform structure sheet, and the specific foaming process comprises the following steps:

(1) raising the temperature of the flat foaming mold to a foaming temperature, a foaming temperature of 148 ° C;

(2) Put a polypropylene mother board (22mm) with uniform structure into the flat foaming mold, the hydraulic system drives the flat foaming mold to mold, the hydraulic system is pressurized to 30MPa, and the high pressure gas conveying system is introduced into the flat foaming mold. 25MPa high temperature carbon dioxide gas, foaming temperature T is 148 ° C, foaming time t (minutes) meet the following formula:

t=0.227*(T-150) ² +0.004083*(P-17.5) ⁴ +40, (where t is 54 min; T is 148 ° C, P is 25 MPa);

(4) After reaching the diffusion and dissolution equilibrium, the rapid pressure relief system quickly releases the gas in the flat foaming mold and recovers it through the gas recovery system. The mold is opened, and the polypropylene mother board is ejected from the mold and foamed to obtain polypropylene micropores. The foaming material is 64.3 mm.

Example 9

The invention discloses a method for producing a uniform thick plate of polypropylene microporous foaming structure, which uses a flat foaming device to foam a polypropylene mother board, and the mother board is a uniform structural sheet, and the specific foaming process comprises the following steps:

(1) raising the temperature of the flat foaming mold to a foaming temperature, a foaming temperature of 148 ° C;

(2) Put the polypropylene mother board (7mm) with uniform structure into the flat foaming mold, the hydraulic system drives the flat foaming mold to mold, the hydraulic system is pressurized to 10MPa, and the high pressure gas conveying system is introduced into the flat foaming mold. 5MPa high temperature carbon dioxide gas, foaming temperature T is 148 ° C, foaming time t (minutes) meet the following formula:

t=0.227*(T-150) ² +0.004083*(P-17.5) ⁴ +40, (where t is 141 min; T is 148 ° C, P is 5 MPa);

(4) After reaching the diffusion and dissolution equilibrium, the rapid pressure relief system quickly releases the gas in the flat foaming mold and recovers it through the gas recovery system. The mold is opened and the polypropylene mother board is removed from the mold. The inside was ejected and foamed to obtain a polypropylene microcellular foamed material of 13.4 mm.

The foamed materials prepared in Examples 1-9 were compared with the comparative examples, wherein the comparative example was a foamed material with a core hole prepared according to Example 4 of CN201210443118, and the foamed structure of the foamed material prepared in Example 1 was The comparison of the comparative examples is shown in Figure 1 and Figure 2. The performance index pairs are shown in Table 1:

Table 1 Performance comparison between the foamed material of the present invention and the foamed material with a core

As can be clearly seen from the comparison of FIG. 1 and FIG. 2, CN201210443118 Embodiment 4 There is a void left in the core inside the prepared foamed material. Due to the existence of the void, in the subsequent processing of the sheet, the remaining void can not be used as a sheet, and a large amount of waste is generated, and the method described in the present application is prepared. The foamed material structure has no such problem; secondly, the void structure becomes larger after the foaming, and the structure is different, so that the overall structure of the foamed material is not uniform, which affects the overall mechanical properties and thermal insulation properties of the sheet. The effect is more obvious in the case where the expansion ratio is larger, and the method described in the present application can achieve uniform structure and excellent performance regardless of the expansion ratio, for example, under the same expansion ratio of 28 times. The polypropylene foamed sheet with core has a lower strength than the structurally uniform coreless polypropylene foamed sheet, as shown in Table 2, and the tensile strength and compressive strength are both shown by comparison in Table 2. Significant differences, in which the foamed slab without core structure increased the tensile strength by about 50.4% and the compressive strength by 25.6%. Table 2 Performance comparison of foamed materials with core structure and without core structure at 28 times expansion ratio

	With core	Coreless
			Tensile strength (MPa)	0.717949	1.079487
Compressive strength (MPa)	0.273333	0.343189

Example 10

The preparation method of the polypropylene mother board used in the embodiments 1-9 is prepared by an extrusion molding line, and the complete extrusion line includes a mixer, a screw extruder, a special flat extrusion die, a cooling setting table, Spray water tank, tractor and cutting machine; the specific preparation process is:

(1) Inhale the polypropylene raw material into the hopper of the screw extruder and dry it at 70-80 °C. The polypropylene raw material is a general-purpose polypropylene, specifically a homopolypropylene or a random copolymer polypropylene. The melt index is from 0.1 to 5.0 g/10 min, preferably from 1.0 to 3.0 g/10 min;

(2) The dried raw materials are plasticized and mixed by the screw extruder. The parameters of the screw extruder are set as follows: screw temperature 160-250 ° C, die temperature 160-180 ° C, melt pressure 5-15 MPa, The host speed is 10-50 rpm;

(3) The plasticized polypropylene melt is formed by a special flat extrusion die;

(4) The molten polypropylene extrusion plate is cooled and shaped under the tension of the tractor to obtain preliminary cooling and setting. The traction rate of the tractor is 10-50cm/min, and the temperature of the cooling setting table is 5-20. °C;

(5) The preliminary shaped polypropylene extrusion plate exits the cooling setting table and enters the spray water tank for further cooling, and the spray water temperature is 10-30 ° C;

(6) The sprayed polypropylene extrusion plate is cut by a cutter to a certain length to obtain a polypropylene mother plate.

In addition, according to the requirements of the specific product, the addition of the auxiliary agent to the polypropylene raw material in the step (1), the specific addition ratio and mixing method are: 100 parts by weight of the polypropylene raw material, 0-2 parts by weight of the color masterbatch 0-10 parts by weight of inorganic filler, 0-30 parts by weight of flame retardant, 0-15 parts by weight of antistatic agent, premixed by mixer, then sucked into the hopper of screw extruder and dried at 70-80 °C Whether the above additives are added and the type is determined according to the specific product requirements, wherein the flame retardant and the antistatic agent respectively achieve flame retardant performance and antistatic property, and the application field with high fireproof requirements generally requires polypropylene foam material to have resistance Burning performance, adding flame retardant at this time; and in the field of electronic product packaging applications, polypropylene foaming materials are generally required to have antistatic properties, and an antistatic agent is added at this time.

Claims (10)

1. A method for producing a uniform polypropylene microporous foamed structural thick plate, characterized in that the specific process comprises the following steps:

   (1) a temperature control system for providing heat to raise the flat foaming mold to a foaming temperature;

   (2) Put the polypropylene mother board with uniform structure into the flat foaming mold, the hydraulic system drives the flat foaming mold to clamp, the hydraulic system is pressurized to 10-35MPa, and the high pressure gas conveying system introduces high temperature into the flat foaming mold. The pressure of high pressure gas, high temperature and high pressure gas is 5-30 MPa, preferably 5-25 MPa, and the foaming temperature and time should be satisfied: t=0.227*(T-150) ² +0.004083*(P-17.5) ⁴ +40, where t For foaming time / min; T is foaming temperature / ° C; P is foaming pressure / MPa, that is, the pressure of high temperature and high pressure gas, high temperature and high pressure gas diffuses from the surface of the polypropylene mother board into the polymer matrix;

   (3) After reaching the dissolution equilibrium, the rapid pressure relief system quickly releases the gas in the flat foaming mold and recovers it through the gas recovery system. The mold is opened, and the polypropylene mother board is ejected from the mold and foamed to obtain polypropylene micropores. foaming material.
2. The method for producing a uniform polypropylene microcellular foamed structural thick plate according to claim 1, wherein the value of t is from 30 to 250 min, preferably from 40 to 230 min.
3. The method for producing a uniform polypropylene microcellular foamed structural thick plate according to claim 1, wherein the polypropylene master has a thickness of 2 to 30 mm.
4. The method for producing a uniform polypropylene microcellular foamed structural thick plate according to claim 1, wherein said foaming temperature is lower than a melting point of polypropylene, preferably, a foaming temperature of from 130 to 160 °C.
5. The method for producing a uniform polypropylene microcellular foamed structural thick plate according to claim 1, wherein the high temperature and high pressure gas is carbon dioxide or nitrogen or a mixture of the two in any ratio.
6. The production method of the uniform polypropylene microcellular foamed structural thick plate according to claim 1 The method is characterized in that the flat foaming mold has a sealing material, and the sealing material is a composite of any one or more of beryllium copper, aluminum, graphite or polytetrafluoroethylene.
7. A method for preparing a polypropylene mother board as claimed in any one of claims 1 to 6, characterized in that it is prepared by an extrusion molding line, and the complete extrusion line includes a mixer, a screw extruder, and a dedicated flat plate extrusion. Die, cooling setting table, spray water tank, tractor and cutting machine; the specific preparation process is:

   (1) sucking the polypropylene raw material into the hopper of the screw extruder and drying at 70-80 ° C;

   (2) The dried raw materials are plasticized and mixed by the screw extruder. The parameters of the screw extruder are set as follows: screw temperature 160-250 ° C, die temperature 160-180 ° C, melt pressure 5-15 MPa, The host speed is 10-50 rpm;

   (3) The plasticized polypropylene melt is formed by a special flat extrusion die;

   (4) The molten polypropylene extrusion plate is cooled and shaped under the tension of the tractor to obtain preliminary cooling and setting. The traction rate of the tractor is 10-50cm/min, and the temperature of the cooling setting table is 5-20. °C;

   (5) The preliminary shaped polypropylene extrusion plate exits the cooling setting table and enters the spray water tank for further cooling, and the spray water temperature is 10-30 ° C;

   (6) The sprayed polypropylene extrusion plate is cut by a cutter to a certain length to obtain a polypropylene mother plate.
8. The method for preparing a polypropylene mother board according to claim 7, wherein the polypropylene raw material is a general-purpose polypropylene, specifically a homopolypropylene or a random copolymer polypropylene, and the melt index is 0.1-5.0. g/10 min, preferably 1.0-3.0 g/10 min.
9. The method for preparing a polypropylene mother board according to claim 7, wherein the polypropylene raw material in the step (1) is added to an auxiliary agent, premixed by a mixer, and then sucked into a screw extruder hopper. Dry at 70-80 °C.
10. A method of preparing a polypropylene mother board according to claim 9, wherein The auxiliary agent includes a color master batch, an inorganic filler, a flame retardant, and an antistatic agent, and the color masterbatch is 0-2 parts by weight, the inorganic filler is 0-10 parts by weight, and the flame retardant is 0. -30 parts by weight, antistatic agent 0-15 parts by weight.

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