CN116175860B - Device and method for preparing polypropylene foamed board by irradiation chain extension modification - Google Patents

Abstract

The device comprises a high-speed mixer, a first-order double-screw extruder, a material strip die, an air cooling device, a stretching ultraviolet irradiation device, a feeding device, a second-order supercritical foaming double-screw extruder, a third-order single-screw extruder, a melt pump, a foaming sheet die, a leveling and shaping device, a traction device and a cutting device which are sequentially arranged. The irradiation chain extension modification is completed in the stretching process, and the chain orientation of the polypropylene molecular chain in the stretching process can limit the fluidity of the chain, effectively inhibit the beta chain from breaking, further prevent the degradation of the polypropylene molecular chain, thereby realizing the efficient chain extension modification and further improving the melt strength and foaming effect of the polypropylene.

Description

Device and method for preparing polypropylene foamed board by irradiation chain extension modification

Technical Field

The invention relates to the field of preparing polypropylene foamed plates, and in particular to a device and a method for preparing polypropylene foamed plates by irradiation chain extension modification.

Background technique

Polymer foam materials have the characteristics of lightweight, sound insulation, heat insulation, cushioning and shock absorption, and are widely used in construction, automotive industry, aerospace, cold chain logistics and other fields. Among the commonly used polymer foam materials, polypropylene (PP) foam material is the new foam material with the fastest domestic demand and production growth. Polypropylene foam material is more environmentally friendly than polyurethane (PU), and has higher temperature resistance and better mechanical properties than polyethylene (PE). Therefore, polypropylene foam material has a broad development prospect and a wide range of applications, and is gradually becoming a new favorite in industries such as cushioning, packaging, automotive interiors, and catering.

However, conventional PP is a semi-crystalline polymer that lacks mutually entangled side chains, so the melt strength is low. At the same time, the processing temperature range of extrusion foaming is very small, which greatly limits the PP foaming material to obtain a stable and controllable pore structure and is not suitable for the preparation of foamed products. Therefore, improving the melt strength of PP is of great significance for the application of extrusion foaming. At present, the main modification methods for improving the melt strength of PP are: blending modification, grafting modification and cross-linking modification. Blending modification to improve melt strength will cause adverse changes in mechanical properties, the mechanical properties of the product will decrease significantly, tensile fracture will easily occur, and the impact resistance will decrease; the chemical synthesis process of grafting modification is relatively complicated, the product performance consistency is low, and the control is difficult; cross-linking modification cross-links PP through electron beam irradiation, gamma ray method, etc., thereby improving the melt strength.

The equipment cost of ultraviolet irradiation grafting branching is low, and it can basically be strictly confined to the surface or subsurface of the material, without excessively damaging the performance of the material. The degree of reaction is easy to control, and it is more suitable for industrial production. However, the branching and breaking of the polymer molecular chain exist simultaneously during the ultraviolet irradiation modification process, because the polypropylene molecular chain carries active α-methyl hydrogen atoms, which form tertiary carbon freedom under the action of ultraviolet irradiation, and then β-breakage occurs, which in turn causes the degradation of the polymer. The degradation process plays an important role in the breakage and branching recombination of the PP molecular chain, which directly affects the degree of branching cross-linking and the structure of the modified molecule. In view of this problem, it is necessary to provide a method that can control the β-breakage of the polypropylene molecular chain during the irradiation process, inhibit the degradation of the polymer, improve the ultraviolet irradiation chain extension modification effect, and thus improve the melt strength and foaming effect of the polymer.

Summary of the invention

The technical problem to be solved by the present invention is to achieve chain extension modification of polypropylene molecular chains by ultraviolet irradiation, and at the same time be able to control the β-fracture of the polypropylene molecular chains during the irradiation process, inhibit the degradation of the polymer, improve the chain extension modification effect of ultraviolet irradiation, and then significantly improve the melt strength of polypropylene to achieve an ideal foaming effect.

In order to achieve the above object, the present invention adopts the following technical solution:

A device for preparing polypropylene foamed board by irradiation chain extension modification, comprising a high-speed mixer, a first-stage twin-screw extruder, a material strip mold, an air cooling device, a stretching ultraviolet irradiation device, a feeding device, a second-stage supercritical foaming twin-screw extruder, a third-stage single-screw extruder, a melt pump, a foamed board mold, a leveling and shaping device, a traction device, and a cutting device arranged in sequence;

The second-stage supercritical foaming twin-screw extruder and the third-stage single-screw extruder are connected via a transition channel;

The stretching ultraviolet irradiation device is internally provided with a first stretching roller, a second stretching roller, a third stretching roller, a fourth stretching roller, a first ultraviolet irradiation lamp group and a second ultraviolet irradiation lamp group, wherein the first stretching roller, the second stretching roller and the first ultraviolet irradiation lamp group constitute a first chain extension and modification section, the third stretching roller, the fourth stretching roller and the second ultraviolet irradiation lamp group constitute a second chain extension and modification section, the first ultraviolet irradiation lamp group and the second ultraviolet irradiation lamp group are both irradiated and heated by heating lamp tubes, and the combined action of the stretching roller and the ultraviolet irradiation lamp group enables the polypropylene strip to be stretched while being irradiated and chain extended in the stretching ultraviolet irradiation device.

Among them, the length of the first chain extension modification section is 1000-1500mm, the length of the second chain extension section is 500-1000mm, the first ultraviolet irradiation lamp group and the second ultraviolet irradiation lamp group include ultraviolet irradiation lamp tubes evenly arranged on the upper and lower parts, and the distance between the upper and lower ultraviolet irradiation lamp tubes is 200-300mm.

Among them, the first-stage twin-screw extruder has a diameter of 40mm, a length-to-diameter ratio of 48:1, an outlet hole diameter of the material strip mold is 5mm, and a screw speed of 100-400rpm; the feeding device is a pair of traction rollers.

Among them, the second-stage supercritical foaming twin-screw extruder has a diameter of 52mm, an aspect ratio of 42:1, a screw speed of 200-300rpm, a lead of the screw element at the feed port of 2-3 times the screw diameter, and a steam injection port is provided at the position where the extruder screw aspect ratio is 30.

Among them, the diameter of the third-stage single-screw extruder is 120mm, the aspect ratio is 32:1, and the screw speed is 5-30rpm.

Among them, the thickness of the foam board mold is 5-10mm and the width is 300-600mm.

The present invention also provides a method for preparing a polypropylene foam plate by using a device for preparing a polypropylene foam plate by irradiation chain extension modification, comprising the following steps:

(1) Raw material mixing

First, put polypropylene and chain extender into a high-speed mixer in proportion, set the temperature of the high-speed mixer to 75-80℃, stir for 5 minutes, then add the auxiliary chain extender and continue stirring for 5 minutes;

(2) Stretch chain extension

The mixture obtained in step (1) is added to a first-stage twin-screw extruder, wherein the temperatures of the screw zone of the first-stage twin-screw extruder are 40°C, 100°C, 160°C, 180°C, 190°C, 190°C, 180°C, and 170°C, respectively; the material strip extruded from the material strip mold is first cooled by an air cooling device, and then irradiated and stretched by a stretching ultraviolet irradiation device; the material strip is stretched and folded multiple times on two sets of parallel rollers in the first chain extension and modification section and the second chain extension and modification section; the stretching ultraviolet irradiation device irradiates the material strip with ultraviolet light while stretching the material strip; the coupling effect of ultraviolet irradiation and chain extender causes the polypropylene molecular chain to rapidly deaminate, generating a large number of macromolecular free radicals; these free radicals combine with each other to form a long branched structure on the long chain of the polypropylene; at the same time, the chain orientation of the polypropylene molecular chain during the stretching process can effectively inhibit the breakage of the β chain, thereby preventing the degradation of the polypropylene molecular chain, thereby achieving efficient chain extension modification;

(3) Steam injection and mixing

The chain-extended and modified polypropylene strips of step (2) are fed into the feeding port of the second-stage supercritical foaming twin-screw extruder through the traction of the conveying roller in the feeding device. The temperature settings of the second-stage supercritical foaming twin-screw extruder from the feeding port to the outlet are 150°C, 210°C, 210°C, 210°C, 205°C, 195°C, 190°C, and 190°C, respectively, and the screw speed is 200-300rpm; at the same time, supercritical fluid _CO2 is injected into the extruder through the steam injection port, and the injection amount of _CO2 is controlled by a flow control valve to be 5-10% of the mass of the polypropylene. Under the mixing and shearing action of the screw, the polypropylene and _CO2 are mixed into a uniform melt;

(4) Extrusion foaming

The melt mixed by the second-stage supercritical foaming twin-screw extruder enters the feeding port of the third-stage single-screw extruder through the transition flow channel. The screw of the third-stage single-screw extruder includes a feeding section, a first compression section, a first metering section, a decompression section, a second compression section and a second metering section. The temperatures of each section are 150°C, 180°C, 190°C, 180°C, 170°C and 150°C respectively; the temperature of the melt pump is 150°C, the temperature of the foaming sheet mold is 155°C, the pressure before and after the melt pump is 8MPa and 10MPa respectively. After the melt passes through the foaming sheet mold, the pressure is released and the bubbles grow. The polypropylene melt modified by chain extension has a higher strength, and there will be no gas molecule escape and pore collapse. The pore morphology is maintained, and the foaming ratio is 8-15 times.

(5) Shape cutting

The foamed sheet is cooled and shaped by a leveling and shaping device, and is then pulled and cut to obtain a foamed sheet.

The chain extender used is benzophenone, the auxiliary chain extender is trimethylolpropane triacrylate or pentaerythritol triacrylate, the mass content of the chain extender is 0.2%-1.0%, and the content of the auxiliary chain extender is 1%-2%.

The first chain extension and modification section and the second chain extension and modification section are heated by internally arranged radiation heating lamps at a heating temperature of 150-200°C, and the ultraviolet radiation dose of the first ultraviolet radiation lamp group and the second ultraviolet radiation lamp group is 2000mj/ ^cm2 to 10000mj/ ^cm2 .

Among them, the stretching ratio of the first stretching roller and the second stretching roller is 2-5, and the stretching ratio of the third stretching roller and the fourth stretching roller is 2-4.

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

(1) The irradiation chain extension modification is completed during the stretching process. The chain orientation of the polypropylene molecular chain during the stretching process can limit the chain fluidity and effectively inhibit the β-chain breakage, thereby preventing the degradation of the polypropylene molecular chain, thereby achieving efficient chain extension modification. The long-chain branching of polypropylene can be controlled by controlling the stretching ratio.

(2) UV radiation modification is carried out after the material strip leaves the mold and solidifies. The depth of UV radiation penetration is increased by reducing the wire diameter through stretching, which can greatly improve the irradiation efficiency. The equipment is simple, the process is continuous, and it will not affect the performance of the product itself. It has a long service life, stable product quality, and low energy consumption.

(3) Polypropylene modified by UV irradiation chain extension has high melt strength, good quality consistency, high process reliability, high foaming quality and good performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of the method for preparing a polypropylene foam plate by irradiation chain extension modification of the present invention.

FIG. 2 is a schematic diagram of a device for preparing a polypropylene foam plate by irradiation chain extension modification according to the present invention.

FIG. 3 is a diagram showing the internal structure of the device for preparing polypropylene foamed board by irradiation chain extension modification according to the present invention.

Among them, 1-high-speed mixer, 2-first-stage twin-screw extruder, 3-material strip mold, 4-air cooling device, 5-stretching ultraviolet irradiation device, 6-feeding device, 7-second-stage supercritical foaming twin-screw extruder, 8-transition flow channel, 9-third-stage single-screw extruder, 10-melt pump, 11-foaming board mold, 12-leveling and shaping device, 13-traction device, 14-cutting device, 15-first stretching roller, 16-second stretching roller, 17-third stretching roller, 18-fourth stretching roller, 19-first ultraviolet irradiation lamp group, 20-second ultraviolet irradiation lamp group.

Detailed ways

In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

As shown in Figures 1 to 3, it includes a high-speed mixer 1, a first-stage twin-screw extruder 2, a material strip mold 3, an air cooling device 4, a stretching ultraviolet irradiation device 5, a feeding device 6, a second-stage supercritical foaming twin-screw extruder 7, a third-stage single-screw extruder 9, a melt pump 10, a foaming board mold 11, a leveling and shaping device 12, a traction device 13, and a cutting device 14, wherein the second-stage supercritical foaming twin-screw extruder 7 and the third-stage single-screw extruder 9 are connected via a transition channel 8;

The first-stage twin-screw extruder 2 is used to pre-treat and mix the raw materials, achieve effective mixing of PP and initiator before initiating the reaction, and activate the photoinitiator benzophenone (BPH) by ultraviolet radiation. The stretching ultraviolet irradiation device 5 is used for stretching and chain extension. Ultraviolet radiation is used to extend and modify the PP chain. It includes two chain extension and modification sections consisting of four stretching rollers and two groups of ultraviolet irradiation lamps. The stretching ultraviolet irradiation device 5 is internally arranged with heating lamps for heating. The material strips are stretched and folded multiple times on two parallel rollers. The second-stage supercritical foaming twin-screw extruder 7 is used to prepare PP foaming materials. The stretched and modified PP is added to the extruder of the twin-screw mixing assembly for melt plasticization, and supercritical fluid _CO2 is injected through a high-pressure injection system. The third-stage single-screw extruder 9 is used to further mix the material that has reached a certain degree of plasticization and the foaming agent, and then cool the material in a molten state. When it reaches a suitable cooling temperature, the molten mixed material becomes a suitable viscous body. After being extruded through a mold, the pressure is quickly released to form a foamed board with closed cells, thereby obtaining a uniformly mixed low-temperature extrudate to improve the quality of extrusion foaming. As shown in FIG3 , the stretching ultraviolet irradiation device 5 is internally provided with a first stretching roller 15, a second stretching roller 16, a third stretching roller 17, a fourth stretching roller 18, a first ultraviolet irradiation lamp group 19 and a second ultraviolet irradiation lamp group 20, wherein the first stretching roller 15, the second stretching roller 16 and the first ultraviolet irradiation lamp group 19 constitute a first chain extension and modification section, the third stretching roller 17, the fourth stretching roller 18 and the second ultraviolet irradiation lamp group 20 constitute a second chain extension and modification section, the first ultraviolet irradiation lamp group 19 and the second ultraviolet irradiation lamp group 20 are both irradiated and heated by heating lamp tubes, the heating temperature is 150-200° C., the stretching ratio of the first stretching roller 15 and the second stretching roller 16 is 2-5, the stretching ratio of the third stretching roller 17 and the fourth stretching roller 18 is 2-4, and the ultraviolet irradiation dose of the first ultraviolet irradiation lamp group and the second ultraviolet irradiation lamp group is 2000mj/cm ² to 10000mj/cm ² . The combined effect of the stretching rollers and the UV lamp group allows the polypropylene strip to be stretched while being UV-irradiated and chain-extended in the stretching UV irradiation device 5 .

The length of the first chain extension modification section is 1000-1500mm, the length of the second chain extension section is 500-1000mm, the first ultraviolet irradiation lamp group and the second ultraviolet irradiation lamp group both include ultraviolet irradiation lamp tubes evenly arranged up and down, and the distance between the upper and lower ultraviolet irradiation lamp tubes is 200-300mm. The PP material strip is irradiated and stretched between the stretching rollers. Due to the action of the external stretching force, effective radiation can be generated at the optimal thickness of the sample, and the resulting chain orientation will reduce the degradation of the polypropylene molecular chain.

The first-stage twin-screw extruder 2 has a diameter of 40 mm and a length-to-diameter ratio of 48:1. The outlet hole diameter of the strip mold 3 is 5 mm and the screw speed is 100-400 rpm. The feeding device is a pair of traction rollers.

The second-stage supercritical foaming twin-screw extruder 7 has a diameter of 52 mm, an aspect ratio of 42:1, a screw speed of 200-300 rpm, a lead of the screw element at the feed port of 2-3 times the screw diameter, and a steam injection port is provided at a position where the extruder's screw aspect ratio is 30.

The diameter of the third-stage single-screw extruder 9 is 120 mm, the aspect ratio is 32:1, and the screw speed is 5-30 rpm; the thickness of the foamed board mold is 5-10 mm, and the width is 300-600 mm.

The raw materials include: the polymer raw material is polypropylene, the chain extender is benzophenone, and the auxiliary chain extender is trimethylolpropane triacrylate or pentaerythritol triacrylate. The mass contents of the raw materials are: the content of polypropylene is 97%-99%, the mass content of the chain extender is 0.2%-1.0%, and the content of the auxiliary chain extender is 1%-2%.

The co-chain extender is used to reduce the duration of ultraviolet radiation and reduce degradation by stabilizing free radical centers.

The chain extenders (photoinitiators) are activated by UV radiation and are less toxic than peroxides.

As shown in FIG1-2, the polypropylene foam sheet is prepared by chain extension modification using the above device, comprising the following steps:

(1) Raw material mixing (pretreatment)

First, the weighed polypropylene and chain extender are put into the high-speed mixer 1, the temperature of the high-speed mixer 1 is set to 75-80°C, the stirring time is 5 minutes, and then the auxiliary chain extender is added, and the stirring is continued for 5 minutes. Then, the auxiliary chain extender is added and the stirring is continued for 5 minutes.

(2) Stretch chain extension

The mixture obtained in step (1) is added to a first-stage twin-screw extruder 2, wherein the temperatures of the screw region of the first-stage twin-screw extruder 2 are 40°C, 100°C, 160°C, 180°C, 190°C, 190°C, 180°C, and 170°C, respectively. The strip extruded from the strip mold 3 is first cooled by an air cooling device 4, and then irradiated and stretched by a stretching ultraviolet irradiation device 5. The strip is stretched and folded multiple times on two sets of parallel rollers in the first chain extension and modification section and the second chain extension and modification section. The stretching ultraviolet irradiation device 5 irradiates the strip with ultraviolet light while stretching the strip. The coupling effect of ultraviolet light irradiation and chain extender causes the polypropylene molecular chain to rapidly deaminate, generating a large number of macromolecular free radicals. These free radicals combine with each other to form a long branched structure on the long chain of the polypropylene. At the same time, the chain orientation of the polypropylene molecular chain during the stretching process can effectively inhibit the breakage of the β chain, thereby preventing the degradation of the polypropylene molecular chain, thereby achieving efficient chain extension and modification;

(3) Steam injection and mixing

The chain-extended and modified polypropylene strips in step (2) are fed to the feeding port of the second-stage supercritical foaming twin-screw extruder 7 through the traction of the conveying roller in the feeding device 6. The temperature settings of the second-stage supercritical foaming twin-screw extruder from the feeding port to the outlet are 150°C, 210°C, 210°C, 210°C, 205°C, 195°C, 190°C, and 190°C, respectively, and the screw speed is 200-300rpm; at the same time, supercritical fluid _CO2 is injected into the extruder through the steam injection port, and the injection amount of _CO2 is controlled by a flow control valve to be 5-10% of the mass of the polypropylene. Under the mixing and shearing action of the screw, the polypropylene and _CO2 are mixed into a uniform melt;

(4) Extrusion foaming

The melt mixed by the second-stage supercritical foaming twin-screw extruder 7 enters the feeding port of the third-stage single-screw extruder 9 through the transition flow channel 8. The screw of the third-stage single-screw extruder includes a feeding section, a first compression section, a first metering section, a decompression section, a second compression section and a second metering section. The temperatures of each section are 150° C., 180° C., 190° C., 180° C., 170° C., and 150° C., respectively; the temperature of the melt pump 10 is 150° C., the temperature of the foaming sheet mold is 155° C., the pressure before and after the melt pump is 8MPa and 10MPa, respectively. After the melt passes through the foaming sheet mold, the pressure is released and the bubbles grow. The polypropylene melt modified by chain extension has a higher strength, and there will be no gas molecule escape and pore collapse. The pore morphology is maintained, and the foaming ratio is 8-15 times;

(5) Shape cutting

The foamed board is cooled and shaped by a leveling and shaping machine, and a high-quality foamed board is obtained by pulling and cutting.

Polypropylene foam material has excellent comprehensive performance and high cost performance. However, due to the lack of branched and cross-linked molecular chains, its melt strength is low and is not suitable for the preparation of foam materials. Maximizing the melt strength of polypropylene without losing the mechanical properties of the material is the difficulty and key to improving the quality of polypropylene foam materials. The device for preparing polypropylene foam sheet by chain extension modification of the present application utilizes ultraviolet light irradiation to increase the melt strength of polypropylene, and adding photoinitiators and chain extenders to the raw materials can increase the thickness of the ultraviolet light treated sample. The foaming effect of the sheet is significantly improved through the optimization of the formulation and processing technology, as well as the modification by ultraviolet radiation.

Specific embodiment 1:

The device for preparing polypropylene foamed plate by irradiation chain extension modification of the present invention comprises the following steps: 0.2% of benzophenone and 98.8% of polypropylene by mass are respectively fed into a high-speed mixer for stirring, and then 1% of trimethylolpropane triacrylate is added and stirred to prepare a raw material, which is then fed into a first-stage twin-screw extruder hopper for further mixing, and the temperatures of various sections of the barrel are sequentially set to 40° C., 100° C., 160° C., 180° C., 190° C., 190° C., 180° C., 170° C. and a screw speed of 100 rpm. After the molten material strips come out of the material strip mold, they are first cooled by the air cooling device and then sent to the stretching ultraviolet irradiation device. The stretching ultraviolet irradiation device irradiates the ultraviolet light while stretching the material strips. The heating temperature of the ultraviolet device heating lamp is 150°C, the stretching ratio of the first stretching roller and the second stretching roller is 2, the stretching ratio of the third stretching roller and the fourth stretching roller is 2, and the ultraviolet irradiation dose of the first ultraviolet irradiation lamp group and the second ultraviolet irradiation lamp group is 2000mj/ ^cm2 . The feeding device feeds the material strips after passing through the stretching ultraviolet irradiation device into the feeding port of the second-stage supercritical foaming twin-screw extruder, adds the foaming gas _CO2 with a mass of 5% of the mass of polypropylene, and further mixes with the raw materials. The lead of the screw element at the feeding port is 2 times the screw diameter, and the temperature of each section of the barrel and the screw speed of 200rpm are set. The second stage supercritical foaming twin screw extruder and the third stage single screw extruder are connected through a transition channel. The third stage single screw extruder cools down and depressurizes the prepared foaming material to realize the foaming process. The temperature of each section of the barrel and the screw speed of 5rpm are set. The thickness of the foaming board mold is 5mm and the width is 300mm. After the melt passes through the foaming board mold, the pressure is released and the bubbles grow. The foamed board is cooled and shaped by a leveling and shaping machine, and a high-quality foamed board is obtained by traction and cutting.

According to the test, the melt strength of polypropylene after chain extension modification by the first-stage twin-screw extruder is 14.7 cN, the density of the foamed sheet is 0.25 g/cm ³ , the cell density is 2.0×10 ⁸ cells/cm ³ , and the average cell diameter is 90 μm.

Specific embodiment 2:

The device for preparing polypropylene foamed plate by irradiation chain extension modification of the present invention comprises the following steps: 0.35% of benzophenone and 98.15% of polypropylene are respectively fed into a high-speed mixer for stirring, and then 1.5% of trimethylolpropane triacrylate is added and stirred to prepare raw materials, which are then fed into a first-stage twin-screw extruder hopper for further mixing, and the temperatures of various sections of the barrel are sequentially set to 40° C., 100° C., 160° C., 180° C., 190° C., 190° C., 180° C., 170° C. and the screw speed is 300 rpm. After the molten material strips come out of the material strip mold, they are first cooled by the air cooling device and then sent to the stretching ultraviolet irradiation device. The stretching ultraviolet irradiation device irradiates the ultraviolet light while stretching the material strips. The heating temperature of the ultraviolet device heating lamp is 150°C, the stretching ratio of the first stretching roller and the second stretching roller is 3, the stretching ratio of the third stretching roller and the fourth stretching roller is 3, and the ultraviolet irradiation dose of the first ultraviolet irradiation lamp group and the second ultraviolet irradiation lamp group is 6000mj/ ^cm2 . The feeding device feeds the material strips after passing through the stretching ultraviolet irradiation device into the feeding port of the second-stage supercritical foaming twin-screw extruder, adds the foaming gas _CO2 with a mass of 8% of the mass of polypropylene, and further mixes with the raw materials. The lead of the screw element at the feeding port is 2.5 times the screw diameter, and the temperature of each section of the barrel and the screw speed of 250rpm are set. The second stage supercritical foaming twin screw extruder and the third stage single screw extruder are connected through a transition channel. The third stage single screw extruder cools down the prepared foaming material to realize the foaming process. The temperature of each section of the barrel and the screw speed of 15rpm are set. The thickness of the foaming board mold is 8mm and the width is 450mm. After the melt passes through the foaming board mold, the pressure is released and the bubbles grow. The foamed board is cooled and shaped by a leveling and shaping machine, and a high-quality foamed board is obtained by traction and cutting.

According to the test, the melt strength of polypropylene after chain extension modification by the first-stage twin-screw extruder is 18.5 cN, the density of the foamed sheet is 0.15 g/cm ³ , the cell density is 1.5×10 ⁹ cells/cm ³ , and the average cell diameter is 60 μm.

Specific embodiment 3:

The device for preparing polypropylene foamed plate by irradiation chain extension modification of the present invention is adopted, 0.5% of benzophenone and 97.5% of polypropylene by mass content are respectively sent into a high-speed mixer for stirring, and then 2% of trimethylolpropane triacrylate is added and stirred to prepare raw materials, which are further mixed in the feeding hopper of a first-stage twin-screw extruder, and the temperatures of various sections of the barrel are set to be 40° C., 100° C., 160° C., 180° C., 190° C., 190° C., 180° C., 170° C. and the screw speed is 400 rpm. After the molten material strips come out of the material strip mold, they are first cooled by the air cooling device and then sent to the stretching ultraviolet irradiation device. The stretching ultraviolet irradiation device irradiates the ultraviolet light while stretching the material strips. The heating temperature of the ultraviolet device heating lamp is 150°C, the stretching ratio of the first stretching roller and the second stretching roller is 5, the stretching ratio of the third stretching roller and the fourth stretching roller is 4, and the ultraviolet irradiation dose of the first ultraviolet irradiation lamp group and the second ultraviolet irradiation lamp group is 10000mj/ ^cm2 . The feeding device feeds the material strips after passing through the stretching ultraviolet irradiation device into the feeding port of the second-stage supercritical foaming twin-screw extruder, and adds the foaming gas _CO2 with a mass of 8% of the mass of polypropylene, and further mixes with the raw materials. The lead of the screw element at the feeding port is 3 times the screw diameter, and the temperature of each section of the barrel and the screw speed of 300rpm are set. The second stage supercritical foaming twin screw extruder and the third stage single screw extruder are connected through a transition channel. The third stage single screw extruder cools down and depressurizes the prepared foaming material to realize the foaming process. The temperature of each section of the barrel and the screw speed of 30rpm are set. The thickness of the foaming board mold is 10mm and the width is 600mm. After the melt passes through the foaming board mold, the pressure is released and the bubbles grow. The foamed board is cooled and shaped by a leveling and shaping machine, and a high-quality foamed board is obtained by traction and cutting.

According to the test, the melt strength of polypropylene after chain extension modification by the first-stage twin-screw extruder is 24.3 cN, the density of the foamed sheet is 0.09 g/cm ³ , the cell density is 2.0×10 ⁹ cells/cm ³ , and the average cell diameter is 50 μm.

The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims (8)

1. A device for preparing polypropylene foamed board by irradiation chain extension modification, characterized in that it comprises a high-speed mixer (1), a first-stage twin-screw extruder (2), a material strip mold (3), an air cooling device (4), a stretching ultraviolet irradiation device (5), a feeding device (6), a second-stage supercritical foaming twin-screw extruder (7), a third-stage single-screw extruder (9), a melt pump (10), a foamed board mold (11), a leveling and shaping device (12), a traction device (13), and a cutting device (14) which are arranged in sequence; the second-stage supercritical foaming twin-screw extruder (7) and the third-stage single-screw extruder (9) are connected by a transition channel (8); the stretching ultraviolet irradiation device (5) is internally provided with a first stretching roller (15), a second stretching roller (16), a third stretching roller (17), a fourth stretching roller (18), a first ultraviolet irradiation lamp group (19) and a second ultraviolet irradiation lamp group (20), wherein the first stretching roller (15), the second stretching roller ( 16) and the first ultraviolet irradiation lamp group (19) constitute a first chain extension and modification section, the third stretching roller (17), the fourth stretching roller (18) and the second ultraviolet irradiation lamp group (20) constitute a second chain extension and modification section, the first ultraviolet irradiation lamp group (19) and the second ultraviolet irradiation lamp group (20) are both irradiated and heated by heating lamp tubes, and the stretching roller and the ultraviolet irradiation lamp group work together to make the polypropylene strips stretch while being irradiated and chain extended in the stretching ultraviolet irradiation device (5); the first The length of the chain extension modification section is 1000-1500 mm, the length of the second chain extension section is 500-1000 mm, the first ultraviolet irradiation lamp group (19) and the second ultraviolet irradiation lamp group (20) include ultraviolet irradiation lamp tubes evenly arranged at the top and bottom, and the distance between the upper and lower ultraviolet irradiation lamp tubes is 200-300 mm; the stretching ratio of the first stretching roller (15) and the second stretching roller (16) is 2-5, and the stretching ratio of the third stretching roller (17) and the fourth stretching roller (18) is 2-4. 2. The device for preparing polypropylene foamed board by irradiation chain extension modification according to claim 1 is characterized in that the diameter of the first-stage twin-screw extruder (2) is 40 mm, the aspect ratio is 48:1, the outlet hole diameter of the strip mold (3) is 5 mm, and the screw speed is 100-400 rpm; the feeding device (6) is a pair of traction rollers. 3. The device for preparing polypropylene foamed board by irradiation chain extension modification according to claim 1 is characterized in that the second-stage supercritical foaming twin-screw extruder (7) has a diameter of 52 mm, an aspect ratio of 42:1, a screw speed of 200-300 rpm, a lead of the threaded element at the feed port of 2-3 times the screw diameter, and a steam injection port is provided at a position where the aspect ratio of the screw of the extruder is 30. 4. The device for preparing polypropylene foamed board by irradiation chain extension modification according to claim 1 is characterized in that the diameter of the third-stage single screw extruder (9) is 120 mm, the aspect ratio is 32:1, and the screw speed is 5-30 rpm. 5. The device for preparing polypropylene foamed board by irradiation chain extension modification according to claim 1, characterized in that the foamed board mold (11) has a thickness of 5-10 mm and a width of 300-600 mm. 6. The method for preparing a polypropylene foamed board according to any one of claims 1 to 5, characterized in that it comprises the following steps: (1) Raw material mixing First, polypropylene and chain extender are put into a high-speed mixer (1) according to a certain proportion, the temperature of the high-speed mixer (1) is set to 75-80° C., the stirring time is 5 minutes, and then the auxiliary chain extender is added, and the stirring is continued for 5 minutes; (2) Stretch chain extension The mixture obtained in step (1) is added to a first-stage twin-screw extruder (2), wherein the temperatures of the screw region of the first-stage twin-screw extruder (2) are 40°C, 100°C, 160°C, 180°C, 190°C, 190°C, 180°C, and 170°C in sequence. The material strip extruded from the material strip mold (3) is first cooled by an air cooling device (4), and then irradiated and stretched by a stretching ultraviolet irradiation device (5). The material strip is stretched and folded multiple times on two sets of parallel rollers in the first chain extension and modification section and the second chain extension and modification section. The stretching ultraviolet irradiation device (5) irradiates ultraviolet light while stretching the material strip. The coupling effect of ultraviolet irradiation and chain extender causes the polypropylene molecular chain to deaminate rapidly, generating a large number of macromolecular free radicals. These free radicals combine with each other to form a long branched structure on the long chain of the polypropylene. At the same time, the chain orientation of the polypropylene molecular chain during the stretching process can effectively inhibit the breakage of the β chain, thereby preventing the degradation of the polypropylene molecular chain, thereby achieving efficient chain extension and modification; (3) Steam injection and mixing The polypropylene material strips after chain extension and modification in step (2) are fed to the feeding port of the second-stage supercritical foaming twin-screw extruder (7) through the traction effect of the conveying roller in the feeding device (6), and the temperature settings of the second-stage supercritical foaming twin-screw extruder from the feeding port to the outlet are 150°C, 210°C, 210°C, 210°C, 205°C, 195°C, 190°C, and 190°C in sequence, and the screw speed is 200-300rpm; at the same time, supercritical fluid _CO2 is injected into the extruder through the steam injection port, and the injection amount of _CO2 is controlled by a flow control valve to be 5-10% of the mass of the polypropylene, and under the mixing and shearing action of the screw, the polypropylene and _CO2 are mixed into a uniform melt; (4) Extrusion foaming The melt mixed by the second-stage supercritical foaming twin-screw extruder (7) enters the feeding port of the third-stage single-screw extruder (9) through the transition flow channel (8). The screw of the third-stage single-screw extruder includes a feeding section, a first compression section, a first metering section, a pressure reduction section, a second compression section and a second metering section. The temperatures of each section are 150° C., 180° C., 190° C., 180° C., 170° C. and 150° C., respectively. The temperature of the melt pump (10) is 150° C., the temperature of the foaming plate mold (11) is 155° C., the pressure before and after the melt pump are 8 MPa and 10 MPa, respectively. After the melt passes through the foaming plate mold, the pressure is released and the bubbles grow. The polypropylene melt modified by chain extension has a high strength, and gas molecules will not escape and the pores will not collapse. The pore morphology is maintained, and the foaming ratio is 8-15 times. (5) Shape cutting The foamed plate is cooled and shaped by a flattening and shaping device (12), and is then pulled and cut to obtain a foamed plate. 7. The method for preparing a polypropylene foamed plate according to claim 6, characterized in that the chain extender used is benzophenone, the auxiliary chain extender is trimethylolpropane triacrylate or pentaerythritol triacrylate, the mass content of the chain extender is 0.2%-1.0%, and the content of the auxiliary chain extender is 1%-2%. 8. The method for preparing a polypropylene foamed board according to claim 7, characterized in that the first chain extension and modification section and the second chain extension and modification section are heated by internally arranged radiation heating lamps, the heating temperature is 150-200°C, and the ultraviolet radiation dose of the first ultraviolet radiation lamp group (19) and the second ultraviolet radiation lamp group (20) is 2000mj/ ^cm2 to 10000mj/ ^cm2 .