CN114437397A

CN114437397A - Foaming device of foaming beads, production method and application thereof, and foaming beads

Info

Publication number: CN114437397A
Application number: CN202011112536.4A
Authority: CN
Inventors: 徐耀辉; 吕明福; 郭鹏; 张师军; 侴白舸; 高达利; 尹华; 王宇飞; 白弈青; 杨庆泉
Original assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petroleum and Chemical Corp
Current assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petroleum and Chemical Corp
Priority date: 2020-10-16
Filing date: 2020-10-16
Publication date: 2022-05-06

Abstract

The invention relates to the field of high polymer material processing, and discloses a foaming device of foaming beads, a production method and application of the foaming device and the foaming beads. The foaming device comprises the following equipment: the device comprises a weighing bin 1, an auxiliary agent preparation kettle 2, a loop reactor 3, an axial flow pump 4, a supercritical foaming agent storage tank 5, a supercritical foaming agent generator 6, a foaming agent storage tank 7 and at least one reaction kettle 9. The foaming device can obviously reduce the process temperature and pressure in the foaming kettle, shortens the impregnation saturation time, effectively reduces the equipment cost and the production energy consumption, shortens the production period of a single kettle, improves the production efficiency and effectively reduces the production cost of the polymer foaming beads.

Description

Foaming device of foaming beads, production method and application thereof, and foaming beads

Technical Field

The invention relates to the field of processing of high polymer materials, in particular to a foaming device of foaming beads, a production method and application thereof, and the foaming beads prepared by the method.

Background

The development and application of the light weight material have very important significance for reducing energy consumption and carbon emission. An epp (expanded polypropylene) member overmolded with kettle-expanded polypropylene beads may be used instead of the conventional plastic article. The EPP beads belong to environment-friendly materials, have excellent mechanical, heat-resistant, shock-resistant and shock-absorbing, corrosion-resistant and other properties, and have the greatest advantage that the free formability can produce products with complex geometric structures and high dimensional precision. Can be widely applied to the fields of automobiles, cushion packaging, buildings, sports, and the like.

CN103788502A, CN103665583A, CN103665567A, CN103665420A and the like all adopt a tank method (also called batch tank method) to prepare epp (expanded polypropylene) beads. As can be seen from reports, in the conventional EPP production device and method, polypropylene, color master and other functional additives are blended to prepare spherical particles with the diameter of about 1mm, and then the particles are soaked and saturated in supercritical carbon dioxide in a liquid-phase dispersion system, and then are quickly decompressed and discharged to obtain foamed particles with a large amount of uniform and fine cells dispersed inside. And then the foamed particles are subjected to secondary molding in a mold to obtain products with different shapes. The key technical index lies in the quality control of the EPP beads. The beads should be smooth on the surface, uniform in size, and free of adhesion. The foaming multiplying power, the diameter of the foam holes and the closed hole rate are all adjustable within a certain range. In order to achieve the above performance smoothly, a special kettle pressure foaming device is required to be used for reaction under the control of process conditions such as precise process temperature and pressure, and in order to avoid uneven foaming of EPP beads caused by temperature fluctuation and even blocking and locking of the EPP beads in a liquid phase dispersion system, a relatively stable temperature rise speed is required to be set to avoid temperature runaway. After the process temperature is reached, the process can be realized by soaking the gas foaming agent for a long time under higher pressure, so that the kettle pressure foaming process in the prior production is intermittent production with long reaction time, which causes quick equipment loss and depreciation, large energy consumption, long production period of a single kettle, low production efficiency and high production cost.

Disclosure of Invention

The invention aims to overcome the defects that the processes for producing the polymer expanded beads in the prior art are all intermittent production, the expansion period is long, the production efficiency is low, and the foaming process has higher requirements on pressure and temperature, the device used for foaming has large load, high production energy consumption and the like, provides a foaming device of foaming beads, a production method and application thereof, and the foaming beads prepared by the method, the foaming device comprises a loop reactor, after the processing of the loop reactor, the thermoplastic polymer microparticles, the foaming medium, the foaming auxiliary agent, the supercritical foaming agent and the like can form a solid-liquid mixture which is uniformly mixed, the process temperature and pressure reduction in a foaming kettle are obviously reduced, the impregnation saturation time is shortened, the equipment cost and the production energy consumption are effectively reduced, the single kettle production period is shortened, the production efficiency is improved, and the production cost of the polymer foaming beads is effectively reduced.

In order to achieve the above object, a first aspect of the present invention provides an expansion device for producing expanded beads, characterized in that the device comprises: the system comprises a weighing bin 1, an auxiliary agent preparation kettle 2, a loop reactor 3, an axial flow pump 4, a supercritical foaming agent storage tank 5, a supercritical foaming agent generator 6, a foaming agent storage tank 7 and at least one reaction kettle 9;

the loop reactor 3 is provided with a material inlet, a material outlet, a gas phase inlet and a gas phase outlet, the material inlet is connected with a discharge port of the weighing bin 1 and a discharge port of the auxiliary agent preparation kettle 2, the material outlet is connected with a feed port of at least one reaction kettle 9, the gas phase inlet is connected with a discharge port of the supercritical foaming agent storage tank 5, and the gas phase outlet is connected with a feed port of the foaming agent storage tank 7;

the axial flow pump 4 is connected with the loop reactor 3 and is used for uniformly mixing materials under the dipping of the supercritical foaming agent;

the supercritical foaming agent storage tank 5, the supercritical foaming agent generator 6 and the foaming agent storage tank 7 are connected in sequence.

A second aspect of the invention provides a process for producing expanded beads, characterized in that it is carried out in an expansion device as described above.

A third aspect of the present invention provides a method for producing expanded beads, characterized in that the method comprises the steps of:

(1) adding thermoplastic polymer microparticles from a weighing bin 1 and a foaming auxiliary agent solution and/or suspension from an auxiliary agent preparation kettle 2 into a loop reactor 3, and mixing to obtain a mixed material;

(2) adding a supercritical foaming agent from a supercritical foaming agent storage tank 5 into the loop reactor 3, and mixing the supercritical foaming agent with the mixed material under the action of an axial flow pump 4 to obtain a multiphase mixture;

(3) conveying the multiphase mixture into a reaction kettle 9 under the condition of stirring, and carrying out impregnation foaming;

(4) discharging and cooling to obtain the expanded beads.

The fourth aspect of the present invention provides expanded beads obtained by the above production method.

In a fifth aspect, the invention provides the use of a foaming apparatus or production process as described above for foaming a polymer.

Through the technical scheme, the foaming device of the foaming beads, the production method and the application thereof, and the foaming beads prepared by the method have the following beneficial effects:

1. in the foaming device provided by the invention, the loop reactor is arranged among the auxiliary agent preparation kettle, the weighing bin and the foaming reaction kettle, and in the loop reactor, a solid-liquid mixture consisting of thermoplastic polymer microparticles, a foaming medium and a foaming auxiliary agent can be fully and uniformly mixed with the supercritical foaming agent, so that a solid-liquid homogeneous mixture can be formed, and the heat and mass transfer effects are greatly improved. The use of foaming auxiliary agents can be effectively reduced, the stirring speed and the stirring time of the reaction kettle are reduced, the process temperature rising speed can be properly accelerated, and the foaming period is shortened.

2. In the invention, the adopted loop reactor has high production capacity per unit volume and large heat transfer area. The jacket of the loop reactor is used for preheating the multiphase mixed material, and compared with the method that the multiphase mixed material is directly fed into an intermittent reaction kettle at normal temperature, the heating speed is higher, and the energy consumption is lower.

3. In the present invention, the thermoplastic composition microparticles and the supercritical blowing agent move together at a high speed in the loop reactor at a certain linear velocity, so that the reaction speed of the supercritical blowing agent permeating into the solid thermoplastic composition microparticles is greatly increased, and a large amount of the blowing agent permeates into the thermoplastic resin. The thermoplastic composition microparticles after being swelled by the foaming agent can reach a saturated state quickly after being added into the reaction kettle, so that the impregnation time of the foaming procedure can be greatly shortened, and the production efficiency is improved.

Drawings

FIG. 1 is a schematic view of a process flow for preparing polymer expanded beads by expanding microparticles of a thermoplastic composition by an expansion device according to the present invention;

FIG. 2 is a schematic view of a single loop reactor used in example 1 of the present invention.

Description of the reference numerals

1: a weighing bin; 2: an auxiliary agent preparation kettle; 3: a loop reactor; 4: an axial flow pump; 5: a supercritical gas storage tank; 6: a supercritical gas generation device; 7: a foaming agent storage tank; 8: a compressed air pressure supplementing tank; 9-1: a reaction kettle; 9-2: a reaction kettle; 9-3: a reaction kettle; 9-4: a reaction kettle; 10-1: a material collecting tank; 10-2: a material collecting tank; 10-3: a material collecting tank; 10-4: a material collecting tank.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For numerical ranges, each range between its endpoints and individual point values, and each individual point value can be combined with each other to give one or more new numerical ranges, and such numerical ranges should be construed as specifically disclosed herein.

The invention provides, in a first aspect, a foaming apparatus for producing expanded beads, characterized by comprising: the system comprises a weighing bin 1, an auxiliary agent preparation kettle 2, a loop reactor 3, an axial flow pump 4, a supercritical foaming agent storage tank 5, a supercritical foaming agent generator 6, a foaming agent storage tank 7 and at least one reaction kettle 9;

In the invention, a loop reactor is arranged among an auxiliary agent preparation kettle, a weighing bin and a foaming reaction kettle in the foaming device, and a solid-liquid mixture consisting of thermoplastic polymer microparticles, a foaming medium and a foaming auxiliary agent in the loop reactor can be fully and uniformly mixed with a supercritical foaming agent to form a solid-liquid homogeneous mixture, thereby greatly improving the heat and mass transfer effects. The use of foaming auxiliary agents can be effectively reduced, the stirring speed and the stirring time of the reaction kettle are reduced, the process temperature rising speed can be properly accelerated, and the foaming period is shortened.

In the invention, the supercritical foaming agent is in a supercritical state in the foaming reaction kettle and the loop reactor, and the supercritical foaming agent has unique physical properties, low viscosity, high density, good flowing, mass transfer, heat transfer and dissolving performances, and can form a uniformly mixed solid-liquid homogeneous mixture with a solid-liquid mixture containing thermoplastic polymer microparticles, a foaming medium and a foaming auxiliary agent.

In the invention, thermoplastic polymer microparticles from a weighing bin 1, a foaming auxiliary agent from an auxiliary agent preparation kettle 2 and softened water are mixed in a loop reactor to obtain a mixed material, the mixed material circularly flows at a high speed in the loop reactor under the action of an axial flow pump 4 under the impregnation of a supercritical foaming agent from a supercritical foaming agent storage tank 5, so that the thermoplastic polymer microparticles and the foaming auxiliary agent are mixed more uniformly, and part of the foaming agent enters the thermoplastic polymer microparticles to swell the thermoplastic polymer microparticles. The thermoplastic polymer microparticles swelled by the foaming agent can reach a saturated state quickly after being added into the reaction kettle, so that the impregnation time of the foaming process can be greatly shortened, and the production efficiency is improved.

In the present invention, the number of reaction vessels is mainly determined by the size of the loop reactor, the size of the reaction vessel, and the space available in the foaming plant. In the present invention, the number and volume of the loop reactor and the reaction tank are not limited. A plurality of reaction kettles 9 may be provided as needed, for example, as shown in fig. 1, the foaming apparatus includes 4 reaction kettles, i.e., reaction kettle 9-1, reaction kettle 9-2, reaction kettle 9-3, and reaction kettle 9-4.

In the invention, a discharge valve is arranged on a discharge pipe line at the lower part of the reaction kettle 9.

According to the invention, the device also comprises at least one material collecting tank 10, wherein the material collecting tank 10 is connected with the discharge hole of the reaction kettle 9 and is used for collecting the foaming beads.

In the invention, according to actual needs, a plurality of material collecting tanks 10 can be arranged, for example, as shown in fig. 1, the foaming device comprises 4 material collecting tanks, namely a material collecting tank 10-1, a material collecting tank 10-2, a material collecting tank 10-3 and a material collecting tank 10-4. The material collecting tank 10 corresponds to the reaction kettle 9.

According to the invention, the weighing silo 1 is used for metering thermoplastic polymer microparticles.

According to the invention, the auxiliary preparation vessel 2 is used to prepare the foaming auxiliaries required for producing the expanded beads as a solution and/or suspension.

According to the invention, the interior of the auxiliary preparation kettle 3 comprises a stirring device.

In one embodiment of the present invention, the auxiliary preparation kettle 3 is connected with a solid feeder and a softened water pipeline.

According to the invention, the loop reactor 3 is a single loop reactor and/or a double loop reactor.

In the present invention, the loop reactor is a closed loop tubular reactor. The working principle is that reaction materials circularly flow in the reactor, and mass transfer and heat transfer are realized in the flowing process. It can be operated continuously or intermittently. The complex inner components can be arranged in the pipe, or the complex inner components can be not arranged.

According to the invention, said loop reactor 3 comprises at least 4 straight pipes, preferably 6 to 10 straight pipes; the straight pipes are connected through bent pipes and form a saddle-shaped closed loop.

According to the invention, the outside of the straight pipe is provided with a jacket for controlling the temperature of the loop reactor.

In the invention, a cooling water inlet and a cooling water outlet are respectively arranged at the upper part and the lower part of the jacket, and the temperature of the loop reactor is kept at the working temperature by controlling the temperature of the jacket water.

According to the invention, a stirring device is arranged inside the reaction kettle 9.

According to the invention, the reaction vessel 9 further comprises a heater and a temperature control instrument.

According to the invention, the device also comprises a compressed air pressure supplementing tank 8, wherein the compressed air pressure supplementing tank 8 is connected with the reaction kettle 9 and is used for maintaining the pressure in the reaction kettle 9 unchanged during discharging, so that the uniform and stable quality of the EPP beads is ensured.

In the invention, a gas phase outlet of the loop reactor 3 is connected with a feeding hole of the foaming agent storage tank 7 after drying treatment.

In the present invention, the apparatus further comprises collecting, washing and drying means.

(4) and discharging and cooling to obtain the expanded beads.

In the production method of the expanded beads, the thermoplastic polymer microparticles and the foaming auxiliary agent solution and/or suspension are mixed to obtain a mixed material, and the mixed material is mixed with the supercritical foaming agent in the loop reactor 3 under the action of the axial flow pump 4 to obtain a multiphase mixture, so that the heat and mass transfer effects can be greatly improved. The use of foaming auxiliary agents can be effectively reduced, the stirring speed and the stirring time of the reaction kettle are reduced, the process temperature rising speed can be properly accelerated, and the foaming period is shortened.

According to some embodiments of the invention, step 1) comprises the following specific steps: the auxiliary agent is weighed and then added into an auxiliary agent preparation kettle 2 containing softened water, the kettle is started to stir to obtain foaming auxiliary agent solution and/or suspension, and the foaming auxiliary agent solution and/or suspension is added into a loop reactor 3. Meanwhile, the thermoplastic polymer microparticles in the weighing bin 1 are metered by a weighing module and then added into the loop reactor 3 with the jacket preheated to the working temperature by starting a heater.

In the present invention, the thermoplastic polymer microparticles can be prepared according to the following method: starting from thermoplastic polymers, the thermoplastic polymer can be extruded into strands through one or more dies of a twin-screw or single-screw extruder and cut to give thermoplastic polymer microparticles. Preferably, the thermoplastic polymer microparticles are obtained using an underwater microparticle pelletizing system. The process comprises blending the base resin, antistatic agent and antioxidant with a high-speed mixer, extruding with a twin-screw extruder, hot-cutting, and cutting into fine particles in water at 70 deg.C or below, preferably 65 deg.C or below, more preferably 45-55 deg.C to obtain particles with length/diameter ratio of 0.5-2.0, preferably 0.8-1.3, more preferably 0.9-1.1, and average weight of 0.1-20mg, preferably 0.2-10mg, more preferably 1-3 mg. The average weight is the average of 200 randomly selected microparticles.

In the present invention, the base resin, the antistatic agent and the antioxidant may be used in amounts conventionally used in the art.

According to the present invention, in the step (1), the foaming aid includes a dispersion medium, a surfactant, a dispersant, and a dispersion enhancer.

In the present invention, any component in which thermoplastic resin microparticles are dispersed without dissolving the microparticles may be used as the dispersion medium. The dispersion medium may be water, ethylene glycol, glycerol, methanol, ethanol or a mixture thereof. Preferably an aqueous based dispersion medium, more preferably water, most preferably deionized water. 10m relative to the volume of the loop reactor³The amount of the dispersion medium is 0.1-2m³Preferably 0.3 to 1m³。

In order to facilitate the dispersion of the microparticles in the dispersion medium, a surfactant is used, which may be stearic acid, sodium dodecylbenzenesulfonate, quaternary ammonium compounds, lecithin, amino acids, betaine, fatty acid glycerides, sorbitan fatty acids, polysorbates, preferably sodium dodecylbenzenesulfonate, which is an anionic surfactant, and is used in an amount of generally 0.01 to 0.2 parts by weight, preferably 0.02 to 0.1 parts by weight, per 100 parts by weight of the thermoplastic polymer microparticles.

In order to prevent the thermoplastic polymer microparticles from melt-adhering to each other during the foaming step, it is desirable to add a dispersant which is a fine organic or inorganic solid to the dispersion medium. For convenience of handling, it is preferable to use an inorganic powder. The dispersant may be natural or synthetic clay minerals (e.g., kaolin, mica, magnesium aluminum garnet and clay), alumina, titanium dioxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, silica, zinc borate and iron oxide, with kaolin being preferred. The dispersant is generally used in an amount of 0.01 to 0.3 parts by weight, preferably 0.02 to 0.1 parts by weight, per 100 parts by weight of the thermoplastic polymer microparticles.

In order to improve the dispersion efficiency of the dispersant, i.e., to reduce the amount of the dispersant while retaining its function of preventing the fusion bonding of microparticles, a dispersion-enhancing agent may be added to the dispersion medium. The dispersion enhancer is an inorganic compound having a solubility of 1mg in 100mL of water at 40 ℃ and providing a divalent or trivalent anion or cation. Examples of the dispersion-enhancing agent include magnesium nitride, magnesium nitrate, aluminum phosphate, magnesium sulfate, aluminum nitride, aluminum nitrate, aluminum sulfate, ferric chloride, ferric sulfate and ferric nitrate, with aluminum sulfate being preferred. The dispersion-enhancing agent is used in an amount of generally 0.001 to 0.1 part by weight, preferably 0.005 to 0.03 part by weight, per 100 parts by weight of the thermoplastic polymer microparticles.

The blowing agent may be any physical blowing agent which can give a supercritical state, and it may be used alone or in combination of two or more. Carbon dioxide and nitrogen are preferred blowing agents for the present invention.

According to some embodiments of the invention, step (2) comprises the following specific steps: the foaming agent in a supercritical state is injected into the loop reactor 3 from a supercritical foaming agent storage tank 5, and is mixed with the thermoplastic polymer microparticles and the auxiliary agent solution and/or suspension in the loop reactor 3 under the action of the axial flow pump 4, and the formed multiphase mixture circulates in the loop reactor 3 for a period of time at a certain linear speed, so that the materials are uniformly dispersed, and the thermoplastic polymer microparticles are swelled.

In the invention, under the action of the axial flow pump 4, the multiphase mixture moves at a high speed at a certain linear speed, so that the reaction speed of the supercritical foaming agent permeating into the solid thermoplastic polymer microparticles is greatly increased, and a large amount of foaming agent permeates into the thermoplastic resin. The thermoplastic polymer microparticles swollen by the foaming agent can reach a saturated state quickly after being added into the reaction kettle, so that the impregnation time of the foaming procedure can be greatly shortened, and the production efficiency is improved.

According to the invention, the operating temperature of the loop reactor 3 is between 50 and 120 ℃, preferably between 75 and 100 ℃; the working pressure is 6.3-16MPa, preferably 7-10 MPa.

According to the invention, in step (2), the multiphase mixture circulates in the loop reactor 3 at a linear velocity of between 1 and 8m/s, preferably between 2 and 6m/s, for a period of between 5 and 60min, preferably between 10 and 30 min.

According to some embodiments of the invention, step (2) comprises the following specific steps: adding a certain amount of softened water into at least one reaction kettle 9, starting a stirring device of the corresponding reaction kettle, starting a material outlet of the loop reactor 3, simultaneously starting a supercritical foaming agent storage tank 5 for pressure compensation when the loop reactor 3 discharges materials, and keeping the foaming agent in the loop reactor 3 in a supercritical state. The mixed material can be discharged completely at the same time or a part of it can be discharged as required, the rest of the material continues to circulate in the loop reactor 3. The discharged materials are respectively added into at least one reaction kettle 9. And starting a heater to heat the corresponding reaction kettle to the foaming temperature, and setting the corresponding reaction kettle to the foaming pressure through a pressure regulating valve.

According to the invention, in step (3), the rotation speed of the stirring is 25 to 80rpm, preferably 35 to 50 rpm.

According to the invention, the impregnation foaming conditions comprise that the impregnation temperature is from the melting point Tm-9 ℃ to Tm +9 ℃ of the thermoplastic polymer, and the heat preservation is carried out for 1-60 min.

According to the invention, the conditions of the impregnation foaming comprise: the dipping temperature is the melting point Tm-5 ℃ Tm +5 ℃ of the thermoplastic polymer, and the temperature is kept for 3-20 min.

According to the invention, the thermoplastic polymer is a polyolefin, preferably polypropylene.

According to the invention, the method further comprises: and (4) opening the compressed air pressure supplementing tank 8 to maintain the pressure of the reaction kettle 9 constant while discharging in the step (4).

According to some embodiments of the invention, step (4) comprises the following specific steps: according to the requirements of different foaming bead products on foaming multiplying power and foam structures, after continuously stirring for a certain time at a foaming temperature and under a foaming pressure, respectively or simultaneously opening a discharge valve at the bottom of at least one reaction kettle 9 to start discharging, and simultaneously starting a compressed air pressure supplementing tank 8 to supplement pressure into the reaction kettle and discharge the materials in at least one reaction kettle 9 into a corresponding at least one material collecting tank 10, so that the foaming beads meeting different production requirements can be obtained simultaneously or sequentially. The collection, washing and drying of the expanded beads are well known methods in the art and will not be repeated here.

According to some embodiments of the invention, step (3) and step (4) are performed simultaneously. And (3) repeating the work of the step (1) and the step (2). And (3) injecting the multiphase mixture in the step (2) into at least one reaction kettle 9 after discharging, and repeating the step (3) and the step (4).

The method and apparatus of the present invention are further described with reference to FIG. 1.

The device for foaming beads comprises: the system comprises a weighing bin 1, an auxiliary agent preparation kettle 2, a loop reactor 3, an axial flow pump 4, a supercritical foaming agent storage tank 5, a supercritical foaming agent generator 6, a foaming agent storage tank 7 and four reaction kettles 9-1, 9-2, 9-3 and 9-4;

a material inlet, a material outlet, a gas phase inlet and a gas phase outlet are arranged on the loop reactor 3, the material inlet of the loop reactor 3 is connected with a discharge port of the weighing bin 1 and a discharge port of the auxiliary agent preparation kettle 2, the material outlet of the loop reactor 3 is respectively connected with feed ports of the reaction kettles 9-1, 9-2, 9-3 and 9-4, the gas phase inlet of the loop reactor 3 is connected with a discharge port of the supercritical foaming agent storage tank 5, and the gas phase outlet of the loop reactor 3 is connected with a feed port of the foaming agent storage tank 7;

The discharge ports of the reaction kettles 9-1, 9-2, 9-3 and 9-4 are respectively connected with material collection devices 10-1, 10-2, 10-3 and 10-4.

The present invention will be described in detail below by way of examples.

The following examples and comparative examples of the starting materials and the equipment and equipment used included:

kaolin: carbofuran, ACROS, analytically pure;

sodium dodecylbenzenesulfonate: the Tianjin Guangfu Fine chemical research institute is analytically pure;

aluminum sulfate: tianjin Guangfu technology development Limited company, analytically pure;

softening water: beijing chemical research institute of petrochemical corporation of China;

polypropylene: w331, polypropylene random copolymer, melting point 146 ℃, Singapore TPC.

All other starting materials are commercially available.

The EPP bead related data in the examples were obtained according to the following test methods:

1. expanded bead density test method: the apparent densities of the polypropylene base resin and of the EPP expanded beads were obtained by draining using the density attachment of a Satorius balance, measured according to the method described in the national Standard GB/T1033.1-2008. The expansion ratio of the obtained EPP expanded beads was calculated by the formula, where b represents the expansion ratio, ρ 1 represents the density of the polypropylene base resin, and ρ 2 represents the apparent density of the expanded material.

2. Open-closed porosity of EPP beads: the test was carried out using an open-closed porosity tester ULTRAFOAM 1200e manufactured by Quantachrome instruments, USA. The test method comprises the following steps: according to GB/T10799-2008.

Preparation example

Preparation of polypropylene microparticles:

taking W331 as a raw material, extruding the raw material into a wire by a double-screw extruder, and cutting the wire to obtain the polypropylene microparticles. The polypropylene microparticles were obtained using an underwater microparticle pelletizing system. Specifically, the method comprises the following steps: 1000kg of base resin, 5kg of antistatic agent ATMER129, 2kg of antioxidant 1010 and 1kg of antioxidant 168 were blended by a high-speed mixer, extruded by a twin-screw extruder, hot-cut, and then introduced into 68 ℃ water to cut fine particles so that the length/diameter ratio of each particle was 1.2 and the average weight was 2 mg.

Example 1

The foaming device comprises, as shown in fig. 1: the system comprises a weighing bin 1, an auxiliary agent preparation kettle 2, a loop reactor 3, an axial flow pump 4, a supercritical foaming agent storage tank 5, a supercritical foaming agent generator 6, a foaming agent storage tank 7 and four reaction kettles 9-1, 9-2, 9-3 and 9-4;

the loop reactor 3 is provided with a material inlet, a material outlet, a gas phase inlet and a gas phase outlet, and the material inlet of the loop reactor 3 is connected with the discharge port of the weighing bin 1 and the discharge port of the auxiliary agent preparation kettle 2.

The material outlet of the loop reactor 3 is connected with the feed inlets of the reaction kettles 9-1, 9-2, 9-3 and 9-4 respectively, the reaction kettle body is provided with an electric heater and a temperature control instrument, the reaction kettles 9-1, 9-2, 9-3 and 9-4 are all provided with stirring devices, and the discharge pipelines at the lower parts of the reaction kettles 9-1, 9-2, 9-3 and 9-4 are provided with discharge valves.

The discharge ports of the reaction kettles 9-1, 9-2, 9-3 and 9-4 are respectively connected with material collecting tanks 10-1, 10-2, 10-3 and 10-4.

A gas phase inlet of the loop reactor 3 is connected with a discharge hole of the supercritical foaming agent storage tank 5, and a gas phase outlet of the loop reactor 3 is connected with a feed hole of the foaming agent storage tank 7 after being dried;

the axial flow pump 4 is connected with the loop reactor 3, and the polypropylene microparticles, the foaming auxiliary agent and softened water are mixed to obtain slurry, so that the materials circularly flow at a high speed under the dipping of the supercritical foaming agent;

the feed inlet of the supercritical foaming agent storage tank 5 is connected with the discharge outlet of the supercritical foaming agent generator 6, and the feed inlet of the supercritical foaming agent generator 6 is connected with the discharge outlet of the foaming agent storage tank 7.

In this embodiment, 10m is selected³The single loop reactor of (2) as shown in figure. The inner diameter of the pipe is 600mm, 6 straight pipes are arranged, each straight pipe is 5m high, and the straight pipes are connected into a saddle-shaped closed loop through 6 bent pipes. In order to prevent the polypropylene microparticles or the foaming aid from sticking to the inner wall, the inner wall of the pipe is polished. The straight pipe part of the loop reactor is provided with a jacket, the outer diameter of the jacket is 690mm, the upper part and the lower part of the jacket are provided with jacket water inlets and outlets, and the temperature of the jacket water is controlled to keep the temperature of the loop reactor at the working temperature. The lower part of the loop reactor is provided with an axial flow pump which enables the mixed material of the polypropylene microparticles, the foaming auxiliary agent and the supercritical foaming agent to directionally and circularly flow at a certain speed.

In this embodiment, 4 pieces of 0.2m are selected³The reaction kettle is provided with an electric heater and a temperature control instrument on the kettle body, a stirring device is arranged in the reaction kettle, and a discharge valve is arranged on a discharge pipe line at the lower part of the reaction. The reaction kettle is connected with an independent material collecting tank.

Example 2

This example provides a method for preparing EPP beads using the kettle pressure foaming apparatus of example 1, comprising the steps of:

1) 10g of surfactant sodium dodecyl benzene sulfonate, 100g of dispersant kaolin and 7g of dispersion reinforcing agent aluminum sulfate are weighed and added into an auxiliary preparation kettle 2 containing 200L of softened water, the kettle is opened to stir, a foaming auxiliary suspension is obtained by stirring, and the auxiliary suspension is added into a loop reactor 3. Meanwhile, 250kg of the polypropylene W331 microparticles in the weighing bin 1 are measured by a weighing module and then added into the loop reactor 3 with a heater started to preheat a jacket to 80 +/-2 ℃.

2) Supercritical carbon dioxide is injected into the loop reactor 3 from a supercritical foaming agent storage tank 5, and is mixed with the polypropylene microparticles and the foaming auxiliary suspension in the loop reactor 3 under the action of the axial flow pump 4, so that the formed multiphase mixture circulates in the loop reactor 3 at a linear speed of 3m/s for 15 minutes, the materials are uniformly dispersed, and the polypropylene microparticles are swelled. The working temperature of the loop reactor is adjusted to 80 +/-2 ℃, and the working pressure is 7.5 +/-0.1 MPa.

3) Adding 40L of softened water into the reaction kettles 9-1, 9-2, 9-3 and 9-4, starting a stirring device of the corresponding reaction kettle at a rotating speed of 40rpm, starting a discharge hole of the loop reactor 3, simultaneously starting a supercritical foaming agent storage tank 5 for pressure compensation when the loop reactor 3 discharges, and maintaining the supercritical state of the foaming agent in the loop reactor 3. Simultaneously, discharging all the mixed materials, and averagely adding the mixed materials into reaction kettles 9-1, 9-2, 9-3 and 9-4. Heaters of the reaction kettles 9-1 and 9-2 are started to heat the corresponding reaction kettles to 149 ℃ within 30 minutes, and meanwhile, the pressure in the corresponding reaction kettles is set to be 2.5MPa through a pressure regulating valve. Heaters of the reaction kettles 9-3 and 9-4 are started to heat the corresponding reaction kettles to 146 ℃ within 30 minutes, and meanwhile, the corresponding reaction kettles are set to 2MPa through pressure regulating valves.

4) After the mixture is continuously stirred for 5 minutes at the pressure and the temperature, discharge valves at the bottoms of the reaction kettles 9-1 and 9-3 are opened simultaneously to discharge, and a compressed air pressure supplementing tank 8 is started to supplement pressure into the reaction kettles 9-1 and 9-3 and discharge the materials in the reaction kettles 9-1 and 9-3 to corresponding material collecting pools 10-1 and 10-3 at the same time to simultaneously obtain 25 times of polypropylene foaming beads and 15 times of polypropylene foaming beads. After the mixture is continuously stirred for 15 minutes at the pressure and the temperature, discharge valves at the bottoms of the reaction kettles 9-2 and 9-4 are opened simultaneously to discharge, and the compressed air pressure supplementing tank 8 is started to supplement pressure into the reaction kettles 9-2 and 9-4 and discharge the materials in the reaction kettles 9-2 and 9-4 to corresponding material collecting pools 10-2 and 10-4 at the same time of discharging, so that 30 times of polypropylene foaming beads and 18 times of polypropylene foaming beads can be obtained simultaneously. The EPP beads are cooled by spraying in the discharging process, float on the water surface, and become EPP bead products after collection, washing and drying. The expansion ratio, bead yield and open/closed cell ratio of EPP beads are shown in Table 1. The collection, washing and drying of the expanded beads are well known methods in the art and will not be repeated here.

Example 3

steps 1) and 2) are the same as in example 2, except that: the resulting multiphase mixture was circulated in the loop reactor 3 at a linear velocity of 4m/s for 25 minutes.

3) Adding 40L of softened water into the reaction kettles 9-1, 9-2, 9-3 and 9-4, starting a stirring device of the corresponding reaction kettle at the rotating speed of 35rpm, starting a discharge hole of the loop reactor 3, simultaneously starting a supercritical foaming agent storage tank 5 to supplement pressure when the loop reactor 3 discharges, and maintaining the supercritical state of the foaming agent in the loop reactor 3. Simultaneously, discharging all the mixed materials, and averagely adding the mixed materials into reaction kettles 9-1, 9-2, 9-3 and 9-4. Heaters of the reaction kettles 9-1 and 9-2 are started to heat the corresponding reaction kettles to 149 ℃ within 30 minutes, and meanwhile, the pressure in the corresponding reaction kettles is set to be 2.5MPa through a pressure regulating valve. Heaters of the reaction kettles 9-3 and 9-4 are started to heat the corresponding reaction kettles to 146 ℃ within 30 minutes, and meanwhile, the corresponding reaction kettles are set to 2MPa through pressure regulating valves.

4) After continuously stirring for 4 minutes at the pressure and temperature, simultaneously opening discharge valves at the bottoms of the reaction kettles 9-1 and 9-3 to start discharging, and simultaneously starting the compressed air pressure supplementing tank 8 to supplement pressure into the reaction kettles 9-1 and 9-3 and discharge the materials in the reaction kettles 9-1 and 9-3 to the corresponding material collecting tanks 10-1 and 10-3, so that 27 times of polypropylene expanded beads and 18 times of polypropylene expanded beads can be simultaneously obtained. After the continuous stirring is carried out for 12 minutes under the pressure and the temperature, discharge valves at the bottoms of the reaction kettles 9-2 and 9-4 are opened simultaneously to start discharging, and the compressed air pressure supplementing tank 8 is started to discharge the materials in the reaction kettles 9-2 and 9-4 to the corresponding material collecting tanks 10-2 and 10-4 while supplementing pressure to the reaction kettles 9-2 and 9-4, so that 33 times of polypropylene foaming beads and 20 times of polypropylene foaming beads can be obtained simultaneously. The EPP beads are cooled by spraying in the discharging process, float on the water surface, and become EPP bead products after collection, washing and drying. The expansion ratio, bead yield and open/closed cell ratio of EPP beads are shown in Table 1. The collection, washing and drying of the expanded beads are well known methods in the art and will not be repeated here.

Comparative example 1

This comparative example is illustrative of an EPP expanded bead production apparatus well known in the art. The method comprises the following steps: a reaction kettle, an auxiliary agent preparation kettle, a weighing bin, a foaming agent pressure supplementing tank, a compressed air pressure supplementing tank and a material collecting pool,

wherein, a feed inlet, a discharge outlet, a gas phase inlet and a gas phase outlet are arranged on the reaction kettle, the feed inlet is connected with the auxiliary agent preparation kettle and the discharge outlet of the weighing bin, the gas phase inlet and the gas phase outlet are connected with the air outlets of the foaming agent pressure supplementing tank and the compressed air pressure supplementing tank, and the discharge outlet of the reaction kettle is connected with the material collecting pool;

the kettle pressure foaming device further comprises a solid feeder and a deionized water pipe, wherein a discharge port of the solid feeder and a water outlet of the deionized water pipe are respectively connected with a feed port of the auxiliary agent preparation kettle.

Comparative example 2

This example provides a process for producing EPP beads using the pot pressure foaming apparatus of comparative example 1 at the same material addition amount as in example 2 and the same process temperature and pressure as in reaction pots 9-1 and 9-2, comprising the steps of:

1) weighing 10g of surfactant sodium dodecyl benzene sulfonate, 100g of dispersant kaolin and 7g of dispersion reinforcing agent aluminum sulfate, adding the mixture into an auxiliary agent preparation kettle containing 200L of softened water, uniformly stirring, adding an auxiliary agent suspension into a reaction kettle with the volume of 800L, simultaneously adding polypropylene W331 particles in a weighing bin into the reaction kettle after 250kg of particles are measured by a weighing module, and then adding 120L of softened water;

2) and (3) starting a stirring device in the reaction kettle, introducing carbon dioxide at the rotating speed of 40rpm for pressurization, starting a heater for heating materials, adjusting the kettle pressure, setting the foaming temperature to be 149 ℃, and setting the foaming pressure to be 2.5 MPa.

3) After the reaction kettle is continuously stirred for 1 hour, the temperature is 146 ℃ and the pressure is 2.46 MPa. The rotating speed of the stirring paddle suddenly and rapidly drops to 0, and noises are transmitted from the transmission bearing and the reaction kettle. The material can not be discharged when the blanking valve is opened. And after emergency pressure relief is carried out from a vent hole at the top of the kettle, opening a kettle cover after the reaction kettle is cooled to below 60 ℃. It is found that the mixing of the stirring paddle is not uniform enough due to the excessively high solid content in the kettle, so that the polypropylene microparticles are continuously adhered to the stirring kettle until being agglomerated with the kettle bottom, so that the foaming production fails, and qualified beads are not obtained.

Comparative example 3

This example provides a method for preparing EPP beads using the kettle pressure foaming apparatus of comparative example 1, after determining the charge amount according to the actual production formulation, at the same stirring speed and the same process temperature and pressure of reaction kettles 9-1 and 9-2 as in example 2, comprising the steps of:

1) weighing 30g of sodium dodecyl benzene sulfonate as a surfactant, 500g of kaolin as a dispersing agent and 17g of aluminum sulfate as a dispersion reinforcing agent into an auxiliary agent preparation kettle containing 200L of softened water, uniformly stirring, adding an auxiliary agent suspension into a reaction kettle with the volume of 800L, simultaneously adding 150kg of polypropylene W331 particles in a weighing bin into the reaction kettle after metering by a weighing module, and then adding 180L of softened water;

3) After the reaction kettle is continuously stirred for 1.5 hours, the process temperature is 139 ℃ and the process pressure is 2.5 MPa. After the reaction kettle is saturated and soaked for 30 minutes at constant temperature and constant pressure, a discharge valve at the bottom of the reaction kettle is opened, and a compressed air pressure supplementing tank is opened simultaneously to supplement pressure and discharge materials in the reaction kettle into a material collecting pool. The obtained product is mostly swollen polypropylene microparticles, and the foaming ratio is extremely low. The expansion ratio, bead pass rate and open/close cell ratio of the product are shown in Table 1.

Comparative example 4

This example provides a method for preparing EPP beads using the kettle pressure foaming device of comparative example 1, with the same process temperature and pressure and the same impregnation time of the reaction kettle 9-1 of example 2, after determining the charge amount according to the actual production formula, comprising the steps of:

1) weighing 30g of surfactant sodium dodecyl benzene sulfonate, 500g of dispersant kaolin and 17g of dispersion reinforcing agent aluminum sulfate, adding the mixture into an auxiliary agent preparation kettle containing 200L of softened water, uniformly stirring, adding an auxiliary agent suspension into a reaction kettle with the volume of 800L, simultaneously adding polypropylene W331 particles in a weighing bin into the reaction kettle after measuring 150kg by a weighing module, and then adding 180L of softened water;

2) and (3) starting a stirring device in the reaction kettle, introducing carbon dioxide at the rotating speed of 85rpm for pressurization, starting a heater for heating materials, adjusting the kettle pressure, setting the foaming temperature to be 149 ℃, and setting the foaming pressure to be 2.5 MPa.

3) After the reaction kettle is continuously stirred for 1.5 hours, the process temperature is 149 ℃, and the process pressure is 2.5 MPa. After the reaction kettle is saturated and soaked for 5 minutes at constant temperature and constant pressure, a discharge valve at the bottom of the reaction kettle is opened, and a compressed air pressure supplementing tank is opened simultaneously to supplement pressure and discharge materials in the reaction kettle into a material collecting pool. Most of the obtained products can be seen by naked eyes to have uneven foaming, and a large amount of unfoamed dead particles are doped in the beads. The expansion ratio, bead pass rate and open/close cell ratio of the product are shown in Table 1.

Comparative example 5

This example provides a process operating according to the feed recipe and process conditions for the actual production of 25 times beads using the kettle pressure foaming apparatus of comparative example 1. The method comprises the following steps:

2) starting a stirring device in the reaction kettle, introducing carbon dioxide at the rotating speed of 85rpm for pressurization, starting a heater for heating materials, adjusting the kettle pressure, setting the foaming temperature to be 152 ℃, and setting the foaming pressure to be 3.5 MPa.

3) After the reaction kettle is continuously stirred for 1.5 hours, the process temperature is 152 ℃, and the process pressure is 3.5 MPa. After the reaction kettle is saturated and impregnated for 45 minutes at constant temperature and constant pressure, a discharge valve at the bottom of the reaction kettle is opened, and a compressed air pressure supplementing tank is opened at the same time, so that the materials in the reaction kettle are discharged into a material collecting pool while pressure supplementing is carried out. The obtained product has full and smooth appearance and uniform particle size distribution, and dead particles which are not foamed can not be observed by naked eyes. The expansion ratio, bead pass rate and open/close cell ratio of the product are shown in Table 1.

TABLE 1 Performance index of EPP beads prepared in examples and comparative examples

As can be seen from example 2, with the kettle pressure foaming device in example 1, the foaming material is fed into different reaction kettles after being pretreated by the supercritical foaming agent in the loop reactor, and EPP beads with different foaming ratios and open-close porosity can be obtained at one time by setting different process temperatures, pressures and impregnation times according to actual production needs.

As can be seen from example 3, increasing the time for pretreatment in the loop can further improve the expansion ratio and production quality of the beads, and can further shorten the dipping time in the reactor.

It can be seen from comparative examples 2 and 3 that, by using the kettle pressure foaming device in example 1, the solid-liquid system is mixed more uniformly after the foaming material is pretreated by the supercritical foaming agent in the loop reactor, and compared with the existing device in comparative example 1, less foaming medium and foaming auxiliary agent can be added, and the foaming agent and the polypropylene microparticles can be fully contacted and infiltrated by using a lower stirring speed, so that the raw material cost, the energy consumption cost and the labor intensity are effectively saved.

As can be seen from comparative example 4, with the kettle pressure foaming device of example 1, the temperature of the foaming material after passing through the loop reactor is increased faster and the energy consumption is less after passing through the loop reactor and preheating the foaming material when passing through the loop reactor; meanwhile, the foaming agent permeates into the polypropylene microparticles to a certain degree, so that the impregnation saturation time in the foaming kettle is shorter. Compared with the device in the prior comparative example 1, the device can effectively save energy consumption cost and production period, and improve the qualified yield and product quality of EPP bead products, thereby greatly improving production efficiency.

As can be seen from comparative example 5, if one wants to use the apparatus of the prior art comparative example 1 to produce a product having properties similar to those of the beads obtained in example 2, a higher process temperature and process pressure, and a longer impregnation time are required.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims

1. An expansion device for producing expanded beads, characterized in that it comprises the following means: the system comprises a weighing bin (1), an auxiliary agent preparation kettle (2), a loop reactor (3), an axial flow pump (4), a supercritical foaming agent storage tank (5), a supercritical foaming agent generator (6), a foaming agent storage tank (7) and at least one reaction kettle (9);

the loop reactor (3) is provided with a material inlet, a material outlet, a gas phase inlet and a gas phase outlet, the material inlet is connected with a discharge port of the weighing bin (1) and a discharge port of the auxiliary agent preparation kettle (2), the material outlet is connected with a feed port of at least one reaction kettle (9), the gas phase inlet is connected with a discharge port of the supercritical foaming agent storage tank (5), and the gas phase outlet is connected with a feed port of the foaming agent storage tank (7);

the axial flow pump (4) is connected with the loop reactor (3) and is used for uniformly mixing materials under the dipping of the supercritical foaming agent;

the supercritical foaming agent storage tank (5), the supercritical foaming agent generator (6) and the foaming agent storage tank (7) are connected in sequence.

2. The apparatus according to claim 1, wherein the apparatus further comprises at least one material collection tank (10), the material collection tank (10) being connected to the outlet of the reaction vessel (9) for collecting the expanded beads.

3. The apparatus according to claim 1 or 2, wherein the weighing silo (1) is used for the metering of thermoplastic polymer microparticles;

preferably, the aid preparation tank (2) is used for preparing foaming aids required for producing expanded beads into a solution and/or a suspension;

preferably, the inside of the auxiliary agent preparation kettle (2) comprises a stirring device.

4. The apparatus according to any one of claims 1-3, wherein the loop reactor is a single loop reactor and/or a double loop reactor;

preferably, the loop reactor (3) comprises at least 4 straight pipes, preferably 6 to 10 straight pipes; all the straight pipes are connected through bent pipes and form a saddle-shaped closed loop;

preferably, the outside of the straight pipe is provided with a jacket for controlling the temperature of the loop reactor.

5. The apparatus according to any one of claims 1 to 4, wherein the reaction vessel (9) is internally provided with stirring means;

preferably, the reaction kettle (9) further comprises a heater and a temperature control instrument.

6. The apparatus according to any one of claims 1 to 5, further comprising a compressed air pressure supplement tank (8), the compressed air pressure supplement tank (8) being connected to the reaction vessel (9) for maintaining the pressure in the reaction vessel (9).

7. A process for producing expanded beads, characterized in that it is carried out in an expansion device according to any one of claims 1 to 6.

8. A method for producing expanded beads, characterized in that it comprises the following steps:

(1) adding thermoplastic polymer microparticles from a weighing bin (1) and a foaming auxiliary agent solution and/or a foaming suspension from an auxiliary agent preparation kettle (2) into a loop reactor (3), and mixing to obtain a mixed material;

(2) adding a supercritical foaming agent from a supercritical foaming agent storage tank (5) into the loop reactor (3), and mixing with the mixed material under the action of an axial flow pump (4) to obtain a multiphase mixture;

(3) conveying the multiphase mixture into a reaction kettle (9) under the condition of stirring, and carrying out impregnation foaming;

(4) discharging and cooling to obtain the expanded beads.

9. Production process according to claim 8, wherein the operating temperature of the loop reactor (3) is between 50 and 120 ℃, preferably between 75 and 100 ℃; the working pressure is 6.3-16MPa, preferably 7-10 MPa;

preferably, in step (2), the multiphase mixture circulates in the loop reactor (3) at a linear velocity of 1 to 8m/s, preferably 2 to 6m/s, for a period of 5 to 60min, preferably 10 to 30 min.

10. The production method according to any one of claims 8 or 9, wherein in the step (3), the rotation speed of the stirring is 25 to 80rpm, preferably 35 to 50 rpm;

preferably, the conditions of the impregnation foaming include: the dipping temperature is between the melting point Tm-9 ℃ and Tm +9 ℃ of the thermoplastic polymer, and the heat preservation is carried out for 1-60 min;

more preferably, the conditions for the impregnation foaming include: the dipping temperature is the melting point Tm of the thermoplastic polymer-5 ℃ Tm +5 ℃, and the temperature is kept for 3-20 min;

preferably, the thermoplastic polymer is a polyolefin.

11. The production method according to any one of claims 8 to 10, wherein the method further comprises: and (4) opening the compressed air pressure supplementing tank (8) to maintain the pressure of the reaction kettle (9) constant while discharging.

12. Expanded beads produced by the production method according to any one of claims 8 to 11.

13. Use of the expansion device for the production of expanded beads according to any one of claims 1 to 7 or the process for the production of expanded beads according to any one of claims 8 to 11 for the expansion of polymers.