CN103895146B - A kind of polymer micro foaming product progressive forming apparatus and method - Google Patents

Abstract

The invention provides a continuous molding device and method for polymer microcellular foamed products, the device includes: at least one extruder, at least two sets of counter-pressure foaming molds, at least two compression molding machines, and melt delivery pipelines System and back pressure gas delivery pipeline and control system. The method comprises the steps of forming a foamable polymer melt, mold clamping and back pressure gas controlled injection, foamable melt injection, microcellular foaming and the like. The cell size of the polymer microcellular foamed product of the present invention is micron order, and the cross section of the product is relatively large, and at the same time, continuous production can be carried out, the production efficiency can be improved, and the production cost can be reduced.

Description

A continuous molding device and method for polymer microcellular foamed products

technical field

The invention belongs to the field of polymer material processing, and in particular relates to a polymer microcellular foam molding device and method.

Background technique:

Microcellular foamed polymer material is a new type of foaming material with a cell diameter of micron scale. Its biggest feature is that the cells are small and dense, evenly distributed, with a cell diameter of 0.1-10 μm and a cell density of 109-1015 /cm3. Microporous plastic improves the toughness of the product while reducing the amount of plastic used, and is considered a "new material in the 21st century". Compared with traditional foamed plastics with cell size in millimeters, microcellular foamed polymer materials have more excellent mechanical properties, dimensional stability, thermal stability, dielectric properties, etc., and are widely used in automobiles, aircraft and various transportation equipment. The field has special application value; in addition, it can also be used in food packaging, biomedicine, building materials, home appliances, information engineering and sports equipment, etc.

Although microcellular foamed polymer materials have many excellent properties, their preparation often requires harsh conditions. Usually, in order to increase the nucleation density of bubbles, the melt pressure at the die of the equipment is required to be higher than 10MPa, and the pressure drop rate through the die outlet is greater than 1GPa/s.

CN03817185.6 discloses a method that uses a screw to dissolve gas into the melt to form a homogeneous solution, and then through the axial movement of the screw, the material quickly passes through the nozzle to form a high pressure drop rate to form a large number of cell nuclei. The growth of the cell core in the mold is limited, and the skin layer usually does not foam, but only forms cells in the core. The expansion ratio of this process is usually low, and the weight loss of the general product is controlled below 15%.

US Patent No. 4479914 discloses a method for reverse pressure injection molding of foamed products. The method is to inflate and pressurize the injection mold to prevent the foaming agent in the melt from overflowing the pre-foaming during the injection filling process; during the injection process, the pressure in the mold is kept constant by venting at the same time; after the injection is completed , the remaining pre-pressurized gas is released into the vacuum cavity, so that the pressure in the mold is reduced, and the molten resin foams and fills the mold. In this method, the back pressure gas pressure is generally low, lower than 2MPa, and the purpose is to improve the surface quality of the product. Usually, the expansion ratio of the product is low, and the weight loss of the product is below 15%.

Japanese Patent No.S39-022213 discloses a foam molding method of coreback (coreback), which is to inject the resin melt containing the foaming agent into the mold, and in the uncured state of the foamed resin, Through the retraction of the core, the volume of the mold is enlarged to reduce the pressure in the mold, and the foaming agent in the melt is precipitated to form cells to obtain a foamed product.

CN101914247A discloses a continuous molding device and method for thermoplastic foamed slabs. By connecting the storage cylinders in series behind the extruder, the residence time of the plastic melt containing the foaming agent in the storage cylinders is longer, enabling the The temperature and pressure distribution of the plastic melt containing foaming agent is more uniform, and continuous extrusion and foaming can be realized by switching between two or more storage tanks, which can prepare foamed sheets with uniform quality and large thickness . However, the cells of its products are difficult to reach the micropore scale.

CN103042647A discloses a production method of polypropylene microporous foam thick board, adopts flat foaming equipment to foam the polypropylene mother board, and is characterized in that: the used polypropylene master board has a core structure; The pore structure of the core of the foam master board shortens the path for supercritical carbon dioxide to diffuse into the polypropylene matrix, thereby reducing the saturation time required to reach diffusion equilibrium and significantly improving production efficiency, but this pore structure will inevitably affect the product. overall mechanical properties.

CN1021677840A discloses a method for preparing polymer microcellular foamed materials by supercritical molding and foaming. First, the foaming mold on the molding machine is heated up. After reaching the foaming temperature, the polymer is put into the mold, and the molding machine is closed. The mold is sealed, and the supercritical fluid is filled into the mold. The supercritical fluid swells and diffuses to the polymer, and then the molding machine opens the mold to release the pressure and foam, and then the polymer microcellular foam with small cell size and high cell density can be obtained. Material. In this method, the supercritical fluid still needs 10 minutes to 60 minutes to swell and diffuse to the polymer, and the time required to reach the homogeneous phase is relatively long.

It is difficult to realize the continuous process to prepare microcellular foamed articles with large cross-sections using the aforementioned techniques. The present invention aims to provide an equipment and method for continuously preparing microcellular foamed polymer products. It can not only obtain foamed products with micron-level cell size and larger product cross-section, but also can carry out continuous production, improve production efficiency and reduce production cost.

Contents of the invention

The invention provides a continuous molding device and method for polymer microporous foam products, in particular to a device and method for extruding microfoam assisted by gas back pressure, so as to overcome the defects in the prior art.

The invention provides a continuous molding device for polymer microcellular foamed products, which includes: at least one extruder, at least two sets of counter-pressure foaming molds, at least two compression molding machines, a melt delivery pipeline system and a counter-pressure foaming mold. Compressed gas delivery pipeline and control system. The outlet of the extruder is connected to the melt of the melt delivery pipeline system, and the melt delivery pipeline system is provided with a reversing valve and at least two melt delivery manifolds; Each set of pressure foaming molds is respectively arranged in one of the at least two compression molding machines, respectively forming a closed chamber together with the upper pressing plate and the lower pressing plate of the compression molding machine; At least one melt injection port and at least one backpressure gas inlet/outlet are provided on the wall of the chamber; through the melt injection port, the backpressure foaming chamber is connected to the at least two melt delivery manifolds A melt connection; through the back pressure gas inlet/outlet, the back pressure foaming chamber is gas connected to the back pressure gas delivery pipeline.

According to one aspect of the present invention, an injection port is provided approximately in the middle of the extruder so as to inject the physical blowing agent. According to one aspect of the present invention, the continuous molding device for polymer microcellular foamed products further includes a physical foaming agent injection system, which is used to stably inject the physical foaming agent into the extruder through the injection port at a certain flow rate.

According to one aspect of the present invention, the counter-pressure foaming mold is a mold set composed of multi-layer molds.

According to one aspect of the present invention, the continuous molding device for polymer microcellular foamed products further includes a static mixer, the inlet of the static mixer is connected to the outlet of the extruder melt, and the outlet of the static mixer is connected to the outlet of the extruder. The melt delivery pipeline is connected.

According to one aspect of the present invention, the continuous molding device for polymer microcellular foamed products further includes a melt pump, the inlet of the melt pump is connected to the outlet melt of the extruder, and the outlet of the melt pump is connected to the outlet of the extruder. The melt delivery piping systems are connected.

The present invention also provides a method for continuous molding of polymer microcellular foamed products, comprising the following steps:

The polymer resin, chemical blowing agent and additives are fed into the extruder through the extruder inlet, and the polymer/blowing agent mixture is formed by the melt mixing action of the extruder, thereby forming a foamable polymer melt;

Or polymer resin and additives are added in the extruder through the feed port of the extruder, and a certain amount of physical foaming agent is injected into the polymer melt in the middle section of the extruder, and in the extruder, the The screw mixing action makes the polymer melt and the physical foaming agent mix uniformly to form a polymer/gas homogeneous solution, forming a foamable polymer melt;

Put the first counter-pressure foaming mold between the upper and lower templates of the first compression molding machine, control the first compression molding machine to close the mold, and control the temperature control system of the first compression molding machine to heat the first cavity , so that the temperature in the first cavity reaches a certain value, then open the control valve located in the back pressure gas injection system, inject high-pressure gas into the first cavity, and make the gas pressure in the first cavity reach a certain value, which is greater than or equal to 5 MPa;

The reversing valve is used to make the foamable melt enter the first mold cavity through the first melt delivery pipeline, and the first mold pressure relief back pressure valve installed on the first back pressure gas pipeline controls the pressure inside the first mold cavity. The back pressure gas is kept at a constant pressure, which is higher than the dissolution pressure of the foaming agent in the polymer melt, so as to ensure that the polymer/foaming agent solution injected into the first cavity remains homogeneous, and the first back pressure After injecting a certain amount of melt into the foaming mold, close the on-off valve of the first melt inlet;

During this process, the second counter-pressure foaming mold is placed between the upper and lower templates of the second compression molding machine, and the second compression molding machine is controlled to close the mold, and at the same time, the temperature control system of the second compression molding machine is controlled to control the temperature of the second compression molding machine. The mold cavity is heated to make the temperature in the second mold cavity reach a certain value, and then the control valve located in the back pressure gas injection system is opened to inject high-pressure gas into the second mold cavity, so that the gas pressure in the second mold cavity reaches a certain value, The value is greater than or equal to 5MPa; then, the melt flows through the second inlet manifold through the reversing valve, and the second melt inlet enters the second counter-pressure foaming mold. While the melt continuously enters the second cavity, the second The gas in the mold cavity is controlled by the back pressure valve installed on the second back pressure gas pipeline system to keep the melt pressure in the second back pressure foaming mold constant;

During the film filling process of the second cavity, the melt in the first cavity stays for a certain period of time after being filled with a certain amount, the residence time is 0-10 minutes, and then the upper and lower molds or molds are quickly opened by controlling the first compression molding machine. The pressure is relieved through the back pressure gas inlet/outlet, so that the pressure in the first cavity is rapidly reduced, and the pressure drop rate is not less than 5MPa/s, and the melt in the first cavity is foamed and filled to obtain the product;

The first back pressure foaming mold is prepared for the next filling, the mold cavity is sealed, and the back pressure is loaded;

When the filling of the second counter-pressure foaming mold is completed, the pressure is released and foamed, the product is molded and taken out, and the next film filling preparation is carried out;

This cycle makes the product forming process continuous.

The present invention utilizes extruder mixing to increase the dissolution rate of gas in polymers, greatly reduces the diffusion time and molding cycle, and has higher efficiency; it breaks through the limitations of existing foaming technology to produce thinner microcellular foamed products, and can It is used in the production process of thick products; the gas back pressure can inhibit the pre-foaming of the foamable melt in the mold cavity, and quickly reduce the pressure in the mold cavity by controlling the opening of the upper and lower mold plates of the molding machine or the back pressure gas pipeline, so that the foamable Foam melt has greater foaming power, high cell nucleation rate, smaller cell size, higher cell density, and better performance; controlled foaming in the mold, determined product shape, The foam ratio is controllable, and its cell structure is controllable; the requirements for material properties are reduced, which overcomes the defect that the existing foaming technology is not suitable for microcellular foaming of low-melt strength polymers; one extruder can be installed Multiple molds enable continuous production and are suitable for industrial applications.

Brief description of the drawings

The present invention will be described in detail below in conjunction with the accompanying drawings.

Fig. 1 is a schematic diagram of a continuous molding device for polymer microcellular foamed products according to an embodiment of the present invention.

Fig. 2 is a schematic diagram of a continuous molding device for polymer microcellular foamed products according to another embodiment of the present invention.

Fig. 3 is a schematic diagram of a continuous molding device for polymer microcellular foamed products according to another embodiment of the present invention.

Fig. 4 is a flowchart of a continuous molding method for polymer microcellular foamed products according to an embodiment of the present invention.

detailed description

See Figure 1-2, in the figure: 11 extruder, 12 screw, 13 hopper, 14 foaming agent injection port, 15 injection system, 16 reversing valve, 61 first melt delivery manifold, 62 second melt Delivery manifold, 171 first mold melt inlet pressure sensor, 172 second mold melt inlet pressure sensor, 81 first back pressure foaming mold, 82 second back pressure foaming mold, 801 first mold cavity, 802 first mold cavity Two cavity, 71 first molding machine, 72 second molding machine, 811 first melt inlet, 821 second melt inlet, 611 first melt inlet on-off valve, 612 second melt inlet on-off Valve, 91 first backpressure gas delivery pipeline, 92 second backpressure gas delivery pipeline, 812 first backpressure gas inlet, 822 second backpressure gas inlet, 31 first gas pressure regulating branch ,32 The second gas pressure regulating branch, 51 The first mold pressure relief stop valve, 52 The second mold pressure relief stop valve, 41 The first mold pressure relief back pressure valve, 42 The second mold pressure relief back pressure valve, 911 1st mold intake stop valve, 912 second mold intake stop valve, 21 back pressure gas delivery stop valve, 20 high pressure gas pumping device, 19 gas source,

As shown in Figure 1, the continuous molding device 1 of polymer microcellular foamed products of the present invention comprises: an extruder 11, a first back pressure foaming mold 81 and a second back pressure foaming mold 82, two compression molding Extruders 71, 72, melt delivery pipeline system and back pressure gas delivery and control system, the outlet of the extruder 11 is connected with the melt of the melt delivery pipeline system, and a reversing valve is installed on the melt delivery pipeline system 16 and the first melt delivery manifold 61 and the second melt delivery manifold 62, the first melt delivery manifold 61 is connected with the first back pressure foaming mold 81 inlet melt, the second melt delivery manifold 62 is connected with the entrance of the second counter-pressure foaming mold 82, and the first counter-pressure foaming mold 81 is placed in the first compression molding machine 71 to form a closed first mold together with the upper and lower platens of the first compression molding machine 71. Cavity 801; the second counter-pressure foaming mold 82 is placed in the second compression molding machine 72, together with the upper and lower platens of the second compression molding machine 72 to form a closed second cavity 802; in the counter-pressure foaming cavity One side of the cavity wall of 801, 802 is respectively connected with back pressure gas delivery pipelines 91, 92.

The extruder 11 is a polymer extrusion processing equipment, including a single-screw extruder, a counter-rotating twin-screw extruder, a co-rotating twin-screw extruder, a triple-screw extruder, and the like. The extruder is mainly used to melt and plasticize the polymer resin, and mix the chemical foaming agent or physical foaming agent with the polymer melt evenly. Preferably, a single-screw extruder with a specific mixing structure, a co-rotating twin-screw extruder or a three-screw extruder is used; more preferably, two extruders are used in series, and a single-screw extruder is connected in series with a single screw Extruder, or co-rotating twin-screw tandem single-screw extruder. The extruder 11 shown in Fig. 1 is a single-screw extruder, comprises screw rod 12 and hopper 13, and the position of extruder 11 machine barrels is opened with foaming agent injection port 14 so that inject physical foam by injection system 15 foaming agent.

The melt delivery manifolds 61 , 62 shown in FIG. 1 connect the outlet of the extruder 11 and the inlets of the back pressure foaming dies 81 , 82 . A reversing valve 16 is installed on the melt conveying manifolds 61 and 62 to control the flow direction of the melt.

There is a temperature control system (not shown) external to the melt delivery manifolds 61, 62, and the temperature control system is used to control the temperature of the melt delivery lines. The temperature control system may be an electric heating temperature control system or an oil heating temperature control system, preferably, an electric heating temperature control system is used.

The melt delivery manifolds 61, 62 have a pressure resistance capability exceeding 10 MPa, preferably exceeding 20 MPa. The melt conveying manifolds 61, 62 are sealingly connected with the outlet of the extruder 11 and the inlets of the counter-pressure foaming molds 81, 82.

The anti-pressure foaming molds 81 and 82 of the device of the present invention are high-pressure molds with a pressure resistance greater than or equal to 20 MPa, and each of the back-pressure foaming molds 81 and 82 includes melt injection ports 811 and 821 and back-pressure gas inlet/outlet ports 812 and 822 . The counter-pressure foaming molds 81, 82 are respectively placed in two compression molding machines 71, 72 which are symmetrically arranged with the extruder 11, and the counter-pressure foaming molds 81, 82 and the compression molding machines 71, 72 are connected by hydraulic pressure. , The lower pressing plate forms airtight chambers 801,802.

As shown in Figures 1-3, according to an embodiment of the present invention, the melt injection ports 811, 821 are arranged on one side of the counter-pressure foaming molds 81, 82, and are preferably located at the middle height of the mould, and more suitably located below the middle height Close to the press plate position of the molding machine 71,72. The back pressure gas inlet/outlet 812,822 is arranged on the mold 81,82 or on the pressing plate of the molding machine 71,72. If it is arranged on the mould, it is more suitable to be located above the height of the middle position of the mould, close to the upper platen position of the compression molding machine 71,72.

According to an embodiment of the present invention, the back pressure foaming mold can also be a mold set, the so-called mold set is formed by a multi-layer mold, such as 3 to 10 layers, and each layer is provided with a melt injection port respectively, through which the melt is injected into the manifold. The switching of the tubes supplies materials to each layer of the mold separately, and each mold group is provided with at least one back pressure gas inlet/outlet.

The melt inlet is set on one side of the mold, preferably at the middle height of the mold, and more preferably at a position lower than the middle height and close to the lower platen of the compression molding machine. According to another embodiment of the present invention, the melt inlet is arranged on the lower die plate of the compression molding machine. The back pressure gas inlet/outlet is arranged on the mold and is located above the height of the middle position of the mold and close to the position of the upper mould. According to another embodiment of the present invention, the back pressure gas inlet/outlet port is located on the upper mold plate of the compression molding machine. The back pressure gas inlet/outlet is connected with the high pressure gas source through the gas pipeline. Melt pressure sensors 171, 172 and temperature sensors (not shown) are installed on the mold.

The reversing valve 16 of the present invention is a melt reversing valve commonly used in plastic processing, and the outlet of the reversing valve is switched between the melt conveying manifolds 61 and 62 under the control of the control system. Melt inlet on-off valves 611, 612 are installed at the melt inlets 811, 821 of the mold. The mold inlet on-off valve of the present invention is a melt gate valve, a stop valve, etc. commonly used in plastic processing to realize the on-off switching of the inlet. The outlets of the melt inlet on-off valves 611, 612 are controlled by the control system to isolate the polymer melt in the mold from the melt in the melt delivery manifold.

The back-pressure gas delivery and control system mainly includes a gas source 19, a high-pressure gas pumping device 20, a pressure sensor, and a gas pipeline. The more suitable gas source is nitrogen (N2), air, carbon dioxide (CO2) or other types of gas; the high-pressure gas pumping device 20 is a gas booster pumping device commonly used in industry; a back pressure gas delivery shut-off valve 21 is installed on the gas pipeline In order to control the gas flow, the gas pressure regulating branch 31, 32 is connected in parallel in the air inlet pipeline close to the air inlet of the mold, and the pressure relief back pressure valve 41, 42 and the intake stop valve 51 are installed on the pressure regulating branch 31, 32 ,52.

As shown in FIG. 2 , according to another embodiment of the present invention, the device of the present invention may further include a static mixer 23 , and the inlet of the static mixer 23 is connected to the outlet of the extruder 11 by melt. The static mixer 23 is a melt mixer commonly used in the field of polymer processing, in order to make the temperature of the polymer melt more uniform. In this embodiment, the outlet of the static mixer 23 is connected to the melt inlets 811, 821 of the back pressure mold through the melt delivery manifolds 61,62.

As shown in Figure 3, according to another embodiment of the present invention, the device of the present invention can also include a melt pump 22, which is a general pumping device for plastic processing, and plays a role in stabilizing or increasing the melt pressure . In this embodiment, the inlet of the melt pump 22 is connected to the melt outlet of the extruder 11 , and the outlet of the melt pump is connected to the melt inlets 811 , 821 of the back pressure mold through the melt delivery manifolds 61 , 62 .

The device of the present invention can also contain a static mixer 23 and a melt pump 22 at the same time, the inlet of the static mixer 23 can be connected with the melt at the outlet of the extruder 11, and the outlet of the static mixer 23 can be connected with the inlet of the melt pump 22; A form in which the inlet of the melt pump 22 is connected to the outlet of the extruder 11 and the outlet of the melt pump 22 is connected to the inlet of the static mixer 23 may also be adopted.

Fig. 4 is a flowchart of a continuous molding method for polymer microcellular foamed products according to an embodiment of the present invention. The continuous molding method of polymer microcellular foam thick plate of the present invention mainly comprises the following steps:

(1) Formation of foamable polymer melt

According to one embodiment of the method of the present invention, the foamable polymer melt is formed by adding polymer resin, chemical foaming agent and additives into the extruder 11 through the hopper 13 of the extruder 11, and passing through the extruder The melt mixing action of 11 forms the polymer/chemical blowing agent mixture, and the temperature of the foamable polymer melt can be controlled further by controlling the temperature of each section near the exit section of the extruder 11.

According to another embodiment of the method of the present invention, the foamable polymer melt is formed by adding polymer resin and additives into the extruder 11 through the feeding port 13 of the extruder 11, and polymerizing in the middle section of the extruder 11 A certain amount of physical foaming agent is injected into the material melt, and the polymer melt and the physical foaming agent are mixed uniformly in the extruder 11 through the mixing action of the screw 12 to form a polymer/gas homogeneous solution, which can be foamed and polymerized material melt.

Polymer resins can be thermoplastic polymers such as polystyrene, polyethylene, polypropylene, polylactic acid, polyurethane, polymethyl methacrylate, polyvinyl chloride, polyethylene terephthalate, polycarbonate, and their copolymers or blends. Resin raw materials usually also include processing aids, such as masterbatches, inorganic fillers, flame retardants, nucleating agents, etc., which are pre-mixed with polymer resin raw materials and then added to the extruder.

The chemical foaming agent can be an inorganic foaming agent such as sodium bicarbonate, sodium carbonate, ammonium carbonate, or an organic foaming agent such as azodicarbonamide (AC) or citric acid.

According to an embodiment of the present invention, the temperature of the foamable polymer melt can be further controlled by controlling the temperature of each section of the extruder 11 to make it more suitable for foaming.

(2) mold clamping and back pressure gas control injection

Put the molds 81, 82 between the upper and lower templates of the molding machines 71, 72, control the mold closing of the molding machines, and control the temperature control system of the molding machines 71, 72 to control the molds 81, 82 and the mold cavities 801, 802 Heating to make the temperature in the cavity 801, 802 reach a certain value. Then open the back pressure gas delivery cut-off valve 21 located in the back pressure gas injection system, and inject high pressure gas into the mold cavities 801, 802, so that the gas pressure in the mold cavities 801, 802 reaches a certain value, and the pressure value is greater than or equal to 5MPa, preferably greater than or equal to 8MPa.

(3) Foamable melt injection

The reversing valve 16 is used to make the foamable melt enter the first mold cavity 801 through the first melt delivery manifold 61, and pass through the first mold relief backpressure valve installed on the first backpressure gas delivery pipeline 91 41 Control the back pressure gas in the mold cavity to maintain a constant pressure, which is higher than the dissolution pressure of the foaming agent in the polymer melt, so as to ensure that the polymer/foaming agent solution injected into the first cavity 801 remains homogeneous ; After injecting a certain amount of melt into the first back pressure foaming mold 81, close the first melt inlet on-off valve 611. At the same time, the reversing valve 16 turns to the second melt delivery manifold 62 to inject the foamable polymer melt into the second cavity 802 of the second counter-pressure foaming mold 82 . The volume of the melt filling the mold cavities 801, 802 is 2%-30% of the volume of the mold cavities. Regulating the volume of the melt injected into the mold cavity 801, 802 can be used to adjust the expansion ratio. When the melt injection volume is lower than 2% of the cavity volume, the final foamed product cannot completely fill the cavity, and the shape of the product cannot be finalized. Rough; when the melt injection amount is higher than 30% of the cavity volume, the expansion ratio of the final product is lower than 3 times. The volume of melt filled into the cavity can be controlled by controlling the time when the melt is filled into the cavity and the output of the extruder.

(4) Microcellular foaming

After a certain amount of foamable melt is injected into the cavity 801 of the first back pressure foaming mold 81, stay for 0-10 minutes, control the first molding machine 71 to quickly open the upper and lower molds, so that the first back pressure foaming mold 81 The pressure in the mold cavity 801 drops rapidly, and the foamable polymer melt undergoes bubble nucleation, bubble growth, and shaping as the pressure drops. Controlling the injection amount of the foamable melt can conveniently adjust the expansion ratio of the final product. The pressure in the cavity 801 of the first counter-pressure foaming mold 81 drops rapidly, and the pressure drop rate is greater than 5MPa/min, preferably greater than 20MPa/min, and more suitably greater than 100MPa/min, thereby increasing the nucleation density of the bubbles and obtaining microcellular foaming products. According to the back pressure in the mold cavity, the pressure drop rate is controlled by controlling the opening time of the upper and lower templates of the hydraulic press of the molding machine.

According to another embodiment of the present invention, when the melt in the first back pressure foaming mold 81 is injected with a certain amount of foamable melt, stay for 0-10 minutes, then quickly open the upper and lower molds or molds by controlling the first compression molding machine Relieve the pressure through the back pressure gas inlet/outlet, so that the pressure in the first mold cavity is rapidly reduced, and the pressure drop rate is not less than 5MPa/s, more preferably not less than 20MPa/s, more preferably not less than 100MPa/s. The melt in the first counter-pressure foaming mold 81 is foamed and filled to obtain a product;

During this process, the melt flows through the reversing valve 16 through the second melt delivery manifold 62, the second melt inlet 821 and enters the second counter-pressure foaming mold 82. When the melt continuously enters the second counter-pressure foaming mold At the same time as the mold 82, the gas in the second back pressure foaming mold 82 is controlled by back pressure to keep the melt pressure in the mold constant at 5-30MPa;

While the second back pressure foaming mold 82 is filling the mould, the melt in the first back pressure foaming mold 81 is depressurized and foamed, and the product is molded and taken out for the next filling preparation: the second back pressure foaming mold 82 sealed, back pressure loaded;

After the filling of the second back-pressure foaming mold 82 is completed, the melt is injected into the first back-pressure foaming mold 81 , and the second mold 81 is taken out for molding and ready for the next filling. This cycle makes the product forming process continuous.

Example 1

Material: polypropylene, grade E02, China Petrochemical Corporation Zhenhai Refining and Chemical Branch,

Nucleating agent: talcum powder, particle size: 0.8um, the amount added is 1% of the total weight of polypropylene

Chemical blowing agent: azodicarbonamide, added in an amount of 2% of the total weight of polypropylene

Lubricant: glyceryl monostearate, added in an amount of 2% of the total weight of polypropylene

Back pressure gas: Nitrogen

The microcellular foam molding device is shown in Figure 1. The diameter of the single-screw extruder is 60mm, and the ratio of length to diameter of the screw is 40.

The microcellular foaming process flow is shown in Figure 4, and the process parameters are shown in Table 1. Test the apparent density of the obtained samples according to GB/T6342-2009; randomly sample the obtained foamed samples, cut the section with a sharp knife, spray gold, observe its microstructure with a scanning electron microscope, and use the imager software to count the cell size, according to Calculate the cell density according to the following formula, and test the compressive strength of the foamed sample according to GB/T8813-2008. The test results are shown in Table 2.

Example 2

Material: polystyrene, brand MG33, Chi Mei Chemical Co.

Nucleating agent: talcum powder, particle size 0.8um, the amount added is 0.8% of the total weight of polystyrene

Lubricant: glyceryl monostearate, added in an amount of 1% of the total weight of polystyrene

The blowing agent is carbon dioxide, and the addition amount is 4.2% of the total weight of polystyrene

Back pressure gas: air

The foaming device is shown in Figure 2. The extruder adopts a twin-screw extruder in series with a static mixer. The microcellular foaming process is shown in Figure 4. The process parameters are shown in Table 1. The samples obtained were tested according to GB/T6342-2009 The apparent density of the obtained foaming sample is randomly sampled, the section is cut with a sharp knife, and after spraying gold, the microstructure is observed with a scanning electron microscope, and the cell size is counted with imager software, and the cell density is calculated according to the following formula, according to GB /T8813-2008 Test the compressive strength of foamed samples. The test results are shown in Table 2.

Example 3

Material, polypropylene, grade E02, China Petrochemical Corporation Zhenhai Refining & Chemical Co., Ltd.

Nucleating agent: talcum powder, particle size: 0.8um, the amount added is 1% of the total weight of polypropylene

Lubricant: glyceryl monostearate, added in an amount of 2% of the total weight of polypropylene

Back pressure gas: Nitrogen

The foaming agent is carbon dioxide, and the addition is 6.0% of the total weight of polypropylene. The microcellular foaming device is as shown in Figure 2. The extruder is a twin-screw extruder (first-order) series static mixer, and the microcellular foaming The process flow is shown in Figure 4, and the process parameters are shown in Table 1. The apparent density of the obtained sample is tested according to GB/T6342-2009; the foamed sample is randomly sampled, and the section is cut with a sharp knife. After spraying gold, use a scanning electron microscope Observe its microstructure, and use the imager software to count the cell size, calculate the cell density according to the following formula, and test the compressive strength of the foamed sample according to GB/T8813-2008. The test results are shown in Table 2.

Example 4

Material: polyethylene terephthalate (PET), intrinsic viscosity 1.3

Nucleating agent: talcum powder, added in an amount of 1% of the total weight of PET

The blowing agent is isopentane, and the addition amount is 1.8% of the total weight of PET

Back pressure gas: Nitrogen

Before processing, PET resin needs to be vacuum dried at 80°C for 12 hours to remove moisture

The foaming device is shown in Figure 3, the extruder is a twin-screw extruder connected with a melt pump, and the microcellular foaming process is shown in Figure 4, except that there is no second-stage extruder and static mixer, but in The outlet of the extruder is connected with the melt pump. The process parameters are shown in Table 1. The apparent density of the obtained samples was tested according to GB/T6342-2009; the obtained foamed samples were randomly sampled, and the section was cut with a sharp knife. After spraying gold, the microstructure was observed with a scanning electron microscope, and imager software The cell size is counted, the cell density is calculated according to the following formula, and the compressive strength of the foamed sample is tested according to GB/T8813-2008. The test results are shown in Table 2.

Example 5

Material, polypropylene, grade E02, China Petrochemical Corporation Zhenhai Refining & Chemical Co., Ltd.

Nucleating agent: talcum powder, particle size: 0.8um, the amount added is 1% of the total weight of polypropylene

Lubricant: glyceryl monostearate, added in an amount of 2% of the total weight of polypropylene

Back pressure gas: Nitrogen

The foaming agent is carbon dioxide, and the addition amount is 6% of the total weight of polypropylene. As shown in Figure 4, the process parameters are shown in Table 1, and the apparent density of the obtained sample is tested according to GB/T6342-2009; the obtained foamed sample is randomly sampled, and the section is cut with a sharp knife. After spraying gold, use a scanning electron microscope to observe its microscopic Structure, and use the imager software to count the cell size, calculate the cell density according to the following formula, and test the compressive strength of the foamed sample according to GB/T8813-2008. The test results are shown in Table 2.

Example 6

The material, device and foaming process are the same as those in Example 5, except that the pressure release rate is 100 MPa/min during back pressure foaming. The performance test results of the samples are shown in Table 2.

Comparative example 1

The raw materials are the same as in Example 3, and the extruder part of the foaming device is the same as in Example 3. The difference is that the comparative example adopts conventional extrusion foaming molding, the head is a sheet head, and the temperature setting of each section of the extruder is the same as that of Example 3. The same as in Example 3, the temperature of the die is 160° C., the pressure of the die is 10 MPa, and after exiting the die, it is cooled and shaped by multiple sets of cooling rolls commonly used in the plastics processing industry. The test results of the obtained samples are shown in Table 2.

Comparative example 2

The raw materials are the same as in Example 4, and the extruder part of the foaming device is the same as in Example 4. The difference is that the comparative example uses a conventional extrusion foaming device to directly extrude and foam, and the head is a sheet foaming head, and the extruder The temperature setting of each section of the machine is the same as that of Example 4, the temperature of the machine head is 240°C, the pressure of the machine head is 5MPa, and the shape is finalized by the shaping device. The test results of the obtained samples are shown in Table 2.

Compared with the prior art, the present invention has the advantages of: using the extruder to mix and increase the dissolution rate of the gas in the polymer, greatly reducing the diffusion time and molding cycle, and having higher efficiency; breaking through the existing foaming technology that can only The limit of microcellular foaming in the production of thinner products can be used in the production process of thicker products; by using back pressure gas to prevent the foamable melt from pre-foaming in advance, by quickly opening the pressure relief device on the molding machine or mold , achieve high pressure drop rate, high cell nucleation rate, smaller cell size, more number, higher cell density, and better performance; controlled foaming in the mold, determined product shape, foaming The magnification is controllable, and the cell structure is controllable; the requirements for material properties are reduced, which overcomes the defect that the existing foaming technology is not suitable for microcellular foaming of low-melt strength polymers; one extruder can be installed with multiple A mold, to achieve continuous production, suitable for industrial applications. The microcellular foam material produced by the continuous molding device and method of the polymer microcellular foam thick plate of the present invention has excellent shock absorption, sound absorption and heat insulation properties, and can be widely used in building heat preservation, cushioning packaging, sound insulation and shock absorption and other fields.

Table 1 Back pressure foaming process parameters

Table 2

Claims (10)

1. A continuous molding device for polymer microcellular foamed products, comprising: at least one extruder, at least two sets of back pressure foaming molds, at least two compression molding machines, melt delivery pipeline system and back pressure The gas conveying pipeline and control system are characterized in that: the outlet of the extruder is connected to the melt of the melt conveying pipeline system, and the melt conveying pipeline system is provided with a melt reversing valve and at least Two melt conveying manifolds; each set of the at least two sets of counter-pressure foaming molds is respectively arranged in one of the at least two compression molding machines, and is respectively connected to the upper platen and the lower compression molding machine of the compression molding machine. The pressure plates form a closed chamber together; at least one melt injection port and at least one back pressure gas inlet/outlet are opened on the wall of the back pressure foaming chamber; through the melt injection port, the back pressure foaming The chamber is connected to one of the at least two melt delivery manifolds; through the backpressure gas inlet/outlet, the backpressure foaming chamber is connected to the backpressure gas delivery pipeline gas connection. 2. The continuous molding device for polymer microcellular foamed products according to claim 1, characterized in that: the extruder is provided with a foaming agent injection port approximately in the middle, and the extruder also includes a foaming agent. An agent injection system is used to stably inject the physical foaming agent into the extruder through the foaming agent injection port at a certain flow rate. 3. The continuous molding device for polymer microcellular foamed products according to claim 1, characterized in that: the counter-pressure foaming mold is a mold set composed of multi-layer molds. 4. The continuous molding device for polymer microcellular foamed products according to claim 1, characterized in that: it also includes a static mixer, the inlet of the static mixer is connected with the outlet melt of the extruder, and the The outlet of the static mixer is connected with the melt delivery pipeline. 5. The continuous molding device for polymer microcellular foamed products according to claim 1, characterized in that: it also includes a melt pump, the inlet of the melt pump is connected with the outlet melt of the extruder, The outlet of the melt pump is connected with the melt delivery pipeline system. 6. A continuous molding method for polymer microcellular foamed products, characterized in that, comprising the following steps: The polymer resin, chemical blowing agent and additives are introduced into the extruder through the extruder inlet, and the polymer/blowing agent mixture is formed by the melt mixing action of the extruder to form a foamable polymer melt; or Add polymer resin and additives into the extruder through the feed port of the extruder, inject a certain amount of physical foaming agent into the polymer melt in the middle section of the extruder, The mixing action makes the polymer melt and the physical blowing agent uniformly mixed to form a polymer/gas homogeneous solution, forming a foamable polymer melt; Put the first counter-pressure foaming mold between the upper and lower templates of the first compression molding machine, control the first compression molding machine to close the mold, and control the temperature control system of the first compression molding machine to heat the first cavity , so that the temperature in the first cavity reaches a certain value, then open the control valve located in the back pressure gas injection system, inject high-pressure gas into the first cavity, and make the gas pressure in the first cavity reach a certain value, which is greater than or equal to 5 MPa; The reversing valve is used to make the foamable melt enter the first mold cavity through the first melt delivery pipeline, and the first mold pressure relief back pressure valve installed on the first back pressure gas pipeline controls the pressure inside the first mold cavity. The back pressure gas is kept at a constant pressure, which is higher than the dissolution pressure of the foaming agent in the polymer melt, so as to ensure that the polymer/foaming agent solution injected into the first cavity remains homogeneous, and the first back pressure After injecting a certain amount of melt into the foaming mold, close the on-off valve of the first melt inlet; During this process, the second counter-pressure foaming mold is placed between the upper and lower templates of the second compression molding machine, and the second compression molding machine is controlled to close the mold, and at the same time, the temperature control system of the second compression molding machine is controlled to control the temperature of the second compression molding machine. The mold cavity is heated to make the temperature in the second mold cavity reach a certain value, and then the control valve located in the back pressure gas injection system is opened to inject high-pressure gas into the second mold cavity, so that the gas pressure in the second mold cavity reaches a certain value, The value is greater than or equal to 5MPa; then, the melt flows through the second inlet manifold through the reversing valve, and the second melt inlet enters the second counter-pressure foaming mold. While the melt continuously enters the second cavity, the second The gas in the mold cavity is controlled by the back pressure valve installed on the second back pressure gas pipeline system to keep the melt pressure in the second back pressure foaming mold constant; During the filling process of the second cavity, the melt in the first cavity stays for a certain period of time after being filled with a certain amount, the residence time is 0-10 minutes, and then the upper and lower molds or The pressure is relieved through the back pressure gas inlet/outlet, so that the pressure in the first cavity is rapidly reduced, and the pressure drop rate is not less than 5MPa/s, and the melt in the first cavity is foamed and filled to obtain the product; The first back pressure foaming mold is prepared for the next filling, the mold cavity is sealed, and the back pressure is loaded; When the filling of the second counter-pressure foaming mold is completed, the pressure is released and foamed, the product is molded and taken out, and the next filling preparation is carried out; This cycle makes the product forming process continuous. 7. The method for continuously molding polymer microcellular foamed products according to claim 6, wherein the volume of the melt filled into the first or second mold cavity is 2%-30% of the volume of the mold cavity. 8. The method for continuously molding polymer microcellular foamed products according to claim 6, wherein the pressure drop rate in the first or second mold cavity is not less than 20 MPa/s. 9. The method for continuously molding polymer microcellular foamed products according to claim 6, wherein the pressure drop rate in the first or second mold cavity is not less than 100 MPa/s. 10. The method for continuously molding polymer microcellular foamed products according to claim 6, wherein the back pressure gas is nitrogen or air.