CN111300713B

CN111300713B - One-time foaming forming process in mold and foaming product

Info

Publication number: CN111300713B
Application number: CN202010157235.7A
Authority: CN
Inventors: 姜修磊; 李期筠; 余加保
Original assignee: Suzhou Shensai New Materials Co ltd
Current assignee: Suzhou Shensai New Materials Co ltd
Priority date: 2020-03-09
Filing date: 2020-03-09
Publication date: 2022-04-26
Anticipated expiration: 2040-03-09
Also published as: CN111300713A; WO2021179645A1

Abstract

The invention discloses an in-mold one-step foaming forming process, which comprises the following steps: s1: pre-impregnating resin beads in supercritical gas to obtain beads to be foamed; s2: transferring the beads to be foamed into a closed space, and introducing wet air to ensure that the beads to be foamed are in a fluidized state; s3: heating the beads to be foamed and the humid air using microwaves; s4: and (5) exhausting, foaming and molding to obtain a foamed product. The foaming product is obtained by one-step molding, the interior of the product is free of defects, and the performance is good; the microwave is used for heating the beads to be foamed, so that the heat efficiency is high, the heat transfer depth is large, and the heating time is short; the mold is made of nonpolar materials with dense small holes on the upper and lower surfaces, is easy to process and low in cost, and the air blowing device is arranged below the mold to ensure that the beads are in a fluidized state during microwave irradiation, are uniformly heated and cannot generate stacking defects; the supercritical fluid is used as a physical foaming agent for dipping and foaming, the production process is green and environment-friendly, and the method is suitable for industrial production.

Description

One-time foaming forming process in mold and foaming product

Technical Field

The invention relates to the field of processing of high polymer materials, in particular to an in-mold one-step foaming forming process and a foaming product.

Background

The polymer foam material refers to a polymer composite material having a porous structure formed by a gas phase uniformly distributed in a polymer solid phase. Due to the existing porous structure, the polymer foam material has excellent sound insulation and heat insulation properties, shock resistance and buffering properties and the like. The forming process of the thermoplastic polymer foaming material mainly comprises three main types, namely extrusion foaming forming, injection foaming forming and bead molding forming. The extrusion foaming molding process can only produce products with single cross section, such as sheets, plates, pipes and the like; the injection foaming molding can produce products with complex structures, but the injection foaming molding is limited by the process, the product density is high, and the foaming multiplying power is low; bead molding, which can produce low-density, complex-shaped foamed articles, is the focus of recent research.

The currently common method of bead molding in industry is a two-step process. The resin beads are firstly foamed by using a chemical foaming agent or a physical foaming agent to obtain foamed beads, then the foamed beads are filled into a mold, and heating molding is carried out through a medium such as water vapor, so that the foamed particles are mutually welded to obtain a complex foamed product. This method has the following problem that the loss of the properties of the molded article obtained is large. The bead has defects inside during primary foaming, the bead which has been foamed during secondary molding inevitably has gaps when being stacked, the mechanical property of the molded body is reduced due to the accumulation of the defects twice, the application scene is limited, meanwhile, the heating molding time is long by using water vapor, and the industrialization efficiency is low.

Disclosure of Invention

Therefore, the invention aims to solve the technical problems that the mechanical property of a formed body is reduced and the application scene is limited due to the accumulation of defects in the conventional two-step method, and simultaneously, the forming time is long and the industrialization efficiency is low due to the heating of water vapor, and provides an in-mold one-step foaming forming process and a foaming product.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

the invention provides a one-time foaming forming process in a mold, which comprises the following steps:

s1: pre-impregnating resin beads in supercritical gas to obtain beads to be foamed;

s2: transferring the beads to be foamed into a mold, introducing wet air into the mold, and heating the beads to be foamed and the wet air by using microwaves;

s3: and (5) exhausting, foaming and molding to obtain a foamed product.

Preferably, in the step S2, the microwave power is 2000-3000MHz, and the heating time is 30-180S.

The relative humidity of the humid air in the mold is 10-50%, and the pressure is 0.2-0.8 MPa.

In step S1, the resin beads are polar thermoplastic polymer resin beads having a particle diameter of 0.5 to 5mm, and the polar thermoplastic polymer resin beads are microwave-absorbing materials and can be heated by microwaves.

Preferably, the polar thermoplastic polymer resin beads are at least one of a polyurethane elastomer, a polyamide elastomer, and a polyester elastomer.

The supercritical gas is nitrogen and/or carbon dioxide;

preferably, the supercritical gas is a mixed gas of nitrogen and carbon dioxide, and the volume ratio of the nitrogen to the carbon dioxide in the mixed gas is (3-49): 1.

furthermore, the temperature of the preimpregnation is 50-100 ℃, the pressure is 10-40MPa, and the time is 10-480 min.

Further, in the S3, the exhaust foaming molding is carried out, the pressure relief rate is reduced to the standard atmospheric pressure at 1-40MPa/S, and then the cooling air at 0-5 ℃ is introduced for cooling.

Further, the surface of the mould is distributed with airflow holes, the diameter of the airflow holes is smaller than that of the resin beads, the mould is made of microwave-permeable non-polar polymer or ceramic, and the non-polar polymer is polymer with polymer side chains without polar functional groups, such as polyethylene and/or polypropylene;

wet air is continuously introduced into the mold through the airflow holes to enable the beads to be foamed to be in a fluidized state, and a blowing device is arranged below the mold.

The invention also provides a foaming product prepared by adopting the foaming process.

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

1. the invention obtains the foaming product by one-step molding, firstly, resin beads are dipped in supercritical fluid, so that gas molecules are dissolved in the resin beads; transferring the beads to be foamed into a mold, and introducing wet air into the mold to ensure that the beads to be foamed are in a fluidized state; after microwave heating, the temperature of the resin beads is increased, and the solubility of the gas in the resin beads is reduced; then exhausting air and releasing pressure, foaming the beads and welding and molding. The invention avoids the reduction of the mechanical property of the product caused by the defect accumulation caused by multiple foaming in a two-step method, and the product has no defect and good performance.

2. The invention uses microwave to heat the bead to be foamed, has high thermal efficiency and large heat transfer depth, and can obtain a foamed product in a short time. Under microwave irradiation, internal molecules of the polar thermoplastic polymer generate dielectric loss through polarization, and the microwave is converted into heat energy. Meanwhile, wet air with certain pressure is introduced, and water molecules dispersed in the air are heated up under microwave heating, so that the surfaces and the interiors of the beads in the foaming box are uniformly heated, and the combination of the beads during foaming is facilitated.

3. The invention uses the mould with dense small holes on the upper and lower surfaces, and the diameter of the small holes is smaller than that of the resin beads. And an air blowing device is arranged below the mold to ensure that the beads are in a fluidized state during microwave irradiation, are uniformly heated and cannot generate stacking defects. Meanwhile, the mold is made of wave-transparent nonpolar polymer or ceramic, is easy to process and low in cost. When the traditional bead is molded, the requirement on the mold is high due to high temperature and pressure, and the traditional bead is usually made of metal materials such as aluminum alloy and the like, so that the cost is high and the processing is difficult. The invention utilizes microwave to heat and mold the beads, the foaming temperature and pressure are lower, more easily obtained nonpolar polymer and ceramic molds can be used, and the production and development cost is greatly reduced.

4. The supercritical fluid is used as the physical foaming agent for dipping and foaming, the production process is green and environment-friendly, and the method is suitable for industrial production.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a schematic view showing the structure of a foaming apparatus used in examples 1 to 3 of the present invention.

Reference numerals:

1-a foaming box; 2-a microwave emitting device; 3-molding; 4-a blower device; 5-inlet valve, 6-exhaust valve; 7-a pressure monitoring device; 8-a humid air compression device; 9-cold air compression unit.

Detailed Description

The following examples are provided to further understand the present invention, not to limit the scope of the present invention, but to provide the best mode, not to limit the content and the protection scope of the present invention, and any product similar or similar to the present invention, which is obtained by combining the present invention with other prior art features, falls within the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

The examples do not show the specific experimental steps or conditions, and can be performed according to the conventional experimental steps described in the literature in the field. The reagents or instruments used are not indicated by manufacturers, and are all conventional reagent products which can be obtained commercially.

The dies 3 used in the following examples 1 to 3 were made of wave-transparent polyethylene material, and the diameter of the air flow holes distributed on the surface of the dies was 0.3 mm.

Example 1

The embodiment provides an in-mold one-time foaming molding process, which comprises the following steps:

(1) thermoplastic polyurethane elastomer (TPU) beads having a melting point of 165 ℃, a hardness of 85A and a particle size of 0.5 to 5mm were immersed in an autoclave for 10 min. Wherein the dipping temperature is 100 ℃, the dipping pressure is 40MPa, and the used supercritical gas is nitrogen: carbon dioxide volume ratio 3: 1;

(2) paving the impregnated TPU beads in a mold 3, closing the mold, placing the mold in a foaming box 1, opening a wet air compression device 8, filling wet air with the relative humidity of 50% into the foaming box through an air inlet valve 5, enabling the pressure in the foaming box 1 to reach 0.2MPa by using a pressure monitoring device 7, and simultaneously opening a blast device 4 to enable the beads to be in a fluidized state;

(3) turning on the microwave emitting device 2, carrying out microwave heating on the beads, setting the microwave frequency to be 2000MHz, and the heating time to be 180 s;

(4) opening the exhaust valve 6, releasing air at the standard atmospheric pressure at the rate of 1MPa/s, opening the cold air compression device 9, and introducing cold air at 0 ℃ into the foaming box 1 for cooling to obtain the foamed product.

The final foamed product was visually observed to have no defects on the surface, dense fusion of particles, and a density of 0.18g/cm³The right-angle tear strength (test standard: ISO 8067:2008) was 140N/cm, and the ball rebound (test standard: ASTM D3574) was 62%.

Example 2

(1) thermoplastic polyamide elastomer (TPAE) beads having a melting point of 170 ℃, a hardness of 94A and a particle size of 0.5-5mm were immersed in an autoclave for 480 min. Wherein the dipping temperature is 50 ℃, the dipping pressure is 10MPa, and the used supercritical gas is nitrogen: volume ratio of carbon dioxide 49: 1;

(2) the impregnated TPAE beads are paved on a mould 3, the mould is closed, the mould is placed in a foaming box 1, a wet air compression device 8 is opened, wet air with the relative humidity of 10 percent is filled into the foaming box through an air inlet valve 5, the pressure in the foaming box 1 is enabled to reach 0.8MPa through a pressure monitoring device 7, and meanwhile, a blowing device 4 is opened to enable the beads to be in a fluidized state;

(3) turning on the microwave emitter 2, carrying out microwave heating on the beads, setting the microwave frequency to be 3000MHz, and the heating time to be 30 s;

(4) opening the exhaust valve 6, releasing air at the standard atmospheric pressure at the rate of 40MPa/s, opening the cold air compression device 9, and introducing cold air at 5 ℃ into the foaming box 1 for cooling to obtain the foamed product.

The final foamed product was visually observed to have no defects on the surface, dense fusion of particles, and a density of 0.07g/cm³The right-angle tear strength (test standard: ISO 8067:2008) was 60N/cm, and the ball rebound (test standard: ASTM D3574) was 72%.

Example 3

(1) thermoplastic polyester elastomer (TPEE) beads having a melting point of 160 ℃ and a hardness of 98A and a particle diameter of 0.5 to 5mm were immersed in an autoclave for 200 min. The impregnation temperature is 70 ℃, the impregnation pressure is 20MPa, and the used supercritical gas is nitrogen: carbon dioxide volume ratio of 4: 1;

(2) the impregnated TPEE beads are fully paved on a mould 3, the mould is closed, the mould is placed in a foaming box 1, a humid air compression device 8 is opened, humid air with the relative humidity of 30 percent is filled into the foaming box through an air inlet valve 5, the pressure in the foaming box 1 reaches 0.4MPa by using a pressure monitoring device 7, and meanwhile, a blowing device 4 is opened to enable the beads to be in a fluidized state;

(3) turning on a microwave emitter, carrying out microwave heating on the beads, setting the microwave frequency to be 2500MHz, and the heating time to be 60 s;

(4) opening the exhaust valve 6, releasing air at the standard atmospheric pressure at the rate of 6MPa/s, opening the cold air compression device 9, and introducing cold air at the temperature of 2 ℃ into the foaming box 1 for cooling to obtain a foaming product.

The final foamed product was visually observed to have no defects on the surface, tightly welded particles, and a density of 0.15g/cm³The right-angle tear strength (test standard: ISO 8067:2008) was 95N/cm, and the ball rebound (test standard: ASTM D3574) was 70%.

Comparative example 1

This comparative example compares to example 1 the conventional two-step process for preparing a foamed article, comprising the steps of:

(1) thermoplastic polyurethane elastomer (TPU) beads having a melting point of 165 ℃ and a hardness of 85A were dipped in an autoclave and foamed under pressure. The dipping time is 30min, the dipping temperature is 110 ℃, the dipping pressure is 40MPa, and the practical supercritical fluid is nitrogen: carbon dioxide volume ratio 3: 1, the pressure relief rate is 400 MPa/s.

(2) And (3) paving the expanded TPU beads in a steam hot-pressing mold, closing the mold, introducing steam, keeping the steam pressure at 0.18MPa for 3min, closing the steam, and inputting cold water for cooling.

The resulting foamed article had a surface defect, as observed by naked eye, and had a density of 0.2g/cm³The right-angle tear strength (test standard: ISO 8067:2008) was 34N/cm, and the ball rebound (test standard: ASTM D3574) was 60%.

Compared with example 1, the foamed product obtained in comparative example 1 has defects, the tearing strength is obviously lower than that of example 1, and the quality difference is obvious.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.

Claims

1. The in-mold one-step foaming molding process is characterized by comprising the following steps of:

s3: exhausting, foaming and molding to obtain a foamed product;

in the step S2, the relative humidity of the humid air in the mold is 10 to 50%, and the pressure is 2 to 8 bar;

airflow holes are distributed on the surface of the mold, and the diameters of the airflow holes are smaller than those of the resin beads;

continuously introducing wet air into the mold through the airflow holes to ensure that the beads to be foamed are in a fluidized state;

the supercritical gas is a mixed gas of nitrogen and carbon dioxide, and the volume ratio of the nitrogen to the carbon dioxide in the mixed gas is (3-49): 1;

the temperature of the preimpregnation is 50-100 ℃, the pressure is 10-40MPa, and the time is 10-480 min;

and in the S3, the air is discharged and foamed to be formed, the pressure is reduced to the standard atmospheric pressure at the pressure relief rate of 1-40MPa/S, and then the cooling is carried out by introducing cold air at the temperature of 0-5 ℃.

2. The foam molding process of claim 1, wherein in step S2, the microwave power is 2000-3000MHz, and the heating time is 30-180S.

3. The foam molding process according to any one of claims 1 to 2, wherein in step S1, the resin beads are polar thermoplastic polymer resin beads having a particle diameter of 0.5 to 5 mm.

4. The foam molding process of claim 3, wherein the polar thermoplastic polymer resin beads are at least one of a polyurethane elastomer, a polyamide elastomer, and a polyester elastomer.

5. A foamed article produced by the foaming process according to any one of claims 1 to 4.