Low-temperature supercritical foaming process

Abstract

Disclosed is a low-temperature supercritical foaming process, comprising the following steps: (1) bringing a polyolefin material or a thermoplastic elastomer material into contact with at least one inert gas in a reactor at a pressure higher than atmospheric pressure to drive the gas into the material, the pressure holding temperature of the polyolefin material or thermoplastic elastomer material being lower than the melting temperature of the material by 5-40 C.; (2) reducing the pressure to expand the material so as to produce a primary foamed material, and taking out the primary foamed material; and (3) taking out the primary foamed material and putting same into a tunnel furnace for secondary foaming, the temperature of the tunnel furnace being higher than the melting temperature of the material. Compared with the prior art, the present invention features high production efficiency, energy saving, and improvement of the reactor utilization rate.

Claims

1. A low-temperature supercritical foaming process, characterized in that it comprises the following steps: step 1: saturation of a polyolefin-based material or a thermoplastic elastomer-based material, at a saturation temperature, by at least one inert gas in an autoclave at a pressure higher than atmospheric pressure to drive the gas into the polyolefin-based material or the thermoplastic elastomer-based material; wherein the saturation temperature of the polyolefin-based material or the thermoplastic elastomer-based material is 5 to 40 C. lower than the melting temperature of the polyolefin-based material or the thermoplastic elastomer-based material; step 2: release the pressure to foam the polyolefin-based material or the thermoplastic elastomer-based material, thereby forming a primary foamed polyolefin-based material or a primary foamed thermoplastic-elastomer material, and taking the primary foamed polyolefin-based material or the primary foamed thermoplastic-elastomer material out of the autoclave; step 3: placing the primary foamed polyolefin-based material or the primary foamed thermoplastic-elastomer material into a tunnel furnace for a secondary foaming, wherein a temperature of the secondary foaming in the tunnel furnace is higher than the melting temperature of the polyolefin-based material or the thermoplastic elastomer-based material.

2. The low-temperature supercritical foaming process according to claim 1, wherein the temperature of the tunnel furnace in step 3 is 10 to 40 C. higher than the melting temperature of the polyolefin-based material or the thermoplastic elastomer-based material, and the secondary foaming occurs for a time of 5 to 60 minutes.

3. The low-temperature supercritical foaming process according to claim 1, wherein the polyolefin-based material is one of PE, PP or EVA, or a mixture of two or more of these, and the thermoplastic elastomer-based material is one of TPE, TPU, TPEE or a mixture of two or more of these.

4. The low-temperature supercritical foaming process according to claim 1 or 3, characterized in that the polyolefin-based material or the thermoplastic elastomer-based material in step 1 is crosslinked by a crosslinking agent, or by irradiation.

5. The low-temperature supercritical foaming process according to claim 1, wherein the at least one inert supercritical fluid gas is nitrogen, carbon dioxide, or a mixture thereof, and the pressure during saturation is from 10 to 70 MPa.

6. The low-temperature supercritical foaming process according to claim 5, wherein the pressure during saturation is from 50 to 70 MPa.

7. The low-temperature supercritical foaming process according to claim 1, wherein the saturation temperature in step 1 is 5 to 10 C. lower than the melting temperature of the polyolefin-based material or the thermoplastic elastomer-based material.

8. The low-temperature supercritical foaming process according to claim 1, wherein the pressure higher than atmospheric pressure is held for a time of 0.5 hour to 24 hours.

9. The low-temperature supercritical foaming process according to claim 1, wherein the release of pressure in step 2 is achieved by quenching, and a quenching speed is 5 s to 600 s.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) To further explain the technical solution of the present invention, the present invention is explained in detail through the following specific embodiments.

(2) The present invention relates to a low-temperature supercritical foaming process, which includes the following steps: Step 1: Saturate polyolefin materials or thermoplastic elastomer materials by at least one inert gas in an autoclave at a pressure higher than atmospheric pressure to drive the gas into the material; The saturation temperature of the polyolefin-based material or thermoplastic elastomer-based material is 5-40 C lower than the melting temperature of the material, preferably 5-10 C lower than the melting temperature of the material; Step 2: Release the pressure to foam the material, and produce a foamed material and take out the foamed material; Step 3: Take out the primary foaming material and put it into a tunnel furnace for secondary foaming, where the temperature of the tunnel furnace is higher than the melting temperature of the material.

(3) In this way, in the present invention, the saturation temperature of the polyolefin material or thermoplastic elastomer material in the autoclave is 5-40 C. lower than the melting temperature of the material, that is, there is lots of inert gas being retained inside the material after the material is reduced in pressure to complete a foaming. Just because of the residual of a large amount of inert gas within the matires, the materials cannot expand too much with the autoclave. Therefore, in the same space in the autoclave, more materials can be placed, and thereby improving the utilization efficiency and reduces the processing cost.

(4) Secondly, the present invention uses a tunnel furnace to perform secondary foaming. The main purpose is to cooperate with the previous two steps to perform secondary foaming of the material that retains the inert gas, that is, to allow the inert gas inside the material to be released, and to achieve the purpose of secondary foaming. As a specific example, in the step 3, the temperature of the tunnel furnace is 10-40 C. higher than the melting temperature of the material, and the secondary foaming time is 5-60 minutes; During the secondary foaming process within the tunnel furnace, the higher the temperature of the tunnel furnace, the greater the foaming ratio. The secondary foaming time of the entire tunnel furnace can be set according to the thickness of the material, and the thicker the material, the longer the time.

(5) The invention uses a tunnel furnace for secondary foaming, which has the characteristics of continuous foaming, uniform temperature, uniform foaming ratio, good performance consistency, time controllable, low-temperature pressure and high space utilization rate. Meanwhile, the whole process has high efficiency and low cost.

(6) Because the temperature of the autoclave is relatively low, the autoclave is always in a constant temperature during the process, which can greatly save energy and reduce production costs.

(7) In the present invention, the polyolefin material in the step 1 is one or a mixture of two or more materials of PE, PP or EVA; the thermoplastic elastomer material in the step 1 is TPE, TPU. TPEE, PEBAX or a mixture of two or more materials.

(8) Preferably, the polyolefin-based material or the thermoplastic elastomer-based material in step 1 is cross-linked by a cross-linking agent, or irradiated, or the cross-linking operation may not be performed.

(9) In the present invention, at least one inert gas in step 1 is a supercritical fluid, which is nitrogen, carbon dioxide, or a mixed gas of the two, and its saturation pressure is 10-70 MPa, preferably 50-70 MPa.

(10) It should be noted that the saturation time in step 1 is 0.5-24 hours, and the specific holding time is determined according to the thickness of the material.

(11) The higher the material thickness, the longer the holding time.

(12) In the step 2, the pressure is released by quenching, and the exhaust speed is 5 s-500 s, and the pressure is released to the atmospheric pressure at a time within this time period. The faster the speed, the finer the cells, while the slower the speed, the larger the cells are. The exhaust speed can be adjusted according to actual needs during production.

(13) The foregoing embodiments do not limit the product form and style of the present invention, and any appropriate changes or modifications made by those of ordinary skill in the art should be regarded as not departing from the patent scope of the present invention.