CN111283946A - Material foaming method for in-mold foaming molding - Google Patents

Abstract

A material foaming method for foaming and forming in a mold comprises the following steps: step A, introducing plastic particles into a mold; step B, a pressurizing and heating device pressurizes and heats the mold, if the plastic particles are made of polyolefin materials, the step C is carried out, and if the plastic particles are made of thermoplastic elastomers, the step D is directly carried out; c, performing high-pressure impregnation by using a supercritical fluid in a mould, and impregnating the plastic particles by using the supercritical fluid to obtain the plastic particles impregnated by the supercritical fluid; step D, after pressure relief, the plastic particles are placed in the mold 1: 1, foaming and forming, cooling the mould after foaming and forming, opening the mould after cooling the mould, and taking out a foamed product. The foaming method does not need to use an injection molding machine or an extruder, and simultaneously does not need to arrange a buffer tank, thereby greatly reducing the equipment cost of material foaming. In addition, the foaming method adopts a heating mode, the material is in a molten or softened state during foaming, the foaming efficiency is high, and the plastic particles can be fully foamed and molded.

Description

A kind of material foaming method for in-mold foam molding

technical field

The invention relates to a physical foaming method, in particular to a material foaming method for in-mold foaming.

Background technique

In the foam molding process or foamed polymer material, a cellular or cellular structure is formed through the addition and reaction of physical or chemical blowing agents. The basic steps of foam molding are the formation of the cell nucleus, the growth or expansion of the cell nucleus, and the stabilization of the cell nucleus.

Chinese patent CN109517262A discloses a supercritical fluid foaming method with full pressure maintaining. The supercritical fluid foaming method is to make infiltrated plastic pellets in a storage tank, and then inject or extrude the product through an injection molding machine or an extruder. out of shape. However, the cost of injection molding machines and extruders is high, and the purchase and maintenance of the above equipment will greatly increase the overall cost of the foaming process.

Chinese patent CN110157086A discloses a physical foaming method for directly forming a foamed product in a mold. In the physical foaming method, the mold is put into an autoclave, and the semi-finished product is directly foamed in the mold at a ratio of 1:1 when the autoclave is depressurized. . However, the parison of the above-mentioned physical foaming method still needs to be produced by an injection machine, an extruder or a molding machine, which also restricts the reduction of the cost of the foaming process. In addition, the above-mentioned physical foaming method performs 1:1 foaming at normal temperature, and the foaming efficiency is low.

SUMMARY OF THE INVENTION

The technical solution of the present invention is aimed at the above-mentioned situation, and in order to solve the above-mentioned problems, a material foaming method for foaming molding in a mold is provided, and the foaming method comprises the following steps:

Step A. Introduce the plastic pellets into the mold;

Step B, the pressure heating device applies pressure to and heats the mold, if the plastic pellets are polyolefin materials, proceed to step C, and if the plastic pellets are thermoplastic elastomers, proceed directly to step D;

Step C, carry out high pressure impregnation with supercritical fluid in the mold, and supercritical fluid impregnates plastic particles to obtain plastic particles infiltrated by supercritical fluid;

Step D. After the pressure is released, the plastic pellets are foamed and molded in the mold at a ratio of 1:1, the mold is cooled after the foaming molding, and the mold is cooled to perform a mold opening operation, and the foamed product is taken out.

Further, the supercritical fluid includes one or more of carbon dioxide, water, methane, ethane, ethylene, propylene, methanol, ethanol, acetone, and nitrogen.

Further, the pressure range of the high pressure infiltration is 5-60MPa, the temperature range is 5°C higher than the softening point of the plastic pellets to 3°C lower than the melting point of the plastic pellets, and the infiltration duration is 0.5-8h.

Further, in the step D, the temperature range inside the mold is 25°C lower than the melting point of the plastic pellets to 25°C higher than the melting point of the plastic pellets, and before the pressure is released, the pressure range inside the mold is greater than 0.1 MPa and less than or equal to 40 MPa , the pressure holding time is 0.2~5h; after the pressure is released, the foaming duration is 5~10min, and the mold is cooled to below 40 ℃ before the mold opening operation.

Further, if the plastic particles are polyolefin materials, before step A, the following steps are further performed: step E, crosslinking the plastic particles to obtain cross-linked plastic particles.

Further, in the step E, the cross-linking reaction is carried out by chemical cross-linking or electron beam irradiation.

Further, the polyolefin composition includes a polyolefin material, and the polyolefin composition material is further doped with one or more of a crosslinking agent, a filler, and an auxiliary agent.

Further, the polyolefin material includes one or more of ethylene-vinyl acetate copolymer (EVA), polyolefin elastomer (POE), low density polyethylene (LDPE), and ethylene propylene diene rubber (EPDM).

Further, the thermoplastic elastomer includes one or more of thermoplastic polyurethane (TPU), thermoplastic polyester elastomer (TPEE), block polyetheramide elastomer (Pebax), polyethylene (PE), and polypropylene (PP). .

After the above technical solution is adopted, the effect of the present invention is that the above foaming method does not need to use an injection molding machine or an extruder, and also does not need to set a buffer tank, which greatly reduces the equipment cost of material foaming. In addition, the above foaming method adopts a heating method, and the material is in a molten or softened state when foaming, and the foaming efficiency is high, and the plastic particles can be fully foamed and formed.

Description of drawings

Fig. 1 is the schematic diagram of the foaming equipment that adopts the autoclave involved in the present invention;

FIG. 2 is a schematic diagram of a foaming device using a molding press according to the present invention.

Detailed ways

The technical scheme of the present invention is further described below by the examples:

The present invention provides a material foaming method for in-mold foaming. As shown in Figures 1 and 2, the equipment used in the foaming method includes: a material storage tank 1, a transmission pipeline 2, and a pressure heating device 3 With the mold 4, one end of the transmission line 2 is communicated with the interior of the storage tank 1, and the other end is communicated with the interior of the mold 4. The mold 4 is located inside the pressure heating device 3, and the transmission line 2 has a valve 20. In this embodiment, the pressure heating device 3 may be an autoclave or a molding machine (also called an oil press). When the pressure heating device 3 is an autoclave, the mold 4 has through holes 40 ; when the pressure heating device 3 is a molding machine, the molding machine has a high-pressure pipeline 30 that communicates with the inside of the mold 4 .

The foaming method includes the following steps:

Step A, open the valve 20 of the transmission pipeline 2, and introduce the plastic pellets into the mold 4 from the storage tank 1 through the transmission pipeline 2;

Step B, the pressure heating device 3 presses and heats the mold 4, if the plastic pellets are polyolefin materials, proceed to step C, and if the plastic pellets are thermoplastic elastomers, proceed directly to step D;

Step C, high-pressure impregnation is carried out with supercritical fluid in the mold, and the supercritical fluid infiltrates the plastic particles through the high-pressure pipeline 30 or the through holes 40 of the mold to obtain the plastic particles infiltrated by the supercritical fluid;

Step D, after pressure relief, the plastic pellets are foamed and molded in the mold 4 at a ratio of 1:1, the mold 4 is cooled after the foam molding, and the mold 4 is cooled to perform a mold opening operation (that is, to separate the upper mold and the lower mold of the mold), and take out the mold. foam products.

As a preferred solution, if the plastic particles are polyolefin materials, before step A, the following steps are also performed: step E, crosslinking the plastic particles to obtain cross-linked plastic particles.

The above-mentioned foaming method does not need to use an injection molding machine or an extruder, and also does not need to set a buffer tank, which greatly reduces the equipment cost of material foaming. In addition, the above foaming method adopts a heating method, and the material is in a molten or softened state when foaming, and the foaming efficiency is high, and the plastic particles can be fully foamed and formed.

-Introduction of plastic pellets-

Open the valve of the transfer line, and introduce the plastic pellets from the storage tank into the mold through the transfer line.

Plastic pellets useful in the supercritical fluid foaming method of the present invention include polyolefin compositions and thermoplastic elastomers.

The polyolefin composition includes a polyolefin material, and the polyolefin material is doped with one or more of a crosslinking agent, a filler, and an adjuvant. The cross-linking agent can interact with the polyhydrocarbon resin to form bridge bonds between the polymer molecular chains and become an insoluble substance with a three-dimensional structure; the filler can improve the properties of the material, increase the capacity, increase the weight, and reduce the cost of the material. Solid substance; additives can improve the fluidity of the main material. Wherein, based on the weight part of the polyolefin material as 100 phr, the amount of the crosslinking agent can be 0.15phr-1.1phr, preferably 0.25phr～1.0phr, the amount of the filler can be less than 30phr, and the amount of the auxiliary agent can be less than 10phr .

The polyolefin material may include one or more of ethylene-vinyl acetate copolymer (EVA), polyolefin elastomer (POE), low density polyethylene (LDPE), and ethylene propylene diene rubber (EPDM). For example, the polyolefin material can be EVA, wherein the molar content of vinyl acetate is 5% to 40%, or it can be a mixture of EVA/POE with a blending ratio of 100/0.1 to 0.1/100, or it can be a polyolefin material Blends with rubber materials, such as EVA/POE/EPDM (ethylene-propylene-diene rubber) blends, with a blending ratio of 100/0.1/0.1 to 0.1/100/20.

The cross-linking agent may include peroxides, including, for example, one or more of dicumyl peroxide (DCP), bis-tert-butyl dicumyl peroxide (BIPB).

The filler may include one or more of calcium carbonate, talc, zinc oxide powder, and titanium dioxide.

The adjuvant may include one or more of paraffin wax and stearic acid.

The thermoplastic elastomer may include one or more of thermoplastic polyurethane (TPU), thermoplastic polyester elastomer (TPEE), block polyetheramide elastomer (Pebax), polyethylene (PE), polypropylene (PP).

-Pressure and heat-

Open the valve of the transfer line, the plastic pellets are transferred from the storage tank to the inside of the mold through the transfer line, and the inside of the pressure heating device pressurizes and heats the mold until the pressure and temperature inside the mold are constant.

As a preferred solution, the pressure heating device is a molding machine. Compared with the autoclave, due to the fast heat conduction of the molding machine, the heating temperature that the molding machine needs to provide is relatively low, which is more energy-saving; in addition, due to the good thermal conductivity of the molding machine, the impregnation time is short, and the product is easy to take, which can greatly reduce the energy consumption. Increase productivity.

-Infiltrated plastic pellets-

The supercritical fluid is used for high-pressure infiltration in the mold, and the supercritical fluid infiltrates the plastic particles through the high-pressure pipeline or through holes of the mold to obtain the supercritical fluid-impregnated plastic particles. The supercritical fluid may include one or more of carbon dioxide, water, methane, ethane, ethylene, propylene, methanol, ethanol, acetone, and nitrogen. The pressure range of high pressure infiltration is 5-60MPa, the temperature range is 5°C higher than the softening point of the plastic pellets to 3°C lower than the melting point of the plastic pellets, and the duration of infiltration is 0.5-8h. In the obtained supercritical fluid-impregnated plastic particles, the supercritical fluid permeation amount of the plastic particles is 1-10% by weight. When the temperature of high-pressure infiltration is close to the melting point of the raw material, the raw material will become a molten state, and the supercritical fluid cannot be infiltrated smoothly; when the temperature of high-pressure infiltration is close to the softening temperature of the raw material, the raw material will be in a relatively hard state (that is, the strength is too high). , the supercritical fluid cannot remain in the raw material.

Claims (10)

1. A material foaming method for foaming and forming in a mold is characterized in that: the foaming method comprises the following steps:

step A, introducing plastic particles into a mold;

step B, a pressurizing and heating device pressurizes and heats the mold, if the plastic particles are made of polyolefin materials, the step C is carried out, and if the plastic particles are made of thermoplastic elastomers, the step D is directly carried out;

c, performing high-pressure impregnation by using a supercritical fluid in a mould, and impregnating the plastic particles by using the supercritical fluid to obtain the plastic particles impregnated by the supercritical fluid;

step D, after pressure relief, the plastic particles are placed in the mold 1: 1, foaming and forming, cooling the mould after foaming and forming, opening the mould after cooling the mould, and taking out a foamed product.

2. The material foaming method for in-mold foam molding according to claim 1, characterized in that: the supercritical fluid comprises one or more of carbon dioxide, water, methane, ethane, ethylene, propylene, methanol, ethanol, acetone, and nitrogen.

3. The material foaming method for in-mold foam molding according to claim 1, characterized in that: the pressure intensity of high-pressure infiltration is 5-60 MPa, the temperature range is 5 ℃ higher than the softening point of the plastic particles to 3 ℃ lower than the melting point of the plastic particles, and the infiltration duration is 0.5-8 h.

4. The material foaming method for in-mold foam molding according to claim 1, characterized in that: in the step D, the temperature range inside the mold is 25 ℃ lower than the melting point of the plastic particles to 25 ℃ higher than the melting point of the plastic particles, the pressure range inside the mold is more than 0.1MPa and less than or equal to 40MPa before pressure relief, and the pressure maintaining time is 0.2-5 h; and after pressure relief, the foaming duration is 5-10 min, and the mold is cooled to below 40 ℃ and then opened.

5. The material foaming method for in-mold foam molding according to claim 1, characterized in that: if the plastic particles are polyolefin material, before the step A, the following steps are further carried out: and E, performing a crosslinking reaction on the plastic particles to obtain crosslinked plastic particles.

6. The material foaming method for in-mold foam molding according to claim 1, characterized in that: the pressurizing and heating device is a molding press.

7. The material foaming method for in-mold foam molding according to claim 1, characterized in that: the polyolefin composition comprises a polyolefin material, and the polyolefin composition material is further doped with one or more of a cross-linking agent, a filler and an auxiliary agent.

8. The material foaming method for in-mold foam molding according to claim 7, wherein: the polyolefin material comprises one or more of ethylene-vinyl acetate copolymer, polyolefin elastomer, low-density polyethylene and ethylene propylene diene monomer.

9. The material foaming method for in-mold foam molding according to claim 7, wherein: the cross-linking agent is peroxide; the filler comprises at least one of calcium carbonate, talcum powder, mica powder, argil, zinc oxide powder and titanium dioxide; the auxiliary agent may comprise at least one of paraffin, stearic acid, zinc salt, calcium salt.

10. The material foaming method for in-mold foam molding according to claim 1, characterized in that: the thermoplastic elastomer comprises one or more of thermoplastic polyurethane, thermoplastic polyester elastomer, block polyether amide elastomer, polyethylene and polypropylene.

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