A transparent foam material with large pores and its preparation method and application

Abstract

The present invention discloses a transparent foam material with large pores, a preparation method thereof and an application in daily necessities. In terms of mass percentage, the raw material composition of the transparent foam material includes 99%-100% of a transparent plastic matrix and 0-1% of a cell nucleating agent. The present invention adopts a low-pressure injection molding physical foaming method, gets rid of the limitation of chemical foaming agents, does not have any small molecule chemical raw materials, and has greater advantages in terms of safety and environmental protection. The prepared product has a smooth appearance and uniform bubble distribution, reaching or even exceeding the effect brought about by using chemical foaming. At the same time, the introduction of bubbles achieves the purpose of lightweighting, and preserves the corresponding mechanical properties and optical properties to a certain extent, and has a very broad market prospect.

Description

Technical Field

[0001] The invention relates to the technical field of polymer material foaming, and in particular to a transparent foaming material with large pores, a preparation method and application thereof. Background Art

[0002] As an important part of the material system of human society, polymer materials are ubiquitous in human life. With the increasing use of polymer materials, a series of environmental pollution problems are inevitably brought about. And because of the decreasing oil resources, how to save limited polymer materials is also a key issue for human society.

[0003] As the main way to reduce weight, polymer foaming materials have been widely used in human society. However, most of the current foaming methods are chemical foaming. Physical foaming is gradually being accepted by production due to its unique advantages.

[0004] The patent specification with publication number CN 111117053 A discloses a highly transparent coarse-pore foam material and a preparation method thereof. The material comprises 1-2% of a nucleating agent, 60-100% of EVA, 40-0% of EPDM, 1-3% of STA, 0.4-0.8% of a cross-linking agent, 2-4% of a foaming agent, 2-4% of urea, and 1-3% of a cell fixing agent. A coarse-pore foam material with a closed-cell structure can be obtained by granulation and foaming. The material has the characteristics of large cell diameter and high light transmittance.

[0005] The patent specification with the publication number CN 111286070 A discloses a supercritical fluid injection foaming polylactic acid foam material and its preparation method. Cellulose nanofibers are used as biological fillers to modify and prepare lightweight and high-strength polylactic acid foam materials, and cellulose nanofibers are used as nucleating agents to improve the crystallization and melt properties of polylactic acid materials. The prepared cellulose nanofiber-modified polylactic acid composite material is mixed evenly with a supercritical fluid foaming agent in a microporous foaming injection molding machine, and combined with an opening and closing mold foaming device, microporous injection molding and foaming molding are performed to obtain a fully bio-based polylactic acid foam material.

[0006] At present, most foam materials mainly pursue small cell size and high cell density, and such foam materials can be widely used in structural parts and supporting parts. However, due to the high cell density and small cell size, light cannot penetrate, thus greatly sacrificing the aesthetics of some plastics with transparent properties.

[0007] In some daily necessities, some people have proposed to make large and small bubbles to improve the aesthetics. However, the scope involved is very small, and the foaming method used is limited to chemical foaming, which not only causes environmental pollution, but also may cause direct harm to human health. Moreover, changing different base materials may also bring certain changes to the selection of chemical foaming agents, thereby affecting the foaming process, and therefore is largely not conducive to industrial production. Summary of the invention

[0008] In response to the above-mentioned technical problems and the shortcomings in the field, the present invention provides a transparent foam material with large pores, which is based on a low-pressure injection molding foaming method, is environmentally friendly, energy-saving, and can be universally manufactured to have a transparent foam material with large pores that can be applied to surface structures.

[0009] A transparent foaming material with large pores comprises, by mass percentage, 99%-100% of a transparent plastic matrix and 0-1% of a pore nucleating agent.

[0010] In a preferred embodiment, the cell density of the transparent foam material with large cells is 3-50 cells / cm 3 , the pore size is 0.3-4mm.

[0011] In the transparent foamed material with large pores, the transparent plastic matrix can be a polymer that is transparent itself, and specifically can include at least one of SAN (styrene acrylonitrile), SMMA (styrene dimethyl methacrylate), PMMA (polymethyl methacrylate), and PC (polycarbonate).

[0012] In a preferred example, in the transparent foamed material with large cells, the cell nucleating agent is an inorganic silicate nucleating agent.

[0013] The present invention also provides a method for preparing the transparent foam material with large pores, comprising: adding the raw material of the transparent foam material with large pores into the barrel of an injection molding machine for low-pressure injection molding and foaming, injecting foaming gas during pre-molding, wherein the pressure of the foaming gas is 4-8 MPa, and then uniformly mixing the foaming gas with the raw material melt through the mixing and conveying function of the injection molding machine screw to obtain a mixed melt of the composite material / foaming gas;

[0014] During the pre-plasticization process, the screw speed is 5-40rpm and the back pressure is 4-8MPa;

[0015] After obtaining the mixed melt of the composite material / foaming gas, steps (1) to (4) are performed:

[0016] (1) Mold filling:

[0017] Open the injection molding machine nozzle and inject the composite material / foaming gas mixed melt into the mold cavity until it is completely filled;

[0018] The injection pressure of the mixed melt of composite material / foaming gas is 60-200MPa, and the injection speed is 40-200mm / s. Too low injection speed and injection pressure will lead to insufficient filling of the cavity.

[0019] (2) Maintaining pressure:

[0020] After the mixed melt of composite material / foaming gas completely fills the mold cavity, the pressure is maintained at 10-150MPa;

[0021] (3) Open and close mold foaming:

[0022] The moving platen of the mold opens rapidly, at which point the pressure of the composite material / foaming gas mixed melt drops rapidly and foaming begins;

[0023] (4) Finished product:

[0024] After the foaming is completed, the foam is cooled and the mold is opened to obtain a transparent foam material with large cells, wherein the weight loss of the obtained transparent foam material with large cells is 5%-50%;

[0025] Alternatively, the under-shot method is adopted: the nozzle of the injection molding machine is opened, and the mixed melt of the composite material / foaming gas is injected into the mold cavity, and partially filled according to the weight reduction. During the injection into the mold cavity, foaming is achieved due to the pressure drop of the gas, thereby obtaining a transparent foam material with large pores of the mold cavity size. After the foaming is completed, the mold is cooled and opened to obtain the transparent foam material with large pores. The weight reduction of the obtained transparent foam material with large pores is 5%-10%.

[0026] The foaming gas pressure used in the conventional physical foaming process is usually as high as 20-30 MPa, and the air intake is large. The resulting product has a large cell density and a small size, making it difficult to produce the transparent foamed material with large cells required by the present invention.

[0027] In order to obtain a transparent foam material with large pores, the present invention adopts low-pressure injection molding foaming. Through a specific screw pre-molding process, the intake pressure can be reduced to 4-8MPa, significantly reducing the intake volume, thereby obtaining a transparent foam material with large pore size, low pore density and number.

[0028] Too high an inlet pressure will result in too much gas, making the product not transparent. Too low a pre-molding back pressure will make it difficult for the gas to fully dissolve into the melt during the pre-molding process, resulting in insufficient filling of the mold cavity. Too high a pre-molding back pressure will prevent the gas from entering the melt, making it difficult to introduce bubbles. Too fast a pre-molding speed will result in less gas dissolution.

[0029] In the process of preparing the mixed melt of composite material / foaming gas, in a preferred example, the raw material of the transparent foaming material with large pores contains a pore nucleating agent, and the pore nucleating agent is evenly dispersed in the transparent plastic matrix through shearing and melt blending by the extruder screw to obtain the raw material of the transparent foaming material with large pores.

[0030] In the above process, in a preferred embodiment, the screw temperature of the extruder is 150-280°C;

[0031] In the preparation method of the present invention, each component of the raw material of the transparent foam material with large pores is dried in advance before use, the drying temperature is 60-80° C., and the drying time is 4-8 hours. Too low drying temperature or too short drying time will cause the plastic matrix to degrade during processing, thereby affecting the corresponding mechanical properties and optical properties.

[0032] In the process of preparing the composite material / foaming gas mixed melt, in a preferred embodiment, the foaming gas is nitrogen or carbon dioxide.

[0033] In a preferred embodiment, in the preparation method, the temperature of the injection molding machine from the material port to the nozzle is 50-250°C.

[0034] In a preferred embodiment, in the preparation method, the mold temperature is 40-120° C. Too low a mold temperature will result in too small bubbles, while too high a mold temperature will result in the formation of bubbles agglomerating, thus affecting the appearance and mechanical properties.

[0035] In a preferred embodiment, in the preparation method, in step (2), the holding time is 0.5-20s.

[0036] The invention also provides application of the transparent foaming material with large pores in daily necessities.

[0037] Compared with the prior art, the present invention has the following significant technical effects:

[0038] The present invention adopts a low-pressure injection molding physical foaming method, gets rid of the limitation of chemical foaming agents, does not have any small molecule chemical raw materials, and has greater advantages in terms of safety and environmental protection. In addition, the present invention is based on low-pressure injection molding foaming equipment. This equipment is not bound by the Mucell supercritical system, reduces the equipment cost of production, and avoids the equipment energy consumption caused by the high pressure process. The prepared product has a smooth appearance and uniform bubble distribution, reaching or even exceeding the effect brought by the use of chemical foaming. At the same time, the introduction of bubbles achieves the purpose of lightweighting, and preserves the corresponding mechanical properties and optical properties to a certain extent, and has a very broad market prospect. At the same time, the raw material preparation in its preparation process is simpler, the cost is lower, the preparation process is simple, the equipment cost is low, it is safe and environmentally friendly, and has good prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a photo of the transparent foamed material with large pores prepared in Example 1;

[0040] Figure 2 This is a photo of the transparent foamed material with large pores prepared in Example 2;

[0041] Figure 3 This is a real photo of the transparent foamed material with large cells prepared in Example 3;

[0042] Figure 4 This is a photo of the transparent foamed material with large pores prepared in Example 4;

[0043] Figure 5 This is a photo of the unfoamed material of Comparative Example 1. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer.

[0045] Example 1

[0046] The pure SAN material was placed in an oven at 80℃ and dried for 4h. The dried material was added to the injection molding machine, and the SAN melt was mixed with 5MPa of CO2 at a speed of 10rpm and a back pressure of 4.7MPa. Then, it was injected into the mold cavity at a temperature of 60℃ at an injection speed of 100mm / s and an injection pressure of 90MPa. After holding the pressure at 60MPa for 1s, the mold was opened once, and the mold opening distance was 1mm. After cooling for 50s, the following was obtained. Figure 1 The product shown has a cell size of 2.5-3.5 mm and a cell density of 3-3.5 cells / cm 3 .

[0047] Example 2

[0048] The difference between this embodiment and embodiment 1 is that the storage speed of this embodiment is 20rpm, the back pressure is 5.7MPa, the gas is 6MPa CO2, and the product is as follows: Figure 2 As shown, the cell size is 2-3.5 mm and the cell density is 8-10 / cm 3 .

[0049] Example 3

[0050] The difference between this embodiment and embodiment 1 is that the storage speed of this embodiment is 20rpm, the back pressure is 6MPa, the gas is 6.3MPa CO2, and the product is as follows: Figure 3 As shown, the cell size is 1-2.8 mm and the cell density is 15-23 / cm 3 .

[0051] Example 4

[0052] The difference between this embodiment and embodiment 1 is that the storage speed of this embodiment is 20rpm, the back pressure is 5.7MPa, the gas is 6MPa N2, and the product is as follows Figure 4 As shown, the cell size is 0.5-2 mm and the cell density is 14-20 / cm 3 .

[0053] Comparative Example 1

[0054] Place the pure SAN material in an oven at 80℃ and dry it for 4 hours; add the dried material to the injection molding machine, plasticize the material evenly at a speed of 60rpm, and inject the plasticized material into the mold at an injection pressure of 80-120MPa. The holding pressure is 60MPa, the holding time is 15s, and the mold is opened after cooling for 50s. Figure 5 Products shown.

[0055] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for preparing a transparent foam material with large pores, characterized in that: The raw material composition of the transparent foaming material with large cells includes 99%-100% of a transparent plastic matrix and 0-1% of a cell nucleating agent in terms of mass percentage; The preparation method comprises: adding the raw material of the transparent foaming material with large pores into the barrel of an injection molding machine for low-pressure injection molding and foaming, injecting foaming gas during pre-molding, the pressure of the foaming gas being 4-8 MPa, and then uniformly mixing the foaming gas with the raw material melt through the mixing and conveying function of the injection molding machine screw to obtain a mixed melt of the composite material / foaming gas; During the pre-plasticization process, the screw speed is 5-40rpm and the back pressure is 4-8MPa; After obtaining the mixed melt of the composite material / foaming gas, steps (1) to (4) are performed: (1) Mold filling: Open the injection molding machine nozzle and inject the composite material / foaming gas mixed melt into the mold cavity until it is completely filled; The injection pressure of the composite material / foaming gas mixed melt is 60-200MPa, and the injection speed is 40-200mm / s; (2) Maintaining pressure: After the mixed melt of composite material / foaming gas completely fills the mold cavity, the pressure is maintained at 10-150MPa; (3) Open and close mold foaming: The moving platen of the mold opens rapidly, at which point the pressure of the composite material / foaming gas mixed melt drops rapidly and foaming begins; (4) Finished product: After the foaming is completed, the foam is cooled and the mold is opened to obtain a transparent foam material with large cells, wherein the weight loss of the obtained transparent foam material with large cells is 5%-50%; Alternatively, the under-shot method is adopted: the nozzle of the injection molding machine is opened, and the mixed melt of the composite material / foaming gas is injected into the mold cavity, and partially filled according to the weight reduction. During the injection into the mold cavity, the gas has a pressure drop and foaming is achieved to obtain a transparent foam material with large pores of the mold cavity size. After the foaming is completed, the mold is cooled and opened to obtain the transparent foam material with large pores. The weight reduction of the obtained transparent foam material with large pores is 5%-10%; The mold temperature is 40-120℃.

2. The preparation method according to claim 1, characterized in that: The cell density of the transparent foamed material with large cells is 3-50 cells / cm 3 , the pore size is 0.3-4mm.

3. The preparation method according to claim 1 or 2, characterized in that: The transparent plastic matrix is ​​a transparent polymer, including at least one of SAN, SMMA, PMMA and PC; The cell nucleating agent is an inorganic silicate nucleating agent.

4. The preparation method according to claim 1, characterized in that: In the process of preparing the composite material / foaming gas mixed melt, the raw material of the transparent foaming material with large cells contains a cell nucleating agent, and the cell nucleating agent is evenly dispersed in the transparent plastic matrix through shearing and melt blending by the extruder screw to obtain the raw material of the transparent foaming material with large cells; The extruder screw temperature is 150-280°C; In the raw materials of the transparent foaming material with large pores, each component is dried in advance before use, the drying temperature is 60-80° C., and the drying time is 4-8 hours.

5. The preparation method according to claim 1, characterized in that: In the process of preparing the composite material / foaming gas mixed melt, the foaming gas is nitrogen or carbon dioxide.

6. The preparation method according to claim 1, characterized in that: The temperature of the injection molding machine from the material port to the nozzle is 50-250℃.

7. The preparation method according to claim 1, characterized in that: In step (2), the holding time is 0.5-20s.

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