Foaming EVA material and preparation method thereof

Abstract

The invention belongs to the technical field of EVA foaming materials, and particularly relates to a foaming EVA material and a preparation method thereof. The foaming EVA material comprises the following raw materials: a microwave absorbent, a heat-conducting filler, a lubricant, an antioxidant, a bridging agent and EVA, and further comprises a raw material elastomer in some schemes. Under the proportion of the raw materials, the foaming EVA material is prepared by dipping in carbon dioxide gas with the pressure of 5-7MPa and then carrying out microwave treatment. Under the support of the preparation method and raw material selection, low-pressure carbon dioxide gas (5-7 MPa) is adopted for impregnation and microwave treatment to obtain the foamed EVA material, compared with a traditional supercritical foaming technology under the high-pressure condition (generally larger than or equal to 12 MPa), the pressure resistance requirement and the operation risk of equipment are remarkably reduced, the production cost is reduced, and the production efficiency is improved. And the safety of the production process is also improved.

Description

Technical Field

[0001] The invention belongs to the technical field of EVA foaming materials, and more specifically relates to a foaming EVA material and a preparation method thereof. Background Art

[0002] Ethylene-vinyl acetate copolymer (EVA) foam materials are widely used in the fields of footwear, sporting goods, packaging materials, floor mats, toys, etc. due to their excellent properties such as light weight, softness, good elasticity, and strong cushioning and shock absorption. However, the existing preparation methods of foamed EVA materials are mainly divided into physical foaming and chemical foaming, but both have certain limitations.

[0003] Chemical foaming EVA usually uses azodicarbonamide (AC) and the like as a foaming agent, but these foaming agents will produce harmful substances such as semicarbazide during the decomposition process, which is considered to have a potential carcinogenic risk. In addition, the decomposition products of the chemical foaming agent may remain in the EVA, resulting in the continuous precipitation of harmful substances, causing potential harm to human health and the environment. Physical foaming mainly relies on supercritical gas to dissolve in EVA under high temperature and high pressure, followed by rapid pressure reduction foaming. Although the toxicity problem of chemical foaming agents is avoided, expensive high-pressure equipment and high operating pressure (greater than 12MPa) are required, which limits its application in large-scale production. Therefore, the preparation method of the existing foaming EVA material has obvious deficiencies in terms of environmental protection, production cost and equipment requirements. It is of great practical significance to develop an environmentally friendly, efficient and low-cost foaming EVA material and its preparation method. Summary of the invention

[0004] The purpose of the present invention is to provide a foamed EVA material and a preparation method thereof, so as to solve the problems existing in the above-mentioned prior art and realize the environmentally friendly, efficient and low-cost preparation of the foamed EVA material.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention is to provide a foamed EVA material, wherein the raw materials include, by weight:

[0007] 1.5-4 parts of microwave absorbent, 2-5 parts of thermal conductive filler, 1-10 parts of lubricant, 0.2-1 parts of antioxidant, 1-2.5 parts of bridging agent and 70-85 parts of EVA.

[0008] Furthermore, the microwave absorbent includes polyvinylidene fluoride and / or ferrosoferric oxide.

[0009] Furthermore, the thermally conductive filler includes nano boron nitride and thermally conductive fibers.

[0010] Optionally, the thermally conductive fibers include boron nitride fibers and / or silicon carbide fibers.

[0011] Furthermore, the lubricant includes at least one of stearic acid, zinc stearate and talc.

[0012] Furthermore, the antioxidant includes butylated hydroxytoluene (BHT) and / or dilauryl thiodipropionate (DLTDP).

[0013] Furthermore, the bridging agent includes one of dicumyl peroxide (DCP), di-tert-butyl dicumyl peroxide (BIPB), benzoyl peroxide (BPO), N,N'-m-phenylene bismaleimide (HVA-2) and triallyl isocyanurate (TAIC).

[0014] Furthermore, the raw materials of the foamed EVA material also include 5-12 parts of elastomer by mass.

[0015] Optionally, the elastomer includes at least one of styrene-ethylene / butylene-styrene block copolymer (SEBS), styrene-butadiene-styrene block copolymer (SBS), ethylene-octene copolymer (POE), butyl methacrylate-styrene copolymer (MBS), ethylene-propylene rubber (EPR) and ethylene-propylene diene monomer rubber (EPDM).

[0016] The second technical solution of the present invention is to provide a method for preparing the above-mentioned foamed EVA material, the steps comprising:

[0017] The raw materials except the bridging agent are fully mixed by extrusion, and then the bridging agent is added and mixed by milling, and then the EVA composition is prepared by hot pressing;

[0018] The EVA composition is impregnated with carbon dioxide gas at a pressure of 5-7 MPa at room temperature to obtain an impregnated EVA material;

[0019] The impregnated EVA material is subjected to microwave treatment to obtain the foamed EVA material.

[0020] Furthermore, the temperature of the hot pressing molding is 170-190° C., the time is 5-15 min, and the pressure is 2.5-5 MPa.

[0021] Optionally, the temperature of the hot pressing molding is 172° C., the time is 10 min, and the pressure is 3 MPa.

[0022] Furthermore, the room temperature immersion time is 1.5-2.5 hours, preferably 2 hours.

[0023] Furthermore, the power of the microwave treatment is 300-1200W, and the time is 60-300s.

[0024] Optionally, the power of the microwave treatment is 900 W and the time is 180 s.

[0025] The microwave absorbent added in the present invention can effectively absorb microwave energy, promote the rapid heating of EVA materials, and improve foaming efficiency. At the same time, nano boron nitride and thermal conductive fibers have excellent thermal stability and thermal conductivity, can provide a good heat conduction path during the foaming process, and further optimize the foaming effect. In addition, the boron nitride whiskers and silicon carbide fibers in the filler also have a certain microwave absorption capacity, can synergize with the microwave absorbent, and improve the electromagnetic properties of the material.

[0026] The present invention discloses the following technical effects:

[0027] With the support of the preparation method and raw material selection of the present invention, low-pressure carbon dioxide gas (5-7MPa) is used for impregnation, and then the foamed EVA material is obtained by microwave treatment. Compared with the high-pressure conditions (usually ≥12MPa) required by traditional supercritical foaming technology, the pressure resistance requirements and operation risks of the equipment are significantly reduced, the production cost is reduced, and the safety of the production process is improved.

[0028] The present invention utilizes microwave heating for foaming, which can rapidly heat the material to the temperature required for foaming in a short time, greatly shortening the foaming time. The rapid heating characteristics of microwaves make the foaming process more efficient. In addition, by simultaneously adding nano and two-dimensional heat-conducting fibers to form a heat-conducting channel, the foaming temperature can be accurately controlled, ensuring a uniform cell structure, further improving the performance and quality of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0030] Figure 1 In the figure, a is a physical picture of the EVA composition prepared in Example 1, b is a physical picture of the EVA foam material prepared in Example 1, and c is a SEM picture of the EVA foam material prepared in Example 1.

[0031] Figure 2 In the figure, a is a physical picture of the EVA composition prepared in Example 2, b is a physical picture of the EVA foam material prepared in Example 2, and c is a SEM picture of the EVA foam material prepared in Example 2.

[0032] Figure 3In the figure, a is a physical picture of the EVA composition prepared in Comparative Example 1, b is a physical picture of the EVA foam material prepared in Comparative Example 1, and c is a SEM picture of the EVA foam material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0033] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0034] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0035] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0036] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0037] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0038] The raw materials and reagents involved in the specific embodiments of the present invention are all commercially available products.

[0039] All “parts” involved in the specific embodiments of the present invention are “parts by mass”.

[0040] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in the art and are not the focus of the present invention.

[0041] Unless otherwise specified, the room temperature and normal temperature referred to in the specific embodiments of the present invention refer to 20-30°C.

[0042] The specification parameters of the talc powder used in the specific embodiment of the present invention are: BHS-818, purchased from Xufeng Powder Raw Materials Co., Ltd.; the specification parameters of the stearic acid used are: 95%, purchased from Aladdin Biochemical Technology Co., Ltd.; the specification parameters of the EVA used are: 7350M, purchased from Formosa Plastics Co., Ltd., Taiwan Province, China; the specification parameters of the nano-boron nitride used are: <150nm, purchased from Aladdin Biochemical Technology Co., Ltd.; the specification parameters of the boron nitride fiber used are: 10-20μm, purchased from Beijing Dekedao Jin Technology Co., Ltd.; the specification parameters of the polyvinylidene fluoride used are: 720, Arkema, France; the specification parameters of the SEBS used are YH-502T, purchased from Baling Petrochemical Branch of China Petrochemical Group Asset Management Co., Ltd.; the specification parameters of the ferroferric oxide used are: ≥97%, purchased from Aladdin Biochemical Technology Co., Ltd.; the specification parameters of the silicon carbide fiber used are: specific surface area 30±2m 2 / g, purchased from Beijing Dekedao Gold Technology Co., Ltd.

[0043] Example 1

[0044] The preparation steps of the foamed EVA material include:

[0045] S1. Raw material preparation: 8.9 parts of talc, 0.9 parts of stearic acid, 84.5 parts of EVA, 0.7 parts of nano-boron nitride, 1.5 parts of boron nitride fiber, 2.2 parts of polyvinylidene fluoride and 1.3 parts of bridging agent BIPB, set aside;

[0046] S2, talcum powder, stearic acid, polyvinylidene fluoride, nano boron nitride, boron nitride fiber and EVA are fully mixed by a twin-screw extruder to prepare modified EVA;

[0047] S3, after the modified EVA and the bridging agent BIPB are mixed by open milling, they are hot pressed at 172° C. for 10 min (pressure 3 MPa) by a hot press to obtain an EVA composition;

[0048] S4. Place the EVA composition in a carbon dioxide impregnation tank, set the pressure to 6 MPa, and impregnate it at room temperature for 2 hours. Then transfer it to a microwave oven, set the microwave power to 900 W, and treat it for 180 seconds to obtain an EVA foam material.

[0049] Figure 1 In the figure, a is a physical picture of the EVA composition prepared in Example 1, b is a physical picture of the EVA foam material prepared in Example 1, and c is a SEM picture of the EVA foam material prepared in Example 1.

[0050] Example 2

[0051] The preparation steps of the foamed EVA material include:

[0052] S1. Prepare raw materials: 8.9 parts of SEBS, 8.9 parts of talc, 0.9 parts of stearic acid, 75.6 parts of EVA, 0.7 parts of nano-boron nitride, 1.5 parts of boron nitride fiber, 2.2 parts of polyvinylidene fluoride and 1.3 parts of bridging agent BIPB, set aside;

[0053] S2, SEBS, talc, stearic acid, polyvinylidene fluoride, nano boron nitride, boron nitride fiber and EVA are fully mixed by a twin-screw extruder to prepare modified EVA;

[0054] S3, after the modified EVA and the bridging agent BIPB are mixed by open milling, they are hot pressed at 172° C. for 10 min (pressure 3 MPa) by a hot press to obtain an EVA composition;

[0055] S4. Place the EVA composition in a carbon dioxide impregnation tank, set the pressure to 6 MPa, treat at room temperature for 2 h, then transfer to a microwave oven, set the microwave power to 900 W, treat for 180 s, and obtain an EVA foam material.

[0056] Figure 2 In the figure, a is a physical picture of the EVA composition prepared in Example 2, b is a physical picture of the EVA foam material prepared in Example 2, and c is a SEM picture of the EVA foam material prepared in Example 2.

[0057] Example 3

[0058] Compared with Example 2, the only difference is that the microwave power is 300W.

[0059] Example 4

[0060] Compared with Example 2, the only difference is that the microwave power is 1200W.

[0061] Example 5

[0062] Compared with Example 1, the only difference is that polyvinylidene fluoride is replaced by an equal amount of ferrosoferric oxide.

[0063] Example 6

[0064] Compared with Example 2, the only difference is that the boron nitride fiber is replaced with an equal amount of silicon carbide fiber.

[0065] Comparative Example 1

[0066] The preparation steps of the foamed EVA material include:

[0067] S1. Prepare raw materials: 9.3 parts of talc, 0.9 parts of stearic acid, 88.4 parts of EVA and 1.4 parts of bridging agent BIPB, set aside;

[0068] S2, talcum powder, stearic acid and EVA are fully mixed by a twin-screw extruder to prepare modified EVA;

[0069] S3, after the modified EVA and the bridging agent BIPB are mixed by open milling, they are hot pressed at 172° C. for 10 min (3 MPa) to obtain an EVA composition;

[0070] S4. Place the EVA composition in a carbon dioxide impregnation tank, set the pressure to 6 MPa, and impregnate it at room temperature for 2 hours. Then transfer it to a microwave oven, set the microwave power to 900 W, and treat it for 180 seconds to obtain an EVA foam material.

[0071] Figure 3 In the figure, a is a physical picture of the EVA composition prepared in Comparative Example 1, b is a physical picture of the EVA foam material prepared in Comparative Example 1, and c is a SEM picture of the EVA foam material prepared in Comparative Example 1.

[0072] Comparative Example 2

[0073] Compared with Example 2, the only difference is that the power of the microwave is 200W.

[0074] Comparative Example 3

[0075] Compared with Example 2, the only difference is that the power of the microwave is 1500W.

[0076] Comparative Example 2

[0077] Compared with Example 2, the only difference is that the boron nitride fiber is replaced with an equal amount of aluminum oxide.

[0078] Comparative Example 3

[0079] Compared with Example 2, the only difference is that the nano boron nitride is replaced by an equal amount of boron nitride fibers.

[0080] Test example

[0081] The volume changes of the EVA compositions and EVA foamed materials prepared in Examples 1-2 and Comparative Example 1 are shown in Table 1. It can be seen from the data in Table 1 that the EVA composition prepared in the method embodiment of the present invention is immersed in low-pressure carbon dioxide gas and combined with microwave heating foaming to have an excellent foaming ratio.

[0082] Table 1

[0083]

[0084]

[0085] Depend on Figure 1-3 It can be seen that the samples of Examples 1 and 2 show obvious signs of foaming, and the foaming ratio of the sample of Example 1 is higher than that of Example 2, while the sample of Comparative Example 1 shows no obvious signs of foaming; according to the SEM image, the pore size of the foamed sample of Example 1 is uniform, the pore size of the sample of Example 2 is slightly different, and the pore size of the sample of Comparative Example 1 is different.

[0086] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0087] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A foamed EVA material, characterized in that: By mass, the raw materials include: 1.5-4 parts of microwave absorbent, 2-5 parts of thermal conductive filler, 1-10 parts of lubricant, 0.2-1 parts of antioxidant, 1-2.5 parts of bridging agent and 70-85 parts of EVA.

2. The foamed EVA material according to claim 1, characterized in that: The microwave absorbent includes polyvinylidene fluoride and / or ferrosoferric oxide; and / or the thermal conductive filler includes nano boron nitride and thermal conductive fiber; and / or the lubricant includes at least one of stearic acid, zinc stearate and talc.

3. The foamed EVA material according to claim 2, characterized in that: The thermally conductive fibers include boron nitride fibers and / or silicon carbide fibers.

4. The foamed EVA material according to claim 1, characterized in that: The antioxidant includes butylated hydroxytoluene and / or dilauryl thiodipropionate; and / or the bridging agent includes one of dicumyl peroxide, di-tert-butyl dicumyl peroxide, benzoyl peroxide, N,N'-m-phenylene bismaleimide and triallyl isocyanurate.

5. The foamed EVA material according to claim 1, characterized in that: The raw materials of the foamed EVA material also include 5-12 parts of elastomer by mass.

6. The foamed EVA material according to claim 5, characterized in that: The elastomer includes at least one of styrene-ethylene / butylene-styrene block copolymer, styrene-butadiene-styrene block copolymer, ethylene-octene copolymer, butyl methacrylate-styrene copolymer, ethylene-propylene rubber and ethylene-propylene-diene monomer rubber.

7. A method for preparing the foamed EVA material according to any one of claims 1 to 6, comprising: The raw materials except the bridging agent are fully mixed by extrusion, and then the bridging agent is added and mixed by milling, and then the EVA composition is prepared by hot pressing; The EVA composition is impregnated with carbon dioxide gas at a pressure of 5-7 MPa at room temperature to obtain an impregnated EVA material; The impregnated EVA material is subjected to microwave treatment to obtain the foamed EVA material.

8. The preparation method according to claim 7, characterized in that: The temperature of the hot pressing molding is 170-190° C., the time is 5-15 min, and the pressure is 2.5-5 MPa.

9. The preparation method according to claim 7, characterized in that: The room temperature immersion time is 1.5-2.5h.

10. The preparation method according to claim 7, characterized in that: The power of the microwave treatment is 300-1200W, and the time is 60-300s.

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