Chemical foaming agent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of macromolecular polyethylene foam materials, and discloses a chemical foaming agent as well as a preparation method and application thereof. The chemical foaming agent contains azodicarbonamide and ammonium dihydrogen phosphate, and on the basis of the total weight of the chemical foaming agent, the content of the azodicarbonamide is 10-40 wt%, and the content of the ammonium dihydrogen phosphate is 60-90 wt%. According to the chemical foaming agent, the thermal decomposition initial temperature of azodicarbonamide is promoted to be reduced through ammonium dihydrogen phosphate, the decomposition process is controllable, foam pore distribution is more uniform, and foaming gas released in the polyethylene rotational molding foaming forming process is mainly CO2, so that the chemical foaming agent is more environment-friendly and energy-saving when being used in the polyethylene rotational molding foaming forming process.

Description

Technical Field

[0001] The invention relates to the technical field of high molecular polyethylene foaming materials, and in particular to a chemical foaming agent and a preparation method and application thereof. Background Art

[0002] In the science of foaming materials, the thermal decomposition characteristics of chemical foaming agents have a decisive influence on the performance of foaming materials. At present, there is still a blank of special foaming agents for roto-molded polyethylene foaming materials. The high-temperature decomposition characteristics of traditional foaming agents require higher processing temperatures to achieve ideal foaming effects, which poses a process challenge with the lower melting point of roto-molding grade polyethylene. During the roto-molding process, excessively high temperatures will cause the viscosity of the polyethylene melt to decrease, which is not conducive to high-quality molding of roto-molding foaming, and may cause inhomogeneity in the pore structure due to the temperature difference between the inside and the outside. The outer layer shows more large-sized pores due to the high temperature, while the inside shows small pores due to insufficient foaming.

[0003] In view of this, the thermal effect and decomposition rate of polyethylene foaming agents need to be considered for their adaptability to the rotational molding process. The thermal decomposition starting point of traditional foaming agents such as azodicarbonamide (about 210°C) is much higher than the melting point of polyethylene (usually below 130°C), which makes it easy to cause polyethylene aging and viscosity out of control while ensuring foaming. Therefore, the development of a new type of foaming agent composition with a moderate decomposition temperature and a controllable decomposition process has become a difficulty in the current industry. In order to meet the needs of refined polyethylene foaming, the research direction focuses on optimizing the decomposition kinetics of foaming agents and reducing by-products, exploring strategies such as silicic acid-modified azodicarbonamide to improve decomposition products and promote cell uniformity, as well as the combined use of azodicarbonamide and other types of foaming agents (such as sulfonylhydrazides), aiming to synergistically regulate the decomposition temperature and control the generation of by-product cyanuric acid, although this combination has the challenge of self-catalytic acceleration of the reaction. In order to further balance the thermal effect, research has also turned to compounding azodicarbonamide with endothermic foaming agents such as NaHCO3 and citric acid derivatives to regulate the thermal effect during the foaming process. However, how to match the appropriate decomposition temperature range to avoid the formation of bubbles with uneven structure remains a problem to be solved.

[0004] Therefore, technological innovation around rotomolding polyethylene foaming agent compositions, especially by precisely controlling the thermal decomposition behavior and kinetics of the foaming agent in order to optimize the polyethylene foaming effect and material properties, is becoming the key to current research. Its purpose is to overcome existing technical difficulties, promote the advancement of foaming technology and improve the quality of polyethylene foam materials. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems of the polyethylene foaming agent in the prior art that the decomposition temperature is too high and the decomposition process is uncontrollable, and to provide a chemical foaming agent and a preparation method and application thereof. The chemical foaming agent promotes the reduction of the thermal decomposition starting temperature of azodicarbonamide through ammonium dihydrogen phosphate, and its decomposition process is controllable, the pore distribution is more uniform, and the foaming gas released during the polyethylene rotational molding foaming process is mainly CO2. Therefore, the chemical foaming agent is more environmentally friendly and energy-saving when used in the polyethylene rotational molding foaming process.

[0006] In order to achieve the above-mentioned object, the first aspect of the present invention provides a chemical foaming agent, which contains azodicarbonamide and diammonium phosphate, wherein, based on the total weight of the chemical foaming agent, the content of azodicarbonamide is 10-40% by weight, and the content of diammonium phosphate is 60-90% by weight.

[0007] Preferably, the ammonium dihydrogen phosphate is distributed on the surface of the azodicarbonamide.

[0008] Preferably, the particle size of the azodicarbonamide is less than 30 μm, preferably 1-15 μm.

[0009] A second aspect of the present invention provides a method for preparing a chemical foaming agent, the method comprising the following steps:

[0010] (1) mixing azodicarbonamide and water and performing a first stirring to obtain a first suspension;

[0011] (2) mixing the first suspension and phosphoric acid and performing a second stirring to obtain a second suspension;

[0012] (3) mixing the second suspension and aqueous ammonia, performing a third stirring, and adjusting the pH value to 6.5-7.5 to obtain a third suspension;

[0013] (4) vacuum drying the third suspension.

[0014] Preferably, in the first suspension, the concentration of azodicarbonamide is 10-60 g / L.

[0015] Preferably, the mass ratio of the azodicarbonamide to the phosphoric acid is 1:(1.5-7).

[0016] Preferably, in step (1), the first stirring conditions include: temperature of 70-95° C., stirring rate of 200-600 r / min, and time of 2-10 h.

[0017] Preferably, in step (2), the second stirring conditions include: temperature of 70-95° C., stirring rate of 200-600 r / min, and time of 10-60 min.

[0018] Preferably, in step (3), the conditions for the third stirring include: temperature of 70-95° C., stirring rate of 200-600 r / min, and time of 10-30 min.

[0019] Preferably, in step (4), the conditions for the first vacuum drying include: temperature of 45-65° C., vacuum degree of 0.2-1 bar, and time of 20-30 h.

[0020] The third aspect of the present invention provides a chemical foaming agent prepared by the above method.

[0021] The fourth aspect of the present invention provides the use of the above-mentioned chemical foaming agent in polyethylene rotational foaming molding.

[0022] Through the above technical scheme, the foaming mechanism of the chemical foaming agent described in the present invention is different from that of the existing chemical foaming agent. The ammonium dihydrogen phosphate in the chemical foaming agent described in the present invention promotes the reduction of the initial thermal decomposition temperature of azodicarbonamide, wherein the ammonium dihydrogen phosphate thermally decomposes at about 180°C to generate ammonium metaphosphate, phosphoric acid, ammonia and water, while the polyethylene foaming molding processing temperature needs to be higher than 150°C, so it has a suitable decomposition temperature, its decomposition process is controllable, and the pore distribution is more uniform; in addition, azodicarbonamide reacts with water under the catalysis of phosphoric acid to release CO2 and NH3 and a small amount of N2, wherein NH3 will react with phosphoric acid to be absorbed, and the release is mainly CO2 gas. Therefore, it is more environmentally friendly and energy-saving when used in the polyethylene rotational molding foaming process, and the heat absorption of ammonium dihydrogen phosphate and the heat release of azodicarbonamide can form heat coupling during the polyethylene foaming process to achieve controllable thermal effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a thermogravimetric analysis diagram of the solid chemical foaming agent prepared in Example 1 and Comparative Example 2;

[0024] Figure 2 It is an optical microscope cell image of the polyethylene foam material prepared by the solid chemical foaming agent of Example 1 and Comparative Example 2;

[0025] Figure 3 It is a comparison diagram of the pore diameters of the inner and outer surfaces of the polyethylene foam materials prepared by the solid chemical foaming agents of Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0026] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0027] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0028] The chemical foaming agent of the present invention contains azodicarbonamide and ammonium dihydrogen phosphate, wherein, based on the total weight of the chemical foaming agent, the content of the azodicarbonamide is 10-40% by weight, and the content of the ammonium dihydrogen phosphate is 60-90% by weight. According to the chemical foaming agent of the present invention, the thermal decomposition starting temperature of azodicarbonamide is reduced by ammonium dihydrogen phosphate, so that its initial foaming temperature is about 180°C, at which time the polyethylene melt has high viscosity, good fluidity, and a certain viscosity, and the formed bubbles are smaller and more uniform, thereby improving the foaming effect. When the temperature is too high, the polyethylene viscosity is low, the formed pores are large, and the pores are easily melted; and the polyethylene foaming molding processing temperature needs to be higher than 150°C, so the chemical foaming agent of the present invention has a suitable decomposition temperature and a more matching decomposition temperature. In addition, azodicarbonamide reacts with water under the catalysis of phosphoric acid to produce and release CO2, NH3 and a small amount of N2, among which NH3 will react with phosphoric acid and be absorbed, and the main released gas is CO2. Therefore, its use in the polyethylene rotational molding foaming process is more environmentally friendly and energy-saving. In addition, during the polyethylene foaming process, the heat absorption of ammonium dihydrogen phosphate and the heat release of azodicarbonamide can form thermal coupling, thereby achieving controllable thermal effect.

[0029] In the chemical foaming agent of the present invention, in order to make the contact between azodicarbonamide and diammonium phosphate more complete, thereby improving the foaming effect, the diammonium phosphate is preferably distributed on the surface of the azodicarbonamide.

[0030] In the chemical foaming agent of the present invention, the particle size of the azodicarbonamide is less than 30 μm, preferably 1-15 μm. By limiting the particle size range of the azodicarbonamide, it is beneficial to prepare a more uniform cell distribution and obtain a better foaming effect.

[0031] In some embodiments, the chemical foaming agent of the present invention contains azodicarbonamide and diammonium phosphate, wherein, based on the total weight of the chemical foaming agent, the content of the azodicarbonamide is 10-40% by weight, the content of the diammonium phosphate is 60-90% by weight, the diammonium phosphate is distributed on the surface of the azodicarbonamide, and the particle size of the azodicarbonamide is less than 30 μm.

[0032] The present invention also provides a method for preparing a chemical foaming agent, the method comprising the following steps:

[0033] (1) mixing azodicarbonamide and water and performing a first stirring to obtain a first suspension;

[0034] (2) mixing the first suspension and phosphoric acid and performing a second stirring to obtain a second suspension;

[0035] (3) mixing the second suspension and aqueous ammonia, performing a third stirring, and adjusting the pH value to 6.5-7.5 to obtain a third suspension;

[0036] (4) vacuum drying the third suspension.

[0037] According to the method of the present invention, small-sized ammonium dihydrogen phosphate is synthesized by in-situ reaction, and the ammonium dihydrogen phosphate can be more evenly distributed on the surface of the azodicarbonamide, so that the azodicarbonamide and the ammonium dihydrogen phosphate are in contact more fully, thereby improving the foaming effect.

[0038] In the method of the present invention, in the first suspension, the concentration of the azodicarbonamide can be 10-60 g / L, preferably 20-50 g / L, for example, 10 g / L, 11.6 g / L, 14.5 g / L, 20 g / L, 25 g / L, 29 g / L, 35 g / L, 40 g / L, 45 g / L, 50 g / L, 55 g / L, 58 g / L or 60 g / L.

[0039] In the method of the present invention, in order to improve the foaming effect, the mass ratio of the amount of the azodicarbonamide and the phosphoric acid is preferably 1: (1.5-7), more preferably 1: (2-6), for example, 1: 1.5, 1: 1.69, 1: 2, 1: 2.5, 1: 3, 1: 3.5, 1: 3.38, 1: 4, 1: 4.5, 1: 5, 1: 5.5, 1: 6, 1: 6.5, 1: 6.76 or 1: 7. The concentration of the phosphoric acid can be 90-98wt%, preferably 95-98wt%. The concentration of the ammonia water can be 20-30wt%, preferably 25-30wt%.

[0040] In the method described in the present invention, in step (1), the first stirring conditions include: the temperature can be 70-95°C, preferably 75-85°C; the stirring rate can be 200-600r / min, preferably 300-400r / min; the time can be 2-10h, preferably 5-10h.

[0041] In the method described in the present invention, in step (2), the conditions for the second stirring include: the temperature can be 70-95°C, preferably 75-85°C; the stirring rate can be 200-600r / min, preferably 300-400r / min; the time can be 10-60min, preferably 30-60min.

[0042] In the method described in the present invention, in step (3), the conditions for the third stirring include: the temperature can be 70-95°C, preferably 75-85°C; the stirring rate can be 200-600r / min, preferably 300-400r / min; the time can be 10-30min, preferably 20-30min.

[0043] In the method of the present invention, in step (4), the conditions of the vacuum drying include: the temperature can be 45-65°C, preferably 45-55°C; the vacuum degree can be 0.2-1 bar, preferably 0.5-1 bar; the time can be 20-30 hours, preferably 22-26 hours. In this article, the vacuum degree is atmospheric pressure minus absolute pressure.

[0044] In some embodiments, the method for preparing the chemical foaming agent of the present invention comprises the following steps:

[0045] (1) mixing azodicarbonamide and water and performing a first stirring at 70-95° C. and a stirring rate of 200-600 r / min for 2-10 h to obtain a first suspension;

[0046] (2) mixing the first suspension and phosphoric acid and performing a second stirring at 70-95° C. and a stirring rate of 200-600 r / min for 10-60 min to obtain a second suspension;

[0047] (3) mixing the second suspension and aqueous ammonia, stirring for a third time at 70-95° C. at a stirring rate of 200-600 r / min for 10-30 min, and adjusting the pH value to 6.5-7.5 to obtain a third suspension;

[0048] (4) vacuum drying the third suspension at a temperature of 45-65° C. and a vacuum degree of 0.2-1 bar for 20-30 hours,

[0049] Wherein, in the first suspension, the concentration of the azodicarbonamide is 10-60 g / L; the mass ratio of the azodicarbonamide to the phosphoric acid is 1:(1.5-7).

[0050] In other embodiments, the method for preparing the chemical foaming agent of the present invention comprises the following steps:

[0051] (1) mixing azodicarbonamide and water and performing a first stirring at 75-85° C. and a stirring rate of 300-400 r / min for 5-10 h to obtain a first suspension;

[0052] (2) mixing the first suspension and phosphoric acid and performing a second stirring at 75-85° C. and a stirring rate of 300-400 r / min for 30-60 min to obtain a second suspension;

[0053] (3) mixing the second suspension and aqueous ammonia, stirring for a third time at 75-85° C. at a stirring rate of 300-400 r / min for 20-30 min, and adjusting the pH value to 6.5-7.5 to obtain a third suspension;

[0054] (4) vacuum drying the third suspension at a temperature of 45-55° C. and a vacuum degree of 0.5-1 bar for 22-26 hours,

[0055] Wherein, in the first suspension, the concentration of the azodicarbonamide is 20-50 g / L; the mass ratio of the azodicarbonamide to the phosphoric acid is 1:(2-6).

[0056] The present invention also provides a chemical foaming agent prepared by the above method. According to the chemical foaming agent of the present invention, the starting temperature of thermal decomposition of azodicarbonamide is lowered by ammonium dihydrogen phosphate, so that the starting foaming temperature of the chemical foaming agent is lower, the decomposition process is controllable, and the pore distribution is more uniform; in addition, the chemical foaming agent can achieve controllable thermal effect by heat coupling through the endothermic absorption of ammonium dihydrogen phosphate and the heat release of azodicarbonamide during the foaming process of polyethylene. The chemical foaming agent can be in a solid form.

[0057] The present invention also provides the application of the above-mentioned chemical foaming agent in polyethylene rotational molding and foaming. According to the application described in the present invention, the chemical foaming agent has a suitable decomposition temperature and a starting foaming temperature in polyethylene rotational molding and foaming, and its decomposition process is controllable, and the pore distribution is more uniform, wherein diammonium phosphate is thermally decomposed at about 180°C to generate ammonium metaphosphate, phosphoric acid, ammonia and water; in addition, azodicarbonamide reacts with water under the catalysis of phosphoric acid to release CO2 and NH3 and a small amount of N2, wherein NH3 will react with phosphoric acid and be absorbed, and the release is mainly CO2 gas, therefore, it is more environmentally friendly and energy-saving when used in the polyethylene rotational molding and foaming process, and diammonium phosphate can absorb heat and azodicarbonamide can release heat to form heat coupling during the polyethylene foaming process, so as to achieve controllable thermal effect.

[0058] In the application of the present invention, the reaction equation for the thermal decomposition of diammonium phosphate is as follows:

[0059] 2NH4H2PO4(s)→(NH4)2H2P2O7(s)+H2O(g)

[0060] NH4H2PO4(s)→NH3(g)+H3PO4(l);

[0061] The reaction equation for the reaction of azodicarbonamide with water under the catalysis of phosphoric acid to produce a large amount of CO2 and a small amount of N2 is as follows:

[0062] 3C2H4N4O2(s)+6H2O(g)→2N2(g)+6CO2(g)+8NH3(g).

[0063] The chemical foaming agent and its preparation method and application of the present invention are further illustrated by examples. The examples are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following examples.

[0064] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available. The azodicarbonamide in the examples was purchased from Shanghai Linuo New Materials Technology Co., Ltd., with an average particle size of 13.5 μm; the phosphoric acid in the examples was purchased from Chengdu Cologne Chemicals Co., Ltd., analytically pure, with a phosphoric acid concentration of 98 wt%; the ammonia water in the examples was purchased from Chengdu Cologne Chemicals Co., Ltd., analytically pure, with a ammonia water concentration of 25 wt%.

[0065] Example 1

[0066] (1) mixing 1.16 g of azodicarbonamide and 100 mL of water and stirring for 10 h at 80° C. at a stirring rate of 300 r / min to obtain a first suspension;

[0067] (2) mixing the first suspension obtained in step (1) with 7.84 g of phosphoric acid and performing a second stirring at 80° C. at a stirring rate of 300 r / min for 60 min to obtain a second suspension;

[0068] (3) mixing the second suspension obtained in step (2) with aqueous ammonia, stirring for a third time at 80° C. at a stirring rate of 300 r / min for 30 min, and adjusting the pH value to 7 to obtain a third suspension;

[0069] (4) The third suspension obtained in step (3) is vacuum dried at a temperature of 50° C. and a vacuum degree of 0.8 bar for 24 hours to obtain a solid chemical foaming agent.

[0070] Example 2

[0071] (1) mixing 1.16 g of azodicarbonamide and 80 mL of water and stirring for 8 h at 80° C. at a stirring rate of 350 r / min to obtain a first suspension;

[0072] (2) mixing the first suspension obtained in step (1) with 5.88 g of phosphoric acid and performing a second stirring at 80° C. at a stirring rate of 350 r / min for 60 min to obtain a second suspension;

[0073] (3) mixing the second suspension obtained in step (2) with aqueous ammonia, stirring for a third time at 80° C. at a stirring rate of 350 r / min for 30 min, and adjusting the pH value to 7 to obtain a third suspension;

[0074] (4) The third suspension obtained in step (3) is vacuum dried at a temperature of 50° C. and a vacuum degree of 0.8 bar for 24 hours to obtain a solid chemical foaming agent.

[0075] Example 3

[0076] (1) mixing 1.16 g of azodicarbonamide and 40 mL of water and stirring for 6 h at 80° C. at a stirring rate of 400 r / min to obtain a first suspension;

[0077] (2) mixing the first suspension obtained in step (1) with 3.92 g of phosphoric acid and performing a second stirring at 80° C. at a stirring rate of 400 r / min for 60 min to obtain a second suspension;

[0078] (3) mixing the second suspension obtained in step (2) with aqueous ammonia, stirring for a third time at 80° C. at a stirring rate of 400 r / min for 30 min, and adjusting the pH value to 7 to obtain a third suspension;

[0079] (4) The third suspension obtained in step (3) is vacuum dried at a temperature of 50° C. and a vacuum degree of 0.8 bar for 24 hours to obtain a solid chemical foaming agent.

[0080] Example 4

[0081] (1) mixing 1.16 g of azodicarbonamide and 20 mL of water and stirring for 4 h at 80° C. at a stirring rate of 450 r / min to obtain a first suspension;

[0082] (2) mixing the first suspension obtained in step (1) with 1.96 g of phosphoric acid and performing a second stirring at 80° C. at a stirring rate of 450 r / min for 60 min to obtain a second suspension;

[0083] (3) mixing the second suspension obtained in step (2) with aqueous ammonia, stirring for a third time at 80° C. at a stirring rate of 450 r / min for 30 min, and adjusting the pH value to 7 to obtain a third suspension;

[0084] (4) The third suspension obtained in step (3) is vacuum dried at a temperature of 50° C. and a vacuum degree of 0.8 bar for 24 hours to obtain a solid chemical foaming agent.

[0085] Example 5

[0086] (1) mixing 3.48 g of azodicarbonamide and 100 mL of water and stirring for 10 h at 80° C. at a stirring rate of 500 r / min to obtain a first suspension;

[0087] (2) mixing the first suspension obtained in step (1) with 7.84 g of phosphoric acid and performing a second stirring at 80° C. at a stirring rate of 500 r / min for 60 min to obtain a second suspension;

[0088] (3) mixing the second suspension obtained in step (2) with aqueous ammonia, stirring for a third time at 80° C. at a stirring rate of 500 r / min for 30 min, and adjusting the pH value to 7 to obtain a third suspension;

[0089] (4) The third suspension obtained in step (3) is vacuum dried at a temperature of 50° C. and a vacuum degree of 1 bar for 24 hours to obtain a solid chemical foaming agent.

[0090] Example 6

[0091] (1) mixing 1.0 g of azodicarbonamide and 100 mL of water and stirring for 2 h at 70° C. at a stirring rate of 200 r / min to obtain a first suspension;

[0092] (2) mixing the first suspension obtained in step (1) with 7.0 g of phosphoric acid and performing a second stirring at 70° C. at a stirring rate of 200 r / min for 10 min to obtain a second suspension;

[0093] (3) mixing the second suspension obtained in step (2) with aqueous ammonia, stirring for a third time at 70° C. at a stirring rate of 200 r / min for 10 min, and adjusting the pH value to 6.5 to obtain a third suspension;

[0094] (4) The third suspension obtained in step (3) is vacuum dried at a temperature of 65° C. and a vacuum degree of 1 bar for 20 hours to obtain a solid chemical foaming agent.

[0095] Example 7

[0096] (1) mixing 6 g of azodicarbonamide and 100 mL of water and stirring for 10 h at 95° C. at a stirring rate of 600 r / min to obtain a first suspension;

[0097] (2) mixing the first suspension obtained in step (1) with 9 g of phosphoric acid and performing a second stirring at 95° C. at a stirring rate of 600 r / min for 60 min to obtain a second suspension;

[0098] (3) mixing the second suspension obtained in step (2) with aqueous ammonia, stirring for a third time at 95° C. at a stirring rate of 600 r / min for 30 min, and adjusting the pH value to 7.5 to obtain a third suspension;

[0099] (4) The third suspension obtained in step (3) is vacuum dried at a temperature of 45° C. and a vacuum degree of 0.2 bar for 30 hours to obtain a solid chemical foaming agent.

[0100] Comparative Example 1

[0101] A solid chemical foaming agent was prepared according to the method of Example 1, except that the amount of azodicarbonamide was changed to 7.84 g, and the amount of phosphoric acid was changed to 1.16 g.

[0102] Comparative Example 2

[0103] The purchased azodicarbonamide was directly used as a solid chemical foaming agent.

[0104] Comparative Example 3

[0105] 2.5g of azodicarbonamide was dissolved in 100mL of dimethyl sulfoxide, and stirred and mixed at a constant temperature of 60°C for 20min to obtain a foaming agent solution; 2.0g of α-zirconium phosphate (α-ZrP) was added to the foaming agent solution, and stirred and mixed at 70°C for 15 hours to obtain a mixed solution; the mixed solution was precipitated and filtered, and the filter cake was washed twice with dimethyl sulfoxide, then filtered, placed in a vacuum oven, and dried at 70°C to obtain a nanocomposite foaming agent. Thermogravimetric analysis (the method refers to the national standard GB / T17050-1997 "Thermal Radiation Terminology") shows that the mass ratio of azodicarbonamide to α-ZrP is 1:1.

[0106] Test Example 1

[0107] The solid chemical foaming agents prepared in Examples 1-7 and Comparative Examples 1-3 were subjected to thermogravimetric analysis by a thermogravimetric analyzer. The thermogravimetric analysis method refers to the national standard GB / T 17050-1997 "Thermal Radiation Terminology". The thermogravimetric analysis graphs of the solid chemical foaming agents prepared in Example 1 and Comparative Example 2 are as follows: Figure 1As shown; the measured mass proportions of azodicarbonamide and ammonium dihydrogen phosphate in the solid chemical foaming agent of Examples 1-7 and Comparative Examples 1 and 2 are recorded in Table 1; the measured initial decomposition temperatures of the solid chemical foaming agents prepared in Examples 1-7 and Comparative Examples 1-3 are recorded in Table 1.

[0108] Table 1

[0109]

[0110] Depend on Figure 1 It can be seen that the initial decomposition temperature of the solid chemical foaming agent of Example 1 is 30° C. lower than that of the solid chemical foaming agent of Comparative Example 2, and the initial decomposition temperature of the solid chemical foaming agent of Example 1 is more suitable for polyethylene foaming molding.

[0111] It can be seen from the results in Table 1 that, compared with Comparative Examples 1-3, the thermal decomposition starting temperature of the embodiment using the chemical foaming agent of the present invention is more suitable for polyethylene foaming molding.

[0112] Test Example 2

[0113] The polyethylene rotomolding foaming performance test was performed on the solid chemical foaming agents prepared in Examples 1-7 and Comparative Examples 1-3. The test method is as follows: polyethylene and solid chemical foaming agent are melt blended at a mass ratio of 100:1.5, and a twin-screw extruder with a diameter of 16 mm and an aspect ratio (L / R) of 40 is used for melt processing at 150°C. The blend is then ground into powder at 60°C for subsequent rotomolding foaming processing and molding tests. The size of the rotomolding experimental mold is 450mm×370mm×200mm, the rotomolding processing temperature is 270°C, and the heating time is set to 24min. The rotational speeds of the main shaft and secondary shaft of the rotomolding machine are set to 5r / min and 8r / min, respectively; the pores of the polyethylene foam material prepared by the solid chemical foaming agent of Example 1 and Comparative Example 2 are characterized by an optical microscope, and the optical microscope pore images of the polyethylene foam material prepared by the solid chemical foaming agent of Example 1 and Comparative Example 2 are analyzed and measured, as shown in FIG. Figure 2 As shown, Figure 2 a is an optical microscope cell image of the inner surface of the polyethylene foam material of Comparative Example 2, Figure 2 b is an optical microscope cell image of the outer surface of the polyethylene foam material of Comparative Example 2, Figure 2 c is an optical microscope cell image of the inner surface of the polyethylene foam material of Example 1, Figure 2d is an optical microscope cell image of the outer surface of the polyethylene foam material of Example 1; the cell diameters of the inner and outer surfaces of the polyethylene foam materials prepared by the solid chemical foaming agents of Examples 1-7 and Comparative Examples 1-3 were measured by optical microscopy and recorded in Table 2, a comparison diagram of the cell diameters of the inner and outer surfaces of the polyethylene foam materials prepared by the solid chemical foaming agents of Example 1 and Comparative Example 2, as shown in Table 2. Figure 3 shown.

[0114] Table 2

[0115] serial number Inner surface cell diameter (μm) Cell diameter on the outer surface (μm) Example 1 401 492 Example 2 422 531 Example 3 435 552 Example 4 450 568 Example 5 447 554 Example 6 408 497 Example 7 461 577 Comparative Example 1 573 986 Comparative Example 2 594 1022 Comparative Example 3 503 923

[0116] Depend on Figure 2 It can be seen that the inner and outer surface pore morphologies of the polyethylene foam material prepared by the chemical foaming agent of Comparative Example 2 are not uniform; the inner and outer surface pore morphologies of the polyethylene foam material prepared by the chemical foaming agent of Example 1 are more uniform.

[0117] Depend on Figure 3 It can be seen that the inner and outer pore diameters of the polyethylene foam material prepared by the chemical foaming agent of Comparative Example 2 are quite different, while the inner and outer pore diameters of the polyethylene foam material prepared by the chemical foaming agent of Example 1 are slightly different, and the pore diameter is smaller.

[0118] It can be seen from the results in Table 1 that, compared with Comparative Examples 1-3, the polyethylene foam material prepared using the chemical foaming agent of the present invention has a smaller difference in pore diameter between the inner surface and the outer surface, and has a smaller pore diameter, and has a better foaming effect.

[0119] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A chemical foaming agent, characterized in that The chemical foaming agent contains azodicarbonamide and diammonium phosphate, Wherein, based on the total weight of the chemical foaming agent, the content of the azodicarbonamide is 10-40% by weight, and the content of the diammonium phosphate is 60-90% by weight.

2. The chemical foaming agent according to claim 1, characterized in that The ammonium dihydrogen phosphate is distributed on the surface of the azodicarbonamide.

3. The chemical foaming agent according to claim 1 or 2, characterized in that The particle size of the azodicarbonamide is less than 30 μm, preferably 1-15 μm.

4. A method for preparing a chemical foaming agent, characterized in that: The method comprises the following steps: (1) mixing azodicarbonamide and water and performing a first stirring to obtain a first suspension; (2) mixing the first suspension and phosphoric acid and performing a second stirring to obtain a second suspension; (3) mixing the second suspension and aqueous ammonia, performing a third stirring, and adjusting the pH value to 6.5-7.5 to obtain a third suspension; (4) vacuum drying the third suspension.

5. The method according to claim 4, characterized in that In the first suspension, the concentration of azodicarbonamide is 10-60 g / L; and / or The mass ratio of the azodicarbonamide to the phosphoric acid is 1:(1.5-7).

6. The method according to claim 4 or 5, characterized in that: In step (1), the first stirring conditions include: temperature of 70-95° C., stirring rate of 200-600 r / min, and time of 2-10 h.

7. The method according to any one of claims 4 to 6, characterized in that: In step (2), the second stirring conditions include: temperature of 70-95° C., stirring rate of 200-600 r / min, and time of 10-60 min.

8. The method according to any one of claims 4 to 7, characterized in that: In step (3), the conditions for the third stirring include: temperature of 70-95° C., stirring rate of 200-600 r / min, and time of 10-30 min.

9. The method according to any one of claims 4 to 8, characterized in that: In step (4), the vacuum drying conditions include: temperature of 45-65°C, vacuum degree of 0.2-1 bar, and time of 20-30 hours.

10. A chemical foaming agent prepared by the method according to any one of claims 4 to 9.

11. Use of the chemical foaming agent according to any one of claims 1 to 3 and 10 in polyethylene rotational foaming molding.

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