An adc foaming agent for improving the density of foaming pores and a preparation method thereof
By surface-modifying the inorganic nucleating agent and adding it in the later stage of the oxidation reaction, the problem of uneven mixing of the nucleating agent was solved, resulting in a significant increase in pore density and improvement in material properties.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NINGXIA RISHNEG HIGH NEW IND CO LTD
- Filing Date
- 2026-04-02
- Publication Date
- 2026-07-10
AI Technical Summary
In the process of preparing synthetic materials, uneven mixing of nucleating agents and host materials leads to uneven and limited pore density, and existing technologies are unable to effectively improve pore density.
By surface modification of the inorganic nucleating agent, a uniform and stable suspension slurry is prepared. The modified inorganic nucleating agent is added in the later stage of the oxidation reaction to make it uniformly adhere to the surface of the ADC crystal, avoid agglomeration, and achieve high bonding strength.
It significantly improved the foam pore density, increasing the pore density by at least 3 times, while also improving the mechanical properties and yield of the material.
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Abstract
Description
Technical Field
[0001] This application relates to the field of foaming agent preparation, and in particular to an ADC foaming agent that improves the density of foamed pores and its preparation method. Background Technology
[0002] ADC foaming agent (i.e., azodicarbonamide foaming agent) is widely used in synthetic materials such as polyvinyl chloride, polyethylene, polypropylene, polystyrene, polyamide, and various rubbers. Applications include, but are not limited to, slippers, shoe soles, insoles, plastic wallpaper, ceilings, linoleum flooring, artificial leather, thermal insulation, and sound insulation materials. ADC foaming agent is characterized by stable performance, non-flammability, non-polluting nature, non-toxicity, odorless nature, non-corrosiveness to molds, non-staining effect on products, adjustable decomposition temperature, and no impact on curing and molding speed.
[0003] Pore density is a crucial technological direction for the current foaming materials industry to transform towards high performance, low carbonization, and high added value. To improve pore density, nucleating agents are incorporated during the preparation of synthetic materials. However, due to the relatively small amounts of foaming agents and nucleating agents incorporated, uneven mixing is easily achieved when combined with the main material. This results in both uneven pore density and limited pore density. Summary of the Invention
[0004] In view of this, this application proposes an ADC foaming agent that improves the foaming pore density and its preparation method.
[0005] A method for preparing an ADC foaming agent that increases the density of foamed pores includes the following steps:
[0006] The modified inorganic nucleating agent was mixed with water at a predetermined mass ratio, a dispersant was added, and the mixture was stirred to prepare a uniform and stable suspension slurry to prevent the nucleating agent from agglomerating.
[0007] Biurea is added to an oxidation reactor and chlorine gas is introduced to carry out the oxidation reaction. When the conversion rate of biurea reaches 80% to 85%, a suspension slurry is added to make the inorganic nucleating agent uniformly adhere to the surface of the ADC crystal.
[0008] The oxidation reaction continues until the biuret conversion rate reaches over 92%, then the mixture is washed, centrifuged, and dried to obtain the ADC foaming agent.
[0009] An ADC foaming agent that improves the density of foamed pores is prepared by the above method.
[0010] The technical effect of this application is that the preparation method of the ADC foaming agent that improves the foaming pore density first performs surface modification treatment on the inorganic nucleating agent, so that the inorganic nucleating agent is not easy to agglomerate and the pore density is relatively uniform.
[0011] In the later stage of the oxidation reaction process, when the biuret conversion rate reaches 80% to 85%, a modified inorganic nucleating agent is added. This not only avoids the nucleating agent being destroyed by the strong oxidation system, but also ensures that the nucleating agent and ADC crystals are fully combined.
[0012] This application incorporates an inorganic nucleating agent during the preparation of the ADC foaming agent, which significantly improves the foaming pore density compared to adding the inorganic nucleating agent during the subsequent preparation of the foam material. Detailed Implementation
[0013] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.
[0014] A method for preparing an ADC foaming agent that increases the density of foamed pores includes the following steps:
[0015] Step 1: Mix the modified inorganic nucleating agent with water at a predetermined mass ratio, add a dispersant, mix well, and prepare a uniform and stable suspension slurry to prevent the nucleating agent from agglomerating.
[0016] Step 2: When the biuret conversion rate reaches 80% to 85%, add a suspension slurry to allow the inorganic nucleating agent to adhere evenly to the surface of the ADC crystal.
[0017] Step 3: Continue the oxidation reaction until the biuret conversion rate reaches more than 92%, then wash, centrifuge and dry to obtain ADC foaming agent.
[0018] ADC foaming agent is obtained by oxidizing biuret with chlorine. Inorganic nucleating agents are chemically stable and do not easily decompose, dissolve, or structurally damage themselves in acidic or oxidizing environments. Extensive testing has shown that by modifying inorganic nucleating agents, they can adhere during the later stages of oxidation, accompanying the ADC crystal growth process, achieving higher bonding strength. Adding inorganic nucleating agents in the post-processing stage of ADC foaming agent leads to agglomeration and very poor dispersion. When organic nucleating agents, such as organophosphates, PMP microspheres, and cellulose, are added during the reaction stage, they undergo hydrolysis, oxidative degradation, or even complete loss of nucleating activity. Directly mixing inorganic nucleating agents into dry ADC powder results in uneven dispersion, requiring the addition of coupling agents, and the final distribution uniformity of the nucleating agent in the ADC foaming agent remains relatively poor.
[0019] In a preferred embodiment, the inorganic nucleating agent is selected from one of nano-silica, nano-calcium carbonate, and mesoporous silica.
[0020] In a preferred embodiment, the nano-silica is modified with a silane coupling agent KH550, and the amount of nano-silica added is 0.5% to 2% of the total mass of the ADC foaming agent. The ADC foaming agent prepared by adding modified nano-silica is suitable for shoe materials, thermal insulation materials, and other applications.
[0021] Experiments showed that when the content of modified nano-silica was below 0.5%, there were insufficient nucleation sites, and the increase in cell density was less than 30%, failing to achieve the desired modification effect. When the content of nano-silica was above 2%, the nano-silica was prone to agglomeration, which led to uneven cell structure, decreased mechanical properties, and a significant increase in cost.
[0022] In a preferred embodiment, the surface hydroxyl content of the nano-silica is ≥3 hydroxyl groups / nm. 2 The particle size is 20–50 nm.
[0023] In a preferred embodiment, the surface of the nano-calcium carbonate is coated with stearic acid, and the amount of nano-calcium carbonate added is 2% to 4% of the total mass of the ADC foaming agent. The ADC foaming agent with modified nano-calcium carbonate is suitable for PVC foamed sheets, pipes, shoe materials, and other applications.
[0024] Experiments showed that when the amount of modified nano-calcium carbonate added was less than 2%, the coverage of nucleation sites on the surface of ADC particles was less than 40%, and the increase in pore density was less than 10 times, failing to meet the requirements for microporous foaming. When the amount of nano-calcium carbonate added was greater than 4%, the excess nano-calcium carbonate could not be completely attached to the surface of the ADC crystals and would agglomerate in the aqueous phase, forming large particles of 1-3 μm. The loss rate during washing exceeded 30%, and the actual effective loading no longer increased linearly with the increase of the added amount.
[0025] In a preferred embodiment, the nano-calcium carbonate has an activation degree ≥95% and a particle size of 30–80 nm.
[0026] In a preferred embodiment, the mesoporous silica is modified by amylation, and the amount of mesoporous silica added is 0.3% to 1% of the total mass of the ADC blowing agent. The ADC blowing agent with modified mesoporous silica is suitable for high-end microporous foaming applications such as automotive lightweighting and electronic packaging.
[0027] Experiments showed that when the amount of modified mesoporous silica added was <0.3%, the coverage of mesoporous nucleation sites on the ADC crystal surface was <30%, the pre-existing gas nucleation effect of the mesopores could not be fully realized, and the increase in cell density was less than 10 times, failing to meet the requirements for microporous foaming. Excessive mesoporous particles would form additional heterogeneous interfaces during the foaming process, leading to an increased cell merging rate. In PP / PE and other polyolefin foaming systems, problems such as bubble breakage and collapse could even occur, resulting in a 10%–15% decrease in mechanical properties.
[0028] In a preferred embodiment, the mesoporous silica has a specific surface area ≥ 600 m². 2 / g, with a particle size of 50-100nm and a pore size of 2-5nm.
[0029] In a preferred embodiment, the mass ratio of the inorganic nucleating agent to water is 1:8 to 10.
[0030] In a preferred embodiment, the dispersant is sodium dodecylbenzenesulfonate, and the amount added is 0.1% to 0.2% of the water mass.
[0031] In a preferred embodiment, in step 2, the reaction temperature is 35–40°C, the pH value of the system is 1.5–2.5, and the reaction is continuously stirred.
[0032] In a preferred embodiment, during washing, the ADC foaming agent is washed with hot water at 60-70°C until the pH of the filtrate is 6-7, in order to remove residual oxidants and salts and prevent the surface modification layer of the inorganic nucleating agent from being damaged.
[0033] In a preferred embodiment, during drying, the ADC foaming agent is dried by airflow with an inlet air temperature of 110-120°C and an outlet air temperature of 60-70°C to prevent excessively high temperatures from causing the surface modifier of the nucleating agent to decompose.
[0034] The effects of the preparation method of the ADC foaming agent for improving the foaming pore density of this application will be explained below through examples and comparative examples.
[0035] Example 1
[0036] Take 1 kg of KH550 modified nano-silica (particle size 30 nm, surface hydroxyl content 3.2 hydroxyl groups / nm). 2 Mix with 8 kg of deionized water, add 8 g of sodium dodecylbenzenesulfonate, and disperse at 3000 rpm for 30 min to obtain a uniform suspension slurry;
[0037] 1000 kg of biuret was put into an oxidation reactor and chlorine gas was introduced to carry out the oxidation reaction. When the biuret conversion rate reached 82%, the above suspension slurry was slowly added dropwise. The addition was completed in 30 minutes. The reaction temperature was controlled at 38℃, the pH value at 2.0, and the stirring speed at 130 rpm. The mixture was kept warm and stirred for another 30 minutes.
[0038] Continue oxidation until the biuret conversion rate reaches 92%. Wash with 65°C hot water until the filtrate pH=6.5. After centrifugation, use airflow drying with an inlet air temperature of 115°C and an outlet air temperature of 65°C to obtain the ADC product. The amount of nano silica added is 0.91% of the total mass of ADC.
[0039] Comparative Example 1
[0040] Without adding nano-silica nucleating agent, the other processes are the same as in Example 1. Then, in the downstream EVA foaming stage, the same KH550 modified nano-silica as in Example 1 is added at 0.91% of the ADC mass. It is then mixed with ADC and EVA resin in a high-speed mixer at 1000 rpm for 5 minutes before foaming.
[0041] Example 2
[0042] Inorganic nucleating agent: Nano-silica, modified with KH550, with a particle size of 25nm and a surface hydroxyl content of 3.5 hydroxyl groups / nm. 2 The amount added is 1.5% of the total mass of the ADC. The rest of the process is the same as in Example 1.
[0043] Comparative Example 2
[0044] Unmodified ordinary nano-silica was used, and the other parameters were the same as in Example 2.
[0045] Example 3
[0046] Inorganic nucleating agent: stearic acid-coated nano-calcium carbonate, particle size 50 nm, activation degree 96%, added at 3% of the total mass of ADC. The inorganic nucleating agent to water mass ratio is 1:9, and the dispersant added is 0.15% of the water mass. The remaining processes are the same as in Example 1.
[0047] Comparative Example 3
[0048] Ordinary nano-calcium carbonate without stearic acid coating was used, with an activation degree of 65%, and the remaining parameters were the same as in Example 3.
[0049] Example 4
[0050] Inorganic nucleating agent: Aminated mesoporous silica, particle size 70nm, pore size 3nm, specific surface area 720m² 2 / g, the amount added is 0.8% of the total mass of the ADC. The rest of the process is the same as in Example 1.
[0051] Comparative Example 4
[0052] Ordinary nano-silica was used instead of mesoporous silica, with the same amount added, and all other parameters were the same as in Example 4.
[0053] Comparative Example 5
[0054] The nano-silica suspension slurry was added to the reaction system at the very beginning of the oxidation reaction (when the biuret conversion rate was <5%), and the remaining process parameters were the same as in Example 1.
[0055] Comparative Example 6
[0056] The nano-silica suspension slurry was added after the oxidation reaction was complete (biurea conversion rate ≥92.0%), and the remaining process parameters were exactly the same as in Example 1.
[0057] The ADC foaming agents prepared in each embodiment and comparative example were treated under the same foaming conditions, as follows:
[0058] The formulation system is completely consistent: all samples use the same formulation, 100 parts of EVA resin (VA content 18%, melt index 2.5g / 10min), 1.5 parts of zinc oxide, 0.8 parts of stearic acid, 0.6 parts of crosslinking agent DCP, and the amount of ADC foaming agent added is uniformly 4 parts, with no other additional additives.
[0059] The processing technology is completely identical:
[0060] Mixing: A two-roll open mill is used, the mixing temperature is 110℃, the mixing time is 8 minutes, and the number of thin passes is 6 to ensure that the material is mixed evenly.
[0061] Compression molding: Temperature 120℃, pressure 10MPa, pre-compression time 5min, to prepare a preformed sheet with a thickness of 2mm;
[0062] Foaming process: Flat vulcanizing machine compression molding foaming, temperature 170℃, pressure 15MPa, foaming time 5min, rapid pressure release and mold opening, foaming ratio uniformly controlled at 5 times ± 0.2 times.
[0063] The performance test conditions were exactly the same:
[0064] Cell structure test: Scanning electron microscope (SEM) was used to photograph the cross section of the sample, and ImageJ software was used to count the diameter and number of at least 1000 cells, and calculate the cell density and average diameter.
[0065] Mechanical property testing: Dumbbell-shaped specimens were prepared according to GB / T 528-2009 standard, with a tensile rate of 500 mm / min. Five specimens were tested in each group, and the average value was taken.
[0066] Yield rate statistics: The percentage of products without large bubbles, cross-bubbles, dents, or holes in each batch of 100 foam samples is counted.
[0067] Note: All samples were tested under the same EVA foaming system, with a foaming temperature of 170℃, a molding pressure of 15MPa, a foaming time of 5min, and a foaming ratio uniformly controlled at 5 times to eliminate the influence of process differences on performance.
[0068] The final test results are shown in Table 1.
[0069] Table 1
[0070]
[0071] As shown in Table 1, Example 1 and Comparative Example 1, inorganic nucleating agents can significantly improve the yield and foaming density of EVA resin during the foaming process. However, the improvement effect is more significant when inorganic nucleating agents are added during the preparation of ADC foaming agent compared to adding them during the foaming stage. Especially in terms of increasing foaming density, the effect is three times that of adding inorganic nucleating agents during the foaming stage.
[0072] Modified inorganic nucleating agents, such as nano-silica, calcium carbonate, and mesoporous silica, are less prone to agglomeration and exhibit higher dispersibility during the preparation of ADC foaming agents compared to unmodified inorganic nucleating agents. As shown in Tables 1 (Examples 2-4 and Comparative Examples 2-4), the ADC foaming agents prepared with modified inorganic nucleating agents, when used in EVA resin foam materials, increase the foam density by at least three times compared to those without modified inorganic nucleating agents, while also significantly improving the tensile strength of the material.
[0073] Meanwhile, the timing of adding the modified inorganic nucleating agent in this application is also very important. As can be seen from the comparison of data from Example 1 and Comparative Examples 5 and 6, adding the modified inorganic nucleating agent earlier or later will significantly reduce the final cell density.
[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.
Claims
1. A method for preparing an ADC foaming agent that improves the density of foamed pores, characterized in that: The modified inorganic nucleating agent was mixed with water at a predetermined mass ratio, a dispersant was added, and the mixture was stirred to prepare a uniform and stable suspension slurry. Biurea is added to an oxidation reactor, and chlorine gas is introduced to carry out the oxidation reaction. When the conversion rate of biurea reaches 80% to 85%, a suspension slurry is added. The oxidation reaction continued until the biuret conversion rate reached over 92%, then the mixture was washed, centrifuged, and dried to obtain the ADC foaming agent. The inorganic nucleating agent is selected from one of nano-silica, nano-calcium carbonate, and mesoporous silica. The nano-silica is modified with silane coupling agent KH550, and the amount of nano-silica added is 0.5% to 2% of the total mass of ADC foaming agent; The surface of the nano-calcium carbonate is coated with stearic acid, and the amount of nano-calcium carbonate added is 2% to 4% of the total mass of the ADC foaming agent; The mesoporous silica is modified by amylation, and the amount of mesoporous silica added is 0.3% to 1% of the total mass of the ADC foaming agent.
2. The preparation method of the ADC foaming agent for improving foam pore density as described in claim 1, characterized in that: The surface hydroxyl content of the nano-silica is ≥3 per nm. 2 The particle size is 20–50 nm.
3. The method for preparing the ADC foaming agent with increased foaming pore density as described in claim 1, characterized in that: The nano-calcium carbonate has an activation degree of ≥95% and a particle size of 30-80 nm.
4. The method for preparing the ADC foaming agent with improved foam pore density as described in claim 1, characterized in that: The mesoporous silica has a specific surface area ≥600 m². 2 / g, with a particle size of 50-100nm and a pore size of 2-5nm.
5. The method for preparing the ADC foaming agent with improved foam pore density as described in claim 1, characterized in that: The dispersant is sodium dodecylbenzenesulfonate, and the amount added is 0.1% to 0.2% of the water mass.
6. The method for preparing the ADC foaming agent with improved foam pore density as described in claim 1, characterized in that: After adding the suspension slurry, the reaction temperature is 35-40℃, the pH value of the system is 1.5-2.5, and the reaction is continuously stirred.
7. The method for preparing the ADC foaming agent with increased foaming pore density as described in claim 1, characterized in that: During washing, the ADC foaming agent is washed with hot water at 60-70℃ until the pH of the filtrate is 6-7.
8. The method for preparing the ADC foaming agent with improved foam pore density as described in claim 1, characterized in that: During drying, the ADC foaming agent is dried by airflow, with an inlet air temperature of 110-120℃ and an outlet air temperature of 60-70℃.
9. An ADC foaming agent, characterized in that: The ADC foaming agent is prepared by the method of any one of claims 1 to 8.