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CN-122011566-A - Light EVA (ethylene-vinyl acetate) foaming material based on intermittent foaming and heating and preparation method thereof

CN122011566ACN 122011566 ACN122011566 ACN 122011566ACN-122011566-A

Abstract

The invention relates to the technical field of high molecular foaming materials, and discloses a light EVA foaming material based on intermittent foaming and heating and a preparation method thereof, the raw materials of the catalyst comprise ethylene-vinyl acetate copolymer, maleic anhydride grafted ethylene-vinyl acetate copolymer, azodicarbonamide, basic zinc carbonate, triallyl isocyanurate, stearic acid and dicumyl peroxide. The preparation adopts a double-machine-position step heating and mechanical mode locking transfer process. The first stage of heating is initiated by dicumyl peroxide to construct a covalent cross-linking framework, and the second stage of foaming is carried out, wherein basic zinc carbonate is decomposed by heating, so that acid anhydride groups are hydrolyzed and combined with released zinc oxide in situ to form ionic cross-linking. The double-order cross-linked network formed by covalent bonds and ionic bonds can absorb the expansion stress of bubbles and stabilize the internal microstructure. The invention reduces the occurrence rate of cell combination and rupture under the low density condition, and obtains the foaming material with low apparent density and small compression set.

Inventors

  • CHEN JINSHUI
  • CHEN GUIQIANG
  • CHEN WENPING

Assignees

  • 锋特(福建)新材料科技有限公司

Dates

Publication Date
20260512
Application Date
20260307

Claims (10)

  1. 1. The light EVA foaming material based on intermittent foaming heating is characterized by being prepared from the following raw materials in parts by weight: 90-95 parts of ethylene-vinyl acetate copolymer; 5-10 parts of maleic anhydride grafted ethylene-vinyl acetate copolymer; 10-15 parts of azodicarbonamide; 2-4 parts of basic zinc carbonate; 0.5-1.0 parts of triallyl isocyanurate; 0.5-1.0 part of stearic acid; 0.8-1.2 parts of dicumyl peroxide.
  2. 2. The light EVA foam material based on intermittent foaming and heating according to claim 1, wherein the foam material is made of raw materials comprising the following parts by weight: 92 parts of ethylene-vinyl acetate copolymer; 8 parts of maleic anhydride grafted ethylene-vinyl acetate copolymer; 12 parts of azodicarbonamide; 3 parts of basic zinc carbonate; 0.8 parts of triallyl isocyanurate; 0.8 part of stearic acid; 1.0 part of dicumyl peroxide.
  3. 3. The light EVA foam material based on intermittent foaming temperature rise according to claim 1, wherein the maleic anhydride grafted ethylene-vinyl acetate copolymer is prepared by reactive extrusion of raw materials comprising the following parts by weight: 100 parts of ethylene-vinyl acetate copolymer; 1.5-2.5 parts of maleic anhydride; 0.05-0.10 part of 2, 5-dimethyl-2, 5-bis (tertiary butyl peroxy) hexane; the grafting rate of the maleic anhydride grafted ethylene-vinyl acetate copolymer is 0.82% -1.46%.
  4. 4. The light EVA foam material based on intermittent foaming and heating according to claim 3, wherein the preparation method of the maleic anhydride grafted ethylene-vinyl acetate copolymer comprises the following steps: Weighing raw materials according to parts by weight, and mixing for 3-5 minutes in a high-speed mixer at normal temperature to obtain a mixed material; Adding the mixed materials into a main feeding port of a homodromous double-screw extruder for reactive extrusion, setting the temperature of a feeding section to be 140-150 ℃, the temperature of a reaction section to be 170-190 ℃, the temperature of a metering and head section to be 160-170 ℃, and the rotating speed of a screw to be 150-250rpm; and opening a vacuum exhaust port at the tail end of the extruder, controlling the vacuum degree to be-0.08 MPa to-0.09 MPa to remove volatile substances, and performing water-cooling shaping, granulating and drying on the extruded polymer to obtain the maleic anhydride grafted ethylene-vinyl acetate copolymer.
  5. 5. The light EVA foam based on intermittent foaming and warming according to claim 1, wherein in the foam: the sum of the parts by weight of the ethylene-vinyl acetate copolymer and the maleic anhydride grafted ethylene-vinyl acetate copolymer is 100 parts; the weight ratio of triallyl isocyanurate to stearic acid is 1:1.
  6. 6. The preparation method of the light EVA foaming material based on intermittent foaming heating is characterized by comprising the following steps of, a process for the preparation of a light EVA foam based on intermittent foaming elevated temperature according to any one of claims 1 to 5, comprising the steps of: adding the ethylene-vinyl acetate copolymer and the maleic anhydride grafted ethylene-vinyl acetate copolymer into a pressurized internal mixer for mixing, then adding azodicarbonamide, basic zinc carbonate, triallyl isocyanurate and stearic acid, and continuing mixing; Starting an internal mixer for cooling, adding dicumyl peroxide for mixing after the materials are cooled, discharging the materials to a double-roller open mill, thin-passing out sheets, cutting the sheets into mother sheets, standing and curing; placing the cured master batch in a mold cavity provided with a mechanical mold locking and fastening device, pushing the master batch into a first press vulcanizer, closing a mold, pressurizing, and maintaining the temperature and pressure at a first temperature; After the pressure maintaining is finished, the upper plate and the lower plate of the die are rigidly locked by using the mechanical die locking fastening device to maintain the internal pressure of the die cavity, the pressure of the first vulcanizing machine is unloaded, the locked die is moved out and directly pushed into a second flat vulcanizing machine which is preheated to a second temperature, and the second temperature is higher than the first temperature; And (3) reapplying the mold closing pressure on the second plate vulcanizing machine, maintaining the temperature and pressure, instantly unloading the pressure after timing is finished, synchronously unlocking the mechanical mold locking device, expanding and ejecting the polymer matrix out of the mold, and cooling and shaping to obtain the product.
  7. 7. The method for preparing the light EVA foam material based on intermittent foaming and heating according to claim 6, wherein the temperature for mixing the ethylene-vinyl acetate copolymer and the maleic anhydride grafted ethylene-vinyl acetate copolymer in a pressurized internal mixer is 90-100 ℃ and the mixing time is 3-5 minutes; after the azodicarbonamide, the basic zinc carbonate, the triallyl isocyanurate and the stearic acid are added, the continuous mixing temperature is 95-105 ℃ and the time is 3-5 minutes.
  8. 8. The preparation method of the light EVA foaming material based on intermittent foaming heating as claimed in claim 6, wherein the adding of dicumyl peroxide is performed when the temperature of a material body is reduced to 85-90 ℃, and the mixing time after the adding of the dicumyl peroxide is 1-2 minutes; When the materials are discharged onto a double-roller open mill, the double-roller open mill is preheated to 75-80 ℃; The standing and ripening condition is that standing and ripening is carried out for 12-24 hours at room temperature.
  9. 9. The preparation method of the light EVA foaming material based on intermittent foaming heating of claim 6, wherein the glue filling rate of the mother film in a mould cavity is 95% -100%; the die closing pressure of the first press vulcanizer is 10-15MPa, the first temperature is set to be 130-145 ℃, and the constant temperature and pressure maintaining time at the first temperature is 8-12 minutes.
  10. 10. The method for preparing the light EVA foaming material based on intermittent foaming and heating according to claim 6, wherein the reapplication mold closing pressure of the second press vulcanizer is 10-15MPa, the second temperature is set to 160-180 ℃, and the constant temperature and pressure maintaining time at the second temperature is 5-10 minutes; The time for instantaneously unloading the pressure and synchronously unlocking the mechanical mode locking device is controlled to be less than 2 seconds.

Description

Light EVA (ethylene-vinyl acetate) foaming material based on intermittent foaming and heating and preparation method thereof Technical Field The invention relates to the technical field of high molecular foaming materials, in particular to a light EVA foaming material based on intermittent foaming and heating and a preparation method thereof. Background Ethylene-vinyl acetate copolymer (EVA) foaming materials are widely applied to the fields of shoe materials, packaging, sports equipment and the like because of good buffering and damping properties and easiness in processing. With the increasing demand for light weight, the preparation of light weight EVA foam with lower apparent density is becoming an important research point in this field. In conventional manufacturing processes, to reduce material density, it is often necessary to increase the amount of chemical blowing agent to increase the expansion ratio. However, a large amount of foaming agent instantaneously releases a large amount of gas upon thermal decomposition, resulting in extremely high internal gas pressure. Conventional single covalent crosslinking systems provide limited melt strength at the high temperature foaming stage and are difficult to withstand severe gas expansion stretching. When the expansion rate of the gas exceeds the deformation limit of the polymer matrix melt, the cell walls are susceptible to cracking, leading to cell consolidation and collapse of the internal structure of the material. Meanwhile, a conventional chemical foaming agent such as azodicarbonamide releases a large amount of heat upon decomposition. This concentrated exothermic phenomenon can cause excessive local temperature of the polymer matrix, further reducing the melt viscosity of the matrix, and making the expanded cell structure difficult to solidify and set. In the traditional single-stage hot-pressing foaming process, the crosslinking reaction and a large amount of decomposition processes of foaming agents are difficult to effectively separate, and a crosslinking network inside a material is impacted by high-pressure gas when the crosslinking network is not yet developed completely. The limitation on the process not only causes uneven cell size distribution of the light EVA foaming material, but also causes large shrinkage and high compression set of the final formed product, so that the existing foaming material is difficult to realize ultralow density and simultaneously has good mechanical stability and dimensional stability. Disclosure of Invention Aiming at the defects of the prior art, the invention provides the light EVA foaming material based on intermittent foaming heating and the preparation method thereof, and solves the problems that when the existing ethylene-vinyl acetate copolymer foaming material is used for preparing a low-density light foaming body, the melt strength of a polymer matrix and the gas release rate of a foaming agent are poor in matching, the phenomena of cell merging, collapse and cracking are easy to occur, and the foaming material with low density and high structural stability is difficult to obtain. In a first aspect, the invention provides a light EVA foaming material based on intermittent foaming and heating, which adopts the following technical scheme: the light EVA foaming material based on intermittent foaming heating is prepared from the following raw materials in parts by weight: 90-95 parts of ethylene-vinyl acetate copolymer; 5-10 parts of maleic anhydride grafted ethylene-vinyl acetate copolymer; 10-15 parts of azodicarbonamide; 2-4 parts of basic zinc carbonate; 0.5 to 1.0 parts of triallyl isocyanurate; 0.5-1.0 part of stearic acid; 0.8-1.2 parts of dicumyl peroxide. By adopting the technical scheme, the raw material system can spontaneously construct a double-order crosslinking network compounded by covalent bonds and ionic bonds in the processing process. Specifically, dicumyl peroxide is thermally decomposed to generate free radicals, and hydrogen atoms on macromolecular chains of the ethylene-vinyl acetate copolymer are abstracted with the aid of triallyl isocyanurate. The process initiates a radical coupling reaction between molecular chains, thereby forming a preliminary carbon-carbon covalent cross-linking framework and playing a role in improving the initial melt strength of the polymer system. As the system temperature increases to the foaming stage, azodicarbonamide is largely decomposed to produce nitrogen and carbon monoxide. During this period, basic zinc carbonate is heated to undergo decomposition reaction to produce nascent zinc oxide, carbon dioxide and water vapor. Notably, in a high-temperature and high-pressure closed environment, the water vapor released by decomposition attacks the anhydride groups on the maleic anhydride grafted ethylene-vinyl acetate copolymer chain segments to generate dicarboxylic acid through hydrolysis ring-opening reaction, and the generated dicarboxylic acid i