Preparation method of ptfe dispersion resin with core-shell structure
Disclosed is a preparation method of a PTFE dispersion resin with a core-shell structure, including: adding a fluorine-containing hydrocarbon and a fluorine-containing modifying monomer as nucleating agents in an initial nucleating stage of polymerization, adding a small amount of a non-PFOA surfactant to regulate a particle core structure, and adding the same or different non-PFOA surfactant during a growth stage to stabilize a dispersion. The method can avoid the use of PFOA surfactants, consume less surfactants and achieve good emulsion stability. The PTFE dispersion resin thus prepared has a core-shell multilayer structure, low extrusion pressure, good thermal stability, and excellent mechanical properties, and is especially suitable for the preparation of small-diameter tubes by high-compression-ratio paste extrusion.
1 . A preparation method of a polytetrafluoroethylene (PTFE) dispersion resin with a core-shell structure, comprising the following steps:
(1) stage I: adding water to a polymerization reactor, adding a fluorine-containing hydrocarbon nucleating agent, a fluorine-containing modifying monomer, a stabilizer, and a non-perfluorooctanoic acid (non-PFOA) surfactant in sequence, and then introducing a TFE monomer to form a solution; heating the solution to a reaction temperature, and dispersing the solution with stirring, then adding an initiator to start a polymerization reaction; emptying and replacing the unreacted monomer and modifying monomer in the polymerization reactor to remove the fluorine-containing modifying monomer to complete the reaction in a nucleating stage;
(2) stage II: adding the tetrafluoroethylene (TFE) monomer to a certain pressure to enter a homopolymerization reaction in a growth stage, and adding the same or different non-PFOA surfactant at this stage to stabilize the dispersion, and keeping the reaction pressure constant by further adding the TFE;
(3) stage III: adding a chain transfer agent or adding the fluorine-containing modifying monomer at the same time to continue the reaction until the end of the reaction; and
(4) cooling the dispersion to remove the stabilizer and then carrying out post-treatment to obtain the PTFE dispersion resin;
wherein the non-PFOA surfactant is one or more of a fluoroether acid or salt, a fluoroether sulfonic acid or salt, a fluoropolyether carboxylic acid or salt, a fluoropolyether sulfonic acid or salt, a hydrofluoroalkyl carboxylic acid or salt, a hydrofluoroalkyl sulfonic acid or salt, and a hydrocarbon-containing surfactant.
2 . The preparation method of a PTFE dispersion resin with a core-shell structure according to claim 1 , wherein the nucleating agent is used in an amount of 0.01-2 wt % of the solution.
3 . The preparation method of a PTFE dispersion resin with a core-shell structure according to claim 1 , wherein the non-PFOA surfactant is added to the polymerization reactor in two steps, respectively in the nucleating stage and the growth stage, and the total amount of the non-PFOA surfactant added in two steps is controlled to be 0.05-0.6 wt % of the solution, wherein the amount of the non-PFOA surfactant added in the nucleating stage is 5-50 wt % of the total amount of the non-PFOA surfactant added.
4 . The preparation method of a PTFE dispersion resin with a core-shell structure according to claim 1 , wherein the fluorine-containing modifying monomer is a fluorine-containing vinyl monomer and comprises a core-modifying monomer and a shell-modifying monomer.
5 . The preparation method of a PTFE dispersion resin with a core-shell structure according to claim 4 , wherein the core-modifying monomer is perfluoroalkyl vinyl ether, and the content of the perfluoroalkyl vinyl ether is 0.02-0.5 wt %; the shell-modifying monomer is fluorinated olefin, and the content of the fluorinated olefin is 0-0.5 wt % of the PTFE dispersion resin.
6 . The preparation method of a PTFE dispersion resin with a core-shell structure according to claim 1 , wherein the stage I refers to a stage of reaction proceeding to 5-20 wt % of the total addition of TFE, and the stage II refers to a stage of reaction proceeding to 80-95 wt % of the total addition of TFE.
7 . The preparation method of a PTFE dispersion resin with a core-shell structure according to claim 1 , wherein the PTFE dispersion resin with a core-shell structure has a core-shell-shell three-layer structure, wherein a core is made of a fluorine-containing olefin-modified PTFE, a middle shell is made of a PTFE homopolymer, and an outer shell is made of a lower-molecular-weight PTFE homopolymer or fluorine-containing olefin-modified PTFE.