Method for producing polymethacrylimide foams
View Patent ↗The invention relates to an improved method for producing foamed material, especially poly(meth)acrylimide foams, which are foamed from polymer plates produced according to the casting method. The two-step method consists of a pre-heating step and at least one foaming step. The product obtained has a significantly smaller compressive strain, measured according to DIN 53425(ASMD 621), than prior art products.
1. A method for production of polymethylacrylimide foamed materials in the form of blocks or plates, comprising:
copolymerizing methacrylic acid and methacrylonitrile and optionally a copolymerizable monomer and additive in the presence of a radical-forming initiator, thereby obtaining a copolymer;
postpolymerizing and cyclizing said copolymer to said polymethylacrylimide, and
transforming said polymethylacrylimide to a foamed material, in a two-stage process step,
wherein
a first stage of said two-stage process step comprises preheating of the polymethylacrylimide to be foamed in a first hot-air oven or hot air oven section at a heating rate used to raise the temperature of between 0.001 K/min and 10 K/min,
while foaming of the preheated polymethylacrylimide takes place in a second stage of said two-stage process, in a second hot-air oven or hot-air ovens or hot air oven section.
2. The method according to claim 1 , in which the two hot-air ovens or hot-air oven sections used for the two-stage process have different temperatures.
3. The method according to claim 1 , in which the temperature of the hot-air oven used for preheating is lower, while being constant in time, than that of the hot-air oven or hot-air oven section used for foaming.
4. The method according to claim 1 , in which the temperature of the hot-air oven used for preheating is lower, while rising over the course of time, than that of the hot-air oven or hot-air oven section used for foaming, and wherein the temperature in the hot-air oven used for preheating can once again be equal, at the end of the heating cycle, to the temperature in the hot-air oven or hot-air oven section used for foaming.
5. The method according to claim 1 , in which the heating rate used to raise the temperature is between 0.01 K/min and 5 K/min.
6. The method according to claim 1 , in which the heating rate used to raise the temperature is between 0.1 K/min and 1 K/min.
7. The method according to claim 6 , in which different heating rates in combination with one another can be used for the average linear temperature rise.
8. The method according to claim 6 , in which the final temperature of the temperature rise can be higher than the temperature that is needed for foaming and that exists in the hot-air oven used for foaming.
9. The method according to claim 1 , wherein said copolymerizable monomer is present.
10. The method according to claim 1 , wherein said additive is present.
11. The method according to claim 1 , wherein said first stage of said two-stage process step is performed in at least one hot air oven.
12. The method according to claim 1 , wherein said first stage of said two-stage process step is performed in at least one hot air oven section.
13. The method according to claim 1 , wherein said second stage of said two-stage process step is performed in at least one hot air oven.
14. The method according to claim 1 , wherein said second stage of said two-stage process step is performed in at least one hot air oven section.