Prefoaming of poly(meth)acrylimide particles for subsequent foam moulding in closed tools
The invention relates to a process for the production of prefoamed poly(meth)acrylimide (P(M)I) particles which can be further processed to give foam mouldings or composites. A feature of this process is that a polymer granulate is first heated and thus prefoamed in an apparatus by means of IR radiation of a wavelength suitable for this purpose. Said granulate can be further processed in subsequent steps, e.g. in a press mould with foaming to give a moulding or a composite workpiece with foam core.
1. A process for the production of prefoamed poly(meth)acrylimide (P(M)I particles, comprising prefoaming unfoamed P(M)I particles by infrared radiation (“IR”) with an IR source, at least 80% of which has a wavelength of from 1.4 to 10.0 μm,
wherein the IR source used emits to an extent of at least 5% in a wavelength range from 5.0 to 9.0 μm, and
wherein the temperature of the IR source, calculated by Wien's method, is from 780 K to 1800 K.
2. The process according to claim 1 , wherein the IR source used emits to an extent of at least 5% in the wavelength range from 5.3 to 6.5 μm or from 7.8 to 8.9 μm.
3. The process according to claim 1 , wherein the temperature of the IR source, calculated by Wien's method, is from 800 to 1200 K.
4. The process according to claim 1 , wherein the unfoamed P(M)I particles have a particle size of from 0.5 to 5.0 mm.
5. The process according to claim 1 , wherein the prefoaming is carried out within at most 5 min.
6. The process according to claim 1 , wherein the unfoamed P(M)I particles are transported in a single layer on a conveyor belt through a heater unit having sources of IR.
7. The process according to claim 1 , wherein the unfoamed P(M)I particles are obtained as granulate from a semifinished P(M)I product by grinding.
8. The process according to claim 1 , wherein the unfoamed P(M)I particles are a suspension polymer.
9. The process according to claim 1 , wherein the maximum size of the prefoamed P(M)I particles is from 1.0 to 25 mm.
10. The process according to claim 1 , wherein a bulk density of the prefoamed P(M)I particles is from 60 to 300 kg/m.
11. A process, comprising:
prefoaming unfoamed P(M)I particles by infrared radiation (“IR”) with an IR source, at least 80% of which has a wavelength of from 1.4 to 10.0 μm,
wherein the IR source used emits to an extent of at least 5% in a wavelength range from 5.0 to 9.0 μm,
wherein the temperature of the IR source, calculated by Wien's method, is from 780 K to 1800 K,
wherein the unfoamed P(M)I particles are transported in a single layer on a conveyor belt through a heater unit having sources of IR, and
wherein after transport through the heating unit, the prefoamed P(M)I particles are transported directly into a shaping mould or into a storage container from which material is charged to at least one shaping mould.