Pressure-dependent foam moulding of poly(meth)acrylimide particles in closed moulds for producing rigid foam cores

• US 10,207,435 B2
• Filed: 06/25/2015
• Issued: 02/19/2019
• Est. Priority Date: 06/27/2014
• Status: Active Grant

• Current Assignee: Evonik Operations GmbH (Rag-Stiftung)
• Original Assignee: Evonik Rã¶Hm GmbH (Rag-Stiftung)
• Inventors: Bernhard, Kay, Liebl, Ina, Denk, Tim, Becker, Florian, Richter, Thomas
• Primary Examiner(s): Yi, Stella K
• Application Number:
  US15/321,845
• Publication Number:
  US 20170136665A1
• Time in Patent Office: 1,335 Days
• CPC Class Codes: B29C 44/143 Means for positioning the lining in the mould in general B29C33/12
• CPC Class Codes: B29C 44/3415 Heating or cooling
• CPC Class Codes: B29C 44/3426 Heating by introducing steam in the mould
• CPC Class Codes: B29C 44/3461 Making or treating expandable particles
• CPC Class Codes: B29C 44/445 in the form of expandable granules, particles or beads
• CPC Class Codes: B29K 2033/00 Use of polymers of unsaturated acids or derivatives thereof as moulding material B29K2035/00 takes precedence
• CPC Class Codes: B29K 2033/26 Polymers of acrylamide or methacrylamide
• CPC Class Codes: B29L 2031/30 Vehicles, e.g. ships or aircraft, or body parts thereof vanes or blades B29L2031/08, air bags B29L2022/027
• CPC Class Codes: B32B 15/046 of foam
• CPC Class Codes: B32B 15/18 comprising iron or steel B32B15/011, B32B15/012 and B32B15/013 take precedence
• CPC Class Codes: B32B 2266/0242 Acrylic resin
• CPC Class Codes: B32B 2605/08 Cars
• CPC Class Codes: B32B 2605/18 Aircraft blades, propellers B32B2603/00
• CPC Class Codes: B32B 5/245 another layer next to it being a foam layer
• CPC Class Codes: B32B 7/12 using interposed adhesives or interposed materials with bonding properties
• CPC Class Codes: C08J 2205/10 Rigid foams
• CPC Class Codes: C08J 2333/24 Homopolymers or copolymers of amides or imides
• CPC Class Codes: C08J 2333/26 Homopolymers or copolymers of acrylamide or methacrylamide
• CPC Class Codes: C08J 9/04 using blowing gases generated by a previously added blowing agent
• CPC Class Codes: C08J 9/232 by sintering expandable particles

Abstract

The invention relates to a process for the production of mold-foamed poly(meth)acrylimide (P(M)I) cores, in particular of polymethacrylimide (PMI) cores, which can be used by way of example in automobile construction or aircraft construction. A feature of this process is that polymer granules or polymer powder preheated under pressure are moreover charged under pressure to a compression mold where they are foamed with depressurization. In particular, a feature of the process is that it optionally uses a preferably two-shell compression mold for the heating and also for the cooling of the granules and, respectively, the rigid foam core formed therefrom.

Claims

1. A process for the production of a rigid poly(meth)acrylimide foam core, the process comprising:

heating poly(meth)acrylimide particles to an atmospheric-pressure-foaming temperature T₁ under a pressure p₁ wherein a volume of the poly(meth)acrylimide particles increases by at most 10% by volume in 10 min,

charging the poly(meth)acrylimide particles to a mould and closing the mould, wherein the charging takes place at a pressure p₂,

depressurizing a space within the mould to a pressure p₃ at a temperature T₂ and foaming the particles,

cooling the space within the mould to a temperature T₃ thereby obtaining a rigid poly(meth)acrylimide foam core,

opening the mould and removing the rigid poly(meth)acrylimide foam core.

2. The process according to claim 1, wherein the poly(meth)acrylimide particles are prefoamed poly(meth)acrylimide particles of size from 1.0 to 25.0 mm.

3. The process according to claim 1, wherein the poly(meth)acrylimide particles are poly(meth)acrylimide suspension polymers of size from 0.1 to 1.0 mm.

4. The process according to claim 1, wherein the foaming is performed within a time period of at most 2 min, and

wherein the process including the heating, the charging and closing, the depressurizing and foaming, and the opening and removing together are performed within a time period of from 5 to 45 min.

5. The process according to claim 1, wherein the charging of poly(meth)acrylimide particles to the mould and closing the mould is performed before the heating of polym(meth)acrylimide particles to an atmospheric-pressure-foaming temperature T₁.

6. The process according to claim 1, wherein the heating, the charging and closing, the depressurizing and foaming, and the opening and removing together are performed in sequence, and

wherein the pressure p₂ is at most 10% smaller than p₁.

7. The process according to claim 1, wherein the temperature T₁ is from 150 to 250°

C., and wherein the pressure p₁ and the pressure p₂ are from 2 to 20 bar.

8. The process according to claim 1, wherein the temperature T₂ is from 150 to 250°

C., and wherein the pressure p₃ is from 0.1 to 2.0 bar.

9. The process according to claim 1, wherein the temperature T₂ is from 180 to 220°

C., and wherein the pressure p₃ is from atmospheric pressure to 1.5 bar.

10. The process according to claim 1, wherein during the charging the poly(meth)acrylimide particles are sucked into the mould, blown into the mould, or both.

11. The process according to claim 1, wherein a mould fill level reached during the charging of the poly(meth)acrylimide particles to the mould is from 50 to 100%.

12. The process according to claim 1, wherein the particles are held during the heating of poly(meth)acrylimide particles in a holding vessel at temperature T₁ and at the pressure p₁,

the charging of poly(meth)acrylimide particles to the mould is performed in a batchwise manner, and

after the charging a connection between the holding vessel and the mould is closed before the depressurizing of the space within the mould to a pressure p₃ is performed.

13. The process according to claim 1, wherein the mould comprises at least two shells and each shell comprises a cavity of thickness from 2 to 20 cm which conforms to an internal shape of the mould and which covers an area of the space within the mould in a manner such that each cavity conforms to a shape of the space within the mould,

wherein a heating liquid is optionally passed through each cavity during the depressurizing of the space within the mould to a pressure p₃, and

wherein a cooling liquid is passed through each cavity during the cooling of the space within the mould to a temperature T₃.

14. The process according to claim 13, wherein

the heating liquid and the cooling liquid are both oils which do not comprise low-boiling fractions and which resist temperature up to at least 300°

C., and

the heating liquid and the cooling liquid are passed from two different holding vessels with different temperatures into each cavity, in a manner such that the temperature of the heating liquid is from 180 to 250°

C. and the temperature of the cooling liquid is from 20 to 40°

C.

15. The process according to claim 13, further comprising

equipping an internal side of each mould shell with prepregs or organopanels prior to the charging of the poly(meth)acrylimide particles to the mould, and

wherein the rigid poly(meth)acrylimide foam core is in the form of a composite material comprising outer layers.

16. The process according to claim 13, wherein the heating liquid is passed through each cavity during the depressurizing of the space within the mould to a pressure p₃.