KIT FOR PRODUCING COMPOSITE SEMI-FINISHED PRODUCTS COMPRISING REVERSIBLY CROSSLINKED POLYMER EMULSIONS

Abstract

The invention concerns specifically emulsion polymers which are intraparticulately crosslinked via a hetero-Diels-Alder (HDA) mechanism. The crosslinked polymers can then be wholly or partly decrosslinked by thermal processing, for example in the form of a composite matrix, via a retro-Diels-Alder or retro-hetero-Diels-Alder reaction and interparticulately recrosslinked on cooling. This makes it possible to prepare long shelf life prepregs for composites. But it is also possible to thus realize other materials that have thermoset properties at use temperature but thermoplastic processing properties at a higher temperature.

Claims

1. A kit for producing a semi-finished composite product, the kit comprising: A) a fibrous backing, B) an aqueous polymer dispersion, comprising: B1) a first reactive component comprising two or more dienophilic double bonds, and B2) a second reactive component comprising two or more diene functionalities, wherein the first reactive component and the second reactive component are crosslinkable with each other via a Diels-Alder or hetero-Diels-Alder reaction and one or more than one of said two components B1) and B2) is an emulsion polymer.

2. The kit according to claim 1, wherein the fibrous backing A) comprises glass, carbon, a plastic, a natural fibre, or a mineral fibre, in the form of a nonwoven web, an interlooped fabric, a formed-loop knit, a drawn-loop knit, a non-interlooped construct, a unidirectional fibre textile, a long-fibre textile, or short-fibre textile.

3. The kit according to claim 1, wherein the dienophilic double bonds are carbon-sulphur double bonds.

4. The kit according to claim 1, wherein the dienophilic double bonds are groups comprising the structure ##STR00009## wherein Z is a 2-pyridyl group, a cyano group, a phosphoryl group or a sulphonyl group; wherein R.sup.m is a multivalent organic group or a polymer, and wherein n is a number between 2 and 20.

5. The kit according to claim 1, wherein the second reactive component B2) is a polymer obtained via emulsion polymerization, wherein the emulsion polymerization is caused by copolymerization of monomers comprising at least one polymerization-active group and at least one diene functionality.

6. The kit according to claim 1, wherein the emulsion polymer is a poly(meth)acrylate.

7. The kit according to claim 1, wherein the second reactive component B2) is the emulsion polymer.

8. A composite material or semi-finished composite product, obtained by the kit according to claim 1.

9. A process for producing a semi-finished composite product or a moulded part of the semi-finished composite product, the process comprising: I. optionally shaping a fibrous material, II. preparing an aqueous poly(meth)acrylate dispersion via emulsion polymerization of a monomer composition, wherein the monomer composition comprises monomers having a group copolymerizable with (meth)acrylates and a diene functionality, III. mixing the dispersion with a compound comprising two or more dienophilic double bonds to produce a second composition, IV. directly impregnating the fibrous material with the second composition and shaping into an uncured shaped composition, V. curing the uncured shaped composition at a crosslinking temperature T.sub.1 thereby obtaining the semi-finished composite product or the moulded part of the semi-finished composite product.

10. The process according to claim 9, further comprising: VI. heating the semi-finished composite product or the moulded part of the semi-finished composite product to a decrosslinking temperature T.sub.2 to produce a decrosslinked product, VII. reshaping the decrosslinked product into a reshaped composition, and VIII. newly curing the reshaped composition at the crosslinking temperature T.sub.1.

11. The process according to claim 10, wherein the crosslinking temperature T.sub.1 in step V., VIII., or both is between 0 and 60° C.

12. The process according to claim 10, wherein steps V., VIII., or both are performed at room temperature, wherein at least 50% of crosslinks are redetached in step VI. at the decrosslinking temperature T.sub.2 via a retro-hetero-Diels-Alder reaction, and wherein the decrosslinking temperature T.sub.2 is between 50 and 150° C. above the crosslinking temperature T.sub.1.

13. The process according to claim 9, wherein steps III. and IV. are carried out at a temperature T.sub.3 which is at least 40° C. above the crosslinking temperature T.sub.1, and wherein step V. is preformed by cooling down to the crosslinking temperature T.sub.1.

14. The process according to claim 10, wherein steps VI. to VIII. are repeated.

15. The process according to claim 9, wherein after process step IV. the uncured shaped composition is dried at a temperature T.sub.2 in a step IVa.

16. The process according to claim 10, further comprising cutting, milling, polishing, painting, or coating the semi-finished composite product or the moulded part of the semi-finished composite product after step V. or VIII. to form a shaped article in a process step IX.

17. The process according to claim 10, further comprising recycling the semi-finished composite product or the moulded part of the semi-finished composite product from step V. or VIII. in a step X. at a temperature T.sub.4, wherein said temperature T.sub.4 is not less than the decrosslinking temperature T.sub.2.

18. A semi-finished composite product or a moulded part of the semi-finished composite product obtained by the process of claim 9, wherein the semi-finished composite product is at least one selected from the group consisting of a boat- or shipbuilding product, an aerospace technology product, an automobile construction product, a two-wheeler product, a civil engineering product, a biomedical engineering product, a sports sector product, an electrical product, an electronics industry product and a power generation product.

19. A shaped article obtained from the process of claim 16, which is at least one selected from the group consisting of a boat- or shipbuilding product, an aerospace technology product, an automobile construction product, a two-wheeler product, a civil engineering product, a biomedical engineering product, a sports sector product, an electrical product, an electronics industry product and a power generation product.

20. The process according to claim 16, further comprising recycling the shaped article from step IX. in a step X. at a temperature T.sub.4, wherein said temperature T.sub.4 is not less than the decrosslinking temperature T.sub.2.

Description

EXAMPLES

Producing an Emulsion Polymer

[0093] A 2 L stirred reactor designed for emulsion polymerization is charged with 183 g of completely ion-free water and also 0.24 g of Disponil SUS IC 875 emulsifier. The completely ion-free water is heated to the target temperature of 75° C. Stirrer speed is 180 rpm. Starting at an internal temperature of 60° C., the reactor is purged with inert gas for 10 minutes. Thereafter, constant blanketing with inert gas is ensured.

[0094] Subsequently, a Woulff bottle purged with inert gas is initially charged in succession with the components for the emulsion:

[0095] 0.96 g of Disponil SUS IC 875

[0096] 0.72 g of 2-ethythexyl thioglycolate (TGEH)

[0097] 108.00 g of methyl methacrylate

[0098] 53.30 g of n-butyl methacrylate

[0099] 8.0 g of furfuryl methacrylate

[0100] 85.0 g of completely ion-free water

[0101] 0.4 ml of 10 wt % tert-butyl hydroperoxide solution

[0102] After the components have been weighed into the bottle, they are stirred for 5 minutes, followed by a quiescent period of 5 minutes and then renewed stirring for 30 minutes. Stirring is only discontinued again 20 minutes after starting the emulsion metering.

[0103] Once an internal temperature of 75° C. is attained in the reactor, 0.7 ml of 10 wt % tert-butyl hydroperoxide solution and 2.3 mL of 5 wt % sodium formaldehydesulphoxylate solution are admixed in succession.

[0104] Initiation is immediately followed by 1.1 g of emulsion/min being metered from the emulsion reservoir into the reactor for 15 minutes. The internal temperature of the reactor rises, attaining a 3° C. higher internal temperature in less than 5 minutes.

[0105] This is followed by gradual cooling down to a process temperature between 75 and 77° C. The 15 minutes of pre-metering are followed directly thereafter by the main metering at a metering rate of 2.4 g of emulsion/minute at said process temperature between 75 and 77° C. During the polymerization time the stirrer speed is set as high as 200 rpm.

[0106] An overall polymerization time of 120 minutes is followed by a 60 minute postreaction time at the process temperature. On completion of postreaction the stirrer contents are cooled down to room temperature at a stirrer speed of 200 rpm and filtered through a 250 μm nylon gauze to separate off solid constituents.

[0107] The yield is 98%. The amount of coagulum separated off in said filtration is less than 1 g based on a batch size of 450 g.

[0108] Reacting the Emulsion with MXBI Compimide:

[0109] Substances Employed:

[0110] Emulsion Polymer

[0111] Dehydran 150 defoamer

[0112] MXBI Compimide meta-xylyenebismaleimide

Procedure:

[0113] The emulsion as per the above description is initially charged to a large vessel and then admixed with about 0.1% of Dehydran 150 defoamer before the MXBI Compimide is gradually added (at about 500 rpm) and further stirring at 1000 rpm for a further 4 hours.

[0114] The required MXBI quantity corresponds to 90% of the stoichiometric equivalent based on the repeat units of furfuryl methacrylate in the polymer.

Tests with the Converted Emulsion Polymer in a Press:

[0115] Dry the material at 50° C. under reduced pressure for about 12 hours.

[0116] The dried powder is then comminuted until homogeneous and the homogeneous powder obtained in the process is placed in a compression mould and compression moulded into tablets or rodlets.

[0117] A moulding force of 50 to 55 kN is applied at a temperature between 160 and 180° C. for a period of 10 min.

Producing a Prepreg

[0118] Process step IV of directly impregnating the fibrous backing of glass, carbon or plastic from process step I. with the dispersion from process step III. is effected on commercially available coater systems, here a vertical coater. The fibrous backing is introduced into the process by clamping into the coater system. The dispersion from process step III. has a viscosity of 700 mPas and is introduced into the coater process via a pumped system with upstream stirring mechanism. In contradistinction to the usual methods of impregnation with thermoplastic matrices, which are impregnated with solid powder or at elevated temperatures in the melt, there is the option here of a liquid impregnation with the hereinabove detailed advantages of very good and homogeneous fibre impregnation.

[0119] The fibre material moves through this continuous process at a linear speed vi of 0.7 m/min. Impregnation is by kiss coating or alternatively by pad-mangling.

[0120] The vertical direction of the web minimizes matrix loss and additionally improves the homogeneity of impregnation and thus the quality of the prepreg. The matrix content is controllable within a range from 15 wt % to 60 wt % via the viscosity of the dispersion and downstream squeegees. In the case of the 700 mPas viscosity dispersion used in this example and two downstream squeegees to additionally enhance the impregnation quality by further squeezing through the matrix, the matrix content is 40 wt %. The fibre material saturated with dispersion is dried at a temperature of 130° C., i.e. at above T.sub.1 but below T.sub.2, for 5 minutes in a circulating air oven, or alternatively with IR radiators. Residual volatility as quantified via mass loss and DSC is below 1 wt %.

[0121] Since drying is carried out at a temperature above T.sub.1, the dried polymer is in the form of a crosslinked film. So a polymeric film has formed in contrast with, for example, prepregs produced by powder impregnation. The continuous prepreg obtained in this process accordingly remains flexible and allows simplified winding via suitable winding means without matrix fracture. Direct cutting within the impregnating process is not required because winding is possible, even to very low radii, without loss of matrix and/or quality.

Producing a Laminate

[0122] The crosslinked and dried semi-finished composite products (prepregs) are mouldable into a component part via process steps VI, VII and VIII. In this example an 8 ply prepreg construction having a matrix content of 40 wt % is IR heated to 200° C. in the course of 60 seconds and immediately placed in a cold mould. The heated multi-ply prepreg construction is subjected in the mould to a surface pressure of 40 bar for a further 60 seconds while being cooled down to room temperature and shaped. Once the temperature is below T.sub.1, the component part formed is in a crosslinked state having the above-described properties and a part thickness of 2 mm. Overall cycle time including heating, shaping and cooling is 2 minutes.

[0123] In contradistinction to other crosslinking prepreg systems such as epoxides, crosslinking takes place during cooling and not at elevated temperatures. This shortens the cycle time from above 10 minutes to 2 minutes. The shaped component part was reshaped and cured in three identical cycles in order to verify the reversibility of the crosslinking. The component part obtained is in a crosslinked and dry state at a temperature below T.sub.1, like the prepregs. At temperatures above T.sub.2, the component part is a non-crosslinked thermoplastic melt having a viscosity of 150 Pas and is newly shapeable and, by cooling, curable.