PROCESS FOR PRODUCING OPTICAL MOLDING MATERIALS

Abstract

A process can be used for producing optical molding materials on the basis of methyl methacrylate (MMA). The MMA produced by an optimized method and the molding materials feature in particular a very low yellowness index. This MMA has been produced by direct oxidative esterification of methacrolein. An optimized workup of the reactor output from the oxidative esterification of methacrolein can be used for removing particularly discoloring byproducts. This process moreover has the advantage that fewer demands are placed on plant apparatus configuration.

Claims

1-20. (canceled)

21: An alkyl methacrylate, produced by a process comprising: a. producing methacrolein in a reactor I, b. oxidatively esterifying the methacrolein in the presence of an alcohol, oxygen, and a heterogeneous noble metal-containing catalyst, at a water content between 0.1% and 10% by weight and a pH between 5 and 8 in at least one reactor II, to obtain a reactor output, c. after-treating the reactor output from the at least one reactor II in a reactor III, to obtain a crude alkyl methacrylate, and d. isolating and purifying the crude alkyl methacrylate from the reactor III, wherein the alkyl methacrylate comprises dimethoxyisobutene (DMIB) and methyl isobutyrate, and has a DMIB content of less than 300 ppm and a methyl isobutyrate content of less than 600 ppm, and wherein in process step c, in the reactor III, a water content is at least 0.5% by weight higher than in the at least one reactor II.

22: The alkyl methacrylate according to claim 21, wherein the alkyl methacrylate has a content of DMIB of less than 100 ppm and a methyl isobutyrate content of less than 300 ppm.

23: An alkyl methacrylate resin, produced from a monomer mixture containing: 30% to 100% by weight of the alkyl methacrylate according to claim 21, 0% to 70% by weight of a monomer copolymerizable with the alkyl methacrylate and/or an alkyl methacrylate produced by another process, and optionally, 0% to 5% by weight of an added substance.

24: The alkyl methacrylate according to claim 21, wherein process step a in the reactor I is a reaction of propanal with formaldehyde in the presence of at least one acid and optionally, in the presence of an amine.

25: The process according to claim 21, wherein the alcohol is methanol and the alkyl methacrylate is methyl methacrylate (MMA).

26: The alkyl methacrylate according to claim 21, wherein in process step c, an organic and/or a mineral acid is added to the reactor III to adjust the pH, and wherein in the reactor III, dimethoxyisobutene is cleaved with water to obtain methacrolein and methanol.

27: The alkyl methacrylate according to claim 26, wherein the acid is sulfuric acid, and wherein a liquid phase in the reactor III is at a temperature between 0° C. and 140° C.

28: The alkyl methacrylate according to claim 26, wherein the reactor III is a distillation column into the bottom of which the acid and optionally additional water are introduced, and in which methacrolein and portions of a remaining alcohol are separated from the crude alkyl methacrylate at a temperature between 50° C. and 100° C.

29: The alkyl methacrylate according to claim 26, wherein the reactor III is a phase separator into whose aqueous phase the acid and optionally additional water are introduced, and in which an aqueous phase containing a remaining alcohol is separated from an organic phase containing the crude alkyl methacrylate at a temperature between 0° C. and 100° C.

30: The alkyl methacrylate according to claim 26, wherein the reactor III is a tubular reactor in which the reactor output from the at least one reactor 1 having an internal temperature between 50° C. and 140° C., the acid, and optionally additional water are mixed to obtain a mixture, and the mixture is subsequently passed into a distillation column or a phase separator.

31: The alkyl methacrylate according to claim 26, wherein the reactor III is a continuously operated stirred reactor in which the reactor output from the at least one reactor II having an internal temperature between 50° C. and 140° C., the acid, and optionally additional water are mixed to obtain a mixture, and the mixture is subsequently passed into a distillation column or a phase separator.

32: The alkyl methacrylate according to claim 21, wherein in process step d, isolation and purification stages comprise at least one phase separator, at least one high boiler column, at least one low boiler column, and optionally at least one crystallization chamber, wherein the at least one phase separator, the at least one high boiler column, the at least one low boiler column, and optionally the at least one crystallization chamber are traversed in series.

33: A method for producing a transparent article, the method comprising: molding an alkyl methacrylate resin comprising the alkyl methacrylate according to claim 21 into a transparent article, wherein the transparent article is at least one selected from the group consisting of an optically conductive sheet, a headlight lens, a headlight cover, a cover for a light source, a display cover, a noise barrier, and a construction material for a greenhouse.

34: A method for producing a colored article, the method comprising: molding an alkyl methacrylate resin comprising the alkyl methacrylate according to claim 21 into a colored article, wherein the colored article is at least one selected from the group consisting of a molding in covers, a molding in a pillar trim, and a molding in decorative strips in passenger car interior and/or exterior applications.

Description

EXAMPLES

[0054] in order to investigate the quality of the alkyl methacrylate resins methyl methacrylate according to process steps a to d from the process according to the invention was polymerized to produce PMMA. Test specimens of 145 mm in length were subsequently produced from the obtained polymer and used to measure the optical properties.

[0055] Production of the polymers employed the following raw materials:

[0056] Methyl methacrylate from Evonik Industries and from process a to d stabilized with 3 ppm of hydroquinone monomethyl ether.

[0057] N-dodecylmercaptan was obtained from Chevron Philips and

[0058] tert-butylperisononanoate was obtained from United Initiator GmbH.

[0059] For polymerization the reactants were continuously suppled to a continuously operated stirred tank having an internal volume of 2.4 L ensuring that the polymerization temperature is always in the range between 120° C. and 150° C. The polymerization proceeded up to a monomer conversion of 55%. The residual monomers of the output polymer syrup were continuously degassed in an extruder at 250° C. The thus obtained polymer strands of the degassed polymer melt were cooled in air and subsequently granulated.

[0060] Reactor feed for the polymerization

[0061] 3500 g/h of methyl methacrylate

[0062] 7.0 g/h of n-dodecylmercaptan

[0063] 2.0 g/h of tert-butylperisononanoate

[0064] To evaluate the optical quality of the polymers polymer granulate was pressed at 220° C. and 50 bar of pressure to afford moldings from which rods having dimensions of 10 mm×10 mm×145 mm were then cut and the surfaces polished by means of a diamond polisher.

[0065] The yellowness index Y.I. and D65/10° transmission coefficient of this molding were measured over the 145 mm length in a Varian Cary 5000 instrument.

[0066] For the specific examples the respective byproduct proportions or DMIB and methyl isobutyrate in the monomers from process step d are also reported. The MMA batches employed in examples 3 and 4 serve as a reference. This particular MMA was produced by means of a C3 process and accordingly contains neither DMIB nor methyl isobutyrate.

Example 1

[0067] Methyl methacrylate from process a to d with

[0068] <6 ppm of DMIB; 230 ppm of methyl isobutyrate

[0069] (after process step d)

[0070] The following process was employed in particular in relation to process step c:

[0071] The output from process step b, reactor II was passed into the process step c, reactor III for workup. Reactor III was in the form of a continuously operated stirred tank with a decanter connected downstream.

[0072] pH in stirred tank: 2

[0073] Residence time in stirred tank: 60 min

[0074] Temperature in stirred tank: 25° C.

[0075] Residence time in decanter 60 min

[0076] Temperature in decanter: 25° C.

[0077] Feeds into reactor III, process step c:

[0078] 1. Acidic aqueous phase:

[0079] Sulfuric acid 100% H2SO4=1.05 g/h

[0080] Water=106.05 g/h

[0081] 2. Feed from process step b:

[0082] MMA=56.11% by weight

[0083] Methanol=13.67% by weight

[0084] DMIB=1659 ppm

[0085] Methyl isobutyrate=305 ppm

[0086] Organic residues=18.57% by weight

[0087] H2O=11.44% by weight

[0088] Total flow: 150 g/h

[0089] Composition of crude alkyl methacrylate after process step c:

[0090] DMIB <6 ppm (1 ppm in organic phase)

[0091] Organic phase methyl isobutyrate=449 ppm

[0092] Aqueous phase methyl isobutyrate=14 ppm

Example 2 (Comparative Example)

[0093] Methyl methacrylate from process a, b and d, without process step c with

[0094] 1550 ppm of DMIB; 475 ppm of methyl isobutyrate

Example 3 (Reference Example)

[0095] Methyl methacrylate from Evonik Industries admixed with

[0096] 1000 ppm of DMIB; 50 ppm of methyl isobutyrate

Example 4 (Reference Example)

[0097] Methyl methacrylate from Evonik Industries as reference with

[0098] <5 ppm of DMIB; 50 ppm of methyl isobutyrate

[0099] In example 1 MMA according to process steps 1 a to d was employed and a low yellowness index and a high transmission achieved. The content of DMIB is low at less than 6 ppm. Example 2 (comparative example) employs MMA according to process steps a, b and d, but without the workup step c. The content of DMIB is higher than in example 1 at 1550 ppm, thus resulting in a higher yellowness index and a lower transmission of the polymethacrylate resin.

[0100] In examples 3 and 4 (reference examples) Evonik MMA from the ACH process h which no DMIB is formed was used in each case. Once with an artificially added 1000 ppm of DMIB and in example 4 without any addition of DMIB. Example 3 again shows a higher yellowness index and a lower transmission than example 4.

[0101] The condensates of the degassed residual monomers were, with high DMIB contents in the employed MMA, very yellow, example 2 and example 3.

TABLE-US-00001 TABLE 1 Comparison of results Y.I. Transmission Y.I. Methyl 145 mm D65/10° 10 mm DMIB isobutyrate Polymer Polymer Condensate MMA [ppm] [ppm] [—] [%] [—] Example 1 Process a-d <6 230 4.1 92.2 3.2 Example 2 Process a-d/ 1550 475 12.0 91.5 9.8 without c Example 3 Evonik Ind. 1000 50 7.0 91.8 8.7 Example 4 Evonik Ind. <1 50 4.1 92.7 3.5

[0102] The respective yellowness indices for the condensates of the degassed polymer syrups are affected by DMIB concentration in the employed alkyl methacrylate. Thus the yellowness indices of the vacuum condensates from examples 1 and 4 are very low while the vacuum condensates of examples 2 and 3 are markedly higher.