PROCESS FOR THE PREPARATION OF LOW HAZE AND COLOR STABLE STYRENIC POLYMERS

Abstract

Process for the preparation of very low haze and color stable styrenic polymers by anionic polymerization wherein the obtained terminated polymer solution is passed through a first filter, fed to a dispersing device to which water is added, fed to a buffer vessel and then is impregnated in a static mixer by addition of further water, carbon dioxide and one or more stabilizers.

Claims

1-19. (canceled)

20. A process for the preparation of homopolymers or block copolymers of vinyl aromatic monomers by anionic polymerization comprising the following steps: (i) polymerization of at least one vinyl aromatic monomer and optionally at least one conjugated diene in an inert non-polar solvent in the presence of an organometal initiator in a reactor, and subsequent deactivation of the obtained living polymer chains with a terminating agent to obtain a polymer solution; (ii) passing the polymer solution obtained in step (i) through a first filter; (iii) feeding the polymer solution obtained in step (ii) to a dispersing device to which water is added in a continuous or in a discontinuous mode; (iv) feeding the polymer solution obtained in step (iii) to a buffer vessel; and (v) feeding the continuously withdrawn polymer solution from the buffer vessel into a static mixer for impregnation by addition of further water, carbon dioxide, and one or more stabilizers; wherein: subsequent to step (iv), the process is conducted in a continuous mode; in step (ii): no water is present in the first filter; the first filter has a mesh size of 200 to 1500 m; the flow rate of the polymer solution is 10 to 500 m.sup.3/h at a temperature of from 50 to 130 C.; in step (iii): the dispersion device is a second filter having a mesh size of 200 to 1500 m, a static mixer, or a process flow part in which the characteristic length of the process flow part, the velocity, the density, and the dynamic viscosity of the polymer solution are chosen in such a way that a transitional or turbulent flow with a Reynolds number above 2300 occurs; water is added in amounts of 0.01 to 0.50 l/m.sup.3 polymer solution; in step (v): the flow rate of the additional water is more than 0.05 l/m.sup.3 polymer solution, and the flow rate of the carbon dioxide is more than 5l/m.sup.3 polymer solution; and in steps (iii) and (v), the pH of the water is in the range of from 5 to 7.

21. The process according to claim 20, wherein the reactor is a batch reactor.

22. The process according to claim 20, wherein in step (iii), the dispersing device is a filter.

23. The process according to claim 20, wherein in step (iii), the dispersing device is a process flow part in which the polymer solution has a transitional flow with a Reynolds number between 2300 and 4000.

24. The process according to claim 20, wherein in step (iii), the dispersing device is a process tube having a characteristic length of from 0.05 to 1.0 m, and the polymer solution has a velocity of from 1.0 to 10.0 m/s, density of from 750 to 900 kg/m.sup.3, and a dynamic viscosity of from 0.01 to 10 Ns/m.sup.2 at a temperature of from 60 to 80 C.

25. The process according to claim 20, wherein in step (iii), the dispersing device is a process tube having a characteristic length of from 0.05 to 5 m, and the polymer solution has a velocity of from 1.0 to 10.0 m/s, density of from 750 to 900 kg/m.sup.3, and a dynamic viscosity of from 0.01 to 10 Ns/m.sup.2 at a temperature of from 60 to 95 C.

26. The process according to claim 20, wherein in steps (ii) and (iii), the filter is a bagfilter.

27. The process according to claim 20, wherein in step (ii), the mesh size of the filter is 500 to 1000 m.

28. The process according to claim 20, wherein in step (iii), the water is added in amounts of 0.05 to 0.20 l/m.sup.3 polymer solution.

29. The process according to claim 20, wherein the polymer solution obtained in step (v) is fed to a further buffer vessel.

30. The process according to claim 20, wherein prior to step (v), the polymer solution continuously withdrawn from the buffer vessel is filtered by a third filter.

31. The process according to claim 30, wherein the third filter is a cartridge filter with a mesh size between 50 m and 300 m.

32. The process according to claim 20, wherein in step (v), the stabilizers are added as a solution with a flow rate of 1 to 8 l/m.sup.3 polymer solution.

33. The process according to claim 20, wherein in step (v), the stabilizers are dissolved in a nonpolar solvent where the concentration of each of the one or more stabilizers is in the range of from 3.5 to 15 wt.-%, preferably 5 to 12 wt.-%.

34. The process according to claim 20, wherein in step (v), a plasticizer is added with an injection flow of 0.1 to 30 l/m.sup.3 polymer solution.

35. The process according to claim 23, wherein the process flow part is a tube or pipe.

Description

EXAMPLES

[0113] All solvents and monomers used in the following examples were dried to use over aluminum-oxide columns or using a destillation process. Unless otherwise stated, the water used in all process steps was demineralized water (pH 6.4).

Example 1 Polymerization of a Star Shaped SBC-Block Copolymer (=Step (i) of the Process According to the Invention)

[0114] A star-shaped styrene-butadiene block copolymers of the structure

##STR00001##

wherein, S.sub.1, S.sub.2 and S.sub.3 denote different styrene polymer blocks, (B/S).sub.1 and (B/S).sub.2 are different random styrene/butadiene copolymer blocks and X denotes the coupling center derived from the coupling agent, was prepared by sequential anionic polymerization of styrene (monomers S1 to S5) and butadiene (monomers B1 and B2), and subsequent coupling using epoxidized soybean oil.

[0115] In a batch reactor (stainless steel reactor, stirred, 50 m.sup.3) 21600 l of cyclohexane at 40 C. was used as initial charge (ic) and 2803 l styrene (S1) was added at 20 m.sup.3/h. When 280 l of S1 had been dosed, 32.19 l of a 1.4 M sec-butyllithium solution (BuLi 1) for initiation (Ini1) had been dosed at once. The reaction was allowed to proceed under continuous stirring and reflux cooling to complete monomer consumption (identified by a decrease in temperature of the reaction mixture). Next, 77.97 l of a 1.4 M sec-butyllithium (BuLi 2) solution was added, as the second initiator mixture (Ini 2), together with 13.48 l of a potassium tert-amyl alcoholate (PTA) solution (5.26 wt.-% in cyclohexane) as randomizer under continuous stirring.

[0116] In a next step, again 1756 l styrene (S2) was added and the polymerization reaction, under continuous stirring, was allowed to run to complete monomer consumption (identified by a decrease in temperature of the reaction mixture). After complete monomer consumption, the polymerization mixture was cooled by means of reflux cooling to a temperature below 75 C. Then, 858 l butadiene (B1) and 573 l styrene (S3) were added simultaneously and the polymerization reaction, with continuous stirring, was allowed to run to complete monomer consumption (identified by a decrease in temperature of the reaction mixture). After complete monomer consumption, the polymerization mixture was cooled by means of reflux cooling to a temperature below 60 C.

[0117] In a next step, again 2290 l butadiene (B2) and 754 l styrene (S4) were added simultaneously and the polymerization reaction, with continuous stirring, was allowed to run to complete monomer consumption (identified by a decrease in temperature of the reaction mixture). After complete monomer consumption, the polymerization mixture was cooled by means of reflux cooling to a temperature below 90 C.

[0118] Then, again 214 l styrene (S5) was added and the polymerization reaction, with continuous stirring, was allowed to run to complete monomer consumption (identified by a decrease in temperature of the reaction mixture).

[0119] Finally, 10 minutes after the last complete monomer consumption, 17.2 l EfkaPL 5382 (epoxidized soya bean oil, BASF), heated to a temperature of 85 C., as coupling agent was added to the polymer solution and allowed to react for 10 minutes at a temperature of 90 C. while stirring.

[0120] Table 1 shows the amounts of the components used.

TABLE-US-00001 TABLE 1 wt.-% Components (phm) kg liter Styrene I 34.00% 2551 2803 Styrene II 21.30% 1598 1756 Styrene III 6.95% 521 573 Butadiene I 7.08% 531 857 Styrene IV 9.15% 687 754 Butadiene II 18.92% 1420 2290 Styrene V 2.60% 195 214 Edenol D82 17.1 17.2 phm = per hundred parts by weight of monomer (wt.-% of component (initiator, coupling agent etc.) is calculated on the total mass of the monomers.

[0121] The polymer solution obtained in step (i) was processed according to the following process flow:

BATCH REACTOR (step (i))->FILTER (step (ii))->DISPERSING DEVICE WITH WATER ADDITION (step (iii))->BUFFER VESSEL 1 (step (iv))->CARTRIDGE FILTER->IMPREGNATION (step (v) continuous) [INJECTION OF WATER, CO.sub.2 and STABILIZERS->STATIC MIXER->INJECTION OF MINERAL OIL->STATIC MIXER]->BUFFER VESSEL 2->DEVOLATIZER->DEGASSING EXTRUDER->PELLETIZER.

[0122] One reactor volume was from 31 to 34 m.sup.3.

[0123] The polymer solution obtained in step (i) was fed through a filter with the below specifications in step (ii): [0124] MAXILINE MBF of HAYWARD Filter Technik [0125] Type: MBF-0802-AB16-150DS-11GEN-M: [0126] Innerdiameter filter: 778 mm [0127] Filterbags: 8diameter 168 mm, Height 660 mm, mesh size 800 m [0128] Flow rate when emptying the reactor: 180 m.sup.3/h [0129] Flow rate over filter bag area: 0.017 m/s [0130] Temperature polymer solution: 89.2 C.

[0131] Afterwards, water was added to the process tube between the filter of step (ii) towards the buffer of step (iv) at a rate of 12 I/h or 0.07l/m.sup.3 polymer solution.

[0132] The process tube, with a round cross-section, has an inner diameter of 0.15 m. The density of the polymer solution at that stage is 750 kg/m.sup.3 and the dynamic viscosity is 0.08 Pa.Math.s (N.Math.s/m.sup.2) at a temperature of 78 C. The polymer solution is being pumped at a rate of 180 m.sup.3/h through this process tube (=pipe).

[0133] The Reynolds number is calculated as:

Re=(u.sup.2)/(u/L)=uL/=3978

With

[0134] Re=Reynolds number
=density
u=velocity based on the actual cross section area of the process tube (m/s)
=dynamic viscosity (Pa.Math.s, N.Math.s/m.sup.2)
L=characteristic length (m)=the diameter for a process tube with a round cross section (=pipe)

[0135] Then, the polymer solution obtained in step (iii) was fed to a first buffer vessel (100 m.sup.3) (=step iv).

[0136] Prior to step (v), the polymer solution continuously withdrawn from the first buffer vessel was filtered through a cartridge filter. The filter used was G78W84HCB from CUNO MICRO-KLEAN with a mesh size of 125 m. The filter material is consisting of acryl fiber and phenol resin and has a length of 100 cm.

[0137] Then, the polymer solution from the buffer vessel in step (iv) of the inventive process, which prior to step (v) was filtered through a cartridge filter, was impregnated (step (v) of the inventive process) under the following conditions (continuous process): [0138] Continuous flow of the polymer solution: 15 m.sup.3/h; [0139] Temperature of the polymer solution: 70 to 80 C.; [0140] Injection flow water=0.18 l/m.sup.3 polymer solution; [0141] Injection flow CO.sub.2=16.32 l/m.sup.3 polymer solution; [0142] Pressure in carbon dioxide feeding tube: 16 to 22 bar; [0143] Injection flow stabilizers=4.07 l/m.sup.3 polymer solution; [0144] Injection flow mineral oil=3.12 l/m.sup.3 polymer solution; [0145] all tubing is DN80, except tubing for CO.sub.2 injection (=DN 50).

[0146] As stabilizers Irganox 1010 (BASF SE, Germany), Irgaphos 168 (BASF SE) and Sumilizer GS (Sumitomo Corp., Japan) were used as a solution in cyclohexane in the following concentrations: Irganox 1010 (7 wt.-%), Irgaphos 168 (10 wt.-%) and Sumilizer GS (7 wt.-%). As mineral oil WINOG 70 (medical white oil, H&R (Klaus Dahleke KG)) was used.

[0147] As static mixer (step (v)) a Sulzer mixer of the type SMX with 2 SMX mixing elements arranged in series had been used. Each mixing element had a length of 840 mm and a tube diameter of 80 mm. Before entering the first SMX mixing element water, carbon dioxide and all stabilizers (in solution) were injected to the polymer solution, then before entering of the second SMX mixing element white oil was injected. Then, the polymer solution obtained in step (v) was fed to a second buffer vessel. At last, after feeding the continuously withdrawn polymer solution from the second buffer vessel to a degassing device for degassing, the obtained polymer was fed into a twin-screw extruder for degassing extrusion under vacuum and under water pelletization. The obtained block copolymer had a Melt Flow Index (MFI, determined according to ISO 1133-1-2011 at 200 C. and a load of 5 kg) of 13.5 cm.sup.3/10 min.

Comparative Example 1

[0148] Example 1 was repeated, except that no water was added in step (iii) of the process. The water was added only in the impregnation step (iv). As such, the process flow of the polymer solution obtained in step (i) was:

BATCH REACTOR (step (i))->FILTER (step (ii))->BUFFER VESSEL 1 (step (iv))->CARTRIDGE FILTER->IMPREGNATION (step (v) continuous) [INJECTION OF WATER, CO.sub.2 and STABILIZERS->STATIC MIXER->INJECTION OF MINERAL OIL->STATIC MIXER]->BUFFER VESSEL 2->DEVOLATIZER->DEGASSING EXTRUDER->PELLETIZER.

[0149] The obtained block copolymer had a Melt Flow Index (MFI, determined according to ISO 1133-1-2011 at 200 C. and a load of 5 kg) of 13.5 cm.sup.3/10 min.

Comparative Example 2

[0150] Step (i) of Example 1 was repeated. Before emptying the batch reactor with the polymer solution obtained in step (i), 2.7 l of water (20 l/h during 8.1 min) were added to the filter used in step (ii) (using the same type of filter and throughput as described for example 1) and afterwards pumped towards a buffer vessel (step (iv)).

[0151] As such, the process flow of the polymer solution obtained in step (i) was:

BATCH REACTOR (step (i))->FILTER WITH WATER ADDITION->BUFFER VESSEL 1 (step (iv))->CARTRIDGE FILTER->IMPREGNATION (step (v) continuous) [INJECTION OF WATER, CO.sub.2 and STABILIZERS->STATIC MIXER->INJECTION OF MINERAL OIL->STATIC MIXER]->BUFFER VESSEL 2->DEVOLATIZER->DEGASSING EXTRUDER->PELLETIZER.

[0152] The subsequent work-up from the first buffer vessel, through the impregnation towards the degassing and pelletization was the same as described in Example 1. The same amount and type of water, CO.sub.2, stabilizers and mineral oil and under the same processing conditions was added during the impregnation step (v) as described for Example 1.

[0153] Two hours after production, samples (injection molded plates, thickness 4 mm) of the obtained SBC-polymer pellets of Example 1 and Comparative Example 1 were used for color measurements (see Table 2) according to DIN 5033 and DIN 6174 (CIE LAB). For the measurements a LUCI 100 spectrophotometer (light source: Xenon lamp D65, D65=T=6504 K, measurement geometry: D/8) has been used. The haze was measured on injection molded plates (thickness 4 mm) of the obtained polymer pellets of Example 1, Comparative Example 1 and Comparative Example 2 using a BYK-Gardner Haze-gard.

[0154] The obtained block copolymer had a Melt Flow Index (MFI, determined according to ISO 1133-1-2011 at 200 C. and a load of 5 kg) of 13.5 cm.sup.3/10 min.

TABLE-US-00002 TABLE 2 Example 1 Comp. Example 1 Comp. example 2 YI 5.93 9.66 6.3 L-value 94.89 93.97 94.67 a-value 0.27 0.04 0.21 b-value 3.23 5.06 3.37 Haze 1.4 1.2 1.7 YI = Yellowness index

[0155] Samples according to Example 1 have a better color stability compared to Comparative Example 1 (the higher the b-value and the higher the YI, the more yellow) and a better color stability and haze compared to Comparative example 2. The results clearly show that the sequence of a filter (step (ii)) and the addition of water in a dispersing device (step (iii)) is beneficial.