METHOD FOR THE PRODUCTION OF A COLORED POLYOXYMETHYLENE COPOLYMER

Abstract

The present invention relates to a method for the production of a colored polyoxymethylene copolymer by mixing a raw polyoxymethylene copolymer in particulate form, comprising 2 to 30% by weight of unreacted residual monomers, with a coloring agent in particulate form, in a degassing apparatus. In addition, the present invention relates to the colored polyoxymethylene copolymer obtainable by the process and the use of the colored polyoxymethylene copolymer for the production of molding parts.

Claims

1-14. (canceled)

15. A method for the production of a colored polyoxymethylene copolymer comprising the following steps: a) providing a component (A1) and a component (A2), wherein component (A1) contains a raw polyoxymethylene copolymer in particulate form, comprising a polyoxymethylene copolymer and 2 to 30% by weight of unreacted residual monomers with regard to the total weight of the raw polyoxymethylene copolymer, and component (A2) contains a coloring agent in particulate form, b) simultaneously feeding components (A1) and (A2) to a degassing apparatus, in which the raw polyoxymethylene copolymer is melted and mixed with component (A2), and whereby the unreacted residual monomers are at least partially removed from the raw polyoxymethylene copolymer to obtain the colored polyoxymethylene copolymer, c) removing the colored polyoxymethylene copolymer from the degassing apparatus, wherein the degassing apparatus comprises viewed in the direction of flow a melting device and a degassing device and wherein the degassing device comprises viewed in direction of flow a first degassing zone, a second degassing zone and optionally a third degassing zone.

16. The method according to claim 15, wherein the components (A1) and (A2) are simultaneously fed to the melting device of the degassing apparatus.

17. The method according to claim 15, wherein in direction of flow the melting device is the foremost part of the degassing apparatus.

18. The method according to claim 15, wherein the degassing apparatus consists of a melting device, which consists of a melting zone, and a degassing device, which consists of a first degassing zone, a second degassing zone and a third degassing zone.

19. The method according to claim 15, wherein at least the degassing device is carried out as a twin screw extruder.

20. The method according to claim 15, wherein the melting device is also carried out as a twin screw extruder.

21. The method according to claim 15, wherein the first degassing zone of the degassing device has a volume of gaseous phase in the range of 80 to 20% by volume, the second degassing zone of the degassing device has a volume of the gaseous phase in the range of 70 to 30% by volume and the third degassing zone of the degassing device has a volume of gaseous phase in the range of 30 to 0% by volume.

22. The method according to claim 15, wherein the melting device is operated at a temperature of from 130 to 220 C. without applying vacuum.

23. The method according to claim 15, wherein the melting device is operated at a temperature of from 150 C. to 200 C. without applying vacuum.

24. The method according to claim 15, wherein the degassing device is operated at a temperature of from 155 to 270 C. and a pressure of from 0.1 mbara to 10 bara.

25. The method according to claim 15, wherein the degassing device is operated at a temperature of from 160 to 240 C. and a pressure of from 10 mbara to 2 bara.

26. The method according to claim 15, wherein the degassing device is operated at a temperature of from 170 to 230 C. and a pressure of from 10 mbara to 400 mbara.

27. The method according to claim 15, wherein the coloring agent is at least one black coloring agent selected from the group consisting of carbon black, activated carbon, carbon nanotubes, graphen black, black organic pigments and black organic dyes.

28. The method according to claim 15, wherein the polyoxymethylene copolymer comprises at least 50 mol % of CH.sub.2O recurring units and up to 50 mol %, of recurring units according to formula (I) ##STR00006## where R.sup.1 to R.sup.4 are each, independently of one another, a hydrogen atom, a C.sub.1-C.sub.4-alkyl group or a alkoxy-substituted alkyl group having from 1 to 4 carbon atoms and R.sup.5 is a CH.sub.2, CH.sub.2O, a C.sub.1-C.sub.4-alkyl- or C.sub.1-C.sub.4-alkoxy-substituted methylene group of a corresponding oxymethylene group and n is from 0 to 3.

29. The method according to claim 15, wherein the polyoxymethylene copolymer comprises at least 50 mol % of CH.sub.2O recurring units and from 0.01 to 20 mol % of recurring units according to formula (I) ##STR00007## where R.sup.1 to R.sup.4 are each, independently of one another, a hydrogen atom, a C.sub.1-C.sub.4-alkyl group or a alkoxy-substituted alkyl group having from 1 to 4 carbon atoms and R.sup.5 is a CH.sub.2, CH.sub.2O, a C.sub.1-C.sub.4-alkyl- or C.sub.1-C.sub.4-alkoxy-substituted methylene group of a corresponding oxymethylene group and n is from 0 to 3.

30. The method according to claim 15, wherein the polyoxymethylene copolymer comprises at least 50 mol % of CH.sub.2O recurring units and from 0.5 to 6 mol % of recurring units according to formula (I) ##STR00008## where R.sup.1 to R.sup.4 are each, independently of one another, a hydrogen atom, a C.sub.1-C.sub.4-alkyl group or a alkoxy-substituted alkyl group having from 1 to 4 carbon atoms and R.sup.5 is a CH.sub.2, CH.sub.2O, a C.sub.1-C.sub.4-alkyl- or C.sub.1-C.sub.4-alkoxy-substituted methylene group of a corresponding oxymethylene group and n is from 0 to 3.

31. The method according to claim 15, wherein the unreacted residual monomers are trioxane, formaldehyde and/or formals of alpha-omega-hydroxyglycoles, which may be substituted in the CC-chain.

32. A colored polyoxymethylene copolymer obtained by the method according to claim 15.

33. Use of a colored polyoxymethylene copolymer according to claim 32 for the production of molded parts.

Description

INVENTIVE EXAMPLES 1-4

[0152] Raw polyoxymethylene copolymer (rPOM; component (A1)) including additives was added with a feed rate of 2000 kg/hr and the coloring agent (A2) was added with a feed rate of 20 kg/hr into barrel C1 of a twin-screw-extruder from JSW, with a total L/D of 56, a screw diameter d=196 mm. The twin-screw-extruder comprised the following defined zones as shown in table 3. On 1.sup.st, 2.sup.nd and 3.sup.rd degassing zone a vacuum (p=40 mbara) is applied.

TABLE-US-00003 TABLE 3 Description of used twin-screw-extruder barrel number of extruder C4 to C5 C6 to C8 C9 to C12 C13 to C15 L/D: 7 14 14 10.5 Function: Melting 1.sup.st degassing 2.sup.nd degassing 3.sup.rd degassing zone zone zone zone

[0153] The polymer melt leaving the twin-screw-extruder was pelletized using a water-ring-pelletizer. In a final step the pellets are heated up by hot air to 140 C. for 6 hours for means of deodorization to obtain low level of residual volatile components especially formaldehyde in the final product.

TABLE-US-00004 TABLE 4 Parameters for producing colored polyoxymethylene copolymer (cPOM) and characterization of pellets (Examples 1 to 4) Example 1 Example 2 Example 3 Example 4 rPOM (A1) A1a A1a A1b A1b Coloring agent (A2) A2a A2b A2a A2b Screw speed in rpm 165 165 180 180 Barrel Temperature in C. melting zone 205-220 205-220 205-220 205-220 first degassing zone 240-190 240-190 240-230 240-230 second degassing 185-140 185-140 190-150 190-150 zone third degassing zone 140-140 140-140 150-150 150-150 MVR in cm.sup.3/10 min 7.6 7.7 11.3 11.5 according to ISO 1133 (190 C./2.16 kg) Weight loss in % 0.18 0.20 0.19 0.18 under N.sub.2 (222 C./2 hr) Residual 10 13 11 14 formaldehyde content in ppm

COMPARATIVE EXAMPLES 1A, 2A, 3A, 4A

[0154] The comparative examples 1a, 2a, 3a, 4a were produced by secondary compounding of finished uncolored polyoxymethylene copolymer in a twin-screw-extruder together with a coloring agent (A2).

[0155] Preparation of the Finished Uncolored Polyoxymethylene Copolymer:

[0156] In a first step, a finished uncolored polyoxymethylene copolymer was produced under identical conditions as A1a/Example 1 (POM UN (1)) and A1b/Example 3 (POM UN (3)), however without dosing of coloring agent (A2). The resulting properties are shown in table 5.

TABLE-US-00005 TABLE 5 Pellet properties of finished uncolored polyoxymethylene copolymer POM UN (1) POM UN (3) Manufacturing conditions identical to, A1a/ A1b/ without dosing of coloring agent (A2) Example 1 Example 3 MVR in cm.sup.3/10 min according to ISO 1133 7.3 10.9 (190 C./2.16 kg) Weight loss in % under N.sub.2 (222 C./2 hr) 0.14 0.16 Residual formaldehyde content in ppm 8 9

[0157] In a second step, 99 wt.-% of POM UN was melt kneaded with 1.0 wt.-% of a coloring agent (A2) in a twin-screw extruder, type ZSK90, underfollowing conditions: barrel temperature from 140-210 C., screw speed 150 rpm, total throughput of 350 kg/hr. The polymer melt leaving the twin-screw-extruder was pelletized using water-ring-pelletizer. In a final step the pellets are heated up by hot air to 120 C. for 4 hours for means of deodorization to obtain low level of residual volatile components especially formaldehyde in the final product. The resulting materials were characterized as shown in table 6.

TABLE-US-00006 TABLE 6 Characterization of black colored pellets Compara- Compara- Compara- Compara- tive ex- tive ex- tive ex- tive ex- ample 1a ample 2a ample 3a ample 4a POM UN (1) (1) (3) (3) Coloring agent A2a A2b A2a A2b (A2) MVR in cm.sup.3/10 min 7.8 7.9 11.5 11.8 according to ISO 1133 (190 C./2.16 kg) Weight loss in % 0.27 0.25 0.24 0.22 under N.sub.2 (222 C./2 hr) Residual 10 13 11 14 formaldehyde content in ppm

COMPARATIVE EXAMPLES 1B, 2B, 3B, 4B

[0158] The comparative examples 1b, 2b, 3b, 4b were produced by self coloring of finished uncolored polyoxymethylene copolymer from table 5 with coloring agent (A2) at the injection molding machine. Hence a homogenous dry-blend pellet mixture of 99 wt.-% of POM UN and 1.0 wt.-% of component (A2) was prepared as summarized in table 7.

TABLE-US-00007 TABLE 7 Dry-blend pellet mixtures of POM UN with coloring agent (A2) Compara- Compara- Compara- Compara- tive ex- tive ex- tive ex- tive ex- ample 1b ample 2b ample 3b ample 4b POM UN (1) (1) (3) (3) Coloring agent (A2) A2a A2b A2a A2b

[0159] Table 8 shows the final properties on molded parts of inventive examples 1-4, comparative examples 1a-4a and comparative examples 1b-4b.

TABLE-US-00008 TABLE 8 Properties measured on injection molded black colored specimens Comparative examples Comparative examples 1b to 4b Inventive examples 1a to 4a (self-coloring injection (primary compounding) (2.sup.nd compounding step) molding) 1 2 3 4 1a 2a 3a 4a 1a 2a 3a 4a Color L 5.7 6.7 5.9 6.8 6.9 7.7 6.7 7.9 7.1 8.0 7.1 8.1 Color a 0.5 0.6 0.6 0.7 0.7 0.7 0.6 0.7 0.7 0.7 0.6 0.7 Color b 1.6 1.3 1.7 1.4 1.4 1.0 1.3 0.9 1.3 0.9 1.3 0.8 Gloss 83.9 84.0 84.9 85.2 82.1 82.2 83.0 83.2 81.8 81.7 82.4 82.3 Formaldehyde 19 21 16 17 25 26 22 21 20 20 17 16 emission in ppm according to VDA 275

[0160] Examples based on colored rPOM exhibit a lower L-value and higher gloss value compared to comparative examples 1a to 4a and 1b to 4b. Therefore, examples based on colored rPOM show a more intensive and more brilliant black color compared to comparative examples 1a to 4a and 1b to 4b. In addition, the inventive examples based on colored rPOM show low level of formaldehyde emissions.

[0161] Consequently, the inventive method provides a simple and cost-efficient way for the production of a colored polyoxymethylene copolymer. Furthermore, the moldings obtained from the colored polyoxymethylene copolymer exhibit outstanding deep and brilliant black color with low emission of formaldehyde.