Polyester compositions

Abstract

The invention relates to compositions based on polyethylene terephthalate and polybutylene terephthalate with optimized crystallization behavior and consequently with optimized processing behavior in the injection molding process, and also to products to be produced therefrom, in particular with optimized crystallinity.

Claims

1. A process for optimizing the crystallization behaviour of polyester moulding compositions or the crystallinity of products to be produced from the polyester moulding compositions, the process comprising producing a polyester moulding composition comprising polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) at a PBT:PET ratio by weight of 5:1 to 0.2:1, wherein the polyethylene terephthalate has an alkali metal content of 1 to 10,000 ppm, and the polybutylene terephthalate and the polyethylene terephthalate each individually have an intrinsic viscosity of about 0.3 cm.sup.3/g to 1.5 cm.sup.3/g, measured in phenol/o-dichlorobenzene (1:1 parts by weight) at 25° C.

2. The process according to claim 1, wherein the polyethylene terephthalate is otained from a process comprising: washing polyethylene terephthalate with aqueous alkali metal hydroxide solution; melting and mixing the polyethylene terephthalate to form a polyethylene terephthalate melt; and removing contaminants, if present, from the polyethylene terephthalate melt.

3. The process according to claim 2, wherein the aqueous alkali metal hydroxide solution comprises 1% to 10% alkali metal hydroxide.

4. The process according to claim 2, wherein the process further comprises: prior to washing, comminuting the polyethylene terephthalate; melting and mixing the comminuted polyethylene terephthalate in a compounder; and forming solidified portions of polyethylene terephthalate, wherein, if contaminants are present, the solidified portions are formed after removal of the contaminants.

5. The process according to claim 4, wherein removing the contaminants comprises removing volatile contaminants by subjecting the melt to a vacuum.

6. The process according to claim 4, wherein removing the contaminants comprises removing volatile contaminants by solid-phase post-condensation of the melt in vacuo, optionally with stripping and/or with passage of an inert gas, to remove residual contaminants and/or increase viscosity.

7. The process according to claim 6, wherein after washing with aqueous alkali metal hydroxide solution, and prior to melting, the process further comprises additional cleaning by at least one of: steaming the polyethylene terephthalate, and washing the polyethylene terephthalate with water with admixed surfactant.

8. The process according to claim 6, wherein the aqueous alkali metal hydroxide solution comprises at least one of: aqueous sodium hydroxide solution and aqueous potassium hydroxide solution, and the alkali metal content is correspondingly at least one of: sodium and potassium.

9. The process according to claim 7, wherein: the compounder comprises a plurality of screws; the polyethylene terephthalate is previously used polyethylene terephthalate; and the contaminants comprise aldehydes and oligomers.

10. The process according to claim 1, wherein the alkali metal content is 3 to 5000 ppm.

11. The process according to claim 1, wherein the alkali metal content is 7 to 1000 ppm.

12. A process for using recycled polyethylene terephthalate for optimizing the crystallization behaviour of polyester moulding compositions or the crystallinity of products to be produced from the polyester moulding compositions, the process comprising producing a polyester moulding composition comprising polybutylene terephthalate (PBT) and only recycled polyethylene terephthalate (PET) at a PBT:PET ratio by weight of 5:1 to 0.2:1, wherein the recycled polyethylene terephthalate has an alkali metal content of 1 to 10,000 ppm, and the polybutylene terephthalate and polyethylene terephthalate each individually have an intrinsic viscosity of about 0.3 cm.sup.3 to 1.5 cm.sup.3/g, measured in phenol/o-dichlorobenzene (1:1 parts by weight) at 25° C.

13. The process according to claim 12, wherein the recycled polyethylene terephthalate is prepared by a process comprising: comminuting used polyethylene terephthalate; washing the polyethylene terephthalate with aqueous alkali metal hydroxide solution; melting and mixing the comminuted polyethylene terephthalate in a compounder to produce a polyethylene terephthalate melt; removing contaminants, if present, from the polyethylene terephthalate melt; and forming solidified portions of recycled polyethylene terephthalate.

14. The process according to claim 13, wherein: washing the polyethylene terephthalate comprises washing the polyethylene terephthalate with aqueous alkali metal hydroxide solution comprising 1% to 10% alkali metal hydroxide; and the alkali metal content in the recycled polyethylene terephthalate is 3 to 5000 ppm.

15. The process according to claim 14, wherein the aqueous alkali metal hydroxide solution comprises at least one of: aqueous sodium hydroxide solution and aqueous potassium hydroxide solution, and the alkali metal is correspondingly at least one of: sodium and potassium.

16. A method for optimizing crystallization behavior and processing behavior of polyester compositions in an injection molding process, the method comprising injection molding a composition comprising polybutylene terephthalate (PBT) and only recycled polyethylene terephthalate (PET) at a PBT:PET ratio by weight of 5:1 to 0.2:1, wherein the recycled polyethylene terephthalate has an alkali metal content of 1 to 10000 ppm, the polybutylene terephthalate and the polyethylene terephthalate each individually have an intrinsic viscosity of about 0.3 cm.sup.3/g to 1.5 cm.sup.3/g, measured in phenol/o-dichlorobenzene (1:1 parts by weight) at 25° C., and the composition is prepared by a process comprising: comminuting used polyethylene terephthalate; washing polyethylene terephthalate with aqueous alkali metal hydroxide solution to provide the alkali metal in the recycled polyethylene terephthalate; melting and mixing the comminuted polyethylene terephthalate in a compounder to produce a polyethylene terephthalate melt: removing contaminants, if present, from the polyethylene terephthalate melt; and forming solidified portions of recycled polyethylene terephthalate comprising the alkali metal.

Description

EXAMPLES

(1) The compositions described in the invention are produced by mixing the individual components (PBT, PET, glass fiber, others) in a twin-screw extruder (ZSK 26 Mega Compounder from Coperion Werner & Pfleiderer (Stuttgart, Germany)) at temperatures from 260 to 290° C. in the melt, discharging them in the form of a strand, cooling until the material is pelletizable, and pelletizing. Prior to further steps, the pellets are dried for about 2 h at 120° C. in a vacuum drying oven. Each of the investigations described in experiments 1 to 5 uses pellets (DSC) or is carried out with pellets (injection molding).

(2) The flow spiral of width 8 mm and thickness 2.0 mm is injection-molded at a melt temperature of 260° C. and mold temperature of 80° C. in a commercially available injection molding machine. The setting of the machine here is such that switchover to hold pressure occurs when the internal mold pressure is 650 bar.

(3) The injection pressure is the internal mold pressure measured close to the gate, and is applied in order to charge material to the mold cavity. In the pressure profile curve it is a characteristic point of inflection between the phase in which material is charged to the mold and the compaction phase, and can be determined by way of the process data collected. For experiment 4, it is determined during the injection molding of flat bars (80×10×4 mm.sup.3) (melt temperature 260° C., mold temperature 80° C.).

(4) Determination of Enthalpy of Fusion:

(5) Enthalpy of fusion is determined on the basis of DSC measurements (differential scanning calorimetry) in STAR 822e DSC equipment from Mettler Toledo (STARe SW 9.01 software).

(6) The measurement schedule is as follows: from 0° C. to 300° C. at 20° C./min (1.sup.st heating procedure), then from 300° C. to 0° C. at −10° C./min (cooling), then 2 min at 0° C. (maintaining temperature), then from 0° C. to 300° C. at 20° C./min (2.sup.nd heating procedure).

(7) Enthalpy of fusion is determined with the aid of the abovementioned software in the form of integral from the 2.sup.nd heating curve (temperature plotted against watts/gram). It is a measure of crystallinity.

(8) Determination of Isothermal Crystallization Time:

(9) Isothermal crystallization time is determined on the basis of DSC measurements (differential scanning calorimetry) in STAR 822e DSC equipment from Mettler Toledo (STARe SW 9.01 software).

(10) The measurement schedule is as follows: Heating to 280° C. (40° C. per minute); then maintaining temperature at 280° C. for 1 minute; then cooling to 210° C. (−400° C. per minute); then maintaining temperature at 210° C.

(11) The isothermal crystallization time is the time at which, at the maintained temperature of 210° C., no further heat flux is measured (crystallization completed). This numerical value is an index of crystallization rate.

(12) Determination of sodium content and potassium content in PET: a conventional analytic method is used; by way of example: PET is digested in nitric acid at elevated temperature and pressure; water is then used for dilution; sodium content and potassium content are then determined by the ICP-OES method.

(13) PBT: Polybutylene terephthalate (Pocan® B 1300, commercially available product from LANXESS Deutschland GmbH, Leverkusen, Germany) with intrinsic viscosity about 0.93 cm.sup.3/g (measured in phenol:1,2-dichlorobenzene=1:1 at 25° C.).

(14) Glass fiber: Glass fiber of diameter 10 nm (CS 7967, commercially available product from LANXESS N.V., Antwerp, Belgium) sized with silane-containing compounds.

(15) Others: other additives commonly used in polyesters, for example mold-release agents (e.g. pentaerythritol tetrastearate (PETS)), and heat stabilizers (e.g. those based on phenyl phosphites).

(16) PET, Type A:

(17) Plus 80 from PET Kunststoffrecyciing GmbH (PKR); comprises 20 ppm of sodium and <1 ppm of potassium; recyclate from PET bottles; isophthalic acid content about 1-3%.

(18) Alternative: CL80 from PET Recycling Team; comprises 9 ppm of sodium and <1 ppm of potassium; recyclate from PET bottles; isophthalic acid content about 1-3%.

(19) (The experiments were carried out with PET Plus 80.)

(20) This type of PET with sodium content and/or potassium content >1 ppm is usually produced in the following way: collection of used PET bottles; shredding to give flakes, removal of labels, caps, and foreign bodies; washing with aqueous solutions of alkali metal hydroxides (preferably aqueous solutions of alkali metal hydroxides comprising sodium and/or potassium, in particular aqueous solution of sodium hydroxide) and with other cleaning agents; drying of the cleaned flakes; compounding in the melt; optionally devolatilization in the melt and optionally filtration in the melt; pelletization; optionally solid-phase postcondensation.

(21) PET, type B: Lighter C93 from Equipolymers Global GmbH (Horgen, Switzerland); comprises <1 ppm of sodium and <1 ppm of potassium; PET copolymer with isophthalic acid content of about 1-3%. This type of PET is usually produced via polycondensation of glycol and dicarboxylic acid or, respectively, dimethyl dicarboxylate with antimony catalyst or, respectively, titanium catalyst.

(22) PET, type C: Polyclear T86 from Invista (Wichita, USA); comprises <1 ppm of sodium and <1 ppm of potassium; PET copolymer with isophthalic acid content of about 3-5%. This type of PET is usually produced via polycondensation of glycol and dicarboxylic acid or, respectively, dimethyl dicarboxylate with antimony catalyst or, respectively, titanium catalyst.

(23) PET, type D: T49H from Invista (Wichita, USA); comprises <1 ppm of sodium and <1 ppm of potassium; PET homopolymer. This type of PET is usually produced via polycondensation of glycol and terephthalic acid or, respectively, dimethyl terephthalate with antimony catalyst or, respectively, titanium catalyst.

Experimental Series 1

(24) Composition 1A: 38% of PBT+31% of PET type A+30% of glass fiber+1% of others;

(25) Composition 1B: 38% of PBT+31% of PET type B+30% of glass fiber+1% of others;

(26) Composition 1C: 38% of PBT+31% of PET type C+30% of glass fiber+1% of others;

(27) Composition 1D: 38% of PBT+31% of PET type D+30% of glass fiber+1% of others.

(28) The enthalpies of fusion of the compositions were measured, wide the following results: 1A (31.1 J/g), 1B (29.9 J/g), 1C (295 J/g), 1D (29.6 J/g).

(29) High enthalpy means high degree of crystallization (equivalent to a relatively large extent of crystallization). A high degree of crystallization is important for high dimensional stability of the injection moldings (otherwise disadvantageous postcrystallization effects occur). This experiment reveals that enthalpy of fusion is significantly higher for the composition (1A) of the invention.

Experimental Series 2

(30) Composition 2A: 34.5% of PBT+34.5% of PET type A+30% of glass fiber+1% of others;

(31) Composition 2B: 34.5% of PBT+34.5% of PET type B+30% of glass fiber+1% of others;

(32) Composition 2C: 34.5% of PBT+34.5% of PET type C+30% of glass fiber+1% of others;

(33) Composition 2D: 34.5% of PBT+34.5% of PET type D+30% of glass fiber+1% of others.

(34) The enthalpies of fusion of the compositions were measured, with the following results: 2A (29.0 J/g), 2B (26.6 J/g), 2C (28.0 J/g), 2D (23.6 J/g).

(35) High enthalpy means high degree of crystallization (equivalent to a relatively large extent of crystallization). A high degree of crystallization is important for high dimensional stability of the injection moldings (otherwise disadvantageous postcrystallization effects occur). This experiment reveals that enthalpy of fusion is significantly higher for the composition (2A) of the invention.

Experimental Series 3

(36) Composition 3A: 38% of PBT+31% of PET type A+30% of glass fiber+1% of others;

(37) Composition 3B: 38% of PBT+31% of PET type B+30% of glass fiber+1% of others.

(38) The isothermal crystallization of the compositions was measured, with the following results: 3A (2.8 min), 3B (4.6 min).

(39) Isothermal crystallization is a measure of crystallization rate. Faster crystallization means shorter cycle time in the injection molding process. Here, the composition (3A) of the invention is to lead to markedly faster isothermal crystallization, and this leads to a shorter cycle time in industrial use.

Experimental Series 4

(40) Composition 4A: 38% of PBT+31% of PET type A+30% of glass fiber+1% of others;

(41) Composition 4D: 38% of PBT+31% of PET type D+30% of glass fiber+1% of others.

(42) Injection pressure was measured during injection of the compositions, with the following results: 4A (289 bar), 4D (367 bar).

(43) Lower injection pressure opens up the possibility of operating at lower melt temperatures. This leads to a shorter cooling time for the melt and consequently to shorter cycle times. A precondition for lower melt temperature is rapid and adequate crystallization. The test result reveals that the composition (4A) of the invention exhibits a markedly reduced injection pressure. This opens up the possibility of achieving shorter cycle times.

Experimental Series 5

(44) Composition 5A: 34.5% of PBT 34.5% of PET type A+30% of glass fiber+1% of others;

(45) Composition 5D: 34.5% of PBT 34.5% of PET type D+30% of glass fiber+1% of others.

(46) The length of the flow spiral of the compositions was measured in each case, with the following results: 5A (286 mm), 5D (275 mm).

(47) The composition (5A) of the invention exhibits a longer flow spiral, and therefore better flowability in the melt. Better flowability opens up the possibility of operating at lower melt temperatures—with the precondition of rapid and adequate crystallization. This leads to a shorter cooling time for the melt and consequently to shorter cycle times.