AU5742994A

AU5742994A - Polymer compositions having improved melt strength

Info

Publication number: AU5742994A
Application number: AU57429/94A
Authority: AU
Inventors: Ronald Richard Light; James Wilson Mercer Jr.; Emerson Eston Sharpe Jr.
Original assignee: Eastman Kodak Co
Current assignee: Eastman Chemical Co
Priority date: 1992-12-28
Filing date: 1993-12-09
Publication date: 1994-07-19
Also published as: MX9400006A; CA2151836A1; WO1994014894A1; EP0675922A1

Description

POLYMER COMPOSITIONS HAVING IMPROVED MELT STRENGTH

Technical Field

This invention relates to polymer compositions having improved melt strength which are useful for forming extrusion blow molded articles. The compositions contain a high molecular weight polyester such as polyethylene terephthaiate, a functional additive which has the ability of changing at least one physical property of the polyester but has the disadvantage of lowering the melt strength thereof, and a polycarbonate.

Background of the Invention Patents relating to polycarbonate and polyester alloys include U.S. Patent No. 3,218,372. The alloys described in this patent contain 5 to 95 wt % polycarbonate blended with 95 to 5 wt % PET. Other patents pertaining to polycarbonate and PET alloys include U.S. Patent Nos. 4,123,473; 4,175,147;

4,230,656; and 4,788,251. However, none of these patents disclose an extrusion blow molded article produced from a high molecular weight polyester having a weight average molecular weight of between 75,000 and 85,000 which contains a functional additive which has the ability to change at least one physical property of the polyester but has the disadvantage of lowering the melt strength thereof, and a polycarbonate.

High molecular weight PET homopolymer has sufficient melt strength for extrusion blow molding processes. However, it is sometimes desirable to incorporate certain functional additives in these polyesters to alter a physical property, such as incorporating pigment into the polyester to change its color. Ordinarily, such functional additives have the adverse effect of degrading some of the physical properties such as melt strength. In extrusion blow molding processes, such as in the production of bottles, it is very desirable for the polymer to have good melt strength, because the extrudate must be self—supporting while in the melt for a period of time.

In accordance with the present invention, it has been discovered that functional additives can be incorporated in certain polyesters while maintaining melt strength thereof, if a small amount of ^~~ polycarbonate is also incorporated in the composition.

By the term "functional additive" it is meant a substance or material which has the ability of altering some property of the polyester, but when incorporated alone in the polyester, has the disadvantage of lowering the melt strength. Examples include pigments, dyes, stabilizers, reinforcing materials such as glass fiber, etc.

By the term polyethylene terephthalate (PET) used herein, it is meant polyethylene terephthalate or polyethylene terephthalate modified with up to 10 mol % of another conventional dicarboxylic acid or glycol, preferably 1,4—cyclohexanedimethanol (CHDM) .

Description of the Invention

According to the present invention, there is provided a polymeric composition having improved melt strength comprising a) 90 to 99.5 wt % of a polyester containing repeat units from at least 90 mol % terephthalic acid and

90 to 100 mol % ethylene glycol, said polyester having a weight average molecular weight of 75,000- 85,000, b) 0.05 to 9.9 wt % of a polymeric material containing 5-100 wt % polycarbonate and 0-95 wt % polyethylene terephthalate wherein the wt % of polymeric material is inversely proportional to polycarbonate level, and c) 0.005 to 6 wt % of a functional additive. wherein a), b) , and c) total 100 wt %.

Also, according to the present invention there is provided a polymeric concentrate which comprises a) 95 to 0 wt % of a polyester containing repeat units from at least 90 mol % terephthalic acid and 90 to 100 mol % ethylene glycol, said polyester having a weight average molecular weight of 40,000—85,000, b) 5 to 99.5 wt % of a polymeric material containing 90 to 100 wt % polycarbonate, and c) 0.5 to 60 wt % of a functional additive, wherein a), b) , and c) total 100 wt %.

While the polyester specified in a) above is a high molecular weight polyester (i.e., 75,000—85,000), the polyester if used in b) is a carrier resin and may be of lower molecular weight (i.e., 40,000—85,000). PET which may be used in the blends of the present invention are well known and are available commercially. Methods for their preparation are described, for example, in U.S. Patent No. 2,465,319 and U.S. Patent No. 3,047,539. The dicarboxylic acid component may contain up to 10 mol % of other conventional aromatic, aliphatic or alicyclic dicarboxylic acids or polyfunctional anhydrides such as isophthalic acid, naphthalene— dicarboxylic acid, cyclohexanedicarboxylic acid, succinic acid, sebacic acid, adipic acid, glutaric acid, azelaic acid and the like.

The glycol component may contain up to 10 mol % of other conventional aliphatic or alicyclic glycols such as diethylene glycol, triethylene glycol, ethylene glycol, propanediol, butanediol, pentanediol. hexanediol, 1,4—cyclohexanedimethanol and the like. 1,4—Cyclohexanedimethanol is preferred.

Higher molecular weight PET, i.e., weight average of 75,000—85,000 may be made by conventional methods such as melt phase polymerization followed by polymerization in the solid phase. I.V.s (inherent viscosity) representing these molecular weights are 0.9 to 1.1, preferably about 0.95. The PET may be modified up to 10 mol % with other conventional trifunctional or tetrafunctional glycols, acids, and anhydrides.

Polycarbonate resins which are suitable for use in the present invention are well known in the art and are generally commercially available. These polycarbonates may be prepared by a variety of conventional and well known processes which include transesterification, melt polymerization, interfacial polymerization, etc. The polycarbonates are generally prepared by reacting a dihydric phenol with a carbonate precursor such as, for example, phosgene. Suitable processes for. preparing the polycarbonates of the present invention are described in, for example, U.S. Patent Nos. 4,018,750, 4,123,436 and 3,153,008. However, other known processes for producing polycarbonates are suitable. Particularly preferred polycarbonates are aromatic polycarbonates, prepared by reacting bisphenol—A [2,2—bis(4—hydroxy— phenyl)propane] with phosgene.

The compositions of the present invention may be subject to conventional processing methods such as injection molding, extrusion, etc. Prior to such processing, pellets of the PET, pellets of polycarbonate and the functional additive are mixed at the desired ratios. Specific industrial applications may require the addition of functional additives such as stabilizers, pigments, flame retardants, fillers, reinforcing agents, and/or processing aids. Other features of the invention will become apparent in the course of the following descriptions of exemplary embodiments which illustrate the invention and are not intended to be limiting thereof. The polyester used in the examples is poly(ethylene terephthalate) modified with 3.5 mol % 1,4—cyclohexane¬ dimethanol having an I.V. of 0.95, which is 80,000 weight average molecular weight.

Examples

Compositions of the following examples were extrusion blow molded into 18—ounce (510 g) wide mouth containers on a Bekum H—12IS extrusion blow molding machine equipped with an 80—mm high density polyethylene screw and a single head with a 0.70—inch (1.78 cm) ID die and a 0.675—inch (1.71 cm) OD mandrel. Melt strength improvements were evaluated by measuring the time and weight of an extruded parison from the extrusion blow molding machine to travel a distance of 24 inches (61 cm) below the die tip opening for a given die gap setting. The initial die gap setting, extruder screw speed and temperatures were established for a control sample and allowed to remain constant for all subsequent measurements on samples containing 3 wt % of the color concentrates.

Example 1 (Control, PET only) — PET containing 3.5 mol % CHDM was dried at 350°F (177°C) for 4 hours in a dehumidifying dryer and extrusion blow molded on the extrusion blow molding machine at a melt temperature of around 450°F (232°C) to 500°F (260°C) . The die gap was set at 52% on the electronic control panel and the extruder speed was maintained at around 7 rpm. An average parison drop time for the extruded parison to travel a distance of 24 inches (61 cm) was around 21 seconds. The average weight of the parison produced during this time for the control was 92 grams for this set of conditions. The results were normalized by multiplying the parison weight times the drop time. The normalized value for the control was 1,932 grams— seconds.

Example 2 (Control, PET and Functional Additive) — In this example, PET described above having a weight- average molecular weight between 75,000 and 85,000 was mixed with 3 wt % of a white color concentrate identify and having a weight—average molecular weight range of between 40,000 and 55,000, at the feed throat of the hopper on the extrusion blow molding machine with an additive feeder. After waiting 30 minutes to allow the system to equilibrate, average drop time for the molten parison to cover the same distance as described in

Example 1 was 20 seconds and it weighed on the average 83 grams. The normalized results are 1,600 grams- seconds. In comparison with Example 1, these results are 14% lower than the control described in Example 1. Example 3 (According to Invention) — While continuing the extrusion of the extrusion blow moldable PET copolymer having a weight—average molecular weight between 75,000 and 85,000, a second white color concentrate prepared with 48.526 wt % of PET having a weight—average molecular weight of 40,000 to 55,000, 42.0 wt % TiO , 9.3 wt % of a polycarbonate and 0.174 wt % of a blue pigment and stabilizer was added with the additive feeder at 3 wt % of the total composition. After waiting for a period of 30 minutes, the parison drop times and weights were measured again without changing the die gap and extruder speed settings that were established in Example 1. In this example, the average parison drop time was around 21 seconds. The average parison weight was about 89 grams. The normalized value was determined to be 1869. Surprisingly, adding the small amount of polycarbonate to the white color concentrate brought the melt strength of the PET containing the white pigment within 3% of the neat PET. Example 4 (According to Invention) — While continuing to extrude the PET copolymer under the conditions given in Example 1, 3 wt % of a red concentrate prepared in a base poly(ethylene terephthalate) having weight—average molecular weight of 40,000 to 55,000 and containing 9.3 wt % polycarbonate was added from the additive feeder attached to the feed hopper. The red concentrate was melt mixed in a Werner— Pfleiderer ZSK twin screw extruder and consisted of 76.643 wt % poly(ethylene terephthalate) having weight— average molecular weight of 40,000 to 55,000, 9.3 wt % polycarbonate, 6.671 wt % Solvaperm (trademark) Red G R—88 dye, 6.526 wt % TiO pigment, 0.750 wt % Solvaperm Red BB R—91 dye and 0.110 wt % Solvaperm Blue B—51 due. After 30 minutes the parison weight and drop time were measured as described above. The parison drop time over the 24—inch (61 cm) distance was 21 seconds and the parison weight was determined to be 92 grams. The normalized value was found to be 1932 which is very similar to that described in Example 1. This clearly demonstrates that adding a small amount of polycarbonate to the red color concentrate prevents a reduction in the overall melt strength of PET copolymer during the extrusion blow molding process.

Example 5 — In this Example, a black color concentrate was prepared by melt mixing in the twin screw extruder 20 wt % of Black Pigment BK 59 with 80 wt % of a poly(ethylene terephthalate) having a weight—average molecular weight of around 55,000. The concentrate was subsequently blended with the higher molecular weight PET in the Bekum H-121S extrusion blow molding machine as described previously. In this case, the parison drop time over the 24—inch (61 cm) distance was around 16 seconds and the parison weight was measured to be 77 grams. The normalized results were 1,232 gm—seconds. Again, in comparison with the normalized value determined for Example 1, the normalized value as a measure of melt strength for this Example was determined to be 36% lower than the control which, surprisingly, is a significant reduction in melt strength.

Example 6 — A black concentrate was prepared by melt compounding in a twin screw extruder a mixture of 70 wt % polycarbonate, 20 wt % Black Pigment BK 59 and 10 wt % a poly(ethylene terephthalate) copolyester modified with 3.5 mol % 1,4—cyclohexanedimethanol which had a weight—average molecular weight between 40,000 and 55,000. As previously described, the concentrate was dried and added to the high molecular weight PET in the Bekum extrusion blow molding machine. Again, the average parison drop time and weight was determined without changing the conditions established in Example 1. The average parison drop time was surprisingly observed to be significantly long, 31 seconds and average parison weight much heavier, 128 grams. The normalized value was found to be 3,960 which is over two times greater than the normalized value for the control sample described in Example 1. Again, this clearly demonstrates that adding the polycarbonate to the color concentrates will surprisingly overcome the reduction in melt strength usually observed if the concentrates are prepared without the polycarbonate.

The higher normalized values in the examples indicate higher melt strength. As used herein, inherent viscosity (I.V.) is measured at 25°C using 0.50 gram of polymer per 100 mL of a solvent consisting of 60% by weight phenol and 40% by weight tetrachloroethane.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

CLAIMSI claim:

1. A polymeric composition having improved melt strength characterized as comprising a) 90 to 99.5 wt % of a polyester containing repeat units from at least 90 mol % terephthalic acid, 90 to 100 mol % ethylene glycol, said polyester having a weight average molecular weight of 75,000—85,000, b) 0.05 to 9.9 wt % of a polymeric material containing 5—100 wt % polycarbonate and up to 0—95 wt % polyethylene terephthalate, and c) 0.005 to 6 wt % of a functional additive, wherein the total of a), b) and c) is 100 wt %.

2. A composition according to Claim 1 wherein the functional additive is a pigment.

3. A composition according to Claim 1 wherein the polyethylene terephthalate is modified with up to 10 mol % 1,4—cyclohexanedimethanol.

4. A polymeric concentrate which is characterized as containing a) 95 to 0 wt % of a polyester containing repeat units from at least 90 mol % terephthalic acid and 90 to 100 mol % ethylene glycol, said polyester having a weight average molecular weight of 40,000-85,000, b) 5 to 99.5 wt % of a polymeric material containing about 90 to 100 wt % polycarbonate, and c) 0.5 to 60 wt % of a functional additive, wherein the total of a) , b) and c) is 100 wt %.

5. A polymeric concentrate according to Claim 4 wherein said functional additive is a pigment.

6. A polymeric concentrate according to Claim 4 wherein said polyethylene terephthalate is modified with up to 10 mol % 1,4—cyclohexanedimethanol.