WO2010027351A1

WO2010027351A1 - Fluid-assisted injection molded articles and process

Info

Publication number: WO2010027351A1
Application number: PCT/US2008/074994
Authority: WO
Inventors: Kenneth Leon Price
Original assignee: Ticona, Llc.
Priority date: 2008-09-02
Filing date: 2008-09-02
Publication date: 2010-03-11

Abstract

Fluid-assisted injection molding articles and processes for producing the articles are described. In one embodiment, a fluid-assisted injection molded article is formed from a polymeric composition containing a polyethylene terephthalate polymer in combination with another polyester polymer, such as polybutylene terephthalate. The polyethylene terephthalate polymer may comprise a copolymer of polyethylene terephthalate with isophthalic acid. The polymeric composition can also contain a reinforcing agent, such as glass fibers. Products made in accordance with the present disclosure have shown dramatically improved surface characteristics. In particular, pitting on the surface of the molded article is minimized.

Description

FLUID-ASSISTED INJECTION MOLDED ARTICLES AND PROCESS

BACKGROUND OF THE INVENTION

Semi-crystalline polymers are useful as engineering thermoplastics because they possess advantageous chemical, physical and electrical properties. Semi- crystalline thermoplastic polymers, for instance, can be readily processed by thermal means and formed into numerous and different shapes. For instance, thermoplastic polymers can be formed into various articles through one of many different molding processes such as extrusion, rotational molding, blow molding, and injection molding.

One particular type of injection molding that is used to produce plastic articles is typically referred to in the art as fluid-assisted injection molding. In fluid- assisted injection molding, a molten polymer composition is injected into a mold in conjunction with a fluid, such as a gas. The fluid is injected into the mold under pressure placing a force on the molten polymer composition. In this manner, the fluid not only forces the polymeric composition into the extremities of the mold, but also creates an internal hollow cavity or void space in the resulting article. During the process, a single fluid can be introduced into the mold or multiple fluids. For instance, in one particular embodiment, a gas is injected into the mold followed by a liquid. The fluid maintains pressure against the polymeric composition until the polymeric composition substantially cools. Once the article is cooled, the fluid pressure is reduced and the article is removed from the mold.

During fluid-assisted injection molding, the fluid provides numerous benefits. For instance, by forming a hollow cavity or void on the interior of the article, less plastic is used to produce the article and the resulting article is lighter. The fluid can also be used to speed up the cycle time or the time it takes to produce the article. As described above, the fluid also forces the polymer composition into the different parts of the mold and potentially improves the surface characteristics of the resulting article. The present disclosure is directed to further improvements in fluid-assisted injection molding processes. In particular, in the past, although fluid-assisted injection molding can produce products having relatively favorable surface characteristics, pitting on the surface still remains a problem, especially when producing fiber reinforced articles. The present disclosure is directed particularly to the production of fluid-assisted injection molding articles that have reduced surface imperfections, such as pits or glass fiber on the surface.

SUMMARY The present disclosure is directed to improved fluid-assisted injection molded articles and to corresponding processes for producing the articles. More particularly, the present disclosure is directed to a fluid-assist injection molded article having low surface imperfections by way of a combination of increased gloss and low incidence of surface pits. The fluid-assist molded article is molded from a composition comprising particular polyester(s) and from 10 wt.% to 25 wt.%, preferably from 10 wt. % to 20 wt.% of a filler selected from platelet filler (i) having an aspect ratio of from 3 to 25, and fibrous fillers (ii) having a diameter of from 7 to 21 μm and length up to 5 mm, and combinations of (i) and (ii) thereof, the filler properties being characterized prior to incorporation into the composition; and wherein the polyester polymers include from 99% to 60% by weight a polyethylene terephthalate polymer characterized in that in addition to terephthalic acid and/or napthalenedicarboxylic acid there may also be from 0.25 mol% to 10 mol% (based on total acid content), such as from about 2.5 mol% to about 10 mol%, of isophthalic acid and/or 2,6- napthalene dicarboxylate including combinations; and from 1 wt.% to 40 wt.% of a second polyester polymer selected from polybutylene terephthalate, polytrimethylene terephthalate, polycyclohexylene dimethyl terephthalate, polybutylene napthalate, or mixtures thereof.

The filled polyester compositions defined herein being processed under fluid- assist injection conditions to result in hollow molded articles showing significant and unexpected improvement in surface quality, as measured by instrumented gloss readings and reduced surface imperfections as evaluated by ImagePro® digitized micrograph analysis of the exterior molded surface of the formed article which is shaped by the interior mold cavity. Of particular advantage, the invention further provides a balance to minimize sacrifices in melt flow rate, and the rate of crystallization while providing improved surface quality. A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is one embodiment of a schematic diagram of a fluid-assisted injection molding process that may be used in accordance with the present disclosure; and

Figures 2 to 12 are micrographs illustrating the surface of samples made in the Examples. Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.

DETAILED DESCRIPTION

It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention.

In general, the present disclosure is directed to filled polyester compounds processed via the fluid-assisted injection molding process to make superior shaped articles. The articles in accordance with the invention exhibit dramatically improved surface characteristics compared to controls derived from filled compounds containing PET homopolymer, a PET copolymer only, and embodiments comprising a filled mixture of polyester resins characterized by a major amount of polyester derived from butane diol ("PBT").

In one embodiment of the present disclosure, for instance, a fluid-assisted injection molded article is formed from a filled polymeric composition containing a polymer mixture of a polyethylene terephthalate copolymer and another polyester polymer other than one derived from a diol solely comprised of ethylene glycol. The polymer mixture, in one embodiment, may contain a polyethylene terephthalate copolymer in an amount from about 55% by weight to about 99% by weight based on 100% of the total weight of the polyester polymers present. For example, the polyethylene terephthalate copolymer may be present in the polymer mixture in an amount from about 60% to about 90% by weight, such as in an amount from about 65% to about 75% by weight of the total polyester polymers present.

The polyethylene terephthalate suitable under the invention is one which exhibits a comparatively slower crystallization half-time versus a PET homopolymer, in the compounded formulation. For example, in one compound where PET homopolymer is present at 98.5% of the total polyester polymers present, the crystallization half-time at 220⁰C is 0.32 min. In another compound where the polyester copolymer is present at 98.5% of the total polyester polymers present, the crystallization half-time at 22O⁰C is 2.35 min. The crystallization half time can be important in delaying the onset of polymer skin formation during the fluid injection stage after the molten compound has been introduced by the short-shot method. Thus, in one embodiment, a polymer is used having a crystallization half-time of greater than 0.75 min, such as greater than 1.5 min, such as greater than 2 min. In one embodiment, the polyester copolymer comprises, but is not limited to the following diacids: terephthalic acid, isophthalic acid, 2,6-napthalenedicarboxylic acid, phthalic acid, adipic acid, sebacic acid, decanedicarboxylic acid, azelaic acid, and cyclohexanedicarboxylic acid; and diols: ethylene glycol, diethylene glycol, propylene glycol, neopentyl glyol, butanediol, pentanediol, hexanediol, 2-methyl-1 ,3- propane diol, bisphenol A, polyethylene glycol and polypropylene glycol, and cyclohexane dimethanol; and combinations of multiple diacids and diols. For example, in one particular embodiment, the polyethylene terephthalate may be copolymerized with isophthalic acid. For instance, in one embodiment, a copolymer of polyethylene terephthalate and isophthalic acid may be used wherein the copolymer is formed from primarily ethylene glycol, terephthalic acid copolymerized with isophthalic acid; the isophthalic acid being present in the copolymer in an amount from about 0.25 mole percent to about 10 mole percent, such as from about 2.5 mole percent to about 7 mole percent, such as from about 3 mole percent to about 6 mole percent. In addition to a polyethylene terephthalate copolymer, the polymer mixture may further contain another polyester, such as polytrimethylene terephthalate, polypropylene terephthalate, polycyclohexylene dimethyl terephthalate, polybutylene terephthalate, polybutylene napthalate, or mixtures thereof. One or more of the above polyesters may be contained in the polymer mixture, in one embodiment, in an amount from about 1 % by weight to about 40% by weight with about from 99% to 60% polyethylene terephthalate copolymer, such as from about 10% to about 30% by weight of another polyester and 90% to 70% polyethylene terephthalate of copolymer. For example, in one particular embodiment, polybutylene terephthalate may be used in an amount from about 18% to about 25% by weight, with about 82% to about 75% polyethylene terephthalate copolymer. In another embodiment, the other polyester may be present in the polymer mixture in an amount less than about 10% by weight, such as from about 3% by weight to about 1 % by weight. When formulating the polymer mixture, the viscosity of the mixture, and/or the crystallization rate of the mixture can be important factors determining in part whether excellent surface gloss can be obtained in processing by fluid-assisted injection molding. The relative amounts of the polymers can be adjusted to ensure there is sufficient melt flow. For example, in one embodiment, the polymer mixture may be formulated so as to have a melt viscosity at 265°C of less than about 300 Pa-s, such as less than about 250 Pa-s, such as less than about 225 Pa-s, such as even less than about 200 Pa-s. For example, in one embodiment, the melt viscosity may be from about 120 Pa-s to about 225 Pa-s at 265°C . In addition to the viscosity, the crystallization rate of the polymer mixture can also be adjusted based upon the relative amounts of the components. The crystallization half-time is an indication of the crystallization rate and is measured using a Differential Scanning Calorimeter (DSC) by raising the material above its melt point and then reducing the temperature to a set point and holding it constant. The time between the onset of crystallization and the peak of crystallization is the crystallization half-time. The longer the crystallization half-time, the slower the material crystallizes. The crystallization half-time at 220⁰C of the polymer mixture, for instance, can be adjusted so as to be between about 0.32 minutes in the case where a PET homopolymer comprises 98.5% of the total polyester polymers present to about 2.35 minutes in the case where a PET copolymer comprises 98.5% of the total polyester polymers present. Although not to be bound by any theories, it has been observed that processes made according to the present disclosure result in reducing skin formation before the flowing composition completely expands to fill the mold cavity. Delaying the onset of skin formation tends to result in reduced or eliminated surface pitting. The presence of a slower crystallizing polymer mixture allows the extremities of the mold cavity to fill prior to skin formation and then the fluid acts to pack the polymer against the cavity wall during skin formation, producing fewer pits and less glass on the surface.

In addition to the fiber reinforced polymer mixture, the composition used to form the fluid-assisted injection molded article can contain various other ingredients and components, for example, platelet shaped filler particles, and mixtures thereof. Exemplary fibers include carbon fibers, wollastonite fibers, and particularly glass fibers. Exemplary platelet fillers are talc and mica. Glass fibers that may be used include, for instance, fibers comprised of lime-aluminum borosilicate glass. Fibers are typically employed in an amount from about 5% to about 50% by weight, such as in an amount from about 10% to about 35% by weight. Chopped fibers can generally have an initial length before compounding of from about 3 mm to about 5 mm.

Nonreinforcing fillers, otherwise referred to as particulate fillers defined by an aspect ratio of less than about 3, may be incorporated into the composition for various purposes. Suitable particulate filler include various mineral fillers such as, clay, silica, calcium silicate (wollastonite), mica, calcium carbonate, titanium dioxide, and the like. The fillers may be present in the composition in an amount from about 0.5% to about 50% by weight, such as from about 0.5% to about 15% by weight. One or more coloring and/or opacifying pigments may also be incorporated into the composition, for instance, titanium dioxide, iron oxide and other metallic pigments. Metallic pigments can include, for instance, aluminum pigments, gold pigments, copper pigments, bronze pigments, and the like. Metallic pigments provide the article with a brushed or polished metal appearance. Pigment particles are effective typically in an amount from about 0.1 % to about 5% by weight.

Perferably the compositions further comprise a stabilizer. Preferred are phosphorous-containing stabilizers. In one embodiment, for instance, the phosphite stabilizer may be obtained from GE Specialty Chemicals under the trade name ULTRANOX 626. A useful phosphite stabilizer is bis(2,4-di-t-butylphenyl) pentaerythritol diphosphite. Other phosphorous-containing stabilizers include phosphates or phosphonates. Phosphorous stabilizers are effectively employed in an amount from about 0.1 % to about 5% by weight, such as in an amount from about 0.1 % to about 1 % by weight.

Another ingredient that may be contained in the composition is a lubricant. The lubricant can be used in order to facilitate mold release. One example of a lubricant that may be used includes any suitable wax, such as an amide wax, a montan wax, esters of montan wax, stearic acide, stearyl alcohol, stearamides, and the like.

The present invention results in reducing or eliminating surface pitting. For instance, articles made according to the present invention can have pits appearing on the exterior surface of the article in an amount less than 3% of the surface area, such as in an amount less than about 2.5% of the surface area, such as in an amount less than about 2% of the surface area, such as in an amount less than about 1.5% of the surface area, such as even in an amount less than about 1 % of the surface area of the article. The above results can be obtained even when the composition used to form the article contains a significant amount of reinforcing fibers or fillers, such as even when the composition contains fibers or reinforcing fillers in an amount greater than 10% by weight. Of particular advantage, surface imperfections are minimized without adversely interfering with the mechanical properties of the molded part.

In general, any suitable fluid-assisted injection molding process may be used to produce articles in accordance with the present disclosure. Fluid-assisted injection molding processes, for instance, are disclosed in U.S. Patent No.

5,049,056, U.S. Patent No. 5,354,523, and U.S. Patent No. 6,896,844 which are all incorporated herein by reference.

During a fluid-assisted injection molding process, generally the polymeric composition is introduced into a mold cavity in the form of a molten stream. One or more fluids at one or more selected locations is injected into the mold cavity and applies pressure against the molten polymeric composition. The pressure of the fluid is controlled so as to create a fluid containing cavity surrounded by the molten polymeric material. The pressurized fluid is then continuously injected into the mold cavity at a controlled rate and pressure causing the molten polymer to flow through the mold space, into all of the extremities of the mold, and be pushed against the walls of the mold cavity.

After a sufficient amount of polymeric composition has been injected into the mold cavity, fluid pressure is held against the polymeric material until the material cools. In particular, the polymeric material is positively held against the mold surfaces as it solidifies into a self-supporting article. In one embodiment, a blowing agent may be premixed with the polymeric material.

In one embodiment, the rate of introduction of the polymeric material and the rate of injection of the fluid are controlled one relative to the other whereby the pressure of the fluid injected fluctuates with the pressure of the polymeric material. During this process, however, the pressure of the fluid remains higher than the pressure of the polymeric material to ensure a uniform injection during the process.

In one embodiment, the fluid may be initially introduced at a relatively high pressure in conjunction with the polymeric material in order to create a hollow cavity within the mold. The fluid pressure can then be subsequently decreased as the cavity extends within the inner region of the flowing polymeric material.

Referring to Fig. 1, for exemplary purposes only, one embodiment of a fluid- assisted molding process is shown. As illustrated, the injection molding system includes a polymer supply 10 which introduces molten polymeric material into a mold 12 that defines a mold cavity 14. The polymer supply 10, for instance, may comprise an extruder that receives the polymer material from a hopper in the form of pellets or a powder.

As shown in Fig. 1 , the system can further include at least one fluid supply. For instance, in the embodiment illustrated, the system includes a first fluid supply 16 and a second fluid supply 18.

During the formation of a molded article, the process involves the step of injecting the molten polymeric material into the mold cavity 14. A first fluid, such as a liquid or a gas, is also injected into the mold cavity 14 with the polymeric material. Initially, the fluid assists in the movement of the polymeric material into the mold cavity 14, forcing the polymeric material into the extremities of the mold. The fluid also forms a void or cavity on the interior of the article being formed. Forming a cavity within the polymeric article significantly reduces the amount of polymeric material needed to produce the article, thus reducing the material cost and the weight of the finished part.

As described above, in one embodiment, the fluid entering the mold cavity 14 from the fluid supply 16 can be a gas or a liquid. In one embodiment, for instance, a gas is used such as nitrogen, air, or an inert gas. The fluid pressure is maintained against the polymeric material until the polymeric material hardens sufficiently to form a self-supporting article. The pressure can then be reduced and the article may be removed from the mold cavity 14.

In one embodiment, a first fluid, such as a gas, can be injected into the mold cavity 14 from the first fluid supply 16. After the polymeric material has been injected into the mold cavity 14, a second fluid from the second fluid supply 18 can then be injected into the mold cavity for cooling the polymeric article. In one embodiment, for instance, the second fluid may comprise a liquid, such as water. Once the polymeric article is cooled sufficiently, the fluid can then be drained from the mold cavity and the article can be removed.

In another embodiment, the second fluid injected into the mold cavity may comprise a liquid that vaporizes as the polymeric article cools. For instance, in one embodiment, liquid carbon dioxide can be injected into the mold cavity. Once contacted with the polymeric material, the carbon dioxide evaporates into a vapor which increases the fluid pressure and further forces the polymeric material against the walls of the mold cavity.

Fluid-assisted molding processes provide numerous advantages and benefits. As described above, for instance, less polymeric material may be needed to produce the polymeric article. Depending upon the pressure of the fluid against the polymeric material, for instance, an article can be formed having relatively thin walls. For instance, the average wall thickness of the resulting article can be less than 0.5 inches, such as less than 0.25 inches, such as even less than 0.1 inches. The actual wall thickness, however, will depend upon the intended use of the article being formed. Another advantage to fluid-assisted injection molding is that the fluid prevents the polymeric material from shrinking away from the mold cavity during cooling. In addition, the fluid facilitates flowing the polymeric material throughout the mold so that the polymeric material is evenly distributed. In addition, the fluid also can minimize cycle times by serving to cool the polymeric material once injected into the mold cavity.

The present disclosure may be better understood with reference to the following examples. EXAMPLE 1

The following Example demonstrates how polymeric compositions made in accordance with the present disclosure reduce surface pitting in fluid-assisted injection molded samples. More particularly, in this Example, various different polymeric compositions were formulated and formed into molded articles using a gas-assisted injection molding process. During molding, nitrogen gas was introduced into the mold cavity. The articles formed comprised oven handles.

The particular compositions that were formulated and tested include the following:

TABLE NO. 1

Micrograph images of each sample were taken using reflected light optical microscopy. The results are illustrated in Fig. 2 through Fig. 5. As shown, in comparison to the images of the comparative samples, the molded articles made in accordance with the present disclosure have dramatically and unexpectedly improved surface characteristics. In particular, a significant reduction in surface pitting and a reduction of glass at the surface is shown.

In addition to Comparative Sample A above as shown in Fig. 3 and in addition to Comparative Sample D above as shown in Fig. 5, another comparative sample (Comparative Sample C) is shown in Fig. 6. Comparative Sample C is intended to represent a current commercial embodiment that is believed to contain a polyethylene terephthalate copolymer combined with 15% by weight fiberglass. The polyethylene terephthalate copolymer is believed to contain polyethylene terephthalate copolymerized with isophthalic acid. The isophthalic acid is present in the polymer in relatively low amounts, such as in an amount of 2.3 mol%. It is unknown what other additives may be contained in the polymer. As shown, Comparative Sample C displays a greater amount of surface pitting, surface fibers and other surface imperfections in comparison to the samples made according to the present disclosure. EXAMPLE 2

This Example quantitatively demonstrates the reduction of surface pitting when producing fluid-assisted injection molded articles in accordance with the present disclosure. Two polymeric compositions were formulated and formed into fluid-assisted injection molded articles using the process described in Example 1. The polymeric compositions that were formulated included the following:

TABLE NO. 2

To assess the relative area of pitting on the surface the same technique of reflected light optical microscopy presented in Example 1 was used to obtain micrographs. Images were taken from about 3 cm areas from the middle and from the end near the gate of each handle. The micrographs were imaged using Image Pro software. The pits were identified using color sensitivity, with the dark areas representing surface pits. The total area counts for all the pits in the micrograph was divided by the total area count of the entire micrograph to determine the percent relative area of pitting. The results of 12 micrographs were averaged. The following results were obtained.

TABLE 3

Additionally, the following tests were performed on the sample made according to the present disclosure to measure mechanical properties of the material:

Tensile Strength and Strain The tensile strength and strain properties of the sample were tested according to ISO Test No. 527. Calculations of tensile strength at break, percent elongation at break, and tensile modulus were performed. Flexural Strength and Strain

The flexural strength of a sample is defined as its ability to resist deformation under load. More particularly, the flexural test was conducted according to ISO Test No.178 and measures the force required to bend the specimen under three point loading conditions. The flexural strength as well as the flexural modulus were recorded.

Notched Izod The impact resistances of a sample were tested according to ISO Test No.

180. The test was performed at 23⁰C and measures energy absorbed by the sample material during impact.

Notched Charpy

The impact resistances of a sample were tested according to ISO Test No. 179. The test was performed at 23⁰C and measures energy absorbed by the sample material during fracture.

The results of mechanical properties tests are given in the following table.

TABLE 4

EXAMPLE 3 The mechanical property tests as described in Example 2 were used to test injection molded samples with varying PET/PBT ratios. Tests were also conducted to measure the melt viscosity at 265⁰C and melt flow rate at 265⁰C of the polymeric compositions. The melt viscosity test was performed using a capillary rheometer with an orifice of 1.0160 mm diameter and 15.240 mm length. Melt flow rate was determined according to ISO Test No. 1 133. The compositions tested and the results of the mechanical property tests as well as the physical property tests are shown in the following table.

TABLE 5

TABLE 6

EXAMPLE 4

The following Example further demonstrates how polymer compositions made in accordance with the present disclosure reduce surface pitting in fluid- assisted injection molded samples. Reduction of the microscopic surface pitting is advantageous because it produces a surface that appears to have an improved finish. In this Example, samples were produced containing primarily a PET copolymer in the polymer mixture. The PET copolymer used contained from 2 mole percent to 4 mole percent isophthalic acid.

The results of experiments testing the effect of different compositions with respect to the percentage of microscopic surface pitting is demonstrated quantitatively in the following table.

TABLE NO. 7

The type of PET polymer used influences the surface appearance. The data above demonstrates that a mixture of PBT with PET copolymer (isophthalic acid co-monomer) shows an improved surface appearance compared with a PET homopolymer alone and is believed to be improved over certain PET copolymers alone. Although Table 7 shows a PET homopolymer (see e.g., Comparative N) having a lower pitted area per square millimeter percentage value than the PET copolymer of Sample K, the micrographs were observed to have more glass fibers at the surface and physical observation of the molded samples with the naked eye indicates that Sample K has a superior surface versus Sample N. Micrograph images of each sample were taken using a reflected light optical microscopy. The results were illustrated in Figs. 7 through 12.

These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in such appended claims.

Claims

What Is Claimed:

1. A molded product comprising: an injection molded article defining an exterior surface having a surface area and an internal fluid-formed hollow cavity, the article being made from a composition containing a polymer mixture and reinforcing fibers or reinforcing fillers, the polymer mixture comprising from about 60% to about 99% by weight of a polyethylene terephthalate polymer, the polyethylene terephthalate polymer comprising a copolymer of polyethylene terephthalate, and from about 1 % to about 40% by weight of a polybutylene terephthalate, a polybutylene naphthalate, a polytrimethylene terephthalate, a polypropylene terephthalate or polycyclohexylene dimethyl terephthalate, the polymer mixture having a melt viscosity at 265°C of less than about 350 Pa-s, the exterior surface of the article containing pits in an amount less than about 2.5% of the surface area of the exterior surface.

2. A molded product as defined in claim 1 , wherein the polyethylene terephthalate polymer is preset in the polymer mixture in an amount from about 65% to about 85% by weight.

3. A molded product as defined in claim 1 , wherein the polyethylene terephthalate polymer comprises a copolymer of polyethylene terephthalate with isophthalic acid, the isophthalic acid being present in the copolymer in an amount from about 0.5 mole percent to about 10 mole percent of the diacids.

4. A molded product as defined in claim 1 , wherein the injection molded article further comprises a particulate filler.

5. A molded product as defined in claim 1 , wherein the article contains reinforcing fibers comprising glass fibers, the fibers being present in the injection molded article in an amount from about 5% to about 50% by weight.

6. A molded product as defined in claim 1 , wherein the polymer mixture has a melt viscosity at 265°C of from about 120 Pa-s to 250 Pa-s .

7. A molded product as defined in claim 2, wherein the polyethylene polymer comprises a copolymer of polyethylene terephthalate with isophthalic acid, the isophthalic acid being present in the copolymer in an amount from about 0.5 mole percent to about 10 mole percent, the article containing reinforcing fibers comprising glass fibers in an amount from about 5% to about 25% by weight, the polymer mixture having a melt viscosity at 265°C of from about 120 Pa-s to about 250 Pa-s.

8. A molded product as defined in claim 1 , wherein the exterior surface of the article contains pits in an amount less than about 1.5% of the surface area of the exterior surface.

9. A molded product as defined in claim 1 , wherein the injection molded article has a cylindrical-like shape.

10. A molded product as defined in claim 1 , wherein the polymer mixture has a crystallization temperature of from about 185⁰C to about 220°C.

1 1 . A molded product as defined in claim 1 , wherein the composition used to form the injection molded article contains a stabilizer comprising a phosphite.

12. A molded product as defined in claim 1 , wherein the injection molded article has an average wall thickness of less than about 0.25 inches.

13. A process for molding a plastic article comprising: injecting a viscous polymeric composition into a hollow mold, the polymeric composition comprising a polymer matrix, the polymer matrix comprising:

(a) a polyethylene terephthalate polymer present in the polymer matrix in an amount from about 70% to about 90% by weight, the polyethylene terephthalate polymer comprising a copolymer of polyethylene terephthalate, the polymer matrix further comprising from about 30% to about 10% by weight of polybutylene terephthalate, a polybutylene naphthalate, polytrimethylene terephthalate, polypropylene terephthalate, or polycyclohexylene dimethyl terephthalate, or

(b) a copolymer of polyethylene terephthalate present in the polymer matrix in an amount from about 90% by weight to 99% by weight, the polyethylene terephthalate being copolymerized with isophthalic acid, the isophthalic acid being present in the copolymer in an amount from about 0.5 mole percent to about 10 mole percent, the polymer matrix further containing from 1 % to about 10% by weight of polybutylene terephthalate, a polybutylene naphthalate, polytrimethylene terephthalate, polypropylene terephthalate, or polycyclohexylene dimethyl terephthalate, the polymer matrix having a melt viscosity at 265⁰C of from about 120 Pa-s to about 225 Pa-s, the polymeric composition further containing reinforcing fibers or reinforcing fillers in an amount from about 5% to about 50% by weight; injecting a fluid into the hollow mold, the fluid exerting a pressure on the viscous polymeric composition in an amount sufficient to push the composition against the walls of the mold and form a cavity surrounded by the polymeric composition; maintaining a fluid pressure against the polymer composition in the mold until the polymeric composition cools forming a self-supporting article; and removing the fluid pressure and removing the molded article from the mold.

14. A process as defined in claim 13, wherein the polymeric composition further comprises a stabilizer comprising a phosphite.

15. A process as defined in claim 13, wherein the molded article includes an exterior surface and an internal hollow cavity, the exterior surface defining a surface area, and wherein the article includes pits that cover less than about 2.5% of the surface area of the exterior surface.

16. A process as defined in claim 13, wherein the fluid comprises nitrogen.

17. A process as defined in claim 13, wherein the polymer matrix comprises the copolymer of polyethylene terephthalate combined with polybutylene terephthalate, the polybutylene terephthalate being present in the polymer matrix in an amount from about 10% to about 30% by weight.

18. A process as defined in claim 13, wherein the polymer composition contains reinforcing fibers comprising glass fibers, the glass fibers being present in an amount from about 5% to about 25% by weight.

19. A process as defined in claim 17, wherein the polymer composition contains reinforcing fibers comprising glass fibers, the glass fibers being present in an amount from about 5% to about 25% by weight.

20. A process as defined in claim 13, wherein the copolymer of polyethylene terephthalate contains isophthalic acid in an amount from about 2.5 mol% to about 10 mol%.