WO2013040096A1

WO2013040096A1 - Low pearlescence compositions

Info

Publication number: WO2013040096A1
Application number: PCT/US2012/054947
Authority: WO
Inventors: David Voisin; Andre Rannard Cotterlaz
Original assignee: E. I. Du Pont De Nemours And Company
Priority date: 2011-09-12
Filing date: 2012-09-12
Publication date: 2013-03-21

Abstract

Described is a method for reducing pearlescence of polyethylene terephthalate injection stretch blow molded bottles comprising preparing a melt blend of 85 percent to 97 weight percent of a poly(ethylene terephthalate) and 3 to 15 weight percent of a poly(trimethylene terephthalate) and injection stretch blow molding bottles therefrom.

Description

TITLE

Low Pearlescence Compositions

FIELD OF THE INVENTION

The present invention relates to compositions for preparing shaped articles such as bottles using polyester pellet blend and melt extruded blend compositions comprising poly(trimethylene terephthalate) and polyethylene terephthalate, as well as the use thereof.

BACKGROUND OF THE INVENTION

The most common polyester currently used is poly(ethylene terephthalate) (PET). It is widely used in the manufacture of shaped articles such as bottles, containers, compression- or injection-molded parts, tiles, films, engineered components, etc. Due to recent trends toward sustainability and reduced use of petroleum, alternatives to PET are being investigated.

A common package currently made from PET is an injection- stretch-blow-molded (ISBM) bottle, jar or other container. In an ISBM process, the polymer resin is heated to the molten form in an extruder and then injection-molded in a mold to provide a "preform" or parison. The preform is then heated and stretched or expanded by application of air pressure to its final shape.

In an effort to provide economically attractive packaging solutions, there is constant effort in the field of injection-stretch-blow-molding (ISBM) to obtain larger bottles having a higher volume capacity from the same amount of PET by pushing back the stretch/expansion limits of PET parisons.

While PET parisons that are expanded to a high degree yield mechanically stable bottles that may be suitably used as containers for liquids, these bottles will also display a whitening of the bottle walls, especially towards the bottom end of the bottle. This whitening is also known as "pearlescence" in the art, because of its luminous sheen reminiscent of an oyster pearl. Without wishing to be bound to a particular theory, it is believed that the pearlescence is due to the formation of multiple, tiny microscopic cracks in the walls of the PET bottle when reaching higher stretch ratios.

While bottles displaying pearlescence can be used to package opaque or strongly colored liquids, such as lemonades, milk or red wine, a bottle displaying pearlescence cannot be used to contain drinking water, since the pearlescence is easily detected upon visual inspection, and turns off prospective customers.

It is therefore desirable to provide for a composition suitable for manufacturing injection-stretch-blow-molded (ISBM) polyester bottles that do not display pearlescence, even when stretch blow molded to high stretch ratios.

SUMMARY OF THE INVENTION

The present invention provides for a process or method for reducing pearlescence in shaped articles, comprising the steps of preparing a thermoplastic composition; heating the composition to a melt; molding the melt into a substantially tubular hollow perform; bringing the preform to a temperature between the glass transition temperature and the temperature of crystallization from the glass or cold crystallization of the composition; and stretching the preform in the axial direction, radial direction or combination thereof; wherein the composition comprises from 85 percent to 97 weight percent of a poly(ethylene terephthalate) and from 3 to 15 weight percent of a poly(trimethylene terephthalate), based on the total weight of the composition; wherein the composition does not contain a crystallization accelerator or nucleating agent; wherein the preform has one closed end and one open end; and wherein the stretching is optionally carried out by application of air pressure, mechanical pressure to the interior of the perform, or both to provide a shaped article.

BRIEF DESCRIPTION OF THE FIGURE FIGURE 1 shows a perspective drawing of the lower portion of an injection blow molded bottle.

DETAILED DESCRIPTION

The technical and scientific terms, unless otherwise indicated, have the meanings that are commonly understood by one of ordinary skill in the art to which this invention belongs. Tradenames or trademarks are in uppercase.

As used herein, the term "produced from" is synonymous to "comprising".

As used herein, the terms "3GT" and "PTT" are synonymous to

"poly(trimethylene terephthalate)".

Homopolymer means a polymer containing many repeat units of one kind. For example, a 3GT homopolymer means a polymer substantially derived from the polymerization of 1 ,3-propanediol with terephthalic acid, or alternatively, derived from the ester-forming equivalents thereof (e.g., any reactants such as dimethyl terephthalate which may be polymerized to ultimately provide a polymer of

poly(trimethylene terephthalate).

Copolymer refers to polymers comprising repeat units of two or more different kinds. For example, a 3GT copolymer means any polymer comprising (or derived from) at least about 70 mole percent trimethylene terephthalate and the remainder of the polymer being derived from monomers other than terephthalic acid and 1 ,3-propanediol (or their ester forming equivalents).

All references are incorporated by reference as if fully set forth herein.

Compositions useful in the process for reducing pearlescence according to the present invention may compositions comprising of from 3 to 15 weight percent, preferably of from 3 to 10 weight percent, and more preferably of from 3 to 8 weight percent of 3GT or poly(trimethylene terephthalate), based on the total weight of the composition, while the remaining weight percent may be of PET or poly(ethylene terephthalate).

Polyester polymers are well known to one skilled in the art and may include any condensation polymerization products derived from, by esterification or transesterification, an alcohol and a dicarboxylic acid including ester thereof. Alcohols include glycols having 2 to about 10 carbon atoms such as ethylene glycol, propylene glycol, butylene glycol, methoxypolyalkylene glycol, neopentyl glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, diethylene glycol,

polyethylene glycol, cyclohexane dimethanol, or combinations of two or more thereof. Dicarboxylic acids include terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, glutaric acid, isophthalic acid, 1 ,10- decanedicarboxylic acid, phthalic acid, dodecanedioic acid, the ester- forming equivalents (e.g., diesters such as dimethylterephthalate), or combinations of two or more thereof.

Polyethylene terephthalate is a polyester prepared by the

condensation polymerization of ethylene glycol and terephthalic acid (or dimethyl terephthalate). The PET may be a PET homopolymer or a copolymer that preferably contains 70 percent or more of poly(ethylene terephthalate) in mole percentage, or blends thereof. These may be modified with up to 30 mol percent of polyesters made from other diols or diacids.

Poly(trimethylene terephthalate) is a polyester that may be prepared by the condensation polymerization of 1 ,3-propanediol and terephthalic acid. A 3GT may also be prepared from 1 ,3-propane diol and dimethylterephthalate (DMT), for example, in a two-vessel process using an organotitanate catalyst, e.g., tetraisopropyl titanate catalyst, TYZOR TPT (E. I. du Pont de Nemours and Company (DuPont), Wilmington, Del.). Molten DMT is added to 1 ,3-propanediol and the catalyst at about 185°C in a transesterification vessel, and the temperature is increased to 210°C while methanol is removed. The resulting intermediate is transferred to a polycondensation vessel where the pressure is reduced to one millibar (10.2 kg/cm²) and the temperature is increased to 255°C. When the desired melt viscosity is reached, the pressure is increased and the polymer may be extruded, cooled and cut into pellets.

The 3GT may be a homopolymer or a copolymer that preferably contains 70 percent or more of 3GT in mole percentage, or blends thereof. These may be modified with up to 30 mol percent of polyesters made from other diols or diacids. The most preferred resin is 3GT homopolymer.

Other diacids that are useful to polymerize 3GT resin include isophthalic acid, 1 ,4-cyclohexane dicarboxylic acid, 1 ,3-cyclohexane dicarboxylic acid, succinic acid, glutahc acid, adipic acid, sebacic acid, 1 ,12-dodecane dioic acid, and the derivatives thereof such as the dimethyl-, diethyl-, dipropyl esters of these dicarboxylic acids, or combinations of two or more thereof.

Other diols include ethylene glycol, 1 ,4-butanediol, 1 ,2-propanediol, diethylene glycol, triethylene glycol, 1 ,3-butanediol, 1 ,5-pentanediol, 1 ,6- hexanediol, 1 ,2-, 1 ,3- and 1 ,4-cyclohexane dimethanol (CHDM), the longer chain diols and polyols made by the reaction product of diols or polyols with alkylene oxides, or combinations of two or more thereof.

Because polyesters and processes for making them are well known to one skilled in the art, further description is omitted herein for the interest of brevity.

Intrinsic viscosity (IV) is a measure of the capability of a polymer in solution to enhance the viscosity of the solution. IV may be measured according to ASTM D2857.95. For example, a Viscotek Forced Flow Viscometer model Y-900 may be used and the polymers dissolved in 50/50 w/w trifluoroacetic acid/methylene chloride at a 0.4percent (wt/vol) concentration and tested at 19 C°. Intrinsic viscosity typically increases with increasing polymer molecular weight, but is also dependent on the type of macromolecule, its shape or conformation, and the solvent it is measured in. Because 3GT and PET polymers have different shapes, 3GT has higher IV than PET for a given molecular weight. For example, 3GT with IV of about 1 .0 corresponds to PET with IV of about 0.7.

Differential Scanning Calorimetry (DSC) may be used to determine glass transition temperature (T_g), temperature of crystallization from the glass or cold crystallization (T_cg or T_cc), crystallization from the melt, and melting point (T_m). A 10-mg sample of polymer, ground to pass a 20- mesh (7.9 cm^"1) screen, was analyzed with a TA Instruments 2920 DSC, with a refrigerated cooling accessory for controlled cooling, from room temperature to 280°C. using a heating rate of 10°C/min. The sample was then held at 280°C for two minutes, quenched in liquid nitrogen, and then reheated from room temperature to 280°C. Procedures for measurement of Tg, Tec or Teg, and T_m were used as described in the TA Instruments manual for the 2920 DSC.

The compositions may additionally comprise small amounts of optional materials commonly used and well known in the polymer art. Such materials include conventional additives used in polymeric materials including plasticizers, stabilizers including viscosity stabilizers and hydrolytic stabilizers, primary and secondary antioxidants such as for example IRGANOX 1010, ultraviolet ray absorbers and stabilizers, antistatic agents, dyes, pigments or other coloring agents, fire-retardants, lubricants, processing aids, slip additives, antiblock agents such as silica or talc, release agents, and/or mixtures thereof. Additional optional additives may include inorganic fillers; acid copolymer waxes, such as for example Honeywell wax AC540; T1O2, which is used as a whitening agent; optical brighteners; surfactants; and other components known in the art to be useful additives. These additives are described in the Kirk Othmer Encyclopedia of Chemical Technology.

Additives such as antioxidants (e.g., hindered phenols

characterized as phenolic compounds that contain sterically bulky radicals in close proximity to the phenolic hydroxyl group) may be used. Hindered phenols may include 1 ,3,5-trimethyl-2,4,6-tris-(3,5-di-tert-butyl-4- hydroxybenzyl)-benzene; pentaerythrityl tetrakis-3(3,5-di-tert-butyl-4- hydroxyphenyl)-propionate; n-octadecyl-3(3,5-di-tert-butyl-4- hydroxyphenyl)-propionate; 4,4'-methylenebis-(2,6-tert-butyl-phenol); 4,4'- thiobis-(8-tert-butyl-o-cresol); 2,6-di-n-tert-butylphenol; 6-(4- hydroxyphenoxy)-2,4-bis(n-octyl-thio)-1 ,3,5 triazine; di-n-octylthioethyl- (3,5-di-tert-butyl-4-hydroxy)-benzoate; sorbitol hexa[3-(3,5-di-tert-butyl-4- hydroxy-phenyl)-propionate], or combinations of two or more thereof. An antioxidant of note is bis-(2,4-di-t-butylphenyl)pentaerythritol diphosphite, CAS Number 26741 -53-7, available under the tradename ULTRANOX 626 from Chemtura.

These additive(s) may be present in the compositions in quantities that are generally from 0.01 to 15 weight percent, preferably from 0.01 to 10 weight percent, so long as they do not detract from the basic and novel characteristics of the composition and do not significantly adversely affect the performance of the composition, i.e. the reduction of pearlescence (the weight percentages of such additives are not included in the total weight percentages of the compositions as defined above in the Summary of the Invention). Many such additives may be present in amounts from 0.01 to 5 weight percent.

The optional incorporation of such additives into the compositions may be carried out by any known process, for example, by dry blending, by extruding a mixture of the various constituents, by the conventional masterbatch technique, or the like.

The compositions disclosed do not contain crystallization

accelerators, also known as nucleating agents or nucleators. The compositions are used in preparing injection molded preforms, which desirably comprise amorphous polymer compositions to allow for orientation in a subsequent blowing step (see below). Accordingly, use of crystallization accelerators that promote crystallization is undesirable. In addition, crystallization accelerators may reduce transparency and/or clarity of the shaped articles.

The process or method comprises preparing a thermoplastic composition as disclosed above. The composition may be prepared by blending the components by any means known to one skilled in the art, e.g., dry blending/mixing, extrusion, co-extrusion, to produce the composition. The composition may be a pellet blend or melt extruded blend. The composition may be prepared by a combination of heating and mixing (melt-mixing or melt-blending). For example, the component materials may be mixed to be substantially dispersed or homogeneous using a melt-mixer such as a single or twin-screw extruder, blender, Buss Kneader, double helix Atlantic mixer, Banbury mixer, roll mixer, etc., to give a resin composition. Alternatively, a portion of the component materials may be mixed in a melt-mixer, and the rest of the component materials subsequently added and further melt-mixed until substantially dispersed or homogeneous. For example, a salt and pepper blend of the components may be made and the components may then be melt-blended in an extruder. Alternatively, the components may be fed to the extruder separately and melt-blended.

The blended composition may be further processed. For example, the composition may be processed into pellets by a combination of extruding the melt into a strand, cutting the strand and cooling. Cooling may be effected by exposure to cool air or water. For example, a Gala underwater pelletizing system may be used to pelletize the extrudates into small pellet size.

Alternatively, the blended composition may be passed directly from the extruder into an injection molding apparatus as a melt. In this embodiment, the first and second steps of the process may be

accomplished in a continuous operation, eliminating the need for a second heating operation.

The composition is then heated to a melt and molded into a shaped preform by injection molding. A preform or parison is a substantially tubular hollow article having a closed end and an open end having relatively thick walls that is adapted for subsequent blow molding into a finally desired container form. The preform may be produced with the necks of the bottle, including threads or other means for attaching as closure (the "finish") on one end.

Injection molding of preforms for later blow molding into container configurations may include some balancing of factors (See, e.g., Blow Molding Handbook, by Rosato and Rosato, Hanser Publishers, New York, N.Y., 1988). See also U.S. Pat. Nos. 5,914,138, 6,596,213, 5,914,138, and 6,596,213.

Injection molding a bottle preform may be conducted by

transporting a molten material into a mold and allowing the molten material to cool. The mold includes a first cavity extending inwardly from an outer surface of the mold to an inner end, an article formation cavity, and a gate connecting the first cavity to the article formation cavity. The gate defines an inlet orifice in the inner end of the first cavity, and an outlet orifice that opens into the article formation cavity. The article formation cavity typically may be cylindrical (but other profiles are contemplated) with an axially centered projection at the end opposite the gate. The molten material flows through the gate into the cavity, filling the cavity. The molding may provide an article that is substantially a tube with an "open" end and a "closed" end encompassing a hollow volume. The open end may provide the neck of the bottle and the closed end may provide the base of the bottle after subsequent blow molding. The molding may be such that various flanges and protrusions at the open end provide strengthening ribs and/or closure means, for example screw threads, for a cap. Parison programming to change wall thickness and die shaping to adjust wall distribution, mainly for non-round containers, may be used to modify the resultant parison for improved blow molding performance.

Transporting the material extends from a melt source to the vicinity of the inlet orifice of the gate and includes an elongated bushing residing at least partially within the first cavity. This bushing defines an elongated, axial passageway therethrough that terminates at a discharge orifice. A "gate area", therefore, is defined by the assembled mold and bushing between the discharge orifice of the bushing and the outlet orifice of the gate. Ideally, this gate area is the portion of the system/apparatus in which the transition of the material from the molten phase present in the "runnerless" injection apparatus to the glassy phase of the completed article occurs during the time period between sequential "shots" of material.

During the injection of a "shot" of molten material (i.e., melt), the melt may flow from the discharge orifice of the bushing, through the gap between the discharge orifice of the bushing and the inlet of the gate, through the gate, and into the article formation cavity of the mold. The preform mold is ideally maintained at a temperature below the minimum T_g of the polymer resin, which enables the polymer to be quenched in the amorphous phase.

Because the temperature is maintained above its maximum crystal melt temperature in the bushing, and the temperature of the mold is maintained well below the T_g of the material, the majority of each shot cools quickly to its glassy state in the article formation cavity of mold. This results in the preform having low crystallinity levels (i.e., an article made up of substantially amorphous material) because the material temperature does not remain within its characteristic crystallization range for any appreciable length of time.

At the end of each "shot" injection pressure may be maintained on the melt for between about 1 and 5 seconds in order to assure that the melt is appropriately packed into the article formation cavity of the mold. Thereafter, the injection pressure on the melt is released, and the article may be allowed to cool in the mold for about 10 to 20 seconds.

Subsequently, the mold is opened, the article is ejected therefrom, and the mold is re-closed. The latter operations may take on the order of about 10 seconds. The temperature of the melt material may transition in the gate area of the system/apparatus during the time interval between successive material "shots" between its molten phase temperature and its glassy (rigid) phase temperature in a controlled manner.

In addition, the preforms and final shaped articles prepared from the preforms, may comprise materials other than the polyester blend, such as layers of polymeric material other than the polyester blend. Various additives as generally practiced in the art may be present in the respective layers including the presence of tie layers and the like, provided their presence does not substantially alter the properties of the article. Such additives including antioxidants and thermal stabilizers, ultraviolet light stabilizers, pigments and dyes, fillers, anti-slip agents, plasticizers, other processing aids, and the like may be employed in the layers other than the polyester blend layer.

For example, preforms may be prepared by coinjection molding wherein two melt streams are injected into a mold in such a way that one polymeric material (for example, the more expensive and/or more functional material) is on the exterior of the article while another polymer is in the interior.

For a multilayer preform molding, the molten materials may be injected into the mold from an annular die such that they form a laminar flow of concentric layers. For example, in a three-layer preform, the inside layer and the outside layer comprise the polyester blend composition and the interior layer (a layer in which both faces of the layer are in contact with another layer) comprises a different material such as, for example, a barrier material. The molten materials are introduced into the mold such that the material for the outside layer and the inside layer enter the mold cavity before the material for the interior layer enters. Thus, the material for the outside and inside layer forms a leading edge of the laminar flow through the cavity. For a period of time, the three layers enter the mold cavity in a three-layer concentric laminar flow. Next, flow of the material for the interior layer is halted and the material for the outside and inside layers provides a trailing edge of the laminar flow. The flow continues until the entire cavity is filled and the trailing edge seals or fuses to itself at the gate area to form the closed end of the preform. The molding process for a three-material, four-layer preform is similar except that two different materials are provided for the two interior layers.

Positioning of the various layers in a cross-section of the preform may be adjusted by controlling relative volumetric flow rates of the inside and outside layers to enable relative shifting of the position of the core, and also the relative thickness of the inside and outside layers in the molded articles (see U.S. Patent 6,596,213).

Molding of three materials to form a four-layer or five-layer object may include a plastic container comprising two interior layers (one layer selected for its gas barrier or gas scavenger properties, and the other layer for its UV protection or for some other property such as a structural layer or a recycled layer). In a 5-layer object, an additional interior structural layer may be between these interior layers. The leading edge of gas barrier and/or gas scavenger property may preferably be such that one of the two interior layers is uniform in its penetration around the circumference of the molded object. This uniform penetration may be achieved by starting the flow of this one interior layer before starting the flow of the second interior layer, so that the leading edge of this first- flowing interior layer starts on the zero gradient of the velocity profile.

Subsequent initiation of the flow of the second interior layer offsets the later-flowing portions of the first interior material from the zero gradient, but the uniform leading edge is established by the initial flow of the first interior layer on the zero gradient.

The relative thickness and position of each of the interior layers may be chosen to enhance the properties of the final molded object. For example, if one of the interior layers is a gas scavenger, the chosen position of the gas scavenger layer may be the innermost interior layer to reduce the permeation rate of gas through the outer layers of the container into the scavenger, and to increase the rate of gas scavenging from the contents of the container. Such a position may extend the shelf life of the container contents if the purpose of the scavenger layer is to absorb gas permeating from the atmosphere exterior to the container. As another example, the position of outermost interior layer may enhance the performance of a humidity-sensitive gas barrier layer, by moving the barrier layer away from the 100 percent relative humidity of the contents of a beverage that is to fill the container to a position in the wall that is closer to the lower relative humidity of the atmosphere surrounding the container.

Injection molded preforms may include mostly amorphous material to allow the preform to be blow-molded into a desired shape easily and with a minimum of reheating and avoiding the formation of undesirable cracks or haziness in the finished article/preform caused by the presence of excessive crystallized material therein.

To prepare a bottle, the preform may be reheated and biaxially expanded by axial stretching and radial stretching in a blow molding operation (as described below), usually in a shaped mold so that it assumes the desired configuration. The neck region is unaffected by the blow molding operation while the bottom and particularly the walls of the preform are stretched and thinned. The resulting thickness of the exterior layers and the interior layers may provide sufficient strength and barrier properties to allow the bottle to contain and protect the product packaged within.

This process involves the production of hollow objects, such as bottles, jars and other containers having biaxial molecular orientation (radial and axial). Biaxial orientation provides enhanced physical properties such as higher mechanical strength and rigidity, clarity

(transparency), and gas barrier properties, which are all very desirable in products such as bottles, vials, jars and other containers. Biaxial orientation allows bottles to resist deforming under the pressures formed by carbonated beverages, which may approach 60 psi.

A practical processing window for thermoplastic materials may be the temperature range between T_g and T_cc or T_cg. 3GT has a relatively narrow processing window. Blends of 3GT and PET provide a broader processing window by shifting the crystallization temperature from glass to a higher temperature region.

The compositions may be used to produce dimensionally-stable ISBM bottles with shrinkage in height and diameter that are statistically equivalent to the control, higher-T_g PET copolymer resin and do not display the pearlescence found in PET copolymer or homopolymer ISBM bottles, especially at overall stretch ratios in excess of 15.

The computation of stretch ratios is further described in the experimental section of the present application.

When measured according to standard ASTM D1003, the bottles manufactured according to the process of the present invention display haze values below 1 .5, or of from 1 .5 to 0.1 , even at overall stretch ratios in excess of 15, in contrast to bottles consisting purely of poly(ethylene terephthalate).

Of note are compositions wherein the T_g is from about 45 to about 90°C and the T_cg is from about 70°C to about 150°C, as determined by differential scanning calorimetry by heating from room temperature to 280°C using a heating rate of 10°C/min, holding at 280°C for two minutes, cooling to below room temperature, and then reheating from room temperature to 280°C. Also of note are compositions wherein the T_g is from about 45 to about 80°C. and the T_cg is from about 70 to about 130, and compositions wherein the T_g is from about 65 to about 80°C and the Ten is from about 90 to about 150. The preforms are heated (for example, using infrared heaters) above their T_g, then blown using high pressure air into the final desired shape. In some cases, the blowing operation is conducted in the absence of a mold cavity that defines a predetermined volume (free-blowing).

Free-blowing allows the investigation of stretch ratios for the compositions.

In most cases, the blowing operation is performed using metal blow molds having an inner volume equal to the size and shape of the desired article. The blowing operation may also be performed using a core rod. The core rod may stabilize the preform in the proper orientation in the mold cavity and may be used to help heat the preform as it is blown. The preform optionally may also be stretched axially (lengthwise) with a core rod as part of the process.

Accordingly, a representative process for producing an article such as container or bottle includes (i) preparing a composition as disclosed herein; (ii) injection molding or extrusion molding a closed-end hollow preform; (iii) (re)heating the preform to the blow molding temperature, such as about 5°C to about 30°C lower than, or about 10°C to 20°C above, the glass transition temperature range of the preform material; (iv) stretching the preform axially in the blow mold by means of a stretch rod; and (v) simultaneously with the axial stretching, introducing compressed air into the preform so as to biaxially expand the preform outwardly against the walls of the blow mold so that it assumes the desired

configuration.

Generally, the molding temperature for the composition containing a poly(trimethylene terephthalate) can be carried out at about 15°C to about 30°C lower than the molding temperature of a polyester composition comprising no poly(trimethylene terephthalate). Also, molding can be carried out at a pressure about 10 psi to about 25 psi lower than the pressure necessary to blow mold the composition

There are two types of stretch-blow-molding techniques. In the one-stage process, preforms are injection molded, conditioned to the proper temperature, and blown into containers all in one continuous process. This technique is most effective in specialty applications, such as wide-mouthed jars, where very high production rates are not a requirement.

In the two-stage process, preforms are injection molded, stored for a short period of time (for example 1 to 4 days) at a temperature below the T_g of the composition, and blown into containers using a reheat-blow (RHB) machine. Because of the relatively high cost of molding and RHB equipment, this is the best technique for producing high-volume items such as carbonated beverage bottles.

In addition, the shaped articles (e.g., preforms and bottles) may comprise materials other than the polyester blend, such as layers of polymeric material other than the polyester blend, or nonpolymeric substrates. For example, articles may be prepared by coinjection molding as described above wherein multiple melt streams are injected into a mold in such a way that one polymer is on the exterior of the article while at least one additional layer is in the interior.

Vials, bottles, jars and other containers comprising the modified polyester composition may be prepared, for example by injection-stretch- blow-molding. Bottle and/or jar sizes may range from under 2-ounce to 128-ounce capacity or larger. Although containers are generally described herein as bottles, other containers such as vials, jars, drums and fuel tanks may be prepared as described herein from the

compositions described herein. Larger capacity containers such as drums or kegs may be similarly prepared, as are smaller vials, bottles and other containers. The present process or method is particularly suitable to reduce pearlescence in shaped articles having one or more corners or salient angles or edges, such as for example in bottles having triangular, square, rectangular or polygonal shapes, since the edges of a bottle are the parts experiencing the most important amount of stretching.

The article disclosed above has reduced heat deformation or shrinkage, as compared to an article made from 3GT or a composition comprising more than 50 weight percent 3GT, when the article is aged at high temperature of about 30 to about 55°C or about 35 to about 45°C and at a high relative humidity of from about 60 to about 100, about 70 to about 100, or about 80 to about 95 percent. In other words, the article is a heat stable article where the article is substantially the same as an article made from PET in heat deformation or shrinkage. Furthermore,

byproducts such as acrolein, is absent from the article.

EXAMPLES

Materials Used

Poly(ethylene terephthalate) is commercially obtainable from M&G under the trademark CLEARTUF P76.

Poly(trimethylene terephthalate) is commercially obtainable from E. I. du Pont de Nemours and Company under the trademark BIOMAX PTT 1002.

In order to test the influence of poly(trimethylene terephthalate) on pearlescence in injection stretch blow molded articles, compositions 1 to 6, having varying percentages of poly(trimethylene terephthalate) and poly(ethylene terephthalate), were prepared.

Composition 1 consisted of pure polyethylene terephthalate.

Composition 2 consisted of 3 weight percent of poly(trimethylene terephthalate) and 97 weight percent of poly(ethylene terephthalate).

Composition 3 consisted of 5 weight percent of poly(trimethylene terephthalate) and 95 weight percent of poly(ethylene terephthalate).

Composition 4 consisted of 7 weight percent of poly(trimethylene terephthalate) and 93 weight percent of poly(ethylene terephthalate).

Composition 5 consisted of 15 weight percent of poly(trimethylene terephthalate) and 85 weight percent of poly(ethylene terephthalate).

Composition 6 consisted of 27 weight percent of poly(trimethylene terephthalate) and 73 weight percent of poly(ethylene terephthalate).

The ingredients for compositions 1 to 6 were melt blended, pelletized and then dried for a minimum of 8 hours at 160°C.

In order to be injection molded into a parison, the compositions 1 to 6 were heated to a melt at 280 °C for 150 seconds and were then injected for 3 seconds into a mold under a pressure of 800 bar. After the injection of molten composition filled up the mold cavity, the mold was cooled within 30 seconds to a temperature of 60 °C and the solidified parisons were then ejected from the mold. The parisons were then allowed to cool to ambient storage temperature and each had a weight of 80 g.

After being preheated to a temperature of 105 C°, the parisons were then stretch blow molded on a SIDEL SBO-2XL platform to yield sample bottles 1 , 2, 3, 4, 5 and 6 each having a volume of 6 liters and made with compositions 1 , 2, 3, 5 and 6 respectively, by first applying a preblow pressure of 7 bar and then a high pressure of 30 bar.

For each sample bottle, an overall stretch ratio was computed. The overall stretch ratio is defined as the product of the length stretch ratio and the hoop stretch ratio.

The length stretch ratio is defined as the length of the middle contour line of the injection stretch blow molded sample bottle, divided by the length of the middle contour line of the parison and characterizes the lengthwise stretch along the central axis of the parison into the stretch blow molded bottle.

The middle contour line is equidistant to the inner and outer contour lines and characterizes a contour line unaffected by localized variations in wall thickness.

The hoop stretch ratio is defined as the middle radius of the injection stretch blow molded sample bottle, divided by the middle radius of the parison and characterizes the increase in diameter of the parison when stretch blow molded into a bottle.

The middle radius is equidistant to the inner and outer radius characterizes a radius unaffected by localized variations in wall thickness.

The overall stretch ratio can be computed for 3 directions, the directions being front-to-back, side-to-side and diagonal.

In the direction of front-to-back, the contour lines measured are defined by the intersection between the surface of the parison or bottle and a plane passing through the central axis of the parison or bottle and which is perpendicular to the front and back faces of the bottle.

In the direction of side-to-side, the contour lines measured are defined by the intersection between the surface of the parison or bottle and a plane passing through the central axis of the parison or bottle and which is perpendicular to the side faces of the bottle.

In the direction of diagonal, the contour lines measured are defined by the intersection between the surface of the parison or bottle and a plane which passes through the central axis of the parison or bottle and through opposed rims of the bottle or parison.

The sample bottles 1 to 6, made from the corresponding

compositions 1 to 6, were then tested for pearlescence according to ASTM D1003 (Procedure B) using a Minolta M3600D spectrometer.

On visual inspection, the sample bottles displayed the most prominent pearlescence in their bottom section, so measuring samples were cut out from the bottommost sidewall of the sample bottles, as indicated by the arrow in Figure 1 .

The pearlescence measurement results for sample bottles 1 to 6 having a volume of 6 litres are summarized in the Table 1 . The

pearlescence can be correlated to the haze (more haze means more pearlescence). Haze was measured according to ASTM D1003

(Procedure B) using a Minolta M3600D spectrometer. The sample bottles exhibited an overall stretch ratio in front-to-back, side-to-side and diagonal directions of 1 1 .98, 17.70 and 19.54, respectively.

In Table 1 , the haze values are shown for samples cut out from the bottommost sidewall of 6 liter sample bottles obtained by stretch blow molding of parisons made with compositions 1 , 2, 3, 4, 5 and 6

respectively. Measurements were made in duplicate and the values shown are the arithmetic average thereof.

Table 1

Sample 1 2 3 4 5 6

Weight % PTT 0 3 5 7 15 27

Haze value¹ 3.73 2.95 1.07 1.84 0.6 7.09

As can be seen from the measurements in Table 1 , the haze value, which can be correlated to the pearlescence, decreased with the addition of poly(trimethylene terephthalate) when compared to pure poly(ethylene terephthalate). Sample 6 showed an increase in haze value, which resulted from a dramatically increased wall thickness in the bottommost sidewall due to an inhomogenous distribution of polymer along the length of the stretch blow molded bottle, and not de facto from an increase in pearlescence

Claims

CLAIMS What is claimed is:

1 . A process for reducing pearlescence in shaped articles, comprising the steps of

a. preparing a thermoplastic composition;

b. heating the composition to a melt;

c. molding the melt into a substantially tubular hollow perform; d. bringing the preform to a temperature between the glass

transition temperature and the temperature of crystallization from the glass or cold crystallization of the composition; and e. stretching the preform in the axial direction, radial direction or combination thereof;

wherein the composition comprises of from 85 percent to 97 weight percent of a poly(ethylene terephthalate) and of from 3 to 15 weight percent of a poly(trimethylene terephthalate), based on the total weight of the composition;

wherein the composition does not contain a crystallization accelerator or nucleating agent;

wherein the preform has one closed end and one open end; and wherein the stretching is optionally carried out by application of air pressure, mechanical pressure to the interior of the perform, or both to provide a shaped article.

2. A method for reducing pearlescence in shaped articles, comprising the steps of

a. preparing a thermoplastic composition;

b. heating the composition to a melt;

transition temperature and the temperature of crystallization from the glass or cold crystallization of the composition; and e. stretching the preform in the axial direction, radial direction or combination thereof; wherein the composition comprises of from 85 percent to 97 weight percent of a poly(ethylene terephthalate) and of from 3 to 15 weight percent of a poly(trimethylene terephthalate), based on the total weight of the composition;

wherein the preform has one closed end and one open end; and wherein the stretching is optionally carried out by

application of air pressure, mechanical pressure to the interior of the perform, or both to provide a shaped article.