HK1087665A - Extrusion blow molded articles - Google Patents

Description

Extrusion blow molded articles

Technical Field

The present invention relates to shaped articles produced by extrusion blow molding of linear copolyesters containing 1, 4-cyclohexanedimethanol and neopentyl glycol residues. More particularly, the present invention relates to shaped articles, such as containers, produced by extrusion blow molding of a crystallizable copolyester comprising 1, 4-cyclohexanedimethanol and neopentyl glycol residues, wherein the copolyester has improved shear thinning properties.

Background

Extrusion blow molding is a common method for making hollow articles from polymeric materials. A typical extrusion blow molding manufacturing process includes: 1) melting the resin in an extruder; 2) extruding the molten resin through a die to form a molten polymer tube (i.e., parison) having a uniform sidewall thickness; 3) clamping a mold having a desired finish shape around the parison; 4) blowing air into the parison causing the extrudate to stretch and expand to fill the mold; 5) cooling the molded article; and 6) removing the article from the mold.

In order to form good quality containers with uniform sidewall thickness and to prevent the parison from tearing during expansion (i.e., blowing), the polymer extrudate must have good melt dimensional stability, also known as melt strength. Materials with good melt dimensional stability (i.e., high melt strength) have a tendency to resist stretching and flow due to gravity when in the softened or molten state. Excessive stretching of the extrudate parison causes the walls to become too thin. This results in uneven wall thickness. Thin walls also have a higher tendency to tear under the influence of the air pressure used to expand the extrudate into the die wall.

In extrusion blow molding, the polymer melt is extruded generally vertically from a die to form a parison, whereby the melt strength can be determined by measuring the vertical length of the extrudate after a certain time to determine the extent of extrudate stretching or "drawdown". When sag is measured, the extrusion throughput and die gap are fixed, whereby a given volume and weight of material is extruded in a fixed length of time. Under these conditions, polymer extrudates with low melt strength will be thin and long. In contrast, polymer extrudates with high melt strength will be short and thick. Furthermore, the sag of the extruded parison is directly related to the weight of the parison, so larger and heavier parisons will have a higher tendency to sag. Thus, larger and heavier parisons, such as those used to make larger bottles, require higher melt strength materials to maintain their shape. The higher the melt strength, the larger bottles can be produced.

Because melt strength is associated with slow flow induced primarily by gravity, it can be associated with polymer viscosity measured at low shear rates (e.g., 1 rad/sec). Viscosity can be measured by a typical viscometer such as a parallel plate viscometer. Generally, viscosity is measured at typical polymer processing temperatures and at a range of shear rates, typically between 1 radian/second and 100 radians/second. In extrusion blow molding, a viscosity of greater than 30,000 poise at 1 rad/sec at the processing temperature is typically required for blowing bottles. Larger parisons require higher viscosities.

However, melt strength only specifies one of the important processing properties in extrusion blow molding. The second important feature is the ease of flow at high shear rates. In the die/extruder, the polymer was in about 10s^-1To 1000s^-1Are "melt processed" at shear rates within the range. A typical shear rate in a barrel or die during extrusion blow molding or profile extrusion is 100 radians/second. These high shear rates are achieved as the polymer flows along the extruder screw, or as it passes through the die. In order to maintain a reasonably high production rate,these high shear rates are required. Unfortunately, at high shear rates, high melt viscosity can lead to viscous dissipation of heat in a process known as shear heating. Shear heating increases the polymer temperature and the degree of temperature rise is proportional to the viscosity at that shear rate. Because viscosity decreases with increasing temperature, shear heating reduces the low shear rate viscosity of the polymer and thus its melt strength.

In addition, high viscosity at high shear rates (e.g., as found in a die) can produce a condition known as melt fracture or "sharkskin" on the surface of the extruded part or article. Melt fracture is a flow instability phenomenon that occurs at the processing surface/polymer melt interface during extrusion of a thermoplastic polymer. The occurrence of melt fracture creates severe surface irregularities in the extrudate as it emerges from the orifice. This surface roughness in the melt fractured samples appeared to the naked eye as a frosty appearance or a matte finish, while the extrudates without melt fracture appeared clear. Melt fracture occurs when the wall shear stress in the die exceeds a certain value, which is typically 0.1 to 0.2 MPa. Wall shear stress is directly related to the volumetric throughput or line speed (which determines the shear rate) and the viscosity of the polymer melt. By reducing the line speed or viscosity at high shear rates, the wall shear stress is reduced, thereby reducing the likelihood of melt fracture. While the exact shear rate at the die wall is a function of the throughput and geometry and surface of the apparatus, a typical shear rate associated with the onset of melt fracture is 100 radians/second. Also, the viscosity at this shear rate typically needs to be below 30,000 poise.

To combine all of these desirable properties, an ideal extrusion blow molding polymer should have high viscosity at low shear rates, while having low viscosity at high shear rates from a processability standpoint. These properties are also useful in other fusion processes. For injection molding, a low viscosity at high shear rates will allow the polymer to flow easily into the mold. However, once the flow has stopped and the shear is removed, the polymer will quickly become highly viscous and the part can be quickly removed from the mold. For profile extrusion, high viscosity at low shear rates maximizes melt strength, while low viscosity at high shear rates minimizes screw motor loading, pump pressure, shear heating, and melt fracture.

Fortunately most polymers themselves have at least some degree of viscosity reduction between low and high shear rates, which is referred to as "shear thinning," which aids processing. Without shear thinning, extruders processing high melt viscosity polymers would require extremely high motor loads and/or high melt temperatures, both of which could lead to polymer degradation and excessive energy consumption. The ideal polymer mentioned above will have a high degree of shear thinning. Based on the foregoing discussion, one definition of shear thinning that is important for the process discussed in this invention will be the ratio of the viscosity measured at 1 rad/sec to the viscosity measured at 100 rad/sec. These viscosities will all be determined at the same temperature (typical of the actual processing conditions). This definition will be used to describe shear thinning for the purposes of the present invention.

Unfortunately, certain polymers such as polycarbonates and polyesters, for example polyethylene terephthalate (PET) and poly (ethylene terephthalate-co-1, 4-cyclohexanedimethanol terephthalate) (PETG), have a very low degree of shear thinning compared to polymers such as PVC, polystyrene, acrylics, and polyolefins. Because these other polymers have one or more of their own drawbacks (e.g., cost, odor, clarity, toughness, chemical resistance), polyesters would be a desirable alternative material in similar applications if the processing difficulties of polyesters could be overcome.

The melt strength of the polymer can be increased by lowering the melting temperature, but because the high shear rate viscosity also increases, the final temperature will be lowered to the point where melt fracture occurs. Lowering the temperature also increases the degree of shear thinning, and thus does enable the processing of articles having a certain maximum size, but the increased degree of shear thinning is generally insufficient to produce large articles.

The molecular weight and molecular weight distribution of the polyester can also be increased by solid state polymerization to increase melt strength and the degree of shear thinning. However, again, the improvement in shear thinning obtained by this method is generally insufficient to produce large articles. In addition, any polyester capable of solid stating is crystallizable and therefore cannot be processed at temperatures below its melting point. Certain solid stated polymers may also have a phenomenon known as "no melt" in which a portion of the solid stated pellets have a very high melting point, or very high viscosity, so that they cannot be dispersed in the melt pool. The resulting pellet sized particles are readily observed in the parison and the bottle produced. This lack of melting is an unacceptable visible defect. To eliminate unmelted, the material must be processed at higher temperatures, which often results in an unacceptable reduction in melt strength.

Linear polyester is defined as a polyester prepared from A-A and B-B monomers or A-B monomers or a mixture of these with the correct stoichiometric balance. The a-a monomer can represent a dibasic acid such as terephthalic acid, isophthalic acid, and the B-B monomer can represent a diol such as ethylene glycol and 1, 4-cyclohexanedimethanol. The A-B monomer can represent p-hydroxybenzoic acid, and the like. When the stoichiometry of these polymerization systems is correct, linear high molecular weight polyesters can be easily prepared. Diesters of dicarboxylic acids can be used instead of dicarboxylic acids, and high molecular polyesters can be produced by an ester exchange method.

The branching agent may be added to the reactor so that the resulting polymer chains are no longer linear. Branching agents are generally defined by the number of functional groups attached and can take the form of A3 or B3 molecules, where A3 is a tricarboxylic acid or tricarboxylic acid ester and B3 is a triol. Likewise, branching can be performed using A2B and AB2 monomers, where A2B represents a monomer having 2 acid functional groups and 1 alcohol group, and AB2 represents a molecule having 1 acid functional group and 2 alcohol groups. Higher functionality branching groups, including tetrafunctional groups, such as pentaerythritol and phenomellitic dianhydride, may also be used for this purpose. The science associated with polyester branching is well known in the polyester art. Chain branching is the most common method used to increase the melt strength of polymers, especially polyesters. However, the use of branching agents can lead to unacceptable gel formation in the melt, particularly if the branched material has already been solid stated. Gels are simply points in the polyester where too much local branching occurs, which effectively creates a network of closely interconnected molecular chains, which do not easily melt. This gel is present in the final molded/extruded part as an unacceptable visible defect. To minimize gelling, the branching agent is added in low levels and is uniformly dispersed in the reactor. Thus, it is difficult to produce branched polyesters and the increase in melt strength is limited to the maximum amount of branching agent that can be added without causing gel formation.

Amorphous copolyesters containing terephthalic acid (T) residues with varying proportions of 1, 4-Cyclohexanedimethanol (CHDM) and Ethylene Glycol (EG) residues are well known in the plastics market. Herein, the abbreviation PETG is used for compositions wherein the diacid component comprises or includes terephthalic acid residues and the diol component comprises up to 50 mole percent CHDM residues, with the remaining diol component being ethylene glycol residues. PCTG is used herein to refer to copolyesters in which the diacid component comprises terephthalic acid residues and the diol component comprises greater than 50 mole percent CHDM residues, the remainder being ethylene glycol residues.

Neopentyl glycol (NPG, 2, 2-dimethyl-propane-1, 3-diol) is another common diol used to make polyesters. Like CHDM, NPG has been used in combination with EG and terephthalic acid to form useful amorphous copolyesters. However, the combination of NPG and CHDM has attracted little attention as the sole diol component of the copolyester.

Several early references disclose polyesters containing both CHDM and NPG residues with terephthalic acid residues as the diacid component. Example 46 of U.S. Pat. No. 2,901,466 describes copolyesters prepared from CHDM and NPG residues that are solid stated to an IV of 1.06. CHDM is said to be "75% trans". The copolyester is reported to have a crystalline melting point of 289-297 ℃. The exact composition of this polyester is not disclosed, but the melting point of this polymer is very different from that of pure poly (1, 4-cyclohexanedimethanol terephthalate) (PCT, Tm ═ 293 ℃).

U.S. patent 3,592,875 discloses polyester compositions containing both NPG and CHDM residues with added polyol for branching. U.S. Pat. No. 3,592,876 discloses polyester compositions comprising EG, CHDM and NPG residues, the level of NPG residues being limited to up to 10 mole percent. U.S. Pat. No. 4,471,108 discloses low molecular weight polyesters, some of which contain CHDM and NPG residues, but which also contain a polyfunctional branching agent. U.S. patent 4,520,188 describes novel low molecular weight copolyesters having a mixture of aliphatic and aromatic diacid residues with both NPG and CHDM residues.

U.S. Pat. No. 4,182,841 describes compositions containing 80 to 70 mole percent ethylene glycol and 20 to 30 mole percent neopentyl glycol, which also contain a polyfunctional modifying material, i.e., a branching agent. Terephthalic acid is the only acid used in the composition. CHDM is not mentioned. U.S. Pat. Nos. 5,523,382 and 5,442,036 describe branched copolyesters suitable for extrusion blow molding. The copolymer comprises Ethylene Glycol (EG) residues in addition to 0.5 to 10 mole percent CHDM residues and 3 to 10 mole percent diethylene glycol (DEG) residues. The diacid component comprises terephthalic acid residues and up to 40 mole percent of isophthalic acid (IPA) or 2, 6-naphthalenedicarboxylic acid (NDA) residues. The branching agent preferably consists of trimellitic acid or anhydride. NPG is not mentioned.

U.S. Pat. No. 4,983,711 describes branched copolyesters consisting of EG and CHDM residues and containing 0.05 to 1 mole percent of a trifunctional branching agent, preferably trimellitic acid or anhydride. Preferred levels of branching agent are 0.1 to 0.25 mole percent. The patent discloses CHDM residue levels of 25 to 75 mole percent and relates to extrusion blow molding applications. There is no mention of preventing melt fracture. NPG is not discussed. U.S. patent 5,376,735 describes branched polyethylene terephthalate modified with up to 3 mole percent IPA for extrusion blow molding applications. A number of branching agents are mentioned, including TMA.

U.S. patent 5,235,027 describes branched co-polyethylene terephthalate for extrusion blow molding. The PET contains 0.5 to 5 weight percent IPA residues, 0.7 to 2.0 weight percent DEG residues, 300-2500ppm tri-or tetrahydroxyalkane residues, 80-150ppm antimony, phosphorus in an amount of at least 25% by weight of antimony, red and blue toners (no more than 5ppm), and various branching agents, of which pentaerythritol is preferred. NPG is not discussed.

U.S. patents 4,234,708, 4,219,527 and 4,161,579 describe branched and end-capped modified PET polyesters for extrusion blow molding. Various chain branching agents (0.025 to 1.5 mole percent) and 0.25 to 10 equivalents of nonionic chain terminators are described for controlling reaction conditions and preventing gelation. NPG is not discussed. U.S. Pat. No. 4,398,022 describes high melt strength copolyesters composed of terephthalic acid and 1, 12-dodecanedioic acid residues, and a diol component containing CHDM residues. No branching agent was used. Japanese patent publication JP3225982B2 discloses amorphous copolyesters purportedly useful for formulating coating compositions for steel sheets. The disclosed copolyesters comprise a diacid component comprising a mixture of aliphatic and aromatic acid residues and a diol component comprising NPG and CHDM residues.

Disclosure of Invention

In view of the state of the art as described above, there is a need for a shaped article and an extrusion blow molding method for producing the shaped article, which uses a linear polyester having improved processability for extrusion blow molding by simultaneously having higher melt strength without gel formation and improved shear thinning. Accordingly, the present invention is directed generally to providing such articles, methods, and polyesters. One embodiment of the present invention is a process for making a shaped article by extrusion blow molding comprising the steps of:

(1) extruding the copolyester through a die to form a tube of molten copolyester;

(2) positioning a mold having a desired final shape around a tube of molten copolyester; and

(3) introducing a gas into the tube of molten copolyester causing the extrudate to stretch and expand to fill the die;

wherein the copolyester is a linear copolyester having an Inherent Viscosity (IV), as measured at a temperature of 25 ℃ in a solvent mixture of symmetric tetrachloroethane and phenol having a weight ratio of symmetric tetrachloroethane to phenol of 2: 3, at a concentration of 0.25 grams per deciliter, of at least 0.7dL/g, and comprising:

(i) a diacid component consisting essentially of: 90 to 100 mole percent terephthalic acid residues and 0 to 10 mole percent isophthalic acid residues, naphthalenedicarboxylic acid residues, biphenyldicarboxylic acid residues or a mixture of two or more of isophthalic acid residues, naphthalenedicarboxylic acid residues or biphenyldicarboxylic acid residues; and

(ii) a diol component consisting essentially of: 70 to 90 mole percent 1, 4-cyclohexanedimethanol residues and 30 to 10 mole percent neopentyl glycol residues;

wherein the copolyester comprises 100 mole percent of a diacid component and 100 mole percent of a diol component. The linear polyester chain consists essentially of the diacid and diol components defined above, meaning that the polyester is free or substantially free of residues derived from monomers or reactants having three or more functional groups, which residues are typically present in branched polyesters. It has been found that these copolyesters have very high melt strength and a degree of shear thinning for linear polyesters. The significant shear thinning of these copolyesters makes them particularly suitable for extrusion blow molding applications.

We have found that the linear copolyesters defined above are crystallizable. Herein, the term "crystallizable" refers to copolyesters that exhibit a substantially crystalline melting point when scanned by Differential Scanning Calorimetry (DSC) at a rate of 20 ℃/minute. These crystallizable compositions, unlike amorphous compositions, are capable of being solid stated. Solid stating is a process for increasing the IV of a polyester beyond that which can be readily obtained by standard melt phase polymerization. It has been found that these solid stated, NPG-containing copolyesters shear-thin to a much greater degree than similar linear solid stated polyesters that do not contain NPG. These solid stated NPG-containing polyesters have rheological properties that are particularly suitable for extrusion blow molding of large articles.

Another embodiment of the present invention is an extrusion blow molded article produced from a linear copolyester having an Inherent Viscosity (IV), measured at a temperature of 25 ℃ in a solvent mixture of symmetric tetrachloroethane and phenol having a weight ratio of symmetric tetrachloroethane to phenol of 2: 3, at a concentration of 0.25g/dL, of at least 0.7dL/g and comprising:

(i) a diacid component consisting essentially of: 90 to 100 mole percent terephthalic acid residues and 0 to 10 mole percent isophthalic acid residues, naphthalenedicarboxylic acid residues, biphenyldicarboxylic acid residues or a mixture of two or more of isophthalic acid residues, naphthalenedicarboxylic acid residues or biphenyldicarboxylic acid residues; and

(ii) a diol component consisting essentially of: 70 to 90 mole percent 1, 4-cyclohexanedimethanol residues and 30 to 10 mole percent neopentyl glycol residues;

wherein the copolyester comprises 100 mole percent of a diacid component and 100 mole percent of a diol component.

Detailed Description

In the first step of the extrusion blow molding process of the present invention, the copolyester is extruded through a die to form a tube of molten polyester. This step may be carried out using a conventional extruder in which the copolyester is heated to a temperature of 250 to 300 ℃ to form a melt of the copolyester. The melt is then extruded through a die, usually downward, to form a tube of molten copolyester. The width of the tube is typically in the range of 50 to 200 mm.

In the second step of the extrusion blow molding process, a mold having the desired final shape is clamped or positioned around a tube of molten copolyester that depends or hangs from the die. In the third step of the process, a gas such as air or nitrogen is injected into the tube of molten copolyester causing the extrudate to stretch and expand to fill the die. The mold and the shaped article contained therein are cooled to a temperature of, for example, 20 to 50 c, and then the article is removed from the mold. The extrusion blow molding process of the present invention is particularly useful for making large containers, such as large bottles or jars for packaging liquids such as water. Because the copolyesters used in the present invention have the desired combination of properties, large containers, for example containers having a volume of from 2 to 50 liters, can be produced by the novel process.

The linear copolyesters used in the present invention can be prepared by conventional polymerization methods known in the art, such as those disclosed in U.S. Pat. Nos. 4,093,603 and 5,681,918, the disclosures of which are incorporated herein by reference. Examples of polycondensation processes that can be used to prepare the novel copolyesters of the present invention include: melt phase processes, which are carried out by introducing a flow of inert gas, such as nitrogen, to shift the equilibrium and reach high molecular weights, or more generally vacuum melt phase polycondensation, which is carried out at temperatures of 240 to 300 ℃ or higher, which is practiced industrially. The diacid residues of the copolyester may be derived from a dicarboxylic acid or its ester-producing equivalent, such as esters, e.g., dimethyl terephthalate and dimethyl isophthalate, or acid halides, e.g., acid chlorides. Although not required, conventional additives may be added to the copolyesters of the invention in typical amounts. Such additives include pigments, colorants, stabilizers, antioxidants, extrusion aids, slip agents, carbon black, flame retardants, and mixtures thereof.

The polymerization reaction may be carried out in the presence of one or more conventional polymerization catalysts. Typical catalysts or catalyst systems for polyester condensation are well known in the art. Suitable catalysts are disclosed in, for example, U.S. Pat. nos. 4,025,492, 4,136,089, 4,176,224, 4,238,593, and 4,208,527. Typical catalysts which can be used in the polyester-making process are also described by r.e. wilfong in the Journal of polymer Science, 54, 385 (1961). Preferred catalyst systems include Ti, Ti/P, Mn/Ti/Co/P, Mn/Ti/P, Zn/Ti/Co/P, Zn/Al. When cobalt is not used in the polycondensation, it may be desirable to use polymerizable toners to control the color of these copolyesters so that they are suitable for their intended use where color may be an important property. In addition to the catalyst and toner, other additives, such as antioxidants, dyes, and the like, may be used for the copolyesterification.

Solid state polymerization is a well known process in the art, for example as described in U.S. Pat. No. 4,064,112. In this process, amorphous precursor pellets that have been prepared by melt phase polymerization are first crystallized at a temperature of 10 to 100 ℃ below their melting temperature and then further held at a temperature of at least 10 ℃ below their melting temperature for a sufficient period of time, e.g., 2 to 40 hours, in the presence of a vacuum or a stream of dry nitrogen to increase the IV. These high temperatures are required to allow the polymerization to proceed at relatively rapid and economical rates. At these high temperatures, the amorphous pellets will soften and fuse together to form a highly viscous mass. In contrast, crystallized pellets will not stick together at these temperatures. Therefore, solid-phase polymerization can be carried out only on crystalline pellets. Typically, when producing molding grade pellets, either a batch or continuous process is used. In a batch process, the pellets are fed into a large vessel which is heated in accordance with the two-stage process described above. The container is continuously rotated to provide uniform heating of the pellets and to prevent the pellets from sticking to the container walls during initial crystallization. In a continuous process, the pellets fall first by gravity into a crystallizer unit and then flow by gravity through a large heated vessel that raises the IV. For industrial operations, a continuous process is preferred for economic reasons. Generally, in solid stating pellets, particles having regular or irregular shapes may be used. The particles may have various shapes and sizes, such as spherical, cubic, irregular as described in U.S. Pat. No. 5,145,742, cylindrical, or as described in U.S. Pat. No. 4,064,112. "particles" also include shapes that are generally flat.

Solid stating is generally accomplished by subjecting the copolyester particles to a temperature of 140 ℃ below the melting point of the polyester to 2 ℃ below the melting point, preferably 180 ℃ below the melting point of the polyester to 10 ℃ below the melting point. The time for solid stating can vary over a wide range (1 to 100 hours) depending on the temperature to achieve the desired IV, but at higher temperatures, typically 10 to 60 hours is sufficient to achieve the desired i.v. or molecular weight. During this time of solid stating, it is common to flow an inert gas stream through the pellets to aid in temperature control of the polyester pellets and to carry away reaction gases such as ethylene glycol and acetaldehyde. Nitrogen is particularly suitable for use as the inert gas as it helps to improve the overall economics of the process. For economic reasons, it is preferred to recycle the inert gas. Other inert gases that may be used include helium, argon, hydrogen, and mixtures thereof. It should be understood that the inert gas may contain some air or oxygen-depleted air.

It is generally observed in solid stating processes that the rate of IV increase may slow significantly over time. Thus, the maximum IV that can be obtained may be limited by the initial IV of the precursor copolyester material. To this end, the IV of the copolyester precursor pellets prior to introduction into the solid stating process is typically between 0.4 and 0.9, preferably between 0.6 and 0.85, most preferably between 0.65 and 0.8.

The diacid component of the copolyesters used in the present invention preferably consists essentially of at least 95 mole percent, or more preferably 100 mole percent, of terephthalic acid residues. In a preferred embodiment, wherein the diacid component of the copolyester consists essentially of terephthalic acid residues, the IV of the solid stated copolyester is from 0.9 to 1.2 dL/g.

A second embodiment of the present invention is a shaped article prepared from the copolyester as described above. Examples of typical shaped articles include containers, water cooler boxes, toys, cabinets, medical devices and instrument parts. The shaped articles provided by the present invention are preferably bottles, in particular bottles having a volume of 2 to 50 liters, which are prepared by the extrusion blow molding process described herein.

Examples

The copolyesters provided by the present invention and their methods of preparation are further illustrated by the following examples. The inherent viscosity was determined at a temperature of 25 ℃ in a solvent mixture of symmetric tetrachloroethane and phenol having a weight ratio of symmetric tetrachloroethane to phenol of 2: 3 at a concentration of 0.25 g/dl. The first cycle melting temperature (Tm1) was measured by DSC at a heating rate of 20 ℃ per minute to a temperature of 280 ℃ to 300 ℃. Second-cycle glass transition temperature (Tg), crystallization temperature (Tch), and melting temperature (Tm2) were determined by DSC heating to a temperature of 280-300 ℃ at a heating rate of 20 ℃/min, quenching to 0 ℃ in liquid nitrogen, and reheating the sample. The final copolyester composition was determined by proton NMR analysis on a 600MHz JEOL instrument. Melt viscosity was determined by dynamic rheometry (RDA II) with 25 mm diameter parallel plates with a gap of 1 mm and 10% strain at the indicated temperature. The samples were dried in a vacuum oven at 60 ℃ for 24 hours before being subjected to the sweep test. The bottles were prepared using an 80 mm Bekum H-121 continuous extrusion blow molding machine equipped with a barrier-type screw containing a Maddock mixing section. The material was dried at 121 ℃ (250 ° F) for 12 hours prior to extrusion. The extruder was operated at 16 Revolutions Per Minute (RPM). The material was extruded into a water bottle having a volume of 3.785 liters (1 U.S. gallon) using a 100 mm die. The bottle weighs 145 to 160 grams. Melt strength was also measured by recording the time elapsed for the parison to exit the die to the point where it reached 20 inches below the head. At this point the parison is cut and weighed. The "melt strength" is reported as the product of the time the parison is dropped and the weight in grams-seconds.

Example 1

Melt phase polymerization of a copolyester comprising a diacid component consisting of 100 mole percent terephthalic acid residues and a diol component consisting of 83 mole percent CHDM residues and 17 mole percent NPG residues (hereinafter 100T/83CHDM/17NPG) was conducted in a 65 gallon (245 liter) stainless steel batch reactor with an intermeshing screw agitator. To the reactor were charged 39.64kg (87.39 lbs, 204.5 moles) of dimethyl terephthalate, 11.48kg (25.30 lbs, 110.4 moles) of neopentyl glycol (NPG), 28.25kg (62.27 lbs, 196.3 moles) of 1, 4-Cyclohexanedimethanol (CHDM), and 112.56 grams of a butanol solution containing a titanium catalyst. The reactor was heated to 200 ℃ and held for 2 hours with stirring at 25 RPM. The temperature was increased to 260 ℃ and held for 30 minutes. The temperature was increased to 270 c and the pressure was reduced to full vacuum at a rate of 13 torr per minute. After the vacuum reached < 4000 microns (< 4 torr), these conditions were held at 25RPM for 1 hour and 15 minutes. The RPM was reduced to 15RPM and the conditions were maintained, reaching the peak of the power meter. The pressure was increased to normal pressure with nitrogen, and the copolymer was pelletized. The copolymer had a melt phase Inherent Viscosity (IV) of 0.758, color number L ═ 68.50, a ═ 0.30, b ═ 6.47, and a composition of 100T/83CHDM17NPG as determined by Nuclear Magnetic Resonance (NMR). The polymer was then crystallized at 150 ℃ for 2 hours and then solid state polymerized in a static bed reactor under a nitrogen purge at 230 ℃ for 24 hours. The IV of the solid stated material was 1.11 dL/g. The polymer had a second cycle DSC glass transition temperature of 92.5 deg.C, a crystallinity (Tch) of 191.7 deg.C (2.59 cal/g) and a melting point of 251.0 deg.C (3.08 cal/g) upon heating. The first cycle melting point was 262.3 deg.C (10.01 cal/g). The melt viscosity of the copolyester was 134880 poise at 1 radian per second and 21162 poise at 100 radians per second when measured at a temperature of 270 ℃. The ratio of melt viscosity at 1 radian per second to melt viscosity at 100 radians per second was 6.37. Surprisingly, the copolyester of example 1 exhibits shear thinning properties superior to any other solid stated copolyester. In fact, the shear thinning properties of the copolyester of example 1 were even better than the branched copolyester described in comparative example 2. The melt strength of the copolyester of example 1 was much higher than any other sample, even when studied under conditions that produced a viscosity of about 23,000 poise at 100 radians/second (melt fracture started). The bottles were prepared at a barrel and head assembly temperature of 260 ℃ (500 ° F). The melt temperature was measured to be 282 deg.C (539 deg.F). Under these conditions, the material has excellent melt strength and the resulting bottle does not contain any unmelts or gels. The "melt strength" measured at this temperature was 4775 g-sec.

The following comparative examples provide melt viscosity data for a number of copolyesters not according to the invention. These samples were prepared using the same general procedure as described in example 1.

Comparative example 1

Copolyesters were prepared by melt phase polymerization comprising a diacid component consisting of terephthalic acid residues and a diol component consisting of 69 mole percent EG residues and 31 mole percent CHDM residues with an IV of 0.74 dL/g. It was not solid stated. The melt viscosity of the polymer, measured at 210 ℃, was 56396 poise at 1 radian per second and 21728 poise at 100 radians per second. The ratio of melt viscosity at 1 radian per second to melt viscosity at 100 radians per second was 2.60. At this temperature, the viscosity at 1 rad/sec is high enough to give the critical melt strength of the material. However, the copolyester cannot be processed at lower temperatures, since the viscosity at 100 rad/s has increased to a limit. Experience with a particular, but typical set of equipment has shown that if the viscosity becomes greater than about 23,000 at 100 radians/second, the material will melt fracture during extrusion blow molding. The melt strength of the material at this temperature is sufficient to blow smaller bottles, but not sufficient to produce large bottles.

Comparative example 2

Copolyesters were prepared by melt phase polymerization comprising a diacid component consisting of terephthalic acid residues and a diol component consisting of 69 mole percent EG residues and 31 mole percent CHDM residues with 0.18 mole percent trimellitic anhydride residues with an IV of 0.74 dL/g. It was not solid stated. The melt viscosity of the polymer, measured at 217 ℃ was 99377 poise at 1 radian per second and 23232 poise at 100 radians per second. The ratio of melt viscosity at 1 radian per second to melt viscosity at 100 radians per second was 4.28. This lower temperature indicates the onset of melt fracture (relative to viscosity at 100 rad/sec). However, at this temperature, the melt strength of the material is almost twice that of the polyester in comparative example 2. Thus, the size of the bottles that can be produced with this material is significantly larger than the size of the bottles that can be produced from the copolyester of comparative example 2. However, this sample was branched.

Comparative example 3

A copolyester comprising a diacid component consisting of terephthalic acid residues and a diol component consisting of 97 mole percent EG residues and 3 mole percent CHDM residues was prepared and solid stated to an IV of 0.98 dL/g. The melt viscosity of the copolyester, measured at 265 ℃, was 72000 poise at 1 radian per second and 23000 poise at 100 radians per second. The ratio of melt viscosity at 1 radian per second to melt viscosity at 100 radians per second was 3.11.

Comparative example 4

Copolyesters were prepared by melt phase polymerization comprising a diacid component consisting of terephthalic acid residues and a diol component consisting of 19 mole percent EG residues and 81 mole percent CHDM residues with an IV of 0.75 dL/g. The polymer had a melting point of 250 ℃ and a melt viscosity, measured at 270 ℃, of 9166 poise at 1 radian per second and 6842 poise at 100 radians per second. The ratio of melt viscosity at 1 radian per second to melt viscosity at 100 radians per second was 1.34. The polymer does not have sufficient melt strength, cannot be processed into large bottles, and cannot be processed at lower temperatures because it crystallizes in the extruder.

Comparative example 5

Copolyesters were prepared by melt phase polymerization comprising a diacid component consisting of 74 mole percent terephthalic acid residues and 26 mole percent isophthalic acid residues and a diol component consisting of 100 mole percent CHDM residues with an IV of 0.72 dL/g. The polymer had a melting point of 245 ℃ and a melt viscosity, measured at 270 ℃, of 5042 poise at 1 radian per second and 4274 poise at 100 radians per second. The ratio of melt viscosity at 1 radian per second to melt viscosity at 100 radians per second was 1.18. The polymer does not have sufficient melt strength, cannot be processed into large bottles, and cannot be processed at lower temperatures because it crystallizes in the extruder.

Comparative example 6

The copolyester prepared in comparative example 4 was solid stated to an IV of 1.03 dL/g. The melt viscosity of the polymer, measured at 270 ℃, was 50482 poise at 1 radian per second and 21434 poise at 100 radians per second. The ratio of melt viscosity at 1 radian per second to melt viscosity at 100 radians per second was 2.36. The bottles were prepared at a barrel and head assembly temperature of 260 ℃ (500 ° F). The measured melt temperature was 283 ℃ (541 ° F). Under these conditions, the material has a critical melt strength and the resulting bottle contains a lot of unmelts. The "melt strength" measured at this temperature was 1830 g-sec. Increasing the temperature eliminates unmelts, but the parison does not have sufficient melt strength and therefore cannot be made into bottles.

Comparative example 7

The copolyester prepared in comparative example 5 was solid stated to an IV of 1.07. The melt viscosity of the polymer, measured at 270 ℃, was 49321 poise at 1 radian per second and 23091 poise at 100 radians per second. The ratio of melt viscosity at 1 radian per second to melt viscosity at 100 radians per second was 2.14. The bottles were prepared at a barrel and head assembly temperature of 260 ℃ (500 ° F). The measured melt temperature was 283 ℃ (542 ° F). Under these conditions, the material has a critical melt strength and the resulting bottle contains a lot of unmelts. The "melt strength" measured at this temperature was 2000 g-sec. Increasing the temperature eliminates unmelts, but the parison does not have sufficient melt strength and therefore cannot be made into bottles. The melt strength is not sufficient to make large bottles.

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 (12)

1. A process for manufacturing a shaped article by extrusion blow molding, comprising the steps of:

(1) extruding the copolyester through a die to form a tube of molten copolyester;

(2) positioning a mold having a desired final shape around a tube of molten copolyester; and

(3) introducing a gas into the tube of molten copolyester causing the extrudate to stretch and expand to fill the die;

wherein the copolyester is a linear copolyester having an Inherent Viscosity (IV), as measured at a temperature of 25 ℃ in a solvent mixture of symmetric tetrachloroethane and phenol having a weight ratio of symmetric tetrachloroethane to phenol of 2: 3, at a concentration of 0.25 grams per deciliter, of at least 0.7dL/g, and comprising:

(1) a diacid component consisting essentially of: 90 to 100 mole percent terephthalic acid residues and 0 to 10 mole percent isophthalic acid residues, naphthalenedicarboxylic acid residues, biphenyldicarboxylic acid residues or a mixture of two or more of isophthalic acid residues, naphthalenedicarboxylic acid residues or biphenyldicarboxylic acid residues; and

(2) a diol component consisting essentially of: 70 to 90 mole percent 1, 4-cyclohexanedimethanol residues and 30 to 10 mole percent neopentyl glycol residues;

wherein the copolyester comprises 100 mole percent of a diacid component and 100 mole percent of a diol component.

2. The method of claim 1 wherein the copolyester comprises a diacid component consisting essentially of at least 95 mole percent terephthalic acid residues.

3. The method of claim 1 wherein the copolyester comprises a diacid component consisting essentially of 100 mole percent terephthalic acid residues.

4. The process of claim 3 wherein the Inherent Viscosity (IV) of the copolyester is from 0.9 to 1.2 dL/g.

5. The process of claim 4 wherein said copolyester is made by a solid state polymerization process.

6. The process of claim 1, wherein the shaped article is a container having a volume of 2 to 50 liters; the mold of step (2) has the shape of the desired final container; the copolyester has an Inherent Viscosity (IV) of at least 0.9 to 1.2 dL/g; and the diacid component consists essentially of terephthalic acid residues.

7. The process of claim 6 wherein said molten copolyester has a temperature of from 250 to 300 ℃.

8. An extrusion blow molded article produced from a linear copolyester having an Inherent Viscosity (IV), measured at a temperature of 25 ℃ in a solvent mixture of symmetric tetrachloroethane and phenol having a weight ratio of symmetric tetrachloroethane to phenol of 2: 3, at a concentration of 0.25g/dL, of at least 0.7dL/g and comprising:

(1) a diacid component consisting essentially of: 90 to 100 mole percent terephthalic acid residues and 0 to 10 mole percent isophthalic acid residues, naphthalenedicarboxylic acid residues, biphenyldicarboxylic acid residues or a mixture of two or more of isophthalic acid residues, naphthalenedicarboxylic acid residues or biphenyldicarboxylic acid residues; and

(2) a diol component consisting essentially of: 70 to 90 mole percent 1, 4-cyclohexanedimethanol residues and 30 to 10 mole percent neopentyl glycol residues;

wherein the copolyester comprises 100 mole percent of a diacid component and 100 mole percent of a diol component.

9. An extrusion blow molded article according to claim 8 wherein said copolyester comprises a diacid component consisting essentially of at least 95 mole percent terephthalic acid residues.

10. An extrusion blow molded article according to claim 8 wherein said copolyester comprises a diacid component consisting essentially of 100 mole percent terephthalic acid residues.

11. An extrusion blow molded article according to claim 10 wherein the Inherent Viscosity (IV) of the copolyester is from 0.9 to 1.2 dL/g.

12. An extrusion blow molded article according to claim 8 wherein said copolyester comprises a diacid component consisting essentially of 100 mole percent terephthalic acid residues; the Inherent Viscosity (IV) of the copolyester is 0.9 to 1.2 dL/g; and the shaped article is a bottle having a volume of 2 to 50 liters.