CN116635449A - Improved polyester compositions for extrusion blow molded containers - Google Patents

Abstract

The present invention relates to a polyester resin for extrusion blow molding bottles comprising a branched aliphatic diol and a branched comonomer.

Description

Improved polyester compositions for extrusion blow molded containers

Cross reference to related applications

The present patent application claims priority from the provisional patent application No. 63/129,305 filed on 12 months 22 in 2020 and entitled "improved polyester composition for extrusion blow molded containers (Improved Polyester Composition For Extrusion Blow Molded Containers)" and the provisional patent application No. 63/288,894 filed on 12 months 13 in 2021 and entitled "improved polyester composition for extrusion blow molded containers", the contents of both provisional patent applications being incorporated herein by reference in their entirety.

Technical Field

The present invention relates to polyester polymers and more particularly to polyethylene terephthalate copolyesters for transparent extrusion blow molded containers.

Background

Aromatic polyesters are generally semi-crystalline and have low melt strength. Containers made from polyethylene terephthalate (PET) with small amounts of modifying comonomers are the most common transparent containers on the market by the injection stretch molding process (ISBM). However, the ISBM process is limited to uniform shapes and cannot produce bottles with handles. Handles are a desirable feature for larger bottles and containers to facilitate handling by consumers. Such larger bottles and containers with handles may be produced by an Extrusion Blow Molding (EBM) process.

A typical EBM process involves: a) melting the resin in an extruder, b) extruding the molten resin through a die (die) to form a tube (parison) of molten polymer, c) clamping a shaping die (mold) of the desired finished shape around the parison, d) blowing air into the parison causing the extrudate to stretch and expand to fill the die, e) cooling the shaped container, f) ejecting the container from the shaping die and g) removing excess plastic (flash/spill) from the container.

The hot parison extruded in this process must typically hang under its own weight for a few seconds before the forming die is clamped around it. During this time, the extrudate must have high melt strength-a feature that enables the material to resist stretching, flow and sagging that would cause uneven distribution in the parison and thinning of the parison wall. Sagging of the extruded parison is directly related to the weight of the parison, so a larger and heavier parison will have a greater tendency to sag. The melt strength is directly related to the viscosity of the polyester resin at zero shear rate and the temperature of the molten extrudate as it exits the die. However, the process is not limited to the above-described process,resins with high melt strength or high melt viscosity at zero shear rate are too viscous to be extruded and pumped through a die in an extruder without the use of high temperatures that cause the polymer to degrade and lose its melt viscosity. Thus, the best polyester resin tailored for EBM end use must have rheology such that viscosity at shear rates associated with the extrusion process (typically 100 to 1000s ^-1 ) Below the viscosity at zero shear rate (i.e., it exhibits shear thinning).

Typical PET resins for ISBM beverage containers are not suitable for EBM because of their relatively low intrinsic viscosity (IV <0.85 dl/g) and high melting point (> 245 ℃) which gives low melt strength at the temperatures required to handle them.

In the EBM process, the molten polyester cannot be thermally crystallized upon cooling; otherwise, a cloudy container may be created. Unlike the ISBM process, the EBM process produces scrap from flash (e.g., pinch points) that must be cut from the formed container. Such scrap (or recycled material) from the EBM process must be ground and blended with the virgin resin and dried prior to re-extrusion. Such scrap (regrind) typically represents about 40-50% of the raw materials in the EBM manufacturing process.

The prior art has met these requirements for extrusion blow molding by using comonomers such as isophthalic acid (IPA) and 1, 4-Cyclohexanedimethanol (CHDM) to reduce the thermal crystallization rate (Modern Polyesters: chemistry and Technology of Polyesters and Copolyesters2003 (modern polyesters: chemistry of polyesters and copolyesters and technical 2003), 246-247). The use of CHDM as an amorphous copolyester of comonomers for EBM has been disclosed, for example, in US 4,983,711, 6,740,377, 7,025,925, 7,026,027, 7,915,374, 8,431,068, 8,890,398 and 2011/0081510. Amorphous copolyesters using IPA as comonomer have been disclosed, for example in U.S. Pat. No. 4,182,841.

By using a branching comonomer in a copolyester containing CHDM or IPA as a modifying comonomer, higher melt strength at zero shear rate and shear thinning to reduce melt viscosity at higher shear rate have been achieved. Typical branched comonomers such as trimellitic anhydride (TMA) and Pentaerythritol (PENTA) are disclosed in US 4,132,707 and 4,999,388. To date, most copolyester formulations designed for EBM containers are substantially amorphous, with the use of branched comonomers to achieve proper balance of processing and good container appearance and properties. However, inclusion of the branched comonomer may produce gels, which then produce poor bottle appearance (e.g., increased haze, reduced gloss, etc.). In addition, the high degree of branching may cause melt fracture at the die, giving the surface of the container a speckled appearance.

Containers made from amorphous copolyesters (when added to post-consumer PET recycle streams) tend to cause sticking, caking, and bridging problems during the drying process. This makes such EBM PET resins unsuitable for reuse in post-consumer polyester recycle streams that are used in blends with virgin resins for standard container and bottle ISBM processes.

Alternatively, high melt strength copolyester resins with ultra high molecular weight (IV >1.1 dl/g) containing small amounts of IPA or CHDM may be used to provide the necessary melt strength because they exhibit some degree of shear thinning (US 9,399,700). These ultra-high IV polyester resins must be processed at higher temperatures that cause thermal degradation of the resin, resulting not only in increased yellowness in the container, but also in a narrower EBM processing window. Lowering the temperature can result in melt fracture and a significant increase in the pressure required to feed the molten polymer from the extruder to the die. In addition, these tough resins are more difficult to cut and more difficult to cleanly remove flash from the finished container.

One key requirement for an EBM container is its ability to drop without breaking if it contains a liquid (i.e., it must have acceptable drop impact properties when filled). It is well known that amorphous polyesters age over time-this aging effect translates into containers made from amorphous polyesters becoming more brittle (i.e., lower impact resistance) over time and thus more susceptible to breakage when dropped.

EBM resins (aurega Polymers inc., spartanburg, SC USA) are a commercial resin (partially crystalline) that has been approved by the post-consumer plastic recycling society (Association of Postconsumer Plastic Recyclers, APR) for recycling in post-consumer recycle streams. However, such resins have poor aged bottle drop performance. US 9,815,964 improves the aged drop resistance of such IPA modified co-branched copolyester resins by adding fillers, especially fumed silica.

Polymers made via stepwise condensation chemistry contain a certain amount of cyclic comonomers (e.g., cyclic dimers, cyclic trimers, etc.). For example, the problem with isophthalic acid as a crystallization retardant is that it forms high melting point oligomers that deposit not only on the container forming die but also on cooler surfaces in/around the extrusion point. These deposits are undesirable because they can cause downstream processors/converters to clean and/or shut down more frequently.

None of the prior art patents discloses a composition for EBM that meets all of the following market needs:

a) Approved for recovery in post-consumer recycle streams, and

b) High melt viscosity at zero shear rate to provide a non-sagging parison, and

c) Low melt viscosity at shear rate in extruder and die head (die head) to reduce extrusion temperature, thereby minimizing degradation and minimizing the energy required to melt and extrude the resin, and

d) Low deposit formation during extrusion blow molding process to minimize machine downtime for cleaning, and

e) The crystallization rate is slow so that the container does not become cloudy during the cooling cycle due to crystallization of the resin.

It is therefore highly desirable to find a novel polyester resin that meets all of these requirements for extrusion blow molding processes.

Disclosure of Invention

In its broadest sense, the present invention relates to a polyester resin for extrusion blow molded bottles comprising a copolyester comprising:

a) An alkyl branched aliphatic diol represented by formula I:

wherein R is ₁ Is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and

R ₂ is an alkyl group having 1 to 6 carbon atoms, and a and b are each independently an integer of 1 to 2,

and

b) A branched comonomer.

In its broadest sense, the present invention relates to a method of preparing EBM bottles from such compositions.

In its broadest sense, the present invention relates to EBM containers made from such compositions.

Detailed Description

The ranges set forth herein include two numbers at the endpoints of each range, as well as any possible number therebetween, as that is the definition of the range.

Polyester EBM resins are typically prepared by adding a comonomer (to retard the crystallization rate of the polyester resin) along with a multifunctional branching comonomer (to increase the melt strength and provide the shear thinning rheological behavior to the resin).

Polyester compositions suitable for use in the present invention typically comprise:

(a) A diacid component comprising 95 to 100 mole percent of the residues of terephthalic acid, naphthalene dicarboxylic acid, or mixtures thereof, based on the total mole percent of diacid residues in the polyester composition, and

(b) A glycol component comprising 90 to 98 mole percent of residues of ethylene glycol, diethylene glycol, or mixtures thereof, based on the total mole percent of glycol residues in the polyester composition, and

(c) A glycol component comprising 2 to 10 mole% of an aliphatic branched glycol represented by the following formula I, based on the total mole% of glycol residues in the polyester composition:

wherein R is ₁ Is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R ₂ Is an alkyl group having 1 to 6 carbon atoms, and a and b are each independently an integer of 1 to 2, and

d) A branched comonomer.

As used herein, the term "polyester" is intended to include "copolyesters" and is understood to mean a synthetic polymer prepared by the reaction of one or more difunctional carboxylic acids and/or polyfunctional carboxylic acids with one or more difunctional hydroxyl compounds and/or polyfunctional hydroxyl compounds, such as branched comonomers. Typically, the difunctional carboxylic acid may be a dicarboxylic acid and the difunctional hydroxyl compound may be a dihydric alcohol such as, for example, a glycol (diol) and a diol (diol). As used herein, the term "glycol" includes, but is not limited to, glycols (diols), diols, and/or polyfunctional hydroxy compounds, such as branched comonomers. Alternatively, the difunctional carboxylic acid may be a hydroxycarboxylic acid such as, for example, p-hydroxybenzoic acid, and the difunctional hydroxyl compound may be an aromatic ring bearing 2 hydroxyl substituents such as, for example, hydroquinone, resorcinol, or other heterocyclic diols such as, for example, isosorbide.

As used herein, the term "residue" means any organic structure that is incorporated into a polymer from the corresponding monomer by polycondensation and/or esterification reactions. As used herein, the term "repeat unit" means an organic structure having dicarboxylic acid residues and diol residues bonded through a carbonyloxy group. Thus, for example, the dicarboxylic acid residues may be derived from dicarboxylic acid monomers or its related acid halides, esters, salts, anhydrides, and/or mixtures thereof. Thus, as used herein, the term "dicarboxylic acid" is intended to include dicarboxylic acids and any derivative of dicarboxylic acids, including the acid halides, esters, half-esters, salts, half-salts, anhydrides, mixed anhydrides, and/or mixtures thereof associated therewith, which can be used in a reaction process with a glycol to make a polyester. As used herein, the term "terephthalic acid" is intended to include terephthalic acid itself and its residues as well as any derivatives of terephthalic acid, including the acid halides, esters, half-esters, salts, half-salts, anhydrides, mixed anhydrides, and/or mixtures thereof or residues thereof associated therewith, which derivatives are useful in the reaction process with a glycol to make a polyester.

The polyesters used in the present invention can typically be prepared from dicarboxylic acids and diols that react in substantially the same proportions and are incorporated into the polyester polymer at their respective residues. Thus, the polyesters of the invention may contain substantially equimolar proportions of acid residues (100 mole%) and glycol (and/or polyfunctional hydroxy compound) residues (100 mole%) such that the total moles of repeating units is equal to 100 mole%. Thus, the mole% provided in the present disclosure may be based on the total moles of acid residues, the total moles of glycol residues, or the total moles of repeat units. For example, a polyester containing 1 mole% isophthalic acid based on total acid residues means that the polyester contains 1 mole% isophthalic acid residues in a total of 100 mole% acid residues. Thus, there are 1 mole of isophthalic acid residues per 100 moles of acid residues. In another example, a polyester containing 1.5 mole% diethylene glycol in a total of 100 mole% diol residues refers to a polyester having 1.5 mole diethylene glycol residues per 100 mole diol residues.

In other polyesters of the invention, the glycol component employed in preparing the polyesters useful in the invention may comprise, consist essentially of, consist of, or consist of ethylene glycol and one or more difunctional diols selected from the group consisting of diethylene glycol, 1, 2-propanediol, 1, 5-pentanediol, 1, 6-hexanediol, and mixtures thereof. The preferred diol is ethylene glycol.

The dicarboxylic acid component of the polyesters useful in the present invention may comprise up to 5 mole% or up to 1 mole% of one or more modified aromatic dicarboxylic acids in addition to terephthalic acid and/or dimethyl terephthalate. Examples of modified aromatic dicarboxylic acids that may be used in the present invention include, but are not limited to, 4 '-biphthalic acid, 1, 4-naphthalene dicarboxylic acid, 1, 5-naphthalene dicarboxylic acid, 2, 6-naphthalene dicarboxylic acid, 2, 7-naphthalene dicarboxylic acid, and trans-4, 4' -stilbene dicarboxylic acid, and esters thereof. Heterocyclic dicarboxylic acids, such as 2, 5-furandicarboxylic acid, may also be used. The preferred modified aromatic dicarboxylic acid is 2, 6-naphthalene dicarboxylic acid.

The dicarboxylic acid component of the polyesters useful in the present invention may be further modified with up to 5 mole% or up to 1 mole% of one or more aliphatic dicarboxylic acids containing 2 to 16 carbon atoms such as, for example, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, caprylic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid (dodecanedioic-dicarboxylic acids), diethyl di-n-propylmalonate, benzyl-dimethyl malonate, 2-dimethyl-malonic acid and 2, 3-dimethyl glutaric acid. The preferred aliphatic dicarboxylic acid is adipic acid.

The polyesters of the invention may further comprise at least one chain extender. Suitable chain extenders include, but are not limited to, polyfunctional (including, but not limited to difunctional) isocyanates, polyfunctional epoxides including, for example, epoxidized novolacs, and phenoxy resins. In certain embodiments, the chain extender may be added at the end of the polymerization process or after the polymerization process. If added after the polymerization process, the chain extender may be introduced by mixing or by addition during the conversion process, such as injection molding or extrusion. The amount of chain extender used may vary depending on the particular monomer composition used and the physical properties desired, but is generally from about 0.1 to about 5 weight percent, or from about 0.1 to about 2 weight percent, based on the total weight of the polyester.

In addition, the polyester compositions and polymer blend compositions useful in the present invention may also contain any amount of at least one additive, for example, common additives such as colorants, dyes, mold release agents, flame retardants, plasticizers, stabilizers (including but not limited to UV stabilizers, heat stabilizers and/or reaction products thereof) and impact modifiers in an amount of from 0.01 to 2.5 weight percent of the total composition. Examples of typical commercially available impact modifiers well known in the art and useful in the present invention include, but are not limited to: ethylene/propylene terpolymers, functionalized polyolefins such as those containing methyl acrylate and/or glycidyl methacrylate, styrenic block copolymer impact modifiers, and various acrylic core/shell impact modifiers. For transparent EBM containers, the refractive index of these additives must closely match the refractive index of the polyester composition to prevent haze in the container. Residues of such additives are also contemplated as part of the polyester composition.

In addition, certain agents for tinting polymers may be added to the melt. Bluing toners (bluing toners) may be used to reduce the yellow color of the resulting polyester polymer melt phase product. Such bluing agents include cobalt salts, one or more blue inorganic and organic toners, and the like. In addition, one or more red toners may also be used to adjust the red color. One or more organic toners, such as one or more blue and red organic toners, may be used. One or more toners may be fed as a pre-mix composition. The pre-mix composition may be a neat blend of red and blue compounds, or the composition may be pre-dissolved or slurried in one of the raw materials of the polyester (e.g., ethylene glycol).

The total amount of toner components added depends on the amount of yellow color inherent in the base polyester and the effectiveness of the toner. In general, the combined toner uses no more than about 15ppm concentration and a minimum of about 0.5ppm concentration, with the total amount of the blueing additive typically being in the range of about 0.5ppm to about 10 ppm.

Conventional production of polyesters may be accomplished by batch, semi-continuous or continuous processes. Typical polyesterification processes involve multiple stages and are commercially carried out in one of two common paths. For a process employing direct esterification, the initial stages of the process react dicarboxylic acids with one or more diols at a temperature of about 200 ℃ to about 250 ℃ to form a macromonomer structure and small condensed molecules, i.e., water. Because the reaction is reversible, water is continuously removed to drive the reaction toward the desired first stage product. The branched comonomer is typically added at this stage of the process. In a similar manner, when a diester (for diacid) is used, an transesterification process is used to react the ester groups of the diester with the diol using some well known catalyst such as manganese acetate, zinc acetate or cobalt acetate. After the transesterification reaction is completed, these catalysts are sequestered with phosphorus compounds such as phosphoric acid to avoid degradation during the polycondensation process.

Then, in the second stage of the reaction, the macromonomer structure (direct esterification product) or exchange part (transesterification product) is subjected to polycondensation reaction to form a polymer. In this process, the temperature of the molten mass is raised to a final temperature in the range of about 280 ℃ to 300 ℃ and a vacuum (about 150 Pa) is applied to remove excess glycol and water. The polymerization is stopped when the desired/target molecular weight is achieved and/or the maximum molecular weight of the design of the equipment is reached. The polyester is extruded through a die into strands which are quenched and cut into pellets. The catalysts generally used for the polycondensation reaction are compounds containing antimony, germanium, aluminum, titanium or other catalysts known to the person skilled in the art, or mixtures thereof. The specific additives used and the points of introduction during the reaction are known in the art and do not form part of the present invention. Any conventional system may be used and one skilled in the art may choose among various commercially viable systems for introducing additives to achieve the desired result. The polyester pellets may be further polymerized to higher molecular weights by well known solid state polymerization processing techniques.

Preferably, the terephthalic acid and/or ethylene glycol are derived from biomass feedstock rather than petroleum-based feedstock. In addition, the use of chemically recycled terephthalic acid (or dimethyl terephthalate) and ethylene glycol from post consumer polyester waste is also preferred for the polyesters of the invention. Another preferred method of making the polyester resins of the present invention utilizes bis- (hydroxyethyl) terephthalate which is purified from the reaction product of glycolysis of post-consumer polyester waste-such monomers can be added to the polymerization process, preferably prior to the polycondensation stage.

Polyester compositions suitable for use in the present invention include those having an intrinsic viscosity of at least about 0.90dl/g, preferably at least about 1.0dl/g, and more preferably between about 0.9 to about 1.2 dl/g. Lower intrinsic viscosity resins have insufficient melt strength for EBM processes, while higher intrinsic viscosity resins have too high melt viscosity at extrusion temperatures above which thermal degradation and molecular weight loss can occur.

Branched aliphatic diols

Preferred examples of branched aliphatic diols suitable for use in the present invention include 2-methyl-1, 3-propanediol, 2-ethyl-1, 3-propanediol, 2-butyl-1, 3-propanediol, 2' -dimethyl-1, 3-propanediol, 2-methyl-1, 4-butanediol, 2-ethyl-1, 4-butanediol, 2-butyl-1, 4-butanediol, 3-methyl-1, 5-pentanediol, 2, 4-dimethyl-1, 5-pentanediol, or mixtures thereof. The most preferred branched aliphatic diol is 2,2' -dimethyl-1, 3-propanediol. The amount of branched aliphatic diol is preferably in the range of about 2.0 mole% to about 10.0 mole%, preferably about 3.0 mole% to about 7.0 mole%, based on the total mole% of diol residues in the composition. Lower amounts of branched aliphatic diols do not sufficiently retard the crystallization rate to be used in EBM processes and do not become hazy after the container is cooled in the forming mold. Higher amounts of branched aliphatic diols do not provide the high melt strength required in EBM processes.

Branched comonomers

The branched comonomer present in the composition has 3 or more carboxyl substituents, hydroxyl substituents, or a combination thereof. Examples of branching monomers include, but are not limited to, polyfunctional acids or alcohols such as trimellitic acid, trimellitic anhydride, pyromellitic dianhydride, benzene-1, 3, 5-tricarboxylic acid, trimethylol propane, glycerol, sorbitol, 1,2, 6-hexanetriol, pentaerythritol, citric acid, tartaric acid, 3-hydroxyglutaric acid, trimesic acid, and the like. Ethoxylated or oxypropylated triols may also be used. In a preferred embodiment, the branching monomer residues are selected from at least one of the following: pentaerythritol, trimethylol propane, trimethylol ethane, trimellitic acid, trimellitic anhydride and/or benzene-1, 3, 5-tricarboxylic acid. The branched comonomer may be present in an amount in the range of 50 to 2000 μmol based on the copolyester.

Extrusion blow molding

In another aspect, the present invention relates to a method for preparing an extrusion blow molded container. The extrusion blow molding process may be accomplished via any EBM manufacturing process known in the art. Although not limited thereto, one exemplary description of an extrusion blow molding manufacturing process involves: 1) melting the resin in an extruder, 2) extruding the molten resin through a die to form a tube of molten polymer (i.e., a parison), 3) clamping a forming die having a desired finished shape around the parison, 4) blowing air into the parison to stretch and expand the extrudate to fill the forming die, 5) cooling the formed container, 6) ejecting the container from the forming die, and 7) removing excess plastic (commonly referred to as flash/overflow) from the container.

As used herein, the term "container" is understood to refer to a receptacle in which material is contained or stored. Containers include, but are not limited to, bottles, bags, vials, tubes, and cans. Applications in industry for these types of containers include, but are not limited to, food, beverage, cosmetic, household or chemical containers, and personal care applications. As used herein, the term "bottle" is understood to mean a resin-containing receptacle capable of storing or containing a liquid.

The exact resin formulation must provide such a melt: the melt has a high melt strength that resists stretching and flow, sagging, or other undesirable aspects that can lead to uneven material distribution in the parison and thinning of the parison wall during extrusion. The melt strength is directly related to the viscosity of the polyester resin at zero shear rate and the temperature of the molten extrudate as it exits the die. However, resins with high melt strength or high melt viscosity at zero shear rate are too viscous to be used without the use of high temperatures which cause the polymer to degrade and lose its melt viscosityExtruded in an extruder and pumped through a die. Thus, the optimal polyester resin designed for EBM end use must have rheology such that viscosity at shear rates associated with the extrusion process (typically 100 to 1000s ^-1 ) Below the viscosity at zero shear rate (i.e., exhibits shear thinning). Melt strength can be measured using a melt index apparatus that extrudes the resin through a capillary die at zero shear rate. The length of the extrudate after a period of time (L ₁ ) And the length (L) after the same period of time ₂ ) A comparison is made. L (L) ₂ /L ₁ The ratio (melt strength) gives a measure of the sag of the extrudate, which is 1.0 if there is no sag. This ratio increases as the melt strength becomes weaker and L2 increases because the extrudate is unable to support its own weight. For the EBM resin of the invention, the melt strength should be in the range of about 1 to about 1.6 when measured at an extrusion temperature corresponding to a melt index of 2.6.+ -. 0.2g/10min under a load of 2.16 kg.

Furthermore, during the EBM process, the molten polyester should not thermally crystallize; otherwise, a cloudy container may be created. The EBM process can produce scrap from burrs that have to be cut from the formed container (where it has been clamped, for example). This waste from the EBM process must be ground and mixed with the virgin resin and dried before re-extrusion. Thus, the resins of interest are designed to have and maintain a low level of crystallinity so that they do not agglomerate during drying.

In order to pass the APR critical guidance protocol for post-consumer clear polyester recycle streams, the polyester resins of the present invention must be semi-crystalline (i.e., exhibit a melting endotherm as measured by differential scanning calorimetry). In this regard, the melting point of the EBM resin should be in the range of 235-255 ℃.

Another parameter that must be met by the resin relates to the drop resistance of the EBM container containing the liquid from a height of 4 feet (122 cm). After such drop tests, no more than one tenth of the containers are expected to rupture, split or leak. As the copolyester ages over time, it is important to measure the drop resistance after several weeks (e.g., 4 to 6 weeks) from the start of manufacture.

Testing and preparation methods

1. Test method

a. The intrinsic viscosity of the polyesters is measured in accordance with ASTM D4603-96 and reported in dl/g.

b. The melting point of the polyester is taken as the peak of the melting endotherm of the copolyester as measured according to ASTM D3418-03. The sample was heated from 30 ℃ to 300 ℃ at a rate of 10 ℃/min, held for 5 minutes, and quenched to 10 ℃ (at a rate of about 320 ℃/s). The sample was then heated to 300 ℃ at a rate of 10 ℃/min and the peak melting endotherm temperature was recorded.

c. The drop resistance of the container was measured according to bruton's step method (Bruceton Staircase Method) of procedure B of ASTM D2463-95. The container was filled with 1.5 liters of water (23 ℃) before dropping. The containers were stored at 23 ℃ and 50% relative humidity for aging (1 day, 1 week, 2 weeks, 3 weeks, 4 weeks, etc.).

d. The melt strength of the polymer was measured using ASTM D1238-04 c, "Standard test method for melt flow Rate of thermoplastics by extrusion plastometer (Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer)". The temperature used for this measurement was a temperature corresponding to a melt flow index of the polymer of 2.6.+ -. 0.2g/10min (with a load of 2.16 kg). The length of the extrudate after 50s was measured (L ₁ ) And the total length (L) after 100s was measured. Length of extrusion within the second 50s (L ₂ ) From L ₁ And L is calculated:

L ₂ ＝L-L ₁ ,

and defines the melt strength as L ₂ /L ₁ 。

h. The polyfunctional hydroxy-branched comonomer content of the polymer was determined by hydrolyzing the polymer with an aqueous solution of ammonium hydroxide at 220+5 ℃ for about two hours in a sealed reaction vessel. The liquid portion of the hydrolysate was then analyzed by gas chromatography. The gas chromatography apparatus was a FID detector from Hewlett Packard (HP 5890, HP 7673A). Ammonium hydroxide is 28 to 30 wt% ammonium hydroxide from Fisher Scientific and is reagent grade.

i. The diacid and diol (including DEG (diethylene glycol)) content of the polymer was determined from proton nuclear magnetic spectroscopy (1H MNR) using a JOEL ECX-300 (300 MHz) instrument. The general samples were prepared as follows:

20mg of the polyester was placed in an appropriate 2mL glass reaction vessel or vial having 1mL of 10:1 chloroform-d: TFA-d [ Cambridge Isotope Laboratories, inc. chloroform-d (d, 98.9%) +0.05% V/V TMS: cambridge Isotope Laboratories, inc. trifluoroacetic acid-d (d, 99.5%) ] and capped. The reaction vessel/vial was placed on a heated block at 100 ℃ for about 10 minutes, or until the sample was completely solvated. The samples were then removed from the heating block and placed in a fume hood to equilibrate to RT. The solvated samples were then transferred to standard NMR tubes and analyzed via a predefined NMR protocol. The resulting spectral integral was processed via Excel macros to determine the reported monomer content.

2. Preparation method

a) Extrusion Blow Molded (EBM) bottle

The shaped EBM containers were produced using a 90mm Bekum H-155 continuous EBM machine equipped with a Glycon DM2 screw. These containers are standard 1.75 liter rectangular handled containers weighing 110 g. The extrusion temperature was adjusted to 245 ℃ to 260 ℃ to obtain a uniform polymer distribution in the vessel. The copolyester is dried to a moisture level of less than 50ppm prior to extrusion.

b) Preparation of polyesters

A series of copolyesters were prepared from purified terephthalic acid, ethylene isophthalate, aliphatic branched acids, pentaerythritol using standard procedures known in the art, with antimony trioxide as polycondensation catalyst. The amorphous IV of these copolyesters is in the range of about 0.66 to about 0.68 dl/g.

These amorphous copolyesters are further polymerized in the solid state to achieve the target IV.

Examples

The compositions and properties of the polyesters used in the examples are listed in Table 1. The comparative examples represent prior art EBM polyester resins. The abbreviations for the monomers used in these compositions are:

PTA purified terephthalic acid

PIA purified isophthalic acid

DEG diethylene glycol

DPD 2,2' -dimethyl-1, 3-propanediol

MPD 2-methyl-1, 3-propanediol

Penta pentaerythritol

The remaining diols added to these compositions are ethylene glycol and diethylene glycol formed during polymerization. The amount of monomer is expressed in mole% based on the moles of diacid or diol suitable and the branched comonomer is expressed in micromoles.

TABLE 1

The melt strengths of these resins are listed in table 2.

TABLE 2

Bottles were made from these resins and the process conditions required to make bottles of the desired size are listed in table 3. Note that when comparative example 2 was run, there was more oligomer deposition on the EBM machine.

TABLE 3 Table 3

Inventive examples can be processed at lower temperatures, melt pressures and motor loads, providing a wider operating window than prior art comparative examples 1 and 2.

The drop resistance of freshly prepared and aged EBM bottles is listed in table 4.

TABLE 4 Table 4

The bottles of the inventive examples had better drop resistance after aging than the comparative examples.

A series of experiments were performed to determine the sensitivity of aged bottle drop performance at a range of molecular weights (IV) for a constant DPD of 5.7 mole%, DEG of 1.4 mole% and Penta of 85 μmol. EBM extrusion conditions are listed in table 5 and the drop resistance of freshly prepared and aged EBM bottles are listed in table 6.

TABLE 5

TABLE 6

These results indicate that the drop resistance of EBM bottles prepared from alkyl branched aliphatic diols is not aged compared to prior art EBM formulations using ultra high IV and aromatic or cycloaliphatic crystallization inhibitors or higher levels of branched comonomers.

While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

Claims (20)

1. A copolyester for an extrusion molded container, the copolyester comprising:

(a) An aromatic dicarboxylic acid component comprising 95 to 100 mole% of dicarboxylic acid residues based on the total mole% of dicarboxylic acid residues in the polyester composition;

(b) A glycol component comprising:

(i) 90 to 98 mole percent of ethylene glycol residues based on the total mole percent of glycol residues in the polyester composition, and

(ii) 2 to 10 mole% of an aliphatic branched diol represented by the following formula I:

wherein R is ₁ Is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and

R ₂ is an alkyl group having 1 to 6 carbon atoms, and

a and b are each independently an integer from 1 to 2, and

(c) A branched comonomer.

2. The copolyester of claim 1, wherein the aromatic dicarboxylic acid residues comprise terephthalic acid, 2, 6-naphthalene dicarboxylic acid, or mixtures thereof.

3. The copolyester of claim 1, wherein the glycol component further comprises diethylene glycol.

4. The copolyester of claim 1, wherein the branching agent is present in an amount of 50 to 2000 μmol based on the copolyester.

5. The copolyester of claim 1 wherein the aromatic dicarboxylic acid component further comprises up to 5 mole% of one or more modified aromatic dicarboxylic acids selected from the group consisting of 4,4 '-biphthalic acid, 1, 4-naphthalene dicarboxylic acid, 1, 5-naphthalene dicarboxylic acid, 2, 6-naphthalene dicarboxylic acid, 2, 7-naphthalene dicarboxylic acid, trans-4, 4' -stilbenedicarboxylic acid, heterocyclic dicarboxylic acid and esters thereof.

6. The copolyester of claim 1 further comprising an intrinsic viscosity of at least about 0.90 dl/g.

7. The copolyester of claim 1, further comprising at least one additive selected from the group consisting of colorants, toners, dyes, mold release agents, flame retardants, plasticizers, stabilizers, impact modifiers, or mixtures thereof.

8. The copolyester of claim 1 further comprising up to 5 mole percent of one or more aliphatic dicarboxylic acids selected from malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, caprylic acid, azelaic acid, sebacic acid, dodecanedioic acid, diethyl di-n-propylmalonate, dimethyl benzyl malonate, 2-dimethyl-malonic acid, and 2, 3-dimethyl glutaric acid.

9. An extrusion blow molding process for forming a container, the extrusion blow molding process comprising:

(a) Melt blending a resin comprising:

(i) An aromatic dicarboxylic acid component comprising 95 to 100 mole% of dicarboxylic acid residues based on the total mole% of dicarboxylic acid residues in the polyester composition;

(ii) A glycol component comprising:

90 to 98 mole percent of ethylene glycol residues based on the total mole percent of glycol residues in the polyester composition, and

2 to 10 mole% of an aliphatic branched diol represented by the following formula I:

wherein R is ₁ Is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and

R ₂ is an alkyl group having 1 to 6 carbon atoms, and

a and b are each independently an integer from 1 to 2, and

(iii) A branched comonomer of the type described above,

(b) Forming a forming blank;

(c) Blowing the parison into the shape of the container;

(d) The waste polymer composition is removed.

10. The extrusion blow molding process of claim 9 wherein the aromatic dicarboxylic acid residues comprise terephthalic acid, 2, 6-naphthalene dicarboxylic acid, or mixtures thereof.

11. The extrusion blow molding process of claim 9 wherein the glycol component further comprises diethylene glycol.

12. The extrusion blow molding process of claim 9 further comprising grinding the scrap polymer composition and then mixing with the resin in step (a).

13. The extrusion blow molding process of claim 9 wherein the resin has a melting point between 235 ℃ and 255 ℃.

14. The extrusion blow molding process of claim 9 wherein the container is a bottle.

15. An extrusion blow molded container comprising a copolyester, the copolyester comprising:

(a) An aromatic dicarboxylic acid component comprising 95 to 100 mole% of dicarboxylic acid residues based on the total mole% of dicarboxylic acid residues in the polyester composition;

(b) A glycol component comprising:

(i) 90 to 98 mole percent of ethylene glycol residues based on the total mole percent of glycol residues in the polyester composition, and

(ii) 2 to 10 mole% of an aliphatic branched diol represented by the following formula I:

wherein R is ₁ Is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and

R ₂ is an alkyl group having 1 to 6 carbon atoms, and

a and b are each independently an integer from 1 to 2, and

(c) A branched comonomer.

16. The extrusion blow molded container of claim 15 wherein the branching agent is present in an amount of 50 to 2000 μmol based on the copolyester.

17. The extrusion blow molded container of claim 15 wherein the dicarboxylic acid residues comprise terephthalic acid, 2, 6-naphthalene dicarboxylic acid, or mixtures thereof and the diol residues comprise ethylene glycol, diethylene glycol, or mixtures thereof.

18. The extrusion blow molded container of claim 15 further comprising a drop height of greater than 160cm after four weeks when tested according to bruton's step method of procedure B of ASTM D2463-95.

19. The extrusion blow molded container of claim 15 wherein the copolyester further comprises an intrinsic viscosity of at least about 0.90 dl/g.

20. The extrusion blow molded container of claim 15 wherein the container is a bottle.