HK1117097B - Compartmentalized chips with similar polymers of different viscosities for improved processability - Google Patents

Description

Compartmentalized chips of similar polymers of different viscosities for improved processability

Priority and cross-reference

The present invention claims priority from the following patent documents: U.S. provisional patent application serial No. 60/644,613 filed on day 18/1/2005, U.S. provisional patent application serial No. 60/646,329 filed on day 24/1/2005, U.S. provisional patent application serial No. 60/677,829 filed on day 5/2005, U.S. provisional patent application serial No. 60/731,789 filed on day 31/10/2005, and U.S. provisional patent application serial No. 60/644,622 filed on day 18/1/2005. These provisional patent applications are incorporated herein by reference.

Background

Technical Field

The present invention generally relates to multicomponent compartmentalized or zoned thermoplastic sheets or pellets that provide compositions with slower crystallization half-times than uniformly dispersed sheets of the same intrinsic viscosity. The sheet may be used in an injection molding process.

Background

In an injection molding process, a polymer is injected into a mold, where the thickest part is usually the location where the material is injected into the mold, called the tip. Because the tip will crystallize first, the part must be held in the mold long enough to cool it, thereby avoiding crystallinity in the tip. If the polymer crystallizes more slowly, the part can be removed from the mold earlier, thereby reducing cycle time and improving the economics of the molding operation.

It is also advantageous to incorporate materials such as post-consumer recycled polyester and virgin polyester into one sheet. However, when this is done as a homogeneous blend, the resulting polymer has a much faster crystallization rate (or shorter crystallization half-life). This increased crystallization rate allows for extended injection molding cycles.

There is also a need for a method of combining two materials and achieving a more uniform intrinsic viscosity (i.v.) distribution, or a reduced i.v. gradient, from the surface of the pellet to the core. The advantages of a more uniform i.v. distribution are described in U.S. patent application 2005/0196566, the teachings of which are incorporated by reference. The key advantage of having a more uniform trans-tablet IV distribution is lower molecular weight drop and lower energy consumption during extrusion.

However, U.S. patent application 2005/0196566 accomplishes this goal by: a molten product having an intrinsic viscosity of 0.70(dl/g) was extruded, and then the i.v. was slightly increased by solid-phase polymerization. Although U.S. patent application 2005/0196566 contemplates the use of recycled polyester, it does not mention its incorporation into a zoned or compartmentalized pellet structure.

Thus, there is a need to combine two similar polymers in a way that can achieve slower crystallization rates and provide the benefit of having a reduced i.v. gradient from the core to the surface.

Summary of The Invention

A compartmentalized chip comprising a first compartment and a second compartment, the first compartment comprising a first crystallizable thermoplastic polymer and the second compartment comprising a second crystallizable thermoplastic polymer, wherein the second compartment is positioned such that at least a portion of the second compartment is between the centroid of the chip and the first compartment, and wherein the melt viscosity of the first crystallizable thermoplastic polymer is different from the melt viscosity of the second crystallizable thermoplastic polymer.

It is still further disclosed that the first and second crystallizable thermoplastic resins are polyesters, and that the resins may also be similar in that at least 85 mole percent of the polymeric repeat units of the second crystallizable thermoplastic resin are identical to the majority of the repeat units of the first crystallizable thermoplastic resin. Preferred embodiments are selected from crystallizable polyethylene terephthalate polymers.

The invention also discloses that the second crystallizable thermoplastic polymer is selected from the group consisting of industrial waste or used waste or FDA specified used recycled polyester.

The second thermoplastic resin has a melt viscosity greater than the melt viscosity of the first thermoplastic resin.

The invention also discloses a method of preparing pellets with reduced i.v. gradient comprising the steps of: 1) producing a compartmentalized chip comprising a first compartment and a second compartment, the first compartment comprising a first crystallizable thermoplastic polymer and the second compartment comprising a second thermoplastic crystallizable polymer, wherein the second compartment is positioned such that at least a portion of the second compartment is between the centroid of the chip and the first compartment, and wherein the intrinsic viscosity of the second crystallizable thermoplastic polymer is greater than the intrinsic viscosity of the first crystallizable thermoplastic polymer, 2) crystallizing the first crystallizable thermoplastic polymer, 3) heating the compartmentalized chip in the presence of a driving force to a temperature of 140 ℃ to 1 ℃ below the temperature at which the first crystallizable polymer becomes liquid; and 4) maintaining the sheet in this temperature range in the presence of a driving force for a time sufficient to increase the intrinsic viscosity of the sheet by at least 0.05 dl/g.

Further, the present invention discloses that the process uses a sheet wherein at least 85% of the recurring polymer units of the second crystallizable thermoplastic polymer have the same chemical structure as at least 85% of the recurring units of the first crystallizable thermoplastic polymer, and/or wherein 85% of the polymer recurring units of the first crystallizable thermoplastic polymer are ethylene terephthalate.

The invention further discloses that the second crystallizable thermoplastic polymer used in the process is selected from the group consisting of thermoplastic polymers that have been made solid and have undergone at least one remelting after their initial production, industrial and used waste, used polyester, and FDA regulated recycled polyester. The present invention also discloses that at least 85% of the recurring polymer units of the second crystallizable thermoplastic polymer have the same chemical structure as at least 85% of the recurring units of the first crystallizable thermoplastic polymer. The invention also discloses that 85% of the polymer repeating units of the first crystallizable thermoplastic polymer used in the process are ethylene terephthalate.

It is also preferred that the second crystallizable thermoplastic polymer is selected from the group consisting of: at least 85% of the recurring polymer units of the second crystallizable thermoplastic polymer have the same chemical structure as at least 85% of the recurring units of the first crystallizable thermoplastic polymer, or even further, 85% of the polymer recurring units of the first crystallizable thermoplastic polymer are ethylene terephthalate.

Drawings

Fig. 1 shows a resin pellet having two compartments or zones in a core-shell configuration.

Fig. 2 shows a resin pellet having two compartments or zones in a core-shell configuration, wherein the core is enclosed, surrounded, or enclosed by an outer shell layer.

Fig. 3 shows a resin pellet having three compartments or zones in a multilayer or sandwich configuration.

Figure 4 shows a resin pellet with three compartments configured as two concentric layers surrounding a core.

Detailed Description

Higher molecular weight polycondensation polymers are typically produced in a two-step process. The melt process converts the raw materials to low molecular weight oligomers, which are then increased in molecular weight to polymers by removing reaction by-products from the liquid. The molecular weight or intrinsic viscosity is increased until the melt viscosity reaches a level where it is too difficult, either physically or economically, to transport the liquid or renew the surface of the liquid for the removal of by-products. At this point, the polymer is cured and cut into small particles, flakes, or sheets, all of which are referred to as sheets. The sheet is then subjected to solid state polymerization which increases the molecular weight of the material in the sheet by exposing the sheet to a temperature below the melting point of the polymer and an external driving force (e.g., vacuum or inert gas). Typically, the temperature is 140 ℃ to 1 ℃ below the temperature at which the sheet becomes liquid or the polymer melts.

Conventional tablets prepared from melt phase polymerization or extruders are homogeneous with a very narrow molecular weight distribution (small i.v. gradient). The epidermis of the tablet has the same molecular weight as the core of the tablet. Intrinsic viscosity and subsequent melt viscosity changes within the chip (intrachip) can be determined by the experiments described below, which determine intrinsic viscosity changes within the chip.

In solid state polymerization, reaction by-products diffuse through the sheet and then escape from the skin into an inert gas or vacuum. It is even proposed to use air as the driving force. Air is not preferred because the presence of oxygen causes competing reactions that reduce the surface melt viscosity and result in color in the polymer.

The solid phase polymerization reaction in the sheet is initially kinetically controlled and rapidly transitions to diffusion controlled because the polymerization of the material closer to the surface proceeds faster than the polymerization of the material inside. Thus, unlike melt polymerization, solid state polymerization produces a sheet with a higher molecular weight material at the sheet surface than at the center of the sheet. Since the melt viscosity increases with increasing molecular weight (intrinsic viscosity), the melt viscosity of the surface is greater than that of the core.

As solid state polymerization designs have become more advanced, the molecular weight in the melt sheet has become lower and lower in the industry. The lower the molecular weight of the melt, the longer the solid phase polymerization time required to reach the aggregate molecular weight as determined by intrinsic viscosity. It is important to understand that intrinsic viscosity is merely a measure of the flow time of a known quantity of tablets dissolved in a predetermined quantity of solvent. Thus, in practice, intrinsic viscosity measurements are only a substitute for molecular weight. As set forth in the examples below, the two sheets may have the same intrinsic viscosity (or flow time through the orifice when dissolved in a solvent), but have a completely different intrinsic viscosity distribution in the sheet, and thus different thermal properties and melt viscosities. Note that melt viscosity is measured by the time required for the molten polymer composition to flow through the orifice, while intrinsic viscosity measures the time for the solvated composition to flow through the orifice. After the sheet is solid phase polymerized, the use of lower molecular weight feeds creates a larger molecular weight difference from the core to the sheet skin. In some cases, the molecular weight of the center of the sheet may even remain unchanged. This molecular weight gradient and melt viscosity of the sheet is so great as to negatively impact the injection molding operation as compared to sheets prepared from molten polymers having higher molecular weights. The reason for the large difference in properties is that the melt viscosity increases exponentially with each increase in intrinsic viscosity.

The following table illustrates this effect with respect to standard commercial uniformly dispersed resins. Table I shows the intrinsic viscosity of a 1g tablet from which the continuous layer of the tablet has dissolved as described in the test methods section. The theoretical zero shear melt viscosity of the polymer at each intrinsic viscosity is also listed. The molecular weight distribution in the sheet can be characterized by the delta intrinsic viscosity (dl/g), which is the intrinsic viscosity of the outer layer minus the intrinsic viscosity of the inner layer, and by the zero shear melt viscosity ratio, which is the zero shear melt viscosity of the surface layer divided by the zero shear melt viscosity of the center. A larger delta intrinsic viscosity (i.v.) indicates a much higher i.v. at the surface, as does a larger zero shear melt viscosity ratio. In contrast, the uniformly prepared sheet should have a Δ i.v. of almost 0.0 and a zero shear melt viscosity ratio of 1.0 immediately after melt production and before solid state polymerization.

TABLE I Concentric weights of 1.0GM polyester starting from 0.58(dl/g) molten polymeric material and solid state polymerized to 0.81(dl/g)

Dissolution time (min)	Weight of dissolved sample (gm)	Percent of initial 1gm sample dissolved		Cumulative weight%	Intrinsic viscosity (dl/g)	Theoretical zero shear melt viscosity at 290 ℃ (1000 poise)
							0.5	0.0451	4.45		4.45	0.914	15.2
1.0	0.0697	6.88		11.33	0.890	13.3
							1.5	0.0865	8.53		19.86	0.886	13.0
3.0	0.1443	14.24		34.1	0.868	11.8
							2.0	0.0920	9.08		43.18	0.860	10.6
2.0	0.0858	8.46		51.64	0.832	9.5
							2.5	0.0981	9.68		61.32	0.807	8.1
2.8	0.0889	8.77		70.09	0.784	7.1
							3.5	0.100	9.87		79.96	0.757	5.9
8.0	0.1265	12.48		92.44	0.789	7.3
							*	0.0619	6.11		98.55	0.706	4.2

^*There was no dissolution time for this sample becauseThis is the amount left after the previous dissolution.

Table II shows the effect of starting from various melt intrinsic viscosities and solid phase polymerizing the material to 0.81 and 0.84 dl/g. The lower the initial intrinsic viscosity and the higher the final intrinsic viscosity, the greater the intrinsic viscosity at the surface and the greater the difference between the surface and the core.

TABLE II intrinsic viscosity Change in sheets for different melt intrinsic viscosities

Starting melt I.V. (dl/g)	Final composite I.V. (dl/g)	Surface I.V. (dl/g)	Central I.V. (dl/g)	Theoretical surface zero shear melt viscosity at 290 ℃ (1000 poise)	Theoretical centre zero shear melt viscosity (1000 poise) at 290 DEG C		Δ IV (surface-center)	Zero surface to center shear MV ratio
									0.46	0.79	1.051	0.667	30.7	3.1		0.384	9.8
0.58	0.806	0.967	0.713	20.2	4.4		0.254	4.6

0.46	0.830	1.115	0.693	41.3	3.8		0.422	10.9
									0.58	0.808	1.003	0.694	24.3	3.8		0.309	6.4

The gradient and associated high melt viscosity of the surface is reduced by extruding the sheet from the melt reactor as a compartmentalized or zoned sheet, wherein the outer compartment or zone comprises a low molecular weight melt material and the inner compartment or zone comprises a similar polymer, but with a higher molecular weight or intrinsic viscosity. The term similar polymer is defined hereinafter, but generally means that 85% of the polymer repeat units are the same.

It is also advantageous in many cases to combine two materials of the same chemical structure, for example in recycling operations. However, when materials are combined, compositions are often produced that crystallize much faster than either of the two starting materials. While not being bound by any theory, it is postulated that this is because the two separate entities, which are uniformly dispersed throughout the tablet, act as nucleating agents for each other. This conclusion is demonstrated in the experimental part in table III, where the compartmentalized pellets have a longer crystallization half-life compared to the same composition in homogeneously dispersed tablets. It is also noted that the total amount of crystallization of the solid article of the present invention is less, and therefore less energy is used to melt the material during the injection operation.

As described below, the following embodiments will illustrate how the compartmentalized or zoned structure overcomes the problems of making low molecular weight chips and solid state polymerizing the chips to higher intrinsic viscosities; how to combine the two materials into the same tablet and achieve a slower crystallization half-time than if the combined materials were uniformly dispersed throughout the tablet.

The words tablet, pellet and particle are used interchangeably. Preferred forms and/or dimensions of the sheet are spheres having a preferred diameter of 0.05cm to 0.3cm, hemispheres having a largest cross-section of preferably 0.1cm to 0.6cm, or right circular cylinders having a preferred diameter of 0.05mm to 0.3mm and a length of 0.1cm to 0.6 cm. The sheet will not be confused with fibres, which will have a large aspect ratio (long strand to diameter) of at least 15, whereas the sheet aspect ratio is below 15, preferably below 10.

U.S. patent application nos. 5627218 and 5747548 and U.S. non-provisional application serial No. 11/130961, filed 5/17/2005, the teachings of which are incorporated herein in their entirety, teach a number of techniques for producing compartmentalized tablets. In one embodiment, there are at least two zones, or regions, in the sheet, preferably a core and a shell. In this embodiment and all embodiments hereafter, a core-shell with sealed ends (as taught in U.S. patent 6669986, all of the teachings of which are incorporated herein) is the preferred sheet structure.

The core-shell structure is obtained by using two feeders. If a third endless loop is desired, then an additional feeder is required. The feeder may be an extruder or a gear pump that discharges the polymer from the melt reactor. Any suitable device capable of forcing the polymer into the nozzle is possible. The first feeder supplies a liquid feed of the material forming the core, which is linearly extruded in the centre of the strand. At the same time, the sheath material is extruded in a second feeder into a sheath layer concentrically covering the core. U.S. patent No.6669986 discloses a multi-orifice die apparatus for producing core-shell sheets.

The preferred embodiment as shown in fig. 2 is to close the pellet ends so that the inner core 21 is completely surrounded and enclosed by the shell 22. Us patent No.6669986 teaches that such spherical or ellipsoidal or disc-shaped multilayer sheets, in which all the boundaries (including the end faces of the core material) are covered with the shell material, can be prepared by rounding the cut end faces. One method of making a sheet having an outer layer enclosing the contents of the inner layer is by cutting a strip of sheet material under water immediately adjacent to a die.

It is obvious to the person skilled in the art that the strand may consist of more than two annular concentric layers. This can be done by using additional feeders and different dies. Figure 4 shows a sheet with three compartmentalized zones having a core 41 comprising a higher intrinsic viscosity thermoplastic, wherein the core is surrounded by an intermediate layer 42 comprising a material, which intermediate layer 42 in turn is surrounded by an outer layer 43 comprising a lower molecular weight thermoplastic, such a sheet may also be used.

The first step is extrusion to form a multi-layer strand. The higher melt viscosity component is fed into the center of the sheet, while the lower melt viscosity component is extruded around the higher melt viscosity component. The extruded multilayer strand is cut and formed into multilayer sheets, as required, before or after cooling.

For the cooling, a usual cooling device is used. For example, a method of immersing the multilayer strand in cooling water in a water tank is employed. The water-cooled multilayer strand is preferably fed to a cutter after removing water adhering to the surface by means of a water dropping device.

The cutter cuts the multilayer strand into a specific length by driving a hob or the like. By cutting the multilayer strand like this, a double cylindrical multilayer sheet comprising a high melt viscosity core and a low melt viscosity shell is obtained.

Typically, multilayer tablets having an outer diameter of about 2-8mm are prepared.

It should be recognized that absolute separation of the compartmentalized zones is not necessary. For all embodiments of the invention, absolute separation is lacking.

Thermoplastic polymers can be cast into layered sheets and then also cut into cube shapes. The minimum structure is two layers, but the preferred structure of the cast structure of the present invention is shown in fig. 3. In a sandwich or layered construction, there are at least three layers, with the middle layer 33 sandwiched between the first and second outer layers 31, 32.

The core region or core compartment is a compartment having a portion between the centroid of the chip and the region having the largest exposed surface area for contact with air. The centroid of a chip is the center of the plane through the chip perpendicular to the extrusion direction of the strand cutting the chip. Typically, this will be the longest dimension of the sheet. It is clear for the ball that any face is satisfactory.

Suitable thermoplastic polymers suitable for use in the present invention include any crystallizable thermoplastic homopolymer or copolymer. The term crystallizable means that the thermoplastic polymer can become semicrystalline through orientation or thermally induced crystallization. It is well known that no plastic is completely crystalline, more precisely the crystalline form shall be described as semi-crystalline. The term semicrystalline is well known in the art and is intended to describe X-ray patterned polymers that exhibit sharp features with crystalline regions and typical diffusion features with amorphous regions. It is also well known in the art that semi-crystallization should be distinguished from pure crystalline and amorphous states.

The crystallizable polymer will form crystals as the polymer is gradually cooled from the molten state. These crystals produce diffraction that can be observed by X-rays.

Preferably, the thermoplastic polymer used in the present invention includes a polyester polymer, which means a homopolymer or a copolymer, such as polyethylene terephthalate or a crystallizable copolymer of polyethylene terephthalate. For the sake of clarity, the term crystallizable polyethylene terephthalate, the group consisting of crystallizable polyethylene terephthalate, refers to a polymer that is crystallizable and comprises at least 85% polyethylene terephthalate repeating segments. The remaining 15% may be any other acid-diol repeating unit combination as long as the resulting polymer is capable of achieving at least 5%, more preferably 10% crystallinity.

The term crystallizable polyester refers to polymers that are crystallizable and have at least 85% of their acid moieties selected from the group consisting of terephthalic acid, 2, 6-naphthalenedicarboxylic acid, or their corresponding dimethyl esters.

In a preferred embodiment, the high and low melt viscosity materials are similar. Similarity does not mean exact molecular formula repeats. For example, a crystallizable polyethylene terephthalate homopolymer (100% of the repeat units are ethylene terephthalate) can be placed in the core, while a crystallizable polyethylene terephthalate copolymer (85% to almost 100% of the repeat units are ethylene terephthalate, with the other repeat units being modified with different diol-acid repeat units) can be placed in the shell. Possible diols include, but are not limited to, cyclohexanedimethanol, ethylene glycol, butanediol, and possible acids include, but are not limited to, isophthalic acid, 2, 6-naphthalenedicarboxylic acid, sebacic acid, or azelaic acid. Mixtures of the foregoing combinations may of course also be used.

For clarity, the use of the term polymer repeat unit refers to the chemical structure that forms the primary mode of reaction (pattern). For example, for polyesters, the units are chemical structures formed by the reaction of diacids and diols. Thus, for polyethylene terephthalate, the repeat unit is the reaction product of terephthalic acid and ethylene glycol, or ethylene terephthalate. The repeating unit, often referred to as "species" in the term polymeric "species", does not have a functional end group attached because it has been reacted into the polymer chain.

It is particularly contemplated that the high melt viscosity core comprises recycled industrial or post consumer recycled polyester. These materials are commonly available from used soft drink bottles and are available worldwide. For recycling, the material must already be present at least once as a solid before being extruded into the core. The core of the recycled polyester used will have a composition typical of the various polyesters used in packaging at the time and therefore contain a mixture of the various packaging polyesters in the market.

Although it is preferred to avoid the use of non-crystallizable polyesters in the core, it is possible that the used polyesters may contain a limited amount of non-crystallizable polyesters. However, this is hardly a problem because crystallizable and non-crystallizable resins react with each other when producing cores to produce a crystallizable core composition. There are therefore used recycled polyesters which do not contain non-crystallizable polyesters and used recycled polyesters which contain non-crystallizable polyesters. However, as part of the present invention, post consumer or industrial recycled polyester compositions must still be crystallizable.

One particular type of post consumer recycled polyester is the type referred to as FDA regulated post consumer recycled polyester. The FDA is the United States food and Drug Administration (United States food and Drug Administration) and is responsible for issuing regulations governing the use of plastics in food packaging. FDA regulated means that recycled polyester that has been used before being placed in a compartmentalized sheet meets FDA regulations governing the use of plastics in food and beverage packaging. In order to comply with FDA regulations, the resin must be of suitable purity for use in Food packaging as required by the Food Drug and Cosmetic Act revision and practice regulations. Some used recycled polyesters are produced using a process that has been reviewed by the FDA and that has been published by the FDA to identify whether the material from the process has the proper purity according to 21 c.f.r174.5, provided that it additionally complies with 21 c.f.r 177.1630. This is commonly referred to as a "letter of nonobject". These post-consumer recycled polyesters are also considered to meet FDA specified limits and will be considered to be FDA specified post-consumer recycled polyesters. It is important to understand that recycled post-consumer polyester specified for purposes of this specification can meet the requirements and comply with FDA regulations, and that the process of cleaning polyester does not have "no objection notice".

It should be understood that the thermoplastic polymers suitable for use in the present invention may be fabricated into films, sheets, or injection molded articles. The present invention is not limited to sheets made from strands. The thermoplastic polymer may also be made into a laminar sheet and then cut into cube form, for example, as disclosed in U.S. patent No. 5627218. While this layered sheet structure may not be as excellent as the core-shell construction, it is expected that placing a higher molecular weight material into the center layer will reduce the overall melt viscosity of the sheet.

The polymers used in the present invention may be prepared by conventional polymerization procedures well known in the art. The polyester polymers and copolymers may be prepared by melt phase polymerization involving the reaction of a diol and a dicarboxylic acid or its corresponding diester. Various copolymers obtained by using various diols and diacids may also be used. Polymers containing repeat units having only one chemical composition are homopolymers. Polymers having two or more chemically different repeat units in the same macromolecule are referred to as copolymers. For clarity, polymers of terephthalate, isophthalate, and naphthalate with ethylene glycol, diethylene glycol, and cyclohexanedimethanol contain six different monomers and are considered copolymers. The diversity of the repeating units depends on the number of different types of monomers present in the initial polymerization reaction. In the case of polyesters, copolymers include reacting one or more diols and one or more diacids, also referred to in some cases as terpolymers.

Suitable dicarboxylic acids include those containing from about 6 to about 40 carbon atoms. Specific dicarboxylic acids include, but are not limited to, terephthalic acid, isophthalic acid, 2, 6-naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid, diphenyl-4, 4' -dicarboxylic acid, 1, 3-phenylenedioxydiacetic acid, 1, 2-phenylenedioxydiacetic acid, 1, 4-phenylenedioxydiacetic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and the like. Specific esters include, but are not limited to, phthalates and naphthalenedicarboxylic esters.

These acids or esters may be reacted with aliphatic diols having from about 2 to about 10 carbon atoms, cycloaliphatic diols having from about 7 to about 14 carbon atoms, aromatic diols having from about 6 to about 15 carbon atoms, or glycol ethers having from 4 to 10 carbon atoms. Suitable diols include, but are not limited to: 1, 4-butanediol, trimethylene glycol, 1, 6-hexanediol, 1, 4-cyclohexanedimethanol, diethylene glycol, resorcinol and hydroquinone.

Polyfunctional comonomers may also be used, typically in amounts of about 0.1 to about 3 mole%. Suitable comonomers include, but are not limited to: trimellitic anhydride, trimethylolpropane, pyromellitic dianhydride (PMDA) and pentaerythritol. Polyester-forming polyacids or polyols may also be used. It is also possible to vary the solid phase polymerization rate of one of the zones or compartments by placing different concentrations of the polyfunctional comonomer in different zones.

One preferred polyester is selected from polyethylene terephthalate formed from the reaction of terephthalic acid or an ester thereof with ethylene glycol at about 1: 1 stoichiometry. Another preferred polyester is selected from polyethylene naphthalate formed by reacting a naphthalene dicarboxylic acid or ester thereof with ethylene glycol in a stoichiometric ratio of from about 1: 1 to about 1: 1.6. Polybutylene terephthalate (PBT) is another preferred polyester. PET copolymers, PEN copolymers and PBT copolymers are also preferred. Specific copolymers and terpolymers of interest are PET in combination with isophthalic acid or its diester, 2, 6-naphthalene dicarboxylic acid or its diester, and/or cyclohexane dimethanol.

The esterification reaction or polycondensation reaction of a carboxylic acid or ester with a diol is usually carried out in the presence of a catalyst. Suitable catalysts include, but are not limited to: antimony oxide, antimony triacetate, antimony glycollate (antimony ethylene glycol), organomagnesium, tin oxide, titanium alkoxides (titanium alkoxides), dibutyltin dilaurate, and germanium oxide. These catalysts may be used in combination with acetic acid or zinc, manganese or magnesium benzoate. Catalysts containing antimony are preferred.

Poly (1, 3-trimethylene terephthalate) (PTT) is another preferred polyester. It can be prepared, for example, by reacting 1, 3-propanediol and at least one aromatic diacid or alkyl ester thereof. Preferred diacids and alkyl esters include terephthalic acid (TPA) or dimethyl terephthalate (DMT). Accordingly, the PTT preferably comprises at least about 80 mole% TPA or DMT. Other diols that may be copolymerized into such polyesters include, for example, ethylene glycol, diethylene glycol, 1, 4-cyclohexanedimethanol, and 1, 4-butanediol. Aromatic and aliphatic acids that may be used simultaneously to make the copolymer include, for example, isophthalic acid and sebacic acid.

Preferred catalysts for the production of PTT include titanium and zirconium compounds. Suitable catalytic titanium compounds include, but are not limited to: titanium alkylate and its derivatives, titanium complex salts, titanium complexes with hydroxycarboxylic acids, titanium dioxide-silica coprecipitates and hydrated alkali-metal-containing titanium dioxide (hydrated alkali-linking titanium dioxide). Specific examples include tetrakis (2-ethylhexyl) -titanate, tetrastearyl titanate, diisopropoxy-bis (acetylacetonate) titanium, di-n-butoxy-bis (triethanolaminato) titanium, tributylmonoacetyl titanate, triisopropylmonoacetyl titanate, tetraphenyl formate titanate, alkali metal titanium oxalates (alkali titanium oxalates) and alkali metal titanium malonates, potassium hexafluorotitanate, and titanium complexes with tartaric acid, citric acid, or lactic acid. Preferred titanium compounds of the catalyst are titanium tetrabutoxide and titanium tetraisopropoxide. The corresponding zirconium compounds can also be used.

Preferred polymers of the invention may also contain small amounts of phosphorus compounds, such as phosphates/phosphates, and catalysts such as cobalt compounds (which tend to impart a blue hue). Other agents that may also be included are infrared absorbers such as carbon black, graphite, and various iron compounds.

The above melt phase polymerization may be followed by a crystallization step and a subsequent solid phase polymerization (SSP) step to increase the molecular weight (as determined by intrinsic viscosity). The crystallization and polymerization may be carried out in a tumble drier reaction in a batch type system. Alternatively, crystallization and polymerization may be accomplished in a continuous solid phase process whereby the polymer flows from one vessel to another after each vessel has been subjected to a predetermined heat treatment.

The crystallization conditions preferably include a temperature of about 100 ℃ to about 150 ℃. The solid phase polymerization conditions preferably include a temperature of from about 200 ℃ to about 232 ℃, more preferably from about 215 ℃ to about 232 ℃. The solid phase polymerization may be carried out for a time sufficient to increase the molecular weight to a desired level, depending on the application. For typical bottle applications, the preferred molecular weight corresponds to an intrinsic viscosity of about 0.65 to about 1.0 deciliter per gram (as determined in 60/40 weight mixtures of phenol and tetrachloroethane at 30 ℃ C. according to ASTM D-4603-86). The time required to reach this molecular weight can be from about 8 to about 45 hours.

In one embodiment, the sheet may be prepared by: the core of the polymer strand was extruded from 0.65dl/g of crystallizable polyethylene terephthalate and the sheath above the core was extruded from 0.48dl/g of polyester prepolymer in an amount of 95-5% by weight of the strand. The strand is then cut into solid core-shell sheets.

In another embodiment, the core may be derived from post consumer recycled polyester. The important factor is that the melt viscosity of the polymer in the core is greater than the melt viscosity of the polymer in the sheath.

As the experimental data indicate, this effect becomes less pronounced when there is less material blended or placed into the core or the i.v. is closer to the i.v. of the main composition.

Experiment of

The following experiments demonstrate the utility of the compartmentalized pellets of the present invention.

Various compartmentalized pellets were made in the core-shell configuration described above (fig. 1). Each compartmentalized pellet had a sheath consisting of a crystallizable polyethylene terephthalate with a low molecular weight (i.v. ═ 0.499dl/g (0.50dl/g)) of 98.2 mole% terephthalic acid and 1.8 mole% isophthalic acid and a core of a higher molecular weight crystallizable polyethylene terephthalate consisting of 98.2 mole% terephthalic acid and 1.8 mole% isophthalic acid. The intrinsic viscosity and the amount of material used in the core are shown in the headings of the data table.

Comparative pellets without compartments were prepared in which two polyethylene terephthalate polymers having the same intrinsic viscosity and amount used in the compartmentalized pellets were uniformly dispersed with each other. The samples were not analyzed for any chemical interaction or degree of transesterification.

Each sample was crystallized by maintaining exposure to a stream of nitrogen heated at 178 ℃ for one hour.

The pellets were then subjected to solid phase polymerization conditions by placing the pellets on a frit in a vertical tube. The tube was placed in a hot oil bath. Nitrogen was heated to the oil temperature by passing it through a series of coils immersed in the hot oil bath and then introduced into the bottom of the vertical tube below the frit. The hot nitrogen then passes through the frit and into the pellets, exiting from the top of the vertical tube. Samples were taken at the intervals.

The solid phase polymerization was carried out at two temperatures (215 ℃ and 230 ℃). A sample of the pellets was removed near the time indicated. The intrinsic viscosity, crystallinity level and crystallization half-life of the whole pellet were analyzed by DSC.

It can be seen that the crystallization half-life of the homogeneously dispersed pellets is in virtually all cases lower than that of the same composition in zoned pellets.

As can be expected, this effect becomes less pronounced as the material blended or placed into the core becomes less or the i.v. becomes closer to the i.v. of the main composition. Thus, the present invention can be viewed as any amount in the core as long as the i.v. is different from the i.v. of the shell.

In one embodiment, the i.v. (melt viscosity) of the material in the core is greater than the i.v. of the material in the sheath. This embodiment describes pellets immediately after they are first made (e.g., by placing fresh polyester from a melt reactor into the shell and used recycled polyester into the core). The greater the amount of material in the core, the greater the difference from the homogeneously dispersed comparative example. Although the aging should not be so great when the amount of material in the core is low, this effect occurs even at 5% in the core. Thus, the core may be as small as 1% by volume of the pellet, preferably at least 5%, with 10% or more being preferred for the desired effect. The maximum volume will be less than 50% because 50% of the core is no longer a minor component.

This embodiment is described by the following pellets, which are the pellets in the experimental section immediately after the pellets are prepared and still amorphous, and the same pellets after crystallization but before significant solid state polymerization.

Another embodiment discloses a pellet wherein the core has an i.v. lower than the i.v. of the sheath. After solid state polymerization, the intrinsic viscosity of the material in the shell increases such that it is greater than the intrinsic viscosity of the material in the core. However, as shown in table VII, compartmentalized pellets with a core molecular weight higher than the shell exhibited a reduction in i.v. gradient by solid phase polymerization.

Test method

Measurement of in-sheet intrinsic viscosity

There are two ways to determine intrinsic viscosity in the sheet. In one method, different sequential samples consisting of 1.0g of a particular product piece were exposed to 50/50 trifluoroacetic acid/dichloromethane mixtures, the longer the exposure time, the more and more of each 1.0g piece was dissolved. The dissolved fraction was then subjected to intrinsic viscosity analysis. This yields intrinsic viscosity data for the surface, and then the weight fraction of the tablets is increased continuously. Thus, the intrinsic viscosity data is initially high (surface intrinsic viscosity) and is continuously close to the intrinsic viscosity of the sample as a whole, referred to as the composite intrinsic viscosity. Intrinsic viscosity for each successive concentric layer can be calculated from a weighted average, unfortunately, the value becomes inaccurate as the center is approached. This is because the difference in the intrinsic viscosity data of fractions fast to the center is very small. This inaccuracy can be overcome by actually measuring the center fraction. The advantage of this method is that using multiple 1.0g samples, a much more reliable description of the product being analyzed is obtained. This is important for aggregate products with large chip-to-chip intrinsic viscosity variation and 1g chips not representative.

Another method is to peel the layers apart. Stripping is accomplished by exposing the same 1.0g piece of the particular product to the solvent used in the intrinsic viscosity test at the same temperature, typically for the same duration, resulting in the layer of the piece being dissolved away. This technique produces a series of intrinsic viscosities that show the change in intrinsic viscosity for each successive layer. The benefit of this procedure is that the intrinsic viscosity of each layer is given and is more accurate for the inner layer. However, it is disadvantageous in that only data of 1.0g of sample is provided.

There are different techniques for handling the dissolved fraction. One is to precipitate the material from the solvent and the other is to analyze the solution directly. Direct analysis of the dissolved fraction is preferred because precipitation of the dissolved fraction introduces an extra step and low molecular weight fractions tend to be lost.

The separation of the undissolved fraction is more difficult for PET than for polyethylene naphthalate (PEN), since PET is more soluble. The undissolved pieces can be separated by filtration through a 325 mesh screen and immediately transferred to a Teflon coated aluminum foil tray. The tray was weighed before and after transfer and weighed again when the undissolved pieces were removed. Generally, nothing remains in the disc. The PET or PEN pieces need to be separated on the tray to ensure that they separate quickly once placed back in the solvent. The tablets retain their shape throughout the dissolution process. There is generally no evidence of pitting or other non-uniform corrosion by the solvent.

Removal of solvent from the undissolved portions of the sheet sample is accomplished by: the sheet was filtered of the solvent using a 325 mesh screen, rinsed, and dried on a hot plate with a surface temperature of 150 ℃ for 30 minutes. The drying time can be extended and additionally dried in a vacuum oven at 150 ℃, but generally does not show weight change.

Melt viscosity

Melt viscosity can be determined by a number of techniques in the industry. The temperature of the melt viscosity is taken to be 40 ℃ above the melting point of the tablet. For sheets with two or more polymers, the temperature at which the melt viscosity is measured is 40 ℃ above the melting point of the highest melting polymer. For example, a sheet made from two copolymerized ethylene terephthalates of different melt viscosities would have a melt viscosity that is the melting point of the copolymerized ethylene terephthalate (approximately 248-252 ℃ C., as determined by differential scanning calorimetry at a scanning rate of 10 ℃ C. per minute). The melt viscosity of a sheet with two polymers melting at 246 ℃ will be measured at 286 ℃.

Alternatively, the melt viscosity of a sheet comprising a co-polyethylene terephthalate with a melting point of 246 ℃ and a polyethylene terephthalate homopolymer with a melting point of 265 ℃ will be measured at 305 ℃.

Intrinsic viscosity

The intermediate molecular weight and low crystalline poly (ethylene terephthalate) soluble in 60/40 phenol/tetrachloroethane and the intrinsic viscosity of the related polymers were determined as follows: 0.1g of polymer or ground pellets was dissolved in 25ml of 60/40 phenol/tetrachloroethane solution and the viscosity of the solution was measured at 30 ℃ C. +/-0.05 using an Ubbelohde 1B viscometer against the solvent at the same temperature. Intrinsic viscosity was calculated based on relative viscosity using the Billmeyer equation.

The intrinsic viscosity of high molecular weight or high crystallinity poly (ethylene terephthalate) and related polymers that are insoluble in phenol/tetrachloroethane is determined by: 0.1g of polymer or ground pellets was dissolved in 25ml of 50/50 trifluoroethane/dichloromethane and the viscosity of the solution was measured at 30 ℃ C. +/-0.05 using an OC Ubbelohde type viscometer against the solvent at the same temperature. Intrinsic viscosity was calculated using the Billmeyer equation and converted using linear regression to yield results consistent with those obtained using 60/40 phenol/tetrachloroethane solvent. The linear regression is:

IV in phenol/tetrachloroethane at 60/40 ═ 0.8229 × IV in trifluoroacetic acid/dichloromethane at 50/50 +0.0124

The intrinsic viscosity measurements for all of the resins in tables II-IV were determined using the method used for the high molecular weight polyesters.

I.v. determination of the outer 10% and inner 10% of the pellets

The outer 10% of the pellets were analyzed as follows. Three 325 mesh screens were folded into a funnel, rinsed with 20-30ml of filtered dichloromethane, dried on a hot plate for at least 10 minutes, and tared to constant weight.

1g of pellets or tablets were weighed into each of three 25ml volumetric flasks without a stir bar.

5ml of filtered I.V. solvent from the IV assay method was added to the flask via a funnel containing a tared 325 mesh screen and gently swirled for 0.5-1 min. The time will vary from sample to sample and some experimentation may be required to determine the appropriate time for 5-11% of the surface of the sample to enter the solution.

The solvent and undissolved pellets were transferred through a screen into a tared flask. The solvent was allowed to drain completely and the vial mouth was allowed to contact the screen several times. The screen was transferred to a wire holder on a hot plate set to a surface temperature of 150 ℃ and dried for about 5 minutes.

The flask was quickly rinsed approximately 4 times with approximately 5ml of filtered solvent and the rinse was transferred through the funnel to the tared flask, rinsing all surfaces of the funnel.

The tared flask was immediately sealed with a stopper and set aside for i.v. measurement. After 5 minutes in the grips, the screens were transferred to an aluminum tare pan on the surface of the heated plate and dried for at least 30 minutes.

The flask was weighed to determine the weight of the solvent and the IV was determined according to the conventional method described above. After the undissolved sample was dried, it was weighed to determine the weight of the undissolved pellet and the weight of the dissolved fraction was determined by subtraction.

The i.v. of the inner 10% of the pellet is determined by: three 325 mesh screens were folded into a funnel, rinsed with 20-30ml of filtered dichloromethane, dried on a hot plate for at least 10 minutes, and tared to constant weight.

1g of pellets were weighed into each of three 25ml volumetric flasks by means of a stir bar.

12ml of filtered IV solvent from the IV process was added to a flask and stirred until 89-95% of the pellets were dissolved. If the weight is not within this range, the sample is repeated. The solvent and undissolved pellets were transferred through a screen mesh into a filter flask.

The volumetric flask was rinsed with approximately 5ml of filtered solvent and the rinsing liquid was transferred through the sieve. If necessary, repeat to transfer all undissolved sample to the screen.

The whole surface of the undissolved pellets and screen were immediately rinsed with about 20ml of filtered dichloromethane.

The screen was transferred to an aluminum tared pan on the surface of a hot plate (150 ℃) and dried for at least 30 minutes, then cooled to room temperature, followed by weighing.

The screen was weighed and the weight of undissolved pellets determined. The IV of the undissolved pellets was determined in a conventional manner as described above.

Claims (35)

1. A compartmentalized chip comprising at least two compartments wherein a first compartment having a maximum surface area for contacting air comprises a first crystallizable thermoplastic resin and a second compartment comprises a second crystallizable thermoplastic resin, wherein the second compartment is positioned such that at least a portion of the second compartment is between the centroid of the chip and the first compartment and the second thermoplastic resin has a melt viscosity greater than the melt viscosity of the first thermoplastic resin, the centroid of the chip being the center of a plane through the chip perpendicular to the direction of extrusion of a strand cutting the chip.

2. The compartmentalized sheet of claim 1, wherein the second thermoplastic resin has a melt viscosity at least 5% greater than the melt viscosity of the first thermoplastic resin.

3. The sheet of claim 1 wherein said first and second crystallizable thermoplastic resins are polyesters.

4. A sheet according to claim 3 wherein at least 85 mole% of the repeat polymer units of the second crystallizable thermoplastic resin are identical to the majority of the repeat units of the first crystallizable thermoplastic resin.

5. The sheet of claim 1 wherein said first and second crystallizable thermoplastic resins are selected from crystallizable polyethylene terephthalate polymers.

6. A compartmentalized chip comprising a first compartment and a second compartment, the first compartment comprising a first crystallizable thermoplastic polymer and the second compartment comprising a second thermoplastic crystallizable polymer, wherein the second compartment is positioned such that at least a portion of the second compartment is between the centroid of the chip and the first compartment, and wherein the melt viscosity of the first crystallizable thermoplastic polymer is different from the melt viscosity of the second crystallizable thermoplastic polymer, the centroid of the chip being the center of the plane through the chip perpendicular to the direction of extrusion of the strand cutting the chip.

7. The compartmentalized chip of claim 6, wherein at least 85% of the repeat polymer units of the second crystallizable thermoplastic polymer have the same chemical structure as at least 85% of the repeat units of the first crystallizable thermoplastic polymer.

8. The compartmentalized sheet of claim 7, wherein 85% of the polymer repeating units of the first crystallizable thermoplastic polymer are ethylene terephthalate.

9. The compartmentalized chip of claim 6, wherein the second crystallizable thermoplastic polymer has been solid and remelted at least once again from its initial production.

10. The compartmentalized chip of claim 9, wherein at least 85% of the repeat polymer units of the second crystallizable thermoplastic polymer have the same chemical structure as at least 85% of the repeat units of the first crystallizable thermoplastic polymer.

11. The compartmentalized sheet of claim 10, wherein 85% of the polymer repeating units of the first crystallizable thermoplastic polymer are ethylene terephthalate.

12. The compartmentalized chip of claim 6, wherein the second crystallizable thermoplastic polymer is selected from the group consisting of industrial waste and used waste.

13. The compartmentalized chip of claim 12, wherein at least 85% of the repeat polymer units of the second crystallizable thermoplastic polymer have the same chemical structure as at least 85% of the repeat units of the first crystallizable thermoplastic polymer.

14. The compartmentalized sheet of claim 13, wherein 85% of the polymer repeating units of the first crystallizable thermoplastic polymer are ethylene terephthalate.

15. The compartmentalized chip of claim 6, wherein said second crystallizable thermoplastic polymer is post consumer polyethylene terephthalate.

16. The compartmentalized chip of claim 15, wherein at least 85% of the repeat polymer units of the second crystallizable thermoplastic polymer have the same chemical structure as at least 85% of the repeat units of the first crystallizable thermoplastic polymer.

17. The compartmentalized sheet of claim 15, wherein 85% of the polymer repeating units of the first crystallizable thermoplastic polymer are ethylene terephthalate.

18. The compartmentalized chip of claim 6, wherein said second crystallizable thermoplastic polymer is an FDA specified post consumer recycled polyester.

19. The compartmentalized chip of claim 18, wherein at least 85% of the repeat polymer units of the second crystallizable thermoplastic polymer have the same chemical structure as at least 85% of the repeat units of the first crystallizable thermoplastic polymer.

20. The compartmentalized sheet of claim 18, wherein 85% of the polymer repeating units of the first crystallizable thermoplastic polymer are ethylene terephthalate.

21. A method of producing a sheet having a reduced i.v. gradient, comprising the steps of:

producing a compartmentalized chip comprising a first compartment and a second compartment, the first compartment comprising a first crystallizable thermoplastic polymer and the second compartment comprising a second thermoplastic crystallizable polymer, wherein the second compartment is positioned such that at least a portion of the second compartment is between the centroid of the chip and the first compartment, wherein the intrinsic viscosity of the second crystallizable thermoplastic polymer is greater than the intrinsic viscosity of the first crystallizable thermoplastic polymer, and the centroid of the chip is the center of a plane through the chip perpendicular to the extrusion direction of the strands cutting the chip;

crystallizing a first crystallizable thermoplastic polymer;

heating the compartmentalized sheet to a temperature of 140 ℃ to 1 ℃ below the temperature at which the first crystallizable polymer becomes liquid in the presence of a driving force;

maintaining the sheet in the temperature range in the presence of a driving force for a time sufficient to increase the intrinsic viscosity of the sheet by at least 0.05 dl/g.

22. The method of claim 21 wherein at least 85% of the repeating polymer units of the second crystallizable thermoplastic polymer have the same chemical structure as at least 85% of the repeating units of the first crystallizable thermoplastic polymer.

23. The process of claim 21, wherein 85% of the polymer repeat units of the first crystallizable thermoplastic polymer are ethylene terephthalate.

24. The process of claim 21 wherein the second crystallizable thermoplastic polymer is already solid and remelted at least once from its initial production.

25. The method of claim 24 wherein at least 85% of the repeating polymer units of the second crystallizable thermoplastic polymer have the same chemical structure as at least 85% of the repeating units of the first crystallizable thermoplastic polymer.

26. The process of claim 24 wherein 85% of the polymer repeat units of the first crystallizable thermoplastic polymer are ethylene terephthalate.

27. The process of claim 21 wherein said second crystallizable thermoplastic polymer is selected from the group consisting of industrial waste and used waste.

28. The method of claim 27 wherein at least 85% of the repeating polymer units of the second crystallizable thermoplastic polymer have the same chemical structure as at least 85% of the repeating units of the first crystallizable thermoplastic polymer.

29. The process of claim 27, wherein 85% of the polymer repeat units of the first crystallizable thermoplastic polymer are ethylene terephthalate.

30. The process of claim 21 wherein the second crystallizable thermoplastic polymer is a post consumer polyester.

31. The method of claim 30 wherein at least 85% of the repeating polymer units of the second crystallizable thermoplastic polymer have the same chemical structure as at least 85% of the repeating units of the first crystallizable thermoplastic polymer.

32. The process of claim 31 wherein 85% of the polymer repeat units of the first crystallizable thermoplastic polymer are ethylene terephthalate.

33. The process of claim 21 wherein the second crystallizable thermoplastic polymer is an FDA specified post consumer recycled polyester.

34. The method of claim 33, wherein at least 85% of the repeating polymer units of the second crystallizable thermoplastic polymer have the same chemical structure as at least 85% of the repeating units of the first crystallizable thermoplastic polymer.

35. The process of claim 33, wherein 85% of the polymer repeat units of the first crystallizable thermoplastic polymer are ethylene terephthalate.