Patent Description:
There are some non-nucleated polypropylene (PP) grades, for example biaxially oriented polyproplylene (BOPP), where a consistent base-line crystallization temperature is required. In BOPP, changes in crystallization rates may affect several processing variables- the point in the process where the film is quenched (or freezes), the temperature at which the film is successfully oriented, and the amount of orientation that can be achieved under standard processing conditions. If a BOPP film becomes inadvertently nucleated, it is well known in the industry that processing problems may be encountered - chief among these is for the film to tear or split in the machine direction as it is being oriented transversally.

Likewise if an injection molding polypropylene grade becomes inadvertently nucleated, it is possible that the shrinkage characteristics may be altered. Therefore, an injection molded article having demanding dimensional tolerances may shrink too much and fall out of specification if made with the inadvertently nucleated composition.

Similar processing problems and/or physical property problems may exist with a wide variety of part fabrications when the incoming polypropylene becomes inadvertently nucleated if the part fabrication was initially established with non-nucleated polypropylene. <CIT> discloses a biaxially oriented film comprising a nucleating agent, a potassium salt of a fatty acid and a thermoplastic resin consisting of polypropylene.

A need therefore exists for additives and processes that can reduce or eliminate any residual nucleation in non-nucleated polypropylene grades.

In a first aspect, the invention provides the use of a potassium salt of a fatty acid in a process for extruding polypropylene comprising the steps of forming a first extrudate by extruding a first composition and then forming a second extrudate by extruding a second composition in the same extrusion system as the first composition. The first composition contains a first polypropylene, a first acid scavenger and ≥ <NUM> ppm of a nucleating agent. The second composition contains a second polypropylene and the potassium salt of a fatty acid as a second acid scavenger and where the second extrudate contains less than about <NUM> ppm of this nucleating agent and the content of all nucleating agents in the second extrudate is < <NUM> ppm. In a second aspect, the invention provides a biaxially oriented polypropylene film as defined in claim <NUM>.

<FIG> illustrates a graph showing the Tc of the formulation of Examples <NUM>, <NUM>, and <NUM> versus time.

The following definitions are provided to define several of the terms used throughout this application.

When the term "stearate" is used in the application, the term is used to include mono, di, and tri stearates depending on the metal cation and its valency. Additionally, when a compound is designated a "stearate", the compound may also contain low amounts of other fatty acids such as palmitate, myristate, etc which are characteristic of commercial grades of stearates. The term "fatty acids" may also include chemical derivatives such as (but not limited to) <NUM>-hydroxy stearates, lactylates, and lactate esters.

As used herein, the term "acid neutralizer" or "acid scavenger" refers to those classes of additives which may be used to neutralize acidic species related to or created by residual amounts of catalyst used in the polymerization reaction in polypropylene manufacturing. These neutralizers or scavengers may also serve other purposes as well in the formulation such as color improvement, lubricity, or as a mold release agent.

Unless otherwise indicated, conditions are <NUM>, <NUM> atmosphere of pressure and <NUM>% relative humidity, concentrations are by weight, and molecular weight is based on weight average molecular weight. The term "polymer" as used in the present application denotes a material having a weight average molecular weight (Mw) of at least <NUM>,<NUM>. The term "copolymer" is used in its broad sense to include polymers containing two or more different monomer units, such as terpolymers, and unless otherwise indicated, includes random, block, and impact copolymers. The concentration of ethylene or propylene in a particular phase or in the heterophasic composition is based on the weight of reacted ethylene units or propylene units relative to the total weight of polyolefin polymer in the phase or heterophasic composition, respectively, excluding any fillers or other non-polyolefin additives. The concentration of each phase in the overall heterogeneous polymer composition is based on the total weight of polyolefin polymers in the heterophasic composition, excluding any fillers or other non-polyolefin additives or polymers.

The process begins with extruding a first composition forming a first extrudate, wherein the first composition comprises a first polypropylene, a nucleating agent, and a first acid scavenger. The first composition is defined as the composition entering the extruder and the first extrudate is defined as the composition exiting the extrusion die. The first composition contains a nucleating agent in an amount of at least about <NUM> ppm and the nucleating agent is selected from the group consisting of phosphate ester salts, sodium benzoate, lithium benzoate, bis(<NUM>-tert-butyl-benzoate) aluminum hydroxide (also known commercially as Al-PTBBA), talc, and compounds conforming to the structure of Formula (I) or Formula (II) illustrated below.

The first extrudate of the invention is useful in producing thermoplastic articles. The first extrudate may be used to create a finished good or resin that may be used in a secondary operation. The first extrudate can be formed into the desired thermoplastic article by any suitable technique, such as injection molding, blow molding (e.g., injection blow molding or injection stretch blow molding), extrusion, extrusion blow molding, thermoforming, rotomolding, film blowing (blown film), film casting (cast film) and compression molding. The first extrudate may be biaxially oriented to form a BOPP film (biaxially oriented polypropylene), extruded into a fiber, or extruded into a pipe and may also be used as an intermediate resin (pelletized or powdered) that is then feed into another process to create a finished good.

The first extrudate is preferably purposefully nucleated polypropylene, meaning that the nucleating agent is intentionally added to the first composition in an amount great enough to significantly nucleate the first polypropylene. As such, the temperature of crystallization (Tc) will be higher than for the PP in the absence of a nucleating agent. Additionally, the crystalline morphology of the polymer may differ in orientation as dictated by the epitaxial match between the polymer and the unique nucleating substrate. Intentional loadings of commercially available nucleating agents may increase the crystallization temperature of the polymer between <NUM> and <NUM>.

Nucleated polypropylene is highly desired in many markets because of the attributes it brings to the processor and/or end-user. The higher crystallization temperature associated with nucleated polypropylene generally translates into faster processing speeds since parts solidify faster and at a higher temperature. The reduction in crystal size that is caused by the nucleating agent also may translate into greater transparency and gloss. With regard to physical properties, nucleated polypropylene generally has higher modulus, greater temperature resistance, and unique shrinkage properties that are dependent upon the type of nucleating agent which is being incorporated. In addition, tensile strength may be improved but this may come with a decrease in tensile elongation. While these types of properties are generally desirable, these attributes can be problematic in situations where these attributes are not desired and where needed accommodations to the process cannot be readily made to suit variability in the degree of nucleation present in the incoming polypropylene composition.

The first polypropylene may be any suitable polypropylene including polypropylene homopolymers, polypropylene copolymers (polypropylene block copolymers (e.g., impact copolymer), polypropylene random copolymers and mini random copolymers), and mixtures thereof. The copolymers may contain comonomers of ethylene, butene, or pentene.

The first composition comprises the nucleating agent in an amount of at least about <NUM> ppm of the nucleating agent, more preferably at least about <NUM> ppm. In another embodiment, the first composition comprises the nucleating agent in an amount of at least about <NUM> ppm of the nucleating agent, more preferably at least about <NUM> ppm. In another embodiment, the first composition comprises the nucleating agent in an amount of at least about <NUM>,<NUM> ppm of the nucleating agent, more preferably at least about <NUM>,<NUM> ppm.

In one embodiment, the nucleating agent is a cycloaliphatic metal salt. In one embodiment, the nucleating agent comprises specific metal salts of hexahydrophthalic acid (and will be referred to herein as HHPA). In this embodiment, the nucleating agent conforms to the structure of Formula (I):
<CHM>.

R<NUM>, R<NUM>, R<NUM>, R<NUM>, R<NUM>, R<NUM>, R<NUM>, R<NUM>, R<NUM>, and R<NUM> are either the same or different and are individually selected from the group consisting of hydrogen, C<NUM>-C<NUM> alkyl, hydroxy, C<NUM>-C<NUM> alkoxy, C<NUM>-C<NUM> alkyleneoxy, amine, and C<NUM>-C<NUM> alkylamine, halogens, and phenyl. M<NUM> is a metal or organic cation, x is an integer from <NUM> to <NUM>, and y is an integer from <NUM> to <NUM>. Preferably, M<NUM> is selected from the group of calcium, strontium, lithium, and monobasic aluminum.

In one preferred embodiment, M<NUM> is a calcium cation and R1-R10 are hydrogen. Ca HHPA as referred to herein refers to Formula (IA). One may employ HYPERFORM™ HPN-20E from Milliken & Company of Spartanburg, S. C which is commercially sold, and comprises Ca HHPA and is described for example in <CIT> which is hereby incorporated by reference in its entirety.

In another embodiment, the nucleating agent is a bicyclic dicarboxylate metal salt described, for example, in <CIT> and <CIT>. The nucleating agent conforms to the structure of Formula (II):
<CHM>
where M<NUM> and M<NUM> are the same or different, or M<NUM> and M<NUM> are combined to form a single moiety, and are independently selected from the group consisting of metal or organic cations. Preferably, M<NUM> and M<NUM> (or the single moiety from the combined M<NUM> and M<NUM>) are selected from the group consisting of: sodium, calcium, strontium, lithium, zinc, magnesium, and monobasic aluminum. Wherein R<NUM>, R<NUM>, R<NUM>, R<NUM>, R<NUM>, R<NUM>, R<NUM>, R<NUM>, R<NUM>, and R<NUM> are independently selected from the group consisting of: hydrogen and C<NUM>-C<NUM> alkyls; and further wherein any two adjacently positioned R<NUM>-R<NUM> alkyl groups optionally may be combined to form a carbocyclic ring. Preferably, R<NUM>-R<NUM> are hydrogen and M<NUM> and M<NUM> are a sodium cations.

In particular, suitable bicyclic dicarboxylate metal salts include disodium bicyclo [<NUM>. <NUM>] heptane-<NUM>,<NUM>-dicarboxylate, calcium bicyclo [<NUM>. <NUM>] heptane-<NUM>,<NUM>-dicarboxylate, and combinations thereof. One may employ HYPERFORM™ HPN-<NUM> or HPN-<NUM> from Milliken & Company of Spartanburg, S. HPN-<NUM> is commercially sold, and comprises the disodium bicyclo [<NUM>. <NUM>] heptane-<NUM>,<NUM>-dicarboxylate shown in Formula (IIA).

In another embodiment, the nucleating agent is a phosphate ester salt. Phosphate ester salts suitable for use as the nucleating and/or clarifying agent include, but are not limited to, sodium <NUM>,<NUM>'-methylene-bis-(<NUM>,<NUM>-di-tert-butylphenyl)phosphate (from Asahi Denka Kogyo K. , known as "NA-<NUM> ™"), aluminum hydroxy bis[<NUM>,<NUM>'-methylene-bis-(<NUM>,<NUM>-di-tert-butylphenyl)phosphate] and lithium myristate (from Asahi Denka Kogyo K. , known as "NA-<NUM> ™"), and other such phosphate esters such as NA-<NUM> (lithium phosphate salt and lithium stearate) as disclosed for example in <CIT> and <CIT>.

In another embodiment, the nucleating agent is sodium benzoate. When the nucleating agent is sodium benzoate, the sodium benzoate may function as both the nucleating agent and the acid scavenger and thus a separate and additional acid scavenger may not need to be employed. In one embodiment where the nucleating agent is sodium benzoate, the acid scavenger is the same composition as the nucleating agent (sodium benzoate).

In another embodiment, the nucleating agent is lithium benzoate. In another embodiment, the nucleating agent is bis(<NUM>-tert-butyl-benzoate) aluminum hydroxide (also known commercially as Al-PTBBA). In another embodiment, the nucleating agent is talc (hydrated magnesium silicate).

The first composition comprises a first acid scavenger in addition to the first polypropylene and the nucleating agent. The acid scavengers suitable for use in the composition of the invention can be any suitable acid scavenger, including but not limited to, aluminum stearate, manganese stearate, calcium stearate, sodium stearate, lithium stearate, magnesium stearate, zinc stearate, cobalt stearate, cerium stearate, potassium stearate, copper stearate, ferric stearate, nickel stearate, calcium lactate, calcium stearoyl lactylate, synthetic hydrotalcites, zinc oxide, calcium oxide, magnesium oxide, and calcium hydroxide. Preferably, the first acid scavenger is selected from the group consisting of metal salts of stearic acid, such as calcium stearate, zinc stearate, magnesium stearate, and mixtures thereof. Calcium stearate may be preferred for some applications due to its low cost, low coloration, and good performance. In another embodiment, the first acid scavenger is hydrotalcite (i.e. DHT-4A) due to its efficacy and low migration characteristics. In one embodiment, the first acid scavenger is a blend of two or more acid scavengers.

The first acid scavenger can be present in the first composition in any suitable amount. The level of acid scavenger (first and second) may be chosen based on the nature of the polymerization catalyst, the amount of residual catalyst, and/or the amount required to effectively stabilize the composition.

Preferably, the first acid scavenger is present in the composition in an amount of about <NUM> ppm to about <NUM> ppm, based on the total weight of the first composition. The first acid scavenger is more preferably present in the composition in an amount of about <NUM> ppm to about <NUM> ppm and most preferably about <NUM> ppm to about <NUM> ppm, based on the total weight of the first composition.

Resin extruders will sometimes follow a nucleated polypropylene run with a non-nucleated polypropylene run. In the second step of the process, a second extrudate is formed by extruding a second composition in the same extrusion system as the first composition , wherein the second composition comprises a second polypropylene and the potassium salt of a fatty acid as a second acid scavenger, wherein the second extrudate contains less than about <NUM> ppm of the nucleating agent.

The second polypropylene may be any suitable polypropylene, including the polypropylene types disclosed as for the first polypropylene. The second polypropylene may be the same or different polypropylene than the first polypropylene.

In one embodiment, the second extrudate contains less than about <NUM> ppm of the nucleating agent, more preferably less than about <NUM> ppm. In another embodiment, the second extrudate contains less than about <NUM> ppm of the nucleating agent, more preferably less than about <NUM> ppm. In another embodiment, the second extrudate contains between about <NUM> ppm and <NUM> ppm of the nucleating agent.

Preferably, no additional nucleating agent is intentionally added to the second composition at any point during the preparation and extrusion of the second composition. The nucleating agent may be added inadvertently to the second composition through residual amounts of nucleating agent retained in the extrusion die/screw/barrel, hoppers, feeders, feed lines, additive masterbatch blenders, or any other part of the extrusion system. It has been found that extruded polypropylene containing residual, low levels of nucleating agent and certain acid scavengers can produce inadvertently nucleated polypropylene. This nucleation may be undesired and cause undesirable properties in the inadvertently nucleated polypropylene such as high crystallization temperatures (Tc) and difficulty producing BOPP films without tears.

The content of all nucleating agents in the second extrudate is less than <NUM> ppm, preferably less than <NUM> ppm, more preferably less than <NUM> ppm, more preferably less than <NUM> ppm, more preferably less than <NUM> ppm.

Preferably, the Tc of the second extrudate is within approximately <NUM> of the Tc of the second polypropylene uncontaminated baseline state. The method for determination of this baseline state for a given polypropylene is defined in the Test Methods section of the specification. In another embodiment, the Tc of the second extrudate is within approximately <NUM> of the Tc of the second polypropylene uncontaminated baseline state, more preferably within approximately <NUM>. In another embodiment where the polypropylene comprises homopolymer polyproylene, the Tc of the second extrudate is less than about <NUM>, more preferably less than about <NUM>, more preferably less than about <NUM>.

Preferably, the difference between the Tc of the first extrudate and the second extrudate is greater than approximately <NUM>, more preferably greater than approximately <NUM>, even more preferably between approximately <NUM> and <NUM> and most preferably greater than approximately <NUM>.

Without being bound to any single theory, it is hypothesized that the preferred second acid scavengers are thought to be de-activating the residual amounts of nucleator. This de-activation may be enabled through an ion-exchange mechanism between the residual nucleator and the acid neutralizer; thereby, changing the chemical nature of the nucleating species. This de-activation may also occur by the acid neutralizer coating the surface of the nucleator, thereby altering the epitaxial match between the nucleator and the polypropylene.

The second acid scavenger is a potassium salt of a fatty acid. It has been found that the potassium salt of a fatty acid results in low nucleation of a polypropylene with all known nucleating agents described above and the like. Preferably, the second acid scavenger comprises a potassium cation and a C<NUM>-C<NUM> fatty acid anion. More preferably, the second acid scavenger comprises potassium stearate. In the embodiment where the nucleating agent is a composition corresponding to Formula (I), then the second acid scavenger is is potassium stearate. It has been found that potassium stearate is able to prevent or significantly reduce any unwanted nucleation of polypropylene extrudates having low amounts of residual nucleating agents corresponding to Formula (I). In one embodiment, the second acid scavenger is a blend of two or more acid scavengers. In the embodiment where the nucleating agent is a composition corresponding to Formula (II), then the second acid scavenger is potassium stearate. It has been found that potassium stearate is able to prevent or significantly reduce any unwanted nucleation of polypropylene extrudates having low amounts of residual nucleating agents corresponding to Formula (II). In one embodiment, the second acid scavenger is a blend of two or more acid scavengers.

In one embodiment, the first acid scavenger and the second acid scavenger are the same composition. This may be preferred in manufacturing environments to lower costs and simplify raw material streams.

The process in which the potassium salt of a fatty acid is used may be used to form polypropylene finished goods or resins having significantly reduced undesired nucleation due to residual amounts of nucleating agents. In one embodiment, the biaxially oriented polypropylene film may be produced. In this specification, biaxially oriented polypropylene film is defined to include oriented polymer films such as tentered or blown polypropylene films.

In one embodiment, the BOPP film comprises a nucleating agent, a potassium salt of a fatty acid and a thermoplastic essentially consisting of polypropylene. The content of all nucleating agents in the film is less than <NUM> ppm, and wherein the nucleating agent preferably conforms to the structure of Formula (I) or (II). The film may contain one or more layers and at least one of the layers contains a nucleating agent, a potassium salt of a fatty acid, and thermoplastic essentially consisting of polypropylene, wherein the content of all nucleating agents in the film is less than <NUM> ppm, and wherein the nucleating agent conforms to the structure of Formula (I) or (II). Preferably, all of the thermoplastic polymer within the film essentially consists of polypropylene. In this application, "essentially consisting of polypropylene" means that the polypropylene polymer contains less than <NUM>% by weight of other thermoplastic polymers.

Peak Crystallization Temperature (Tc) - The peak crystallization temperature (Tc) for all examples was determined in accordance with ASTM D3418-<NUM>, modified with a profile of heating from <NUM> to <NUM> at a rate of <NUM>/min, holding for <NUM> minutes, and cooling at a rate of <NUM>/min back to <NUM>. Under these conditions, the peak Tc was then determined from the crystallization exotherm. Two instruments were involved in the measurement of samples - a Mettler Toledo DSC <NUM> and Mettler Toledo DSC <NUM> Star. The Tc bias between the <NUM> instruments was approximately <NUM>.

Baseline Tc - The baseline value of <NUM> was established by a) making a <NUM> batch consisting of PRO-FAX™ <NUM> reactor flake, <NUM> ppm of IRGANOX™ <NUM>, <NUM> ppm of IRGAFOS™ <NUM>, and <NUM> ppm of calcium stearate, b) vigorously mixing the batch in a sterile plastic bag, c) molding the powder mixture into discs having a thickness of <NUM> with a Carver Press exerting a hydraulic pressure of <NUM>,<NUM> psi and a temperature of <NUM>, d) obtaining specimens from these discs for differential scanning calorimetry, and e) determining the peak crystallization temperature (Tc) in accordance with ASTM D3418-<NUM> (modified with a profile of heating from <NUM> to <NUM> at a rate of <NUM>/min, holding for <NUM> minutes, and cooling at a rate of <NUM>/min back to <NUM>) whereby the peak Tc value was determined from the crystallization exotherm. In this manner, the Tc was determined from the polymer having a standard additive package whereby the risk of introducing contaminants capable of nucleating the polymer could be essentially eliminated.

Some polypropylene extrusion systems first extrude a polypropylene with a nucleating agent (in an amount greater than <NUM> ppm), then switch over to a non-nucleated grade polypropylene. The non-nucleated grade polypropylene may still contain residual amounts (<NUM> ppm) of nucleating agent. This example simulates the non-nucleated grade polypropylene with residual amounts of nucleating agent and the effect of various acid scavengers on the Tc of the polypropylene composition.

To create polypropylene compositions having low levels of nucleating agents, a concentrated nucleating agent mixture was first formed by adding the following ingredients to PRO-FAX™ <NUM><NUM> MFR PP homopolymer reactor flake: IRGANOX™ <NUM> in an amount of <NUM> ppm, IRGAFOS™ <NUM> in an amount of <NUM> ppm, and HYPERFORM™ HPN-<NUM> (abbreviated in this application as HPN-<NUM>) available from MILLIKEN & COMPANY™ or HYPERFORM™ HPN-20E (abbreviated in this application as HPN-20E) available from MILLIKEN & COMPANY™ nucleator in an amount of <NUM> ppm. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter HENSCHEL™ mixer for <NUM> minute forming the concentrated nucleating agent mixture.

Next, to a reactor flake of a polypropylene homopolymer used for manufacturing bi-axially oriented polypropylene film, the following ingredients were added: IRGANOX™<NUM> in an amount of <NUM> ppm, IRGAFOS™ <NUM> in an amount of <NUM> ppm, and the concentrated nucleating agent mixture in an amount of <NUM> ppm. This serial dilution resulted in approximately <NUM> ppm nucleating agent in the formulation. In addition, the acid scavenger to be screened was also added at a concentration consistent with its use in commercial formulations. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter HENSCHEL™ mixer for <NUM> minute.

The diluted formulations were then compounded on a DELTAPLAST™ extruder (typical output of approximately <NUM>/hr) having a <NUM> single screw with an LID ratio of <NUM>:<NUM> and equipped with a Maddocks mixer. The barrel temperature profile was set with a maximum zone setting of approximately <NUM>. The molten polymer was filtered through a <NUM> mesh screen pack and then extruded through a strand die. The strand was subsequently quenched in a water bath, dried, and pelletized.

The extruded pellets were molded into discs having a thickness of <NUM> with a Carver Press exerting a hydraulic pressure of <NUM>,<NUM> psi and a temperature of <NUM>. Specimens were taken from these discs for differential scanning calorimetry.

The baseline Tc of the polypropylene used for manufacturing bi-axially oriented film was <NUM>. As can be seen from the results set forth in the Table <NUM>, the Tc of Examples <NUM>-<NUM> were within +/- <NUM> of the BOPP grade polypropylene. These data illustrate that the harmful effects (i.e. Tc values <NUM>-<NUM> over baseline) from residual amounts of HPN-20E and HPN-<NUM> can be essentially eliminated through the selection of preferred acid scavengers. The baseline (for only Example Set <NUM>) was not measured in the manner described in the Test Methods section. This baseline value of <NUM> was established by a) making a <NUM> batch consisting of the subject polypropylene reactor flake, <NUM> ppm of Irganox <NUM>, <NUM> ppm of Irganox <NUM>, and <NUM> ppm of calcium stearate, b) vigorously mixing the batch in a sterile plastic bag, c) molding the powder mixture into discs having a thickness of <NUM> with a Carver Press exerting a hydraulic pressure of <NUM>,<NUM> psi and a temperature of <NUM>, d) obtaining specimens from these discs for differential scanning calorimetry, and e) determining the peak crystallization temperature (Tc) in accordance with ASTM D3418-<NUM> (modified with a profile of heating from <NUM> to <NUM> at a rate of <NUM>/min, holding for <NUM> minutes, and cooling at a rate of <NUM>/min back to <NUM>) whereby the peak Tc value was determined from the crystallization exotherm. In this manner, the Tc was determined from the polymer having a standard additive package whereby the risk of introducing contaminants capable of nucleating the polymer could be essentially eliminated.

To illustrate how quickly a preferred acid neutralizer could diminish the unwanted effects from residual nucleation, an experiment was designed on a DELTAPLAST™ <NUM> single screw extruder (<NUM>:<NUM>/d) equipped with a MADDOCKS™ mixer (typical output of approximately <NUM>/hr). The barrel temperature profile was set with a maximum zone setting of approximately <NUM>. The molten polymer was filtered through a <NUM> mesh screen pack and then extruded through a strand die. The strand was subsequently quenched in a water bath, dried, and pelletized.

Prior to extrusion, all samples were pre-blended on a <NUM> liter HENSCHEL™ high intensity mixer for <NUM> minute. Before introducing the samples into the extruder, the extruder was purged with <NUM> of a commercial non-nucleated <NUM> MFR polypropylene homopolymer.

Following the <NUM> purge, a <NUM> nucleated "contamination" batch was extruded into strands that were subsequently water-cooled and chopped into pellets. This batch consisted of PRO-FAX™ <NUM> homopolymer with the following additive package: IRGANOX™ <NUM> - <NUM> ppm, IRGAFOS™ <NUM> - <NUM> ppm, DHT-4A - <NUM> ppm, and HPN-20E - <NUM> ppm.

The extruded pellets from the "contamination" batch were molded into discs having a thickness of <NUM> with a Carver Press exerting a hydraulic pressure of <NUM>,<NUM> psi and a temperature of <NUM>. Specimens were taken from these discs for differential scanning calorimetry.

Immediately following the "contamination" batch, a compound was extruded for <NUM> minutes that consisted of PRO-FAX™ <NUM> homopolymer and the following additive package: IRGANOX™ <NUM> - <NUM> ppm, IRGAFOS™ <NUM> - <NUM> ppm, and sodium stearate - <NUM> ppm forming Example <NUM>.

Extruded pellet samples were collected after <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> minutes. The extruded pellets were molded into discs having a thickness of <NUM> with a Carver Press exerting a hydraulic pressure of <NUM>,<NUM> psi and a temperature of <NUM>. Specimens were taken from these discs for differential scanning calorimetry to determine the peak crystallization temperature (Tc).

The steps in Example Set <NUM> were repeated with the exception that calcium stearate was substituted for sodium stearate forming Example <NUM>. The steps in Example Set <NUM> were repeated with the exception that DHT-4A (a synthetic hydrotalcite) was substituted for sodium stearate forming Example <NUM>.

As seen from <FIG>, the Tc of the formulation of Example <NUM> (containing the sodium stearate) drops almost immediately to baseline of the polypropylene (<NUM> ) and is <NUM> - <NUM> lower than Examples <NUM> and <NUM> that contained the commonly used acid neutralizers, DHT-4A and calcium stearate. For the remaining <NUM> minutes of the test, Example <NUM> (DHT-4A) appeared to plateau around <NUM> while only a modest reduction was observed in Example <NUM> (CaSt). Examples <NUM> and <NUM> typify the problem of ridding an extrusion system of nucleator to enable truly non-nucleated crystallization values to be attained. On the other hand, by a mechanism which is not fully understood, the sodium stearate (Example <NUM>) apparently deactivates the residual amounts of the HPN-20E remaining in the system.

Some polypropylene extrusion systems first extrude a polypropylene with a nucleating agent (in an amount greater than <NUM> ppm), then switch over to a non-nucleated grade polypropylene. The non-nucleated grade polypropylene may still contain residual amounts (<NUM> ppm) of nucleating agent. This example simulates the non-nucleated grade polypropylene with residual amounts of various commercially available nucleating agents and the effects of various preferred acid scavengers on the Tc of the polypropylene composition.

To create polypropylene compositions having low levels of nucleating agents, a concentrated nucleating agent mixture was first formed by adding the following ingredients to PRO-FAX™ <NUM><NUM> MFR PP homopolymer reactor flake: IRGANOX™ <NUM> in an amount of <NUM> ppm, IRGAFOS™ <NUM> in an amount of <NUM> ppm, and nucleator (either FLUID ENERGY™ sodium benzoate, ASAHI DENKA™ NA-<NUM>, ASAHI DENKA™ NA-<NUM>, ASAHI DENKA™ NA-<NUM>, GCH aluminum p-tertiary butyl benzoic acid (also known as AI-PTBBA and also bis(<NUM>-tert-butyl-benzoate) aluminum hydroxide), IMERYS™ Jetfine 3CA talc, or SIGMA ALDRICH™ lithium benzoate) in an amount of <NUM> ppm. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter Henschel mixer for <NUM> minute forming the concentrated nucleating agent mixture.

Next, to PRO-FAX™ <NUM><NUM> MFR PP homopolymer reactor flake, the following ingredients were added: IRGANOX™<NUM> in an amount of <NUM> ppm, IRGAFOS™<NUM> in an amount of <NUM> ppm, and the concentrated nucleating agent mixture in an amount of <NUM> ppm. This serial dilution resulted in <NUM> ppm nucleating agent in the formulation. In addition, the acid scavenger to be screened was also added at a concentration consistent with its use in commercial formulations. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter HENSCHEL™ mixer for <NUM> minute.

The diluted formulations were then compounded on a DELTAPLAST™ extruder (typical output of approximately <NUM>/hr) having a <NUM> single screw with an LID ratio of <NUM>:<NUM> and equipped with a MADDOCKS™ mixer. The barrel temperature profile was set with a maximum zone setting of approximately <NUM>. The molten polymer was filtered through a <NUM> mesh screen pack and then extruded through a strand die. The strand was subsequently quenched in a water bath, dried, and pelletized.

The extruded pellets were molded into discs having a thickness of <NUM> with a Carver Press exerting a hydraulic pressure of <NUM>,<NUM> psi and a temperature of <NUM>. Specimens were taken from these discs for differential scanning calorimetry to determine the peak crystallization temperature (Tc).

Reviewing Examples <NUM>-<NUM>, each Example when used in conjunction with residual amounts of various nucleators resulted in imparted Tc values that were either below baseline or no more than about <NUM> above baseline. Examples <NUM>-<NUM> and <NUM>-<NUM> when used in conjunction with residual amounts of various nucleators resulted in an imparted Tc values that were either below baseline or no more than about <NUM> above baseline. Therefore, it appears that the preferred stearates would have broad applicability for use in non-nucleated polypropylene where baseline Tc performance is desired.

Some polypropylene extrusion systems first extrude a polypropylene with a nucleating agent (in an amount greater than <NUM> ppm), then switch over to a non-nucleated grade polypropylene. The non-nucleated grade polypropylene may still contain residual amounts (<NUM> ppm) of nucleating agent. This example simulates the non-nucleated grade polypropylene with residual amounts of HPN-20E and the effects of various acid scavengers from the class comprising metallic salts of stearic acid.

To create the polypropylene compositions having low levels of HPN-20E nucleating agent, a concentrated nucleating agent mixture was first formed by adding the following ingredients to PRO-FAX™ <NUM><NUM> MFR PP homopolymer reactor flake: IRGANOX™ <NUM> in an amount of <NUM> ppm, IRGAFOS™ <NUM> in an amount of <NUM> ppm, and HPN-20E nucleator in an amount of <NUM> ppm. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter HENSCHEL™ mixer for <NUM> minute forming the concentrated HPN-20E nucleating agent mixture.

Next, to PRO-FAX™<NUM><NUM> MFR PP homopolymer reactor flake, the following ingredients were added: IRGANOX™ <NUM> in an amount of <NUM> ppm, IRGAFOS™<NUM> in an amount of <NUM> ppm, and the concentrated nucleating agent mixture in an amount of <NUM> ppm. This serial dilution resulted in <NUM> ppm of HPN-20E nucleating agent in the formulation. In addition, the acid scavenger to be screened was also added at a concentration consistent with its use in commercial formulations. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter HENSCHEL™ mixer for <NUM> minute.

The extruded pellets were molded into discs having a thickness of <NUM> with a Carver Press exerting a hydraulic pressure of <NUM>,<NUM> psi and a temperature of <NUM>. Specimens were taken from these discs for differential scanning calorimetry to determine the peak crystallization temperature (Tc).

In general, the monovalent metal salts of stearic acid (examples <NUM>-<NUM>) produced the lowest peak crystallization temperatures when used in conjunction with residual amounts of HPN-20E, imparting Tc values that were within about <NUM> above the baseline. Among these types, the potassium stearate provided the lowest Tc response. In this Example Set, no significant differences in the above examples were apparent between the divalent and trivalent salts that were tested.

Some polypropylene extrusion systems first extrude a polypropylene with a nucleating agent (in an amount greater than <NUM> ppm), then switch over to a non-nucleated grade polypropylene. The non-nucleated grade polypropylene may still contain residual amounts (<NUM> ppm) of nucleating agent. This example simulates the non-nucleated grade polypropylene with residual amounts of HPN-<NUM> and the effects of various acid scavengers from the class comprising metallic fatty acid salts.

To create the polypropylene compositions having low levels of HPN-<NUM> nucleating agent, a concentrated nucleating agent mixture was first formed by adding the following ingredients to PRO-FAX™ <NUM><NUM> MFR PP homopolymer reactor flake: IRGANOX™ <NUM> in an amount of <NUM> ppm, IRGAFOS™ <NUM> in an amount of <NUM> ppm, and HPN-<NUM> nucleator in an amount of <NUM> ppm. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter HENSCHEL™ mixer for <NUM> minute forming the concentrated HPN-<NUM> nucleating agent mixture.

Next, to PRO-FAX™ <NUM><NUM> MFR PP homopolymer reactor flake, the following ingredients were added: IRGANOX™<NUM> in an amount of <NUM> ppm, IRGAFOS™<NUM> in an amount of <NUM> ppm, and the concentrated nucleating agent mixture in an amount of <NUM> ppm. This serial dilution resulted in <NUM> ppm of HPN-<NUM> nucleating agent in the formulation. In addition, the acid scavenger to be screened was also added at a concentration consistent with its use in commercial formulations. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter HENSCHEL™ mixer for <NUM> minute.

No correlation appeared to exist between the valency of the metallic stearate and peak crystallization temperature when the salt was used in conjunction with residual amounts of Hyperform HPN-<NUM>. In fact, low Tc values were observed with the monovalent potassium salt (example <NUM>); divalent magnesium, manganese, and zinc salts (examples <NUM>, <NUM>, <NUM> respectively); and the trivalent aluminum salt (example <NUM>). All of these previously mentioned salts imparted Tc values that were within about <NUM> above baseline.

Potassium stearate (examples <NUM> and <NUM>) provides a low Tc response with either HPN-<NUM> or HPN-20E and is preferred. With respect to the <NUM>-hydroxy stearates (examples <NUM>-<NUM>), the magnesium and zinc salts provided Tc values within about <NUM> above baseline.

With respect to the calcium lactates and lactylates (examples <NUM>-<NUM>), none provided the desirable low peak crystallization temperature in the presence of residual amounts of HPN-<NUM> nucleator except for the calcium stearoyl lactylate (Pationic <NUM>). This acid neutralizer is the only Ca salt that has provided a low crystallization temperature in the presence of either HPN-20E or HPN-<NUM>.

Except for potassium stearate, all of the stearates tested seem to have differing responses when used with residual amounts of HPN-<NUM> versus HPN-20E with respect to the peak crystallization temperature of the PP composition.

Some polypropylene extrusion systems first extrude a polypropylene with a nucleating agent (in an amount greater than <NUM> ppm), then switch over to a non-nucleated grade polypropylene. The non-nucleated grade polypropylene may still contain residual amounts (<NUM> ppm) of nucleating agent. This example simulates the non-nucleated grade polypropylene with residual amounts of HPN-20E and the effects of various inorganic additives and acid scavengers.

Next, to PRO-FAX™ <NUM><NUM> MFR PP homopolymer reactor flake, the following ingredients were added: IRGANOX™ <NUM> in an amount of <NUM> ppm, IRGAFOS™<NUM> in an amount of <NUM> ppm, and the concentrated nucleating agent mixture in an amount of <NUM> ppm. This serial dilution resulted in <NUM> ppm of HPN-20E nucleating agent in the formulation. In addition, the inorganic additives and acid scavengers to be screened were all added at a concentration of <NUM> ppm. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter HENSCHEL™ mixer for <NUM> minute.

As can be seen in Table <NUM>, some inorganic additives are also effective at reducing the Tc in the presence of residual amounts of the HPN-20E nucleator. Some of the higher performers (i.e., titanium dioxide, calcium silicate, and silica, examples <NUM>, <NUM>, and <NUM> respectively) were <NUM> - <NUM> above the polypropylene baseline crystallization temperature.

Some polypropylene extrusion systems first extrude a polypropylene with a nucleating agent (in an amount greater than <NUM> ppm), then switch over to a non-nucleated grade polypropylene. The non-nucleated grade polypropylene may still contain residual amounts (<NUM> ppm) of nucleating agent. This example simulates the non-nucleated grade polypropylene with residual amounts of HPN-<NUM> and the effects of various inorganic additives and acid scavengers.

Next, to PRO-FAX™ <NUM><NUM> MFR PP homopolymer reactor flake, the following ingredients were added: IRGANOX™ <NUM> in an amount of <NUM> ppm, IRGAFOS™ <NUM> in an amount of <NUM> ppm, and the concentrated nucleating agent mixture in an amount of <NUM> ppm. This serial dilution resulted in <NUM> ppm of HPN-<NUM> nucleating agent in the formulation. In addition, the inorganic additives and acid scavengers to be screened were all added at a concentration of <NUM> ppm. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter HENSCHEL™ mixer for <NUM> minute.

In the presence of residual amounts of HPN-<NUM> nucleator, calcium silicate (example <NUM>) and titanium dioxide (example <NUM>) strongly reduce the peak crystallization value. In these cases, both were within about <NUM> above the polypropylene baseline crystallization temperature. Similarly, magnesium oxysulfate (example <NUM>) and silica (example <NUM>) were found to provide suppressed peak crystallization values that were within about <NUM> above the polypropylene baseline crystallization temperature.

Previous studies have shown that potassium stearate imparts a preferred low peak crystallization value in the presence of residual amounts of both HPN-20E and HPN-<NUM>. On the other hand, calcium stearate consistently imparted an undesirably high peak crystallization value in the presence of residual amounts of both HPN-20E and HPN-<NUM>. This study was undertaken to understand if the carbon chain length would affect the behavior of either the potassium or calcium fatty acid salt.

To create the polypropylene compositions having low levels of Hyperform HPN-<NUM> nucleating agent, a concentrated nucleating agent mixture was first formed by adding the following ingredients to PRO-FAX™ <NUM><NUM> MFR PP homopolymer reactor flake: IRGANOX™ <NUM> in an amount of <NUM> ppm, IRGAFOS™ <NUM> in an amount of <NUM> ppm, and HPN-<NUM> nucleator in an amount of <NUM> ppm. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter HENSCHEL™ mixer for <NUM> minute forming the concentrated HPN-<NUM> nucleating agent mixture.

Next, to PRO-FAX™ <NUM><NUM> MFR PP homopolymer reactor flake, the following ingredients were added: IRGANOX™ <NUM> in an amount of <NUM> ppm, IRGAFOS™ <NUM> in an amount of <NUM> ppm, and the concentrated nucleating agent mixture in an amount of either <NUM> ppm or <NUM> ppm. In addition, the acid scavenger to be screened was also added at a concentration consistent with its use in commercial formulations. This serial dilution resulted in either <NUM> ppm or <NUM> ppm of HPN-<NUM> nucleating agent in the formulation. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter HENSCHEL™ mixer for <NUM> minute.

The composite peak crystallization value for the calcium salts (Examples <NUM>-<NUM>) was <NUM> +/- <NUM> while the composite peak crystallization value for the potassium salts (Examples <NUM>-<NUM>) was <NUM> +/- <NUM>.

These data indicate that the carbon chain length does not have a very significant effect with respect to the acid neutralizer's ability to subdue residual nucleation. On the other hand the metal associated with fatty acid salt appears to be the most significant factor with regard to the acid neutralizer's ability to provide the desired low crystallization temperature of the polypropylene composition.

All of the previous studies illustrated how certain acid neutralizers can provide desired low or baseline crystallization temperatures in polypropylene systems containing residual amounts of nucleator of <NUM> ppm and less. This experiment evaluates how potassium stearate affects nucleation in PP systems having nucleator concentrations of <NUM> ppm all the way up to conventional usage loadings of <NUM> ppm and <NUM> ppm. Comparisons were also made to similarly nucleated systems containing calcium stearate rather than potassium stearate.

To create the polypropylene compositions containing various levels of HPN-<NUM> nucleating agent, a concentrated nucleating agent mixture was first formed by adding the following ingredients to PRO-FAX™ <NUM><NUM> MFR PP homopolymer reactor flake: IRGANOX™ <NUM> in an amount of <NUM> ppm, IRGAFOS™ <NUM> in an amount of <NUM> ppm, and HPN-<NUM> nucleator in an amount of <NUM> ppm. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter HENSCHEL™ mixer for <NUM> minute forming the concentrated HPN-<NUM> nucleating agent mixture.

Next, to PRO-FAX™ <NUM><NUM> MFR PP homopolymer reactor flake, the following ingredients were added: IRGANOX™ <NUM> in an amount of <NUM> ppm, IRGAFOS™ <NUM> in an amount of <NUM> ppm, and the concentrated nucleating agent mixture in amounts ranging from <NUM>% to <NUM>%. In addition, the acid scavenger to be screened was also added at a concentration consistent with its use in commercial formulations. This serial dilution resulted in final concentrations ranging from <NUM> to <NUM> ppm of HPN-<NUM> nucleating agent in the formulation. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter HENSCHEL™ mixer for <NUM> minute.

The preceding table illustrates again the effect of potassium stearate and calcium stearate on the polymer Tc at various nucleator loadings.

At low nucleator levels, potassium stearate provides Tc values near those from baseline polymer. As the amount of nucleator is increased, it begins to outcompete this suppressive effect and can effectively perform as a nucleating agent. While the Tc is never as high as with calcium stearate, this may provide a useful process in manufacturing to simplify material supply or cleanout.

Previous studies evaluated fatty acid salts at a typical commercial loading of around <NUM> ppm to understand their interaction with residual amounts of nucleator. This experiment seeks to determine if the desired low crystallization temperature can be enhanced by using higher loadings of the acid scavenger.

To create polypropylene compositions having low levels of nucleating agents, a concentrated nucleating agent mixture was first formed by adding the following ingredients to PRO-FAX™ <NUM><NUM> MFR PP homopolymer reactor flake: IRGANOX™ <NUM> in an amount of approximately <NUM> ppm, IRGAFOS™ <NUM> in an amount of <NUM> ppm, and nucleator (either HPN-<NUM> or HPN-20E) in an amount of <NUM> ppm. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter HENSCHEL™ mixer for <NUM> minute forming the concentrated nucleating agent mixture.

Next, to PRO-FAX™ <NUM><NUM> MFR PP homopolymer reactor flake the following ingredients were added: IRGANOX™ <NUM> in an amount of <NUM> ppm, IRGAFOS™ <NUM> in an amount of <NUM> ppm, and the concentrated nucleating agent mixture in an amount of <NUM> ppm. This serial dilution resulted in <NUM> ppm nucleating agent in the formulation. In addition, the acid scavenger to be screened was also added at a concentration consistent with its use in commercial formulations and then also at a significantly higher loading. Utilizing a <NUM> batch size, these ingredients were high intensity blended in a <NUM> liter HENSCHEL™ mixer for <NUM> minute.

Moving to higher loadings of acid scavenger did not appear to significantly affect the interaction of the fatty acid salt with the residual amount of either HPN-<NUM> or HPN-20E nucleator except for magnesium stearate. In this case (examples <NUM>, <NUM>, <NUM>, and <NUM>), moving from <NUM> ppm to <NUM> ppm lowered the Tc by <NUM> and <NUM> in the presence of <NUM> ppm HPN-20E and <NUM> ppm HPN-<NUM> respectively.

Claim 1:
Use of a potassium salt of a fatty acid in a process for extruding polypropylene comprising, in order, the steps of
(a) forming a first extrudate by extruding a first composition comprising a first polypropylene, a first acid scavenger, and ≥ <NUM> ppm of a nucleating agent; and
(b) forming a second extrudate by extruding a second composition in the same extrusion system as the first composition, the second composition comprising a second polypropylene and the potassium salt of a fatty acid, wherein the second extrudate contains < <NUM> ppm of the nucleating agent and the content of all nucleating agents in the second extrudate is < <NUM> ppm;
as a second acid scavenger for deactivating residual amounts of nucleating agent in the second extrudate,
wherein the nucleating agent is selected from phosphate ester salts, sodium benzoate, lithium benzoate, bis(<NUM>-tert-butyl-benzoate) aluminum hydroxide, talc, compounds of formula (I)
<CHM>
wherein
M<NUM> is an organic or inorganic cation,
x is <NUM> or <NUM>,
y is <NUM> or <NUM>,
R<NUM>-R<NUM> each independently are H, OH, C<NUM>-<NUM>-alkyl, C<NUM>-<NUM>-alkoxy, C<NUM>-<NUM>-alkyleneoxy, amine, C<NUM>-<NUM>-alkylamine, halogen or phenyl, wherein any two vicinal or geminal alkyl groups may be combined to form a carbocyclic ring of up to six carbon atoms and wherein the carboxyl moieties of Formula (I) are present in cis configuration;
and formula (II)
<CHM>
wherein
M<NUM> and M<NUM> are each independently selected from metal or organic cations, or are combined to form a single moiety, and
R<NUM>-R<NUM> each independently are H, OH, C<NUM>-<NUM>-alkyl, C<NUM>-<NUM>-alkoxy, C<NUM>-<NUM>-alkyleneoxy, amine, C<NUM>-<NUM>-alkylamine, halogen, phenyl, alkylphenyl, or geminal or vicinal C<NUM>-<NUM>-carbocyclic.