WO2008024154A1

WO2008024154A1 - High clarity polymer compositions, methods and articles made therefrom

Info

Publication number: WO2008024154A1
Application number: PCT/US2007/015643
Authority: WO
Inventors: Bryan G. Wells; Susan Chia-Yu Yeh
Original assignee: Exxonmobil Chemical Patents Inc.
Priority date: 2006-08-22
Filing date: 2007-07-09
Publication date: 2008-02-28

Abstract

The present invention relates to polymer compositions with high clarity and low haze that exhibit superior strength and stiffness, methods for making the same and useful articles formed therefrom. In particular, the invention relates to a polymer composition comprising a mixture of at least two olefin polymers and a sorbitol compound. In another aspect, the invention relates to shaped articles formed from the polymer composition, in particular, blow molded articles, injection blow molded articles, injection stretch molded articles, shallow- and deep-draw thermoformed articles, sheet extrusion, films, containers, medical devices and eating and drinking utensils such as cups, plates and plasticware. Also provided are methods for making high clarity shaped articles.

Description

HIGH CLARITY POLYMER COMPOSITIONS, METHODS AND ARTICLES MADE THEREFROM

FIELD OF THE INVENTION

[0001] The present invention relates to polymer compositions with high clarity and low haze that exhibit superior strength and stiffness, methods for making the same and useful articles formed therefrom. In particular, the invention relates to a polymer composition comprising a mixture of at least two olefin polymers and a sorbitol compound. In another aspect, the invention relates to shaped articles formed from the polymer composition.

BACKGROUND OF THE INVENTION

[0002] Crystalline or semi-crystalline polyolefϊns, including, but not limited to polypropylene and propylene/ethylene copolymers, have long been sought after in the polymer industry. These polymers are used extensively in many molding processes because they exhibit desirable physical properties (i.e., rigidity, clarity and impact or chemical resistance). However, often a particular combination of characteristics is desired and a balancing of one property versus another must be struck.

[0003] "Nucleation" is the term given to the onset of polymer crystallization, an event that usually occurs randomly throughout a polymer matrix as individual molecules align. Sometimes, though, nucleation will begin at a point of interface between the polymer and a foreign body, possibly an intentionally added nucleating agent. A number of such nucleating agents are known in the art, including dibenzylidene sorbitol acetal derivative compounds ("DBSs"), sodium benzoate, sodium phosphates and talc. Usually, in the presence of a nucleating agent, crystallization will result in a large number of small crystals. A polymer with small crystals will generally have better optical clarity because less light is scattered by the small crystals as it passes through the polymer. Informed use of nucleating agents can impart uniquely desirable characteristics to the polymer, including clarity and improved molding cycling times through faster crystallization.

[0004] It is known that a polymer's crystalline structure greatly influences its physical characteristics. For example, crystalline propylene homopolymer ("CPH") is rigid and highly chemically resistant, but is brittle. To obtain increased impact resistance, a blend of CPH and an elastomeric compound, such as ethylene/propylene rubber or ethylene-propylene-diene rubber may be used. However, addition of such materials often reduces the optical clarity of the CPH. As a result, a need exists for a polymer composition that retains the rigidity of CPH while simultaneously exhibiting impact resistance, high clarity and low haze.

[0005] The present invention provides polymer compositions with high clarity and low haze that exhibit superior strength and stiffness, methods for making the same and useful articles formed therefrom. In particular, the invention relates to a polymer composition comprising a mixture of at least two olefin polymers and a sorbitol compound having the following structure:

wherein Rl and R2 are the same or different and selected from C6 to C24 aryls and substituted derivatives thereof, C7 to C30 alkylaryls, and C7 to C30 arylalkyls; and R3 and R4 are the same or different and selected from the group consisting of hydrogen, Cl to ClO alkyls and Cl to ClO substituted alkyls.

SUMMARY OF THE INVENTION

[0006] The present invention provides polymer compositions with high clarity and low haze that exhibit superior strength and stiffness, methods for making the same and useful articles formed therefrom. In particular, the invention relates to a polymer composition comprising a mixture of at least two olefin polymers and a sorbitol compound having the following structure:

wherein R¹ and R² are the same or different and selected from Ce to C₂₄ aryls and substituted derivatives thereof, C₇ to C3₀ alkylaryls, and C₇ to C30 arylalkyls; and R³ and R⁴ are the same or different and selected from the group consisting of hydrogen, Ci to Cio alkyls and Ci to Cio substituted alkyls and the composition exhibits a clarity percentage of Y or more, where Y = 0.09293x + 28.9 and x is an amount of the sorbitol compound measured in parts per million by weight of polyolefin polymer and is from about 0 to about 750.

[0007] The polymer composition may be further processed to form useful or shaped articles by the following methods: blow molding, injection blow molding, injection stretch molding, thermoforming, shallow- and deep-draw thermoforming and sheet extrusion.

[0008] Further, the useful or shaped articles of the invention include, but are not limited to, beverage containers, food storage containers, food product packaging, bottles, baby bottles, digital video disk ("DVD") packaging, labware, medical devices, personal care product packaging, pharmaceutical packaging, office supplies and closures (i.e., screw-on bottlecaps).

DETAILED DESCRIPTION

[0009] As used herein, the new numbering scheme for the Periodic Table of

Elements Groups are used as in Hawley's Condensed Chemical Dictionary 852

(John Wiley & Sons, 13th ed. 1997).

[0010] As used herein, the term "polymer" refers to the product of a polymerization reaction, and is inclusive of homopolymers, copolymers, terpolymers, etc.

[0011] As used herein, unless specified otherwise, the term "copolymer(s)" refers to polymers formed by the polymerization of at least two different monomers. For example, the term "copolymer" includes the copolymerization reaction product of ethylene and an alpha-olefϊn, such as 1-hexene. However, the term "copolymer" is also inclusive of, for example, the copolymerization of a mixture of ethylene, propylene, 1-hexene, and 1-octene.

[0012] As used herein, when a polymer is referred to as "comprising a monomer," the monomer is present in the polymer in the polymerized form of the monomer or in the derivative form the monomer.

[0013] As used herein, "molecular weight" means weight average molecular weight ("Mw"). Mw is determined using Gel Permeation Chromatography. Molecular Weight Distribution ("MWD") means Mw divided by number average molecular weight ("Mn"). (For more information, see US Patent No. 4,540,753 to Cozewith et al. and references cited therein, and in Verstrate et al., 21 Macromolecules 3360 (1998)). The "Mz" value is the high average molecular weight value, calculated as discussed by A.R. Cooper in Concise Encyclopedia of Polymer Science and Engineering 638-39 (J.I. Kroschwitz, ed. John Wiley & Sons 1990). [0014] As used herein, "isotactic" is defined as having at least 40% isotactic pentads according to analysis by C-NMR. "Substantially isotactic" is defined as having at least 97% isotactic pentads.

[0015] As used herein, "thermoplastic" includes only those thermoplastic materials that have not been functionalized or substantially altered from their original chemical composition. For example, as used herein, polypropylene, propylene ethylene copolymers, propylene alpha-olefin copolymers, polyethylene and polystyrene are thermoplastics. However, maleated polyolefins are not within the meaning of thermoplastic as used herein.

[0016] As used herein, weight percent ("wt%"), unless noted otherwise, means a percent by weight of a particular component based on the total weight of the mixture containing the component. For example, if a mixture contains three pounds of sand and one pound of sugar, then the sand comprises 75 wt% (3 lbs. sand / 4 lbs. total mixture) of the mixture and the sugar 25 wt%. [0017] As used herein, a "tailored crystallinity resin" ("TCR") is a modified polypropylene comprising an in situ reactor blend of a higher molecular weigh propylene/ethylene random copolymer and a lower molecular weight substantially isotactic homopolypropylene such as those described in United States Patent No. 4,950,720, incorporated, by reference as if fully disclosed herein.

[0018] For purposes of the invention, the melting point (T_M) is determined by differential scanning calorimetry (DSC). For example, the method proceeds as follows. From 6 to 10 mg of a sheet of a polymer is pressed at approximately 200⁰C to 230⁰C and is removed with a punch die. The sample is then annealed at room temperature for 80 to 100 hours. At the end of the annealing period, the sample is placed in a differential scanning calorimeter (Perkin Elmer 7 Series Thermal Analysis System) and cooled to -50⁰C to -70⁰C. The sample is then heated at a rate of 20°C/min to a final temperature of 200⁰C to 220⁰C. The thermal output is recorded as the area under the melting peak curve of the sample, which is typically peaked at 3O⁰C to 185⁰C, and occurs between the temperatures of 0⁰C and 200⁰C. The thermal output in joules is a measure of the heat of fusion. The melting point is recorded as the temperature of the greatest heat absorption within the range of melting of the sample. This is called the first melt. The sample is then cooled at a rate of 20°C/min to 25°C. The non- isothermal crystallization temperature (Tc) is recorded as the temperature of greatest heat generation, typically between 100⁰C and 125°C. The area under the peak corresponds to the heat of crystallization. The sample is remelted by heating a second time, called the second melt, and is more reproducible than the first melt.

[0019] When referred to herein, a polymer's "clarity," "clarity percentage," "haze" or "haze percentage" are determined in the absence of any colorant, colored pigments, dyes or other additives meant to affect the final color or opacity of the polymer. In particular, if an inventive composition described herein satisfies the clarity and haze percentages of the given formulae before the addition of colorants, colored pigments, dyes or other additives, but does not after the addition of some additive, it does not cease to be an inventive composition according to the present invention.

[0020] For purposes of the invention, clarity (measured in %) is determined according to ASTM D 1746 using a 50 mil thick, injection molded plaque.

[0021] For purposes of the invention, haze (measured in %) is determined according to ASTM D 1003-61, using a 50 mil thick, injection molded plaque and a BYK-Garder USA Haze-Gard Plus hazemeter.

[0022] For purposes of the invention, Melt Flow Rates (MFR) are determined in accordance with ASTM D 1238 at 230⁰C and 2.16 Kg weight.

[0023] One aspect of the present invention is directed to a polymer composition comprising at least two olefin polymers and a sorbitol compound having the following structure:

where R¹ and R² are the same or different and selected from Ce to C₂₄ aryls and substituted derivatives thereof, C₇ to C₃₀ alkylaryls, and C₇ to C₃₀ arylalkyls; and R³ and R⁴ are the same or different and selected from the group consisting of hydrogen, Ci to Cio alkyls and Ci to C_1O substituted alkyls.

[0024] Preferably, the sorbitol compound is a DBS. A number of preferred DBS compounds are commercially available including, but not limited to, 1,2-O- 2,4-bis(3,4-dimthylbenzylidene) sorbitol (available from Milliken Chemical under the trade name Millad® 3988) and l,3-O-2,4-bis(p-methylbenzylidene) sorbitol (also available from Milliken Chemical under the trade name Millad® 3940). The sorbitol compound may be present in the amount of from greater than zero to about 5000 parts per million by weight (PPMW). The sorbitol compound is preferably present in an amount of from 5 PPMW to 3000 PPMW₃ preferably of from 25 PPMW to 2000 PPMW, more preferably of from 50 PPMW to 1500 PPMW, even more preferably of from 100 PPMW to 1000 PPMW and even more preferably of from about 250 PPMW to about 750 PPMW. [0025] The olefin polymers that make up part of the inventive polymer compositions may be polypropylene (optionally isotactic or syndiotactic), propylene ethylene copolymer (optionally block or random copolymer), propylene alpha-olefin copolymer (optionally block or random copolymer) and mixtures thereof. The at least two olefin polymers of the present invention may be the same, but are preferably different. Preferably, the olefin polymers of the present invention are polypropylene and propylene alpha-olefin copolymer. More preferably they are polypropylene homopolymer and propylene alpha-olefin random copolymer. Even more preferably, they are substantially isotactic propylene homopolymers and propylene alpha-olefin random copolymer. Even more preferably, they are lower molecular weight substantially isotactic propylene homopolymers and higher molecular weight propylene alpha-olefin random copolymer. Even more preferably, they are tailored crystallinity resins. [0026] Preferably, the propylene alpha-olefin copolymers used in the present invention are comprised of alpha-olefin based units chosen from ethylene and C₄ to C_1O alpha olefin based units. More preferably, the alpha-olefin based units are ethylene based units.

[0027] In an embodiment, the composition exhibits clarity of C or more, where C = 0.09293x + 28.9 and x is an amount of the sorbitol compound measured in PPMW of olefin polymer and is from greater than 0 to about 750. [0028] In another embodiment, the composition exhibits haze of H or less, where H = -O.O588x + 46.3, where x is an amount of the sorbitol compound measured in PPMW of olefin polymer and where x is from greater than 0 to about 750.

[0029] In one aspect, the polymer compositions of the present invention exhibit clarity at least 10% greater than the clarity of the base polymer blend absent the sorbitol compound. Preferably, the clarity is at least 15% greater; more preferably at least 25% greater; and even more preferably at least 35% greater. [0030] In another aspect, the polymer compositions of the present invention exhibit haze of at least 10% less than the haze of the base polymer blend absent the sorbitol compound. Preferably, the haze is at least 15% less; more preferably at least 20% less; more preferably at least 25% less; and even more preferably at least 40% less.

[0031] The polymer compositions may further comprise an effective amount of a stabilizer to prevent color formation. Many such stabilizers are known in the art, any of which may be used with the present invention. Preferred stabilizers include phosphorus oxo acids, acid organo phosphates, acid organo phosphates, acid phosphate metal salts, acidic phosphate metal salts and mixtures thereof. [0032] The polymer compositions of the present invention may also further contain an effective amount of a colored pigment. Many colored pigments for use with polyolefins are known in the art, any of which may be used. Among the pigments available for use with the present invention are carbon black, phthalocyanine blues, phthalocyanine greens, anthraquinone dyes, scarlet 2b Lake, azo compounds, acid azo pigments, quinacridones, chromophthalocyanine pyrrols, halogenated phthalocyanines, quinolines, heterocyclic dyes, perinone dyes, anthracenedione dyes, thiozanthene dyes, parazolone dyes, polymethine pigments and mixtures thereof.

[0033] The polymer compositions of the present invention may also be combined with additional additives or compounds to provide the compositions with particular, desirably characteristics. Many such additives and compounds are known in the art. The use of appropriate additives or compounds is well within the skill of one in the art. Examples of such include UV stabilizers, antioxidants, light stabilizers, flame retardants, antistatic agents, biocides, viscosity- breaking agents, impact modifiers, plasticizers, fillers, reinforcing agents, lubricants, mold release agents, blowing agents, nucleating agents and the like. [0034] The olefin polymers used in the present invention may be produced using any technique known in the art for production of olefinic polymers, such as solution polymerization, slurry polymerization or gas phase polymerization techniques, with liquid-phase polymerization being a preferred technique. Similarly, the olefin polymers may be produced using any known polyolefin catalyst system, such as Zeigler-Natta catalysts or metallocene catalysts, Zeigler- Natta catalysts being preferred.

[0035] Ziegler-Natta-type catalysts are well known in the art, and are discussed, for example, by in Concise Encyclopedia of Polymer Science and Engineering, 1087-1107 (Jacqueline I. Kroschwitz ed., 1990) and by F. A. Cotton & G. Wilkinson, Advanced Inorganic Chemistry, 1280-1282 (4th ed. 1980). Typical solid magnesium supported catalyst systems and preparations thereof are outlined in U.S. Patent Nos. 4,990,479 and 5,159,021, and WO 00/44795. For example, Ziegler-Natta catalysts are typically composed of a transition metal compound from groups 4-7 and an organometallic compound of a metal from groups 11-13 of the periodic table. Well-known examples include TiCb- Et₂AlCl, AlR₃-TiCl₄ wherein Et is an ethyl group and R represents an alkyl group. These catalysts include mixtures of halides of transition metals, especially titanium, chromium, vanadium, and zirconium, with organic derivatives of nontransition metals, particularly alkyl aluminum compounds. The Ziegler- Natta-type catalysts are usually combined with an electron donor. Electron donors are typically used in two ways in the formation of a Ziegler-Natta catalyst system. First, an internal electron donor may be used in the formation reaction of the solid catalyst. Examples of internal electron donors include: amines, amides, ethers, esters, aromatic esters, ketones, nitriles, phosphines, stibines, arsines, phosphoramides, thioethers, thioesters, aldehydes, alcoholates, and salts of organic acids. The second use for an electron donor in a catalyst system is as an external electron donor and stereoregulator in the polymerization reaction. The same compound may be used in both instances;, although typically they are different. Organic silicon compounds are generally known in the art for use as electron donors. Examples of electron donors that are organic silicon (or "silane") compounds are disclosed in U.S. Patent Nos. 4,218,339; 4,395,360; 4,328,122; 4,473,660; 6,133,385; and 6,127,303. A description of the two types of electron donors is provided in U.S. Patent No. 4,535,068. [0036] In an embodiment, the present invention envisions shaped parts and articles formed from any of the polymer compositions of the present invention. [0037] In other embodiments, the shaped parts and articles of the present invention may be formed from any of the inventive polymer compositions discussed herein.

[0038] In certain embodiments of the present invention, the shaped parts and articles may be bottles, deli trays, food packaging, containers, medical devices, such as syringes, and eating and drinking utensils such as cups, plates and plasticware.

[0039] In certain embodiments, the shaped parts and articles are shaped by blow molding, injection blow molding, injection stretch molding, thermoforming, shallow-draw thermoforming, deep-draw thermoforming and sheet extrusion. [0040] In an embodiment, the present invention provides a method for producing a shaped article including the steps of (1) melt mixing at least two olefin polymers and a sorbitol compound to form a clarified polyolefin composition and (2) shaping the clarified polyolefin composition to form a shaped article. The clarified polyolefin compositions shaped in the methods of the present invention may be any of the polyolefin compositions of the present invention.

[0041] The melt mixing step may be accomplished through any means or device known to those of skill in the art for melt mixing materials with thermoplastics. The devices may include, but are not limited to a Banbury mixer, Buss co-kneader, Farrel continuous mixer, planetary extruder, single screw extruder, co-rotating multi-screw screw extruder, counter rotating multi-screw screw extruder, co-rotating intermeshing extruder or ring extruder. [0042] In certain embodiments, the shaped articles of the method herein described is shaped by blow molding, injection blow molding, injection stretch molding, thermoforming, shallow-draw thermoforming, deep-draw thermoforming and sheet extrusion. In yet other embodiments, the shaped articles of the method herein described may be bottles, deli trays, food packaging, containers, medical devices, such as syringes, and eating and drinking utensils such as cups, plates and plasticware.

[0043] In other embodiments, the methods of the present invention may also include other steps including, but not limited to, mixing additional additives with the polymer compositions. Many additives are known in the art for modifying polymer compositions to provide particular physical characteristics or effects. The use of appropriate additives is well within the skill of one in the art. Examples of such additives include colored pigments, UV stabilizers, antioxidants, light stabilizers, flame retardants, antistatic agents, biocides, viscosity- breaking agents, impact modifiers, plasticizers, fillers, reinforcing_^, agents, lubricants, mold release agents, blowing agents, nucleating agents and the like. [0044] The above description is intended to be illustrative of the invention, but should not be considered limiting. Persons skilled in the art will recognize that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention will be deemed to include all such modifications that fall within the appended claims and their equivalents.

EXAMPLES

[0045] Sheet samples of the inventive polymers were extruded on a

Reifenhauser Mirex-W sheet extruder equipped with an 80 mm, 33:1 L/D barrier screw with Maddox and pineapple mixing sections. The sheet die has a symmetrical, coathanger manifold. The polishing stack, consisting of 16 inch wide rolls equipped with temperature controls, was run in an upstack configuration.

[0046] The shaped parts and articles were formed with an Illig RDM 54k thermoformer equipped with longitudinal row control for both upper and lower infrared ceramic heaters. The forming mold was polished aluminum and produced (1) drinking cups 1 1 mil thick, 93.1 mm wide and 127 mm deep from

1.9 mm sheet or (2) portion cups 93.1 mm wide and 51 mm deep from 1.9 mm sheet.

Claims

CLAIMSWHAT IS CLAIMED IS:

1. A polymer composition comprising at least two olefin polymers and a sorbitol compound having the following structure:

wherein Rl and R2 are the same or different and selected from C6 to C24 aryls and substituted derivatives thereof, C7 to C30 alkylaryls, and C7 to C30 arylalkyls; and R3 and R4 are the same or different and selected from the group consisting of hydrogen, Cl to ClO alkyls and Cl to ClO substituted alkyls;

the polymer composition exhibiting clarity of C or more, where C = 0.09293x + 28.9, where x is an amount of the sorbitol compound measured in parts per million by weight of olefin polymer and where x is from greater than 0 to about 750.

2. The polymer composition of claim 1, wherein the olefin polymer is a tailored crystallinity resin polymer.

3. The polymer composition of claim 2, wherein the clarity is at least 10% greater than the tailored crystallinity resin polymer absent the sorbitol compound.

4. The polymer composition of claim 1, wherein the clarity is at least 10% greater than the olefin polymers absent the sorbitol compound.

5. The composition of claim 1, wherein the clarity is at least 35% greater than the olefin polymers absent the sorbitol compound.

6. The polymer composition of claim I₃ wherein the polymer composition exhibits a haze at least 10% less than the olefin polymers absent the sorbitol compound.

7. A shaped article comprising the polymer composition of claim 1.

8. The shaped article of claim 7, wherein the shaped article is selected from the group consisting of bottles, deli trays, food packaging, containers, medical devices, cups, plates and plasticware.

9. The shaped article of claim 7, wherein the shaped article is shaped by blow molding, injection blow molding, injection stretch molding, thermoforming, shallow-draw thermoforming, deep-draw thermoforming and sheet extrusion.

10. The polymer composition of claim 1, where the olefin polymers are independently selected from isotactic polypropylene, syndiotactic polypropylene and propylene-alpha olefin copolymers.

11. A polymer composition comprising at least two olefin polymers and a sorbitol compound having the following structure:

wherein Rl and R2 are the same or different and selected from C6 to C24 aryls and substituted derivatives thereof, C7 to C30 alkylaryls, and C7 to C30 arylalkyls; and R3 and R4 are the same or different and selected from the group consisting of hydrogen, Cl to ClO alkyls and Cl to ClO substituted alkyls; the polymer composition exhibiting haze of H or less, where H = -0.0588x + 46.3, where x is an amount of the sorbitol compound measured in parts per million by weight of olefin polymer and where x is from greater than 0 to about 750.

12. The polymer composition of claim 11, wherein the haze is at least 10% less than the olefin polymers absent the sorbitol compound.

13. The polymer composition of claim 11, wherein the polymer composition exhibits a clarity at least 10% greater than the olefin polymers absent the sorbitol compound.

14. A shaped article comprising the polymer composition of claim 11.

15. The shaped article of claim 14, wherein the shaped article is selected from the group consisting of bottles, deli trays, food packaging, containers, medical devices, cups, plates and plasticware.

16. The shaped article of claim 14, wherein the shaped article is shaped by blow molding, injection blow molding, injection stretch molding, thermoforming, shallow-draw thermoforming, deep-draw thermoforming and sheet extrusion.

17. The polymer composition of claim 11, where the olefin polymers are independently selected from isotactic polypropylene, syndiotactic polypropylene and propylene-alpha olefin copolymers.

18. A method for producing a shaped article comprising: contacting at least two olefin polymers and a sorbitol compound to form a clarified polyolefin composition, the sorbitol compound having the following structure:

wherein Rl and R2 are the same or different and selected from C6 to C24 aryls and substituted derivatives thereof, C7 to C30 alkylaryls, and C7 to C30 arylalkyls; and R3 and R4 are the same or different and selected from the group consisting of hydrogen, Cl to ClO alkyls and Cl to ClO substituted alkyls and, the composition exhibiting haze of Z or less, where Z = -0.0588x + 46.3, where x is an amount of the sorbitol compound measured in parts per million by weight of polyolefin polymer and where x is from greater than 0 to about 750; and shaping the clarified polyolefin composition to form a shaped article.

19. The method of claim 18, wherein the olefin polymers are an isotactic polypropylene and a propylene-alpha olefin copolymer.

20. The method of claim 19, wherein the shaped article is selected from the group consisting of bottles, deli trays, food packaging, containers, medical devices, cups, plates and plasticware.

21. The method of claim 19, wherein the shaping step is accomplished by blow molding, injection blow molding, injection stretch molding, thermoforming, shallow-draw thermoforming, deep-draw thermoforming and sheet extrusion.