High melt-strength polyolefin composites and methods for making and using same Number:6,770,697 from the United States Patent and Trademark Office (PTO) owispatent The invention includes a process for preparing an improved melt-strength polyolefin blend by incorporating a polyolefin/clay nanocomposite product. The nanocomposite-modified polyolefin blend is used to form articles through processing operations that involve stretching and/or drawing, such as thermoforming, melt spinning, blow molding and foaming. The addition of the nanocomposite product to the polyolefin blend improves the sag resistance of the polyolefin and broadens the processing window of the operation.<H composites, polyolefin, High, melt, stren, 6770697.html, Patent, pto, 6770697

Title: High melt-strength polyolefin composites and methods for making and using same

Abstract: The invention includes a process for preparing an improved melt-strength polyolefin blend by incorporating a polyolefin/clay nanocomposite product. The nanocomposite-modified polyolefin blend is used to form articles through processing operations that involve stretching and/or drawing, such as thermoforming, melt spinning, blow molding and foaming. The addition of the nanocomposite product to the polyolefin blend improves the sag resistance of the polyolefin and broadens the processing window of the operation.

Patent Number: 6,770,697 Issued on 08/03/2004 to Drewniak, et al.

Inventors: Drewniak; Marta (Carrollton, TX), Zhao; Xia (Garfield, NJ), Srinivasan; Satchit (Carrollton, TX)
Assignee: Solvay Engineered Polymers (Grand Prairie, TX)

Appl. No.: 10/072,536

Filed: February 7, 2002

Current U.S. Class: 524/445 ; 264/349; 264/41; 264/540; 523/351; 524/321; 524/425; 524/538; 525/70

Current International Class: C08L 23/00 (20060101); C08J 3/20 (20060101); C08L 23/04 (20060101); C08J 3/22 (20060101); C08L 23/10 (20060101); C08L 23/08 (20060101); C08L 51/00 (20060101); C08L 51/06 (20060101)

Field of Search: 524/445,321,538,425 523/351 525/70 264/540,349,41

References Cited [Referenced By]

U.S. Patent Documents


4810734	March 1989	Kawasumi et al.
5164460	November 1992	Yano et al.
5552469	September 1996	Beall et al.
5759938	June 1998	Cody et al.
5853886	December 1998	Pinnavaia et al.
5910523	June 1999	Hudson
5973053	October 1999	Usuki et al.
5985971	November 1999	Srinivasan et al.
6036765	March 2000	Farrow et al.
6051643	April 2000	Hasegawa et al.
6103817	August 2000	Usuki et al.
6117541	September 2000	Frisk
6117932	September 2000	Hasegawa et al.
6121361	September 2000	Usuki et al.
6136908	October 2000	Liao et al.
6153680	November 2000	Shah et al.
6225394	May 2001	Lan et al.
6337046	January 2002	Bagrodia et al.
6380295	April 2002	Ross et al.
6451897	September 2002	Niyogi
6462122	October 2002	Qian et al.
6583209	June 2003	Mehta et al.
2002/0161096	October 2002	Loontjens et al.

Foreign Patent Documents


0 807 659	Nov., 1999	EP
1 055 706	Nov., 2000	EP
51075761	Mar., 1976	JP
WO 00/12572	Mar., 2000	WO
WO 01/30864	May., 2001	WO
WO 01/48080	Jul., 2001	WO
WO 02/066553	Aug., 2002	WO

Other References

Kato, M.; Usuki, A.; Okada, A., "Synthesis of Polypropylene Oligomer-Clay Intercalation Compounds," Journal of Applied Polymer Science, vol. 66, pp. 1781-1785, 1997. .
Kawasumi, M.; Hasegawa, N.; Kato, M.; Usuki, A.; and Okada, A., "Preparation and Mechanical Properties of Polypropylene-Clay Hybrids," Macromolecules, vol. 30, No. 20, pp. 6333-6338, Aug. 1997. .
Hasegawa, N.; Kawasumi, M.; Kato, M.; Usuki, A.; Okada, A., "Preparation and Mechanical Properties of Polypropylene-Clay Hybrids Using a Maleic Anhydride-Modified Polypropylene Oligomer," Journal of Applied Polymer Science, vol. 67, pp. 87-92, 1998. .
Lau, H.C.; Bhattacharya, S.N.; Field, G.J., "Melt Strength of Polypropylene: Its Relevance to Thermoforming," Polymer Engineering and Science, vol. 38, No. 11, Nov. 1998. .
Hasegawa, N.; Okamoto, H.; Kawasumi, M.; Kato, M.; Tsukigase, A.; Usuki, A., "Polyolefin-clay hybrids based on modified polyolefins and organophilic clay," Macromolecular Materials and Engineering, vols. 280/281, pp. 76-79, 2000. .
Alexandre, M.; Dubois, P., "Polymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials," Materials Science and Engineering, vol. 28, pp. 1-63, 2000. .
Galgali, O., et al., "A Rheological Study on the Kinetics of Hybrid Formation in Polypropylene Nanocomposites," Macromolecules, vol. 34, pp. 852-858 (2001). .
Kim, K-N, et al., "Mixing Characteristics and Mechanical Properties of Polypropylene-Clay Composites," ANTEC 2000, vol. 3, pp. 3782-3786 (2000). .
Kodgire, P., et al., "PP/Clay Nanocomposites: Effect of Clay Treatment on Morphology and Dynamic Mechanical Properties," J. Applied Science, vol. 81, pp. 1786-1792 (2001). .
Kurokawa, Y., et al., "Structure and Properties of a Montmorillonite/Polypropylene Nanocomposite," J. Materials Science Letters, vol. 16, pp. 1670-1672 (1997). .
Oya, A., "Polypropylene-Clay Nanocomposites," Wiley Series in Polymer Science, John Wiley & Sons, Ltd., Chapter 8, pp. 152-172 (2000). .
Oya, A., et al., "Factors Controlling Mechanical Properties of a Clay Mineral/Polypropylene Nancomposite," J. Materials Science, vol. 35, pp. 1045-1050 (2000). .
Reichert, P., et al., "Poly(propylene)/Organoclay Nanocomposite Formation: Influence of Compatibilizer Functionality and Organoclay Modification," Macromot. Mater. Eng., vol. 275, pp. 8-17 (2000). .
Solomon, M.J., et al., "Rheology of Polypropylene/Clay Hybrid Materials," Macromolecules, vol. 34, pp. 1864-1872 (2001). .
Svoboda, P., et al.: "Structure and Mechanical Properties of Polypropylene and Polystyrene/Organoclay Nanocomposites," Department of Chemical Engineering, The Ohio State University, Jun. 25-27, 2001..

Primary Examiner: Wu; David W.
Assistant Examiner: Hu; Henry S
Attorney, Agent or Firm: Winston & Strawn LLP

Parent Case Text

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of provisional application No. 60/269,386, filed Feb. 20, 2001, the entire contents of which is hereby incorporated herein by express reference thereto.

Claims

What is claimed is:

1. A method of manufacturing an article which comprises: providing a polyolefin/clay nanocomposite masterbatch formed from about 0 to 99 percent by weight of polyolefin, from about 1 to 100 percent by weight of functionalized polyolefin, and from about 10 to 50 percent by weight of an organically modified clay; melt blending from about 1 to 30 percent by weight of the nanocomposite masterbatch and from about 70 to 99 percent by weight of a polyolefin blend comprising a non-functionalized homopolymer or copolymer of propylene, and either (a) copolymer of ethylene and an alpha-olefin with an optional diene: or (b) a styrene copolymer of ethylene or propylene; or a mixture thereof, to form a final polyolefin blend and to ensure sufficient exfoliation of the organically modified clay into the final polyolefin blend so that the melt strength of the final polyolefin blend is greater than the melt strength of the polyolefin blend before modification with the nanocomposite masterbatch; and forming the article using the final polyolefin blend.

2. The method of claim 1, wherein the masterbatch present in an amount from about 2 to 27 percent by weight and which comprises from about 50 to 80 percent by weight of polyolefin, from about 20 to 50 percent by weight of functionalized polyolefin, and from about 20 to 48 percent by weight of organically modified clay, and the polyolefin blend present in an amount from about 73 to 98 percent by weight, are melt blended to form the final polymer blend which has a modified melt strength so that the ratio of the modified melt strength to the melt strength before modification measured at 220.degree. C. is at least about 1.5 but no more than about 15.

3. The method of claim 1, wherein the masterbatch present in an amount from about 3 to 25 percent by weight and which comprises from about 60 to 70 percent by weight of polyolefin, from about 30 to 40 percent by weight of functionalized polyolefin, and from about 30 to 45 percent by weight of organically modified clay, and the polyolefin blend present in an amount from about 75 to 97 percent by weight are melt blended to form the final polyolefin blend which has a modified melt strength so that the ratio of the modified melt strength to the melt strength before modification measured at 220.degree. C. is at least about 1.6 but no more than about 14 and the final polyolefin blend has a shear viscosity that is at least about 5 times that of the shear viscosity of the polymer blend measured under the same conditions but without the organically modified clay.

4. A method of manufacturing an article which comprises a polyolefin/clay nanocomposite blend comprising: combining from about 50 to 98 percent by weight of a polyolefin comprising a non-functionalized homopolymer or copolymer of propylene, and either (a) copolymer of ethylene and an alpha-olefin with an optional diene; or (b) a styrene copolymer of ethylene or propylene; or a mixture thereof, from about 1 to 20 percent by weight of a functionalized polyolefin, and an organically modified clay in an amount sufficient to provide a modified melt strength, so that a ratio of the modified melt strength of the final polyolefin blend to the melt strength of the polyolefin blend before modification with the organically modified clay measured at 220.degree. C. is at least about 1.5 but no more than about 15; and forming the article using the polyolefin/clay nanocomposite blend.

5. The method of claim 4, wherein the polyolefin blend in the article comprises from about 70 to 95 percent by weight of polyolefin, from about 1 to 10 percent by weight of functionalized polyolefin, and from about 4 to 20 percent by weight of organically modified clay to provide a ratio of the melt strength of the modified blend to the melt strength of the blend before modification measured at 220.degree. C. of at least about 1.6 but no more than about 14.

6. The method of claim 4, wherein the polyolefin blend in the article comprises from about 85 to 92 percent by weight of polyolefin, from about 2 to 5 percent by weight of functionalized polyolefin, and from about 6 to 10 percent by weight of organically modified clay to provide a ratio of the melt strength of the modified blend to the melt strength of the blend before modification measured at 220.degree. C. of at least about 1.6 but no more than about 14.

7. The method of claim 1 wherein the forming comprises at least one of thermoforming, extrusion, melt spinning, blow molding or foam processing.

8. An article formed from a final polyolefin blend containing a polyolefin/clay nanocomposite masterbatch comprising: from about 0 to 99 percent by weight of polyolefin from about 1 to 100 percent by weight of a functionalized polyolefin, and from about 10 to 50 percent by weight of an organically modified clay, and any optional additive components, wherein the final polyolefin blend comprises from about 1 to 30 percent by weight of the nanocomposite masterbatch and about 70 to 99 percent by weight of a polyolefin blend comprising a non-functionalized homopolymer or copolymer of propylene, and either (a) copolymer of ethylene and an alpha-olefin with an optional diene; or (b) a styrene copolymer of ethylene or propylene; or a mixture thereof, and wherein the organoclay is sufficiently exfoliated into the polyolefin blend to provide the final polyolefin blend with a modified melt strength so that the ratio of the modified melt strength of the final polyolefin blend to the melt strength of the polyolefin blend before modification with the organically modified clay measured at 220.degree. C. is at least about 1.5 but no more than about 15.

9. The article of claim 8, wherein the masterbatch is present in an amount from about 2 to 27 percent by weight and comprises from about 50 to 80 percent by weight of polyolefin, from about 20 to 50 percent by weight of functionalized polyolefin, and from about 20 to 48 percent by weight of organically modified clay, and the polyolefin blend is present in an amount from about 73 to 98 percent by weight, to form the final polymer blend which has a modified melt strength so that the ratio of the modified melt strength to the melt strength before modification measured at 220.degree. C. is at least about 1.5 but no more than about 15.

10. The article of claim 8, wherein the masterbatch is present in an amount from about 3 to 25 percent by weight and comprises from about 60 to 70 percent by weight of polyolefin, from about 30 to 40 percent by weight of functionalized polyolefin, and from about 30 to 45 percent by weight of organically modified clay, and the polyolefin blend is present in an amount from about 75 to 97 percent by weight, to form the final polyolefin blend which has a modified melt strength so that the ratio of the modified melt strength to the melt strength before modification measured at 220.degree. C. is at least about 1.6 but no more than about 14 and the final polyolefin blend has a shear viscosity that is at least about 5 times that of the shear viscosity of the polymer blend measured under the same conditions but without the organically modified clay.

11. The article of claim 8, wherein the functionalized polyolefin comprises a homopolymer or copolymer of propylene, a homopolymer or copolymer of ethylene, or a mixture thereof, wherein a functional monomer with a pendant reactive polar group is grafted onto the polyolefin.

12. The article of claim 8, wherein the nanocomposite-modified polyolefin blend further comprises one or more optional additive components including nucleating agents, fillers, plasticizers, impact modifiers, colorants, mold release agents, lubricants, antistatic agents, pigments, fire retardants, and ultraviolet stabilizers, or mixtures thereof, and the alpha-olefin comprises octene.

13. The article of claim 8, wherein the addition of the nanocomposite masterbatch provides a range of temperatures for forming the article that is at least about 10.degree. C. greater than without the inclusion of a sufficient amount of the clay nanocomposite.

14. An automotive component, a building material, a packaging material, an electrical material, or a nonwoven fabric or fiber comprising the article of claim 8.

15. An article formed from a modified polyolefin blend comprising from about 50 to 98 percent by weight of polyolefin comprising a non-functionalized homopolymer or copolymer of propylene, and either (a) copolymer of ethylene and an alpha-olefin with an optional diene; or (b) a styrene copolymer of ethylene or propylene; or a mixture thereof, from about 1 to 20 percent by weight of functionalized polyolefin, and from about 1 to 30 percent by weight of organically modified clay that is sufficiently dispersed in the polyolefin and functionalized polyolefin to provide a modified melt strength of the final polyolefin blend that is greater than the melt strength of the polyolefin blend before modification with the or organically modified clay.

16. The article of claim 15, wherein the polyolefin blend comprises from about 70 to 95 percent by weight of polyolefin, from about 1 to 10 percent by weight of functionalized polyolefin, and from about 4 to 20 percent by weight of organically modified clay.

17. The article of claim 15, wherein the polyolefin blend comprises about 85 to 92 percent by weight of polyolefin, from about 2 to 5 percent by weight of functionalized polyolefin, and from about 6 to 10 percent by weight of organically modified clay.

18. The article of claim 15, wherein the polyolefin blend has a ratio of the melt strength of the modified blend to the melt strength of the blend before modification measured at 220.degree. C. of at least about 1.5 but no more than about 15.

19. The article of claim 15, wherein the polyolefin blend has a ratio of the melt strength of the modified blend to the melt strength of the blend before modification measured at 220.degree. C. of at least about 1.6 but no more than about 14.

20. The article of claim 15, wherein the organically modified clay comprises a reaction product of at least one organoclay and at least one swelling agent.

21. The article of claim 20, wherein the swelling agent comprises at least one of cationic surfactants; amphoteric surface active agents; derivatives of aliphatic, aromatic or arylaliphatic amines, phosphines and sulfides; organosilane compounds; protonated amino acids and salts thereof; and combinations thereof.

22. A method of manufacturing an article which comprises: providing a polyolefin/clay nanocomposite masterbatch formed from about 0 to 99 percent by weight of polyolefin, from about 1 to 100 percent by weight of functionalized polyolefin, and from about 10 to 50 percent by weight of an organically modified clay that comprises a smectite clay that has been ion-exchanged and intercalated with a quaternary ammonium compound of the formula: (R).sub.n (CH.sub.3).sub.m N.sup.+ Cl.sup.-, where R represents a hydrogenated tallow moiety, n is 1 to 4, m is 0 to 3 with the proviso that n+m=4; melt blending from about 1 to 30 percent by weight of the nanocomposite masterbatch and from about 70 to 99 percent by weight of a polyolefin blend comprising a functionalized homopolymer or copolymer of propylene, and either (a) copolymer of ethylene and an alpha-olefin with an optional diene; or (b) a styrene copolymer of ethylene or propylene; or a mixture thereof, to form a final polyolefin blend and to ensure sufficient exfoliation of the organically modified clay into the final polyolefin blend so that the melt strength of the final polyolefin blend is greater than the melt strength of the polyolefin blend before modification with the nanocomposite masterbatch; and forming the article using the final polyolefin blend.

Description

FIELD OF THE INVENTION

This invention relates to blends including polymer/clay nanocomposite materials containing a polyolefin polymer, a functionalized or grafted polymer, and an organically modified clay material therein, as well as articles made therefrom and processes for stretching and/or drawing such high melt-strength blends.

BACKGROUND OF THE INVENTION

Amorphous polymers, such as acrylonitrile-butadiene-styrene (ABS) and polystyrene, are typically used in industrial processes where stretching and/or drawing of the material is required (i.e., thermoforming, melt spinning, blow molding and foaming.) Polyolefins, including polypropylene (PP) and polyethylene (PE), can potentially replace ABS or polystyrene blends in order to manufacture articles, such as automotive parts, electronic components, fibers, household equipment, containers and bottles, packaging material, and construction equipment. The advantages of polyolefins over ABS or polystyrene blends are improved, long-term ultraviolet and heat resistance, reduced fogging, better recyclability, and lower raw material costs.

To be useful in such industrial processes, the polymer material must exhibit sufficient elastic behavior to resist sagging, but remain viscous enough to flow into the mold under stress. One advantage of ABS and polystyrene is that their rubbery elastic state exists over a wider temperature range compared to that of the semi-crystalline polyolefins. Due to their sharp melting point, polyolefins such as polypropylene pass through the viscoelastic plateau very rapidly on heating, resulting in poor melt strength and sag. In thermoforming, for example, deformations in the thermoformed sheet caused by sagging may in turn lead to irregularities in articles made by the process, such as unacceptable variations in weight and thickness, which may even result in tearing of the sheet.

To address the problems associated with thermoforming polyolefins, Japanese Patent Publication No. 51-75761, published in June, 1976, discloses a polypropylene sheet laminated onto a sagging-free sheet of a resin different from polypropylene in attempts to solve the problem of sagging; however, this may be unsuitable for general use since it raises problems as to lamination means, selection of resins used and the like. WO 00/12572 details a long-chain branched polypropylene with high melt strength and good processability formed by contacting propylene monomers in a reactor with an inert hydrocarbon solvent and one or more single site catalysts capable of producing stereospecific propylene at 40-120.degree. C. However, the use of this high-melt-strength polypropylene (HMS-PP) gives only limited improvements, since it affects only one component of the polyolefin compound (i.e., polypropylene). It is currently recognized, for example, in Lau et al., Polymer Eng. Sci. 38 (1998), page 1915, that for a material to have good thermoformability, it must exhibit high melt strength.

Nancomposites are a new class of composites that are particle-filled polymers for which at least one dimension of the dispersed particle is in the nanometer range (10.sup.-9 meter). Because of the size of the dispersed particles, the nanocomposites exhibit modified mechanical, thermal and optical properties as compared to pure polymers or conventional composites.

The most commonly used and investigated types of polymer nanocomposites are those based on clays and layered silicates. The nanocomposites are obtained by the intercalation or penetration of the polymer (or a monomer subsequently polymerized) inside the galleries of layered clay material and the subsequent exfoliation or dispersion of the intercalate throughout the final polymer blend. To be more compatible with organic polymers, the layered clay material is usually modified by an ion exchange process with cationic surfactants, such as alkylammonium or alkylphosphonium ions.

The great difficulty when using clay in a polyolefin matrix is the opposing nature of the materials. The polymeric portion of the matrix is usually a nonpolar organic material, whereas the clay is a much more polar inorganic material. This incompatibility hinders the direct intercalation or exfoliation of the clay in the final polymer blend. See, for example, Alexandre et al., Mater. Sci. Eng. Rpts. 28 (2000), page 1. To introduce favorable interactions between the polymer and the layered clay material, a functionalized polyolefin such as a maleic-anhydride-modified polypropylene must be added to the composite. This method has been reported in Kawasumi et al., Macromolecules 30 (1997), page 6333.

Increased interest in developing a polymer/clay nanocomposite to improve the stiffness/impact balance of polyolefins has been reported. See, for example, Hasegawa et al., J. App. Pol. Sci. 67 (1998), page 87. No applications have been commercialized at the present time, however, presumably as a result of the lack of direct intercalation or exfoliation of the organically modified clay in the polyolefin matrix that renders such materials difficult to prepare.

U.S. Pat. No. 5,552,469 describes the preparation of intercalates derived from certain clays and water soluble polymers, such as polyvinyl alcohol and polyacrylic acid. Although the specification lists a wide range of resins including polyesters and rubbers that can be used in blends with these intercalates, there is no teaching of how to make such blends. Further, the water soluble polymer/clay mixture is taught to be incompatible with hydrophobic polyolefins (i.e., all blends containing polypropylene).

U.S. Pat. No. 5,910,523 describes a process wherein the clay layer is functionalized with an aminosilane and then grafted to a carboxylated or maleated polyolefin through an amine-carboxyl reaction. The use of xylene solvent in this process, however, makes the method cumbersome, environmentally unfriendly, and expensive to commercialize.

U.S. Pat. No. 6,121,361 describes a process wherein a composite clay material is formed of a clay mineral having an interlayer section by first bonding a swelling agent such as an onium ion having 6 or more carbon atoms to the clay mineral via an ionic bond for expanding the interlayer section and rendering the interlayer section compatible with an organic molecule, and then introducing a polymer having a polar group in a main chain and/or a side chain. Degradation of the mechanical properties of the composites, however, can occur whenever excess amounts of the swelling agent precipitates out of solution.

U.S. Pat. No. 6,153,680 discloses a composition useful for automotive interior parts which includes a blend of polypropylene, an uncrosslinked ethylene copolymer, an ionomer, a crosslinking agent and a silicone elastomer. Clay fillers in the nanometer-size range are listed as optional fillers, but there is no teaching that the use of such fillers improves the mechanical properties of the blend and no teaching of the details of any such filled-blends.

Moreover, none of the prior art references described above teaches the surprising discovery of the present invention, i.e., that the addition of polymer/clay nanocomposites to such polyolefins improves the melt strength of the final polymer blend. Thus, there remains a need to develop processes using polyolefins in thermoforming, melt spinning, blow molding, and foaming, and the improved articles resulting from the processes of the invention.

SUMMARY OF THE INVENTION

The invention encompasses methods of manufacturing an article by providing a polyolefin/clay nanocomposite masterbatch formed from about 0 to 99 percent by weight of polyolefin, from about 1 to 100 percent by weight of functionalized polyolefin, and from about 10 to 50 percent by weight based on the total masterbatch of an organically modified clay, melt blending from about 1 to 30 percent by weight of the nanocomposite masterbatch and from about 70 to 99 percent by weight of a polyolefin blend to form a final polyolefin blend and to ensure sufficient exfoliation of the organically modified clay into the final polyolefin blend so that the melt strength of the final polyolefin blend is greater than the melt strength of the polyolefin blend before modification with the nanocomposite masterbatch, and forming the article using the final polyolefin blend.

In one embodiment, the masterbatch present in an amount from about 2 to 27 percent by weight and which includes from about 50 to 80 percent by weight of polyolefin, from about 20 to 50 percent by weight of functionalized polyolefin, and from about 20 to 48 percent by weight of organically modified clay, and the polyolefin blend present in an amount from about 73 to 98 percent by weight, are melt blended to form the final polymer blend which has a modified melt strength so that the ratio of the modified melt strength to the melt strength before modification measured at 220.degree. C. is at least about 1.5 but no more than about 15. In a preferred embodiment, the masterbatch present in an amount from about 3 to 25 percent by weight and which includes from about 60 to 70 percent by weight of polyolefin, from about 30 to 40 percent by weight of functionalized polyolefin, and from about 30 to 45 percent by weight of organically modified clay wherein the amounts total to 100 percent, and the polyolefin blend present in an amount from about 75 to 97 percent by weight are melt blended to form the final polyolefin blend which has a modified melt strength so that the ratio of the modified melt strength to the melt strength before modification measured at 220.degree. C. is at least about 1.6 but no more than about 14 and the final polyolefin blend has a shear viscosity that is at least about 5 times that of the shear viscosity of the polymer blend measured under the same conditions but without the organically modified clay.

The invention also encompasses methods of manufacturing an article which includes a polyolefin/clay nanocomposite blend by forming a final polymer blend. This method includes combining from about 50 to 98 percent by weight of a polyolefin, from about 1 to 20 percent by weight of a functionalized polyolefin, and an organically modified clay in an amount sufficient to provide a modified melt strength, so that a ratio of the modified melt strength to the melt strength before modification measured at 220.degree. C. is at least about 1.5 but no more than about 15, and forming the article using the polyolefin/clay nanocomposite blend.

In one embodiment, the polyolefin blend in the article includes from about 70 to 95 percent by weight of polyolefin, from about 1 to 10 percent by weight of functionalized polyolefin, and from about 4 to 20 percent by weight of organically modified clay to provide a ratio of the melt strength of the modified blend to the melt strength of the blend before modification measured at 220.degree. C. of at least about 1.6 but no more than about 14. In a preferred embodiment, the polyolefin blend in the article includes from about 85 to 92 percent by weight of polyolefin, from about 2 to 5 percent by weight of functionalized polyolefin, and from about 6 to 10 percent by weight of organically modified clay, wherein the total amoutns to 100%, to provide a ratio of the melt strength of the modified blend to the melt strength of the blend before modification measured at 220.degree. C. of at least about 1.6 but no more than about 14.

In either method of forming articles, the forming can include at least one of thermoforming, extrusion, melt spinning, blow molding or foam processing.

The invention also encompasses articles formed from a final polyolefin blend containing a polyolefin/clay nanocomposite masterbatch including from about 0 to 99 percent by weight of polyolefin, from about 1 to 100 percent by weight of a functionalized polyolefin, and from about 10 to 50 percent by weight based on the final polyolefin blend of an organically modified clay, and any optional components, wherein the final polyolefin blend includes from about 1 to 30 percent by weight of the nanocomposite masterbatch and about 70 to 99 percent by weight of a polyolefin blend, and wherein the organoclay is sufficiently exfoliated into the polyolefin blend to provide the final polyolefin blend with a modified melt strength so that the ratio of the modified melt strength to the melt strength before modification measured at 220.degree. C. is at least about 1.5 but no more than about 15.

In one embodiment, the masterbatch is present in an amount from about 2 to 27 percent by weight and includes from about 50 to 80 percent by weight of polyolefin, from about 20 to 50 percent by weight of functionalized polyolefin, and from about 20 to 48 percent by weight of organically modified clay, and the polyolefin blend is present in an amount from about 73 to 98 percent by weight, to form the final polymer blend which has a modified melt strength so that the ratio of the modified melt strength to the melt strength before modification measured at 220.degree. C. is at least about 1.5 but no more than about 15. In a preferred embodiment, the masterbatch is present in an amount from about 3 to 25 percent by weight and includes from about 60 to 70 percent by weight of polyolefin, from about 30 to 40 percent by weight of functionalized polyolefin, and from about 30 to 45 percent by weight of organically modified clay, and the polyolefin blend is present in an amount from about 75 to 97 percent by weight, to form the final polyolefin blend which has a modified melt strength so that the ratio of the modified melt strength to the melt strength before modification measured at 220.degree. C. is at least about 1.6 but no more than about 14 and the final polyolefin blend has a shear viscosity that is at least about 5 times that of the shear viscosity of the polymer blend measured under the same conditions but without the organically modified clay.

In one embodiment, the functionalized polyolefin includes a homopolymer, copolymer, and/or mixture of ethylene and/or propylene, wherein a functional monomer with a pendant reactive polar group is grafted onto the polyolefin. In another alternative or additional embodiment, the nanocomposite-modified polyolefin blend further includes one or more optional additive components including nucleating agents, fillers, plasticizers, impact modifiers, colorants, mold release agents, lubricants, antistatic agents, pigments, fire retardants, and ultraviolet stabilizers, or mixtures thereof. The addition of the nanocomposite masterbatch provides a range of temperatures for forming the article that is at least about 10.degree. C. greater than without the inclusion of a sufficient amount of the clay nanocomposite.

The invention also encompasses articles formed from a modified polyolefin blend including from about 50 to 98 percent by weight of polyolefin, from about 1 to 20 percent by weight of functionalized polyolefin, and from about 1 to 30 percent by weight of organically modified clay that is sufficiently dispersed in the polyolefin and functionalized polyolefin to provide a modified melt strength that is greater than the melt strength of the blend before modification.

In one embodiment, the polyolefin blend includes from about 70 to 95 percent by weight of polyolefin, from about 1 to 10 percent by weight of functionalized polyolefin, and from about 4 to 20 percent by weight of organically modified clay. In a preferred embodiment, the polyolefin blend includes about 85 to 92 percent by weight of polyolefin, from about 2 to 5 percent by weight of functionalized polyolefin, and from about 6 to 10 percent by weight of organically modified clay. In one embodiment, the polyolefin blend has a ratio of the melt strength of the modified blend to the melt strength of the blend before modification measured at 220.degree. C. of at least about 1.5 but no more than about 15. In a preferred embodiment, the polyolefin blend has a ratio of the melt strength of the modified blend to the melt strength of the blend before modification measured at 220.degree. C. of at least about 1.6 but no more than about 14.

The organically modified clay preferably includes a reaction product of at least one organoclay and at least one swelling agent. The swelling agent can include at least one of cationic surfactants; amphoteric surface active agents; derivatives of aliphatic, aromatic or arylaliphatic amines, phosphines and sulfides; organosilane compounds; protonated amino acids and salts thereof; and combinations thereof.

The invention also encompasses an automotive component, a building material, a packaging material, an electrical material, or a nonwoven fabric or fiber formed from the articles described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention can be ascertained from the following detailed description that is provided in connection with the drawing(s) described below:

FIG. 1 is a graphical depiction of viscosity versus shear rate for a masterbatch of the current invention and for controls;

FIG. 2 is a graphical depiction of melt strength of the polyolefin/clay nanocomposite masterbatch over a range of processing temperatures as compared to controls;

FIG. 3a is a photograph of sheets of material formed from Examples 6-8 and of Controls 7-8 after a sag test;

FIG. 3b is a photograph of a frontal view of Control 8 after a sag test, showing the thinning and tearing thereof;

FIG. 4 is a graphical depiction of melt strength determination using Example 5; and

FIG. 5 is a graphical depiction of the tensile force of examples and controls as a function of elongation ratio, .lambda., for the rotating rollers on the Gottfert.TM. Rheotens Melt Tension instrument Model 10.1. The elongation ratio is defined as the ratio of the wheel velocity of the instrument's rotating rollers to the initial wheel velocity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It has now been discovered that melt strength in polyolefin/functionalized polyolefin final blends can be improved by including clay nanocomposites therein. The current invention involves melt-strength polyolefin blends containing a polyolefin/clay nanocomposite, methods of using such blends for manufacturing articles through conventional industrial processes, such as thermoforming, extrusion, melt spinning, blow molding or foaming, that involve stretching and/or drawing, and the resultant articles. The thermoforming process, for example, requires that a material be pre-heated without sagging under the force of gravity and then stretched over a thermoforming mold without tearing.

Thus, the present invention can provide one or more of the following advantages: improved melt strength of polyolefin blends; increased sag resistance of polyolefin blends; maximized range of operating temperatures during processing; ability to thermoform polyolefin sheets with less variation in weight and thickness; and minimized polymer sheet deformation and distortion.

In each of the processes noted herein, the melt strength of the final polymer tends to be critical to its success, since the melted and/or softened polymer must retain its intended shape while being handled and/or cooled. Melt strength is the characteristic that keeps a polymeric material from exhibiting tearing or excessive deformation when subjected to stress while in the melted state. The melt strength of a polymer is determined by a Gottfert.TM. Rheotens Melt Tension instrument Model 10.1 which measures the force in centi-Newtons (cN) required to pull a polymer melt strand from a capillary die at constant acceleration.

In addition to increased melt strength, the processing window of the heating step in these commercial processes must include a broad enough range of temperatures to ensure the practicality of the use of the composite in industrial applications. The processing window is defined as the range of temperatures at which a material has a characteristic that allows for a given process to be performed. Pure polypropylene, for example, can only be thermoformed in the range of temperatures between 143.degree.-166.degree. C., representing a very narrow processing window. On the other hand, ABS has a wider processing temperature window of 127.degree. C.-182.degree. C.

It has now been discovered that the polyolefin/clay nanocomposites of the invention surprisingly exhibit very high viscosity under low shear rates. Shear rate is defined as the rate at which a material is undergoing deformation, or movement, in response to a shear stress, which is the force applied to a material to cause flow. Shear rate is expressed in reciprocal seconds (l/s). A low shear rate is less than or equal to 10 l/s, while a high shear rate is greater than 900 l/s. This high viscosity under low shear rates translates into a high melt strength for the blend as a whole. The improved melt strength, in turn, helps increase the range of acceptable temperatures available for many beneficial industrial applications. It should be understood that masterbatches of the present invention have a higher melt strength than the final polymer blends, and that dilution into a final polymer blend reduces the higher melt strength to a melt strength that is still significantly higher than conventional polymer blends lacking the polyolefin/functionalized polyolefin/clay nanocomposite structure of the invention.

The incorporation of a polyolefin/clay nanocomposite into the final polymer blend is important in any manufacturing process that requires stretching and/or drawing according to the invention. Any suitable method of incorporation can be used. The preferred method of incorporation can either be: by adding a masterbatch of polyolefin/clay nanocomposite to a final polymer blend; or by exfoliating the organically modified clay directly into a polymer matrix containing, for example, an impact-modified polypropylene; or both. Both the masterbatch and the directly compounded polyolefin blend contain a polyolefin; a polyolefin functionalized with a hydrophilic moiety; and an organically modified clay (also referred to herein as "organoclays").

Any suitable polyolefin can be used, particularly those having narrow processing windows or low melt strength. Preferably, the polyolefin includes C.sub.2 to C.sub.20 polyolefins. The more preferred polyolefin of the polyolefin/clay nanocomposite in the present invention includes be a homopolymer or copolymer of ethylene; a homopolymer or copolymer of propylene; a copolymer of ethylene and an alpha-olefin; a terpolymer of ethylene, an alpha-olefin and a diene; a styrene copolymer of ethylene or propylene; or mixtures thereof.

Similarly, any suitable functionalized polyolefin can be used as the functionalized polyolefin component of the invention, including those polyolefins described above but including functionalization (e.g., grafting). Preferably, the functionalized polyolefin can also be a homopolymer, copolymer, and/or mixture of ethylene and/or propylene. The functionalized polyolefin preferably contains one or more types of polar moieties that are either grafted onto the polyolefin base or copolymerized with the polyolefin. Preferably, the one or more polar moieties are grafted onto the polyolefin base as a pendant reactive polar group. Any unsaturated carboxylic acid monomer that provides a polar moiety can be used in the manufacture of functionalized polyolefins of this invention. Representative unsaturated organic compounds that contain at least one carbonyl group include the ethylenically unsaturated carboxylic acids, anhydrides, esters, and their salts. Representative compounds include maleic, fumaric, acrylic, methacrylic, itaconic, crotonic, alpha-methyl crotonic, cinnamic, and the like, acids and their anhydride, ester and salt derivatives, if any. Additional unsaturated organic compounds and other compounds available to those of ordinary skill in the art may also be used, as well as combinations of functionalizing compounds, such as methacrylate-vinyl acetate mixtures or acrylic acid/methacrylic acid mixtures. Preferably, maleic anhydride, acrylic acid, methacrylic acid, or combinations thereof are used. More preferably, maleic anhydride is used.

An unsaturated hydrophilic organic compound can be grafted to the base polymer by any technique known to one of ordinary skill in the art, such as those taught in U.S. Pat. No. 3,236,917 and U.S. Pat. No. 5,194,509, both of which are incorporated herein by express reference thereto. For example, in the '917 patent, the base polymer is introduced into a two-roll mixer and mixed at a temperature of 60.degree. C. The unsaturated organic compound is then added along with a free radical initiator, such as benzoyl peroxide, and the components are mixed at 30.degree. C. until the grafting is completed. In the '509 patent, the procedure is similar except that the reaction temperature is higher, e.g., 210.degree. to 300.degree. C., and a free radical initiator is not used. Such functionalized polyolefins are also available from Crompton Corporation (formerly Uniroyal Chemical Company) of Greenwich, Conn. under the trademark Polybond and from Eastman Chemical Company of Kingsport, Tenn. under the trademark Epolene.

The organically modified clays of the present invention may be prepared by any available methods, preferably from any suitable, swellable, layered clay mineral including natural or synthetic phyllosilicates, particularly smectite clays such as montmorillonite, nontronite, beidellite, hectorite, saponite, sauconite, vermiculite and the like, as well as magadiite, kenyaite, stevensite, halloysite, aluminate oxides, hydrotalcite, and the like, and combinations thereof. Typically, the swellable clays have a negative charge on the surface, preferably of at least about 20 milliequivalents, preferably at least about 50 milliequivalents, and more preferably from about 50 to 150 milliequivalents, per 100 grams of the layered clay material.

Certain clays can be treated with organic molecules that are capable of being absorbed within the clay material, e.g., between layers of clay, thereby expanding (swelling) the volume of the clay. For example, the space between adjacent layers can be expanded from about 0.4 nanometers (nm) or less to at least about 1 nanometer or even more. Although the clay can have any cation exchange capacity, the clay must still be able to properly expand. Preferably, the cation exchange capacity of the clay is at least about 20 milliequivalents/100 grams since organic molecules are not exchanged as well at lower cation exchange capacities and will have reduced expansion of the clay. Preferably, the cation exchange capacity is no more than about 200 milliequivalents/100 grams. If the exchange capacity exceeds about 200 milliequivalents/100 grams, the bonding strength between the clay mineral layers becomes fairly strong and it becomes more difficult to expand the clay.

"Organically modified clay," as used herein, refers to a clay that has been modified by the addition of a swelling agent. Any organic molecules suitable as swelling agents may be used. Preferably, the swelling agents include cationic surfactants, for example including ammonium, phosphonium or sulfonium salts; amphoteric surface active agents; derivatives of aliphatic, aromatic or arylaliphatic amines, phosphines and sulfides; and organosilane compounds; and combinations thereof. Other suitable swelling agents include protonated amino acids and salts thereof containing 2-30 carbon atoms, such as 12-aminododecanoic acid, epsilon-caprolactam, and like materials, as well as any combinations thereof. This process of swelling the clay, particularly layered clay, known as intercalation, results in the development of intercalates (stacks) which are more organophilic and which can be more readily exfoliated (dispersed) during admixture with a polymer to form a polymer/clay nanocomposite. These clay intercalates are often about 1 nanometer thick, but about 100 to 1,000 nanometers across. This high aspect ratio, and the resulting high surface area, helps provides high reinforcement efficiency at low loading levels. In one embodiment, the clays of the invention are preferably at least substantially exfoliated (dispersed) throughout the polyolefin/functionalized polyolefin polymer matrix, and more preferably are completely exfoliated throughout the polymer matrix.

The clay mineral or other layered silicate can be organically modified by any technique known to one of ordinary skill in the art, such as those taught in U.S. Pat. Nos. 5,728,764, 4,810,734 and 3,671,190, each of which is incorporated herein by express reference thereto. However, it is not intended that these methods be limited to any specific process or procedure. Organoclays are also available commercially from Nanocor, Inc. of Arlington Heights, Ill. under the trademark Nanomer and from Southern Clay Products, Inc. of Gonzales, Tex. under the trademark Closite.

However, treating the hydrophilic clay to increase its organophilic aspect tends to be insufficient to generate a reaction with nonpolar polyolefins. Most reports of increased mechanical properties using nanocomposites have been obtained by utilizing the more reactive polyamides in the polymer matrix. In order to incorporate the use of polyolefins, the polarity of the polymer matrix is preferably enhanced by adding a functional monomer with a pendant reactive polar group to a small percentage of the polyolefin blend, as described above. The functionalized monomer, such as a maleic anhydride group, reduces interfacial tension and partly acts as a nucleating agent for the main polyolefin component of the nanocomposite. The reactive polar group on the functionalized polyolefin also interacts with the highly polar organoclays, serving to increase the distance between the clay layers and increasing the potential of exfoliation into the polyolefin/clay nanocomposite, as well as the final polymer blend.

The polyolefin/clay nanocomposite may be incorporated into the final polymer blend in a two-step mixing process by adding a masterbatch of polyolefin/clay nanocomposite to the final polymer blend. The polymeric portion of the nanocomposite masterbatch typically includes from about 0 to 99 wt % of polyolefin and from about 1 to 100 wt % of functionalized polyolefin, preferably from about 50 to 80 wt % of polyolefin and from about 20 to 50 wt % of functionalized polyolefin, and more preferably from about 60 to 70 wt % of polyolefin and from about 30 to 40 wt % of functionalized polyolefin. The amount of layered clay material may vary widely but generally can be about 10 to 50 wt % of the total mixture of polyolefin blend and nanocomposite clay (the "nanocomposite mixture"), preferably from about 20 to 48 wt % of the total nanocomposite mixture, and more preferably from about 30 to 45 wt % of the total nanocomposite mixture. Preferably, the clay material delaminates to form layers or stacks of layers that are substantially homogeneously dispersed in the polymer matrix. In general, at least about 50 wt %, preferably at least about 70 wt %, more preferably at least about 80 wt % of the clay material delaminates. In one more preferred embodiment, at least about 90 wt % of the clay delaminates.

The final polymer blend can include, for example, from about 1 to 30 percent by weight of the nanocomposite masterbatch and from about 70 to 99 percent by weight of a polyolefin blend. In another embodiment, the final polymer blend can include from about 2 to 27 percent by weight of the masterbatch and from about 73 to 98 percent by weight of a polyolefin blend. In yet another embodiment, the final polymer blend can include from about 3 to 25 percent by weight of the masterbatch and from about 75 to 97 of a polyolefin blend.

Such a masterbatch has higher shear viscosity at low shear rates than straight polypropylene or conventionally filled polypropylene. The masterbatch shear viscosity at 10 l/s, a low shear test, and at 60.degree. C. over the melting point of the polymer (i.e., typical peak melting temperature of polypropylene is approximately 165.degree. C.) should be a factor of at least about 5, preferably a factor of at least about 8, over the viscosity of the polymer at the same conditions without the addition of the layered clay material. For example, if the polymer without the clay has a viscosity at 230.degree. C. of about 300 Pascal seconds (Pa.multidot.s) at 10 l/s, the viscosity of the masterbatch should be at least about 1500 (Pa.multidot.s). The absolute value will, of course, depend on the viscosity of the base polymer.

Any available technique for using a polymer masterbatch to form a final polymer blend that is available to those of ordinary skill in the art may be used according to the invention. The final polymer blend can contain, for example, from about 1 to 10 weight percent of the clay nanocomposite, i.e., after the masterbatch has been formed into the final polymer blend.

In another embodiment, the individual components of the polyolefin/clay nanocomposite can be added directly to the final polymer blend in one step, provided that significant clay exfoliation is achieved in the compound. Surprisingly, the interlayer section of the clay mineral in some cases is sufficiently expanded in a one-stage mixing. As a result, an increase in low shear viscosity is observed, as well as improvement in melt strength and sagging resistance, from simply combining the polyolefin component, functionalized polyolefin component, and clay nanocomposite. The final polymer blend containing the polyolefin/clay nanocomposite includes from about 50 to 98 percent by weight (wt %) of polyolefin, from about 1 to 20 wt % of functionalized polyolefin, and from about 1 to 30 wt % of organically modified clay. In one embodiment, the final polymer blend containing the polyolefin/clay nanocomposite includes from about 70 to 95 wt % of polyolefin, from about 1 to 10 wt % of functionalized polyolefin, and from about 4 to 20 wt % of organically modified clay. In another embodiment, the final polymer blend containing the polyolefin/clay nanocomposite includes from about 85 to 92 wt % of polyolefin, from about 2 to 5 wt % of functionalized polyolefin, and from about 6 to 10 wt % of organically modified clay.

The final polymer blend may include various optional components which are additives commonly employed with polymers. Such optional components include nucleating agents, thermal stabilizers, mineral fillers, plasticizers, impact modifiers, colorants, mold release agents, lubricants, antistatic agents, pigments, fire retardants, conductive fillers, ultraviolet stabilizers and the like. These can be added for any of a variety of reasons, as desired and as readily determined by those of ordinary skill in the art, e.g., as processing aids, to improve or obtain desired characteristics, for cost considerations, or the like.

Preferred mineral fillers include, but are not limited to, talc, ground calcium carbonate, precipitated calcium carbonate, precipitated silica, precipitated silicates, precipitated calcium silicates, pyrogenic silica, hydrated aluminum silicate, calcined aluminosilicate, clays, mica, and wollastonite, and combinations thereof.

Foaming agents can be included in the mixture to produce foamed articles. The expanding medium, or foaming agent, can include a physical foaming agent or a chemical foaming agent. A physical foaming agent is a medium expanding composition that is a gas at temperatures and pressures encountered during the foam expanding step. Typically, a physical foaming agent would be introduced to the polymer blend in the gaseous or liquid state and expands, for example, upon a rapid decrease in pressure. A chemical foaming agent is a compound or mixture of compounds that decompose at elevated temperatures to form one or more gases, which can be used to expand the polymer blend into a foam.

Melt blending is one method for preparing the polyolefin/clay nanocomposite and for incorporating the nanocomposite into the final polymer blend of the present invention. Techniques for melt blending of a polymer with additives of all types are known in the art and can typically be used in the practice of this invention. Typically, in a melt blending operation useful in the practice of the present invention, the individual components of the composite are combined in a mechanical extruder or mixer, and then heated to a temperature sufficient to form a polymer melt. The mechanical mixer can be a continuous or batch mixer. Examples of suitable continuous mixers include single screw extruders, intermeshing co-rotating twin screw extruders such as Werner & Pfleiderer ZSK.TM. extruders, counter-rotating twin screw extruders such as those manufactured by Leistritz.TM., and reciprocating single screw kneaders such as Buss.TM. co-kneaders. Examples of suitable batch mixers include lateral 2-roll mixers, such as Banbury.TM. or Boling.TM. mixers.

The composite may be prepared by shear mixing the polyolefin blend and the clay material in the melt at a temperature equal to or greater than the melting point of the polymer. Melting point is defined as the first order transition temperature at which a crystalline solid changes from a solid state to a fluid state. The temperature of the melt, residence time of the melt within the mixer, and the mechanical design of the mixer are several variables that control the amount of shear to be applied to the composition during mixing. The melt of the polyolefin blend and the clay material is subjected to shear mixing until the desired amount of material exfoliates or delaminates to the desired extent.

Alternatively, the polyolefin blend may be granulated and dry-mixed with the organoclay, and thereafter, the composition heated in a mixer until the polymer is melted to form a flowable mixture. This flowable mixture can then be subjected to a shea