This invention relates to polymer compositions. In particular, this invention relates to soft, flexible polymer compositions with improved abrasion resistance. One aspect of this invention relates to polymer compositions containing linear or substantially linear α-olefin polymers and high molecular weight polydimethylsiloxane. Another aspect of this invention relates to polymer compositions containing linear or substantially linear α-olefin polymers in which the addition of polydimethylsiloxane does not substantially affect the coefficient of friction of the polymer composition nor the adhesion or heat seal strength of the composition. In yet another aspect, this invention relates to articles made from the above-mentioned polymer compositions.

Applications such as tarps, shoe soles, wire and cable insulation and jacketing where surface abrasion may occur require flexible polymers with good surface abrasion resistance. Low density (density < 0.9 g/cm ³ ) ethylene/alpha olefin copolymers have good flexibility and toughness and thus are candidates for these applications; however, the low density polymers lack the surface abrasion resistance needed for these applications. Furthermore, although additives exist which may improve the processability and other properties of the polymer composition, these same additives can change the coefficient of friction (COF) and create undesirable effects in particular applications such as in shoe soles, where surface traction is important.

A polyolefin composition is needed which has improved abrasion resistance. Another desirable feature of such a polyolefin composition is that it possess a desirable coefficient of friction. Yet another desirable feature of such a polyolefin composition is that it be easily processed, thus requiring less energy to process. These and other advantages are taught by the polyolefin composition of the present invention. In one aspect, the invention is a polymer composition comprising:

(A) at least one ethylene interpolymer and

(B) at least one polydimethylsiloxane (PDMS) having a viscosity at 25°C of greater than 100,000 centistokes, said PDMS comprising 0.1 to 10 weight percent of the polymer composition. Preferably, (A) comprises at least one ethylene interpolymer selected from the group consisting of homogeneously branched linear ethylene/α-olefin interpolymer, homogeneously branched substantially linear ethylene/α-olefin interpolymer and ethylene/alpha-olefin/diene terpolymers. The compositions of the invention can have a NBS abrasion resistance tested in accordance with ASTM D1630-83 of at least 20 percent greater that of component (A) alone and wherein a plaque made from said composition has a coefficient of friction (COF) tested in accordance with ASTM D 1894 not less than 90 percent of the COF of component (A) alone.

In another aspect, the invention comprises an article made from the polyolefin compositions disclosed herein. In still another aspect, the invention is a method of improving the abrasion resistance of an ethylene polymer while maintaining at least 90 percent of the coefficient of friction of said ethylene polymer, said method comprising the step of incorporating into said ethylene polymer from 0.1 to 10 weight percent of at least one polydimethylsiloxane having a viscosity at 25°C greater than 100,000 centistokes.

The term "ethylene interpolymer" used herein means either a homogeneously branched linear or substantially linear ethylene polymer or interpolymer of ethylene with at least one alpha-olefin, and it can mean a heterogeneously branched interpolymer of ethylene with at least one alpha- olefin, but the term does not refer to homopolymer polyethylene.

The term "linear ethylene polymers" used herein means that the ethylene polymer does not have long chain branching. That is, the linear ethylene polymer has an absence of long chain branching, as for example the traditional heterogeneous linear low density polyethylene polymers or linear high density polyethylene polymers made using Ziegler polymerization processes (for example, USP 4,076,698 (Anderson et al.), sometimes called heterogeneous polymers. The Ziegler polymerization process, by its catalytic

nature, makes polymers which are heterogeneous, that is, the polymer has several different types of branching within the same polymer composition as a result of numerous metal atom catalytic sites. In addition, the heterogeneous polymers produced in the Ziegler process also have broad molecular weight distributions (MWD); as the MWD increases, the I-I Q/12 ^rat i° concurrently increases.

The term "linear ethylene polymers" does not refer to high pressure branched polyethylene, ethylene/vinyl acetate copolymers, or ethylene/vinyl alcohol copolymers which are known to those skilled in the art to have numerous long chain branches. The term "linear ethylene polymers" can refer to polymers made using uniform branching distribution polymerization processes, sometimes called homogeneous polymers. Such uniformly branched or homogeneous polymers include those made as described in USP 3,645,992 (Elston), and those made using so-called single site catalysts in a batch reactor having relatively high olefin concentrations (as described in U.S. Patent 5,026,798 (Canich) or in U.S. Patent 5,055,438 (Canich), or those made using constrained geometry catalysts in a batch reactor also having relatively high olefin concentrations (as described in U.S. Patent 5,064,802 (Stevens et al.), or in EPA 0 416 815 A2 (Stevens et al.)). The uniformly branched/homogeneous polymers are those polymers in which the comonomer is randomly distributed within a given interpolymer molecule and wherein substantially all of the interpolymer molecules have the same ethylene/comonomer ratio within that interpolymer, but these polymers too have an absence of long chain branching, as, for example, Exxon Chemical has taught in their February 1992 Tappi Journal paper.

The term "substantially linear" means that the polymer has long chain branching and that the polymer backbone is substituted with 0.01 long chain branches/1000 carbons to 3 long chain branches/1000 carbons, more preferably from 0.01 long chain branches/1000 carbons to 1 long chain branches/1000 carbons, and especially from 0.05 long chain branches/1000 carbons to 1 long chain branches/1000 carbons. Similar to the traditional linear homogeneous polymers, the substantially linear ethylene/α-olefin

copolymers used in this invention also have a homogeneous branching distribution and only a single melting point, as opposed to traditional Ziegler polymerized heterogeneous linear ethylene/α-olefin copolymers which have two or more melting points (determined using differential scanning calorimetry (DSC)). The substantially linear ethylene polymers are described in USP 5,272,236 and USP 5,278,272.

Long chain branching for the substantially linear ethylene polymers is defined herein as a chain length of at least 6 carbons, above which the length cannot be distinguished using ¹³ C nuclear magnetic resonance spectroscopy. The long chain branch of the substantially linear ethylene polymers is, of course, at least one carbon longer than two carbons less than the total length of the comonomer copolymerized with ethylene. For example, in an ethylene/1-octene substantially linear polymer, the long chain branch will be at least seven carbons in length. However, the long chain branch can be as long as about the same length as the length of the polymer backbone. For substantially linear ethylene/alpha-olefin copolymers, the long chain branch is also itself homogeneously branched, as is the backbone to which the branch is attached.

For ethylene homopolymers and certain ethylene/alpha-olefin copolymers, long chain branching is determined by using ¹³ C nuclear magnetic resonance spectroscopy and is quantified using the method of Randall (Rev. Macromol. Chem. Phvs.. C29 (2&3), pp. 285-297).

The SCBDI (Short Chain Branch Distribution Index) or CDBI (Composition Distribution Breadth Index) is defined as the weight percent of the polymer molecules having a comonomer content within 50 percent of the median total molar comonomer content. The CDBI of a polymer is readily calculated from data obtained from techniques known in the art, such as, for example, temperature rising elution fractionation (abbreviated herein as "TREF") as described, for example, in Wild et al, Journal of Polymer Science, Poly. Phvs. Ed.. Vol. 20, p. 441 (1982), or as described in U.S. Patent

4,798,081 or as is described in USP 5,008,204 (Stehling). The CDBI for the homogeneously branched linear or homogeneously branched substantially

linear olefin polymers of the present invention is greater than about 30 percent, preferably greater than about 50 percent, and especially greater than about 90 percent.

A unique characteristic of the substantially linear olefin polymers used in the present invention is a highly unexpected flow property where the I-1 ₀ /I2 value is essentially independent of polydispersity index (that is M _w /M _n ). This is contrasted with conventional Ziegler polymerized heterogeneous polyethylene resins and with conventional single site catalyst polymerized homogeneous linear polyethylene resins having rheological properties such that as the polydispersity index increases (or the MWD), the H0/I2 value also increases.

The density of the ethylene interpolymer, including the substantially linear homogeneously branched ethylene or linear homogeneously branched ethylene/α-olefin polymers, used in the present invention is measured in accordance with ASTM D-792 and is generally from 0.85 g/cm ³ to 0.945 g/cm ³ , preferably from 0.85 g/cm ³ to 0.93 g/cm ³ , and especially from 0.87 g/cm ³ to 0.9 g/cm ³ .

Melting point (and Vicat softening point) of the homogeneously branched linear or homogeneously branched substantially linear olefin polymers used in the present invention correlates primarily with the density of the polymer since the substantially linear ethylene polymers lack a high density (that is, linear) fraction, with some effects attributable to the molecular weight of the polymer (indicated melt index). Melting point variation of the homogeneously branched linear or homogeneously branched substantially linear olefin polymers used in the present invention is contrasted with heterogeneous ethylene polymers having two or more melting points (due to their broad branching distribution), one of which is about 126°C and is attributable the high density linear polyethylene fraction. The lower the density of the homogeneously branched linear or homogeneously branched substantially linear olefin polymers used in the present invention, the lower the melting and Vicat Softening point and the higher the coefficient of friction (COF). Thus, lower density ethylene polymers (for example, density < 0.9

g/cm ³ ) especially benefit from the present invention, since their COF is quite high (for example, as high as 1 or greater using ASTM D 1894) to begin with and addition of other additives makes the polymer more tacky and difficult to handle, making the formulation disadvantageous in specific applications such as shoe sole and tarps. For example, Table 1 lists Vicat softening point (as measured using ASTM D-1525) versus density for various substantially linear ethylene/1-octene copolymers:

Table 1

The molecular weight of the ethylene polymer, including the homogeneously branched linear or homogeneously branched substantially linear olefin polymers, used in the present invention is conveniently indicated using a melt index measurement according to ASTM D-1238, Condition 190 C/2.16 kg (formally known as "Condition (E)" and also known as I2). Melt index is inversely proportional to the molecular weight of the polymer. Thus, the higher the molecular weight, the lower the melt index, although the relationship is not linear. The melt index for the ethylene interpolymer, including the homogeneously branched linear or homogeneously branched substantially linear olefin polymers, used herein, is generally from 0.01 grams/10 minutes (g/10 min) to 100 g/10 min, preferably from 0.1 g/10 min to 30 g/10 min, and especially from 0.1 g/10 min to 5 g/10 min.

Another measurement useful in characterizing the molecular weight of the ethylene polymer, including the homogeneously branched linear or

homogeneously branched substantially linear olefin polymers, is conveniently indicated using a melt index measurement according to ASTM D-1238, Condition 190°C/10 kg (formerly known as "Condition (N)" and also known as Ho). The ratio of these two melt index terms is the melt flow ratio and is designated as Ho/12- For the substantially linear ethylene/α-olefin polymers used in the invention, the H0/I2 ratio indicates the degree of long chain branching, that is, the higher the I10 I2 ratio, the more long chain branching in the polymer. Generally, the I10/I2 ratio of the substantially linear ethylene/α- olefm polymers is at least 5.63, preferably at least 7, especially at least 8 or above. The upper limit of the H0/I2 ratio can be 50, preferably 20, and especially 15. For the substantially linear ethylene polymers, the melt flow ratio (I10/I2) can be increased to compensate for the use of higher molecular weight polymers (that is, lower melt index polymers). Thus, an elastic substantially linear ethylene polymer having a melt index of about 10 grams/10 minutes, a density of about 0.92 g/cm ³ , M _w /M _n of about 2, and

I10/I2 ^0ι about 10 will have a viscosity similar to a substantially linear ethylene polymer having a melt index of about 30 grams/10 minutes, a density of about 0.92 g/cm ³ , M _w /M _n of about 2, and I ₁ 0/I2 of about 7.5, when using approximately the same shear rate. Additives such as antioxidants (for example, hindered phenolics (for example, Irganox ^* 1010 made by Ciba Geigy Corp.), phosphites (for example, Irgafos ^* 168 made by Ciba Geigy Corp.)), cling additives (for example, polyisobutylene (PIB)), slip additives (for example, erucamide), lubricants (for example, stearic acid), print- or adhesion- enhancing additives which increase the surface tension of the surface comprising the compositions, processing aids (for example, fluoroelastomers), fillers (for example, calcium carbonate, silica dioxide, or talc), plasticizers, oils, antiblock additives, and pigments can also be included in the compositions of the inventions, to the extent that they do not interfere with the enhanced properties discovered by Applicants.

Molecular Weight Distribution Determination

The whole interpolymer product samples and the individual interpolymer components are analyzed by gel permeation chromatography (GPC) on a Waters 150C high temperature chromatographic unit equipped with three mixed porosity columns (Polymer Laboratories 10 ³ , 10 ⁴ , 10 ⁵ , and 10 ⁶ ), operating at a system temperature of 140°C. The solvent is 1,2,4- trichlorobenzene, from which 0.3 percent by weight solutions of the samples are prepared for injection. The flow rate is 1.0 miHiliters/minute and the injection size is 100 microliters. The molecular weight determination is deduced by using narrow molecular weight distribution polystyrene standards (from Polymer Laboratories) in conjunction with their etution volumes. The equivalent polyethylene molecular weights are determined by using appropriate Mark- Houwink coefficients for polyethylene and polystyrene (as described by Williams and Ward in Journal of Polymer Science, Polymer Letters, Vol. 6. (621) 1968) to derive the following equation:

M polyethylene = a ^* (M _p0 |y _S ty _r ene) • In this equation, a = 0.4316 and b = 1.0. Weight average molecular weight, M _w , and number average molecular weight, M _n , is calculated in the usual manner according to the following formula:

Mj = (Σ w^M )) ¹ ; where w. is the weight fraction of the molecules with molecular weight M, eluting from the GPC column in fraction i and j = 1 when calculating M _w and j = -1 when calculating M _n .

The molecular weight distribution (M _w /M _n ) for the substantially linear ethylene interpolymers or the homogeneous linear ethylene interpolymers used in the invention is generally less than 5, preferably from 1.5 to 2.8, and especially from 1.8 to 2.8.

The ethylene interpolymers useful in the present invention, including the substantially linear olefin polymers, can be interpolymers of ethylene with at least one C3-C20 α-olefin and/or C ₄ -C ₁ 8 diolefins. The ethylene interpolymers used in the present invention can also be interpolymers of ethylene with at least one of the above C3-C20 α-olefins, diolefins in

combination with other unsaturated monomers. The term "interpolymer" means that the polymer has at least two comonomers (for example, a copolymer) and also includes more than two comonomers (for example, terpolymers such as ethylene/alpha-olefin/diene (EPDM)). For EPDM, preferably the diene is 5-ethylidene-2-norbomene or piperylene. However, ethylene/alpha-olefin copolymers are preferred however, and ethylene/ C3- C20 α-olefin copolymers are especially preferred.

The compositions of the present invention may also contain polyethylene blends produced by the direct polymerization of various combinations of substantially linear or linear olefin polymers in multiple reactors using either single or multiple catalysts.

The ethylene interpolymers are present in the composition of the present invention in the range of about 30 percent to about 99.9 percent by total weight of the composition. The ethylene interpolymers used in the present invention are mixed with high molecular weight (that is they have a viscosity at 25°C greater than 100,000 centistokes) polydimethylsiloxane (PDMS), such as MB25 or MB 50, which is a 25 percent and 50 percent concentrate in highly branched low density polyethylene available from Dow Corning or POLYBATCH ^* IL 2580- SC, available from Shulman, or RHODORSIL ^* 47 V Silicones, available from Rhone-Poulenc. This does not include the lower molecular weight fluids or lower molecular weight siloxane polymers, such as Dow Corning (R) 200 Fluid silicone Plastic Additive (having a viscosity of about 12,500 centistokes). PDMS can be found in the composition of the present invention in the range of 0.1 percent to 10 percent by total weight of the composition. Preferably,

PDMS can be found in the composition of the present invention in the range of 0.5 percent to 5 percent by total weight of the composition. More preferably, PDMS can be found in the composition of the present invention in the range of 0.5 percent to 3 percent by total weight of the composition. In the examples of the present invention using Dow Corning PDMS, a 50 percent by weight masterbatch PDMS in LDPE is added to the final polyolefin composition.

Other polymers can also be combined with effective amounts of the ethylene interpolymers to make the polyolefin composition of the present invention as well, depending upon the end use properties required. These other polymers are thermoplastic polymers (that is, melt processable) and include polymers such as polypropylene, ethylene/alpha-olefin/diene terpolymers, styrene block co- and ter-polymers, highly branched low density polyethylene, heterogeneously branched linear low density polyethylene, maleic anhydride or succinic acid grafted ethylene interpolymers such as those described and/or claimed in USP 4,684,576, ethylene/vinyl acetate copolymers, and ionomers such as SURLYN ^* made by E.I. duPont de Nemours, Inc., and ethylene/acrylic acid copolymers (for example, PRIMACOR™ Adhesive Polymers made by The Dow Chemical Company). The polyolefin compositions of the present invention may be used for making fabricated articles requiring good wear resistant properties, such as tarpolins (tarps), various automotive applications (for example, cargo covers), coated polyester yarns for outdoor furniture applications, coated fabrics, table-cloths, geotextile type transportation products, secondary containment fabrics or tarps, tents, shoe soles, and cable jacketing. The fabricated articles can incorporate the novel compositions claimed herein can use techniques such as using an extrusion coating operation or cast film or laminating process such that the PDMS component may only be added where it's needed, that is, on the outer surface of the laminate.

Examples

EXAMPLE A:

30 percent (by weight) of a substantially linear ethylene/1-octene copolymer having a melt index of 0.5 g/10 min and a density = 0.868 g/cm ³ , 30 percent (by weight) of a substantially linear ethylene/1-octene copolymer having a melt index of 5 g/10 min and a density = 0.87 g/cm ³ , 28 percent (by weight) of a substantially linear ethylene/1-octene copolymer having a melt index = 1.0 g/10 min and a density = 0.885 g/cm ³ , 10 percent (by weight) of an ethylene/propylene copolymer having a melt index of 65 g/10 min and a density = 0.953 g/cm ³ which was grafted with 1.2 percent of maleic anhydride, 2 percent PDMS master batch (contains 1 percent active PDMS). This composition is used to extrusion coat polyester scrim for tarpolin applications.

OTHER EXAMPLES

In other examples, cast co-extrusion film are made from a substantially linear ethylene/1-octene copolymer with and without 10 percent PDMS in a polypropylene carrier resin. The resins used are ENGAGE ^* 8100 (a substantially linear ethylene/1-octene copolymer having a melt index of 1 g/10 min and a density of 0.87 g/cm ³ ), and ENGAGE 8150 (a substantially linear ethylene/1-octene copolymer having a melt index of 0.5 g/10 min and a density of 0.868 g/cm ³ ). Laminate structures (Film/PET scrim/Film) are prepared by using the hot press at a temperature and pressure sufficient to integrate the film with the scrim. The samples are then tested by a rope abrasion tester (two 19.1 mm (3/4 inch) of 3-strand twisted polypropylene rope (tensile strength of 3469.96 kg (7650 lb)) mounted onto a slide with 9.07 kg (20 lb) of weight at 1 hz for 20 seconds) and ranked by appearance. The sample is placed under the rope and abraded for 20 cycles (about 20 seconds) where a rating of "1" means that the sample is completely abraded where the scrim is completely exposed; "5" means that the sample has a first sign of scrim exposure; and "10" means that the sample has little or no visible

damage. Table 1 shows that the samples containing the PDMS suffered less surface damage than the controls.

Table 1 A/B Coex Films (with PDMS) Laminated to Polyester Scrim (B/A/Scrim/A/B)

A layer = ENGAGE 8100

Weight Percent Rope Abrasion Test

B layer Active PDMS ^** Appearance Rating

ENGAGE* 8100 (0.87 g/cm ³ 0.5 0-1 density)

(95 percent)

ENGAGE 8100 + ENGAGE 1880 0.5 1-2 (0.902 g/cm ³ density) (57 percent + 38 percent)

DOWLEX ^* 2265A (0.924 g/cm ³ ) 0.5 7 (95 percent)

DOWLEX 2265A 1.5 9-10 (85 percent)

ENGAGE 8100 +ENGAGE1880 1.5 2-3 (50 percent + 35 percent)

**Percentages do not add up to 100 percent because the balance of each formulation is the inactive carrier (polypropylene in each case here).

Similar laminate structures (3/4 to 3 percent PDMS MB) were prepared on a Black-Clawson pilot extrusion coating line operating at 287.8-301.7° C(550-575°F). The PDMS was obtained from Dow Corning in a 50 percent masterbatch with LDPE as the carrier. These structures were also tested and compared to a control structure produced using the Shulman PDMS masterbatch using the rope abrasion tester and again significantly less abrasion occurred in the samples containing the PDMS. It was noted in these trials that the extrusion amps were about 30 percent lower when the PDMS was present at the 2 and 3 percent loading. Data regarding these trials is presented in Table 2 below.

Table 2

Rope Abrasion Testing

Monolayer Films

Weight Percent Double Rub

Film Structure Active PDMS Rating

ENGAGE 8100 (0.870) 1.5 8.0 +ENGAGE 8003 (0.885) + PDMS# (55 + 35 +15 percent)

ENGAGE 8100 (0.870) 0.3 8.5 +ENGAGE 8003 (0.885) + PDMS ^* (557+ 40 + 3 percent)

ENGAGE 8100 (0.870) 0.15 7+ +ENGAGE 8003 (0.885) + PDMS* (58.5 + 40 + 1.5 percent)

ENGAGE 8100 (0.870) 0.075 7

+ENGAGE 8003 (0.885)

+ PDMS*

(59.25 + 40 + 0.75 percent)

# Schulman masterbatch with 10 percent PDMS

*Dow Corning masterbatch with 50 percent PDMS

NB: Film Extrusion Coated to Polyester Scrim (Film/Scrim/Film)

Polymer samples were prepared containing Shellflex oil and calcium carbonate to determine if PDMS would still produce the desired effect. Table 3 shows that the addition of the oil and filler reduced the abrasion somewhat.

Table 3

Weight Rope Abrasion Resistance

Structure Percent Ratinα

Active

PDMS

PVC Control* 0 9

ENGAGE 8003 + Oil + CaCO ₃ + 1 7-8

MB50

(54 + 15 + 29 + 2 wt percent)

ENGAGE 8150 + ENGAGE 1880 1 7

+Oil +CaCO ₃ + MB50

(27.5 + 25.5 + 15 + 2 wt percent)

ENGAGE 8003 + Oil + CaCO ₃ 0 6 (55 + 15 + 30 wt percent)

* This commercial tarp was obtained from Hendee Corp, Houston, Texas.

The PDMS is evaluated in shoe sole formulations comprising substantially linear ethylene polymers to try to reduce abrasion. These formulations also contain oil to increase flexibility. Again the formulations with the PDMS showed significantly lower abrasion via NBS tester. COF was not effected by the addition of PDMS to our surprise.

Table 4 Coefficient of Friction (ASTM D 1894)

Discussion It has been found that when high molecular weight (>1 x 10 ⁶ centistokes viscosity) polydimethylsiloxane (PDMS) like one supplied by Dow Corning is incorporated into the polymer or formulation at 0.5 to 3 percent by weight improved abrasion resistance is achieved sometimes without effecting the coefficient of friction (COF). This has allowed the soft flexible polymer compositions to meet the requirements for applications like tarps where rope abrasion is a problem, shoe soles and wire applications where abrasion can occur when it is being installed in conduit. This result is also totally unexpected, as one would not expect to be able to improve the abrasion resistance without changing the coefficient of friction or slip properties of the material. See, White et al., New Silicone Modifiers for Improved Physical Properties and Processing of Thermoplastics and Thermoset Resins, ANTEC

'91, pp. 1904-7 (1991) and Abouelwafa et al., The Wear and Mechanical Properties of Silicone Impregnated Polyethylene.

Another advantage that is often achieved by using the PDMS is lower processing amps. In some case as much as 30 percent reduction in amps has been achieved which is quite significant for the narrow molecular weight homogenous alpha olefin copolymers. See Table 4 above.