POLYMERS BLENDS, FILMS AND ARTICLES THEREOF

Abstract: Polymer blends, films and articles having improved hot tack strength properties. The polymer blend comprises a polymer having a narrow molecular weight and composition distribution and a high pressure ethylene homopolymer or copolymer. The articles and films have significantly improved physical characteristics and remarkably high hot tack and low heat seal initiation temperatures and therefore provide improved processibility at higher line speeds on commercial heat sealing equipment.

Description: POLYMER BLENDS, FILMS AND ARTICLES THEREOF FIELD OF THE INVENTION The present invention relates to heat sealable films and articles. In particular, the invention relates to a blend of polymers one of which has a narrow molecular weight distribution and narrow composition distribution, the other being a high pressure low density polymer. The blends of the invention exhibit excellent hot tack, heat sealing and other physical properties. The blends may be used to make films, bags, pouches, tubs, trays, lids, packages, containers and other articles employing a heat seal. BACKGROUND OF THE INVENTION Many articles of manufacture employing heat seals are currently available in the marketplace. For example, plastic parts usefully employed in machines and toys may be constructed by joining together two individual plastic pieces by heating one or both of the plastic pieces, pressing them together, and then, allowing them to cool. Heat sealing is very important in packaging applications. Packages formed by a heat seal provide for the efficient transportation of a consumer item within the package, provide a display of the consumer item that promotes sales, and, in the food industry, the packaging is employed to preserve the freshness of the consumer item. Most importantly and related to heat seal a manufacturer of packages or any other like article requiring a seal also requires excellent processibility. Various types of polymers are used to form articles, which include packages, that may be joined together or sealed by the application of heat and/or pressure. Polymers or blends of polymers used to make the articles are selected for use because they provide a strong seal, which is easily and rapidly formed by a single short application of heat and/or pressure. Occasionally, the entire heat sealed article is constructed from the same polymer or a blend of polymers or by the coextrusion of the same or different polymers. More often, the article is constructed of various areas or layers of different materials, and polymers which provide good heat sealing properties are utilized only in areas, or layers, where heat sealing will ultimately be necessary. This type of construction is employed because the articles, for instance multilayer films, should have desirable physical and mechanical properties such as clarity, strength, resistance to puncture and tearing, in addition to heat sealing properties, and should be easily processed by high speed equipment. Many plastic materials are known to possess good physical and mechanical properties but often do not also possess good heat sealing properties. In the commercial packaging industry, assembly line speeds are very important to a manufacturer. In the packaging business, the faster the line speeds, the higher production, and thus, a lowering of overall cost. There are several important characteristics of a polymer or polymer blend that make it particularly suitable to the packaging industry. One of those important characteristics is a polymer composition's heat seal initiation temperature. This is the temperature to which the polymer composition must be heated before it will usefully bond to itself under stress and/or strain. Relatively low heat seal initiation temperatures are desirable in commercial heat sealing equipment. The lower temperatures provide for higher production rates of the packages on the equipment because the polymer does not need to be heated to as great a temperature to make the seal. Also, cooling of the seal to attain adequate strength will be faster. Qualitatively, every 10°C decrease in seal initiation temperature will result in 30% improvement in line speed productivity. There are various polymers in the art that have a low seal initiation temperature. For example, ethylene vinyl acetate (EVA) and ethylene methyl acrylate (EMA) copolymers have low seal initiation temperatures but these high pressure low density copolymers have poor hot tack strength. Thus, in the past in order to improve these poor properties, manufacturers have been blending EMA and EVA copolymers with, for example, linear low density polyethylene (LLDPE). However, LLDPE's because they have a low comonomer content have less desirable heat sealing properties and tend to be hazy. Thus, blends of LLDPE with these copolymers cause a reduction in the overall blend properties. Another important characteristic that manufacturers require of a polymer composition, particularly in vertical form fill seal (VFFS) and gas-flushed horizontal form fill seal (HFFS) applications, is good hot tack strength. Hot tack is the capability of a heat seal to hold together, when pulled apart, immediately before thoroughly quenching the seal. Hot tack strength is the measure of the maximum stress that can be applied before the seal fails. This is different from seal strength which is a measure of the strength of a seal after the seal has cooled. Hot tack strength, on the other hand, is the ability of a heat seal to hold together immediately after sealing, before the seal is cooled. Hot tack properties are important in packaging applications. A high hot tack strength at lower temperatures allows packaging manufacturers to increase line speeds. Hot tack is also the constraining factor in determining the weight of material that can be packaged in a form-fill seal machine. High hot tack is also advantageous in cases where bulky products tend to resist package edge sealing, where vibration or cutting takes place while the seal is hot, or where packages are filled hot. In a typical VFFS or HFFS process a polymer composition is formed into a flexible pouch and almost immediately filled with the contents to be packaged and then the pouch is sealed closed. Since it is often difficult or impossible to maintain commercial sealing equipment at exactly the same sealing temperature throughout a commercial run, a broader range of sealing temperatures would make it easier to assure that all heat seals are made with acceptable strength. Therefore, a need exists for a polymer blend that exhibits improved hot tack strength over a broader sealing temperature window while maintaining other desirable physical properties, such as a low seal initiation temperature and good optical properties. SUMMARY OF THE INVENTION The blend of polymers of the invention generally include a first polymer, component A, which has a narrow molecular weight distribution and composition distribution and a second polymer, component B, which is a high pressure polyethylene homopolymer or copolymer. In one embodiment of the invention, component A comprises between about 10 to 50 weight percent of the total weight percent polymer blend and component B comprises between about 50 to about 90 weight percent of the total weight percent of the polymer blend of the invention. In yet another embodiment, the polymer blend of the invention is useful as a film layer in an article of manufacture, particularly in a heat sealable article where the film layer is a seal layer. BRIEF DESCRIPTION OF THE DRAWINGS The foregoing aspects, features, and advantages of the invention will become clearer and more fully understood when the following detailed description is read in conjunction with the accompanying drawings, in which: Figure 1 is a graph of the relationship between the hot tack strength versus weight percent of component A for samples numbered EX. 1-9. Figure 2 is a graph of the relationship between the hot tack strength versus weight percent of component A for samples numbered EX. 1, 10-12. Figure 3 is a graph of the relationship between the hot tack strength versus weight percent of component A for samples numbered EX. 1, 13-15. Figure 4 is a graph of the relationship between the hot tack strength versus weight percent of component A for samples numbered EX. 9, 16-18. Figure 5 is a graph of the relationship between the hot tack strength versus weight percent of component A for samples numbered EX. 9, 16, 19-20. Figure 6 is a graph of the relationship between the hot tack strength versus weight percent of component A for samples numbered EX. 12, 21-23. Figure 7 is a graph of the relationship between the hot tack strength versus weight percent of component A for samples numbered EX. 9, 21, 24-25. Figure 8 is a graph of the relationship between the hot tack strength versus temperature for samples numbered EX. 1, 10-12. Figure 9 is a graph of the relationship between the hot tack strength versus temperature comparing the inventive blends with a prior art blend. DETAILED DESCRIPTION OF THE INVENTION Introduction The invention concerns a blend of a narrow molecular weight distribution (NMWD) and a narrow composition distribution (NCD) polymer, component A, and a high pressure ethylene homopolymer or copolymer, component B, their production and applications for their use. The polymer blend of the invention has unique properties which make them particularly well suited for use in polymeric films. These films are very useful in applications requiring heat sealability. It has been discovered previously that polymers derived from metallocene catalyst systems heat seal extremely well, as compared to polymers produced by conventional Ziegler-Natta catalysts, see PCT Application No. WO 93/03093, published February 18, 1993. The polymer blends of the invention are not discussed. Surprisingly and unexpectedly, applicants have discovered a polymer blend having an improved hot tack strength while maintaining other desirable physical properties such as heat seal initiation temperature. In certain applications, the line-speed (how fast a package can be made) is limited by the hot tack strength ofa particular film. High hot tack strength during a wider range of lower sealing temperatures significantly increases line speeds and reduces the risk of "burn-through" as well as damage to temperature sensitive packaged goods. Prior art blends typically require higher sealing temperatures. Therefore, dwell times are longer, line speeds are slower and the likelihood of "burn-through" is increased. An added advantage of the inventive blends is a broader hot tack temperature window or range where the hot tack strength is commercially attractive. The inventive blends allow for wider tolerances in packaging operations (seal bar temperature, dwell time, line speed, etc.) resulting in a more economical packaging operation. Production of Polymer Component A of the Invention Polymer Component A, of this invention can be produced using metallocene catalyst systems in a polymerization process in gas, slurry solution or high pressure phase. The process for polymerizing involves the polymerization of one or more of the alpha-olefin monomers having from 2 to 20 carbon atoms, preferably 2-15 carbon atoms. The invention is particularly well suited to the copolymerization reactions involving the polymerization of one or more of the monomers, for example alpha-olefin monomers of ethylene, propylene, butene-1, pentene-1, 4- methylpentene-1, hexene-1, octene-1, decene-1 and cyclic olefins such as styrene. Other monomers can include polar vinyl, dienes, norbornene, acetylene and aldehyde monomers. Preferably a copolymer of ethylene and at least one alpha- olefin comonomer having from 3 to 15 carbon atoms is utilized in the polymer blends of the invention. For the purposes of this patent specification the term "metallocene" is defined to contain one or more cyclopentadienyl moiety in combination with a transition metal. The metallocene catalyst component is represented by the general formula (Cp)mMRnR'p wherein Cp is a substituted or unsubstituted cyclopentadienyl ring; M is a Group 4, 5 or 6 transition metal; R and R' are independently selected halogen, hydrocarbyl group, or hydrocarboxyl groups having 1-20 carbon atoms; m=l-3, n=0-3, p=0-3, and the sum of m+n+p equals the oxidation state of M. The metallocene can be substituted with principally hydrocarbyl substituent(s) but not to exclude a germanium, a phosphorous, a silicon or a nitrogen atom containing radical or unsubstituted or bridged or unbridged or any combination. Various forms of the catalyst system of the metallocene type may be used in the polymerization process of this invention. Exemplary of the development of these metallocene catalysts for the polymerization of olefins is found in U.S. Patent Nos. 4,808,561, 4,871,705, 4,897,455, 4,912,075, 4,937,217, 4,937,299, 4,937,301, 5,008,228, 5,017,714, 5,055,438, 5,064,802, 5,086,025, 5,096,867, 5, 120,867, 5, 147,949, 5,238,892, and 5,240,894, PCT International Publications WO 91/ 04257, WO 92/00333, WO 93/08199, and WO 93/08221 , EP-A-0 129 368, and EP-A-0420436 all of which are herein fully incorporated by reference. These metallocenes are activated by alumoxane described in U.S. Patent No. 4,665,208 or by compounds described in EP-A-0 520 732, EP-A-0277 003 and EP-A-0277004 and U.S. Patent Nos. 5,153,151 and 5,198,401 all of which are herein fully incorporated by reference. All the catalyst systems described above may be, optionally, prepolymerized or used in conjunction with an additive or scavenging component to enhance catalytic productivity. Characteristics of Polymer Component A of the Invention A key characteristic of polymer Component A of the present invention is its composition distribution (CD). As is well known to those skilled in the art, the composition distribution ofa copolymer relates to the uniformity of distribution of comonomer among the molecules of the copolymer. Metallocene catalysts are known to incorporate comonomer very evenly among the polymer molecules they produce. Thus, copolymers produced from a catalyst system having a single metallocene component have a very narrow composition distribution - most of the polymer molecules will have roughly the same comonomer content. Ziegler-Natta catalysts, on the other hand generally yield copolymers having a considerably broader composition distribution. Comonomer inclusion will vary widely among the polymer molecules. A measure of composition distribution is the "Composition Distribution Breadth Index" ("CDBI"). CDBI is defined as the weight percent of the copolymer molecules having a comonomer content within 50% (that is, 25% on each side) of the median total molar comonomer content. The CDBI ofa copolymer is readily determined utilizing well known techniques for isolating individual fractions ofa sample of the copolymer. One such technique is Temperature Rising Elution Fraction (TREF), as described in Wild, et al., J. Poly. Sc Polv. Phvs. Ed., vol. 20, p. 441 (1982) and U.S. Patent No. 5,008,204, which are incorporated herein by reference. To determine CDBI, a solubility distribution curve is first generated for the copolymer. This may be accomplished using data acquired from the TREF technique described above. This solubility distribution curve is a plot of the weight fraction of the copolymer that is solubilized as a function of temperature. This is converted to a weight fraction versus composition distribution curve. For the purpose of simplifying the correlation of composition with elution temperature all fractions are assumed to have a Mn > 15,000, where Mn is the number average molecular weight of the fraction. Low weight fractions generally represent a trivial portion of the polymer, component A, of the present invention. The remainder of this description and the appended claims maintain this convention of assuming all fractions have Mn > 15,000 in the CDBI measurement. From the weight fraction versus composition distribution curve the CDBI is determined by establishing what weight percent of the sample has a comonomer content within 25% each side of the median comonomer content. Further details of determining the CDBI ofa copolymer are known to those skilled in the art. See, for example, PCT Patent Application WO 93/03093, published February 18, 1993. The polymers of the present invention have CDBI's generally in the range of 50-98%, usually in the range of 60-98% and most typically in the range of 65- 95%. Obviously, higher or lower CDBI's may be obtained using other catalyst systems with changes in the operating conditions of the process employed. Molecular Weight Distribution (MWD), or polydispersity, is a well known characteristic of polymers. MWD is generally described as the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn). The ratio Mw/Mn can be measured directly by gel permeation chromatography techniques. Those skilled in the art will appreciate that there are several methods for determining MWD ofa polymer sample. For the purposes of this patent specification the molecular weight distribution of a polymer can be determined with a Waters Gel Permeation Chromatograph equipped with Ultrastyrogel columns and a refractive index detector. In this development, the operating temperature of the instrument was set at 145°C, the eluting solvent was trichlorobenzene, and the calibration standards included sixteen polystyrenes of precisely known molecular weight, ranging from a molecular weight of 500 to a molecular weight of 5.2 million, and a polyethylene standard, NBS 1475. The MWD of the polymer component A of this invention are termed "narrow". For the purposes of this patent specification "narrow" MWD means a Mw/Mn less than about 3.4, preferably less than or equal to 3, more preferably less than 2.5. The MI of the polymers of the invention are generally in the range of about 0.1 dg min to about 1000 dg/min, preferably about 0.2 dg/min to about 300 dg min, more preferably about 0.3 to about 200 dg/min and most preferably about 0.5 dg/min to about 100 dg min. Contemplated densities of component A of the invention are in the range of 0.85 to 0.96 g/cm 3 , preferably 0.87 to 0.940 g/cm 3 , more preferably 0.88 to about 0.935 g/cm 3 . In another embodiment the density of component A is in the range of 0.900 to 0.915 g/cm 3 , 0.915 to 0.940 g/cm 3 , 0.88 to 0.9 g/cm 3 and greater than 0.940 g/cm 3 to 0.96 g cm 3 . A particular attribute of Component A polymers is their very low level of extractable components. The extractable levels for the polymers of Component A are in the range of between 5.5% to below 0.1%, preferably less than 3%, more preferably less than 2% and most preferably less than 1%. For the purposes of this patent specification the extractable level of films made from polymer component A is measured in accordance with the process detailed in 21 CFR 177.1520(d)(3)(ii). In another embodiment, component A can comprise a blend of component A polymers, which can be prepared by blending the desired components in the desired proportion using conventional blending techniques and apparatus, such as, for example, screw-type extruders, Banbury mixers, and the like. .Alternatively, the blends may be made by direct polymerization, without isolation of the blend components, using, for example, two or more catalysts in one reactor, or by using a single catalyst and two or more reactors in series or parallel. Characteristics of Polymer Component B of the Invention Polymer Component B, of the invention is very well known in the art and may be prepared by free radical initiators, typically in a tubular reactor under high pressure, peroxide being the preferred initiator. For example, U.S. Patent No. 4,719,193, incorporated herein by reference, discloses a method of preparing polymer component B . Generally, the molecular weight of the component B of the invention is in the range of 60,000 to 200,000, the melt index (MI) is from 0.2 to 50 and the density ranges from 0.91 to 0.94 g/cm 3 , typical of linear low density polyethylene homopolymer (LDPE) and a linear low density copolymer and the like. For the purposes of this patent specification the term "high pressure polyethylene homopolymer or copolymer", Component B, is defined as a polyethylene homopolymer having a density less than 0.940 g/cm 3 or an ethylene copolymer of ethylene and an ethylenically unsaturated carboxylic acid ester or vinyl acetate. Preferred ethylenically unsaturated acrylic acid esters include, for example, methyl acrylate, butyl acrylate, and ethyl acrylate. A preferred monomer is vinyl acetate. These comonomers are present within a range of from about 1 to about 45 weight percent, preferably from about 1 to about 25 weight percent, based on the total weight of the Component B polymer. Ethylene methyl acrylate copolymers suitable for use in this invention are available from Exxon Chemical Company, Houston, Texas under the trademark Optema™. Ethylene vinyl acetate copolymers suitable for use in the invention are also available from Exxon Chemical Company, Houston, Texas under the trademark ESCORENE™. The B component of the polymer blend of the invention may be a blend of different prior art polymers, each differing in one or more of: molecular weight, MWD, comonomer type and content, density, MI and CD. BLENDS. FILMS AND ARTICLES OF THE INVENTION The polymer blend of the invention, herein referred to as, the "A-B blend", may be used to form articles with particularly desirable heat sealing properties. In particular, the A-B blend may be processed into films which possess particularly desirable heat sealing characteristics. For example, the A-B blend may be used to form films which are in turn formed into bags or pouches by heat sealing techniques known in the art. The heat sealable film may also be used as package sealing material, for example, the film may be placed over the opening ofa container, and then secured to the container by the application of heat. This technique may be used to seal perishable items, such as food, into paper, plastic, glass, ceramic or metallic containers. The articles of the invention may comprise other materials, especially in portions of the article not utilized for heat sealing. In the portions of the article that are used for heat sealing, the language "formed from" is intended to mean "comprising." In one embodiment, all articles or portions of articles described may also be constructed to consist essentially of the inventive A-B blends. In other words, the heat sealing portion of any article described herein may consist essentially of the inventive A-B blend. However, the blend may have additional components as further described below. The A-B blend of polymers may be formed into films by methods well known in the art. For example, the polymers may be extruded in a molten state through a flat die and then cooled. Alternatively, the polymers may be extruded in a molten state through an annular die and then blown and cooled to form a tubular film. The tubular film may be slit and unfolded to form a flat film. The films of the invention may be unoriented, uniaxially oriented or biaxially oriented. The films of the invention may be single layer or multiple layer films. The multiple layer films may comprise of one or more layers formed from the A-B polymer blend. The films may also have one or more additional layers formed from other materials such as other polymers, polypropylene (PP), polyester, LDPE, HDPE, polyamide, polycarbonates, EVA and EVOH for instance, metal foils, paper and the like. Multiple layer films may be formed by methods well known in the art. If all layers are polymers, the polymers may be coextruded through a coextrusion feedblock and die assembly to yield a film with two or more layers adhered together but differing in composition. Multiple layer films may also be formed by extrusion coating whereby a substrate material is contacted with the hot molten polymer as the polymer exits then die. Extrusion coating is particularly useful when the A-B blend heat seal layer is to be applied to substrates that are woven or knitted from natural or synthetic fibers or yams, e.g., textiles, or substrates made from non-polymer materials such as glass, ceramic, paper or metal. Multiple layer films may also be formed by combining two or more single layer films prepared as described above. The two layers ofa film so formed may be adhered together with an adhesive or by the application of heat and pressure. The heat sealed article may be formed by pressing at least two portions of the article together at a temperature sufficient to soften at least one of the article portions. The article portion which has been softened by heat is formed from the A-B blend of polymers. Although it is sufficient if only one of the article portions being heated and pressed to form a heat seal is formed from the A-B, it is preferable for all article portions directly involved in the heat seal to be formed from the A-B blend. Other portions of the article may be constructed of other materials. Articles of the invention include a sealed container comprising a body and a sealing member secured thereto, wherein the sealing member comprises a seal layer comprising the A-B blend polymers. The body may be constructed of any ofa number of different materials such as paper, plastic, glass, ceramics, metals and textiles. The body can be constructed with walls that are impervious to liquids and/or gases or the body may be constructed to allow the passage of liquids and/or gases. The body may also be constructed with one or more portals to allow passage of small items through the body wall or to allow the consumer to inspect the item stored in the container without removing the item from the container. In one embodiment, the polymer blend of the invention contains about 10 to about 50 weight percent of polymer Component A, preferably about 20 to about 50 percent, more preferably about 20 to about 40 weight percent, and most preferably about 20 to about 30 weight percent. In another embodiment of the invention the polymer blend contains about 50 to about 90 weight percent of polymer component B, preferably about 60 to about 90 weight percent, more preferably about 60 to about 80 weight percent, most preferably about 70 to about 80 weight percent. The first component of the polymer blend of the invention contains about 50 to about 100 weight percent of the first polymer, preferably 60 to 95 weight percent, more preferably 65 to 90 weight percent, even more preferably 70 to 90 weight percent and most preferably 75 to 90 weight percent. In another embodiment of the polymer blend of the invention the second component contains about 50 to about 100 weight percent ofa high pressure ethylene homopolymer or copolymer, preferably 60 to 95 weight percent, more preferably 65 to 90 weight percent, even more preferably 70 to 90 weight percent and most preferably 75 to 90 weight percent. The polymer blend of the invention or the individual components A and B may also be compounded with various conventional additives known in the art such as, for example, antioxidants, UV stabilizers, pigments, fillers, slip additives, block additives, and the like. Seal initiation temperature is defined as the temperature at which a hot tack strength of 2 N/15 mm is observed. In one embodiment the films of the invention generally have a seal initiation temperature less than about 110°C, preferably less than about 105 C C, more preferably less than about 100°C, and most preferably less than about 95°C. Hot tack strength is measured in N/15mm. Hot tack temperature range or hot tack temperature window is defined as the temperature range where a hot tack strength of ≥ 2 N/l 5 mm is maintained. In one embodiment the films of the invention have a hot tack strength greater than about 1.5 N/l 5 mm, preferably greater than 2 N/l 5 mm and most preferably greater than 3 N/l 5 mm at a temperature of greater than about 100°C. In another embodiment the films of the invention have a hot tack strength greater than about 1.5 N/l 5 mm, preferably greater than 2 N/l 5 mm and most preferably greater than about 3 N/l 5 mm at a temperature of greater than about 105°C. In yet another embodiment the films of the invention have a hot tack strength greater than about 1.5 N/l 5 mm, preferably greater than 2 N/l 5 mm and most preferably greater than about 3 N/l 5 mm at a temperature of about 110°C. In one embodiment the films of the invention have a hot tack strength temperature window greater than about 10°C at a hot tack strength greater than or equal to about 2 N/l 5 mm. In another embodiment the hot tack strength temperature range is greater than about 12°C to about 40°C, preferably greater than about 15°C to about 40°C, more preferably greater than about 20°C to about 40°C and most preferably greater than about 25°C to about 30°C at a hot tack strength greater than about 2 N/l 5 mm, preferably greater than about 2.5 N/l 5 mm and most preferably greater than 3 N/l 5mm. In still another embodiment the film of the invention has a hot tack strength greater than about 2 N/l 5 mm at a temperature between about 100°C to about 115 °C. In still yet another embodiment the film of the invention has a hot tack strength of greater than about 2.5 N/15 mm at temperature greater than about 100° C. In a further embodiment, the film of the invention has a hot tack strength greater than 2 N/l 5 mm preferably greater than 2.5 N/l 5 mm, more preferably greater than 3 N/l 5 mm at a temperature of greater than about 80°C or in the range of about 80°C to about 95°C. EXAMPLES In order to provide a better understanding of the present invention the following examples are offered as related to actual tests performed in the practice of this invention, and illustrate the surprising and unexpected properties of the A-B blends of the invention and are not intended as a limitation on the scope of the invention. EXAMPLE I; Sample No. Ul and U2 in Table 1, are prepared using free radical initiation of ethylene under high pressure conditions in a tubular reactor. The reactor temperature range is 149-260°C, and pressure range of 36,000 psig (248,220 kPa) to 45,000 psig (310,275 kPa) and a residence time of 2 s to 30 s. Samples No. U3 in Table 1 is prepared similar to Ul and U2 using free radical initiation and high pressure conditions in a tubular reactor, using vinyl acetate as the comonomer. Sample No. U4 in Table 1 is prepared similar to Ul and U2 using free radical initiation and high pressure conditions in a tubular reactor, with methyl acrylate and acrylic acid as the comonomers. EXAMPLE H: Sample No. XI, is prepared using silicon bridged transition metal catalyst. The catalyst preparation and process is outlined in U. S. Patents 5,017,714 and 5,120,867. Sample No. XI is prepared using the catalyst mentioned above, and reaction conditions of ethylene pressure of 19000 psig (131,005 kPa), temperature in zone 1 of 137°C, and zone of 5 166°C, butene 9 mole%, and hexene 45 mole%. Sample No. X2 is prepared similar to XI, except the temperature in zone 1 was 135°C and zone 5 of l63°C. Sample No. X3 is prepared in a similar manner as samples XI and X2, except only hexene is used as a comonomer. The polymer properties and the catalyst and process details on the polymers are shown in Table 1. Blend Preparation: The blend components of the invention were melt homogenized using a Werner Pfleider twin screw extruder followed by pelletization. Films Preparation: The blends and the prior art polyethylenes were used as seal layers on high density polyethylene (HDPE) substrate and were made using a Killion coextrusion line to give A/B construction. The thickness of the HDPE and the seal layers were approximately 1.0 mil each (25 μm). EXAMPLE DJ: The blend samples numbered EX. 2-8, 10, 11, 13, 14, 18, 19, 20, 22, 23, 24, 25, 27, and 28 were made by melt homogenization of the blend components using a Werner Pfleider twin screw extruder followed by pelletization step. EXAMPLE IV: The blend samples numbered EX. 2-8, 10, 11, 13, 14, 16, 17, 19, 20, 22, 23, 24, 25, 27, and 28 and the prior art conventional polyethylene samples numbered EX. 1, 16, 21, and 26, and the polymer samples numbered EX. 9, 12, and 15 were used as seal layers on high density polyethylene (HDPE) substrate and were made using a Killion coextrusion line to result in A/B (A - HDPE, and B - seal layer) type of construction. The thickness of the HDPE and the seal layers were approximately 1.0 mil each (25 μm). EXAMPLE V: The hot tack strength is measured by heat sealing the films at temperatures and separating and measuring the hot tack strength immediately after sealing. A commercial hot tack tester (DTC Hot Tack Tester Model 52-D) is used for hot tack measurement. The conditions for sealing and hot tack strength measurement were as follows: dwell time - 0.5 s, pressure - 0.5 N/mπ-2, delay time - 0.4 s, and peel speed - 200 mm/s. The hot tack strength is measured for the condition of sealing seal layer-to-seal layer, and not for HDPE-to-seal layer or HDPE-to- HDPE. The hot tack strength data for the samples numbered EX. 1-15 (blends of Ul with XI, X2, and X3, and the components) as measured from 90 to 130°C is shown in Table 2. The hot tack strength data for the samples numbered EX. 16-20 (blends of U2 with XI, and X2, and the components) as measured from 90 to 130°C is shown in Table 3. The hot tack strength data for the samples numbered EX. 21-25 (blends of U3 with XI and X2 and the components) as measured from 70-110°C is shown in Table 4. The hot tack strength data for the samples numbered EX. 26-28 (blends of U4 with XI and the components) as measured from 80-120°C is shown in Table 5. Predicted Hot Tack Strength at a selected temperature X°C = F^ x HT^. + Fg x HTJJ where, F^ is the weight fraction of the component A of the blend, HT^ is the hot tack strength for 100% component A at temperature X°C, Fg is the weight fraction of Component B of the blend, and HTg is the hot tack strength for 100% Component B at temperature X°C. The error bars in Figures 1-8 for the observed hot tack strength are based on ± σ, which represents one standard deviation. The predicted maximum hot tack strength and the observed maximum hot tack strength values for the samples numbered EX. 1-15, along with the composition of the blends are shown in Table 6. The predicted maximum hot tack strength and the observed hot tack strength values for the samples numbered 16-28, along with the composition of the blends is shown in Table 7. The predicted maximum hot tack strength shown in Tables 6 and 7 is calculated by using the relationship. Figure 1 represents the maximum observed hot tack strength versus weight percent of XI in Ul for samples numbered EX. 1-9, and the predicted maximum hot tack strength for samples numbered EX. 2-8. The hot tack values for the inventive blends is better than the conventional polyethylene sample EX. 1. In addition, the observed hot tack values for the inventive blends is in general greater than the predicted hot tack values, and this result is unexpected. Figure 2 represents the maximum observed hot tack strength versus weight percent of X2 in Ul for the samples numbered EX. 1, 10-12, and the predicted hot tack values for samples numbered EX. 10 and 11. Clearly, the observed maximum hot tack strength values for samples numbered EX. 10 and 11 are significantly and unexpectedly better than the predicted maximum hot tack strength. Figure 3 represents the maximum hot tack strength versus weight percent of X3 in Ul for the samples numbered EX. 1, 13-15, and the predicted hot tack strength values for samples numbered EX. 13 and 14. Clearly, the observed hot tack values for the inventive blends numbered EX. 13 and 14 are better than the predicted values. Figure 4 represents the maximum observed hot tack strength versus weight percent of XI in U2 for the samples numbered EX. 16-18, and 9, and the predicted hot tack values for samples numbered EX. 17 and 18. Clearly, the observed maximum hot tack strength values for samples numbered EX. 17 and 18 are significantly and unexpectedly better than the predicted maximum hot tack strength. Figure 5 represents the maximum observed hot tack strength versus weight percent of X2 in U2 for the s.amples numbered EX. 16, 19,20, and 9, and the predicted hot tack values for samples numbered EX. 19 and 20. Clearly, the observed maximum hot tack strength values for samples numbered EX. 19 and 20 are better than the predicted maximum hot tack strength. Figure 6 represents the maximum observed hot tack strength versus weight percent of XI in U3 for the samples numbered EX. 21-23, and 12, and the predicted hot tack values for samples numbered EX. 22 and 23. Clearly, the observed maximum hot tack strength values for samples numbered EX. 22 and 23 are significantly and unexpectedly better than the predicted maximum hot tack strength. Figure 7 represents the maximum observed hot tack strength versus weight percent of X2 in U3 for the samples numbered EX. 21, 24, 25, and 9, and the predicted hot tack values for samples numbered EX. 24, and 25. Clearly, the observed maximum hot tack strength values for samples numbered EX. 24 and 25 are significantly and unexpectedly better th.an the predicted maximum hot tack strength. Figure 8 represents the hot tack strength versus temperature for samples numbered EX. 1, and 10-12. The hot tack strength for the inventive blends EX. 10 and 11, is significantly better than the prior art polyethylene EX. 1, and at 40 wt% component X2 in prior art polyethylene sample EX. 1, the maximum hot tack strength is unexpectedly better than one would expect based on linear additivity of the two components involved (Ex. 1 and EX. 12). Figure 9 represents the hot tack strength versus temperature for a prior art polyethylene sample numbered EX. 1, and a prior art blend of LDPE LLDPE (80/20 wt%) in comparison to the inventive blends of samples EX. 3 and 10 which contain 20 wt% of components XI and X2 respectively in the prior art polyethylene EX. 1. As is clearly demonstrated, the inventive blends show improved hot tack between 95-105°C in comparison to the prior art samples EX. 1 and a blend of LDPE/LLDPE. In addition to the higher peak hot tack, the inventive blends show broader sealing window (defined as the temperature range where hot tack strength stays above a certain level, for example 2 N/l 5 mm). While the present invention has been described and illustrated by reference to particular embodiments thereof, it will be appreciated by those of ordinary skill in the art that the invention lends itself to variations not necessarily illustrated herein. For instance, the catalyst system may comprise various other transition metal metallocenes that are activated by alumoxane and/or ionic activators as the cocatalyst to produce polymers having a narrow molecular weight distribution and narrow composition distribution. Further, high pressure ethylene terpolymers can be utilized in the polymer blends of the invention. Also, the polymer blends of the invention are useful in articles of manufacture such as potato chip bags, cereal bags and pouches, cookies and cracker bags and pouches, detergents and other powder bags, condiments or candy containers, liquid containers, such as bag-in-box applications, vegetable or fruit bags and meat and cheese bags. The film of the invention are also useful in shrink packaging or plastic wrap applications. Reference should be made solely to the appended claims for purposes of determining the true scope of the present invention. Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 Sample ID Blend Composition Predicted Maximum Observed Maximum Hot Tack (N/15 mm) Hot Tack (N/15 mm) Ul XI B A EX.1 100 0 n/a 1.65 EX.2 90 10 2.23 2.51 EX.3 80 20 2.32 3.73 EX.4 70 30 3.1 3.30 EX.5 60 40 3.88 4.25 EX.6 50 50 4.66 5.16 EX.7 40 60 5.14 5.21 EX.8 20 80 6.99 7.47 EX.9 0 100 n/a 8.55 Ul X2 EX.10 80 20 2.89 3.65 EX.11 60 40 3.53 5.15 EX.12 0 100 n/a 8.95 Ul X3 EX.13 80 20 2.98 3.45 Table 7

Claims: CLAIMS We Claim: 1. A polymer blend comprising from 10 to 50 weight percent ofa first component of at least one ethylene and at least one C 3 to C 20 alpha-olefin first polymer having a molecular weight distribution less than 3, a composition distribution breadth index greater than 50 percent and a density in the range of 0.87 to 0.940 g/cm 3 and from 50 to 90 weight percent ofa second component of at least one high pressure ethylene copolymer having a density in the range of 0.91 to 0.94 g/cm 3 and a melt index in the range of 0.2 to 50 dg/10 min. 2. A polymer blend comprising from 10 to 50 weight percent of a first component of at least one ethylene and at least one C 3 to C2 0 alpha-olefin first polymer having a molecular weight distribution less than 3, a composition distribution breadth index greater than 50 percent, and a density in the range of 0.87 to 0.94 g/cm 3 , and from 50 to 90 weight percent ofa second component comprising at least one high pressure ethylene interpolymer of ethylene and at least one ethylenically unsaturated carboxylic acid ester or vinyl acetate; wherein films made from said polymer blend have a hot tack strength of greater than 2 N/l 5 mm over a hot tack temperature range of at least 10°C. 3. A film comprising at least one layer of from 10 to 50 weight percent ofa first component of at least one ethylene and at least one C 3 to C 20 alpha-olefin polymer having a molecular weight distribution less than 3, a composition distribution breadth index greater than 50 percent, and a density in the range of 0.87 to 0.94 g/cm 3 , and from 50 to 90 weight percent ofa second component of at least one high pressure ethylene homopolymer or copolymer. 4. The polymer blend of claim 1 or 2 wherein the first polymer has a composition distribution breadth index greater than 60%, preferably greater than 70%. 5. The polymer blend of claim 1 or 2 wherein said polymer blend comprises from 20 to 50, preferably 10 to 30, and more preferably 20 to 30 weight percent of said first component. 6. The polymer blend of claim 1 or 2 wherein said polymer blend comprises 60 to 90 weight percent of said first component, preferably 70 to 90 weight percent of the first component. 7. The polymer blend of claim 1 or 2 wherein said first polymer has a molecular weight distribution less than about 2.5. 8. The polymer blend of claim 1 or 2 wherein said second component includes a LDPE or an EVA copolymer or EMA copolymer. 9. The polymer blend of claim 1 or 2 wherein said blend has a density in the range of 0.88 to 0.94 g/cm- * ** and a melt index in the range of 0.5 to 30 dg/min. 10. The polymer blend of claim 2 wherein the hot tack temperature range is greater than 12°C, preferably greater than 15° C, and more preferably greater than 20° C. 11. The film of claim 3 wherein said film, at a temperature of about 100° C, has a hot tack strength greater than 2 N/l 5 mm, and preferably, at a temperature of greater than 110° C, has a hot tack strength greater than 2 N/l 5 mm.. 12. The film of claim 3 wherein said film has a hot tack strength greater than 2 N/15 mm and a hot tack temperature range of greater than 10°C to 35°C. 13. A container formed from the film of claim 3, wherein said film has a hot tack strength of greater than 2 N/l 5 mm in a hot tack temperature range of at least 10°C to about 35°C. 14. The container of claim 13 formed by a vertical form fill sealed process or by a horizontal form fill sealed process. 15. An article of manufacture comprising a film, said film comprising the polymer blend of claim 1 or 2. 16. The article of claim 15 wherein the film is a seal layer, the seal layer having a seal initiation temperature less than 100°C and wherein said seal layer has a hot tack strength greater than 2 N/l 5mm at a temperature of greater than 100°C to 115°C. 17. The article of claim 15 wherein said seal layer has a hot tack strength greater than 2 N/l 5mm in a hot tack temperature range of greater than 10°C to 30 °C.

Inventors: DAVIS DONNA SUE, FARLEY JAMES MCLEOD, MEKA PRASADARAO, DAVIS, DONNA, SUE, FARLEY, JAMES, MCLEOD, MEKA, PRASADARAO
Applicants: EXXON CHEMICAL PATENTS INC, EXXON CHEMICAL PATENTS INC.
Application year: 1995
Main classification: C08L23
IPC codes: C08L23, C09J123