CA2185469A1 - Polymers blends, films and articles thereof - Google Patents

Abstract

Polymer blends, films and articles having improved hot tack strength prop-erties. 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 character-istics 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

21 8~469 095125141 r_-,u POLYMER BLENDS. FILMS AN-D ARTICLES TlHEREOF
.
FIELD OF THE lN V~;N 1 lUN
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 10 molecular weight dictrih~tion and rlarrow ~ ;. . rlictrih~ti~n, 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, container and other articles employing a heat seal.
BAC~GROUND OF TLE lN Vlsm 1 lUN
Many articles of " ~ employing heat seals are currently available in the ' ~ For example, plastic parts usefully employed in machines and toys may be c.~ J- l ~l by joining together two individual plastic pieces by 20 hesting one or both of the plastic pieces, pressing them together, and then, allowing them to cool.
Heat sealing is very important in packaging ~ ., ' Packages formed by a heat seal provide for the efflcient ll~l~JUIl~Liv~l of a consumer item within the package, provide a display of the consumer item that promotes sales, and, in the25 food industry, the packaging is employed to preserve the freshness of the consumer item. Most . ~.~ and related to heat seal a " Cl of packages or any other like article requiring a seal also requires excellent ~ J.
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 30 pressure. Polymers or blends of polymers used to make the a}ticles 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.
C~ "~, the entire heat sealed article is ~ d from the same polymer or a blend of polymers or by the ~c, - l . l .~ . .. of the same or different 35 polymers. More often, the article is c. .- . ~ " .. l rd of various areas or layers of different materials, and polymers which provide good heat sealing properties are ~185~9 W0 95/2S141 r~ a,. . I

-2-utilized only in areas, or layers, where heat sealing wiD ultimately be necessary.
This type of ~ u~,Lio.~ iS employed because the artides, for instance multilayerfilms, should have desirable physical and mechanical properties such as clarity,strength, resistance to puncture and tearing, in addition to heat sealing properties, 5 and should be easily processed by high speed equipment. Many plastic materialsare known to possess good physical and mechanical properties but often do not also possess good heat sealing properties.
In the ~ ~,;dl packaging industry, assembly line speeds are very imporLant to a ~ ,.. In the packaging business, the faster the line speeds, 10 the higher production, and thus, a lowering of overaD cost.
There are several important ~ of a polymer or polymer blend that make it I ~i ,ul~ul~ suitable to the packaging industry. One ofthose imporLant iS a polymer . ~ heat seal initiation t~ JI~u-~. This is the . ~ to which the polymer ~ ;- ., must be heated before it wiD
15 usefully bond to itself under stress and/or strain. Relatively low heat seal initiation .,~ are desirable in commercial heat sealing equipment. The lower ~ ,~ provide for higher production rates of the packages on the equipment because the polymer does not need to be heated to as great a L~ .at~ to make the seal. Also, coohng of the seal to attain adequate strength will be faster.
20 (~ , every 10C decrease in seal initiation i . . wiD result in 30%
. ., . in line speed ~ JdU~ )l. There are various polymers in the art that have a low seal initiation l~ pc.~u-~. For example, ethylene vinyl acetate (EVA)and ethylene methyl acrylate (EMA) copolymers have low seal initiation t~ ,.a~ul~.~ but these high pressure low density copolymers have poor hot tack 25 strength.
Thus, in the past in order to improve these poor properties, " t:.
have been blending EMA and EVA copolymers with, for example, linear low density ~ul~ DPE). However, LLDPE's because they have a low content have less desirable heat sealing properties and tend to be hazy.
30 Thus, blends of T .T npE with these copolymers cause a reduction in the overall blend properties.
Anotherimportant~ r ;_1;~ that IlI~ Ult:l~ requireofapolymer .ul~lJ in vertical form fill seal (VFFS) and gas-fiushed horizontal form fill seal ~HFFS) ..1~ -- ., is good hot tack strength. Hot tack is 35 the capability of a heat seal to hold together, when pulled apart, ' '.~, before thoroughly quenching the seal. Hot tack strength is the measure of the maximum _ _ _ . . ..

~VO95/25141 _ 3 P~~
stress that can be apphed 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 tackstrength, on the other hand, is the ability of a heat seal to hold together ~.~ after sealin6 before the seal is cooled.
Hot tack properties are important in pachging 1l, ' ' A high hot tack strength at lower i u.~l~aLL..~ allows packaging '` ..~ to increase line speeds. Hot tack is also the . ~ factor in ' ~ the weight of material that can be pachged in a form-fill seal machine. High hot tack is also ~d ~-t..o_uu~ in cases where bulky products tend to resist package edge sealinO,10 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 ~ is formed into a 'dexible pouch and almost i " '~ f lled with the contents to be pachged and then the pouch is sealed closed. Since it is often difiicult or impossible to maintain commercial sealing equipment at exactly the same sealing 15 i . c; throughout a commercial run, a broader range of sealing i ~ . al~
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 i . ~; window while ' ~ other desirable physical properties, such as a low seal initiation i . ~; and good 20 optical properties.
SUI~qMARY OF TME 1N V~N I ION
The blend of polymers of the invention generally include a first polymer, component A, which has a narrow molecular weight ~ietrih~ltinn and ~
25 ~lictrjhlltir~n and a second poly~ner, component B, which is a high pressure l~cl~,lh,l~ , IlUIIIU~JUl~ ,. or copolymer.
In one . ~ ' of the invention, component A comprises between about I û 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 30 weight percent of the polymer blend of the invention.
In yet another . 1 " t, the polymer blend of the invention is useful as a film layer in an article of ~ ~, particularly in a heat sealable article wherethe flm layer is a seal layer.

3, BRIEF D~SOtl/'TION OF T1FIE DRAWINGS

W0 95125141 ~ 1 8 5 1 6 9 ~ OI
The foregoing aspects, features, and advantages of the invention will become clearer and more fully understood when the following detailed descriptionis read in . , with the P . ,:..g drawings, in which:
Flgure I is a graph of the ~ ' ' . between the hot tack strength versus 5 weight percent of component A for samples numbered EX. 1-9.
Figure 2 is a graph of the . .' ' . 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 .~ . 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 .~ ' ' . 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 . ~ ' ' . between the hot tack strength versus weight percent of component A for samples numbered EX. 9, 16, 19-20.
Figure 6 is a graph ofthe .~ ' ' . between the hot tack strength versus weight percent of component A for samples numbered EX. 12, 21-23.
Figure 7 is a graph ofthe ..' ' . 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 .~ ' ' . between the hot tack strength versus c for samples numbered EX. 1, 10-12.
Figure 9 is a graph ofthe .. ~ ' . between the hot tack strength versus tC..l~ t~C comparing the inventive blends with a prior art blend.
DETAILED DESCRIPTION OF T~E INVENTION
25 ~..t~
The invention concerns a blend of a narrow molecular weight distribution (NMWD) and a narrow , distribution (NCD) polymer, component A, and a high pressure ethylene l r ~ ~ or copolymer, component B, their production and ~j r~' ' ' for their use. The polymer blend of the invention has 30 unique properties which make them particularly well suited for use in polymeric films. These films are very useful in ~, ' requiring heat sealability.
It has been discovered previously that polymers derived from "-catalyst systems heat seal extremely weU, as compared to polymers produced by cu..~ ' Ziegler-Natta catalysts, see PCT Application No. WO 93103093, published February 18, 1993. The polymer blends of the invention are not discussed.

~WO9S/25141 ~)1 $~4~ r ~,o.
.

Surprisingly and ~ r~l~, applicants have discovered a polymer blend having an improved hot tack strength while _ other desirable physical properties such as heat seal initiation i . ~;.
In certain ~l, ' the line-speed (how fast a package can be made) is 5 limited by the hot tack strength of a particular film. High hot tack strength during a wider range of lower sealing i . ~ , increases line speeds and reduces the risk of "burn-through" as well as damage to i . ~; sensitive packaged goods.
Prior art blends typically require higher sealing i . ~. Therefore, 10 dwell tirnes 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 .d~lllc window or range where the hot tack strength is; , '~
attractive. The inventive blends allow for wider tolerances in packaging operations (seal bar t~ t...~, dwell time, line speed, etc.) resulting in a more economical5 packaging operation.
of Polvmer Coml~onent A of the Invention Polymer C~ . A, of this invention can be produced using "- catalyst systems in a pVI~,..~,,i~d~iU,, process in gas, slurry solution or high pressure phase.
2û The process for pGI~ _ involves the pul,~ .~d~iU.. 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 cu~,ul) ' ' reactions involving the p~l~..~i,d~;oi~ of one or more of the monomers, for example alpha-olefin monomers of ethylene, propylene, butene-l, pentene-l, 4-' J'~ , hene-1, octene-l, decene-l and cyclic olefins such as styrene.
Other monomers can include polar vinyl, dienes, norbornene, acdylene and aldehyde monomers. Preferably a copolymer of ethylene and at least one alpha-olefin ~ having from 3 to 15 carbon atoms is utilized in the polymer blends of the invention.
For the purposes of this patent ~ the term " " is defined to contain one or more ~ 1 moidy in ~ with a transition mdal. The " catalyst component is ~ c~ by the general formula (Cp)mMRnR'p wherein Cp is a substituted or, ~..I~p. ..~ 1 ring; M is a Group 4, 5 or 6 transition metal; R and R' are 35 ' . ' '.~, selected halogen, IrJ.IIUI~ yl group, or lydlu~,~bu~l groups having 1-20 carbon atoms; m=1-3, n=0-3, p=0-3, and the sum of m+n+p equals the 21 85~q W0 95/25141 r~ u~.. . 1 oxidation state of M. The " can be substihuted with principaily hJI-.,vn byl Cllhctihl~nt(S) but not to exclude a ,, , a I ' ~, ' uuv, a silicon or a nitrogen atom containing radical or . . . l .~l ;l . ~f~ l or bridged or unbridged or any Various forms of the catalyst system of the " type may be used in the pt~ ;., process of this invention. Exemplaiy of the d~v~ of these " cataiysts for the ~ul~ of olefins is found in U.S. Patent Nos. 4,808,561, 4,871,705, 4,897,455, 4,912,0?5, 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 T- t- .- ~ 1 Pl ' '- '-WO 91/ 04257, WO 92/00333, WO 93/08199, and WO 93/08æl, EP-A-0 129 368, and EP-A-0 420 436 ail of which are herein fully ill~.UII ' ' by reference.These " are activated by aiumoxane described in U.S. Patent No. 4,665,208 or by .,~ described in EP-A-0 520 732, EP-A-0 277 003 andEP-A-0277004andU.S.PatentNos.5,153,151and5,198,401allofwhich ~re herein fully l ' by reference.
All the cataiyst systems described above may be, optionally, ~l~.,l~ll~h..,l or used in , ~-vith an additive or scaveni~ing component to enh~ince cataiytic pluJu~,livily.
Cl n~t~ of Polvmer Cl . A of the Invention A key ~ - of polymer Component A of the present invention is its tiictrihlltinn (CD). As is well known to those skilled in the ari, the tiictrihlltinn of a copolymer relates to the uniformity of dictrih~tinn of among the molecules of the copolymer. r ' " cataiysts are known to ~/vl~r ".. ~l.. veiy evenly among the polymer molecules they produce. Thus, copolymers produced fiom a cataiyst system having a single "- componenthaveaveiynariow . distribution-mostofthe polymer molecules will have roughly the same ~ . content. Ziegler-Natta catalysts, on the other h~vnd generaily yield copolymers having a ~iu..v d~
30 broader ~ ;' ' C~ inclusion will vaiy widely among the polymer molecules.
A measure of . distribution is the "C~ . Distribution Breadth Index" ("CDBI"). CDBI is defined as the weight percent of the copolymer molecules having a ~ content within 50% (that is, 25% on 35 each side) of the median totai molar content. The CDBI of a copolymer is readily determined utilizing well known techniques for isolating ~5 ~wo 9snsl4l 2 p~"o~ /~r~o individual fractions of a sample of the copolymer. One such technique is Temperature Rising Elution Fraction ('I~EE7), as described in W~d, et al., I.~, ~;" Poly. Phys. Ed.. vol. 2Q p. 441 (1982) and U.S. Patent No. 5,008,204, which are ~,vl~Lc,l herein by reference.
To determine CDBI, a solubility distribution curve is first generated for the copolymer. This may be ~.. ~l .l; 'h '-~ using data acquired from the TREF
techrlique described above. This solubility distlibution curve is a plot of the weight fraction of the copolymer that is solubilized as a function of t~,...l,~,...~u. ,,. This is converted to a weight fraction versus ~ distribution curve. For the purpose of simplifying the correlation of . . with elution t~ ,,d~ul~ all fractions are assumed to have a Mn > 15,000, where Mn is the number averdge 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
From the weight fraction versus . , ,iicfrih.lfinn curve the CDBI is determined by ~ what weight percent of the sample has a content within 25% each side of the median ~ content. Further details of ~ the CDBI of a 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 CDBrs generally in the rdnge of 50-98%, usually in the range of 60-98% and most typically in the range of 65-95%. Obviously, higher or lower CDBrs may be obtained using other catalyst systems with changes in the operating conditions of the process ernployed.
Molecular Weight Distribution (MWD), or ~ul~ ;ly, is a well known of polymers. MWD is generally described as the ratio of the weiOoht average molecular weight (Mw) to the number average molecular weight (Mn).
The ratio Mw/Mn can be measured directly by gel permeation ~,h., ~ . ' techniques.
Those skilled in the art will appreciate that there are several methods for MWD of a polymer sample. For the purposes of this patent the molecular weight distribution of a polymer can be determined with a Waters Gel Permeation Clu~ O . ' equipped with UIII~Lyl~O_l columns and a refractive index detector. In this d.,~,lvl,,,,~ , the operating t~ UI~ of the instrument was set at 145C, the eluting solvent was WO 95/25141 2 1 ~ 5 4 6 ~ ol ~

Ll;.,llu.ub~ " and the calibration standards included sixteen p~ ty~ ofprecisely known molecular weight, ranging from a molecular weight of 500 to a molecular weight of 5.2 million, and a ~ul~ ~,.l., l~...~ standard, NBS 1475.
The MWD of the polymer component A of this invention are termed 5 "narrow". For the purposes of this patent ~ "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 Ml of the polymers of the irlvention are generally irl the range of about 0.1 dglmin to about 1000 dg/min, preferably about 0.2 dg/mirl 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.
C~ . ' ' densities of component A of the invention are in the range of 0.85 to 0.96 g/cm3, preferably 0.87 to 0.940 g/cm3, more preferably 0.88 to about 0.935 g/cm3. In another ~ ~ - ' the density of component A is in the range ofO.9OOtoO.915g/cm3,0.915toO.940g/cm3,0.8gtoO.9g/cm3andgreaterthan 0.940 g/cm3 to 0.96 g/cm3.
A particular attribute of Component A polymers is their very low level of extractable . The extractable levels for the polymers of C~ , A
are in the range of between 5.5% to below 0.1%, preferably less than 3%, more 20 preferably less than 2% and most preferably less than 1%. For the purposes of this patent .~ the extractable level of films made from polymer component A
ismeasuredinaccordancewiththeprocessdetailedin21 CFR177.1520(d)(3)(u).
In arlother ~ ~ ' t, component A can comprise a blend of component A polymers, which can be prepared by blending the desired . . in the 25 desired proportion using c(,.... ' blending techrliques and apparatus, such as, for example, screw-type extruders, Banbury mixers, and the like. Alternatively, the blends may be made by direct l,c,l~ ;- without isolation ofthe blend using, for example, two or more catalysts in one reactor, or by using a sirlgle catalyst and two or more reactors in series or parallel.
30 Ck~. ~t.. ;,li. . of Polvmer C- B of the Invention Polymer ('~ . 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 ~o.
4,719,193, i~ JlaL~i herein by reference, discloses a method of preparing 35 polymer cDmponel~ B.

4~S
~WO 95/25141 A ~.IIU... ~
_9 _ Generally, the molecular weight of the component B of the invention is m 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/cm3, typical of Gnear low density pf Lu...u~.ul~..._. (IDPE) and a hinear low density copolymer and the like.
S For the purposes of this patent ~ the term "high pressure p~ ,ll.JI~ Ilu...~ul~..._l or copolymer", C~ . B, is defined as a pf l~_LI.~ 1 having a density less than 0.940 g/cm3 or an ethylene copolymer of ethylene and an _L~IJ~ ' ' carboxylic acid ester or vinyl acetate. Preferred ~L~.,' "~,, ~ acrylic acid esters include, for 10 ex~unple, methyl acrylate, butyl acrylate, and ethyl acrylate. A preferred monomer is vinyl acetate. These c~ are present within a range of from about I to about 45 weight percent, preferably from about I to about 25 weight percent, based on the total weight of the Component B polymer.
Ethylene methyl acrylate copolymers suitable for use in this mvention are 15 available from Exxon Chemical Company, Houston, Texas under the trademark Optema~M. Ethylene vinyl acetate copolymers suitable for use in the mvention arealso available from Exxon Chemical Company, Houston, Texas under the trademark ESCORENE7M.
The B component of the polymer blend of the invention may be a blend of 20 different prior art polymers, each differing in one or more of: molecular weight, MWD, .,~ . . . type and content, density, MI and CD.
13LENDS. ~lLMS AND ARTICLES OF TEIE INV~ ON
The polymer blend of the invention, herein referred to as, the "A-B blend", 25 may be used to form articles with pa~ticularly desirable heat sealing properties. In particular, the A-B blei~d may be processed into films which possess pa~ticularly desirable heat seahng . ~
For example, the A-B blend may be used to form films which are m tum fommed into bags or pouches by heat sealing techniques h~own in the art. The heat 30 sealable film may also be used as package sealing material, for example, the film may be placed over the opening of a container, and then secured to the containerby the application of heat. This techrlique 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 35 portions of the article not utilized for heat sealing. In the portions of the article that are used for heat sealh~g, the language "fommed from" is intended to mean WO 95125141 2 ~ ~ 5 ~ ~ q ~o " In one ~ 1 ' t, all articles or portions of articles described may also be cc.. ~.t, u.,Lcd to consist essentially of the inventive A-B blends. In other vords, the heat sealing portion of imy article described herein may consist essentially of the inventive A-B blend. However, the blend may have additional ~ 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 amd cooled to form a tubular film. The tubular film may be slit and unfolded to form a fiat 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 fromother materisls such as other polymers, p~ J~ , (PP), polyester, LDE~E, HDPE, polyamide, p~ 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 ~
feedblock and die assembly to yield a film with two or more layers adhered together but differing in: . 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 pa~ticularly usefiulwhen the A-B blend heat seal layer is to be applied to substrates that are woven or knitted from natural or synthetic fibers or yarns, e.g., textiles, or substrates made from non-polymer rnaterials such as glass, cdc, paper or metal.
Multiple layer films may also be formed by combining two or more single layer films prepared as described aboYe. The two layers of a 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 t~ UI ~ sufficient to sofren at least one of the article portions. The article portion which has been sofrened by heat is formed from theA-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 ~WO9S/25141 218~469 P .~
from the A-B blend. Other portions of the article may be CO;~tl ..~,t~,~ 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 S comprising the A-B blend polymers. The body may be .,usL. u~t~,~ of any of a number of different materials such æ paper, plastic, glass, ceramics, metals andtextiles. Tbe body can be ~ with walls that are impervious to liquids and/or gases or the body may be constructed to allow the pæsage of liquids and/or gases. The body may also be ~ with one or more portals to allow passage of small items through the body wall or to allow the consumer to inspectthe item stored in the container without removing the item from the container.
In one ~ v~ , 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 L ~' 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; ' - " of the polylner blend of the invention the second component contains about 50 to about 100 weight percent of a high pressure ethylene I . '.~ or copolymer, preferably 60 to 95 weight percent, more preferably 65 to 90 weight percent, even more preferably 70 to 90 weight percentand most preferably 75 to 90 weight percent.
The polymer blend of the invention or the individual: -~r A and B
30 rnay also be cv l,v ~1 with various Wll' additives known in the art such æ, for example, ' , W stabilizers, pigments, fillers, slip additives, block additives, and the like.
Seal initiation t~ .. c; is defined as the ~ u.~ at which a hot tack strength of 2 N/15 mm is observed. In one ~ 1 v~ the films of the invention 35 generally have a seal initiation t.,..l~ -L~ Iess than about 110~C, preferably less 2 1 ~5469 WO 95/25 14 1 P ~, I / IJ ~.. _. .

than about 105C, more preferably less than about 100C, and most preferably less than about 95C
Hot tack strength is measured in N/15mm Hot tack t~ lu.~; range or hot tack i . ~; window is defined as the . range where a hot tack 5 strength of 2 2 N/15 mm is maintained In one ' ' the films of the invention have a hot tack strength greater tham about 1 5 N/15 mm, preferably greater than 2 N/15 mm and most preferablygreaterthan3N/15mmataLt...l!~,.~u.cofgreaterthanabout 100C
In amother ' " the fihms of the invention haYe a hot tack strength greater than about 1 5 N/15 mm, preferably greater tham 2 N/15 mm and most preferably greater than about 3 N/15 mm at a tu...~dlu.~ of greater tham about 105C.
In yet another ~, ' ~ " the films of the invention have a hot tack strengh greater than about 1 5 N/15 mm, preferably greater than 2 N/15 mm and most preferably greater than about 3 N/15 mm at a ~ of about 110C
In one ~, l; ,1 the films of the invention have a hot tack strength t~.tJ~a~ ; window greater than about 10C at a hot tack strength greater th~m orequal to about 2 N/15 mm In another ~ ~ - " the hot tack strength L~ ,.dul~ range is greater than about 12C to about 40C, preferably greater than about 1 5C to about 40C, more preferably greater tham about 20C to about 40C and most preferably greater than about 25C to about 30C at a hot tack strength greater than about 2 N/15 mm, preferably greater than about 2 5 N/15 mm and most preferably greater than 3 N/l 5mm In still another ~ ~ " the film of the invention has a hot tack strength greater tham about 2 N/15 mm at a i p~ ~ between about 100C to about 115 C.
In still yet amother ~ " the film of the invention has a hot tack strength of greater than about 2 5 N/15 mm at tu..~ lu. ~; greater than about 100 30 C.
In a fwther l ,, li 1, the film of the invention has a hot tack strength greater than 2 N/15 mm preferably greater than 2 5 N/15 mm, more preferably greater than 3 N/l 5 mm at a t~,...~..,. allll ~ of greater than about 80C or in the range of about 80C to about 95C
EXA~qPLES

- 095125141 2 i a~b~

In order to provide a better, ' " ~ of the present invention the following examples are offered as related to actual tests performed m the practice of this invention, and illustrate the surprising amd unexpected properties of the A-B
blends of the invention and are not mtended 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 i . ~i range is 149-260C, 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 I is prepared similar to Ul and U2 usmg free radical initiation and bigh pressure conditions in a tubular reactor, using vinyl acetate as the Sample No. U4 in Table I is prepared similar to Ul and U2 using free radical initiation and high pressure conditions m a tubular reactor, with methylacrylate and acrylic acid as the;
~XAMPLE II:
Sample No. X1, is prepared using silicon bridged transition metal catalyst.
The catalyst IJl~,lJal~l~iU.I and process is outlined m U. S. Patents 5,017,714 amd 5,120,867. Sample No. Xl is prepared using the catalyst mentioned above, and reaction conditions of ethylene pressure of 19000 psig (131,005 kPa), h.~ lu in zone I of 137C, and zone of 5 166C, butene 9 mole%, and hexene 45 mole%.
SampleNo. X2 is prepared similar to Xl, except the t~~ ul~; in zone I was 135C and zone 5 of 163C.
Sample No. X3 is prepared in a similar malmer as samples Xl and X2, except only hexene is used as a ~.~
The polymer properties and the catalyst and process details on the polymers are shown in Table 1.
Blend r. . .
The blend, . of the invention were melt 1 ~ using a Werner P'deider twin screw extruder followed by ~ " ~i, l i.~. .
Films Pl ~ .
The blends and the prior art p~ L,".,~ were used as seal layers on high density pul~ ,.lc ~PE) substrate and were made using a Killion co ~
, _ . , . . _ . _ . . . . .. . _ . .. . . . .

21~469 wo 95/2514~ . o line to give AIB Co..Jt~ ,,.,liu... The thickness of the HDPE and the seal layers were ~yy~ 1.0 mil each (25 ,um).
F.~MPLE m:
The blend samples numbered EX. 2-8, 10, I l, 13, 14, 18, 19, 20, 22, 23, 24, 25, 27, and 28 were made by melt ~ ' of the blend using a Werner Pneider twin screw e~A~truder followed by ~ 11 t; ~ step.
EX~MPLE IV:
The blend samples numbered EX. 2-8, 10, I l, 13, 14, 16, 17, 19, 20, 22, 23, 24, 25, 27, and 28 and the prior alt .,u.... " ' p~ JL,..~, samples numbcred EX. 1, 16, 21, and 26, and the polymer samples numbered EX. 9, 12, and 15 were used as seal layers on high density yul~.lhJI~ . (HDPE) substrate and were made using a Killion ~". . I . . .- - ..n line to result in A/B (A - HDPE, and B -15 seal layer) type of c.-~ . `t, . .. l ;'~ ~ The thickness of the HDPE and the seal layers were ~yyl~ 1.0 mil each (25 ,um).
E~AMPLE V:
The hot tack strength is measured by heat sealing the films at i . ~.O
20 snd separating and measuring the hot tack strength ' " ',~ after sealing. A
~u.. ~".,;~ hot tack tester (DTC Hot Tack Tester Model 52-D) is used for hot tack ~ ' The conditions for sealing and hot tack strength ..~
were as follows: dwell time - 0.5 s, pressure - 0.5 Nlmm2, 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 Xl, X2, and X3, and the ~ t~) as measured from 90 to 130C is shown in Table 2.
The hot tack strength data for the samples numbered EX. 16-20 (blends of U2 with Xl, and X2, and the ç~ .o~l. .t~) as measured from 90 to 130C is shown in Table 3.
The hot tack strength data for the samples numbered EX. 21-25 (blends of U3 with Xl and X2 and the c~ ) as measured from 70-110C is shown in Table 4.

~WO 95/25141 2 1 ~ ~ ~ 6 ~ ol The hot tack strength data for the samples numbered EX. 26-28 (blends of U4 with Xl and the r ~ ) as measured from 80-120C is shown m Table 5.
Predicted Hot Tack Strength at a selected ~,,..I,~,.~Lu- ~ XC = FA x HTA +
FB x HTB where, FA is the weight fraction of the component A of the blend, HTA
5 is the hot tack strength for 100% component A at i . ~ XC, FB is the weight fraction of Component B of the blend, and HTB is the hot tack strength for 100% Cr~mpr~nr-nt B at i . ~ XC. The error bars in Figures 1-8 for the observed hot tack strength are based on _ ~, which represents one st~mdard deYiation.
The predicted maximum hot tack strength amd the obserYed maximum hot tack strength values for the samples numbered EX. 1-15, along with the r. . ~ of the blends are shown in Table 6.
The predicted maximum hot tack strength and the obserYed hot tack strength values for the samples numbered l6-28, along with the .,.. ~ ofthe blends is shown m Table 7.
The predicted maximum hot tack strength shown in Tables 6 and 7 is calculated by using the . ' ' .
Figure I represents the maximum observed hot tack strength versus weight percent of Xl m Ul for samples numbered EX. 1-9, amd the predicted maximum 20 hot tack strength for samples numbered EX. 2-8. The hot tack values for the inventiYe blends is better than the cu~ Lional ~cl~.,Lhjlu..~ sample EX. 1. In addition, the observed hot tack values for the mventive blends is in general greater than the predicted hot tack values, and this result is l~nr~rt~
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 hottack values for samples numbered EX 10 and 11. Clearly, the observed maximum hot tack strength values for samples numbered EX. 10 amd 11 are S;~ ir.~a...ly and '~ 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 amd 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 Xl in U2 for the samples numbered EX. 16-18, and 9, and the predictedhot tack values for samples numbered EX. 17 and l o. Clearly, the observed .... .. ... .. . . . _ _ 21 ~5~6~
W0 95125141 1~ 9!

maximum hot tack strength Yalues for samples numbered EX. 17 and 18 are ~ amd ~ , 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 samples numbered EX. 16, 19,20, and 9, and the predicted hot tack values for samples numbered EX. 19 ~md 20. Clearly, the observed rnaximum hot tack strength values for samples numbered EX. 19 and 20 are better than the predicted maximum hot tack strength.
FiBre 6 represents the maximum observed hot tack strength versus weight percent of Xl im 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 amd 23 are _ r ' ~ and ~ , better than the predicted maximum hot tack strength.
Figre 7 represents the maximum observed hot tack strength versus weight percentofX2inU3forthesamplesnumberedEX.21,24,25,and9,andthe predicted hot tack values for samples numbered EX. 24, and 25. Clearly, the observed maximum ho~ tack strength values for samples numbered EX. 24 and 25 are ~ and I . ".~, better than the predicted maximum hot tack strength.
Flgre 8 represents the hot tack strength versus t~ J~a~ ; for samples numbered EX. 1, and 10-12. The hot tack strength for the inventive blends EX.
10 and 11, is ~ r ~ better than the prior art ~ ,..c EX. 1, and at 40 wt% component X2 im prior art pul~LhJI~ , sample EX. 1, the maximum hot tack 25 strength is ~ better than one would expect based on linear additivity of the two - r ' involved (Ex. I amd EX. 12).
FiBre 9 represents the hot tack strength versus i . c; for a prior art pGl~,Ll.jl~..., sample numbered EX. 1, and a prior art blend of LI)PEILIDPE
(80/20 wt%) in , to the inventive blends of samples EX. 3 and 10 which 30 contain 20 wt% of r ' Xl and X2 ~ ,Li~ in the prior art p~ ,LhJI. ..~ EX. 1. As is clearly c' i, the mventive blends show improved hot tack between 95-105C in . to the prior art samples EX. I
and a blend of LDPELLDPE. In addition to the higher peak hot tack, the imventive blends show broader sealing window (def ned as the i . ~ range 35 where hot tack strength stays above a certain level, for example 2 N115 mm).

2 ~ ~ ~46~
~WO 9S/25141 r~ a,. I

While the present invention has been described and illustr2ted by reference to particular ~ v l ~ thereof, it will be ~ . by those of ordinary skill in the 2rt that the invention lends itself to variations not necessarily illustrated herein. For instance, the catalyst system may comprise various other transition S metal - th2t are activated by 21umoxane 2nd/or ionic activators as the cocatalyst to produce polymers having a narrow molecular weight di~ 2nd rlarrow ,lictrihlltinn Further, high pressure ethylene ~ /CJI~ can be utilized in the polymer blends of the invention. Also, the polymer blends of the invention 2re useful in 2rticles of r ' ~: such as potato chip bags, cereal bags10 2nd pouches, cookies and cr2cker bags and pouches, detergents and other powder bags, or c2ndy cont2iners, liquid containers, such as bag-in-box ., vegetable or fruit bags and me2t and cheese bags. The film of the irlvention are 21so useful in shrink packaging or plastic wr2p ~ r ' Reference should be made solely to the 2ppended cl2ims for purposes of 15 1 , the true scope of the present invention.
Table Sample ~ 1~ MI/Density (~/10 min/~/cc) - : Iu~lu~t~ . /0.917 : ree ac ca/Ar oclave Iulllu~u r.. ,~ / .925 ree at ca~Tu ular ~inyl Acetate . C ree . .2t ca/Tu~ular _' ., M~.LI~.,I~' ~'ree. at ca~Autoclave and Acrylic Acid Xl A Hexene, 3.510.90 High Pressure Butene X2 A Hene, 1.5/0.90 High Pressure Butene X3 A Hexene 1.2/0.9 High Pressure ~1 8~4~
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Claims (18)

- 22 -

1. A polymer blend comprising from 10 to 20 weight percent of a first component of ethylene and at least one C3 to C20 alpha-olefin copolymer 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 g/cm3 and from 80 to 90 weight percent of a second component of at least one high pressure ethylene homopolymerhaving a density in the range of 0.91 to 0.94 g/cm3 and a melt index in the range of 0.2 to 50 dg/10 min.

2. A polymer blend comprising from 10 to 40 weight percent of a first component of ethylene and at least one C3 to C20 alpha-olefin copolymer 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/cm3, and from 60 to 90 weight percent of a second component at least one high pressure interpolymer comprising ethylene and at least one ethylenically unsaturated carboxylic acid ester or vinyl acetate wherein said second component has a density less than 0.940 g/cm3.

3. A film comprising from 10 to 20 weight percent of a first component of at least one ethylene and at least one C3 to C20 alpha-olefin copolymer 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/cm3, and from 80 to 90 weight percent of a second component of at least one high pressure homopolymer of said second component having a density 0.91 to 0.94 g/cm3.

4. A film comprising from 10 to 40 weight percent of a first component of at least one ethylene and at least one C3 to C20 alpha-olefin copolymer 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/cm3, and from 60 to 90 weight percent of a second component of at least one high pressure interpolymer of ethylene and at least one ethylenically unsaturated carboxylic acid ester or vinyl acetate, said second component having a density less than 0.940 g/cm3.

5. The polymer blend of claim 1 or 2 wherein the first component has a composition distribution breadth index greater than 60%, preferably greater than 70%.

6. The polymer blend of claim 2 wherein said polymer blend comprises 10 to 30, and more preferably 20 to 30 weight percent of said first component.

7. The polymer blend of claim 1 or 2 wherein said first polymer has a molecular weight distribution less than 2.5.

8. The polymer blend of claim 1 wherein said second component comprises a LDPE.

9. The polymer blend of claim 2 wherein said second component comprises an EVA
copolymer or EMA copolymer.

10. The film of claim 3 or 4 wherein said film has a hot tack strength of greater than 2N/15 mm over a hot tack temperature range of 10°C.

11. The film of claim 3 or 4 wherein the hot tack temperature range is greater than 12°C, preferably greater than 15°C, and more preferably greater than 20°C.

12. The film of claim 3 or 4 wherein said film, at a temperature of 100°C, has a hot tack strength greater than 2 N/15 mm, and preferably, at a temperature of greater than 110°C, has a hot tack strength greater than 3 N/15mm.

13. The film of claim 3 or 4 wherein the film comprises 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/15mm at a temperature of greater than 100°C.

14. A container formed from the film of claim 3 or 4, wherein said film has a hot tack strength of greater than 2 N/15mm over a hot tack temperature range of at least 10°C.

15. The container of claim 14 formed by a vertical form fill sealed process or by a horizontal form fill sealed process.

16. An article of manufacture comprising the film of claim 3 or 4.

17. The article of claim 16 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/15 mm at a temperature of greater than 100°C.

18. Use of the polymer blends of claim 1 or 2 to produce a film having a hot tack strength of at least 2N/15 mm over a hot tack temperature range of at least 10°C.