CN1849348B - Polymers of ethylene and, optionally, copolymerizable esters, films using such polymers and stretch hood packaging processes using such films - Google Patents

Abstract

The invention relates to a polymer comprising units derived from ethylene, said polymer having: a) a Melt Index of from 0.05 to 20 g/10 min as determined by ASTM-1238 Condition E; b) at least 10 per 1000 C-atoms of short chain branches, containing five carbon atoms or less, as determined by C13 NMR, and less than 3.5 mol %, of units derived from a copolymerizable ethylenically unsaturated ester, c) a density of from 0.90 to 0.94 g/cm<3>, preferably 0.91 to 0.935 g/cm<3>, especially 0.92 to 0.93 g/cm<3> as determined by ASTM D1505, and d) a relaxation time as described herein of at least 10 s.Such polymers are obtainable by polymerization by free radical polymerization using a chain transfer agent that incorporates into the polymer chain such as an alpha-olefin, preferably propylene, as achain transfer agent, preferably in a tubular reactor under circumstances to favor LCB formation in a down stream part of the tubular reactor. The polymer may be used for stretch hood film, preferablyas a blown film coextruded tube comprising: a) a core of the above polymer; and b) a skin layer, on each side of the core which may be of the same or different composition, comprising at least 60 wt% of an LLDPE having density of 0.91 to 0.94 g/cm<3> as determined by ASTM-D 1238 Condition E and hexane extractables less than 1.5 wt %, said skin layer containing less than 7500 ppm of anti-block particulates and said film having an elastic recovery after a 100 % stretch of at least 40 % and providing a normalized holding force per 100 m thickness pre-stretch at 85 % stretch after an initial stretch of 100 % of at least 20 N/50 mm at a deformation rate of less than 10 % of the starting length per second.

Description

But the polymkeric substance of ethene and the copolyesters of choosing wantonly uses the film of this polymkeric substance and the stretch hood packaging processes of this film of use

FIELD OF THE INVENTION

But the polymkeric substance of the copolyesters class that the present invention relates to ethene and choose wantonly relates to film that uses this polymkeric substance and the stretch hood packaging processes that uses this film.This film can be used to pack in a kind of purposes and generally is supported on backing plate or other bracing frame so that store or the object or the collection of objects of transportation.But the invention particularly relates to polymkeric substance wherein and be ethene and copolyesters class interpretation situation and relate to the multilayer film that epidermal area wherein is provided on the one or both sides of sandwich layer.

Background of the present invention

Term " cover (stretch hood) stretches " refers to a kind of packaging system of form, and wherein the film pipe is used for forming cover with harness and protection article.Article can be Individual Items, as white domestic appliances (washing machine or refrigerator) or electronic product.These article can be object such as bottle, the bag of soil, cement, fertilizer, polymeric aggregate or concrete briquetting, fragment of brick, ceramic tile, the set of thermal insulation material.One or more objects usually are supported on backing plate or other bracing frame, are called the clamping plate shipment here, to allow to utilize the charge and discharge operations of fork truck jacking equipment.The film pipe is produced by blown film extrusion molding (it can involve coextrusion) easily, so that produce the membrane pipe from annular die.By using blown film to extrude, extruded pipe can leveling so that being provided with the back uses, need not to cut in the vertical it.The cover that stretches depends on, tensioning equipment by the film pipe packaged object or collection of objects periphery be in form cover in the stretched condition after, in the elastic shrinkage of the film pipe of the object that will pack or collection of objects periphery.This cover protection, maintenance clamping plate child shipments are together to prevent to come down in torrents (if necessary) and block the clamping plate child shipments in transportation and storage process avoiding damage and environmental factors (moisture) influence.This cover can at one end seal the top with protection and covering clamping plate child shipments.Perhaps, this cover can be at open-top, if provide protection is not too important.

Compare as shrinking cover (wherein the utilization of film pipe heat shrink) or stretch-wraps material (object or collection of objects that wherein flat film parcel will be packed) with the packing of other form of clamping plate shipments, the packaging stretch hood system can provide some advantage.In shrinking cover, contain film fusion orientation when extruding of height-oriented polymkeric substance (usually be LDPE, optional have some LLDPE), when peripheral in the clamping plate child shipments and on it can shrink and thicken when shrinking.Heating can make the position that film is retracted to can provide confining force, and this confining force can keep together child shipments and come down in torrents avoiding.This process can consume more energy, and the use of heat can produce potential safety hazard.Film is thicker and inflexible, and needn't be designed to easily stretch before thermal contraction.In the stretch-wraps material, more linear polymkeric substance (usually be linear low density of polyethylene LLDPE, choosing wantonly has some VLDPE (having the ethylene copolymer than LLDPE less dense)) is extruded, and obtains required tensile properties.Must add Tackified polymeric or other composition so that determine enough clinging powers from the teeth outwards.This film is adhered to consumingly when rolling and (is called adhesion) on itself and can produces big noise when this film of unwinding under high speed.This film approaches and is designed to easily to be stretched to when being applied to the child shipments periphery and is higher than 200% conspicuous level.Confining force is provided by the convergent force that oriented film applied.The stretch-wraps material is used as straight, non-tubular-film, and provides the incomplete protection effect for environmental factors.

The present invention relates to interpretation and multilayer film, they are described with regard to their uses in the cover that stretches is used.Yet these polymkeric substance and film can have some performance characteristics, make that they can be other local application.Suitable purposes can be the flexibility that places labels on bottles or supply that silage or greenhouse films are used or supply arrangement (collation) to shrink to use used agricultural film.

The film pipe is packed object or collection of objects on the packaging stretch hood machine purposes involves the step of giving an example and describing for the sealed situation in cover top that stretches in EP0461667.

(referring to Fig. 1 and 2 of EP0461667) flatted membrane pipe is by unwinding with spread out so that be enclosed within on the stretcher in first step, and the latter can be the form of shown frame form or four jiaos of equipment that show for example in Fig. 6.In this stage, the top of pipe was heat-sealed before periosteum cuts off, and produced the bag of upset.Stretcher equipment can enter into the bag of upset from the below.Mould material utilizes the dismounting roller (not shown in FIG.) on each angle to collect (gathered) on stretcher.Film is sandwiched in the roll gap between stretcher and the roller.Dismounting roller (takedownrollers) causes film laterally folded and collection on stretcher.Enough frictions of having between film and the roller have are so that carry out effective collection (gathering) and dismounting (take down) operation.Heat-sealing on the top of periosteum needs high thermal viscosity and sealing intensity, so that hold out against follow-up stretching.Collect, laterally folded pipe transversely expands at film by stretcher then, exceeds the physical dimension of clamping plate child shipments.This needs predetermined elasticity, so that pass through lax answer (referring to Fig. 3 of EP0461667) after allowing to stretch and stretching.The stretcher of having expanded with cross directional stretch film pipe passes through on the clamping plate child shipments downwards then, launches and this film that gets loose (referring to Fig. 4 of EP0461667).This requires the film pipe appropriate frictional coefficient being arranged so that allow it easily to get loose from stretcher under its tensile state and between the stretcher, allows film be subjected to enough power in the vertical to realize the longitudinal stretching of appropriateness simultaneously.Stretcher remains on extended mode and returns back up to the startposition after the lower rim of film cover that gets loose, and through this cover, seals on the top, shrinks around the clamping plate child shipments now.

Advised that different film tubular constructions is used for the cover that stretches.WO 00/37543 discloses the resulting trilamellar membrane of blend of ethene (E) vinyl-acetic ester (VA) of the plastomer (the 8th page of 10 row is capable to 16) that uses metallocene-produced and the amount of preponderating, high-load VA is arranged, and the EVA upper layer with low VA content contains SiO in sandwich layer ₂As the antiblocking friction modifiers.Term " plastomer " is used to refer to the low density copolymer of ethene and alpha-olefin.The EVA polymkeric substance that is used for WO00/37543 is produced in high-pressure process, in the general autoclave reactor of describing for example in EP0099646.These polymkeric substance generally are divided into two types, referring to WO00/37543: low VA and high VA.

The convergent force of the use restriction film cover of high EVA.It is soft that film tends to, and stretches easily but only apply limited power to be returned to its pretensioned state.Influence and film confining force that high EVA is subjected to environment heat easily die down.These defectives can only be partly compensated by the interpolation of plastomer.The surface friction that is provided by low EVA epidermal area (generally having wider molecular weight distribution) can only come the control of out of true ground by high-load antiblocking agent, and the latter has negative impact for transparency and mechanical property.

The whole film of WO00/37543 provides weak confining force by contraction after it has been stretched to largely in packaging stretch hood.Film thickness has to increase to obtain enough confining forces.In case in peripheral stretching of child shipments and contraction, in a single day this cover has low puncture resistance, and is punctured, have poor anti tear and spread, this easily causes coming down in torrents of clamping plate child shipments.Stretching fully also may cause wash boarding, and wherein the different piece of film differently stretches, and causes forming thicker and thinner membrane portions.In addition, when the clamping plate child shipments is in higher temperature following time, confining force may weaken.The adjusting meeting of special packaging stretch hood machine or packing purpose needed frictional coefficient realizes being restricted inadequately on the scope and/or being difficult under the situation of not damaging other required film properties.Many stretchable elastomeric polymers are viscosity inherently.If this base polymer is selected for the surface of stretch hood film, then need the antiblocking agent of high consumption so that make the heat-sealing top of this cover become smooth and closely tighten up adaptive in clamping plate child shipments periphery.This antiblocking agent consumption can make film opaque and interference machinery and optical property.

US6291038 has described the film of the heat shrinkable with medium VA EVA content, has VA and narrow molecular weight distributions and highly short-chain branched of 9-20wt%.

Here the short-chain branched finger of Shi Yonging is by the detectable alkyl of 13C NMR technology branch, and get rid of since vinyl acetate copolymerization with acetoxyl group branch that monomeric introducing brought.Definedly in the polymkeric substance that in the high-pressure free radical polymerization, makes short-chain branchedly mainly sting mechanism and obtain, caused forming the branching of ethyl and butyl-type branch and some higher degrees from the Roedel tail.Other short chain branch is that these branches generally have effect or the purpose that reduces molecular weight and are called telogen or transfer agent because the introducing on the chain of alpha-olefin causes.The use of propylene transfer agent causes forming methyl type short chain branch.The use of iso-butylene also causes forming methyl type short chain branch.Use the NMR technology, can be determined at carbonatoms in the short chain branch and all types of short chain ramose numbers.When with the 1000C atom when being the amount of basal expression SCB or LCB, be meant whole carbon atoms for the reference of 1000C atom, comprising the carbon atom in the acetoxyl group group, unless otherwise mentioned.

Atofina sells the EVA polymkeric substance of the grade of low VA content: EVATANE (registered trademark) 1005VN3, it has the VA content of 3.5mol% (9.8wt%) and 0.33 melt index.Film has limited short-chain branched and short time of relaxation.

Therefore, be used for packaging stretch hood the known membrane structural limitations performance and the saving (savings) that can obtain from the packaging stretch hood system.Range of application (wherein it plays a role at oriented film or contraction cover packing competitively) is restricted inadequately.

The objective of the invention is to improve the characteristic of packaging stretch hood film.Especially the objective of the invention is between stretchiness and confining force, to realize better balance.The objective of the invention is to allow: the minimizing of the given needed film weight of confining force a) is provided in packaging stretch hood; B) the better friction control and the more even stretching of the film of packaging stretch hood operation, and/or c) improved package integrity properties and transparency, puncture and tearing, and/or the stress relaxation that after the packaging stretch hood operation has been finished, under higher envrionment temperature, has reduced.

General introduction of the present invention

The present invention relates to new vinyl-type polymer in one aspect, and it can be used to improve the oriented film characteristic.The present invention relates to new membrane structure and composition in yet another aspect, and they can be used to improve the oriented film characteristic.Aspect relevant with membrane structure, new ethene polymers can be used as sandwich layer.Perhaps, the different sandwich layers of forming, the EVA interpretation as common can be used for the membrane structure occasion.Each of these aspects can help the stretch hood film characteristic; Excellent properties will have been accumulated owing to the combination of these aspects in these aspects.

The polymkeric substance that comprises units derived from ethylene is provided in one aspect, and this polymkeric substance has:

A) melt index of the 0.05-20g/10min that measures by ASTM-1238 condition E;

B) at least 10 short chain branches of per 1000 C atoms, contain five carbon atoms or still less (measure) by C13 NMR but and be lower than the unit of 3.5mol% derived from the ethylenic unsaturated ester class of copolymerization,

C) 0.90-0.94g/cm that measures by ASTM D1505 ³, preferred 0.91-0.935g/cm ³, 0.92-0.93g/cm especially ³Density and

D) at least 10 seconds the time of relaxation of here describing.

Major part in these parameters is that those skilled in the art are known.Be that rheology is derived and reflected the time that polymer chain relaxes and spent after the distortion in molten state time of relaxation.It will be subjected to all respects influence of polymer architecture, as long chain branching level, molecular weight and molecular weight distribution, if time of relaxation is oversize, and then polymkeric substance strain hardening prematurely in the cold stretching process.The long balance fusing orientation of having impelled film in the blown film extrusion time of relaxation.In use laterally (TD) stretches and will allow vertically on (MD) some stretchings are being arranged under the precondition that does not have fracture, thereby except edgewise confining force is arranged, also provides confining force from top to bottom.

Per thousand carbon atoms of preferred polymers contain at least four, five SCB especially, and this SCB contains three carbon atoms or three following carbon atoms.Preferably, be at least 11 and/or be lower than 20, or be lower than 15 time of relaxation.

Polymkeric substance of the present invention can preferably use tubular reactor production easily in radical polymerization.Units derived from ethylene is suitable to be accounted for more than the 85wt% of polymkeric substance.The short chain ramose amount that contains 5 carbon atoms or 5 following carbon atoms is suitable to be lower than 30, preferably is lower than 20/1000 C atoms.

But the ethylenic unsaturated ester of copolymerization can not exist, but but preferred polymers contains the long chain branches that contains 6 or 6 above carbon atoms of at least 1 in the unit that forms derived from the ethylenic unsaturated ester class of copolymerization of 1-3mol% and/or per 1000 C atoms, measures according to C13 NMR.The ethylenic unsaturated ester class can be the senior analogue such as the ethylene acrylic ethyl ester of ethylene methacrylate and it, but ethene-vinyl acetate copolymer preferably.If VA content is too high, then extending so that polymkeric substance can not shrink fully after producing required confining force.Aptly, polymkeric substance also has the bimodal molecular weight distribution of being measured by GPC DRI and/or is lower than 20 seconds time of relaxation.Bimodal pattern can show as acromion in the collection of illustrative plates of expression molecular weight distribution.

Although polymkeric substance can have the 20g/10min of being lower than, preferably be lower than 15g/10min and especially be lower than the melt index of 10g/10min, preferred polymers has 0.1-4g/10min for blown film is extruded; Preferably be lower than 2g/10min and especially be lower than the melt index of 1g/10min.

In another aspect of the present invention, polymkeric substance is described according to employed technology characteristics in its manufacturing, and this has caused its particular performances.The invention provides the polymkeric substance that comprises units derived from ethylene that can obtain aspect preferred at this by the Raolical polymerizable that uses chain-transfer agent, this polyreaction is introduced preferably propylene as chain-transfer agent so that obtain a kind of polymkeric substance in polymer chain, the latter has the melt index of the 0.05-20g/10min that is measured by ASTM-D 1238 condition E, and but per 1000 at least 10 in C atoms contain the short chain branch (being measured by C13 NMR) of 5 or 5 following carbon atoms and are lower than the unit derived from the ethylenic unsaturated ester of copolymerization of 3.5mol%.

Radical polymerization can be carried out in stirred autoclave, but polymkeric substance preferably helps producing in the envrionment conditions that LCB forms in tubular reactor in the downstream part of tubular reactor, and preferably has the 0.90-0.94g/cm that is measured by ASTM D1505 ³, more preferably 0.91-0.935g/cm ³, 0.92-0.93g/cm especially ³Density, and/or preferably have time of relaxation of describing of at least 10 seconds here.LCB forms and can obtain promoting by transfer agent concentration and/or the intensification in the downstream part of tubular reactor that reduces.Above according to density, time of relaxation, ethylene content, short chain branch level, the feature of the polymkeric substance of the present invention that molecular weight distribution and melt index are discussed can similarly be applicable to this one side of the present invention.

The preferred transfer agent of selecting is to provide high introducing tendency.Therefore propylene is the preferred 60-100% that also preferably accounts for total transfer agent content.Yet can use other transfer agent (iso-butylene, aldehydes) in a small amount.

More broadly, the method of producing polymkeric substance can be a free radical polymerisation process, but it is included in to help stinging by tail and forms short chain branch and help under the condition that propylene introduces obtaining a kind of polymkeric substance with the ethylenic unsaturated ester of ethene and copolymerization with as the propylene input of chain-transfer agent, but the latter has melt index and the optional unit derived from the ethylenic unsaturated ester class of copolymerization that is lower than 3.5mol% of the 0.05-20g/10min that measures according to ASTM-D 1238 condition E.The condition of polyreaction should obtain foregoing optional and preferred polymer features.

Preferred this polyreaction be in tubular reactor under 2200-2700 crust and 180-330 ℃, the repeatedly injection of raw material and initiator is carried out, but the injection that in the downstream reaction district, has reduced or do not had monomer to inject and randomly reduced or do not had transfer agent.The outlet temperature peak value in the downstream reaction district that has reduced or do not had monomer to inject can surpass the thermal spike among at least two thermal spikes of two reaction zones of upstream, end reaction district.The outlet temperature peak value in the downstream reaction district that has reduced or do not had monomer to inject can surpass the thermal spike of at least one thermal spike of the reaction zone that the monomer injection is arranged at its upstream.

Polymkeric substance of the present invention can be by being that film is used for packaging stretch hood with polymer formation, and this film can be the single or multiple lift structure, can TD stretches at least 100% and guarantee that this film utilizes follow-up elastic recovery effect to remain on the child shipments periphery.Membrane structure is suitably selected.

Preferred this film has main stor(e)y, main stor(e)y contains any one or a plurality of polymkeric substance in the feature noted earlier of having of 50wt% (based on the gross weight of polymkeric substance in main stor(e)y) at least, this film has at least 40% elastic recovery rate after 100% stretches, and, under the rate of deformation that is lower than 10% of initial initial length/second, provide 20N/50mm at least after 100% incipient extension rate under 85% extensibility the nominal confining force of preliminary draft/100 μ m thickness.

In industrial application, the behavior and the characteristic that importantly add the film in man-hour under the speed of using in industrial reality generally are higher than those behaviors and the characteristic of using in laboratory equipment.Suitable single or multiple lift structure can provide this class feature under higher deformation rate (as surpassing 12% of initial initial length/second).This type of film can be used at utmost reducing for the amount that forms enough needed mould materials of confining force and in stretching process and after shrinking on child shipments on the packaging stretch hood streamline is optimizing the film behavior, the risk that minimizing is torn or punctured.

When film stretched under the envrionment temperature that packaging stretch hood is used, the behavior of stretching-stress also was to need to pay close attention to.Usually in the graphic representation of the stress of stretch-draw or stretching-right-applied, initial slope is a steepest.This information can be obtained as secant modulus.Preferably, the secant modulus of unstretching film is lower than 180MPa, or is lower than 120MPa.Elmendorf (Elmendorf) tearing strength is 10g/ μ m at least, preferably 12g/ μ m and be lower than 25g/ μ m at least.

Generally speaking, initial slope is steep more, and film has stiffness more, needs bigger strength to stretch it at first.After initial stretch-draw, slope becomes gently, for the power that further increment stretch-draw need be lower each time of film.When the last increment of the further quotient of difference of stretch-draw needed lower power, slope can become negative.Preferred film can stretch-draw up to 100%, the minimum Elongation test slope of 0.01MPa/ elongation % at least is provided simultaneously.This helps avoid " wash boarding ", disfeature quality and produce the part of high elongation of the latter, these parts tend to be punctured and on child shipments, shrink after make the film splitting.Polymkeric substance of the present invention helps to keep the minimum Elongation test slope of 0.01MPa/ elongation % at least in whole drawing process.

In film, polymkeric substance of the present invention can itself use or use with another kind of mixed with polymers.The reason of adding another kind of polymeric constituent comprise by long chain branching or more existence of wide molecular weight distribution improve processing characteristics; Or improve intensity in telolemma by the use that has more crystalline polymkeric substance.If necessary, but film can comprise the ethylenic unsaturated ester (preferred vinyl-acetic ester) of copolymerization, but have the ethylenic unsaturated ester content of the copolymerization of 4-10mol%, and/or help to realize under up to 100% extensibility the ethene-alpha-olefin interpretation of the MI of the density with 0.915-0.86 of the slope that just stretches of 0.01MPa/ elongation % at least and 0.5-5.The existence of ethene-alpha-olefin interpretation can help rapid answer, i.e. the speed of elastic recovery.

Aptly, film have multilayered structure (as three or five-layer structure), its mesexine is arranged on the one or both sides of main stor(e)y.Epidermal area can comprise the linear low density ethylene copolymer (LLDPE) of the density with 0.91-0.94.Structure optimization is the A/B/C structure, and wherein C can be identical or different with A.At least one epidermal area should be LLDPE.Another epidermal area can be different LLDPE or non-LLDPE material.Film of the present invention can be extruded manufacturing by tubular blown film, it should form can at least 100% transverse stretching and a kind of stretching cover of follow-up elastic recovery.

According to a specific embodiments, film of the present invention can be extruded manufacturing by tubular blown film, form the cover that stretches when being suitable for stretching in the horizontal, it can be stretched at least 100% under the total deformation speed of the 12%/second that is surpassing initial initial length under the constant pinblock speed.

The film outward appearance is protected when stretch-draw, and can produce sizable fixing or confining force.The composition that depends on film, when the temperature that is heated to 45 ℃, if possible even during the temperature of 50 ℃ or 55 ℃ or 60 ℃, the loss of the confining force that is run into when the heating of clamping plate child shipments can be restricted to basically and be lower than 40% of initial value.

, provide for what packaging stretch hood was used to have 0.2 to 10 aspect another of the present invention, the film of preferred 0.3 to 0.8 and most preferably 0.4 to 0.7 frictional coefficient, it comprises:

A) core polymer layer; With

B) can have the epidermal area of identical or different composition on each face of sandwich layer, it comprises the 0.91-0.94g/cm that is measured by ASTM-D 1238 condition E that has of 60wt% at least ³Density and be lower than 1.5wt%, preferably be lower than 1wt%, but especially be lower than the LLDPE of the hexane extractives content of 0.6wt%, this top layer is contained and is lower than 7500ppm, preferably be lower than the antiblocking particulate matter of 3000ppm, and this film has at least 40% elastic recovery rate after 100% extensibility and the nominal confining force/100 μ m thickness of preliminary draft under 85% extensibility after the incipient extension rate 100% of 20N/50mm at least is provided.This carries out under the rate of deformation that is lower than 10% of initial length/second usually.But the FDA hexane extractives content that uses here and in an embodiment test is the version on July 7th, 2003.This test is according to 21CFR177.1520 (d) (3) (ii) (e), film is used to extract and for extract and dry after the dry film weighing carry out with measurement weight loss.

According to a specific embodiments, one or two epidermal area contains not transportable polymer surface modification agent in the film of the present invention, so as to be provided at the frictional coefficient of measuring according to ASTMD1894 between the 0.4-0.7 and be provided under the confining force pressure and the clamping plate child shipments between the increase friction.Preferred wherein polymer surface modification agent is to have the high molecular UHDPE that is higher than 500 000 molecular weight and 0.94 or 0.94 above density.

LLDPE can be easily by using transistion metal compound to be prepared by polyreaction as catalyzer.Polyreaction can be, for example, and gas phase, slurry or solution polymerization.

The antiblocking particulate matter is stretched out from the film surface, has reduced intermembranous contact area.Generally at utmost reduce its use, to keep the film transparency.Preferably, epidermal area contains the particulate matter that is lower than 2500ppm, more preferably less than 2000ppm.Can be used for the talcum of antiblocking in the film or the granularity of silica antiblocking agent can be changed, and this is commonly known in the art.Antiseize paste is designed to move to the surface so that the lubricant film of the coefficient of reducing friction to be provided.The relative quantity of antiseize paste and any antiblocking agent is subjected to the basic friction of LLDPE epidermal area and the influence of adhesiveness.The application of the invention can determine to be suitable for the frictional coefficient of packaging stretch hood.

The processing (handling) of film under tension force can be improved and more easily be adapted to different requirements in such a way in the packaging stretch hood operating process.Avoided the use of elastica, elastica has to handle to reduce friction with the antiblocking agent of high consumption.Replacement is from low-level described antiblocking agent, and the target frictional coefficient can obtain by the suitable interpolation of antiseize paste.The wash boarding problem can by make with single-site catalysts (for example metallocenes), have at least under up to 100% stretch-draw that the making of LLDPE of the tension test slope of 0.01MPa/ elongation % is used for alleviating, for example according to preparing in method described in the WO98/44011, this patent is hereby incorporated by reference this LLDPE.The top of stretching cover can seal, so that high bond strength to be provided.

Using after antiseize paste realizes the target frictional coefficient, advantageously after the film manufacturing and be used for keeping this frictional coefficient before the packaging stretch hood.This can be by using a certain amount of transportable component in sandwich layer, utilize to reduce at utmost at the cross transfer between each layer that the variation of frictional coefficient realizes in epidermal area.By using the blown film extrusion molding to make this membrane structure, the film curing afterwards of extruding of steeping at film is affected, thereby improved transparency is provided.

Sandwich layer can be selected from various alterative version, comprising high EVA, and the blend of high EVA and other material.Yet, can obtain excellent result as sandwich layer by using for the described main stor(e)y of polymkeric substance of the present invention.Film covers the stretching of experiencing main level (considerably beyond 50%) in the process that is applied to the clamping plate shipment on the tensioning equipment of packaging stretch hood machine in stretching then.Must control carefully the tensile resistance because the rubbing effect of the jaw face of packaging stretch hood machine is caused, particularly when using film, it becomes in drawing process even is thinner.Therefore, for the use that to combine on the other hand with the present invention of the polymkeric substance that obtains having high-caliber SCB and high time of relaxation and film (it can high elongation) of this one side of the present invention on by the time low top layer of waiting friction in obtaining.

When two epidermal areas account for the 10-60% of whole film thickness together, during preferred 30-50%, obtained gratifying result.Film thickness can change in positive and negative 5% scope of mean thickness, and wash boarding can minimize.Advantageously, the mean thickness of preliminary draft film can change between 25-300 μ m.Advantageously, the overall average film thickness can be 25-75 μ m, and gratifying packaging stretch hood characteristic still is provided simultaneously.Film can carry out formulating of recipe on the whole so that the minimum tension test slope of 0.01MPa at least to be provided; Be lower than the secant modulus before stretching of 120MPa and/or the elmendorf tearing strength of 10g/ μ m at least.Membrane structure is suitably selected.

Height puncture and tear strength can be allowed the production of the film of the fluid permeability that can promote the packaging stretch hood material through boring a hole, and for example allow successive drying or the like.Multilayer film can be extruded manufacturing by tubular blown film, it be suitable for forming can at least 100% transverse stretching and a kind of stretching cover of follow-up elastic recovery.

Epidermal area and sandwich layer also can be used for modification by making of additive.Sandwich layer and/or epidermal area can come modification by the introducing of PPA processing aid or slip additive (comprising PP or HDPE as the polymkeric substance antiblocking agent).

By individually or combine and use all respects of the present invention, the stretching cover system can be optimized farthest to reduce the amount of required film, shrinks and/or the energy expenditure when applying film and be bonding needed viscosity in film.Film can apply and pack well under all temps condition, store.In production, can obtain good bubble stability and gained film owing to the low particulate state antiblocking agent of measuring has high-clarity by blown extrusion.

According to a specific embodiments, the middle layer is inserted between main stor(e)y and one or two epidermal area, and the middle layer is the polymer composition that has than the modulus more than the low 40MPa of modulus of adjacent epidermal area.

According to a specific embodiments, epidermal area has antiblocking additive, antiseize paste and/or the surface-modifying agent of different content.

According to a further aspect in the invention, provide a kind of described polymkeric substance to be used for the purposes of packaging stretch hood, by being multilayer film with polymer formation, it can TD stretches at least 100% and utilize follow-up elastic recovery effect to remain on the child shipments periphery.

Detailed description of the present invention

Ethylenic unsaturated ester can be a vinyl-acetic ester, methyl acrylate, butyl acrylate and ethyl propenoate or their binding substances.The transfer agent that is used for the production of polymkeric substance of the present invention can be introduced in the chain and this helps to produce the short chain branch of polymkeric substance.Preferred this transfer agent is a propylene, though more high-grade alkene such as iso-butylene or 1-butylene also can use.These general name long chain branches (LCB) are distinguished by the branch that the trial of NMR technology will have six or 6 above carbon atoms.No matter LCB exists and can be reflected in time of relaxation with what amount or structure.The molecular weight distribution mw/mn of being measured by DRI preferably at least 8 and preferably bimodal, high in this case load/low load MI ratio not too is suitable for reflecting the influence of LCB.

The LLDPE that is used for the epidermal area of film of the present invention can pass through gas-phase polymerization process, as those technologies that are described among the WO9425495 make, and this patent is hereby incorporated by reference.Preferable material is the LLDPE with some long chain branchings, and it can be made by the method that is described among the WO98/44011, and this patent is hereby incorporated by reference.LLDPE can be 2.0 to 3 by the molecular weight distribution that is expressed as the Mw/Mn value of DRI gpc measurement, preferably at least 2.5, especially at least 4, to 8, especially be lower than 7.Total orientation of extruding can limit by the selection of low Mw/Mn value as 2.3 to 3.5.This allows the sandwich layer orientation, decision film tensile property.Some long chain branchings can assist to set up horizontal orientation, help to prevent wash boarding.Short-chain branched can be by the alpha-olefin copolymer with 3 to 10 C atoms with monomer such as 1-butylene, 1-hexene and 1-octene provide.With I _21.6/ I _2.16The melt index ratio of expression can be from 10, preferably surpasses 30, to 100, especially is lower than 80.The center is catalyst-loaded although the disclosure thing depends on the metallocenes list, but other transition metal component can be used as single-site catalysts and obtains the suitable polymers homogeneity and lack the lower molecular weight extract.But common in addition titanium type ziegler natta catalyst system can be optimized the generation that reduces the lower molecular weight extract.This base polymer is equally applicable in film of the present invention.

Epidermal area in multi-layer film structure of the present invention can contain, and combines with LLDPE, and is a small amount of, generally is lower than the hp-ldpe of 20wt%; Linear high density polyethylene(HDPE) or polypropylene or their binding substances.Sandwich layer can contain on a small quantity, generally is lower than the linear very low density polyethylene of the density with 0.86-0.90 of 40wt%, the LLDPE with density of 0.91-0.94; And/or has a crystalline elastomerics by what ethene or propylene formed.These layers can be inserted between sandwich layer and the epidermal area, and the part purpose can be the amount that restriction is used for epidermal area and the more expensive polymkeric substance of sandwich layer.

The consumption of antiseize paste, especially the consumption in epidermal area preferably is limited to maximum 500ppm.If use too many antiseize paste, then frictional coefficient becomes too low, will cause poor film processing in wrapping machine.More preferably use the slip dosage of 150-300ppm.The example of spendable antiseize paste is uncle or secondary amide, as mustard acid amides and oleylamide.Except antiseize paste or replace antiseize paste, can use anti-coalescing aid, for example stearate.If you are using, examples of such additives will be with than antiseize paste volume more, for example 1000 uses to 5000ppm.

Film does not preferably contain any tackifier such as PIB or Viscotrol C or similar additive.The existence of this type of adhesion promoting additive generally has disadvantageous effect for the control of frictional coefficient.Can believe, be not wishing to be bound by theory that sandwich layer has different contributions to whole film properties separately with epidermal area.When the polymer composition of epidermal area and sandwich layer was mixed into single layer, effect was different when then being used for different layers with them.Each layer has it self contribution.By the suitable combination of epidermal area and sandwich layer, can make film, it allows sizable stretching and has kept its physical integrity and tear strength simultaneously, and meanwhile sandwich layer can provide the convergent force of optimization.

Embodiment

The present invention explains by reference example, has wherein mentioned following accompanying drawing:

Fig. 1 is used to make the synoptic diagram of mentioning in an embodiment according to the tubular reactor equipment of EVA polymkeric substance of the present invention;

Fig. 2 is used for the reactor of service chart 1 so that the temperature profile of the EVA multipolymer of mentioning in an embodiment of the present invention is provided;

Fig. 3 A and 3B have shown EVA multipolymer of mentioning in an embodiment of the present invention and the 13C NMR curve that contrasts level UL00109;

Fig. 4 has shown the graphic representation of describing shearing rate and viscosity of calculating of the time of relaxation of the EVA multipolymer of the present invention that is used for mentioning in an embodiment;

Fig. 5 has shown bar graph, and it has indicated the prepared lax and reservation power of mentioning in an embodiment (75% incipient extension-60% finally stretches) of the stretching cover of film of the present invention under elevated temperature of EVA multipolymer of using;

Fig. 6 A has shown that with 6B explanation comprises the diagram of tearing the behavior of spreading of the different films of film of the present invention; With

Fig. 7 has shown three-dimensional plot, and it has illustrated the Exceed polymkeric substance of different amounts and according to the influence for frictional coefficient of the film thickness of film of the present invention.

Polymers compositions

Usually, the EVA copolymer causes production by free radical in tubular polymerization reactor. Employed initator can be oxygen, peroxide and similar reagent. The chain-transferring agent that helps to increase short-chain branched amount is alpha-olefin, general mainly is comprised of propylene. Highly exothermic reactions carries out under turbulent condition and high temperature (150-330 ℃) in the reactor of the lower operation of high pressure (2000-3200 bar). Heat of polymerization is removed by tube wall. Operating condition such as reactor pressure, the temperature of reactor in the differential responses district and comonomer and chain transfer agent concentration can be realized the required product performance through overregulating. Operating condition for the impact of properties of product (Ehrlich and Pittilo[1], Ehrlich and Mortier[2], Luft[3], Marano and Jenkins[4], Yamamoto and Sugimoto[5], the people such as Goto [6], the people such as Luft [7,8], Ogo[9], Beasly[10]) in discuss.

Reference

[1]P.Ehrlich and R.N.Pitillo，J.Polym.Sci.，43，389(1960).

[2]P.Ehrlich and G.A.Mortimer，Adv.Polym.Sci.，7(3)，386(1970).

[3]G.Luft in″Polymer Handbook″.(Eds.J.Brandrup andE.H.Isnmergut)，Wiley，New York(1975).

[4]J.P.Marano Jr.and J.M.Jenkins，in″High PressureTechnology″(edited by I.L.Spain and J.Paauwe)61(1977).

[5]K.Yamamoto and M.Sugimoto，J.Macrom.Sci.-Chem.，A13(8)，1067(1979).

[6]S.Goto，K.Yamamoto，S.Furui and M.Sugimoto.J.Appl.Polym.Sci.：Appl.Polym.Symp.，36，21(1981).

[7]G.Luft，P.Lim and M.Yakawa，Makromol.Chem.，184，207(1983a).

[8]G.Luft，P.Lim and M.Yakawa，Makromol.Chem.，184，849(1983b).

[9]Y.Ogo，JMS-Rev.Macrom.Chem.Phys.，C24(1)，1(1984).

[10]J.K.Beasly in″Comprehensive Polymer Science″，3，273(1989).

Referring to Fig. 1 and 2, in tubular reactor, the raw material monomer of ethene, vinyl-acetic ester and transfer agent is supplied in the main compressor 4, enters into auxiliary compressor 6 then.The discharging current of auxiliary compressor 6 is split up into the materials flow of the required number of the positive materials flow of tubular reactor 8 and side materials flow, is identified by arrow Ib-IVb in Fig. 2.The streams that flows to the front (upstream extremity) of reactor 8 is heated at 10 places, and the streams that flows to side materials flow inlet point is cooled at 12 places.The side streams is supplied to the decanting point that distributes on the length of tubular reactor 8 then.

Tubular reactor 8 is plug flow reactors of restricted back-mixing.The storage tank supply of peroxide type initiator from 20 with solvent, is fed in the reactor 8 to indicated position, VIa place at Ia in Fig. 2 by pump 22 then.Use a plurality of superoxide decanting points 24 along the length of reactor 8, become the EVA polymkeric substance and optimize product performance so that optimize conversion of ethylene.Use four or more a plurality of decanting point.Should be pointed out that final decanting point is in the pipeline section of not supplying raw material monomer.The reactor transformation efficiency can be near 40%.

Peroxide initiator causes the polyreaction of this free radical, heat release.The rising of utilization of Heat of Reaction ethylene temperature utilizes the injection and the utilization of the cold junction materials flow of ethene to remove to Closed loop jacket water (J.W.) cooling system method via reactor wall is heat passage.The common temperature fluctuation contrast that should be pointed out that and show, temperature shown in collinear B, fluctuate like that (referring to Fig. 2) by line A.Initial temperature is lower than temperature commonly used.Allow to be higher than temperature commonly used in the temperature of can't help in the downstream part of side materials flow supply raw material monomer.Ethene maximizes under suitable temperature of cooling water by using reactor jacket water to the conversion of polymkeric substance.This cooling jacket water has at utmost increased and has passed the heat passage of thick-wall reactor pipe.Pressure drop along the length of reactor minimizes by using fractionated to distribute to reaction tube diameter.Line A has indicated the common pressure drop on the reactor length of producing along common EVA; Line B is the indication that is used for the absolute pressure of EVA of the present invention.This fractionated distribution optimization along the gas velocity of reactor length, it has almost eliminated the incrustation on the inwall of tubular reactor.

The distributed computer control system that extends is used for controlling reactor temperature distribution and other critical process variable.

In polymerization (it is in 1.8km length and the about about 20-40 of cost second in the pipe of 32.65mm diameter) afterwards, reacting fluid is via reduce pressure about 300barg and be used for cooling off from the low pressure quenching medium of main compressor discharge end of reactor pressure control valve 30.Mixture is supplied in the high-pressure separator 32 then, therein polymkeric substance and unreacted monomer separation.The use of low pressure quenching medium at utmost reduces the formation of gel and improves transparency.The monomer that reclaims is recycled in the auxiliary compressor 6 at 33 places.

Melt polymer and a spot of ethene that is embedded are depressurized to about 0.7barg via the low pressure bleed valve once more, are fed to then in the light pressure separator 34.In this, the most remaining monomer that is embedded separates with EVA and delivers in the sweeping gas compression system 35.

Sweeping gas compressor 35 is worked off one's feeling vent one's spleen light pressure separator and rise to the suction pressure of main compressor 4 (operating) under the ethylene tube linear pressure.In this, the part of gas is discharged into from the EVA line in the MONOMER RECOVERY system, and the major part of this gas turns back in the reactor assembly via main compressor simultaneously.

Polymer melt from light pressure separator 34 is supplied in the hot melt forcing machine 36.Additive is sneaked in the hot melt forcing machine.This typically utilizes the masterbatch technology to carry out via side branch forcing machine 38.Should be pointed out that masterbatch can contain additive such as antiseize paste, antiblocking agent and antioxidant.Perhaps, fluid additive injects and also can consider.

The polymkeric substance lines that leave the mouth mould of forcing machine are cut into pellet in water, materials flow is cooled, transfers in weighing storehouse 42 or the blending machine 44 in 40 place's dryings and pneumatically then, therein pellet purged in case with residual ethylene concentration be reduced to safe storage concentration (＜50wppm).After blend, pellet is transported to bulk shipment or bagging equipment 46.

For make special EVA of the present invention and employed in an embodiment those, regulate processing condition so that obtain on polymkeric substance, to have the wide molecular weight distribution of the branching of appropriate amount, simultaneously melt index is kept enough low.By using four or more decanting point for initiator and in the upstream of final initiator decanting point, on one or more positions properties-correcting agent or the transfer agent of vinyl monomer in being diluted in monomer being injected, it is high to make transformation efficiency pursue on target.The consumption of properties-correcting agent makes has branching widely in final polymerization stage.This process can obtain required low MI and wide molecular weight distribution after operation.Reactor pressure is near the low side of normally used scope (2200-2700 crust), and temperature of reactor reduces gradually along length of tube.Medial temperature is brought up to and is higher than 220 ℃, near 300 ℃ of the upper end of usual range (180-330 ℃), therefore helps the short chain ramose and forms and at utmost increase long chain branching.Operational condition contrast with common improves temperature in the downstream of final decanting point and can further increase long chain branching.Propylene is as alkene chain-transfer agent short-chain branched with further raising polymer backbone.VA and propylene separately in the materials flow actual concentrations of VA and propylene can cause that productive rate and molecular weight change.

The EVA of Shi Yonging has following feature in these embodiments:

Table 1

Characteristic	Measuring method	EVA of the present invention	EVA (1) UL00109	EVA (1) UL00018	EVATANE (2) 1005VN3
						Melt index (MI) g/10min	ASTM-D 1238 condition E	0.41	0.49	0.35	0.33

Characteristic	Measuring method	EVA of the present invention	EVA (1) UL00109	EVA (1) UL00018	EVATANE (2) 1005VN3
						The melt index ratio	ASTM D1238 D I 21/I 2	79	80	86	105
VA mol％	NMR 16-1.2L	2.3	3.2	6.9	3.5
						Density (g/cm 3)	ASTM-D 1505	0.9275	0.9324	N/A	N/A
Melting heat	ASTM-D 3417-3418	95.5 J/g	112.5 J/g	69.5J/g	96.9J/g
						The peak value temperature of fusion	ASTM-D 3417-3418	98℃	100.5℃	85℃	97℃
SCB/1000 C with five or five following carbon atoms	NMR 04-1.1	14.3	7.13	6.6	10.4
						SCB/1000 C with three or three following carbon atoms	NMR 04-1.1	6.29	2.66	2.40	3.28
Time of relaxation, 230 ℃ (s)	1-19 is capable for the WO97/45244 page 5	11.7	6.9	15.5	8.8
						Mw/Mn	GPC 03-2.1	9.2	5.1	4.4	5.1

(1) Escorene Ultra (trade mark of ExxonMobil)

(2) trade mark of Atofina.

VA mol% be by use 75 and 68ppm between CH resonance and 50 and 0ppm between resonance (comprise CH from VA ₂, CH ₃With from ethyl structure partial C H ₂, CH and CH ₃) calculate.With the mutual relationship of the wt% of VA be that 1mol%VA equals 2.7wt%VA.

SCB measures with reference to the content of the alkyl type SCB with five or five following carbon atoms as described below.Fig. 3 A has shown the 13C NMR curve of the EVA multipolymer of mentioning in an embodiment of the present invention and the data of table 2 are provided: Fig. 3 B has provided the same curve for the known EVA of contrast usefulness.

Table 2

Measured configuration	The peak position, ppm 4)	The present invention, EVA 3)	EVA (1) UL00109	EVA (1) UL00018	EVATANE (2) 1005VN3
						Methyl 2)	19.948.	1.19	0.00	0.00	0.00
Ethyl	9.539+10.996	5.1022	2.66	2.40	3.28
						Dimethyl	42.7	0	0.87	0.06	0
Butyl	23.359	6.08	3.34	2.89	5.42
						Amyl group	32.679.	2.12	1.13	1.31	1.93
Total SCB with five or five following carbon atoms		14.3	8.00	6.66	10.38
						Hexyl+the have LCB of six or six above carbon atoms 1)	32.165	3.55	1.77	2.04	2.34
The 2-ethylhexyl	24	1.51	0.79	1.13	0.97
						2-ethyl-heptyl	23.6	1.58	0.89	1.12	1.41
The VA carbonyl	169ppm
						VA CH 2O	74ppm

1) gets rid of 2-ethylhexyl and 2-ethyl-heptyl.

2) methyl on the monomer acetoxyl group unit that vinyl-acetic ester forms no matter in main chain or in side chain, is got rid of from SCB measures.

3) by the intensity of " quantity of group/1000 carbon atom ".

4) ppm=1,000,000/.

Be that the following column data that is depicted among Fig. 4 that obtains from the mensuration of the shearing rate of the EVA multipolymer of mentioning in an embodiment of the present invention and viscosity is determined time of relaxation.

Table 3

Temperature: 230 ℃

Predicted data comes from the Cross model, wherein:

Shear-stress=(zero-shear viscosity * shearing rate)/(1+ time of relaxation, λ * shearing rate) ^ power law index, m.

Measure-loss function of the best-fit of right-prediction is defined as the sum of squares of difference: summation=(x-y) ², wherein x and y are the viscosity of measuring and predicting respectively.The instrument of finding the solution that MicrosoftExcel Windows is 2000 editions (solver tool) is utilized to carry out curve fitting.Derive from the Cross model parameter time of relaxation, and it will obtain the minimum summation of squared differences.List in table 4 by the Cross parameter that fitting of a curve provides:

Table 4

The GPC program that is used for this table and follow-up table is as follows.Mw and Mn measure by the GPC (gel permeation chromatography) on Waters 150 gel permeation chromatographs that differential refraction index (DRI) detector and the online light-scattering photometer of Chromatix KMX-6 are housed.With 1,2, the 4-trichlorobenzene uses this system as mobile phase under 135 ℃.Use Shodex (ShowaDenko America, Inc) the polystyrene gel post 802,803, and 804 and 805.This technology is at " Liquid Chromatography of Polymers and Related MaterialsIII ", and J.Cazes edits, Marcel Dekker.1981, and p.207 middle the discussion, the document is hereby incorporated by reference.Do not use and proofread and correct for the post unfolded; Yet, with generally accepted standard substance for example the relevant data of the hydrogenated polyisoprene (alternately ethylene-propylene copolymer) produced of State Bureau of Standardization's polyethylene 1484 and negatively charged ion method show that (=MWD) correction is lower than 0.05 unit for Mw/Mn.Mw/Mn calculates from elution time.The LALLS software of the Beckman/CIS customization of numerical analysis by being purchased combines with standard Gel Permeation routine package to make and is used for carrying out.

Plastomer is to make by the method for generally describing in WO00/24793, and this patent is hereby incorporated by reference, and is sold as EXACT 0201 by ExxonMobil Chemical Company.It has following properties:

Table 5

Characteristic	Measuring method	Numerical value
			Melt index (MI) g/10min	ASTM-D 1238 condition E	1.1
The melt index ratio	ASTM-D 1238I 21/I 2	33
			1-octene mol%	NMR 04-1.1	5.15
Density (g/cm 3)	ASTM-D 1505	0.902
			Melting heat	ASTM-D 3417-3418	86J/g
The peak value temperature of fusion	ASTM-D 3417-3418	94℃
			Mw/Mn	GPC 03-21	2.8

The EXACT grade is to comprise antiseize paste and antiblocking agent but does not contain down the HS of target additive and add and obtain.The polymkeric substance that is used for epidermal area be by general description in WO94/25495 the method manufacturing and by ExxonMobil Chemical Company as do not have antiblocking agent EXCEED 1018CA and have the EXCEED 1018EB of antiblocking agent to sell.These grades contain the antioxidant and the PPA (by the fluoropolymer section bar material of Dyneon with trade mark Dynamar supply) of common amount.Exceed 1018CA does not comprise antiseize paste and antiblocking agent.Exceed1018EB contains the mustard acid amides of 750ppm and 1500ppm talcum as antiblocking agent and have the described extractability according to FDA177.1520d3ii of 0.3-0.4wt% here.

These EB and CA grade have following denominator:

Table 6

Characteristic	Measuring method	Numerical value
			Melt index (MI) g/10min	ASTM-D 1238 condition E	1
The melt index ratio	ASTM D1505	17
			1-hexene mol%	NMR 04-1.1	2.8
Density (g/cm 3)	ASTM D1505	0.918
			Melting heat	ASTM-D 3417-3418	127.5J/g
Mw/Mn	GPC 0.32.1	2.16
			The peak value temperature of fusion	ASTM-D 3417-3418	118℃

Can use dissimilar LLDPE in some embodiments, according to making in the described method of WO9844011.This LLDPE has (can think) some long chain branches formation and has following performance:

Table 7

Characteristic	Measuring method	Numerical value
			Melt index (MI) g/10min	ASTM-D 1238 condition E	1
The melt index ratio	ASTM D1238					40
			1-hexene mol%	NMR 04-1.1	About 2-3mol%
Density (g/cm 3)	ASTM D1238	0.92
			Melting heat	ASTM-D 3417-3418	140.5
Mw/Mn	GPC 0.3-2.1	3
			The peak value temperature of fusion	ASTM-D 3417-3418	117℃

Blend and coextrusion

EVA and EXACT plastomer obtain from the polymkeric substance blend the blown film forcing machine with the pellet form supply.These materials are according to the Windmoeller ﹠amp that describes in embodiment 1,2 and 3; Coextrusion in the Holscher coextrusion blow film line:

Table 8

For embodiment 4,5 and 6, condition is as follows:

Table 9

Resulting structures is as follows:

Table 10

Embodiment		1	2	3	4	5	6	7	Scope
										Sandwich layer B	wt％EVA	100 1)	85 1)	70 1)	70 2)	70 3)	70 3)	100 3)	50-100
	EXACT 4)	0	15	30	30HS	30HS	30HS		0											0-50
										Antiseize paste	The mustard acid amides	150ppm	150ppm	150ppm	0ppm	0ppm		0	0		0-450ppm
Epidermal area A/C	CA+EB wt％ 5)	62.5+37.5	62.5+37.5	62.5+37.5	0+100	0+100	0+100	100+0	0-100
											Talcum ppm	2500	0	2500	0	0	0	0	0-10000
Film	Thickness		140	140	140	150	150	80	80											50-200

Embodiment		1	2	3	4	5	6	7	Scope
											The A/B/C ratio	1/3/1	1/3/1	1/3/1	1/3/1	1/3/1	1/3/1	1/3/1	1/1/1-1/8/1
Extrude	Blow-up ratio	3.18	3.18	3.18	2.85	2.85	2.85	2.85	2-5
											Frost line height	750	750	750	740	885	885	885

¹⁾The EVA of the present invention of table 1.

²⁾Escorene UL00109-is referring to table 1.

³⁾Escorene UL00018-is referring to table 1.

⁴⁾EXACT 0201-is referring to table 5.

⁵⁾EXCEED 1018-is referring to table 6.

Film is gone up at the packaging stretch hood machine Multiflex by Lachenmeier (Denmark) supply and is used, with the fixing lamination of paper.

Table 11

		Numerical value
			Cross directional stretch	By on backing plate, shrink the m/c stretching that stretches and to be applied	106％ 90％
Longitudinal stretching	Estimate	About 25%
			The top seal condition	The thermal pulse sealing	50Hz 0.9-1.1 second

Film after shrinking has following performance.Reference example 4 to 7 is Comparative Examples.Reference example 1 is the product film that is used for packaging stretch hood, and it is the coextrusion structure that the high EVA on internal surface and low EVA are on the outer surface combined.Reference example 2 is the commodity unitary films from the blend acquisition of high and low EVA.

Table 12

Embodiment	1	2	3	4	5	6	7	Reference example 1	Reference example 2
										Thickness	144	143	143	150	150	80	80	153	152
Confining force N/50mm	35.3	35.0	34.6	38.0	34.0	17.8	15.4	26.6	31.3
										Nominal confining force 100 μ m N/50mm	24.7	24.5	24.3	24.0	22.0	22.2	19.5	17.4	20.6
Elastic recovery rate %	50	51	51	51	53	51	53	56	48

Embodiment	1	2	3	4	5	6	7	Reference example 1	Reference example 2
										Stretching TD (MPa) ASTM D 882	36.4	37	37.6	36.8	41.3	46.1	41.7	28.4	26.1
Tangent Mod TD (MPa) ASTM D 882	153	149	147	145	128	119	106	116	126
										Elmendorf MD (g/ μ m) ASTM D1922	12.4	12.1	13.5	15.3	15.3	12.5	11.3	8.4	9.2
Elmendorf TD (g/ μ m) ASTM D1922	16.9	15.6	15.8	17.3	17.5	18.0	14.1	10.9	11.1
										Puncture force N/15mm	2.02	2.14	2.11	2.9	2.4	2.0	2.7	0.96	0.83
Tearing under 100% extensibility spreads	Good	Good	Good	Good	Good	Good	Good	Bad	Bad

Except specified ripe ASTM method, other testing regulation of measuring above film properties is:

A) the ASTM D5459 standard test methods that keeps by means of the elastic recovery that is used for oriented film, tension set and stress is basic method, but improvements are membrane sample and are stretched to some elongation (100%) under certain pinblock speed (1000mm/min), measure confining force/elastic recovery.When reaching 100% elongation, pinblock kept 5 seconds in this position, turned back to certain 85% elongation then.After 60 second waiting time, measured at the load on the sample (N/50mm) and in table, be recorded as confining force.This imitation acts on the confining force on the clamping plate child shipments.Subsequently, to turn back to the power reading be zero position to pinblock.Elongation is recorded as elastic recovery in table.Calculate the nominal confining force by being adjusted to 100 μ m thickness N/50mm (observed value is the twice for the film of the original depth of 50 μ m) according to the confining force of film thickness.

B) based on ASTM 882, but the membrane sample (50*50mm) that improvements are to have little pre-otch (wide at 2mm on the MD direction) reaches 100% elongation at 1000mm/min pinblock velocity pull-down on the TD direction, measure to tear and spread.For by test, film should not torn uncontrollably but show intermittently the behavior of spreading of tearing, wherein tear and be prevented from, can restart to tear just need apply more power.

C) measure the lower velocity puncture resistance that puncture force is determined the plastic film sample.This method target is to be provided under the low trial speed (500mm/min) of fixed at the load-deformation response of multiaxis under texturizing condition, with the imitation condition of cover when fixedly having the clamping plate child shipments of sharp-pointed article that stretch.In this test, have the piston that is fixed to the standard probe on the load cell (cell) and pushed the membrane sample that is passed in the circular sample retainer with 90mm diameter, until perforate membrane and breaking.Sensing lead on load cell is by the operating measurement deformation rate of pinblock.

In order to further specify the benefit that obtains by embodiment, carry out following discussion with reference to the accompanying drawings and about accompanying drawing.

Fig. 4 is the bar graph that has shown that confining force changes along with heating and cooling cycle temperature.The testing regulation (the cover relaxation test stretches) of estimating the effect in heating and cooling cycle is as follows:

The test fixture that the horizontal bar of two perpendicular separations is housed by use carries out relaxation test.The top rod in vertical direction can be movable so that for film applies predetermined elongation, on the rod of wide * 100mm long sleeve form that it is attached to 50mm.The below rod is attached to the power and this power usage data record device that act on the film with measurement on the strain gage and comes record.By the whole test anchor clamps being placed on the test of carrying out in the hot-air heated baking oven under temperature required under elevated temperature.For the original pressure of dummy activity on shrinkable film, film is pre-stretched to 3% elongation, and this is corresponding to the stretch-draw of typically seeing in the backing plate shrink film of commercialization.The predetermined elongation rate on underproof film of putting on is by incipient extension 75%, allows then film is loose to be got back to 60% and produce.Anchor clamps can experience required heating and cooling program with the increase and decrease of record from initial tension.

The data that are reflected among Fig. 4 are given in the table 10.At first, drop sharply to the sub-fraction of initial confining force at room temperature at the confining force that is heated to after 60 ℃ for 150 microns LDPE type shrinkable films shown in A.After cooling, very limited answer is arranged.Confining force further reduces in subsequent cycle.All these require to use the film thicker than this situation.The film that shows at the B place is the high EVA (18wt%VA) with EXCEED top layer that is coextruded on the 80 micron thickness films.In this case, be heated to confining force after 60 ℃ initial sharply descend after, confining force follow-up be cooled to envrionment temperature after further decline.Film must have enough thickness to adapt to the loss on confining force.Corresponding to the film in table 12 5, but has 80 microns reduction thickness at the film at C place.In this case, the loss of confining force reduces to some extent than the loss on film A and B.Yet they remain significant.D be according to the present invention and corresponding in table 12 to film 1, but have 80 microns reduction thickness.Still retentive loss after being heated to 60 ℃ in this case.For given thickness, film D provides the better confining force than film C under 60 ℃, and this characteristic is kept in heating and cooling program process subsequently, has caused the remarkable advantage at the week of heating and cooling repeatedly after date.

Table 13

A: shrink cover (LDPE type), 150 microns

B:Coex (EVA sandwich layer 18%VA), 80 microns

C:Coex (0201,80 micron of EVA sandwich layer 18%VA+30%Exact)

D:Coex (EVA sandwich layer of the present invention), 80 microns

Fig. 6 A has illustrated that with 6B tearing of different films spread in table 12.Indication as in the weight savings of the obtainable cover of the present invention compares according to film 1 of the present invention and reference example 1.Should be noted that, 100% stretch under, it is poor that the tearing of reference example 1 spread.This illustrates that it can only be stretched to level well below 100% in practice, thereby protects package integrity properties in the situation that membrane puncture and follow-up tearing spread.And then the confining force of degree of drawing explanation for given film weight of the minimizing of the reference example 1 that adapts with package integrity properties will reduce.Therefore must use thicker film.In addition, contrast shows, even ignore the requirement for package integrity properties, film according to the present invention provides higher confining force for identical film weight.

Have " tearing intermittently " characteristic according to embodiments of the invention: behind incipient extension, if load further increases, puncture only little by little progressively launches.Interfering section, tearing spreads and can access prevention.As illustrated, the section of tearing at intermittence begins after about 70% extensibility.Reference example 1 in above table 12 and 2 meets with to tear afterwards and spreads in about 60% extensibility (not stoping platform but interfere to tear).If being punctured, the prior art film of this class high elongation may calamity tear the child shipments of coming down in torrents when containing child shipments.

For the present invention, can apply the stretching of higher degree safely.

Fig. 7 is diagram, has shown the susceptibility that frictional coefficient is formed the difference of epidermal area.Referring to Fig. 7, it is apparent that utilize the desired combination of antiblocking agent and antiseize paste, frictional coefficient (COF) can be adapted to special packaging stretch hood machine desired numerical value in the wide region of 0.2-1.2, has covered the preferable range of 0.4-0.6.Required combination can realize by the mixture of LLDPE grade that use has inherently an existing metallocene-produced of low blocking characteristics.This characteristic comprises to come stabilization by the coupling of transportable examples of such additives (as antiseize paste) in sandwich layer.Fig. 7 shows that also COF is a substantially constant in the thickness of wide region, and this shows that film has good mechanical property.This also additional following advantage: for the different thickness needs that design or reconciliation statement cortex form of reformulating are reduced.

Data at the frictional coefficient shown in Fig. 7 are to utilize designed experiment (4 factors, 3 levels) obtain, in experiment, studied following four parameters [(a) antiblocking agent of the further interpolation except the amount that in the additivated polymeric constituent of epidermal area, exists already, (b) film thickness, (c) the plastomer level in sandwich layer and (d) as the amount of antiseize paste that additive added and antiblocking agent Exceed-1018EB (as all additivated and do not add the per-cent of (Exceed 1018CA) polymkeric substance in epidermal area of interpolation)] for the influence of frictional coefficient.Underproof film is produced by reference table 8 described method and apparatus, and layer is distributed as A=20%, B=60%, C=20%.Measure frictional coefficient (COF) according to ASTM D1894.A series of underproof film forms by the various combination that uses above-mentioned four parameters, and each parameter is used on three levels.These levels are: (a) 0,2500, and 5000ppm, antiblocking agent, (b) 80,110,140 microns, film thickness, (c) 0,37.5,75%, additivated Exceed EB, (d) 0,15,30% plastomer.Data are analyzed by using Designof Experiment software package (DesignExpert).Fig. 7 is the statistical model that draws from the result that obtains the experiment of design and has represented wherein that antiblocking agent level (a) is 1250ppm; Film when being zero with plastomer level (c) in sandwich layer.The figure illustrates when parameter (b) and (c) the kinetics COF characteristic of film when changing.

With the prior art film that is used to contain the clamping plate child shipments Comparatively speaking, can utilize the stretching of higher degree and the influence of thinner film, and the better maintenance of the confining force when temperature variation saves more than 50% on a consumption/clamping plate child shipments of polymkeric substance.Have EVA and/or the blend of EXACT and/or the LLDPE that use contains LCB of low VA content and high SCB content by use, wash boarding can minimize, and thicker especially if desired film is all the more so.This step makes the stress strain curve corrigendum or not too negative that becomes on film greatly stretches.

The benefit of film of the present invention and the optimization EVA that here describes can be utilized in every way.Although the present invention is described at the background that packaging stretch hood requires, the characteristic of the uniqueness of EVA also is suitable for shrinking the improvement of cover film or the stretch-wraps film and the performance of other film application.In the field of packaging stretch hood, improved characteristic can be utilized to reduce the cost of packing by using film thinner and/or more high elongation to reduce the weight of used film.Improved characteristic also can be used to strengthen confining force, transparency etc., so that promote the application that the quality of packaging stretch hood film makes it can be used for requirements at the higher level, their characteristic is inadequate so far in these are used.

Claims (22)

1. the polymkeric substance that comprises units derived from ethylene, this polymkeric substance has:

A) melt index of the 0.05-10g/10min that measures by ASTM-1238 condition E;

B) per 1000 C atom 10-are lower than 30 short chain branches, this short chain branch measures according to C13NMR contains five carbon atoms or still less, with 1-3mol% derived from vinyl-acetic ester, methyl acrylate, ethyl propenoate, butyl acrylate or their bonded unit

C) 0.90-0.94g/cm that measures by ASTM D1505 ³Density and

D) 10-is lower than 20 seconds time of relaxation, uses the Cross model by measuring shearing rate and viscosity calculations down at 230 ℃.

2. according to the polymkeric substance of claim 1, wherein polymkeric substance has 0.91-0.935g/cm ³Density.

3. according to the polymkeric substance of claim 1 or claim 2, wherein polymkeric substance contains contain 6 or greater than whole long chain branches of 6 carbon atoms of at least 1 in per 1000 C atoms, measures according to C13NMR.

4. according to the polymkeric substance of claim 1 or claim 2, wherein polymkeric substance has the bimodal molecular weight distribution of being measured by GPC DRI.

5. according to the polymkeric substance of claim 1 or claim 2, wherein extrude for blown film, polymkeric substance has 0.1 to 4g/10min melt index.

6. preparation is according to each the free radical polymerisation process of polymkeric substance of claim 1-5, it is included in and helps stinging under the condition that forms short chain branch and help the propylene introducing ethene by tail, and vinyl-acetic ester, methyl acrylate, ethyl propenoate, butyl acrylate or their combination and as the input of the propylene of chain-transfer agent, wherein polyreaction in having the tubular reactor of a plurality of reaction zones under 2200-2700 crust and 180-330 ℃, repeatedly injection by raw material and initiator is carried out, but the injection that in the downstream reaction district, has reduced or do not had monomer to inject and reduced or do not had transfer agent.

7. according to the method for claim 6, the outlet temperature peak value that has wherein reduced or do not had the final downstream reaction district that monomer injects surpasses the thermal spike among at least two thermal spikes of two reaction zones of this upstream, end reaction district.

8. multilayer film, it comprises main stor(e)y, main stor(e)y contain based on the gross weight of polymkeric substance in main stor(e)y at least 50wt% according to any one polymkeric substance among the claim 1-5, this film has at least 40% elastic recovery rate after 100% stretches, and provide 20N/50mm at least after 100% incipient extension rate under 85% extensibility the nominal confining force of preliminary draft/100 μ m thickness, described nominal confining force is based on ASTM D5459 and by following step measurements: a) the pinblock speed with 1000mm/min is stretched to 100% elongation with membrane sample; B) kept 5 seconds at this elongation; C) turn back to 85% elongation; D) load under measuring N/50mm after 60 second waiting time; And e) calculates the nominal confining force by confining force being adjusted to 100 μ m thickness films.

9. film according to Claim 8, wherein film can stretch-draw up to 100%, the minimum Elongation test slope of 0.01MPa/ elongation % at least is provided simultaneously.

10. according to Claim 8 or 9 film, wherein the secant modulus of unstretching film is lower than 180MPa.

11. wherein be aligned to according to Claim 8 or 9 film, the linear low density ethylene multipolymer that epidermal area on the one or both sides of main stor(e)y comprises the density with 0.91-0.94.

12. according to the film of claim 11, wherein this film has the A/B/C structure, wherein C and A are identical or different.

13. according to Claim 8 or 9 film, it extrudes manufacturing by tubular blown film, forms the cover that stretches when being suitable for stretching in the horizontal, it can surpassing under the constant pinblock speed 12% of initial initial length/second total deformation speed under be stretched at least 100%.

14., wherein be lower than 3000ppm antiblocking particulate and have 0.91-0.94g/cm by containing according to the film of claim 11 ³The frictional coefficient that provided of the LLDPE epidermal area of density be 0.4-0.7, measure by ASTM D1894.

15. according to the film of claim 11, one of them or two epidermal areas are included in up to having the linear low density ethylene multipolymer of the use single-site catalysts manufacturing of the Elongation test slope of 0.01MPa/ elongation % at least under 100% extensibility.

16. film according to claim 11, one of them or two epidermal areas contain transportable antiseize paste to be provided at the frictional coefficient according to ASTM D1894 mensuration between 0.4 to 0.7, and main stor(e)y contains a certain amount of transportable component, so that by farthest the reduce friction variation of coefficient of the cross transfer of antiseize paste between main stor(e)y and epidermal area.

17. film according to claim 11, one of them or two epidermal areas contain not transportable polymer surface modification agent, so as to be provided at the frictional coefficient of measuring according to ASTM D1894 between the 0.4-0.7 and be provided under the confining force pressure and the clamping plate child shipments between the increase friction.

18. according to the film of claim 11, wherein the middle layer is inserted between main stor(e)y and one or two epidermal area, the middle layer is the polymer composition that has than the modulus more than the low 40MPa of modulus of adjacent epidermal area.

19. according to the film of claim 11, wherein epidermal area has antiblocking additive, antiseize paste and/or the surface-modifying agent of different content.

20. according to the film of claim 11, wherein epidermal area accounts for the 10-60% of whole film thickness together.

21. according to the film of claim 17, wherein the polymer surface modification agent is to have the high molecular UHDPE that is higher than 500000 molecular weight and 0.94 or 0.94 above density.

22. be used for the purposes of packaging stretch hood according to each polymkeric substance of claim 1-5, by being multilayer film with polymer formation, it can TD stretches at least 100% and utilize follow-up elastic recovery effect to remain on the child shipments periphery.

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