How to extrude HMW-LDPE film.Extrude extrude /ex·trude/ (ek-strldbomacd´)
1. to force out, or to occupy a position distal to that normally occupied.
2. in dentistry, to occupy a position occlusal to that normally occupied. HMW-LDPE Film
HMW-LDPE is not brand new, though it is still unfamiliar to most film producers. It has been offered commercially on a small scale for several years, but may have been "ahead of its time" when first unveiled in the early 1980s (see PT, Nov.'84, pp. 47, 55). Last year, the USI Div. of Quantum Chemical Corp., cincinnati, felt the time was right to "reintroduce Re`in`tro`duce´
v. t. 1. To introduce again.
Verb 1. reintroduce - introduce anew; "We haven't met in a long time, so let me reintroduce myself"
re-introduce " this material, since the expanded use of long-stalk HDPE HDPE
high-density polyethylene blown film machinery has created a new window of opportunity for HMW-HDPE. Quantum, believed to be the only producer of this material, currently offers three grades of Petrothene HMW-LDPE resin, ranging from 0.25 to 0.5 melt index.. Two grades are homopolymers (0.925 density), while the third is an EVA Eva
to marry winner of singing contest. [Ger. Opera: Wagner, Meistersinger, Westerman, 225–228]
See : Prize
1. Eva - A toy ALGOL-like language used in "Formal Specification of Programming Languages: A Panoramic Primer", F.G. copolymer copolymer: see polymer. . Petrothene NA 351 (0.3 MI) is suitable for a broad range of applications. NA 355 (0.5 MI) is recommended where clarity is most important or where better drawdown Drawdown
The peak to trough decline during a specific record period of an investment or fund. It is usually quoted as the percentage between the peak to the trough.
Notes: is required. NA 357 (4.5% VA content) is for uses demanding exceptional toughness, low-temperature properties, or low sealing temperatures. These high-strength resins are also suitable for combination with other plastics through coextrusion or blending.
With long-stalk equipment now more prevalent in the market, the resin may be re-examined by processors as a means of boosting their equipment's utilization as well as tapping into niche markets A niche market also known as a target market is a focused, targetable portion (subset) of a market sector.
By definition, then, a business that focuses on a niche market is addressing a need for a product or service that is not being addressed by mainstream providers. such as merchandise bags, clarity shrink film, high-gloss coextruded film, heavy textiles and heavy-duty produce bags. Other potential applications include ice bags, quickfreeze food bags, drum liners and clarity film where downgauging is desired.
HWM-LDPE's higher viscosity than conventional LDPE LDPE
low-density polyethylene and LLDPE LLDPE Linear Low Density Polyethylene provides excellent bubble stability. The combination of high viscosity and molecular chain branching gives rheological rhe·ol·o·gy
The study of the deformation and flow of matter.
rheo·log properties that permit extrusion under a broad range of operating conditions.
Because of its unique properties, HMW-LDPE can compete in applications with a variety of resins. Compared with conventional PE clarity packaging films, HMW-LDPE is stiffer, has better tensile tensile,
adj having a degree of elasticity; having the ability to be extended or stretched. , puncture puncture /punc·ture/ (-cher) the act of piercing or penetrating with a pointed object or instrument; a wound so made.
cisternal puncture and impact strengths, and equivalent optical properties. Extrusion can be with either long-stalk or "pocket" bubble, better optical properties usually resulting with the latter.
HMW-LDPE also can compete in heavy-duty film applications. When compared with a standard 7.5% EVA copolymer of 0.5 MI, used for heavy-duty liner film, HMW-LDPE has lower impact strength but better tear resistance (both MD and TD), puncture resistance and stiffness. Compared with an LDPE homopolymer of 0.3 MI and 0.918 density, HMW-LDPE film impact properties are similar, tear and stiffness again are better, and optical properties are much better.
Table : HMW-LDPE VS. OTHER PE FILMS
Conditions HMW-LDPE LLDPE HMW-HDPE Melt Temperateture Lowest Medium Highest Long Stalk Desirable Not Normally Necessary Blow-Up Ratio 3:1 2:1 3.2:1 Die Gap 40 mil >89 mil 40 mil Melt Strength Excellent Poor Excellent Optical Properties Excellent Poor Very Poor Impact Strength Very Good Good Excellent Elmendorf Tear Low, but High and Low MD, Balanced Balanced High TD Stiffness Good Good Excellent Softness Good Good Poor MVTR Good Good Excellent
Dart-drop impact strength of HMW-LDPE per mil per mil also per mill
[per + mil (short for Latin m of thickness is higher than that of conventional LDPE, and even higher than LLDPE. This emphasizes the orientation effect of long-stalk extrusion. Standard LDPE and LLDPE impact/mil values remain relatively constant with increasing gauge. HMW-LDPE has remarkably high impact/mil for films under 1 mil An Internet address domain name for a military agency. See Internet address.
(networking) mil - The top-level domain for entities affiliated with US armed forces. , decreasing with gauge, and eventually leveling off at about 2 mils. HMW-LDPE also has better optical properties than the other two high-strength resins, HMW-HDPE and LLDPE.
Table : HMW-LDPE & HMW-HDPE IN LONG-STALK EXTRUSION
Petrothene Petrothene NA 351 LY600 Properties HMW-LDPE HMW-HDPE
g/10 min. 0.3 8.0 HLMI Density, g/cc 0.925 0.951 Film Gauge, mil 0.75 0.75 Haze, % 6.0 High Gloss, 45 [degrees] 67 Low Drop dart, g 238 414
Total Energy Dart dart
see blow dart.
see blow dart.
Body 1.9 2.2 Creased 1.7 2.1
Tens. Str., psi
MD 6090 11,600 TD 5900 9010
Elongation elongation, in astronomy, the angular distance between two points in the sky as measured from a third point. The elongation of a planet is usually measured as the angular distance from the sun to the planet as measured from the earth. , %
MD 130 260 TD 320 380
1% Secant Mod., psi
MD 32 128 TD 33 144
Output, lb/hr 116 120 Screw Speed, rpm 175 125 Pressure, psi 2420 5100 Drive, amps 23 31 Melt Temp., [degrees] F 396 397 Blow-Up Ratio 3.2:1 3.2:1 Stalk Height, in. 28 30
HMW-LDPE can be blown into film by either of two standard bubble shapes: a conventional "pocket" bubble, used with LDPE gives high clarity and high output, but film cannot readily be drawn down to 1.5 mils, unless blended with LLDPE. Long-stalk extrusion, characteristic of HDPE, provides twice as much impact/mil and permits drawdowns to 0.5 mil, though clarity is somewhat lower. These two methods may be obtained by changing the type of air ring used in the process.
A dual-lip air ring pulls the bubble down into the air-ring pocket in the conventional bubble shape. A single-lip air ring allows the bubble to rise in a stalk stalk (stawk) an elongated anatomical structure resembling the stem of a plant.
allantoic stalk and expand when the viscoelastic Adj. 1. viscoelastic - having viscous as well as elastic properties
natural philosophy, physics - the science of matter and energy and their interactions; "his favorite subject was physics" forces of the melt have been overcome by the drawing forces. During this rapid expansion just below the frost line frost line
The depth to which frost penetrates the earth.
1. In regions where there is no permafrost, the maximum depth to which frost penetrates the ground in the winter.
2. , significant molecular orientation is created that optimizes the film's impact strength. This effect is enhanced by the resin's high melt viscosity and molecular weight.
HMW-LDPE can be extruded through grooved-feed extruders developed for HWM-HDPE long-stalk film. Gauges usually range between 0.5 and 1.5 mil. HMW-LDPE long-stalk extrusion uses the same die gaps - about 40 mils - as for HMW-HDPE. Extruded under these conditions, melt temperatures can be as low as 370-380 F, which is about 50 [degrees] lower than for HMW-HDPE. In addition, there is a less tendency for melt-temperature override with HMW-LDPE because less shear heat is generated in the extruder than with HWM-HDPE.
Output per screw rpm of HMW-LDPE is lower than with HMW-HDPE, meaning that extruder screw speed would have to be increased in order to achieve equivalent outputs through grooved-feed extruders. Normally this isn't a problem since HME-LDPE generally runs cooler and at a lower backpressure back·pres·sure
Residual pressure opposing the free flow of a gas or liquid, as in a pipe or an exhaust system. than HMW-HDPE.
For example, HMW-HDPE was run on quantum's 100-mm laboratory grooved-feed extruder with a 4-in. diam. die at 120 lb/hr at 125 rpm; to match this output with HMW-LDPE, screw speed was increased to 175 rpm.
HMW-LDPE has the high melt strength required for a long stalk. Good gauge control is possible, with no special die adjustments necessary, other than standard gap adjustments in order to get a symmetrical bubble.
Long-stalk film optical properties and puncture resistance are unaffected by blow-up ration ration
a fixed allowance of total feed for an animal for one day. Usually specifies the individual ingredients and their amounts and the amounts of the specific nutriments such as carbohydrate, fiber, individual minerals and vitamins. (BUR bur or burr, popular name for fruits that have barbed, pointed, or rough outgrowths. By clinging to the fur or hair of animals and the clothing of man they are transported from the parent plant, often great distances. ). However, dartdrop impact increases dramatically with BUR. MD tear strenght and stiffness decrease with BUR. Since these resins are stiffer than normal, a film blown with a large 4:1 BUR has a modulus See modulo. similar to a normal 0.922-density homopolymer film. Optimum properties are achieved at about 3:1 BUR.
TANDEM AIR-RING BENEFITS
Several years ago, the former Chemplex Co., now merged into Quantum, found that a tandem air ring was one way to improve output rate and clarity in HMW-LDPE long-stalk extrusion (see PT Nov. '84, pp.47, 55). In the tandem setup, the primary air ring is a conventional single-lip type mounted directly onto the die. The secondary ring is a dual-lip model attached 30 to 51 in. above the first ring. A moderately shallow lip was found to give the best results. The secondary air ring "locks" the bubble in place, increasing stability and providing up to 14% higher throughput rates Throughput rate is an obsolete term in the terminology of automated chemical analysis. It may mean either:
1. ^ International Union of Pure and Applied Chemistry. "throughput rate". , while reducing gauge variation by about 60%. And while film toughness and strength were somewhat reduced by the tandem air-ring method, these properties remained well above levels of conventional clarity LDPE, suggesting potential downgauging. Clarity of HMW-LDPE is also better with dual-air-ring long-stalk extrusion than by any other method. On the other hand, it can be somewhat tricky to set up a dual air ring to achieve these benefits, and some trial and error may be necessary.
USING LDPE FILM LINES
Standard LDPE film extrusion lines can also be used to run HMW-LDPE. Although it is difficult to extrude below 1.5 mil in the pocket, favorable properties can be attained at all gauges. Pocket extrusion results in significantly less TD orientation than long-stalk extrusion, so film impact strength may be lower. Optical properties of HMW-LDPE generally improve when going from long-stalk to pocket extrusion. Compared with typical LDPE clarity films, HMW-LDPE extruded in the pocket has better impact, stiffness and strength properties, with equivalent opticals.
To improve drawdown of HMW-LDPE when extruding a conventional pocket bubble, 10-30% LLDPE can be dry-blended into the resin. Film gauges as low as 0.5 mil have been reached in Quantum's applications research laboratory, where HMW-LDPE is blended with 30% of a hexene LLDPE with a 2.5 MI and 0.918 density at a 3:1 BUR. The addition of the 30% LLDPE had little effect on film haze or gloss, although "see-through clarity" (NAS (1) See network access server.
(2) (Network Attached Storage) A specialized file server that connects to the network. A NAS device contains a slimmed-down operating system and a file system and processes only I/O requests by supporting the popular ) was decreased relative to 100% HMW-LDPE. Tensile and tear strengths were improved; and though total dart-drop impact energy decreased, puncture resistance improved with addition of LLDPE.
HMW-LDPE also is a good candidate for coextrusion. When used as the outside layer in HMW-HDPE structures, the low-density resin provides high gloss and a good heat seal. And since it's a natural in long-stalk extrusion, the coextruded material runs with a more stable bubble, which gives better gauge control. It also allows the coextrusion to be run with a high frost line, providing excellent orientation.
PHOTO : High strength of HMW-LDPE film suggests uses in heavy produce bags, ice bags, quick-freeze bags, drun liners, shrink films, heavy textile, and even downgauged clarity films.