Shrink Film
SHRINK WRAP
SHRINK FILM BASICS
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The shrink film market is comprised of two basic categories; the polyvinyl chlorides (PVC) and the polyolefin. Shrink polyethylene is not typically included in the competitive polyolefin category; "poly" lacks the clarity, gloss and the tight second skin polyolefin provide. These attributes are critical for retail appeal.The polyolefin "family" consists of films made from polyethylene or polyethylene and polypropylene copolymer resins. All Cryovac shrink films are polyolefin.
PVC shrink films derive their properties from additives, which are primarily plasticizers. As these films age, the plasticizers. migrate and the film reverts to its brittle state, turning to a yellowish color. Also, PVC films tend to be temperature-sensitive, developing a tendency to shatter and split at cold temperatures (below freezing), and "shrink-back" and! or block when exposed to high temperatures over a period of time. The color may also change to yellow when exposed to heat (such as being stored in a non-air-conditioned warehouse over the summer).
FILM SEALING SYSTEMS For pictures and a comparison of other shrink wrap methods click here
Until recently, most sealing systems used a hot wire in order to seal and cut-off the film at the same time; now, a knife system has gained in popularity on many models, due to its durability. The wire or knife seals the film against a pad, covered with Teflon tape to protect the pad. Time, temperature and pressure are the three most critical elements affecting the seal quality. If the sealing head is not held on the film long enough, the temperature is too low, or the pressure is insufficient or uneven, the seal quality will be poor, and/or won’t cut. However, if the sealing temperature is too low, or the pressure is insufficient or uneven, the seal quality will be poor, and/or won’t cut. However, if the sealing temperature is too high, the film may break just behind the seal. Following the impulse sealing cycle, a cooling cycle allows the film to "solidify" into a solid seal. This dwell-time is critical in order for a seal to hold.SHRINK FILM BASICS
PVC films require only heat in order to cut seal and cut. When run on a sealing system as previously described, build-up of carbon char (black specs and flakes) will occur. The char will need to be cleaned from the sealing head on a regular basis; otherwise, the carbon will interfere with the sealing process, and will look unsightly on the sealed ends of the package.Since only heat is needed to form a PVC seal, some machines use a hollowed out bottom platen instead of the foam pad; direct contact with the seal wire is eliminated. Other systems employ a much thinner nichrome wire (.020" diameter versus. a standard .036" to .040" for polyolefin) against a hard bottom sealing pad. This system is insufficient to create strong polyolefin seals.
One other sealing system designed for PVC is called a Universal Sealing System. Despite the name, the hot knife is typically too sharp to form a quality polyolefin seal. A rounded knife is better suited.
FILM SHRINKING SYSTEMS
In order for proper shrinking to take place, polyolefin films need an air evacuation hole or multiple perforations. A bag formed with PVC film does not need "artificially created" air escape holes. Because of the makeup of PVC, the seal typically is full of small pinholes; this is where the air escapes during the shrinking process. While this may seem advantageous (a step can be eliminated), the small holes actually weaken the seal area. These holes are often located near or in the package corners.In order for proper shrinkage to occur, polyolefin film must be exposed to the correct temperature for the correct amount of time (which is controlled by conveyor speed), and also be surrounded by the correct air velocity, or wind turbulence. The air allows the film to stand away from the product, and a "bubble" is formed around it. A good, even shrink should result when this occurs.
FILM TYPES & CHARACTERISTICS TERMINOLOGY
BACK TO TERMINOLOGY
Balanced - Equal orientation in both LD and TD, i.e., 3 x 3 or 5 x 5.
Basic Film -A film made of one material.
Biaxially Oriented Film - Oriented along X and Y axes.
Blown Film -A film extruded by the blown (air inflation) system. Sometimes erroneously called "extruded" film.
Coextrusion -Two or more polymers extruded and combined in a die, each forming a distinct layer in the final film.
Copolymer - Polymers such as polyethylene/polypropylene are composed of repeating monomers and are actually homopolymers. Copolymers result when two monomers are combined during polymerization.
Composite Film -A film made by joining two or more basic films. Composite films include laminates, co-extrusions, and coated films.
EVOH - Ethylene vinyl alcohol (EVOH) resins are hydrolyzed copolymers of vinyl acetate and ethylene. EVOH has excellent gas, aroma, and solvent-barrier properties.
Heat Shrinkable Films -Films which have gone through an orientation step in the manufacturing process, which shrink significantly with application of heat, generating a substantial shrink force.
Laminate - A general term used to describe packaging structures composed of two or more materials, each designed to contribute one or more desirable properties to the final construction. There are many techniques for producing laminate materials, i.e., extrusion, adhesive laminating or extrusion coating. Syn. Composite.
Monoaxial - A film which is oriented to shrink in one direction (longitudinal or transverse) only.
MonolayerFilm - A single layer film extruded from one or a blend of several raw materials (resins).
Multilayer Shrink Film - A film formed with multiple layers of similar or differing polymers. The purpose is to obtain specific properties and characteristics.
Polyethylene - A simple thermoplastic polymer of ethylene. Each molecule consists of hundreds/thousands of carbon atoms. The length of molecules and the amount of side branching determine the characteristics of the film, i.e., LDPE, LLDPE, HDPE, etc. Polyethtlene is used for general wrapping, when appearance is not critical.
Polymer - A gas heated under pressure goes from a gas to a solid. This is called "polymerization". The resultant material is called polymer.
Polyolefin - A term used to describe ethylene and/or propylene-based films that are generally a composite of several different types of film. The shrink wrap industry uses this film because it can provide a very high strength to gauge ratio and the film is generally very good for retail applications. Cryovac leads the industry in the highest performance shrink film available.
Polypropylene - A thermoplastic polymer of propylene. Polypropylene materials are generally oriented, heat-set (OPP) materials which do not shrink.
Preferential Shrink - The characteristics of a shrink film which enable it to shrink more in on direction (longitudinal or transverse) than the other. Longitudinal orientation is accomplished by a device which stretches the film in the machine direction. Transverse orientation is induced by a process such as tentering which applies across the web stretching.
PVC (Polyvinyl Chloride) - Compounding modifications and a variety of production processes adapt PVC to a wide variety of end uses. In manufacturing, the film can be blown, solution case, calendered, and slot die chill cast-in thicknesses from 0.0004-0.010 mil. It is readily oriented to produce a shrink film.
Saran (Polyvinylidene Chloride) - Saran films are made from copolymer that is predominately vinylidene chloride (PVDC). Due to the very high chlorine content of the polymer, unplasticized saran film is highly crystalline and has high barrier to passage of oxygen and other gases, water vapor, odors, aromas, and flavors.
Unbalanced - Unequal orientation in LD and TD; preferential or monoaxial orientation.
Cryovac D-955
D-955 Film has been specially formulated by Cryovac scientists to meet the demand for a shrink film with exceptional toughness combined with excellent merchandisability. It can well be described as a "work-horse" film: tough, durable, with the versatility to be used in a wide range of applications.Superior abuse and puncture resistance make D-955 ideal for packaging products that must survive rough handling in distribution, such as multipackaging for warehouse clubs. Its high shrink energy tightly unitizes multiple items, often eliminating the need for supporting trays or banding.
Because of its wide range of shrink properties, D-955 Film performs equally well for unusual-shape objects, window boxes, and heavy products with premium add-ons or "pack-ons." The film's excellent memory prevents it from relaxing under fluctuating temperatures. This same memory feature is especially important if a product is handled a great deal while on retail display; the package stays taut and wrinkle-free.
Exceptional tensile strength enables D-955 Film to be used in thinner gauges than competitive films while delivering the same degree of protection. It also produces very high-integrity seals over a broad temperature range, and runs at excellent speeds on various types of packaging equipment.
At the point of sale, D-955 outperforms other films in merchandising appeal with excellent optics. Its exceptional clarity (both see-through and contact), high gloss and sheen impart a premium look to consumer products, giving them a distinct advantage in eye appeal.
The versatile way to unlimited packaging
If versatility is what you need, Cryovac® D-955 Shrink Film is what you are looking for. Everything from complementary products like motor oil and transmission fluid to sampling products like mouthwash and chewing gum, and multiple packages of shutters, canned goods, aerosol cans and so much more. /
/ ® D-955 offers both excellent strength and world class optics. Its exceptional tensile strength means you can save on packaging costs by utilizing thinner gauges. This strength assures abuse and puncture resistance and subsequent product protection.
This makes D-955 ideal for multipacking and shrink-wrapping products with premium add-ons. Its high shrink energy tightly unitizes multiple items while its clarity lends a premium look to products that depend heavily on eye appeal at the retail level.
Film Highlights
Type of Material.Extremely tough, multilayer, cross-linked polyolefin. / Appearance.
Superior clarity, gloss and sheen give products maximum appeal at point of sale.
Machineability.
Medium to high slip enables it to be run on various types of equipment: centerfold, reverse-fold and form-fill seal machines. / Toughness.
Superior abuse and puncture resistance; can be used in thinner gauge.
Forms available.
Singlwound (SW) in widths to 63"; centerfolded (CF) in widths to 58".
Gauges.
60, 75, 100 and 125. / Sealing techniques.
Impulse, constant heat, electrostatic.
Comparative Properties Chart
CRYOVAC Series D-955 FilmsGauge / 60 / 75 / 100 / 125
Minimum Use Temp. / -60 deg. F.
Maximum Storage Temp.
(two years maximum) / 90 deg. F.
Shrink Temp. , Air / 250-350 deg. F.
Density @ 73 deg. F.(g/cc) / 0.922
Haze (%) / 2.4 / 2.6 / 2.7 / 2.7
Gloss (%) / 87.3 / 88.2 / 88.8 / 86
Ball Burst Impact Strength (cm/kg) / 17.7 / 21.7 / 28.5 / 30.3
Oxygen Transmission Rate
(cc/m*m/24hrs., 73 deg. F., 1 atm) /
8,548 /
6,726 /
4,941 /
3,350
Water Vapor Transmission Rate
(gms/100 sq. in./24 hrs., 73 deg. F., 100% RH) /
1.38 /
1.09 /
0.82 /
0.74
LD* / TD** / LD* / TD** / LD* / TD** / LD* / TD**
Tensile Strength (psi) / 14,300 / 17,300 / 15,400 / 16,800 / 15,200 / 17,900 / 14,700 / 16,400
Elongation at Break (%) / 120 / 105 / 130 / 110 / 140 / 110 / 155 / 135
Modulus of Elasticity(psi) / 50,100 / 55,800 / 52,500 / 57,200 / 52,900 / 58,600 / 47,400 / 52,800
Tear Propagation (gms) / 6.1 / 4.6 / 8.7 / 7.1 / 13.2 / 9.5 / 17.5 / 14.5
Unrestrained Shrink (%)
@200 deg. F.
@220 deg. F.
@240 deg. F.
@260 deg. F. /
13
21
47
78 /
19
30
54
78 /
16
24
51
78 /
18
30
56
79 /
13
20
48
77 /
22
35
59
76 /
9
20
62
76 /
20
32
66
77
Note: These are typical values for Cryovac films. They are intended for use as limiting specifications.
*Longitudinal Direction **Transverse Direction
This information represents Cryovac's best judgement base on work done, but Cryovac & Pierce Packaging assumes no liability whatsoever in connection with the use of information or findings contained herein.
D-955 complies with the requirements of the Federal Food, Drug and Cosmetics Act, as amended, for the packaging of all foods, with the exception of high alcoholic substances, at temperatures of 100 degrees C. and below.
Cryovac D-940
D-940 Film is the result of break-through technology that creates the first true polyolefin soft shrink film.D-940 Film is a multilayer, electronically cross-linked film produced through a proprietary coextrusion process and designed to provide a low shrink energy. This unique property enables a variety of products to be effectively shrink-packaged without distortion or buckling to detract from their sales appeal.
D-940 Film is ideal for paper products such as stationery, magazines, greeting cards and computer manuals.
Excellent clarity and gloss of D-940 Film enhance merchandising of products whose true colors are critical to the sale (wallpaper, giftwrap, textiles, etc.).
It is specifically suitable for window box packaging and for products that use lightweight chipboard trays or containers.
D-940 Film provides excellent machinability on automatic equipment and produces high-integrity heat seals. Unlike PVC films, D-940 is noncorrosive and causes no carbon buildup on sealing wires.
Superior cold-flex properties keep the film pliable even at sub-freezing temperatures.
Sometimes the softest things are the hardest things to package.
Products like linens, bedding, gift wrap, stationary and snack foods. Ironically, the very thing that makes them so appealing also makes them difficult to package. Cryovac® D-940 soft-shrink film allows you to package soft goods without the buckling and distortion that can turn shoppers off at the point of sale.
D-940 film from Cryovac eliminates unsightly dog ears, fish eyes and crow's feet, and it gives products an additional merchandising advantage with reduced haze and greater sparkle. This translates into great appeal on the retail shelf. /
/ This soft-shrink film helps showcase items such as books, magazines, computer manuals, notebooks, photo albums, school supplies and printed or converted paper products. It's ideal for products packaged in lightweight chipboard trays or containers that normally buckle when wrapped with most shrink films. Since this film conforms to odd shapes, it creates a beautiful package for hard-to-package
Film Highlights
Type of Material.Multilayered, coextruded polyolefin. / Appearance.
Superior optics with low shrink energy.
Machineability.
Very "forgiving" film, because it runs on just about any kind of equipment, under just about any conditions. / Toughness.
Excellent seal strength.
Forms available.
Singlwound (SW) in widths to 63"; centerfolded (CF) in widths to 58".
Gauges.
60 and 75. / Sealing techniques.
Impulse, constant heat, electrostatic.
Comparative Properties Chart
CRYOVAC Series D-940 FilmsGauge / 60 / 75
Minimum Use Temp. / 0 deg. F. / 0 deg. F.
Maximum Storage Temp.
(two years maximum) / 90 deg. F. / 90 deg. F.
Shrink Temp. , Air / 200-325 deg. F. / 200-325 deg. F.
Density @ 73 deg. F.(g/cc) / 0.932 / 0.932
Clarity (%) / 83 / 85
Gloss (%) / 86 / 95
Ball Burst Impact Strength (cm/kg.) / 8 / 11
Oxygen Transmission Rate
(cc/m*m/24hrs., 73 deg. F., 1 atm) /
13,800 /
12,000
Water Vapor Transmission Rate
(gms/100 sq. in./24 hrs., 73 deg. F., 100% RH) /
2.8 /
2.4
LD* / TD** / LD* / TD**
Tensile Strength (psi) / 11,300 / 9,800 / 10,980 / 11,042
Elongation at Break (%) / 98 / 130 / 110 / 100
Modulus of Elasticity(psi @ 73 deg. F.) / 29,000 / 29,000 / 29,000 / 29,000
Tear Propagation (gms) / 11 / 15 / 23 / 13
Unrestrained Shrink (%) @160 deg. F.
@180 deg. F.
@200 deg. F.
@220 deg. F.
@240 deg. F.
@260 deg. F.
@280 deg. F. / 8
9
23
44
69
81
82 / 7
15
28
45
68
77
77 / 8
15
28
43
69
81
82 / 6
14
32
44
68
78
79
Note: These are typical values for Cryovac films. They are intended for use as limiting specifications.
*Longitudinal Direction **Transverse Direction
This information represents Cryovac's best judgement base on work done, but Cryovac & Pierce Packaging assumes no liability whatsoever in connection with the use of information or findings contained herein.
D-940 complies with the requirements of the Federal Food, Drug and Cosmetics Act, as amended, for the packaging of all foods, with the exception of high alcoholic substances, at temperatures of 65 degrees C. and below.