This story explains the various steps in manufacturing calendered vinyl films: blending, fluxing, milling, calendering, embossing...
I usually
compare the calendering process to
rolling out pie dough. In reality, the manufacturing process is a little more
complex than that. In the calendering process, PVC material is squeezed between
gigantic, heated, polished-steel rollers that form the vinyl into a very thin
sheet of film.
A modern
calendering line is also more expensive than grandma’s rolling pin, with
capital equipment investments ranging typically from $10 million to $15
million. In addition, the calendering rolls alone cost several hundreds of
thousands of dollars.
The
production lines at companies, such as Achilles, feature advanced computer
controls, which allowed continuous monitoring and in-process adjustments of
machine functions.
In addition
to focusing on the raw materials that create calendered vinyl, I’ll review the
calendering process’s basic steps: blending, fluxing, milling, calendering,
embossing, cooling and winding.
Raw materials.
PVC resin is
the key ingredient. However, by itself, it’s a very hard and brittle plastic
material. Additives — plasticizers, stabilizers, lubricants, pigments and
processing aids — change the film’s physical properties and make it easier to
process.
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PVC resin, pigments and additives comprising the “dry blend” are
combined with the liquid plasticizer in a giant mixer. Photo courtesy of
Achilles USA, Inc.
|
Plasticizers,
which are liquids incorporated into the formulation, soften the hard PVC resin
and make the films more flexible.
Plasticizers
in polymeric calendered vinyls are more complex than those in monomeric films.
Monomeric plasticizer comprises linear (sometimes branched) molecular chains,
whereas polymeric plasticizer features complex branched chains of a higher
molecular weight. The weightier polymeric molecules resist migration and create
a more stable and longer-life plastic.
Plasticizers
add flexibility to the final film. Plasticizer additions soften the film’s
feel, or “hand.” Normal vinyl films used in graphics applications contain
between 20% and 25% plasticizer. The higher-molecular-weight,
polymeric-plasticized mixes have a higher viscosity (rheology) than monomeric
systems, and are processed at slower production speeds. These plasticizers are
more expensive than the monomerics, and are less efficient, which means they
require a higher content of a more expensive material manufactured at lower
speeds.
The
plasticizer’s molecular weight helps determine its stability.
Higher-molecular-weight, polymeric plasticizer comprises very big, bulky,
slow-moving molecules. Hence, they stay in the film.
The early,
lower-molecular-weight monomeric plasticizer molecules were more mobile. They
moved around easily and readily migrated out of the PVC into other adjoining
materials, such as the adhesive coated on the film. Modern monomeric plasticizers
are less mobile, which limits migration into the adhesive.
Heat and UV
light prematurely age products, especially vinyl. As the film ages, it yellows
and degrades. Films can lose their elasticity and become brittle. Heat and UV
stabilizers slow down this aging process. Although monomeric vinyl formulations don’t
usually contain UV absorbers, they’re often incorporated into the vinyl (and
adhesive) — for overlaminating applications — to impart some UV protection to
the digital image or photograph being protected.
Lubricants
assist the film’s release from the hot calender rolls during production and act
as internal processing aides during production. They not only prevent PVC film
from sticking to the rollers, they also improve the compound’s process.
Pigmentation
is achieved via inorganic and organic pigments, which are usually first ground
into the plasticizer to achieve a specified particle size (for full-color
development). The pigment selection will depend upon the vinyl’s end
application.
Economical
inorganic pigments provide higher opacity than organics. High-performance
calendered vinyls use the same pigment opportunities as the more expensive cast
products.
The Calendering Process.
By itself,
the PVC resin is as hard and brittle as a saltine cracker. Thus, to transform
the PVC resin into a flexible plastic, it must be compounded with other
vinyl-film ingredients.
 |
The dry blend and plasticizer are combined in a giant mixer.
Imagine the margaritas that you could make in blender like this? Photo courtesy
of Achilles USA, Inc.
|
Once all the
raw materials are weighed and blended, into a very fine powder with the
consistency of cake flour, the blend is fed into the extruder’s screw — the
machine’s fluxing section. Under heat and pressure, the extruder continues the
mixing process, evenly dispersing all the additives with the PVC resin. In the
fluxing or plastification process, all the separate ingredients fuse together
into one homogenous mass of plastic called the “melt.” As the fine powder
melts, at approximately 300°F, the extruder kneads the material into a hot,
twisted plastic rope. The extruder also helps strain out any foreign particles,
which could damage the machinery.
 |
In the extruder the ingredients are heated and fused together in
what is called the plastification process. Photo courtesy of Achilles USA, Inc.
|
Next, the
hot, plastic rope is fed into a two-roll mill bin and rolled into a rough sheet
of film. In the manufacturing process, the heat is continually increased,
making the film more malleable so it can be rolled increasingly thinner. During
this milling process, edge trim can be reworked into the mix.
 |
In the two-roll mill the hot plastic rope is squeezed into a
thick, rough sheet of plastic. Photo courtesy of Achilles USA, Inc.
|
After the
two-roll mill, the material passes a metal detector. This inspection step
prevents any metal from reaching the calendering rolls. Even the tiniest metallic speck could cause
irreparable damage and necessitate roller replacement.
Calender Rolls.
The calender
comprises four, rather heavy, highly polished, 2-ft.-diameter steel rolls.
Calendering rolls can be arranged into various configurations, such as “L,” “F”
(or inverted “L”) and “Z”. The plant I visited utilized a four-roll “L”
configuration.
 |
The thick sheet of plastic is fed into the top of the calendering stack.
Photo courtesy of Achilles USA, Inc.
|
During the
calendering process, the heat increases, and the vinyl sheet passes between the
rollers. During this process, the film is squeezed into a much thinner and
wider sheet.
The calender
rolls subject the vinyl sheet to thousands of pounds of pressure per square
inch. Such intense forces and rapid production speeds can bend and deflect
these massive rolls.
To compensate
for the rolls’ deflection, some complex
mechanical-engineering ideas have been incorporated into modern machinery,
including crowned rolls (which are thicker in the middle than on the edges) and
rolls that are crossed slightly to one another, rather than perfectly parallel,
and designed to counter the rolls’ bending by applying pressure in the
counter-direction.
 |
In the calendering stack the plastic film is squeezed into a much
thinner and wider sheet. Photo courtesy of Achilles USA, Inc.
|
These
measures ensure an optimum profile so the vinyl’s caliper remains uniform.
After the web travels through the production line’s calender section, the
strip-off, or pick-off roll, strips the sheet from the calendering rolls.
To impart the
film’s surface finish, the sheet goes through an embossing unit. Here, the film
is pressed onto an embossing cylinder with a matte-rubber pressure cylinder.
The resultant surface finish depends upon this embossing cylinder’s condition.
A high-gloss surface is achieved from a highly polished chrome cylinder,
whereas a matte surface is achieved from a matte-engraved emboss cylinder. The
film’s reverse side has an unspecified matte surface.
 |
After the sheet is calendered, it is passed through a series of
rollers, which impart a surface finish.
In this manufacturing stage, the thickness of the sheet is measured
continually across the web to ensure product consistency. Photo courtesy of
Achilles USA, Inc.
|
As the vinyl
sheet passes over and under a series of chilling rolls in the cooling section,
the vinyl quickly cools. The cooling process anneals the vinyl into its final
form.
The vinyl
film is then wound, using highly sophisticated, progressive-tension winders, to
minimize any tension that could result in future, dimensional-stability issues.
For high-gloss films with a soft hand, it’s important to keep roll lengths to a
minimum, with controlled winding tension, to reduce the tendency for gloss
reduction through the roll. This reduction is caused by “cold embossing” — the
matte reverse side presses onto the roll’s high-gloss surface. This is
temporary “damage,” and the gloss can easily be refreshed with heat during
subsequent processing.
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After the film is wound into a master roll, it is shipped to an
adhesive coater, such as RTape. Photo courtesy of Achilles USA, Inc.
|
Although the
facestock is a vinyl film’s key ingredient, it’s only one ingredient in the
pressure-sensitive sandwich. How a film cuts, weeds and handles depends on how
all the components work together. Two rolls of the same facestock, coated with
different adhesives, will likely perform differently. Remember this why it is important that you
evaluate each new vinyl film product.
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SEALITPEN
● Felt tipped marker filled with acrylic clear coat.
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3M Brand 3950 Edge Sealer
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● Suitable for graphics applications in temperatures from 50°F to 100°F.
3M Tape Primer 94 1/2 Pint 8oz For Vinyl
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● Use when vinyl graphics will be stretched into concave areas.
Steinel HG 2510 ESD Programmable IntelliTemp Heat Gun with a LDC Display
● Temperature range: 120°F -
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Visit My Vinyl Sign Techniques Community
Additional Vinyl Graphics Articles
Vinyl Application Videos
Squeegee Technique. Nothing is more basic in vinyl application than the squeegee. But some squeegees work better than others. And there are right ways and wrong ways to use this simple tool. This video clip reviews squeegee selection, squeegee care and squeegee technique. Click to Link
Wet Applications. Dry applications are typically recommended for most vinyl applications. For those exceptions to the rule, this instructional video explains the right way to perform a wet application. Click to Link
Application of Window Graphics. Installing vinyl graphics on glass can be challenging, because the adhesive aggressively grabs onto this high energy surface. Repositioning graphics on window is generally difficult, if not impossible. This instructional video explains how to dry apply window graphics right the first time. It also describes the necessary steps required for surface preparation. Click to Link
Transferring Frosted Window Graphics Films. Because frosted window films are highly textured, transferring cut vinyl graphics can be problematic. This video provides direction in selection of the right application tape and how to apply these films quickly, easily and without problems. Click to Link
3-Step Surface Prep. This instructional video describes how to properly clean the surface of a vehicle before applying pressure sensitive vinyl graphics to a trailer or doing a full wrap of a car or van. This three step surface prep involves detergent washing, solvent cleaning and a final wipe down with IPA. Click to Link
Vinyl Application Over Rivets. Applying vinyl graphics on vehicle surfaces with rivets is challenging for most sign makers. Vinyl failures to these surfaces are all too common. This video demonstrates some tips and procedures, used by professional decal installers, which will make these demanding applications easier and more trouble-free. Click to Link
Vinyl Application to Corrugations. Learn how to apply vinyl graphics to corrugations in a relaxed state. Forcing films into the valleys of corrugations puts too much mechanical stress on the film. Sooner or later, the vinyl will lift or tent in valleys. Click to Link
Applying Air Egress Vinyls. Vinyl films with air egress release liners have almost eliminated bubbles and wrinkles from applied graphics. Air egress release liners with their highly textured surface structure are problematic. Not much will stick to these liners other than the vinyl film. At RTape our best premask solution for air egress liners is a special Conform® tape called 4761RLA. Click to Link
About Jim Hingst: After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.
Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer. Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.
Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 150 articles for publications, such as Signs Canada, SignCraft, Signs of the Times, Screen Printing, Sign and Digital Graphics and Sign Builder Illustrated. He also posted more than 325 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published. Vinyl Sign Techniques is available at sign supply distributors and at Amazon.
© 2016 Jim Hingst
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