Plastisol
vs. Water-based Ink for Textile Printing
There are
two main types of ink that are used for textile printing. Water-based ink
utilizes either dyes or pigments in a suspension with water as the solvent.
The evaporation of the water is necessary to set or cure the ink. This
curing can take place either at room temperature or using a forced-air dryer
depending upon the specific water-based ink used and the speed or volume of
production.
Plastisol
ink is a PVC (Some inks are Phalide Free) based system that essentially
contains no solvent at all. Along with UV ink used in graphic screen
printing, it is referred to as a 100% solid ink system. Plastisol is a
thermoplastic ink in that it is necessary to heat the printed ink film to a
temperature high enough to cause the molecules of PVC resin and
plasticizer to cross-link and thereby solidify, or cure. The
temperature at which most plastisol for textile printing cures at is in the
range of 300 °F to 330°F
Both types
of ink are very popular. However, for the most part, they are used in very
different applications. Plastisol is the ink of choice for printing of
finished goods such as T-shirts, sweatshirts, jackets, and tote bags.
Water-based ink is the ink of choice for the printing of yard goods; either
in piece form or on the roll. Both inks have technical advantages and
disadvantages for use in specific applications. They also each have their
own environmental impacts and these should be considered for the particular
application and shop setup.
Advantages of Plastisol
-
Plastisol can be left in the screen for extended periods of time without
clogging the mesh. It is ready to use right out of the container more
than 90% of the time. In most applications, it can be printed
wet-on-wet, which allows for increased production speeds. It comes in
formulations that can be printed on light and dark fabrics. And, in most
municipalities, the disposal of waste plastisol is a very simple
process.
-
Plastisol does not “dry”. In order for a compound to dry, there must be
evaporation of some kind of solvent. Since plastisol has little or no
solvent, it cannot dry. Because of this characteristic, plastisol can be
left in screens, the lids can be left off of the ink containers
(although keeping them covered is a good practice to keep lint and dirt
out of the ink). And ink left at the end of the job can be returned to
the container for reuse without any adverse affects. This last practice
is a great benefit in reducing waste product.
-
Plastisol is extremely versatile in that most printers never have to
amend the ink. They are able to use it direct from the container without
ever adjusting the viscosity or the strength.
-
Plastisol comes in strengths from transparent to very opaque and most
printers will have the various versions available to use, depending upon
the type and color of fabric they are printing on. The various opacities
of ink also vary greatly in price with the most opaque being the most
expensive, mainly due to the cost of the increased pigment. So, good
shop management dictates that the proper opacity be applied to each
fabric in order to be cost effective.
Plastisol Disadvantages
- Since
Plastisol is a thermoplastic, it will remelt if it comes in contact with
anything hot enough. For that reason, plastisol prints cannot be ironed.
If an iron touches a print, it will smear the ink.
-
Plastisol ink also creates an ink film that can be felt with the hand.
The higher the opacity of the ink, the greater the hand. This heavy hand
is considered a disadvantage at the consumer level. One of the most
important practices when using plastisol ink is to keep the ink clean.
What this
statement means, is that it is very beneficial, and cost effective, to keep
plastisol colors from being contaminated by dirt, lint, or even other colors
of ink. By maintaining clean shop practices, there will be a great reduction
in ink waste. Clean ink can be returned to the original ink container for
reuse. There is no degradation in the quality of plastisol as long as it is
not mixed with other colors or contaminated with foreign materials.
Plastisol
that has been contaminated with other colors is can still be retained in a
separate container for blending with other waste ink. Often times this waste
ink can be used to create new colors or, it can be over pigmented with fresh
pigment to create a dark color, such as black, for use on less critical
jobs.
With good
plastisol ink management, waste can be reduced to a very small percentage.
Plastisol product that is unusable is not considered hazardous waste in most
municipalities as long as it is solidified (cured). The best way to achieve
this cure is to heat the waste container itself to 160 °C (320 °F) for a
period long enough to cure the ink all the way through. In practice, a one
gallon container of plastisol will cure all the way through in approximately
one hour.
If the
plastisol needs to be disposed of in an uncured state, then hazardous
chemical regulations usually apply. For either cured or uncured disposal, it
is recommended that you always check
with local regulatory agencies.
The
biggest environmental hazard in the use of plastisol comes in the screen and
equipment cleaning steps. In order to emulsify the ink for easy removal from
screens, squeegees, flood bars, spatulas, and work surfaces, it is necessary
to use some type of solvent. The waste ink and the solvent must be disposed
of properly in order to minimize environmental impact.
The screen
printing industry has been very proactive in the creation of products that
can minimize the impact of these cleaning processes. Solvents are available
that are “more” environmentally sensitive
http://www.silkscreeningsupplies.com/site/799934/product/CCCPG
than the traditional petroleum based solvents. In addition, there are many
types of filtration and cleaning systems available to capture inks and
solvent residues to minimize the solids that are discharged into the sewer
system.
Water-based Ink Systems
Water-based inks are defined as those that utilize water as the main
solvent. That does not mean, however that water is the only solvent. It is
significant to note that many water base inks contain “co-solvents” which
may even be petroleum based solvents. The reason these co-solvents are used
varies, but one of the key reasons is to decrease the time and heat
necessary to cure the ink film on the fabric.
Advantages of Water-based
Inks
-
Water-based inks are a good choice when a “soft hand” is desirable. A
soft hand is the condition where the ink film cannot easily be felt with
the hand when passed across the surface of the fabric. This affect is
often used as an argument for why water-based is preferable to plastisol
as plastisol has more of a hand than water-based.
-
Water-based ink also has the advantage of being an excellent ink system
for high speed roll-to-roll yardage printing. Such printing is done on
large sophisticated equipment that has very large drying (curing)
capacity.
-
Water-based ink also is a good choice where ink penetration is
desirable, such as in towel printing. Towels have a high nap fabric that
must be printed in a manner where the ink penetrates or wicks through to
the base fabric for adequate coverage.
-
Waterbased inks that are designed to wick into the fabric are excellent
for this application. Ink wicking is not a desirable affect in most
other fabric printing as it will destroy the design and registration of
multiple colors.
Disadvantages of
Water-based Ink
-
Water-based ink is much more difficult to cure than plastisol. A shop
that is interested in printing water-based ink must have the drying
capacity to remove the water. The dryers used for water-based printing
tend to be larger than those needed for plastisol. In plastisol
printing, the ink film must only reach the cure temperature for a brief
moment. With water-based ink, the temperature must be reached and then
held until all of the solvent (water) is removed. There are water-based
inks that will air dry but they are usually only acceptable for craft
level printing as the room required for curing greatly reduces
productivity.
- Many
water-based inks can also be more quickly cured with the addition of a
catalyst that will assist the heat in the curing of the ink by
continuing the cure even if all of the water is not removed in the
dryer. The disadvantage of a catalyst is that once it is added to a
water-based ink, it creates a time limit or “pot life” where the ink
must be all used in a certain time or be discarded. Most catalyzed
water-based ink pot life’s are between four and twelve hours. Since
water-based inks contain water as an evaporative solvent, care must be
taken to prevent the ink from drying in the screen. If water-based ink
is left in open mesh for even a short period of time, it can clog the
mesh and ruin the screen.
-
Practiced water-based ink printers must always be conscious of how long
a screen sits between prints to prevent the ink from “drying in”. While
modern water-based inks are less prone to this phenomenon, it is still a
concern. In addition, when a water-based print job will take more than
one day, the ink must be removed and the screen cleaned with to prevent
drying. The ink is then put back in the screen on the next work day and
the job is continued.
-
Water-based ink is also much more aggressive than plastisol towards the
emulsion that is used to create the screen stencil. Emulsion
manufacturers all make “water-resistant” emulsions that must be used for
water-based printing. If standard emulsion is used, the water-based ink
will destroy the stencil by melting the emulsion is as little as a few
minutes. Even when the proper emulsion is used, screen life tends to be
much less with water-based printing than it is for plastisol printing.
Water-based Ink Cleanup
There is a
common misconception that because water can be used for cleaning screens,
squeegees and tools, that the waste water can just be discharged in the
sewer. However, the water-based ink is not just water. There are pigments,
binders, thickeners, and sometimes, even co-solvents in the ink residue.
Screen
cleaning systems that can at least capture the solids are still recommended.
In addition, water-based that has not been catalyzed can be returned to its
container for reuse. If the ink has been catalyzed, it should be considered
hazardous waste unless it can be dried out (all water and solvent removed)
before discarding. If it cannot be dried, it should be disposed of as
hazardous waste.
Summary
Whether
printing with plastisol or a water-based ink system, you are still printing
a chemical compound. Therefore, it is essential that proper handling and
disposal methods be practiced. As stated above, there are advantages and
disadvantages to each ink system. The key is to use the proper ink for the
application, minimizing waste product, and always dispose of waste properly.
| Type |
Print Ease |
Opacity |
Hand/Feel |
Curing |
Ink Recovery |
| Plastisol |
Easy |
Low-High |
Med-Heavy |
Easy |
Easy |
| Water Base |
Med (Dries Fast) |
Low-Med |
Low-Med |
Med |
Easy |
Usage Recommendations
Plastisol Water-base
T-Shirts/light
colors Excellent
Excellent
T-Shirts/dark colored
Good Poor
Nylon Jackets
Good Poor
Towels
Poor Excellent
Yard
goods
Poor Excellent
Sporting Goods
Excellent
Poor