Pigment dispersion processing, optimization for higher pigmentation

Abstract

One way to make a UV curable ink is to mix a pigment dispersion with monomers, oligomers,
photoinitiators and additives. Creating a pigment dispersion is in many cases the first processing
step of making a UV curable ink and is of large importance. To process pigment dispersions
of Pigment red 2 and Pigment red 122 a premixing step with a dissolver is used followed
by a grinding step employing a three-roll mill. The components for the dispersions are
a monomer/oligomer blend of acrylates, pigment and a dispersing agent. The optimal monomer/oligomer
blend of acrylates were determined by the Daniel flow point method. When
processing using a three-roll mill the process time becomes of great importance, alongside
with the final viscosity of the dispersion. Each dispersion was passed three times over the
three-roll mill and the passing times were recorded to get the processing time. To find a correlation
between processing time and viscosity a design of experiment was conducted for the
two different pigments. The design of experiment model was of the extreme vertices design
type which allows setting upper and lower boundaries for the input variables. From the design
of experiment an expected viscosity and processing time could be estimated. For Pigment red
2 the model suggested a processing time of 14.47 grams/min and a viscosity of 44.58 Pa*s.
The actual processing time came out as 16.46 grams/min with a viscosity of 49.10 Pa*s. For
Pigment red 122 the estimated processing time was 24.35 grams/min with a viscosity of 43.04
Pa*s. The results were a processing time of 22.98 grams/min with a viscosity of 43.80 Pa*s.
The use of the Daniel flow point method combined with design of experiment allows for an
efficient way of screening new pigments and monomer/oligomer optimums for UV curable
inks.

Popular Abstract

Printing inks cured by ultraviolet light (UV) can be found in many places of our everyday life.
These printing inks are found on very many packaging and label applications, such as beer
bottles, milk cartons and bottles of soap. These type of inks first hit the market in the early
1960’s and have since then seen a steady growth. Because of this steady growth and wide
application range there are several demands that need to be met by a printing ink.
One of the most important demands on the printing ink is the type of color that the ink shows.
As one of the large applications for UV printing inks is packaging, the color should in many
cases be very bright and intense to attract the shopping customers. Besides the intensity and
shade of the printing ink, it is important that the printing ink gives a label with high durability.
This high durability is often characterized by that the print on the label does not change due to
twisting of the label, spilling liquids on the label, or that the product sits on the shelf for a
long time. All of these different types of demands put a high pressure on the formulation of
the printing inks, and especially a high pressure on the
pigment in the ink.
Because of the pressure on the printing inks and especially
on the pigment, there needs to be a way to check if a new
pigment is suitable for packaging and label applications. In
many cases, it is the pigment that is the most important
factor for deciding if a printing ink has a high durability or
not. In my study I have been trying to develop a method
for the investigation of new pigments for UV-curable
printing inks. More specifically, I have been looking at
two different types of pigment, one that shows a shade of
warm-red and another that shows a shade of rhodamine
red. The reason for why new pigments are needed is in
many cases related to cost, and trying to be cost
competitive on the market.
When looking at these two types of pigments, there are more things to keep in mind besides
the durability of the pigment in the printing ink. One of these things is to investigate the flow
behavior the pigment has in its concentrated state. This concentrated state is known as a
pigment dispersion. In comparison, the example of a juice concentrate comes very handy. A
juice concentrate you dilute in water to obtain the drinkable juice. For a pigment dispersion,
the same type of dilution is made to obtain a printing ink. However, the dilution step for the
pigment dispersion has several components and does not contain any water. The flow
behavior in the concentrated state is very important for the printing ink, but also for the
production workers. If the concentrated state has a free flowing behavior, meaning that you
can easy pour it out from a bucket, it becomes easier to handle in production, as well as giving
a better flow property for the printing ink.
The goal of my study has been to employ the method how to investigate new pigments, and
then implement it on the warm-red and rhodamine red pigment to create new pigmentdispersions. The results were successful and the new pigment dispersion will in a near future
be produced on a larger scale in the production Flint Group has in Trelleborg. Eventually
these new pigment dispersions will end up in printing inks, which will be used on the
different types of packaging that are used on a daily basis in very many households.

• author: Paajanen, Hans
• supervisor: Baozhong Zhang
• organization: Centre for Analysis and Synthesis
• course: KASM15 20181
• year: 2018
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: polymer technology, polymerteknologi
• language: English
• id: 8947886
• date added to LUP: 2018-06-18 14:07:55
• date last changed: 2018-06-18 14:07:55