more efficient processing and better quality
thermoformed food packaging
key advantages
• more efficient processing
• improved overall quality
• potential to reduce costs
introduction
With global demand for beverage cups, containers and
lids projected to rise five percent per year to $23.4 billion
in 2014, according to The Freedonia Group Inc.,
manufacturers are looking for ways to improve
processing efficiency and product quality. Many are
discovering that polypropylene (PP) blended with
Vistamaxx™ propylene- based elastomer (PBE) from
ExxonMobil Chemical provides a better balance
of impact resistance, clarity and stiffness, as well
as being more efficient to process.
Manufacturers of beverage cups and containers face a number of challenges, especially
when they use homopolymer polypropylene (hPP) in thermoforming. Some of these
issues include lack of detail, incomplete forming or cracking during manufacture. This is
due to the poor flexibility and low-temperature impact resistance of PP. Because of low
impact resistance, products can be damaged during handling and transportation. Another
problem is poor clarity, which can result from using a polyethylene-based impact modifier.
Honghua Machinery Plastic & Rubber Co. Ltd. (Honghua) of China, a manufacturer of
extrusion, thermoforming and molding machines used for the production of food and
beverage containers, is committed to helping manufacturers solve these challenges.
Their approach is to consider and evaluate the materials being used.
material challenges
Materials typically used by manufacturers include polyethylene
terephthalate (PET), polystyrene (PS), homopolymer polypropylene
(hPP) or random copolymer PP (RCP).
• PET provides good clarity but exhibits poor heat resistance.
As a result, PET containers cannot be used for hot beverages
or used in a microwave, as they may warp. PET is also difficult
for masterbatch dispersion and cannot be used long-term,
refilled or re-used.
• PS can either be transparent or colored and offers good
processability, but it has poor heat resistance and inadequate
impact and tear resistance, especially at low temperatures.
• while hPP offers good heat resistance and broad food contact
compliance, it lacks flexibility. This can result in unsatisfactory
detail and incomplete forming or cracking during manufacture,
leading to higher rejection rates than with other materials.
It also exhibits low impact resistance during transportation
and can be brittle at low temperatures.
• RCP can be a more expensive option than hPP but while
it provides good clarity and flexibility its impact resistance
remains inadequate at low temperatures.
To improve flexibility, Honghua initially recommended
a “three-in-one” polymer formulation. Comprising 15 percent
low density polyethylene (LDPE), 15 percent high density
polyethylene (HDPE) and 70 percent PP, it improved flexibility
during processing, but reduced clarity. Incorporating a fourth
ingredient, a nucleating or clarifying agent, can improve clarity
but it also can introduce a problem of odor during processing.
new possibilities with Vistamaxx™
Honghua turned to ExxonMobil Chemical to explore
the solutions that Vistamaxx PBE could offer for flexibility.
Together, the companies developed two solutions.
For applications requiring a balance of impact resistance,
clarity and stiffness, they developed a dry blend formulation of
5-10 percent Vistamaxx 3020 PBE with PP. This has been proven
to reduce cup breakage during production and transportation.
In the second solution, a low dosage of Vistamaxx 6102 PBE
is added to PP. This improves impact resistance and maintains
clarity, while avoiding die cutting issues, at low cost.
more efficient processing
Vistamaxx PBE can easily be blended with hPP and RCP.
Compatibility with polypropylene, combined with improved
flexibility and elasticity, results in a simpler molding process which
is important for complex shapes, such as deep-draw cups.
Compounders can target the flexibility that is best-suited for the
application, giving them a broader choice than the original hPP
or RCP grades.
The lower melt temperature and higher flow of Vistamaxx
PBE allow the processing temperature to be reduced and the
processing rate to increase. This can reduce energy consumption
and improve processing efficiency. Its flexibility helps to increase
the draw ratio resulting in fewer flow marks, better product
quality and lower scrap rate. The scrap rate can also be
reduced because the elastomer shrinks less than PP, making
the production process easier to control and die cutting more
accurate, for improved cup and lid matching.
better products
Vistamaxx™ PBE can cost-effectively improve overall product
quality for attractive packaging with more customer appeal. It
helps to maintain clarity, color dispersion and reduces or eliminates
stress whitening to maintain the color and quality of the part. This
is important for cups and other containers, such as sheets, trays,
hinges and profiles.
Enhanced impact strength enables downgauging opportunities
for lower material usage and costs. Breakage during storage
and handling is minimized, and cups are less prone to collapse
when stacked, making transportation easier. Even at low
temperatures, Vistamaxx PBE helps to improve the impact
strength of PP due to a glass transition temperature of -28° C
(-18.4° F).
Low seal initiation temperatures and excellent heat-sealing
characteristics can lead to energy savings and reduced costs.
Mr. Wang Zhiqiang, Manager,
Zhejiang Honghua Machinery Plastic & Rubber Co. Ltd.
For applications that require a greater degree of slip resistance,
such as sheets, grips, and cups, it can be used to increase
the coefficient of friction. This results in better traction, so that
products are less likely to slip during use.
Complying with US and EU food contact regulations, Vistamaxx
PBE is creating new possibilities for thermoformed cups and
other food packaging applications.
“The collaboration with ExxonMobil Chemical has helped us
to better address customer queries on process efficiency and
product quality,” said Mr. Wang Zhiqiang, Manager, Zhejiang
Honghua Machinery Plastic & Rubber Co. Ltd. “Because
Vistamaxx delivers excellent performance for thermoformed cups,
we recommend that customers use it in other applications, such
as food boxes, trays and other plastics containers. Customers
can have better quality products that are more efficient to process,
giving them a competitive advantage in a growing market.”
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