VIEW THE ONLINE EDITION
High-Tech Contract Decorating at Emerald Corporation
2012 SGIA Expo Show Preview
Ask the Expert
Plastics Surface Energy Wetting Test Methods
Scratch-resistant in One Step
Letter from the Chair
TopCon Rolls Through Indy
Digital Decorating Webinar Scheduled for August 28
Ultrasonic Welding: The Need for Speed Control
How to Close Sales that are Over the Budget
PLASTEC West, Anaheim Convention Center, Anaheim, CA, www.plastecwest.com
Plastics Crossroads Summit,
Sheraton Hotel, Anaheim, CA, www.rjginc.com/plasticscrossroads
PLASTEC South, Orange County Convention Center, Orlando, FL, www.plastecsouth.com
AWA DecTec USA, Orange County Convention Center, Orlando, FL, www.awa-bv.com
SPE ANTEC® 2013, Duke Energy Convention Center, Cincinnati, OH, www.antec.ws
HBA, June 18-20, Jacob K. Javits Convention Center, New York City, NY, www.hbaexpo.com
PLASTEC East, , Pennsylvania Convention Center, Philadelphia, PA, www.plasteceast.com
Copyright 2010 Peterson Publications, Inc.
Plastics Decorating Magazine
2150 SW Westport Dr., Suite 101
Topeka, KS 66614
(785) 271-5801Â Fax (785) 271-6404
Wear Damage of Decorated Parts - Techniques to Understand and Improve Testing
by By Alan D. Jaenecke, TABER® Industries
The objective of a laboratory test method is to define the approach that will
permit an operator to obtain meaningful, reliable data. As materials and
decoration techniques evolve, commonly used test methods to measure abrasion
resistance of decorated plastics may no longer be sufficient. To ensure a robust
product, it is essential to understand how to recreate and measure “real-world”
damage. This article presents a process to develop (or improve) test methods
intended to quantify the resistance of surface wear on decorated plastics.
Emphasis is placed on reducing common sources of test procedure variation and
advanced techniques to interpret and quantify the results
For many products, it is easy to identify something that is worn. But
understanding how it got to that state is not as simple! The process of wear is
a complex phenomenon and trying to replicate it exactly in a laboratory setting
is often extremely difficult. ASTM International defines wear as “damage to a
solid surface (generally involving progressive loss of material), caused by the
relative motion between that surface and a contacting substance or substances
. In most instances, the material removal is a gradual process and the motion
is a repetitive action.
Two common types of wear
that occur with plastics are wear abrasion and mar abrasion. Wear abrasion is
the removal of a portion of the surface by some kind of mechanical action (e.g.,
rubbing or sliding back and forth of an object). Mar abrasion is the permanent
deformation of a surface but the deformation does not break the surface. Wear
and abrasion should not be confused. Although the terms are frequently used
interchangeably, wear is “the wearing away of any part of a material by rubbing
against another surface
 and abrasion is the action that causes it.
Laboratory wear tests have the potential to provide
considerable insight into the various factors that contribute to a material’s
techniques do not exactly duplicate the mechanics seen in real-life.
This is because there
are often multiple influences that impact the rate of wear.
It is imperative that the limitations of testing be understood because
accelerated wear testing may not always identify potential problems or predict
field performance results. Despite this,
a controlled laboratory test allows the user to approximate field
conditions and eliminate extraneous variables. This enables
the life span of a product to be compressed into a much
shorter duration, and allows
materials to be evaluated
in the same manner within a controlled environment. Additionally, the cost of a laboratory test is significantly less than a field
Attempting to recreate wear damage in a laboratory setting involves determining
a complex combination of interrelated properties. The objective of the test is
to provide predictive performance under a specified set of criteria and
correlate with end-use performance. Yet when evaluating the conditions a product
is exposed to during its life, one quickly realizes the task of developing a
test methodology is both multifaceted and difficult. A basic principal of
establishing new abrasion tests is to use the simplest technique first and to
stop once the required information is available. Quite often, the additional
information that is obtained by studying additional factors does not justify the
additional time and cost.
An engineer concerned
with reliability and product life may require precise simulation of the wear
system. In contrast, a material developer looking to rank the wear resistance of
materials may accept a convenient test that does not exactly replicate intended
use. In either case, to generate useful data careful consideration must be given to the wear
system and failure mode. The wear system is
comprised of the test piece and contacting material(s) along with the relative
movement that causes the wear. The failure mode is established by how the system
wears and which wear modes are involved. (For additional information on wear
modes, see ASTM International, G40 Terminology).
Wear is a response
resulting from the conditions to which the whole system is exposed. Resistance
to abrasion is affected by the nature of abradant, variable action of the
abradant over the area of specimen being abraded, tension of the specimen, the
pressure between the specimen and abradant, and the dimensional changes in the
specimen. While most standardized test methods specify the parameters that must
be adhered to when conducting tests, it should be accepted that all of the
influences that create wear conditions probably will not be able to be
accurately identified. However, give careful consideration to contact geometry,
length of exposure, interacting material surfaces, normal force, sliding speed,
environmental conditions, and material composition and hardness. (Note: Do not become distracted when
attempting to isolate and replicate the influence of each parameter.)
How does one determine the conditions to which a product might be exposed? The
first approach is to consider prior knowledge. If studying a field failure,
examine the appearance of the surface wear from an actual application. Keep in
mind there may be multiple wear modes occurring at the same time and recognize
that matching conditions in a laboratory are usually not perfect. The following
parameters are normally associated with sliding wear on plastic materials :
Intrinsic parameters relating to the materials involved, such as their nature,
surface condition, and finish. These include bulk properties (e.g., chemical
composition, physical characteristics, mechanical properties, and hardness) and
surface properties (roughness, physico-chemical characteristics).
External parameters relating to the sliding conditions, such as applied load,
sliding velocity, characteristics of the motion, mode of contact, ambient
conditions (temperature, humidity), and the interstitial substances (lubricant,
Parameters depending on both the nature of the materials involved and the
sliding conditions, particularly surface temperature of the rubbing surfaces.
Many industries have established test procedures and recommend abrasion
instruments that might be used to simulate the wear. Unfortunately, “there are a
lot of customer and industry specifications that really are not an indicator of
meaningful product performance or durability” . If a method does not exist or it is decided that the industry standard
will not be followed, a test modeling the system to be studied should be
If unsure of where to start, begin by contacting research industry
associations to determine if an accepted abrasion test procedure exists. Other
sources of information include organizations that develop test standards, such
as ASTM International and ISO.
instruments exist to evaluate a material’s resistance to surface wear damage.
Because the results for each apparatus are based on that tester’s unique system,
data is generally not comparable between different instruments. And
occasionally, materials may not
exhibit the same relative order of resistance to abrasion when tested by
The primary elements involved in simulating a
wear system include apparatus design, specimen preparation, test protocol, and
measurement. Whether or not a particular type of abrasion test correlates with
end-use performance depends not only on a similarity of abrading mechanisms but
also, on the extent to which that mechanism is maintained during the course of
the abrasion test. The following describe the important features that should be
Motion. The type of relative motion is often
used to define the wear that is generated. Because of its complexity, a number
of different wear modes have been recognized and include rubbing, sliding,
rolling, and scuffing. Wear can occur in combination or on different areas of
the same component.
Apparatus. The test apparatus should be of a
rugged design to provide repeatable and reproducible results. Parameters such as
load, speed, rigidity of apparatus construction, alignment, and supply of
abrasive require adequate control to ensure stable wear conditions. The most
commonly used testers for decorated plastics involve a reciprocating movement;
rotating abrasive disc/wheel; or point contact.
Materials involved. The structure of the wear
system includes the specimen and counter-body (usually an abradant of some
sort). Basic properties such as elasticity, hardness, strength (including
cohesive, tensile, and shear strength), toughness and especially in the case of
wear resistance, thickness can all influence wear resistance of the materials.
Be aware that a material can wear differently when exposed to different
situations, or may be influenced by the wear of the other contacting body.
Abradant (Wear Agent). The mechanism of wear
depends upon the topography of the counterface abradant. Popular types of
abrasives include textiles, engineered abrasives, and sandpaper. Although
abrasive particles may not be the primary cause of actual wear, they are often
used to accelerate the test. Abrasive particles, regardless if they are embedded
in a binder material or are loose, have a strong influence on the rate of wear.
It is preferable in most cases to use an abrasive only once, unless it can be
refreshed. Consider the following:
- Shape –
Particles that are angular or “blocky” in shape can cause up to ten times the
wear rate as compared to rounded particles.
- Size - The size
of the particle is critical, as smaller particles cause proportionally less wear
than larger particles. Particles responsible for abrasion or erosion are
typically between 1 µm and 500 µm in size.
- Type – Popular
abrasive particles include silicon carbide and aluminum oxide. With sandpaper,
silicon carbide creates a thinner scratch pattern due to being a sharper grain
than aluminum oxide and will typically cut faster.
- Friability –
How easy the abradant breaks down and fragments under localized heat and
pressure, creating new sharp edges.
Contact Geometry. This includes the shape of the
abrading head or abradant, and contact between it and the specimen. Some systems
may require the specimen and abradant to “wear-in”, thus establishing a uniform
and stable contact geometry. Although point-contact eliminates many alignment
problems associated with other contact geometries, stress levels may change as
wear progresses, requiring more complex data analysis and comparison techniques.
Contact Pressure (Applied Load). With an
accelerated test, the load may exceed what is actually seen in the field. This
parameter usually involves the amount of force used to push the abrading
material against the specimen during the rubbing action. Do not use a load that
exceeds the ultimate strength of a material.
Sliding Speed (Sliding Velocity). This is the
speed of the abradant as it moves over the specimen. While acceleration in a
test is desirable, if the speed is too fast for the material (abradant), the
precision of the test may be compromised by introducing different phenomena.
Excessive speeds can cause a typical thermal condition on the test specimen.
State of lubrication. Lubrication will affect
the frictional characteristics of a material. Usually involved with metals, many
plastics formulations also include a lubricant additive.
Specimen Preparation. Specimen preparation and
the details of test control vary with the test and materials involved. For
example, surface roughness, geometry of the specimens, homogeneity, and hardness
should be controlled for reproducible test results. Similar controls also are
necessary for the counter-face and the wear-producing mediums. When evaluating multilayered systems, the substrate plays an important
Environment. Many materials are sensitive to
changes in temperature and humidity, and changing the test environment may
A well thought out wear
test can provide valid data without exactly replicating the application. Before
attempting to recreate surface damage, a step that is often overlooked is to
establish the purpose of the test and how the data will be used. Taking the time
to state the objective(s) before conducting any tests will help keep focus and
The majority of companies conduct testing only because they have a customer or
industry specification they must satisfy in order to sell their product. Others
utilize testing to better understand their product/process. Regardless of
whether the decoration is for cosmetic appeal or functional performance, the
primary reason companies conduct surface damage tests on decorated plastics is
to ensure that they are producing a quality finish that will endure throughout
the product’s life cycle. The goal is to make certain the product maintains a
minimum performance over its estimated life and withstands deterioration or
wearing out in use. This becomes challenging because customers have a habit of
using products in applications for which they were not originally designed or
tested. A common problem facing the industry today is the chemical attacks that
household cleaning agents and personal care products have on coatings. Due to
the many different formulations of hand creams, sunscreens, insect repellants,
etc., available to consumers, it is not feasible to test the effects of each. In
this case, having a stated test objective will help keep testing on track.
Sources of Variation
stated in the introduction, the process of replicating wear in a laboratory
setting is a complex phenomenon. There are multiple sources of variation that
can influence test results. Being aware of each allows the development of an
approach that can provide a means to generate repeatable and reproducible data.
developing a new protocol, keep in mind
that test development is dependent on the capability of the developer. It may
take some trial and error to establish a test procedure that provides useful
information. An exact simulation is generally neither practical nor possible and
some differences will have to be accepted. This is because wear involves two or
more bodies, one or more materials, and is dependent on a wide range of
influences. Once a procedure is identified, it must be documented. Test methods
that lack critical procedural information could introduce problems with
reproducibility, as much of the variation that occurs with abrasion tests result
from operator error.
Depending on the apparatus, any of the aforementioned parameters may introduce
variation into test results. This is normally seen with companies that do not
an established test method or are utilizing a procedure
that is missing critical information.
Review the test set-up parameters to ensure they are the same for each
test. For example, operators often overlook the importance of sample
positioning. If the apparatus being used does not secure specimens in the same
position, consider a fixture or other device. Furthermore, the rate of abrasion
may change as debris adheres to the body that is generating the wear. Failure to
change or refresh the abradant may cause a decrease in the abrasion rate.
Another issue may be the age or condition of the abradant, especially if it has
a shelf life or is adversely impacted by environmental/storage conditions.
Finally, do not overlook the importance of providing effective training for
laboratory personnel. Variation also can be introduced if the technician does not understand
the proper usage of the device and is utilizing it incorrectly.
Techniques to Interpret and Quantify the Results
Abrasion resistance is normally calculated using one of
three methods: loss in weight for a specified number of abrasion cycles (mass
loss); number of abrasion cycles required to wear the coating through to the
substrate material (wear cycles per mil); or a visual change in the appearance
of the specimen (amount of coating removed compared to predetermined standards).
Other methods that have been used include volume loss, depth of wear, haze
measurement (for transparent materials), and strength testing.
Most of the recognized abrasion test methods provide a comparative measurement of wear resistance and
the results are used to rank materials. For decorated plastics, results
are normally interpreted by a subjective assessment of the appearance or
condition of the specimen after a fixed number of abrasion test cycles. For
repeatable results, a standardized grading system (e.g., 1 – 5 visual scale)
should be used to measure the change in appearance and rank performance.
Reference photographs along with an associated verbal description are often
provided to indicate an evenly spaced ranking. Another popular option is to
determine the number of cycles required to generate a specified level of
destruction (e.g., change in gloss, color, thickness, wear through).
As technology advances, magnification of the test sample can be accomplished
in-house at a relatively modest cost. With the electronic industry striving to
continue miniaturizing components, tools are available that can be used to
magnify parts in all cost ranges. A 10x enlargement using a reticle eyepiece or
microscope may continue to be sufficient if the application is for decoration.
But a magnification of 200x or 300x may be necessary if the application is
performance-based. In these cases, software may be utilized for conducting
analysis of surface damage or for generating a 3D surface mapping of the part.
Whatever the method of evaluation, wear rate may not
always be a linear function of time or number of contact cycles – it depends
very much on the materials, type of wear, and the contact conditions.
Extrapolate results only with great care. The primary reason that companies conduct abrasion
tests is to ensure that they are producing a quality product that is free from
defects, consistent in characteristics and quality, and will endure throughout
its life cycle. Through testing, a company can monitor quality assurance of the
manufacturing process; conduct product research and development; demonstrate its
product conforms to industry standards; develop new products; provide
information to buyers; establish criteria for warranties; etc.
Employing a meaningful test program is a necessary step to validate product
quality and to ensure that the specified material or surface finish meets the
Unfortunately no laboratory abrasion test can
guarantee success in the field; there are just too many influences to be modeled
in the lab. The effect of abrasion is generally only one of
several factors that contribute to product durability, and the relationship may
vary with different end uses. It is not recommended to rely solely on abrasion
results to predict wear-life, unless there is data showing a specific
relationship between laboratory abrasion tests and actual wear in the intended
it is advisable to establish a predictive wear model for design and component
life estimation, no model is universally satisfactory.
But with proper
consideration, abrasion test results can provide meaningful, reliable data.
G40 Terminology Wear & Erosion
International Standard ISO 6601,
Plastics – Friction and wear by sliding
–identification of test parameters
A.F. Zielnik, Test of Time: Will
Your Finish Last? Finishing Today,
p. 28 (June 2007)
Alan Jaenecke is VP of marketing; materials test and
measurement/press divisions for Taber Industries
and plays a critical role in the company’s Materials Test and Measurement
division. In charge of new product development and strategic planning, he has
given presentations on physical property testing of numerous materials and has
written new test methods and coordinated numerous reviews for existing methods.
For over 65 years, Taber®
Industries has been helping companies understand wear resistance.
Taber instruments have been utilized in diverse applications including paints
and coatings, textiles, paper, laminate flooring, plus many more. For more
information on Taber Industries, call (716) 694-4000, email
firstname.lastname@example.org or visit