September 2009

President’s Message

Greetings! I hope that all of you had an enjoyable summer.

We will kick off our 2009-2010 program year with the Astros vs. the Braves baseball mixer on Tuesday, September 8. Please express your appreciate to our sponsors that make this event possible. This year’s Gold sponsors are Ticona and Centerpoint Energy. This year’s Silver sponsors are Vertec Polymers, Ashland, Osco, and ThomasNet. This is the third year we have held this fun event that welcomes all friends and family of the plastics industry to the new SPE membership year. The event will be held in the Champions Pavilion at Minute Maid Park and begins at 5:30 when the park opens. Tickets (includes reception, dinner and seat at the game) are $25 each and. Tickets available online at www.spe-stx.org. Tickets ordered 10 days prior to the event can be mailed. Tickets ordered within 10 days of the event will be available at will call.

I am very excited about the board of directors as we have many new faces that are bringing new ideas and enthusiasm to the section. At the baseball game, our directors and chairpersons will have information about the various opportunities to serve in the section. Please consider joining one of our committees and finding an opportunity to participate in the section. We have a very active section that covers a large geography. As such we have many opportunities each month to serve and network. In addition to our monthly technical programs, International Polyolefins Conference and golf tournament, we have a monthly breakfast bunch meeting the first Tuesday at 7:00 a.m. at the IHOP at I-10 and Washington. We also have a lunch meeting the third Friday of each month at the Steel City Pizzeria on Sawdust road in The Woodlands.

The mission of the SPE is to promote scientific and engineering knowledge relating to plastics. In addition to our professional technical programs, we continue our commitment to support local SPE student chapters, scholarships and grants at 10 colleges and Universities in our region.

Our section seeks to engage our young professionals and this year Ayush Bafna of Dow Chemical will be leading a new Young Professionals Committee. Ayush will host periodic fun social and business networking events at times and locations that may be more attractive to our younger professionals. Joe Nelson has taken on the role to expand our use of social networking sites as another tool to communicate with members. If you use these sites or want to try them out we encourage your participation in these groups.

On behalf of all of the directors and chairpersons, we look forward to serving you in a way that will grow our businesses, expand our technical knowledge and our relationships.

Best wishes,

Jeff Applegate
SPE South Texas President 2009-2010

Extrusion of Engineering Plastics Seminar

November 9, 2009 9:00am–November 11, 2009 4:30pm
Instructor: Dr. Pravin Shah
Houston, Texas USA
Expertise Level: II

Purpose & Overview
This seminar, developed for plant managers, production engineers and process engineers as well as extrusion supervisors and technicians, provides a simplified and thorough treatment of the extrusion of engineering plastics and exotic polymers, with major emphasis on:

(1) How to select the right grade of each material to extrude strip, tubing, profile, and rod.

(2) How to develop critical process parameters such as barrel temperature profile and screw design requirements for extruding exotic materials of today, using melt rheology as a practical tool.

Utilizing a workshop approach this seminar teaches how to correlate materials, process, and equipment parameters for extruding engineering plastics into various shapes. Attendees learn how to improve extrusion of current and new engineering plastics, reduce scrap and downtime, and improve yield and output rates.

The laboratory session will take place at Killion Laboratories and will focus on extrusion runs with engineering or novel polymers; attendees receive hands-on training.

Instructor:
Dr. Pravin Shah - Biography

Seminar Content
• Introduction to Engineering Plastics
• Basic Understanding of the Extrusion Process
• A Simple Guide to Selecting Critical Materials and Extrusion Parameters From Melt Rheology Data
• Introduction to Die Design (for Tubing, Blown Film, Flat Film, and Sheet)
• A Processor's Guide to Extrusion of Engineering Plastics
• A Workshop Session to Solve Extrusion Problems

Hotel Information:
Sheraton Houston Brookhollow Hotel
3000 North Loop West Freeway
Houston, Texas 77092
+1 888-627-8196
Rate: $129.00 plus tax
Attendees are responsible for making their own hotel reservations.

Transportation:
The Sheraton Houston Brookhollow Hotel is located approximately 30 minutes from George Bush International Airport and approximately 45 minutes from Hobby Airport in Houston. Transportation to the hotel from these airports should be arranged through your travel agent.

Seminar Hours:
Monday, November 9: 9:00 a.m. to 4:30 p.m. with lunch from 12:00 p.m. to 1:00 p.m
Tuesday, November 10: 9:00 a.m. to 4:30 p.m. with lunch from 12:00 p.m. to 1:00 p.m.
Wednesday, November 11: 9:00 a.m. to 3:00 p.m.
Please schedule your departures after this 3:00 p.m. ending time.

Suggested Attire:
Casual Business attire is appropriate. Please be prepared for moderate temperature variations in the seminar room.

Seminar Cancellation Policy:
Refunds will not be granted five (5) days prior to seminar. Substitutes may be sent in place of the registrant with prior notification to SPE. Cancellations are subject to a $100 processing fee. Written cancellations must be received at SPE headquarters prior to the seminar.

SPE reserves the right to cancel a seminar or substitute instructors. If SPE should cancel, the attendee will be contacted as soon as possible prior to the seminar. It is recommended that a refundable airline ticket be purchased. SPE is not responsible for penalty fees or any costs incurred by the attendee due to cancellation of the seminar.

Registration Fees:
Your registration fee covers classroom instruction, educational materials, transportation to and from the laboratory session at Davis-Standard, refreshment breaks, and lunch on Monday and Tuesday. It does not include hotel accommodations.

Registration Information:
You may register for this seminar online or by phone +1 203-740-5403.

Registration is limited and on a first-come, first-served basis. Early registration is strongly recommended.

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http://www.facebook.com/group.php?gid=35280334773&ref=ts

Join the South Texas Section of the Society of Plastics Engineers on Facebook. Click on the above link and you will be directed to our group page. We hope that this will serve as another communication tool for our Professional Section and be a familiar platform to welcome and inform the Student Sections. It is easy and free, so join in. (TTYL = Talk To You Later)

Bulletin Board

Plastics Information: Check it Out

The Houston Public Library on McKinney has resources on plastics and polymers. Check out their catalog at www.hpl.lib.tx.us. If you are not near the McKinney location, you can arrange to pick up your books at your local branch.

The Fondren Library at Rice University has the most complete collection of books on plastics and polymers. This is also a prime resource for patent and trademark information, as well as other US Government documents. You cannot check out books there unless you join Fondren Library [$50], but you can arrange for books to be sent to your library by inter-library loan. Use their catalog at http://library.rice.edu/.

The next best place to browse is at the MD Anderson Library at the University of Houston central campus. South Texas Section has donated many plastics books to this library. If you plan ahead, you can get a TexShare library card from a library where you are a member, which will allow you to check out books from any U of H library. Their catalog is at www.library.uh.edu/.

Book Bag

	ANTEC™@NPE 2009 Conference Proceedings - Thumb Drive SPE, Chicago, Illinois USA, June 2009, Thumb Drive $250.00 In Chicago in 2009, ANTEC® (Annual Technical Conference), sponsored by the Society of Plastics Engineers, celebrated its 67th year of excellence. The largest peer-reviewed technical conference serving the plastics industry, ANTEC® is perfectly positioned to help the plastics specialist achieve new levels of professional development. Order the ANTEC® 2009 proceedings on thumb drive or CD-ROM. Includes 700+ papers detailing the latest developments in: Alloys and Blends, Applied Rheology, Automotive, Biopolymers, Blow Molding, Color and Appearance, Composites, Decorating and Assembly, Electrical and Electronic, Engineering Properties and Structure, Extrusion, Failure Analysis and Prevention, Flexible Packaging, Injection Molding, Joining of Plastics and Composites, Marketing and Management, Medical Plastics, Mold Making and Mold Design, Nano/Micro Molding, Plastic Pipe & Fittings, Plastics in Building and Construction, Plastics Environmental, Polymer Analysis, Polymer Modifiers and Additives, Process Monitoring and Control, Product Design and Development, Radiation Processing of Polymers, Rotational Molding, Thermoforming, Thermoplastic Elastomers, Thermoplastic Materials and Foams, Thermoset, and Vinyl Plastics.
	Thermal Analysis of Polymers: Fundamentals and Applications Joseph D. Menczel, R. Bruce Prime, 2009; 688 pages ISBN: 978-0-471-76917-0 $150.00 This book emphasizes the practical uses of thermal analysis. Each chapter guides readers through the applications of thermal analysis for polymer characterization, with detailed examples that show how to perform each step. Chemists and engineers new to thermal analysis, whether in industry, government, or academia, can quickly learn to use the techniques to generate high-quality results. More experienced researchers can expand their repertoire to include a broader range of sophisticated techniques and applications. Essential theoretical background is included, but the focus is on how to perform thermal analysis measurements and tests, with detailed coverage of methods, applications, instrumentation, and calibrations. Moreover, readers learn how to correctly interpret their results..
	Polymeric Foams: Technology and Developments in Regulation, Process, and Products Shau-Tarng Lee, Dieter Peter Klaus Scholz, 2008, 352 pages ISBN: 9781420061253 $140.00 Exploring new concepts, innovations, and developments in the field, Polymeric Foams: Technology and Development in Regulation, Process, and Products provides an international perspective on the direction of foam technologies and applications, focusing on the progress in blowing agent research and hydrofluorocarbons for the polyurethane foam industry. The text covers new foam products, including PP/PS interpolymer, nano-, and biodegradable foams. It also examines new technologies, such as injection foam molding and PVC foam; industry and environmental regulations; and research on foam performance, emission impact, and economic effects. As in most fields these days, efforts to be environmentally friendly and achieve enhanced performance for specialty applications drive research and development. Presenting a clear picture of the development process, this book covers not only new directions in the industry, but how they will impact current and future development.

SPE-STX Board Meeting

Location: Spaghetti Warehouse, downtown Houston
Date: July 27, 2009

Techniques to Determine Resistance to Surface Damage on Decorated Plastics

Alan Jaenecke, Taber^® Industries

Abstract

Most consumers believe the price paid for a product is directly related to its inherent level of quality. With decorated plastics, how robust the product finish is before it becomes damaged or “worn out” is an essential element of this perceived quality. This paper presents an introduction to the mechanisms of surface wear and scratch damage, and the importance of conducting controlled laboratory tests. An overview of several commercially available instruments is offered including suggestions on how to recreate and measure “real-world” damage.

Introduction

Wear is defined 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 [1]. In most instances, the material removal is a gradual process and the motion is a repetitive action.

The process of wear is a complex phenomenon and trying to replicate it exactly in a laboratory setting is often extremely difficult. This is because there are often multiple influences that impact the rate of wear. To better understand the challenges, consider wear generated on a television remote control unit. How quickly the wear occurs will be influenced by the individuals’ hand size and shape (contact geometry); average time spent operating the television remote (length of exposure); cleanliness and ‘roughness’ of the individuals’ skin (interacting material surfaces); technique for using the remote (normal force and sliding speed); and location where the television is viewed (climate & environment). If there are multiple people using the remote, it is easy for the researcher to quickly become distracted when attempting to isolate and replicate the influence of each parameter.

Another influence on the rate of wear is the composition and hardness of the materials involved. Wear caused by rubbing a product against a flexible material (e.g. pants pocket or liner of a purse) may be significantly different than a rigid material (e.g. table or countertop). In most instances, the product and contacting surfaces appear to be relatively smooth but there are actually asperities that form the contact junctions of the materials. Similar to the peaks and valleys shown in figure 1, these asperities support the load and tend to deform when the surfaces slide over one another. With repeated movement, there is elastic and plastic deformation of the asperities and over time, material is eventually removed from one or both surfaces.

Due to the complexity of recreating wear, the ideal solution is to analyze the product in actual use under the actual intended use conditions. Unfortunately, it often takes many years before useful data becomes available. Additionally, the cost of conducting a field test could be prohibitive and the complexity of identifying the influences can be unwieldy. While laboratory techniques usually do not exactly duplicate the mechanics seen in real-life, a controlled test allows the user to approximate field conditions and eliminate extraneous variables. This enables materials to be evaluated using the same set of criteria. This is important, because the resistance to abrasion is affected by conditions of the tests such as the nature of abradant, variable action of the abradant over the area of specimen being abraded, the pressure between the specimen and abradant, and the dimensional changes in the specimen.

Scratch and mar are another type of mechanical surface damage that impacts decorated plastics. Scratching is defined as the resistance of a solid body to penetration by an edge or protuberance on a second body that is moving along its surface [2], and usually associated with a single occurrence in the specimen surface. Normal scratching includes deformation such as plowing (figure 2), but might also involve material cracking, peeling and removal. In comparison, marring is the term used to describe relatively fine surface scratches generally characterized by shallow damage, distributed over a relatively large area that typically spoils the appearance of a surface coating.

For laboratory scratch and mar tests, a stylus with a defined geometry is drawn across a specimen surface at a known speed and with a known force. This is done to simulate damage that might occur during normal usage and handling, shipping or assembly procedures. For polymers, the objectives of most scratch and mar resistance studies are to determine the behavior of the material under specific test conditions or to establish a relative ranking of similar materials. When evaluating decorated plastics, the purpose of the test is most often to determine the failure limit of the surface coating.

Similar to wear, the amount of scratch damage on a material surface can be influenced by test parameters (e.g. stylus composition and geometry, loading, and speed) and requires an appropriate procedure to minimize these influences. As an example, different mechanical deformations may be generated using different scratch indenter geometries: 1mm spherical ball (hardened stainless or tungsten steel); conical diamond; cube corner; pyramidal; cylinder sectioned at 45° to the axis; 0.8mm diameter helix and the radius edge of a paperclip. Variation can also be introduced by the speed the stylus is drawn across the specimen surface. Another consideration is the length of time a stylus sits on a specimen surface before the test commences, and how deep the stylus “sinks” in. Material properties such as surface roughness, hardness, modulus of elasticity, texture, grain, gloss level, and coating thickness will also influence the severity of scratch damage.

Scratching appears to be a relatively simple concept, but trying to evaluate and describe the results on a plastic material is not always easy. Many plastics have visco-elastic properties and the stresses in the plastic may relax during loading. Plus, plastics demonstrate an elastic recovery after applied stresses are removed so scratch width; groove depth; displaced material; and severity of the damage may change over time. Other issues that affect the visual perception of scratches include the color of the sample; amount of strain whitening; scratch direction; lighting and viewing conditions; and time an observer is allowed to view the sample.

Prior to Conducting Tests

Laboratory tests have the potential to provide considerable insight into the various factors that contribute to a material’s performance. Before attempting to recreate surface damage, the first step must be to establish the purpose of the test. Taking the time to state the objective(s) before conducting any testing will help keep you focused and minimize the distractions. For example, the purpose may be to rank varying coatings and surface treatments for wear resistance. By performing this test, the results can be used to develop selection guidelines and criteria for optimum serviceability.

To generate useful data, careful consideration must be given to the test system and failure mode. For wear tests, the test 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]. If the dominant wear mechanism is identified and selected at the beginning, the results will be more representative of the failure you are attempting to recreate. How do you determine the conditions a product might be exposed to? The first approach is to consider prior knowledge. If you are studying a field failure, examine the appearance of the surface wear from an actual application. The following parameters are normally associated with sliding wear on plastic materials [3]:

1. 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, hardness) and surface properties (roughness, physico-chemical characteristics).
2. 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, wear debris).
3. Parameters depending on both the nature of the materials involved and the sliding conditions, particularly surface temperature of the rubbing surfaces.

The next step is to develop a testing methodology and select a tester. Many industries have established test procedures and recommend instruments that might be used. This information can usually be obtained by contacting a testing laboratory, industry association, or organization such as ASTM International. If a method does not exist or you decide not to follow the industry standard, you need to select a test that models the system you wish to study.

Understanding the Test Instruments

There are numerous instruments to evaluate a material’s resistance to surface wear or scratch damage. To understand the available options, the following describes the basic principle of commonly used instruments. The results from these testers are usually not equivalent, and caution must be taken when making any comparison of the data.

Abrasion Testers
The Rotary Platform Abrasion Tester (Taber^® Abraser or Abrader) requires a flat specimen be mounted to a turntable platform that rotates at a fixed speed. Two abrasive wheels, which are applied with a specific load, are lowered onto the specimen surface. As the turntable rotates, the wheels are driven by the sample in opposite directions about a horizontal axis displaced tangentially from the axis of the sample. One abrading wheel rubs the specimen outward toward the periphery and the other, inward toward the center while a vacuum system removes loose debris during testing. A characteristic rub-wear action (sliding rotation) is produced on the surface of the test piece and the resulting abrasion marks form a pattern of crossed arcs in a circular band that cover an area of 30 cm2. An important feature of this instrument is the wheels traverse a complete circle on the specimen surface, revealing abrasion resistance at all angles relative to the weave or grain of the material.

Genuine Taber wheels are comprised of silicon carbide or aluminum oxide abrasive particles embedded in a resilient or vitrified (clay) binder. Available in different levels of abrasiveness, the wheels are designed so the binder material breaks down during use – thus exposing and creating a new abrading surface. For decorated plastics, the CS-10F and CS10 wheels are most popular, and intended to simulate an abrading action like that of normal handling, cleaning, and polishing.

The ‘RCA’ Abrasion Wear Tester (RCA Tape Tester) is a point contact abrasion tester offered by Norman Tool, Inc. This apparatus is typically used to quantify abrasion and wear resistance of painted or plated organic finishes, foil, and printed ink deposits (such as key pad lettering). Two rollers constantly pull an abrading material, either abrasive paper or polyester tape, over a specimen surface. A vertically mounted “O” ring presses the abrading material onto the specimen at a known force and the movement of the paper causes the “O” ring to rotate. This action generates surface wear the size of the contact area of the “O” ring. The abrading material eliminates any build up error and ensures a fresh surface for each abrasion cycle. Due to the small area that is worn, a magnifier is suggested when evaluating coating breakthrough.

Because of its ease of use and low cost, the Crockmeter has been employed to conduct both wet / dry scuffing, abrasion, and rubbing tests on flat specimens. A 50 mm square crocking cloth is affixed to a 16 mm diameter acrylic rubbing finger, and weighted at a force of 9N. The finger traverses 100 mm back and forth over the specimen surface to elicit a change in the appearance. After rubbing specimens, the staining of the crocking cloth is assessed by comparing the degree of ‘dirtiness’ with an approved grey scale rating. Performance is normally measured by 1 – 5 rating scale. Modifications to how the test is performed include moving a weighted felt pad across a surface or using abrasive paper to mimic the effects of random scratching.

Taber Industries’ Linear Abraser incorporates a horizontal arm that reciprocates in a linear motion. Attached to the end of the arm is a ‘free-floating’ test system that is placed onto the specimen at the start of the test. As the arm cycles back-and-forth, a spline shaft raises or lowers as the test attachment follows the contours of the specimen being tested. To simulate real-world conditions, parameters such as speed, stroke length and load can be altered according to the material and test being conducted. Typically, there is not much weight loss generated using the Linear Abraser for abrasion tests, therefore results are most often determined by a visual inspection after a fixed number of abrasion cycles.

The basic configuration allows the operator to conduct wear tests using an abradant referred to as a Wearaser^®. Manufactured from the same abrasive formulations used in the Genuine Taber wheels, wearasers are available in the standard 6.5 mm configuration, a 12.7 mm diameter Jumbo Wearaser and 19 mm diameter Weardisc™.

To allow the operator to evaluate other material physical properties, interchangeable attachments are available. The Universal Attachment has a 25.5 mm diameter flat head, which enables the operator to affix their own abradant material with a double-sided adhesive tape. This attachment is useful to test the ability of the product to withstand repeated rubbing by a flat object, such as rub damage caused by shipping cartons during transport. The Scotchbrite^® Pad Kit simulates abrasion damage that might be generated by a consumer while cleaning with a scouring pad. The CrockMeter Attachment converts the Linear Abraser into a crockmeter and can be used in a similar fashion, or to conduct smudge resistance testing. Manufactured from a porous material, the Fluid Delivery Tip enables the operator to evaluate chemical and solvent resistance of their product. This 6.5 mm spherical tip features an intricate network of open-celled, omni-directional pores which absorbs and retains fluids. The Spherical Rub Attachment utilizes a compressible membrane rubber as the test media. Placed over a steel ball and held in place with a threaded retaining ring, this attachment can be employed to simulate the wear generated by rubbing a fingertip on the product surface.

INNOWEP GmbH manufactures the ABREX^® Abrasion Tester which is described as a chemo-mechanical abrasion tester and intended to simulate print and coating wear caused by hand contact on flat or curved surfaces. According to the manufacturer’s website, this is achieved by imitating the natural movement of finger / hand contact through a defined force, contact angle, “smear” geometry and “finger” texture. Specimens are held in place, perpendicular to the test finger. Pneumatically operated, a finger made from silicone rubber (44 Shore A) is pressed against the test specimen at an angle of 45° to generate an impact and friction movement. Between the finger and test specimen is a standard test fabric. In addition to the mechanical resistance, an option for an automatic fluid delivery system can be utilized to apply artificial sweat, cleaning products, hand lotions and oils to the product during testing.

Norman Tool, Inc. also offers a Pneumatic Finger Abrasion Wear & Contact Tester that can be used for endurance testing of printed surfaces. A foam finger pad is inserted into a rod adapter body mounted at the end of a cylinder rod. Interchangeable springs placed in the rod adapter assembly provide force settings of 8oz., 16oz. and 32 oz. to simulate different amounts of finger pressure. To mimic a finger tip striking a printed surface, the air cylinder is set to an angle of 15°. The cylinder can also be positioned vertically to test switch endurance.

Using a Scuffing Head Attachment in place of the abrading wheels, the Rotary Platform Abrasion Tester has the ability to generate adhesion or ‘scrape’ tests. Mounted to the left hand abraser arm mount, one of three unique profile scuff heads is attached such that it is held at a 100° angle. The vertical centerline of the scuff head is 32 mm from the specimen holder center pin, and the tip is centered under a weight (0.45 kg or 0.9 kg) in a horizontal alignment with the center pin. The scuffing head is dragged across the specimen as the table rotates to determine the resistance to scuffing of the test specimen. Results are compared to a master specimen and ranked as PASS or FAIL based on any observed changes.

Other abrasion testers worth mentioning are primarily are used in other industries, but occasionally are used for decorated plastics. With the Falling Sand Tester, graded quartz silica sand particles fall from a specified height through a guide tube onto a test panel placed 12.7 mm underneath at an angle of 45°. The test is continued until the substrate material is exposed. For rub and smear tests on flat printed surfaces, the Sutherland^® Ink Rub Tester manufactured by the Danilee Company may be used. A film or paper receptor is mounted to a 2 or 4 pound weighted block, which is moved over the test specimen in an arc, causing print degradation and / or ink transfer. The Washability Tester uses a brush, sponge, or scouring pad as the abrading material to perform wet or dry abrasion tests. A weighted sled is pulled back and forth approximately 10 inches over the specimen surface at a rate of 35 to 60 cycles per minute. The Oscillating Abrasion Tester requires the specimen to be mounted in the bottom of a tray and covered with abrading media (such as quartz silica). The test consists of reciprocating the tray over a distance of 100mm at a speed of 300 strokes per minute. Utilizing the Grit Feeder Attachment enables three-body abrasion to be performed with the Taber Abraser. For this type of test, loose grit particles are evenly distributed on the specimen surface and passed under a pair of leather wheels. The grit particles aid in the rolling action of the wheels and contribute to the physical breakdown of the material.

Scratch / Mar Testers
Perhaps the most widely used apparatus for evaluating scratch adhesion and mar resistance of coatings is the Balanced Beam Scrape Adhesion and Mar Tester. The instrument consists of a pivoted balanced beam equipped with a holder that sets the stylus at an angle of 45° in the direction of test sample travel. A test panel is affixed to a movable platform, which is manually pushed against the stylus at a rate of 6.5 mm per second for a distance of at least 76 mm. After each stroke, the specimen is visually examined for surface damage. If none is observed, additional weights are added to the beam in increments of 0.5 kg until a scrape or mar is apparent. If damage is produced in the initial test, testing is continued using lighter weights. The weight required to just produce visible marring is taken as the mar resistance value. The tester is supplied with a “U” shape loop stylus, and can also be used with a 1 mm diameter needle stylus.

Taber Industries’ Linear Abraser can also emulate the physical contact made with various scratch media. The Multi-Mar Attachment allows you to conduct similar tests as the balance beam tester using mar and scratch tools such as a paperclip, loop stylus, needle stylus, Hoffman type stylus and coin. For soft materials, a 1.0mm diameter hemisphere Scratch Tip is suggested. For harder materials, a conical tool such as the Diamond Scratch Kit or Tungsten Carbide Scratch Tips may be used.

A popular scratch test for plastics used in automotive applications is the Five Finger Scratch and Mar Tester. This apparatus includes a movable sledge and five “fingers” that include scratch pins, either 1.0 mm or 7.0 mm spherical balls. Each pin is loaded with different weights, such that they exert a standard force on the test surface ranging from 0.6N to 25N. The speed of the test is 100 mm/second.

UV formulators and other coating manufacturers have used the Taber Shear / Scratch Tester to measure a material’s resistance to gouging, scratching, engraving or shearing. A precision cutting tool is affixed to a balanced scale beam. Test pieces are mounted to a turntable, which rotates at a constant speed when actuated. By changing the position of a sliding weight(s), loads from 0 to 1000 grams may be applied to the cutting tool. Evaluation is determined by the minimal load to produce a continuous mark on the coating surface.

A common apparatus used in the paint industry to measure scratch resistance on smooth surfaces and coatings is the Wolff-Wilborn Pencil Hardness Test. Using constant pressure and pencils of varying hardness (usually 6B to 6H), the pencil is held at a fixed angle of 45° to the specimen surface and pushed about 6.5 mm away from the operator under a fixed pressure of 7.5N. This test is repeated using softer lead until one is found that will not cut through the coating or indent the surface.

The Hoffman Scratch Hardness Tester is a simple, portable device to rate scratch resistance and adhesion. This hand operated tool consists of a four-wheeled carriage, scale arm (or fulcrum) and a cylindrical shaped tool which has a circular rim mounted at 45° to the test surface.

Despite their poor repeatability and reproducibility, both fingernail and coin mar tests continue to be employed. In the Fingernail Test, the back of a fingernail is dragged across the surface of a coating and the degree of marring is visually observed. Alternatively, a fingernail can also be used for adhesion tests to determine if the coating will be ‘scratched’ off. Similarly, the Coin Mar Test consists of dragging the edge of a coin across the surface of a coated panel and visually determining the degree of marring produced.

The most common method for evaluating scratch and mar has been a visual observation and rating. For scratching, this might include reporting any change in color, minimum load that causes a visible scratch, or the load at first sign of whitening. Quantitative assessment can also be performed with more sophisticated tools that measure change in gloss, haze, scratch depth, material removed, etc. A time period must be specified for materials that are elastic in nature.

Understanding the Results

As demonstrated, there are numerous options that can be used to simulate surface damage of decorated plastics. Because the results for each apparatus are based on that tester’s unique system, data is generally not comparable between different instruments. So how does one evaluate and interpret the test outcome to make meaningful decisions?

Abrasion resistance is normally calculated using one of three methods; loss in weight for a specified number of abrasion cycles (weight loss), number of abrasion cycles required to wear 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. Note, the rate of wear may not be a linear function of time or contact cycles.

For wear resistance of 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. a 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, wear through).

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 end-use.

For scratch resistance, results are typically reported as the load to generate a visible scratch and a description of the scratch (e.g. scratch topography, deformation, and color change). The deformation caused when testing plastic materials is highly dependent on the material properties and stylus geometry. Often scratching in polymers progresses from elastic deformation to viscoelastic-plastic plowing followed by crack formation in the edges of the scratch groove and then by even more severe types of deformation.

Abrasion and scratch resistance are not unique or isolated material properties; they are related to many other physical characteristics. If you are following a test protocol that does not provide enough useful information or reflect the appropriate wear damage, it may be time to reevaluate the tests you are conducting. A word of caution if test results are questionable: do not automatically assume that testing was conducted in the same manner. Quite often, test procedures lack important details which cause the operator to make assumptions. Or perhaps the technician does not understand the proper usage of the device, and is utilizing it incorrectly.

Significance of Testing for Resistance to Surface Damage

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 visual appearance over its estimated life and withstands deterioration or wearing out in use. Regardless of whether the decoration is for cosmetic appeal or functional performance, surface damage that occurs too soon will detracts from a consumer’s perception of product quality.

While accelerated laboratory tests may not always identify potential problems or provide predictive performance results, they can be an inexpensive means to generate useful data in a relatively short period of time and are a key step for monitoring manufacturing processes. Testing also provides an opportunity to create value with your product, and can be invaluable in solving related coating and printing issues. Starting with the product concept and design phase, you can use test procedures for product research and development by evaluating available decorating options. During this step, minimum quality assurance test specifications might be established. Once a coating (material) has been selected, incoming inspections and pre-production testing of the part can be performed as an initial step in quality control. During or after the manufacturing process, product testing should be conducted to assure the product meets all specifications prior to shipment. Finally, you should monitor consumer feedback and evaluate product returns to ensure that test specifications are meeting their objective.

In today’s competitive environment, manufacturers put significant efforts into minimizing production costs to remain competitive. These efforts might involve changing material suppliers or specifying a different type of finish. Unfortunately, changes are often made without the proper consideration of how they will impact product performance. When problems do occur in the field, they can often be tied to a lack of testing and validation. If you find yourself responding to warranty claims, it is already too late to prevent the problem. However, you can use benchmarking techniques to identify the cause, and adjust formulations to improve and maximize performance. Employing a meaningful test program is a necessary step to validate your product quality, and to ensure that the surface finish you specify meets the customer’s expectations.

[1] ASTM International, G40 Terminology Wear & Erosion
[2] P.J. Blau, The Lab Handbook of Scratch Testing, Oak Ridge: Blue Rock Technical Publications, p. 1.2 (2002)
[3] International Standard ISO 6601, Plastics – Friction and wear by sliding –identifation of test parameters