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Keep your
color under control!
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Portable color measurement - The portable spectrophotometer, color-guide from BYK-Gardner is ideal for easy color measurement in the plastic industry. EMSA Werke Wulf GmbH & Co., Emsdetten, Germany, uses the instrument predominantly in the inspection area, for the adjustment of color hues. color-guide is a great support tool to objectively determine color differences and reduce the number of inspection steps.
The age of visual inspection and therefore, subjective color control is over. Visual results are always influenced by different color sensitivity from person to person, varying environments such as lightness and color as well as the deficiency to communicate and document color and color differences.
The color must be right
New developments in the area of color measurement eliminate these subjective factors. Today, medium and small sized companies perform color control according to ISO 9000 with reliable, easy-to-use and affordable test instruments. This is of particular importance whenever the individual components of the final product are produced at different manufacturing sites of one company, or even more complicated when several suppliers are involved. Nevertheless, at the end, the color must be right. Wherever you look, the quality criteria "color" is gaining importance in every industry – automotive interior and exterior, appliances, electronic parts or packaging.
Adjustment of new colorsEMSA Werk Wulf GmbH & Co. has experienced the advantages of the new color-guide for portable color measurement. Since the spring of 1997, the color-guide is used to ensure consistent color quality. Prior to purchasing the instrument, an older laboratory instrument was used. The company had technical problems and most important, the unit was stationary in the screen printing department. That meant that all parts had to be carried there, even for a "quick" color inspection. "Because of this, we just stopped using the instrument and went back to old-fashioned visual inspection", says Mr. Willers, member of the quality control team at EMSA. Portability is the main advantage for Mr. Willers. The instrument is small, light weight, and battery powered, which permits color measurement where ever it is necessary, even at a suppliers site. The main area of application for the color-guide at EMSA is in inspection where colors are adjusted. Adjustment is necessary whenever new colors are introduced, alternative raw materials are evaluated, or when a raw materi als supplier is changed. In this application, a color instrument helps to objectively determine color differences and reduce inspection steps.
Color control is of particular importance for
multi-component products. EMSA produces thermo pots, which consist of three different
components; lid, body, and bottom. Often, individual components are over produced and put
into stock. If the raw material supplier has changed, color-guide allows hue adjustment
and ensures that the stock component will still match. Color adjustment is done by use of
a master sample that is submitted by the raw material supplier whenever a new color is
introduced. If the color is approved by R&D and general management, plastic plaques
are injected molded using a pilot injection machine (figure 1). The
plaques have areas which differ in surface roughness and include one polished area. These
master plaques are used to produce several sample plaques for each color and raw material,
which are stored in black envelopes for protection. Sample plaques are also used at the
production site when a new color is transferred to production. Prior to color-guide,
everything was done visually at the production sites. Today the standards are stored in
the instrument (standard memory capacity is 200) with visual evaluation supported by
objective measurement results. Once the injection molding machine is running and all its
parameters are set, random checks are sufficient for color control. (Figure 2)
color-guide -- your
color under control The portable spectrophotometer, color-guide offers the
plastics manufacturer a new way for easy and secure color control in incoming outgoing
quality inspection and process control. The optical design of the instrument is in
accordance with the 45/0 geometry defined in international specifications (ASTM, DIN,
ISO), which guarantees correlation to visual color evaluation (figure
a). The specimen is circumferentially illuminated at 45?using 30 Light
Emitting Diodes (LED’s). Due to their long life, LED’s are used in many other
applications such as stereo systems, automotive turn signals, etc.. In order to cover the
entire visible spectrum (380 - 720 nm) differently colored LED’s are used.
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Three LED’s of the same color are circumferentially arranged 120?apart
(figure b). The sample is illuminated from three
different positions, thus minimizing the effect of structure and direction. During
one measurement, the individual LED triplet sequentially illuminates the specimen. One
detector collects and measures the reflected light (from the specimen) at 0?and
transfers it to an internal processor to calculate the color values.
LED’s possess typical emission curves within the visible spectrum. As
these curves are overlapping, additional spectral information is available (figure c). A patented, automated, complex calibration routine
and the information from the LED curves allows calculation of spectral data every 20 nm. A
new, state-of-the-art electro-optical reference principle controls the temperature of each
LED triplet during measurement, thus an excellent repeatability and inter-instrument
agreement is achieved. This allows color-guide to competently compete with traditional
spectrophotometers.When outsourcing a product, a color is defined using a color plaque. One standard plaque remains with EMSA while others are given to third party suppliers for production control. In addition, EMSA supplies the required raw materials. With these steps taken, the final color should be on target. When incoming QC measures a difference for the sample plaques or first batch deliveries, it is obvious that the machine parameters have not been optimized. These deviations could be caused by process variables such as injection mold temperature, pressure, cooling rate, or speed of the injection screw. Long lasting discussions about color differences are eliminated, as color-guide documents the measurement results in black and white (figure 3). A computer interface allows to directly transfer measurement data to Windows™ applications, where they can be further processed. The spreadsheet program Microsoft Excel™ can be used to create trend graphs and statistical evaluation. No time consuming manual entry of data is required.
No need to be a color expert
color-guide makes color control easy. "The instrument is very easy to
operate and can be reduced to a minimum of options", says Mr. Willers. The capability
to configure the instrument allows it to be customized to meet individual needs.
Therefore, production workers who might not be color experts can easily use the
color-guide without any problems.
The outdoor product line is especially difficult to control. Lately, color-guide was a great help to us for our "outdoor line", states Willers. This product family consists of flower pots and buckets. They are constantly exposed to wind and weather, which requires usage of UV absorbing raw materials. Consumers expect that a recently purchased flower pot matches the one purchased last year.
Secure and consistent productionWith the objective of security and consistency in production, Mr. Willers has greater control on products that are colored by EMSA. Transparent pellets are colored with masterbatches. If there is too much or not enough colorant used, a major color difference can be seen. Visually, this inspection is done by holding the samples up to a light: too little colorant allows more transmission compared to the correct amount, which is opaque. color-guide measures such differences in the light-dark scale, when deviations in the colored components are negligible. Too little colorant will make the product too light and too much will make it appear too dark. In the future, the measurement data will help EMSA to optimize the mix ratio and save money.
EMSA-Werke Wulf GmbH & Co. mainly supplies large department stores chains and catalog houses in nearly 100 countries. They are in the fortunate position to not be held to specific color tolerances (to give acceptable color differences) because "EMSA sets the standard of what will be delivered." But there is always room for improvement. Visually acceptable color deviations need to be determined for their own production as well as for the cooperation with raw materials suppliers. "We want to use the instrument to get a certain security and consistency in our production, to see where we are. For this, color-guide is a non-replaceable support tool."
Sandra Welker,
Product Manager Color at
BYK-Gardner, GmbH, Geretsreid, Germany
| EMSA Werke Wulf GmbH & Co. is a medium sized company with approximately 600 employees. They have been located at Emsdetten, Germany since 1956. Over 1600 products are manufactured on a 40,000 m2 site. The product line ranges from flower and garden supplies, to kitchen products and thermo pots. Over 60 injection molding machines process between 20 - 25 tons of materials on a daily basis. As a leading company of high quality products, EMSA always strives to satisfy requirements and trends from tomorrow with high quality products. Therefore, the quality parameter of "color" needs to be measured and documented to be in compliance with ISO 9000. |
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