In-Line Color Measurement in the Molten Polymer

Color measurement is a widely used technology for ensuring the quality of color values during the manufacturing process. Typically, these measurements happen offline. The time it takes between sampling and receiving results from the laboratory can be lengthy. A significant disadvantage is that only one measurement occurs during this period, and the color quality during, before, and after the sampling point is unknown. A complete analysis is possible because inline color measurements are performed directly in the melt, but when color variations occur, immediate intervention is possible.

Inline color measurement will provide product-quality indicators for immediate and automatic adjustment of process parameters. The outcome is to maintain the highest possible product quality without waiting for sample analysis from the plant's laboratory.

Equitech International Corp. has been in business since 1995, supplying fiber-optic spectroscopic instruments for process analysis to pharmaceutical, chemical, and food manufacturers. In 2005 they entered the plastics market and began extending their technology into inline color monitoring and real-time closed-loop process control. They published a helpful Technical Paper titled In-Line Color Measurement in the Molten Polymer. You can download that paper here.

In-Line Turbidity and Haze Measurement

Photo 1: Equitech's Retro-Reflection Probe

Monitoring turbidity and haze of liquids and sheet is an indicator for product quality. Examples include: polymer extrusion, resins and chemical production. Real-time adjustments of the process parameters are therefore possible through immediate "off-specification" detection.

INTRODUCTION 

Turbidity and haze measurement is a well-accepted technology to check the consistency some production processes. Usually these measurements are performed ‘off-line’.  

The delay between sampling and obtaining the results from the laboratory can be time consuming. A significant disadvantage is that only a single measurement is generated in this time period and the concentration during, before and after the sampling point is unknown.  

With the inline turbidity and haze measurements taking place directly in the process, not only is complete documentation possible, but when variations occur, immediate intervention can take place.

INNOVATION 

The Equispec™ In-line Color Spectrophotometer (ICS) is a high performance instrument designed for use in an industrial pro-cess. Its excellent sensitivity and flexibility make it useful for process applications. The ICS and process probes are designed to be used in high-temperature, high-pressure and corrosive environments. It can be used to analyze  liquids and solids. 

The analyzer supports one or two probes with dedicated lamp compensation channels [all fiber-optic double-beam design]. 

Photo 3: Trend charts of EquiColor Software

TURBIDITY AND HAZE MEASUREMENT 

Equitech’s fiber-optic probes allow for easy access into the process. Equitech offers probes for both turbidity and haze measurements.  This includes insertion/immersion probes (see Photo 1). 

The spectrophotometer is integrated in a NEMA4 box with an industrial computer and touch-screen (see photo 4). The appropriate spectral range is 380-780 nm (resolution 1 nm). The NEMA4 box is made from stainless steel. It is designed and equipped specifically for use in the production environment where the ambient conditions can be dusty, vary in temperature, subject to vibration etc. The box also contains a thermoelectric cooling and heating device to eliminate the influences from ambient temperature by keeping the temperature inside the box at a constant level. 

Photo 2: ICS stainless steel NEMA4 box with touch-screen

INSTALLED APPLICATIONS INCLUDE 

Resin Production, Sheet Production,  Filter Breakthrough, Surfactants 

Turbidity and haze are calculated from the spectral curve,  and displayed as trend charts by the EquiColor™ software (see photo 3). 

For more information, contact AP Corp. Call them at (508) 351-6200 or visit https://a-pcorp.com.

DOWNLOAD THE PDF HERE

In-Line Color Measurement for Recycled Plastic

Photo 1 - Recycled Plastic with Color

INTRODUCTION 

Color measurement is a well-accepted technology to check the quality of the color values in the production process. Usually these measurements are performed "off-line".

The delay between sampling and obtaining the results from the laboratory can be time consuming. A significant disadvantage is that only a single measurement is generated in this time period and the quality of the color during, before and after the sampling point is unknown.

With the in-line color measurements taking place directly in the melt, not only is complete documentation possible, but when color variations occur, immediate intervention can take place.

Photo 2 - Reflection probe in strand pelletizer.

When recycling plastic to convert to new uniform  colored pellets many challenges can take place. Recycled plastic is much more inconsistent than virgin material. Understand-ing this inconsistency will help on your color dosing to provide a more homogeneous final product. With the proper color measurement system you can know the color values of your extrudate in real time. This allows for closing the loop on your color by changing your dosing rates to meet your specifications.

INNOVATIVE NEW TECHNOLOGY

Photo 4 - Stainless Steel NEMA4 box with touch-screen.

Technology from Equitech, a manufacturer of in-line process instrumentation, deploys a probe directly in the molten polymer. Their Reflection Polymer Melt Probe (RPMP, Photo 2) is installed on the exit (adapter) of the extruder by using ½”-20 UNF thread (typically Dynisco®). The RPMP is screwed into position in the adapter between the extruder and the die. The RPMP consists of the threaded body and optical fibers. The sapphire lens on the tip of the probe is the observation window and is very well suited to the harsh conditions in the extruder (temperature, pressure, and friction through flowing material). The self-cleaning function of the sapphire is ensured by the shear force of the material flow. Ideal installation is directly into the melt stream in the adapter.

Off-line measurements are used more effectively by downloading them to the Equitech Inline Color Spectrophotometer. This can be done manually or through OPC communications. By having the laboratory target values displayed on the Equitech system the operator can view trends of L*, a*, b* and Delta E.

This method provides complete documentation of a particular extrusion run. It also matches the known laboratory measurements giving confidence that an extrusion run has maintained specifications throughout its entirety. When color variations occur, notification can take place via digital alarms. Intervention can take place via OPC or analog signals i.e. L* feedback for closed loop color control.

Photo 3 - Trend charts of EquiColor Software

COLOR MEASUREMENT 

Illumination of the polymer through the sapphire window is achieved by 6 circumferentially-positioned glass fibers which convey the light of a xenon flash lamp. The reflection from the illuminated surface is detected by one center-positioned optical fiber. This reflected light is then interpreted by the spectrophotometer. Color values such as L*, a*, b* C*, h are calculated from this spectral curve, and displayed as trend charts, (see Photo 3).

For a continuous process monitoring, 10 to 60 seconds is recommended as the measurement interval. Intervals as fast as 1 to 2 seconds are possible. The calibration of the spectrophotometer is designed specifically for the demands of the production process. Calibration can be done without interruption of the process.

USER BENEFITS

• Real-time information about process stability & quality
• Impact of speed changes on the quality of the extrusion
• Controlled color changes: start phase, end of run  
• Avoid off-specification batches & waste production
• Detection of dosage elevations
• Optimized recipe formulation & process design
• Available feedback loop for L* closed loop control via feeder
• Comprehensive quality audit trail customer documentation

For more information, contact AP Corp. by calling (508) 351-6200 or visiting https://a-pcorp.com.

Reprinted with permission from Equitech International Corporation.