Which colorimeter is suitable for measuring plastics

All roles in plastic production have their difficult areas, but working to achieve the correct color for molded parts for automotive dashboards, extruded films for packaging, or mixed raw masterbatch, is particularly challenging. During production, unanticipated color inconsistencies in materials can result in the scrapping of the production run, loss of machine time, and add to the frustration of a customer. It is of the utmost importance to achieve color consistency for production runs.

The materials in the plastics industry make simple color matching by eye nearly impossible. A high gloss and a matte plastic with the same dye formulation can appear different. With varying color options in raw form, layers of transparent materials or varying shapes and sizes, and glossy surfaces, the eye is always taking a guess.

That's where colorimeters and spectrophotometers come in! Based on your specific needs, we're going to outline the most critical variables to consider so we can simplify the process and make colorimeter shopping less overwhelming.

Why Your Eyes Can't Be Trusted

Let's start with some reasons why standard visual inspection doesn't work on the shop floor. Human vision is very easily deceived. Depending on the temperature of the lights in the QC lab compared to the factory floor, the inspector could see a radically different color of plastic. Color perception is also reduced at the end of a shift, so an operator could be fatigued during the inspection.

There are also physical properties of plastics to consider. A shiny surface can make the color of an object look different because of the way the surface reflects light. A curved surface creates shadows that can effect the perception of color. If the materials involved are either colored or clear plastic, the color of the background can distort color perception.

The only way to avoid this is to use a device that takes objective, reproducible measurements in the form of lab, LCh, and ΔE values. These values measure the degree of variation from the standard regardless of light or surface reflections.

Must Haves: D/8 Optical Geometry

One thing that is most important when buying a plastic colorimeter is the Optical Geometry. If you are measuring ever so slightly opaque plastic sheets, a basic 0/45 device is fine. But, for everything else in the plastics industry, you would need a D/8 Optical device

• Here is the importance of D/8: The device usually supports two different measurement modes called, SCI, SCE. Both are needed to understand different aspects of your plastic

• SCI (Specular Component Included): This setting records light that is reflecting off the sample regardless of the texture of the surface. This shows the color of the plastic resin, regardless of surface texture. If you are color matching, adjusting your masterbatch, or formulate new dyes, you have to have SCI. It shows whether your recipe is right.

• SCE (Specular Component Excluded): This setting shows the color the way a human eye actually sees it, without the gloss.

Having a D/8 device that can toggle between SCI and SCE is helpful. When a batch seems to have issues, looking at both the SCI and SCE data can tell you whether the pigment recipe is the issue, or if it is the mold's surface texture that has changed and impacted the gloss.

Matching the Aperture to Your Plastic

Your next important choice is the measuring aperture, which is the size of the window that the sensor looks through. Data will be completely useless if the size is not chosen correctly.

1. The 8mm Standard for Everyday Parts Measuring standard, opaque molded parts—such as appliance casings, thick bottles, toy parts, or flat interior panels—an 8mm aperture is the industry standard. It reads a large area to stabilize the average, and it small enough to has to be flat against most everyday products.

2. Small Apertures for Small or Bent Parts If you are producing very small electronics, wire connectors, or components that are heavily bent, an 8mm aperture will not sit flush against the plastic. The edges will let in ambient light, which will interfere with the readings. Here you will need a small-aperture device. Colorimeters with a 1mm to 4mm opening (like the ST70 with its 1x3mm tiny footprint) can measure with great precision narrow or tightly bent surfaces, as edge interference will not interfere with the readings.

3. Large Apertures for Pellets and Powders Measuring raw plastic pellets or pigment powders is challenging in terms of the physical gaps and shadows found within and around each individual element. If you are using standard or small aperture, you will most likely be measuring a dark shadow, which will give you a darker reading. 

4. Transmission Mode for Clear Plastics Standard colorimeters reflect the light back off the surface of the plastic. For clear beverage bottles, plastic films, or transparent acrylic sheets, the light passes right through. Reflective measurement will not work for these materials. You will need to get a spectrophotometer with a transmission mode (like the TS8260) that shoots light through the material to assess transmittance, haze, and yellowing.

Top Models by Scenario and Budget

So, what should you actually buy? Here is a practical breakdown of reliable models based on different shop-floor needs and budgets.

Entry-Level QC for Small to Medium Shops ($800--$2,000)

If you just need basic, reliable quality control that will catch obvious color drift on the production line, you really don’t need to spend ten grand.

3NH NH310 & NR60CP: These are great, portable D/8 units with the standard 8mm aperture. They operate simply, are very economical, and achieve a ΔE ≤ 0.03 repeatability. They are ideal for routine inspection of opaque injection-molded parts.

Professional Grade for High-End Manufacturing ($3,000 - $8,000)

You need higher stability and better tracking software if your clients have strict color tolerances, and especially if that involves automotive parts or high-end consumer electronics.

• Threenh TS7700: flagship grating spectrophotometer, excellent repeatability (ΔEab ≤ 0.02), handles 8mm and 10mm apertures.

• PS2080: needs testing for small, curved electronic parts, this model has that critical 1x3mm small aperture for tight areas.

• 3nh TS2010: stable workhorse, 4mm and 8mm options, versatile for mixed production lines with varying sized components.

Specialty Equipment for Specific Materials

• YS6060: You’ll want this benchtop model for raw masterbatch and pellets due to the giant 50mm aperture. It makes sure your raw materials are in range before you do any melting.

• TS8560 and YH1010: If you deal with transparent plastics, or you operate an upscale formulation laboratory, these devices are dual transmission/reflection mode and provide excellent laboratory precision (ΔE ≤ 0.001).

Don’t let bad color matches eat into your profit margins and ruin your production efficiency. If you still use a visual light booth and human eyes, you urgently need to invest in a colorimeter which will pay for itself in a few months due to the reduced amount of scrap.

Plastic Color Measurement Standards

When measuring and evaluating the color of plastics, it is essential to adhere to established international standards such as ASTM E1164 (ASTM International), JIS Z 8722 (Japanese Industrial Standards), ISO 11664, ASTM D6290, ASTM E313, and ISO 17223:2014. These frameworks ensure accuracy and consistency across the industry. Within these standards, visual appearance is quantified using several specific metrics tailored to the material's characteristics:

• Yellowness Index (YI): Crucial for evaluating the degree of yellowing in resins, which frequently occurs due to heat exposure or environmental degradation.

• Whiteness Index (WI): Primarily used to assess the effectiveness of whitening agents, such as titanium dioxide (TiO₂).

• Opacity: Measures the amount of light transmittance in transparent or translucent plastics, providing a complete profile of the material's optical properties.

Final Words

Most plastics manufacturers find that a portable D/8 integrating sphere colorimeter with an 8mm aperture and switchable SCI/SCE modes offers the best safety and versatility.

With that being said, it is important to always consider the shape of your item. Choose the best instrument for the particular type of plastic you're processing, and the quality control uncertainty will be gone for good.