Visible Defect Analysis in the Consumer Products Industry

Consumer product manufacturing is a huge industry and the identification of materials is a consistent need throughout it. From defect or contaminant identification to incoming material verification, there is a constant requirement to positively identify materials.

Frequently, the material in question is physically small, particularly in the case of contaminants and defects, but the key to solving the problem is establishing the true identity, and likewise the source.

The quicker the material is identified, the quicker the source is found and the line can continue. Often, the gating factor in solving contamination and visible defect issues is the identification of the “black spot”. Luckily, material identification of even small spots can be acquired using infrared (IR) microscopy.

The chemical identity of samples that are barely visible to the human eye can be identified by combining the precise focus and spatial resolution of a microscope with the analytical power of a Fourier transform infrared (FTIR) spectrometer.

The majority of visible defects range from 100 – 300 micrometers in size. IR microscopes can measure the IR spectrum of a micron-sized area or samples by focusing and masking the IR beam to the size of the sample. IR spectra contain information about the chemical bonds that are present in a sample.

The sample can be identified easily by matching the spectrum to a library of known materials. The measurement times using this technology are also fairly quick. FTIR spectrometers can gather a spectrum in well under a minute for most samples.

In most cases results can be gathered in under 30 minutes if sample collection and preparation time is included. So if they can be easily identified with a relatively short measurement time, why are visible defects such a concern? Usually, the problem is where the IR microscope is located.

Traditionally, IR microscopes were difficult to use and were usually expensive. In order to keep them running, they frequently required cryogenic cooling of the detector along with expert alignment.

Consequently, bigger companies purchased IR microscopes for their research and development labs; likewise, smaller companies relied on outside contract labs for microscope analysis. Long-standing backlogs often added to the time needed to solve a problem.

The analysis may be fast, but sample backlog and transportation often lengthen the time until a solution is found. So, the root cause of delays in material identification go back to the location of the measurement equipment; moving the measurement technology closer to labs directly affected by the issue, and to the problem, leads to quicker analysis and so, substantial cost savings.

Instrumentation

Recent advances in IR microscope technology enable measurements to be performed at on-site labs by process or quality control engineers.

As shown in Figure 1, the IRSpirit™ FTIR spectrophotometer by Shimadzu coupled with the SurveyIR™ FTIR Microscope Accessory by Redwave Technologies, combines a high-performance, rugged design with usability features to provide a system which is simple and durable enough for quality control or production labs.

SurveyIR FTIR microspectroscopy accessory mounted in IRSpirit FTIR spectrometer’s sample compartment

Figure 1. SurveyIR FTIR microspectroscopy accessory mounted in IRSpirit FTIR spectrometer’s sample compartment. Image Credit: Shimadzu Scientific Instruments

The system installs quickly with no adjustment, facilitating rapid results anywhere it is needed, even to remote sites. High-throughput optics enable utilization with the spectrometer’s internal room temperature detector, avoiding the expense and complication of cryogenic liquids commonly utilized with conventional FTIR microscopes.

Some benefits of the SurveyIR™ FTIR Microscope Accessory are:

  • No maintenance
  • Large, 1900 µm field of view
  • Transmission/Reflection/Oblique illumination modes
  • Affordable compact design
  • No alignment
  • Transmission/Reflection/ATR IR collection modes
  • Simplified user controls
  • 5 MP Digital camera with 2X optical magnification resulting in 0.7 µm/pixel at the sample plane
  • View-through, clip-on diamond ATR

Defect Analysis and Discussion

An example of a defect found in a plastic component is used to show how this analysis works. Visual inspection revealed dark marks throughout a plastic packaging material. As shown in Figure 2, the marks were viewed under a stereo microscope and found to be dark, fiber-like contaminants.

One of these fibers was taken from the plastic with a needle and rolled onto an IR reflective slide for measurement. The contaminant had a dark blue tint under the microscope, as shown in Figure 2.

(Left) Visible defect found in plastic packaging viewed with a stereo microscope; (Right) Excised fiber rolled flat on a low-E microscope slide and imaged with the SurveyIR.

Figure 2. (Left) Visible defect found in plastic packaging viewed with a stereo microscope; (Right) Excised fiber rolled flat on a low-E microscope slide and imaged with the SurveyIR. Image Credit: Shimadzu Scientific Instruments

Shown in Figure 3 (red), the IR spectrum of the contaminant was measured and searched against a spectral library. The blue library match which is shown in Figure 3 shows that the fiber was clearly made from cotton.

A secondary component that was also matched was indigo dye and a reference spectrum is shown in black in Figure 3. including sample prep, the analysis took under an hour. With the identity of the material, the plant engineer was able to look for the source of the issue.

IR spectra of excised blue fiber and corresponding library matches.

Figure 3. IR spectra of excised blue fiber and corresponding library matches. Image Credit: Shimadzu Scientific Instruments

Visible defects can also happen in raw materials. Manufacturers must identify any visible defect and establish if they will cause a problem in their production, whether these materials are in use or incoming.

Recently a cosmetics manufacturer discovered a discoloration in the citric acid powder which was utilized in one of their products. A sample of the discolored powder was placed on a microscope slide for analysis. The visible image that was gathered with oblique illumination on the SurveyIR is shown in Figure 4.

Visible image of contaminated citric acid captured with the SurveyIR microscope using oblique illumination showing both discolored (A) and white (B) crystals.

Figure 4. Visible image of contaminated citric acid captured with the SurveyIR microscope using oblique illumination showing both discolored (A) and white (B) crystals. Image Credit: Shimadzu Scientific Instruments

Excellent color representation is supplied by oblique illumination. Discolored powder is seen in the center of the image compared to the typical white-colored citric acid crystals on the outside.

A spectrum of the discolored crystal was measured with the SurveyIR diamond attenuated total reflectance (ATR). ATR is a surface-sensitive method where only the samples that are touching the ATR crystal directly are measured.

The spectrum of the crystal is shown in Figure 5 (Red); features are present from both the contaminant and the citric acid. In Figure 5 (Blue) a comparison to hydraulic fluid is also shown and matches the spectral features attributed to the contaminant closely.

The source of the hydraulic fluid contamination was identified as a leaking seal on a pump utilized in the manufacturing process. The manufacturer was able to find a compromised seal in a pump quickly and resume manufacturing having identified the contaminant.

IR spectra collected using the SurveyIR diamond ATR of contaminated citric acid (red) compared to hydraulic fluid (blue) that was identified as the contaminant.

Figure 5. IR spectra collected using the SurveyIR diamond ATR of contaminated citric acid (red) compared to hydraulic fluid (blue) that was identified as the contaminant. Image Credit: Shimadzu Scientific Instruments 

Cost Analysis

In order to show the economic benefits of quicker sample measurement, a simple cost analysis can be done. For this example of a manufacturing production line producing a product is considered as leading to $ 500,000 in yearly revenue, or $ 1,370 per day. Defects do not happen every day, but they could happen six times per year.

It may take up to three days to get results because of the transportation of the samples and laboratory backlog if the company has an internal R&D laboratory capable of analyzing these samples.

In this instance, each incident would cost the company around $ 4,000 in lost production or $ 24,000 per year. Smaller companies may be forced to utilize an outside laboratory. Usually, these labs take longer; furthermore, each analysis may cost as much as $ 2,000 per test.

In these instances, the company suffers a cost of $ 2,000 for each test, plus a $ 5,500 loss in production. The yearly cost may total near to $ 45,000. By moving the analysis to the quality control or production lab immediately adjacent to the production line, the IRSpirit coupled with SurveyIR system supplies a way to decrease these costs.

The analysis can be accomplished in less than half a day in this instance; the yearly cost in this case would be less than $ 4,000 in lost production. Given these numbers, the system would pay for itself in about a year compared to using an internal R&D laboratory.

The SurveyIR would pay for itself in about 6 months for companies using contract labs. This calculation only considers savings, which are due to lost production time. By providing higher quality control in addition to increased incoming material identification, the total savings in the cost of poor quality can be even higher.

Conclusion

The fast identification of contaminants can enhance efficiency and reduce costs. New products, like the compact IRSpirit FTIR spectrophotometer with SurveyIR FTIR microscope, make this analysis accessible to quality control and production laboratories.

This information has been sourced, reviewed and adapted from materials provided by Shimadzu Scientific Instruments.

For more information on this source, please visit Shimadzu Scientific Instruments.

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