Advanced online inspection techniques are used in coating operations for two essential purposes in the production of high quality finished films:
- Real-time process control
- Defect mapping.
Accurate monitoring and correction capabilities are made possible with online inspection. Some insight into the methods a premier contract manufacturing company uses are detailed below.
Coatings are applied to substrates to achieve properties in mechanical, electrical, optical or other attributes in finished products used in packaging, electronics, display, energy devices, and many others. Film coatings supply various engineered properties such as barrier qualities, selective permeability, reflectivity, conductivity, or other attributes. Frequently advanced coating materials can be applied in different layers, each meeting a unique purpose.
Quality control in design and manufacturing is essential to achieve optimal performance and:
- Ensure uniform thickness control
- Identify and characterize contaminants
- Prevent or minimize other anomalies and defects.
While coating formulations can be precisely regulated and applied on a high-speed roll-to-roll coating web, online inspection techniques allow the coating process to run continuously while monitoring deviations that would negatively affect product performance. Online inspection and defect mapping can also enable automated culling and discarding of substandard material.
Inspection technology choice depends on the material being inspected. Typical inspection online is done with:
- A beta gauge which measures thickness via absorption from a radiation source
- Optical with various wavelengths from a laser or visual light source
- Electrical methods such as eddy current, or
- Other capacitive or resistive methods.
When implementing optical methods, inspection can be reflective or transmissive with darkfield and brightfield results. Another consideration with optical inspection technology is the angle of incidence between light source and the inspected web material. Spotting anomalies in the web are often enhanced by optimizing incidence angles and correlating multiple inspection methods’ results.
In coating a clear product for example, a darkfield inspection might be performed with the signal reflected because dark particles and clear gels will reflect light differently. By using multiple channel (brightfield and darkfield / transmissive and reflective) inspection methods, technicians can get a good understanding of any defects and begin to characterize and correct them.
Sophisticated inspection methods are required to keep up with the high-speed coating process. For example, Carestream uses multi-million-dollar laser scanning systems to scan across the web. With optimum laser spot size and scan rates fast enough to insure scan overlap, 100% inspection can be obtained. Carestream’s inspection systems can also display an image of each defect to avoid cutting into a roll for a sample. This visualization capability accelerates root cause determination and resolution of the problem – ultimately increasing yield.
At Carestream, online inspection is made far more efficient and informative by the company’s experience, which is documented in a searchable database. This database enables the user to insert keywords that identify the defect and access information on defects previously encountered with similar descriptions. They can then search by inorganic or organic matches from the FTIR or SEM to identify repeat sources of contamination. Once a search is done, micrographs of past defects can be examined to determine the similarity to the defect at hand. This has been a major source of improvement in cycle time and cost in classifying defects.
The automated inspection results are reported and translated by Carestream’s proprietary software. Thus defects and anomalies are precisely identified, characterized and resolved.
Online inspection is a never-ending improvement process, and has been automated over time at Carestream. The company’s skill and experience building a repertoire of best-practice inspection techniques for substrates and coatings, along with solutions to a large number of issues encountered, allows for fast correction.
No single technology works for every application and coating. Carestream uses both best-of-class technology and proprietary software/ methods for online inspection. There are many different suppliers of inspection sources to choose from as well. Carestream blends them and selects the best methodologies for each case as an integral part of the process design service provided to its customers.