Extrusion Cross-Directional Hot Melt Die Bolt Coatings
High viscosity, hot melt Pressure Sensitive Adhesives (PSAs) are often applied to substrates via die bolt coaters in tape manufacturing. The die bolt zones are located across the web to minimize interactions, streaks and voids.
Summary of Process
The die width and flow rate of PSAs are critical in maintaining a uniform adhesive across the web. Die gaps are initially set at their previously known optimal settings. System is started up and halted for sample collection to lab when thought to be at optimum with extruder and web speed. Process is repeated to confirm product is in specification.
The viscous liquid flows through the die slot onto paper, film or other substrate. The slot gap width is adjusted by die bolts manually (screw extrusion) or via pump pressure.
Quality Parameters and Measuring Points
The hydrocarbon extrusion is a strong NIR absorber. Our MCT Series of NIR stand-alone transmitters are usually mounted in the center of the web or in series on the left, right and center of the web. This is of great value to the converter. The Guardian Cross Direction Web Profile System supplies a cross-direction, zoned web profile and machine direction trend for system operation. The color-coded CD profile visually displays in-spec product as green zones, alerts in yellow and red alarms. This is often connected to a color-coded Stack Light with annunciator to alert operator when product is in the alarm condition. Machine Direction Trends allows troublesome zones to be diagnosed and corrected.
The Cross Direction Web Profile System or fixed-point transmitter is usually mounted at an angle of 15–20 degrees off the normal, 6–16 inches from the web. The system is calibrated in engineering units such as GSM or mil thickness.
Process Sensors has been measuring extrusions for over 25 years. This is a mature application measuring the organic hydrogen carbon stretch.
Value and Quality
Implementation of NIR technology to measure extrusions improves speed at start up, increases production, reduces scrap and allows for data archiving by roll or run. Without an on-line measurement system, the line must be started up, a sample collected for laboratory analysis, the system optimized, and it started up again with another sample collected in order to confirm the optimization. With an on-line system, this process is streamlined, resulting in much greater efficiency. The data archiving, whether from fixed or scanning transmitters via Ethernet communications, protects against customer complaints and allows data histories to be associated with modifications to unit operations or work shifts.
