Hot melt adhesives are a nearly $7 billion market growing at 6.5% annually. Hot melts are a unique class of bonding materials used in a wide range of industrial applications and consumer products including pressure sensitive adhesive labels and disposable hygiene products. While solid at room temperature, these adhesives melt readily when heated, becoming free-flowing liquids which can be applied to a desired bonding site in a precisely-controlled manner. Upon cooling, the adhesive solidifies to rapidly form a strong bond between two materials.
In packaging, converting, assembly, bookbinding, nonwovens, footwear and many other applications, hot melt glues and adhesives offer the critical advantage of fast bonding.
Unlike water-based or solvent-based adhesives, hot melt adhesives do not require lengthy drying times. Hot melts begin bonding almost immediately after application, as they cool down to their solidification point. This fast solidification is ideal for use on highly automated manufacturing lines that require rapid bond formation.
Paraffin wax is largely acknowledged as the original hot melt adhesive coating. Modern polymer and copolymer resin formulations continue to be developed to outperform earlier predecessors, opening up innovative applications for today’s hot melt adhesives.
Roll and die coaters, extruders and doctor blade configurations are among the many methods of applying hot melt adhesive. Roll coaters offer more flexibility than die application methods as they can be changed over more quickly and allow for stripe coating. Die coaters offer more precision, especially in the 15-20 grams/sqaure meter (GSM) range, whereas hot melt applications can range from 0-400 GSM.
Manufacturers need to apply just enough hot melt adhesive for proper bonding and for efficient operations. Excess adhesive is not only costly, it adversely affects the bond strength. To maintain this critical specification, the Process Sensors Corporation (PSC) sensor is recommended for accurate and stable coating measurements of paper, plastic, nonwovens or other substrate.
The hot melt coat weight thickness can be measured using a fixed on-line PSC sensor. Or for a more comprehensive view, the Guardian Cross Direction Web Profile System is recommended.
The Guardian Cross Direction Web Profile System supplies a cross direction (CD) 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 operators when product is in the alarm condition. Machine Direction Trends allows troublesome zones to be diagnosed and corrected.
Implementation of the Process Sensors Corporation sensors and Guardian Cross Direction Web Profile Systems for the measurement of hot melt coatings speeds start up, increases production output, reduces scrap and allows for data archiving by roll or production run for traceability.
Without an on-line measurement system, the line must be started, a sample collected and sent to the factory laboratory for analysis, then system adjustments can be done. This manual process is then repeated until the line is running efficiently. With an on-line system, this process is done in real-time, resulting in increased efficiency and cost savings.
Sensors and Guardian Cross Direction Web Profile Systems configured with Ethernet communications also provide data archiving, allowing production lots to be associated with modifications to unit operations, setups, operators or work shifts, for quality control purposes.
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Accurate moisture, coat weight and film thickness profiles for process control in converting applications
Reliable in-process monitoring of multiple constituents for improved process control, increased yield and maximum production efficiency