Protein adhesives or gelatin glue are known for their excellent performance in applications such as casemaking, bookbinding, paper converting, and rigid box manufacturing. When properly matched to the application, they offer excellent tack, fast set speeds, strong bonds, and clean machining.
However, protein adhesives can also be sensitive to changes in the production process. When a glue application suddenly isn't performing as expected, it's easy to assume there is something wrong with the adhesive. In reality, the glue itself is only one part of the equation.
Equipment settings, adhesive temperature, production speed, substrates, dilution, plant conditions, and even changes elsewhere in the production process can all affect adhesive performance.
When customers contact LD Davis because their protein glue isn't running as well as expected, our adhesive specialists start by gathering information. Troubleshooting isn't about immediately changing the adhesive—it's about understanding what is happening throughout the entire application.
Before assuming your protein adhesive is the problem, consider these six questions a glue expert is likely to ask.
Your equipment is the foundation of a successful adhesive application.
Protein adhesives are used on many different types of equipment, and not every adhesive will perform the same way on every machine. Glue pot design, roller configuration, application method, operating temperature, and production speed can all affect which adhesive formulation best suits the application.
One of the first things an adhesive specialist will want to know is the make and model of the equipment you're running.
They may also ask:
If an application has historically run well and suddenly starts having problems, also investigate equipment condition. Worn rollers, uneven pressure, incorrect settings, or adhesive buildup can change the amount and consistency of glue being transferred to the substrate.
Temperature is one of the most important variables when working with protein adhesives.
Protein glue needs to remain within an appropriate operating temperature range throughout the application process. Temperature directly affects viscosity, flow, transfer, tack, and set speed.
If the adhesive is too cool, it can become too thick or begin setting prematurely. This may prevent the glue from transferring properly from the roller to the substrate or cause it to lose tack before the materials are joined.
If the adhesive becomes excessively hot, prolonged exposure to high temperatures can reduce performance and may eventually damage the adhesive.
One common troubleshooting mistake is relying exclusively on the machine's temperature display.
The temperature shown on the control panel isn't necessarily the exact temperature of the adhesive at every point in the system. For this reason, we recommend verifying the actual glue temperature with a thermometer.
Check the adhesive temperature:
The roller temperature can be especially important because this is where the adhesive is transferred immediately before reaching the substrate.
Even relatively small temperature differences can change how a protein adhesive behaves.
For example, if the glue pot is at the correct temperature but the rollers are significantly cooler, the adhesive may increase in viscosity or begin setting before it ever reaches the material.
Understanding the actual operating temperature throughout the system gives an adhesive specialist valuable information when diagnosing a problem.
One of the most important troubleshooting questions is also one of the simplest:
Has anything changed with the materials you're using?
Substrate changes happen more frequently than many manufacturers realize.
A new production job may require a different paper, board, cloth, or cover material. In other cases, your material supplier may change a coating, treatment, or manufacturing process without the material appearing significantly different.
Even subtle changes to a substrate's surface can affect adhesive performance.
Protein adhesives typically need to interact with the surface of the material to develop a strong bond. If a substrate becomes more resistant to moisture or has a lower surface energy, the adhesive may have difficulty wetting or penetrating the surface.
A simple water drop test can provide useful information. Place a small drop of water on the substrate and observe how the surface reacts. If the water readily wets or absorbs into the surface, the material may be receptive to a water-based adhesive. If the water beads tightly on the surface, the coating may be preventing proper wetting.
A dyne pen test can provide additional information by measuring the surface energy of the material.
These simple tests can help determine whether the substrate is "glueable" with the existing protein adhesive or whether additional testing, surface treatment, or a different adhesive may be required.
Production speed directly influences how quickly an adhesive needs to develop tack and set.
The faster the machine runs, the less time the adhesive has between application and bonding.
On high-speed production lines, an adhesive may need to develop tack very quickly, so materials remain securely positioned as they move through the machine. An adhesive that sets too slowly can result in shifting, opening seams, poor corner adhesion, or other quality problems.
Slower production speeds create different requirements.
If an adhesive sets too quickly on a slower line, it may begin drying before the substrates are joined. In these applications, an adhesive with a longer open time may provide better performance.
It's also important to consider whether the production speed has changed since the adhesive was originally selected. A glue that performed perfectly when a machine was running at one speed may not be the ideal formulation after production has been significantly increased.
Matching adhesive characteristics to actual operating conditions is essential for maintaining consistent production.
Another valuable troubleshooting tool is a refractometer.
A refractometer is a small handheld instrument that can be used to monitor the solids concentration of a protein adhesive. Regular readings can help operators verify that the adhesive remains within the desired operating range.
This is particularly important when water is added to the glue during production.
Protein adhesives may lose moisture while heated in an open glue pot. Depending on the application and equipment, operators may add water to maintain the desired viscosity and operating characteristics.
However, operators must carefully control dilution.
If too little water is present, the adhesive may become excessively thick. This can contribute to poor transfer, excessive glue film, buildup on equipment, stringing, and other application problems.
If too much water is added, the adhesive can become overly thin. Excessive dilution may reduce tack, slow set speed, increase drying time, and potentially affect bond performance.
A refractometer gives operators a measurable value rather than relying solely on how the adhesive looks or feels.
Maintaining records of solids readings can also be extremely helpful when troubleshooting recurring problems. If operators know the typical solids range when the application is running well, they have a useful benchmark when performance changes.
Troubleshooting Tip: Don't wait for a problem to start checking solids. Establishing normal operating readings during successful production gives you something to compare against later.
Environmental conditions are often overlooked during adhesive troubleshooting.
Temperature and humidity within the production area can influence how quickly moisture leaves the adhesive, which can affect open time, tack, set speed, and overall bonding performance.
That is why some adhesive problems seem seasonal.
A production line may run perfectly throughout spring and fall but behave differently during extremely hot, humid summer weather or cold, dry winter conditions.
For example, dry conditions can cause moisture to leave the adhesive more quickly, potentially shortening open time. Higher humidity can slow moisture evaporation and may increase the amount of time required for the adhesive to set or dry.
Facilities without climate-controlled production areas may experience more noticeable seasonal changes.
When troubleshooting an application, consider:
Substrate storage can also matter. Paper, board, and other materials can respond to environmental conditions before they ever reach the production line.
If your application begins behaving differently at the same time every year, environmental conditions may be worth investigating.
While these six questions cover many of the most common causes of protein adhesive problems, troubleshooting sometimes requires looking even deeper into the process.
More adhesive doesn't always create a stronger bond.
Applying too much protein glue can increase drying time, create squeeze-out, contribute to warping, and cause unnecessary buildup on equipment. Applying too little adhesive may result in incomplete coverage and insufficient bond strength.
The goal is to create a consistent, appropriate glue film for the materials and applications.
If you're experiencing bonding problems, inspect the glue pattern across the entire substrate. Look for areas where the adhesive film is heavier, lighter, or missing altogether.
Protein adhesive buildup on rollers, glue pots, hoses, or other machine components can interfere with consistent adhesive application.
A dirty or partially obstructed application system may create an uneven glue film even when the adhesive performs correctly.
Establishing a regular cleaning and preventative maintenance schedule can help prevent many application problems before they begin.
Applying the adhesive is only part of the bonding process.
The two substrates also need sufficient contact and pressure while the adhesive develops its initial bond. Inadequate compression can sometimes appear to be an adhesive failure when the actual issue is elsewhere in the machine.
If you're seeing areas that aren't bonding consistently, inspect how the substrates are coming together after glue application.
When troubleshooting, it's helpful to determine whether the problem occurs across every shift or only under certain operating conditions.
Different operators may dilute glue differently, use different temperature settings, adjust rollers differently, or follow slightly different startup and shutdown procedures.
Documented operating procedures can help eliminate these variables and create more consistent adhesive performance from shift to shift.
One of the best ways to make troubleshooting easier is to document your process when everything is running correctly.
Record information such as:
Think of these numbers as your application's baseline.
When a problem occurs, you can compare current production conditions with your normal operating parameters. This can make it much easier to identify what has changed.
Instead of asking, "Why isn't my glue working?" you can begin by asking a much more useful question:
"What is different today compared with the last time this application ran successfully?"
That question can significantly narrow the troubleshooting process.
Successful Adhesive Performance Starts with the Right Questions
Troubleshooting a protein adhesive application isn't about guessing or immediately replacing the glue. It's about understanding the entire bonding process.
Equipment, adhesive temperature, substrate characteristics, production speed, solids content, environmental conditions, glue film thickness, and operating procedures all work together to determine adhesive performance.
A change in just one variable can sometimes create a noticeable difference in production.
Before switching adhesives, take time to evaluate the process as a whole. In many cases, something as simple as adjusting the glue temperature, correcting dilution, cleaning an application roller, or identifying a substrate change can restore performance without requiring a new adhesive.
And when the cause isn't obvious, detailed process information makes it much easier for an adhesive specialist to help.
At LD Davis, we've been manufacturing industrial adhesives since 1926, and our team understands that every application is different. Whether you're running protein adhesive for rigid boxes, casemaking, bookbinding, paper converting, or another manufacturing application, our adhesive specialists can help evaluate your process and troubleshoot performance issues.
If you're experiencing an ongoing protein adhesive challenge, contact the LD Davis team. We'll work with you to identify the variables affecting your application and find a solution that keeps your equipment—and your production—running efficiently.