How to Improve the Mixing Process for Adhesive Manufacturing

In order to maximize adhesive performance, you must ensure the quality and consistency of the mix of your input materials. When you find reliable processes for adhesive mixing, you can minimize batch failures, support product performance, and reduce waste. This article outlines common issues that arise when mixing adhesives and provides ways to mix adhesives efficiently.

Signs Your Adhesive Mixing Process Needs Improvement

When mixing adhesives, you may encounter various issues that affect product quality and performance. These signs likely indicate that you should improve your mixing process:

• Product quality issues: Batches may vary in viscosity, texture, or even color.
• Defects: You may notice visual defects such as agglomerates (clumps), streaks, or gels in the adhesive.
• Trapped air: Any voids or trapped air bubbles in the adhesive mix can weaken bond strength and affect the product’s structural integrity.
• Dead zones: In larger containers or inefficient mixing systems, dead spots can occur, resulting in uniformity issues in the product. Often, denser materials separate from the mixture and do not disperse properly.
• Curing issues: Some particles in the adhesive mix will be hotter than others due to uneven shearing rates. This can cause inconsistent curing.

Solving Mixing Issues With Traditional Batch Equipment

Traditional batch mixing systems have evolved to tackle some mixing issues. These are best practices to follow when mixing adhesives:

Use High-Shear Mixers for Better Dispersion

The more viscous your adhesive mixture is, the greater the shearing force required to disperse all the particles, creating a clump-free and uniform product. This minimizes weak spots and ensures your product performs as designed. A high-shear mixer typically creates a vortex that pulls materials down into the blade.

This only works with materials that are fluid enough to flow back toward the blade. It would not be suitable for thicker pastes, as the material would not flow back, and no mixing would occur.

It is essential to use the correct shear for the mixture, particularly with more sensitive components. Otherwise, high-shear mixers can cause breakdowns in polymer chains, weakening the adhesives’ overall durability. These mixers can also damage or crush fillers, which can lead to a denser product or undesirable changes in viscosity, rather than the expected results.

Use Planetary Mixers for High-Viscosity Pastes

The orbital motion of planetary mixers helps to mix thicker putties or caulks. Double planetary mixers are typically more common, with two identical arms that perform a kneading, folding, and wiping motion. The movement of the arms allows the whole batch to be mixed, minimizing dead zones.

Planetary mixers are better suited for handling more sensitive materials. They generate less shearing force compared to high-shear mixers. The drawbacks of planetary mixers include their relatively long cycle times. Despite the coverage provided by the orbital path of the mixer’s arms, batch-to-batch consistency also remains a challenge, which relies on the operator’s skill and procedure.

Use Multi-Shaft Mixers for All-in-One Processing

Like the double planetary mixer, multi-shaft mixers have more than one arm or tool. While multi-shaft mixers also have multiple tools, their individual shafts typically rotate rather than orbiting the container as a single unit, allowing for precise, independent control over each mixing element. For example, one blade scrapes the sides and pushes material inward toward a high-shear dispersing blade in the center.

Rather than having to use different containers and mixing equipment, multi-shaft mixers can combine these two types of mixing. However, these mixers are still part of a batch process and its stop-and-go pattern of production. This means there is still downtime between batches and some potential for variation.

Why Continuous Processing Is Superior

One of the biggest issues with batch mixing adhesives is the process’s intermittent nature. You manually load each container or batch, which is the reason why variations can occur between batches made at the start versus the end of a day, for example. There is a fragmented workflow because of the need to intervene and get production moving. This can make it difficult to scale your operations without significant investment in more machines and labor.

With Continuous Processing, rather than having multiple mixing machines, there is a single continuous processor that can perform multiple mixing operations in one unit. A continuous processor takes much smaller amounts of material and mixes them in a short period of time, and does this continuously to meet various run rates up to thousands of pounds of material per hour.

Here’s why continuous processing is the best way to mix adhesives efficiently:

• Ensure consistency: Feeders and pumps help add precisely the right amount of raw materials to ensure consistent ratios. This can be enhanced by using loss-in-weight technology to maintain a specific throughput. Continuous processors can work at different throughputs and shear intensities as needed.
• Maintain shear and heat history: Unlike in batch mixing, where some material can be overworked and cause uneven curing rates, the particles in continuous processing are exposed to the same conditions, giving them the same shear and heat history.
• Maximize efficiency: The continuous processor requires fewer steps. It can perform multiple mixing operations and eliminates the need for manual loading of containers. In addition, you can run your operations 24/7 to increase throughput.
• Reduce waste: By metering the precise amounts of materials as required, there is less waste compared to batch mixing large containers. Continuous processors also require less energy.
• Less cleaning: Cleaning out batch mixers can take as long as eight hours. Continuous processors can be self-cleaning, which saves time and gets you back to productive work more quickly.
• Increase safety: Continuous processors are enclosed units, which means there are fewer safety issues compared to loading batch mixers. The closed units also reduce exposure to chemicals. This can help you comply with OSHA regulations on substance exposure more easily — dust and contaminants are kept inside the processor.
• Better space utilization: Continuous processing requires less factory floor space as there are fewer pieces of equipment involved.
• Increase output: Using a dependable continuous processor can increase output from the non-productive downtime of loading and handling containers in batch mixing.