One Solution to the Problem Of Char: Metallocene-Based Adhesives

Clear with MetalloceneIn the past few years metallocene-based polymer hot-melt adhesives have become more widely available in the marketplace, and more affordable for use in the packaging field.

Metallocene-based hot melt offers superior performance and char-free operation, because the chemical composition means they are not subject to carbon buildup, gelling, or any other changes over extended high temperature storage and use.

As a result, metallocene-based adhesives can be stored indefinitely in glue tanks at high temperatures. The glue will flow clearly at all times through the application cycle, without char buildup or any other material change. Also, unlike EVA-based adhesive, metallocene-based adhesives won’t cause poor or blocked adhesive flow through pumps, hoses, or nozzles.

Next Time: Key Benefits of Metallocene-based Adhesives.

(Excerpted from “No More Char”, a recent issue of Evans Adhesive Solution Advisor. Download entire issue here.)

Preventive Maintenance Can’t Solve Char Buildup

Preventive maintenance, which involves systematic monitoring and periodic flushing of the adhesive application system, can substantially reduce the incidence of charring and gelling and extend the life of applicator hoses and extrusion nozzles.

However, the unfortunate fact is that charring is an inherent problem with EVA-based adhesives (see previous posts). No matter how diligent the preventive maintenance program, charring will eventually occur in any hot melt system using EVA-based adhesive kept at an operating temperature above 350º for prolonged periods. Since prolonged high temperature operation naturally occurs in any production environment, char resulting from EVA will eventually pose a problem, regardless of the steps taken to prevent it. (Read more about the impact of char.)

In some cases, the maintenance required when using EVA is considered part of the cost of choosing this type of adhesive. However, in other cases, finding an alternate adhesive may address some of the drawbacks inherent with EVA-based adhesive.

Next Time:  One Solution to the Problem of Char.

(Excerpted from “No More Char”, a recent issue of Evans Adhesive Solution Advisor. Download entire issue here.)

The Problem of Char: Negative Effects

Before char is apparent oChar Clogs Hoses and Nozzlesr clogging occurs, char creates a thermal barrier in hose linings. This lowers the optimal operating temperature of the adhesive, causing poor flow performance. When your system applies more heat to compensate, even more char build up results.

When char buildup occurs, pieces break loose in your application system. These pieces clog applicator hoses and nozzles, causing uneven adhesive application and eventually, production stoppages. (Read more about Common Causes of Char.)

Even when charring isn’t immediately visible, hidden char deposits contribute to poor adhesive application due to clogged or char-degraded tanks, hoses, or nozzles. This leads to improperly and insufficiently glued packages, plus unsightly char deposits on packaged products.

Next Time:  Can char build-up be prevented?.

(Excerpted from “No More Char”, a recent issue of Evans Adhesive Solution Advisor. Download entire issue here.)

The Problem of Char: Common Causes

Ethylene vinyl acetate (EVA) adhesive is widely used for packaging hot melt applications. However, because of its chemical composition, EVA tends to develop carbon buildup, or char, inside of adhesive application tanks, lines, hoses, and nozzles.

Char — carbon buildup — occurs when EVA oxidizes at prolonged high temperatures above 350º. This heat and oxidation reaction creates carbon buildup during idle periods when adhesive is not flowing through the system, due to degradation of the EVA.

During packaging operations, Char Clogs Applicatorsince adhesive which flows closer to the walls of a hot melt applicator hose moves more slowly than the adhesive flowing in the center of the hose, adhesive nearer to the outer wall of the hose wall tends to degrade more readily, becoming thicker and sticking to the inner walls of the hoses, and eventually forming char on the inside of the hoses, adhesive tank, and nozzles of your hot melt adhesive application system.

 

Next Time: What happens when char is present.

(Excerpted from “No More Char”, a recent issue of Evans Adhesive Solution Advisor. Download entire issue here.)

Dextrin vs. Resin Part 2: With Hybrid Adhesives, You Don’t Have to Make a Choice

Hybrid adhesives combine the flexibility of resin-based adhesive with the lay-flat attributes of dextrin-based adhesives to solve many of your moisture-related production problems. (Read more here.)

One such hybrid — Evans Adhesive’s ResDex™ — is suitable for the majority of litho lamination jobs, and provides key advantages compared to resin-based adhesive.

  • ResDex hybrid adhesive benefitsProduction speeds are equal to those for resin-based adhesives, so production rates will be unaffected by the changeover.
  • Hybrid adhesives can be applied at a lower thickness (as low as 6 lbs. per M.S.F compared to 8-9 lbs. per M.S.F for dextrin-based adhesive), lowering material costs for each job.
  • Hybrids are approximately 10-20% less expensive than resin-based adhesives.
  • Unlike resin-based adhesives, hybrid adhesives do not cause early deterioration of neoprene bands in your Automatän machine; this saves repair cost and downtime in your production flow

With hybrid adhesives, you no longer have to make tradeoffs between the speed of resin and the easier workability of dextrin: This is one instance where you can truly have the best of both for the majority of your litho lamination projects.

(Excerpted from “Fighting Warp,” a recent issue of Evans Adhesive Solution Advisor. Download entire issue here.)

Dextrin vs. Resin Part 1: With Hybrid Adhesives, You Don’t Have to Make a Choice

Benefits of Hybrid AdhesivesUsing dextrin-based adhesive potentially increases the risk of warping. Fortunately, there is a workable adhesive solution for most of your litho lamination projects that also greatly reduces the risk of warp and other moisture-induced problems.

Hybrid adhesives, which contain a mix of both dextrin and resin emulsion, combine the flexibility of resin-based adhesives with the lay-flat attributes of dextrin-based adhesives. These formulations have been problem solvers in many litho lamination jobs.

Hybrid adhesives, such as Evans Adhesive’s ResDex™, are suitable for most litho lamination jobs, and provide key advantages compared to resin-based adhesive.

With hybrid adhesives, you have the advantages of both for your litho lamination projects.

(Excerpted from “Fighting Warp,” a recent issue of Evans Adhesive Solution Advisor. Download entire issue here.)

Solving Moisture-Related Problems in Litho Lamination Part 2: Key Steps Before Running the Job

Previous posts described the role of moisture in causing warpage.

Here are more key steps you can take to identify and mitigate the effects of moisture before running a litho lamination job. (Read Steps 1 and 2 here.)

3)  Reverse-stack finished sheets

When the job is completed, operators can sometimes mitigate warp problems by reverse-stacking finished sheets to attempt to equalize the direction of warp between one stack of sheets and another. However, this approach can’t always be relied on to completely eliminate warp in the final product (especially true with fast setting adhesives), so it’s better to deal with these potential moisture problems before the job is run.

Next time: the role of adhesives in controlling unwanted moisture.

(Excerpted from “Fighting Warp,” a recent issue of Evans Adhesive Solution Advisor. Download entire issue here.)

Solving Moisture-Related Problems in Litho Lamination Part 1: Key Steps Before Running the Job

Previous posts described the role of moisture in causing warpage.

Here are a few key steps you can take to identify and mitigate the effects of moisture before running a litho lamination job.

Check your adhesive to find cost-killing problems1)     Examine moisture content of stock before running job

Many litho lamination operations maintain a humidity controlled environment. However, stock received from other vendors and locations should always be checked for both high and low moisture levels; if high moisture or low moisture is detected, this material should either be rejected or be given sufficient time to reach the appropriate humidity level on your shop floor before processing (generally 48 hours minimum).

A Cobb test is a simple way to measure the moisture content of the paper prior to running.

2)     Choose the right adhesive

Another key factor in preventing warp is the choice of adhesive you use in your lamination projects. Selecting the wrong adhesive for a project, or applying the right adhesive incorrectly, not only introduces unwanted moisture into a job, but also adds its own complications to the moisture problems that cause stock warp.  Because of this, there’s a need for a better understanding of the role adhesives play in causing these problems—and in solving them.

Next time: more moisture-control steps to take before running your litho lamination job.

(Excerpted from “Fighting Warp,” a recent issue of Evans Adhesive Solution Advisor. Download entire issue here.)

Fighting Warp in Litho Lamination (Part 2): More About How Moisture Causes Warp

In the ongoing fight against warpage and other moisture-related issues, it’s important to understand what’s causing the warpage and why. (See previous post for more.)

At a microscopic level, the printed litho sheet and corrugated substrates contain fibers that run in an opposite direction to the grain of the paper. From job to job, fibers in the cross direction react differently to conditions of added moisture or humidity, whether from the ambient air or by direct contact from inks, varnishes, adhesives, or other coatings.

How moisture creates warpage

When exposed to moisture, paper fibers swell and grow. Paper fibers in printed litho stock may expand at a different rate than those in the corrugated board to which they are laminated.

It is these different rates of expansion that cause warp in the finished sheet. Too much adhesive, or not checking moisture content prior to starting a job will many times create unnecessary waste and complicate final die-cutting and finishing operations.

Next time: how to prevent major causes of moisture in litho lamination jobs.

(Excerpted from “Fighting Warp,” a recent issue of Evans Adhesive Solution Advisor. Download entire issue here.)

Fighting Warp in Litho Lamination (Part 1): How Moisture Causes Warp

Before you try to fight warpage and other moisture-related issues, it’s important to understand what’s causing it and why.

When substrates are laminated and die-cut, a variety of problems can occur.  For example, differences in moisture content between the printed topsheet and corrugated substrate can lead to warp in the finished product. Also, variations in moisture, combined with misapplication of the wrong adhesive, can create bubbles, “tunnelling,” and score crack between the printed topsheet and corrugated substrate.

How moisture creates warpage

Next Time

A closer look at what happens when moisture and paper fibers meet.

(Excerpted from “Fighting Warp,” a recent issue of Evans Adhesive Solution Advisor. Download entire issue here.)

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