Two-component adhesive system eliminates mixups

Minneapolis-based CSD/WestPac Division solves unpredictable moisture-curing problems by switching to a two-component laminating adhesive that allows total proportion control.

In switching from a single-component, solventless adhesive system, CSD/WestPac Division of Minneapolis was unwilling to forego control over the proportioning process that it perceived typical of two-component systems. The company had tried this method once before and found that the uncertainty of two-component mixing and the attending possibility of mixing errors was, in a word, unacceptable.

West-Pac wanted something that was 'mistake-proof' from a mixing standpoint," says Tom Ruppert, CSD/WestPac Division director of technical services. As a printer and laminator of packaging materials for salted, meat and confection snacks, the converter chose to avoid solvent-based laminating systems, instead using a single-component, moisture-curing adhesive, but the product's performance still left a good deal to be desired.

The reason for wanting to switch from the one-component system made sense to Jerry Finch, vice president of operations for CSD/WestPac. He explains, "We were using a moisture-curing product that worked on most films - but the curing was so unpredictable." Even external spraying did not provide the uniform application of moisture required, which could lead to unpredictable, inconsistent and longer cure times.

In order to maintain process control with the one-component system, Finch recalls having to keep the plant at 50% relative humidity. "At times, that posed a big problem," particularly during seasonal changes. There were other attending problems, including some of the following:

* Water spots on films.

* CO2 generation if too much moisture was applied.

* Inability to trace the source of application problems after they occurred.

* Possible residual monomers that could migrate to film surfaces and contribute to anti-sealing.

Going Beyond Price and Product

Although seeking an alternative adhesive system to solve their moisture problems was alone justifiable, there were other mandatory criteria that a new adhesive supplier must satisfy, Ruppert explains. Besides simply obtaining a viable two-component, 100% solids system that met CSD/WestPac's production concerns, recalls Ruppert, "We wanted something beyond price, beyond product. We wanted a true partnership so that we could develop something new and different."

According to Ruppert, among the many suppliers available, only one, H.B. Fuller, St. Paul, responded with a "can-do" attitude in promising to develop the proper product and sourcing the right adhesive proportioning system. Fuller immediately went to work formulating a solvent-free polyester system to suit CSD/WestPac's needs.

Fuller also determined that Graco Inc., another Minneapolis-based firm, offered the reliability that CSD/WestPac required for two-component proportioning technology. Quinton Ford, who coordinated Graco's efforts in the partnership with H.B. Fuller and CSD/WestPac, recollects, "This technology had proven itself to be highly reliable in other critical two-component applications where the costs of mix-ratio failure could be high. CSD/WestPac's needs met the same profile, so we were sure that we could offer significant benefits over traditional proportioning methods."

Proportioning Controller Self-Adjusts

An attractive feature of Graco's PrecisionMix proportioning controller is its ability to self-adjust the desired mix ratio of adhesive components. If the mix ratio cannot be maintained within an operator-specified tolerance, delivery of adhesive to the applicator rubber roll of the laminator automatically stops, preventing production errors. Production reports can be printed to track mix-ratio performance and adhesive quantities used for specific orders.

The success of the two-component adhesive system can be credited, say Finch and Ruppert, to the synergy that developed among CSD/WestPac, H.B. Fuller and Graco. "CSD/WestPac had experience in the solventless laminating process and a vision of what it wanted," explains Finch. "By combining that with H.B. Fuller's adhesive formulating expertise and Graco's knowledge of application equipment, the team was able to create something entirely new."

In addition, having been a player in the converting industry only since 1990 has been helpful to CSD/WestPac Division. Finch asserts, "I think our fresh approach has helped us spearhead some new technological advancements for a rather traditional, conventional industry. We are not hampered by the old ways typically practiced by others."

100% Solids Offers Other Advantages

The 100% solids system has offered other benefits, including increased production speeds, faster turnaround for customers and an improved end product.

* The curing process is much easier to control because of measured doses of basic component A and Curing Agent B. The process no longer depends on moisture. Full cure with film-destruct bonds, explains Finch, takes a total of three days' time. Slitting can be accomplished only 24 hrs. after laminating, and materials can be ready for shipment in just one week of processing time.

* Increased production speeds are possible without fear of delamination because of the dependability of process control. Ruppert explains, "Before this, we were at the mercy of a spray head, some water droplets and the humidity. Now we can increase the speed and still know the adhesive is properly mixed." CSD/WestPac currently uses the product on various films, including polypropylene, polyethylene, metallized and coated films, nylon and polyester.

* There is a greatly reduced likelihood of monomer migration because of low residual monomers in CSD/WestPac's laminations. This also reduces resulting problems with food contamination and anti-sealing. H.B. Fuller's Robert Arquette, who helped formulate the flexible packaging adhesive, reveals, "The urethane pre-polymer developed for this application is subjected to a proprietary, patented process by which the residual monomer is reduced to very, very low levels." This minimizes the presence of unreacted polymer that usually results from any polymerization process and which has posed a problem for the food packaging converting industry.

* Operator exposure has been reduced and volatile-organic compound emissions virtually eliminated because of low residual monomer levels. This provides advantages for the machinery operator, the consumer and the environment.

* A consistent low viscosity results from controlled mixing of the adhesive's two components. Graco's PrecisionMix proportioning controller delivers adhesive in a specific ratio to a solventless laminator from Paper Converting Machine Co., Green Bay WI. A heated, three-roll applicator/metering system then applies it to the primary web.

* Tight control of the application rate and fluid viscosity leads to constant coat weights due to the adhesive proportioning system. CSD/WestPac now averages around 700 fpm but has targeted 1,000 to 1,200 fpm. The coat weight hovers between .7 and .8 lb./3,000 sq. ft. of laminated ream. According to Ruppert, "It's similar to what we were using with the one-component adhesive. But we are going to aim for lower weights to further experience an improvement in economies.

The greatest advantage, professes Finch, is the control we have over the whole curing process. "We've been able to introduce statistical process control into our production process because we have computerized controls reading out second by second."

Ruppert adds, "Throughout this process, our goal was to develop something that would better the industry. We wanted to go beyond where we are today and work to revolutionize the industry. I hope we've done that."

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