Lay-up operations look to new glues.

Water-based and reactive hotmelt adhesives are gaining popularity with lay-up operations as pending regulations may eliminate many solvent-based adhesives.

Solvent-based contact adhesives have been among the most-commonly used adhesives in the woodworking industry for laying-up laminates and veneers in panel processing operations. Yet, the levels of VOCs (volatile organic compounds) produced from solvent evaporation as contact cements cure has become a target of federal, state and even some local governments.

"Three years ago when we said we had a water-based adhesive, woodworkers were saying 'So What?'," said Ed McHugh, vice president of sales and marketing with National Casein Co. "Today we've got some forward-minded customers who want to see what these low VOC-emitting adhesives can offer."

Faced with these stringent regulations, many adhesive manufacturers have developed reformulated products, such as water-based glues which will be able to meet new environmental regulations.

"Many cabinetmakers will go into water-based adhesives kicking and screaming," said Kent Pitcher, president of Custom-Pak Wood Adhesives."Solvent-based products dry quickly and are a tried and true adhesive. Woodworkers want these new products to perform at the same levels that their solvent-based products did, and that's quite a challenge."

Two of the most popular types of new adhesive technology making appearances in today's lay-up operations are reactive or urethane hotmelts and water-based contact adhesives. Both not only offer acceptable VOC levels, but additional benefits to the operations which use them, such as fast curing times and high solids content.

Reactions to reactive glues

Reactive or urethane hotmelts are a 100 percent solids, low VOC type of adhesive which have technological roots tracing back to European laminating operations. There manufacturers discovered benefits from their adhesive's ability to maintain a strong bond, resistance to solvents and water, and the variety of application options.

Reactive hotmelts must be applied through a sealed system heated to around 250F because they will cure when exposed to the moisture found in air, according to Jack Dutney, business director for Bondmaster Adhesives with National Starch and Chemical Co. Application methods include roll coaters and spray applicators. Reactive hotmelts can be an attractive substitute to solvent-based adhesives when applying a veneer or laminate to the substrate.

Although reactive hotmelt must be kept in a sealed environment before application, immediate curing following exposure to air can be a benefit to help production.

"Reactive hotmelts cure so rapidly that we've seen a freshly laminated board come out of the nip roller and have a handling bond that will permit machining immediately," said Dutney. "However, it takes anywhere from 24 to 72 hours to reach 100 percent cure."

One consideration that companies need be aware of is the added expense of not only the reactive hotmelt itself, but also the sealed system required for application.

"On a price per pound basis, reactive hotmelts are more expensive," said Dutney. "But you get better mileage out of reactive hotmelts because it is a 100 percent solid adhesive versus a solvent-based adhesive that may only be 22 percent solids."

Water-based contact cement

Another adhesive choice available to layup operations is water-based contact cements. Also high in solids and low in VOC emissions, water-based adhesives can be a rubber or neoprene based product. There are two different types of water-based cements, according to Jack Chambers, director of product assembly with Swift Adhesives with Reichhold Chemicals Inc.

"Single component water-based adhesives typically have a longer drying time while two component water-based adhesives cure faster so set up time can be faster," Chambers said.

Some benefits of water-based cements are that they are non-creeping, have good water resistance and offer a longer open time, according to Pitcher.

"Just because they offer a longer open life, don't assume that they have a longer shelf life." Pitcher said. "All adhesives should be used as close to the purchase date as possible."

Because water-based adhesives can cause rust in spray lines and other metal application equipment, companies that switch to water-based adhesives may have to purchase new equipment that contains staintess steel, plastic or fiberglass parts which come into contact with the water-based adhesive.

"Water-based adhesives work best when applied through a spray gun and that may require a new equipment purchase," said Pitcher.

Both share benefits

Because of the low VOC emissions, reactive hotmelts and water-based adhesive are non-flammable and non-combustible. This property has gained the attention of the insurance industry, and use of either adhesive can lower the risk of possible fire, making chances of obtaining fire insurance for a woodworking operation a possibility.

"When we look at a business for fire insurance coverage, we look at four elements: construction, occupancy, protection and exposure (COPE)," said Don Brackins, national account executive with CNA Insurance Cos. "COPE deals with building construction and what a company is making. Do they have sprinklers/extinguishers and where they are located. Although woodworking facilities have historically been categorized as high risk by insurance companies, using water-based adhesives is a plus for obtaining insurance. But remember that water-based adhesives are only one factor in making or breaking policy acceptance," he added.

Change is good but...

A gluing operation, regardless of the application, is a critical process that must be carefully monitored in order to obtain superior bonds.

"There are so many combinations where a glue will or will not properly bond to another component," said Dutney. "Woodworkers don't have to be experts on adhesives, but a good general knowledge of adhesives is necessary."

Any change in production or materials used can affect proper bonding. Adhesive manufacturers urge end users to test the water before diving in.

"Trial testing is the best way to see if an adhesive is the right one," said McHugh. "Every change in production doesn't require an adhesive change. A good example would be if a company switches to the thinner veneers that are becoming ever more popular. Will your adhesive bleed through the thinner veneer? Trials are the best way to prevent the headaches that can come from costly returns or rejects."

Conclusion

Exploring solvent-free adhesives in a panel lay-up operation is not only a good idea for piece of mind regarding future VOC legislation, but also because of additional benefits such as reducing the amount of flammable materials in a shop. Users will find that many of these low or VOC-free products can offer similar performance characteristics to their solvent-based counterparts.

Experimenting with these new products before applying them exclusively is suggested for users to not only conform with regulations, but also to offer comparable or superior bonds to current adhesives.

Available adhesives

The following is a review of some adhesives available to the woodworking industry. For more information, circle the corresponding numbers on the Reader's Service Card. For a more comprehensive overview of the wood glue market, consult the 1995 Red Book Annual Buyer's Specification Guide.

Hotmelts

Pro Coat 100% solids adhesives from Swift Adhesives reportedly will not cause grain to rise and contains no VOCs. Designed for application to laminated decorative papers, the adhesive is applied with slot coating equipment and then reactivated with heat from a conventional laminator. Benefits of the product include heat resistance and a mirror-like finish on particleboard or MDF, the company says.

Jowatherm 204 30 and 206 00 reactive polyurethane adhesives from Jowat Corp. are general purpose adhesives that are suitable for profile wrapping and edgebanding.

Type II hotmelt adhesives from Therm O Web are available in both pellet and cartridge form and feature high viscosity EVA suited to handle any edgebanding requirements. The hotmelt can be used on high pressure laminate, thin and thick PVC and real wood. Colors include natural, white, brown and black.

Dorus PVA and hot melt (granular and cartridge) adhesive products from Woodtape can be used in edgebanding, lamination, postforming, dowel insertion, membrane press and numerous other woodworking applications.

GreenPak hotmelt adhesive from Brockton Adhesives is a low temperature (125F) hotmelt adhesive and is a water-based colloidal hydrogel which emits no harmful vapors. Brockton says the product sets up quickly, is non-toxic, non-flammable and cleans up with warm water. Upon curing, the adhesive is said to exhibit high heat resistance and keep a strong bond in the presence of oils and vapors.

Contact cements

Lokweld brand adhesives from Ralph Wilson Plastics Co. are formulated to be compliant to meet government regulations. LW H20 is a water based contact adhesive with a VOC level reported to be less than 20 grams per liter. The VOC level makes LW H20 exempt from the most stringent regulations, according to the company.

Duration is a solvent-free, water-based contact cement from Para-Chem Southern Inc. and is reported to deliver a strong, safe performance in a variety of industrial applications. A non-hazardous, high solids latex product, the product also features spray/brush/roll application capabilities and can be purchased in quart, 1-, 5-, and 55-gal sizes.

The Flexweld line of water-based contact adhesives from Imperial Adhesives are reported to offer high temperature performance, contactability, postformability and shelf life. High solids allow for fast drying and improved mileage.

Hybond brand contact adhesives from Pratt & Lambert are available in a variety of formulations and can be applied with brush, roller or spray. The adhesives can be applied to a variety of substrates.

AZ Bond instant adhesives from AZ Laboratories provide bonding of wood, plastics and other materials. The company says molded plastics can be bonded to wood surfaces in 10 to 30 seconds. The product is non-aqueous and non-solvent so slow bonding and emissions are eliminated.

Famobond industrial wood glue from Eclectic Products Inc. has been developed for bonding wood to other porous and semi-porous substrates. Benefits include fast setting rates, long shelf life, and no mixing or staining, according to the company.

Custom-Pak Adhesives Inc. offers powder and liquid urea resins for veneer work and cross-linking PVA's and resorcinols for exterior exposure. The company works with small- to medium-size wood product manufacturers to find the correct adhesive, regardless of container size or amount used.

Titebond's series of aliphatic resin glues from Franklin International was designed specifically for the woodworking industry. The adhesives feature wet tack, low temperature usage, sandability and are resistant to solvents, creep and high temperatures. Uses for the adhesives include edge gluing, assembly gluing and laminating.

Bostik's 8155 water-based contact adhesive is designed to bond HPL (high pressure laminate) to chipboard, wood and other similar woodworking assemblies. Non-VOC and non-flammable, according to the company, the product is also resistant to heat and offers a long open time. The product is available in 5-, 54-, and 300 gal totes. The company also offers a wide variety of adhesives for the woodworking industry.

Miscellaneous adhesives

The National Casein product line consists of crosslinking (Type I and II) adhesives, PVA assembly, UF resins, casein powder, melamine and modified melamine powder adhesive for a wide variety of applications.

Liquid melamine resin from ARC Resins Corp. is reported to offer for use on ether a radio frequency press or a hot press. Called MUF-9430, the resin is reported to feature high water resistance, gap filling capabilities and is sold in tank truck quantities or in smaller quantities through a distributor.

EXCEL polyurethane wood glue from AmBel Corp. can be applied to wood directly with a brush, roller or spatula and reportedly expands as it dries, filling gaps in the wood. Available for interior or exterior use, the product is resistant to water, temperature extremes and chemical exposure. The product can be used for underwater applications provided the joints are covered with a protective coating such as quality paint or varnish.

Available from Eastman Chemical/Lenderink Technologies Inc., DriBond is a sheet adhesive which can be applied between veneers and substrates. Additional benefits of DriBond include elimination of moisture and blowout related problems, bonding of substrates of entirely different composition, elimination of glue spreaders and reduced press times, the company says.

A variety of Rubinate brand binders from ICI Polyurethanes Group are offered to enhance the performance and processing ease of board products. Rubinate 1041 is a cold adhesive designed for bonding LVL, I-beams and solid lumber Rubinate 1780 is a water-emulsifiable binder designed for efficient distribution.

High temperature resistant, room temperature curing epoxy from Master Bond is a two component system called EP30HT. The manufacturer says it has a service operating range of -100F to 400F and will adhere to wood, many plastics and other materials. Bonds are resistant to thermal cycling, water, oil, fuels, and most organic solvents. The epoxy is available in pint, quart, 1-, 5-, and 55-gal. kits.

Jet-Weld brand adhesives from 3M are one-part moisture curing urethane adhesives that give thin glue lines, structural strength, long open times and fast times.

H.B. Fuller Co.'s finger joint adhesives meets or exceeds the ASTM D-3110 wet use application standard and feature low formaldehyde levels. Working equally well with ambient or RF curing, the company can also customize an adhesive to do the job.

Edgebander glues from Edging Plus Inc. are 100 percent solids and can be used to glue a wide variety of edge-banding including PVC, wood, HPL, melamine and other types of edgebanding.

Bondmaster adhesives from National Starch and Chemical Co. are available in a full range of performance adhesives designed to increase productivity, satisfy environmental concerns and control costs.

RELATED ARTICLE: TIPS FOR BETTER GLUING

1 Be sure you have a good understanding of all materials utilized to complete/produce the end product. If uncertain, pre-production evaluations should be conducted.

2 When edge or face gluing, keep the time to a minimum. For best results, they should take place on the same day.

3 When mixing multiple component adhesive systems, accurately weigh out each item, add them in the correct order and mix thoroughly.

4 Observe temperature recommendations for the adhesive. Remember that colder temperatures require longer press times.

5 Be aware of your assembly times. Look for squeeze out as a check for precure or insufficient glue spread.

6 Keep your glue spread accurate and even. Too little or too much glue may cause problems.

7 Keep gluing equipment clean and well maintained.

8 When curing at ambient temperatures, make sure glue lines are cured and set prior to releasing pressure.

9 Be aware of your clamping pressures and the conditions of your joints. For good results, surfaces must be in intimate contact with each other.

10 When gluing multiple stacks in a press, thickness variations will cause uneven pressure distribution in the load which can yield poor bonds.

11 Check press platens for warpage and unevenness.

12 When hot pressing, ensure the platens have equal heat throughout the entire surface and the temperature gauge accurately reflects the platen temperatures.

13 Check the moisture content of stock to be glued with, 6-10 percent m.c. being ideal. High or low m.c. will cause adhesion, warpage end shrinkage problems.

14 All materials to be glued must be clean and free of contamination. Avoid oil, wax or grease on the stock. Sawdust and chips between the surfaces to be glued will prevent intimate contact and may show through on veneers or overlays.

15 Check and properly rotate adhesive inventory.