Fast-Dry Adhesive Aids Automation Effort For Paint Brush Maker
By Tony Ring, senior technical director, and Amedeo Granata, vice president, technical sales, Fielco Adhesives, Huntingdon Valley, Pa.

Waiting for glue to dry has been an obstacle to in-line processing of paintbrushes. Room temperature cure times of 4-6 hr are disrupting to a rapid flow of products through an assembly process. Use of a faster-drying epoxy adhesive is facilitating productivity at a Canadian paintbrush manufacturer.

Through its in-line use of a two-component, medium-viscosity, filled epoxy adhesive that oven cures in 5 min at, 175ºF, T.S. Simms and Co. Ltd., Canada's largest producer of paint applicators, has taken an important step toward total automation of its paint brush manufacturing facilities.

Earlier efforts to perfect fast cure systems aimed at accelerating brush production failed because of excessive shrinkage during cure, reduced solvent resistance, non-uniform material penetration and unsafe fuming of emissive gases.

The shortened curing time required by Sure Cure epoxy adhesive (see Figures 1 and 2), enables in-line pouring of the adhesive that fastens the bristle or synthetic filaments to the brush. According to Heinz Schmidt, manager of plant operations at Simms' factory in Saint John, New Brunswick, Sure Cure cuts down on rejects by providing early data concerning the degree of adhesive penetration. According to Don Sheehan, machinery division manager at Simms, Sure Cure has had no negative impact on conventional glue dispensing equipment.

Inefficient manufacturing caused by lengthy adhesive penetration and curing time has plagued the brush industry since the advent of the assembly line. Work began on a successful effort to solve the problem when Simms agreed to work closely with Fielco Adhesives, Huntingdon Valley, Pa.,a specialist in the formulation and manufacture of high performance polymer products. Fielco has been a Simms supplier for nearly 15 years, and distributes its materials to manufacturers throughout the world.

The two companies began a joint search for a fast-setting brush epoxy about five years ago when Simms agreed to try out in production the experimental formulations developed by Fielco's staff and senior technical director, Tony Ring. In laying out the desired parameters of the product. Simms was definite. They needed an epoxy system that, would facilitate the in-line automated production of paint brushes. The adhesive had to leave uniform wetting and flowability to offer consistent depth of penetration into bristle and filament bundles. Additionally, the penetration lengths of the epoxy through the filament shafts had to be consistent, and wrap-around to the filaments by the adhesive had to be controlled. Also, the adhesive needed to adhere well to materials commonly used for ferrule fabrication, such as tin, nickel and chrome, and offer high resistance to solvents, petroleum products, acids, alkalis and to both salt and fresh water.

In responding to thc assignment, Fielco engineered a flexi- ble set of parameters into Sure Cure so the overall paint brush manufacturing industry could use the product over a range of production line speeds. For example, for temperatures at ambient (not requiring capital investment), the new formulation cures effectively at a 30 min span instead of requiring the presently common 5 hr span. By changing products, the manufacturer can increase his processing throughput by more than 80%, according to Fielco. Except for mechanization, little had changed in the manufacture of brushes. In-line processing of paintbrushes was previously not attainable due to the curing times required by then current brush epoxy technology. Because 4-6 hr cure times at room temperature (68-72 "F) were the norm, the brush-making technician had to put his work aside for several hours to allow for curing of the prior materials. Thus, assembly line interuptions for bristle bonding took far too long to incorporate any type of in-line processing schedule. Such interruptions had been too frequent, irregular and time consuming to allow for the development of consistent in-line processing schedules.

The long curing time required by the earlier adhesives also had been expensive to the brush industry in terms of rejected product. Under pressure to produce, when deciding whether the adhesive had hardened sufficiently to resume manufacture, plant personnel sometimes incorrectly estimated the penetration state of the curing adhesive, resulting in product rejection. At Simms, where the process is speeded by oven-generated higher temperatures, only 2 min are needed after pouring to evaluate penetration effects. Once they are known, the in-line process can speedily resume. For brush assembly plants preferring to operate at ambient temperatures, materials for immediate conversion to a 30 min available.

In approving the use of Fielco's Sure Cure epoxy, Tom Simms, chairman and chief executive officer of the corporation, noted the absence of odor in the product, its less toxic qualities, and praised it, in terms of environmental considerations. Pleased with the results for brush manufacturing, Fielco has developed a fast, cure adhesive to be used in the assembling of paint roller products.

The cooperation between Simms and Fielco has also resulted in a range of curing times wide enough to satisfy the needs of' a variety of paint, thrush and other manufacturers. Examples of Sure Cure curing schedule vari- ants are: 5 min at 175"V (Shore D-80) 30 min at ambient temperatures (Shore D-60); 1 min at 200ºF (Shore D-70).

Additional applications include an infrared curing as short as 15 sec and other variant which uses an ultraviolet light as an accelerant. Because of the capital investment required, however, those two techniques have proved too costly for the paint brush industry. It seems clear, though, that technologically driven factories, including those making composite, laminated and abrasive products, are turning to fast setting epoxies for their in-line processing to gain a competitive advantage in today's global market.