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In looking at my experience in the adhesive industry related to solid surface and engineered stone products, I hope you can find some insight into what makes a good adhesive. And if I can assist you in understanding adhesives better, then perhaps you can use the information to improve your own processes. Sometimes even the smallest refinements can mean putting out a better product.
Adhesives For Solid Surface Materials
Our experience in the solid surface industry started in 1984, at the time as Duraglas Composites. We were in the fiber-reinforced plastics (FRP) industry; our manufacturing processes required the blending of various polyester resins and additives for specialty bonding and casting applications. It was at that time we discovered solid surface at a kitchen manufacturer that was a dealer for Corian™. The company thought Corian was a great product, but was frustrated that it was priced very high relative to competitive products (tile, laminate) and at the time was only available in a few conservative colors. They posed the question, "Can you make something like this in more colors and maybe at a lower cost?"
We were so intrigued by the product that we started a project to develop a competitive product (which eventually became Karadon). We had to develop the entire formulation from the ground up, including the base resin, which we worked to develop with Ashland Chemical (GWIL Industries at the time). Then we developed a manufacturing system, produced prototypes and built a market for what was an almost unknown product group. The term "solid surface" would not be coined for years, so we had to explain our products over and over again. As Corian eventually became known, we were finally able to say, "it's like Corian but . . ."
In order to go to market, we needed a reliable installation system to ensure that our product would meet the customers' expectations for appearance and long-term durability. That brings us to the subject of glue.
Early Adhesives
At the time, Corian was being installed with silicone in the joints, and some installers were using Cyanoacrylate (Crazy Glue). The cyanoacrylates provided a better joint than silicone because it was rigid and allowed the fabricator to sand seams level for a less conspicuous joint. However, the cyanoacrylate joints soon discolored and eventually failed.
DuPont was the first to offer a color-matched acrylic seam kit. The first one we saw was in a foil tube. It was inconvenient to use compared to today's dispensing systems, but provided a monumental improvement to the product line. The joints were nearly invisible and stayed that way.
We fell back on our experience formulating with polyesters and developed a seam kit of our own. We had great color matching and a reasonably durable joint, but were unable to provide the same strength, speed of cure and color stability offered by acrylic systems. As a short-term solution we were able to purchase acrylic-based resins, which we stabilized, tinted and packed to go along with our sheet stock. This bought us the time to consider the market needs and develop an adhesive with exactly the properties our fabricators were looking for.
In 2002, I sold my remaining shares in Karadon Corp and formed a company to focus on the development and production of adhesives for markets other than our captive clientele, and our products were made available direct to fabricators, as well as private labeled for various solid surface manufacturers.
Challenges
Some of the challenges we faced and continue to face as an industry are:
- To develop the product and a route to market that meets the needs of fabricators
- To provide technical support to ensure the successful use of products
- To provide high bond strength to a variety of substrates — polyesters/acrylic/hybrid solid surfaces, engineered stone and natural stone
- To provide color accuracy, repeatability, stability and UV resistance
- To provide the correct gloss, clarity and opacity for invisible seams
- To provide a system with the desired viscosity and flow properties
- To provide a system with the desired miscibility of components to allow for thorough mixing with low-cost static mixers.
- To provide a product with a long shelf life (storage stability) that remains consistent in cure, color and viscosity for a year or more after packaging
- To provide a stable system using FDA-approved color pigments
- To provide a system with accurate, on-ratio (even) curing
- To provide for quality control and thereby consistency
- To ensure products are used and disposed of in an environmentally responsible manner compliant with environmental regulations
Manufacturing Process
In order to produce adhesives with optimum color and extended shelf life, impurities in the mixture must be eliminated. Using pharmaceutical-grade stainless steel chemical reactors helps to achieve the highest level of purity. Also, processing each batch under vacuum at elevated temperature to polymerize the monomers allows the desired viscosity to be achieved. The mixture must then be rapidly cooled to prevent the adhesive from hardening in the reactor. At this point the mixture is stabilized and various additives (adhesion promoters, cross linkers, tougheners, etc) are mixed in to achieve the final properties.
Samples of the finished product should be taken to the lab and, if required, adjustments made to ensure the cure profile — bond strength, color and viscosity — are within specification. Also, samples should be retained and QA certificates from each batch should be stored and made available to the fabricator on request.
Expectations
There are certain standards that all fabricators should be aware of. We believe that a fabricator should expect the following:
- A minimum of six to 12 months of shelf life (stored correctly)
- Color stability
- A flexural bond strength of 4,000 psi or higher
- That handling strength should develop within 30 minutes at normal room temperature
- Ease of sanding; adhesive should not clog sand paper
- A consistently even cure
- A product warranty that covers, at minimum, the replacement of defective materials
- Technical support; fabricators should be able to call and speak with a knowledgeable representative that can provide application advice and assist with solving technical difficulties
- Reasonable pricing
- Off-the-shelf availability of all colors and accurate color matches without the use of clear adhesives to substitute for unmatched/unavailable colors
Current Products On The Market
Solid Surface Adhesives. Solid surface adhesives are generally acrylic based, except for a few regional solid surface brands that use resin from their casting operations to bond their products. Most are cured with a form of peroxide. Some have added tougheners to increase impact resistance, although this usually reduces flexural strength. Some have added performance-enhancing polymers to improve cure, bond strength or flexibility. Most are designed for a 10:1 ratio of adhesive to activator; however, some 1:1 systems have been used with limited success.
Most of the adhesives on the market are produced by three or four manufacturers. Products are often sold under private label or are purchased in bulk and packaged by repacking companies. The quality of the tinting and filling process and the quality of filling equipment can have a dramatic effect on the finished product's performance, just as storage conditions can dramatically extend or reduce shelf life.
Adhesives For Engineered And Natural Stone. Quartz material and natural stone adhesives are offered in a variety of polymers, each with their respective advantages.
Acrylics: Available clear or in a wide range of colors, they provide strong, fast curing bonds to properly prepared dry surfaces. They are UV stable. They do not cure well below 50° F and will not cure or bond well to surfaces where moisture is present when applied. Acrylics can shrink 1 to 5 percent during cure, depending on the formulation. They are tolerant of off-ratio dispensing and are easily mixed. They work well for laminating, top seams and repairs.
Epoxy-modified Acrylics: These have the same properties as acrylic, but with reduced shrinkage and improved bond strength. They are available in varying formulations to provide bond strength as desired, up to 6,000-psi flexural strength and work well for laminating, top seams and repairs.
Epoxies: Available in a variety of colors and clear for tinting, epoxies exhibit low shrinkage (less than 1 percent) and provide high bond strength, particularly with slow cure versions. Fast-cure systems typically have lower strength. Epoxies require accurate proportioning and thorough mixing to achieve good physical properties. They are not as sensitive to moisture as acrylics or polyesters. Cure is temperature-dependent and some formulations require 24 hours to cure, or require heat to produce a full cure. They work well for laminating.
Polyesters: Polyesters are available in a wide variety of colors and transparent for tinting. Their curing system usually causes a yellowing, so whites can be difficult to produce. Their bond strength is typically lower than epoxies or acrylics, and they will not cure or bond well to surfaces where moisture is present. The cost of polyesters is lowest of all categories and the material is quite soft, so it is easy to finish. It produces good sacrifice joints and top seams, especially for installers needing to open seams for adjustment or repair.
Urethanes: Urethanes are not common in the finishing side of the industry because they are not as color-stable as the other categories. They do, however, have good physical properties and can be used for many structural applications, such as installing wall panels or attaching plywood substrate to countertops. Urethanes have an extremely wide range of properties; they can be formulated to cure within a few seconds or as slowly as several hours and provide either flexible or rigid bonds. They bond well to most surfaces including stone, glass, wood and solid surface.
Products Under Development
Aside from the ongoing development work to improve properties for existing applications, we see the development of adhesives tailored specifically for use on new products and fabrication processes.
There are several examples of developing technology:
- Fast cure or UV light-cured adhesives for automated production lines
- Highly flexible adhesives for shower wall installations with quartz surfaces
- High-impact adhesives for v-groove joints
- Modified gloss adhesives to improve the appearance of joints in textured stone and quartz finishes.
Moving Ahead
While it is important for manufacturers to continue to refine their adhesive offerings and develop new products that address the needs of emerging applications, this cannot be done without the input of the fabricators who use the product everyday. As a parting word, I want to encourage end users to discuss their needs and share their information so manufacturers can work to produce systems that benefit the industry as a whole.
About the author:
Doug Turner is president of Integra Adhesives Inc., 4-33759 Morey Ave., Abbotsford, BC V2S2W5; P.O. Box 970 Sumas, WA 98295; 888-862-6665; dturner@integra-adhesives.com; www.integra-adhesives.com.
author: By Doug Turner