Urea resin is a truly versatile adhesive capable of most assembly gluing, surface and edge gluing, lamination and finishing. Urea resin binders are available as liquid resins with powdered catalysts, or as pre-formulated pre-catalyzed powders. Powdered urea is preferably used where production runs are infrequent, where ambient temperatures are high, and where longer shelf life is required. The shelf life of urea powder is one year. They are pre-formulated with the required fillers, additives and catalysts to meet a wide range of process requirements. CPi's Powder Plastic Resin (PPR) products can be hot-pressed, cold-pressed or radio frequency (RF) cured. Both result in similar glue line properties: strong, rigid, thermoset, Type II water repellent and excellent heat resistance.
Water is necessary to reconstitute the powder resin. The amount of water should be 50-65% by weight of the dry powder to be mixed.65% is the ideal water level. Once you have determined the amount of water you need, first add 2/3 of the amount of water to the mixing vessel. Add the powder slowly while stirring the mixture with a mechanical mixer at low speed (<2,000). Continue mixing for 3-5 minutes, using a spatula to scrape the sides of the powder back into the liquid. At this point the mixture should be creamy with few lumps. Add the remaining 1/3 of the water and mix for another minute. The mixture should be smooth, creamy and free of lumps.
**Note: This product should not be used if the powder does not dissolve easily in water, or if the mixture is sandy and/or granular. These working characteristics provide a built-in safety check that the powder is past its shelf life.
**Note: Keep in mind that the rated shelf life applies to unopened containers stored in a cool (60°-70°F) and dry place. Higher temperatures can seriously shorten shelf life (only 6 months @ 90°F), and exposure to high humidity can cause severe agglomeration or actual catalysis of the powder resin.
Spread rates are highly dependent on the nature of the work being done and the curing method employed. Rates are usually defined by pounds. Glue is required per 1,000 square feet of board surface (MSGL). In many cases, it may be more practical to remove a zero from each side of the equation and express it in pounds. For example, you are veneering a 4 x 6 surface area per 100 square meters and you are looking for a spread of 30#/1,000 MSGL, then figure 3#/100'sq.. The board area is 24'sq., you can deduce that you will need 0.5# glue. Spread rates vary from 25# to 50#/MSGL depending on the nature of the job, glue time constraints and curing method. In general, solid wood gluing uses a higher coating weight (40-50#) than veneer work. RF curing, the coating rate is lower than the normal level (32-36#), to prevent interference with the operation of the equipment. The diffusion rate should be sufficient to show slight extrusion of the beads when pressure is applied. Lighter, heavy mixes are generally preferred over heavier, leaner mixes. Press pressure also has a large effect on spread. Lower pressure should have less glue on the glue line, as thick glue lines will take longer to cure and are weak spots in the glue line. Only one surface needs to be spread, however, breaking the rated assembly time limit may require coating on both surfaces. Likewise, the use of harder-to-moist woods (such as hard maple, ash, hickory) may also require double-sided cladding. Of course, it all boils down to the ability to measure and control the spread. When working with virgin veneers, a thin application is critical in order to reduce the effects of leakage. Bleeding is when glue seeps out of the pores of the wood and appears on the surface of the panel. Pay attention to the thickness of your veneer and the relative porosity of the species you are working with, and adjust the distribution accordingly. In many cases, thin coating and forced open assembly times (possibly up to 10 minutes) are required to prevent excessive leakage. Be careful not to let the glue dry if you allow time to open up for assembly. It must still be wet enough to transfer to the mating surface. Lower spread rates are also standard for pressing high pressure laminate (HPL) to board, in part due to the good consistency of the surfaces being bonded. Application can be done very roughly with a brush or paint roller, or in a complex way with automatic gluing equipment. The more accurately the spread is controlled, the better your success will be. Although the adhesive is somewhat forgiving, reducing the variables yields better results. If a lot of bonding is going to be done, it is recommended to upgrade to better spreading equipment. With rougher equipment, it is often impossible to differentiate spread rates. Measuring spread is usually done by gravimetric or thin film measurements.
Also known as formaldehyde resin glue, this adhesive is one of the oldest synthetic polymers, first developed in 1872. As one of the least expensive glues, it is generally used to bond thin sheets of wood together to form plywood or wood chip to make particleboard. Polyurethane or epoxy adhesives have replaced phenolic resin glues in some applications over the last few decades. Advantages include superior adhesion to most substrates, good high temperature properties, water and weather resistance, resistance to burning, and high strength. Phenolic resins are sometimes used as a base resin or a modifier in an adhesive formulation.
This type is used to improve a product’s durability as well as to make it waterproof and resistant to solvents, heat, and flames. Applications include compression molding for hard plastic furniture and dishes, and to bond together cellulosics in the manufacture of Formica, Melmac, and similar products.
Commonly known as yellow glue or carpenter's glue, this adhesive is similar to plain white glue, but has been modified in structure to be stronger and more resistant to moisture. It is particularly effective on brown hardwoods and provides strong initial tack and fast setting to diminish clamping time. Unaffected by finishes, this adhesive may be fully sanded. Aliphatic resins may be used only on porous materials, dries quickly, and is easy to clean.
Available in powdered or liquid forms, urea resin glues are used for laminating and veneering. This glue is ideal for water- and heat-resistant construction applications. In liquid form, it has a powdered catalyst, while the powdered version has the urea and formaldehyde components already mixed. Respirators are generally recommended when mixing the powdered version as it is toxic. These glues usually do not need hardeners when mixed. One of the biggest advantages of urea resin glue is its long open life, meaning that the container can be left open for a long time while using the product without it drying or becoming rigid.