The type of adhesive or coating will influence the way the liquids are brought to the metering point. Although most adhesives will work for short periods of time in any type of rollcoater, problems can occur with certain adhesives that would cause the coating results to become inconsistent as the material runs for longer periods. Some general guidelines are as follows:
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1) Evaporation of the solvent or water in an adhesive is a major consideration in how well it will run in a roll coater. When running solvent based materials, as little surface area as possible should be exposed, and material should be in constant agitation to prevent dead areas which can form a skin of partially dried adhesive. Machines designed for solvent base adhesives or fast setting water based adhesives would have rollers shielded as much as possible, and would include pumps or other methods to keep the material in constant circulation.
2) Machines for latex-based adhesives would be designed to minimize areas where the adhesive would be subject to a shearing action which could cause clumps to form.
3) It should be easy to add fresh adhesive to any machine. The design of the tank should be a compromise between the capacity and the exposed surface area. Too large a tank may cause too much surface area to be exposed to evaporation, but too small a tank may require constant refilling. Automatic refill systems can be fitted to some machines to alleviate the need to refill constantly.
4) Some types of materials do not flow well, and need to be pumped to the metering point. In some cases these materials can be carried up by a pickup roll that rotates slowly enough to be wetted by the adhesive, but in other cases pumping systems are required. This is especially true with certain high viscosity materials such as epoxies, solvent cements and urethane adhesives.
5) Certain types of adhesives and coatings have special characteristics that must be taken into account when selecting or designing a rollcoater to handle them. An example of this are Ultraviolet cured coatings (UV cure). Machines that are used to apply these coatings must have shielding or guarding in place to keep the coating shielded from light as much as possible, since light exposure can cause UV cure coatings to catalyze earlier than desired or can degrade the characteristics of the coating.
The type of adhesive will affect the choice of materials for the rollers and reservoir, the approach to coating thickness control, the method of machine cleanup, and the way that coating gets delivered to the metering point. Certain types of adhesives (such as hotmelts, waxes and certain high viscosity materials) require that the machine or the rollers be heated to melt the material or lower the viscosity to a point where it can be applied. Some adhesives or coatings will react with certain metals or other materials, and this can degrade the adhesive as the machine runs, or cause damage to the coater. Examples of this are the reactions of copper containing alloys with latex cements and U.V. cured adhesives. Other examples of incompatible materials would be aluminum components used with highly acidic adhesives (such as hot animal glue). In this case the metal components would be attacked and damaged by the glue.
Some adhesives are sensitive to a shearing action which occurs with a scraper blade, and can tend to congeal when subjected to this type of force. These adhesives and coatings must be run in machines having metering rollers.For adhesives and coatings that must be heated either the rollers must be heated directly or the tank which holds the material must be heated, and the heat from the tank and material transferred to the application roller. The need for heating can limit the choice of materials for the roller, since any material selected must be capable of maintaining critical dimensions when heated to the operating temperature.
With any type of coating machine the type of adhesive or coating will affect the cleanup method. Some types of materials can be easily cleaned &#; others require extensive washing with solvents or water to remove any residue. Most machines used for the application of hotmelts do not require cleanup. The adhesive is simply allowed to cool and hardens up in the machine. One exception to this are the &#;reactive&#; hotmelts or &#;moisture cure&#; hotmelts which must be purged from the equipment before it is shut down.
The common goal of the different type coating technologies is to increase the usefulness of the roller, thereby increasing production efficiency. Different coating technologies are suitable for different application scenarios, and choosing the right coating technology is crucial to ensure the performance and durability of the roller.
Ceramic coatings
Ceramic coatings include alumina, titania, zirconia, chromium oixde, silicon carbide, silicon nitride, and boron carbide, as well as oxides of many of these materials. It can provide wear protection to guide rollers for films, fibers, paper and cardboard. In recent years, it has also been active in biomaterials. Usually the plasma coatings system to spray ceramic powder material with the temperature range from &#; to &#;. Main properties of ceramic coatings include high chemical corrosion resistance, anti-static, excellent wear resistance, mirror surface finished, oxidation resistance, excellent electrical insulation, high hardness. Ceramic coating apply to CFRP, aluminum, steel roller.
Non-stick wear coatings
Use a kind of special polymer combined with metal powder by plasma coatings process which can form dural layer extremely wear resistant and non stick functional surface for hot melt glue. Non-stick wear coatings widely used in adhesive tape, sanitary napkins, diaper, film industry. Non-stick wear coatings main properties include prevent adhesive build-up, web tension control, superior wear proformance, superior anti-corrosion, reduce roller/parts work noise. Non-stick wear coatings apply to CFRP, aluminum, steel roller.
Tef-lok coatings
Low friction fluoropolymer with outstanding chemical resistance and weathering resistance. It has excellent electrical insulating properties. It can also solve the contamination problem for ink, plastic, water-based glue. Tef-lok coatings main properties include smooth finished surface, low friction, high temperature applications up to 240&#;, easy clean. Tef-lok coatings apply to CFRP, aluminum, steel roller.
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Tungsten carbide coatings
Tungsten carbide hard facing coatings are a kind of coating with high hardness, erosion resistance, excellent wear resistance up to HV . Coatings exhibit a strong metallurgical bond with the substrate. It mostly used in film, paper-making, turbine blade, cardboard industry. Tungsten carbide coatings main properties include excellent corrosion and wear resistance, high hardness, high-conductivity, scratch resistance, impact resistance, heat and oxidation resistance, ultra mirror surface finished Ra 0.02um.
Stainless steel coatings
Stainless steel is an iron-based alloy that contains an appreciable percentage of chromium and nickel. It enhanced surface quality as well as increased corrosion and wear resistance. It mostly used to spray onto CFRP roller surface what can make it like a 'steel roller' with lightweight. Stainless steel coatings main properties include corrosion resistance, durable, hygienic, temperature resistance, mirror surface finished, apply to CFRP roller.
With Huatao's product range, we are able to cover the entire spectrum of converting industry roller for the film, nonwoven, paper, rubber, textiles printing, hygiene products and packaging.
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